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- Photophysics and photochemistry of azole fungicides: triadimefon and triadimenolPublication . Silva, José P. da; Silva, Abílio M. da; Khmelinskii, Igor; Martinho, J. M. G.; Ferreira, Luís F. VieiraPhotophysics and photochemistry of pesticides triadimefon {1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butanone} and triadimenol {1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl) butan-2-ol} were studied in the solution. The excited singlet states were identified by comparison with the absorption spectra of adequate model compounds, in several solvents. The first excited singlet state of triadimefon is an n, pi* state localized on the carbonyl group, while higher excited states are localized on the chlorophenoxy group and have a pi, pi* character. The lowest singlet state of triadimenol is pi, pi* state, since a methoxyl group replaces the carbonyl group of triadimefon. Triadimefon shows a weak fluorescence from the n, pi* state, upon excitation at both 310 and 250 nm. This suggests a fast intramolecular energy transfer process from the localized pi, pi* state of the chlorophenoxy group to the n, pi* state of the carbonyl group. The photodegradation quantum yield of triadimefon in cyclohexane at 313 run is 0.022. Triadimenol is photostable, under the same conditions. Two major photodegradation products of triadimefon and triadimenol were identified: 4-chlorophenol and 1,2,4-triazole. 4-Chlorophenoxyl radicals were detected by flash photolysis, suggesting a homolytic cleavage of the C-O bond of the asymmetric carbon. (C) 2001 Elsevier Science B.V. All rights reserved.
- Discrimination of beer flavours by analysis of volatiles using the mass spectrometer as an electronic nosePublication . Sikorska, Ewa; Chmielewski, Jaroslaw; Gorecki, Tomasz; Khmelinskii, Igor; Sikorski, Marek; De Keukeleire, DenisEntire mass spectra of beer headspace components were used as fingerprints for beer brand classification and differentiation of beer samples stored under various conditions. Chemometric analysis of the mass spectra allowed for the discrimination of beer brands and for the detection of beer aging and photodegradation. The numeric methods used include unsupervised PCA modelling and discrimination using kappa NN, LDA, and D-PLS methods.
- TiO2 thin film synthesis from complex precursors by CVD, its physical and photocatalytic propertiesPublication . Bessergenev, V.; Pereira, R. J. F.; Mateus, M. C.; Khmelinskii, Igor; Nicula, R. C.; Burkel, E.Photocatalytic TiO2 films on glass and quartz plates were obtained by the chemical vapour deposition using Ti(dpm)(2)(Opr(i))(2) complex compound (CC-CVD method) in a standard vacuum apparatus at 1.2-2.0 x 10(-4) mbar. The substrate temperature was stabilised in the range of 450-600 degreesC. The growth rate varied from several nanometres to several dozen of nanometres per minute. Structural information on TiO2 thin films was obtained from synchrotron radiation experiments. High-resolution grazing incidence X-ray diffraction (GIXRD) experiments were performed at the high-resolution powder diffractometer at the DESY/HASYLAB beamline B2 (Hamburg, Germany). Thin films deposited on either single-crystal Si wafers or on amorphous quartz substrates were analysed. The photocatalytic activity of the TiO2 thin films was studied using a photocatalytic reactor. The fungicide Fenarimol was chosen as chemical indicator and its degradation kinetics was followed by High-Performance Liquid Chromatography (HPLC).
- Novel efficient synthesis of 3,4-dihydro-6-substituted-3-phenylpyrimidin-2(1H)-onesPublication . Frija, L.; Khmelinskii, Igor; Cristiano, Maria Lurdes SantosA new attractive and convenient strategy for the synthesis of 3,4-dihydro-6-substituted-3-phenylpyrimidin-2(1H)-ones is described. Photolysis (k = 254 nm) of 4-allyl-tetrazolones in alcoholic solutions produces the corresponding pyrimidinones as the sole product in nearly quantitative yields, with simultaneous extrusion of molecular nitrogen. Work-up procedures consist in the simple evaporation of the solvent under reduced pressure, in mild conditions. Heats of reaction for the photocleavage process of 4-allyltetrazolones were calculated, indicating high stability of the resulting products.
