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81.
F. Akbarian A. Lin B.S. Dunn J.S. Valentine J.I. Zink 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1067-1070
Biological activity of cholinesterases can be determined by optically monitoring the enzymatic reaction with indophenyl acetate,
(N-4′-acetoxyphenyl)-4-quinone imine. At pH 8.0 cholinesterases hydrolyze this yellow dye to yield a blue reaction product.
Cholinesterase inhibitors reduce the rate of this hydrolysis. Thus, by monitoring absorbance of the hydrolysis product at
its maximum (630 nm) as a function of time, reaction rates of both cholinesterase activity and cholinesterase inhibition may
be quantified spectroscopically. Using this technique, we measured the enzymatic activity of butyrylcholinesterase (BuChE)
molecules encapsulated in tetramethyl orthosilicate (TMOS) silicate gel-glass prepared by hydrolysis and condensation. This
activity is reduced, in a concentration-dependent manner, by the reversible cholinesterase inhibitors 1,5-bis(4-allyldimethyl-ammoniumphenyl) pentan 3-one dibromide (BADAPP) and 9-amino-1,2,3,4-tetrahydroacridine (THA; tacrine, Cognex).
The gel-glasses are rigid, and compact, transparent and porous enough to allow reagents to diffuse in and out. 相似文献
82.
Wong IY Gardel ML Reichman DR Weeks ER Valentine MT Bausch AR Weitz DA 《Physical review letters》2004,92(17):178101
We study the thermal motion of colloidal tracer particles in entangled actin filament (F-actin) networks, where the particle radius is comparable to the mesh size of the F-actin network. In this regime, the ensemble-averaged mean-squared displacement of the particles is proportional to tau(gamma), where 0相似文献
83.
We measure the viscoelasticity of entangled F-actin over length scales between 1 and 100 microm using one- and two-particle microrheology, and directly identify two distinct microscopic contributions to the elasticity. Filament entanglements lead to a frequency-independent elastic modulus over an extended frequency range of 0.01-30 rad/sec; this is probed with one-particle microrheology. Longitudinal fluctuations of the filaments increase the elastic modulus between 0.1 and 30 rad/sec at length scales up to the filament persistence length; this is probed by two-particle microrheology. 相似文献
84.
Lefebvre BG Liu W Peterson RW Valentine KG Wand AJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,175(1):158-162
Traditionally, large proteins, aggregation-prone proteins, and membrane proteins have been difficult to examine by modern multinuclear and multidimensional solution NMR spectroscopy. A major limitation presented by these protein systems is that their slow molecular reorientation compromises many aspects of the more powerful solution NMR methods. Several approaches have emerged to deal with the various spectroscopic difficulties arising from slow molecular reorientation. One of these takes the approach of actively seeking to increase the effective rate of molecular reorientation by encapsulating the protein of interest within the protective shell of a reverse micelle and dissolving the resulting particle in a low viscosity fluid. Since the encapsulation is largely driven by electrostatic interactions, the preparation of samples of acidic proteins suitable for NMR spectroscopy has been problematic owing to the paucity of suitable cationic surfactants. Here, it is shown that the cationic surfactant CTAB may be used to prepare samples of encapsulated anionic proteins dissolved in low viscosity solvents. In a more subtle application, it is further shown that this surfactant can be employed to encapsulate a highly basic protein, which is completely denatured upon encapsulation using an anionic surfactant. 相似文献
85.
