Ni Octaethylporphyrin Research Articles

Preferential adsorption of nickel porphyrin to resin to increase asphaltene precipitation

This paper incorporates a multi-scale approach to evaluate the contribution of nickel porphyrin to the aggregation and precipitation of asphaltenes in a medium of solvent/precipitator. This study provides an in-depth understanding of the role of metalloporphyrins in the complex matrix of petroleum/bitumen. Density functional theory (DFT) calculations and laboratory experiments were performed to examine the changes in physicochemical and rheological properties of a selected bituminous structure when doped with Ni octaethylporphyrin (NiOEP). Based on the DFT results, light and small assemblies of asphaltene-resin (in the limit of a single asphaltene molecule) are easily attracted to NiOEP. This in turn may help establish the role of a metal center as a nucleating agent promoting formation of small nanoaggregates in solution. Our experiment results using size-exclusion chromatography and rheological analysis of bitumen doped with NiOEP indicate an increased number of small-size nanoaggregates, as evidenced by a reduction in large molecular size (LMS) and a reduction in the polydispersity index. The latter is indicative of the formation of uniform particle size within the matrix after being doped with NiOEP. The modeling results further show that in larger nanoaggregates, asphaltene-asphaltene intermolecular interactions are too strong to allow an asphaltene core to be affected by NiOEP. In such cases, small resin molecules surrounding asphaltenes show preferential adsorption to NiOEP and take distance from the original nanoaggregates, reducing nanoaggregates’ overall size. This was in line with UV–Vis absorption spectroscopy of a NiOEP-doped solution of bitumen showing that at least 95% of the added NiOEP remained in the maltenes portion containing resin, while only a trace amount of NiOEP was found in the asphaltenes. Considering the role of resins in stabilizing asphaltene aggregates, their departure can promote precipitation of asphaltene nanoaggregates. The latter was also evidenced by TLC-FID chromatography measurement, showing a substantial increase in asphaltene extracts in NiOEP-doped specimens compared to a control sample.

Biocatalytic activity of methyl-modified microperoxidase-11 in transformation of nickel- and vanadium-porphyrins

► Application of peroxidases as useful biocatalysts in green chemistry has been proved. ► Microperoxidase-11 (MP-11) was chemically modified to methylated MP-11 (mMP-11). ► We examined porphyrin transformation activity of MP-11 and its methylated derivative. ► mMP-11 showed higher activity against porphyrins in organic solvents than native MP-11. ► mMP-11 also exhibited a good degradation potential in the presence of 35% kerosene. Microperoxidase-11 (also known as MP-11) was chemically modified by boron trifluoride–methanol reagent to obtain methylated MP-11 (mMP-11). Porphyrin transformation capability of mMP-11 in a ternary solvent system was investigated by spectroscopic and kinetic techniques and compared with those of native MP-11. Methyl-modified MP-11 showed higher porphyrin transformation efficiency for synthetic nickel- and vanadium-porphyrins than native MP-11. Upon the chemical modification, the initial rates of porphyrin transformation in a solvent mixture of methylene chloride, methanol and water (up to 5%, v/v) were increased by 60.0-, 4.1-, 7.0- and 1.13-fold for VTPP (V-tetraphenyl porphyrin), VOEP (V-octaethyl porphyrin), NiTPP (Ni-tetraphenyl porphyrin) and NiOEP (Ni-octaethyl porphyrin), respectively. Modified MP-11 also exhibited a good degradation potential in the presence of kerosene (a crude oil fraction). In an organic solvent mixture containing kerosene (35%, v/v), mMp-11 in compared to unmodified MP-11 showed 46.0-, 2.1-, 14.1- and 3.1-times higher activity for VTPP, VOEP, NiTPP and NiOEP, respectively. Experimental data showed that concentration and type of organic hydroperoxides, temperature, and pH of the added water play significant roles on the porphyrin degradation.

