Different Weak C−H···O Contacts in <i>N</i>-Methylacetamide-Water System: Molecular Dynamics Simulations and NMR Experimental Study

Abstract

An all-atom N-methylacetamide (NMA) model and a refined SPC water model have been adopted for molecular dynamics simulations. 1H NMR chemical shifts of water, as well as the relative chemical shifts of the NMA methyl group and amide hydrogen atom in the NMA-water system, are measured and calculated over an entire composition range at different temperatures: 308, 323, 338, and 353 K. NMA molecules can act as a hydrogen bonding acceptor or a donor competing with water molecules. Interestingly, the two methyl groups in the NMA molecule are found to have different capabilities in forming weak C−H···O contacts in the mixtures from the radial distribution functions (RDFs). Also, temperature-dependent NMR results of the different methyl groups show excellent agreements with the MD simulations.