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971.
J. Popplewell A. Al-Qenaie S. W. Charles R. Moskowitz K. Raj 《Colloid and polymer science》1982,260(3):333-338
The thermal conductivity of a number of ferrofluids consisting of colloidally dispersed Fe3O4 particles in diester, hydrocarbon, water and fluorcarbon carriers have been measured at 38°C. The variation in thermal conductivity with particle concentration is well described by Tareef's equation (1940). This has enabled the ratio of the physical to magnetic size to be determined and compared with estimates of the ratio obtained from electron micrographs and magnetic measurements.The fit between theory and experiment is particularly good for hydrocarbon carrier fluids giving the ratio of solid to magnetic radiusR
i/R
m=1.24±0.03 compared with the value obtained from magnetic data and electron micrographs of 1.19±0.07. The corresponding value from the fluids with a diester carrier ranges between 1.1<R
d/R
m<1.3 which is again consistent with microscopy and magnetic data.The application of a magnetic field of 0.1 T had no noticeable effect on the thermal conductivities of ferrofluids. 相似文献
972.
A ten-residue fragment of an antibody (mini-antibody) directed against lysozyme as ligand in immunoaffinity chromatography 总被引:1,自引:0,他引:1
G W Welling J van Gorkum R A Damhof J W Drijfhout W Bloemhoff S Welling-Wester 《Journal of chromatography. A》1991,548(1-2):235-242
The interaction between an antibody molecule and a protein antigen is an example of "natural" protein modelling. Amino acids of the antigen-binding site consisting of three hypervariable segments (L1, L2, L3) of the light (L) and three (H1, H2, H3) of the heavy (H) chain of an antibody molecule interact with amino acids present in an epitope of a protein. A ten-residue peptide was synthesized with an amino acid sequence analogous to the hypervariable L3 segment of a monoclonal antibody directed against lysozyme. The peptide was immobilized on CH-Sepharose 4B and the affinity adsorbent was used to purify lysozyme added to a detergent extract of insect cells infected with a recombinant baculovirus. This methodology may also be applicable to other antigen-antibody combinations, in immunoaffinity chromatography for selective purification of a protein or in an immunosensor for detection of a protein. 相似文献
973.
Summary AT-x phase diagram of the system sodium stearate (NaSt)-stearic acid (HSt) has been determined by DTA. It shows the existence
of five defined association compounds, three of them (2 NaSt · 3 HSt, NaSt · HSt and 3 NaSt · 2 HSt) with an incongruent melting
point and the others (5 NaSt · 2 HSt and 5 NaSt · HSt) with a congruent melting point. The latter two compounds pass through
various mesomorphic phases before melting.
The components do not form solid solutions and are even non-miscible in the mesomorphic state below 200 °C. Mutual miscibility
is only observed above this temperature in the subneat and neat region, occurring in the HSt composition range from 0 to 15
and from 0 to 5 mole% respectively.
The existence of molecular associations in the liquid state is very probable, particularly in the composition range between
30 and 40 mole% stearic acid. This might result in a liquid structure similar to that present in the melt of anhydrous soaps.
Zusammenfassung EinT-x Zustandsdiagramm des Natriumstearat (NaSt)- Stearins?ure (HSt)-Systems wurde mittels DTA bestimmt. Es weist fünf definierte assoziierte Verbindungen auf, drei (2 NaSt · 3 HSt, NaSt · HSt und 3 NaSt · 2 HSt) mit einem inkongruenten Schmelzpunkt und zwei (5 NaSt · 2 HSt und 5 NaSt · HSt) mit einem kongruenten Schmelzpunkt. Die zwei letzteren Verbindungen durchlaufen verschiedene mesomorphe Phasen, bevor sie schmelzen. Die Komponenten bilden keine festen L?sungen und sind im mesomorphen Zustand unter 200 °C nicht einmal miteinander mischbar. Nur bei h?heren Temperaturen sind sie v?llig mischbar, und zwar in der “subneat” und “neat” Region, die im HSt-Bereich von 0 bis 15 bzw. von 0 bis 5 Mol% reicht. Die Existenz molekularer Assoziate im flüssigen Zustand ist sehr wahrscheinlich, vor allem im Bereich zwischen 30 und 40 Mol% Stearins?ure. Dies k?nnte zur Bildung von Strukturen in der Flüssigkeit führen ?hnlich, wie dies bei der Schmelze wasserfreier Seifen der Fall ist.相似文献
974.
