David E. Nicodem

Photochemical processes and the environmental impact of petroleum spills

A review of the photochemical processes involved in the degradation of petroleum,its products, and some model compounds found in petroleum. Emphasis is given to processes which affect emulsification, water solubility, and toxicity. Waterphase photodegradation is also treated. The interaction of these processes withbiodegradation is discussed. Areas requiring further work are indicated. 96references.

Photochemistry of petroleum: I. Systematic study of a brazilian intermediate crude oil

The photochemical weathering of a crude Brazilian petroleum as a film over sea-water by sunlight has been studied using a combination of analytical tools including elemental analysis, GC, UV-VIS, IR, Fluorescence, and NMR. Fluorescence intensity decreased rapidly upon irradiation, whereas only slight weathering could be observed by GC and IR even after 100 h of exposure to full tropical sunlight. The other methods used did not reveal observable changes in petroleum composition.

PHOTOCHEMISTRY OF PETROLEUM

The current knowledge of photochemical weathering of petroleum and its fractions in the environment is reviewed, mostly in relation to petroleum films over water. Literature results are compared with the authors’ work. The effects of photochemical oxidation of petroleum on the physical and biological properties of petroleum are examined as well as suggested mechanisms for the observed transformations.

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*).

The use of fluorescent probes in the characterization of lignin: the distribution, by energy, of fluorophores in Eucalyptus grandis lignin

Four fluorescent probes (biphenyl, naphthalene, pyrene and phenanthrene) were used to map the energy distribution of the structural units present in lignin fragments from Eucalyptus grandis wood. This distribution shows that these fragments present two regions with a high concentration of chromophores, one between 418 and 385 kJ/mol, and the other below 322 kJ/mol. When this lignin was treated with NaBH4, the two more intense regions occurs between 418 and 346 kJ/mol, followed by a significant increase in the concentration of chromophores in almost all the studied energy range. Lifetime distributions present a bimodal pattern, with two typical peak lifetime values, the first of 1 :36 0:17 ns, with a relative amplitude above 80%, and the second of 8:48 2:32 ns, for both species, with some fluctuation for different em. The synchronous spectra indicates, for this lignin, at least three broad spectral envelopes, with a large superposition of the emission maxima. The results indicate the existence of at least three most representative fluorophores, most probably due to biphenyl, coniferyl alcohol and stilbene structures, with varying substituents. The majority of the fluorescence complexity of this lignin seems to be associated with the inhomogeneous emission decay kinetics associated with ground state heterogeneity, due to the complex mixture of the different fluorophores, on which are superimposed different distributions of environments.

Investigation of asphaltene association by front-face fluorescence spectroscopy.

The tendency of asphaltenes to aggregate and form clusters in solvents was studied by fluorescence spectroscopy. This was done by evaluating the relative fluorescence quantum yield of asphaltenes diluted at several concentrations in toluene and by studying the changes in the fluorescence spectra of asphaltene solutions as the composition of the solvent, toluene and cyclohexane, is changed. The asphaltene fraction (heptane insoluble) was collected from a Brazilian heavy crude oil, and solutions of this material varying from 0.016 g/L up to 10 g/L were prepared in toluene. Front-face emission spectra were obtained in two wavelength ranges, from 310 to 710 nm, excited at 300 nm (short range), and from 410 to 710 nm, excited at 400 nm (long range). Severe quenching was observed at concentrations above about 0.1 g/L. Stern–Volmer plots (reciprocal of quantum yield against concentration) exhibited nonlinear, downward-curved behavior, indicating that a more complex suppression mechanism, probably influenced by the association of the asphaltene molecules, is taking place. The same asphaltenes were dissolved (0.1 g/L) in binary mixtures of toluene and cyclohexane, and emission spectra in both the short range and long range were obtained. Fluorescence was progressively quenched at longer wavelengths of the spectra as the proportion of cyclohexane in the solvent grew. Cyclohexane, a poor asphaltene solvent, is probably inducing static quenching through association of asphaltenes.

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.

Standardization of the potassium ferrioxalate actinometer over the temperature range 5 – 80 °C

Abstract The quantum yield of ferrous ion formation on irradiation at 313 nm is constant and has a value of 1.24 in the temperature range 5 – 80 °C. At temperatures above ambient the samples should be deoxygenated to eliminate reoxidation of Fe 2+ by O 2 . At 80 °C there is a competing thermal reduction producing Fe 2+ which is first order in ferrioxalate.

Time-Resolved Single Photon Counting Study of the Quenching of Fluorescent Probes by Petroleum: Probing the Energy Distribution of the Nonaliphatic Components

Index Headings: Petroleum; Fluorescence; Time-resolved single photon counting; TRSPC; Quenching.

Theoretical study of photochemical hydrogen abstraction by triplet aliphatic carbonyls by using density functional theory.

The density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) have been used to study the lowest lying spin states of the photochemical hydrogen abstraction reaction by formaldehyde, acetaldehyde, and acetone in the presence of different hydrogen donors: propane, 2-propanol, and methylamine. Calculations of all the critical points on the PES of these reactions were performed at uB3LYP/6-311++G(d,p). Methylamine is the best hydrogen donor, in thermodynamic and kinetic terms, followed by 2-propanol and finally propane. Secondary C-H hydrogen abstraction in 2-propanol and C-H abstraction in methylamine is thermodynamically and kinetically favored with respect to hydrogen abstraction from the OH and NH functional groups. Charge transfer takes place before the transition state when methylamine is the hydrogen donor, and for other hydrogen donors, charge transfer begins only in the transition state. The extent of the charge transfer in the transition states corresponds to about 50% of the total change in electron density of the oxygen atom of the T(1) carbonyl compounds during the course of the hydrogen abstraction reactions. The effect of solvent was investigated using the continuum solvation model for the reaction of triplet acetaldehyde in acetonitrile, which resulted in a barrierless transition state for hydrogen abstraction from methylamine.