Abilio J. F. N. Sobral

One-step synthesis of dipyrromethanes in water

In this communication we describe the first results of an efficient synthesis of β-free-dipyrromethanes in water. This new method affords very pure products in moderate to high yields, using a cheap, non-toxic, environment friendly solvent, in a one-step procedure from pyrrole and carbonyl compounds, needing little or no work up procedures.

Porphyrins as nanoreactors in the carbon dioxide capture and conversion: a review

On account of their unique properties and robust structures, porphyrins are natures favorite catalysts. Porphyrins have attracted the attention of researchers for many decades as a result of their intense colors; but in recent years, interest in these molecules has sharply increased, due to their potential use in solving difficult problems in the fields of medicine and environmental protection. Much attention is currently focused on the development of materials for the capture and conversion of CO2 into value-added products, and porphyrins are proving to be of interest in this area of research. Porphyrins were previously thought to be poorly-absorbant materials, as they are generally planar compounds. However, the development of new, efficient porphyrin-based materials and reliable synthetic routes for porphyrin-based nanoreactors, such as covalent–organic frameworks and metal–organic frameworks, for use as porous materials has helped to overcome the underlying challenges in CO2 reactivity. Porphyrin-based materials that behave as nanoreactors are promising candidates in the capture and conversion of CO2 as a result of the presence of the basic pyrrole structure that contains a macrocyclic cavity and large aromatic rings, which facilitate strong interactions with CO2. This review provides an overview of progress in the area of CO2 capture and conversion using porphyrin-based molecular materials and nanoreactors. These materials have important structural features in terms of surface area, porosity, CO2 uptake and the possibility of the catalytic conversion of CO2 to chemically valuable products.

Metal-assisted reactions. Part 22. Synthesis of perhalogenated prophyrins and their use as oxidation catalysts

Abstract Meso-tetrakisarylporphyrins have been perchlorinated and perbrominated at peripheral (β)-positions of the pyrrole rings by high-yielding procedures. These halogenated porphyrins show enhanced catalytic activity towards oxidation of alkanes and alkenes but are not stable when hydrogen peroxide is used as the oxygen donor. The reason for this instability appears to lie in excessive homolytic dissociation of H 2 O 2 with consequent rapid attack at the porphyrin β-position.

An investigation of the optical properties of tetraphenylporphyrin derivatives in Langmuir and Langmuir-Blodgett films

Abstract The optical properties of two tetraphenylporphyrin derivatives based on tetra(4-aminosulphonyl) phenylporphyrin have been examined. These porphyrins can exist in both free-base and dication states with their Soret absorption band occurring near 420 and 440 nm respectively. Floating monolayers can show the occurence of a new state characterized by two additional bands near 490 and 700 nm. The formation of this unknown state is dependent on both the subphase pH and the area occupied per monomer unit at the air-water interface. The effect of the subphase pH on the production of this state has been investigated systematically for both porphyrins and comparisons between the two habe been made. The optical absorption of Langmuir-Blodgett films for one of the porphyrins has also been examined. This has shown that the unknown state can be transferred on to glass substrates, though it is found not to be stable if stored in air.

Conformational studies of poly(9,9-dialkylfluorene)s in solution using NMR spectroscopy and density functional theory calculations.

Relationships have been obtained between intermonomer torsional angle and NMR chemical shifts ((1)H and (13)C) for isolated chains of two of the most important poly(9,9-dialkylfluorenes), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6) and the copolymer poly(9,9-dioctylfluorene-co-[2,1,3]benzothiadiazole-4,7-diyl) (F8BT), using DFT calculations. The correlations provide a model for NMR spectral data interpretation and the basis for analysis of conformational changes in poly(9,9-dialkylfluorene-2,7-diyl)s. The correlations obtained for PF2/6 indicate that the (13)C chemical shifts of the aromatic carbons close to the intermonomer connection (C1, C2, and C3) have minimum values at planar conformations (0 degrees and 180 degrees ) and maximum values at 90 degrees conformations. In contrast, the (1)H chemical shifts of the corresponding aromatic ortho protons (Ha and Hb) are greatest for planar conformations, and the minimum values are seen for 90 degrees conformations. For the F8BT copolymer, similar relationships are observed for the (1)H (Ha, Hb, and Hc) aromatic shifts. Considering the aromatic carbons of F8BT, the behavior of C2, C4, C5, and C6 is similar to that found for the PF2/6 carbons. However, C1 and C3 of the fluorene moiety behave differently with varying torsion angle. These are in close proximity to the fluorene-benzothiadiazole linkage and are markedly affected by interactions with the thiadiazole unit such that delta(C1) is a maximum for 180 degrees and a minimum for 0 degrees , whereas delta(C3) is a maximum for 0 degrees and minimum for 180 degrees. We have studied the (1)H and (13)C spectra of the two polymers at temperatures between -50 degrees C and +65 degrees C. The observed changes to higher or lower frequency in the aromatic resonances were analyzed using these theoretical relationships. Fluorescence studies on PF2/6 in chloroform solution suggest there are no significant interchain interactions under these conditions. This is supported by variable-temperature NMR results. Polymer-solvent and polymer intramolecular interactions were found to be present and influence all of the alkylic and one of the aromatic (1)H resonances (Hb). The detailed attribution of the (1)H and (13)C NMR spectra of the two polymers was made prior to the establishment of the relationships between torsion angle and NMR chemical shifts. This was carried out through DFT calculation of the (1)H and (13)C shielding constants of the monomers, coupled with distortionless enhancement by polarization transfer and heteronuclear correlation NMR spectra. Several DFT levels of calculation were tested for both optimization of structures and shielding constants calculation. The B3LYP/6-31G(d,p) method was found to perform well in both cases.