James F. Sanders John D. Ferry Robert H. Valentine 《Journal of Polymer Science.Polymer Physics》1968,6(5):967-980
Viscoelastic properties of uncrosslinked 1,2-polybutadiene (91.5% vinyl, 7.0% cis, 1.5% trans, number-average molecular weight 99,000) were studied by dynamic shear measurements between 0.15 and 600 cps (torsion pendulum and Fitzgerald transducer) and shear creep measurements over time periods up to 3.7 × 104 sec., in the temperature rang from 5 to 50°C. More limited dynamic measurements were made on a sample of unvulcanized natural rubber with number-average molecular weight 350,000 at frequencies from 0.4 to 400 cps and temperatures from 13 to 48°C. All data were reduced to 25°C. by shift factors calculated from equations of the WLF form with the following coefficients: 1,2-polybutadiene, c1 = 6.23, c2 = 72.5; natural rubber, c1 = 5.94, c2 = 151.6. In the transition zone, the relative positions of the loss tangent curves on the logarithmic frequency scale for these and other rubbers (1,4-polybutadiene with 50% trans configuration; styrene–butadiene rubber with 23.5% styrene content; and polyisobutylene) provided relative measures of local segment mobility. At 25°C., these ranged over a factor of 3700 with 1,2-polybutadiene and polyisobutylene the lowest and 1,4-polybutadiene the highest. When the frequency scale of each rubber was reduced to a temperature 100°C. above its glass transition temperature, however, the loss tangent curves for all except polyisobutylene were nearly coincident; the latter still showed a lower mobility by a factor of about 1/800. The terminal relaxation time and steady-state compliance for the 1,2-polybutadiene calculated from the Rouse theory were larger than those observed experimentally. The level of compliance corresponding to the entanglement network of 1,2-polybutadiene, JeN, was calculated by integration over the loss compliance, J″, to be 1.62 × 10?7 cm.2/dyne; integration over G″ to obtain the corresponding modulus gave reasonable agreement. From such JeN, values, the average number of chain atoms between entanglement points, jZe, was estimated as follows: 1,2-polybutadiene, 132; natural rubber, 360; 1,4-polybutadiene, 110; styrene–butadiene rubber, 186; polyisobutylene, 320. Values of jZe were also estimated from the minimum in the loss tangent and compared with those reported from the molecular weight dependence of viscosity. The three sources were in generally good agreement. 相似文献
86.
Paul J. Robinson Julen Munarriz Michael E. Valentine Austin Granmoe Natalia Drichko Juan R. Chamorro Priscila F. Rosa Tyrel M. McQueen Anastassia N. Alexandrova 《Angewandte Chemie (International ed. in English)》2020,59(27):10996-11002
Samarium hexaboride is an anomaly, having many exotic and seemingly mutually incompatible properties. It was proposed to be a mixed‐valent semiconductor, and later a topological Kondo insulator, and yet has a Fermi surface despite being an insulator. We propose a new and unified understanding of SmB6 centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm?B bonding modes within SmB6, corresponding to different oxidation states of the Sm. The mixed valency arises in SmB6 from thermal population of these distinct minima enabled by motion of B. Our model simultaneously explains the thermal valence fluctuations, appearance of magnetic Fermi surface, excess entropy at low temperatures, pressure‐induced phase transitions, and related features in Raman spectra and their unexpected dependence on temperature and boron isotope. 相似文献
87.
88.
Prof. Dr. Valentine G. Nenajdenko Dr. Aleksey A. Goldberg Dr. Vasily M. Muzalevskiy Prof. Dr. Elizabeth S. Balenkova Dr. Aleksey V. Shastin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(7):2370-2383
A convenient and simple three‐step pathway to the new family of CF2CF2S‐bridged alkanes and CF2S‐, CF2O‐bridged alkenes and alkynes was elaborated by using catalytic olefination reaction as a key step of the synthetic sequence. The obtained compounds revealed attractive liquid crystalline characteristics. 相似文献
89.
90.
Yury Yu. Rusakov Leonid B. Krivdin Nikolay V. Orlov Valentine P. Ananikov 《Magnetic resonance in chemistry : MRC》2011,49(9):570-574
Stereochemical study of five sterically crowded phenylselanylalkenes obtained via the hydroselenation of either terminal or internal alkynes with benzeneselenol catalyzed by the nanosized Ni complexes has been carried out based on the experimental HMBC measurements and theoretical second order palarization propagator approach (SOPPA) calculations of their 77Se? 1H spin–spin coupling constants across double bond in combination with the energy‐based theoretical conformational analysis performed at the MP2/6‐311G** level. It has been found that studied phenylselanylalkenes adopt mainly skewed s‐cis conformation with the noticeable out‐of‐plane deviations of the phenylselanyl and phenyl groups. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献