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1.
Laurens Kooijman Dr. Matthias Schuster Christian Baumann Simon Jurt Dr. Frank Löhr Dr. Boris Fürtig Prof. Dr. Peter Güntert Prof. Dr. Oliver Zerbe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21151-21158
To achieve efficient proton pumping in the light-driven proton pump bacteriorhodopsin (bR), the protein must be tightly coupled to the retinal to rapidly convert retinal isomerization into protein structural rearrangements. Methyl group dynamics of bR embedded in lipid nanodiscs were determined in the dark-adapted state, and were found to be mostly well ordered at the cytosolic side. Methyl groups in the M145A mutant of bR, which displays only 10 % residual proton pumping activity, are less well ordered, suggesting a link between side-chain dynamics on the cytosolic side of the bR cavity and proton pumping activity. In addition, slow conformational exchange, attributed to low frequency motions of aromatic rings, was indirectly observed for residues on the extracellular side of the bR cavity. This may be related to reorganization of the water network. These observations provide a detailed picture of previously undescribed equilibrium dynamics on different time scales for ground-state bR. 相似文献
2.
B. M. Azizur Rahman A. K. M. Saiful Kabir Muttukrishnan Rajarajan Kenneth T. V. Grattan 《Optical and Quantum Electronics》2005,37(1-3):171-183
Modal solutions of planar photonic crystal waveguides with rectangular air-holes are presented by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations. 相似文献
3.
A test statistic is developed that checks the validity of the extreme value conditions without specifiying the shape parameter of the limiting extreme value distribution. 相似文献
4.
Mulder FM Stride J Picken SJ Kouwer PH de Haas MP Siebbeles LD Kearley GJ 《Journal of the American Chemical Society》2003,125(13):3860-3866
Discotic molecules have planar, disklike polyaromatic cores that can self-assemble into "molecular wires". Highly anisotropic charge transfer along the wires arises when there is sufficient intermolecular overlap of the pi-orbitals of the molecular cores. Discotic materials can be applied in molecular electronics, field-effect transistors, and-recently with record quantum efficiencies-photovoltaics (Schmidt-Mende, L.; Fechtenk?tter, A.; Müllen, K.; Moons, E.; Frien, R. H.; MacKenzie, J. D. Science 2001, 293, 1119). A combination of quasielastic neutron scattering (QENS) measurements with molecular dynamics simulations on the discotic molecule hexakis(n-hexyloxy)triphenylene (HAT6) shows that the dynamics of the cores and tails of discotic molecules are strongly correlated. Core and tail dynamics are not separated, the system being characterized by overall in-plane motion, on a time scale of 0.2 ps, and softer out-of-plane motions at 7 ps. Because charge transfer between the molecules is on similar time scales, these motions are relevant for the conducting properties of the materials. Both types of motion are dominated by van der Waals interactions. Small-amplitude in-plane motions in which the disks move over each other are almost entirely determined by tail/tail interactions, these also playing an important role in the out-of-plane motion. The QENS measurements reveal that these motions are little changed by passing from the columnar phase to the isotropic liquid phase, just above the clearing temperature. The model of four HAT6 molecules in a column reproduces the measured QENS spectrum of the liquid phase, suggesting that correlations persist within the liquid phase over about this number of disks. 相似文献
5.
The gas chromatographic determination of trace gaseous impurities in highly reactive fluorinated gaseous matrices presents unique requirements to both equipment and techniques. Especially problematic are the gases normally present in ambient air namely oxygen and nitrogen. Analysing these gases at the low microl/l (ppm) level requires special equipment and this publication describes a custom-designed system utilising backflush column switching to protect the columns and detectors. A thermal conductivity detector with nickel filaments was used to determine ppm levels of impurities in ClF3. 相似文献
6.
