Pressure-induced isomerization of retinal on bacteriorhodopsin as disclosed by fast magic angle spinning NMR

Bacteriorhodopsin (bR) is a retinal protein in purple membrane of Halobacterium salinarum, which functions as a light-driven proton pump. We have detected pressure-induced isomerization of retinal in bR by analyzing 15N cross polarization-magic angle spinning (CP-MAS) NMR spectra of [zeta-15N]Lys-labeled bR. In the 15N-NMR spectra, both all-trans and 13-cis retinal configurations have been observed in the Lys N(zeta) in protonated Schiff base at 148.0 and 155.0 ppm, respectively, at the MAS frequency of 4 kHz in the dark. When the MAS frequency was increased up to 12 kHz corresponding to the sample pressure of 63 bar, the 15N-NMR signals of [zeta-15N]Lys in Schiff base of retinal were broadened. On the other hand, other [zeta-15N]Lys did not show broadening. Subsequently, the increased signal intensity of [zeta-15N]Lys in Schiff base of 13-cis retinal at 155.0 ppm was observed when the MAS frequency was decreased from 12 to 4 kHz. These results showed that the equilibrium constant of [all-trans-bR]/[13-cis-bR] in retinal decreased by the pressure of 63 bar. It was also revealed that the structural changes induced by the pressure occurred in the vicinity of retinal. Therefore, microscopically, hydrogen-bond network around retinal would be disrupted or distorted by a constantly applied pressure. It is, therefore, clearly demonstrated that increased pressure induced by fast MAS frequencies generated isomerization of retinal from all-trans to 13-cis state in the membrane protein bR.     

Lewis acid catalyzed benzylic C-H bond functionalization of azaarenes: addition to enones

A Lewis acid catalyzed benzylic C-H bond functionalization of alkyl-substituted azaarenes is described. Sc(OTf)(3) and Y(OTf)(3) promoted the direct addition of alkyl-substituted azaarenes and benzoxazole to enones and an α,β-unsaturated N-acylpyrrole. Products were obtained in 60-96% yield.     

Efficient catalytic decomposition of sulfuric acid with copper vanadates as an oxygen-generating reaction for solar thermochemical water splitting cycles

Copper pyrovanadate (Cu(2)V(2)O(7)) was found for the first time to achieve the high catalytic activity for the decomposition of sulfuric acid to evolve O(2) at moderate temperatures around 650 °C, which is essential for the development of solar thermochemical water splitting cycles.     

Rheo-SANS studies on shear-thickening/thinning in aqueous rodlike micellar solutions

Shear-induced thickening/thinning phenomena of aqueous rodlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium p-toluene sulfonate (NapTS) were investigated by means of simultaneous measurements of rheology and small-angle neutron scattering (SANS), the so-called Rheo-SANS. The aqueous CTAB/NapTS solutions were classified into five different categories dependent on their flow behavior and micellar structure. By increasing salt concentration and/or shear rates, the micelles underwent morphological transition from (i) spherical or short rodlike micelles to (ii) long rodlike micelles without entanglements, followed by (iii) those with entanglements. These transitions were recognized as changes in flow behavior from Newtonian to shear-thickening and shear-thinning flow, respectively. In the latter two cases, anisotropic SANS patterns appeared around these critical shear rates. The physical meaning of the anisotropic SANS patterns accompanied by shear-thickening flow behavior is discussed in conjunction with other shear-thickening systems.     

Small hepatocellular carcinomas in cirrhosis: differences in contrast enhancement effects between helical CT and MR imaging during multiphasic dynamic imaging

