Origin of Enantioselectivity in Engineered Cytochrome c-Catalyzed Carbon-Radical FePP Hydrolysis Revealed Using QM/MM (ABEEM Polarizable Force Field) and MD Simulations.

The origin of highly efficient asymmetric aminohydroxylation of styrene catalyzed by engineered cytochrome c is investigated by the developed Atom-Bond Electronegativity Equalization Method polarizable force field (ABEEM PFF), which is a combined outcome of electronic and steric effects. Model molecules were used to establish the charge parameters of the ABEEM PFF, for which the bond-stretching and angle-bending parameters were obtained by using a combination of modified Seminario and scan methods. The interactions between carbon-radical Fe-porphyrin (FePP) and waters are simulated by molecular dynamics, which shows a clear preference for the pre-R over the pre-S. This preference is attributed to the hydrogen-bond between the mutated 100S and 101P residues as well as van der Waals interactions, enforcing a specific conformation of the carbon-radical FePP complex within the binding pocket. Meanwhile, the hydrogen-bond between water and the nitrogen atom in the active intermediate dictates the stereochemical outcome. Quantum mechanics/molecular mechanics (QM/MM (ABEEM PFF)) and free-energy perturbation calculations elucidate that the 3RTS is characterized by sandwich-like structure among adjacent amino acid residues, which exhibits greater stability than crowed arrangement in 3STS and enables the R enantiomer to form more favorably. Thus, this study provides mechanistic insight into the catalytic reaction of hemoproteins.

Development of a QM/MM(ABEEM) method for the deprotonation of neutral and cation radicals in the G-tetrad and GGX(8-oxo-G) tetrad.

The rapid deprotonation of G˙+ in the DNA strand impedes positive charge (hole) transfer, whereas the slow deprotonation rate of G˙+ in the G-tetrad makes it a more suitable carrier for hole conduction. The QM/MM(ABEEM) combined method, which involves the integration of QM and the ABEEM polarizable force field (ABEEM PFF), was developed to investigate the deprotonation of neutral and cation free radicals in the G-tetrad and GGX(8-oxo-G) tetrad (xanthine and 8-oxoguanine dual substituted G-tetrad). By incorporating valence-state electronegativity piecewise functions χ*(r) and implementing charge local conservation conditions, QM/MM(ABEEM) possesses the advantage of accurately simulating charge transfer and polarization effect during deprotonation. The activation energy calculated by the QM method of X˙ is the lowest among other bases in the GGX(8-oxo-G) tetrad, which is supported by the computation of the average electronegativity calculated by ABEEM PFF. By utilizing QM/MM(ABEEM) with a two-way free energy perturbation method, the deprotonation activation energy of X˙ in the GGX(8-oxo-G) tetrad is determined to be 33.0 ± 2.1 kJ mol-1, while that of G˙+ in the G-tetrad is 20.7 ± 0.6 kJ mol-1, consistent with the experimental measurement of 20 ± 1.0 kJ mol-1. These results manifest that X˙ in the GGX(8-oxo-G) tetrad exhibits a slower deprotonation rate than G˙+ in the G-tetrad, suggesting that the GGX(8-oxo-G) tetrad may serve as a more favorable hole transport carrier. Furthermore, the unequal average electronegativities of bases in the GGX(8-oxo-G) tetrad impede the deprotonation rate. This study provides a potential foundation for investigating the microscopic mechanism of DNA electronic devices.

A simple, rapid method for simultaneous determination of multiple elements in serum by using an ICP-MS equipped with collision cell.

