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781.
Fosnaric M Bohinc K Gauger DR Iglic A Kralj-Iglic V May S 《Journal of chemical information and modeling》2005,45(6):1652-1661
A membrane inclusion can be defined as a complex of protein or peptide and the surrounding significantly distorted lipids. We suggest a theoretical model that allows for the estimation of the influence of membrane inclusions on the curvature elastic properties of lipid membranes. Our treatment includes anisotropic inclusions whose energetics depends on their in-plane orientation within the membrane. On the basis of continuum elasticity theory, we calculate the inclusion-membrane interaction energy that reflects the protein or peptide-induced short-ranged elastic deformation of a bent lipid layer. A numerical estimate of the corresponding interaction constants indicates the ability of inclusions to sense membrane bending and to accumulate at regions of favorable curvature, matching the effective shape of the inclusions. Strongly anisotropic inclusions interact favorably with lipid layers that adopt saddlelike curvature; such structures may be stabilized energetically. We explore this possibility for the case of vesicle budding where we consider a shape sequence of closed, axisymmetric vesicles that form a (saddle-curvature adopting) membrane neck. It appears that not only isotropic but also strongly anisotropic inclusions can significantly contribute to the budding energetics, a finding that we discuss in terms of recent experiments. 相似文献
782.
H. Ratajczak J. Barycki A. Pietraszko J. Baran S. Debrus M. May J. Venturini 《Journal of Molecular Structure》2000,526(1-3)
-Histidinium dihydrogenarsenate orthoarsenic acid (LHA) crystal ;
belongs to P21 space group of the monoclinic system, Z=2, a=9.264(2) Å, b=8.929(2) Å, c=8.874(2) Å, β=108.61(3)°. The crystal is isomorphous to
(LHP) crystal. The H2AsO4− anions and H3AsO4 molecules are joined into layers parallel to the (100) crystallographic planes by the O–HO type hydrogen bonds. The histidinium cations occupy the space between the layers. The histidinium cation posses the carboxylic COO− group. The positive charges appear in the ring (the proton is attached to the =N(3)– nitrogen) and in the ammonium group. The differential scanning calorimetric (DSC) diagram does not show any phase transition till 100 K. The infrared spectrum fully confirms the X-ray crystal structure. The LHA crystal is a good second harmonic generator (0.46 relative to KDP) 相似文献
Full-size image
Full-size image
783.
Malte Behrens Enno May Wolfgang Bensch Dietrich Häußler 《Journal of solid state chemistry》2006,179(11):3330-3337
The reactivity of [Cr/Se/Te] multilayers under annealing was investigated using X-ray reflectometry, in situ X-ray diffraction, X-ray absorption fine structure (XAFS) measurements and transmission electron microscopy. For all samples, interdiffusion was complete at temperatures between 100 and 300 °C, depending on the repeating tri-layer thickness. A crystalline phase nucleated approximately 20 °C above the temperature where interdiffusion was finished. The first crystalline phase in a binary Cr/Te sample was layered CrTe3 nucleating at 230 °C. In ternary samples (Se:Te=0.6-1.2), the low-temperature nucleation of such a layered CrQ3 (Q=Se, Te) phase is suppressed and instead the phase Cr2Q3 nucleates first. Interestingly, this phase decomposes around 500 °C into layered CrQ3. In contrast, binary Cr/Se samples form stable amorphous alloys after interdiffusion and Cr3Se4 nucleates around 500 °C as the only crystalline phase. Evaluation of the XAFS data of annealed samples yield Se-Cr distances of 2.568(1) and 2.552(1) Å for Cr2Q3 and CrQ3, respectively. In the latter sample, higher coordination shells around Se are seen accounting for the Se-Te contacts in the structure. 相似文献
784.
