Specific Association of Riboflavin and Adenine Derivatives in Chloroform Solution and the Effect of Barbiturates on the Association

Riboflavin-2′,3′,4′,5′-tetraacetate and tetrabutyrate have been found to associate with 9-ethyladenine. They form stronger complexes with each other than with themselves and with other nucleic acid purine and pyrimidine derivatives. The association constants of the formation of the complexes were determined from the infrared spectra to be 130 and 95m−1 respectively. The complex is a 1 : 1 cyclic hydrogen bonded dimer through the imino and the 2-C carbonyl groups of the isoalloxazine ring and the amino group of the adenine residue. 9-Ethyladenine is an effective quencher of the fluorescence of riboflavin tetraacetate. The quenching appears mainly due to the coplanar interaction through hydrogen bonds and partly due to the collision interaction with the purine rings. Some barbiturates were found to prevent the formation of the complex of the adenine and riboflavin derivatives by the formation of more stable complexes with ethyladenine.