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The use of an oxidizing matrix for matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) specifically induces the cleavage of Cα-C bonds on the peptide backbone, except for bonds located on the N-terminal side of proline residues. To examine the effect of Pro residues on bond cleavage induced by MALDI-ISD with an oxidizing matrix, the small dipeptides AcAA-NH 2 and AcAP-NH 2 were used as models. As the fragmentation is initiated by electron transfer from the peptide to the oxidizing matrix, the dissociation chemistry of the cation radical forms of the model peptides [AcAA-NH 2 ]+• and [AcAP-NH 2 ]+• was investigated using quantum chemistry calculations. The [AcAA-NH 2 ]+• can produce fragment ions not only due to Cα–C bond cleavage, but also peptide bond cleavage. Quantum chemistry calculations indicated that peptide bond cleavage of [AcAA-NH 2 ]+• occurs more slowly compared to Cα–C bond cleavage. Instead of Cα–C bond cleavage, the bond on the N-terminal side of Pro residue undergoes peptide bond cleavage during MALDI-ISD with an oxidizing matrix, due to the lack of an amide hydrogen in the Pro residue. The [AcAP-NH 2 ]+• undergoes proton migration from the δ-carbon of the Pro residue. Depending on the proton binding site in the peptide cation radical, the peptide bond cleavage of [AcAP-NH 2 ]+• results in the formation of either [b 1 ]+, and [y 1 ]•, or [a 1 ]• and [y 1 ]+. These theoretical results are consistent with experimental findings, and the newly proposed mechanism involving peptide cation radical formation followed by proton migration provides a more accurate model for the MALDI-ISD processes. [Display omitted] • MALDI-ISD with an oxidizing matrix preferentially induces the cleavage of Cα−C bond on peptide backbone, producing [a n ]+ and [x m ]+. • As exception, the bonds located on the N-terminal side of proline residues provide [a n ]+, [b n ]+, and [y m ]+, which is called as proline effect. • The proline effect can be explained by peptide cation radical formation and subsequent proton migration from the δ-carbon in the Pro residue. [ABSTRACT FROM AUTHOR]

• The role of supported Au and Pd in oxygen activation under irradiation. • Dissociation of O 2 evidenced by NAP-XPS and in-situ spectroscopy. • Both Au and Pd prolong the lifetime of reactive oxygen species. • Au bonds O atom stronger and promotes the selective oxidation. • Pd bonds O atom weaker and promotes the complete oxidation. Activation of molecular oxygen plays an important role in photocatalytic selective oxidation reactions and complete degradation of organic pollutants. Noble metal cocatalysts are often employed to modulate the activation of oxygen to reach an optimum photocatalytic performance. However, the role of the metal nanoparticles (NPs) still remains unclear and deserves investigation for the design of efficient photocatalysts. Here, Au and Pd NPs are deposited on the TiO 2 photocatalyst to study the promotional mechanism of O 2 dissociation with the presence of glycerol under irradiation by near-ambient-pressure photoelectron spectroscopy and in-situ spectrometry approaches. While both Au and Pd NPs can dissociate O 2 into activated oxygen species, a relatively strong bonds of dissociated oxygen atom is observed on Au NPs than on the Pd NPs. This results in a moderate reduction rate of O 2 and eventually favors a mild oxidation reaction process for Au, and a rapid reduction rate of O 2 and eventually a deep oxidation reaction process for Pd, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

• The OH group at the primary carbon plays an important role in cleavage of the C-O bond at the secondary carbon. • Primary and secondary OH groups were dissociated via completely different mechanisms. • Both the position and structure of the substrate on the catalyst surface must be controlled for selective hydrogenolysis. The hydrogenolysis of various polyols and ethers over a Pt/WO 3 /Al 2 O 3 catalyst was investigated. The hydrogenolysis rate of a C O bond at a secondary carbon was higher than that at a primary carbon, indicating that a hydroxyl (OH) group at a primary carbon played an important role in the dissociation of a C O bond. Moreover, the dissociation position of the C O bond in alcohols and ethers strongly depended on the stability of the carbocation intermediate, and hydrogenolysis via a secondary carbocation as an intermediate proceeded preferentially to that via a primary carbocation. The kinetics of the hydrogenolysis of C 3 polyols were also investigated. The reaction orders with respect to the concentrations of glycerol, 1,2- and 1,3-propanediol were almost the same. In contrast, different reaction orders with respect to the H 2 pressure were observed for the hydrogenolysis of C 3 polyols with or without vicinal OH groups, indicating that the dissociation of a C O bond at primary and secondary carbons proceeded via completely different mechanisms. These investigations suggested that both the structure and position of a substrate on the catalyst surface must be controlled for highly selective hydrogenolysis. [ABSTRACT FROM AUTHOR]

First-principle density functional theory (DFT) calculations are performed to study the active sites in FeN 4 G electrocatalysts, as well as ORR activity and mechanism. The possible intermediates and transition states existing in the possible reaction paths from Langmuir-Hinschelwood (LH) mechanism are investigated. The results show that the associative pathways of OOH∗ formation is prior to that of O 2 ∗ dissociation. The condition of proton adsorbed on top N sites (T2) is more beneficial to the reduction of O-contained species adsorbed on top Fe site (T1) compared to the conditions of proton adsorbed on top C sites (T3). However, the dissociation of O 2 ∗, OOH∗ and H 2 O 2 ∗ is more likely to occur on the paired T1-T3 sites, since their lower energy barriers compared to other paired sites. The most favorable four-electron reduction pathway follows the mechanisms: O 2 ∗→ OOH∗→ O∗+H 2 O→ OH∗+H 2 O→ 2H 2 O. The rate determining step for ORR on FeN 4 G is the reduction of O∗ into OH∗ (barrier, 0.47 eV). The most feasible pathway for ORR is downhill at a high electrode potential (0.76 V vs. SHE at pH = 0) according to the free energy diagram. Compared to the ideal catalyst, the adsorption energy of OOH∗ on FeN 4 G is much lower in free energy, while those of OH∗ and O∗ are slightly higher. Additionally, the elementary reaction rate for OOH∗→O∗+H 2 O is much larger than that of OOH∗→H 2 O 2 based on the parameter of activation barrier. Therefore, the formation of H 2 O 2 (l) is unfavorable on FeN 4 G catalysts. Feasible reaction network for the oxygen reduction reaction on FeN 4 G. 1st, 2nd, 3rd and 4th represent first, second, third and fourth reduction products, respectively. Image 1 • The condition of proton adsorbed on N site is more favored to the reduction of O-contained species. • The most feasible four-electron reduction path on FeN 4 G is O 2 ∗→OOH∗→O∗+H 2 O→OH∗+H 2 O→2H 2 O. [ABSTRACT FROM AUTHOR]

The supramolecular complexes of metallofullerenes and carbon nanoring were constructed and their properties were studied. The size-selective encapsulation of metallofullerene Sc 3 N@C 78 , Sc 3 N@C 80 and Sc 2 C 2 @C 82 by a carbon nanoring of [12]Cycloparaphenylene ([12]CPP) was found. Fluorescence spectral titration experiments showed the different quenching effect of matallofullerenes on photoluminance of [12]CPP. It was found that Sc 2 C 2 @C 82 has a stronger affinity to [12]CPP, and their supramolecular complex has a stronger host-guest interaction. Electrochemical results revealed that the redox potentials of encapsulated matallofullerenes are shifted compared to pristine species. Moreover, these supramolecular complexes can be dissociated using a metal-organic framework (MOF-177), which can only absorb the metallofullerene, leaving behind hollow [12]CPP. These results reveal the special supramolecular chemistry for metallofullerenes, [12]CPP nanoring, and porous MOF-177. In addition, the powerful attraction of porous MOF-177 for metallofullerene can break the host-guest interaction between metallofullerene and nanoring, which is applicable in separation. Image 1 [ABSTRACT FROM AUTHOR]

In this work, initial activation mechanism of CO 2 over MgO supported Ni catalysts has been systematically studied through the periodic DFT calculations. In addition, the role of metal cluster, interface and support for CO 2 activation is investigated and the active site is identified. CO 2 is most favored to be activated on the interface instead of neither Ni cluster nor MgO support. The effective energy for this process is around 0.67 eV, and the dissociation of CO 2 (0.62 eV) is the rate-determining step, since it requires much higher energy than that of the CO 2 adsorption process (0.05 eV). Thus, the interface between metal cluster and support plays a key role for C=O bond activation. Moreover, CO∗ is preferred to be adsorbed on the Ni cluster, while the O∗ is likely to bind on Mg atom of support. To illustrate the adsorption behavior of CO 2 at different sites, the Mulliken atomic charge and electron density difference have been calculated. It was found that the total amount of electron gain for CO 2 binding at different sites follows the order of Interface (−0.03 e) < MgO support (−0.05 e) < Ni cluster (−0.07 e), and effective energy barrier rises linearly with the increase of electron gain of CO 2 binding at different sites. In addition, electron gain of oxygen atom O1 and oxygen atom O2 of CO 2 is the same for Ni cluster and MgO support, however, the electron gain of O1 and O2 is different for Interface. The difference of electron gain for two oxygen atoms shows the electron unbalance of CO 2 molecule, which is in favor of C=O activation. This study could shed some light on understanding the active sites of CO 2 thermal-catalytic activation over MgO supported Ni catalysts, and is helpful to elucidate the reaction on an atomic level. Image 1 • CO 2 prefers to bind on the interface and support instead of metal cluster. • CO 2 is most favored to be activated on the interface. • Effective energy barrier rises with the increase of electron gain of CO 2. • The difference of electron gain for two O atoms is in favor of C=O activation. [ABSTRACT FROM AUTHOR]

