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At least 973 records · Page 54Linked to original sources
PubMed2001

Prenylated flavonoids from Deguelia hatschbachii and their systematic significance in Deguelia.

Chemical investigation of dichloromethane and petrol extracts from the roots of D. hatshbachii A. M. G. Azevedo furnished thirteen compounds from which five are described for the first time and their structures were determined to be 3-(4'-hydroxyphenyl)-5-methoxy-6-( 3,3-dimethylallyl)-2"2"-dimethylchromene-(5",6":8,7)-3-(propyl-2-one)-4H-1-benzo-2,3-dihydropyran-2,4-dione; 6,4'-dihydroxy-3-(3,3-dimethylallyl)-2",2"-dimethylchromene (5",6":5,4)-2-methoxy deoxybenzoin; 6.4'-dihydroxy-3-(3,3-dimethylallyl)-2",2"-dimethylchromene (5",6":5,4)-2-methoxy-8-(propyl-2-one) deoxybenzon; 6-(3,3-dimethylallyl)-2",2"-dimethylchromene (5",6":4.5)-4'-hydroxy-3-methoxy stilbene and 3,5-dimethoxy-4'-hydroxy-4-(3,3-dimethylallyl) stilbene by spectral analysis (UV, IR, MS and ID- and 2D- NMR experiments). The root extracts and some isolated compounds were bioactive, as revealed by bioautography and brine shrimp lethality assays.

Fabaceae↗
PubMed1994

The expression of carbonic anhydrases II and IV in the human pancreatic cancer cell line (Capan 1) is associated with bicarbonate ion channels.

Human pancreatic ductal cells of the Capan 1 cell line differentiate progressively during growth. After the exponential growth phase, the cells elongate and become polarized with their apical poles covered by microvilli and separated from the basolateral pole by tight junctions. In this stationary phase, they form domes, which are thought to result from the exchange of water and electrolytes. In this study, we demonstrated, using patch-clamp techniques, that HCO3- ions exit via the g350 high conductance anionic channel we observed recently at the Capan 1 cell surface. This g350 channel was thought to be either a Cl-/HCO3- antiport or a simple HCO3- channel. The stilbene derivatives 4-acetamido-4 isothiocyano-2-2'-disulfonic acid (SITS) and 4,4' diisothiocyano stilbene-2,2' disulfonic acid (DIDS) reduced both the number of domes and the Cl- and HCO3- flux through the g350 channel. Moreover, using histochemical, immunocytochemical and biochemical methods we showed that Capan 1 cells express a specific pattern of carbonic anhydrases (CA). Two types of CA were detected: the CA II isozyme mainly localized in the cytoplasm, but also found beneath the inner leaflet of the apical plasma membrane, and the CA IV isozyme localized on the outer leaflet of the apical plasma membrane and microvilli. Their molecular masses were 30 (CA II) and 55 kDa (CA IV), respectively. They were expressed continuously during the exponential growth phase, although their activity increased greatly during the stationary phase. Inhibition of dome formation by acetazolamide indicated the existence of a direct relationship between dome formation and CA. Characteristic structures with a central electron-dense core surrounded by a light halo were observed on the surface of cell membrane using histochemical and immunocytochemical methods. These structures were thought to represent a channel, corresponding possibly to CA IV. Our observations suggest that Capan 1 cells, despite their neoplasic transformation, produce HCO3- ions in the same way as normal human pancreatic ductal cells. Capan 1 cells in culture may therefore represent a suitable model for studying pancreatic duct HCO3- secretion at the cellular and molecular levels.

Acetazolamide↗
PubMed1989

Multi-residue screening of bovine urine on xenobiotic oestrogens with an oestrogen radioreceptor assay.

An improved radioreceptor assay (RRA) is used for the screening of urine samples from cattle for the presence of exogenous oestrogenic anabolic compounds, e.g., stilbenes and zeranol. The method includes extraction of the hormones from urine samples with simultaneous purification using reversed-phase C18 cartridges. High-performance liquid chromatography is used to isolate the anabolics from the naturally occurring oestrogens. Fractions containing the stilbenes and zeranol are collected and subsequently analysed using the RRA with the oestrogen receptor, isolated from immature calf uteri, as a binder and tritiated 17 beta-oestradiol as a tracer. Urine samples from untreated calves and cows and samples from calves treated with zeranol-trenbolon acetate, dienoestrol or hexoestrol or samples containing diethylstilboestrol were analysed with this RRA method. Sensitivity, specificity and predictive values were calculated at different classification levels (0.4, 0.5, 0.6 and 1.0 ng/ml 'apparent' oestradiol in urine). An optimum sensitivity (89%) with a maximum specificity (95%) was reached at a classification level of 0.6 ng/ml. At this level the detection limits in urine samples are 0.5 ng/ml for hexoestrol, 0.6 ng/ml for diethylstilboestrol, 0.9 ng/ml for dienoestrol and 5.0 ng/ml for zeranol.

