The crystal and molecular structure of guanine hydrochloride dehydrate

Abstract

The structure of guanine hydrochloride monohydrate has been determined by X-ray single crystal analysis and the parameters (including anisotropic temperature vibrations) have been refined by the three-dimensional least squares method. The unit cell is monoclinic with a = 14.69 ± 0.01, b = 13.40 ± 0.01, c = 4.840 ± 0.005 Å; β = 93.8°± 0.1°; space group P2₁/a. For 1600 independent reflexions the final value of the agreement index R was 0.07 and the standard deviations of atomic coordinates are in the region of 0.0035 Å. Two guanine molecules are linked together by hydrogen bonds to form a centrosymmetrical dimer. The dimer is linked by hydrogen bonds to four water molecules which are then hydrogen bonded to two chlorine ions. It is shown that the guanine molecule has associated with it six centres of electron density corresponding to hydrogen atoms and it is therefore in the form (H guanine)⁺ with protonation at the N₇ position.