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This study aimed to address the issue of the low solubility in the model drug probenecid (PRO) and its impact on bioavailability. Two salts of probenecid (PRO), 4-aminopyridine (4AMP), and 4-dimethylaminopyridine (4DAP) were synthesized and characterized by PXRD, DSC, TGA, FTIR, and SEM. The crystal structures of the two salts were determined by SCXRD, demonstrating that the two salts exhibited different hydrogen bond networks, stacking modes, and molecular conformations of PRO. The solubility of PRO and its salts in a phosphate-buffered solution (pH = 6.8) at 37 °C was determined, the results showed that the solubility of PRO salts increased to 142.83 and 7.75 times of the raw drug, respectively. Accelerated stability experiments (40 °C, 75% RH) showed that the salts had good phase stability over 8 weeks. Subsequently, Hirshfeld surface (HS), atom in molecules (AIM), and independent gradient model (IGM) were employed for the assessment of intermolecular interactions. The analyses of salt-forming sites and principles were conducted using molecular electrostatic potential surfaces (MEPs) and pKa rules. The lattice energy (EL) and hydration-free energy (EHF) of PRO and its salts were calculated, and the relationships between these parameters and melting points and the solubility changes were analyzed. [ABSTRACT FROM AUTHOR]

This study undertakes a detailed theoretical investigation into the iso‐pentanol radical isomerization and decomposition kinetics and the mechanism development of the iso‐pentanol oxidation. The CCSD(T)/CBS//M08‐HX/6‐311+G(2df,2p) method was adopted to calculate the reaction potential energy surface. The reaction rate coefficients were calculated by variational transition state theory (VTST) with multistructural torsional (MS‐T) partition function and small curvature tunneling (SCT) correction. Moreover, the pressure‐dependent rate coefficients were determined using the system‐specific quantum Rice‐Ramsperger‐Kassel theory (SS‐QRRK). The variational and tunneling effects were discussed, and the dominant reaction channels were identified. It reveals that the isomerization reactions play a significant role at low temperatures, while the decomposition reactions dominate the high‐temperature regime. Notably, the quantitative rate expressions for iso‐pentanol radical decomposition reactions were also obtained. Furthermore, a new kinetic model incorporating the calculated rate coefficients was constructed, exhibiting satisfactory prediction performance on ignition delay times and improved predictive accuracy of species mole fractions. This work provides accurate rate data of isomerization and decomposition kinetics and contributes to a more comprehensive understanding of the iso‐pentanol oxidation mechanism. [ABSTRACT FROM AUTHOR]

In this work, a novel organic–inorganic hybrid-based Fe3O4 nanoparticles was developed to remove metal ion and organic contaminants from aqueous solutions with the most serious environmental problems. In order to remove pollutants including Mercury(II) chloride (HgCl2), Alpha lipoid acid (ALA), Methyl orange (MO), Fe3O4@SiO2@APTS functionalized oxidized chitosan (Fe3O4@SiO2@APTS-OCS) was synthesized, and these composites were characterized by FT-IR, XRD, FE-SEM, VSM and BET techniques. In addition, a simple and fast multi-stage heating method was provided to produce mercury chloride under a closed laboratory system. The purification of mercury (II) chloride showed > 99.99%. Then, Hg2+, ALA and MO removal can be carried out by Fe3O4@SiO2@APTS-OCS with the optimum equilibrium conditions. The adsorbent catalyst dosage Fe3O4@SiO2@APTS-OCS was obtained 0.35 g/L. The initial concentration parameter for Hg2+, ALA and MO removal was calculated 30 mg/L. In addition, optimum initial pH value for Hg2+, ALA and MO removal was obtained 11, 1 and 1, respectively. After six consecutive cycles, Hg2+, ALA and MO adsorption by nano-composite were decreased from 89.0 to 78.0%, 85.0 to 76.0%, and 92 to 79, respectively. The quantum and molecular dynamic calculations were studied to obtain optimization of structures and removal of Hg2+, ALA and MO by Fe3O4@SiO2@APTS-OCS in Materials Studio 2017 software. Based on the negative adsorption energy (ΔEads) of Hg2+, ALA and MO on nanoparticles, the simulation system was the stability and placed spontaneously in parallel above Fe3O4@SiO2@APTS-OCS by forming hydrogen bonds and van der Waals. [ABSTRACT FROM AUTHOR]

