Search

Conjugating the porphyrin ring with an amino acid via amide linkage represents a straightforward way for conferring both amphiphilicity and chirality to the macrocycle. Proline residue is a good choice in this context since its conformational rigidity allows for porphyrin assembling where molecular chirality is efficiently transferred and amplified using properly honed aqueous environments. Herein, we describe the evolution of the studies carried out by our group to achieve chiral systems from some porphyrin-proline derivatives, both in solution and in the solid state. The discussion focuses on some fundamental aspects reflecting on the final molecular architectures obtained, which are related to the nature of the appended group (stereochemistry and charge), the presence of a metal ion coordinated to the porphyrin core and the bulk solvent properties. Indeed, fine-tuning the mentioned parameters enables the achievement of stereospecific structures with distinctive chiroptical and morphological features. Solid films based on these chiral systems were also obtained and their recognition abilities in gaseous and liquid phase are here described.

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 FeCl 3 . 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.

Porphyrinoids are considered perfect candidates for their incorporation into electron donor-acceptor (D-A) arrays due to their remarkable optoelectronic properties and low reorganization energies. For the first time, a series of subphthalocyanine (SubPc) and corrole (Cor) were covalently connected through a short-range linkage. SubPc axial substitution strategies were employed, which allowed the synthesis of the target molecules in decent yields. In this context, a qualitative synthetic approach was performed to reverse the expected direction of the different electronic events. Consequently, in-depth absorption, fluorescence, and electrochemical assays enabled the study of electronic and photophysical properties. Charge separation was observed in cases of electron-donating Cors, whereas a quantitative energy transfer from the Cor to the SubPc was detected in the case of electron accepting Cors., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Electron-donating corroles (Cor) were integrated with electron-accepting phthalocyanines (Pc) to afford two different non-covalent Cor ⋅ Pc systems. At the forefront was the coordination between a 10-meso-pyridine Cor and a ZnPc. The complexation was corroborated in a combination of NMR, absorption, and fluorescence assays, and revealed association with binding constants as high as 10 6  m -1 . Steady-state and time-resolved spectroscopies evidenced that regardless of exciting Cor or Pc, the charge-separated state evolved efficiently in both cases, followed by a slow charge-recombination to reinstate the ground state. The introduction of non-covalent linkages between Cor and Pc induces sizeable differences in the context of light harvesting and transfer of charges when compared with covalently linked Cor-Pc conjugates., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Corrole chemistry has witnessed an impressive boost in studies in the last 20 years, thanks to the possibility of preparing corrole derivatives by simple synthetic procedures. The investigation of a large number of corroles has highlighted some peculiar characteristics of these macrocycles, having features different from those of the parent porphyrins. With this progress in the elucidation of corrole properties, attention has been focused on the potential for the exploitation of corrole derivatives in different important application fields. In some areas, the potential of corroles has been studied in certain detail, for example, the use of corrole metal complexes as electrocatalysts for energy conversion. In some other areas, the field is still in its infancy, such as in the exploitation of corroles in solar cells. Herein, we report an overview of the different applications of corroles, focusing on the studies reported in the last five years.

Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of the macrocycle (i.e., D - or L -proline moieties), in the presence of chiral amines as co-solute, such as chiral benzylamine derivatives. The aggregation process, steered by hydrophobic effect, has been studied in aqueous solvent mixtures by combined spectroscopic and topographic techniques. The results obtained pointed out a dramatic effect of these ligands on the morphology and on the supramolecular chirality of the final self-assembled structures. Scanning electron microscopy topography, as well as fluorescence microscopy studies revealed the formation of rod-like structures of micrometric size, different from the fractal structures formerly observed when the self-assembly process is carried out in the absence of chiral amine co-solutes. On the other hand, comparative experiments with an achiral porphyrin analogue strongly suggested that the presence of the prolinate moiety is mandatory for the achievement of the observed highly organized suprastructures. The results obtained would be of importance for unraveling the intimate mechanisms operating in the selection of the homochirality, and for the preparation of sensitive materials for the detection of chiral analytes, with tunable stereoselectivity and morphology.

