Jacques Antonio de Miranda

Photophysics and spectroscopic properties of 3-benzoxazol-2-yl-chromen-2-one

The photophysics of 3-benzoxazol-2-yl-chromen-2-one was studied in different solvents. High molar absorptivities, between 14,800 and 22,900 dm3/mol cm, were observed for the absorption peak related to the S0 --> S1 transition which suggests a pi --> pi* character. This compound presents a limited solvatochromism, attributed to the benzoxazole group, and high fluorescence quantum yields, phi(f). The fluorescence quantum yield is lowered with the increase of solvent polarity, favouring the participation of internal conversion as deactivation path of the S1 state. The Stokes shift shows that the excited state is stabilised with increasing solvent polarity. The dipole moment was estimated by ab initio calculations as being between 5.28 and 5.62 Debye for S1, and 4.75 Debye for S0. Phosphorescence was not observed. A small but not negligible quantum yield of singlet oxygen generation (phidelta = 0.15) was measured in chloroform. The geometric parameters obtained by semi-empirical calculation (PM3) are in good agreement with crystallographic data, showing a r.m.s. deviation of 0.153 A for the superposition of both structures. The predicted structure is all planar, while the crystallographic data reveal a dihedral angle of 6.5 degrees, between the coumarin and benzoxazole rings. The theoretical description of the electronic spectra, obtained from a PM3 CI calculation, shows excellent agreement with the experimental data. Deviations lower than 2% are observed in the predicted absorption maxima, with best results when solvation is considered. For electronic states calculation, ZINDO/S gave a better prediction of excited state energies, with a deviation lower than 7% for the S1 energy. The most probable sequence for the first four excited states is: Ti(n pi*) < T2(pi pi*) < S1(pi pi*) < S2(n pi*).

Photophysical properties of two new psoralen analogs

Abstract The photophysics of two new psoralen analogs has been examined using absorption and emission spectroscopy. Both compounds efficiently absorb radiation in the UVA region (320 nm ) which are weakly fluorescent and sensitize the generation of singlet oxygen with a quantum efficiency near unity.

Construção e estudos de perfomance de um reator fotoquímico tipo CPC ("Compound Parabolic Concentrator")

A CPC (Compound Parabolic Concentrator) reactor was projected and constructed aiming to promote the degradation of the organic matter present in considerable volumes of aqueous effluents, under the action of solar radiation. The essays were done using a model effluent which consists of a mixture of fragments of a sodium salt of lignosulphonic acid possessing a mean molecular weigth of 52,000 Daltons, and a real effluent, from a chip board industry. The volume of effluent in each test was about 50 L. The tests involved heterogeneous (TiO2 P25 Degussa and formulations made from the association of TiO2 with a photosensitiser), and homogeneous (thermal and photochemical Fenton reactions) catalysis of the effluents. The results demonstrate the viability of application of this kind of reactor even when the load of organic pollutants is high.

Comparison of the photodynamic action of methylene blue and zinc phthalocyanine on TG-180 tumoral cells

The efficiency of zinc phthalocyanine and methylene blue (CI 52015) in compromise the viability of TG 180 malignant cells by photodynamic action, was compared by counting the number of killed cells. The results show that, under the observed experimental conditions, zinc phthalocyanine (ZnPc) is at least two times more efficient than methylene blue (MB), and possesses a very low citotoxicity and high capacity to penetrate the cellular membrane. Quenching experiments using β-carothene evidence the importance of a type II mechanism during cell inactivation by ZnPc.

Degradação Fotocatalítica de Corante Alimentício Azorrubina e Monitoramento de Redução de Toxicidade

In present work, simples of the food dyes organic synthetic (C 2 OH 12 N 2 Na 2 O 7 S 2 ) was submitted to photodegradation with a support of the Fenton and photo-Fenton reactions and measure toxicity with a support of essays germination of the lettuce seeds ( Lactuca sativa ). The results showed that, using Fenton and photo-Fenton reactions and simples dyes with a concentration of the 2500 ppm, were achieved 100% discoloration in only 30 minutes. The photocatalytic of the uv-vis light, uv-vis and H 2 O 2 , Fenton and photo-Fenton reactions, constant values presented apparent discolored of the, k ap = 0.02161 min -1 , k ap = 0.04939 min -1 , e k ap = 0.1244 min -1 , respectively. The reduction toxicity assays presented a significant reduction of toxicity after analyzing the samples collected in 120 minutes of the photolysis. The toxicity reduction achieved, compared to the control sample, was 17.43% for the growth of the radicle and 32.35% for the growth of the hypocotyl. DOI: http://dx.doi.org/10.17807/orbital.v1i1.717