May BL Gerber J Clements P Buntine MA Brittain DR Lincoln SF Easton CJ 《Organic & biomolecular chemistry》2005,3(8):1481-1488
alpha-Cyclodextrin, beta-cyclodextrin, N-(6(A)-deoxy-alpha-cyclodextrin-6(A)-yl)-N'6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea and N,N-bis(6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea (alphaCD, betaCD, 1 and 2) form inclusion complexes with E-4-tert-butylphenyl-4'-oxyazobenzene, E-3(-). In aqueous solution at pH 10.0, 298.2 K and I = 0.10 mol dm(-3)(NaClO(4)) spectrophotometric UV-visible studies yield the sequential formation constants: K(11) = (2.83 +/- 0.28) x 10(5) dm(3) mol(-1) for alphaCD.E-(-), K(21) = (6.93 +/- 0.06) x 10(3) dm(3) mol(-1) for (alphaCD)(2).E-3(-), K(11) = (1.24 +/- 0.12) x 10(5) dm(3) mol(-1) for betaCD.E-(-), K(21) = (1.22 +/- 0.06) x 10(4) dm(3) mol(-1) for (betaCD)(2).E-(-), K(11) = (3.08 +/- 0.03) x 10(5) dm(3) mol(-1) for .E-3(-), K(11) = (8.05 +/- 0.63) x 10(4) dm(3) mol(-1) for .E-3(-) and K(12) = (2.42 +/- 0.53) x 10(4) dm(3) mol(-1) for .(E-3(-))(2). (1)H ROESY NMR studies show that complexation of E-3(-) in the annuli of alphaCD, betaCD, 1 and 2 occurs. A variable-temperature (1)H NMR study yields k(298 K)= 6.7 +/- 0.5 and 5.7 +/- 0.5 s(-1), DeltaH = 61.7 +/- 2.7 and 88.1 +/- 4.2 kJ mol(-1) and DeltaS = -22.2 +/- 8.7 and 65 +/- 13 J K(-1) mol(-1) for the interconversion of the dominant includomers (complexes with different orientations of alphaCD) of alphaCD.E-3(-) and (alphaCD)(2).E-3(-), respectively. The existence of E-3(-) as the sole isomer was investigated through an ab initio study. 相似文献
785.
Optimal control theory (OCT) is formulated for the case of a two-color pump-probe experiment. The approach allows to calculate the pump-pulse shape in such a way that the probe-pulse absorption signal is maximized. Since the latter quantity is given by the time-averaged expectation value of a time dependent operator (the probe-pulse field-strength times the dipole operator) a version of OCT has to be used where the target state is distributed in time. The method is applied to a molecular three-level system with the pump-pulse driving the transition from the electronic ground state into the first-excited electronic state and the probe-pulse connecting the first-excited state with a higher lying electronic state. Depending on the probe-pulse duration, the vibrational wave packet becomes localized or at least highly concentrated in the Franck-Condon window for the transition into the higher-excited state. The dependence on the probe-pulse duration and on the delay time between the optimized pump-pulse and the probe-pulse is discussed in detail. The whole study demonstrates the feasibility of laser pulse induced temporal wave packet localization and the use of spectroscopic quantities as target states in experiments on femtosecond laser pulse control. 相似文献
786.
Simándi TM May Z Szigyártó IC Simándi LI 《Dalton transactions (Cambridge, England : 2003)》2005,(2):365-368
Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases. 相似文献
787.
(E)-4-tert-Butyl-4'-oxystilbene, 1(-), is thermally stable as the (E)-1(-) isomer but may be photoisomerized to the (Z)-1(-) isomer as shown by UV-vis and (1)H NMR studies in aqueous solution. When (E)-1(-) is complexed by alphaCD two inclusion isomers (includomers) form in which alphaCD assumes either of the two possible orientations about the axis of (E)-1(-) in alphaCD.(E)-1(-) for which (1)H NMR studies yield the parameters: k(1)(298 K)= 12.3 +/- 0.6 s(-1), DeltaH(1)(++)= 94.3 +/- 4.7 kJ mol(-1), DeltaS1(++)= 92.0 +/- 5.0 J K(-1) mol(-1), and k(2)(298 K)= 10.7 +/- 0.5 s(-1), DeltaH(2)(++)= 93.1 +/- 4.7 kJ mol(-1), DeltaS2(++)= 87.3 +/- 5.0 J K(-1) mol(-1) for the minor and major includomers, respectively. The betaCD.(E)-1(-) complex either forms a single includomer or its includomers interchange at the fast exchange limit of the (1)H NMR timescale. Complexation of 1(-) by N-(6(A)-deoxy- alpha-cyclodextrin-6(A)-yl)-N'-(6(A)-deoxy- beta-cyclodextrin-6(A)-yl)urea, results in the binary complexes 2.(E)-1(-) in which both CD component annuli are occupied by (E)-1(-) and which exists exclusively in darkness and 2.(Z)-1(-) in which only one CD component is occupied by (Z)-1(-) and exists exclusively in daylight at lambda > or = 300 nm. Irradiation of solutions of the binary complexes at 300 and 355 nm results in photostationary states dominated by 2.(E)-1(-) and 2.(Z)-1(-), respectively. In the presence of 4-methylbenzoate, 4(-), 2.(Z)-1(-) forms the ternary complex 2.(Z)-1(-).4(-) where 4(-) occupies the second CD annulus. Interconversion occurs between 2.(Z)-1(-).4(-) and 2.(E)-1(-)+4(-) under the same conditions as for the binary complexes alone. Similar interactions occur in the presence of 4-methylphenolate and 4-methylphenylsulfonate. The two isomers of each of these systems represent different states of a molecular device, as do the analogous binary complexes of N,N-bis(6(A)-deoxy- beta-cyclodextrin-6(A)-yl)urea, 3, [3.(E)-1(-) and 3.(Z)-1(-), where the latter also forms a ternary complex with 4(-). 相似文献
788.
