Vanadyl Octaethylporphyrin Research Articles

Spectral characteristics and DFT Study of vanadyl octaethylporphyrin complex

<p>The chemistry of vanadyl porphyrins has been explored using vanadyl octaethylporphyrin as a substance in petroleum porphyrins, crude oils and bitumen. The structural, electronic, thermodynamic, spectroscopic properties are described. The geometry’s optimization of this molecule was done by Density Functional Theory (DFT) using the hybrid Beck three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional (B3LYP) and 6-31G(d) standard basis set. All calculations have been made in the gas phase and in different solvents: benzene, benzonitrile, tetrachloromethane and chloroform. The calculated infrared spectrum was compared with experimental spectroscopic data, and the vibrational assignment was provided. An electron density analysis in terms of natural bond orbitals was conducted to determine the nature of the bonds between the vanadium and nitrogen atoms. The spatial representation of the associated molecular orbitals helped to explain the formation of the V-N bonds and to interpret the chemical reactivity of the compound studied. The electrostatic potential was calculated in order to investigate the reaction properties of the molecule.<strong></strong></p>

Spectral characteristics and DFT Study of vanadyl octaethylporphyrin complex

The chemistry of vanadyl porphyrins has been explored using vanadyl octaethylporphyrin as a substance in petroleum porphyrins, crude oils and bitumen. The structural, electronic, thermodynamic, spectroscopic properties are described. The geometry’s optimization of this molecule was done by Density Functional Theory (DFT) using the hybrid Beck three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional (B3LYP) and 6-31G(d) standard basis set. All calculations have been made in the gas phase and in different solvents: benzene, benzonitrile, tetrachloromethane and chloroform. The calculated infrared spectrum was compared with experimental spectroscopic data, and the vibrational assignment was provided. An electron density analysis in terms of natural bond orbitals was conducted to determine the nature of the bonds between the vanadium and nitrogen atoms. The spatial representation of the associated molecular orbitals helped to explain the formation of the V-N bonds and to interpret the chemical reactivity of the compound studied. The electrostatic potential was calculated in order to investigate the reaction properties of the molecule.

High field electron paramagnetic resonance characterization of electronic and structural environments for paramagnetic metal ions and organic free radicals in Deepwater Horizon oil spill tar balls.

In the first use of high-field electron paramagnetic resonance (EPR) spectroscopy to characterize paramagnetic metal-organic and free radical species from tar balls and weathered crude oil samples from the Gulf of Mexico (collected after the Deepwater Horizon oil spill) and an asphalt volcano sample collected off the coast of Santa Barbara, CA, we are able to identify for the first time the various paramagnetic species present in the native state of these samples and understand their molecular structures and bonding. The two tar ball and one asphalt volcano samples contain three distinct paramagnetic species: (i) an organic free radical, (ii) a [VO](2+) containing porphyrin, and (iii) a Mn(2+) containing complex. The organic free radical was found to have a disc-shaped or flat structure, based on its axially symmetric spectrum. The characteristic spectral features of the vanadyl species closely resemble those of pure vanadyl porphyrin; hence, its nuclear framework around the vanadyl ion must be similar to that of vanadyl octaethyl porphyrin (VOOEP). The Mn(2+) ion, essentially undetected by low-field EPR, yields a high-field EPR spectrum with well-resolved hyperfine features devoid of zero-field splitting, characteristic of tetrahedral or octahedral Mn-O bonding. Although the lower-field EPR signals from the organic free radicals in fossil fuel samples have been investigated over the last 5 decades, the observed signal was featureless. In contrast, high-field EPR (up to 240 GHz) reveals that the species is a disc-shaped hydrocarbon molecule in which the unpaired electron is extensively delocalized. We envisage that the measured g-value components will serve as a sensitive basis for electronic structure calculations. High-field electron nuclear double resonance experiments should provide an accurate picture of the spin density distribution for both the vanadyl-porphyrin and Mn(2+) complexes, as well as the organic free radical, and will be the focus of follow-up studies.

Membrane Diffusion Measurements Do Not Detect Exchange between Asphaltene Aggregates and Solution Phase

