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Solvent effects have always been a non-negligible factor for aqueous catalytic reactions, though few studies have been devoted towards the molecular understanding and impact of solvent effects on catalysis. In this work, we investigated ethanol dehydrogenation and C-C bond cleavage over Ir(100) in an aqueous solution using density functional theory calculations with both the implicit and explicit solvent models and transition state theory-based kinetics simulations. The results show that solvent polarization assists the α- and β-dehydrogenation of ethanol on Ir(100) in the aqueous solution and hydrogen bonding also assists the ethanol β-dehydrogenation and C-C bond cleavage in CH

Activity, cost, and durability are the trinity of catalysis research for the electrochemical oxygen reduction reaction (ORR). While studies towards increasing activity and reducing cost of ORR catalysts have been carried out extensively, much effort is needed in durability investigation of highly active ORR catalysts. In this work, we examined the stability of a trimetallic PtPdCu catalyst that has demonstrated high activity and incredible durability during ORR using density functional theory (DFT) based computations. Specifically, we studied the processes of dissolution/deposition and diffusion between the surface and inner layer of Cu species of Pt

Fluoride is abundantly used in dental healthcare and pharmaceutical industry, it is harmful if it is found over certain concentration in drinking water and in soil. It is therefore essential to develop portable tools to detect fluoride. Fluorescence sensing can be used as a simple and sensitive tool to detect fluoride anions. Fluorescent detection of anions is less widely studied compared to metal cation and neutral organic small molecules. As such, the interactions between F- anion and two silyl-fluorescein based sensors were studied here using density functional theory (DFT). Chemical shifts and electronic properties of the free sensor and the sensors in the presence of different number of fluoride anions were obtained and compared. The DFT results show that strong binding responses can be found as a function of fluoride concentration. The change in UV-Vis spectra due to the presence of fluoride indicates they are promising sensor candidates for fluoride detection and further studies on fluorescence response of these sensors are worthwhile.

Fluorescence sensors are an important analytical tool for monitoring biologically relevant analytes. For instance, an anthracene based sensor was designed and characterized for the detection of Zn2+ in our previous studies. However, the selective detection of such a sensor in the presence of other metal cations is a critically important factor for its practical application. In this work, we employed density functional theory calculations to study the selectivity of this anthracene sensor in the detection of Zn2+ in the presence of Ca2+, Mg2+, Cu2+, and Hg2+. DFT results indicate that the selectivity of the sensor on Zn2+ detection over the cations Ca2+, Mg2+, and Hg2+ due to the binding selectivity as Zn2+ binds favorably to the sensor while Ca2+, Mg2+, and Hg2+ are no binding. Although Cu2+ binds to the sensor stronger than Zn2+, the chelated sensor by Cu2+ reduces the UV-Vis absorption at the free sensor wavelength by 10 times and the fluorescence pathway is also enhanced by the chelation, thus resulting response selectivity of Zn2+ over Cu2+ . Therefore, the present DFT study shows that the sensor selectivity on Zn 2+ detection in the presence of Ca2+, Mg2+, Cu2+, and Hg2+ is due to a combination of binding selectivity and response selectivity.

In this work, the proton transfer and photophysical properties of 2,4-dihydroxybenzoic acid and its chlorinated and brominated derivatives were studied using Density Functional Theory (DFT) to understand the proton transfer mechanism of these molecules as matrices in matrix-assisted laser desorption-ionization (MALDI). Structures, IR, UV-Vis, and fluorescence spectra were obtained together with the energies of frontier orbitals from DFT and time-dependent DFT calculations. In addition, the proton affinity (PA) and gas phase acidity (GPA) of the molecules were determined to understand the heavy atom substitution effect. Upon substitution of Cl and Br, the UV-Vis absorption at ~330 nm increases with heavy atom substitutions. While no apparent change in the OH bond strength at the ground state, it is substantially weakened upon electronic excitation at both the first singlet and triplet excited states under heavy atom substitution. These results demonstrate that both the UV-Vis absorption and intersystem crossing play important roles in facilitating proton transfer in heavy atom substitution of 2,4-dihydroxybenzoic acid.