Dislocation plasticity in the vicinity of grain boundaries (GBs) plays a critical role in H-induced intergranular failure. Their interaction mechanisms under H environment, however, remain largely unexplored. Here, the underlying interaction of a screw dislocation with [ 1 1 ¯ 0 ] symmetric tilt GBs was studied by using molecular dynamics simulation, with special concerns on the role of solute H in it. Our results show several interaction mechanisms including dislocation dissociation, transmission, nucleation and reflection, depending on different glide planes and GB structures. The presence of H tends to transform these reactions into ones involving dislocation absorption due to H-hindered GB migration and H-enhanced localised plasticity. Furthermore, it is quantified that solute H leads to an increase in energy barrier for dislocation-grain-boundary interaction. After dislocation absorption, the GB segregated with H atoms is activated to a more disordered atomic structure, which can be correlated to the crack nucleation and hence the ultimate fracture. These findings advance a mechanistic understanding on H-induced plasticity-mediated intergranular failure. • DGB reactions (nucleation, transmission, dissociation and reflection) are observed. • The presence of H atoms generally increases the energy barrier for DGB interactions. • Solute H transforms those reactions into ones involving dislocation absorption. • Dislocation absorption causes local GB activation, which greatly aids decohesion. [ABSTRACT FROM AUTHOR]

• Nine ϴ-Fe 3 C surface terminations explored for CO bond dissociation • Pre-activation CO important for lowering the overall activation barrier • (111), 1 1 ¯ 1 , (010): direct CO dissociation B 5 sites • 0 1 ¯ 1 , (001), (100) H-assisted CO dissociation • (111) & 0 1 ¯ 1 dominate CO conversion rate (28% of Wulff particle surface) Spin-polarized density functional theory was employed to determine the preferred CO bond dissociation mechanism on low-index Miller surfaces of ϴ-Fe 3 C in the context of Fischer-Tropsch synthesis. Compared to the most reactive (111) surface of bcc-Fe on which CO binds in a 7-fold coordination, CO prefers to locate in 3-fold or 4-fold sites on the carburized surfaces due to the presence of interstitial C atoms at or below the surface. An important finding is that the lowest activation energies for direct CO bond dissociation are associated with the presence of step-like sites, similar to the case of metallic surfaces. We could identify such sites for 3 out of the 9 investigated surfaces, namely the (111), 1 1 ¯ 1 , and (010) terminations of ϴ-Fe 3 C. On the other hand, H-assisted CO dissociation is preferred on the 0 1 ¯ 1 , (001), and (100) surfaces. The other (011), (110), and (101) surfaces are inert with CO dissociation barriers close to or exceeding the CO adsorption energy. A kinetic analysis shows that the (111) surface (direct CO dissociation) and the (0 1 ¯ 1) surface (H-assisted CO dissociation via HCO) display comparable CO bond dissociation rates, much higher than the rates computed for the other surfaces. Together these two surfaces make up ca. 28% of the surface enclosing a Wulff nanoparticle of ϴ-Fe 3 C. Using an atomic population analysis, we show that the activation barrier for C-O bond dissociation correlates well with the bond order of adsorbed CO. This implies that pre-activation of CO is important for lowering the overall activation barrier. The present work demonstrates that the high-temperature ϴ-Fe 3 C phase is highly active towards CO bond dissociation, which is the essential first step in the Fischer-Tropsch reaction. Several of the exposed surfaces present lower overall CO dissociation barriers than α-Fe (known to be unstable under Fischer-Tropsch conditions) and the χ-carbide of Fe (usually assumed to be the most stable phase of Fe-carbide under Fischer-Tropsch conditions). Notably, the activity of the (111) surface is higher than that of a stepped cobalt surface. [ABSTRACT FROM AUTHOR]

In the never ending quest for clean energy, storing chemical energy in the form of hydrogen molecules in solid state materials is a premier choice. The release of H 2 from the H-storage (absorbent) material is hindered by the on-set of reaction mechanism which depends on the energy barrier. In a search for efficient onset (re)hydrogenation temperature, stimuli like catalysts have drawn more attention in the hydrogen fuel economy. It is laborious to down-select the aspirant candidates by screening their material properties and the thermochemical energy which are required for bond breaking. An understanding on perceptible energies involved in breaking/creating bonds has been obtained using the novel "Interface Reaction tool". To enlighten the underpinning catalytic reaction mechanism to the absorbent, the energetics of interactions between the catalyst and the solid metal hydrides have been derived. For this test study, a leading catalyst TiF x (x = 4,3, and 2) has been added to the well-studied high gravimetric metal hydrides such as MgH 2 , Mg(BH 4) 2 , and Mg(AlH 4) 2. The reaction equation at ambient condition has been validated using the total energies from Kohn-Sham density-functional-theory, and the outcome emphasizes the importance of bonding analysis. Hence, we exemplified the bonding states of all the Ti–F derivatives namely TiF 4 , TiF 3 and TiF 2 in an effort to elucidate the role of fluorine for the onset of catalytic reaction. Our detailed analysis of reaction pathways indicate the vitality of TiF 4 as an additive before and after the H 2 release. Our work pioneers the study on often overlooked reaction possibilities at ambient condition. The calculated reaction energy of less than 40 kJ/mol and 4.64 wt % of H 2 release for TiF 4 and TiF 3 underscores their catalytic activity and meet the system targets set by DoE for the year 2020. This work presents "significant disclosures" on the hydrogen decomposition mechanism and provides a platform for the feasibility study of a new material. This proposes an innovative methodology for predicting the suitability of a new material for efficient production of H 2 fuel. Image 1 • For the first time, H 2 dissociation energy and reaction equations are predicted. • Potential catalysts are identified to make metal hydrides meet targets of DoE _2020. • 4.6 wt% H 2 released with <40 kJ/mol energy when TiF 4 & TiF 3 are added to Mg(BH 4) 2. • Bond strength analysis explains the catalytic activity of the titanium fluorides. [ABSTRACT FROM AUTHOR]

The development of highly active and low-cost catalysts for electrochemical reactions is one of the most attractive topics in the renewable energy technology. Herein, the site-specific nitrogen doping of graphdiyne (GDY) including grap-N, sp-N(I) and sp-N(II) GDY is systematically investigated as metal-free oxygen reduction electrocatalysts via density functional theory (DFT). Our results indicate that the doped nitrogen atom can significantly improve the oxygen (O 2) adsorption activity of GDY through activating its neighboring carbon atoms. The free-energy landscape is employed to describe the electrochemical oxygen reduction reaction (ORR) in both O 2 dissociation and association mechanisms. It is revealed that the association mechanism can provide higher ORR onset potential than dissociation mechanism on most of the substrates. Especially, sp-N(II) GDY exhibits the highest ORR electrocatalytic activity through increasing the theoretical onset potential to 0.76 V. This work provides an atomic-level insight for the electrochemical ORR mechanism on metal-free N-doped GDY. [ABSTRACT FROM AUTHOR]

Schematic of H permeation of dense metallic membrane. • Interaction between H and V surface and bulk are fully studied. • H coverage (θ) effects the adsorption energy of H/V(1 0 0). • H solubility and diffusivity depend slightly on the H concentration. To investigate the H 2 purification mechanism of V membranes, we studied the adsorption, dissociation, and diffusion properties of H in V, an attractive candidate for H 2 separation materials. Our results revealed that the most stable site on the V (1 0 0) surface is the hollow site (HS) for both adsorbed H atoms and molecules. As the coverage range increases, the adsorption energy of H 2 molecules first decreases and then increases, while that of H atoms remains unchanged. The preferred diffusion path of atoms on the surface, surface to first subsurface, and first subsurface to second subsurface is HS → bridge site (BS) → HS, BS → BS, and BS → tetrahedral interstitial site (TIS) → BS, respectively. In the V bulk, H atoms occupy the energetically favourable TIS, and diffuse along the TIS → TIS path, which has a lower energy barrier. This study facilitates the understanding of the interaction between H and metals and the design of novel V-based alloy membranes. [ABSTRACT FROM AUTHOR]

• Pd/CoAl-HTs catalysts show high activity and selectivity in furfural hydrogenation. • Water promotes the hydrogenation of furfural to cyclic compounds. • The interaction between metal and support be tuned by CoAl-HTs microenvironment. • H 2 dissociative and activation ability be adjusted by interlayer anion and spaces. The conversion of biomass-based compounds into highly value-added chemicals has received extensive attention in recent years. This work reports the liquid-phase selective hydrogenation and furan ring-rearrangement of furfural (FFL) into cyclopentanone (CPO) and cyclopentanol (CPL) over Pd/Co 4 Al 1 -HTs catalysts and water as the solvent. The specific reaction rate of the optimal catalyst at 160 °C reaches 538 h–1, and the selectivity of CPO/CPL is 77.5 %. By adopting the ion-exchange and formamide treatment methods, the type of the interlayer anions and interlayer spacing for the CoAl-HTs supports can be regulated, which can affect the state of the supported Pd sites and their catalytic activity and selectivity towards the ring-rearrangement products. Furthermore, the H 2 /D 2 exchange experimental results demonstrate that the presence of the interlayer NO 3 – anions of CoAl-HTs support promotes the activation and dissociation of H 2 , thereby accelerating the hydrogenation of FFL to cyclic compounds. [Display omitted] [ABSTRACT FROM AUTHOR]