We developed an inductively coupled plasma mass spectrometry method for testing 23 elements, namely, Mg, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Cd, Sn, Sb, Ba, W, Tl, Pb, and U, in human serum. The serum samples were analyzed after diluting 1/25 with 0.5% nitric acid, 0.02% Triton-X-100, and 2% methanol. Sc, In, Y, Tb, and Bi were assigned internal standards to correct the baseline drift and matrix interference. The kinetic energy discrimination mode of the instrument with helium gas as the collision gas eliminated polyatomic interference. All 23 elements exhibited excellent linearity in their testing range, with a coefficient of determination ≥ 0.9996. The limits of detection of the 23 elements were within the range of 0.0004-0.2232 µg/L. The intra- and inter-day precision (relative standard deviation) were < 12.19%. The recoveries of the spiked standard for all elements were 88.98-109.86%. Among the 23 elements of the serum reference materials, the measured results of Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Se were within the specified range of the certificate, and the results of the other elements were also satisfactory. The developed method was simple, rapid, and effective, and only 60 µL sample was consumed. A total of 1000 serum samples from healthy individuals were randomly selected from the Henan Rural Cohort, which reflects the status of serum elements in rural adults from the Northern Henan province of central China.

Atomic charges in molecules defined by molecular real space partition into atomic subspaces.

Atomic charge (AC), which is the charge distribution of a molecule, is an important property that is closely associated with structures, reactivities, and intra- and inter-molecular interactions among molecules. Several theoretical models or methods can be used to obtain the magnitudes of AC with different characteristics. These models can be classified into fuzzy-atoms models and models partitioning a molecule into individual atoms with sharp boundaries. The first category includes Mulliken, natural population analysis (NPA), Hirshfeld, Merz-Kollman-Singh (MK), CHELPG, the electronegativity equalization method (EEM), the atom-bond electronegativity equalization method (ABEEM), and atomic polar tensor (APT). The second category is derived from quantum chemical topology (QCT) and includes the quantum theory of atoms in molecules (QTAIM) and QCT analysis based on the potential acting on one electron in a molecule (PAEMQCT). Herein, after giving a bird's-eye view of the population methods of the first category, we specifically describe some features of the second category. We only present the basic framework of QCT for obtaining ACs from QTAIM and PAEMQCT and show their important characteristics. QCT establishes the basis of the following chemical concept: a molecule is spatially partitioned into individual atoms with sharp boundaries. The ACs from QTAIM are close to the atomic valence in chemistry, and ACs from PAEMQCT may be practically suitable for modeling intra- and inter-molecular interactions.

Development of a QM/MM(ABEEM) method combined with a polarizable force field to investigate the excision reaction mechanism of damaged thymine.

This paper focuses on the development of a quantum mechanics/molecular mechanics method using the ABEEM polarizable force field (QM/MM(ABEEM) method) to investigate the excision reaction mechanism of damaged thymine. This method does not simply combine the QM method with the polarizable force field. A valence electronegativity piecewise function with the distance between atoms as a variable is introduced to describe the atomic partial charges, and changes greatly during the reaction process. At the same time, the charge transfer effect is treated using the condition of local charge conservation. Compared with the traditional QM/MM method, the QM/MM(ABEEM) method can more accurately simulate the polarization effect and charge transfer effect in the reaction process. Focusing on the controversial problems of the excision of damaged bases, six reaction pathways were designed for monofunctional and difunctional deglycosylation of neutral bases and protonated bases. The results show that the QM/MM(ABEEM) method accurately simulates the polarization effect, charge transfer effect, activation energy and other properties of the reaction process. The process in which the active residue Asp activates the nucleophile H2O to attack the protonated base is the preferred path. The average activation energy and free activation energy of the protonated base are 7.00-14.00 kcal mol-1 lower than that of the neutral base. The study in this paper is helpful to understand the mechanism of repair enzymes in repairing bases.

Development of QM/MM (ABEEM polarizable force field) method to simulate the excision reaction mechanism of damaged cytosine.

