ABSTRACT
Infrared and Raman spectroscopies measure the vibrational frequencies of a group of bonded atoms in a molecule. The frequencies are determined by the masses of the atoms, the force constants, and the geometry of the molecule. Thus, it is possible, at least in principle, to determine structural properties of a molecular group, such as bond orders, bond length/angle, and ionization state of ionizable moieties, from vibrational frequencies. Furthermore, the interactions that take place between molecular groups when a small molecule binds to a protein, such as hydrogen bonding and other bond-polarizing electrostatic interactions, geometry distortion from steric clashes, and the formation of new bonds, affect vibrational frequencies and, hence, are reported by the changes in frequencies. The accuracy of determining these parameters from vibrational frequencies is very high, gener ally much better than probes of protein structure such as x-ray crystallographic and multidimensional NMR studies. On the other hand, while vibrational spectros copy is a very fine-scale probe, it is not (currently) feasible to determine the full structure of a protein from its vibrational spectrum. There is thus a high degree of synergism among these experimental probes in the information they provide.