PICOSECOND FLUORESCENCE STUDY OF PHOTOSYNTHETIC MUTANTS OF Chlamydomonas reinhardii: ORIGIN OF THE FLUORESCENCE DECAY KINETICS OF CHLOROPLASTS 总被引:3,自引:0,他引:3
Robert J. Gulotty Laurens Mets Randall S. Alberte Graham R. Fleming 《Photochemistry and photobiology》1985,41(4):487-496
Abstract— The fluorescence decay kinetics of photosynthetic mutants of Chlamydomonas reinhardii which lack photosystem II (PS II), photosystem I (PS I), and both PS II and PS I have been measured. The PS II mutant strain8–36C exhibits fluorescence decay lifetime components of 53, 424 and 2197 ps. The fluorescence decay of a PS I mutant strain12–7 contains two major fluorescence decay components with lifetimes of 152 and 424 ps. The fluorescence decay of mutant strain C2, which lacks both PS II and PS I, is nearly single exponential with a lifetime of 2561 ± 222 ps. In simulations in which it is assumed that wild-type decays are a simple sum of the major decay components of the isolated parts of the photosynthetic unit as measured in the mutants, curves are obtained that fit the wild-type C. reinhardii fluorescence decay data when the absorption cross-sections of PS II and PS I are weighted approximately equally. The 89 ps lifetime component in the wild-type is an average of 53 and 152 ps components arising from excitation transfer to and trapping in PS I and PS II. The single step transfer time in PS I is estimated to be between 100 and 700 fs depending on assumptions about array size. We find that between two and four visits to the PS I reaction center are required before final trapping. 相似文献
7.
Begum N Hyder MI Kabir SE Hossain GM Nordlander E Rokhsana D Rosenberg E 《Inorganic chemistry》2005,44(26):9887-9894
Treatment of Mn(2)(CO)(10) with 3,4-toluenedithiol and 1,2-ethanedithiol in the presence of Me(3)NO.2H(2)O in CH(2)Cl(2) at room temperature afforded the dinuclear complexes Mn(2)(CO)(6)(mu-eta(4)-SC(6)H(3)(CH(3))S-SC(6)H(3)(CH(3))S) (1), and Mn(2)(CO)(6)(mu-eta(4)-SCH(2)CH(2)S-SCH(2)CH(2)S) (2), respectively. Similar reactions of Re(2)(CO)(10) with 3,4-toluenedithiol, 1,2-benzenedithiol, and 1,2-ethanedithiol yielded the dirhenium complexes Re(2)(CO)(6)(mu-eta(4)-SC(6)H(3)(CH(3))S-SC(6)H(3)(CH(3))S) (3), Re(2)(CO)(6)(mu-eta(4)-SC(6)H(4)S-SC(6)H(4)S) (4), and Re(2)(CO)(6)(SCH(2)CH(2)S-SCH(2)CH(2)S) (5), respectively. In contrast, treatment of Mn(2)(CO)(10) with 1,3-propanedithiol afforded the trimanganese compound Mn(3)(CO)(6)(mu-eta(2)-SCH(2)CH(2)CH(2)S)(3) (6), whereas Re(2)(CO)(10) gave only intractable materials. The molecular structures of 1, 3, and 6 have been determined by single-crystal X-ray diffraction studies. The dimanganese and dirhenium carbonyl compounds 1-5contain a binucleating disulfide ligand, formed by interligand disulfide bond formation between two dithiolate ligands identical in structure to that of the previously reported dimanganese complex Mn(2)(CO)(6)(mu-eta(4)-SC(6)H(4)S-SC(6)H(4)S). Complex 6, on the other hand, forms a unique example of a mixed-valence trimangenese carbonyl compound containing three bridging 1,3-propanedithiolate ligands. The solution properties of 6 have been investigated by UV-vis and EPR spectroscopies as well as electrochemical techniques. 相似文献
8.
