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981.
Sergi A Watney JB Wong KF Hammes-Schiffer S 《The journal of physical chemistry. B》2006,110(5):2435-2441
Constraining a single motion between distal residues separated by approximately 28 A in hybrid quantum/classical molecular dynamics simulations is found to increase the free energy barrier for hydride transfer in dihydrofolate reductase by approximately 3 kcal/mol. Our analysis indicates that a single distal constraint alters equilibrium motions throughout the enzyme on a wide range of time scales. This alteration of the conformational sampling of the entire system is sufficient to significantly increase the free energy barrier and decrease the rate of hydride transfer. Despite the changes in conformational sampling introduced by the constraint, the system assumes a similar transition state conformation with a donor-acceptor distance of approximately 2.72 A to enable the hydride transfer reaction. The modified thermal sampling leads to a substantial increase in the average donor-acceptor distance for the reactant state, however, thereby decreasing the probability of sampling the transition state conformations with the shorter distances required for hydride transfer. These simulations indicate that fast thermal fluctuations of the enzyme, substrate, and cofactor lead to conformational sampling of configurations that facilitate hydride transfer. The fast thermal motions are in equilibrium as the reaction progresses along the collective reaction coordinate, and the overall average equilibrium conformational changes occur on the slower time scale measured experimentally. Recent single molecule experiments suggest that at least some of these thermally averaged equilibrium conformational changes occur on the millisecond time scale of the hydride transfer reaction. Thus, introducing a constraint that modifies the conformational sampling of an enzyme could significantly impact its catalytic activity. 相似文献
982.
We have synthesized a series of novel coplanar chromophores in which heteroarenes, namely, thiophene, benzothiophene, and carbazole, were fused to neighboring phenylene ring(s) through intramolecular annulation via sp(3)-hybridized carbon atoms bearing two p-tolyl groups as peripheral substituents. The molecular configurations of the pi-conjugated backbones were determined by X-ray crystallographic analysis; the heteroarene-fused molecular frameworks of these novel molecules exhibit nearly coplanar conformations. [structure: see text] 相似文献
983.
Ping Wong Ng 《Proceedings of the American Mathematical Society》2006,134(8):2223-2228
Let be a unital, simple, separable -algebra with real rank zero, stable rank one, and weakly unperforated ordered group. Suppose, also, that can be locally approximated by type I algebras with Hausdorff spectrum and bounded irreducible representations (the bound being dependent on the local approximating algebra). Then is tracially approximately finite dimensional (i.e., has tracial rank zero).
Hence, is an -algebra with bounded dimension growth and is determined by -theoretic invariants.
The above result also gives the first proof for the locally case.
984.
Chen JS Wong GK Murdoch SG Kruhlak RJ Leonhardt R Harvey JD Joly NY Knight JC 《Optics letters》2006,31(7):873-875
We report on the observation of cross-phase modulation instability in a highly nonlinear photonic crystal fiber. In such fibers the presence of higher orders of dispersion results in a complex phase-matching curve. We are able to observe this behavior experimentally and obtain excellent agreement between the measured and predicted shifts. 相似文献
985.
We demonstrate continuous-wave cascaded optical parametric oscillation in which the signal field of the primary parametric oscillator internally pumps the secondary parametric oscillator. Wavelength tuning is achieved with temperature tuning and a fan-out grating structure of a dual-grating periodically poled lithium niobate crystal. Above the secondary threshold the primary signal power is clamped, and all the other output powers increase linearly with the input pump power, in accordance with theory. Cascaded parametric oscillation offers a convenient and efficient way to generate multiple tunable outputs. 相似文献
986.
Fu-Hsiang Wong Shiueh-Ling Yu Cheh-Chih Yeh Wei-Cheng Lian 《Applied Mathematics Letters》2006,19(12):1293-1299
The purpose of this work is to establish the timescale version of Lyapunov’s inequality as follows: Let be a nontrivial solution of satisfying . Then, under suitable conditions on , , and , we have where and satisfies if . Here is a timescale (see below). 相似文献
987.
As a chromatographic column, the high-speed counter-current chromatography system was equipped with a preparative HPLC series, enabling the successful isolation of hydrolysable tannins from the fruits of Terminalia chebula, a traditional Chinese medicine. The two-phase solvent system was composed of n-hexane-ethyl acetate-methanol-water (1:20:1:20 v/v). As a result, 33.2 mg chebulagic and 15.8 mg chebulinic acids were obtained in one step from 300 mg of crude extract. Their purities were determined by HPLC to be 95.3 and 96.1%, respectively. The chemical structures were identified by their MS and 1H NMR spectra. 相似文献
988.
We investigate the formation of ringlike deposits in drying drops of DNA. In analogy with the colloidal "coffee rings," DNA is transported to the perimeter by the capillary flow. At the droplet edge, however, DNA forms a lyotropic liquid crystal (LC) with concentric chain orientations to minimize the LC elastic energy. During the final stages of drying, the contact line retracts, and the radial stress causes undulations at the rim that propagate inward through the LC and form a periodic zigzag structure. We examine the phenomenon in terms of a simple model based on LC elasticity. 相似文献
989.
Uniform asymptotic formulas are obtained for the Stieltjes-Wigert polynomial, the q−1-Hermite polynomial and the q-Laguerre polynomial as the degree of the polynomial tends to infinity. In these formulas, the q-Airy polynomial, defined by truncating the q-Airy function, plays a significant role. While the standard Airy function, used frequently in the uniform asymptotic formulas for classical orthogonal polynomials, behaves like the exponential function on one side and the trigonometric functions on the other side of an extreme zero, the q-Airy polynomial behaves like the q-Airy function on one side and the q-Theta function on the other side. The last two special functions are involved in the local asymptotic formulas of the q-orthogonal polynomials. It seems therefore reasonable to expect that the q-Airy polynomial will play an important role in the asymptotic theory of the q-orthogonal polynomials. 相似文献
990.
P. H. Kropholler S. J. Pride W. A. M. Othman K. B. Wong P. C. Wong 《Semigroup Forum》2010,81(1):172-186
In this paper, we study some properties of semigroups with presentation 〈a,b ; a
p
=b
r
,a
q
=b
s
〉. We will also study their potential as platforms for the Diffie-Hellman key exchange protocol. 相似文献