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The studies have shown that in both native and reconstituted [4Fe-4S] FNR, the reaction environment and the presence of [Fe.sup.2} and [Fe.sup.3} chelators have influenced the cluster conversion reactions. The sensitivity of FNR cluster conversion kinetics to chelators has disclosed mechanism by which the cell can fine-tune its response to the onset of aerobic conditions.

A magneto-optical study is undertaken of the mixed-valence single-molecule magnet [MnIV (sub 4)MnIII (sub 8) O12 L16] in which the ligands, L, are acetate (Mn12Ac) or the long-chain carboxylic acid, C14 H-29COOH(Mn12C15) that confers better solubility in organic solvents. The optical polarization and the selection rules for field magnetic circular dichroism (MCD) select a subset of molecular orientations with respect to the direction of field.

The blue copper protein azurin was studied using optically detected electron paramagnetic resonance spectroscopy.

The reactive 3Fe cluster in the 7Fe ferredoxin from Desulfovibrio africanus, incorporating Fe and other metals to to form cubanes (M3Fe-4S) has a non-cystein ligation to the added metal (M). Connectivities among interconversion with different M, the influence of pH and the reactivities of certain cluster oxidation levels have been studied using electrochemical and spectroscopic methods.

Characterization of the novel 'hyper-reduced' form of protein-bound (3Fe-4S) clusters showed that its formation is reversible. It was also determined that in the weakly acidic/neutral region of pH, the cluster consumes a total of three protons for the overall three-proton reduction of (3Fe-4S)(super 1+). In the two-electron reduction of (3Fe-4S)(super 0) in a range of proteins, the product is surprisingly inert each time and the pH-dependent reduction potential is in the region of -700 mV vs SHE at pH 7.

The redox-coupled binding of a thiolate ligand to an Fe-S protein cluster has been characterized by voltammetry. The protein ligand of Ferrodoxin III which contains seven cysteines capable of ligating both (4Fe-4S) and (3Fe-4S) clusters, utilized for characterization has been isolated from the Desulfovibrio africanus strain. The kinetics and equilibrium constants of the ligation has also been measured. Findings show no definite interaction betweeen either of the protein clusters and thiolate. However, voltammetric characterization demonstrated the time-separated coupling of electron transfer to conformational change.

The synthesis experiments have shown that while no Re-Zn alloy or solid solution is formed, a novel [Re.sub.3]Zn[N.sub.x] ordered solid solution is formed with nitrogen occupying Re-coordinated cages. The studies have shown that unlike pure [Re.sub.3]Zn, the novel hexagonal [Re.sub.3]Zn[N.sub.x] structure is stabilized by nitrogen bond formation with rhenium.

Synthesis experiments at 10 GPa and 1500 K followed by annealing at 770 K using Ge and Sn starting materials and ex-situ analysis have documented the recovery of a [Ge.sub.0.9][Sn.sub.0.1] solid solution.

Catenanes and rotaxanes are prepared by using the hard trivalent transition metal ion cobalt(III) as a template. The removal of the metal ion for both catenanes and rotaxanes via reduction under acidic conditions to the more labile Co(II) has given neutral interlocked molecules with well-defined co-conformations stabilized by intercomponent hydrogen bonding.

An algorithm is designed to search coiled-coil specificity space, along with a few modest multicomponent structures to show the ability to build peptide-based nanostructures from the bottom up. This concept can be expanded to longer coiled coils and larger number of domains and the extensions have provided the extra versatility and stability required for achieving programmed multicomponent self-assembling systems.

The rise to similar fast-relaxing broad features in the dual-mode X-band EPR spectra is caused by spin-coupled high-spin Fe(lll) heme O3 and CuB(ll) ion. The MCD data, independent of the EPR study shows the spin-coupling with the active site.

Rotaxanes can be prepared from a class of cyclic peptides and nonpeptic threads. Cyclo(L-ProGly)4 and cyclo(L-ProGly)5 are prepared from cyclic peptides by a solid-phase backbone amide-linking approach, by removing the macrocycles from a rotaxane-forming reaction mixture through simple aqueous extraction.

