Vibrational circular dichroism in amino acids and peptides. 3. Solution- and solid-phase spectra of alanine and serine

Vibrational circular dichroism (VCD) in solution and solid phases is reported for alanine and serine in vibrational modes involving hydrogen and deuterium stretching motions. The quality of the solution-phase VCD spectra was significantly enhanced by on-line computer averaging techniques. Solid-phase spectra were obtained as mulls in halocarbon oil and this method promises to be a useful new sampling technique in VCD spectroscopy. VCD signals in the solid phase are considerablq larger than the solution spectra for the same molecules. The increased magnitude is attributed to such effects as conformational uniformity, local ordering, and crqstal lattice interactions between molecules. A neb vibrational assignment of solutionphase alanine in the carbon-hydrogen stretching region is presented as determined from the solid-phase Ranian spectra of alaninc-do and alanine-C*-dl. The basic features of the observed VCD spectra of alanine and serine are discussed in terms of their constituent normal modes and the chiral perturbation of locally symmetric groups