RESUMO
Interactions between two negatively charged mica surfaces across aqueous solutions containing various amounts of a 10% charged cationic polyelectrolyte have been studied. It is found that the mica surface charge is neutralized when the polyelectrolyte is adsorbed from a 10-50 ppm aqueous solution. Consequently no electrostatic double-layer force is observed. Instead an attractive force acts between the surfaces in the distance regime 250-100 A. We suggest that this attraction is caused by bridging. Additional adsorption takes place when the polyelectrolyte concentration is increased to 100 and 300 ppm, and a long-range repulsion develops. This repulsive force is both of electrostatic and steric origin. The polyelectrolyte layer adsorbed from a 50 ppm solution does not desorb when the polyelectrolyte solution is replaced with an aqueous polyelectrolyte-free solution. Injection of sodium dodecyl sulfate (SDS) into the measuring chamber to a concentration of about 0.01 CMC (8.3 x 10(-5) M ) does not affect the adsorbed layers or the interaction forces. However, when the SDS concentration is increased to 0.02 CMC (0.166 mM ) the adsorbed layer expands dramatically due to adsorption of SDS to the polyelectrolyte chains. The sudden swelling suggests a cooperative adsorption of SDS to the preadsorbed polyelectrolyte layer and that the critical aggregation concentration between the polyelectrolyte and SDS at the surface is about 0.02 CMC. The flocculation behavior of the polyelectrolyte in solution upon addition of SDS was also examined. It was found that 0.16-0.32 mol SDS/mol charged segments on the polyelectrolyte is enough to make the solution slightly turbid.
RESUMO
Amphipols are a new class of surfactants that make it possible to handle membrane proteins in detergent-free aqueous solution as though they were soluble proteins. The strongly hydrophilic backbone of these polymers is grafted with hydrophobic chains, making them amphiphilic. Amphipols are able to stabilize in aqueous solution under their native state four well-characterized integral membrane proteins: (i) bacteriorhodopsin, (ii) a bacterial photosynthetic reaction center, (iii) cytochrome b6f, and (iv) matrix porin.
Assuntos
Proteínas da Membrana Bacteriana Externa/química , Bacteriorodopsinas/química , Grupo dos Citocromos b/química , Proteínas de Membrana/química , Estrutura Secundária de Proteína , Tensoativos , Animais , Proteínas da Membrana Bacteriana Externa/isolamento & purificação , Bacteriorodopsinas/isolamento & purificação , Chlamydomonas reinhardtii/metabolismo , Grupo dos Citocromos b/isolamento & purificação , Complexo Citocromos b6f , Estabilidade de Medicamentos , Escherichia coli/metabolismo , Halobacterium/metabolismo , Cinética , Modelos Estruturais , Solubilidade , Tensoativos/síntese química , Fatores de Tempo , ÁguaRESUMO
A chiral polymer easily obtained by treatment of a linear polyacrylamide with L-proline was adsorbed on a silica support treatment of a linear polyacrylamide with L-proline. After complexation with copper(II), and in spite of a rather low efficiency due to slow ligand exchange, such packing are very convenient for the resolution of amino acid enantiomers eluted in water (relative retention, k'L/k'D, higher than 2 may be observed). Other eluents may also be used. The chiral polymer was studied in solution by potentiometry and nuclear magnetic resonance spectroscopy (13C relaxation measurement). A model of the complex involved in the stereoselection is proposed which accounts for the chromatographic results obtained.
