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Not only pH. Specific buffer effects in biological systems
No full textThe aim of this work is to overview the specific effect of pH buffers in biological systems. The pH of a buffer solution changes only slightly when a small amount of a strong acid or bases is added to it. This is widely accepted and applied both in chemical and in biological (i.e. enzyme catalysis) systems. Here we show some examples - spanning from pH measurements, enzyme activities, electrophoretic mobilities, antibody aggregation, protein thermal stability - that demonstrate additional roles of buffers. They not only set pH, but also address specific ion effects, in terms of Hofmeister series, when strong electrolytes are also added. From the experimental data referred to some charged biological moieties it emerges that different buffers, at the same nominal pH, can specifically adsorb at the charged surface. Buffer specific adsorption modifies several molecular and macroscopic properties amongst which electrophoretic mobilities, and hence effective surface charges, are particularly significant. More importantly, buffers' weak electrolytes, even at low concentration, are found to compete for the adsorption at the charged surfaces with strong electrolytes, thus modulating Hofmeister effect
DDAB vesicles and lamellar liquid crystals. A multinuclear NMR and Optical Microscopy Study
No full textOn microstructural transitions of lamellar phase forming surfactants
No full textIn binary or ternary surfactant systems, if a complete segregation at an interface between the hydrophilic and lipophilic domains is assumed, the microstructure is related to the interfacial geometry. This is determined by two factors: the local interfacial curvatures set by the balance of molecular forces at the interface, and the interfacial topology and degree of connectivity that is imposed by the need to satisfy global packing constraints. The local constraint is characterized by the packing parameter of the surfactant, upsilon/al. For lipids and membrane mimetic systems this is close to unity.
Several microemulsions and liquid-crystalline phases formed from surfactants with surfactant parameter close to unity are shown to exhibit peculiar structural transitions. This is demonstrated by NMR and conductivity experiments. This feature, upsilon/al = 1, shared by lipids, seems to allow quite diverse flexibility in microstructure. This is despite the very different molecular structures of the surfactants studied (DDAB, AOT, MO, PFPE). Microemulsions and liquid-crystalline phases exhibit drastic structural changes on addition of a very small amount of a further new component, or with minimal variation in the composition of the system.
Other properties exhibited by such systems are shared and quite general: on increasing the volume fraction of the hydrophobic domain in binary surfactant/water system, or upon water and oil dilution, for microemulsions, an evolution of microstructure from a continuous water network towards closed water domains is observed
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