Pietro Tagliatesta

Oxidation of unsaturated monoterpenes with hydrogen peroxide catalysed by manganese(III) porphyrin complexes

Oxidation of (+)-3-carene (1), nerol (2) and geraniol (3) by hydrogen peroxide in the presence of catalytic amounts of several manganese(III) porphyrin complexes with electron withdrawing and electron donating groups was examined. The reactions were carried out at room temperature in acetonitrile, using aqueous hydrogen peroxide as oxidant and ammonium acetate as co-catalyst. The oxidation reactions of 3-carene (1) showed high conversion of the substrate with all metalloporphyrins tested and four major products were identified and characterised, namely α-3,4-epoxycarane (7), β-3,4-epoxycarane (8), 3-caren-5-one (9) and 3-carene-2,5-dione (10). Nerol (2) oxidation reactions gave rise to 2,3-epoxynerol (11), 6,7-epoxynerol (12) and 2,3,6,7-diepoxynerol (13). In the case of geraniol (3), besides 2,3-epoxygeraniol (14), 6,7-epoxygeraniol (15) and 2,3,6,7-diepoxygeraniol (16), the oxidation reactions afforded 6,7-epoxygeranial (17). The terminal 6,7 double bond of nerol and geraniol was preferentially epoxidised. The regioselectivity induced by different porphyrins was investigated.

Transport and equilibrium characteristics of γ-lithium vanadium bronze

Abstract The diffusion coefficient of Li + in the γ-lithium vanadium bronze (Li 1+ x V 3 O 8 ) has been measured with the long-pulse galvanostatic technique. Values ranging from 1.7×10 −7 cm 2 s −1 , at x =0.3, to 2.2×10 −8 cm 2 s −1 , at x = 1.4, have been measured. The thermodynamic factors, d ln a/d ln c , determined from the OCV/ x curve and from voltage relaxation after the current pulse, have a mean value of ∼15. The pseudo two-phase region observed in the OCV/ x curve at high Li + concentrations seems attributable to ordering of Li + in specific sites and to alteration of the unit cell. This process is reversible as shown by X-ray diffractometry. Finally, from OCV/ t plots at different x , the partial molar entropy of Li + was determined. The values, on account of the large d E ( x )/d t measured, are higher than those found for V 6 O 13 or TiS 2 .

Metalloporphyrin catalysts for organic synthesis

Novel chiral systems for the catalytic asymmetric oxidation and cyclopropanation of olefins based on metalloporphyrins containing iron, ruthenium and manganese, have been recently introduced. High catalyst turnover numbers and sometimes high enantiomeric excess were observed. New catalytic reactions with metalloporphyrins have recently been reported; these are the olefination of aldehydes and cyclotrimerization of terminal alkynes. Dendrimers and polymers containing metalloporphyrins, have also been found to be efficient catalysts for oxidation and carbene transfer.

Micelle‐Bound Metalloporphyrins as Highly Selective Catalysts for the Epoxidation of Alkenes

The porphyrin-surfactant interaction determines the activity of the title catalysts. Amphiphilic porphyrin derivatives (e.g. 1 with M=MnCl, R=CH2 CH2 (OCH2 CH2 )2 OH) are easy to prepare and can be included in micellar phases.

Epoxidation and hydroxylation reactions catalysed by β-Tetrahalogeno and β-octahalogeno manganese porphyrins

Abstract β-Tetrahalogenated manganese(III) porphyrins are more efficient catalysts than the β-octahalogenated ones in oxidations promoted by H 2 O 2 .

Redox mechanism and cycling behaviour of nonylbenzo-hexaquinone electrodes in Li cells

Abstract Nonylbenzo-hexaquinone (NBHQ), a quinonoid polymer of low molecular weight, has been reinvestigated as a cathode material for Li cells. Its reduction mechanism gives rise at first, in a 3-electron process, to an irreversible species involving the formation of radical anions. Successively, a direct two-electron reduction of other quinone groups occurs. This second step, which involves 4 e in quasi-thermodynamic conditions, is reversible and allows cells of the type Li/LiClO 4 -PC,DME/NBHQ,C to be cycled for more than 500 cycles at the C/2 rate between 3.5 and 2.0 V. The average energy density during this cycling was 160 Wh/kg, based on the weight of the cathode material (additives included).

Conjugated eicosapentaenoic acid inhibits human topoisomerase IB with a mechanism different from camptothecin

Conjugated eicosapentaenoic acid (cEPA) has been found to have antitumor effects which has been ascribed to their ability to inhibit DNA topoisomerases and DNA polymerases. We here show that cEPA inhibits the catalytic activity of human topoisomerase I, but unlike camptothecin it does not stabilize the cleavable complex, indicating a different mechanism of action. cEPA inhibits topoisomerase by impeding the catalytic cleavage of the DNA substrate as demonstrated using specific oligonucleotide substrates, and prevents the stabilization of the cleavable complex by camptothecin. Preincubation of the inhibitor with the enzyme is required to obtain complete inhibition. Molecular docking simulations indicate that the preferred cEPA binding site is proximal to the active site with the carboxylic group strongly interacting with the positively charged K443 and K587. Taken together the results indicate that cEPA inhibitor does not prevent DNA binding but inhibits DNA cleavage, binding in a region close to the topoisomerase active site.

Epoxidation and hydroxylation reactions catalyzed by the manganese and iron complexes of 5,10,15,20-tetrakis(2,6-dimethoxyphenyl)porphyrin

Abstract Manganese(III) and iron(III) complexes of 5,10,15,20-tetrakis-(2,6-dimethoxyphenyl)porphyrin (H2TDMeOPP) were tested as catalysts in the epoxidation of alkenes and in the hydroxylation of adamantane with H2O2 (in the presence of imidazole) or PhIO as oxidants. The behavior of the two catalysts is compared with that of the corresponding manganese(III) and iron(III) complexes of 5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin and 5,10,15,20-tetraphenylporphyrin, and the observed differences ascribed to the electron donating effect of the methoxy groups.

Synthesis of unsymmetrical porphyrin dimers containing β-octaalkyl and meso-tetraphenylporphyrin subunits

Methodology for synthesis of phenyl-linked unsymmetrical dimers containing 8,12-diethyl 2,3,7,12,13,17,18-hexamethylporphyrin and meso-tetraphenylporphyrin subunits is reported. Hetero metal complexes of these dimers can be prepared by following two different routes.

Remarkable selectivity in the cyclopropanation reactions catalysed by an halogenated iron meso-tetraphenylporphyrin

Abstract Iron(II) meso -tetra(2′,6′-dichlorophenyl)porphyrin, Fe II (TDCPP) catalyses the cyclopropanation of styrenes by ethyldiazoacetate with high yields and remarkable anti selectivities. The reaction mechanism is discussed and compared with that for the rhodium catalysts. Some evidences for the presence of a radical intermediate in the iron catalysed reactions are also discussed.