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51.
Hsu MF Dufresne ER Weitz DA 《Langmuir : the ACS journal of surfaces and colloids》2005,21(11):4881-4887
While the important role of electrostatic interactions in aqueous colloidal suspensions is widely known and reasonably well-understood, their relevance to nonpolar suspensions remains mysterious. We measure the interaction potentials of colloidal particles in a nonpolar solvent with reverse micelles. We find surprisingly strong electrostatic interactions characterized by surface potentials, |ezeta|, from 2.0 to 4.4 k(B)T and screening lengths, kappa(-1), from 0.2 to 1.4 microm. Interactions depend on the concentration of reverse micelles and the degree of confinement. Furthermore, when the particles are weakly confined, the values of |ezeta| and kappa extracted from interaction measurements are consistent with bulk measurements of conductivity and electrophoretic mobility. A simple thermodynamic model, relating the structure of the micelles to the equilibrium ionic strength, is in good agreement with both conductivity and interaction measurements. Since dissociated ions are solubilized by reverse micelles, the entropic incentive to charge a particle surface is qualitatively changed from aqueous systems, and surface entropy plays an important role. 相似文献
52.
This article outlines some of the factors influencing the choice of a suitable reactor for using immobilized biocatalysts.
We have concentrated on biochemical engineering parameters of immobilized biocatalysts, which are important with respect to
their application in industrial processes. 相似文献
53.
The electric conduction in the fibrous medium constructed by a homogeneous array of parallel, identical, charged, circular cylinders having an arbitrary zeta potential filled with the solution of a symmetrically charged electrolyte is analytically examined. The thickness of the electric double layers surrounding the dielectric cylinders is assumed to be small relative to the radius of each cylinder and to the gap width between two neighboring cylinders, but the polarization of the mobile ions in the diffuse layers is allowed. The effect of interactions among individual cylinders is taken into explicit account by employing a unit cell model. The appropriate equations of conservation of electrochemical potential energies of ionic species are solved for each cell, in which a cylinder is envisaged to be surrounded by a coaxial cylindrical shell of the fluid solution. Analytical expressions for the effective electric conductivity are obtained in closed forms as functions of the porosity of the fiber matrix and other characteristics of the porous system. Comparisons of the results of the cell model with different conditions at the outer boundary of the cell are made. Under an otherwise identical condition, the electric conductivity in a porous medium composed of an array of parallel cylinders in the transverse direction is smaller than that of a suspension of spheres. The effect of interactions among the cylinders or spheres on the effective conductivity can be quite significant under appropriate conditions. 相似文献
54.
The determination of glutamate pyruvate activity (GPT) is of particular clinical importance. A portable GPT sensor for both diagnostic and home-care purpose is highly expected. A highly sensitive and stable l-glutamate sensor was fabricated for the rapid detection of the GPT activity in serum. The sensor is composed of immobilized l-glutamate oxidase in a photo-crosslinkable polymer (PVA-SbQ) membrane on a palladium-deposited screen-printed carbon electrode. The sensor exhibited high sensitivity (detection limit of 50 nM for monosodium glutamate), remarkable long-term stability in storage (5 months in the dry dark state and 1 month in buffer solution) and good reproducibility (R.S.D.=2.6%, n=100). The electrode-to-electrode reproducibility was found to depend on the composition of the polymeric matrix. The optimal substrate composition for the detection of GPT activity was 1 mM α-ketoglutarate and 100 mM l-alanine. The GPT activity in serum can be determined within 3 min. The response of the sensor to GPT activity is linear over the range of 8-250 U/l. Good correlation between the sensor and the Sigma GPT assay kit was achieved (R2=0.9958). The sensor is potentially applicable to a home-care purpose when a portable measuring device is adapted. 相似文献
55.
A new approach to a CD45 protein tyrosine phosphatase inhibitor, pulchellalactam, is described. The key step of the sequence involves addition and elimination of an enolic lactam in a single step and 70% yield, employing an organocuprate reagent. The resulting alpha,beta-unsaturated lactam could be condensed with isobutyraldehyde to produce Z-pulchellalactam or converted into siloxypyrrole, which was subjected to the BF(3) x Et(2)O-promoted coupling reaction with isobutyraldehyde to afford E-pulchellalactam after E1-cB elimination and TFA deprotection. This first total synthesis afforded Z-pulchellalactam in six steps and 32% overall yield from Boc-glycine. The same sequence of reactions could also be applied to the liquid- or solid-phase synthesis of trifunctionalized pulchellalactam derivatives. 相似文献
56.
Hsu CL Chang SJ Lin YR Tsai SY Chen IC 《Chemical communications (Cambridge, England)》2005,(28):3571-3573
Vertically well aligned P-doped ZnO nanowires were prepared on ZnO-Ga/glass templates at 550 degrees C by reactive evaporation without metal catalysts and the nanowires were found to be single crystalline with the würtzite structure, oriented in the c-axis direction; the P-doping shortened the physical lengths of the ZnO nanowires without changing their diameter, and furthermore, the introduction of P atoms resulted in a much weaker and broader ZnO band edge emission. 相似文献
57.
