Pierluigi Polese

Lanthanide(III) complex formation with diethylenetriamine in anhydrous N,N-dimethylformamide

Abstract The formation of diethylenetriamine (dien) complexes of the lanthanide(III) ions has been studied in N,N-dimethylformamide (dmf) containing 0.1 mol dm−3 tetraethylammoniumtrifluoromethanesulfonate as constant ionic medium at 298 K. The stability constants have been obtained by potentiometry using the method of competitive reactions, silver(I) being the auxiliary central ion. The thermodynamic investigations have therefore been extended also to this metal ion. The data concerning lanthanide(III) complexation are well explained in terms of formation of two successive mononuclear complexes which are enthalpy stabilized, entropy changes being unfavourable. Dien coordinates with all N atoms both in ML and ML2 lanthanide(III) complexes; with silver(I), tridentation is achieved only when the first mononuclear complex is formed. The trends in enthalpy and entropy values of the lanthanide(III) complexes are discussed taking into account the presence of multiple solvation equilibria which involve the bare ions and the complexes in solution. Comparison with similar data previously obtained in dimethylsulfoxide (dmso) both for the lanthanide(III)- and silver(I)-dien systems, shows the remarkable influence of the solvent on the thermodynamics of complex formation.

Oxygenation reaction of Co(trien)2+ complex in dimethylsulfoxide and the aerobic oxidation of 2,6-di-tert-butylphenol catalyzed by Co(II)–amine complexes

Abstract The kinetics and the thermodynamics of the oxygenation reaction of Co(trien)2+ complex (trien=1,4,7,10-tetraazadecane) have been studied in dimethylsulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm−3 with Et4NClO4 by means of UV–Vis spectrophotometric technique. The reaction mechanism is consistent with the fast formation of an initial CoL–O2 species, followed by a rate determining step which gives the final (CoL)2O2 adduct. The results are compared with similar data in water and discussed considering the effects of ligand/solvent substitution. The catalytic activity of Co(trien)2+ as well as that of other diamine complexes, CoL2 (L=ethylenediamine (en), N,N′-dimethylethylenediamine) has also been tested towards the aerobic oxidation of 2,6-di-tert-butylphenol in mild conditions and the results are discussed in term of both catalytic ability and selectivity.

A simplified approach for modelling the bacterial growth/no growth boundary.

A simplified growth/no growth (G/NG) model, conceptually derived from the Gamma model and making direct and explicit use of growth limits of bacteria through a normalization constant (η), was proposed. The η value, which quantifies the product of the cardinal optimal distances for growth probability, is a species-independent constant. This is of importance when experimental data is missing or insufficient. The simplified G/NG model was developed including the effect of temperature, pH and water activity, and was expanded incorporating the preservative effects. As a practical application, the model was investigated for its ability to describe published data. The successful validation of the simplified G/NG model is discussed in regard to its potential applicability as a first estimate method for the development of safe food products.

Thermodynamics of complex formation of silver(I) with N-donor ligands in non-aqueous solvents

The results of a potentiometric and calorimetric study on the complexation reactions of neutral N-donor ligands with silver(I) in propylenecarbonate (PC) and dimethylformamide (DMF) are reported. The ligands concerned in DMF are butylamine (n-but), 1,2-diaminoethane (EN), bis(2-aminoethyl)amine (DIEN) and N,N’-bis(2-aminoethyl)ethane-1,2-diamine (TRIEN) whereas in PC results are provided for EN and DIEN, because of side reactions occurring for n-but and TRIEN. The data are compared to those previously reported in dimethylsulfoxide (DMSO), acetonitrile (AN) and water solvent media which present quite different dielectric constants (ε) and donor numbers (Dn). The trend of stabilities of the mononuclear AgL and AgL2 formed is discussed in terms of different cation and amines solvation in the different solvents. TRIEN can form bimetallic species in DMF, but not in DMSO. Given the lower ε value for DMF than for DMSO, Ag2TRIEN formation is evidently more influenced by the lower solvation of Ag(I) ion in DMF, rather than by difference in dielectric constants of these two solvents. In PC in addition to mononuclear complexes of higher stability with respect to the former solvents, also polynuclear Ag2L and Ag3L2 species are found.

cEST: a flexible tool for calorimetric data analysis

A new MS-Excel utility based on the EST speciation tool (cEST) specifically designed to be applied to the analysis of calorimetric data is presented in this work. The cEST utility is able to fit calorimetric data with species of arbitrary stoichiometry and also automatically provides a complex statistical analysis of data fitting. This latter aspect is often very useful to discriminate the goodness of fit for different models. As cEST runs under MS-Excel, it is flexible in its implementation and allows a straightforward data import and graphing. Furthermore, it is open source and can be used within both Windows and MacOS operating systems. The applicability of cEST is tested toward data of different origin: experimental data, where the complex formation between Ag+, Co2+ and Cd2+ ions and terpyridine in anhydrous DMSO is studied, and simulated ITC points for biomolecular interactions with either two- or three-binding sites. In the case of metal complex formation, the combination with regression statistics allows the choice of the best model among those for which convergence is achieved. In this case, the Akaike Information Criterion is employed for selecting the model for the metal-terpyridine speciation. Our analysis, based on independent calorimetric data, provides models and thermodynamic parameters which are in good agreement with those of the original works obtained by combining different complementary techniques. Also, in all the examined cases, the results obtained for the biomolecular interactions provide thermodynamic parameters which are strictly in line with the published results.

Praedicere Possumus: An Italian web-based application for predictive microbiology to ensure food safety

The use of predictive modelling tools, which mainly describe the response of microorganisms to a particular set of environmental conditions, may contribute to a better understanding of microbial behaviour in foods. In this paper, a tertiary model, in the form of a readily available and userfriendly web-based application Praedicere Possumus (PP) is presented with research examples from our laboratories. Through the PP application, users have access to different modules, which apply a set of published models considered reliable for determining the compliance of a food product with EU safety criteria and for optimising processing throughout the identification of critical control points. The application pivots around a growth/no-growth boundary model, coupled with a growth model, and includes thermal and non-thermal inactivation models. Integrated functionalities, such as the fractional contribution of each inhibitory factor to growth probability (f) and the time evolution of the growth probability (Pt), have also been included. The PP application is expected to assist food industry and food safety authorities in their common commitment towards the improvement of food safety.