DNA damages are regarded as having harmful effects on cell. The base excision repair mechanism combats these effects by removing damaged bases. The deglycosylation mechanism of excising damaged bases by DNA glycosylase and the state of the leaving base have been controversial. The enzymatic reaction of DNA glycosylase to remove the damaged bases involves not only the formation and breaking of chemical bonds, but also complex polarization effect and charge transfer, which cannot be accurately simulated by the QM/MM method combined with the fixed charge force field. This work has developed the ABEEM fluctuating polarizable force field combining with the QM method, that is (QM/MM[ABEEM]), to accurately simulate the proton transfer, charge transfer and the charge distribution. The piecewise function is used as the valence-state electronegativity in the QM/MM (ABEEM) to realize the accurate fitting of the charge distribution in reaction. And the charge transfer is accurately simulated by the local charge conservation conditions. Four deglycosylation mechanisms including the monofunctional and difunctional mechanisms of four neutral and protonated cytosine derivatives are explored. It is confirmed that the monofunctional mechanism of Asp-activated nucleophile water is a better deglycosylation mechanism and the base is protonated before the reaction occurs. Protonization of the base reduced the activation energy by 10.00-17.00 kcal/mol. Asp provides the necessary charge for the reaction, and DNA glycosylase preferentially cleaves ɛC. This work provides a theoretical basis for the research of excising damaged bases by DNA glycosylase.

A daily carbon emission prediction model combining two-stage feature selection and optimized extreme learning machine.

Global warming caused by increased carbon emissions is a common challenge for all mankind. Facing the unprecedented pressure of carbon emission reduction, it is particularly important to grasp the dynamics of carbon emission in time and accurately. This paper proposes a novel daily carbon emission forecasting model. Firstly, the daily carbon emission data is decomposed into a series of completely noise-free mode functions by improved complete ensemble empirical mode decomposition method with adaptive noise (ICEEMDAN). Then, a two-stage feature selection method composed of partial autocorrelation function (PACF) and ReliefF is applied to select appropriate input variables for the next prediction process. Finally, the extreme learning machine optimized by improved sparrow search algorithm (ISSA-ELM) is used to predict. The empirical results show that the proposed two-stage feature selection method can further improve the prediction accuracy. After two-stage feature selection, the values of R2, MAPE, and RMSE were improved by 0.55%, 30.23%, and 28.46%, respectively. It can also be found that ISSA has good optimization performance. By combining with ISSA, R2, MAPE, and RMSE improved by 7.60%, 31.97%, and 44.79%, respectively. Therefore, the proposed model can provide a valuable reference for the formulation of carbon emission reduction policies and future carbon emission prediction research.

Conjunctional Relationship between Serum Uric Acid and Serum Nickel with Non-Alcoholic Fatty Liver Disease in Men: A Cross-Sectional Study.

Serum uric acid (SUA) and heavy metals are closely related to non-alcoholic fatty liver disease (NAFLD). Yet, the conjunctional relationship between SUA and serum nickel (Ni) concentrations with the risk of NAFLD in men has not yet been investigated. Therefore, we designed this cross-sectional study to investigate the association of SUA or serum Ni with NAFLD in men. The cross-sectional study was based on data obtained from a prospective cohort study of common chronic non-communicable diseases in Central China, conducted in Xinxiang city, Central China's Henan Province, between April and June 2017. A total of 1709 male participants completed the physical examination. B-ultrasound was used to examine the liver and to diagnose NAFLD. Binary logistic regression models and restricted cubic splines were performed to estimate the association of the SUA and serum Ni with NAFLD. The prevalence of NAFLD among 1709 male participants was 46.6%. After adjusting for potential confounders, with the highest quartile compared to those with the lowest quartile, SUA (OR = 1.579, 95% CI: 1.140-2.189) and serum Ni (OR = 1.896, 95% CI: 1.372-2.625) were associated with NAFLD, respectively. At the same time, the associations for the second and third SUA quartiles were null. Restricted cubic splines showed a positive linear relationship between serum Ni (ln-transformed) and NAFLD risk. Intriguingly, high SUA and high Ni (OR = 2.370, 95% CI: 1.577-3.597) increased the risk of NAFLD, compared with those with low SUA and low Ni. Our findings demonstrate a positive linear trend between serum Ni concentrations and NAFLD risk. Men with elevated serum Ni had a higher risk of developing NAFLD when compared to those with high SUA. Furthermore, the conjunctional relationship of SUA and serum Ni with NAFLD risk was observed in men.

A novel short-term carbon emission prediction model based on secondary decomposition method and long short-term memory network.

