CRYSTAL AND MOLECULAR STRUCTURE OF A HYDROGEN-BONDED COMPLEX CONTAINING ADENINE AND HYPOXANTHINE DERIVATIVES - 9-ETHYL-8-BROMOADENINE-9-ETHYL-8-BROMOHYPOXANTHINE

9-Ethyl-8-bromoadenine and 9-ethyl-8-bromohypoxanthine form a 1:1 hydrogen-bonded complex in the crystalline state. The structure has been determined by three-dimensional X-ray diffraction methods and refined by block diagonal least squares to a final residual of 9.1%. The crystals are triclinic, space group P1 ̄, with a = 8.55 A ̊, b = 7.23 A ̊, c = 14.65 A ̊, α = 87 ° 8′, β = 102 ° 34′ and γ = 92 ° 25′. The adenine and hypoxanthine bases form a planar complex, joined by two hydrogen bonds; an N-H...N bond involving N(1) of hypoxanthine and N(7) of adenine, and an N-H...O bond involving the amino group of adenine and the carbonyl oxygen of hypoxanthine. The over-all crystal structure is a sheet-like structure, in which adjacent base pairs are related by a center of symmetry and are connected by hydrogen bonds between the adenine residues. The possible significance of this structure to Crick's wobble" hypothesis is discussed. © 1969."