An overview of the solvent-driven aggregation of a series of chiral porphyrin derivatives studied by optical methods (UV/Vis, fluorescence, CD and RLS spectroscopies) is herein reported. The investigated porphyrins are characterized by the presence in the meso-positions of glycol-, steroidal- and glucosteroidal moieties, conferring amphiphilicity and solubility in aqueous media to the primarily hydrophobic porphyrin platform. Aggregation of the macrocycles is driven by a change in bulk solvent composition, forming architectures with supramolecular chirality, steered by the stereogenic centers on the porphyrin peripheral positions. The aggregation behavior and chiroptical properties of the final aggregated species strongly depend on the number and stereogenicity of the ancillary groups that dictate the mutual spatial arrangement of the porphyrin chromophores and their further organization in larger structures, usually detectable by different microscopies, such as AFM and SEM. Kinetic studies are fundamental to understand the aggregation mechanism, which is frequently found to be dependent on the substrate concentration. Additionally, Molecular Mechanics calculations can give insights into the intimate nature of the driving forces governing the self-assembly process. The critical use of these combined methods can shed light on the overall self-assembly process of chirally-functionalized macrocycles, with important implications on the development of chiral porphyrin-based materials.

The reaction of 5,10,15-tritolylcorrole with 3-dimethylaminoacrolein (3-DMA) and POCl 3 gives a further example of the rebel reactivity of this contracted macrocycle. While no evidence was obtained for the formation of the expected β-acrolein corrole, the inner core substituted N21,N22-3-formylpropylcorrole and the 10-acrolein isocorrole were the reaction products. By increasing the temperature or the amount of the Vilsmeier reagent, the 10-isocorrole became the unique reaction product. The formation of the isocorrole by electrophilic attack of the Vilsmeier reagent to the 10-position of the corrole is unprecedented in the porphyrinoids field and it could pave the way for a novel route to the preparation of stable isocorroles.

The interest in assembling porphyrin derivatives is widespread and is accounted by the impressive impact of these suprastructures of controlled size and shapes in many applications from nanomedicine and sensors to photocatalysis and optoelectronics. The massive use of porphyrin dyes as molecular building blocks of functional materials at different length scales relies on the interdependent pair properties, consisting of their chemical stability/synthetic versatility and their quite unique physicochemical properties. Remarkably, the driven spatial arrangement of these platforms in well-defined suprastructures can synergically amplify the already excellent properties of the individual monomers, improving conjugation and enlarging the intensity of the absorption range of visible light, or forming an internal electric field exploitable in light-harvesting and charge-and energy-transport processes. The countless potentialities offered by these systems means that self-assembly concepts and tools are constantly explored, as confirmed by the significant number of published articles related to porphyrin assemblies in the 2015-2019 period, which is the focus of this review.

The importance of allosteric proteasome inhibition in the treatment of cancer is becoming increasingly evident. Motivated by this urgent therapeutic need, we have recently identified cationic porphyrins as a highly versatile class of molecules able to regulate proteasome activity by interfering with gating mechanisms. In the present study, the mapping of electrostatic contacts bridging the regulatory particles with the α-rings of the human 20S proteasome led us to the identification of (meso-tetrakis(4-N-methylphenyl pyridyl)-porphyrin (pTMPyPP4) as a novel non-competitive inhibitor of human 20S proteasome. pTMPyPP4 inhibition mechanism implies a positive cooperative binding to proteasome, which disappears when a permanently open proteasome mutant (α-3ΔN) is used, supporting the hypothesis that the events associated with allosteric proteasome inhibition by pTMPyPP4 interfere with 20S gating and affect its "open-closed" equilibrium. Therefore, we propose that the spatial distribution of the negatively charged residues responsible for the interaction with regulatory particles at the α-ring surface of human 20S may be exploited as a blueprint for the design of allosteric proteasome regulators.

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.