Grasping the dynamics of carbon emission in time plays a key role in formulating carbon emission reduction policies. In order to provide more accurate carbon emission prediction results for planners, a novel short-term carbon emission prediction model is proposed. In this paper, the secondary decomposition technology combining ensemble empirical mode decomposition (EEMD) and variational mode decomposition (VMD) is used to process the original data, and the partial autocorrelation function (PACF) is applied to select the optimal model input. Then, the long short-term memory network (LSTM) is chosen for prediction. The secondary decomposition algorithm is innovatively introduced into the field of carbon emission prediction, and the empirical results illustrate that the secondary decomposition technology can further improve the prediction accuracy. Combined with the secondary decomposition, the R2, MAPE, and RMSE of the model are improved by 2.20%, 43.08%, and 36.92% on average. And the proposed model shows excellent prediction accuracy (R2 = 0.9983, MAPE = 0.0031, RMSE = 118.1610) compared with other 12 comparison models. Therefore, this model not only has potential value in the formulation of carbon emission reduction plans, but also provides a valuable reference for future carbon emission forecasting research.

Refined models of coordination between Al3+/Mg2+ and enzyme in molecular dynamics simulation in terms of ABEEM polarizable force field.

MFX (AlF30, AlF4- and MgF3-) as transition state analogues of phosphoryl transfer enzymes (enzyme-MFX-TSAs) is of great significance for study of the catalytic mechanism of phosphoryl transfer enzymes. Bonded model and non-bonded model based on the ABEEM polarizable force field (ABEEM PFF) are developed and applied to study the coordination of enzyme-MFX-TSAs. The bond stretching of the bond containing metal is simulated by Morse potential energy function, because the change of chemical bond is described more accurately in a large range. The charge distribution of the system is distributed to multiple-charge-sites, including atomic site, σ bond site, π bond site and lone pair electron site. Partial charge can fluctuate according to the surrounding environment and molecular conformation. The reasonable charge distribution of 68 model molecules can be obtained, and the energy minimizations are performed in vacuum. Then, with the same parameters the charge distribution and the charge transfer of four complexes are obtained, and the energy minimization and molecular dynamics simulation in NVT ensemble are carried out in vacuum and explicit water solution. The results verify the correctness, rationality and transferability of the new parameters of ABEEM PFF, and the bonded model simulates more reasonable charge distribution and geometry. The parameters determined in this paper make up the blank of the parameters of MFX and phosophoryl transfer enzymes containing Mg2+. The development of ABEEM PFF provides a refined tool for MFX-TSAs to study the catalytic mechanism of phosphoryl transfer enzymes.

Energetics and J-coupling constants for Ala, Gly, and Val peptides demonstrated using ABEEM polarizable force field in vacuo and an aqueous solution.

The development of an atom-bond electronegativity equalisation method at the σπ-level (ABEEM) polarisable force field (PFF) for peptides is presented. ABEEM PFF utilises a fluctuating charge model to explicitly describe the polarisation effects in an extensive environment. The partial charge of any individual site changes in response to changes in its surroundings. The peptide parameters are derived from ab initio methods in vacuum using a consistent and automatic protocol. By including explicit σ- and π-bond sites and lone pair sites, the anisotropy around an atom has been characterised. The fluctuating charge at each site ensures the distinction between the intrinsic behaviour observed among the various conformations of peptides, as corroborated by the agreement between quantum mechanics (QM) and ABEEM PFF concerning the calculated energy order, charge distribution, locations of minima, and potential energy surface (PES) in vacuo. The energy barriers in the PES have been clearly described using ABEEM PFF, in which a good charge distribution plays a vital role. Molecular dynamic simulations have been performed for short peptides in explicit ABEEM 7P-water boxes to examine their conformational properties in solution. The J-coupling constants obtained using ABEEM PFF are consistent with the experimental nuclear magnetic resonance (NMR) spectra and the influence of the chain length and temperature also investigated. The results demonstrate that the ABEEM PFF method is capable of locating conformations and describing the energetics of peptides with high accuracy and efficiency both in vacuo and an aqueous solution.

