The Anharmonic Vibrational Potential and Relaxation Pathways of the Amide I and II Modes of N-Methylacetamide

Citations Over TimeTop 10% of 2006 papers

Abstract

We investigate the influence of isotopic substitution and solvation of N-methylacetamide (NMA) on anharmonic vibrational coupling and vibrational relaxation of the amide I and amide II modes. Differences in the anharmonic potential of isotopic derivatives of NMA in D2O and DMSO-d6 are quantified by extraction of the anharmonic parameters and the transition dipole moment angles from cross-peaks in the two-dimensional infrared (2D-IR) spectra. To interpret the effects of isotopic substitution and solvent interaction on the anharmonic potential, density functional theory and potential energy distribution calculations are performed. It is shown that the origin of anharmonic variation arises from differing local mode contributions to the normal modes of the NMA isotopologues, particularly in amide II. The time domain manifestation of the coupling is the coherent exchange of excitation between amide modes seen as the quantum beats in femtosecond pump-probes. The biphasic behavior of population relaxation of the pump-probe and 2D-IR experiments can be understood by the rapid exchange of strongly coupled modes within the peptide backbone, followed by picosecond dissipation into weakly coupled modes of the bath.

Related Papers

• → Vibrational relaxation of CO2 in CO2-N2 and CO2-O2 mixtures(1974)21 cited
• → Concentration and temperature dependence of electronic and vibrational energy relaxation of O2 in liquid mixtures(1981)65 cited
• → Anharmonic Effects on the Rate of Relaxation of Vibrational Energy in Rapidly Expanding Flows(1972)15 cited
• → On the phonon mechanism of vibrational relaxation of adsorbed particles(1988)9 cited
• → A comment on the vibrational relaxation of anharmonic oscillators(1972)1 cited