THE NATURE OF DRASTIC DIFFERENCES IN THE RECOGNITION OF PROTONATED CYTIDINIUM AND DEOXYCYTIDINIUM CATIONS BY THEIR PARENT NUCLEOSIDES WITHIN DIHYDROGENPHOSPHATE SALTS IN THE LIGHT OF THE COMPUTER-SIMULATED CRYSTAL-STRUCTURE OF DCYD HEMIPHOSPHATE (DCYD)2H+H2PO4-]

In the crystal structures of cytidine (Cyd), deoxycytidine (dCyd) and their dihydrogen phosphates, we have found important information about their abilities to resist transformation in the solid phase. On this basis we predicted and realised the transformation of the monophosphate into the hemiphosphate of dCyd and vice versa [dCydH+ H2PO-4 ⇌ (dCyd)2H+ H2PO-4], and simulated the latter structure by computer modelling of the former. We also discuss the molecular mechanism of both transformations in which protonation and deprotonation processes play leading roles. In the light of observations accumulated in this paper, further progress in the crystal engineering of nucleosides appears to be promising. © 1990.