Magnetite-functionalized biochar (MBC) is a promising engineered material for remediation of antibiotic-contaminated fields. However, sorption mechanisms of ionizable organic compounds such as sulfonamide antibiotics (SAs) on MBC are still unclear. This study employed four representative SAs including sulfamethazine (SMT), sulfamerazine (SMR), sulfadiazine (SDZ), and sulfamethoxazole (SMX), to compare the difference in sorption on MBC. Results showed that the sorption capacities and affinities of the four SAs varied with their substituents, hydrophobic properties, and dissociation constants (pKa). Synergistic effect during co-pyrolysis with Fe3+ enhanced the sorption performance of MBC towards SAs compared to original BC. Spectral methods confirmed structural changes of MBC such as the variance in oxygen-containing groups and defective/graphitized phases. Results of modeling pH-dependent sorption revealed that H-bonding or π-bond assisted H-bonding determined the sorption affinities and capacities of SAs. In particular, the SAs with lower pKa were thermodynamically favorable to form H-bonding with MBC via proton exchange with water molecules. Quantum calculation results quantified the contributions of H-bonding strengths and found that the energies of H-bonding were correlated with affinities of SAs. Moreover, contributions of oxygen-containing groups instead of minerals dominated the H-bonding energies. Mechanistic insights from this study can be valuable in exploring engineered BC composites for practical application in field remediation. Highlights: Sorption capacity and affinity of four SAs varied with substituents, Kow, and pKa Copyrolyzed carbon matrix and Fe3+ synergistically enhanced SA sorption performance H-bonding or π-bond assisted H-bonding determined SA sorption affinity and capacity Contributions of O-containing groups instead of minerals dominated H-bonding energy [ABSTRACT FROM AUTHOR]

Context: Benzene and other aromatic groups, as planar groups with π electrons cloud, tend to form stacking interactions which have an important role in various chemical and biological processes. In order to have a better insight in the nature of these interactions, we have performed a fractal analysis on patterns of electron density and electrostatic potential for two benzenes in stacking interaction. The calculated fractal dimension follows the trend of the calculated interaction energy for the interplanar distances of 4.0 to 6.0 Å, which partially coincides with the strongest attractive stacking interactions. The fractal dimension vs. energy dependences were fitted with the logistic curve, and the fitting coefficient was 0.96 up to 1.00. Methods: For the benzene stacking interaction energy, with a range of conformations and distances between two benzenes, DFT calculations at the B3LYP+D3/aug-cc-pVDZ level were performed with the TURBOMOLE software. The fractal analysis for electron density and electrostatic potential has been done by python scripting. [ABSTRACT FROM AUTHOR]

One of the main ways that metallic materials lose their useful qualities is through dissolution; hence corrosion management is crucial for protecting the metal. In this paper, new thienylpicolinamidine derivatives, namely; 5-[5-(3,4,5-trimethoxyphenyl)thiophen-2-yl]picolinamidine hydrochloride salt (MA-1517), 5-[5-(4-methoxyphenyl)thiophen-2-yl]picolinamidine hydrochloride salt (MA-1543), and 5-[5-(3-chloro-4-methoxyphenyl)thiophen-2-yl]picolinamidine hydrochloride salt (MA-1516), were utilized as corrosion inhibitors for C-steel in 1.0 mol L−1 HCl. Their corrosion inhibiting impact can be demonstrated by experimental methods as chemical approaches (mass reduction) and electrochemical techniques (electrochemical impedance examination, EIS, and Tafel polarization). These methods gave inhibition efficiencies (IE%) of 97.41 %, 93.84 % and 91 % for MA-1517, MA-1543 and MA-1516, respectively at 323 K and concentration 17 × 10−6 mol. L−1. The rise in IE% with rising inhibitor concentration and temperature illustrate that the adsorption of these studied compounds is chemisorption, declared via the Langmuir isotherm. Thermodynamic and kinetic parameters are computed and discussed. Polarization research exhibits that these thienylpicolinamidines act as mixed type inhibitors. The outer part morphology of C-steel surfaces and the adsorption of these compounds on C-steel outer part can be checked by atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX). The mechanism of inhibition can be backed by quantum chemical examination and Monte Carlo model. A theoretical estimate proves that the use of cationic derivatives of pyridine is good impediments versus corroding of C-steel in HCl medium. [ABSTRACT FROM AUTHOR]

Aim: To evaluate using bioinformatics tools the interactions between plant protease inhibitors (PIs) and SARS-CoV-2 Mpro. Materials & methods: This was an in silico study based on molecular docking, molecular dynamics simulations and quantum biochemistry calculations. Results: The plant PIs pineapple cystatin and sesame cystatin interacted allosterically with Mpro, leading to significant structural alterations. These conformational changes lead to a reduction of the area and volume of the Mpro proteolytic site, likely affecting the protease activity and, consequently, reducing viral replication. Conclusion: This work highlights the therapeutic potential of plant PIs as candidates for future in vivo investigations into new therapeutics for COVID-19. [ABSTRACT FROM AUTHOR]

The quantum transport properties of ZnO devices with five different bulk configurations are investigated with numerical methods. The calculation results reveal that the transport property at a higher energy range can be tuned by changing the length of central scattering. By substituting some Zn atoms with Cu atoms, it is found that the doped Cu atoms have an obvious effect on the quantum properties at the entire energy range investigated, and could result in different transmission. The properties of ZnO devices are also influenced by the doping positions of Cu atoms. The tuning mechanism relies on the shifting of carrier distributions in the scattering center of the device. [ABSTRACT FROM AUTHOR]

