INFRARED-ANALYSIS OF PEPTIDE SUCCINIMIDE DERIVATIVES

In order to establish parameters to identify imide derivatives formed during in vitro aging of aspartylalanyl-containing proteins, a dipepti de and a tetrapeptide containing this sequence were acidified and heat ed in vacuo. The formation of succinimide derivatives could be confirm ed by FTIR and Raman spectroscopy. Hereto, earlier assignments of succ inimide vibrations had to be revised. FTIR absorbance spectra of the s uccinimide, derived from H-Asp-Ala-OH, in the solid state give five ba nds between 1700 and 1800 cm-1. In this case, owing to Fermi resonance , the antisymmetric imide carbonyl stretching vibration gives rise to an apparent doublet, centered around 1715 cm-1. The symmetric stretchi ng mode is found at 1793 cm-1. The other bands are assigned to carboxy lic acid stretching modes (I 728 cm-1: COOH dimer and 1751 cm-1: COOH monomer). Fermi resonance does not occur in succinimide derivatives oc curring in larger peptides. As a consequence, the imide bands of the s uccinimide, generated from H-Val-Asp-Ala-Gly-OH, are observed at 1716 and 1791 cm-1 (antisymmetric and symmetric stretching modes, respectiv ely). (C) Munksgaard 1993.