This work reports the synthesis and spectral properties of meso-styryl substituted triphenylamine-porphyrin derivatives, mP-BLP, mPPC-BLP and their metal coordinated complexes. The photophysical processes were analyzed and related to the meso-groups and centre metal ions. The meso styryl substituent in mP-BLP and its complexes are able to extend the conjugation of porphyrin macrocycle to the styryl motif, increase light harvesting ability and accelerate intersystem crossing (ISC) process. A large dihedral angle between the meso-styryl group and porphyrin macrocycle would prohibit the delocalization of electrons between the two motifs and induce the occurrence of solvation decay process. Increasing the electron-withdrawing ability of meso-substituent via additional pyrimidine group could promote the photoinduced intramolecular electron transfer (PIET) process for mPPC-BLP. Moreover, the coordination of metal ions would significantly accelerate the photophysical processes of both mP-BLP and mPPC-BLP. Specially, the Mg[Formula: see text] is helpful to the ISC process whereas Zn[Formula: see text] is adverse to the ISC process, while Cu[Formula: see text] would boost the non-radiation process. Furthermore, Zn[Formula: see text] is able to promote the PIET process of mPPC-BLP, exhibiting the highest charge-separated tendency among these porphyrins. mPPC-ZnBLP-based dye-sensitized solar cell (DSSC) devices show the highest power conversion efficiency (PCE). The photovoltaic performance of DSSC devices reveals the significancy of the photoinduced charge-separated tendency for the design of porphyrin sensitizers.

An in situ analysis for DNA content detection without DNA separation in samples, which circumvents the influence of the chromophore, fluorophore and other interferents in vivo, based on long-persistent luminescence of organic doped-crystals.

p-CuO/n-ZnO heterostructures with a sea urchin-like hierarchical structure exhibit outstanding photodegradation abilities toward MO under UV light.

Fluorescein derivatives play an important role in the field of biological and fluorescent sensors. To tune the spectroscopic properties many attempts have been made including extending conjugation, substituting the central carbon by nitrogen or introducing electron withdrawing groups and replace the oxygen bridge atom by other elements such as N, C, S, Se, and Te. In this paper we report density functional theory (DFT) and time-dependent DFT (TDDFT) studies of silicon analog of fluorescein derivatives with oxygen replaced by Si, C, and Ge. Among the different silicon analogs, the most conjugated molecule 4 showed red shift in absorption wavelength (495 nm). The OH position of molecule 2 has a significant effect on the spectral properties of the silicon analogs of the fluorescein. Since aggregation is very common in most of the fluorescein and it is interesting to study the effect of aggregation, we also studied dimerization of molecule 1 in silicon analog of fluorescein derivative and the results show that two absorption bands are formed with red shift compared to monomer.

Perylenetetracarboxylic dianhydride (PTCDA) and perylene diimide (PDI) have been widely used as photosensitizers in many applications. Photophysical properties are key factors for efficient application of these materials. Furthermore, many functionalization of these materials come from the motivation of tuning their solubility, which may affect the photophysical properties of the resulting materials. As such, it is imperative to study the electronic and photophysical properties of PTCDA and PDI derivatives. In this work, we report DFT studies of 36 molecules consisting 18 PTCDA molecules and 18 PDI derivatives with the same set of functionalization at the bay positions. DFT results show that the impact of functionalization is similar in HOMO and LUMO energies to both PTCDA and PDI derivatives. Analysis of electronic results indicates extension of electron delocalization along the bay positions 1 and 7 is important in altering absorption wavelengths or HOMO-LUMO gaps

