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The morphology of the film created by the aggregation of corrole molecules from ethanol solution onto the surface of gold substrate was studied by scanning tunneling microscopy both: (i) in situ, namely in quasi-equilibrium (wet sample), and (ii) ex situ, i.e., removing the substrate from the fluid cell and leaving the residual amount of solution on the substrate to desiccate (dry sample). Despite the different conditions, the morphology of the corrole overlayer formed on the film of molecules is reminiscent, in both cases, of the leopard skin; the “speckles” are actually areas where the molecular overlayer of flat molecules is not completed. We quantitatively compared these two similar morphologies by studying the power spectral density of the images, the fractal dimension DPof the hole perimeters, and the cumulative distribution function of the hole areas. We found that the last layer of both films, in spite of very different formation conditions, differed from each other only by a scale factor.

Enantiorecognition of a chiral analyte usually requires the ability to respond with high specificity to one of the two enantiomers of a chiral compound. However, in most cases, chiral sensors have chemical sensitivity toward both enantiomers, showing differences only in the intensity of responses. Furthermore, specific chiral receptors are obtained with high synthetic efforts and have limited structural versatility. These facts hinder the implementation of chiral sensors in many potential applications. Here, we utilize the presence of both enantiomers of each receptor to introduce a novel normalization that allows the enantio-recognition of compounds even when single sensors are not specific for one enantiomer of a target analyte. For this purpose, a novel protocol that permits the fabrication of a large set of enantiomeric receptor pairs with low synthetic efforts by combining metalloporphyrins with (R,R)- and (S,S)-cyclohexanohemicucurbit[8]uril is developed. The potentialities of this approach are investigated by an array of four pairs of enantiomeric sensors fabricated using quartz microbalances since gravimetric sensors are intrinsically non-selective toward the mechanism of interaction of analytes and receptors. Albeit the weak enantioselectivity of single sensors toward limonene and 1-phenylethylamine, the normalization allows the correct identification of these enantiomers in the vapor phase indifferent to their concentration. Remarkably, the achiral metalloporphyrin choice influences the enantioselective properties, opening the way to easily obtain a large library of chiral receptors that can be implemented in actual sensor arrays. These enantioselective electronic noses and tongues may have a potential striking impact in many medical, agrochemical, and environmental fields.

Tissue engineering offers attractive strategies to develop three-dimensional scaffolds mimicking the complex hierarchical structure of the native bone. The bone is formed by cells incorporated in a molecularly organized extracellular matrix made of an inorganic phase, called biological apatite, and an organic phase mainly made of collagen and noncollagenous macromolecules. Although many strategies have been developed to replicate the complexity of bone at the nanoscale in vitro, a critical challenge has been to control the orchestrated process of mineralization promoted by bone cells in vivoand replicate the anatomical and biological properties of native bone. In this study, we used type I collagen to fabricate mineralized scaffolds mimicking the microenvironment of the native bone. The sulfated polysaccharide κ-carrageenan was added to the scaffolds to fulfill the role of noncollagenous macromolecules in the organization and mineralization of the bone matrix and cell adhesion. Scanning electron microscopy images of the surface of the collagen/κ-carrageenan scaffolds showed the presence of a dense and uniform network of intertwined fibrils, while images of the scaffolds’ lateral sides showed the presence of collagen fibrils with a parallel alignment, which is characteristic of dense connective tissues. MC3T3-E1 osteoblasts were cultured in the collagen scaffolds and were viable after up to 7 days of culture, both in the absence and in the presence of κ-carrageenan. The presence of κ-carrageenan in the collagen scaffolds stimulated the maturation of the cells to a mineralizing phenotype, as suggested by the increased expression of key genes related to bone mineralization, including alkaline phosphatase (Alp), bone sialoprotein (Bsp), osteocalcin (Oc), and osteopontin (Opn), as well as the ability to mineralize the extracellular matrix after 14 and 21 days of culture. Taken together, the results described in this study shed light on the potential use of collagen/κ-carrageenan scaffolds to study the role of the structural organization of bone-mimetic synthetic matrices in cell function.

