pH effect of· OH radical induced oxidation of phosphoryl- methionine in aqueous solution

Conclusion The results of pulse radiolytical research on the · OH radical-induced oxidation of NDM in aqueous solution demonstrate that pH value has a great influence on the radiolytical mechanism of NDM. At low pH value, the product is mainly stabilization of the oxidizing sulfur centre in the three-electron-bonded cation radical NDM₂ ·⁺ [S]; with the increase of pH value, NDM₂ ·⁺ [S] gradually decays to become the reducing α-amino radical which was verified by the chemical method and whose yield was also calculated. Compared with Met₂ ·⁺ [S] produced by the · OH radical-induced oxidation in aqueous solution [1], the stability of NDM₂·⁺ [S] increases and the yield of α-amino radical decreases. This suggests that the introduction of phosphoryl group has a coordinating effect on the radioprotection of methionine to biological systems, and provides the essentially theoretical foundation for the thorough clarification of the reversible phosphorylation of proteins.     

The strong cooperativity of dioxygen binding by dicobalt (II) diporphyrin compounds in nonaqueous solution at room temperature

Thermodynamic data were determined for the reversible binding of O₂ to two compounds of dicobalt(II) di(meso-tetra-phenyl)porphyrin derivatives with different lengths of diamidoaliphatic bridge (abbreviated to Co₂PP₈ and Co₂PP₄) in N,N-dimethylformamide at room temperature. The partial pressure of dioxygen necessary for half-oxygenation (P _1/2) and hill coefficient (n) at 298 K were determined as follows:P _1/2=54.2 kPa,n=2.0 for Co₂PP₈ andP _1/2=6.8 kPa,n=1.8 for Co₂PP₄, respectively. The rate equations of reversible oxygen binding by Co₂PP₈ were determined and the reaction path was proposed. The results of ther-modynamic and kinetic studies indicate that there exists strong cooperative effect during oxygenation of the compounds. The ESR observation reveals that the dioxygen complexes formed in the solutions are of superoxo (Co-O ₂ ⁻ ) type. Supported by the Research Foundation of the State Education Commission of China Zhou Xiaohai: born in 1962, Ph.D. Associate professor