Tuning the HOMO and LUMO energy strategically of triphenylamine derivatives plays an important role towards understanding and design of high performance organic photovoltaics. To improve on the charge separation and electron transfer properties, twenty one D-pi-A organic dyes with nitrostyryl triphenylamine-based structures (NTPAs) were designed and computationally studied, in which triphenylamine, carbazole, or indoline structures were used as donor and NO2 group as acceptor. The LUMOs of these dyes are more localized at the nitrostyryl moiety with almost the same energy and the HOMOs, which are orthogonal to the LUMOs, can be conveniently tuned by changing the donor structure and using different functional groups substituted on the donor. Compared with triphenylamine molecules, carbazole molecules decrease the HOMO energy of NTPA, whereas cis N-phenylindoline structure increase the HOMO energy. In addition, the exciton sizes generated by these dyes are also tuned in a range of 7.0-12.7 A. These results show that introduction of dimethylamino group on the triphenylamine moiety greatly increases the HOMO energy and prolongs the maximum absorption wavelength as well as increases the exciton size, indicating that NTPA dyes containing strong electron donating dimethylamino group on the donor part are promising candidates as sensitizers in the dye-sensitized solar cell applications. The results of the structural and spectral properties show good correlation with the experimental results, which confirms that the DFT method employed in this work is an effective way to design organic small molecule based sensitizers.

The interaction energies of five pairs of interactions: CH3OH-CH3OH, CH3OH-CO2, CO2-CO2, CH3OH-CH3CH2OH, and CH3CH2OH-CH3CH2OH were obtained using MP2, B3LYP, and B3LYP-D3 methods. Activity coefficients of CH3CH2OH-CH3OH and CH3OH-CO2 systems were calculated using the UNIQUAC equation and the phase diagrams of these binary systems were constructed based on the Raoult's law. The B3LYP-D3 methanol/ethanol isothermal phase diagram at 298K is in good agreement with the experimental data and the agreement is slightly better than the MP2 result and much better than the B3LYP result. Thus, the B3LYP-D3 method is promising to obtaining activity coefficients and illustrates the promise of molecular simulation of phase diagram of binary systems. A carbon dioxide/ethanol isothermal phase diagram at 230K was constructed. The current results showed that CO2 and CH3OH are hardly mixed under the simulation conditions.

The ability to produce cheap and efficient catalysts for oxygen reduction is essential for cost reduction in fuel cells. This work reports the density functional theory (DFT) results of the investigation of ~1 nm trimetallic nanocatalysts of 26 atoms with a composition of Pt8V4Fe14. The relative stability of ~50 Pt8V4Fe14 nanoparticles (NPs) were analyzed to conclude that the most stable NPs had vanadium atoms located at the center of the NP with scattered platinum atoms attached to them from the outside. Adsorption of O2 on the most stable nanocatalyst was also analyzed at 14 various adsorption sites; it was determined that oxygen preferred to bond to vanadium and iron atoms located at the surface of the NP. Compared to the small sub-nanometer PtVFe clusters of the same composition, the O2 adsorption strength is slightly decreased on the ~1nm PtVFe NPs. These findings provided important insights into the effectiveness of PtVFe nanocatalysts towards oxygen reduction.

The reaction mechanisms of hydrogen and ethyl acetate formation from ethanol dehydrogenation in the presence of a single Cu atom, Cu2, and Cu13 were studied using density functional theory (DFT) calculations. The rate-limiting step was found to be dependent on the Cu cluster size. The acetaldehyde prefers desorbing from Cu clusters due to its low adsorption energy on Cu, rather than dehydrogenating to acetyl. The vibrational frequencies of the system and temperature also affect the reaction mechanism. The HOMO-LUMO gap of the Cu13 cluster rarely altered by adsorption species while that of a single Cu and Cu2 changed substantially when reactive species adsorbed on a single Cu atom or Cu2 cluster. This work also illustrates that the reaction mechanisms are sensitive to the size of Cu clusters.