• In-situ IR characterization shows more C x H y * species from cracking of butanol while more unsaturated ketones from diethyl ether (DEE). • Reforming of ethanol generates more O-containing species, making coke more aliphatic and thermally unstable. • Reforming of butanol and DEE forms much more coke than from ethanol, due to aggregation of abundant carbonaceous intermediates. • Carbon-rich intermediates from butanol or DEE forms coke of aromatic nature with high crystallinity. • Coke from DEE is more defective with rough surface, while that from butanol is more graphitic with smooth surface. Molecular structures of organics play key roles in determining the tendency of coking and property of coke through governing reaction intermediates formed. Diethyl ether (DEE) can be produced from etherification of ethanol and has same carbon number with n-butanol (butanol), while they may show distinct coking behaviors in steam reforming (SR). Herein, SR of DEE, ethanol and butanol over Ni/SBA-15 catalyst were performed, aiming to probe impacts of ether functionality and length of carbon chain of the alcohols on coke formation. The results indicated that cracking of DEE formed C x H y * species and unsaturated ketone intermediates, serving as precursors of coke. Dissociative adsorption of butanol formed abundant C x H y * species even from 100 °C, due to its longer carbon chain and lower oxygen content. In comparison, abundant oxygen-containing intermediates were generated from degradation of ethanol and reactions with steam. Abundant C x H y * species from DEE and butanol prompted formation of more coke than that from ethanol (60.6 % of coke in the catalyst for DEE, 66.8 % for butanol and 32.9 % for ethanol). Moreover, the coke from SR of ethanol was thermally less stable than that from DEE or butanol, due to the involvement of more oxygen-containing intermediates, which resulted in more aliphatic coke of amorphous form in ethanol reforming. Additionally, the coke from DEE reforming was more defective with carbon nanotube form of thick walls and little internal cavity. The coke produced from butanol reforming was more graphitic and mainly in carbon nanotube form of smooth surface. Varied abundance of C x H y * and ketone species in reforming of DEE and butanol created such a difference. [Display omitted] [ABSTRACT FROM AUTHOR]

It remains challenging to achieve the selective cleavage of C–C bonds in lignin or lignin model compounds to produce aromatic products in high yield and selectivity. We have developed a redox-neutral photocatalytic strategy to accomplish this goal in both β-O-4 and β-1 lignin models at room temperature (RT) via proton-coupled electron transfer (PCET) process without any pretreatments of substrate, by adjusting the alkalinity of base to obtain a lignin models/base PCET pair with a bond dissociation free energy close to 102 kcal/mol. Without breaking down C β –C γ bond and any C–O bonds, this PCET method is 100% atom economy and produces exclusive C α –C β bond cleavage products, such as benzaldehydes (up to 97%) and phenyl ethers (up to 96%), in high to excellent yields and selectivities. Preliminary studies indicated that the PCET strategy is also effective for the depolymerization of native lignin at RT, thus providing significantly important foundation to the depolymerization of lignin. [ABSTRACT FROM AUTHOR]

The behaviors of H 2 O adsorption and dissociation on the Zr 5n O 10n (n = 4–9) nanoparticles are investigated by density functional theory calculations. We find that the coordination number of Zr plays a significant role in H 2 O and OH adsorption. Our results demonstrate that the adsorption of H 2 O and OH on the Zr CN5 (Zr atom with five coordination number) site is stronger than that on the Zr CN6 site (Zr atom with six coordination number), while hydrogen is easily absorbed on the O CN2 (the O atom with two coordination number) site. Particularly, the coordination number of Zr also influences the H 2 O dissociation reaction. Through analyzing the reaction pathways of H 2 O dissociation on Zr CN5 and Zr CN6 site of the Zr 5n O 10n (n = 4–9) nanoparticles, we explore that the H 2 O molecules can be easily decomposed on Zr CN5 and Zr CN6 sites. The largest energy barrier of H 2 O dissociation is 0.247 eV, which is found on the Zr CN6 of Zr 20 O 40 nanoparticles. For the Zr CN6 of Zr 20 O 40 nanoparticles, this energy barrier is even smaller. We found that the adsorption energy and H 2 O dissociation are sensitive to the coordination number of nanoparticles. Besides, the reaction rate constant of H 2 O dissociation on Zr CN5 site of all nanoparticles are larger than that on Zr CN6 site. Image 1 • Structures of (ZrO 2) 5n (n = 2–9) nanoparticles are generated by artificial bee colony algorithm and optimized by DFT. • Adsorption energies of H 2 O, OH and H are affected by the size and coordination number. • We analyze the reaction pathways of H 2 O dissociation on different coordination number sites. • H 2 O dissociation is much stronger sensitive to the coordination number. [ABSTRACT FROM AUTHOR]

An investigation is reported of possible kinetic limitations to MgB 2 hydrogenation. The role of H–H bond breaking, a necessary first step in the hydrogenation process, is assessed for bulk MgB 2 , ball-milled MgB 2 , as well as MgB 2 mixed with Pd, Fe and TiF 3 additives. The Pd and Fe additives in the MgB 2 material exist as dispersed metallic particles in the size range ~5–40 nm diameter. In contrast, TiF 3 reacts with MgB 2 to form Ti metal, elemental B and MgF 2 , with the Ti and the MgF 2 phases proximate to each other and coating the MgB 2 particulates with a film of thickness ~3 nm. Sieverts studies of hydrogenation kinetics are reported and compared to the rate of H–H bond breaking as measured by H-D exchange studies. The results show that H–H bond dissociation does not limit the rate of hydrogenation of MgB 2 because H–H bond cleavage occurs rapidly compared to the initial MgB 2 hydrogenation. The results also show that surface diffusion of hydrogen atoms cannot be a limiting factor for MgB 2 hydrogenation. Instead, it is speculated that it is the intrinsic stability of the B–B extended hexagonal ring structure in MgB 2 that hinders the hydrogenation of this material. This supposition is supported by B K-edge x-ray absorption measurements of the materials, which showed spectroscopically that the B–B ring was intact in the material systems studied. The TiF 3 /MgB 2 system was examined further theoretically with reaction thermodynamics and phase nucleation kinetic calculations to better understand the production of Ti metal when TiB 2 is thermodynamically favored. The results show that there exist physically reasonable ranges for which nucleation kinetics supersede thermodynamics in determining the reactive pathway for the TiF 3 /MgB 2 system and perhaps for other additive systems as well. [ABSTRACT FROM AUTHOR]

Sea-salt aerosol (SSA) has significant impact on the formation of secondary nitrate and its dry deposition in the coastal region. In this study, size-segregated aerosols were collected for water-soluble ions analysis in the coastal cities and sea cruises in the western Taiwan Strait of China from 2016 to 2017 to investigate the impact of SSA on particulate inorganic N deposition. The size distributions of NH 4 + were characterized by a unimodal pattern peaking at 0.44–1.0 μm while NO 3 − exhibited typical bimodal distributions peaking at 0.44–1.0 μm and 2.5–10 μm. Furthermore, the fine mode peaks of NO 3 − became insignificant or disappeared in summer and fall due to the volatilization and dissociation of NH 4 NO 3 at higher temperatures. Elevated sea-salt contributions in the largest size bin (>16 μm) during sea cruises were attributed to vessel induced wave breaking, while there was no peak for NO 3 − at this range due to its short atmospheric lifetime. Although the concentrations of particulate NH 4 +-N showed higher levels than those of NO 3 −-N for both coastal and marine aerosols, the dry deposition fluxes of the particulate NO 3 −-N were significant higher than those of the particulate NH 4 +-N due to their different size distributions. The contribution of SSA to particulate inorganic N deposition was estimated on average to be 20.33% and 36.91% in the coastal and offshore region, respectively, assuming all of the chlorine depletion was caused by the reaction between nitric acid and SSA in the coarse mode. In addition, dry deposition fluxes using constant deposition velocities for fine/coarse particles and NH 4 +/NO 3 − were higher than those using size-dependent dry deposition velocities. Considering the increasing human activities at the coastal urban zone in the western Taiwan Strait, the atmospheric N deposition could have an important ecological impact on the marine environment that is already under pressure from riverine inputs and urban waste discharges. • The size distribution of inorganic N species were determined in the western Taiwan Strait. • The impact of sea-salt aerosols to particulate inorganic N deposition was quantified. • Size-dependent dry deposition velocities greatly improved estimated deposition fluxes. [ABSTRACT FROM AUTHOR]

• Salts have surface charge. • Surface charge will affect removal and deposition of ions. • Surface charge must affect rate of ionic dissociation and dissolution. • Surface charge has not been accounted for in crystallization and dissolution models. • Model of dissociation proposed to account for charge and kinetics. The ionic dissociation of NaCl has long been thought to be fully understood in terms of the simultaneous removal and hydration of the constituent ions from the surface. However, there are two observations that trouble the current model of ionic dissociation. The first of these observations is that the surface is charged. This has been established by several of studies using laser doppler electrophoresis and membrane electrochemistry. This has not been accounted for in descriptions of ionic dissociation, dissolution or crystallization of salt. The second observation is that the current model, which envisages sodium and chloride ions hydrating and departing the surface, does not yield a rate law consistent with experimental data. These two observations are resolved in this work. It is proposed that the removal of ions form ionic vacancies while deposition forms excess ions on the surface. Vacancies and excess ions are the source of surface charge. The effect of this surface charge affects the rate of removal of ions from the surface, resulting in a feedback mechanism: ionic vacancies are formed by the removal of ions, which affects the rate at which ions are removed. From this model, expressions are derived for the establishment of the charge on the surface and for the kinetics of ionic dissociation, dissolution and crystallization of NaCl. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MnNi x oxides with irregular pits were synthesized via hydrothermal method. • The addition of Ni into MnO 2 promoted the catalytic activity for propane oxidation. • The MnNi 0.09 sample could convert 90% propane at 220 °C. • The MnNi 0.09 sample with pits exhibited the lowest apparent activation energy (33.6 kJ mol−1). Abstract Series of nickel doping MnO 2 with irregular surface pits were synthesized and employed for propane deep oxidation. The partial substitution of Ni for Mn resulted in the formation of structural defects, which could be observed by high-resolution transmission electron microscopy. The MnNi 0.09 sample exhibited the best catalytic activity for propane oxidation with the conversion of 90% at 220 °C. The presence of pits on the MnNi 0.09 sample could facilitate the dissociation of propane and mobility of oxygen along the conduction channels of surface pits, thus promoting the catalytic efficiency. Moreover, the in situ studies found that different intermediates were formed on the MnO 2 and MnNi 0.09 catalysts during the propane oxidation process. The propane was oxidized to propanoyl species on the surface of MnO 2 catalyst, while it was oxidized to hydrogen carbonates and carbonates on the surface of MnNi 0.09 sample, which were thermally less stable and converted into CO 2 at lower temperature. The finding provides a new perspective on understanding the effect of cation doping. [ABSTRACT FROM AUTHOR]

