7,916 research outputs found
Gian-Carlo Rota, Mathematician and Philosopher
No full textTraduzione dell'edizione italiana: Vite Matematiche, curata da C. Bartocci, R. Betti, A. Guerraggio, R. Lucchetti, copyright 2007,
Springer-Verlag Italia
Catalytic reduction of CCl4 by a meso-tetraphenyl porphyrin excited state in benzene/ethanol mixed solvent.
No full textThe irradiation of benzene/CCl4 solutions of meso-tetraphenyl porphyrin (TPP) leads to an electron transfer from an electronic excited state of the porphyrin to CCl4 giving an intermediate which is likely to be the encounter pair, (TTP+.. CCl4-.). This is completely reconverted to the original species by a fast back electron transfer except in the presence of ethanol where the reduction products of CCl4, Cl- and CHCl3, are formed with catalytic yield. A mechanism is proposed where ethanol plays the twofold role of favouring the dissociation of the encounter pair by increasing the polarity of the reaction environment, and of restoring TPP by reducing the TPP+. radical cation. The oxidation of ethanol produces H+ ions which give rise to the protonation of the pyrrolic nitrogens to give the TPPH22+ dication, which, however, fails to form in KOH containing solutions
In vivo or in vitro modulating effects of vincristine on the generation of allogeneic cytotoxic lymphocytes in vitro
No full textPhotochemistry of iron porphyrins in homogeneous and heterogeneous catalysis
No full textThe results illustrated in this report show that photochemistry is a praticable way to obtain catalytic redox systems based on metalloporphyrins working in mild conditions and exhibiting the high selectivity of enzymatic systems
Riduzione fotochimica di Fe(III) tetrafenilporfirina tetrasolfonata in solvente misto piridina-etanolo-acqua
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Photochemistry of dimeric and trimeric hydroxo-bridged diammine platinum(II) complexes in aqueous solution
No full textThe irradiation of aerated aqueous solutions containing cis-Pt(NH3)2(H2O)2+2 with 254-nm light gives rise to the formation of a blue product identified as a mixed valence (Pt(II)/Pt(IV) = 2) hydroxo bridged trinuclear cationic complex [Pt3(NH3)4(OH)6]2+. The photoreactive species have been identified as the dimeric and trimeric hydroxo bridged platinum compounds that are present in solution and have the maximum concentration at pH 6.5. The reaction is initiated in a OH → Pt charge transfer excited state, to give a primary photoreaction intermediate which undergoes thermal air oxidation to give the final blue product. © 1982
Ohotochemical formation of a mixed valence platinum compound
No full textThe excited state of a platinum trimer complex leads to the formation of a poly-nuclear species that is partially oxidized by oxygen giving rise to the formation of a mixed valence Pt(II)-Pt(IV) trinuclear blue complex
Oxidative addition - reductive elimination sequences in the photochemistry of some bis(phosphine)platinum complexes
No full textThe photolysis of [L2Pt(C2H4)] (L = PPh3, P(p-C6H4CH3)3 complexes in halocarbon solvents (CH2Cl2, CH2Br2) gives C2H4 and the coordinatively unsaturated species [L2Pt]. Photolysis of platinum metallacycles [L2Pt(CH2)4] (L = PPh3, P(n-Bu)3) generates alkanes, alkenes and [L2Pt]. The [L2Pt] centers are very reactive, and under prolonged photolysis undergo oxidative addition of CH2Cl2 forming the trans-[L2Pt(CH2Cl)Cl] complexes. Under appropriately controlled conditions the trans complexes isomerize to cis species before bimolecular C2H4 elimination occurs and [L2PtCl2] is formed as the final product. The oxidative addition-reductive elimination mechanism is discussed on the basis of spin-trapping experiments, quantum yield values, and the sensitivity to radical inhibitors and to solvents. © 1983
An ESR spin trapping investigation on the photoreduction of chlorohemin in mixed solvents
No full textRadical scavenging by nitrone compounds is used in conjunction with ESR spectroscopy in order to obtain evidence for radical formation in the photoreduction of chlorohemin in aqueous alcoholic mixed solvents. The formation of adducts between hydrogen atoms and the spin traps appears to be the most important process in aerated and in pyridine-containing solutions. Evidence for the formation of hydroxyethyl adducts is obtained when the alcoholic component of the solvent is ethanol. In deaerated solutions not containing pyridine, no evidence is obtained for radical formation. The results are interpreted in terms of hydrogen abstraction by the nitrone from an alkoxy radical formed together with Fe(II) in the primary photoreduction. The abstraction process strongly competes with cage re-oxydation, as well as with the diffusion of the alkoxy radical in the solvent bulk where it would rapidly react to give hydroxy radicals. The role of pyridine and oxygen may respectively be stabilizing and oxidizing the Fe(II) species before it undergoes cage re-oxidation. © 1983
Photoreduction of fe(iii) protoporphyrin ix in ethanol-water solutions containing bifunctional ligands
No full textThe irradiation of Fe(III) protoporphyrin IX [Fe(III)PPIX) in a thoroughly deoxygenated 35% ethanol-water solution containing pyrazine (pyz) leads to changes in the visible spectrum that are indicative of Fe(II)PP species formation. With a large excess of pyz the spectrum is similar to that of the Fe(II) pyridine hemochrome, suggesting that the monomer Fe(II)PP(pyz)2 is formed. With a lower pyz content, the photochemically formed bis-pyz complex converts to a polymeric Fe(II)PP species. A similar photochemical behaviour is observed when piperazine or 4,4′-bipyridine are used as bridge ligands instead of pyz. The origin of the absorptions characteristic of the photoreaction products is discussed on the basis of the dependence of the spectra on the nature of the bridge ligands. © 1986
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