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Values of binary mutual diffusion (interdiffusion) coefficients, obtained by using the Taylor dispersion method, for aqueous solutions of γ-cyclodextrin in the concentration range from (0.002 to 0.010) mol · dm -3 and temperatures (298.15 and 310.15) K are reported. From these experimental results, the hydrodynamic radius values for the γ-cyclodextrin are estimated. Also, the measured diffusion coefficients are used with both Hartley's and Gordon's equations to estimate activity coefficients for aqueous γ-cyclodextrin. These studies are complemented by some density and viscosity measurements, carried out at the same range of concentrations and temperatures. The effect of both the viscosity of the medium and the formation of γ-cyclodextrin dimers on the estimated hydrodynamic radius is discussed.

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The adsorption of the antineoplastic drug mitomycin C (MC) on the hanging mercury drop electrode (HMDE) surface by means of stripping voltammetry measurements is studied. With this technique, a cathodic peak is obtained at −0.47 V (vs Ag/AgCl) in phosphate buffer pH 7.1 after accumulation onto HMDE surface by applying −0.35 V. Peak current variations with the accumulation time, MC concentration, and temperature are presented. The Langmuir isotherm is employed for adjusting the experimental results, and the values of the Gibbs free energy, enthalpy, and entropy of adsorption are calculated, the adsorption process being entropically governed. The results and data presented can provide useful information on the mechanism of penetration across the cellular membrane, which is of clinical interest since MC exerts its antineoplastic activity by interaction with biological membranes.

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Electrochemical laboratory classes are frequently limited to processes that follow the Nernst equation. However, most electrochemical processes take place at potentials far from the equilibrium potential, that is, with an overvoltage. This paper presents a simple laboratory experiment designed to acquaint the student with overvoltage in the hydrogen evolution reaction.The experiment is done in two stages. The first shows that hydrogen evolution takes place at different potentials depending on the electrode material (mercury, platinum, or silver). The overvoltage on each material is calculated. In the second stage the exchange current density, a kinetic parameter, is obtained from the Tafel equation.