In future fusion devices, tungsten (W) and W-based alloys are the primary candidates for plasma facing materials, which experience high-energy neutron and high-flux hydrogen (H) isotopes and helium. Since mono-vacancy and di-vacancy are considered respectively as the common point defect and cluster under irradiation, the interaction between H and vacancies is concerned. In this work, the models to abstract the dynamical parameters, including the effective capture radii (ECRs) and dissociation coefficients, for various trapping and dissociation processes (V n H x + H ⇌ V n H x +1), were firstly extended based on molecular dynamics (MD) simulations. It was found that the ECRs and dissociation coefficients are dependent not only on the reaction types but also on the temperatures. As the increase of the trapped H atoms in the mono-/di-vacancy, the ECRs decrease gradually and the dissociation energies of H decrease gradually. It is not always valid that ECR is commonly assumed as one lattice constant or pre-exponential factor is commonly assumed as 10 ps−1. The number of trapped H in the vacancies should be related to the dwell time, and is also related to the temperature. These results should be potentially applicable for the long-term simulation methods such as kinetic Monte Carlo (KMC) and rate theory (RT) models. [ABSTRACT FROM AUTHOR]

The short operation lifetime is a major factor which hinders the large-scale commercialization of phosphorescent organic light-emitting diodes (OLEDs). Unveiling the intrinsic degradation mechanism of phosphorescent material may be a feasible method for exploring the determined factors of operation lifetime. In this article, the ligand dissociation reactions and phosphorescent quantum yields of various bidentate Pt (II) complexes were investigated by means of the density functional theory (DFT) and time-dependent (TD)-DFT. The calculated results indicate for phosphorescent quantum yields, sulphur heterocycle can facilitate the radiative decay process and suppress the temperature-dependent nonradiative channel. In the aspect of ligand dissociation reactions, the corresponding dissociations of Pt (II) complexes can be effectively avoided via changing the coordinate forms of ligands. In addition, the relationship between geometric tailor and stability, emission color was also taken into account. An analysis of computed results can conclude that the electron-withdrawing and electron-dominating substituents can tune the emissive wavelengths from 477 to 624 nm and cause minor effect on the stability. This investigation could some meaningful information for designing stable Pt (II) complexes. Pt (II) complexes pictured in the graph are explored in detail to unveil the influence of auxiliary ligand and electron-donating/withdrawing groups on stability and provide valuable strategy for designing the stable phosphorescent emitters doped in OLEDs. Image 1 • Sulphur heterocycle can facilitate the radiative decay process. • Stability of platinum (II) complexes can be controlled via auxiliary ligand. • Substituents cause minor effect on the stability, but tune the emissive colors. [ABSTRACT FROM AUTHOR]

Abstract The catalytic mechanism of HFC-245fa on clean and O atom pre-adsorbed Cu(1 1 1) surfaces are investigated by using Density Functional Theory (DFT) calculation. Six initial dissociation reaction pathways of HFC-245fa on clean and O atom pre-adsorbed Cu(1 1 1) surfaces and the related homolytic reactions of HFC-245fa molecule via initial C F, C H and C C bonds breakages are investigated, respectively. The reaction energies, energy barriers, and bond dissociation energies are calculated and compared to investigate the catalytic mechanism of HFC-245fa on clean and oxygen atom pre-adsorbed Cu(1 1 1) surfaces, this result shows that while the energy barriers of C F bond and C H bond decomposition pathways in HFC-245fa on the clean Cu(1 1 1) surface are much smaller than the corresponding bond dissociation energies in the homolytic reactions of HFC-245fa molecule, the breakage energy barriers of C C bond are comparable in these two cases. The energy barriers of all initial decomposition reaction pathways for HFC-245fa on clean Cu(1 1 1) surface are higher than that of HFC-245fa on O atom pre-adsorbed Cu(1 1 1) surface. It is indicated that the Cu(1 1 1) surface can effectively catalyze the scission reactions of HFC-245fa and the O atom can facilitate these dissociation reactions. When the temperature of heat source is close to the decomposition temperature of HFC-245fa, copper used in the components of ORC system (such as evaporator) which works in the higher temperature, should be avoided, because copper can catalyze the decomposition of HFC-245fa. Highlights • The dissociation mechanism of HFC-245fa on clean and oxygen-adsorbed Cu(1 1 1) surfaces are investigated. • The dissociation reactions of HFC-245fa on Cu(1 1 1) surface are easier occur than homolytic reactions • The presence of oxygen atom on the Cu(1 1 1) surface can promote the dissociation of HFC-245fa. • The Cu(1 1 1) surface had good catalytic effect on the decomposition of HFC-245fa. [ABSTRACT FROM AUTHOR]

Highlights • The inhibitory effect of drilling fluids on hydrate dissociation was studied. • An unexpected inhibitory effect occurred with EG at concentrations below 10 wt%. • PVP and lecithin could inhibit hydrate dissociation. • A combination of PVP and lecithin was selected as a hydrate dissociation inhibitor. Abstract Hydrate dissociation poses a significant problem during drilling operations in hydrate-bearing sediments. The drilling fluid is in direct contact with hydrates, and understanding its inhibitory effect on hydrate dissociation is important for stabilizing hydrates during drilling operations. In this work, an apparatus was designed for investigating hydrate dissociation in drilling fluids, and the effects of thermodynamic hydrate inhibitors (THIs), polyvinyl pyrrolidone (PVP), and soybean lecithin on hydrate dissociation were studied. The inhibitory effect of a water-based drilling fluid in the presence of the potential hydrate dissociation inhibitors was also studied. An unexpected inhibitory effect occurred with ethylene glycol (EG) at concentrations below 10 wt%, resulting from a range of factors including the dissociation driving force, and mass and heat transfers in the EG solution. PVP and lecithin reduced the hydrate dissociation rate and increased the time required for complete dissociation of hydrates. These can, therefore, be used in water-based drilling fluids to inhibit hydrate dissociation. A combination of 0.1 wt% PVP and 0.5 wt% lecithin was selected as an optimal hydrate dissociation inhibitor, considering its inhibitory effect and compatibility with the drilling fluid. Using EG at a concentration below 10 wt% as a THI instead of NaCl can also help inhibit hydrate dissociation. The findings of this work provide a basis for the development and design of drilling fluids for drilling in hydrate-bearing sediments. [ABSTRACT FROM AUTHOR]

• A novel photocatalyst constructed by BNQDs and UPCN was prepared. • Intensified exciton dissociation and charge transfer across BNQDs/UPCN heterostructure. • Higher photocatalytic efficiency toward molecular oxygen activation under visible light. • Mechanisms of enhanced photocatalytic activities were proposed. Graphitic carbon nitride (g-C 3 N 4) has enormous potential for photocatalysis, but only possesses moderate activity because of excitonic effects and sluggish charge transfer. Herein, metal-free heterostructure photocatalyst constructed by boron nitride quantum dots (BNQDs) and ultrathin porous g-C 3 N 4 (UPCN) was successfully developed for overcoming these defects. Results showed that the BNQDs loaded UPCN can simultaneously promote the dissociation of excitons and accelerate the transfer of charges owing to the negatively charged functional groups on the surface of BNQDs as well as the ultrathin and porous nanostructure of g-C 3 N 4. Benefiting from the intensified exciton dissociation and charge transfer, the BNQDs/UPCN (BU) photocatalyst presented superior visible-light-driven molecular oxygen activation ability, such as superoxide radical (O 2 −) generation and hydrogen peroxide (H 2 O 2) production. The average O 2 − generation rate of the optimal sample (BU-3) was estimated to be 0.25 μmol L−1 min−1, which was about 2.3 and 1.6 times than that of bulk g-C 3 N 4 and UPCN. Moreover, the H 2 O 2 production by BU-3 was also higher than that of bulk g-C 3 N 4 (22.77 μmol L−1) and UPCN (36.13 μmol L−1), and reached 72.30 μmol L−1 over 60 min. This work reveals how rational combination of g-C 3 N 4 with BNQDs can endow it with improved photocatalytic activity for molecular oxygen activation, and provides a novel metal-free and highly efficient photocatalyst for environmental remediation and energy conversion. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • DFS experiment and MD simulation are combined to study thrombin-aptamer binding. • Multiple factors affecting force measurement are comprehensively elucidated. • Enhanced analytical techniques are employed to determine dissociation force quanta. • Dissociation force of the complex is lower than that of G-quadruplex breakdown. Abstract Previous literature on dynamic force spectroscopy of the thrombin-aptamer complex has shown significantly different force magnitudes even at similar AFM tip velocities, implying the need for a more elaborate evaluation of the force interaction. In this study, we employ a combination of experimental and computational methods to reveal comprehensively how the unbinding force can possibly depend on the loading rate, coverage density, binding rate, linker stiffness and binding buffer composition. In addition, we utilize enhanced analytical techniques that include autocorrelation function, probability density convolution, and Poisson distribution to determine the dissociation force quanta of multiple bond dissociation from force spectroscopy experiments. We then predict the unbinding force measured in the experiments by using atomistic simulation data with significantly broader loading rate range following a continuum model. The dissociation forces of thrombin-aptamer complex are found to be lower than forces associated with the breakdown of G-quadruplex on aptamer, while comparable to forces associated with DNA melting, which indicates the complex dissociation could be more likely attributed to the bond breakage between thrombin and aptamer, rather than the collapse of G-quadruplex on aptamer. [ABSTRACT FROM AUTHOR]

