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001-es BibID:	BIBFORM006214
Első szerző:	Polshin, Victor
Cím:	Attaining control by design over the hydrolytic stability of Fe-TAML oxidation catalysts / Polshin, V., Popescu, D. L., Fischer, A., Chanda, A., Horner, D. C., Beach, E. S., Henry, J., Qian, Y. L., Horwitz, C. P., Lente, G., Fabian, I., Munck, E., Bominaar, E. L., Ryabov, A. D., Collins, T. J.
Dátum:	2008
Megjegyzések:	The iron(III) complexes of tetra amidato macrocyclic ligands (TAMLs) ([Fe{1-X-1-2-X2C6H2-4,5-(NCOCMe2NCO)(2)CR2}(OH2)](-), 1: X-1 = X-2 = H, R-2 = Me-2 (a), R-2 = (CH2)(2) (b); X-1 = X-2 = Cl, R-2 = F-2, (c), etc.), which the proton is known to demetalate at pH < 3, are also subject to catalyzed demetalation by Bronsted acid buffer components at pH 4-9 such as H2PO4-, HSO3-, and CH3- CO2H, HO2CCH2CO2-. Buffers based on pyridine (py) and tris(hydroxymethyl)aminomethane (TRIS) are catalytically inactive. Where reactions proceed, the products are demetalated TAMLs and iron species of variable composition. Pseudo-first-order rate constants for the demetalation (k(obs)) are linear functions of the acid concentrations, and the effective second-order rate constants k(1),(eff) have a hyperbolic dependence on [H+] (k(1),eff = a(1)[H+]/(b(1)+[H+]). The rate of demetalation of 1a in H2PO4-/HPO42- buffer is appreciable, but the k(obs) values for 1b and 1c are immeasurably low, showing that the rates are strongly affected by the CR2 or "tail" fragments, which are known to potently affect the TAML basicity. The reactivities of 1 depend insignificantly on the aromatic ring or "head" group of 1. The proposed mechanism involves precoordination of the acidic buffer species followed by hydrolysis. The demetalating abilities of buffer species depend on their structures and acidities. Thus, although pyridine-2-carboxylic (picolinic) acid catalyzes the demetalation, its 3- and 4-isomers (nicotinic and isonicotininc acids) are inactive. The difference is rationalized to result from the ability that only coordinated picolinic acid has to deliver a proton to an amidato nitrogen in an intramolecular manner. The reaction order in picolinic acid equals one for la and two for 1a. For 1b, "inactive" pyridine and nicotinic acid speed up the demetalation in the presence of picolinic acid, suggesting that the second order arises from the axial binding of two pyridine molecules, one of which must be picolinic acid. The binding of pyridine- and imidazole-type ligands was confirmed by UV/vis equilibrium measurements and X-ray crystallography. The implications of these mechanistic findings for designing superior Fe-TAML oxidation catalysts and catalyst formulations are discussed using the results of DFT calculations.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
Megjelenés:	Journal of the American Chemical Society. - 130 : 13 (2008), p. 4497-4506. -
További szerzők:	Popescu, Delia-Laura Fischer, Andreas Chanda, Arani Horner, David C. Beach, Evan S. Henry, Jennifer Qian, Yong-Li Horwitz, Colin P. Lente Gábor (1973-) (vegyész) Fábián István (1956-) (vegyész) Munck, Eckard Bominaar, Emile L. Ryabov, Alexander D. Collins, Terrence J.
Internet cím:	elektronikus változat elektronikus változat
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001-es BibID:	BIBFORM016482
Első szerző:	Popescu, Delia-Laura
Cím:	Thermodynamic, Electrochemical, High-Pressure Kinetic, and Mechanistic Studies of the Formation of Oxo Fe-IV-TAML Species in Water / Delia-Laura Popescu, Melanie Vrabel, Ariane Brausam, Peter Madsen, Gabor Lente, Istvan Fabian, Alexander D. Ryabov, Rudi van Eldik, Terrence J. Collins
Dátum:	2010
ISSN:	0020-1669
Megjegyzések:	Stopped-flow kinetic studies of the oxidation of Fe-II-TAML catalysts, [Fe{1,2-X2C6H2-4,5-(NCOCMe2NCO)(2)CMe2}-(OH2)](-) (1), by t-BuOOH and H2O2 in water affording Fe-IV species has helped to clarify the mechanism of the interaction of 1 with primary oxidants. The data collected for substituted Fe-III-TAMLs at pH 6.0-13.8 and 17-45 degrees C has confirmed that the reaction is first order both in 1 and in peroxides. Bell-shaped pH profiles of the effective second-order rate constants k(1) have maximum values in the pH range of 10.5-12.5 depending on the nature of 1 and the selected peroxide. The "acidic" part is governed by the deprotonation of the diaqua form of 1 and therefore electron-withdrawing groups move the lower pH limit of the reactivity toward neutral pH, although the rate constants k(1) do not change much. The dissection of k(1) into individual intrinsic rate constants k(1) ([FeL(OH2)(2)](-) + ROOH), k(2) ([FeL(OH2)OH)](2-) + ROOH), k(3) ([FeL(OH2)(2)](-) + ROO-), and k(4) ([FeL(OH2)OH)](2-) + ROO-) provides a model for understanding the bell-shaped pH-profiles. Analysis of the pressure and substituent effects on the reaction kinetics suggest that the k(2) pathway is (i) more probable than the kinetically indistinguishable k(3) pathway, and (ii) presumably mechanistically similar to the induced cleavage of the peroxide O-O bond postulated for cytochrome P450 enzymes. The redox titration of 1 by Ir-IV and electrochemical data suggest that under basic conditions the reduction potential for the half-reaction [(FeL)-L-IV(=O)(OH2)](2-) + e(-) + H2O -> [(FeL)-L-III(OH)(OH2)](2-) + OH- is close to 0.87 V (vs NHE).
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban coupled electron-transfer peroxide-activating catalysts tert-butyl hydroperoxide hydrogen-peroxide aqueous-solution oxoiron(iv) porphyrin oxidation catalysts compound-ii azo dyes iron(iii)
Megjelenés:	Journal of Biological Inorganic Chemistry. - 49 : 24 (2010), p. 11439-11448. -
További szerzők:	Vrabel, Melanie Brausam, Ariane Madsen, Peter Lente Gábor (1973-) (vegyész) Fábián István (1956-) (vegyész) Ryabov, Alexander D. Eldik, Rudi, Van Collins, Terrence J.
Internet cím:	DOI Intézményi repozitóriumban (DEA) tárolt változat
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