Structure of the monopotassium salt of adenosine 5'-diphosphate dihydrate, KADP.2H2O

Crystals of the title compound, K ÷.C~0 HI4NsOioP 2. 2H20, were grown at pH 4 from a water/ ethanol mixture. They have space group P2~2~2 with a = 28.502 (5), b = 10.461 (2), c= 6.321 (2) A,Z= 4, D c = 1.76 Mg m -3. The structure was solved from 1726 three-dimensional X-ray diffraction data and refined to Rw = 9.3%. The ribose adopts the C(2')endo conformation, the orientation about the C(4')-C(5') bond is gauche,gauche and the heterocycle is anti with respect to the ribose. The pyrophosphate O(5')-P(1)-O(6') -P(2) chain is in a staggered conformation, with P-O-P angle 130 ° and P(1)-O(6') 1.65, P(2)-O(6') 1.60A. K ÷ is coordinated to pyrophosphate oxygens, to ribose O(2'), to heterocycle N(3) and to water. The two other negative charges of ADP are compensated by protons at N(1) and at 0(23) of the pyrophosphate. This crystal structure is isomorphous with RbADP. H20 [Viswamitra, Hosur, Shakked & Kennard (1976).