Chlorine sensing properties of porphyrin thin films

Abstract This work describes the influence of gaseous chlorine on thin porphyrin films. LB films of metal and free base porphyrins based on meso-tetra (4-amino sulfonyl) phenylporphyrin [1]exhibit intense optical absorption bands in the region 400–700 nm. The change in the molecular environment of the porphyrin which arises as a result of exposure to the sensor gas is reflected in substantial changes to the optical absorption spectrum. This effect is reversible in the absence of the sensor gas. In-situ optical measurements have been performed to quantify the response of the films in a stream of gas of specified concentration and their subsequent recovery in air. Factors affecting the response such as choice of porphyrin, orientation of porphyrin molecules within the LB film, concentration of sensor gas and temperature have been studied.

Interactions of Copper (II) Chloride with β‐Cyclodextrin in Aqueous Solutions

The interaction between copper (II) chloride and the carbohydrate β‐cyclodextrin (β‐CD) has been studied in aqueous solutions (298.15 K and 310.15 K) using measurements of diffusion coefficients and electrical conductivity. Significant effects on the electrical conductivity were observed in the presence of the β‐CD, suggesting interactions between this carbohydrate and copper chloride. Support for this came from diffusion coefficient measurements. These studies have been complemented by molecular mechanics calculations.

Optical response of monolayer films of a metal-free sulfonamido-porphyrin

Abstract The influence of gaseous chlorine on monolayers of metal-free meso-tetra(4-amino sulfonyl)phenylporphyrin is discussed. These films exhibit characteristic intense optical absorption bands in the region 400–700 nm. Upon exposure to chlorine vapour in the concentration range 0.1–10 ppm, the Soret and Q-bands decrease in intensity and new bands at ∼455 nm and ∼660 nm appear. The rate of response has been measured as a function of deposition surface pressure and gas concentration. Repeated dosing experiments have shown that reversible and reproducible sensing action occurs provided that a threshold concentration is not exceeded. The recovery of the original optical spectrum can be accelerated with moderate heat treatment (60°C for 10 min). Ageing experiments have shown that the basic response of the monolayer is not effected over a time period of at least 5 months.

Imidazole clubbed 1,3,4-oxadiazole derivatives as potential antifungal agents.

A series of compounds in which 2-(4-ethyl-2-pyridyl)-1H-imidazole was clubbed with substituted 1,3,4-oxadiazole was synthesized and subjected to antifungal activity evaluation. In vitro assays indicated that several clubbed derivatives had excellent antifungal activity against different strains of laboratory and clinically isolated Candida species. Structural Activity Relationship (SAR) studies revealed that the presence and position of substituents on the phenyl ring of the 1,3,4-oxadiazole unit, guides the antifungal potential of the compounds, where compound 4b, 4c and 4g were found to be active against all the tested fungal strains. Impairment of ergosterol biosynthesis upon the concomitant treatment of 4b, 4c and 4g, revealed the possible mechanisms of antifungal action of these compounds. Inhibitors snugly fitting the active site of the target enzyme, as revealed by molecular docking studies, may well explain their excellent inhibitory activity.

Oxoperoxo vanadium(V) complexes of L-lactic acid: density functional theory study of structure and NMR chemical shifts.

Various combinations of density functionals and pseudopotentials with associated valence basis-sets are compared for reproducing the known solid-state structure of [V 2O 2(OO) 2 l-lact 2] (2-) cis . Gas-phase optimizations at the B3LYP/SBKJC level have been found to provide a structure that is close to that seen in the solid state by X-ray diffraction. Although this may result in part from error compensation, this optimized structure allowed satisfactory reproduction of solution multinuclear NMR chemical shifts of the complex in all-electron DFT-IGLO calculations (UDFT-IGLO-PW91 level), suggesting that it is probably close to that found in solution. This combination of approaches has subsequently been used to optimize the structures of the vanadium oxoperoxo complexes [V 2O 3(OO) l-lact 2] (2-) cis , [V 2O 3(OO) l-lact 2] (2-) trans , and [VO(OO)( l-lact)(H 2O)] (-) cis . The (1)H, (13)C, (51)V, and (17)O NMR chemical shifts for these complexes have been calculated and compared with the experimental solution chemical shifts. Excellent agreement is seen with the (13)C chemical shifts, while somewhat inferior agreement is found for (1)H shifts. The (51)V and (17)O chemical shifts of the dioxo vanadium centers are well reproduced, with differences between theoretical and experimental shifts ranging from 22.9 to 35.6 ppm and from 25.1 to 43.7 ppm, respectively. Inferior agreement is found for oxoperoxo vanadium centers, with differences varying from 137.3 to 175.0 ppm for (51)V shifts and from 148.7 to 167.0 ppm for (17)O(oxo) shifts. The larger errors are likely to be due to overestimated peroxo O-O distances. The chosen methodology is able to predict and analyze a number of interesting structural features for vanadium(V) oxoperoxocomplexes of alpha-hydroxycarboxylic acids.