Animals↗
PubMed2002

Design and synthesis of lignostilbene-alpha,beta-dioxygenase inhibitors.

Lignostilbene-alpha,beta-dioxygenase cleaves the olefinic double bond of phenolic stilbenes by a mechanism similar to that of 9-cis-epoxycarotenoid dioxygenase, a key enzyme in abscisic acid biosynthesis. Several analogues of stilbene were designed and synthesized, and their efficacy as inhibitors of lignostilbene-alpha,beta-dioxygenase was examined. The compound (Z)-1-(4-hydroxyphenyl)-1-fluoro-2-phenylethene (2) was found to be a potent inhibitor of this enzyme with an IC(50) of 3 microM.

Dioxygenases↗
PubMed2002

Synthesis of (bis)sulfonic acid, (bis)benzamides as follicle-stimulating hormone (FSH) antagonists.

Screening efforts identified (bis)sulfonic acid, (bis)benzamides (1-3) as compounds that interact with the follicle stimulating-hormone receptor (FSHR) and inhibit FSH-stimulated cAMP accumulation with IC(50) values in the low micromolar range. Structure-activity relationship studies using novel analogues of 1-3 revealed that two phenylsulfonic acid moieties were necessary for activity and that the carbon-carbon double bond of the stilbene sub-series was the optimum spacer connecting these groups. Selected analogues (2, 14, and 50) were also able to block FSHR-dependent estradiol production in rat primary ovarian granulosa cells and progesterone secretion in a clonal mouse adrenal Y1 cell line. IC(50) values for these compounds in these assays were in the low micromolar range. Optimization of the benzoic acid side chains of 1-3 led to gains in selectivity versus activity at the thyroid stimulating hormone (TSH) receptor (TSHR). For instance, while stilbene (bis)sulfonic acid congener 2 was only 10-fold selective for FSHR over TSHR, analogue 50 with an IC(50) value of 0.9 microM in the FSHR-cAMP assay was essentially inactive at 30 microM in the TSHR-cAMP assay.

Animals↗
PubMed2002

Overexpression of Arabidopsis thaliana soluble epoxide hydrolase 1 in Pichia pastoris and characterisation of the recombinant enzyme.

Epoxide hydrolases are enzymes involved in metabolism and defense of plants. Genome scanning suggested the presence of several genes encoding epoxide hydrolase in Arabidopsis thaliana. To assure that the predicted genes are functional and the translated products have epoxide hydrolase activity analysis at the protein level is needed. We have started to clone the cDNAs and overexpress them for catalytic and physico-chemical analysis. We here report that Pichia pastoris serves as an efficient system for overexpression of soluble epoxide hydrolase 1 (AtsEH1) from A. thaliana. A tag containing six histidine residues was added to the N-terminus to enable efficient one-step purification on nickel-agarose. The enzyme was expressed at levels >18 mg.L(-1) of culture and a French Press was found to be effective to achieve cell lysis. The recombinant enzyme had a molecular mass of 37 or 38 kDa based on SDS-PAGE or MALDI-TOF analysis, respectively. The enzyme was highly active towards the substrate trans-stilbene oxide (TSO) and had a pH optimum at 7 and a temperature optimum at 54 degrees C. Using TSO as substrate the K(m) and V(max) values were determined to 5 micro M and 2 micromol min(-1) mg protein(-1), respectively. The activity was 50-fold lower towards cis-stilbene oxide. The stability over time was tested from 20 to 54 degrees C and the enzyme lost activity at varying degrees at the temperatures tested but was stable for several months at 4 degrees C.

Arabidopsis↗
PubMed2000

Blocking HIV replication by targeting Tat protein.