Hydrolyzable chlorine is a well-known residue issued from the synthesis of epoxy resin, which may impart specific dielectric properties. In this work, the changes in distributed energy levels and charge trap depths of the molecule containing such defects are investigated using quantum chemical calculations. These changes are analyzed from the microscopic perspectives of electron energy structure and electron cloud offset. The charge transport and charge injection behavior in epoxy materials before and after the hydrolysis are predicted using the analysis results. The volume resistivities and space charges of epoxy materials with three different hydrolyzable chlorine contents are tested at different hygrothermal aging times, which are consistent with the previous predictions. These results are used to explain the ac breakdown strength of these epoxy materials at different hygrothermal aging times. It is indicated that the structural changes (electronegativity and atomic position changes) of the molecule containing hydrolyzable chlorine before and after hydrolysis change the spatial distribution of electron cloud density between and on valence bonds, and in turn, change the energy levels of different molecular segments. This results in a large increase in the overall electron trap depth and a small decrease in the overall hole trap depth of the molecule after hydrolysis. [ABSTRACT FROM AUTHOR]

The Aeluropus lagopoides (ALG) was used as an eco-friendly green inhibitor to prevent carbon steel (C.S) corrosion in one molar HCl. Based on the GC-MS results, 36 compounds are identified in the studied extract. The corrosion inhibition efficiency (%IE) of ALG for C.S in one molar HCl has been calculated by utilized chemical technique [weight loss (WL)] and electrochemical tests [potentiodynamic polarization (PP) method and AC impedance spectroscopy (EIS)]. The extract acted as a mixed-type metal corrosion inhibitor according to the potentiodynamic polarization results. The adsorption of ALG on C.S followed the Langmuir adsorption isotherm. The inhibition efficiency increased by lowering the temperature. EIS revealed that the ALG extract formed a thin protective film on the C.S surface. The adsorption of ALG on C.S surface was confirmed via scanning electron microscope (SEM), Energy Dispersion Spectroscopy X-ray spectra (EDX), and Atomic force Microscopy (AFM). Moreover, the biological effect of the ALG was measured and indicate ALG has a kindly impact in preventing multiplying bacteria. Monte Carlo simulations are also executed to simulate the adsorption of ALG extract on iron surface. The theoretical results were in a good agreement with experimental measurements. [ABSTRACT FROM AUTHOR]

The corrosion behavior of Al in 1 M HCl solution with and without thiophene derivatives is studied utilizing altered chemical and electrochemical methods. Thiophene derivatives have been prepared and characterized by infrared (IR), proton nuclear magnetic resonance (1H NMR) and mass spectral studies. The corrosion data were obtained using weight reduction and electrochemical techniques. The outcome data revealed that the efficiency rises with improving the dose of thiophene derivatives in aggressive solution, while it lowered with the rise of temperature. The adsorption of the studied thiophene derivatives on the surface of Al follows Langmuir isotherm. The thermodynamic parameters such as adsorption constant Kads and free energy of adsorption () are calculated and discussed. Polarization curves indicated that the thiophene derivatives are mixed-kind inhibitors. The quantum calculation such as EHOMO, ELUMO and ΔE were obtained and related to the experimental data. The biological effect of these derivatives also discussed. [ABSTRACT FROM AUTHOR]

The anticorrosion potency of Sabic mild steel (MS) in 0.5 M H2SO4 solution was enhanced by three synthetic non-ionic surfactants (NI Surf.) containing pyridine and pyrimidine derivatives. These compounds are safe, environmentally friendly, and harmless to human health. Chemical and electrochemical measurements were used to compute the corrosion parameters. The anticorrosion efficacy increases with increasing the concentration of NI Surf. and with lowering temperature, surface and interfacial tension, and critical micelle concentration. The effectiveness of anticorrosion is interpreted due to the spontaneous horizontal adsorption on the surface of MS by the existence of some active centers that facilitate the adsorption. The adsorption process obeys Temkin isotherm. Potentiodynamic polarization elucidated that the synthetic NI Surf. acted as mixed-type inhibitors. Some surface properties were determined and confirm the anticorrosive effect of these molecules. Quantum chemical parameters as reactivity descriptors were carried out. It should be noted that the results obtained from computational calculations of the specifications are in full agreement with the experimental observations. There is good compatibility between the anticorrosion efficiency obtained from various techniques and surface properties and quantum chemical calculation. [ABSTRACT FROM AUTHOR]