Alam TM Nyman M Cherry BR Segall JM Lybarger LE 《Journal of the American Chemical Society》2004,126(17):5610-5620
Solid-state (1)H, (17)O MAS NMR, (1)H-(93)Nb TRAPDOR NMR, and (1)H double quantum 2D MAS NMR experiments were used to characterize the oxygen, water, and hydroxyl environments in the monoprotonated hexaniobate material, Na(7)[HNb(6)O(19)].15H(2)O. These solid-state NMR experiments demonstrate that the proton is located on the bridging oxygen of the [Nb(6)O(19)](8-) cluster. The solid-state NMR results also show that the NbOH protons are spatially isolated from similar protons, but undergo proton exchange with the water species located in the crystal lattice. On the basis of double quantum (1)H MAS NMR measurements, it was determined that the water species in the crystal lattice have restricted motional dynamics. Two-dimensional (1)H-(17)O MAS NMR correlation experiments show that these restricted waters are preferentially associated with the bridging oxygen. Solution (17)O NMR experiments show that the hydroxyl proton is also attached to the bridging oxygen for the compound in solution. In addition, solution (17)O NMR kinetic studies for the hexaniobate allowed the measurement of relative oxygen exchange rates between the bridging, terminal, and hydroxyl oxygen and the oxygen of the solvent as a function of pH and temperature. These NMR experiments are some of the first investigations into the proton location, oxygen and proton exchange processes, and water dynamics for a base stable polyoxoniobate material, and they provide insight into the chemistry and reactivity of these materials. 相似文献
789.
May Nilsen 《Proceedings of the American Mathematical Society》1998,126(10):2969-2978
Let be a cosystem and be a dynamical system. We examine the extent to which induction and restriction of ideals commute, generalizing some of the results of Gootman and Lazar (1989) to full crossed products by non-amenable groups. We obtain short, new proofs of Katayama and Imai-Takai duality, the faithfulness of the induced regular representation for full coactions and actions by amenable groups. We also give a short proof that the space of dual-invariant ideals in the crossed product is homeomorphic to the space of invariant ideals in the algebra, and give conditions under which the restriction mapping is open.
790.
Jerry L. Atwood Simon G. Bott Kerry D. Robinson Elizabeth J. Bishop Michael T. May 《Journal of chemical crystallography》1991,21(4):459-462
The title compound was synthesized by the reaction of [H3O+·18-crown-6][Cl-H-Cl–]·3.8 C6H5Me with two equivalents of H2O. Colorless crystals, which slowly deposited from the corresponding liquid clathrate, belong to the monoclinic space group P21/n witha=10.648(6),b=9.571(2),c=20.801(6) Å,=98.67(5)°, andD
c=1.24 g cm–3 forZ=4. Refinement based on 1609 observed reflections led to a finalR value of 0.072. In the crystal structure the [H3O+·18-crown-6]+ cations are packed in layers separated by puckered sheets of [(H5O
2
+
)(Cl–)2]–. 相似文献