BACKGROUND: A rapid development of viral drug resistance poses a serious limitation in the current drug development programs against HIV. In turn, this obstacle forms the basis for new efforts, which utilize alternative viral targets. RESULTS: By aiming at the Tat-driven process of HIV gene regulation, we discovered a new class of compounds as well as a novel target. The candidate compound acts on the one hand by classically inhibiting Tat/TAR complexation, however, without binding to nucleic acids. CONCLUSIONS: Structure and molecular modeling/dynamics suggest that the stilbene derivative CGA137053 directly binds to Tat protein but not TAR RNA. As a completely new, second property, the compound also antagonizes a TAR-independent activity of free Tat protein by preventing the recently described upregulation of the HIV coreceptor CXCR4. With the stilbene CGA137053, we have identified a potent, double-hitting and chemically feasible Tat antagonist. The compound possesses high target specificity and low cytotoxicity, is not restricted to the Tat/TAR axis of HIV inhibition and highly active on HIV-infected, primary human cells.

Amides↗
PubMed2002

Pro-oxidant and antioxidant potential of catecholestrogens against ferrylmyoglobin-induced oxidative stress.

Ferryl heme proteins may play a major role in vivo under certain pathological conditions. Catecholestrogens, the estradiol-derived metabolites, can act either as antioxidants or pro-oxidants in iron-dependent systems. The aim of the present work was (1) to determine the effects of ferrylmyoglobin on hepatocyte cytotoxicity, and (2) to assess the pro/antioxidant potential of a series of estrogens (phenolic, catecholic and stilbene-derived) against ferrylmyoglobin induced lipid peroxidation in rat hepatocytes. Cells were exposed to metmyoglobin plus hydrogen peroxide to form ferrylmyoglobin in the presence of the transition metal chelator diethylentriaminepentaacetic acid. Results showed that ferrylmyoglobin induced an initial oxidative stress, mainly reflected in an early lipid peroxidation and further decrease in GSH and ATP. However, cells gradually adapted to this situation, by recovering the endogenous ATP and GSH levels at longer incubation times. Phenolic and stilbene-derived estrogens inhibited ferrylmyoglobin-induced lipid peroxidation to different degrees: diethylstilbestrol>estradiol>resveratrol. Catecholestrogens at concentrations higher than 1 microM also inhibited lipid peroxidation with similar efficacy. The ability of estrogens to reduce ferrylmyoglobin to metmyoglobin may account for their antioxidant activity. In contrast, physiological concentrations (100 pM-100 nM) of the catecholestrogens exerted pro-oxidant activities, 4-hydroxyestradiol being more potent than 2-hydroxyestradiol. The implications of these interactions should be considered in situations where local myoglobin or hemoglobin microbleeding takes place.

Animals↗
PubMed2003

Mono- and multilayer formation by diazonium reduction on carbon surfaces monitored with atomic force microscopy "scratching".

Contact mode atomic force microscopy (AFM) was used to intentionally scratch a monolayer deposited on a pyrolyzed photoresist film (PPF). The force was set to completely remove the monolayer but not to damage the underlying PPF surface. A line profile determined across the scratch with tapping mode AFM permitted determination of the monolayer thickness from the depth of the scratch. A statistical process was devised to avoid user bias in determining the monolayer thickness and was used to determine the thickness as a function of derivatization parameters. PPF surfaces modified by reduction of diazonium ions of stilbene, biphenyl, nitrobiphenyl, terphenyl, and nitroazobenzene (NAB) were scratched and their modification layer thicknesses determined. For single-scan derivatizations of 1 mM diazonium ions to -0.6 V versus Ag+/Ag, the biphenyl and stilbene monolayers exhibited thicknesses close to those expected for true monolayers. However, more extensive derivatization resulted in multilayers up to 6.3 nm thick for the case of NAB. Such multilayers imply that electrons are transmitted through the growing film during diazonium reduction, despite the fact that electron tunneling would not be expected to be operative over such long distances. The results are consistent with a conductance increase in the growing film, which yields a partially conductive layer that can support further diazonium ion reduction and additional layer growth.

Journal Article↗
PubMed1993

Modification of human hemoglobin with methyl acyl phosphates derived from dicarboxylic acids. Systematic relationships between cross-linked structure and oxygen-binding properties.