Background: Lignin peroxidases catalyze a variety of reactions, resulting in cleavage of both β-O-4′ ether bonds and C–C bonds in lignin, both of which are essential for depolymerizing lignin into fragments amendable to biological or chemical upgrading to valuable products. Studies of the specificity of lignin peroxidases to catalyze these various reactions and the role reaction conditions such as pH play have been limited by the lack of assays that allow quantification of specific bond-breaking events. The subsequent theoretical understanding of the underlying mechanisms by which pH modulates the activity of lignin peroxidases remains nascent. Here, we report on combined experimental and theoretical studies of the effect of pH on the enzyme-catalyzed cleavage of β-O-4′ ether bonds and of C–C bonds by a lignin peroxidase isozyme H8 from Phanerochaete chrysosporium and an acid stabilized variant of the same enzyme. Results: Using a nanostructure initiator mass spectrometry assay that provides quantification of bond breaking in a phenolic model lignin dimer we found that catalysis of degradation of the dimer to products by an acid-stabilized variant of lignin peroxidase isozyme H8 increased from 38.4% at pH 5 to 92.5% at pH 2.6. At pH 2.6, the observed product distribution resulted from 65.5% β-O-4′ ether bond cleavage, 27.0% Cα-C1 carbon bond cleavage, and 3.6% Cα-oxidation as by-product. Using ab initio molecular dynamic simulations and climbing-image Nudge Elastic Band based transition state searches, we suggest the effect of lower pH is via protonation of aliphatic hydroxyl groups under which extremely acidic conditions resulted in lower energetic barriers for bond-cleavages, particularly β-O-4′ bonds. Conclusion: These coupled experimental results and theoretical explanations suggest pH is a key driving force for selective and efficient lignin peroxidase isozyme H8 catalyzed depolymerization of the phenolic lignin dimer and further suggest that engineering of lignin peroxidase isozyme H8 and other enzymes involved in lignin depolymerization should include targeting stability at low pH. [ABSTRACT FROM AUTHOR]

Many energetic materials synthesized to date have limited applications because of low thermal and/or mechanical stability. This limitation can be overcome by introducing structural modifications such as a bridging group. In this study, a series of 1,3,4‐oxadiazole‐bridged furazans was prepared. Their structures were confirmed by 1H and 13C NMR, infrared, elemental, and X‐ray crystallographic analyses. The thermal stability, friction sensitivity, impact sensitivity, detonation velocity, and detonation pressure were evaluated. The hydroxylammonium salt 8 has an excellent detonation performance (D=9101 m s−1, P=37.9 GPa) and insensitive properties (IS=17.4 J, FS=330 N), which show its great potential as a high‐performance insensitive explosive. Using quantum computation and crystal structure analysis, the effect of the introduction of the 1,3,4‐oxadiazole moiety on molecular reactivity and the difference between the sensitivities and thermal stabilities of mono‐ and bis‐1,3,4‐oxadiazole bridges are considered. The synthetic method for introducing 1,3,4‐oxadiazole and the systematic study of 1,3,4‐oxadiazole‐bridged compounds provide a theoretical basis for future energetics design. [ABSTRACT FROM AUTHOR]

Many energetic materials synthesized to date have limited applications because of low thermal and/or mechanical stability. This limitation can be overcome by introducing structural modifications such as a bridging group. In this study, a series of 1,3,4‐oxadiazole‐bridged furazans was prepared. Their structures were confirmed by 1H and 13C NMR, infrared, elemental, and X‐ray crystallographic analyses. The thermal stability, friction sensitivity, impact sensitivity, detonation velocity, and detonation pressure were evaluated. The hydroxylammonium salt 8 has an excellent detonation performance (D=9101 m s−1, P=37.9 GPa) and insensitive properties (IS=17.4 J, FS=330 N), which show its great potential as a high‐performance insensitive explosive. Using quantum computation and crystal structure analysis, the effect of the introduction of the 1,3,4‐oxadiazole moiety on molecular reactivity and the difference between the sensitivities and thermal stabilities of mono‐ and bis‐1,3,4‐oxadiazole bridges are considered. The synthetic method for introducing 1,3,4‐oxadiazole and the systematic study of 1,3,4‐oxadiazole‐bridged compounds provide a theoretical basis for future energetics design. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chinese Mass Spectrometry Society is the property of Journal of Chinese Mass Spectrometry Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Chinese Mass Spectrometry Society is the property of Journal of Chinese Mass Spectrometry Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, space charge behavior over a large range of electric field and temperature, of two kinds of epoxy resins are investigated using an improved pulsed electro-acoustic method. Significant influence of high electric field and high temperature on the space charge accumulation in epoxy are found. Hetero charge accumulation starts to build up at 80 °C under 120 kV/mm for amine-type hardener cured epoxy (EP-AM), while at 140 °C under 60 kV/mm for anhydride-type hardener cured epoxy (EP-AH). The accumulated charge increases with the increasing of electric field and temperature. The maximum enhancement of local electric field of is 135 and 123 % at 140 °C for EP-AM and EP-AH, respectively. Quantum chemical calculation is performed to clarify the mechanism of space charge characteristics in the two types of epoxy. It is indicated that ionization of remnant unreacted hardener and electrode injection may be the main sources of space charge. The interaction between molecular chains of EP-AH is stronger than that of EP-AM, which makes it have better space charge characteristics even under high temperature. [ABSTRACT FROM AUTHOR]

Amino acid modified polyaspartic acids were evaluated as calcium‐scale inhibitors. Feasibility of scale inhibition experiments was analyzed by molecular dynamics simulation and Gaussian optimization, and the scale inhibition mechanism was theoretically analyzed. Scale inhibition performance was studied by scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, static scale inhibition experiments, and electrochemical performance testing, which provided an experimental basis for the molecular dynamics simulation. The experimental results showed that Arg‐SA‐PASP has better scale inhibition and corrosion inhibition performance than His‐SA‐PASP. The scale inhibition effect increased with increasing concentration. Electrochemical tests indicated that Arg‐SA‐PASP is an excellent scale and corrosion inhibitor. [ABSTRACT FROM AUTHOR]

