Hydrogen-ion titrationswere conducted for hen-egg-white lysozyme in solutions of potassium chloride, over the range of pH 2.5-11.5 and for ionic strengths to 2. 0 M. The dependence oflysozyme's net proton charge, zP' on pH and ionic-strength in potassium-chloride solution is measured. From the ionic-strength dependence of zP' interactions of lysozynie with potassium and chloride ions are calculated using the molecular-thennodynamic theory of Fraaije and Lyklema 1. Lysozyme interacts preferentially with up to 12 chloride ions at pH 2.5. The observed dependence of ion-protein interactions on pH and ionic strength is explained in terms of electricdouble-layer theory. New experimental pKa data are reported for eleven ammo acids in potassium-chloride solutions of ionic strength to 3.0 M.

The diffusion of hen egg-white lysozyme has been studied by dynamic light scattering in aqueous solutions of ammonium sulfate as a function of protein concentration to 30 g/liter. Experiments were conducted under the following conditions: pH 4-7 and ionic strength 0.05-5.0 M. Diffusivity data for ionic strengths up to 0.5 M were interpreted in the context of a two-body interaction model for monomers. From this analysis, two potential-of-mean-force parameters, the effective monomer charge, and the Hamaker constant were obtained. At higher ionic strength, the data were analyzed using a model that describes the diffusion coefficient of a polydisperse system of interacting protein aggregates in terms of an isodesmic, indefinite aggregation equilibrium constant. Data analysis incorporated multicomponent virial and hydrodynamic effects. The resulting equilibrium constants indicate that lysozyme does not aggregate significantly as ionic strength increases, even at salt concentrations near the point of salting-out precipitation.

Stable gold nanoparticles with average size 1.7 nm synthesized by an amine-terminated ionic liquid showed enhanced electrocatalytic activity and high stability.Electrocatalytically active gold nanoparticles are enjoying increasing applications in electrochemistry, electroanalysis and bioelectronics. 1 Catalytic activity has been shown to depend strongly on the gold oxidation state, nanoparticle size and surface properties. 2 For example, 1.3 nm gold nanoparticles exhibited superior activity in catalysis of aerobic alcohol, relative to larger (9.5 nm) particles. 3 An established method for generating 1-3 nm gold nanoparticles is reduction of AuCl 4 − by sodium borohydride in the presence of an alkanethiol in water-toluene biphasic reaction systems. 4 While the resulting nanoparticles are very stable, the reagents are hazardous. A "greener" route, reduction by citrate in water, yields particles of only limited stability. 5 In general, preparation of gold particles with narrow size distribution in the 1-3 nm range and long-term electrocatalytic activity is difficult, and reports of suitable novel syntheses are few. 6-8Room-temperature ionic liquids (RTILs) seem well positioned to address the challenge of preparing stable, active gold nanoparticles, due to their high chemical and thermal stability, negligible vapor pressure, recyclability, high conductivity and wide electrochemical window. 9 Moreover, low interfacial tensions result in high nucleation rates, allowing formation of very small particles because Ostwald ripening occurs only weakly. 10 RTILs have been successfully employed in "green" preparations of Cu 2 O crystals, 9 gold nanosheets, 11 and nanoparticles of silver, gold or platinum. 12-14 In this work, a functionalized RTIL, 1-(3-aminopropyl)-3-methylimidazolium bromide (IL-NH 2 ), 15 was applied to simultaneously reduce aqueous HAuCl 4 and stabilize the resulting gold nanoparticles, which had an average diameter 1.7 nm and retained long-term stability without special protection. These IL-stabilized gold nanoparticles (Au-IL) showed better electrocatalytic activity in reduction of oxygen