Nuno M. M. Moura

Synthesis, Spectroscopy Studies, and Theoretical Calculations of New Fluorescent Probes Based on Pyrazole Containing Porphyrins for Zn(II), Cd(II), and Hg(II) Optical Detection

New pyrazole-porphyrin conjugates were successfully prepared from a reaction of β-porphyrin-chalcone derivatives with phenylhydrazine in acetic acid followed by an oxidative step. This fast and efficient synthetic approach provided the expected compounds in yields up to 82%. The sensing ability of the new porphyrin-pyrazole derivatives to detect the metal ions Ag(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Cr(3+) was studied by spectrophotometric and spectrofluorimetric titrations. In the presence of Zn(2+), the conjugates exhibit changes in the emission spectra that are desired for a ratiometric-type fluoroionophoric detection probe. The studies were extended to gas phase, where the pyrazole-porphyrin conjugates show ability to sense metal ions with high selectivity toward Cu(2+) and Ag(+), and in poly(methyl methacrylate) doped films with promising results for Zn(2+) detection.

A New 3,5-Bisporphyrinylpyridine Derivative as a Fluorescent Ratiometric Probe for Zinc Ions

A new 3,5-disubstituted pyridine with two porphyrin moieties was prepared through an efficient synthetic approach involving 2-formyl-5,10,15,20-tetraphenylporphyrin (1), piperidine, and catalytic amounts of [La(OTf)3]. 3,5-Bis(5,10,15,20-tetraphenylporphyrin-2-ylmethyl)pyridine (2) was fully characterized and its sensing ability towards Zn(2+), Cu(2+), Hg(2+), Cd(2+), and Ag(+) was evaluated in solution by absorption and fluorescence spectroscopy and in gas phase by using matrix-assisted laser desorption/ionization (MALDI)-TOF mass spectrometry. Strong changes in the ground and excited state were detected in the case of the soft metal ions Zn(2+), Cd(2+), Hg(2+), and Cu(2+). A three-metal-per-ligand molar ratio was obtained in all cases and a significant ratiometric behavior was observed in the presence of Zn(2+) with the appearance of a new band at 608 nm, which can be assigned to a metal-to-ligand charge transfer. The system was able to quantify 79 ppb of Zn(2+) and the theoretical calculations are in accordance with the stoichiometry observed in solution. The gas-phase sensorial ability of compound 2 towards all metal ions was confirmed by using MALDI-TOF MS and in solid state by using polymeric films of polymethylmethacrylate (PMMA) doped with ligand 2. The results showed that compound 2 can be analytically used to develop new colorimetric molecular devices that are able to discriminate between Hg(2+) and Zn(2+) in solid phase. The crystal structure of Zn(II) complex of 3,5-bisporphyrinylpyridine was unequivocally elucidated by using single-crystal X-ray diffraction studies.

Preparation and ion recognition features of porphyrin–chalcone type compounds as efficient red-fluorescent materials

A series of porphyrins containing an α,β-unsaturated ketone unit in a β-pyrrolic position (4a–e) were synthesized and characterized. Their sensing ability towards Ag+, Cu2+, Zn2+, Cd2+, and Hg2+ was evaluated in solution by absorption and fluorescence spectroscopy and in the gas phase using MALDI-TOF-MS spectrometry. The versatility of these types of compounds towards other metals was also analysed by studying the behaviour of compound 4d in the presence of Na+, K+, Tl+, Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Pb2+, Fe2+, Fe3+, Cr3+ and Al3+. Polymeric films of polymethylmethacrylate (PMMA) doped with ligand 4d were prepared and their ability to be used as metal ion-probes in the solid state was studied. Compounds of type 4 showed the best performance to be analytically used in developing new Zn2+ ratiometric molecular devices.

Vilsmeier-Haack formylation of Cu(II) and Ni(II) porphyrin complexes under microwaves irradiation

Microwave irradiation is a powerful tool in organic synthesis allowing for instance, to reduce reaction times and to obtain the desired products in better yields. Contrary to what is reported in literature, the first Vilsmeier-Haack formylation of Ni(II) and Cu(II) complexes of meso-tetraarylporphyrins by using microwave irradiation is described here. Different solvents, irradiation powers and reaction times were studied using the Ni(II) and Cu(II) complexes of 5,10,15,20-tetraphenylporphyrin and the best found conditions were extended to a series of other meso-substituted tetraarylporphyrins. The products, namely the new ones were isolated in good to excellent yields and with a significant reduction on the reaction times. Scaled-up studies have shown that the efficiency of the process is not affected by increasing the amount of porphyrin.