Deep trap sites have been proved able to suppress charge injection into nanocomposites even under high electric field. In order to reveal the mechanism of deep trap sites in epoxy/graphene nanocomposite, the trap distribution was obtained through surface potential decay (SPD) method. The energy levels and 3D potential distributions of epoxy and single-layer graphene under vertical or various parallel electric fields were calculated by using the density functional theory (DFT). The experimental and calculation results indicate that doping with graphene sheets introduces deep trap sites in epoxy/graphene composite. Under parallel electric field, the apparent dipoles of single-layer graphene build positive and negative potential wells in pairs, which capture carriers as the trap sites in epoxy/graphene composite. While a vertical electric field seems to have no effect on the trap sites. For better performance in suppressing charge injection, the doped graphene sheets should be exposed partially to a parallel electric field. [ABSTRACT FROM AUTHOR]

Soluble guanylate cyclase (sGC) is a key enzyme implicated in various physiological processes such as vasodilation, thrombosis and platelet aggregation. The enzyme's Heme-Nitric oxide/Oxygen (H-NOX) binding domain is the only sensor of nitric oxide (NO) in humans, which on binding with NO activates sGC to produce the second messenger cGMP. H-NOX is thus a hot target for drug design programs. BAY60-2770 and BAY58-2667 are two widely studied activators of sGC. Here we present comparative molecular dynamics studies to understand the molecular details characterizing the binding of BAY60-2770 and BAY58-2667 with the human H-NOX (hH-NOX) and bacterial H-NOX (bH-NOX) domains. HartreeFock method was used for parametrization of both the activators. A 50 ns molecular dynamics (MD) simulation was run to identify the functionally critical regions of the H-NOX domains. The CPPTRAJ module was used for analysis. BAY60-2770 on binding with bH-NOX, triggered rotational movement in signaling helix F and significant dynamicity in loops α and β, but in hH-NOX domain the compound showed relatively lesser aforementioned structural fluctuations. Conversely, hH-NOX ligated BAY58-2667 experienced highest transitions in its helix F due to electrostatic interactions with D84, T85 and R88 residues which are not conserved in bH-NOX. These conformational transformations might be essential to communicate with downstream PAS, CC and cyclase domains of sGC. Comparative MD studies revealed that BAY bound bHNOX dynamics varied from that of hH-NOX, plausibly due to some key residues such as R40, F74 and Y112 which are not conserved in bacteria. These findings will help to the design of novel drug leads to cure diseases associated to human sGC. [ABSTRACT FROM AUTHOR]

This work aims to investigate the inhibitory activity of capsaicin, which is one of capsaicinoid compounds, on these enzymes using a molecular docking and quantum calculation. Acarbose, a commercial diabetes drug, was also investigated for comparison. The docking results revealed that acarbose yields better inhibition efficiency with binding free energy (ΔGbinding) of about -8.2 to -11.9 kcal/mol, and inhibition constant (Ki) of about 0.0002 to 0.4 µM, where as capsaicin provided the ΔGbinding of -5.8 to -6.1 kcal/mol and Ki of 23.7 to 45.9 µM. The total binding energy (ΔEbinding) between each inhibitor and amino acids in active site of enzyme obtained from quantum calculation with MP2/6-31G(d,p) level is in agreement with the ΔGbinding, i.e. the ΔEbinding of acarbose was larger negative than that of capsaicin. The amino acids interacting with inhibitor as hydrogen bond mainly contribute to the total binding energy. Nevertheless, it could be concluded that capsaicinoids have high potential to be developed as an alternative drug for diabetes disease. [ABSTRACT FROM AUTHOR]

A global glide disorder has been discovered during an X‐ray investigation of the crystal structure of (Z)‐2‐[(E)‐(4‐methoxybenzylidene)hydrazinylidene]‐1,2‐diphenylethanone (MHDE, C22H18N2O2) at room temperature. In another crystal, however, such disorder disappears (still at room temperature). Even though the disorder may be partly due to the poor quality of the harvested crystal, the structure can shed light on the nature of disorder. With the help of quantum chemical calculations, it is found that the global disorder seems to be connected with the need for stabilization of the somewhat rigid but mobile and unstable molecular structure. The most relevant feature driving the packing of the disordered structure concerns the slight perturbations (such as glide) of two or more disorder components (fractional occupancies) distributed throughout the crystal. [ABSTRACT FROM AUTHOR]

