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21.
Membrane fragments of Heliobacillus (Hc.) mobilis were characterized using resonance Raman (RR) spectroscopy in order to determine the configuration of the neurosporene carotenoid, the pigment-protein interactions of the bacteriochlorophyll (BChl) g molecules, and the Chl a-like chlorin pigments present in the antenna-reaction center complex constituting the photosynthetic apparatus. Using 363.8 nm excitation, the Raman contributions of the BChl g molecules were selectively resonantly enhanced over those of the carotenoid and the Chl a-like chlorin pigments. The RR spectrum of BChl g in these membranes excited at 363.8 nm exhibits bands at 1614 and 1688 cm?1, which correspond to a CaCm methine bridge stretching mode and a keto carbonyl group stretching mode, respectively. Both of these bands are 16 cm?1 wide (full width at half maximum, FWHM), indicating that a sole population of BChl g molecules is being enhanced at this excitation wavelength. The observed frequency of the CaCm stretching mode (1614 cm?1) indicates that the bulk of BChl g molecules is pentacoordinated with only one axial ligand to the central Mg atom while that of the keto carbonyl stretching mode (1668 cm?1) indicates that these groups are engaged in a hydrogen bond. This homogeneous population of BChl g molecules bound to the heliobacterial core polypeptides is in contrast to the heterogeneous population of Chl a molecules bound to the core polypeptides of the reaction center of photosystem I of Synechocystis 6803 as observed by the inhomogeneously broadened C9 keto carbonyl band in its RR spectrum. The RR spectrum of the Chl a-like chlorin pigments in Hc. mobilis excited at 441.6 nm exhibits a broad keto carbonyl band (43 cm?1 FWHM) with components at 1665, 1683 and 1695 cm?1, indicating several populations of these pigments differing in their protein interactions at the level of the keto carbonyl group. Fourier transform (FT) pre-RR spectroscopic measurements of intact whole cells and membrane fragments at room temperature using 1064 nm excitation indicate that high quality vibrational spectra of the BChl g molecules can be obtained with no photodegradation. Low-temperature FT Raman spectra excited at 1064 nm reveals an inhomogeneously broadened 1665 cm?1 band corresponding to the C9 keto carbonyl stretching mode. Spectral deconvolution and second derivative analysis of this band reveal that it is comprised of components at 1665, 1682 and 1695 cm?1, the latter two most likely arising from BChl g photoconversion products. Excitation using 885 nm to enhance the preresonance effect of the BChl g molecules yields an FT Raman spectrum where the keto carbonyl band at 1665 cm?1 is narrow, as is the case in the Soret RR spectra, reflecting a sole population of BChl g molecules, which are engaged in an H bond. The RR spectrum of the neurosporene molecule in Hc. mobilis membranes excited at 496.5 nm is compared to that of 1,2-dihydroneurosporene bound in a cis configuration in reaction centers of Rhodopseudomona viridis and to that of the same carotenoid in its all-trans configuration extracted from these reaction centers in the presence of light. The similarity of this latter RR spectrum with that of neurosporene in the Hc. mobilis membranes indicates that it is bound in an all-trans configuration. 相似文献
22.
K. J. Tony V. Mahadevan J. Rajaram C. S. Swamy 《Reaction Kinetics and Catalysis Letters》1997,62(1):105-116
Thetrans-dioxo ruthenium (VI) complex, [P(C6H5)3C6H5CH2]+[Ru(O)2OAcCl2] or tetrapropylammonium perruthenate catalyzes the oxidation of secondary alcohols to ketones byN-methylmorpholine-N-oxide (NMO). Kinetic studies showed the formation of a complex between catalyst and substrate (alcohol) as the first step
in the mechanism. 相似文献
23.
Collier PN Campbell AD Patel I Raynham TM Taylor RJ 《The Journal of organic chemistry》2002,67(6):1802-1815
The Garner aldehyde-derived methylene alkene 5 and the corresponding benzyloxycarbonyl compound 25 undergo hydroboration with 9-BBN-H followed by palladium-catalyzed Suzuki coupling reactions with aryl and vinyl halides. After one-pot hydrolysis-oxidation, a range of known and novel nonproteinogenic amino acids were isolated as their N-protected derivatives. These novel organoborane homoalanine anion equivalents are generated and transformed under mild conditions and with wide functional group tolerance: electron-rich and -poor aromatic iodides and bromides (and a vinyl bromide) all undergo efficient Suzuki coupling. The extension of this methodology to prepare meso-DAP, R,R-DAP, and R,R-DAS is also described. 相似文献
24.
UV.-irradiation of pivalic and isobutyric acid and their methyl esters as well as of α-hydroxy isobutyric and malonic acid in solution lead to chemically induced dynamic nuclear polarization (CIDNP.) of parent compounds and of various reaction products. CIDNP.-effects and product distributions confirm α-cleavage of the C(α), CO bond to be the major mode of photodecomposition. Scavenger experiments indicate that decomposition of the molecules from a triplet excited state is roughly equally or more probable than from a singlet excited state. Quantum yields of educt disappearance are also given for the methyl esters of pivalic and isobutyric acid. 相似文献
25.
