Tristano Boschi

An electronic nose for food analysis

Since the first developments of electronic noses, food analysis has been considered as one of its most useful applications. In this paper an electronic nose based on quartz microbalances coated with metallo-porphyrins and related compounds is presented and illustrated. Extensive tests on various substances playing key roles in food analysis show that sensing properties of the sensing materials (in terms of sensitivity and selectivity) can be exploited for electronic nose applications devoted to the analysis of various kinds of foods. The versatility of this system has been successfully tested on different kinds of foods, such as fish, meat, vegetable and wine for which results are shown.

The application of metalloporphyrins as coating material for quartz microbalance-based chemical sensors

Abstract The results of both optimization and tests to prove the suitability of an array of quartz microbalance sensors (QMBs) modified with various metalloporphyrins for the determination of food freshness are presented and discussed. As far as optimization is concerned, it was found that a minimum amount of 50 μg of metalloporphyrin must be used for the modification of the quartz microbalance sensors in order to obtain the maximum sensitivity. The sensory behavior of five different porphyrins was subsequently studied. QMBs were modified using four different meso -tetraphenylporphyrins: phenyl, p -nitrophenyl, p -bromophenyl, p -methoxyphenyl and an octa-alkylporphyrin ( etio -porphyrin I), all loaded with a Co 2+ metal ion. A clear decrease in the sensitivity for the etio -porphyrin I was observed whereas for the meso -tetraphenyl-porphyrins the best response was obtained for the p -nitrophenyl derivative. These results can be attributed to the different electron densities which are present at the metal center of the macrocycle. The determination of the response behavior with respect to methanol, thiophene, diethylamine and triethylamine of a sensor array consisting of rhodium, ruthenium, cobalt, and manganese meso -tetraphenylporphyrin revealed that there is a clear difference in terms of the sensitivity and hence, the selectivity for the various QMBs. The rhodium and the cobalt-based QMBs were alike and demonstrated a preference for the gases with soft donating sites, i.e. thiophene and the amines. The QMBs based on ruthenium and manganese demonstrated distinctly different behavior. The ruthenium-based QMB demonstrated no clear preference for gases with either hard or soft donating sites, whereas the manganese-based QMB preferred gases with hard donating sites, i.e. methanol. These results led to the overall conclusion that this sensor array could be used for the analysis of complex gas mixtures, where the most prevalent gases fall under the categories of the amines, the alcohols and the sulphides.

Photophysical Behaviour of Corrole and its Symmetrical and Unsymmetrical Dyads

The luminescence properties at room temperature and 77 K of octamethylcorrole are reported for the first time, together with the photophysical behaviour of corrole-corrole and porphyrin-corrole dyads covalently linked through the 10-position with a phenyl bridge. The photophysical properties of corrole free base are very similar to those of the porphyrin analogues, whereas the dimeric systems show luminescence bands different from those of the parent monomers, indicating an unexpectedly high degree of interaction between the chromophores. The porphyrin-corrole dyad undergoes photocatalysed ring opening of the corrole moiety to give the corresponding porphyrin-biliverdin species.

Recognition of fish storage time by a metalloporphyrins-coated QMB sensor array

`Electronic nose applications have been increasing in number in recent years. The reliability of these applications is mainly based on the selectivity properties of the sensors composing the array and on the stability of their characteristics. In this paper an electronic nose based on metalloporphyrins-coated quartz microbalance sensors is described. Due to the nature of the chosen metals, the sensors are particularly suitable to classify environments in which compounds containing donor atoms, such as amines, alcohols and sulphides, play a key role. The aroma of fish during storage is one of these environments. The array has been applied both for classification and for identification of the degree of freshness of stored cod fish. Data on the recognition of storage days and continuous short time monitoring are reported and discussed. Results of the electronic nose response are displayed by a method that is based on the parametrization of the input temporal evolution and allows an adequate representation of the evolving chemical environment.

The exploitation of metalloporphyrins as chemically interactive material in chemical sensors

Abstract The main features of a chemical sensor are given by the properties of the chemically interactive membranes that accomplish the selective capture of molecules from the environment. The capture of molecules on the surface can originate the variation of a number of different properties of the materials so that a number of different kinds of chemical sensors can be based on the same chemically interactive membrane. In this paper the utilization of metalloporphyrins and related compounds as chemically interactive materials is discussed and preliminary data concerning the performance of mass sensitive sensors and conductivity sensors are reported. Very interesting results have been obtained with quartz microbalances. In this case metalloporphyrin coated sensors show, beside good sensitivity, a selectivity which depends mostly on the metallic ion complexed at the center of the macrocycle. This results in the possibility of changing the sensor selectivity with minor modification of the synthesis process. This property makes metalloporphyrins interesting for electronic nose applications. Results concerning the applications of an electronic nose based on metalloporphyrin coated quartz microbalances are illustrated and discussed. Conductivity measurements confirmed the previously reported character of the charge transport inside the metalloporphyrins. A certain sensitivity to triethylamine and NOx has also been found. Among the measured compounds, a polymer of porphyrins has been included, conductivity measurements indicate the occurrence of a different conduction mechanism.

Technologies and tools for mimicking olfaction: status of the Rome "Tor Vergata" electronic nose.

This paper shows recent results obtained in the field of artificial olfaction by an electronic nose based on quartz microbalances. The chemical interactive material responsible of the sensitivity is, in this case, porphyrin, whose performance and optical characterization will be presented and discussed. The design of the electronic nose and the kind of neural network that has been considered for these applications will be illustrated and commented. Future research and perspectives toward electronic nose miniaturization are also discussed as fundamental milestones for reaching closer biomimicking action.

5,10,15-Triphenylcorrole: a product from a modified Rothemund reaction

One-pot synthesis of 5,10,15-triphenylcorrole has been achieved by reaction of benzaldehyde with an excess of pyrrole; the triphenylphosphinocobalt complex of 5,10,15-triphenylcorrole has been structurally characterized using X-ray crystallography.

Self-assembled monolayers of mercaptoporphyrins as sensing material for quartz crystal microbalance chemical sensors

Abstract Thiol-functionalized metalloporphyrin have been deposited as self-assembled monolayers onto the gold pad of quartz crystal microbalances (QMBs). The sensitivities of the resulting sensors have been measured with respect to model volatile organic compounds (VOCs), interesting for future practical applications. The sensitivities of these functionalized QMBs depend on the number of the sulfide groups present at the peripheral positions of the porphyrins, but they are higher if compared with the corresponding casting coated sensors.

Epoxidation and hydroxylation reactions catalysed by β-Tetrahalogeno and β-octahalogeno manganese porphyrins

Abstract β-Tetrahalogenated manganese(III) porphyrins are more efficient catalysts than the β-octahalogenated ones in oxidations promoted by H 2 O 2 .

Synthesis and characterization of cobalt(III) complexes of meso-phenyl-substituted corroles

Abstract The synthesis and characterization of two new cobalt(III) complexes of corrole: [triphenylphosphine- (2,3,7,8,12,13,17,18-octamethyl-10-phenylcorrolato)cobalt(III)] and [triphenylphosphine(2,3,7,8,12,13,17,18-octamethyl- 5,10,15-triphenylcorrolato)cobalt(III) are reported. Such complexes represent the first examples of meso- substituted corrolates reported in the literature. The insertion of one or three phenyl groups at the meso-positions of the macrocyclic ligand has been achieved by designing different synthetic strategies. The spectroscopic characterization of the complexes shows the peculiarity of the corrole ligand which maintains a planar structure despite the steric hindrance of the peripheral substituents.