The coordination chemistry of corrole has witnessed a great improvement in the past few years and its Periodic Table has been widened to be so large that it is compared with that of porphyrins. However, Ni and Zn ions, commonly used with porphyrins for both synthetic and theoretical purposes, are sparsely reported in the case of corroles. Here, we report synthetic protocols for preparing Ni and Zn triarylcorrole complexes. In the case of Zn, the preliminary oxidation of the free base corrole in DMSO to the neutral corrole radical is a necessary step to obtain the coordination of the metal ion, because the direct reaction led to the formation of an open-chain tetrapyrrole. The Ni complex could be directly obtained by heating the free base corrole and Ni(II) salt to 100 °C in a DMSO solution containing FeCl3. The non-innocent nature of the corrole ligand for both complexes has been elucidated by EPR, and in the case of the Zn derivative the first spectroelectrochemical characterization is presented.

Corroles, a family of contracted porphyrinoids, exhibit broad chemical interactions, undergo straightforward synthetic preparation and functionalization, and enable versatile thin film deposition. These attributes render them promising candidates for use in chemical sensors. Nevertheless, the inherently limited conductivity of corrole solid films constrains their application in mass and optical sensors. Despite this impediment, there is a great interest in matching the sensitive properties of the corrole with the features of facile miniaturization and integration into low‐cost electronic circuits. This work explores the possibility of directly and simply depositing conductometric polymeric films of [5,10,15‐(4‐aminophenyl)corrolato] copper onto interdigitated electrodes. Remarkably, the electropolymerization protocol allows the selection of the semiconductive nature (p‐ or n‐type) of these films, yielding two distinct sensor types: the former exhibiting high sensitivity and selectivity toward nitrogen monoxide (NO) with a slight influence of relative humidity and the other manifesting a broad spectrum of sensitivities. This breakthrough lays the foundation for developing miniaturized conductometric gas detectors, nonlinear conductometric sensing elements, and electronic nose platforms based on polycorroles. Allowing corroles to conduct when linked in chains! The preparation of semiconducting corrole polymers by electropolymerization techniques allows their exploitation in chemoresistive sensors. The preparation protocol allows tuning of the semiconducting nature of the corrole electropolymer, addressing the selectivity of the resulting devices and paving the way for their integration in functional sensor arrays.

Three mono-CN ligated anionic cobalt A3-triarylcorroles were synthesized and investigated as to their spectroscopic and electrochemical properties in CH2Cl2, pyridine (Py), and dimethyl sulfoxide (DMSO). The newly synthesized corroles provide the first examples of air-stable cobalt corroles with an anionic axial ligand and are represented as [(Ar)3CorCoIII(CN)]−TBA+, where Cor is the trivalent corrole macrocycle, Ar is p-(CN)Ph, p-(CF3)Ph, or p-(OMe)Ph, and TBA+is the tetra-n-butylammonium (TBA) cation. Multiple redox reactions are observed for each mono-CN derivative with a key feature being a more facile first oxidation and a more difficult first reduction in all three solvents as compared to all previously examined corroles with similar meso-and β-pyrrole substituents. Formation constants (log K) for conversion of the five-coordinate mono-CN complex to its six-coordinate bis-CN form ranged from 102.8for Ar = p-(OMe)Ph to 104.7for Ar = p-(CN)Ph in DMSO as determined by spectroscopic methodologies. The in situ generated bis-CN complexes, represented as [(Ar)3CorCoIII(CN)2]2–(TBA+)2, and the mixed ligand complexes, represented as [(Ar)3CorCoIII(CN)(Py)]−TBA+, were also investigated as to their electrochemical and spectroscopic properties. UV–visible spectra and electrode reactions of the synthesized mono-CN derivatives are compared with the neutral mono-DMSO cobalt corrole complexes and the in situ generated bis-CN and bis-Py complexes, and the noninnocent (or innocent) nature of each cobalt corrole system is addressed. The data demonstrate the ability of the CN–axial ligand(s) to stabilize the high-valent forms of the metallocorrole, leading to systems with innocent macrocyclic ligands. Although a number of six-coordinate cobalt(III) corroles with N-donor ligands were characterized in the solid state, a dissociation of one axial ligand readily occurs in nonaqueous solvents, and this behavior contrasts with the high stability of the currently studied bis-CN adducts in CH2Cl2, pyridine, or DMSO. Linear free energy relationships were elucidated between the meso-phenyl Hammett substituent constants (Σσ) and the measured binding constants, the redox potentials, and the energy of the band positions in the mono-CN and bis-CN complexes in their neutral or singly oxidized forms, revealing highly predictable trends in the physicochemical properties of the anionic corroles.

