Donato Monti

Novel Aspects of Corrole Chemistry

Corrole is one of the first examples of porphyrin analogs reported in the literature. This class of compounds has received a great attention, because of their promising exploitation in different fields, ranging from medicine to material chemistry. Among them, corrole can be considered the prototypical example of contracted porphyrins, with one of the meso carbon bridges missing. Although this macrocycle was first reported more than thirty years ago, only recently more attention has been devoted to the chemistry of corrole. The recent availability of efficient and facile syntheses of meso-substituted corroles has probably been the shuttle for the impressive flourishing of corrole-related papers appearing in literature in the last few years. The aim of this review is to highlight the latest reports in the synthetic chemistry of corrole, with special attention to the synthetic strategies and peripheral functionalizations of this macrocycle.

Porphyrinoids for Chemical Sensor Applications

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.

Chemical sensitivity of porphyrin assemblies

Porphyrins show unique binding properties that are widely exploited in nature to accomplish essential functions for life; the potential mimic of these functions with synthetic counterparts has provided the basis of many kinds of chemical sensors. This peculiar behaviour can be further enriched when porphyrins do not act as single players, but when they are included in a team, the porphyrin aggregates. Recent investigations point out that the supramolecular frameworks could allow interaction pathways not possible to the individual constituents. In this paper some recent results on supramolecular porphyrin aggregates exploited for chemical sensor development are illustrated and discussed.

New cationic liposomes as vehicles of m-tetrahydroxyphenylchlorin in photodynamic therapy of infectious diseases.

Antimicrobial photodynamic therapy is emerging as a promising therapeutic modality for bacterial infections. For optimizing the antibacterial activity of the photosensitizer m-tetrahydroxyphenylchlorin, it has been encapsulated in mixed cationic liposomes composed of different ratios of dimyristoyl- sn-glycero-phosphatidylcholine and any of four cationic surfactants derived from l-prolinol. The delivery efficiency of the different liposomes formulations has been evaluated on a methicillin-resistant Staphylococcus aureus bacterial strain (MRSA), and one of the tested formulations shows a biological activity comparable to that of the free chlorin. In order to rationalize the physicochemical parameters of the carriers that control the biological activity, the new liposome formulations have been characterized by measuring (a) the zeta potential, (b) their capability of chlorin entrapping efficiency, i.e. entrapment efficacy, (c) the effect of storage on chlorin entrapment and (d) the localization of chlorin in the bilayer. The correlation of the physicochemical and biological features of formulations has allowed us to rationalize, to some extent, some of the parameters that may control the interactions with the biological environment.

Preparation and self-assembly of chiral porphyrin diads on the gold electrodes of quartz crystal microbalances: A novel potential approach to the development of enantioselective chemical sensors

Porphyrin diad 1 was synthesized by reaction of the acyl chloride of porphyrin 2 and trans-1,2-dithiane-4,5-diol. The Co complex of this diad was studied as a potential enantioselective receptor for chiral recognition in solution and in the solid state. In solution both enantiomers of limonene induce significant changes in the visible and circular dichroism (CD) spectra of [Co2(1)], while a different behavior is observed in the case of the enantiomeric pair of trans-1,2-diaminocyclohexane. A different efficiency of [Co2(1)] chiral recognition is obtained for these compounds, with a remarkable degree of enantiodiscrimination observed in the case of limonene. Self-assembled monolayers of [Co2(1)] were deposited onto the gold electrodes of quartz crystal microbalances to be used as sensing materials of nanogravimetric sensors operating in the gas phase. The enantiodiscrimination properties of these sensors towards the enantiomeric pairs of chiral analytes have been studied. While in the case of analytes bearing donor ligand atoms we did not observe a remarkable enantioselectivity, a significant degree of chiral discrimination was observed in the case of limonene; this result is particularly encouraging for the potential development of enantioselective chemical sensors for use in an array configuration.

Porphyrin-Based Nanostructures for Sensing Applications

The construction of nanosized supramolecular hosts via self-assembly of molecular components is a fascinating field of research. Such intriguing class of architectures, beside their intrinsic intellectual stimuli, is of importance in many fields of chemistry and technology, such as material chemistry, catalysis, and sensor applications. Within this wide scenario, tailored solid films of porphyrin derivatives are structures of great potential for, among others, chemical sensor applications. The formation of supramolecules relays on noncovalent interactions (electrostatic, hydrogen bond, 𝜋-𝜋, or coordinative interactions) driven by the chemical information stored on the assembling molecules, such as shape and functional groups. This allows, for example, the formation of large well-defined porphyrin aggregates in solution that can be spontaneously transferred onto a solid surface, so achieving a solid system with tailored features. These films have been used, covering the bridge between nanostructures and microsystems, for the construction of solid-state sensors for volatiles and metal ion recognition and detection. Moreover, the variation of peripheral substituents of porphyrins, such as, for example, chiral appended functionalities, can result in the formation of porphyrin aggregates featuring high supramolecular chirality. This would allow the achievement of porphyrin layers characterised by different chiroptical and molecular recognition properties.

