Spectroscopic Studies of Molecular Interaction in DNA Constituents
Stability of the DNA helix depends in part on the free energy of association of the DNA-base pairs. Similarly, the interaction between DNA and certain biologically active molecules may be determined in large part by the binding of the latter to the DNA bases. It is possible to study the base pair interactions in nonaqueous solvents, such as chloroform, by means of infrared spectroscopy, and the results of a variety of such studies are summarized. The selectivity of base pairing, effects of chemical substitution on base-pairing equilibria, the thermodynamics of base pairing, and ultraviolet hypochromism in chloroform solution are discussed on the basis of the infrared studies. For aqueous solutions, Raman spectra appear to be a more powerful means of investigating associative equilibria, and a number of interesting systems have been examined with this technique. A survey of the Raman spectra of aqueous solutions of individual bases, nucleosides, and nucleotides is given. The spectra of certain mixtures of nucleosides are discussed, and results are reported from the spectroscopic study of nucleoside-metal ion complexes and of interaction between organic phosphates and metal ions. The advantages of excitation of Raman spectra by lasers are illustrated in preliminary fashion by comparison of the spectrum of polyriboadenylic acid excited with mercury blue light with that excited by a helium-neon laser.
KeywordsRaman Spectrum Spectroscopic Study Chloroform Solution Raman Line Raman Effect
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