Combined Matrix-Isolation FT-IR and AB Initio 6-31 + + G** Studies on the Tautomerism and H-bonding Properties of Nucleic Acid Bases and Simpler Model Molecules

Abstract

A step-by-step experimental and ab initio 6–31 + + G** research approach has been developed for interpretation of FT-IR spectra of H-bonded complexes of different tautomers of nucleic acid bases. The first step of this procedure involves a detailed study of a large number of relatively simple compounds, each modeling one or more H-bonding sites of cytosine, adenine and guanine. The application of this method is illustrated with the results obtained for the tautomerism of 1-CH3-adenine and 1-CH3-cytosine, and for some H-bonded complexes of imidazole and 4-NH2-pyridine with water. Comparison between the experimental and ab initio calculated parameters for the H-bonded complexes allows some correlations to be established. Apart from practical application of the correlation curves, e.g. interpretation of the complicated FT-IR spectra of H-bonded nucleic acid bases, more fundamental information can also be obtained from die correlations.