Phosphorus complexes of corrole have recently attracted increasing interest since these compounds can be easily prepared in good yields, are stable, and show unusual optical properties. For these reasons, phosphorus corroles represent a class of interesting compounds to be exploited in the field of material science or for biomedical investigations and the definition of synthetic pathways for their functionalization is an important step to optimize their properties for various applications. We report here the reactivity of the phosphorus complex of 5,10,15-tritolylcorrole in the nitration or bromination reaction. Both these attempts were successful, allowing the preparation of substituted phosphorus corroles, which can be used as intermediates of more complex architectures endowed with useful properties. Furthermore, the crystallographic characterization of both complexes shows that they have an unusual ruffled geometry of the corrole core, a conformation that has not been considered possible for such a macrocycle., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Complexes of 5,10,15-triferrocenylcorrole were synthesized from the crude free-base corrole product obtained by the reaction of ferrocenyl aldehyde and pyrrole. Direct formation of the complex in this manner leads to an increase of the reaction yield by protecting the corrole ring toward oxidative decomposition. The procedure was successful and gave the expected product in the case of the copper and triphenylphosphinecobalt complexes, but an unexpected result was obtained in the case of the nickel derivative, where metal insertion led to a ring opening of the macrocycle at the 5 position, giving as a final product a linear tetrapyrrole nickel complex bearing two ferrocenyl groups. The purified 5,10,15-triferrocenylcorrole complexes have been fully characterized by a combination of spectroscopic methods, electrochemistry, spectroelectrochemistry, and density functional theory calculations. Copper derivatives of 10-monoferrocenyl- and 5,15-diferrocenylcorrole were prepared to investigate how the number and position of the ferrocenyl groups influenced the spectroscopic and electrochemical properties of the resulting complexes. A complete assignment of resonances in the (1)H and (13)C NMR spectra was performed for the cobalt and nickel complexes, and detailed electrochemical characterization was carried out to provide additional insight into the degree of communication between the meso-ferrocenyl groups on the conjugated macrocycle and the central metal ion of the ferrocenylcorrole derivatives.

Two synthetic routes have been defined for the preparation of a 5,10,15-triferrocenylcorrole Cu derivative. This complex has been characterized and the preliminary electrochemical investigation shows a strong interaction among the corrole and meso ferrocenyl substituents. The results obtained suggest that peculiar properties are gained by combining the eccentric characteristics of ferrocenyl substitution with the corrole macrocycle.

The phenyl-iron complex of 5,10,15-tritolylcorrole was prepared by reaction of the starting chloro-iron complex with phenylmagnesium bromide in dichloromethane. The organometallic complex was fully characterized by a combination of spectroscopic methods, X-ray crystallography, and density functional theory (DFT) calculations. All of these techniques support the description of the electronic structure of this phenyl-iron derivative as a low-spin iron(IV) coordinated to a closed-shell corrolate trianion and to a phenyl monoanion. Complete assignments of the (1)H and (13)C NMR spectra of the phenyl-iron derivative and the starting chloro-iron complex were performed on the basis of the NMR spectra of the regioselectively β-substituted bromo derivatives and the DFT calculations.

In this manuscript a multitechnique approach is proposed to characterize the interaction between new tri-N-methylpyridyl corrole (TMPC) and its germanium(IV) derivative (GeTMPC), with single- and double-stranded nucleic acid homopolymers and calf thymus DNA. The specificity of each spectroscopic technique has been exploited to analyze the different aspects of corrole binding. Noteworthy, this approach allows us to distinguish between H aggregation of TMPC in the presence of polyriboadenilic acid (poly(rA)) and J aggregates in the presence of polyribocytidinic acid (poly(rC)) as well as to identify the formation of GeTMPC dimers in the presence of single-stranded poly(rA) and pseudointercalation with single-stranded poly(rC).

5,10,15-Triaryltetrabenzocorrole complexes of aluminum, gallium, germanium, and phosphorus were synthesized by coordination of these metal ions in the preformed triaryltetrabenzocorrole macrocycle, opening a way to the investigation of different metal complexes. The UV-vis spectra of these derivatives exhibit a red shift and broadening of all absorption bands because of the π-extended aromatic system and distortion of the molecular framework. The electrochemical and photophysical behaviors of the free base and the metal complexes of meso-triaryltetrabenzocorrole were investigated and characterized.

Functionalization of the β-pyrrolic positions of the corrole macrocycle with -NO(2) groups is limited at present to metallocorrolates due to the instability exhibited by corrole free bases under oxidizing conditions. A careful choice of the oxidant can limit the transformation of corroles into decomposition products or isocorrole species, preserving the corrole aromaticity, and thus allowing the insertion of nitro groups onto the corrole framework. Here we report results obtained by reacting 5,10,15-tritolylcorrole (TTCorrH(3)) with the AgNO(2)/NaNO(2) system, to give mono- and dinitrocorrole derivatives when stoichiometry is carefully controlled. Reactions were found to be regioselective, affording the 3-NO(2)TTCorrH(3) and 3,17-(NO(2))(2)TTCorrH(3) isomers as the main products in the case of mono- and disubstitution, in 53 and 20% yields, respectively. In both cases, traces of other mono- and disubstituted isomers were detected, which were structurally characterized by X-ray crystallography. The influence of the β-nitro substituents on the corrole properties is studied in detail by UV-visible, electrochemical, and spectroelectrochemical characterization of these functionalized corroles. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations of the ground and excited state properties of these β-nitrocorrole derivatives also afforded significant information, closely matching the experimental observations. It is found that the β-NO(2) substituents conjugate with the π-aromatic system of the macrocycle, which initiates significant changes in both the spectroscopic and redox properties of the so functionalized corroles. This effect is more pronounced when the nitro group is introduced at the 2-position, because in this case the conjugation is, for steric reasons, more efficient than in the 3-nitro isomer.

