排序方式: 共有13条查询结果,搜索用时 15 毫秒
1.
Rongbiao?WangEmail author Herbert?Schmiedel Bernd-Reiner?Paulke 《Colloid and polymer science》2004,283(1):91-97
Isothermal titration calorimetry (ITC) measurements of the mixture of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) with negatively charged, hairy copolymer latices (poly-(2,3-epoxypropylmethacrylate-co-methacrylic acid) in different ratio) at high water excess indicate a monomer adsorption mechanism of CTAB by the polymer particles. The number of adsorbed CTAB molecules at saturation corresponds approximately to the number of negative elementary charges bound at the surface of the latices. The mixing enthalpy is the sum of demicellization and sorption enthalpies. At 25 °C for CTAB the demicellization enthalpy amounts to 10 kJ/mol, whereas the adsorption enthalpy varies from –7 kJ/mol (surface charge density of the latices
=–0.37 C/m2) to +3 kJ/mol (=–0.085 C/m2). The hydrodynamic radius
RH of the latex particles upon titration of cationic detergent and salt (NaBr) decreases by about 2 nm until the onset of aggregation near the isoelectric point. Titration of nonionic or anionic detergents has much less influence on the hydrodynamic radius and produces no measurable adsorption heat. The results are consistent within a model of latex particles with extended negatively charged polymer chains interacting predominantly via Coulombic forces with detergents. 相似文献
2.
3.
S. Schumacher R. Wüstneck B.-R. Paulke R. Cartier U. Pison 《Colloid and polymer science》2009,287(2):203-214
The binding of Gd3+ to two carboxylated polyglycidyl methacrylate latices was investigated. The latices differed in size (60 and 140 nm for CL6
and CL3, respectively) and surface charge density. The Gd3+ concentration in aqueous suspension was determined using an arsenazo (III) assay. Using 153Gd3+, the bound amount was determined directly. Because of the high binding affinity, ligand depletion became evident. The binding
was pH dependent, investigated in buffer solutions not influencing the arsenazo (III) assay. Optimal binding occurs by formation
of sodium salts of the carboxylic groups and replacement of Na+ and H+ by Gd3+. The dissociation constants of the particles were k
D ≈ 5 × 10−5 mol/L (CL3) and 10−4 mol/L (CL6), without cooperativity (Hill plot). Colloidal stability was investigated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
5.
Two-dimensional electrophoresis (2-DE) was previously established for analysis of plasma protein adsorption patterns on particulate carriers for intravenous drug targeting. This study addresses a possible effect of polymeric particles on protein separation in the first dimension, e.g., hindrance of protein entry into the gel or interaction of particles with the gel matrix. Polystyrene beads of mean diameter 100, 200 and 1000 nm were used as model carriers. Two different separation techniques were performed in the first dimension of 2-DE to study possible interactions of the beads with the different gel matrices, i.e., carrier ampholytes (CA) and immobilized pH gradients (IPGs). Comparison of gels obtained from samples including the particles from samples separated from the polystyrene beads showed no noteworthy differences. Therefore, a negative effect of the particles can be excluded, and particle separation from the sample is not necessary. Another goal of this study was the transfer of analytical protocols for isoelectric focusing from CA to IPGs with regard to enhanced reproducibility, faster sample processing, and easier handling. Transfer from CA to IPGs was carried out successfully and showed improved resolution of basic proteins. In contrast to that, lower amounts of a few high molecular mass proteins were detected, especially when sample application cups were employed. A qualitative change in the obtained protein pattern was not observed. Increased entry of high molecular weight proteins was achieved by in-sample rehydration instead of using sample cups. 相似文献
6.
Alexander Paulke Manfred Schubert-Zsilavecz Mario Wurglics 《Monatshefte für Chemie / Chemical Monthly》2008,139(5):489-494
The popularity of St. John’s Wort (SJW) extracts for treating mild to moderate depression has increased over the last decades and great effort has been devoted
to identify the active principle of SJW extract. Previous investigations suggest the contribution of at least three classes of compounds, the phloroglucinols, the
quercetin flavonoids, and the phenanthroperylenequinones, to the clinical efficiency of SJW extracts. Up to now, a plausible molecular mechanism of action has been described only for the phloroglucinols. For the
flavonoids and the phenanthroperylenequinones different targets were proposed on the basis of pharmacological studies. The
vast majority of these targets are located in the CNS and therefore increasing interest in the question of the CNS availability
of these substances arose. Recently, the ability of phloroglucinols and flavonoids to penetrate the blood brain barrier could
be demonstrated. For the phenanthroperylenequinones an examination of CNS bioavailability is still missing.
The aim of this work is to close this gap by developing and validating a HPLC method with electrochemical detection for the
quantification of the phenanthroperylenequinones in brain tissue of rodents after oral application of SJW extract or pure hypericin. In our study, the phenanthroperylenequinone content in the CNS tissue was below the lower limit
of detection of the analytical method and was thus lower than 16 pmol/g brain for hypericin and lower than 52 pmol/g brain
for pseudohypericin after oral administration of 1600 mg/kg SJW extract or pure hypericin (5 mg/kg).
Correspondence: Mario Wurglics, Institute of Pharmaceutical Chemistry, Johann Wolfgang Goethe University/ZAFES, 60438 Frankfurt
am Main, Germany. 相似文献
7.
8.
A. BRÓDKA 《Molecular physics》2013,111(21):3177-3180
The Ewald-type method, its modified version and the Lekner-type method for summing Coulomb interactions in a system periodic along one direction are presented and compared. Advantages and disadvantages of these methods are discussed, and the methods are tested in molecular dynamics simulations of acetone molecules confined to cylindrical silica pores. 相似文献
9.
The Mellin transform and Poisson summation formula are used to derive an expression for the Coulomb interaction energy of a three-dimensional system with periodicity in one direction. Initially, calculations are performed for interactions characterized by any inverse power and, using the analytical continuation of the energy function, one obtains the final expression for the interaction energy of charges. We consider also a special case when two different charges are located on a line parallel to the periodicity direction. The energy and force expressions are identical to those obtained from the Lekner summation which is simply a sum over reciprocal lattice terms. The convergence behaviour of the Lekner summation is compared with that based on the Ewald type approach. 相似文献
10.