Nicolangelo Fanelli

Activity coefficients of lanthanum salts at 298.15 K

Activity coefficients of La(NO3)3, La(ClO4)3, and La2(SO4)3 are determined using the method of liquid membrane cells, which allows us to study high dilution levels previously unattainable (10−4 to 10−5 mol kg−1 depending on the salt). Literature values are found to be correct for La(ClO4)3, moderately biased for La(NO3)3 and completely incorrect for La2(SO4)3. This last salt in the diluted regions displays dramatic negative deviations—not recognised earlier because the measurements terminated at ca. 10−3 mol kg−1, where a Debye–Huckel-like misleading trend occurs. Numerical integration of the Poisson–Boltzmann equation and Bjerrums theory of ion pairing show an astounding ability to reproduce the trend of La2(SO4)3; however, there is evidence of short-range interactions that add to long-range interactions for lanthanum and bivalent metal sulfates, as if sulfate ions were displacing water from the hydration shells of the cations. Pitzers equation parameters that reproduce the activity and osmotic coefficients of the three salts and those (recalculated) of LaCl3 are reported.

Electrochemical Detection of Host–Guest Interactions of Dicarboximide Pesticides with Cyclodextrins

Electrochemical methods sensitively detect the formation of host–guest complexes of cyclodextrins and three redox-active pesticides: vinclozoline (3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-1,3-oxazolidine-2,4-dione), iprodione (3-(3,5-dichlorophenyl)-N-(1-methylethyl)-2,4-dioxo-1-imidazolidinecarboxamide), and procymidone (3-(3,5-dichloro-phenyl)-1,5-dimethyl-3-azabicyclo[3.1.0]hexane-2,4-dione). The protecting environment of the CD cavity allows a four-electron heterogeneous reaction leading to a preferential cleavage of the C–Cl bonds and conservation of the heterocycle structure for a further second electron transfer step. This interpretation is supported by numerical simulation of the voltammetric curves and by quantum-chemical calculations of the LUMO changes of vinclozoline. Electrochemical detection of these host–guest interactions is far superior to the spectral methods.

Adsorption of Papain on solid substrates of different hydrophobicity

Adsorption properties of protein Papain at the solid|liquid (0.1 M KCl) interfaces of different hydrophobicity [highly oriented pyrolytic graphite (HOPG), bare gold, CH3, OH, and COOH-terminated self-assembled monolayers on gold] were studied by a combined quartz crystal microbalance and atomic force microscopy techniques. It was found that Papain forms an incomplete monolayer at hydrophobic interfaces (HOPG and CH3-terminated substrate), whereas on more hydrophilic ones, a complete monolayer formation was always observed with either the onset of the formation of a second layer (bare gold substrate) or adsorption in a multilayer fashion, possibly a bilayer formation (OH-terminated substrate). The surface concentration and compact monolayer film thickness was much lower on the COOH-terminated substrate compared to other surfaces studied. This result was explained by partial dissociation of the interfacial COOH groups leading to additional electrostatic interactions between the positively charged protein domains and negatively charged carboxylate anions, as well as to local pH changes promoting protein denaturation.