NMR Studies on Dynamic Properties of Nucleic Acid Base Pairs in Nonaqueous Solvents

Abstract

In the double-stranded structures of deoxyribonucleic acid and ribonucleic acid, adenine forms specific hydrogen bonds with thymine (or uracil) and guanine with cytosine. The specific bonds are believed to be the molecular basis of information transfer in nucleic acids. Much work has been done to find the basis of this specificity by the use of synthetic poly-and oligonucleotides and single base derivatives. Some infrared (1~8) and proton magnetic resonance studies (9~12) clearly showed that even single base residues interact by means of specific hydrogen bonds in solution. The data obtained in these experiments revealed the strength of interaction on the amino-and imino-protons, but little is known about the acceptor sites of the hydrogen bonds. In the base pair model proposed by Watson and Crick, thymine (or uracil) pairs with adenine by using the C-4 carbonyl group. However, X-ray analyses showed that 5-bromouracil (13) and 4-thiouracil (14) derivatives through the C-2 carbonyl group. In the present experiment we observed ¹³C magnetic resonances of single base derivatives in solution and tried to find interaction sites from the concentration dependency of chemical shifts.