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Transesterification of oxo-osmium(VI) ligand complexes of thymine derivatives
Authors:W.R. Midden  C.-H. Chang  R.L. Clark  E.J. Behrman
Affiliation:Department of Biochemistry, The Ohio State University, Columbus, Ohio, USA
Abstract:We have measured the rate of transesterification reactions between glycols (LO′) and oxo-osmium(VI) esters formed from thymine derivatives and a variety of nitrogen-containing ligands, LOMLN, according to the equation: LOMLN + LO′
/></figure> L<sub>O</sub>′ML<sub>N</sub> + L<sub>O</sub>. We have also measured the rates of transesterification for this system with the addition of external nitrogen-containing ligands, L<sub>N</sub>′. The order of effectiveness of the nitrogen-containing ligands in slowing the rate of transesterification is different depending on whether the ligand is present in the ester (L<sub>N</sub>) or whether it is added externally (L<sub>N</sub>′). Bathophenanthroline disulfonic acid is the most effective ligand when present in the ester. It forms exceptionally inert complexes. <em>N,N,N′,N′</em>-Tetramethylethylenediamine is the most effective ligand when added externally. The order of effectiveness of the nitrogen-containing ligand does not depend on the nature of either L<sub>O</sub> or L<sub>O</sub>′ but the nature of the glycol affects both the rate and the equilibria. We present mechanistic proposals, with limiting assumptions, to account for our findings.</td> </tr> <tr> <td align=
Keywords:Address reprint requests to: Dr. E.J. Behrman   Department of Biochemistry   The Ohio State University   Columbus   OH 43210   USA
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