Economically advantageous Cu-based catalysts have been widely used for a great number of reactions related to ethanol. However, serious obstacles still remain, such as the high reaction energy barrier and low selectivity for the first step of the dehydrogenation of ethanol. In this study, O-H and α-C-H bond cleavages in ethanol on a Cu3X(111) surface (X= Zr, In, Ag, Au) were carried out using DFT to explore the effect of alloying on the selective and effective dehydrogenation of ethanol. Cu3Zr(111) was found to have superior catalytic performances for dehydrogenation with significantly low reaction barriers for both O-H bond cleavage (0.13 eV) and α-C-H bond cleavage (0.73 eV), which are much lower than the results on Cu(111). Thus this work indicates that alloying Zr can selectively break the O-H bond of ethanol, which cannot be accomplished using Pt, Pd, or Cu catalysts. Meanwhile, through PDOS analysis, Mülliken charge analysis, and d-band center analysis, there are two key fac-tors that contribute to the great improvements on the dehydrogenation catalytic activities of Cu3X(111). Firstly, the specific inherent properties of the second alloyed metal X, including the d-band center, are crucial to the adsorption and activation of ethanol on surfaces. Sec-ondly, the electronic distribution on the surfaces resulting from the difference of electronega-tivity between the metals Cu and X is associated with the dehydrogenation reaction barrier. More electron density around the Cu atoms on these surfaces is more beneficial for dehydro-genation reactions, especially when H atoms were adsorbed stably on the Cu sites.

We performed DFT and TDDFT calculations to determine interactions between silver atom and model cell membrane of human hepatocellular carcinoma (HepG2) cells or human liver cells. Specifically, we chose the two major lipid constituents of HepG2 cells which are 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyI-sn-glycero-3-phosphoethanolamine (POPE) to represent HepG2 cell membrane. Silver atom (Ag0) and silver ion (Ag+) are used as silver models to represent possible point-to-point interaction and the effect of silver ion (Ag+) leakage. The results show that exposure of POPC to silver ion (Ag+) at a high concentration can cause structural conformational changes from being originally bent to straight conformation. In addition, the interaction between silver ion (Ag+) and the lipids can cause significant amount of charge transfer that ranges from 0.14 to 0.16 for POPC and 0.12 to 0.14 for POPE. Moreover, though silver ion (Ag+) binds three to five times stronger to the lipids than silver atom (Ag0), both interactions are Van der Waals interaction. Finally, the presence of silver atom (Ag0) in the lipids can be detected using UV-Vis spectrophotometer by occurrence of a red shift which is seen at 376 nm and 372 nm for POPC and POPE respectively. However, detecting silver ion (Ag+) using this method is not feasible as no apparent shifts are shown.

Silver clusters consisting of 2-20 atoms were investigated using spin polarized density functional theory (DFT) calculations with PW91 functional and a plane wave basis set. Linear clusters were found to undergo Peierls bond distortion. The calculated excitation energies for planar Ag clusters are smaller than those predicted from the Plasmon Hybridization method. New global minima were found for clusters of 9, 10, 13–16, 19, 20 atoms. The most stable even numbered clusters are singlet and odd-numbered clusters are doublet. No unexpected magnetisms are obtained. The Sutton-Chen potential was also used to study the relative stability of selected clusters; however, the results showed that it overestimates the binding energies of Ag clusters. In this work, we re-parameterized the Sutton-Chen potential using the DFT results of the selected clusters.

The effects of 10nm citrate-coated silver nanoparticles (AgNPs) to hepatocellular carcinoma (HepG2) cells were investigated to elucidate toxicity mechanisms. Cell viability, oxidative stress, protein expression, and cell morphology were assessed to determine the toxicity of AgNPs at various dose levels. 10nm citrate-coated AgNPs were found to be toxic to HepG2 cells at a dose of > 1.0 ppm and their LD50 was determined to be 3.0 ppm. Oxidative stress levels in the cells were found to increase with the dose of AgNPs and HepG2 cells can withstand high level of reactive oxygen species before cell death. The expressions of heat shock proteins and tubulin proteins were most significantly affected by the presence of AgNPs of 5.0 ppm. The AgNPs were observed to penetrate the cells treated with a dose of 5.0 ppm by transmission electron microscopy. Furthermore, the agglomeration of AgNPs in HepG2 cells was found and generated osmotic pressure that is likely another pathway to be responsible for the toxicity of AgNPs.

