Mechanism and molecular-electronic structure correlations in a novel series of osmium(V) hydrazido complexes

Reaction between the Os(VI) nitrido (OsVI identical to N+) complexes [OsVI(L3)(Cl)2(N)]+ (L3 is 2,2':6',2"-terpyridine (tpy) or tris(1-pyrazolyl)methane (tpm)) and secondary amines (HN(CH2)4O = morpholine, HN(CH2)4CH2 = piperidine, and HN(C2H5)2 = diethylamine) gives Os(V)-hydrazido complexes, [OsV(L3)(Cl)2(NNR2)]+ (NR2 = morpholide, piperidide, or diethylamide). They can be chemically or electrochemically oxidized to Os(VI) or reduced to Os(IV) and Os(III). The Os-N bond lengths and Os-N-N angles in the structures of these complexes are used to rationalize the bonding between the dianionic hydrazido ligand and Os. The rate law for formation of the Os(V) hydrazido complexes with morpholine as the base is first order in [OsVI(L3)(Cl)2(N)]+ and second order in HN(CH2)4O with ktpy(25 degrees C, CH3CN) = (581 +/- 12) M-2 s-1 and ktpm(25 degrees C, CH3CN) = 2683 +/- 40 M-2 s-1. The proposed mechanism involves initial nucleophilic attack of the secondary amine on the Os(VI) nitrido group to give a protonated Os(IV)-hydrazido intermediate. It is subsequently deprotonated and then oxidized by OsVI identical to N+ to Os(V). The extensive redox chemistry for these complexes can be explained by invoking a generalized bonding model. It can also be used to assign absorption bands that appear in the electronic from the visible-near-infrared spectra including a series of d pi-->d pi interconfigurational bands at low energy.     

Improved direct measurement of A(b) and A(c) at the Z(0) pole using a lepton tag

The parity violation parameters A(b) and A(c) of the Zb(b) and Zc(c) couplings have been measured directly, using the polar angle dependence of the polarized cross sections at the Z(0) pole. Bottom and charmed hadrons were tagged via their semileptonic decays. Both the electron and muon analyses take advantage of new multivariate techniques to increase the analyzing power. Based on the 1993-1998 SLD sample of 550,000 Z(0) decays produced with highly polarized electron beams, we measure A(b) = 0.919+/-0.030(stat)+/-0.024(syst), and A(c) = 0.583+/-0.055(stat)+/-0.055(syst).     

M?ssbauer characterization of the iron-sulfur clusters in Desulfovibrio vulgaris hydrogenase.

The periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenbourough) is an all Fe-containing hydrogenase. It contains two ferredoxin type [4Fe-4S] clusters, termed the F clusters, and a catalytic H cluster. Recent X-ray crystallographic studies on two Fe hydrogenases revealed that the H cluster is composed of two sub-clusters, a [4Fe-4S] cluster ([4Fe-4S](H)) and a binuclear Fe cluster ([2Fe](H)), bridged by a cysteine sulfur. The aerobically purified D. vulgaris hydrogenase is stable in air. It is inactive and requires reductive activation. Upon reduction, the enzyme becomes sensitive to O(2), indicating that the reductive activation process is irreversible. Previous EPR investigations showed that upon reoxidation (under argon) the H cluster exhibits a rhombic EPR signal that is not seen in the as-purified enzyme, suggesting a conformational change in association with the reductive activation. For the purpose of gaining more information on the electronic properties of this unique H cluster and to understand further the reductive activation process, variable-temperature and variable-field M?ssbauer spectroscopy has been used to characterize the Fe-S clusters in D. vulgaris hydrogenase poised at different redox states generated during a reductive titration, and in the CO-reacted enzyme. The data were successfully decomposed into spectral components corresponding to the F and H clusters, and characteristic parameters describing the electronic and magnetic properties of the F and H clusters were obtained. Consistent with the X-ray crystallographic results, the spectra of the H cluster can be understood as originating from an exchange coupled [4Fe-4S]-[2Fe] system. In particular, detailed analysis of the data reveals that the reductive activation begins with reduction of the [4Fe-4S](H) cluster from the 2+ to the 1+ state, followed by transfer of the reducing equivalent from the [4Fe-4S](H) subcluster to the binuclear [2Fe](H) subcluster. The results also reveal that binding of exogenous CO to the H cluster affects significantly the exchange coupling between the [4Fe-4S](H) and the [2Fe](H) subclusters. Implication of such a CO binding effect is discussed.     

Subdifferentiation of Regularized Functions

We study the Moreau regularization process for functions satisfying a general growth condition on general Banach spaces. We give differentiability criteria and we study the relationships between the subdifferentials of the function and the subdifferentials of its approximations. We also consider the Lasry-Lions process.