Search

Research was conducted to examine and compare the activation of calcineurin by Mn2+ and Mg2+. Perturbations were introduced into the calcineurin reaction conditions which included the introduction of substrate labeled with heavy atom isotopes and the inclusion of viscogen in the reaction mixture. Results indicate that cleavage of the phosphate ester linkage was the most important factor that contributed to the rate-limiting step of calcineurin catalysis.

A generalized nonlinear least-squares fitting scheme simulates anistropic EPR spectra of mixed valence dimanganese complexes and the dimanganese catalase enzyme from Thermus thermophilus. The simulation yields inherent (super 55)Mn hyperfine tensors for each Mn ion, which illustrates the intermanganese HDVV exchange reaction. The increase in Mn(III) anisotropy magnitudes implies the occurrence of a ligand field variation on reduction.

The bis chelate products chromium (Cr)(V) and Cr(III) are produced from the disproportionation and subsequent ligand oxidation of Cr(IV). The addition of manganese (Mn)(II) in reactions within pH 2.5 to 4 enhances the rate of Cr-disproportionation, but the absence of the Mn-catalysts results in second order reaction and varied formation of hydrogen ions and anionic ligands. Furthermore, the study has shown the effect of Cr(IV)(OH) which interacts with Mn(II) to increase reaction rates in both catalyzed and uncatalyzed mechanisms.

The concerted (3 + 2) cycloaddition mechanism for the permanganate oxidation of alkenes was investigated using high level density functional theory. To this end, the products and transition states for both one-step (3 + 2) and stepwise (2 + 2) mechanisms were calculated to determine the structures and relative energies of the alkenes. Experimental results showed that the activation energy for the (3 + 2) transition state was 9.2 kcal/mol. The kinetic isotope effects for a substituted case were found to be consistent with experimental data.

By reacting manganese nitrate and sodium hydroxide at pH [nearly equal to] 12 and heating the product at 400 [degrees] C for 3 hrs, [Mn.sub.5][O.sub.8] with crystallite size [nearly equal to] 14 nm and the [Cd.sub.2][Mn.sub.5][O.sub.8] structure is produced, as confirmed by x-ray diffraction. Magnetic state of [Mn.sub.5][O.sub.8] is investigated by measuring the temperature variations of the magnetic susceptibility [Chi] and the electron spin resonance spectra. The [Chi] versus T variation is characteristic of antiferromagnetic ordering with Neel temperature [T.sub.N] [nearly equal to] 128 K. For T [is greater than] [T.sub.N], [Chi] follows the Curie-Weiss law, [Chi] = C/(T - [Theta]), with C = 14.26 [cm.sup.13]-K/mole, and [Theta] = -164 K. In ESR, only a single line is observed whose linewidth [Delta]H fits the variation [Delta]H(Oe) = 1570 + A/[(T - [T.sub.N]).sup.[Gamma] with [Gamma] = 1.26, characteristic of a uniaxial antiferromagnet. The magnitude of C is consistent with the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] valence state of [Mn.sub.5][O.sub.8]. Index Terms--Antiferromagnetism, electron spin resonance, mixed valences, synthesis.

Research was conducted to examine the catalytic reaction of the Mn2+ form of the native bacteriophage eta phosphatase and the H76N mutant with the substrate p-nitrophenyl phosphate. Heavy atom isotope effects and pH-dependent rate studies were used in the experiment. Results demonstrate that the chemical step of P-O bond cleavage is rate-limiting. The isotope effects are comparable to those measured for the reactions of protein-tyrosine phosphatases, which suggests that the two families of enzymes share similar dissociative transition states.

The partitioning of Fe2+ and Mn2+ between (Fe, Mn)TiO3 and (Fe, Mn)2SiO4 solid solutions in the system FeO-MnO-TiO2-SiO2 was investigated at 1100 degrees Celsius and pressures of one bar and 25 kilobars. The Fe-Mn partitioning results constrain the difference in the thermodynamic mixing characteristics of the solid solutions. These findings confirm the hypothesis that solid solutions between isostructural end-members have simple thermodynamic mixing properties.