Two different methods for the regioselective nitration of different meso-triarylcorroles leading to the corresponding β-substituted nitrocorrole iron complexes have been developed. A two-step procedure affords three Fe(III) nitrosyl products-the unsubstituted corrole, the 3-nitrocorrole, and the 3,17-dinitrocorrole. In contrast, a one-pot synthetic approach drives the reaction almost exclusively to formation of the iron nitrosyl 3,17-dinitrocorrole. Electron-releasing substituents on the meso-aryl groups of the triarylcorroles induce higher yields and longer reaction times than what is observed for the synthesis of similar triarylcorroles with electron-withdrawing functionalities, and these results can be confidently attributed to the facile formation and stabilization of an intermediate iron corrole π-cation radical. Electron-withdrawing substituents on the meso-aryl groups of triarylcorrole also seem to labilize the axial nitrosyl group which, in the case of the pentafluorophenylcorrole derivative, results in the direct formation of a disubstituted iron μ-oxo dimer complex. The influence of meso-aryl substituents on the progress and products of the nitration reaction was investigated. In addition, to elucidate the most important factors which influence the redox reactivity of these different iron nitrosyl complexes, selected compounds were examined by cyclic voltammetry and thin-layer UV-visible or FTIR spectroelectrochemistry in CH(2)Cl(2)., (© 2012 American Chemical Society)

Copper and germanium complexes of β-substituted nitrocorroles were reacted with 4-amino-4H-1,2,4-triazole to give the corresponding β-amino-β-nitro derivatives, in moderate to good yields. This is the first successful example of a vicarious nucleophilic substitution performed on corrole derivatives, because the same reaction carried out on silver complexes afforded the corresponding 6-azahemiporphycenes by way of corrole ring expansion. The first step of this work is related to the modification of a synthetic protocol for preparation of the β-substituted nitro corroles. The nitration reaction was carried out on a copper corrole using NaNO(2) as the primary source of NO(2)(-) coupled with AgNO(2) used as oxidant. By variation of the molar ratio of the reagents it was possible to direct the product distribution toward mono- and dinitro derivatives. The reaction between mono- and dinitro derivatives of (TtBuCorrCu) with 4-amino-4H-1,2,4-triazole gave good results, leading to the isolation of 2-(NH(2))-3-(NO(2))-TtBuCorrCu and 2,18-(NH(2))(2)-3,17-(NO(2))(2)-TtBuCorrCu in moderate yields. To elucidate factors that influence the reaction, and to highlight the different behavior observed for different metal complex substrates, the electrochemistry of three copper complexes, TtBuPCorrCu, (NO(2))TtBuPCorrCu, and (NO(2))(2)TtBuPCorrCu, was studied by cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry. The nitro groups on (NO(2))(x)TtBuPCorrCu are highly electron-withdrawing, which leads not only to a substantial positive shift of all redox potentials but also to a unique redox behavior and UV-vis spectrum of the singly reduced product as compared to the parent compound, TtBuPCorrCu. Finally, the amination reaction was carried out on a Ge(IV) nitrocorrolate, giving in good yield the 2-amino-3-nitroderivative, which was structurally characterized by single crystal X-ray crystallography.

Two different synthetic routes for the preparation of 5,10,15-triaryl-tetrabenzocorroles have been developed. The first approach is based on the condensation of a tetrahydroisoindole with aryl-aldehydes, and the second pathway involves a cross-coupling reaction between a bromo-substituted corrole and a suitable substrate to form the four β-fused aryl rings. These routes are successful to lead to the target tetrabenzocorroles, obtained in both cases as the corresponding Cu complex and with the highest yield obtained via the one-step cross-coupling methodology. Demetalation of the Cu-tetrabenzocorrole produces the corresponding free base; this macrocycle was further exploited to obtain the Sn and Co complexes in good yields.