A new series of cobalt A3-triarylcorroles were synthesized and the compounds examined as to their electrochemical and spectroscopic properties in CH2Cl2or dimethyl sulfoxide (DMSO) containing 10 different anions added to the solution in the form of tetrabutylammonium salts. The investigated anions were PF6–, BF4–, HSO4–, ClO4–, Br–, I–, Cl–, OAc–, F–, OTs–, and CN–, all but three of which were found to facilitate reduction of the cobalt corrole in dilute CH2Cl2solutions, as determined by a combination of UV–vis spectroscopy and spectroelectrochemistry. The synthesized corroles are represented as (Ar)3CorCo(DMSO), where Ar is a meso-phenyl group containing one of 10 different electron-donating or -withdrawing substituents. The axial DMSO ligand was found to dissociate in dilute (10–5M) CH2Cl2solutions, but this was not the case at the higher electrochemical concentration of 10–3M, where the investigated corroles exhibit a rich redox reactivity, undergoing up to five reversible one-electron-transfer reactions under the different solution conditions. The reversible half-wave potentials for generation of the singly oxidized corroles varied by over 1.0 V with a change in the electron-donating or -withdrawing meso-phenyl substituents and type of anion added to the solution, ranging from E1/2= 0.83 V in one extreme to −0.42 V in the other. Much smaller shifts in the potentials (on the order of ∼210 mV) were observed for the reversible first reduction as a function of changes of the anion and/or corrole substituents, with the only exception being in the case of CN–, where the E1/2values in CH2Cl2ranged from +0.08 V in solutions containing 0.1 M TBAClO4to >−1.8 V upon the addition of CN–.

The development of chiral receptors for discriminating the configuration of the analyte of interest is increasingly urgent in view of monitoring pollution in water and waste liquids. Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and makes the dye@nanohelix system disperse in a suspension of water without aggregation. We noted strong induction and amplification of chiroptical activity in both achiral and chiral (proline-based or hemicucurbituril-based) porphyrin derivatives with and without zinc ions once confined and organized in nanometer silica helices. The results clearly demonstrated that the organization-induced chirality amplification of porphyrins dominates the molecular chirality, and the amplification is more efficient for more flexible porphyrins (especially free-base and achiral).

Recognition of enantiomers is one of the most arduous challenges in chemical sensor development. Although several chiral systems exist, their effective exploitation as the sensitive layer in chemical sensors is hampered by several practical implications that hinder stereoselective recognition in solid state. In this paper, we report a new methodology to efficiently prepare chiral solid films, by using a hybrid material approach where chiral porphyrin derivatives are grafted onto zinc oxide nanoparticles. Circular dichroism (CD) evidences that the solid-state film of the material retains supramolecular chirality due to porphyrin interactions, besides an additional CD feature in correspondence of the absorbance of ZnO (375 nm), suggesting the induction of chirality in the underlying zinc oxide nanoparticles. The capability of hybrid material to detect and recognize vapors of enantiomer pairs was evaluated by fabricating gas sensors based on quartz microbalances. Chiral films of porphyrin on its own were used for comparison. The sensor based on functionalized nanostructures presented a remarkable stereoselectivity in the recognition of limonene enantiomers, whose ability to intercalate in the porphyrin layers makes this terpene an optimal chiral probe. The chiroptical and stereoselective properties of the hybrid material confirm that the use of porphyrin-capped ZnO nanostructures is a viable route for the formation of chiral selective surfaces.

Perovskite solar cells (PSCs) are evolving with an impressive pace, emerging as the most promising next-generation photovoltaic devices. Nevertheless, beside these enormous progresses, the stability of PSCs remains one of the major problems to be challenged, because the most commonly used hole transporting material (HTM), the 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)−9,9′-spirobifluorene (Spiro-OMeTAD), suffers long-term stability. Here, we tackle this long-lasting issue exploiting reduced graphene oxide (RGO), prepared by an easy and efficient reduction method, as HTM in PSCs. We carried out endurance tests over 1987h of shelf life and 120h of light soaking. The PSCs based on RGO have shown power conversion efficiency (PCE) of 6.6%, outperforming the ones achieved with the Spiro-OMeTAD (PCE=6.5%), after the shelf life test. The light soaking test confirmed the better durability of RGO-based PSCs with respect to the Spiro-OMeTAD ones, the latter showing a reduction in PCE 2.7 times higher than the RGO-based cells. Moreover, we demonstrate by Open Circuit Voltage Decay measurements that RGO, beside the HTM function, acts also as an anti-recombination layer, reducing the charge carriers recombination pathways and, hence, increasing their lifetime.

