Spectral manifestations of urea effect on glycylglycine self-association

Abstract

The effect of urea on intermolecular interactions and the infrared spectral characteristics of a glycylglycine dimer was investigated using density functional theory. Quantum-chemical calculations were performed at the B3LYP/6-31G(d) level. Optimized structures and IR spectra were obtained for a glycylglycine monomer, its hydrogen-bonded dimer, and the dimer complex with one urea molecule. The reliability of the computational approach was evaluated by comparison of the calculated spectra of glycylglycine and urea with available experimental data.
Formation of the glycylglycine dimer was accompanied by two intermolecular N–H···O hydrogen bonds with pronounced spectral signatures. Introduction of a urea molecule near one of these interactions caused substantial changes in both its geometric and spectral parameters. The corresponding hydrogen bond became longer, its IR band shifted toward higher wavenumbers, and both the band intensity and the estimated interaction energy decreased. At the same time, the second intermolecular hydrogen bond remained nearly unchanged, indicating a predominantly local effect of urea on the peptide–peptide interaction.
The obtained results demonstrate that weakening of intermolecular hydrogen bonding in peptide systems can produce distinct IR spectral changes detectable by combining infrared spectroscopy with quantum-chemical modeling. The study complements previous molecular-dynamics investigations of peptide self-association and provides a molecular-level interpretation of how urea may weaken peptide–peptide interactions in a minimal model system.

Speaker

Egor V. Nazarev
Saratov State Technical University
Russia

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