Resonance Raman assignment of myeloperoxidase and the selected mutants Asp94Val and Met243Thr. Effect of the heme distortion

AbstractResonance Raman (RR) spectra have been acquired for human myeloperoxidase (MPO), and its Met243Thr and Asp94Val mutants with different excitation wavelengths and in polarized light. The proteins were characterized as ferric, ferrous and ferric–CN complexes in order to study the heme configuration in various coordination, spin and oxidation states. Well‐defined spectra of the five‐coordinate high spin (ferrous), six‐coordinate high spin (ferric) and low spin (ferric–CN) species were obtained. The data allowed us to propose an almost complete assignment of the RR bands. The richness of the RR spectra of MPO is because of the activation of almost all the in‐plane skeletal modes observed for the Ni–octaethylporphyrin model compound, induced by the distortion of the heme imposed by the covalent links with the protein. The two mutants, which lost at least one of the covalent links between the protein and the heme group, were useful to determine the effect of the symmetry lowering of the heme group. Copyright © 2006 John Wiley & Sons, Ltd.

Study of nonplanar distortions of Ni(II)-mesomethylporphyrins using spectroscopy of resonance Raman scattering

The role of mesomethyl substitution and of steric interaction of peripheral substituents in the formation of nonplanar distortions of the porphyrin macrocycle is studied for a series of Ni(II)-porphyrins. Resonance Raman spectra are recorded for Ni(II)-5-methyl-2,3,7,8,12,13,17,18-octaethylporphyrin (1); Ni(II)-2,5,8,12,18-pentamethyl-3,7,13,17-tetraethylporphyrin (2); and Ni(II)-3,5,7,12,17-pentamethyl-2,8,12,17-tetraethylporphyrin (3). The obtained spectra are compared with spectra of Ni-octaethylporphyrin (Ni-OEP) and Ni-etioporphyrin II. It is found that introducing one methyl group into a mesoposition leads to significant low-frequency distortions of the structure-sensitive lines of resonance Raman scattering. Specifically, frequenciesν 3 ,ν 11 ,ν 19 ,ν 2 , andν 10 decrease by 10–44 cm−1 while frequencyν 4 remains practically unchanged. It is shown that the observed spectral variations are caused by nonplanar distortions of the structure of Ni-porphyrins. The same tendency of the line displacement for tetragonal Ni-OEP and for compounds 1, 2, and 3 indicates that CH3-mesosubstituted Ni-porphyrins have a “corrugated” structure. The degree of nonplanarity is modulated by alkyl groups on pyrrole rings and increases in the porphyrin series 3→2→1. All mesomethyl-substituted Ni-porphyrins have spectral indications that the considered compounds are structurally heterogeneous in solution due to the presence of conformers with different degrees of planarity.

Photoluminescent Properties of Cadmium Selenide in Contact with Solutions and Films of Metalloporphyrins. Evidence for Semiconductor-Mediated Adduct Formation of Oxygen with Metalloporphyrins at Room Temperature

The band-edge photoluminescence (PL) intensity of etched n-CdSe single crystals is modulated through adsorption of 17 porphyrins and metalloporphyrins from methylene chloride solution. In nitrogen-saturated solution, the PL intensity is reversibly enhanced through adduct formation with octaethylporphyrin (OEP), tetraphenylporphyrin (TPP), their divalent Co, Cu, and Cd derivatives, and with tetra(pentafluorophenyl)porphyrin (TFP), tetra-(4-tolyl)porphyrin (TTP), and tetra-(4-pyridyl)porphyrin (TPyP); in contrast, the PL intensity is reversibly quenched by exposure to divalent Mg, Ni, and Zn complexes of OEP and TPP. The concentration dependence of the PL changes can be fit to the Langmuir adsorption isotherm model to yield binding constants that range from ∼103 to 105 M-1. Saturating methylene chloride with oxygen rather than nitrogen does not affect the CdSe PL nor does oxygen affect the (metallo)porphyrin absorption spectra in methylene chloride solution. However, many of the metalloporphyrin-induced PL responses and binding constants are substantially affected by the change in dissolved gas ambient, evidencing surface-mediated adduct formation between oxygen and these metalloporphyrins at room temperature. Particularly large effects are observed for the Mg, Ni, and Zn OEP and TPP complexes, which produce PL enhancements in oxygen-saturated solution rather than PL quenching in nitrogen-saturated solution. When a thin film of each metalloporphyrin is deposited onto CdSe substrates by solvent evaporation, oxygen can be detected through reversible PL enhancement (NiTPP and ZnTPP) or quenching (all other metalloporphyrins examined save for CdOEP and CdTPP, which gave no response) relative to a gaseous nitrogen ambient. Binding constants obtained were typically in the range ∼1−10 atm-1. Steric and electronic contributions to these effects are discussed.