Water-Mediated Oxidation of Guanine by a Repair Enzyme: Simulation Using the ABEEM Polarizable Force Field.

The recognition mechanism of oxidative damage in organisms has long been a research hotspot. Water is an important medium in the recognition process, but its specific role remains unknown. There is a need to develop a suitable force field that can adequately describe the electrostatic, hydrogen bond, and other interactions among the molecules in the complex system of the repair enzyme and oxidized base. The developing ABEEM polarizable force field (PFF) has been used to simulate the repaired enzyme hOGG1 and oxidized DNA (PDB ID: 1EBM) in a biological environment, and the corresponding results are better than those of the fixed-charge force fields OPLS/AA and AMBER OL15. 8-Oxo-G is recognized by Gln315 of hOGG1 mainly through hydrogen bonds mediated by continuous exchange of 2 water molecules. Phe319 and Cys253 are stacked on both sides of the π planes of bases to form sandwich structures. The charge polarization effect gives an important signal to drive the exchange of water molecules and maintains the recognition of oxidation bases by enzymes. The mediated main water molecule A and mediated auxiliary water molecule B together pull Gln315 to recognize 8-oxo-G by hydrogen bond interactions. Then, the charge polarization signal of solvent water molecule C with a large absolute charge causes the absolute charge of O atoms in water molecule A or B to increase by approximately 0.2 e, and water molecule A or B leaves Gln315 and 8-oxo-G. The other water molecule and water molecule C synergistically recognize 8-oxo-G with Gln315. Even though the water molecules between Gln315 and 8-oxo-G are removed, the MD simulation results show that water molecules appear between Gln315 and 8-oxo-G in a very short time (<2 ps). The dwell time of each water molecule is approximately 60 ps. The radial distribution function and dwell time support the correctness of the above mechanism. These polarization effects and hydrogen bonding interactions cannot be simulated by a fixed-charge force field.

Enhanced visible light photoelectrocatalytic degradation of tetracycline hydrochloride by I and P co-doped TiO2 photoelectrode.

Elimination of antibiotics such as tetracycline hydrochloride (TC) from wastewater is of great significance, but still faces challenges. Herein, for the first time, I and P co-doped TiO2 catalysts were prepared via a hydrolysis method. We also reported a simple method to prepare I and P co-doped TiO2 photoelectrodes, which exhibited preeminent photoelectrocatalytic (PEC) performance for the decomposition of TC. The synergistic effect of I and P co-doping could significantly improve the charge separation rate and enhance the light absorption capacity of TiO2, leading to an enhancement of PEC activity. The main factors affecting the PEC performance were investigated, and the highest degradation rate constant (4.20 × 10-2 min-1) was achieved when the doping content of P was 4 at% (ITP-4 photoelectrode) at pH 11.02 under visible light. The Langmuir-Hinshelwood kinetic model and active species trapping experiments were selected to investigate the degradation mechanism of TC. The results suggest that the hydroxyl radicals and photogenerated holes were the main active species that were responsible for the decomposition of TC. Moreover, the degradation pathways of TC based on the intermediates also demonstrated that the hydroxyl radicals and holes showed a principal role in degrading TC.

Directional depolymerization of lignin into high added-value chemical with synergistic effect of binary solvents.

This work exploits a one-pot method for directional depolymerizing organosolv lignin into high added-value phenolic monomers with synergistic reaction system consisted of methanol-dimethoxymethane binary solvents and acid catalyst. The influence of solvent composition and reaction parameters such as different catalyst, binary solvents ratio, time, and temperature on the conversion of lignin and yield of products were investigated carefully, the optimum yield of liquid products and phenolic monomers were achieved at 67.39% and 27.67% at 200 °C kept for 60 min with low amount of acid catalyst. The plausible mechanism on the depolymerization of lignin was proposed in view of product distributions. Moreover, the combination of co-solvents and acidic catalyst was also suitable for converting different types of lignin into phenolic monomers, and the recyclability of joint reaction system was satisfactory. These results can provide promising prospects on developing an effective method for achieving high added-value phenolic compounds from lignin.

