CRYSTAL-STRUCTURE OF 2'-DEOXYCYTIDINE HEMIDIHYDROGENPHOSPHATE REVEALSC-DOT-C BASE-PAIRS AND TIGHT, HYDROGEN-BONDED (H2PO4-)INFINITY COLUMNS(CENTER)

2'-Deoxycytidine hemidihydrogenphosphate has been crystallized in the hexagonal space group P6(2) with a = 25.839(3), c = 12.529(1) Angstrom . The structure has been solved using the Patterson search method. The asymmetric unit contains two protonated base-paired 2'-deoxycytidine dimers and two H2PO4- anions. The C+.C base pairs are composed of a pr otonated and a neutral species each and are triple H-bonded, the centr al N(3)...N(3) bonds being 2.850(7) and 2.884(5) Angstrom. The conform ations of the four nucleosides fall in the same category (sugar pucker s 2'-endo, glycosidic links anti) but in one of them the glycosidic to rsion angle is quite low with consequences in other geometrical parame ters. The H2PO4- anions are located on twofold axes and form two types of tight columns with P...P separations about 4.18 Angstrom. The neig hboring units along a column are linked via two very short O...H...O h ydrogen bonds (O...O about 2.49 Angstrom) leading to effective equaliz ation of the P-O bonds. The base pairs of the two dC(+).dC cations are coplanar and form layers perpendicular to the phosphate columns repea ting every c/3. Within the layers, the dimers form a network through O (5')...O(2) hydrogen bonds but their primary intermolecular interactio ns have the form of H-bond anchors [N(4)-H...O-P and O(3')-H...O-P] to the phosphate groups.