The effect of temperature and solvation on the ultrafast dynamics of n-methylacetamide

The ultrafast dynamics of N-methylacetamide (NMA), a peptide-linkage model compound, are reported for the first time as a function of temperature and dilution. The rotational-diffusive timescale of NMA was observed to behave in a manner inconsistent with established hydrodynamic theory for simple liquids, exhibiting sharp decreases at elevated temperatures and low concentrations. These were associated with non-stoichiometric changes in far-infrared and terahertz Raman transition strengths. The data is consistent with a model in which neat NMA forms hydrogen bonded aggregates, featuring cooperative effects upon the polarizability and dipole moment that are disrupted by increased temperature or decreased NMA mole fraction.