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Examines the solid-state 13C chemical shift tensors in terpenes using nuclear magnetic resonance (NMR) analyses. Evidence of mixed polymorphic forms in solid verbenol; Structural predictions from computed and experimental NMR shift tensors; Characterization of the minor polymorphic form of verbenol.

Solution-phase photoinduced low-spin to high-spin conversion in the FeII polypyridyl complex [Fe(tren(py)3)]2+ (where tren(py)3 is tris(2-pyridylmethyliminoethyl)amine) has been studied via picosecond soft X-ray spectroscopy. Following ¹A1 → 1MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L2- and L3-edges were observed concomitant with formation of the transient high-spin 5T2 state. Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of ∼1 eV in the high-spin state relative to the singlet ground state. A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca. 0.2 Å increase in Fe-N bond length upon formation of the high-spin state. The overall occupancy of the Fe-3d orbitals remains constant upon spin crossover, suggesting that the reduction in s-donation is compensated by significant attenuation of π-back-bonding in the metal-ligand interactions. These results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations. [ABSTRACT FROM AUTHOR]

Amide-linkedspiropyran—anthraquinone (SP—AQ) conjugates were shown to mediate ZnTPPS4- photosensitized transmembrane reduction of occluded Co(bpy)33+ within unilamellar phosphatidylcholine vesicles by external EDTA. Overall quantum yields for these reactions were dependent upon the isomeric state of the dye; specifically, 30–35% photoconversion of the closed-ring spiropyran (SP) moiety to the open-ring merocyanine (MC) form caused the quantum yield to decrease by 6-fold in the simple conjugate and 3-fold for an analogue containing a lipophilic 4-dodecylphenoxy substituent on the anthraquinone moiety. Transient spectroscopic and fluorescence quenching measurements revealed that two factors contributed to these photoisomerization-induced changes in quantum yields: increased efficiencies of fluorescence quenching of ¹ZnTPPS4- by the merocyanine group and lowered transmembrane diffusion rates of the merocyanine-containing redox carriers. Transient spectrophotometry also revealed the sequential formation and decay of two reaction intermediates, identified as 3ZnTPpS4 and a species with the optical properties of a semiquinone radical. Kinetic profiles for Co(bpy)33+ reduction under continuous photolysis in the presence and absence of added ionophores indicated that transmembrane redox mediated by SP-AQ was electroneutral, but reaction by the other quinone-containing mediators was electrogenic. The minimal reaction mechanism suggested from the combined studies is oxidative quenching of vesicle-bound ³ZnTPPS4- by the anthraquinone unit, followed by either H+/e- cotransport by transmembrane diffusion of SP-AQH or, for the other redox mediators, semiquinone anion-quinone electron exchange leading to net transmembrane electron transfer, with subsequent one-electron reduction of the internal Co(bpy)33+. Thermal one-electron reduction of Co(bpy)33+ by EDTA is energetically unfavorable; the photosensitized reaction therefore occurs with partial conversion of photonic energy to chemical and transmembrane electrochemical potentials. [ABSTRACT FROM AUTHOR]

The article analyzes the high-affinity binding and direct electron transfer using Shewanella oneidensis cytochrome OmCA. Researchers have shown that purified OmcA binds and densely covers the surface of hematiteand reduces Fe (III) with maximal velocity. It corresponds to an electron flux that approaches observed fluxes in the most efficient bioreactors.