The structure of a hydrated 1:2 complex of adenylyl(3'-5')adenosine–proflavine hemisulphate

Abstract

The 1:2 complex (M r = 1410.28) between adenylyl(3'- 5')adenosine (ApA), C20H25NIoOIoP, and proflavine hemisulphate, 2C 13H ~2N~ - . SO42-, crystallizes with 16.5 water molecules in the space group P21212 and unit-cell parameters a = 32.157 (5), b = 21.450 (4) and c = 10.175 (1) A; V = 7018.4 A 3, Z = 4, d c = 1.33, d m = 1.32 Mgm -3,/z(Cu Ka) = 1.32 mm -~, F(000) = 2980. Crystal data were measured up to 20 = 120 ° with Cu Ka radiation. The structure was determined by a multisolution phase method and refined by a blockedmode full-matrix least-squares procedure. The final R factor is 0.118 for 3507 observed data. The dinucleoside phosphate, ApA, in this structure has a very unusual conformation which is not found in other oligonucleotide structures. The backbone of ApA is extended and each adenine ring is hydrogen bonded to another symmetry-related one forming an adenineadenine base pair. Each base pair is sandwiched by proflavine cations which also stack with each other. Solvent molecules lie in the continuous channels between columns of stacked heterocyclic rings.