PURPOSE: The purpose of this study was to evaluate differences in the degrees of contrast enhancement effects of small hepatocellular carcinomas (HCCs) in patients with cirrhosis between helical computed tomography (CT) and magnetic resonance (MR) imaging during multiphasic contrast-enhanced dynamic imaging and to determine the diagnostic value of MR imaging especially in assessing hypovascular HCCs detected as hypoattenuating nodules on late-phase CT. SUBJECTS AND METHODS: This study included 64 small HCCs (<3 cm in diameter) in 40 patients with chronic hepatitis or cirrhosis who underwent multiphasic (arterial, portal and late phases) contrast-enhanced dynamic helical CT and MR imaging. The contrast enhancement patterns of each lesion in the arterial and late phases were evaluated by two radiologists experienced in liver MR imaging and categorized as one of five grades (1=hypoattenuated/hypointense; 2=slightly hypoattenuated/hypointense; 3=isoattenuated/isointense; 4=slightly hyperattenuated/hyperintense; 5=hyperattenuated/hyperintense), compared with the surrounding liver parenchyma. RESULT: Forty-three (67%) of 64 lesions showed Grade 4 (n=24) or Grade 5 (n=19) enhancement on arterial-phase CT, while 51 (80%) of 64 lesions showed Grade 4 (n=20) or Grade 5 (n=31) enhancement on arterial-phase MR imaging, indicating hypervascular HCCs. The grading score of hypervascular HCCs on arterial-phase MR imaging (mean: 4.61) was significantly (P<.01) higher than that for hypervascular HCCs on arterial-phase CT (mean: 4.20), showing better detection of the hypervascularity (arterial enhancement) of the lesion on arterial-phase MR imaging. Regarding hypovascular HCCs, all (100%) of 21 hypovascular HCCs on CT showed Grade 1 (n=10) or Grade 2 (n=11) enhancement on late-phase CT, seen as hypoattenuation. In contrast, 8 (62%) of 13 hypovascular HCCs on MR imaging showed Grade 1 (n=1) or Grade 2 (n=7) enhancement on late-phase MR imaging, seen as hypointensity. Grading scores of hypovascular HCCs on late-phase images were significantly (P<.001) lower on CT than on MR imaging (mean score: 1.52 vs. 2.31), indicating better washout effects for hypovascular HCCs on late-phase CT. CONCLUSION: The washout effects for small HCCs on late-phase MR imaging were inferior to those for small HCCs on late-phase CT. Especially, hypovascular HCCs demonstrated as hypoattenuating nodules on late-phase CT were often not seen on late-phase MR imaging, requiring careful evaluation of other sequences, including unenhanced T(1)-weighted and T(2)-weighted MR images.     

Analysis of relationship between magnetic property and crystal structure of La1−xSrxCrO3 (x=0.13, 0.15)

Dependence of dc magnetization, $M$, of La_1?xSr_xCrO₃ ($x=0.13$, 0.15) polycrystalline specimens on external magnetic field, $H$, was measured at various temperatures. At higher temperatures above 274 K and 265 K for the specimens with $x=0.13$ and 0.15, respectively, almost linear relationships were observed, indicating paramagnetic property. At the lower temperatures, hystereses, indicating canted antiferromagnetic property, were observed in $M\text{–}H$ curves. The temperatures where the magnetic phase transition was observed showed agreement with those where base line shift was observed in differential scanning calorimetry (DSC) measurement. In the $M\text{–}H$ curves of La_1?xSr_xCrO₃ ($x=0.13$, 0.15), saturation magnetization, $M_s$, was not observed at external magnetic fields as high as 70 kOe. At 226 K and 189 K for the specimens with $x=0.13$ and 0.15, respectively, structural phase transition from orthorhombic- to rhombohedral-distorted perovskite was observed in DSC curves. At the temperature, abrupt decreases of residual magnetization, $M_r$, and variation of temperature dependence of coercive force, $H_c$, were detected. We regard that the abrupt decrease of $M_r$ and the variation of temperature dependence of $H_c$ at the structural phase transition temperature can be ascribed to discontinuous variation of Cr–O–Cr angles.     

Enantioselective Synthesis of 1,2-Benzothiazine 1-Imines via RuII/Chiral Carboxylic Acid-Catalyzed C−H Alkylation/Cyclization

Sulfondiimines are diaza-analogues of sulfones with a chiral sulfur center. Compared to sulfones and sulfoximines, their synthesis and transformations have so far been studied to a lesser extent. Here, we report the enantioselective synthesis of 1,2-benzothiazine 1-imines, i.e., cyclic sulfondiimine derivatives from sulfondiimines and sulfoxonium ylides via C−H alkylation/cyclization reactions. The combination of [Ru(p-cymene)Cl₂]₂ and a newly developed chiral spiro carboxylic acid is key to achieving high enantioselectivity.     

ChemInform Abstract: First‐Principles Investigation of R2O3(ZnO)3 (R: Al,Ga, and In) in Homologous Series of Compounds.

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