Synthesis and reactivity of a bis(disulfide)-bridged RuMo3S4 double-cubane cluster: a new family of nona- or decanuclear mixed-metal sulfide clusters with two RuMo3S4 units

A bis(disulfide)-bridged RuMo3S4 double-cubane cluster [{(Cp*Mo)3(mu3-S)4Ru}(mu2-eta2:eta1-S2)]2[PF6]2 (2, Cp* = eta5-C5Me5) is readily available from cluster [(Cp*Mo)3(mu3-S)4RuH2(PPh3)][PF6] (1) and S8. The reactions of cluster 2 with [M(PPh3)4] (M = Pd, Pt) give rise to the formation of a new family of nona- or decanuclear mixed-metal sulfide clusters, [{(Cp*Mo)3(mu3-S)4Ru}2(mu3-S)2{Pd(S)(PPh3)}][PF6]2 (3), [{(Cp*Mo)3(mu3-S)4Ru}2(mu3-S)2{(Pd(PPh3))2(mu2-S)}][PF6]2 (4), and [{(Cp*Mo)3(mu3-S)4Ru}2(mu3-S)2{Pt(PPh3)2}][PF6]2 (5), with two RuMo3S4 cubane units, the structures of which have been determined by X-ray diffraction studies.     

Electrochemical gate-controlled conductance of single oligo(phenylene ethynylene)s

We have studied electron transport properties of unsubstituted oligo(phenylene ethynylene) (OPE) (1) and nitro-substituted OPE (2) covalently bound to two gold electrodes. The conductance values of single 1 and 2 are approximately 13 and approximately 6 nS, respectively. In addition to a decrease in the conductance, the presence of the nitro moiety leads to asymmetric I-V characteristics and a negative differential resistance-like (NDR-like) behavior. We have altered the nitro-substituted OPE by electrochemically reducing the nitro group and by varying the pH of the electrolyte. The conductance decreases linearly with the electron-withdrawing capability (i.e., Hammett substituent values) of the corresponding reduced species. In contrast, the conductance of 1 is independent of the pH and the electrode potential.     

Synthesis and aldose reductase-inhibitory activity of benzo[b]furan derivatives possessing a carboxymethylsulfamoyl group

Various benzo[b]furan derivatives with a carboxymethylsulfamoyl group were prepared and evaluated for aldose reductase-inhibitory potency. Most of the compounds displayed significant inhibitory activities (IC50, 10(-8)-10(-7) M). Among the test compounds, the compounds having a carboxymethylsulfamoyl group at the 3- or 4-position exhibited the greatest inhibitory potency. Structure-activity trends of the tested compounds are discussed.     

Participation of the BC Loop in the Correct Folding of Bacteriorhodopsin as Revealed by Solid‐state NMR†

Structural changes in bacteriorhodopsin (bR) in two different processes of retinal reconstitutions were investigated by observing the ¹³C and ¹⁵N solid‐state NMR spectra of [1‐¹³C]Val‐ and [¹⁵N]Pro‐labeled bR. We found that NMR signals of the BC loop were sensitive to changes in protein structure and dynamics, from wild‐type (WT) bR to bacterio‐opsin (bO), regenerated bR and E1001 bR. Regenerated bR was prepared following the addition of retinal into bO obtained from photobleached WT‐bR. E1001 bR was cultured from a retinal‐deficient strain termed E1001 following the addition of retinal to growing cells. ¹⁵N NMR signal at Pro70 in the BC loop in WT‐bR was observed at 122.4 p.p.m., whereas signals were not apparent or partly suppressed in bO and regenerated bR, respectively. Similarly, the ¹³C NMR signal at Val69 in the BC loop at 172.0 p.p.m. that was observed in WT‐bR was significantly decreased in both regenerated bR and bO. These results suggest that the dynamic structure of the BC loop in bO was substantially altered following the removal of retinal. As a consequence, the correct protein structure failed to be recovered via the regenerating process of retinal to bO. On the other hand, ¹³C and ¹⁵N NMR signals at the BC loop in E1001 bR appeared at positions identical to those of WT‐bR. The results of the current study indicate that the BC loop may not always fold correctly in the regenerated bR, which leads to different properties in the regenerated bR compared to that of WT‐bR.     

Color‐Discriminating Retinal Configurations of Sensory Rhodopsin I by Photo‐Irradiation Solid‐State NMR Spectroscopy

SRI (sensory rhodopsin I) can discriminate multiple colors for the attractant and repellent phototaxis. Studies aimed at revealing the color‐dependent mechanism show that SRI is a challenging system not only in photobiology but also in photochemistry. During the photoreaction of SRI, an M‐intermediate (attractant) transforms into a P‐intermediate (repellent) by absorbing blue light. Consequently, SRI then cycles back to the G‐state. The photoreactions were monitored with the ¹³C NMR signals of [20‐¹³C]retnal‐SrSRI using in situ photo‐irradiation solid‐state NMR spectroscopy. The M‐intermediate was trapped at ?40 °C by illumination at 520 nm. It was transformed into the P‐intermediate by subsequent illumination at 365 nm. These results reveal that the G‐state could be directly transformed to the P‐intermediate by illumination at 365 nm. Thus, the stationary trapped M‐ and P‐intermediates are responsible for positive and negative phototaxis, respectively.     

Studies of cyclodextrin effect for glycosylation by galactosyltransferase

Cyclodextrins (CDs) do not disturb HPLC purification and do not form lather, which makes them superior to commonly used surfactants. In this paper, the authors describe the utility of CDs, specifically α-CD, β-CD, and γ-CD, for the synthesis of neoglycolipids from insoluble peptide-linked substrates. γ-CD was found to be well matched to the bulky benzyl group and accelerated the reaction for the substrate having Phe (F), while β-CD was well matched to the methyl group and accelerated the reaction for the substrate having Ala (A). Galactosylation to water-insoluble peptide-linked glucosaminide substrate by galactosyltransferase proceeded 63% at the most, but using either β-CD or γ-CD gave quantitative yield within 10 h.     

Molecular recognition of alpha,beta-unsaturated carbonyl compounds using aluminum tris(2,6-diphenylphenoxide) (ATPH): structural and conformational analysis of ATPH complexes and application to the selective vinylogous aldol reaction

Various alpha,beta-unsaturated carbonyl compounds were coordinated with aluminum tris(2,6-diphenylphenoxide) (ATPH) to give the corresponding Lewis acid-base complexes in a distinctive coordination fashion (selective coordination). ATPH recognizes carbonyl substrates and subsequently orients itself as it forms a stable complex through selective coordination with the carbonyl oxygen. Selective coordination also confers a conformational preference to each carbonyl compound under the steric and electronic influence of ATPH, which enables the vinylogous aldol reaction of alpha,beta-unsaturated carbonyl compounds to give the corresponding gamma-aldol products with different regio- and stereoselectivities.