Noncovalent porphyrin deposition onto polylysinated surfaces proceeds by obeying the self-assembly rules experienced in aqueous solution. In particular, the porphyrin’s ability to stack in a face-to-facearrangement, leading to H-aggregate formation, strongly depends on the central metal coordination, even during deposition on surfaces. This aspect is important to control the porphyrin layer density and the related optical properties and reactivity to external stimuli, thus pointing to intriguing sensing applications. In this perspective, we demonstrate the ability of porphyrin-based layers, assembled on polylysinated Quartz Micro Balance (QMB) resonators, to act as humidity sensors, whose sorption behavior depends on the presence of the central metal into the porphyrin cavity. The obtained sensors are fast responsive, reversible and stable over a tested period of 6 months. The straightforwardness, robustness and performance repeatability of the presented functionalization procedure, associated with low cost and green chemistry figure of merits, pave the way to the development of porphyrin-based sensitive layers for humidity sensing applications.

Introduction:The early determination of serious pathologies has so far been an important issue in both the medical and social fields. The search for an instrument able to detect cancers has led to the consideration of the usage of chemicals of the human body, which carry, through its volatile compounds, information coming from or related to defined pathologies.Areas covered:The electronic nose (EN) seems to represent a good solution for the detection of cancers of different types. Recent results showed the utility of an EN to smell chemicals related to lung, melanoma, prostatic, breast and pancreatic cancers. The results obtainable from ENs are chemical images and, as it will be shown in this paper, the probability of cancer recognition is rather high. Main results obtained at international level and by the authors of this paper will be commented upon.Expert opinion:A personal opinion is given trying to foresee future developments of the olfaction strategy. To this purpose, two main aspects are considered: looking for better overall stability of the EN and for a new use of ENs in detecting alterations between blood and pathology components.

Hybrid materials based on wide band gap semiconductors and dye molecules are intensively studied for photovoltaic applications. However, these materials also possess interesting gas sensitivities, besides these photonic effects. In this Article, we report the study, under visible light illumination, of the porphyrin-functionalized ZnO nanorod photoconductivity changes, modulated by exposure to two volatile organic compounds, ethanol and triethylamine, chosen as model analytes. The sensitivity to triethylamine exceeds that to ethanol by more than two orders of magnitude, showing a selectivity that is not found in other porphyrin-based gas sensors. This feature could open the way to a novel generation of sensors, where photoactivation plays a role in determining both sensitivity and selectivity of the resulting device.

The peculiar properties of porphyrins allow their exploitation as sensing materials in chemical sensors having different transduction principles, or even the intriguing possibility to develop sensors where two different transduction mechanisms are hyphenated in the same substrate. This approach can allow a significant increase in the chemical information obtained from the device and it can boost the performances in terms of selectivity and sensitivity. Our recent achievements in the field of functionalized porphyrins application for the development of the hyphenated optoelectrochemical sensors will be discussed in this contribution.

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, 3H2) or anionic (carboxylate residue, 6H2) group. Formation of anionic 6H2aggregates shows a diffusion‐limited kinetic behavior. AFM topography studies show formation of tighter globular structures. On the other hand, the corresponding 3H2aggregates are formed by a cooperative, fractal‐type decay, and appear as long‐fibrous, looser structures. In the templated aggregation of 3H2over preformed 6H2aggregates, 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.

Chemical fingerprinting: The polychromatic fingerprinting of the excitation emission matrix (EEM) of diverse fluorescent substances by using common computer screens as light sources is reported. The modelling of the polychromatically excited spectra (see graphic) establishes the link with the sampling of the EEM of the tested substances and sets the theoretical frame for the interpretation of sensing techniques based on this principle.

Ge complexes of 5,10,15-triphenylcorrole were prepared in refluxing dry DMF using GeCl4 as the source of Ge. Chromatographic separation of the crude reaction mixture afforded the μ-oxo dimer 1 and the methoxy derivative 2a. The corresponding chloride 2b can be obtained by treatment of 1 or 2a with HCl. The reaction of 2a with Br2 in CHCl3/py afforded the hexabromo derivative 3 as the main product, giving the first indication of the regioselective substitution of pyrroles B and C on the corrole ring. The fully brominated open-chain tetrapyrrole 4 was also characterized as a reaction by-product. Different partially brominated Ge complexes 5 and 6 have been obtained by variation of reaction conditions, while the heptabromo derivative was obtained in a mixture with the corresponding fully brominated Gecorrole. Photophysical characterization of Ge corrolates confirmed the high fluorescence quantum yield of such complexes, and also led to the first observation of phosphorescence emissions from corrole complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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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.

