MODEL COMPOUNDS FOR THE INTERACTION OF SILVER(I) WITH POLYURIDINE - CRYSTAL-STRUCTURE OF A 1-1 SILVER COMPLEX WITH 1-METHYLTHYMINE

The neutralization of uridine in the presence of various quantities of Ag+ ions has been followed pHmetrically and the data have been interpreted in terms of complexes with 2:1 and 2:2 metal-ligand ratios. The corresponding equilibrium constants have been refined by least squares. Crystals of the 1:1 silver complex with 1-mcthylthymine (HMT) are monoclinic. space group C2/c, with a = 11.270 Å, b = 13.239 Å, c = 9.647 Å, and β = 100.11°. The structure was refined on 1004 independent nonzero reflections to an R factor of 0.028. One-half of the silver atoms have a linear coordination and bind strongly to N(3) atoms of two deprotonated ligands (Ag-N(3) = 2.081 °). The resulting planar Ag(MT)2- units are connected by the remaining silver atoms, which are tetrahedrally surrounded with oxygen atoms from two Ag(MT)2- units. Binding to O(2) is much weaker (Ag-O(2) = 2.512 Å) than with O(4) (Ag-O(4) = 2.333 Å). Those results are discussed in connection with silver binding to poly(U). © 1979, American Chemical Society. All rights reserved.