Crystal structures of cadmium(II) complexes with uridine 5′-monophosphate (5′-UMP), [Cd(5′-UMP)(H2O)2]·2H2O, and with 2′-deoxyuridine 5′-monophosphate (5′-dUMP), [Cd2(5′-dUMP)2(H2O)6]: phosphate-only metal bonding

Abstract

The crystal structures of the cadmium(II) complexes with uridine 5′-monophosphate (5′-UMP), [Cd(5′-UMP)(H₂O)₂]·2H₂O(1), and with 2′-deoxyuridine 5′-monophosphate (5′-dUMP), [Cd₂(5′-dUMP)₂(H₂O)₆](2), have been determined by X-ray analysis. Complex (1) crystallizes in space group C2 with a= 28.835(7), b= 14.241(4), c= 4.928(3)Å, β= 91.37(1)°, and Z= 4; complex (2) crystallizes in space group P1 with a= 18.278(6), b= 7.572(3), c= 5.356(1)Å, α= 89.76(3), β= 98.22(2), γ= 93.74(3)°, and Z= 1. Both structures have been solved by heavy-atom methods and refined to R= 0.079 for (1) and 0.060 for (2), using 1 236 and 2 530 diffractometer data respectively. Both compounds are one-dimensional polymers of compositions [{Cd₂(5′-UMP)₂(H₂O)₄}_n] for (1) and [{Cd₂(5′-dUMP)₂(H₂O)₆}_n] for (2). The conformation of UMP and dUMP is anti about the glycosyl link, gauche–gauche about the C(4′)–C(5′) bond (except for one of the dUMP molecules which is gauche–trans), and the sugar puckers are endo-C(3′)/exo-C(2′) for UMP but endo-C(1′) and exo-C(4′) in dUMP. UMP or dUMP nucleotides are bonded to metal ions through their phosphate groups only and form columns of metal–phosphate clusters from which sugar–base moieties project outwards. These findings suggest that the helical structure of polyuridylic acid is probably destabilized by Cd^II due to interactions with phosphate groups and not via base co-ordination, as generally assumed.