Conformational preference of short aromatic amino acids from the FT-IR, FT-Raman and Far-IR spectroscopies, and quantum chemical calculations: l-phenylalanine and l-tyrosine

Abstract

From the analysis of the vibrational Mid-IR, Raman and Far-IR spectra of the α-amino acids l-phenylalanine and l-tyrosine, we are able to explain the conformational preference of their zwitterionic forms, which are of biological interest. The recorded spectra of l-Phe and l-Tyr in the solid state have been analyzed and compared with a large set of quantum chemical calculations in order to better understand the zwitterionic structures experimentally detected. In this way, analysis of the low frequency region between 500 and 30cm−1 reveals much information in order to assign the most stable structures. The present work reveals that IR, Raman, and Far-IR, combined with quantum chemical calculations, are helpful and complementary techniques to characterize biological systems, such as amino acids.