The structural and electronic properties of small Cu clusters were studied using density functional theory (DFT) calculations. The Cu clusters consist of up to fifty-five atoms with linear, planar, and three-dimensional structures. Five functionals, the Perdew-Wang 91 form of the generalized gradient approximation (PW91), Perdew-Burk-Ernzerhof functional (PBE), and three Minnesota functionals (M05, M06, and M06-L) were used. The dispersion correction in the format of DFT-D3 was also taken into account to the results of the PBE. The binding energy, average bond length, magnetic moment, and the HOMO-LUMO gap of each cluster were obtained and compared. DFT results for PBE and PW91 are very similar and agree with experimental data well. DFT-D3 corrections have no effect on the stable sequence. The copper clusters are more stable in the planar structure for clusters with n≤6, which agrees with other theoretical studies. In the case of bigger clusters, different DFT methods predicted different most stable structures. As cluster size increases, there was a monotonic decrease in magnetic moment for the odd number of clusters. As the linear cluster size increases, the bond distances between the atoms begin to alternate.

To accurately predict the electron acceptability of cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs), we evaluated the performance of six functionals, B3LYP, CAM-B3LYP, HSEH1PBE, PBE, TPSS, and HCTH, using eight CP-PAHs. The results show that B3LYP is the best to obtain the energy of the highest occupied molecular orbital (HOMO), the energy of the lowest unoccupied molecular orbital (LUMO), and the HOMO-LUMO energy gap of CP-PAHs with a mean absolute error (MAE) of 0.14 eV. The current study also demonstrates that calculations must be carried out for the anion of the corresponding CP-PAH in order to predict LUMO energy of an electron acceptor. Time-dependent CAM-B3LYP with the B3LYP optimized geometry predicts the absorption spectra of CP-PAHs most accurately with a MAE of 29 nm. The results from B3LYP and time-dependent CAM-B3LYP calculations coupled with the new practice in calculating LUMO energy presented in this work show that six of the eight CP-PAHs can accept electrons from the donor material poly(3-hexylthiophene)(P3HT), thus indicating they can be used as electron acceptors of P3HT. Moreover, three pairs of CP-PAHs were identified for their use as highly efficient organic solar cell materials through construction of a P3HT-acceptor1-acceptor2 architecture.

Substituting the middle thiophene ring in the MK-3 dye with a silole ring, the B3LYP calculations have shown that the absorption wavelengths of the new dyes, Me2Si-MK-3 and F2Si-MK-3, are bathochromically shifted by about 100 nm from 436 nm (MK-3). This large red shift is due mainly to a higher HOMO energy level in the Me2Si-MK-3 dye (-5.19 eV) with respect to the MK-3 dye (-5.30 eV) but to a lower LUMO energy level in the F2Si-MK-3 dye (-3.41 eV) compared to the MK-3 dye (-3.09 eV). These results suggest a wide range of alternatives in altering absorption wavelengths in the design of organic dyes for solar cells. Additionally, the calculations have shown the absorption intensities of the proposed new dyes are higher than that of the MK-3 dye. A pragmatic technique is developed to accurately describe the photon excitation of dye molecules by considering higher energy molecular orbital involvement. All three set of data, the HOMO-LUMO gap, the TD-B3LYP, and the calibrated TD-B3LYP, show the consistent red shifts for the new dye molecules with respect to the MK-3 dye.

The high transition dipole strength of the azide asymmetric stretch makes aryl azides good candidates as vibrational probes (VPs). However, aryl azides have complex absorption profiles due to Fermi resonances (FRs). Understanding the origin and the vibrational modes involved in FRs of aryl azides is critically important towards developing them as VPs for studies of protein structures and structural changes in response to the surroundings. As such, we studied vibrational couplings in 4-azidotolune and 4-azido-N-phenylmaleimide in two solvents, N,N-dimentylacetamide and tetrahydrofuran, to explore the origin and the effects of intramolecular group and solvent on the FRs of aryl azides using density functional theory (DFT) calculations with B3LYP functional and seven basis sets, 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p), and 6-311++G(df,pd). Two combination bands consisting of the azide symmetric stretch and another mode form strong FRs with the azide asymmetric stretch for both molecules. The FR profile has been altered by replacing the methyl group with maleimide. Solvent changes the relative peak position and intensity more significantly for 4-azido-N-phenylmaleimide, which makes it a more sensitive VP. Furthermore, the DFT results from different basis sets can be used to predict more reliable vibrational spectra.