Lignin Based Activated Carbon Using H3PO4 Activation.

Activated carbon (AC) with a very high surface area of over 2000 m2/g was produced from low sulfur acid hydrotropic lignin (AHL) from poplar wood using H3PO4 at a moderate temperature of 450 °C (AHL-AC6). ACs with similar surface areas were also obtained under the same activation condition from commercial hardwood alkali lignin and lignosulfonate. Initial evaluation of AC performance was carried out using nitrogen adsorption-desorption and dye adsorption. AHL-AC6 exhibited the best specific surface area and dye adsorption performance. Furthermore, the adsorption results of congo red (CR) and methylene blue (MB) showed AHL-AC6 had greater adsorption capacity than those reported in literature. The dye adsorption data fit to the Langmuir model well. The fitting parameter suggests the adsorption is nearly strong and near irreversible, especially for MB. The present study for the first time provided a procedure for producing AC from lignin with Brunauer-Emmett-Teller (BET) surface area >2000 m2/g using low cost and low environmental impact H3PO4 at moderate temperatures.

Dividing the Periodic Box into Subdivisions with Their Surroundings to Accelerate Molecular Dynamics Simulation with High Accuracy.

A major field of current research in chemistry and biology is the development of the tools that enable in situ analysis of complex systems. However, the long-time dynamics simulation for an extremely large system in solution is almost impossible by an all-atom force field combined with an explicit solvent model. The results show that the larger the periodic box is, the closer the properties of the system are to the experimental values. Therefore, how can we carry out simulations for systems that are fast, accurate, and large enough? A method of dividing the periodic box into subdivisions with their surroundings (DBSS) is presented here, and it clearly increases the computation speed without losing accuracy and enables the simulation of extremely large systems by strongly decreasing the dimension of the charge matrix. The DBSS method divides a single periodic box or unit in an extremely large system into several subdivisions with a suitable choice according to atomic coordinates. This method ensures that these subdivisions are always changing and allows the atoms to communicate with each other. Intermolecular communication is important for molecular properties and functions but is not possible with other fragment methods. The partial charges are calculated in each subdivision with an overlapping surrounding used to take hydrogen bond interaction between the subdivisions into account. This is an iterative process because the charge population will be recalculated at intervals during the dynamics simulations. Taking a water system as an example, each subdivision is extended by 4 Å as the surrounding. The computation time scales almost linearly with the size of the system, and the slope is small. MD simulations for several properties have been performed by the ABEEM-DBSS method. The results indicate that the ABEEM-DBSS method can accurately simulate the properties of water system, and the accuracy can reach or approach that of the experimental data or of other water potentials. Interestingly, the properties become closer to the experimental data as the sizes of the periodic box increase, further validating the need for the simulation of a large system and demonstrating the value of the DBSS method.

Alterations of fatty acid composition and metabolism in APP/PS1 transgenic mice.

Accumulating evidence suggests that abnormal fatty acid composition is related to the development of Alzheimer's disease (AD). However, there is no consistency in the fatty acid profile and metabolism associated with AD pathogenesis. This study aims to define the characteristics of fatty acid composition and metabolism in AD. Using 6-month-old APP/PS1 transgenic mice with wild-type mice as a control, we examined the serum lipids, brain fatty acid composition, and the expression levels of various genes involved in liver fatty acid ß-oxidation. The results of our study demonstrate that APP/PS1 mice present decreased serum free fatty acids, altered brain fatty acid profiles, and minimal change in liver fatty acid ß-oxidation. Our results suggest that abnormal fatty acid compositions and contents may play potential roles in AD progression. This study provides further evidence for the metabolic basis of AD pathogenesis.

Systematic Parameterization and Simulation of Boronic Acid-ß-Lactamase Aqueous Solution in Developing the ABEEMσπ Polarizable Force Field.

