Quantum chemical modeling of the structure and vibrational spectra of two melatonin catabolites: N-γ-acetyl-N-formyl-5-methoxykynuramine and N-γ-acetyl-5-methoxykynuramine

Abstract

Quantum chemical calculations for possible conformers of the melatonin molecule (N-acetyl–5-methoxytryptamine) and its two catabolites, (N-γ-acetyl-N-formyl-5-methoxykynuramine (AFMK) and N-γ-acetyl-5-methoxykynuramine (AMK)), are performed at different theoretical levels with inclusion of the macrohydration effects within the conductor-like polarizable continuum model (CPCM). The influence of the used in biochemical studies CD3-labels on the vibrational spectra of molecules is considered. It is demonstrated that the theoretical (B3LYP/6-31+G**) vibrational spectra and geometric parameters of the most stable melatonin conformers are in good agreement with the experimental data. On a base of analysis of the theoretical frequency shifts in the theoretical B3LYP/6-31+G** vibrational spectra of different conformations of melatonin catabolites and of the influence of the aqueous surrounding and isotopic substitution, the conclusion is made that the region of nitrogen–hydrogen stretching can be proposed for identification of considered compounds.