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761.
Laura Saa Dr. Ana Virel Dr. Jose Sanchez‐Lopez Valery Pavlov Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(21):6187-6192
We have developed an analytical assay to detect the enzymatic activity of acetylcholine esterase and alkaline phosphatase based on the generation of quantum dots by enzymatic products. Acetylcholine esterase converts acetylthiocholine into thiocholine. The latter enhances the rate of decomposition of sodium thiosulfate into H2S, which in the presence of cadmium sulfate yields CdS quantum dots showing a time dependent exponential growth, typical of autocatalytic processes. This assay was also applied to detect acetylcholine esterase inhibitors. Alkaline phosphatase hydrolyzes thiophosphate and yields H2S, which instantly reacts with Cd2+ to give CdS quantum dots. The formation of CdS quantum dots in both reactions was followed by fluorescence spectroscopy and showed dependence on the concentration of enzyme and substrate. 相似文献
762.
763.
Jose Luis Muñoz-Muñoz Francisco Garcia-Molina Ramón Varon Jose Tudela Francisco Garcia-Cánovas Jose N. Rodríguez-López 《Journal of mathematical chemistry》2010,48(2):347-362
Tyrosinase has two types of enzymatic activities: the hydroxylation of monophenols to o-diphenols (monophenolase activity) and oxidation of o-diphenols to o-quinones (diphenolase activity). The action on o-diphenols involves two substrates: oxygen and o-diphenol, while the mechanism proposed is a Uni Uni Bi Bi ping-pong. In this contribution, we demonstrate experimentally that
there is a kinetically preferred pathway, which translates into the appearance of curves of initial velocity vs. initial diphenol concentration shows inhibition by an excess of substrate, while sigmoid curves are obtained when the initial
velocity vs. initial oxygen concentration are graphed. However, the action mechanism of the enzyme on monophenols, which is more complex
because it involves three substrates (monophenol, oxygen and o-diphenol), does behave differently from the hyperbolic behaviour as regards the initial velocity vs. initial monophenol concentration, results that can be explained if the limiting step in the action of tyrosinase is the
hydroxylation of monophenol to o-diphenol. 相似文献
764.
The preparation of sodium phosphate glasses singly and doubly doped with rare earth ions Ce3+ and Eu3+ by melt quench method is described. The spectroscopic characterizations of the samples are done using absorption, excitation and emission spectra. The nonradiative energy transfer between trivalent cerium and europium is achieved through the phosphate lattice and the results are incorporated. The main reason of quenching of Ce3+ ions and the mechanism of energy transfer is mainly electric dipole-dipole in nature for Ce3+:Eu3+ system. 相似文献
765.
Estrogen induced proliferation of existing mutant cells is widely understood to be the major risk determining factor in the
development of breast cancer. Hence determination of the Estrogen Receptor[ER] status is of paramount importance. We have
carried out the synthesis and characterization of a novel NIR fluorescent dye conjugate aimed at measuring ER+ve status in-vivo.
The conjugate was synthesized by ester formation between 17-β estradiol and a cyanine dye namely: bis-1, 1-(4-sulfobutyl)
indotricarbocyanine-5-carboxylic acid, sodium salt. The replacement of the sodium ion in the ester by a larger glucosammonium
ion was found to enhance the hydrophilicity and reduce the toxic effect on cell lines. The excitation and emission peaks for
the dye were recorded as 750 and 788 nm respectively; ideal for non-invasive optical imaging owing to minimal tissue attenuation
and auto-fluorescence at these wavelengths. The dye (NIRDC1) has a significant drop in plasma-protein binding therefore leading to marked improvement in pharmacokinetic profile such
as dye evacuation in comparison to ICG. In addition the dye showed enhanced fluorescence quantum yield, molar extinction coefficient
and linearity in fluorescence relative to ICG. This dye can be potentially used as a target specific exogenous contrast agent
in molecular optical imaging for early detection of breast cancer. 相似文献
766.
Luis Daniel Abreu 《Comptes Rendus Mathematique》2011,349(5-6):255-258
767.
Martín Egozcue Luis Fuentes García Wing-Keung Wong Ričardas Zitikis 《Central European Journal of Mathematics》2011,9(6):1288-1297
We show that Grüss-type probabilistic inequalities for covariances can be considerably sharpened when the underlying random
variables are quadrant dependent in expectation (QDE). The herein established covariance bounds not only sharpen the classical
Grüss inequality but also improve upon recently derived Grüss-type bounds under the assumption of quadrant dependency (QD),
which is stronger than QDE. We illustrate our general results with examples based on specially devised bivariate distributions
that are QDE but not QD. Such results play important roles in decision making under uncertainty, and particularly in areas
such as economics, finance, and insurance. 相似文献
768.
Fabric dependence of quasi-waves in anisotropic porous media 总被引:1,自引:0,他引:1
Assessment of bone loss and osteoporosis by ultrasound systems is based on the speed of sound and broadband ultrasound attenuation of a single wave. However, the existence of a second wave in cancellous bone has been reported and its existence is an unequivocal signature of poroelastic media. To account for the fact that ultrasound is sensitive to microarchitecture as well as bone mineral density (BMD), a fabric-dependent anisotropic poroelastic wave propagation theory was recently developed for pure wave modes propagating along a plane of symmetry in an anisotropic medium. Key to this development was the inclusion of the fabric tensor--a quantitative stereological measure of the degree of structural anisotropy of bone--into the linear poroelasticity theory. In the present study, this framework is extended to the propagation of mixed wave modes along an arbitrary direction in anisotropic porous media called quasi-waves. It was found that differences between phase and group velocities are due to the anisotropy of the bone microarchitecture, and that the experimental wave velocities are more accurately predicted by the poroelastic model when the fabric tensor variable is taken into account. This poroelastic wave propagation theory represents an alternative for bone quality assessment beyond BMD. 相似文献
769.
This article presents a technique for modelling the coupled dynamics of a railway vehicle and the track. The method is especially useful for simulating the dynamics of high speed trains running on nonlinear tracks. The main hypothesis is a cyclic system: an infinite track on which there is an infinite set of identical vehicles spaced at a regular interval of distance. Thus the main problems of the finite-length track models (e.g. the waves that reflect at the end of the track and interact with the vehicle; and the time interval of integration must be shorter than the track length divided by the velocity) are avoided. The flexibility of the method can be observed from the case studies presented in the present work: a vehicle passing over a hanging sleeper, and the vehicle-track dynamics for different ballast compaction cases. The results show the influence of the hanging sleeper gap on the wheel-rail contact forces, and the bending moment at the sleeper for different ballast compaction cases. 相似文献
770.
Ansgar Jüngel José Luis López Jesús Montejo–Gámez 《Journal of statistical physics》2011,145(6):1661-1673
A quantum Navier–Stokes system for the particle, momentum, and energy densities is formally derived from the Wigner–Fokker–Planck
equation using a moment method. The viscosity term depends on the particle density with a shear viscosity coefficient which
equals the quantum diffusion coefficient of the Fokker–Planck collision operator. The main idea of the derivation is the use
of a so-called osmotic momentum operator, which is the sum of the phase-space momentum and the gradient operator. In this
way, a Chapman–Enskog expansion of the Wigner function, which typically leads to viscous approximations, is avoided. Moreover,
we show that the osmotic momentum emerges from local gauge theory. 相似文献