Scheme and atom labeling of trialanine cation .
maps of the mean (top) and the splitting (bottom) of the two amide I frequencies, as obtained for isolated glycine dipeptide (left), isolated trialanine (middle), and trialanine in (right).
Distribution of the frequency splitting without (left) and with (right) the inclusion the solvent contribution, as obtained for the three conformational states of glycine dipeptide (top) and trialanine (bottom).
Distribution of the amide I normal-mode frequencies obtained for the three conformational states of trialanine (a) in the gas phase and (b) in solution. Panel (c) shows the corresponding absorption bands calculated within the cumulant approximation.
Solvent-induced frequency shifts (black solid line) and (red dashed line) of the amide I local modes of trialanine, plotted as a function of the distance between peptide and solvent atoms.
(Left) Distribution of the solvent-induced amide I frequency shifts (black solid lines) and (red dashed lines), as obtained for the three conformational states of trialanine. (b) Radial distribution functions pertaining to the distance between (middle) the oxygen of the peptide unit and a hydrogen of water and (right) the hydrogen of the peptide unit and the oxygen of water , respectively.
Correlation functions of the total transition dipole moment, shown for both amide I normal modes and the conformations , , and .
Amide I absorption bands of trialanine obtained for the conformations , , and . Compared are results calculated directly from semiclassical line-shape theory [via Eq. (5), thick black lines], by invoking only the adiabatic approximation [via Eq. (8), thin red lines], and by invoking adiabatic and cumulant approximations [via Eq. (8), blue dashed lines].
Comparison of experimental (Ref. 39, green dashed line) and calculated amide I absorption spectra of trialanine. The latter were obtained directly from semiclassical line-shape theory [via Eq. (5), thick black line] and by invoking adiabatic and cumulant approximations [via Eq. (8), thin red line].
Solvent-induced frequency shifts and of the amide I local modes of trialanine, comparing various electrostatic models (see text). Shown are the mean frequency shifts and , the full widths at half maximum and of the distributions, as well as the mean frequency gap , as obtained for the conformational states , , and . Units are .
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