Summary: In the modeling of hydrocarbon thermal cracking processes, complicated reaction networks of multicomponent reactants make kinetic parameter predictions very challenging. To solve this problem, the additivity method and Evans‐Polanyi equation were proposed for the prediction of kinetic factors. As the calculation of kinetic parameters using quantum chemical theory was used for higher accuracy, new additivity methods at the quantum theory level were developed for the prediction of thermodynamic kinetic parameters. At the same time, a reaction class transition state theory RC‐TST, analogous to the Evans‐Polanyi equation, was proposed by considering quantum factors for kinetic constant evaluation. Quantum calculation methods promoted mechanistic studies of electronic effects to accurately reveal the kinetic constant rules with different structural factors. Under these circumstances, kinetic parameter predictions by different quantum chemical computation methods were firstly introduced and reviewed. Meanwhile, development of the new additivity method and RC‐TST theory at the quantum chemistry level were summarized, and the new outlook on electronic effects with an appropriate quantum chemical computational method into the new additivity method was conducted to develop more perspicuous and accuracy in a simplified method for the calculation of complicated thermal cracking reaction. [ABSTRACT FROM AUTHOR]

B3LYP, PBE, M06-2X, B2PLYP, BN2PLYP-D, ωB97X-D, and MP2 levels of theory, in combination with the 6-311++G(d,p) and cc-pVTZ basis sets were comprehensively assessed for their ability to reproduce experimental FOX-7 structural and detonation data. ωB97X-D/cc-pVTZ, B3LYP/cc-pVTZ, and M06-2X/cc-pVTZ provided highly accurate optimized structure predictions. M06-2X/cc-pVTZ and ωB97X-D/cc-pVTZ reproduced experimentally determined detonation properties (detonation velocity and detonation pressure) with high accuracy. The results of this study demonstrate that more accurate structure calculation levels provide more reliable detonation property predictions. Moreover, the results show that detonation property prediction is largely dependent on the calculation level. This investigation demonstrates that using a wide range of calculation levels enables the reliable prediction and modeling of novel types of HEDMs. [ABSTRACT FROM AUTHOR]

Anion functionalized strategy has been proposed for the synthesis of macro-porous resins [IRA-900][An] through the neutral reaction of the basic resin [IRA-900][OH] with the corresponding donors. Combining CO2 adsorption results and FT-IR, solid-state 13C NMR characterization as well as quantum chemical calculations, chemical adsorption mechanism was verified and tunable capture of CO2 was realized. Among them, the anion functionalized resin [IRA-900][Triz] exhibits an extremely high adsorption capacity (4.02 mmol g−1 at 25°C, 0.15 bar), outperforming many other good adsorbents. Finally, we discuss the thermostability and recycling stability of [IRA-900][Triz], which shows a great potential in the industrial capture of CO2. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3008-3015, 2017 [ABSTRACT FROM AUTHOR]

IR spectra of heme and different O-content hemoglobin were studied by the quantum computation method at the molecule level. IR spectra of heme and different O-content hemoglobin were quantificationally characterized from 0 to 100 THz. The IR spectra of oxy-heme and de-oxy-heme are obviously different at the frequency regions of 9.08-9.48, 38.38-39.78, 50.46-50.82, and 89.04-91.00 THz. At 24.72 THz, there exists the absorption peak for oxy-heme, whereas there is not the absorption peak for de-oxy-heme. Whether the heme contains Fe-O-O bond or not has the great influence on its IR spectra and vibration intensities of functional groups in the mid-infrared area. The IR adsorption peak shape changes hardly for different O-content hemoglobin. However, there exist three frequency regions corresponding to the large change of IR adsorption intensities for containing-O hemoglobin in comparison with de-oxy-hemoglobin, which are 11.08-15.93, 44.70-50.22, and 88.00-96.68 THz regions, respectively. The most differential values with IR intensity of different O-content hemoglobin all exceed 1.0 × 10 L mol cm. With the increase of oxygen content, the absorption peak appears in the high-frequency region for the containing-O hemoglobin in comparison with de-oxy-hemoglobin. The more the O-content is, the greater the absorption peak is at the high-frequency region. The IR spectra of different O-content hemoglobin are so obviously different in the mid-infrared region that it is very easy to distinguish the hemoglobin variant by means of IR spectra detector. IR spectra of hemoglobin from quantum computation can provide scientific basis and specific identification of hemoglobin variant resulting from different O contents in medical diagnosis. [ABSTRACT FROM AUTHOR]

Benzophenone-3 (BP-3), as an important organic UV filter, is widely used in the sunscreen, cosmetic, and personal care products. The chemical reaction mechanism and kinetics of BP-3 degradation initiated by hydroxyl (OH) radical was investigated in the atmosphere based on the density functional theory (DFT). The results showed that the OH radical is more easily added to the C3 position of the aromatic ring (pathway 3), while the H atom abstraction from the OH group on the aromatic ring (pathway 23) is an energetically favorable reaction pathway. At ambient temperature, 298 K, the overall rate constant for the primary reaction is about 1.50 × 10−10 cm3 mol −1 s−1 with the lifetime of 1.92 h. OH addition reactions play the key role in the OH-initiated reaction of BP-3. The study is helpful for better understanding of the removal, transformation, and fate of BP-3 in the atmosphere. [ABSTRACT FROM AUTHOR]