W. K. Jóźwiak T. P. Maniecki A. Basińska J. Góralski R. Fiedorow 《Kinetics and Catalysis》2004,45(6):879-889
This paper is focused upon the influence of potassium on the reduction behavior and catalytic properties of Fe2O3, Ru/Fe2O3 and Ru/(K)Fe2O3 catalysts for the water gas shift (WGS) reaction. The effect of promotion by potassium is attributed to stabilization of a highly dispersed ruthenium phase on the iron oxide surface. The hydrogen reduction behavior of Fe2O3 catalysts is strongly influenced by time-pressure dependent processes and comprises two or three heavily overlapped TPR peaks which can be ascribed to the following stages of the iron(III) oxide reduction 3Fe2O3 2Fe3O4 6FeO 6Fe. The appearance of FeO as an intermediate phase was confirmed by XRD. The presence of ruthenium(IV) oxide substantially changes the kinetics of the reduction process. In the case of potassium-doped catalysts, the reduction of Fe2O3 is substantially different and is assigned to the reduction phase of KFeO2. Both ruthenium and potassium have a promoting effect on the catalytic activity for the WGS reaction.From Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 930–941.Original English Text Copyright © 2004 by Jówiak, Maniecki, Basiska, Góralski, Fiedorow.This article was submitted by the authors in English. 相似文献
975.
Craft JL Horng YC Ragsdale SW Brunold TC 《Journal of the American Chemical Society》2004,126(13):4068-4069
Magnetic circular dichroism (MCD) spectroscopy and variable-temperature variable-field MCD are used in combination with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to characterize the so-called ox1-silent, red1, and ox1 forms of the Ni-containing cofactor F430 in methyl-coenzyme M reductase (MCR). Previous studies concluded that the ox1 state, which is the precursor of the key reactive red1 state of MCR, is a Ni(I) species that derives from one-electron reduction of the Ni(II)-containing ox1-silent state. However, our absorption and MCD data provide compelling evidence that ox1 is actually a Ni(II) species. In support of this proposal, our DFT and TD-DFT calculations indicate that addition of an electron to the ox1-silent state leads to formation of a hydrocorphin anion radical rather than a Ni(I) center. These results and biochemical evidence suggest that ox1 is more oxidized than red1, which prompted us to test a new model for ox1 in which the ox1-silent species is oxidized by one electron to form a thiyl radical derived from coenzyme M that couples antiferromagnetically to the Ni(II) ion. This alternative ox1 model, formally corresponding to a Ni(III)/thiolate resonance form but with predicted S = 1/2 EPR parameters reminiscent of a Ni(I) (3dx2-y2)1 species, rationalizes the requirement for reduction of ox1 to yield the red1 species and the seemingly incongruent EPR and electronic spectra of the ox1 state. 相似文献
976.
Smith JT Tomfohr JK Wells MC Beebe TP Kepler TB Reichert WM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8279-8286
A novel technique for the quantitative observation of cell migration along linear gradient substrates functionalized with adhesive proteins is presented. Gradients of the cell adhesion molecule fibronectin are generated by the cross diffusion of functionalizable alkanethiols on gold and characterized by X-ray photoelectron spectroscopy and surface plasmon resonance. Two distinct migration assays are described that characterize the movement of either sparsely populated noncontacting cells or a confluent monolayer of cells into free space. The drift speed of bovine aortic endothelial cells is measured and shown to increase along a fibronectin gradient when compared to a uniform control substrate using both assays. The results of these experiments establish reproducible conditions for studies of cell migration on gradients of surface-bound ligands. 相似文献
977.
The potential energy surface (PES) of the CH3OH system has been characterized by ab initio molecular orbital theory calculations at the G2M level of theory. The mechanisms for the decomposition of CH3OH and the related bimolecular reactions, CH3 + OH and 1CH2 + H2O, have been elucidated. The rate constants for these processes have been calculated using variational RRKM theory and compared with available experimental data. The total decomposition rate constants of CH3OH at the high- and low-pressure limits can be represented by k infinity = 1.56 x 10(16) exp(-44,310/T) s-1 and kAr0 = 1.60 x 10(36) T-12.2 exp(-48,140/T) cm3 molecule-1 s-1, respectively, covering the temperature range 1000-3000 K, in reasonable agreement with the experimental values. Our results indicate that the product branching ratios are strongly pressure dependent, with the production of CH3 + OH and 1CH2 + H2O dominant under high (P > 10(3) Torr) and low (P < 1 atm) pressures, respectively. For the bimolecular reaction of CH3 and OH, the total rate constant and the yields of 1CH2 + H2O and H2 + HCOH at lower pressures (P < 5 Torr) could be reasonably accounted for by the theory. For the reaction of 1CH2 with H2O, both the yield of CH3 + OH and the total rate constant could also be satisfactorily predicted theoretically. The production of 3CH2 + H2O by the singlet to triplet surface crossing, predicted to occur at 4.3 kcal mol-1 above the H2C...OH2 van der Waals complex (which lies 82.7 kcal mol-1 above CH3OH), was neglected in our calculations. 相似文献
978.
