Alessandra Di Tullio

Behavioral bioassays testing the methyl 6-methylsalicylate as a component of the female sex pheromone in the slave-making ant Polyergus rufescens (Hymenoptera, Formicidae)

The mating behavior of the slave-making ant Polyergus rufescens is an example of “Female-calling Syndrome” as defined by Hölldobler and Bartz (1985). In this species, in fact, nuptial flights are inconspicuous and not well synchronized between sexes. Moreover, females typically call for males, do not disperse widely, and remain near their natal nest or return to a dulotic colony after mating. Lastly, the virgin queen usually mates only with the first male that is able to locate her and after mating she cuts off her wings and hides in the vegetation surrounding the nest (Mori et al., 2001). Two main aspects of P. rufescens ecology could explain the mating strategy adopted by this species: the relative low density of both sexes and its parasitic nature. As suggested by Bourke and Franks (1995), female calling could be advantageous for species that do not produce a large amount of sexuals: through this mating strategy, females probably maximize their chances of finding a mate. Moreover, female calling is suitable for scattered colonies, like those

ESI-MS in the study of the activity of α-chymotrypsin in aqueous surfactant media

The catalytic activity of α-chymotrypsin on a model and a peptide substrate, in the supramolecular system “enzyme–surfactant” in water solution, has been studied by electrospray ionization mass spectrometry. Hydrolysis of N-succinyl-L-phenylalanine p-nitroanilide as the model compound, catalysed by α-chymotrypsin in the presence of monomeric cetyltributylammonium bromide, has been followed by UV and ESI-MS detection. Kinetic data, which are essentially identical independent of their determination techniques, show a twelve fold improvement of the enzyme catalytic efficiency when compared with the reaction carried out in the absence of the additive. Once validated, the ESI-MS technique was used to study the hydrolytic activity of the enzyme on a peptide substrate like substance P; it is worth emphasising that the spectrophotometric detection cannot be employed on peptides, where the chromophores are untouched by the hydrolytic process. Substance P hydrolyses in aqueous surfactant following dichotomic kinetics, which are initially rapid but then slow down as the reaction progress. The results presented in this paper are expected to extend studies on biocatalysis in aqueous surfactant media to a wide range of substrates, independent of their spectroscopic properties.

Application of multivariate analysis for recognition of organic patinas on stone monuments

Black organic films, which had accumulated over ages on stone monuments in ancient villages located in the Apennines in central Italy, were solvent-extracted and the extracts analyzed by capillary gas chromatography. The overall procedure, selection of the monuments and patina extraction followed by chromatographic analysis and processing of the data, was developed with the purpose of establishing a new methodology for clusterization of ancient monuments located in the same geographic area, or even of different parts of the same monument, according to the chemical substances deposited on their surfaces. This concept relies on the assumption that the black crusts present on the monument surface represent a chemical memory of the work of art itself, related to its history, topological location, and exposure to environmental conditions. Selection of the most appropriate extraction solvent, as well as treatment of the chromatographic data, was carried out with the aid of multivariate chemometric methods to obtain classification models.

Synthesis and Preliminary Biological Evaluation of 3′‐Substituted Cephem Sulfones as Potential β‐Lactamase Inhibitors

3′-Substituted cephem sulfones, as well as the unsubstituted congener, were synthesized and biologically evaluated as β-lactamase inhibitors. Sodium 3′-substituted cephalosporanate sulfones 4 and 5 were prepared starting from 7-aminodeacetoxycephalosporanic acid (7-ADCA, 6) by a bromodeamination reaction, followed by reduction of the 7-halo derivative. Selective, radical bromination at C-3′ on the Δ3-isomer, followed by nucleophilic substitution and then retroisomerization at Δ2, afforded the required derivatives. 3′-Unsubstituted and 3′-acetoxycephem sulfones 2 and 3 were prepared using routine chemistry. The 3′-substituted cephem sulfone derivatives, evaluated as β-lactamase inhibitors by IC50 determinations, behave as weak inhibitors of the class D “oxacillinase” OXA1 from Escherichia coli and the class C β-lactamase of Enterobacter cloacae P99. Conversely, the 3′-unsubstituted cephem sulfone 2 was shown to be comparable to sulbactam and even more active than clavulanic acid against the latter enzyme. The activity of 2 against E. cloacae P99 was also greatly enhanced by prolonging the pre-incubation time. Considerations as to the mechanism of inhibition are also put forward.

ANTIPODAL FORMS OF CEPHEM DERIVATIVES VIA STEREOCHEMICAL MANIPULATIONS OF THE CEPHALOSPORIN NUCLEUS

Two complementary strategies have been developed in order to convert a cephalosporin derivative, characterized by the ‘natural’ absolute configuration of the two stereogenic centers, into its enantiomer, as an optically pure compound.