Strategy and Tactics in the Raman Spectroscopy of Biomolecules

Abstract

The strategic bases for the application of Raman spectroscopy to the problems of molecular biology and the tactics used in exploiting them are examined and discussed with the help of specific examples. The correlation of vibrational frequencies and intensities with molecular geometry is illustrated by several group frequencies of importance in the analysis of the Raman spectra of proteins, including those of the disulfide and amide groups. A new correlation between the amide-III frequency and peptide geometry is proposed and utilized to follow the reversible thermal denaturation of the enzyme ribonuclease. How other physical techniques may be combined with Raman methods is shown by the comparison of the Raman spectrum of a crystalline transfer ribonucleic acid, whose molecular structure is known from x-ray diffraction, with the spectra of the same substance in aqueous solution under different conditions of ionic strength, pH, and temperature. From the quantitative variation of the spectra the structural changes produced by temperature are evaluated. Possible improvements and new developments in the strategy and tactics of Raman spectroscopy are considered briefly.