EAT-by-LIGHT: Fiber-Optic and Micro-Optic Devices for Food Quality and Safety Assessment

A selection is presented of fiber-optic and micro-optic devices that have been designed and tested for guaranteeing the quality and safety of typical foods, such as extra virgin olive oil, beer, and milk. Scattered colorimetry is used to authenticate various types of extra virgin olive oil and beer, while a fiber-optic-based device for UV-VIS-NIR absorption spectroscopy is exploited in order to obtain the hyperspectral optical signature of olive oil. This is done not only for authentication purposes, but also so as to correlate the spectral data with the content of fatty acids, which are important nutritional factors. A micro-optic sensor for the detection of olive oil aroma that is capable of distinguishing different ageing levels of extra virgin olive oil is also presented. It shows effective potential for acting as a smart cap of bottled olive oil in order to achieve a nondestructive olfactory perception of oil ageing. Lastly, a compact portable fluorometer for the rapid monitoring of the carcinogenic M1 aflatoxin in milk, is experimented.

Chemical sensitivity of self-assembled porphyrin nano-aggregates

Nanostructured molecular assemblies may provide additional sensing properties not found in other arrangements of the same basic constituents. Among three-dimensional structures, nanotubes are particularly appealing for applications as chemical sensors, because of the potential inclusion of different guests inside the cavity or the induced modification of the skeletal interaction after analyte binding. Porphyrins are a class of compounds characterized by brilliant sensing properties, appearing also in non-ordered solid-state aggregates. In recent years, it was reported that aggregation of oppositely charged porphyrins led to the formation of self-assembled nanotubes and in this paper their sensing properties, both in solution and in the solid state, have been investigated. The interactions of porphyrin nanotubes with guest molecules have been monitored by following the changes in their UV-vis spectra. The results obtained have been exploited to build up a sensing platform based on a computer screen as a light source and a digital camera as detector. Porphyrin nanostructures exhibited an enhanced sensitivity to different compounds with respect to those shown by single porphyrin subunits. The reason for the increased sensitivity may be likely found in an additional sensing mechanism related to the modulation of the strength of the forces that keep the supramolecular ensemble together.

Micelle‐Bound Metalloporphyrins as Highly Selective Catalysts for the Epoxidation of Alkenes

The porphyrin-surfactant interaction determines the activity of the title catalysts. Amphiphilic porphyrin derivatives (e.g. 1 with M=MnCl, R=CH2 CH2 (OCH2 CH2 )2 OH) are easy to prepare and can be included in micellar phases.

Supramolecular chirality in solvent-promoted aggregation of amphiphilic porphyrin derivatives: kinetic studies and comparison between solution behavior and solid-state morphology by AFM topography.

The solvent-promoted aggregation behavior of some amphiphilic porphyrin derivatives bearing chiral functionality in the form of a charged L-proline group has been investigated by UV/Vis, resonance light scattering, fluorescence and circular dichroism spectroscopy. The investigated macrocycles give rise to aggregates featuring supramolecular chirality with high ellipticity. Kinetic studies reveal peculiar differences in the fashion of aggregation, depending on the intimate nature of the chiral functionality, namely, cationic (nitrogen-quaternized L-proline, 3H(2)) or anionic (carboxylate residue, 6H(2)) group. Formation of anionic 6H(2) aggregates shows a diffusion-limited kinetic behavior. AFM topography studies show formation of tighter globular structures. On the other hand, the corresponding 3H(2) aggregates are formed by a cooperative, fractal-type decay, and appear as long-fibrous, looser structures. In the templated aggregation of 3H(2) over preformed 6H(2) aggregates, AFM images show formation of globular structures with reduced sizes, as a likely consequence of shorter interchromophore distances, due to favorable Coulombic interactions. The results obtained show an interesting parallelism between the solution behavior and the solid-state aggregate structures, corroborating the sergeant-soldier effect observed in the templated aggregation. The results presented give important insights for understanding the complex mechanisms involved in these issues, which are of key importance for the development of chiral supramolecular materials and stereoselective sensors and devices.