Human hemoglobin was reacted with five dicarboxylic acid bis(methyl phosphate) reagents under different ligand conditions. The bis(methyl phosphate) reagents tested were derived from fumaric, isophthalic, terephthalic, trans-stilbene-3,3'-dicarboxylic, and trans-stilbene-4,4'-dicarboxylic acids. These acyl phosphate mixed anhydrides are anionic electrophiles and will react with N-terminal amino and lysyl epsilon-amino groups to form amides. The major and many of the minor reaction products that result have been isolated and structurally characterized by globin chain and peptide analysis. Products which are not cross-linked, intrachain linked, and interchain singly and doubly cross-linked occur in proportions which depend upon the reaction conditions and reagent. Modifications of the beta chains were limited to the amino groups of beta 1Val, beta 82Lys, and, to a minor extent, beta 144Lys. In the case of the smaller reagents, the amino groups of alpha 1Val, alpha 99Lys, and, to a minor extent, alpha 139Lys were modified. The oxygen binding affinities of most of the major modified hemoglobins have been measured and are characterized by P50 values from about 1/2 to over 5 times that of unmodified human hemoglobin. Most show strong cooperativity with Hill coefficients (n) of 2.0 or greater. Several of the products that are cross-linked between the beta 1Val of one chain and the beta 82Lys of the other chain have oxygen affinities in a physiologically useful range for oxygen transport and delivery. An inverse linear correlation has been found between the log of P50 and bridging distances for the hemoglobins cross-linked between beta 1Val of one chain and the beta 82Lys of the other chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

Copper-dependent cleavage of DNA by bleomycin.

DNA strand scission by bleomycin in the presence of Cu and Fe was further characterized. It was found that DNA degradation occurred readily upon admixture of Cu(I) or Cu(II) + dithiothreitol + bleomycin, but only where the order of addition precluded initial formation of Cu(II)--bleomycin or where sufficient time was permitted for reduction of the formed Cu(II)--bleomycin to Cu(I)--bleomycin. DNA strand scission mediated by Cu + dithiothreitol + bleomycin was inhibited by the copper-selective agent bathocuproine when the experiment was carried out under conditions consistent with Cu chelation by bathocuproine on the time scale of the experiment. Remarkably, it was found that the extent of DNA degradation obtained with bleomycin in the presence of Fe and Cu was greater than that obtained with either metal ion alone. A comparison of the sequence selectivity of bleomycin in the presence of Cu and Fe using 32P-end-labeled DNA duplexes as substrates revealed significant differences in sites of DNA cleavage and in the extent of cleavage at sites shared in common. For deglycoblemycin and decarbamoylbleomycin, whose metal ligation is believed to differ from that of bleomycin itself, it was found that the relative extents of DNA cleavage in the presence of Cu were not in the same order as those obtained in the presence of Fe. The bleomycin-mediated oxygenation products derived from cis-stilbene were found to differ in type and amount in the presence of added Cu vs. added Fe. Interestingly, while product formation from cis-stilbene was decreased when excess Fe was added to a reaction mixture containing 1:1 Fe(III) and bleomycin, the extent of product formation was enhanced almost 4-fold in reactions that contained 5:1, as compared to 1:1, Cu and bleomycin. The results of these experiments are entirely consistent with the work of Sugiura [Sugiura, Y. (1979) Biochem. Biophys. Res. Commun. 90, 375-383], who first demonstrated the generation of reactive oxygen species upon admixture of O2 and Cu(I)--bleomycin.

Bleomycin↗
PubMed1996

Metal Complex-Catalyzed Epoxidation of Olefins by Dioxygen with Co-Oxidation of Aldehydes. A Mechanistic Study.

Mechanistic studies of the oxidation of olefins by dioxygen plus aldehyde in the presence of metal complexes such as metalloporphyrins and metal cyclam complexes have been carried out. Epoxides were the predominant products, with trace amounts of allylic oxidation products. cis-Stilbene was oxidized to a mixture of cis- and trans-stilbene oxides. It is concluded from this study that the principal role of the metal complexes is to aid in the initiation step for the free radical autoxidation of the aldehyde and that acylperoxy radicals generated in the autoxidation reaction (or metal complexes formed by complexation of the acylperoxy radicals) are the active epoxidizing agents.

Journal Article↗
PubMed2001

Conformational gating of long distance electron transfer through wire-like bridges in donor-bridge-acceptor molecules.

