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The characterization and preparation of the first sphere mutant of soybean lipoxygenase-1, N694C which allows evaluation of the [sigma]-organoiron mechanism showing a significant deuterium isotope effect for kinetic data of N694C is presented.

A combination of studies is employed to analyze the thiolate bonding to [{FeNO}.sup.2]/[{[FeO.sub.2]}.sup.8] complexes of isopencillin N synthase (IPNS). The determination of oxidase substrate versus the oxygenase activity in nonheme Fe enzymes shows that the single center reaction in IPNS allows it to avoid the oxygen bridged binding completely.

The effect of the three-His motif in Dke1 on the geometric and electronic structure of the [Fe.sup.II] centers is analyzed by a combination of absorption, CD, MCD and VTVH MCD spectroscopies and DFT calculations. The studies have helped in understanding the effects of perturbation of the facial triad ligation of the non-heme ferrous enzymes on their geometric and electronic structure and also their contributions to reactivity.

The article describes a new subclass of [alpha]-ketoglutarate ([alpha]-KG)-dependent oxygenases, which do not contain the conventional facial triad. These compounds are found to exhibit novel reactivity and excellent catalytic activity.

A study was conducted on N694G sLO-1 to probe its contribution to Asn694's weak sixth ligand that is thought to be critical for enzymatic catalysis in wild-type soybean LO-1 (WT sLO-1). It as proposed on the basis of kinetic and structural factors that the Asn694 water-derived ligand could likely be a hydroxide and the active site, water-derived ligand a water in the ferric state, hence lowering the reaction rate of N694G more than would be expected from the lowered reduction potential alone.

A study was conducted, with circular dichroism (CD) and magnetic circular dichroism (MCD), to examine the resting Fe site of (4-hydroxyphenyl)pyruvate dioxygenase (HPPD) and its interaction with (4-hydroxyphenyl)pyrvate (HPP) substrate. The result provides the insight into the mechanism of oxygen binding and activation by HPPD, and its active-site structural relationship to both alpha-KG-dependent dioxygenases and extradiol class of mononuclear non-heme iron enzymes.

Research has been conducted on second coordination sphere mutants from soybean lipoxygenase-1. The solution structure of these mutants has been investigated via the use of MCD and CD spectroscopies, and the results demonstrate that the iron coordination environment relates to activity.

The a-ketoglutarate (α-KG)-dependent oxygenases are a large and diverse class of mononuclear non-heme iron enzymes that require FeII, α-KG, and dioxygen for catalysis with the a-KG cosubstrate supplying the additional reducing equivalents for oxygen activation. While these systems exhibit a diverse array of reactivities (i.e., hydroxylation, desaturation, ring closure, etc.), they all share a common structural motif at the FeII active site, termed the 2-His-1-carboxylate facial triad. Recently, a new subclass of α-KG- dependent oxygenases has been identified that exhibits novel reactivity, the oxidative halogenation of unactivated carbon centers. These enzymes are also structurally unique in that they do not contain the standard facial triad, as a CI ligand is coordinated in place of the carboxylate. An FeII methodology involving CD, MCD, and VTVH MCD spectroscopies was applied to CytC3 to elucidate the active-site structural effects of this perturbation of the coordination sphere. A significant decrease in the affinity of FeII for apo- CytC3 was observed, supporting the necessity of the facial triad for iron coordination to form the resting site. In addition, interesting differences observed in the FeII/α-KG complex relative to the cognate complex in other a-KG-dependent oxygenases indicate the presence of a distorted 6C site with a weak water ligand. Combined with parallel studies of taurine dioxygenase and past studies of clavaminate synthase, these results define a role of the carboxylate ligand of the facial triad in stabilizing water coordination via a H-bonding interaction between the noncoordinating oxygen of the carboxylate and the coordinated water. These studies provide initial insight into the active-site features that favor chlorination by CytC3 over the hydroxylation reactions occurring in related enzymes. [ABSTRACT FROM AUTHOR]