Benzophenone-3 (BP-3), as an important organic UV filter, is widely used in the sunscreen, cosmetic, and personal care products. The chemical reaction mechanism and kinetics of BP-3 degradation initiated by hydroxyl (OH) radical was investigated in the atmosphere based on the density functional theory (DFT). The results showed that the OH radical is more easily added to the C3 position of the aromatic ring (pathway 3), while the H atom abstraction from the OH group on the aromatic ring (pathway 23) is an energetically favorable reaction pathway. At ambient temperature, 298 K, the overall rate constant for the primary reaction is about 1.50 × 10−10 cm3 mol −1 s−1 with the lifetime of 1.92 h. OH addition reactions play the key role in the OH-initiated reaction of BP-3. The study is helpful for better understanding of the removal, transformation, and fate of BP-3 in the atmosphere. [ABSTRACT FROM AUTHOR]

Five kinds of anion-functionalized ionic liquids (ILs) with different basicity and substituent were selected, prepared and applied in the capture of SO2 from flue gas, where the concentration of SO2 is only 2000 ppm. The effect of the anion on SO2 absorption capacity, desorption residue, and available absorption capacity under 2000 ppm was investigated. The relationship between available absorption capacity and absorption enthalpy was also studied. Through a combination of thermodynamic analysis and quantum calculation, the results indicated that the effect of the cation in the IL on absorption enthalpy was significant. However, the effect of chain length in the cation was weak. Hence, a new IL with low molecular weight, [P4442][Tetz], was further designed and applied for the capture of SO2, which shows the high absorption capacity of 0.18 g SO2 per g IL and excellent reversibility for 2000 ppm SO2. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2028-2034, 2015 [ABSTRACT FROM AUTHOR]

The solvation of salts in water and salt-water interactions are important for understanding a large variety of chemical, biological, and atmospheric processes. In this perspective, we summarize our recent studies on the theoretical modeling of salt-water clusters. In these studies, the integrated tempering sampling method was used for structure search and density functional theory was used to optimize the low-energy configurations. The microsolvation mechanisms of three alkali-halide ion pairs in clusters are discussed. We also discuss the implications of these studies to our understanding of corresponding bulk solutions. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Hemagglutinin (HA) is a membrane protein present on the influenza viral envelope. It is responsible for molecular recognition between the viral particle and the host cell, as well as fusion of the viral envelope to the endosome bilayer. Because it is essential for influenza viral infection and replication, it has become a target for the design of anti-influenza drugs. Previous studies have identified two small molecule HA ligands (CL-385319 and 1L) that inhibit infection with pseudovirus H5N1 with different potency. In order to compare their different inhibitory activities and shed light on drug design targeting the HA protein, we conducted a variety of theoretical calculations, including docking, molecular dynamics simulations, free energy calculations, as well as quantum calculations to investigate interactions between these two ligands and the HA protein. We found that molecule 1L has stronger π–π interactions with the side chains of residues F110 2 and M24 1 compared with molecule CL-385319. We propose that these stronger π–π interactions are responsible for the higher inhibitory activity of molecule 1L. Our calculations will aid drug design studies targeting the HA protein. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The synthesis of 5-nitro-2-nitratomethyl-1,2,3,4-tetrazole (4) and its full characterization are given here. Compound 4 was synthesized through the nitration of 5-nitro-2-hydroxymethyl-tetrazole (3) with fuming nitric acid and acetic anhydride and its structure was characterized by MS, FT-IR, 1H-NMR and 13C-NMR techniques. The crystal structure of 4 was determined by X-ray single crystal diffraction analysis. The compound belongs to the orthorhombic system with space group Pna2(1), and its crystal parameters were a = 2.121(8) nm, b = 0.5281(19) nm, c = 0.6246(2) nm, Z = 4, V = 0.6995(4) nm3, Dc = 1.805 g/cm3, F(000) = 384, μ = 0.174 mm-1. A theoretical study of 4 has been performed, using quantum computational density functional theory (B3LYP methods) with 6-31G* basis sets as implemented in the Gaussian 03 program suite. The obtained heat of formation (HOF) for 4 was 228.07 kJ mol-1, the detonation pressure (P) values calculated for 4 was 37.92 GPa, the detonation velocity (D) can reach 9260 ms-1, and the oxygen balance was zero (Q), making 4 a competitive energetic compound. [ABSTRACT FROM AUTHOR]

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The surface reaction pathways of isothiazole and thiazole on Si(100)−2 × 1 surface were theoretically investigated using multireference wavefunctions. In the case of isothiazole, the Si-N dative adduct turned out to be the major surface product. In contrast, a direct reaction competition between a concerted [4 + 2] cycloaddition and Si-N dative adduct was found in the adsorption of thiazole. Therefore, it is concluded that the particular geometric arrangements of heteroatoms exhibit distinctly different initial surface reaction mechanisms. [ABSTRACT FROM AUTHOR]