A series of five donor-bridge-acceptor (DBA) molecules in which the donor is tetracene, the acceptor is pyromellitimide, and the bridge molecules are oligo-p-phenylenevinylenes (OPV) of increasing length has been shown to undergo electron transfer (ET) by means of two mechanisms. When the bridge is short, strongly distance dependent superexchange dynamics dominates, whereas when the bridge is longer, bridge-assisted hopping dynamics prevails. The latter mechanism results in relatively soft distance dependence for ET in which the OPV oligomers act effectively as molecular wires. We now report studies on the critical influence that bridge dynamics have on electron transfer through these oligomers. The temperature dependence of the charge separation (CS) rates in all five molecules does not appear to obey the predictions of standard ET theories based upon the Condon approximation. All five molecules show behavior consistent with CS being "gated" by torsional motion between the tetracene donor and the first bridge phenyl ring. This is based on the near equivalence of the CS activation energies measured for all five molecules with the frequency of a known vibrational mode in 5-phenyltetracene. In the molecule containing a trans-stilbene bridge, a competition occurs between the tetracene-phenyl torsional motion and one that occurs between the vinyl group and the phenyls linked to it. This results in complex temperature-dependent CS that exhibits both activated and negatively activated regimes. The charge recombination (CR) reactions within the molecules which have the two shortest bridges, namely phenyl and trans-stilbene, show a weaker dependence on these molecular motions. The three molecules with the longest bridges all display complex temperature dependencies in both their rates of CS and CR, most likely because of the complex torsional motions, which arise from the multiple phenyl-vinyl linkages. The data show that long-distance electron transfer and therefore wire-like behavior within conjugated bridge molecules depend critically on these low-frequency torsional motions. Molecular device designs that utilize such bridges will need to address these issues.

Journal Article↗
PubMed2002

Unraveling the mechanism of epoxide formation from sulfur ylides and aldehydes.

Sulfur ylides R(2)S(+)-C(-)HR' react with aldehydes R' '-CHO to form epoxides, predominantly as the trans isomers, in a synthetically useful reaction which is increasingly used in its asymmetric variant with chiral sulfides. The mechanisms of the "model" reaction (R = Me, R' = R' ' = H) and the reaction forming stilbene oxide (R = Me, R' = R' ' = Ph) have been studied in detail using density functional theory, the B3LYP density functional, and flexible basis sets. It has been shown that for this reaction involving highly polar intermediates, continuum solvation models need to be used throughout to obtain reasonable results. For the reaction of benzaldehyde with dimethylsulfonium benzylide, the key steps are shown to be quasi [2 + 2] addition of the ylide to the aldehyde to form a betaine R'-CH(S(+)Me(2))-CH(O(-))-R' ' in which the charged groups are gauche to one another, and torsional rotation around the C-C single bond of the betaine to form its rotamer with the two charged groups anti. The final step, elimination of sulfide from this second rotamer of the betaine, is found to be facile. In the case of the anti pathway, leading to trans-stilbene epoxide, the initial addition is found to be rate-determining, whereas for the diastereomeric syn pathway, leading to the cis-epoxide, it is instead the torsional rotation which is slowest. These results are in excellent agreement with experiment, unlike previous computational work. The unexpected and apparently unprecedented (for C-C bond-forming reactions) importance of the torsional rotation step, especially in the syn case, is due to the fact that all the barriers involved are low-lying. This novel picture of the mechanism provides a sound basis for the future development of chiral sulfides for enantioselective epoxide synthesis.

Journal Article↗
PubMed2002

Activation of nitrous oxide and selective epoxidation of alkenes catalyzed by the manganese-substituted polyoxometalate, [Mn(III)2ZnW(Zn2W9O34)2]10-.

A manganese(III)-substituted polyoxometalate of the "sandwich" structure, [MnIII2ZnW(ZnW9O34)2]10-, catalyzed the highly selective (>99.9%) epoxidation of alkenes, such as 1-octene, 2-octene, and cyclohexene with nitrous oxide. Reactions occurred in homogeneous media at 150 degrees C under 1 atm N2O. The epoxidation had a linear reaction profile; turnover frequencies of 0.5-1.4 h-1 were measured. The reactions were also stereoselective; for example, cis-stilbene gave cis-stilbene oxide. From ESR spectroscopy, it was shown that a Mn(II) octahedral species is reversibly formed by reaction between the original Mn(III) polyoxometalate and N2O. Therefore, it would appear that a Mn(V)-oxo active species is not formed; it is possible that the activation of nitrous oxide was by its oxidation by the Mn(III) polyoxometalate.