Rockburst is one of the common geological hazards. It is of great significance to study the evaluation indexes and classification criteria of the bursting liability of hard rocks, which is important for the prediction and prevention of rockbursts in hard rocks. In this study, the evaluation of the rockburst tendency was conducted using two indoor non-energy indexes, namely the brittleness indicator (B2) and the strength decrease rate (SDR). The measuring methods of B and SDR as well as the classification criteria were analyzed. Firstly, the most rational calculation formulas for B and SDR were selected based on previous studies. The B2 equaled to the ratio between the difference and sum of uniaxial compressive strength and Brazilian tensile strength of rocks. The SDR was the average stress decrease rate of the post-peak stage in uniaxial compression tests and equaled the uniaxial compressive strength dividing the duration time of post-peak rock failure in uniaxial compression tests. Secondly, the uniaxial compression tests of different rock types were designed and carried out, and the change trend of B and SDR with the increase of loading rate in uniaxial compression tests were studied in detail. The results showed that after the loading rate was greater than 5 mm/min or 100 kN/min, the B value was affected, limited by the loading rate, while the SDR value was more affected by the strain rate. The displacement control, with a loading rate of 0.1–0.7 mm/min, was recommended for the measurement of B and SDR. The classification criteria of B2 and SDR were proposed, and four grades of rockburst tendency were defined for SDR and B2 according to the test results.

Organic long-persistent luminescent materials can be easily quenched in aqueous solutions or air, which limits their wide applications. Here we report novel doped organic crystals to overcome this challenge. The stable LPL performance of this crystalline material is visible for over 8 s and can be maintained for at least three months even in aqueous solution or in air.

Steam methane reforming (SMR) accounts for 76% of the dedicated hydrogen worldwide, and will remain the process of choice for large-scale hydrogen production for a long time. Durable and efficient catalysts are always desirable for this high-temperature-preferred process. Here, we report the design of a partially oxidized Ni/CeO2 catalyst with enhanced activity and stability for SMR. Density functional theory calculations were performed to identify the influence of Ni oxidation state on the binding energy of the Ni cluster and the energy barrier of the rate-limiting step. The best catalyst predicted was subsequently synthesized and characterized, which showed superior performance, as expected. During the 1500 min performance test at 700 °C, stable SMR operations were well maintained on NiO/CeO2-364 °C with an H2 production rate of 5.0 mmol min−1 and an H2/CO ratio of 4.3.

Effective C–C bond cleavage is a critical concern in the applications of ethanol technologies. The lack of catalytic efficiency toward complete ethanol oxidation reaction (EOR) has hindered the dev...

Steam reforming is a main industrial process for hydrogen production. In particular, with the carbon chain increasing to n-butane, a main component in liquefied petroleum gas (LPG) and shale oil gas, chemically different C-C bonds ((C-C)α,β and (C-C)β,β') will be involved in cleavages. In addition, understanding the role of catalysis in these pathways is critical toward the advancement in technology, yet is largely lacking. As such, we have performed density functional theory (DFT) calculations to study the two possible C-C cleavage pathways of n-butane on Ni(111), i.e., the (C-C)α,β cleavage from the n-butane deep dehydrogenation product of 1-butyne, and the (C-C)β,β' cleavage from 2-butyne. The results indicate that these two different pathways have distinct dehydrogenations to butyne, and that Ni is suitable for the deep dehydrogenation. The C-C cleavage in both pathways serves as the rate-determining step with a higher energy barrier than that for the preceding C-H bond cleavage. In addition, the 1-butyne pathway was found to be more favorable than that of 2-butyne in thermodynamics and kinetics. Our results provide insights into the alkane dehydrogenation and cracking of long-chain hydrocarbons on Ni-based catalysts.