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231.
232.
Helmut Zecha 《Macromolecular Symposia》1990,31(1):169-200
The synthesis of (monodisperse) poly(styrene) latexes was reexamined using sodiumdodecyl sulfate as emulsifier and potassium persulfate as initiator. It has been shown, that at fixed emulsifier concentration cE the variation of persulfate amount produces similar particle size variations as changes of electrolyte (potassium sulfate) concentration at a given low initiator level. For cE << cmc a maximum of particle size versus initiator or electrolyte concentrations has been found. Concentrated monodisperse poly(styrene) dispersions and carboxylated latexes up to 50% have been prepared by a carefully controlled seeding process using monomer feed. Particle size influence on steady shear viscosity has been studied for different kinds of polymer dispersions: for electrostatic stabilized poly(styrene) latexes at high ionic strengths, for electrostatic and sterically stabilized carboxylated latexes at different pH values and for steric stabilized dispersions of poly(vinyl chloride) in plasticizer (dioctyl phthalate). All three kinds of dispersions give pronounced particle size effects on viscosity, which is different from hard-sphere-behaviour. Simple model equations have been formulated to describe the concentration and shear rate dependence on viscosity. Particle size influence may be discussed on the basis of the effective hydrodynamic particle diameter. Causes for the increase of the hydrodynamic particle size are given either by surface swelling or by the formation of particle clusters which are formed and destroyed within the shear field. 相似文献
233.
234.
The anionic and/or insertion copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) with ϵ-caprolactone (ECL), pivalolactone (PVL) and L-lactide (LLA) is presented with special emphasis on the copolymerization mechanism. Statistical copolymers are obtained by copolymerization of DTC with ECL and with LLA, while with PVL a block copolymer is obtained. The role of transesterification on the microstructure is discussed. 相似文献
235.
Xie R Johnson W Rodriguez L Gounder M Hall GS Buckley B 《Analytical and bioanalytical chemistry》2007,387(8):2815-2822
To study the carboplatin–protein interaction, a sensitive method using size exclusion chromatography coupled to inductively
coupled plasma mass spectrometry (SEC–ICP–MS) was developed. The complexes formed between plasma proteins and carboplatin
were monitored and identified with this method. Composite blood plasma samples from patients who were undergoing chemotherapy
were analyzed, and carboplatin was found to bind plasma proteins. In addition, blank plasma samples were spiked with carboplatin
and were analyzed as a time course study, and the results confirmed that carboplatin formed complexes with plasma proteins,
primarily albumin and γ-globulin. To further substantiate the study, these two proteins were incubated with carboplatin. The
binding between carboplatin and these proteins was then characterized qualitatively and quantitatively. In addition to a one-to-one
binding of Pt to protein, protein aggregation was observed. The kinetics of the binding process of carboplatin to albumin
and γ-globulin was also studied. The initial reaction rate constant of carboplatin binding to albumin was determined to be
0.74 M−1 min−1, while that for γ-globulin was 1.01 M−1 min−1, which are both lower than the rate constant of the cisplatin–albumin reaction previously reported. 相似文献
236.
Sylvia Jeney Ernst H K Stelzer Helmut Grubmüller Ernst-Ludwig Florin 《Chemphyschem》2004,5(8):1150-1158
A new method combining three-dimensional (3D) force measurements in an optical trap with the analysis of thermally induced (Brownian) position fluctuations of a trapped probe was used to investigate the mechanical properties of a single molecule, the molecular motor kinesin. One kinesin molecule attached to the probe was bound in a rigorlike state to one microtubule. The optical trap was kept weak to measure the thermal forces acting on the probe, which were mainly counterbalanced by the kinesin tether. The stiffness of kinesin during stretching and compression with respect to its backbone axis were measured. Our results indicate that a section of kinesin close to the motor domain is the dominating element in the flexibility of the motor structure. The experiments demonstrate the power of 3D thermal fluctuation analysis to characterize mechanical properties of individual motor proteins and indicate its usefulness to study single molecule in general 相似文献
237.
Transport behavior of humic acid-modified nano-hydroxyapatite in saturated packed column: effects of Cu, ionic strength, and ionic composition 总被引:1,自引:0,他引:1
Wang D Chu L Paradelo M Peijnenburg WJ Wang Y Zhou D 《Journal of colloid and interface science》2011,360(2):398-407
The surfaces of nano-hydroxyapatite (nHAP) used for contaminated soil and groundwater remediation may be modified to render nHAP highly mobile in the subsurface. Humic acid (HA) is widely used to modify and stabilize colloid suspensions. In this work, column experiments were conducted to determine the effects of contaminant (e.g., Cu) concentration, ionic strength (IS), and ion composition (IC) on the transport behavior of HA-modified nHAP in saturated packed columns. IS and nature of the cation had strong effects on the deposition of nHAP, and the effect was greater for divalent than for monovalent cations. Divalent cations have a greater capacity to screen the surface charge of nHAP, and Ca(2+) bridges the HA-modified nHAP colloidal particles, which causes greater deposition. Moreover, Cu(2+) had a greater effect on the transport behavior than Ca(2+) due to their strong exchange with Ca(2+) of nHAP and its surface complexation with nHAP. The relative travel distance L(T), of the injected HA-modified nHAP colloids, ranges from less than one to several meters at varying Cu concentrations, ISs, and ICs in saturated packed columns. The results are crucial to evaluate the efficacy of nHAP on the remediation of contaminated soil and groundwater environments. 相似文献
238.
Elisabeth Eidenberger Erich Stergar Harald Leitner Peter Staron Jürgen Spitaler Claudia Ambrosch-Draxl Helmut Clemens 《Applied Physics A: Materials Science & Processing》2009,97(2):331-340
Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy.
Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of
matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to
nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism
of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment
of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium
composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences
of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed. 相似文献
239.
240.
Dr. Shaodong Zhou Dr. Jilai Li Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3073-3076
Carbon‐atom extrusion from the ipso‐position of a halobenzene ring (C6H5X; X=F, Cl, Br, I) and its coupling with a methylene ligand to produce acetylene is not confined to [LaCH2]+; also, the third‐row transition‐metal complexes [MCH2]+, M=Hf, Ta, W, Re, and Os, bring about this unusual transformation. However, substrates with substituents X=CN, NO2, OCH3, and CF3 are either not reactive at all or give rise to different products when reacted with [LaCH2]+. In the thermal gas‐phase processes of atomic Ln+ with C7H7Cl substrates, only those lanthanides with a promotion energy small enough to attain a 4fn5d16s1 configuration are reactive and form both [LnCl]+ and [LnC5H5Cl]+. Branching ratios and the reaction efficiencies of the various processes seem to correlate with molecular properties, like the bond‐dissociation energies of the C?X or M+?X bonds or the promotion energies of lanthanides. 相似文献