Mono- and di-substituted β-nitro derivatives have been obtained from the reaction of ttcorrFeCl with sodium nitrite in refluxing DMF. This result is unprecedented for iron corrolates and further evidences the non-innocent character of the corrole ligand.

Bromination of 3-nitro-5,10,15-triarylcorrole selectively provides two regioisomers, depending on the reaction pathway. An isocorrole species is the key intermediate to drive the reaction towards the 2-Br-17-nitro regioisomer.

The reaction of 5,10,15-triarylcorrole with 4-amino-4H-1,2,4-triazole provides another example of corrole ring expansion to give the corresponding 6-azahemiporphycene, a novel porphyrin analogue. The facile oxidation of the corrole ring is a required step for the ring expansion and for this reason the reaction fails in the case of corroles bearing meso-phenyl groups carrying electron-withdrawing substituents. Steric requirements also limited the scope of the reaction, which is not successful in the case of 2,6-disubstituted meso-aryl corroles. The occurrence of an initial oxidation is further supported by formation of the 6-azahemiporphycene derivative when the reaction is carried out under the same conditions, using a 5- or a 10-isocorrole as starting material. (1)H NMR spectra and X-ray crystal characterization of 6-azahemiporphycene evidenced the presence of an intramolecular N-H...N hydrogen bond in the inner core of the macrocycle, while photophysical characterization confirmed the aromatic character of the novel macrocycle, showing an intense Soret-like band around 410 nm in the absorption spectrum. The fluorescence emission is very modest, and 6-azahemiporphycene showed higher photostability than the corresponding corrole species. Different metal complexes of 6-azahemiporphycene were prepared following synthetic protocols usually exploited for the preparation of metalloporphyrins, demonstrating good coordination properties for the macrocycle. Both the free-base and metal derivatives were characterized by cyclic voltammetry and spectroelectrochemistry in dichloromethane and benzonitrile. To further detail the behavior of this novel macrocycle, density functional theory (DFT) calculations were carried out on the basic structure of 6-azahemiporphycene with the aim of assessing aromaticity and tautomerism, as well as calculating its stability with respect to the 5-aza isomer.

Several procedures for the demetalation of silver(III) corrolates have been tested. Acidic conditions induce removal of the silver ion but they can also promote concomitant oxidation of the corrole nucleus to an isocorrole species, the degree of which will depend upon the specific acidic media. This oxidation cannot be completely avoided by addition of hydrazine, particularly in the case of 3-NO(2) substituted complexes which are quantitatively converted into the corresponding 3-NO(2), 5-hydroxy isocorroles upon silver ion removal. Several beta-nitro isocorrole products were isolated, and one was structurally characterized. Electrochemical and chemical reductive methods for silver(III) corrolates demetalation were then tested with the aim to avoid the formation of isocorroles. While reaction with sodium borohydride was shown to be quite effective to demetalate unsubstituted silver corrolates this was not the case for the beta-nitro derivatives where the peripheral nitro group is reduced by borohydride giving the corresponding 3-amino free base corrole species. For the beta-nitro corrole silver complexes, a successful approach was obtained using DBU/THF solutions which afforded the 3-NO(2) corrole free-base compound as a single reaction product in good yield. These conditions were also effective for unsubstituted corroles although longer reaction times were necessary in this case. To study in greater detail the corrole demetalation behavior, selected Ag(III) derivatives were characterized by cyclic voltammetry in pyridine, and the demetalation products spectrally characterized after controlled potential reduction in a thin-layer spectroelectrochemical cell.

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.

Deposition of amphiphilic porphyrin derivatives occurs spontaneously on silanised glass surfaces, in a controlled fashion. The resulting porphyrin films show appreciable fluorescence emission. This emission can be effectively quenched by immersion of the slides into a diluted solution of Hg(2+) (microM concentration). The initial intensity can be restored by washings with a solution of N,N,N',N'-tetrakis(2-pyridilmethyl)ethylenediammine with no loss of efficiency. A remarkable selectivity is featured toward the detection of Hg(2+) over Cu(2+), Cd(2+), Pb(2+) and Zn(2+) counterparts. This protocol can be extended to a flow-through apparatus. The presented results are of importance for the achievement of a solid-state chemosensor for mercuric ions, at micromolar concentration, in water.