'Single-molecule magnets' (SMMs) represent the ultimate limit of miniaturization of magnetic data storage media. An optical method is demonstrated for determining the single-ion ZFS within clusters and the relative orientations of the local and cluster magnetic axes are as important as the sign of the single-ion ZFS in determining whether cluster would be a SMM .

The perpendicular- and parallel-mode X-band EPR spectra of fluoride bo3 was simulated to determine the interaction between high-spin Fe(III) heme and copper(II) ion in the active site of heme-copper oxidases. Results showed a weak coupling between the two metal ions for a heme with a fluoride ligand and for fast, formate and azide derivatives of bo3. This indicates that the intervening exogenous ligands have a small influence in mediating the exchange interaction between the two ions.

High pressure can induce profound changes in solids. A significant barrier to new alloys and ceramics, however, is that targeted starting materials may not react with each other, even with the help of pressure. We. use nitrogen, in a new capacity, to incorporate two otherwise unreactive elements, Re and Zn, in the same structure when pressure alone does not suffice, without nitrogen altering the resulting backbone structure. Synthesis experiments up to 20 GPa and 1800 K show that while no Re-Zn alloy or solid solution is formed, a novel Re3ZnNx ordered solid solution is formed, at 20 GPa, with nitrogen occupying Re-coordinated cages. We put forth that unlike pure Re3Zn, our novel hexagonal Re3ZnNx structure is stabilized by nitrogen bond formation with rhenium. Pressure lifts the pronounced ambient Zn anisotropy, making it more compatible with Re and likely facilitating incorporation of the structure-stabilizing nitrogen anion. This methodology and result denote further options for removing impasses to material preparation, thus opening new avenues for synthesis. These can also be pursued with other ions including carbon, hydrogen, and oxygen, in addition to nitrogen. [ABSTRACT FROM AUTHOR]

The article discusses the designed α-helical tectons for constructing multicomponent synthetic biological systems. As stated, the method applies rules relating sequence and stability in dimeric coiled coils to produce peptidic tectons for use in self-assembly and synthetic biology. The method uses a reduced alphabet and considers only the g, a, d and e positions of the heptad repeat.

In Escherichia coli, the switch between aerobic and anaerobic metabolism is primarily controlled by the fumarate and nitrate reduction transcriptional regulator FNR. In the absence of O2, FNR binds a [4Fe-4S]2+ cluster, generating a transcriptionally active dimeric form. Exposure to O2 results in the conversion of the cluster to a [2Fe-2S]2+ form, leading to dissociation of the protein into transcriptionally inactive monomers. The [4Fe-4S]2+ to [2Fe-2S]2+ cluster conversion proceeds in two steps. Step 1 involves the one-electron oxidation of the cluster, resulting in the release of Fe2+ generating a [3Fe-4S]1+ cluster intermediate, and a superoxide ion. In step 2, the cluster intermediate spontaneously rearranges to form the [2Fe-2S]2+ cluster, with the release of a Fe3+ ion and two sulfide ions. Here, we demonstrate that, in both native and reconstituted [4Fe-4S] FNR, the reaction environment and, in particular, the presence of Fe2+ and/or Fe3+ chelators can influence significantly the cluster conversion reaction. We demonstrate that while the rate of step 1 is largely insensitive to chelators, that of step 2 is significantly enhanced by both Fe2+ and Fe3+ chelators. We show that, for reactions in Fe3+-coordinating phosphate buffer, step 2 is enhanced to the extent that step 1 becomes the rate determining step and the [3Fe-4S]1+ intermediate is no longer detectable. Furthermore, Fe3+ released during this step is susceptible to reduction in the presence of Fe2+ chelators. This work, which may have significance for the in vivo FNR cluster conversion reaction in the cell cytoplasm, provides an explanation for apparently contradictory results reported from different laboratories. [ABSTRACT FROM AUTHOR]

Examines the optical detection of spin polarization in single-molecule magnets. Evaporation of solvents to provide samples for variable-temperature and field magnetic circular dichroism (MCD); Adsorption of spectra in isotropic light; Measurement on MCD magnetization curves.