ABSTRACT
1H NMR spectra of the paramagnetic complexes [L(NH(3))(5)Ru(III)], where L = derivatives of cytosine-kappa(N4) and adenine-kappa(N6), reveal rotameric isomers with distinct acid-base equilibria. (31)P NMR spectra of the 5'CMPkappa(N4) and 5'AMPkappa(N6) complexes indicate little interaction between the metal and phosphate centers. Differences between the (1)H and (31)P NMR of endo- and exocyclically-coordinated nucleosides and nucleotides are discussed and provide a means of distinguishing exocyclic from endocyclic nitrogen coordination.
ABSTRACT
The (1)H-NMR spectra of complexes involving the paramagnetic metal center [(NH(3))(5)Ru(III)] coordinated at ring nitrogens have been examined with pyridine, purine, nucleoside, and nucleotide ligands along with (31)P-NMR of the nucleotide complexes and EPR of representative complexes. Variations in the spectra have been investigated as a function of the coordination site and pH. Pseudocontact and contact shifts have been calculated for various protons, and an attempt has been made to correlate sugar conformations in coordinated 5'GMP, 5'IMP, Guo, and Ino with paramagnetically induced shifts. The compound [(7MeGuakappa(N9))(NH(3))(5)Ru]Cl(3).3H(2)O crystallizes in the orthorhombic space group Pna2(1) with cell parameters a = 25.375(4) Å, b = 11.803(4) Å, c = 6.958(2) Å, Z = 4, and R = 0.042. The autoxidation of [L(NH(3))(5)Ru(III)], where L = Guo, dGuo, and 1MeGuo, to the corresponding 8-oxo complexes under atmospheric oxygen is first order in the complex and [OH(-)]. For L = Guo, k = 6.6 x 10(-5) M(-1) s(-1), DeltaH = 58 kJ/mol, and DeltaS = -124 J/(mol K).