The structures, electron configurations, magnetic susceptibilities, spectroscopic properties, molecular orbital energies and spin density distributions, redox properties and reactivities of iron corrolates having chloride, phenyl, pyridine, NO and other ligands are reviewed. It is shown that with one very strong donor ligand such as phenyl anion the electron configuration of the metal is d(4)S=1 Fe(IV) coordinated to a (corrolate)(3-) anion, while with one weaker donor ligand such as chloride or other halide, the electron configuration is d(5)S=3/2 Fe(III) coordinated to a (corrolate)(2-.) pi-cation radical, with antiferromagnetic coupling between the metal and corrolate radical electron. Many of these complexes have been studied by electrochemical techniques and have rich redox reactivity, in most cases involving two 1-electron oxidations and two 1-electron reductions, and it is not possible to tell, from the shapes of cyclic voltammetric waves, whether the electron is added or removed from the metal or the macrocycle; often infrared, UV-Vis, or EPR spectroscopy can provide this information. (1)H and (13)C NMR spectroscopic methods are most useful in delineating the spin state and pattern of spin density distribution of the complexes listed above, as would also be expected to be the case for the recently-reported formal Fe(V)O corrolate, if this complex were stable enough for characterization by NMR spectroscopy. Iron, manganese and chromium corrolates can be oxidized by iodosylbenzene and other common oxidants used previously with metalloporphyrinates to effect efficient oxidation of substrates. Whether the "resting state" form of these complexes, most generally in the case of iron [FeCl(Corr)], actually has the electron configuration Fe(IV)(Corr)(3-) or Fe(III)(Corr)(2-.) is not relevant to the high-valent reactivity of the complex.

Thin films consisting of a fulleropyrrolidine derivative 1 and a novel water-soluble porphyrin 2 were prepared by the Langmuir-Shäfer (LS, horizontal lifting) method. In particular, a solution of 1 in 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 pi 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.

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.

Reflectance anisotropy spectroscopy (RAS) has been largely used to investigate organic compounds: Langmuir–Blodgett and Langmuir–Schaeffer layers, the organic molecular beam epitaxy growth in situ and in real time, thin and ultrathin organic films exposed to volatiles, in ultra-high vacuum (UHV), in controlled atmosphere and even in liquid. In all these cases, porphyrins and porphyrin-related compounds have often been used, taking advantage of the peculiar characteristics of RAS with respect to other techniques. The technical modification of a RAS spectrometer (CD-RAS: circular dichroism RAS) allows us to investigate the circular dichroism of samples instead of the normally studied linear dichroism: CD-RAS measures (in transmission mode) the anisotropy of the optical properties of a sample under right and left circularly polarized light. Although commercial spectrometers exist to measure the circular dichroism of substances, the "open structure" of this new spectrometer and its higher flexibility in design makes it possible to couple it with UHV systems or other experimental configurations. The importance of chirality in the development of organic materials (from solutions to the solid state, as thin layers deposited—in liquid or in vacuum—on transparent substrates) could open interesting possibilities to a development in the investigation of the chirality of organic and biological layers. In this manuscript, after the detailed explanation of the CD-RAS technique, some calibration tests with chiral porphyrin assemblies in solution or deposited in solid film are reported to demonstrate the quality of the results, comparing curves obtained with CD-RAS and a commercial spectrometer. [ABSTRACT FROM AUTHOR]

A porphyrin derivative functionalized with the L-enantiomer of proline amino acid was characterized at the air–pure water interface of the Langmuir trough. The porphyrin derivative was dissolved in dichloromethane solution, spread at the air–subphase interface and investigated by acquiring the surface pressure vs. area per molecule Langmuir curves. It is worth observing that the behavior of the molecules of the porphyrin derivative floating film was substantially influenced by the presence of L-proline amino acid dissolved in the subphase (10−5 M); on the contrary, the physical chemical features of the floating molecules were only slightly influenced by the D-proline dissolved in the subphase. Such an interesting chirality-driven selection was preserved when the floating film was transferred onto solid supports by means of the Langmuir–Schaefer method, but it did not emerge when a spin-coating technique was used for the layering of the tetrapyrrolic derivatives. The obtained results represent proof of concept for the realization of active molecular layers for chiral discrimination: porphyrin derivatives, due to their intriguing spectroscopic and supramolecular properties, can be functionalized with the chiral molecule that should be detected. Moreover, the results emphasize the crucial role of the deposition technique on the features of the sensing layers. [ABSTRACT FROM AUTHOR]