Boronic acid, an inhibitor of ß-lactamase, has begun to be applied to the treatment of biological infections and tumors. Scientists are working to develop new and more effective boronic acid. Molecular dynamics (MD) simulation provides a powerful auxiliary tool for drug design. However, the current force fields have no boron-related parameters. In this work, an atom-bond electronegativity equalization method at the σπ level (ABEEMσπ) polarizable force field (ABEEMσπ PFF) of boronic acid and ß-lactamase has been developed to determine the potential functions and parameters. The interaction between boron and serine in ß-lactamase is regarded as a bonded mode. The interaction between them is simulated by the Morse potential energy function, which is close to the experimental change of the stretching potential energy in a large range. The potential energy surfaces of the bond length, bond angle, and dihedral angle of boronic acid-ß-lactamase have the same stability point and change trend as M06-2X/6-311G**. For 47 boronic acid-ß-lactamase training molecules, the linear correlation coefficient (R) of the charge distribution between the ABEEMσπ PFF and HF/STO-3G is greater than 0.96. Attributed to the fact that the charge distribution of the ABEEMσπ PFF can fluctuate with the change of geometry and environment, the polarization effect and charge-transfer effect are well reflected. The binding ability of different boronic acids with the same ß-lactamase is different. A total of 10 boronic acid-ß-lactamase model molecules and 10 boronic acid-ß-lactamase and water complexes are simulated. The order of binding energy of five large model molecules calculated by the ABEEMσπ PFF is consistent with that of the MP2 method. The binding energies of boronic acid-ß-lactamase and water complexes are close to those of the MP2 method. The results of MD simulation of five aqueous boronic acid-ß-lactamase complexes in the NVT ensemble verify the rationality of boron-related parameters of the ABEEMσπ PFF, which have a good application prospect. This study lays a solid theoretical foundation for further study of the inhibition of boronic acid on ß-lactamase.

Directional and integrated conversion of whole components in biomass for levulinates and phenolics with biphasic system.

Integrated conversion and stepwise extraction of whole components in biomass with biphasic system are introduced for producing chemicals: levulinates and phenolics. When methanol/dimethoxymethane as biphasic solvent, 46.51% methyl levulinate and 18.78% phenolics were obtained with a conversion of 80.59 wt% per 4 g rice straw under the mild reaction conditions. Levulinates were collected with a 87.5 wt% high purity of methyl levulinate with stepwise precipitation and extraction from the cellulose and hemicellulose. The results of acid value, freezing point, induction period, kinematic viscosity, and flash point supposed that the extracted methyl levulinate could meet the requirements of fuel additives. Depolymerized lignin was consisted of many low-molecular phenolics. These results illustrated that the biphasic system can promote the conversion of cellulose and hemicellulose to the same product methyl levulinate through different intermediate transition compounds, and the catalyst can contribute to directly cleave the glycosidic bonds, ß-O-4, and 4-O-5 with adequate protons.

ABEEM/MM OH- Models for OH-(H2O)n Clusters and Aqueous OH-: Structures, Charge Distributions, and Binding Energies.

Based on the atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM), two fluctuating charge models of OH--water system were proposed. The difference between these two models is whether there is charge transfer between OH- and its first-shell water molecules. The structures, charge distributions, charge transfer, and binding energies of the OH-(H2O)n (n = 1-8, 10, 15, 23) clusters were studied by these two ABEEM/MM models, the OPLS/AA force field, the OPLS-SMOOTH/AA force field, and the QM methods. The results demonstrate that two ABEEM/MM models can search out all stable structures just as the QM methods, and the structures and charge distributions agree well with those from the QM calculations. The structures, the charge transfer, and the strength of hydrogen bonds in the first hydration shell are closely related to the coordination number of OH-. Molecular dynamics simulations on the aqueous OH- solution are performed at 298 and 278 K using ABEEM/MM-I model. The MD results show that the populations of three-, four-, and five-coordinated OH- are 29.6%, 67.1%, and 3.4% at 298 K, respectively, and those of two-, three-, four-, and five-coordinated OH- are 10.8%, 44.9%, 39.2%, and 4.9% at 278 K, respectively; the average hydrogen bond lengths and the hydrogen bond angle in the first shell increase with the temperature decreasing.