Time-resolved resonance-Raman study of porphyrins and metalloporphyrins in the electronic excited states

Current developments of our Time-Resolved Resonance-Raman (TR3) studies on the (ππ*) excited states of free-base porphyrins and (dd) excited state of Ni-OctaEthylPorphyrin (NiOEP) in solutions are described. A device for quasi-simultaneous measurements has been developed to obtain correct difference spectra for pump/probe spectra of various delay times and probe-only spectrum. This technique is practically powerful to obtain TR3 spectra of porphyrins and metalloporphyrins. An orbital-symmetry marker band (ν 2) exhibited upshifts alongS 0→S 1→T 1 transitions for free-base octaethylporphyrin (H2OEP), while downshifts along the same transitions for free-base TetraPhenylPorphyrin (H2TPP). This is interpreted by the symmetry differences in the highest occupied molecular orbitals of H2OEP (a u-orbital) and H2TPP (b 1u-orbital). An intensity-borrowing mode (ν 19) was enhanced by the AlbrechtC-term in resonance with theS 1→S n transition, but not in resonance with theT 1→T n transition for H2OEP. This fact can be considered to be due to different vibronic couplings between the singlet and triplet manifolds. For the (dd) excited state of NiOEP, our TR3 study suggests the excess energy for the (ππ *) to (dd) transition was vibrationally cooled prior to the electronic relaxation from the (dd) state to the ground state with a relaxation time of ca. 300 ps. Comparison between Stokes- and anti-Stokes resonance Raman spectra for the delay time of 0 ps indicated that the lower limit of vibrational temperature in 0–40 ps time range is 750 K.

Time-resolved spontaneous and coherent raman scattering of Ni-octaethylporphyrin in excited electronic states

The results are presented of a detailed analysis of the vibrational structure of the excited triplet electronic state Td of Ni-octaethylporphyrin (Ni-OEP) in solution by means of spontaneous and coherent Raman scattering spectroscopy. The application of these two methods generated complementary information about the characteristics of the Td state.

Nickel porphyrin photophysics and photochemistry. A picosecond investigation of ligand binding and release in the excited state

The photophysical behavior and some photochemical processes for nickel (II) porphyrins have been examined with picosecond transient absorption techniques. Detailed results are reported for Ni-octaethylporphyrin (NiOEP) and Ni-protoporphyrin IX dimethylester (NiPPDME) in toluene, pyridine and piperidine. Excitation flashes at six wavelengths between 355 and 532 nm have been employed. In toluene, rapid (⩽ 15 ps) radiationless decay occurs via several pathways to the low-lying 3B 1g excited state. In the basic solvents pyridine and piperidine, excited states with nickel 1A 1g (d z2) character have a tendency to release ligands bound to the metal. Excited states with nickel 1B 1g or 3B 1g (d z2, d x 2-y 2 ) character on the other hand, have an affinity for basic ligands, which rapidly bind to the metal. The competition between radiationless decay, ligand binding, and ligand release depends on the nickel porphyrin, solvent, and excitation wavelength. A set of “rules” has been developed that gives a consistent view of all of our results and those of previous investigators. These results may be helpful in understanding photoprocesses in other transition-metal porphyrins, including hemes, which have particular biological significance.