The development of chemical sensors is an urgent need for both environmental and health issues. The breakthrough needed for the advancement of these devices is the development of efficient receptors. Porphyrins have been widely used as sensing layers in chemical sensors, but their integration with nanostructures can greatly boost the performance of these macrocycles, improving from one side the stability of the sensing layer, and from the other, offering additional interaction mechanisms with target analytes. We present here some recent examples of hybrid materials prepared by the integration of porphyrins with metal and metal oxide nanoparticles, porphyrin-based metal organic frameworks and their exploitation as sensing layers in chemical sensors. [ABSTRACT FROM AUTHOR]

The coupling of semiconductors with organic molecules results in a class of sensors whose chemoresistive properties are dictated by the nature of dyes. Organic molecules generally reduce conductivity, but in the case of optically active dyes, such as porphyrinoids, the conductivity is restored by illumination with visible light. In this paper, we investigated the gas sensing properties of ZnO nanoparticles coated with porphyrins and corroles. Under light illumination, the resistance of these materials increases with the adsorption of volatile compounds but decreases when these are strong electron donors. The behavior of these sensors can be explicated on the basis of the structural difference between free-base porphyrin and corrole, the influence of coordinated metal, and the corresponding electronic structures. These sensors are promising electronic noses that combine the selectivity to strong electron donors with the broad selectivity toward the other classes of chemicals. An efficient representation of the data of this peculiar array can be obtained by replacing the Euclidean distance with the angular distance. To this end, a recently introduced spherical principal component analysis algorithm is applied for the first time to gas sensor array data. Results show that a minimal gas sensor array (four elements) can produce a sort of chemotopic map, which enables us to cluster a very large class of pure chemical vapors. Furthermore, this map provides information about the composition of complex odor matrices, such as the headspaces of beef meat and their evolution over the time. [ABSTRACT FROM AUTHOR]

Two synthetic routes for the preparation of the water soluble 5,10,15‐tris(4‐sulfonatophenyl)corrole are reported. The first approach explores the chlorosulfonation reaction on the phosphorus complex of 5,10,15‐tris(4‐trimethylsilylphenyl)corrole. Following this route, the P complex of the target corrole has been obtained in low yields, while the major product was the tetrasubstituted complex, with the additional sulfonyl group regioselectively introduced at the 2‐position. To widen the scope of the reaction, the direct preparation of the 5,10,15‐tris(4‐sulfonatophenyl)corrole has been pointed out, affording both the target corrole and the intermediate chlorosulfonyl derivative in reasonable yields. The photophysical properties and the protonation equilibria of both corroles have been investigated, showing that 5,10,15‐tris(4‐sulfonatophenyl)corrole does not aggregate in acidic solutions, different from the analogous porphyrin. [ABSTRACT FROM AUTHOR]

A diminoisoindoline‐tetraphenylporphyrin (as Zn complex) unit has been used as building block for the preparation of a tetraphenylporphyrin‐1,3‐bis(2‐pyridylimino)isoindoline conjugate (3). The chelating system of this molecule possesses two different binding centers. The optimization of the synthetic procedure allowed to obtain the ZnTPP‐BPI moiety in very good yields, the structure of which was identified by means of UV/Vis, NMR, mass and X‐ray methods. The Zn‐porphyrin complex was then subject to Zn ion removal from the porphyrin core, allowing the isolation of the corresponding free base derivative. The optical features of the compound are very interesting, as expected from the fusion of two chromophores active in the UV and visible regions of the optical spectrum; this has also been confirmed by testing ZnTPP‐BPI (3) as chemosensor for metal cations detection. Grab the ions: a fused porphyrin‐bis(2‐pyridylimino)isoindole system has been reported for the first time. The external binding unit is able to interact with cations in solution, allowing the optical detection of some metals. [ABSTRACT FROM AUTHOR]