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Thin films consisting of a fulleropyrrolidine derivative 1and a novel water‐soluble porphyrin 2were prepared by the Langmuir–Shäfer (LS, horizontal lifting) method. In particular, a solution of 1in chloroform and dimethyl sulfoxide was spread on the water surface, while porphyrin 2(bearing peripheral anionic groups) was dissolved into the aqueous subphase. To the best of our knowledge, such a versatile method of film fabrication for fullerene/porphyrin mixed composite films has never been used before. Evidence of the effective interactions between the two moieties at the air–water interface was obtained from the analysis of the floating layers by means of surface pressure versus area per molecule Langmuir curves, Brewster angle microscopy and UV‐visible reflection spectroscopy. The characterisation of the LS films by UV‐visible spectroscopy reveals that the two constituents behave as discrete and weakly interacting π systems. The use of polarised light suggests the existence of a preferential direction of the macrocyclic rings with an edge‐on arrangement with respect to the substrate surface. Finally, photoaction spectra were recorded from films deposited by only one horizontal lifting onto indium–tin–oxide (ITO) electrodes and the observed photocurrent increased notably with increasing transfer surface pressure.

Spontaneous deposition of aggregates of a tetraphenylporphyrin derivative, possessing a cationic appended functionality, straightforwardly occurs from aqueous solutions. Combined spectroscopic studies and AFM morphological characterisation reveal that these layered films feature a consistent degree of order. Deposition of the related manganese or cobalt derivatives analogously occurs and the UV-visible spectral pattern of the films dramatically changes upon exposure to vapours of amines or olefins. This aspect can be of great importance for the construction of solid state chemical sensors.

The sensing properties of functionalized cavitands have been studied by thin‐film coating TMSR chemical sensors and by measuring their responses towards model analytes. We studied the relationship between the sensor performance, in terms of sensitivity and selectivity, and the molecular recognition properties of the cavitands. The Langmuir‐like shape of the adsorption isotherm, obtained in the case of short‐chain alcohols, demonstrated that selective binding can be achieved by the synergistic interactions of the cavity and the bridging POingroups. In the absence of these substituents, the peripheral alkyl chains necessary for the formation of highly permeable thin films attenuate the cavity effect because of nonspecific dispersion interactions. This completely overrides the response originating from molecular recognition. The same effect is observed when the PO groups are oriented outward from the cavity. The use of multivariate chemometrics and the study of the correlations between sensors sensitivity and analyte properties provided further evidence of molecular recognition phenomena, whose intensity is enhanced by the permanent free volume created by the rigid cavity surrounding the POingroup.

5,10,15‐Triphenylcorrole (1) reacts with the Vilsmeier reagent (POCl3/DMF) to give the corresponding 3‐formyl derivative 3as the major product. The regioselectivity of the reaction was proven by X‐ray crystallography and only traces of the 2‐formyl isomer were observed. A more polar product is also observed and this compound becomes the major product when an excess of DMF is used for the preparation of the Vilsmeier reagent, while the formation of the 3‐formyl isomer is almost completely suppressed. X‐ray crystallography allowed us to identify this compound as the fully substituted N‐ethane bridged derivative 4, formed from the attack of the Vilsmeier reagent at the inner core of the macrocycle. This compound is unique among porphyrinoid macrocycles, and further confirms the peculiarity of corrole chemistry.

Porphyrin diad 1was synthesized by reaction of the acyl chloride of porphyrin 2and 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.

New linear diporphyrin arrays and a heteroleptic diad have been synthesized in good yield. ¹H NMR, UV-visible and fluorescence studies reveal that the receptors bind to alkali and alkaline-earth metal ions to give a supramolecular complex in which the ion is nestled within the oligooxaethylene framework. The formation of the host–guest complexes promotes a change in the geometry of the system toward a topology in which the two tetrapyrrolic macrocycles tend to face together. This is evidenced by the mutual ring current anisotropy effect exerted by the porphyrinic platforms, and by the blue shift and broadening of the relative UV-visible bands (Soret). In particular, the changes observed allow the complexation process to be monitored at very low concentrations. The association constants lie within the range 25–1×10⁵ M^-1 (CD₃CN–CDCl₃ 1:1) depending on either the nature of the diporphyrinic receptors or that of the interacting metal ions. The heteroleptic diad shows a very efficient energy transfer process (>99%) between the two different macrocycles in a variety of solvents that is not altered by complexation with metal ions. The systems reported present interesting properties as switchable biomimetics.