• It is possible to separate the IF 5 -BrF 3 -UF 6 system into individual components by sorption on NaF. • The recommended sorption scheme is: separation of IF 5 from BrF 3 and UF 6 ; selective desorption of BrF 3 ; desorption of UF 6. • Kinetics of BrF 3 interaction with NaF is limited by the conditions of new crystalline phase formation for BrF 3 ∙3NaF. • The observed thermal dissociation rate of BrF 3 ∙3NaF under vacuum is acceptable for industrial implementation. Temperature dependence of bromine trifluoride vapor pressure over its adduct with sodium fluoride has been determined; the adduct normal dissociation temperature has been determined. Kinetics of sorption and desorption processes in BrF 3 (gas)–NaF(solid) system have been studied. The equation was proposed to illustrate the link between forward reaction rate (К а) described by Arrhenius equation and experimental value (K i): K i = K а ⋅ (P a /P eq)m, where Ki – observed reaction rate constant, K a – forward reaction rate constant described by Arrhenius equation; P a – partial pressure of BrF 3 ; P eq – equilibrium pressure of BrF 3 above BrF 3 ⋅3NaF; m – factor characterizing the interaction area of BrF 3 with NaF. The application of this equation makes possible to determine the true reaction rate values and reaction activation energy in chemisorption terms; it also helps to calculate the degree BrF 3 sorption on NaF reaction at different temperatures and adsorbate pressures. The possibility of sorption-desorption separation of bromine trifluoride – uranium hexafluoride – iodine pentafluoride system with use of sodium fluoride was shown. [ABSTRACT FROM AUTHOR]

Abstract Gas hydrate dissociation, resulted from temperature and pressure changes in reservoirs, and natural submarine landslides demonstrate spatial consistency. Currently, large-scale production of oceanic gas hydrates is subject to extensive exploration. However, only few studies focus how large-scale hydrate mining affects near-future stability of the submarine slope and landslides. Thus, we used actual exploration data of the hydrate sediment in the Shenhu area in the South China Sea to establish a substantial three-dimensional and multi-field coupled numerical model of the hydrate submarine slope, which take into account dynamic strength changes of the hydrate layer during the hydrate decomposition process. Our numerical study indicated that severe reduction of hydrate sediments strength is the ultimate cause of the seabed settlement and slope instability. When horizontal wells are utilized to produce hydrates on the seabed slope, horizontal wells should be oriented in the vertical slope direction to ensure maximum stability of the slope as well as higher gas yield. Our results also revealed that seafloor subsidence caused by the increased effective stress corresponds to ∼20% of the total subsidence. Excessive production pressure drop (>9 MPa) and heat injection temperature (>80 °C) as well as large production scale (>150 m) will cause sharp decrease in slope stability and trigger submarine landslides. Our study also discussed methods of hydrate recovery and demonstrated benefits of simultaneous implementation of depressurization and the heat injection methods. Highlights • The horizontal well should be oriented vertically to slope to mine oceanic hydrate. • The decrease in strength after hydrate decomposition declines the slope stability. • Seafloor subsidence occurs in the whole process of hydrate decomposition. • High productivity is likely to induce large-scale submarine slope landslides. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sequential BH 4 dehydrogenation have been investigated by DFT for the first time. • Adsorption and decomposition mechanism have been clarified on all surfaces. • Lateral interactions between adsorbates are effective on Reaction Energy Diagram. • Au(1 1 1) is the most active surface, however Cu(1 1 1) can compete with it. Abstract In this study, the catalytic effect of various metal surfaces on the sequential decomposition of BH 4 molecule has been studied by Density Functional Theory (DFT) for the first time. For this purpose, the sequential dissociation of BH x (x = 0 → 4) molecules on Au, Cu, Al and Ag (1 1 1) surfaces were systematically investigated. At first, ground state structures of BH x (x = 0 → 4) molecules and their decomposed versions such as BH x + yH (x + y = 4) were obtained. Then, transition state search calculations were performed to find activation barriers related to every BH x + yH (x + y = 4) decomposition step until x = 0 has been reached. An additional hydrogen atom(s) remaining from a previous step accepted as if they(it) are(is) at infinite distances from the central unit cell of the surface because it is prerequisite to form energy diagram which keeps the number of the atom(s) constant. Our calculations were supported with the lateral interaction energies and the various bond distances to clarify catalytic abilities of the surfaces. It is concluded that Au(1 1 1) surface is the most active surface among the others however the activity of the Cu(1 1 1) surface can compete with it. Al(1 1 1) and Ag(1 1 1) surfaces are the least active surfaces. This knowledge can be used to develop strategies to design Cu-based cheap and active catalyst for hydrogen generation from borohydride dissociation. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Converting lignite into soluble organic compounds (SOCs) under mild conditions is significant for both evaluating molecular structure and producing clean fuels/chemicals. A three-step dissociation, i.e., sequential extraction, sequential thermal dissolution (TD), and ruthenium-ion-catalyzed oxidation (RICO), was adopted to convert the organic matter (OM) in Xiaolongtan lignite (XL) into SOCs. The perspectives on chemicals, geochemical information, and structural characteristics of XL were evaluated based on the molecular compositions of SOCs. Much higher yields of SOCs were obtained from TD than from extraction, which could be attributed to the thermal dissociation of non-covalent interactions in XL. Normal alkanes, alkyl-substituted benzenes, alkyl-substituted phenols, ketones, and aliphatic esters are the main group components released from TD. A series of important biomarkers were released and their distributions and evolution pathways during XL-forming process imply that higher terrestrial plants could be the main input of the OM in XL. Benzenecarboxylic acids were produced from TD residue in high selectivity via the RICO. According to the results from the RICO, the insoluble macromolecular structures in XL are rich in peri-condensed aromatics along with some cata -condensed aromatics and polyaryls, and CH 3 is the major alkyl side chain on the aromatic rings. Adjacent aromatic moieties are mainly connected each other directly by C ar C ar bridged bonds. [ABSTRACT FROM AUTHOR]

Abstract Aptamers represent interesting bioreceptor alternatives to antibodies when developing a bioassay and are selected by the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process. After selection, an extensive characterization process is essential to verify the binding affinity and specificity of aptamer candidates, which is the most time-consuming and costly step. In this study, we assessed a new microfluidic platform, namely Evalution™, as a rapid and high throughput aptamer characterization platform. To do this, we first selected aptamers against influenza A nucleoprotein (infA NP) by performing magnetic bead-based SELEX. The selected aptamer candidates were subsequently screened using Evalution™ for their binding kinetics and specificity towards infA NP. All aptamers showed dissociation constants (K D) in the low nanomolar range (from 13 to 41 nM), and differential binding behavior towards control proteins, such as BSA and influenza B nucleoprotein (infB NP). Among 5 selected candidates, one aptamer (NP5) exhibited a significant discrimination between infA NP and infB NP and was further used to benchmark the kinetic analysis of Evalution™ (K D = 41 nM) with an SPR platform (K D = 17 nM). These results suggested that NP5 has the potential to be used for developing sensitive and infA NP specific aptamer-based assay. Moreover, the presented platform proved to be an efficient aptamer characterization tool for performing typical aptamer characterization experiments like binding kinetics (due to the real-time monitoring feature) and specificity assessment in a high-throughput manner due to the multiplexing capacity. Graphical abstract Image 1 Highlights • The Evalution™ platform was evaluated for aptamer characterization process. • Aptamers against Influenza A nucleoprotein were selected. • Selected aptamers were screened for their binding kinetics and specificity using Evalution™. • The obtained K D values were in accordance with SPR measurement. • The capability of Evalution™ for rapid and high-throughput aptamer characterization was proven. [ABSTRACT FROM AUTHOR]

Abstract The dislocation associated with the (0001)1/3< 11 2 ¯ 0> basal slip in alumina plays an important role on its plastic deformation at elevated temperatures. A 60° mixed basal dislocation was preferentially introduced by in situ transmission electron microscopy (TEM) nanoindentation, and characterized by atomic-resolution scanning TEM (STEM). It was revealed that the 60° mixed basal dislocation dissociates into two partial dislocations via self-climb with a stacking fault on the 1 1 ¯ 00 plane. The dissociation mechanisms of the basal dislocation have been discussed in terms of its core structure and atomic diffusion process. Graphical abstract A 60° mixed basal dislocation was preferentially introduced and revealed to dissociate into two partials via self-climb process with the formation of stacking fault (SF) on the 1 1 ¯ 00 plane. The climb dissociation mechanisms of the basal dislocation were discussed based on its core structure and atomic diffusion process. Unlabelled Image [ABSTRACT FROM AUTHOR]

