Corroles as receptors in liquid membrane electrodes and their potentiometric response towards salicylic acid

Corroles at work: a small macrocycle for great applications

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.

Porphyrinoids for Chemical Sensor Applications

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

Combined MCD/DFT/TDDFT Study of the Electronic Structure of Axially Pyridine Coordinated Metallocorroles

A series of metallocorroles were investigated by UV-vis and magnetic circular dichroism spectroscopies. The diamagnetic distorted square-pyramidal main-group corrole Ga(tpfc)py (2), the diamagnetic distorted octahedral transition-metal adduct Co(tpfc)(py)2 (3), and paramagnetic distorted octahedral transition-metal complex Fe(tpfc)(py)2 (4) [H3tpfc = tris(perfluorophenyl)corrole] were studied to investigate similarities and differences in the electronic structure and spectroscopy of the closed- and open-shell metallocorroles. Similar to the free-base H3tpfc (1), inspection of the MCD Faraday B-terms for all of the macrocycles presented in this report revealed that a ΔHOMO < ΔLUMO [ΔHOMO is the energy difference between two highest energy corrole-centered π-orbitals and ΔLUMO is the energy difference between two lowest energy corrole-centered π*-orbitals originating from ML ± 4 and ML ± 5 pairs of perimeter] condition is present for each complex, which results in an unusual sign-reversed sequence for π-π* transitions in their MCD spectra. In addition, the MCD spectra of the cobalt and the iron complexes were also complicated by a number of charge-transfer states in the visible region. Iron complex 4 also exhibits a low-energy absorption in the NIR region (1023 nm). DFT and TDDFT calculations were used to elaborate the electronic structures and provide band assignments in UV-vis and MCD spectra of the metallocorroles. DFT and TDDFT calculations predict that the orientation of the axial pyridine ligand(s) has a very minor influence on the calculated electronic structures and absorption spectra in the target systems.

Application of metalloporphyrin grafted-graphene oxide for the construction of a novel salicylate-selective electrode

Due to the vast applications of salicylate ion, development of a simple and selective procedure for its determination is of practical interest. Herein, the unique properties of graphene oxide are combined with the anion selectivity of metalloporphyrins to construct a novel salicylate selective electrode. This electrode is prepared by incorporating Cu(II)–5-4 (aminophenyl)-10,15,20-triphenyl porphyrin grafted-grapheneoxide (CuTPP-GO) into the plasticized poly (vinyl chloride) membrane. Effects of plasticizer nature, Cu TPP-GO concentration and anionic and cationic additives on the potential response of the electrode are investigated. The electrode with the membrane composition of 25% PVC, 50% NPOE, 5% NaTPB and 20% Cu TPP-GO provided the best behavior. This sensor shows a Nernstian response (57.8 mV.decade-1) in the concentration range of 5.0 × 10-1–5.0 × 10-7M with detection limit of 8.0 × 10-8M. sensor response is stable in the pH range of 5–7 and shows a discriminating ability for salicylate compared to most common anions. The sensor was successfully used for determination of salicylate in an aspirin tablet.

Recent advances in the functionalization of meso-triarylcorroles via cycloaddition reactions

With reference to the Portugal-Spain Special Issue of the Journal of Porphyrins and Phthalocyanines, this highlight is mainly concerned with the contribution by the University of Aveiro group on the functionalization of the β-pyrrolic positions of triarylcorroles via cycloaddition reactions.

Structure-function relationship in antimony corrole photosensitizers: Time-resolved electron paramagnetic resonance and optical study

Three photosensitizers based on tris-(pentafluorophenyl)antimony corroles that differ in oxidation state and axial ligands, namely, (pyridine) Sb (III)-, (oxo) Sb (V)- and (difluoro) Sb (V) complexes, were studied by time-resolved electron paramagnetic resonance spectroscopy and laser flash photolysis. The magnetic and orientational parameters of the corroles oriented in a nematic liquid crystal as well as their triplet lifetimes in liquid toluene were determined and interpreted in terms of their structure and geometry. The negative zero-field splitting parameter D assigned to all studied corroles is explained by the asymmetric π-electron withdrawal effect caused by perfluorinated peripheral aryl groups, which force the triplet electron spins to align in head-to-tail configuration. The effect of the axial ligands on the photoexcited triplet state properties of the corroles is correlated with their different efficiency to perform photoassisted aerobic oxygenation of some organic molecules. This is explained by the dependence of the main parameters of the photoexcited complexes on the interaction between the central ion and corrole π-system. This interaction is strongly influenced by axial ligands coordination, affecting the macrocycle symmetry, planarity, and rigidity.

Corrole-based ion-selective electrodes

Different corrole derivatives have been exploited as ionophores for the development of ion-selective electrodes (ISEs). The compounds used are free-base 5,10,15-triphenylcorrole, the corresponding Mn and Fe chloride complexes, the Cu complex of 5,10,15-tris(4-tert-butylphenyl)-corrole and the Fe chloride complex of 2,3,17,18-tetraethyl,7,8,12,13-tetramethylcorrole. Corroles have been dispersed in the polyvinyl chloride polymeric matrix and different plasticizers have been used for the preparation of selective membranes. The developed ISEs have been tested for the detection of model analytes and the working mechanism has been investigated in detail. In the case of free-base corrole, the results showed that it is difficult to obtain high selective ISEs, due to the macrocycle high sensitivity to the background solution pH. On the other hand, Mn derivative are shown to be highly selective for chloride ion detection, with performances superior to the corresponding Mn porphyrin-based ISEs. Finally both Cu and Fe derivatives are very promising ionophores for the detection of hydrophilic anions, such as carbonate and monohydrogen phosphate ion.

Corrole-based applications

Despite of the many similarities between corroles and porphyrins, the chemistry of the former remained undeveloped for decades because of severe synthetic obstacles. The recent discoveries of facile methodologies for the synthesis of triarylcorroles and the corresponding metal complexes allowed for their utilization in various fields. This survey reveals many examples where corroles were used as the key components in catalysis, sensing of gaseous molecules and medicine-oriented research. The focus in all these cases was on the special features of corroles: stabilization of high valent transition metal ions, unique photophysical properties, large NH acidity, facile synthetic manipulation and distinct catalytic properties. The latter aspect includes several examples of reactions that are not catalyzed by any non-corrole metal complex, such as the iron-based aziridination by Chloramine-T, the clean disproportionation of peroxynitrite, and the very facile N-H activation of amines.