Journal Article↗
PubMed2003

Highly efficient and selective epoxidation of alkenes by photochemical oxygenation sensitized by a ruthenium(II) porphyrin with water as both electron and oxygen donor.

Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phenylporphyrinatoruthenium(II) (Ru(II)TMP(CO)) as a photosensitizer, hexachloroplatinate(IV) as an electron acceptor, and an alkene in alkaline aqueous acetonitrile induces selective epoxidation of the alkene with high quantum yield (Phi = 0.6, selectivity = 94.4% for cyclohexene and Phi = 0.4, selectivity = 99.7% for norbornene) under degassed conditions. The oxygen atom of the epoxide was confirmed to come from a water molecule by an experiment with H(2)(18)O. cis-Stilbene was converted into its epoxide, cis-stilbeneoxide, without forming trans-stilbeneoxide. trans-Stilbene, however, did not exhibit any reactivity. Under neutral conditions, an efficient buildup of the cation radical of Ru(II)TMP(CO) was observed at the early stage of the photoreaction, while an addition of hydroxide ion caused a rapid reaction with the cation radical to promote the reaction with reversion to the starting Ru(II)TMP(CO). A possible involvement of a higher oxidized state of Ru such as Ru(IV), Ru(V), Ru(VI) through a dismutation of the Ru(III) species was excluded by an experiment with Ru(VI)TMP(O)(2). Decarbonylation of the Ru complex was also proven to be invalid. A reaction mechanism involving an electron transfer from the excited triplet state of Ru(II)TMP(CO) to hexachloroplatinate(IV) and subsequent formation of OH(-)-coordinated Ru(III) species, leading to an oxo-ruthenium complex as the key intermediate of the photochemical epoxidation, was postulated.

Alkenes↗
PubMed2004

Stereochemistry of isoplagiochin C, a macrocyclic bisbibenzyl from liverworts.

Cyclic bisbibenzyls, like isoplagiochins C (1) and D (2), are stereochemically intriguing molecules: Although not equipped with any of the traditional stereogenic elements that render molecules conformationally stable per se, they are sometimes isolated in an optically active form and are thus chiral at room temperature. The paper describes quantum chemical calculations, in particular investigations of the conformational space and molecular dynamics simulations, showing that the helicity is a property of the entire molecule, whose ring strain makes the molecule configurationally stable overall, with (formally) three stereogenic elements (two biaryl axes and one helical stilbene unit). Only one of the biaryl axes (the 'upper' one, joining C-12' and C-14) has a stable configuration, leading to a population of four interconverting diastereomers, yet without racemization at room temperature. On the basis of these conformational and dynamic calculations, the circular dichroism spectrum of isoplagiochin C (1) was calculated, leading to the first assignment of the absolute configuration of a cyclic bisbibenzyl. Accordingly, 1 has the P-configuration at the stereochemically stable biaryl axis and constitutes a mixture of diastereomers with respect to the other biaryl axis and the helical stilbene unit. From the temperature dependence of the racemization rates, an enantiomerization barrier of 101.6 kJ/mol was determined. Likewise, for the first time for cyclic bisbibenzyls, the enantiomeric ratio of this natural product was determined, by chromatography on a chiral phase with CD-coupling. Accordingly, 1 from Plagiochila deflexa is not enantiomerically pure, but occurs in a 85:15 ratio in favor of the enantiomer that has the P-configuration at the stereochemically stable axis.

Bibenzyls↗
PubMed2003

Laser flash photolysis formation and direct kinetic studies of manganese(V)-oxo porphyrin intermediates.

Irradiation of porphyrin-manganese(III) perchlorate complexes in acetonitrile with 355 nm laser light gave MnV-oxo intermediates that were characterized by their UV-vis spectra and reactivities. The MnV-oxo species of tetrakis(pentafluorophenyl)porphyrin (2), tetraphenylporphyrin (4), and tetra-(4-(N-methylpyridiniumyl))porphyrin (6) were generated. Second-order rate constants for reactions of 2 with substrates were as follows: 6.1 x 105 M-1 s-1 (cis-stilbene), 1.3 x 105 M-1 s-1 (diphenylmethane), 1.3 x 105 M-1 s-1 (ethylbenzene), and 0.55 x 105 M-1 s-1 (ethylbenzene-d10). In oxidations of cis-stilbene and diphenylmethane, the order of reactivity of the MnV-oxo species was 2 > 6 > 4.

Kinetics↗