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The study represents the first detection of a tridentate coordination mode for triphosphate in solution. It has utilized advanced electron spin echo modulation and four-pulse- two-dimensional hyperfine sublevel correlation spectroscopic techniques to characterize the solution structure of the 1:1 triphosphate.

The two-dimensional ESEEM spectroscopy, known as HYSCORE, offers higher resolution and substantially more information compared with one-dimensional techniques for the characterization of the paramagnetic centers involving large numbers of magnetically nonequivalent nuclei. This was concluded from the application of the spectroscopic technique to the study of hyperfine couplings from nitrogens of histidine and azide ligands. The hyperfine couplings of all coordinated azide and histidine nitrogens were successfully assigned for a geometry very close to that of the parent differic state.

Electron spin-echo envelope modulation experiments were performed to characterize the nitrogens surrounding the Rieske-type (2Fe-2S) cluster in 2,4,5-trichlorophenoxyacetate monooxygenase from Burkholderia cepacia AC1100. The results showed variations in the isotropic hyperfine couplings of the 'ligated nitrogens in the two histidines coordinated to the iron of the reduced Rieske cluster.'

The pulsed EPR spectroscopy technique is employed to explain the interaction taking place between the various nitrogen donors and the semiquinone in the [Q.sub.B] site of bacterial reaction centers. The formation of hydrogen bonds by these semiquinone forms is also analyzed.

Continuous-wave (CW) EPR spectra of reduced [2Fe-2S][(Cys).sub.3][(His).sub.1] clusters of mammalian mitoNEET soluble domain has produced features resulting from the interaction of the electron spins of the two adjacent clusters. The studies have shown that these quantitative data may be used in the future functional and theoretical studies on the mammalian mitoNEET [2Fe-2S] cluster system.

Escherichia coli (cyt) [bo.sub.3] ubiquinol oxidase has catalyzed the two-electron oxidation of ubiquinol and the four-electron reduction of [O.sub.2] to water. The results have formed a basis for more advanced theoretical analysis of the protein-semiquinone (SQ) interaction in the [Q.sub.H] site, using the model of the neutral radical indicated by the proton hyperfine couplings.

The weakly coupled (super 15)N(sub E) and (super 15)N(sub p) nuclei around the archaeal Rieske center in the uniformly (super 15)N-labeled SDX produce readily observable signatures in the hyperfine sublevel correlation spectroscopic (HYSCORE) spectra. The HYSCORE experiment can be used to study the structure-mechanism studies of a wide range of the biological redox protein system involving these nitrogens.

The presence of two different types of proteins with distinct biological electron-transfer functions is reflected in the redox potential (Em) cluster, and its pH dependence. A comparative study of the pH-dependent RR spectral changes, of three Rieske-type [2Fe-2S] proteins with different redox properties, is presented.

Canthaxanthin and 8' -apo-beta-caroten-8' -al radical cations chemically prepared on activated silica-alumina and in CH2Cl2 solution containing AlCl3 are studied by pulsed EPR and electron nuclear double resonance (ENDOR).

A study reports the orientation-selected hyperfine sublevel correlation (HYSCORE) characterization of the (super 15)N-SDX reduced at pH 13.3 to quantify the deprotonation effects through the hyperfine couplings with (super15)N nuclei in the cluster environment. The HYSCORE data confirms that (super 15)N-SDX treated at very alkaline pH, which exhibits a significantly modified electron paramagnetic resonance (EPR) line shape for the fully deprotonated, reduced protein, partially retians essential geometric features for a Rieske-type [2Fe-2S] cluster.

VO(super2+) was observed to interact with the inorganic fraction of bone, using electron spin-echo envelope modulation spectroscopy.

Histidine is shown to be a polydentante ligand, contrary to prior assumptions. This is shown by a two-dimensional ESEEM analysis of VO2+ complexes having imidazole and histidine.