The aggregation of beta-lactoglobulin (BLG) at ambient temperature was studied using turbidimetry and dynamic light scattering in the range 3.8

Bovine serum albumin (BSA) and poly(diallyldimethylammonium chloride) (PDADMAC) spontaneously form, over a range of ionic strength I and pH, dense fluids rich in both macroions. To study their nanostructure, these coacervates were prepared at low I and high pH (strong interaction) or at high I and lower pH (weaker interaction), with polymer MWs ranging from 90K to 700K, and then examined by dynamic light scattering (DLS) and rheology. DLS shows a dominant and surprisingly fast protein diffusional mode independent of polymer MW; accompanied by robust slow modes, slower by 1-2 orders of magnitude, which are also insensitive to MW and are present regardless of I, pH, and sample aging. High MW sensitivity was observed by rheology for the terminal time (order of milliseconds), which increased as well with the strength of polyelectrolyte-protein interaction. Viscoelastic behavior also indicated a tenuous network, solidlike at low strain but re-forming after breakage by shear. Two models, both of which have strengths and defects, are put forward: (I) macroion-rich domains dispersed in a continuum of macroion-poor domains near the percolation limit and (II) a semidilute solution of PDADMAC chains with interchain friction modulated by transient BSA-PDADMAC association.

The self-aggregation of sodium dodecyl benzene sulfonate (SDBS) and its solution behaviors have been critically assessed by conductometric, tensiometric, spectrophotometric, flourimetric, and calorimetric methods. The interfacial adsorption behaviors of SDBS have also been assessed critically. Based on the isothermal titration calorimetric (ITC) measurements, the thermodynamics of micellization of SDBS have been examined in the light of both "mass action" and "pseudophase" principles. A method of simulation has been used to evaluate the aggregation number and the free energy of micellization according to the mass action model. The thermodynamic parameters derived indirectly from the rationale of van't Hoff and directly by microcalorimetry have been compared and discussed. The interaction of SDBS with the water-soluble polymers poly(vinyl pyrrolidone) (PVP), the chloride salt of the N,N-dimethyl-N-methyl derivative of hydroxyethylcellulose (JR 400), and the chloride salt of the N,N-dimethyl-N-dodecyl derivative of hydroxyethylcellulose (LM 200) have been also investigated by the conductometric and microcalorimetric methods. The critical aggregation concentration (cac) and the thermodynamics of binding of the aggregates with the polymer segments, as well as the thermodynamics of formation of free micelles in solution, in the presence of PVP, JR 400, and LM 200 have been quantitatively assessed.

The solubilization of dimyristoylphosphatidylcholine (DMPC) vesicles by the surfactant sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB), respectively, was studied by isothermal titration calorimetry (ITC) at 30 and 60°C and at different lipid concentrations. The partitioning of surfactant into lipid bilayers and the following solubilization of vesicles show a temperature dependence due to hydrophobic interactions, which is similar to temperature dependence of the cmc of surfactants. From the ITC data, we constructed phase diagrams in the total surfactant vs lipid concentration and surfactant concentration vs temperature plane, respectively. The micellar, the coexistence, and the vesicular region can not only be reached by concentration changes but also by simply raising the temperature of a lipid-surfactant mixture with a fixed concentration. From these phase diagrams, the transition temperature for a particular lipid-surfactant mixture can be predicted. The predictions were verified by following the temperature-induced formation of fluid vesicles from mixed micelles upon heating a lipid-surfactant mixture. The micelle-vesicle transitions of mixtures of DMPC with SDS or DTAB in water and the reverse transition to mixed micelles observed upon cooling was studied by differential scanning calorimetry (DSC), turbidity measurements using UV-vis spectrophotometry, and dynamic light scattering methods. The endothermic effects observed in the DSC curves for the micelle-vesicle transition are a consequence of the endothermic heats of transfer of surfactant as well as lipid from a mixed micelle to a mixed vesicle as determined by ITC.