Rapid kinetic, spectroscopic, and potentiometric studies have been performed on human Theta class glutathione transferase T2-2 to dissect the mechanism of interaction of this enzyme with its natural substrate GSH. Theta class glutathione transferases are considered to be older than Alpha, Pi, and Mu classes in the evolutionary pathway. As in the more recently evolved GSTs, the activation of GSH in the human Theta enzyme proceeds by a forced deprotonation of the sulfhydryl group (pKa= 6.1). The thiol proton is released quantitatively in solution, but above pH 6.5, a protein residue acts as an internal base. Unlike Alpha, Mu, and Pi class isoenzymes, the GSH-binding mechanism occurs via a simple bimolecular reaction with konandkoffvalues at least hundred times lower (kon=(2.7 ± 0.8) × 104m−1s−1, koff= 36 ± 9 s−1, at 37 °C). Replacement of Arg-107 by alanine, using site-directed mutagenesis, remarkably increases the pKavalue of the bound GSH and modifies the substrate binding modality. Y107A mutant enzyme displays a mechanism and rate constants for GSH binding approaching those of Alpha, Mu, and Pi isoenzymes. Comparison of available crystallographic data for all these GSTs reveals an unexpected evolutionary trend in terms of flexibility, which provides a basis for understanding our experimental results.

Steady state, pre-steady state kinetic experiments, and site-directed mutagenesis have been used to dissect the catalytic mechanism of human glutathione transferase T2-2 with 1-menaphthyl sulfate as co-substrate. This enzyme is close to the ancestral precursor of the more recently evolved glutathione transferases belonging to Alpha, Pi, and Mu classes. The enzyme displays a random kinetic mechanism with very lowkcatandkcat/Km(GSH)values and with a rate-limiting step identified as the product release. The chemical step, which is fast and causes product accumulation before the steady state catalysis, strictly depends on the deprotonation of the bound GSH. Replacement of Arg-107 with Ala dramatically affects the fast phase, indicating that this residue is crucial both in the activation and orientation of GSH in the ternary complex. All pre-steady state and steady state kinetic data were convincingly fit to a kinetic mechanism that reflects a quite primordial catalytic efficiency of this enzyme. It involves two slowly interconverting or not interconverting enzyme populations (or active sites of the dimeric enzyme) both able to bind and activate GSH and strongly inhibited by the product. Only one population or subunit is catalytically competent. The proposed mechanism accounts for the apparent half-site behavior of this enzyme and for the apparent negative cooperativity observed under steady state conditions. These findings also suggest some evolutionary strategies in the glutathione transferase family that have been adopted for the optimization of the catalytic activity, which are mainly based on an increased flexibility of critical protein segments and on an optimal orientation of the substrate.

In this paper the performances of an electronic nose based on metalloporphyrin-coated quartz microbalance sensors and of an experienced panel of seven human assessors in the evaluation of gases derived from degradation reactions in tomatoes are presented and discussed. The performances are measured in terms of the capability of both systems to distinguish between samples of different quality coming from conventional and organic production systems. The study deals with the application of pattern recognition techniques based on either multivariate statistical methods (PCA, GPA) or artificial neural networks using a self-organising map (SOM). The response pattern of the sensor array and the sensory data are analysed and compared using these methods. Similarities in the classification of the data by electronic nose and human sensory profiling are found. © 2000 Society of Chemical Industry

A series of Mn^III porphyrins progressively halogenated in the β-pyrrolic positions was employed to catalyse the epoxidation of cis-stilbene by iodosylbenzene, and to study the role of the electronic effects on the stereoselectivity of this process. A gradual improvement in the stereoselectivity on increasing the number of β-halogen atoms was observed. The role of steric effects upon the epoxidation was also investigated by placing ortho-substituents in the meso-phenyl rings, and it was found that steric effects are more important than electronic effects toward the stereoselectivity of this process. These results can be rationalised by proposing a competition between a nonstereoselective electrophilic pathway of addition and a stereospecific pathway of oxygen insertion, the former being disfavoured by electron-withdrawing substituents. Alternatively, the formation of an open intermediate between the Mn^V oxene and the substrate could be suggested, where the stereoselectivity ought to be determined by the competition between closure of the epoxide ring and rotation around the C–C bond. In this case, the enhanced stereoselectivity given by our polyhalogenated porphyrins might be attributed to an acceleration of the epoxide ring closure caused by the electron-withdrawing effect of the halogen substituents.