- Photochemistry of 5-allyloxy-tetrazoles: steady-state and laser flash photolysis studyPublication . Frija, L.; Khmelinskii, Igor; Serpa, C.; Reva, I. D.; Fausto, R.; Cristiano, Maria Lurdes SantosThe photochemistry of three 5-allyloxy-tetrazoles, in methanol, acetonitrile and cyclohexane was studied by product analysis and laser flash photolysis. The exclusive primary photochemical process identified was molecular nitrogen elimination, with formation of 1,3-oxazines. These compounds were isolated in reasonable yields by column chromatography on silica gel and were fully characterized. DFT(B3LYP)/6-31G(d,p)calculations predict that these 1,3-oxazines can adopt two tautomeric forms (i) with the NH group acting as a bridge connecting the oxazine and phenyl rings and (ii) with the –N=bridge and the proton shifted to the oxazine ring. Both tautomeric forms are relevant in the photolysis of oxazines in solution. Secondary reactions were observed, leading to the production of phenyl vinyl-hydrazines, enamines, aniline and phenyl-isocyanate. Transient absorption, detected by laser flash photolysis, is attributed to the formation of triplet 1,3-biradicals generated from the excited 5-allyloxy-tetrazoles. The 1,3-biradicals are converted to 1,6-biradicals by proton transfer, which, after intersystem crossing, decay to generate the products. Solvent effects on the photoproduct distribution and rate of decomposition are negligible.
- Mechanistic Investigations into the photochemistry of 4-allyl-tetrazolones in solution: a new approach to the synthesis of 3,4-dihydro-pyrimidinonesPublication . Frija, L.; Khmelinskii, Igor; Cristiano, Maria Lurdes SantosPhotolysis (ì ) 254 nm) of 4-allyl-tetrazolones 2a-c was carried out in methanol, 1-propanol, 1-hexanol, acetonitrile, and cyclohexane. The sole primary photochemical process identified was molecular nitrogen elimination, with formation of pyrimidinones 6a-c. Following the primary photocleavage, secondary reactions were observed in acetonitrile and cyclohexane, leading to phenyl-isocyanate (7), aniline (9), and 1-phenylprop-1-enyl-isocyanate (10a). In alcoholic solutions, the primary products, 6a-c, remained photostable even under extended irradiation, making possible the isolation of 3,4-dihydro-pyrimidinones as stable compounds in very high yields. The observed photostability of pyrimidinones 6a-c in alcohols is ascribed to the excited state quenching via reversible proton transfer, facilitated by the solvent cage stabilization due to formation of hydrogen bonds. The viscosity of alcohols is directly related to the cage effects observed. The photocleavage of 4-allyl-tetrazolones leads probably to a caged triplet radical pair. This hypothesis is confirmed by the solvent viscosity effect on the photolysis quantum yields. Additionally, dissolved molecular oxygen sensitizes the formation of pyrimidinones, as should be expected for a triplet intermediate that can only form the product molecule after T-S conversion, which is accelerated by oxygen.
- Fluorescence spectroscopy for characterization and differentiation of beersPublication . Sikorska, E.; Gorecki, Tomasz; Khmelinskii, Igor; Sikorski, M.; De Keukeleire, D.Total luminescence and synchronous scanning fluorescence spectroscopic techniques were applied for characterization of the intrinsic fluorescence of eight different beers. Spectra were measured using different geometries to reveal the presence of similar fluorescent components. The total luminescence and synchronous fluorescence spectra exhibit a relatively intense short-wavelength emission ascribed to aromatic amino acids and less intense emission in the long-wavelength region, which may originate from B vitamins. Classification of beers based on their synchronous fluorescence spectra was performed using non-parametrical k nearest neighbours method and linear discriminant analysis. Very good discrimination was obtained in both methods with a low classification error. The results demonstrate the potential of fluorescence techniques to characterize and differentiate beers.
- Dissipation of triadimefon on the solid/gas interfacePublication . Silva, José P. da; Silva, Abílio M. da; Khmelinskii, IgorThe dissipation or triadimefon, as pure solid and in the Bayleton 5 commercial formulation, was studied under controlled and natural conditions. Volatilization and photodegradation were shown to be the main dissipation processes. The volatilization results can be described by an empirical model assuming exponential decay of the volatilization rate. The filler of the commercial formulation is determinant for the volatilization but has little effect on the photodegradation rates. The main photoproducts were identified and a reaction mechanism proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.