Although the aggregation of petroleum asphaltenes has been measured by a variety of methods, little is known about the rate of exchange between aggregated and dissolved components. This work studied the diffusion of asphaltenes from several heavy oils and bitumens in dilute toluene solutions using a stirred diffusion cell equipped with ultrafiltration membranes (Ultracel YM and Anopore). The pore sizes were varied between 3 and 20 nm to retain aggregates while allowing free molecules to diffuse. The permeate was continuously monitored using in situ UV−vis spectroscopy. These experiments demonstrated that the sizes of the asphaltene aggregates at a concentration of 1 g/L in toluene at 25 °C were between 5 and 9 nm and that rates of exchange of material between the aggregates and free solution were extremely low. An increase in the temperature results in an increase in asphaltene mobility but does not reduce the size of the asphaltene structures below 5 nm. Likewise, a decrease in the concentration to 0.1 g/L did not result in a decrease in size. The origin of the asphaltenes (Athabasca, Safaniya, and Venezuela) did not have a significant impact on the observed behavior; therefore, the above observations are widely applicable to C7 asphaltenes. The diffusion of vanadyl porphyrins (vanadyl meso-tetraphenylporphyrin, vanadyl octaethylporphyrin, and native petroporphyrins) in the presence of asphaltenes showed that the native petroporphyrins were larger than the model vanadyl porphyrins based on the appearance of hindered diffusion within smaller pores. An increase in the temperature resulted in an increase in petroporphyrin mobility as per the Stokes−Einstein relationship, although decreasing the asphaltene concentration did not. The mobility of the vanadyl petroporphyrins varied with the origin of the sample (Safaniya, Venezuela, and Athabasca) and is therefore not universal.

Electrochemical removal of metals from crude oil samples

Removal of vanadium from vanadyl (IV) meso-tetra-phenylporphyrin (VO-MTPP) and vanadyl (IV) octa-ethylporphyrin (VO-OEP) and metals removal from Ayacucho Venezuelan crude oil samples were performed using electrochemical techniques. According to cyclic voltammograms, a potential of − 2.3 V vs. Ag/AgNO 3 (0.1 M), LiClO 4 (0.1 M) in acetonitrile, was chosen for running electrolysis at platinum (Pt), graphite (G) and glassy carbon (GC) electrodes. Qualitative analysis was done by cyclic voltammetry (CV) and atomic absorption spectroscopy (AAS) while quantification was performed by AAS and inductively coupled plasma/atomic emission spectrometry (ICP/AES). Three stages (best results) of the study are reported: (a) when using commercial porphyrins; the best conditions for electrolysis were: tetrahydrofuran (THF)/20% methanol (MeOH)/1% perchloric acid (HClO 4) on GC, producing 84% hydro-demetalation (HDM) for VO-MTPP, and 78% HDM for VO-OEP; (b) when using extracts of crude oil; demetalation percentages, after 90 min of electrolysis, on graphite, and after 120 min of electrolysis on platinum, were 66.44% and 64.10% HDM respectively, no discrimination of metals under these conditions (c) from electrolysis in whole crude oil, quantitative analysis gave: vanadium (V) 31.2 mg/kg, iron (Fe) 65, 0 mg/kg and nickel (Ni) 6, 3 mg/kg, with charge efficiencies of V (7.5%), Fe (79.6%) and Ni (8.2%).

Mo/MCM-41-Type mesoporous materials doubly promoted with Fe and Ni for hydrotreating reactions

A Si-MCM-41-type material was synthesized and impregnated with a Mo solution in order to get a 15% MoO 3 by weight. Then, it was doubly promoted with Ni and Fe in different proportions. Information on the structure of the precursors was revealed by XRD, TPR and surface area techniques. XRD results showed that the mesoporous materials were not affected for the successive impregnations carried out; while, their specific surface areas was partially blocked. These solids were tested for vanadyl octaethyl porphyrin hydrodeporphirinization (HDP), and individual and competitive reactions of dibenzothiophene (DBT) hydrodesulfurization (HDS) and 2-methyl naphthalene (2MN) hydrogenation (HYD). The DBT HDS activity was higher than 2MN HYD, and the presence of Fe in the catalysts did not produce a synergetic effect for this reactions. However, HDP activities of doubly promoted catalysts were superior to the monopromoted ones.

Avaliação da atividade fotodinâmica de porfirinas para uso em terapia fotodinâmica através da fotoxidação de triptofano

Neste trabalho investigou-se a atividade fotodinâmica de octaetilporfirina (OEP), octaetilporfirina de vanadil (VOOEP) e meso-tetramesitilporfirina (m-TMP). Este estudo foi realizado através da determinação da constante da velocidade de fotoxidação (k f) do aminoácido triptofano (Trp). A participação do oxigênio singlete nesta fotoxidação foi determinada através da adição de azida de sódio e água deuterada no meio de reação. Os valores de k f/10-4s-1 para a fotoxidação de Trp demonstraram que OEP (2,80 ± 0.05) é mais eficiente do que m-TMP (1,62 ± 0,07) e VOOEP (0,81 ± 0,08). Os valores de k f foram menores na presença de azida de sódio e maiores na presença de água deuterada, sugerindo que o oxigênio singlete é o responsável pela atividade fotodinâmica de OEP, VOOEP e m-TMP. Estes resultados sugerem também que as diferenças na atividade fotodinâmica entre as porfirinas podem ser associadas com as diferenças na estrutura molecular das mesmas. A presença do grupo vanadil (V=O) interfere claramente na atividade fotodinâmica de OEP causando considerável redução na sua eficiência.

Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: I. Characterization of the Excited Quartet State

Laser flash induced spin-polarized transient electron paramagnetic resonance (TREPR) spectra for vanadyl octaethylporphyrin in isotropic and partially ordered frozen solutions are presented and compared with corresponding luminescence data. The TREPR spectra show well-resolved hyperfine couplings to the vanadium nucleus and a multiplet polarization pattern with features typical of zero-field splitting (ZFS). The principal values of the vanadium hyperfine coupling tensor evaluated from the spectra are 1/3 of the corresponding values found from steady-state EPR spectra of the ground state. On the basis of these characteristics and numerical simulations, the polarization patterns are assigned to the excited quartet state. The values of the ZFS parameters of the trip-quartet obtained from simulation of the spectra (D = 17.5 mT and E = 1.5 mT) are comparable to those of the triplet state of the zinc and free base octaethyl porphyrin. The lifetime of the spin polarization is found to be temperature dependent and is essentially the same as that of the optical emission. The temperature dependence is rationalized using a model in which the decay to the ground state occurs from both the trip-quartet and trip-doublet, which are in thermal equilibrium even at 15 K. A fit of the model to the observed spin polarization lifetimes yields an energy gap of 47 cm(-1) between the trip-quartet and trip-doublet. It is shown that the spin polarization evolves from a multiplet pattern at early times to a net absorptive pattern at late times following the laser flash. It is proposed that the establishment of thermal equilibrium leads to the evolution of the spin from multiplet to net polarization.

Light-Induced Electron Spin Polarization in Vanadyl Octaethylporphyrin: II. Dynamics of the Excited States

The dynamics of the low-lying excited states of vanadyl octaethylporphyrin (OEPVO) in frozen solution is investigated by transient electron paramagnetic resonance (TREPR). The observation of spin-polarized TREPR spectra from the lowest excited trip-quartet state of OEPVO, reported in the preceding paper, opens a new avenue for investigation of the excited states of such molecules. Here, a model based on the back-and-forth transitions between the trip-quartet and trip-doublet states is developed and used to explain the time dependence of the low-temperature laser flash-induced electron spin polarization of OEPVO. At early times, the TREPR spectra show predominantly multiplet polarization, whereas strong net polarization develops at later times. An analysis of the time dependence reveals two well-separated processes: (i) fast evolution of the polarization from the multiplet pattern to the net absorptive pattern and (ii) very slow decay of the net polarization. Both processes are temperature dependent and are faster at higher temperature. All of these observed features can be reproduced, and the experimental data can be simulated within the framework of the model. For simplicity, only the two nearly degenerate orbital states resulting from the a(1) --> e triplet excitation of the porphyrin are considered. Each of these is split into a trip-doublet and trip-quartet giving a total of four low-lying excited states. Transitions between the trip-doublet and trip-quartet states are assumed to be governed by spin-orbit coupling, which mixes the four low-lying states. It is known that following light excitation, the molecule initially decays to the lowest trip-doublet state and then to the trip-quartet state. In agreement with the observed TREPR spectra, the model predicts that this decay results in predominantly multiplet polarization of the trip-quartet. However, a small amount of net polarization is also predicted due to the spin selectivity associated with the Zeeman interaction. Because the energy gap between the trip-doublet and trip-quartet states is small, back-and-forth electronic transitions between the trip-doublet and trip-quartet are expected to occur as thermal equilibrium is established. The model predicts that it is these transitions that lead to the observed evolution of the initial multiplet polarization to net absorptive polarization.

Preparation of ZnNiMo/γ-alumina catalysts from recycled Ni for hydrotreating reactions

Ni, recovered from Ni–Cd cellular phone batteries, was used in the preparation of ZnNiMo/Al 2O 3 catalysts. The catalysts were characterized by temperature programmed reductions (TPR), surface area determinations (BET) and chemical analysis. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) and thiophene hydrodesulfurization (HDS) were used as catalytic tests. It was found that the addition of Zn increases the ratio between octahedral and tetrahedral Mo in ZnMo and ZnNiMo catalysts, and that Ni addition lowers the reduction temperature of Mo species. Both results induce a positive synergetic effect for HDP and HDS reactions. An activity maximum was found for the catalyst with a Zn/(Zn + Ni) atomic ratio equal to 0.29, for both reactions. Finally, the use of a possible pollutant (Ni–Cd batteries) to produce a catalyst to eliminate contaminants in fuels was shown to be feasible.

