A series of TpxCu(I) complexes (Tpx=homoscorpionate ligand) have been reacted in solution with dioxygen at room temperature. Two different behaviors have been observed: the already described reaction with O2 or the lack of any transformation. The trend has been correlated with the electronic density at the metal center, and that has been evaluated by means of cyclic voltammometry studies as well as by IR studies with the TpxCu(CO) complexes. The data collected indicate that the former could serve as a better tool to predict such transformation, establishing a limit above which the complexes are stable under oxygen in solution. Catalytic tests carried out under oxygen have demonstrated that the use of an inert atmosphere is not a requirement in some cases.

A detailed investigation of the electrochemical reduction of 2-nitroimidazole ͑2-NIm͒ in a mixed aqueous medium was carried out by means of cyclic voltammetry ͑CV͒ at a mercury electrode. The voltammetric behavior of 2-NIm in 60% dimethylformamide ͑DMF͒ ͑0.1 M tetrabutyl ammonium perchlorate, TBAP͒/40% aqueous buffer ͑0.3 M KCl + 0.015 M citric acid + 0.03 M boric acid͒ is pH-dependent, changing from one irreversible reduction peak at acid pHs to two reduction peaks at alkaline pHs. At pH 2.5 it is possible to obtain a voltammetric pK which is due to the protonation-deprotonation equilibrium produced by the hydroxylamine derivative formed from the reduction of 2-NIm. This indicates that 2-NIm is reduced to the unprotonated hydroxylamine derivative above pH 2.5 and to its protonated form below it. At pH Ͼ 7 it is possible to observe a cyclic voltammetric couple due to the one-electron reduction of 2-NIm to produce the corresponding nitro radical anion. Furthermore, the nitro radical anion disproportionates with a rate constant, k 2 , of 6.78 ϫ 10 5 M s −1 and a half-life, t 1/2 , of 1.5 ms for the first half-life. The voltammetric behavior of 2-NIm in aqueous mixed medium is substantially different from that described in nonaqueous medium; in fact, only in the aqueous medium is it possible to study in isolation the nitro radical anion.

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An ellipsoidal cavity model has been used to study the energy changes in occupied molecular orbitals induced by solute–solvent electrostatic interactions. Some benzene derivatives have been selected as solutes. Calculations have been carried out at the CNDO and abinitio STO-4G levels. Important variations in the molecular orbital sequence, involving a change in the HOMO nature, have been observed. A perturbation analysis is employed to understand the orbital evolution from gas phase to solution.