Flat and gable meso-tetraphenylporphyrin-corrole heterodimers have been synthesized following a stepwise approach. The macrocyclic precursor for both isomers is a functionalized meso-tetraphenylporphyrin (TPP) bearing a formyl group at one of the peripheral phenyl groups. The preparation of these starting materials has been improved with respect to the previously reported method. Acidic condensation with pyrrole 8allows the preparation of a TPP-dipyrromethane intermediate. Subsequent decarboxylation followed by reaction with formylpyrrole 2affords the corresponding TPP–a,c-biladiene species. Final cyclization of this intermediate affords the desired heterodimer. Attempts to use the functionalized corrole 5as starting material were unsuccessful, as this corrole failed to condense with pyrrole and benzaldehyde. This synthetic approach provides new examples of tetrapyrrolic heterodimers, which can represent useful biomimetic models to study photochemical processes.

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.

Flat and gable meso-tetraphenylporphyrin–corrole heterodimers have been synthesized following a stepwise approach. The macrocyclic precursor for both isomers is a functionalized meso-tetraphenylporphyrin (TPP) bearing a formyl group at one of the peripheral phenyl groups. The preparation of these starting materials has been improved with respect to the previously reported method. Acidic condensation with pyrrole 8 allows the preparation of a TPP–dipyrromethane intermediate. Subsequent decarboxylation followed by reaction with formylpyrrole 2 affords the corresponding TPP–a,c-biladiene species. Final cyclization of this intermediate affords the desired heterodimer. Attempts to use the functionalized corrole 5 as starting material were unsuccessful, as this corrole failed to condense with pyrrole and benzaldehyde. This synthetic approach provides new examples of tetrapyrrolic heterodimers, which can represent useful biomimetic models to study photochemical processes. © 1998 John Wiley & Sons, Ltd.

Linear ethynylporphyrin-bridged platinum(II) complexes, [X(R3P)2Pt–C&z.tbd6;C–Zn(por)–C&z.tbd6;C–Pt(PR3)2Y] [Zn(por) is a non-ethynylated porphyrin 1a] and related oligomers have been synthesized. Di- and tri-nuclear platinum centers are linked to different porphyrin arrays; the end groups Pt(PR3)2X and Pt(PR3)2Y (R 4;= 4;n-Bu or Ph; X 4;= 4;Y 4;= 4;Cl or I; X 4;= 4;Cl, Y 4;= 4;I) show that a ligand exchange Cl 4;→ 4;I also occurs. The compounds containing PBu3 as the ligand are more stable than the corresponding PPh3 ones. The dinuclear platinum dimers containing one bridging porphyrin have been isolated and characterized by IR, UV/VIS, 1H NMR and MALDI (matrix assisted laser desorption/ionization) mass spectroscopies. The mixture of longer oligomers was separated from the crude reaction products and could be identified by MALDI. The cis–trans isomerization of the porphyrin complexes with respect to the platinum precursor complexes, i.e. trans-[PtCl2(PBu3)2], cis-[PtCl2(PPh3)2] and trans-[PtH(Cl)(PPh3)2], was observed. The dimers and oligomers are expected to be model molecules for long chain organometallic polymers.

Eine dimere, auch in Lösung stabile Struktur, die auf Wasserstoffbrückenbindungen beruht, charakterisiert das Chloridsalz des abgebildeten expandierten Corrols. Die Synthese, die Röntgenstrukturanalyse sowie die NMR- und UV/Vis-Absorptionsspektren der neuen Spezies bestätigen die Strukturzuordnung sowohl in Lösung als auch im festen Zustand.

Methodology for synthesis of phenyl-linked unsymmetrical dimers containing 8,12-diethyl 2,3,7,12,13,17,18-hexamethylporphyrin and meso-tetraphenylporphyrin subunits is reported. Hetero metal complexes of these dimers can be prepared by following two different routes.