The reported studies deal with the synthesis of porphyrin chemosensor 2, designed for the detection of the emerging pollutant diclofenac. Owing to the peculiar structure of its molecular frame, which is composed of a tetrapyrrolic platform linked to a rhodamine B residue, receptor 2 reversibly interacts with diclofenac sodium salt (DCF)Na. The resulting 2@DCF adduct was detected by UV-Vis spectroscopy in a large pH range (5.5–9.0) as well as in the presence of competitive analytes. Both static and time-resolved fluorescence, resonance light scattering (RLS) and UV-Vis spectroscopies allowed for the evaluation of the binding behaviour, in terms of the association constant and structural features of the formed 2@DCF. In particular, the host–guest recognition event occurs with the growth of large porphyrin aggregates, as stated by the quenching of the fluorescence emission as well as the enhancement of RLS intensities, and with an overall 1 : 1 binding constant of about 105 M−1. [ABSTRACT FROM AUTHOR]

Pheromones are known to play an important role in butterfly courtship and may influence both individual reproductive success and reproductive isolation between species. Recent studies have focused on courtship in Hipparchia butterflies (Nymphalidae: Satyrinae) emphasizing morphological and behavioural traits, as well as genetic differences. Behavioural observations suggested a role for chemical cues in mate and species recognition, where the androconial scales on the forewings of these species may be involved in chemical communication between individuals. Cchemical-mediated signals have received relatively little attention in this genus. Here, we report the results of a three-year investigation of the volatile organic compounds (VOCs) released by Hipparchia fagi and H. hermione in order to identify differences in VOCs between these species where they live in syntopy. Our study was carried out using an array of cross-selective sensors known as an "Electronic Nose" (EN) that operates by converting chemical patterns into patterns of sensor signals. While the identity of volatile compounds remained unknown, sensor signals can be compared to identify similar or dissimilar chemical patterns. Based on the EN signals, our results showed that: 1) the two sexes have a similar VOCs pattern in H. fagi, while they significantly diverge in H. hermione; 2) VOCs patterns were different between females of the two species, while those of males were not. [ABSTRACT FROM AUTHOR]

Chemoresistors working at room temperature are attractive for low-consumption integrated sensors. Previous studies show that this feature can be obtained with photoconductive porphyrins-coated ZnO nanostructures. Furthermore, variations of the porphyrin molecular structure alter both the chemical sensitivity and the photoconductivity, and can be used to define the sensor characteristics. Based on these assumptions, we investigated the properties of an array of four sensors made of a layer of ZnO nanoparticles coated with porphyrins with the same molecular framework but different metal atoms. The array was tested with five volatile organic compounds (VOCs), each measured at different concentrations. Results confirm that the features of individual porphyrins influence the sensor behavior, and the differences among sensors are enough to enable the discrimination of volatile compounds disregarding their concentration. [ABSTRACT FROM AUTHOR]

A diiminoisoindolo-pyrazino unit was annulated to the β-pyrrolic position of the Zn complex of tetraphenylporphyrin, giving a macrocycle with an expanded π system in satisfactory yields. The crystal structure of this derivative evidenced the formation of a hydrogen bond network. The interaction of the β-fused isoindoline porphyrin derivative with nucleotides and nucleic acids has been investigated. [ABSTRACT FROM AUTHOR]

The association between volatile compounds (VCs) and microorganisms, as demonstrated by several studies, may offer the ground for a rapid identification of pathogens. To this regard, chemical sensors are a key enabling technology for the exploitation of this opportunity. In this study, we investigated the performance of an array of porphyrin-coated quartz microbalance gas sensors in the identification of a panel of 12 bacteria and fungi. The porphyrins were metal complexes and the free base of a functionalized tetraphenylporphyrin. Our results show that the sensor array distinguishes the VC patterns produced by microorganisms in vitro. Besides being individually identified, bacteria are also sorted into Gram-positive and Gram-negative. [ABSTRACT FROM AUTHOR]

Porphyrins provide an excellent material for chemical sensors, and they have been used for sensing species both in air and solution. In the gas phase, the broad selectivity of porphyrins is largely dependant on molecular features, such as the metal ion complexed at the core of the aromatic ring and the peripheral substituents. Although these features have been largely exploited to design gas sensor arrays, so far, little attention has been devoted to modify the sensing properties of these macrocycles by variation of the molecular aromatic ring. In this paper, the gas sensing properties of a porphyrin analog, the corrole, are studied in comparison with those of the parent porphyrin. Results show that changes in the aromatic ring have important consequences on the sensitivity and selectivity of the sensors and that porphyrins and corroles can positively cooperate to enhance the performance of sensor arrays. [ABSTRACT FROM AUTHOR]