Infrared spectra of related dipeptides

Abstract

The infrared spectra of a series of glycine dipeptides, a series of tryptophan dipeptides and of l-leucine, l-alanine dipeptides were determined. Assignments of certain absorption bands were related to the amide linkage and to the amino and carboxyl end groups which are possessed in common by all dipeptides except for those of proline and hydroxyproline. While dipeptides containing glycine gave no typical pattern, those containing tryptophan showed a distinctive pattern in the 1068–1156 cm −1 region. Examination of the 1500–1700 cm −1 region, for peptides thus far studied, indicates that infrared spectra can give information about their sequence. In the few instances in which paired dipeptides showed the same number of absorption band in this region, they could be readily differentiated by differences in the 1340–1400 cm −1 region. This study suggests that specific infrared band patterns may exist for other dipeptides which contain a common amino acid residue other than tryptophan.