Effect of polar organic components on wettability as studied by adsorption and contact angles

Adsorption of polar organic components onto the rock surface is one of the mechanisms that is believed to cause wetting alteration of a reservoir rock. Polar compounds in crude oil that are believed to be responsible for surface interactions and wetting properties include carboxylic and phenolic acids, organic bases and metal complexes. Known compounds, representative of these naturally occurring polar organic compounds in crude oil, have been chosen for adsorption and contact angle studies. Contact angles and adsorption isotherms in solid–oil–brine model systems have been examined as a function of component concentration in either water or oil and of salinity and pH of the water phase. The systems investigated consist of isooctane oil phase and water solutions of NaCl and CaCl 2 as the water phase. Silicate glass and α-alumina were used as solid phases. The polar compounds were 1-naphtoic acid, 5-indanol, quinoline, vanadyl–octaethyl–porphyrin (VO OEP) and dihydrogen–octaethyl–porphyrin (H 2 OEP). The compounds chosen represent functionalities that are found in polar crude oil fractions, such as asphaltenes, but still can be considered well-defined model substances. The components were adsorbed from the oil phase as well as from the water phase, both for contact angle and adsorption isotherm experiments. The results demonstrate the difference in adsorption behaviour between compounds with different functional groups of varying polarity and acidity. The importance of solid–solute interactions compared to solvent–solute interactions is demonstrated.

Insensitivity of Vanadyl−Oxygen Bond Strengths to Radical Type (2A1u vs 2A2u) in Vanadyl Porphyrin Cation Radicals

Resonance Raman (RR) spectra are reported for vanadyl octaethylporphyrin, OV(OEP), tetramesityltetramethylporphyrin, OV(TMTMP), and tetramesitylporphyrin, OV(TMP), and their corresponding π-cation radicals obtained by chemical and electrochemical oxidation. The behavior of the ν2 RR porphyrin “marker band”, which moves to higher frequency upon oxidation of the OV(OEP) and OV(TMTMP) and to lower frequency for OV(TMP), shows that the resultant cation radicals have predominantly 2A1u and 2A2u ground states, respectively. In contrast to earlier work (Macor, K. A.; Czernuszewicz, R. S.; Spiro, T. G. Inorg. Chem. 1990, 29, 1996), it is demonstrated here that the shift of the ν(VO) is insensitive to radical type, behavior which is in agreement with similar studies of the ferryl analogues (Czarnecki, K.; et al. J. Am. Chem. Soc. 1996, 116, 2929 and 4680). It is suggested that the observed downshifts of the ν(VO) previously reported for RR spectra of vanadyl porphyrin π-cation radicals, relative to their neutral parents, are most reasonably ascribed to trans oxo ligand coordination (most probably a water molecule) during low-temperature electrochemical oxidation of the neutral species.

HDM of the vanadyl octaethylporphyrin on MoS2-based catalysts: Nature and repartition of the vanadium deposit

Electron microprobe analyses are used for characterizing the repartition of vanadium deposited during the hydrodemetallation of vanadyl octaethyl porphyrin on a classical Ni−MoS2-γ-Al2O3 catalyst. It is found that a part of vanadium can displace Ni initially interacting with the MoS2 platelets (Ni MoS phase) and another part is forming a crown as vanadium sulfide around the catalyst particle. The displaced nickel also formed large nickel sulfide crystallites.

Chemistry of Vanadyl Porphyrins

Abstract The chemistry of vanadyl porphyrins has been explored using vanadyl octaethylporphyrin as the type substance, and with special reference to the occurrence of such substances in petroporphyrins. Spectroscopic properties (electronic spectra, IR spectra, mass spectra) are described, and electronic spectra are employed to detect the occupation of the vacant axial coordination site. Direct substitution of vanadyl octaethylporphyrin furnishes meso -substituted products: various nitro, chloro and benzoyloxy derivatives are characterised. Trans alkylation is observed when vanadyl octaethylporphyrin is heated in vacuo on various supports, including clay minerals: the reaction provides a model for the generation of the homologous series of vanadyl polyalkylporphyrins found in crude oils and bitumens.

Linewidth inversion in electron resonance spectra

The electron resonance spectrum of the cation of vanadyl octaethylporphyrin exhibits an unusual linewidth variation with the outer spectral lines sharper than the inner components. This observation corresponds to an inversion of the line broadening normally observed for vanadium (IV) complexes. The linewidth inversion is found to result from the anisotropy in the vanadium hyperfine interaction and the zero-field splitting which, when coupled with the molecular rotation, provides a powerful relaxation process. It is possible to provide a quantitative account of the observed linewidth variation if the anisotropy in the g tensor for the electron on vanadium is also included in the theory.

On the origin of petroporphyrin homologues: the transalkylation of vanadyl octa-alkylporphyrins

Transalkylation occurs when vanadyl octaethylporphyrin is heated with alumina, with illite, or with montmorillonite.