Rodrigo J. Corrêa

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.

Theoretical study of protonation of butene isomers on acidic zeolite: the relative stability among primary, secondary and tertiary alkoxy intermediates

A density functional theory (DFT) study of the protonation of but-1-ene, (E)-but-2-ene and isobutene over a cluster representing the zeolite acid site (HT3) was carried out. At the B3LYP/6-31+G** level of calculation all the reactions were exothermic, with respect to the isolated reactants, in forming an alkoxy species. Formation of a π-complex involving the double bond and the acidic proton was the first step and shows a small dependence with the olefin structure. The proton transfer involves a transition state with carbenium ion like character, which is reflected in the calculated ΔH‡, being higher for the but-1-ene (to afford the 1-butoxy intermediate) and lower for the isobutene (to afford the tert-butoxy intermediate). However, the stability of the alkoxy formed shows a different trend. The tert-butoxy was computed to be only 1.5 kcal mol−1 lower in energy than the π-complex between isobutene and HT3 at the B3LYP/6-31+G** level of calculation, but the reaction becomes endothermic by 2.5 kcal mol−1 when computed at B3LYP/6-311++G**. The calculated order of stability among the alkoxy species was 2-butoxy > 1-butoxy > tert-butoxy. These results show that electronic effects dominate ΔH‡, which is associated with the kinetics of the protonation process, while steric effects play a major role in the stability of the alkoxy, which in turn is related to the thermodynamics of protonation.

SN2, E2 reactions of butylchlorides on NaY zeolite: A potential method for studying the formation and reactivity of alkoxy species on the zeolite surface

The adsorption and reaction of n-butyl, sec-butyl, isobutyl and tert-butyl chlorides over NaY zeolite was studied by infrared spectroscopy. All the chlorides reacted almost instantaneously with the zeolite, giving rise to CH2 and CH3 bands in the infrared spectra. A band at approximately 1640 cm−1, ascribed to CC vibration, was observed in all experiments, its intensity being dependent upon the structure of the chloride. For tert-butyl chloride the intensity is greatest, and bands at 3550 and 3061 cm−1, ascribed to the acidic OH and olefinic CH, respectively, were observed. The intensity of the olefinic band is weaker in secondary and especially primary chlorides. Calculations at the B3LYP/6-31+G** level, using a T3 cluster to represent the zeolite active site, indicated that, for the secondary and primary chlorides, the formation of the alkoxy species, through an SN2 type reaction mechanism, is lower in energy relative to proton elimination, through an E2 type mechanism. The opposite was observed for the tert-butyl chloride, in agreement with the experimental results. The method can be useful for generating alkoxide species, especially primary and secondary ones, and for studying their reactivity on the zeolite surface.

Understanding the planar tetracoordinate carbon atom: spiropentadiene dication.

The atoms in molecule theory shows that the spiropentadiene dication has a planar tetracoordinate carbon (ptC) atom stabilized mainly through the sigma bonds and this atom has a negative charge. The bonds to the ptC atom have less covalent character than the central carbon from neutral spiropentadiene. The total positive charge is spread along the structure skeleton. The analysis of the potential energy surface shows that the dication spiropentadiene has a 2.3 kcal/mol activation barrier for ring opening.

Singlet oxygen production by pyrano and furano 1,4-naphthoquinones in non-aqueous medium.

The influence of ring size on the photobehaviour of condensed 1,4-naphthoquinone systems, such as pyrano- and furano-derivatives (1 and 2, respectively) has been investigated. The absorption spectra for both families of naphthoquinones reveal clear differences; in the case of 2 they extend to longer wavelengths. A solvatochromic red shift in polar solvents is consistent with the π,π* character of the S(0)→ S(1) electronic transition in all cases. Theoretical (B3LYP) analysis of the HOMO and LUMO Kohn-Sham molecular orbitals of the S(0) state indicates that they are π and π* in nature, consistent with the experimental observation. A systematic study on the efficiency of singlet oxygen generation by these 1,4-naphthoquinones is presented, and values larger than 0.7 were found in every case. In accordance with these results, laser flash photolysis of deoxygenated acetonitrile solutions led to the formation of detectable triplet transient species with absorptions at 390 and 450 nm (1) and at 370 nm (2), with φ(ISC) close to 1. Additionally, the calculated energies for the T(1) states relative to the S(0) states at UB3LYP/6-311++G** are ca. 47 kcal mol(-1) for 1 and 43 kcal mol(-1) for 2. A comparison of the geometrical parameters for the S(0) and T(1) states reveals a marked difference with respect to the arrangement of the exocyclic phenyl ring whilst a comparison of electronic parameters revealed the change from a quinone structure to a di-dehydroquinone diradical structure.

Silica nanoparticles doped with anthraquinone for lung cancer phototherapy.

In the present study, SiO2 nanoparticles functionalized with 3-(2-aminoethylamino)propyl group (SiNP-AAP) were used, for the first time, to covalently bond rose bengal (SiNP-AAP-RB) or 9,10-anthraquinone-2-carboxylic acid (SiNP-AAP-OCAq). The functionalized SiNP were characterized by: Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM); elemental analysis (CHN) for determination of the dye concentration; FTIR and UV-vis diffuse reflectance (DR-UV-vis) and a surface area study (BET). The functionalized SiNPs were applied in photodynamic therapy (PDT) against lung cancer cell lines. The evaluated cytotoxicity revealed 20-30% cell survival after 15min of PDT for both materials but the OCAq concentration was half of the RB nanomaterial. The phototoxicity was mainly related to oxidative stress generated in the cellular environment by singlet oxygen and by hydrogen abstraction as confirmed by the laser flash photolysis technique. The unprecedented results indicate that SiNP-AAP-OCAq is a possible system for promoting cell apoptosis by both type I and type II mechanisms.

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.

Derivatives of Spiropentadiene Dication : New Species with Planar Tetracoordinate Carbon (ptC) atom

In this work, nine tetrasubstituted derivatives [NH(2), OCH(3), Li, Na, Si(CH(3))(3)/SiH(2)CH(3,) P(CH(3))(2), Cl, F, and CN] of the spiropentadiene dication were analyzed within the framework of QTAIM. In the studied series, the electron-withdrawing substituents destabilize the ptC-containing spiropentadiene dication. On the other hand, stabilization of this dication is possible for electron-donating substituents only through sigma bonds, such as Li and Na. In all studied systems, according to QTAIM, the pi-electron system does not participate in the stabilization of the ptC atom in the spiropentadiene dication. sigma-electron-donating groups stabilize the spiropentadiene dication system by increasing the charge density of C(ext)-ptC bonds, whereas electron-withdrawing groups remove the charge density from C(ext)-ptC bonds.