The FT-IR spectra of glycine and glycylglycine zwitterions isolated in alkali halide matrices

The infrared absorption spectra of glycine and the dipeptide glycylglycine have been measured using a novel spray-sampling technique which leads to better resolved spectra than the traditional crystal and solution methods. Spectra were recorded for a number of different alkali halide matrices. Theoretical predictions of the spectra have been undertaken using the self-consistent reaction field Onsager continuum model, without the inclusion of specific solute solvent interactions. Good agreement has been achieved between measured and predicted structures and spectra. For the glycine zwitterion in alkali halide matrices, the measured spectra suggest a trans structure about the NC bond, while for the dipeptide the conformation about the peptide bond is trans as in the crystal. The DSD spectra showed little dependence on the alkali halide matrix used to isolate the amino acid zwitterions in support of the theoretical approach adopted.