Blastulae aggregates: New intermediate structures in the micelle-to-vesicle transition of catanionic systems

A new type of intermediate structure was found in the salt-induced micelle-to-vesicle transition in a catanionic system composed of Na dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in aq. soln. with an excess of anionic surfactant. The appearance of sym. shaped hollow structures, which the authors named blastulae vesicles, is presented

Hofmeister Effect on Enzymatic Catalysis and Colloidal Structures

An attempt is made to decouple the effects that occur when different electrolytes are added to proteins, especially enzymes, in buffer solutions. In particular, direct molecular 'chemical' interactions between ions and specific sites on the enzyme are distinguished from 'physical' interactions due to electrostatic and dispersion forces. The latter are often related to a Hofmeister series. It is shown that bulk effects, usually on the pH via a shift of the buffer equilibria, must be separated from direct enzyme-ion interactions. ABTS oxidation with horseradish peroxidase is taken as an example to show how this separation can be done. The different concentration ranges in which these phenomena occur are also discussed. Finally, the influence of ions on a particular enzyme, the NADH oxidase, is compared to their influence on mixed catanionic micelles. The striking similarities can be associated with the structure-making and -breaking behaviour of the ions and a balanced effect for 'neutral' Hofmeister ions

Specific Anion and Cation Binding to Lipid Membranes Investigated on a Solid Supported Membrane

Ion binding to a lipid membrane is studied by application of a rapid soln. exchange on a solid supported membrane. The resulting charge displacement is analyzed in terms of the affinity of the applied ions to the lipid surface. The authors find that chaotropic anions and kosmotropic cations are attracted to the membrane independent of the membrane compn. In particular, the same behavior is found for lipid headgroups bearing no charge, like monoolein. This general trend is modulated by electrostatic interaction of the ions with the lipid headgroup charge. These results cannot be explained with the current models of specific ion interactions