New Hybrid Adsorbent Based on Porphyrin Functionalized Silica for Heavy Metals Removal: Synthesis, Characterization, Isotherms, Kinetics and Thermodynamics Studies

The pollution of water resources due to the disposal of toxic heavy metals has been a growing global concern for the last decades. For this purpose, the search for effective and economic material based adsorbents is required, due to the efficiency of the process. In this work, a novel inorganic-organic hybrid material based on silica chemically modified with a porphyrin (SiNTPP), with a high metal removal efficiency, was developed. The new material was characterized using a set of suitable techniques such as 13C NMR of the solid state, elemental analysis, FTIR, nitrogen adsorption-desorption isotherm, BET surface area, BJH pore sizes and scanning electron microscopy (SEM). The new material surface exhibits good chemical and thermal stability based on the obtained thermogravimetric curves (TGA). An adsorption study was accomplished to investigate the effect of porphyrin-silica hybrid on the removal of Pb(II), Zn(II), Cd(II) and Cu(II) from aqueous solutions using a batch method. The effect of various parameters, such as initial metal concentration, pH, temperature, as well as the kinetics and thermodynamics for sorption on SiNTPP were investigated. The studies demonstrate that adsorption is fast, as proved by the equilibrium achievement within 25min. The metals removal from aqueous solution are better adapted to the Langmuir isotherm model than to the Freundlich model. The thermodynamic parameters (ΔG°, ΔH° and ΔS°) disclose that the process was endothermic and spontaneous in nature, and the adsorption process follows a pseudo-second order kinetics. The adsorbent can be regenerated continuously without affecting its extraction percentage. Its effectiveness is highly justified compared to previous described materials.

β-Formyl- and β-Vinylporphyrins: Magic Building Blocks for Novel Porphyrin Derivatives

Porphyrins bearing formyl or vinyl groups have been explored as starting materials to prepare new compounds with adequate features for different applications. In this review it is discussed mainly synthetic strategies based on the reaction of meso-tetraarylporphyrins bearing those groups at β-pyrrolic positions. The use of some of the obtained porphyrin derivatives for further transformations, namely via pericyclic reactions, is also highlighted.

Synthesis, characterization and biological evaluation of cationic porphyrin–terpyridine derivatives

A simple access to a new series of cationic porphyrin–terpyridine derivatives is described. The key step to obtain the required neutral precursors as major products involved a Krohnke type approach. The methodology allowed also the isolation of the respective benzoporphyrins and porphyrin–chalcone type derivatives, and in one case a new 2-(2,4-terpyridin-6-yl)-porphyrin. The quaternization of the pyridyl groups was performed in the presence of the adequate alkyl iodide affording the dicationic derivatives in excellent yields. All the new conjugates were fully characterised and it was found that the cationic isomers can be efficiently differentiated by ESI-MS, as their behaviour can be intensively studied by mass spectrometry. The new methylated cationic porphyrin–terpyridine derivatives demonstrate an ability to generate singlet oxygen and their efficacy to photoinactivate bioluminescent Gram-negative E. coli was evaluated. A reduction in the bioluminescence signal, up to 5.4 log, was obtained with the most efficient photosensitiser.

Synthetic access to new porphyrinoids from 2-nitro-5,10,15,20-tetraphenylporphyrin and an arylacetonitrile

In this work, the reactivity of 2-nitro-5,10,15,20-tetraphenylporphyrin with 2-(4-nitrophenyl)acetonitrile in the presence of KOH as base was studied. Under these conditions, three new compounds were isolated: a β-di-substituted derivative, as the major compound, accompanied by two minor products, a π-extended and a β-isoxazoline-fused derivative, all in acceptable yields. A preliminary study was also performed in the presence of K2CO3. It allowed the isolation of a cyclopropyl-annulated chlorin in very good yield. All the obtained products were photochemically and photophysically characterized, some of them showing promising properties to be used as photosensitizers in photodynamic processes.Graphical abstract

N-Confused Porphyrin Immobilized on Solid Supports: Synthesis and Metal Ions Sensing Efficacy

In this work, the N-confused porphyrin 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrin (NCTPP) was immobilized on neutral or cationic supports based on silica and on Merrifield resin. The new materials were characterized by appropriate techniques (UV-Vis spectroscopy, SEM, and zeta potential analysis). Piezoelectric quartz crystal gold electrodes were coated with the different hybrids and their ability to interact with heavy metals was evaluated. The preliminary results obtained showed that the new materials can be explored for metal cations detection and the modification of the material surface is a key factor in tuning the metal selectivity.

Porphyrin-Oligopyridine Triads: Synthesis and Optical Properties

The synthesis of two triads with two porphyrinyl units linked by oligopyridine derivatives and a new β-functionalized porphyrin-dihydroazepine is described. One of the porphyrin-oligopyridine triads has a quinquepyridine unit connecting the porphyrins β-pyrrolic positions, while the other one has an asymmetric quaterpyridine with one of the pyridines fused to the porphyrin. All compounds have fluorescence emission quantum yields in the range of meso-tetraphenylporphyrin (16-22%).