Isopenicillin N synthase (IPNS) is a unique mononuclear nonheme Fe enzyme that catalyzes the four-electron oxidative double ring closure of its substrate ACV. A combination of spectroscopic techniques including EPR, absorbance, circular dichroism (CD), magnetic CD, and variable-temperature, variable-field MCD (VTVH-MCD) were used to evaluate the geometric and electronic structure of the {FeNO}7 complex of IPNS coordinated with the ACV thiolate ligand. Density Function Theory (DFT) calculations correlated to the spectroscopic data were used to generate an experimentally calibrated bonding description of the Fe-IPNS-ACV-NO complex. New spectroscopic features introduced by the binding of the ACV thiolate at 13 100 and 19 800 cm-1 are assigned as the NO π*(ip) → Fe dx2-y2 and S π Fe dx2-y2 charge transfer (CT) transitions, respectively. Configuration interaction mixes S CT character into the NO π*(ip) → Fe dx2-y2 CT transition, which is observed experimentally from the VTVH-MCD data from this transition. Calculations on the hypothetical {FeO2}8 complex of Fe-IPNS-ACV reveal that the configuration interaction present in the {FeNO}7 complex results in an unoccupied frontier molecular orbital (FMO) with correct orientation and distal O character for H-atom abstraction from the ACV substrate. The energetics of NO/O2 binding to Fe-IPNS-ACV were evaluated and demonstrate that charge donation from the ACV thiolate ligand renders the formation of the FeIII-superoxide complex energetically favorable, driving the reaction at the Fe center. This single center reaction allows IPNS to avoid the O2 bridged binding generally invoked in other nonheme Fe enzymes that leads to oxygen insertion (i.e., oxygenase function) and determines the oxidase activity of IPNS. [ABSTRACT FROM AUTHOR]

DNA-templated silver nanoclusters are promising biological fluorescence probes due to their useful fluorescence properties, including tunability of emission wavelength through DNA template sequence variations. Ag K-edge EXAFS analysis of DNA-templated silver nanoclusters has been used to obtain insight into silver nanocluster bonding, size, and structural correlations to fluorescence. The results indicate the presence of small silver nanoclusters (<30 silver atoms) containing Ag-Ag bonds and Ag-N/O ligations to DNA. The DNA sequence used leads to differences in silver-DNA ligation as well as silver nanocluster size. The results support a model in which cooperative effects of both Ag-DNA ligation and variations in cluster size lead to the tuning of the fluorescence emission of DNA-templated silver nanoclusters. [ABSTRACT FROM AUTHOR]

Presents highlights of the meeting of the National Conference on Undergraduate Research held April 8-10, 1999 at the University of Rochester, New York. Activities for intellectual development; Topics discussed; Conference's provision of information about financing and applying for graduate studies; Information about the Council on Undergraduate Research. INSET: About NCUR and CUR..

Interconversion of the oxidation states of uranium enables separations and reactivity schemes involving this element and contributes to technologies for recycling of spent nuclear fuels. The redox behaviors of uranium species impact these processes, but use of electrochemical methods to drive reactions of molecular uranium complexes and to obtain molecular insights into the outcomes of electrode-driven reactions has received far less attention than it deserves. Here, we show that electro-reduction of the uranyl ion (UO 2 2+ ) can be used to promote stepwise functionalization of the typically unreactive oxo groups with exogenous triphenylborane (BPh 3 ) serving as a moderate electrophile, avoiding the conventional requirement for a chemical reductant. Parallel electroanalytical, spectrochemical, and chemical reactivity studies, supported by spectroscopic findings and structural data from X-ray diffraction analysis on key reduced and borylated products, demonstrate that our electrochemical approach largely avoids undesired cross reactions and disproportionation pathways; these usually impact the multicomponent systems needed for uranyl functionalization chemistry. Joint computational studies have been used to map the changes associated with U-O activation and to quantify the free energy differences related to key reactions. Taken together, the results suggest that electrochemical methods can be used for selective interconversion of molecular actinide species, reminiscent of methods commonly employed in transition metal redox catalysis.