Tao Huang Seyyedmohsen Hosseinibarkooie Adam L. Borne Mitchell E. Granade Jeffrey W. Brulet Thurl E. Harris Heather A. Ferris Ku-Lung Hsu 《Chemical science》2021,12(9):3295
Sulfonyl-triazoles are a new class of electrophiles that mediate covalent reaction with tyrosine residues on proteins through sulfur-triazole exchange (SuTEx) chemistry. Recent studies demonstrate the broad utility and tunability of SuTEx chemistry for chemical proteomics and protein ligand discovery. Here, we present a strategy for mapping protein interaction networks of structurally complex binding elements using functionalized SuTEx probes. We show that the triazole leaving group (LG) can serve as a releasable linker for embedding hydrophobic fragments to direct molecular recognition while permitting efficient proteome-wide identification of binding sites in live cells. We synthesized a series of SuTEx probes functionalized with a lipid kinase fragment binder for discovery of ligandable tyrosines residing in catalytic and regulatory domains of protein and metabolic kinases in live cells. We performed competition studies with kinase inhibitors and substrates to demonstrate that probe binding is occurring in an activity-dependent manner. Our functional studies led to discovery of probe-modified sites within the C2 domain that were important for downregulation of protein kinase C-alpha in response to phorbol ester activation. Our proof of concept studies highlight the triazole LG of SuTEx probes as a traceless linker for locating protein binding sites targeted by complex recognition elements in live cells.Sulfonyl-triazole probes modified with a kinase recognition element are developed for live cell activity-based profiling to identify tyrosine sites located in catalytic and regulatory domains that are important for kinase function. 相似文献
58.
Krishnaswamy Vasudevan Sigrid D. Peyerimhoff Robert J. Buenker Wolf E. Kammer Hsiang-lin Hsu 《Chemical physics》1975,7(2):187-209
A series of ab initio calculations is reported for the ground and low-lying valence and Rydberg states of diimide N2H2. Symmetric bending potential curves for both the cis and trans forms of this system have been obtained at the SCF level of treatment. In addition Cl calculations have been carried out for the trans-diimide ground state equilibrium nuclear conformation, using a configuration selection procedure described elsewhere; an associated energy extrapolation scheme is also employed which enables the effective solution of secular equations with orders of up to 40000. The ensuing Cl wavefunctions are interpreted in the discussion and the corresponding calculated energy differences between the various electronic states are compared with experimental transition energy results for both diimide and for related systems such as trans-azomethane. A more detailed analysis of the observed absorption bands in the 1Bg-X1Ag transition in N2H2 is also given, making use of calculated potential curve data as well as the pertinent Cl vertical energy difference. The dipole-forbiddenness of the excitation process is thereupon concluded to result in a distinct non-verticality for this electronic band system, causing its absorption maximum to occur at a position some 0.6 eV to the blue of the so-called vertical transition, i.e., that for which maximum vibrational overlap is obtained. 相似文献
59.
Hsu MH Hu WS Lin JJ Hsu YJ Wei DH Yang CW Chang CS Tao YT 《Langmuir : the ACS journal of surfaces and colloids》2004,20(9):3641-3647
The structure of self-assembled monolayers ofp-terphenyl-4-carboxylic acid and the mixed monolayers of this acid with n-hexadecanoic acid on silver surface were studied by reflection-IR spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) measurement, X-ray photoemission electron microscopy (X-PEEM), and atomic force microscopy. Exposure of the p-terphenyl-4-carboxylate monolayer to H2S vapor resulted in reorganization of the film structure into clusters of the corresponding free acids, in tens of nanometer dimension. Exposure of the mixed monolayer to H2S resulted in reorganization of the mixed monolayer film into phase-separated clusters of respective component molecules. The saturated aliphatic acid formed clusters of submicrometer size, whereas the p-terphenyl-4-carboxylic acid formed clusters of tens of nanometer size, presumably due to different surface mobility and/or intermolecular interaction of the two types of molecule. Restoration of the monolayer film from the clusters, driven by the reaction between the free acid molecules and the basic surface sites, proceeded at different speeds for the two types of molecules. The saturated acid monolayer was restored much faster than the p-terphenyl-4-carboxylic acid monolayer. A domain-separated monolayer in several micrometers scale was obtained. The process was imaged by tapping mode atomic force microscopy. 相似文献
60.
Chen CH Liu KY Sudhakar S Lim TS Fann W Hsu CP Luh TY 《The journal of physical chemistry. B》2005,109(38):17887-17891
Thin films of silica hybrid materials consisting of two to three covalently bound organic chromophores at different ratios were conveniently synthesized and fabricated. The photophysical properties of these materials have been studied. The fluorescence spectra reveal complete fluorescence resonance energy transfer (FRET) from donor to acceptor, and the light-harvesting ability of these hybrid materials increases with increasing the molar fraction of donor chromophore. In a three-chromophore system, the energy is transferred from 300 to 530 nm successfully. Time-resolved fluorescence experiments are employed to elucidate the average rates and efficiencies (84-97%) of energy transfer in these organic/inorganic hybrid systems. The hybrid materials have been shown to provide antenna effect to facilitate energy transfer and light harvesting. 相似文献