Highlights • Dissociation of coal-related model compounds in ILs were studied. • ILs have a significant effect on the thermal dissolution of the model compounds. • ILs promote the dissociation interaction of bridge bonds in model compounds. • B(SO 3 H)mim]OTf has a significant effect on the cleavage of diphenylmethane and diphenyl ketone. • [Bmim]Cl promotes the cleavage of the diphenyl ether. Abstract Ionic liquids have demonstrated to be promising solvents for processing coal and biomass. Aiming to exploit ionic liquids (ILs) as media for degradation of coal, diphenylmethane (DPM), diphenyl ether (DPE), and diphenyl ketone (DPK) were used as coal-related compounds to study the degradation behaviors of weak-bond structures of coal in ionic liquids in this work. It was found that 1-sulfonic acid butyl-3-methylimidazolium 14 trifluoromethanesulfonate ([B(SO3H)mim]OTf), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) and 1-butyl-3-methyl-imidazolium chloride ([Bmim]Cl) have a significant effect on the thermal dissociation of the model compounds. [B(SO 3 H)mim]OTf has a significant effect on the cleavage of DPM and DPK. [Bmim]Cl promotes the cleavage of the DPE. The dissociation effect of the model compound under the action of ionic liquid increases with the increase of reaction temperature. The interaction between the oxygen-containing functional groups in the model compound promotes the respective thermal dissociation of the model compounds. Ionic liquids promote the dissociation interaction of bridge bonds in model compounds. Under the action of ionic liquids, the carbonyl bond promotes the cleavage of the methylene and ether bond cleavage, and the ether bond promotes the methylene bond cleavage. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Both molecular and dissociative adsorption can be found in the adsorption of a single water on a C 3 S low-index surface. • Two-coordinated covalent O atom can adsorb proton in hydration process as well as ionic O atoms. • The adsorption energy of water on the C 3 S surface is affected by the final position of the newly formed OH group significantly. Abstract The adsorption of water molecules on tricalcium silicate (C 3 S), which influences the initial hydration of C 3 S, is still unclear at the atomistic level. In the present paper, density functional theory is employed to depict the adsorption of a single water molecule on seven low-index M 3 -C 3 S surfaces. The calculations show that both molecular and dissociative adsorption can occur on the C 3 S surfaces and that the latter mode is preferential. All of the ionic O atoms on the C 3 S surfaces can adsorb the H atoms from dissociated water molecules, while only two-coordinated covalent O atoms on the surfaces can form O H chemical bonds. The electronic structures of the ionic and two-coordinated covalent O atoms in the first atomic layer of the C 3 S surfaces show similar charge density localization of the valence band maximum (VBM), which can describe the variations in the reactivity of the ionic O atoms in the bulk or exposed on the surface slab. The partial density of states (PDOS) analysis shows that the formation of new Ca O bonds is mainly due to the overlap of O-2s and Ca-3p orbitals and O-2p and Ca-3d orbitals. Furthermore, the position of the OH group generated from the dissociated water molecule is found to significantly affect the adsorption energy. The general order of the adsorption energy in terms of the position of the OH group is E hollow > E bridge > E top. The findings in this study provide additional support for the fundamental understanding of C 3 S hydration. [ABSTRACT FROM AUTHOR]

Graphical abstract Unsupported MoS 2 catalysts were obtained by hydrothermal method at various temperatures ranging from 150 °C to 180 °C. The catalysts obtained at lower temperature show better CO conversion since they have more bridging S 2 2- groups that are beneficial for H 2 dissociation and formation of SH group. Highlights • Unsupported molybdenum sulfide catalysts were synthesized. • The bridging S 2 2- groups increased with the decrease of hydrothermal temperature. • The amount of bridging S 2 2- groups displayed positive effect on methanation. Abstract Unsupported MoS 2 catalysts were synthesized by a one-step hydrothermal method using ammonium heptamolybdate and thiourea at different temperatures ranging from 150 °C to 180 °C. With the decrease of hydrothermal temperature, the obtained MoS 2 catalyst showed an increased sulfur-resistant methanation performance. The physical structure and chemical characteristics of the catalysts were analyzed by N 2 -physisorption, XRD, SEM, HRTEM, Elemental Analyzer, H 2 -TPR, XPS and Raman techniques. Combining the catalytic performance trend with the characterization analysis results, we found that the catalysts obtained at lower temperature contain more bridging S 2 2- groups, that is beneficial for H 2 dissociation and methanation reaction. We deduced that over-stoichiometric sulfur in the catalyst existed in the form of bridging S 2 2- groups, which increased with the decrease of hydrothermal temperature. The finding that the positive role of the bridging S 2 2- groups rather than the S vacancies in MoS 2 catalyst is helpful for designing high efficient MoS 2 catalysts not only for methanation but also for other hydrogenation reactions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Li prefers to adsorb on the Mg-Mg bridge site of the Mg 17 Al 12 (1 0 0) surface. • Adsorption energies of hydrogen on the surfaces with adding Li are enhanced. • Barrier energy of H 2 dissociation on Li-adsorbed surfaces is reduced evidently. • Formation of Li-H bonds in the hydrogenation of the Li-containing surfaces. Abstract The adsorption and dissociation properties of hydrogen on the Li-adsorbed and -substituted Mg 17 Al 12 (1 0 0) surfaces are investigated by using the first principle calculations. Compared with the clean (1 0 0) surface, the adsorption energies of H and H 2 on the Mg 17 Al 12 (1 0 0) surfaces with a small amount of Li are evidently improved. Moreover, the barrier energy of H 2 dissociation on the Li-adsorbed Mg 17 Al 12 (1 0 0) system is notably reduced 0.51 eV. The catalytic effects of Li on the enhanced hydrogenation properties of the Mg 17 Al 12 surfaces are discussed. [ABSTRACT FROM AUTHOR]

Highlights • Methane hydrate dissociation around the freezing point inside the micro porous media channels using depressurization is investigated. • Effects of ice formation/melting on water temperature, distribution of water and methane, pressure, change in cumulative methane generation and residual methane hydrate and change in heat are analyzed. • Heat transfer between phases and the slip velocity and temperature jump at the boundaries in the slip region are considered. • Energy equations and momentum equations for all phases are solved to increase the accuracy of temperature and velocity calculation. Abstract Ice phase affects the methane hydrate dissociation in the porous medium channels. Thus, the investigations on the roles of ice formation and melting in hydrate dissociation around the freezing point are necessary. A model that considers the interphase heat transfer and microscale effects was developed in our previous work. In this study, we extended the work to investigate the effects of ice formation/melting on methane hydrate dissociation in micro porous media channels. Our investigations showed that water temperature, distribution of water and methane, pressure, cumulative methane generation and residual methane hydrate and heat changes in the system are affected seriously by the ice phase. The formation of ice favors the hydrate dissociation for a while, and then inhibits the dissociation of methane hydrate due to the thickening ice. The pressure variations are indications of the possible reformation of methane hydrate and deformation of porous medium channels. The change in heat as one of the key factors for hydrate decomposition shows a more complex changing peculiarity as a result of the ice formation/melting. [ABSTRACT FROM AUTHOR]

Highlights • An extended one-dimensional coarse-grained Helfrich model has been proposed. • Both the tensile and bending energy of the plasma membrane is involved. • The axial strain energy is larger than the bending energy near the neck. • Actin forces is the main mechanism driving the invagination of the plasma membrane. Abstract Endocytosis plays important roles in many cellular physiological processes, such as metabolism and immune. Many theoretical models have been proposed to study the endocytic process, but little has considered the tensile deformation of the membrane and the actin forces. In this paper, a new endocytic model is proposed based on the co-rotational grid method. Our model gives a direct estimation of the in-plane strain of the plasma membrane and provides a basis for the calculation of further scission process of the vesicle. The results fit well with experimental data in the literature. Moreover, it is suggested that the active forces of actin at the endocytic site is the main mechanism driving the invagination of the plasma membrane. [ABSTRACT FROM AUTHOR]

Abstract The paper reports fabrication of electrode containing rGO supported CdS catalyst for photoelectrochemical reduction of water to hydrogen. The reduction of GO to r GO was carried out electrochemically in situ. The catalyst which contained 10 wt % GO with CdS showed the best activity. Catalysts were characterized by XRD, FTIR, DRS, SEM, TEM, SED, XPS, PL, EIS and Mott-Schottky analysis. It is reported that incorporation of r GO to CdS resulted into formation of heterojunction at the interface of CdS and rGO by a chemical interaction between the two. Consequently, a greater band bending, a higher charge carrier density, a low resistance for electronic mobility and low recombination rate result in. The high activity of the catalyst is due to the above mention attributes. These effects become prominent with the increase in the loading of GO, however, any loading in excess of 10 wt % resulted into its shielding of CdS which adversely affected the activity. Highlights • Catalyst containing CdS supported on rGO were prepared for dissociation of water to hydrogen. • GO reduced in situ electrochemically, promoted chemical interaction between CdS and rGO. • Below 10 wt % loading results into trivial interaction whereas higher results into shielding. • Activity has been explained on the basis of microstructure. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • E-beam irradiation at 1.5, 10 and 30 keV passing through graphene on SiO 2 does not etch it. • Results are inconsistent with previously proposed mechanism for wide-area irradiation. • We propose dissociated oxygen from surrounding SiO 2 etches graphene. Abstract We investigate the effects of focused electron-beam irradiation on exfoliated graphene on SiO 2 substrates at energies of 1.5, 10 and 30 keV and dosage of 28.8 C/cm2. Our objective is to understand the mechanism by which wide-area low-energy electron irradiation thins such samples. We test a previously reported mechanism in which the incident electrons produce defects in the graphene, pass through the graphene, and dissociate oxygen from the SiO 2 underneath. The dissociated oxygen then reacts with graphene, etching it from below. We conclude that although oxygen may play a role in the etching, incident electrons at 1.5, 10 and 30 keV that pass through the graphene do not etch it. We propose wide-area irradiation may dissociate oxygen from the uncovered SiO 2 substrate surrounding the graphene and produce etching from above. [ABSTRACT FROM AUTHOR]

