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The first vacuum-ultraviolet absorption spectrum of pyridine-N-oxide has been obtained, and has led to the identification of nearly 30 Rydberg states. These states were identified by use of the vibrational envelope ("footprint") of the UV-photoelectron spectrum, and are based on the first to the third ionization energies (IE). The adiabatic IE order, central to the Rydberg state symmetry identification, is confirmed by multi-configuration SCF calculations as: 1 2 B 1 < 1 2 B 2 < 1 2 A 2 < 2 2 B 1 . Several excited valence state equilibrium structures were determined by multi-configuration SCF and coupled cluster procedures. Multi-reference multi-root CI was used to calculate both Rydberg and valence state vertical excitation energies and oscillator strengths, which were correlated with the experimental measurements. © 2013 AIP Publishing LLC. [http://dx

Models of [FeFe]‐hydrogenases containing diselenolato ligands with different bridge linker length have been prepared: Fe2(μ‐Se(CH2)4Se‐μ)(CO)6 (4DS), and Fe2(μ‐Se(CH2)5Se‐μ)(CO)6 (5DS) as well as dithiolato Fe2(μ‐S(CH2)4S‐μ)(CO)6 (4DT) and compared with Fe2(μ‐S(CH2)3S‐μ)(CO)6 (PDT) and Fe2(μ‐Se(CH2)3Se‐μ)(CO)6 (PDS). Compounds 4DT, PDS, 4DS, and 5DS were characterized by spectroscopic techniques including NMR, IR, mass spectrometry, ultraviolet photoelectron spectroscopy (UPS), elemental analysis, and X‐ray crystal structure analysis. Combinations of electrochemical measurements, UPS, and density functional theory calculations indicate that oxidations of these five compounds are not significantly affected by chalcogen character but instead are governed by linker length. Cations for all compounds are calculated to adopt a bridged CO “rotated” structure with a vacant site on one of the Fe centers. In 4DT, 4DS, and 5DS, the alkane linker forms an agostic interaction with the vacant site on the rotated Fe. The reduction potentials for these compounds shift positively on average 0.16 V for each carbon added to the alkane linker with shifts being as large as 0.23 V between PDT and 4DT, and as small as 0.09 V between 4DS and 5DS. Catalytic reduction of protons from acetic acid in CH2Cl2 occurs at −1.79 and −1.86 V for PDT and 4DT and −2.02, −2.09, and −2.04 V for PDS, 4DS, and 5DS, indicating that chalcogen character is the primary factor that affects catalytic potential. On average the S‐containing compounds catalyze proton reduction at potentials, which are 0.23 V less negative than the Se‐containing compounds in this study.

Abstract— The near UV and visible circular dichroism (CD) spectra of rhodopsin solubilized and purified in sodium cholate have been determined. The CD properties of rhodopsin in 2 and 20mg/ml sodium cholate are substantially different in terms of the α band to β band ratio, and sensitivity of the near UV CD spectra to bleaching. Rhodopsin in 2mg/ml sodium cholate will regenerate (11‐cis‐retinal + opsin → rhodopsin) and has a CD spectrum similar to rhodopsin in rod outer segment membranes and digitonin which will also regenerate. On the other hand rhodopsin in 20mg/ml sodium cholate will not regenerate and has CD properties similar to other nonregenerable detergents (cetyltri‐methylammonium salts and emulphogene). These results indicate that CD reflects the conformational integrity of functional (regenerable) rhodopsin and that sodium cholate can reversibly alter the conformation of rhodopsin. Finally the results further support the validity of using sodium cholate solubilized rhodopsin as a model system for studies on the structure and function of rhodopsin.

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