The synthesis and electrochemical characterization of five covalently linked symmetrical and unsymmetrical metalloporphyrin dimers containing tetraphenylporphyrin (TPP), triphenylporphyrin (TriPP) or diethylhexamethylporphyrin (DEHMP) macrocycles are reported. The investigated compounds are represented as M(TPP-DEHMP)M (M= Co, Ni, Cu) and M(TPP-TriPP)M (M= Ni, Cu), where TPP-DEHMP and TPP-TriPP are the tetraanions of 1-[5-(10,15,20-triphenylporphyrinyl)]-4-[10-(2,18-diethyl-3,7,8,12,13,17-hexamethylporphyrinyl)]benzene and 1,4-bis-[5″-(10″,15″,20″-triphenylporphy-rinyl)]benzene respectively. The UV-vis spectra of the neutral dimers can be simply obtained by superimposing the spectra of the two corresponding monomeric (TPP)M and (DEHMP)M units, the latter of which is approximated by (OEP)M (TPP and OEP are the dianions of tetraphenylporphyrin and octaethylporphyrin respectively). The reduction potentials of the dimeric porphyrins are similar to those of the combined individual monomeric units. This is also the case for all oxidations of M(TPP-TriPP)M as well as the first TPP- and DEHMP-centered oxidations of M(TPP-DEHMP)M to give porphyrin π-cation radicals. However, the second DEHMP macrocycle-centered oxidations of M(TPP-DEHMP)M to give porphyrin dications occur at half-wave potentials which are 50-100 mV easier than E1/2for the same ring-centered oxidations of the corresponding (OEP)M monomers. The electrochemical data indicate that there is an electronic interaction between the (TPP)M and (DEHMP)M units of M(TPP-DEHMP)M only under conditions where both macrocycles of the dimer have been converted to a porphyrin π-cation radical.

This paper describes preliminary results obtained by the Kelvin probe system utilized for the investigation of the sensing behavior of self-assembled-monolayers of thiol functionalized porphyrins. Dynamic aspects related to volatile compounds adsorption have indicated fast responses and a remarkable sensitivity.

The synthesis and electrochemical characterization of five covalently linked symmetrical and unsymmetrical metalloporphyrin dimers containing tetraphenylporphyrin (TPP), triphenylporphyrin (TriPP) or diethylhexamethylporphyrin (DEHMP) macrocycles are reported. The investigated compounds are represented as M(TPP-DEHMP)M (M = Co, Ni, Cu) and M(TPP-TriPP)M (M = Ni, Cu), where TPP-DEHMP and TPP-TriPP are the tetraanions of 1-[5-(10,15,20-triphenylporphyrinyl)]-4-[10-(2,18-diethyl-3,7,8,12,13,17-hexamethylporphyrinyl)]benzene and 1,4-bis-[5'-(10',15',20'-triphenylporphyrinyl)]benzene respectively. The UV-vis spectra of the neutral dimers can be simply obtained by superimposing the spectra of the two corresponding monomeric (TPP)M and (DEHMP)M units, the latter of which is approximated by (OEP)M (TPP and OEP are the dianions of tetraphenylporphyrin and octaethylporphyrin respectively). The reduction potentials of the dimeric porphyrins are similar to those of the combined individual monomeric units. This is also the case for all oxidations of M(TPP-TriPP)M as well as the first TPP- and DEHMP-centered oxidations of M(TPP-DEHMP)M to give porphyrin π-cation radicals. However, the second DEHMP macrocycle-centered oxidations of M(TPP-DEHMP)M to give porphyrin dications occur at half-wave potentials which are 50–100 mV easier than E1/2 for the same ring-centered oxidations of the corresponding (OEP)M monomers. The electrochemical data indicate that there is an electronic interaction between the (TPP)M and (DEHMP)M units of M(TPP-DEHMP)M only under conditions where both macrocycles of the dimer have been converted to a porphyrin π-cation radical. © 1998 John Wiley & Sons, Ltd.

The absolute selectivity of chemical sensors ceased in the last years to be a fundamental feature due to the uprising of many applications, such as electronic noses, which require the presence of broad selectivity sensors. On the other hand for these applications the attention is paid to the development of sensors whose broad selectivity can be oriented towards different classes of molecules representing a given environment in order to optimize the interface between the sensitive layers deposited on transducers and the chemical complexity of the environment itself. In this paper the main problems in the design and characterization of such sensors are presented and discussed in the case of a class of molecules, such as metallo-porphyrins, which have been recently exploited as sensitive layers in electronic nose applications.