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001-es BibID:	BIBFORM085256
Első szerző:	Jászberényi Zoltán
Cím:	Synthesis and complexation properties of DTPA-N,N?-bis[bis(n-butyl)]-N?-methyl-tris(amide). Kinetic stability and water exchange of its Gd3+ complex / Z. Jászberényi, É. Tóth, T. Kálai, R. Király, L. Burai, E. Brücher, A. E. Merbach, K. Hideg
Dátum:	2005
ISSN:	1477-9226
Megjegyzések:	A novel DTPA-tris(amide) derivative ligand, DTPA-N,N -bis[bis(n-butyl)]-N -methyl-tris(amide) (H2L3) was synthesized. With Gd3+, it forms a positively charged [Gd(L3)]+ complex, whereas with Cu2+ and Zn2+ [ML3], [MHL3]+ and [M2L3]2+ species are formed. The protonation constants of H2L3 and the stability constants of the complexes were determined by pH potentiometry. The stability constants are lower than those for DTPA-N,N -bis[bis(n-butyl)amide)] (H3L2), due to the lower negative charge and reduced basicity of the amine nitrogens in (L3)2?. The kinetic stability of [Gd(L3)]+ was characterised by the rates of metal exchange reactions with Eu3+, Cu 2+ and Zn2+. The exchange reactions, which occur via proton and metal ion assisted dissociation of [Gd(L3)]+, are signi?cantly slower than for [Gd(DTPA)]2?, since the amide groups cannot be protonated and interact only weakly with the attacking metal ions. The relaxivities of [Gd(L2)] and [Gd(L3)]+ are constant between 10?20 ?C, indicating a relatively slow water exchange. Above 25 ?C, the relaxivities decrease, similarly to other Gd3+ DTPA-bis(amide) complexes. The pH dependence of the relaxivities for [Gd(L3)]+ shows a minimum at pH?9, thus differs from the behaviour of Gd3+?DTPA-bis(amides) which have constant relaxivities at pH 3?8 and an increase below and above. The water exchange rates for [Gd(L2)(H2O)] and [Gd(L3)(H2O)]+, determined from a variable temperature 17O NMR study, are lower than that for [Gd(DTPA)(H2O)]2?. This is a consequence of the lower negative charge and decreased steric crowding at the water binding site in amides as compared to carboxylate analogues. Substitution of the third acetate of DTPA5? with an amide, however, results in a less pronounced decrease in kex than substitution of the ?rst two acetates. The activation volumes derived from a variable pressure 17O NMR study prove a dissociative interchange and a limiting dissociative mechanism for [Gd(L2)(H2O)] and [Gd(L3)(H2O)]+, respectively.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk
Megjelenés:	Dalton Transactions. - 4 (2005), p. 694-701. -
További szerzők:	Tóth Éva (1960-) (kémikus) Kálai T. Király Róbert (1947-) (vegyész) Burai László Brücher Ernő (1935-) (vegyész) Merbach, André E. Hideg Kálmán
Pályázati támogatás:	T 038 364 OTKA
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001-es BibID:	BIBFORM087718
Első szerző:	Szilágyi Erika
Cím:	Equilibria and formation kinetics of some cyclen derivative complexes of lanthanides / Erika Szilágyi, Éva Tóth, Zoltán Kovács, Johannes Platzek, Bernd Radüchel, Ernö Brücher
Dátum:	2000
ISSN:	0020-1693
Megjegyzések:	The kinetics of the formation reactions between the lanthanide(III) ions Ce 3+, Eu 3+ and Yb 3+ and four cyclen derivative ligands, DO3A-B, DO3A-ME, DO2A and DO2A-2B, were studied by spectrophotometry and a stopped-flow method at 25?C in 1.0 M KCl solutions. The reactions were found to be of first order, which was interpreted in terms of the formation of a diprotonated intermediate, Ln(H 2L) +. The formation of products occurs via deprotonation and rearrangement of the intermediate, characterised by the rate constant, k r. The rate law obtained, k r= k OH[OH ?], is similar to those obtained for the formation reactions of DOTA and DOTA derivative complexes. The rate constants, k OH, decrease with decrease in the number of charged carboxylate functional groups in the ligands; the lowest rates were found for the formation of the DO2A complexes. The formation rates increase significantly from Ce 3+ to Yb 3+. The direct proportionality between the formation rates and [H +] ?1 was interpreted by assuming the equilibrium formation of a monoprotonated intermediate, Ln(HL), which undergoes deprotonation in a slow, rate-determining step. The validity of general base catalysis was detected in the formation reactions, which supports the assumption of the rate-controlling role of deprotonation of the monoprotonated intermediate. The protonation constants of the ligands DO3A-ME and DO2A-2B and the stability constants of their complexes were also determined. The ligand DO2A forms the usual complexes Ln(DO2A) + and the unusual species Ln(DO2A) 2 ? . In the complexes Ln(DO2A) 2 ? , the two ligands exhibit different coordination modes which were demonstrated by 1H NMR spectroscopy.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk Stability constants Lanthanide complexes Cyclen complexes
Megjelenés:	Inorganica Chimica Acta. - 298 : 2 (2000), p. 226-234. -
További szerzők:	Tóth Éva (1960-) (kémikus) Kovács Zoltán Platzek, Johannes Radüchel, Bernd Brücher Ernő (1935-) (vegyész)
Pályázati támogatás:	T 025462 OTKA
Internet cím:	Szerző által megadott URL DOI Intézményi repozitóriumban (DEA) tárolt változat
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