The crystal and molecular structure of an intermolecular complex between riboflavin and an adenosine derivative.

Riboflavin and the adenosine derivative 5'-bromo-5'-deoxyadenosine form a crystalline 1:1 intermolecular complex, the structure of which has been solved by x-ray diffraction analysis. The adenine ring is found to be joined by two hydrogen bonds to the uracillike end of the riboflavin isoalloxazine ring. In addition, the riboflavin and the adenosine molecules associate through the formation of stacks of alternating parallel adenine and isoalloxazine rings. These intermolecular associations are considered to be models for intramolecular association in the coenzyme flavin adenine dinucleotide (FAD), which contains both adenosine and riboflavin.