Constable EC Housecroft CE Neuburger M Schaffner S Shardlow EJ 《Dalton transactions (Cambridge, England : 2003)》2005,(2):234-235
Reaction of 4'-(2-propyn-1-oxy)-2,2':6',2'-terpyridine (HC triple bond CCH2Oterpy) with trans-[PtI2(PEt3)2] regioselectively metallates the alkyne to give trans-[Pt(C triple bond CCH2Oterpy)2(PEt3)2] which, when treated with Fe(II), gives a [2 + 2]-metallocycle. 相似文献
26.
Wei Hu Taotao Qiang Chenchen Li Longfang Ren Fei Cheng Baoshuai Wang Mingli Li Xinjian Song Tony D. James 《Chemical science》2022,13(37):11140
Small-molecule near-infrared (NIR) imaging facilitates deep tissue penetration, low autofluorescence, non-invasive visualization, and a relatively simple operation. As such it has emerged as a popular technique for tracking biological species and events. However, the small Stokes shift of most NIR dyes often results in a low signal-to-noise ratio and self-quenching due to crosstalk between the excitation and emission spectra. With this research, we developed a NIR-based fluorescent probe WD-HOCl for hypochlorous acid (HOCl) detection using the NIR dye TJ730 as the fluorophore, which exhibits a large Stokes shift of 156 nm, with no crosstalk between the excitation and emission spectra. It contains acyl hydrazide as the responsive group and a pyridinium cation as the mitochondria-targeting group. The fluorescence intensity of WD-HOCl was enhanced by 30.1-fold after reacting with HOCl. Imaging studies performed using BV-2 cells indicated that WD-HOCl could be used for endogenous HOCl detection and imaging in living cells exposed to glucose and oxygen deprivation/reperfusion. Finally, we demonstrated that inhibiting the expression of NOX2 reduced the HOCl levels and the severity of oxidative stress during stroke in a mouse model.Small-molecule near-infrared (NIR) imaging facilitates deep tissue penetration, low autofluorescence, non-invasive visualization, and a relatively simple operation. 相似文献
27.
Toward Fluorescence‐Based High‐Throughput Screening for Enantiomeric Excess in Amines and Amino Acid Derivatives
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Elena G. Shcherbakova Dr. Valentina Brega Dr. Tsuyoshi Minami Sara Sheykhi Prof. Dr. Tony D. James Prof. Dr. Pavel Anzenbacher Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10074-10080
A highly accurate and reliable screening method for enantiomeric excess of amine derivatives in the presence of water is reported. The fluorescence‐based screening system has been realized by self‐assembly of chiral diol‐type dyes (BINOL, VANOL and VAPOL), 2‐formylphenylboronic acid, and chiral amines forming iminoboronate esters. The structure and chirality of the amine analytes determine the stability of the diastereomeric iminoboronate esters, which in turn display differential fluorescence. The fluorescence signal reflects the enantiomeric purity of the chiral amines and was utilized in high‐throughput arrays. The arrays were able to recognize enantiomeric excess of amines, amino esters, and amino alcohols. In addition to qualitative analysis, quantitative experiments were successfully performed. Studies of the role of additives such as water or citrate were carried out to gain insight into the stability of the iminoboronate esters. It is shown that the above additives destabilize less stable esters while the stable esters remain unchanged. Thus, the presence of water and citrate leads to increased difference between the diastereomeric iminoboronates and contributes to the enantiodiscrimination of the chiral amines. 相似文献
28.
29.
Seow Jecg Chin Peter Hornsby Damjan Vengust Dragan Mihailović J. Mitra Paul Dawson Tony McNally 《先进技术聚合物》2012,23(2):149-160
Composites of poly(ε‐caprolactone) (PCL) and molybdenum sulfur iodine (MoSI) nanowires were prepared using twin‐screw extrusion. Extensive microscopic examination of the composites revealed the nanowires were well dispersed in the PCL matrix, although bundles of Mo6S3I6 ropes were evident at higher loadings. Secondary electron imaging (SEI) showed the nanowires had formed an extensive network throughout the PCL matrix, resulting in increased electrical conductivity of PCL, by eight orders of magnitude, and an electrical percolation threshold of 6.5 × 10?3 vol%. Thermal analysis (DSC), WAXD, and hot stage polarized optical microscopy (HSPOM) experiments revealed Mo6S3I6 addition altered PCL crystallization kinetics, nucleation density, and crystalline content. A greater number of smaller spherulites were formed via heterogeneous nucleation. The onset of thermal decomposition (TGA) of PCL decreased by 70°C, a consequence of the thermal degradation of Mo6S3I6 to MoO3, which in turn accelerates the formation of volatile gases during the first stage of PCL decomposition. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
30.
Tony Brown 《Research in Mathematics Education》2013,15(1):11-22
Abstract Derrida's revolutionary work in the study of language has seriously challenged the way in which we see words being attached to meanings. This paper makes tentative steps towards examining how his work might assist us in understanding the way in which our attempts to describe or capture our mathematical experiences modify the experience itself. In doing this we draw on the work of Jacques Derrida and John Mason in locating possible frameworks through which to conceptualise the relationship between language and mathematical cognition. It concludes that mathematical meaning never stabilises since it is caught between the individual's ongoing experience and society's ongoing renewal of its conventions. That is, mathematics, language and the human performing them are always evolving in relation to each other. 相似文献