A. M. d'A. Rocha Gonsalves

Photoacoustic Measurements of Porphyrin Triplet-State Quantum Yields and Singlet-Oxygen Efficiencies

Photoacoustic calorimetry was used to measure the quantum yields of singlet molecular oxygen production by the triplet states of tetraphenylporphyrin (TPP), ZnTPP and CuTPP in toluene, yielding values of 0.67 0.14, 0.68 0.19 and 0.03 0.01, respectively. We show that a novel dichlorophenyl derivative of ZnTPP is capable of singlet-oxygen production with a 0.90 0.07 quantum yield. The synthesis and characterisation of a new photostable chlorin with high absorptivity in the red that is capable of singlet-oxygen production with 0.54 0.06 quantum yield is described. Our results suggest that chlorinated chlorins may be interesting new sensitisers for photodynamic therapy.

Heavy-atom effects on metalloporphyrins and polyhalogenated porphyrins

The photophysics of halogenated and metallated tetrakisphenylporphyrins is investigated using single-photon counting, photoacoustic calorimetry and luminescence techniques. The radiationless transition rates in these and related molecules are interpreted with a quantum-mechanical tunnelling model modified to include the effect of spin–orbit coupling in the intersystem crossing rates. It is shown that tetrakisphenylporphyrins with halogens in the ortho positions have long-lived triplet states that are formed in high yields. 2002 Elsevier Science B.V. All rights reserved.

Halogen atom effect on photophysical and photodynamic characteristics of derivatives of 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin.

Brominated and iodinated derivatives of 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin were synthesised directly from the corresponding aldehydes. Photophysical and photochemical properties, singlet oxygen formation quantum yields, photobleaching and log P were measured. Cellular uptake measurements and cytotoxicity assays on WiDr and A375 tumour cell lines were performed. 5,10,15,20-Tetrakis(2-bromo-5-hydroxyphenyl)porphyrin showed the best cytotoxicity with values of IC(50) of 113 nM over WiDr cells and 52nM over A375 cells.

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.

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.

THE USE OF 2-AZADIENES IN THE DIELS-ALDER REACTION

Cysteine methyl ester has been converted into a series of 2-substituted methyl thiazolidine-4-carboxylates by reaction with carbonyl compounds including aromatic aldehydes and a- and P-oxoesters. These thiazolidines react with silver carbonate with the elimination of the elements of H2S and with the formation of transient 1 -substituted 2-azadiene carboxylate esters. The Diels-Alder reactions of these azadienes have been shown to take place with both electron rich dienophiles (enamines) and with electron deficient dienophiles (enones). The cycloaddition reactions are regioselective but not stereoselective. Exceptionally, the intermediates act as dienophiles when reacted with cyclopentadiene. Some of the 2-azadienes derived from oxoesters tautomerise to isolable enamines. A new example of intramolecular 1,3-dipolar cycloaddition of a Schiff base of a S-allylcysteine methyl ester derivative is described.

Asymmetric transfer hydrogenation of acrylic acids catalyzed by rhodium(I) complexes of diphosphine ligands

Abstract A number of chiral 1,2 1,3 and 1,4-diphosphines have been investigated as ligands for the rhodium catalyzed hydrogen transfer from formic acid and its salts to acrylic substrates. The results reveal a strong dependence of the activity and selectivity of the catalytic system on the size of the chelate ring and rigidity of the ligand, the reaction medium, as well as the nature of the substrate.

Ethyl 4-do­decyl-3,5-di­methyl-1H-pyrrole-2-carboxyl­ate: intermolecular interactions in an amphiphilic pyrrole

The title compound, C(21)H(37)NO(2), is a new amphiphilic pyrrole with a long hydrocarbon chain, which will be used as a precursor for the synthesis of Langmuir-Blodgett films of porphyrins. Molecules related by an inversion centre are joined head-to-head into dimers by strong N-H.O hydrogen bonds. The dimers pack in the structure with their carbon chains parallel to one another, thereby forming alternating layers of carbon chains and pyrrole heads. The structure is further stabilized by two weak C-H.pi intermolecular interactions, thereby saturating the hydrogen-bonding capability of the aromatic pi-electron clouds.

Ethyl 3,5-dimethyl-4-phenyl-1H-pyrrole-2-carboxylate.

In the title compound, C(15)H(17)NO(2), the ethoxycarbonyl group is anti with respect to the pyrrole N atom. The angle between the planes of the phenyl and pyrrole rings is 48.26 (9) degrees. The molecules are joined into dimeric units by a strong hydrogen bonds between pyrrole N-H groups and carbonyl O atoms. The geometry of the isolated molecule was studied by ab initio quantum mechanical calculations, employing both molecular orbital Hartree-Fock (MO-HF) and density functional theory (DFT) methods. The minimum energy was achieved for a conformation where the angle between the planes of the phenyl and pyrrole rings is larger, and that between the ethoxycarbonyl and pyrrole planes is smaller than in the solid-state molecule.

2,4-Dibromo-5-hydroxybenzaldehyde

The title compound, C 7 H 4 Br 2 O 2 , crystallizes as cen trosymmetric dimers in which two molecules are linked by two hydrogen bonds between the hydroxyl and carbonyl groups, with an O. . .O distance of 2.839(5)A Other intermolecular interactions are weak. There are no unusual intramolecular bond distances or angles. The atoms of the aldehyde group and the Br atoms, however are found to deviate significantly from the plane of the benzene ring.