Quantum-classical description of the amide I vibrational spectrum of trialanine

摘要

A quantum-classical description of the amide I vibrational spectrum of trialanine cation in D2O is given that combines (i) a classical molecular dynamics simulation of the conformational distribution of the system,(ii) comprehensive density functional theory calculations of the conformation-dependent and solvent-induced frequency fluctuations,and (iii) a semiclassical description of the vibrational line shapes which includes nonadiabatic transitions between vibrational eigenstates.Various assumptions that are usually employed in the calculation of condensed-phase vibrational spectra are tested,including the adiabatic,the Franck-Condon,and the second-order cumulant approximations,respectively.All three parts of the theoretical formulation are shown to have a significant impact on the simulated spectrum,suggesting that the interpretation of peptide amide I spectra may require substantial theoretical support.