The study of the ternary interactions of some phenoxyacetic acids derived from a herbicide, with the heavy metals present in soil in trace amounts has been realized by potentiometric measurements. The stability constants of the ternary complexes have been calculated at 25°C and ionic strength 0.1(NaNO3). The experimental results have confirmed the presence of one ternary hydroxide species MH1(2,4-D)(2,4-MCPA) for Cu(II), Pb(II) and Zn(III) on one hand and MH2(2,4-D)(2,4-MCPA) for Hg(II) on the other. The order of stability constants has been found to be: Cu(II)> Hg(II)> Pb(II)> Zn(II)>Cd(II). Finally, a quantum approach has been achieved by the semi-empirical AM1 method for the mercuric complex. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

Two novel oxo-vanadium complexes of VO(HB(pz)3)(pzH)(SCN) (1) and VO(HB(3,5-Me2pz)3) (3,5-Me2pzH)(SCN)(SCNH)2 (2) with tris(pyrazolyl) hydroborate ligands were prepared by the reaction of VOSO4nH2O, KSCN with Na(HB(pz)3), pyrazole, or Na(HB(3,5-Me2pz)3) and methyl-substituted pyrazole in the solution of MeOH, respectively. The complexes were characterized by element analysis, IR, and UV-vis spectra. In the mean time, the fluorescence spectrum was studied too, and the result indicates that the luminescence of the complexes is related to the interaction between oxovanadium ion and tris(pyrazolyl) hydroborate ligands. In addition, structures of oxovanadium complexes 1 and 2 were determined by X-ray diffraction. The electronic structures and the bonding characters of the two complexes were analyzed with ab initio calculations. [ABSTRACT FROM AUTHOR]

Despite the common use of salens and hydroxyquinolines as therapeutic and bioactive agents, their metal complexes are still under development. Here, we report the synthesis of novel mixed-ligand metal complexes (MSQ) comprising salen (S), derived from (2,2′-{1,2-ethanediylbis[nitrilo(E) methylylidene]}diphenol, and 8-hydroxyquinoline (Q) with Co(II), Ni(II), Cd(II), Al(III), and La(III). The structures and properties of these MSQ metal complexes were investigated using molar conductivity, melting point, FTIR, 1H NMR, 13C NMR, UV–VIS, mass spectra, and thermal analysis. Quantum calculation, analytical, and experimental measurements seem to suggest the proposed structure of the compounds and its uncommon monobasic tridentate binding mode of salen via phenolic oxygen, azomethine group, and the NH group. The general molecular formula of MSQ metal complexes is [M(S)(Q)(H2O)] for M (II) = Co, Ni, and Cd or [M(S)(Q)(Cl)] and [M(S)(Q)(H2O)]Cl for M(III) = La and Al, respectively. Importantly, all prepared metal complexes were evaluated for their antimicrobial and anticancer activities. The metal complexes exhibited high cytotoxic potency against human breast cancer (MDA-MB231) and liver cancer (Hep-G2) cell lines. Among all MSQ metal complexes, CoSQ and LaSQ produced IC50 values (1.49 and 1.95 µM, respectively) that were comparable to that of cisplatin (1.55 µM) against Hep-G2 cells, whereas CdSQ and LaSQ had best potency against MDA-MB231 with IC50 values of 1.95 and 1.43 µM, respectively. Furthermore, the metal complexes exhibited significant antimicrobial activities against a wide spectrum of both Gram-positive and -negative bacterial and fungal strains. The antibacterial and antifungal efficacies for the MSQ metal complexes, the free S and Q ligands, and the standard drugs gentamycin and ketoconazole decreased in the order AlSQ > LaSQ > CdSQ > gentamycin > NiSQ > CoSQ > Q > S for antibacterial activity, and for antifungal activity followed the trend of LaSQ > AlSQ > CdSQ > ketoconazole > NiSQ > CoSQ > Q > S. Molecular docking studies were performed to investigate the binding of the synthesized compounds with breast cancer oxidoreductase (PDB ID: 3HB5). According to the data obtained, the most probable coordination geometry is octahedral for all the metal complexes. The molecular and electronic structures of the metal complexes were optimized theoretically, and their quantum chemical parameters were calculated. PXRD results for the Cd(II) and La(III) metal complexes indicated that they were crystalline in nature. [ABSTRACT FROM AUTHOR]

Using the Iterative Extended Huckel Theory ( IEHT), energy-conformation studies have been carried out for HCN (I), trans-HCNH (IIA), and cis-HCNH (IIB), three possible isomers formed by addition of a hydrogen atom to hydrogen cyanide. Calculations show that the order of decreasing thermodynamic stability is I $$ > $$ IIA > IIB. Results of a series of calculations designed to simulate the stepwise addition of a hydrogen atom to hydrogen cyanide to form both I and IIA indicate that formation of I is also kinetically favored over IIA. Calculated properties of the minimum energy conformers of I and IIA and the nature of the bonding in them are described. The calculated distribution of the unpaired electron density in I compares favorably with results obtained empirically from the ESR spectra of a radical formed by addition of H atoms to HCN. The potential role of HCN (I) as a reactive intermediate in prebiotic organic synthesis and its possible relevance to interstellar organic chemistry are discussed. [ABSTRACT FROM AUTHOR]