All-atom molecular dynamic simulations and relative NMR spectra study of weak C-H•••O contacts in amide-water systems

Amide-water mixtures are studied by all-atom molecular dynamics (MD) simulations and the relative temperature-dependent NMR experiment. The weak C-H (...) O contacts are found in the amide-water systems theoretically and experimentally. The statistical results of the average numbers of hydrogen bonds indicate that the methyl groups in amide molecules represent different capabilities in forming the weak C-H (...) O contacts. The statistics also imply that the C-H (...) O contacts are more obvious in the amide-rich region than those in the water-rich region. The temperature-dependent NMR spectra are also adopted to investigate the weak C-H (...) O contacts in the amide-water systems. The relative chemical shifts of the methyl groups are in good agreement with the MID simulations.