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In view of the widespread glyphosate herbicide (N-(phosphonomethyl) glycine) usage, the physical and chemical properties in aqueous solution have to be exploited to understand its role in environment. In this sense, molecular dynamics (MD) simulations can provide an atomistic detail in the description of such a system. Herein, partial atomic charges and dihedral angles were obtained quantum mechanically for glyphosate molecule. Parameters for MD simulation were implemented in the OPLS-AA force field to better understand the herbicide mechanism action. Results showed that atomic charges were consistent with the database of the force field. Additionally, potential energy curves for the dihedrals were consistent and could be used to run MD simulations. Therefore, the parameterisation reported for this molecule can be useful to explain studies involving its interaction with many enzymes and proteins such as 5-enolpyruvylshikimate 3-phosphate synthase enzyme (EPSP). Furthermore, considering these new data in OPLS-AA, numerous simulations can be proposed to unveil the effects of the glyphosate as an environment contaminant.

The effects of the configuration and temperature on the Young’s modulus of poly (methyl methacrylate) (PMMA) have been studied using molecular dynamics simulations. For the DREIDING force field und...

Interactions between transmembrane (TM) peptides are important in biophysical chemistry, but there are few studies assessing atomistic simulation parameters concerning the energetics of interactions of TM helical peptides. Our potential of mean force analysis using OPLS-AA protein/Berger lipid force fields (FFs) shows that the dimerisation energy of (AALALAA)3 helical peptides in the dioleoylphosphatidylcholine bilayer is −4.4 kJ/mol, which was much smaller than the reported experimental value (−12.7 kJ/mol), thus calling for improvement of parameters of the combined FFs. As each of the FFs has been independently developed, we then tested the effects of downscaling the Lennard-Jones (LJ) energy terms between the OPLS-AA atoms and Berger lipid atoms, preserving the parameters within each FF. A 0.9-fold rescaling of the LJ energies was found to render the dimerisation energy close to the experimental value. Solvation of backbone atoms as well as side chain atoms in lipids is crucial for the TM helix interaction. In similar analyses, GROMOS 53A6 FF exhibited as weak dimerisation propensity (~−5.2 kJ/mol) as OPLS-AA/Berger, but CHARMM36 showed relatively accurate propensity (~−9.9 kJ/mol). Challenges and strategies in rendering the TM interaction energy realistic within the framework of current FFs are discussed.

A set of 13 aliphatic alcohols was modelled by molecular dynamics simulations at temperatures from 288 to 338 K using the optimised potential for liquid simulations (OPLS) united-atom force field, the OPLS all-atom force field and the OPLS all-atom force field with modified partial charges of the hydroxyl group. The set includes primary and secondary alcohols, and mono-, di- and trialcohols, and covers a broad range of polarities from log P = − 0.74 (methanol) to log P = 2.9 (octanol). The density, the radial distribution function, the self-diffusion coefficient and the dielectric constant were evaluated. A long equilibration time of at least 50 ns and a large size of the molecular system of more than 75,000 atoms were used. Except for glycerol, the OPLS all-atom force field reliably reproduced the experimentally determined density with deviations of less than 4% over the whole temperature range. In contrast, the modelled self-diffusion coefficient deviated from its experimental value by up to 55%. To mod...

New force fields for molecular dynamics (MD) simulation of aqueous zwitterionic amino acid simulations were developed. These were especially designed to calculate activity coefficient of water in amino acid solutions with high accuracy. For example, aqueous solutions of the following amino acids were considered: glycine, alanine, α-aminobutyric acid, α-aminovalerianic acid, valine and leucine. The force fields were obtained by quantum chemical calculations using B3LYP/6-31G and MP2/6-311(d,p) model theories in combination with the Merz–Kollmann–Singh scheme. To further increase the accuracy of the force field, a polarised continuum was considered in all quantum chemical calculations. Water activity coefficients obtained from MD using different all-purpose literature force fields, namely, OPLS, AMBER ff03 and GROMOS 53A6 as well as experimental data are compared with the results utilising the new force field. The new force field is shown to give better results compared with experimental data than existing ...

We have previously proposed a method for refining force-field parameters of protein systems, which consists of minimising the summation of the square of the force acting on each atom in the proteins with the structures from the protein data bank (PDB). The results showed that the modified force-field parameters for all-atom model gave structures more consistent with the experimental implications than the original force fields. In this work, we applied this method and a new method to the OPLS–UA force field. In the new method, we perform a minimisation of the average of the root-mean-square deviation of various protein structures from the native structure. We selected some torsion-energy parameters for this optimisation, and 100 molecules from the PDB were used. The results imply that the new force-field parameters gave structures of two peptides more consistent with the experimental implications for the secondary structure-forming tendencies than the original OPLS–UA force field.

The ability of five different force fields (MM2, MM3, AMBER, OPLS, MMFF) to calculate relative conformational energies of seven molecules is compared to results at the MP2/aug-cc-pVTZ level. It is found that the quality of the results deteriorates as the polarity of the molecules increases for all force fields, strongly indicating that the use of fixed partial charges for representing the electrostatic interaction limits the accuracy that can be obtained.

The ability to use computer simulations to predict mixture properties using potential models that have been optimized for the pure compounds is demonstrated. Since the potential models were optimized only for the pure compounds, there is no guarantee that they will describe the interactions between dissimilar molecules in the mixture correctly. In this study, Monte Carlo simulations have been carried out in the isothermal-isobaric (NPT) ensemble to calculate the density and excess enthalpy for 1-butanethiol + n-heptane mixtures at 298.15 K and 1 atm. The OPLS potential-parameters developed by Jorgensen were used to describe the n-heptane molecule. Two models for the butanethiol molecule were employed: PES1 used the OPLS potential-parameters unaltered, while PES2 used the OPLS parameters with slightly modified partial charges. Simulations were performed on mixtures with butyl mercaptan mole fractions of 0.0, 0.23, 0.42, 0.62, 0.83, and 1.0. The average rms deviation between the calculated densitie...