Abstract Hydrate reservoirs generally have some unique characteristics such as hydrate dissociation and reformation, permeability change, which may result in quite different pressure-transient behavior from that in conventional reservoirs. In this work, we develop the pressure-transient analysis method for Class III hydrate reservoirs. By establishing a 2D cylindrical model, we then conduct a pressure buildup test and five flow regimes are identified according to the exhibited characteristics observed from the pressure-transient curves. Furthermore, sensitivity analysis is conducted to study the effects of initial reservoir pressure, initial reservoir temperature, permeability reduction exponent, BHP (bottom-hole pressure), and production time on pressure-transient behavior. We identify five flow regimes on the pressure-transient curves. Due to the dissociation of gas hydrate, the first regime is dominated by the non-uniform distribution of permeability, and the pressure derivative curve exhibits an upward straight line. We identify a " V -shaped" valley in the second regime with a peak in the third regime, which suggests the occurrence of hydrate reformation near the wellbore. Such characteristics exhibited in the three regimes are unique to hydrate reservoirs. In addition, the methodology proposed in this study is successfully applied to analyze the actual well testing data obtained from the Malik hydrate reservoir in Canada. Highlights • The pressure-transient analysis method is proposed for gas hydrate reservoirs. • Five flow regimes are identified on pressure-transient curves in Class III hydrate reservoirs. • Pressure-transient behaviors in Class III hydrate reservoirs are fully analyzed. • Key parameters on pressure-transient behaviors are analyzed. [ABSTRACT FROM AUTHOR]

Abstract Electron capture detectors (ECDs) and detectors used in ion mobility spectrometry (IMS) have been successfully used for the detection of numerous compounds including hazardous substances. The general principles of their operations are similar and based on sample component ionization and measurement of the signal using the differences in the mobility of electric charge carriers. Differences in sensitivity result from various parameters of these instruments. Value of electric field intensity in ionic reactors have an influence on ionization process. The main goal of the performed tests was to compare the analytical properties of ECD and two types of IMS detectors: a drift tube spectrometer (DT IMS) and a differential mobility spectrometer (DMS). In the work performed, the efficiency of ionization and the response of detectors to selected analytes were compared. ECD, DT IMS and DMS were equipped with 63-Ni radioactive sources. Analytes have been ionized via electron capture process or dissociative electron transfer. Results obtained for oxygen and chloro-substituted organic compounds (carbon tetrachloride, benzyl chloride, chloroform, 2-chloroethyl ethyl sulfide) were used to calculate the relative signal and to compare the ionization efficiency for three detectors. The phenomena observed experimentally were related to energy dependencies and electron capture cross-sections of analytes. The efficiency of ionization in DT IMS was also compared for electron capture when nitrogen was used as the carrier gas, and when the ionization process was based on the collisions of the analyte molecules with the O 2 - with the use of air. Graphical abstract fx1 Highlights • Electron capture is effective method of ionization in ion mobility spectrometry. • Different types of detectors are compared. • Limits of detection of below 1 ppb level are achieved. • Electron energy is the factor determining ionization efficiency. • In some cases dissociative charge transfer is the effective way for ionization. [ABSTRACT FROM AUTHOR]

Highlights • H 2 adsorption energies are very similar on different facets and K preadsorbed on hcp Co. • H atom adsorption was site and facet dependent on hcp Co. • H 2 dissociation energy barriers were negligible (0–0.07 eV) on clean hcp Co. • K has a slight inhibiting effect on the H atom adsorption and H 2 dissociation. • Different K species (K and KOH) exhibit similar effect on H 2 dissociation on hcp Co. Abstract Trace amounts of potassium (K) have a significant influence on the activity and selectivity of cobalt-based catalysts in Fischer–Tropsch synthesis (FTS), in which hydrogen adsorption and dissociation is one of the initial and most important steps. In this work, hydrogen adsorption and dissociation behavior on typical facets ((0001), (10–11), (10–12), (10–15) and (11–20)) of hcp Co with and without adsorbed K were systematically studied. H 2 molecular adsorption results showed that H 2 mainly adsorbed in the perpendicular mode and close to the state of free H 2. Different facets and pre-adsorbed K did not show obvious effects on the H 2 adsorption energy. Atomic hydrogen adsorption was site and facet dependent, but the maximum hydrogen adsorption energy on the different facets of hcp Co were similar (-2.64 to -2.67 eV) with the exception on the (11–20) facet where the adsorption energy was significantly lower (-2.44 eV). K had a slight destabilizing effect on the H atom adsorption on the former Co surfaces due to a very weak repulsive interaction between K and H atoms. The initial H 2 dissociation had negligible energy barriers (0–0.07 eV) on the clean surface of hcp Co, suggesting the direct dissociative adsorption of H 2. The energy barriers for H 2 dissociation are mainly caused by the approach of molecular H 2 towards the Co surface and the rotation of the H 2 molecule from the perpendicular mode to the parallel mode. The H 2 dissociation energy barriers increase by 0.02–0.17 eV after the pre-adsorption of K, indicating a slight inhibition of H 2 dissociation by K. However, the energy barriers for H 2 dissociation in the presence of K were also small (0.05–0.21 eV). This indicates that H 2 dissociates readily at typical Co-based FTS reaction temperatures (210–240 °C), both in the absence and presence of K. Different K species (K and KOH) exhibit similar effects on H 2 dissociation on hcp Co. The B 5 sites on the stepped facets, the preferred sites for K adsorption are not the most favorable site for H 2 dissociation, and K slightly hinders H 2 dissociation at the B 5 site of hcp Co. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • A defect-induced preferential etching mechanism of MACE for SiNW formation is proposed. • Theoretical mechanism of Ag modification in NO 2 -response enhancement is demonstrated. • The doped effect of Ag is investigated for understanding the sensing mechanism. • Dissociation reaction and spillover-effect are clarified for NO 2 adsorption on the Ag atom. • The catalyst nature of modified Ag for NO 2 adsorption and reaction is revealed. Abstract Surface modification by noble metal nanoparticles has been proved highly effective on response enhancement of a semiconductor gas sensor. In this work, the adsorption of NO 2 on Ag-modified silicon nanowire (Ag@SiNW) was investigated by means of density functional theory (DFT) calculations with aim to explore the nature and theoretical mechanism of Ag modification for sensing response enhancement. Ag surface modification tunes the electronic structure of SiNW considerably, which is further moderated by the spontaneous adsorptions of NO 2 on surface Si site and on the modified Ag atom. The modified Ag as a donor creates an n-doping state, activating the surface Si atom and promoting the adsorption of Si surface to NO 2 gas. Nevertheless, Mulliken charge transfer calculations clarify that the enhanced response observed experimentally for an Ag@SiNW sensor is mainly attributed from the gas adsorption right on Ag atom. The adsorbed NO 2 on modified Ag atom captures 1.27 e from the nanowire surface, which is more than twice as much as that with Si site adsorption. The calculations on geometry and charge density difference reveal the catalyst nature of the modified Ag for NO 2 adsorption and further clarify theoretically the possible reaction of NO 2 , i.e., dissociation and spillover, occurring on the Ag atom. Besides, a defect-induced preferential etching mechanism of metal (Ag)-assisted chemical etching (MACE) for SiNW was proposed from a new perspective based on the lattice distortion analysis induced by Ag modification. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The nanomechanical interaction mechanism between GO and AOCs was investigated. • The single-molecule bond dissociation energy was evaluated. • Polar and enhanced π interactions introduced by epoxy groups were demonstrated. • Electrostatic interaction introduced by ionized carboxylic groups was also involved. Abstract Graphene oxide (GO) has been extensively applied in environmental and chemical engineering applications, such as wastewater remediation and organic compounds sensing, in which the adsorption of aromatic organic compounds (AOCs) (e.g., dyes, drugs and pesticides) on GO is commonly involved. Understanding the fundamental interaction mechanism of AOCs-GO is critical for these applications and designing advanced functional GO-based nanocomposites. In this work, for the first time, the nanomechanical interaction mechanism between GO and a model AOC molecule is quantitatively characterized using single-molecule force spectroscopy (SMFS) and density functional theory (DFT) simulations. The contributions of major functional groups of GO to the binding affinity and configurations of AOC/GO complex have been investigated. It is found that most binding events in the formation of AOC/GO complex should be attributed to the attraction between the cationic AOC molecule and the regions on GO with epoxy groups, the role of which has been overlooked previously, with an activation Gibbs energy for bond dissociation (Δ G) of −4.61 kcal mol−1. Surprisingly limited occurrence of binding events between the cationic AOC and the regions with ionized carboxylic groups on GO suggests that the role of electrostatic interaction has been overrated traditionally. Our results provide new nanomechanical insights into the interaction mechanism of AOCs-GO with useful implications for developing novel AOC/GO nanocomposites with environmental, biomedical and engineering applications. [ABSTRACT FROM AUTHOR]

