A scheme to describe SDS-lysozyme complex formation has been proposed on the basis of isothermal titration calorimetry (ITC) and FTIR spectroscopy data. ITC isotherms are convoluted and reveal a marked effect of both SDS and lysozyme concentration on the stoichiometry of the SDS-lysozyme complex. The binding isotherms have been described with the aid of FTIR spectroscopy in terms of changes in the lysozyme structure and the nature of the SDS binding. At low SDS concentrations, ITC isotherms feature an exothermic region that corresponds to specific electrostatic binding of SDS to positively charged amino acid residues on the lysozyme surface. This leads to charge neutralization of the complex and precipitation. The number of SDS molecules that bind specifically to lysozyme is approximately 8, as determined from our ITC isotherms, and is independent of lysozyme solution concentration. At high SDS concentrations, hydrophobic cooperative association dominates the binding process. Saturated binding stoichiometries as a molar ratio of SDS per molecule of lysozyme range from 220:1 to 80:1, depending on the lysozyme solution concentration. A limiting value of 78:1 has been calculated for lysozyme solution concentrations above 0.25 mM.

The solubilization of styrene in large unilamellar DODAB vesicles is investigated at a styrene to DODAB molar ratio of 2:1. The combination of various vesicle characterization methods allows a simultaneous look at vesicle morphology (cryo-TEM, DLS) and molecular interactions (micro-DSC, various fluorescence techniques) and gives a complete picture of the DODAB vesicles before and after the addition of styrene. Cryo-TEM and DLS results reveal that the addition of styrene does not break up the DODAB vesicles as an entity, but the peculiar angular DODAB vesicle morphology becomes smoother and the geometries tend to be more curved. The change in morphology is explained by an enhanced bilayer fluidity and the drastic depression of the phase transition temperature as determined from calorimetry and fluorescence experiments. Moreover, micro-DSC scans and fluorescence experiments with two different pyrene probes suggest a nonhomogeneous distribution and partial demixing of solute and bilayer for temperatures below ∼27 °C. Above this temperature, the solute appears uniformly distributed and facilitates molecular motion in the amphiphile aggregate. The diffusion coefficient for the lateral diffusion of an amphiphilic probe is then increased by a factor of 2 compared to the pure DODAB vesicles. The observed solubilization phenomena are rationalized by interactions of the solute with both the hydrocarbon part and the polar headgroup region of the bilayer.

Procedures are described for analysing enthalpograms characterising adsorption by macromolecules in solution recorded using a titration microcalorimeter. The experimental procedure involves injecting small aliquots of a solution containing adsorbate into a sample cell containing a solution of macromolecular adsorbent. Treatments based on both Langmuir and Frumkin adsorption isotherms are described. The procedures are illustrated by application of the derived equations to the interaction of micelles of sodium dodecylsulfate(aq) and of sodium decylsulfate(aq) with the water-soluble polymer, PVP. The dominant features in the recorded enthalpograms are described using equations developed from the Frumkin equation. In both cases the adsorption is endothermic attributed to hydrophobic interactions between polymer and surfactant. However, an important feature of the analysis is the characterisation of adsorbateÈadsorbate interactions using enthalpic interaction parameters. The enthalpograms are characterised by three composition ranges : (i) micelle deaggregation and weak interaction of monomers with polymer, (ii) micelle adsorption on to the soluble polymer up to surface saturation and (iii) micelle dilution.

Differential scanning microcalorimetric data for dimethyldioctadecylammonium bromide (DOAB) in dilute aqueous solutions prepared using different protocols including an ethanol injection method are compared. Reproducible data are obtained for solutions prepared using a hot-water method. Scans for very dilute solutions show evidence for processes controlled by both inter-and intra-vesicular interactions. An extremum in the scans near 47°C is assigned to a gel to liquid crystal transition involving local domains within each vesicle comprising ca. 130 DOAB monomers.

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Solubilities of several complex salts at ambient temperature and pressure are reported for aqueous solutions and for solutions in binary aqueous organic mixtures. The organic cosolvents are ethanol and propan-2-01. These and earlier published solubilities are analysed using the TATB assumption which sets the transfer chemical potentials of Ph,As+ ions equal to those of Ph,B-ions. The calculations yield transfer parameters for various ions including complex metal ions. Derived transfer parameters for ions are compared for a range of solvent systems comprising binary aqueous mixtures, including those systems where the organic cosolvents are methanol, ethanol, propan-2-01 and acetone. These transfer parameters are used in an analysis of kinetic data describing chemical reaction between hydroxide ions and iron(rr) complex cations, [Fe(phen),I2+ in aqueous solutions. Definitions of standard state chemical potentials for solutes and solvents are considered with reference to descriptions of composition of these systems using the mole fraction scale.

Interactions of both cationic and anionic surfactants with vesicles formed by dimethyldioctadecylammonium bromide (DOAB) and by sodium didodecylphosphate (DDP) have been probed using differential scanning microcalorimetry. The scans show that the surfactants are incorporated into the vesicle bilayers. The change in the melting temperature, Tm, characterising the gel to liquid-crystal transition depends on whether the charges on the head groups of surfactant ion and vesicular ion have either similar or opposite signs.