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Pressure effects on solvation structure and dynamics in mixture of cis and trans-Nmethylformamide in a protic and aprotic polar solvent

Authors : Apramita Chand and Snehasis Chowdhuri*



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Abstract

We have explored the effects of variation of pressure on solvation structure, dynamics and hydrogen bonding properties in mixture of cis and trans-N-methylformamide in protic/aprotic medium through classical molecular dynamics simulations. Hydrogen bonding preferences of ONMF-HNMF vary with cis-cis/trans-trans/cis-trans/trans-cis combinations but are overall better in DMSO solution than in aqueous solution. In both water/DMSO solutions, at XNMF = 0.5, the Ocis-Hcis hydrogen bonding probability is enhanced which is boosted at higher pressures. Higher pressures may induce hydrogen bond contacts at intermediate pressures due to close packing but distortion in hydrogen bond network renders such hydrogen bonds less stable. Cis-NMF molecules prefer hydrogen bonding interactions with oxygen of DMSO while trans-NMF molecules engage their Nmethyl groups for hydrophobic interactions with DMSO methyl groups. The disparity between cis and trans-NMF dipole rotations becomes more apparent in aqueous medium at higher pressures and higher NMF concentrations while difference in diffusion coefficients is significant at lower pressures. Higher lifetimes of ODMSO…Hcis hydrogen bonds may be responsible for longer dipole relaxation rates of cis-NMF in DMSO solution as pressure increases.

 

Keyword

cis and trans-NMF mixture, self-diffusion, orientational relaxation, hydrogen bond lifetime.