α-Amino Acids In Water: A Review Of VCD And ROA Spectra

Abstract

An up-to-date perspective on the capability of Vibrational Circular Dichroism (VCD) and Raman Optical Activity (ROA) spectroscopy of the 20 encoded α-amino acids to solve the structural problems appearing in water is provided in this review. VCD and ROA spectroscopy of the α-amino acid molecules reviewed in this chapter refer only to free and single amino acids in water at various pH levels. To well understand the implications of such studies for biology and medicine, we devote one subchapter to the role of free amino acids in an organism’s metabolism and physiology. A variety of side chains that modify the α-amino acids character from acidic to basic and from hydrophilic to hydrophobic makes the possible dissociation equilibria in water very complex and dependent on several factors. Therefore, information on dissociation constants, isoelectric points, and hydrophobicity parameters of α-amino acids is summarised in the next subchapter. The conformational variety, complexity of interactions, and entanglement of equilibria makes considering the influence of these factors on VCD and ROA spectra with quantum chemical analysis absolutely necessary. The elements of the theory of chiroptical vibrational spectra and methods enabling solvent simulations are provided in the subsequent subchapter. We report on experimental methods, techniques and tricks for measuring and simulating the VCD and ROA spectra in water at different pH levels. The review is concluded by listing the not-yet-measured amino acids, a presentation of the main challenges for computational methods, and suggestions for the most promising experimental techniques that may be used in future studies.