Lead(II) 2,2'-bipyridine hexachloroplumba tetetrahydrate was synthesized and investigated by DTA, TG and DTG. IR spectroscopy
and other methods enabled the identification of some of the decomposition products. Comparative studies on the corresponding
chlorides: [Pb(bipy)]Cl2 and [Pb(bipy)3]Cl2, which can be considered as precursors of the hexachloroplumbate, were also undertaken. X-ray measurements enabled the tentative
determination of the crystal structure of [Pb(bipy)]Cl2. Hexachloroplumbate decomposes with the liberation of chlorine, water and organic ligands, and the process is accompanied
by the simultaneous transition of Pb(IV)→Pb(II). Chlorides release only ligands upon heating. Residues comprised always PbCl2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Noorjahan Begum Amarash C. Ghosh Shariff E. Kabir Md. Arzu Miah G.M. Golzar Hossain 《Polyhedron》2005,24(18):3074-3081
Four triosmium carbonyl clusters bearing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands of general formula [Os3(CO)9(μ-OH)(μ-OMeCO)L] (1, L = pyrazine; 2, L = 2-methylpyrazine; 3, L = 2,3-dimethylpyrazine; 4, L = 2,3,5-trimethylpyrazine) were synthesized by the reactions of [Os3(CO)12] with the corresponding pyrazine derivatives and water in the presence of a methanolic solution of Me3NO in moderate yields. Compounds [Os3(CO)9(μ-OH)(μ-OMeCO)L] react with a series of two electron donor ligands, L′ at ambient temperature to give [Os3(CO)9(μ-OH)(μ-OMeCO)L′] (5, L′ = PPh3; 6, L′ = P(OMe)3; 7, L′ = tBuNC; 8, L′ = C5H5N) in good yields by the displacement of the pyrazine ligands. This implies that the pyrazine ligands in 1–4 are relatively labile. Compounds 2, 3, 4, and 8 were characterized by single crystal X-ray diffraction analyses. All the four compounds possess two metal–metal bonds and a non-bonded separation of two osmium atoms defined by Os(1)Os(3), which are simultaneously bridged by OH and MeOCO ligands and a heterocyclic ligand is terminally coordinated to one of the two non-bonded osmium atoms. 相似文献
10.
Kazi A. Azam Rahima Dilshad Shariff E. Kabir Rashid Miah Mohammad Shahiduzzaman Edward Rosenberg Kenneth I. Hardcastle Michael B. Hursthouse K. M. Abdul Malik 《Journal of Cluster Science》1996,7(1):49-70
The reaction of [Os3(CO)12] with tetramethylthiourea in the presence of a methanolic solution of Me3NO·2H2O at 60° yields the compounds [Os3(CO)11{η 1-SC(NMe2)2}] (1) in 56% yield and [Os3(CO)9(μ-OH)(μ-MeOCO){η 1-SC(NMe2)2}] (2) in 10% yield in which the tetramethylthiourea ligand is coordinatedvia the sulfur atom at an equatorial position. Compound2 is a 50 e? cluster with two metal-metal bonds and the hydroxy and methoxycarbonyl ligands bridging the open metal-metal edge. In contrast, the analogous reaction of [Os3(CO)12] with thiourea gives the compounts [(μ-H)Os3(CO)10{μ-NHC(S)NH2}] (3) in 8% yield and [(μ-H)Os3(CO)9{3-NHC(S)NH2}] (4) in 30% yield. In3, the thioureato ligand bridges two osmium atomsvia the sulfur atom, whereas in4 in addition to the sulfur bridge, one of the nitrogen atoms of thioureato moiety bonds to the remaining osmium atom. The decacarbonyl compounds 3 can also be obtained in 50% yield from the reaction of [Os3(CO)10(MeCN)2] with thiourea at ambient temperature. Compound3 converts to4 (65%) photochemically. Compound1 reacts with PPh3 and acetonitrile at ambient temperature to give the simple substitution products [Os3(CO)11(PPh3)] and [Os3(CO)11(MeCN)], respectively, while with pyridine, the oxidative addition product [(μ-H)Os3(CO)10(μ-NC5H4] is formed at 80°C. All the new compounds are characterized by IR,1-H-NMR and elemental analysis together with the X-ray crystal structures of1,2 and4. Compound1 crystallizes in the triclinic space group P $P\bar 1$ with unit cell parametersa = 8.626(3) Å,b = 11.639(3) Å,c = 12.568(3_ Å,α = 84.67(2)°,β = 75.36(2)°,γ = 79.49(3)°,V = 1199(1) Å3, andZ = 2. Least-squares refinement of 4585 reflections gave a final agreement factor ofR = 0.0766 (R w = 0.0823). Compound2 crystallizes in the monoclinic space group P21/n with unit cell parametersa = 9.149(5) Å,b = 17.483(5) Å,c = 15.094(4) Å,β = 91.75(2)°,V = 2413(2) Å3, andZ = 4. Least-squares refinement of 3632 reflections gave a final agreement factor ofR = 0.0603 (R w = 0.0802). Compound4 crystallizes in the monoclinic space group C2/c with unit cell parametersa = 13.915(7) Å,b = 14.718(6) Å,c = 17.109(6) Å,β = 100.44(3)°,V = 3446(5) Å3, andZ = 8. Least-squares refinement of 2910 reflections gave a final agreement factor ofR = 0.0763 (R w = 0.0863). 相似文献