SUMMARYNew theoretical molecular indices are defined. They contain information about the whole molecular structure in terms of size, shape, symmetry and atom distribution. These indices are calculated from the ( x , y , I) co-ordinates of a molecule within different weighting schemes in a straightforward manner and represent a very general approach to describe molecules, molecular fragments, macromolecules and molecular conformations in a unitary conceptual framework. Their interpretability is quite evident and is defined by the same mathematical properties as the algorithm used for their calculation. Examples on the total surface area, toxicity of PCDD and PCDF and reaction rate of catalysed reactions show a high modelling power of these indices.

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Environmentally persistent free radicals (EPFRs) are toxic products deriving from incomplete combustion and are able to generate DNA damage and pulmonary dysfunction. They are formed on particulate matter through interaction with aromatic hydrocarbons, catalyzed by transition metal oxides, and produce reactive oxygen species (ROS) in aquatic media. The processes are already described for substituted aromatic molecules, for example, phenol, but not for unsubstituted aromatic systems, such as benzene. This Article reports on the reaction of benzene with molecular oxygen in the presence of CuxO/SiO2, suggesting a mechanism based on cluster and periodic computational models. The activation of O2 by interaction with silica coordinated Cu(I) centers leads to a peroxy species that yields the phenoxy radical upon reaction with benzene. Dissociation of OH• radical eventually allows for the recovery of the catalyst. The experimental characterization of the CuxO/SiO2 catalyst regarded morphology, crystal structure, copper electronic state, and crystal field around Cu(II). Electron paramagnetic resonance (EPR) spectroscopy revealed the formation of phenoxy radical entrapped in the catalyst upon reaction between benzene and CuxO/SiO2. Moreover, EPR investigation of ROS in aqueous solution evidenced the generation of OH• radicals by benzene-contacted CuxO/SiO2. All of the experimental results nicely fit the outcomes of the computational models