Head group electrostatic interaction

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

The difference in properties when the aliphatic chain of amine oxide contains more than 14 carbons is attributed to the mismatch of the hydrophobic chain with that of the SDS. The extra terminal segment results in a disruptive effect on the packing of the surface active molecules. The observed association behavior in the case of 0 2 C14-DAO with SDS is then also due to the maximum cohesive interaction between hydrocarbon chains in addition to the reduced electrostatic repulsion in the head groups. Solubilization of the 1 1 association is also determined by this chain length compatibility effect which may contribute to the absence of visible precipitation in C12/C12 and C2 2/ -14 mixtures. Chain length compatibility effects in different systems have been discussed by other investigators (24,25,26). 

Effect of salt type and concentration The ionic strength of the aqueous solution in eontaet with a reverse micelle phase affects protein partitioning in a number of ways [18,23]. The first is through modification of electrostatic interactions between the protein surface and the surfaetant head groups by modifieation of the eleetrieal double layers adjacent to both the eharged inner mieelle wall and the protein surface. The second effect is to salt out the protein from the mieelle phase because of the inereased propensity of the ionie speeies to migrate to the micelle water pool, reduee the size of the reverse mieelles, and thus displace the protein. 

Since the stability of CLAs displays a strong dependence on ionic strength, due to electrostatic interactions associated with the surfactant head groups, pH should also have an influence on CLA half-lives. The effect of continuous phase pH on the stability of CLAs dispersed in deionized water at 25°C was investigated by Lye and Stuckey [65]. Above a pH of 6-7, ti/2 values were essentially constant, but began to decline as the continuous phase became more acidic. At low pH values, the excess hydrogen ion concentration led to protonation of the sulfonate head groups of the SDS molecules located at the outer soapy-shell interface. This would have two... 

The aqueous phase pH determines the ionization state of the surface-charged groups on the protein molecule. Solubilization of the protein in RMs is found to be dominated by electrostatic interactions between the charged protein and the inner layer of the surfactant head groups [112]. Solubilization of protein is favored at pH values above the isoelectric point (pi) of the protein in the case of... 

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