Braunstein P Kormann HP Meyer-Zaika W Pugin R Schmid G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(24):4637-4646
Two complementary strategies are presented for the anchoring of molecular palladium complexes, of cobalt or platinum clusters or of gold colloids inside the nanopores of alumina membranes. The first consists in the one step condensation of an alkoxysilyl functional group carried by the metal complex with the hydroxy groups covering the surface of the membrane pores. Thus, using the short-bite alkoxysilyl-functionalized diphosphane ligands (Ph2P)2N(CH2)3Si(OMe)3 (1) and (Ph2P)2N(CH2)4SiMe2(OMe)] (2) derived from (Ph2P)2NH (dppa) (dppa bis(diphenylphosphanyl)amine), the palladium complexes [Pd(dmba)(kappa2-P,P-(Ph2P)2N(CH2)3Si(OMe)3)] Cl (3) and [Pd(dmba)[kappa2-P,P-(Ph2P)2N(CH2)4SiMe2(OMe)]]Cl (4) (dmba-H = dimethylbenzylamine). respectively, were tethered to the pore walls. After controlled thermal treatment. confined and highly dispersed palladium nanoparticles were formed and characterized by transmission electron microscopy (TEM). This method could not be applied to the cobalt cluster [Co4(CO)8(mu-dppa)[mu-P,P-(Ph2P)2N(CH2)4SiMe2(OMe)]] (7) owing to its too limited solubility. However, its anchoring was achieved by using the second method which consisted of first derivatizing the pore walls with 1 or 2. The covalent attachment of the diphosphane ligands provides a molecular anchor that allows subsequent reaction with the cluster [Co4(CO)10(mu-dppa)] 6 to generate anchored 7 and this step was monitored by UV/Vis spectroscopy. In addition, the presence of carbonyl ligands in the cluster provides for the first time a very sensitive spectroscopic probe in the IR region which confirms both cluster incorporation and the retaining of its molecular nature inside the membrane. The presence of the bridging dppa ligand in 6 provides additional stabilization and accounts for the selectivity of the procedure. Using this method, platinum clusters (diameter ca. 2 nm) and gold colloids (diameter ca. 13 nm) were immobilized after passing their solution through the functionalized membrane pores. The resulting membranes were characterized by TEM which demonstrated the efficiency of the complexation and showed the high dispersion of the metal loading. The successful application of these methods has demonstrated that nanoporous alumina membranes are not only unique supports to incorporate metal complexes, clusters, or colloids but can also be regarded as functional matrices or microreactors, thus opening new fields for applications. 相似文献
979.
Harding WW Tidgewell K Schmidt M Shah K Dersch CM Snyder J Parrish D Deschamps JR Rothman RB Prisinzano TE 《Organic letters》2005,7(14):3017-3020
[reaction: see text] Two new neoclerodane diterpenes, salvinicins A (4) and B (5), were isolated from the dried leaves of Salvia divinorum. The structures of these compounds were elucidated by spectroscopic techniques, including (1)H and (13)C NMR, NOESY, HMQC, and HMBC. The absolute stereochemistry of these compounds was assigned on the basis of single-crystal X-ray crystallographic analysis of salvinicin A (4) and a 3,4-dichlorobenzoate derivative of salvinorin B. 相似文献
980.
Experiments have been carried at magnetic-field strengths of 9.4, 14.1, and 17.6 T to explore the evolution of intermolecular multiple quantum coherences in the nonlinear regime where the system evolves for times that are much greater than the characteristic time of action of the long-range dipolar field, tau(d). The results show the expected Bessel function form of the recorded signal as a function of time of evolution, with evident zeros and sign changes. As expected, the rate of signal evolution increases at higher-field strengths as a result of the increased equilibrium magnetization. A numerical method for calculating the evolution of magnetization under the action of the distant dipolar field, relaxation, and diffusion that is based on Fourier analysis of the magnetization distribution has been applied to the correlated two-dimensional spectroscopy revamped by asymmetric z-gradient echo detection sequence in the nonlinear regime and shown to produce results that are in good agreement with experimental data acquired at different magnetic fields and rates of spatial modulation. Experiments and simulations have also been used to explore the evolution of magnetization in a mixture of two interacting spin species in the nonlinear regime. 相似文献