Investigation of the anomalous solvation free energies of amides and amines: FEP calculations in cyclohexane and PS-GVB calculations of amide-water complexes

Article Abstract:

The anomalous ordering of the amide and amine aqueous solvation energies were investigated through free energy perturbation (FEP) calculations of acetamide, N-methylacetamide, N,N-dimethylacetamide, ammonia and methylamine in cyclohexane and PS-GVB calculations of amide-water complexes at the LMP2/cc-pVDZ level. The FEP calculations on cyclohexane showed an additive methyl substitution effect for both amines and amides. The PS-GVB calculations suggested that the anomalous aqueous solvation free energies of amides is due to differences in their hydrated gas-phase geometries.

Amines, Amides, Cyclohexane

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Binding of organic cations to a cyclophane host as studied with molecular dynamics simulations and free energy calculations

Article Abstract:

The binding of two organic cations, an iminium (IM) and a guanidinium (GU), to a cyclophane host P4--4Na+, was investigated through molecular dynamics simulations and free energy computations. Differences in van der Waals interaction energies were mostly responsible for the various binding strengths, and the host adopts various shapes when accommodating IM as compared to GU. The in vacuo interaction energies in the two complexes were computed utilizing a nonadditive force field, previously found to accurately represent alkali cation-aromatic interaction energies in vacuo.

Models, Molecular dynamics, Cations, Cyclophanes

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Application of the RESP methodology in the parametrization of organic solvents

Article Abstract:

Parametrizations of the nonaqueous solvents dimethyl sulfoxide, ethanol, CCl4, CHCl3 and CH2Cl2 have been undertaken using the RESP methodology. The results obtained are similar with those obtained through the AMBER force field of Cornell et al. The method can be used not just with new functional groups in the solute but also when a different solvent or mixture of solvents are used. It makes possible a flexible all-atom solvent model whose density, heat of vaporization, diffusion constant and rotational times agree with experimental data.

Analysis, Atomic structure, Solution (Chemistry), Solutions (Chemistry), Organic solvents

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