Abstract The Nickel/Yttria-stabilized zirconia (Ni/YSZ) Solid Oxide Fuel Cells (SOFCs) anode faces the sulfur-poisoning problem. The criteria of ideal sulfur tolerant anode materials are weak atomic sulfur adsorption, high catalytic activity toward H 2 dissociation and low cost. It is found that H 2 dissociation barriers on Au (111), Au monolayer on WC (0001) (Au ML /WC), Au monolayer doped by Pt atom on WC (0001) (Au ML Pt-d/WC) surface are decreasing from 0.98 to 0.1 eV. The ab initio atomistic thermodynamic data shows that at typical SOFC operating temperatures of 923–1073 K, for any pH 2 S/pH 2 , Au ML Pt-d/WC can be sulfur free clean surface. Therefore, we proposed Au ML Pt-d/WC as ideal sulfur tolerant anode materials. Graphical abstract Image 1 Highlights • A strategy to design an ideal sulfur tolerant anode material is proposed. • H 2 dissociation and sulfur adsorption on fours surfaces are presented. • Au ML Pt-d/WC shows high activity towards H 2 dissociation. • Au ML Pt-d/WC shows high tolerance towards sulfur poisoning. [ABSTRACT FROM AUTHOR]

Abstract Collision-Induced Dissociation and Electron Transfer Dissociation experiments were carried out from various lithium adducts ([M+2Li]2+, [M+3Li]3+) from polycaprolactone diol (pCL), polytetrahydrofurane (pTHF), and one triblock copolymer (pCL-pTHF-pCL). In both cases (pCL and pTHF), CID of triply lithiated precursors led to complex mass spectra compared to corresponding ETD spectra, which remained relatively simple because CID product ions exhibit multiple charge states whereas ETD mainly led to singly charged fragment ions. CID of pCL involves charge-remote rearrangements over the ester groups and intramolecular transesterification reactions, whereas ETD leads to radical and charge induced cleavages leading globally to structurally different product ions but accounting for the same bond cleavages: (CO)O-C and (CO)-O respectively. Both CID and ETD can produce a low amount of undesirable reactions such as consecutive fragmentations especially from 3+ precursors but these fragmentations are absent in ETD from 2+ species. CID of a triply lithiated pTHF involved charge-induced and charge-remote fragmentations. In contrast, under ETD conditions, in the absence of suitable chemical functionality, pTHF did not undergo any backbone fragmentations at all. Nevertheless, proton abstraction by the fluoranthene reagent anion allowed the formation of species that could further be collisionally activated, leading to a depolymerization process from the ends. This strategy combining sequentially ETD and CID led to dramatically simplified product ion spectra. Concerning the supposed triblock copolymer, which was commercially purchased, both CID and ETD led to the same conclusion that at least a part of the copolymer was a diblock rather a triblock. Graphical abstract Image 1 Highlights • Polycaprolactone and polytetrahydrofurane: two polymers that show a completely different behavior under ETD conditions. • For the polyester, ETD leads to backbone fragmentation, whereas for the polyether, ETD leads to proton abstraction. • ETD of polycaprolactone leads to simpler mass spectra than CID especially for the highest charge state (3 + vs 2+). • ETD of polytetrathydrofurane can be combined with CID to produce structural information. • ETD was successfully applied to a triblock copolymer. [ABSTRACT FROM AUTHOR]

Abstract Two non-fullerene electron acceptors (BT-SFIC and BT-FIC) bearing a dithienyl[1,2-b:4,5-b']benzodithiophene core were designed and synthesized. Due to the strong electron-withdrawing ability of fluorine atoms, these two non-fullerene acceptors both show near-infrared absorption around 900 nm, with a narrow bandgap of 1.44 and 1.39 eV for BT-SFIC and BT-FIC, respectively. BT-SFIC and BT-FIC have complementary absorption and matched energy level with PTB7-Th. PSCs based on PTB7-Th donor and these two acceptors both show good charge dissociation and collection, small charge recombination and good active layer morphology. However, BT-FIC bearing much more fluorine have much higher electron mobility. And the PSCs based on PTB7-Th: BT-FIC gives a maximum PCE of 10.10% with a V OC of 0.73 eV, a J SC of 21.28 mA cm−2 and an FF of 65%, which is among in the high-performance polymer organic solar cells based on PTB7-Th. Graphical abstract Image 1 Highlights • Florination can narrow the optical bandgap of non-fullerene acceptors. • BT-SFIC and BT-FIC can increase the PCE to 9.52% and 10.10% respectively. • High-performance PSCs basd on PTB7-Th:non-fullerene system are achived. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Non-covalent interaction between PSS and PLL was characterized by MS n. • Elucidation of the non-covalent binding sites between PSS and substance P. • Supramolecular conjugation for determining surface-accessible basic sites. Abstract Electrospray ionization multistage tandem mass spectrometry (ESI-MS n) was employed to examine the non-covalent complexes between poly(styrene sulfonate) (PSS) and poly- l -lysine (PLL). During single-stage ion activation, the PLL peptide chain mainly underwent backbone cleavages without disruption of the non-covalent interaction which could only be broken via sequential application of electron transfer dissociation (ETD) and collisionally activated dissociation (CAD), indicating strong binding interactions between the two polyelectrolyte chains. Such binding properties make PSS a potential "non-covalent (supramolecular) label" for determining the surface accessibility of basic residues on a peptide or protein. To probe this premise, non-covalent complexes of substance P and PSS were characterized by ESI-MS n using different ion activation methods. Both MS2 and MS3 experiments on the substance P + PSS complex resulted in the formation of b n (on CAD) or c n (on ETD) fragments attached non-covalently to the intact PSS chain. All peptide fragments containing the intact PSS chain included Arg1, Lys3, and Gln5, pointing out that these residues, which are located near the N-terminus, are most likely involved in the non-covalent interaction with PSS. In contrast, Gln6 was excluded from this fragment series, attesting a much weaker interaction with PSS due to lesser accessibility. The strong tendency of PSS to bind peptides non-covalently at sites that can be elucidated by MS n demonstrates a proof-of-concept for the capacity of this approach to unveil higher order structure in proteins. [ABSTRACT FROM AUTHOR]

Graphical abstract Differentation of open-cage fullerene isomers by dissociation of sodiated monomers (using LIFT) and dimers (using CID) reveals multiple interaction motives. Highlights • Ion formation of open-cage fullerenes (OCFs) by DCTB- / pencil lead- MALDI and ESI. • MS2 spectra of the molecular ions of isomeric OCFs are indistinguishable. • MS2 spectra of sodiated and potassiated OCFs differentiate between isomers. • Metal coordination to the heteroatoms at the cage orifice causes differentiation. • Relative sodium ion affinities are obtained by the kinetic method. Abstract Isomeric open-cage fullerenes (OCFs) are studied by MALDI-LIFT. The two types of isomers feature different connectivities of the heteroatoms at the rim of the orifice to the fullerene cage. The molecular ions (radical cations, M+.) are generated by electron transfer MALDI, using DCTB as the matrix. The resulting LIFT spectra are indistinguishable. The alternative use of pencil lead is found inferior as a matrix but proves an exceptionally facile method of creating sodium and potassium adducts. The fragmentation of these metallated OCFs reveals different fragmentation pathways allowing the differentiation of the OCF isomers. This is evidently caused by the different interactions of the metal cation with the heteroatoms at the rim of the orifice. Additionally, the influence of the functionalization and isomer structure on the sodium ion affinity (SIA) is analysed by the kinetic method investigating the dissociations of sodium-bound hetero-dimers in electrospray ionization/ collision-induced dissociation (ESI-CID) experiments. [ABSTRACT FROM AUTHOR]

Highlights • Fragmentations of [b 5 – H]+ ions containing an α-methyltryptophan residue are studied. • All the [b 5 – H]+ radical cations have the radical at the N-terminal residue. • The captodative structure prevents head-to-tail macrocyclization of the [b 5 – H]+ ions. • Non-identical CID spectra are observed among the [b 5 – H]+ ions. Graphical abstract Abstract Collision-induced dissociation (CID) of hexapeptide radical cations consisting of four alanine residues, one α-methyltryptophan and a glycine residue at the C-terminus results predominantly in bond cleavages around the sterically crowded α-methyltryptophan residue, but all generated [b 5 – H]+ ions in moderate abundance. Unlike in the dissociations of the [b 5 – H]+ ions of the analogous [A 4 W oxa ]+ ions, where regardless of the initial location of the unmodified tryptophan residue the CID spectra were identical, the α-methyltryptophan-containing [b 5 – H]+ ions all gave different CID spectra, indicating that there was no evidence of isomerization. Losses of imine-amides and the neutral of mass 141 Da provide evidence that the radical centre is located at the α-carbon of the N-terminal residue. This N-terminal captodative structure inhibits macrocyclization, thereby preventing isomerization and leading to different dissociation products. Density functional theory (DFT) calculations on [AAAW α-Me A oxa ]+, the ion that gave the largest variety of dissociation products, established that the captodative structure at the N-terminus is at the global minimum, 27 kJ mol−1 lower in energy than the π-radical cation. Calculations also showed that losses of the dialanine radical from the captodative structure and the side chain of α-methyltryptophan from the π-radical are the two lowest-energy dissociation pathways, consistent with the onsets observed in the experimental energy-resolved CID curves. The overall conclusion is that [b 5 – H]+ ions that contain an unmodified tryptophan have the radical centre located on the α-carbon of the tryptophan residue, and this leaves the N-terminal amino group free to initiate macrocyclization leading to isomerization prior to dissociation. When the α-carbon is blocked by a methyl group, as in α-methyltryptophan, then the captodative structure at the N-terminal residue is favoured and this prevents macrocyclization and isomerization. [ABSTRACT FROM AUTHOR]