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001-es BibID:	BIBFORM089116
Első szerző:	Sarka Lajos
Cím:	Synthesis, equilibrium and NMR studies of lanthanide(III) complexes of the N-mono(methylamide) and N'-mono(methylamide) derivatives of diethylenetriamine-N,N,N',N'',N''-pentaacetic acid / Lajos Sarka, István Bányai, Ernő Brücher, Róbert Király, Johannes Platzek, Bernd Radüchel, Heribert Schmitt-Willich
Dátum:	2000
ISSN:	0300-9246 1364-5447
Megjegyzések:	Two derivative ligands of diethylenetriamine-N,N,N',N ",N "-pentaacetic acid (H(5)DTPA; H5L1) were synthesized: the symmetric and asymmetric mono(methylamides) DTPA-N'-MA (H4L3) and DTPA-N-MA (H4L4). The protonation constants (log K-i(H)) of L-3 and L-4 were obtained by pH-potentiometric titration: 10.04, 8.41, 2.73, 1.94 and 10.18, 6.19, 3.55, 2.0, respectively. The protonation constants and the sites of protonation were interpreted on the basis of the pH dependence of the chemical shifts of the non-labile protons. The stability constants (K-LnL) of the complexes of these ligands with lanthanide(III) ions were determined by direct pH-potentiometry and competition titration. The stability constants decrease in the sequence LnL(1) > LnL(3) > LnL(4). The log K-LnL values of the complexes LnL(3) and LnL(4) increase with increasing atomic number of Ln(3+) from La to Gd, then remain roughly unchanged up to Er and subsequently decrease slightly to Lu. The H-1 and C-13 NMR spectra reveal the presence of 2 isomers for the complexes LnL(3) and 4 isomers for LnL(4) at around 0 degrees C. The AB multiplets of the acetate methylene protons demonstrate the long lifetime of the Ln(3+)-N bonds. The coupling observed between the methyl and methylene protons of the methylamide group in the 2-D COSY spectra indicates partial double bond character of the C-NMe bond.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk
Megjelenés:	Journal of the Chemical Society. Dalton Transactions. - 2000 : 20 (2000), p. 3699-3703. -
További szerzők:	Bányai István (1953-) (vegyész) Brücher Ernő (1935-) (vegyész) Király Róbert (1947-) (vegyész) Platzek, Johannes Radüchel, Bernd Schmitt-Willich, Heribert
Pályázati támogatás:	OTKA 23810 OTKA OTKA T 026115 OTKA FKFP 0448/1997
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001-es BibID:	BIBFORM087593
Első szerző:	Sarka Lajos
Cím:	The rates of the exchange reactions between [Gd(DTPA)](2-) and the endogenous ions Cu2+, and Zn2+: A kinetic model for the prediction of the in vivo stability of [Gd(DTPA)](2-) used as a contrast agent in magnetic resonance imaging / L. Sarka, L. Burai, E. Brücher
Dátum:	2000
ISSN:	0947-6539 1521-3765
Megjegyzések:	The kinetic stability of the complex [Gd(DTPA)]2?(H5DTPA=diethylenetriamine?N,N,N·,Nı,Nı?pentaacetic acid), used as a contrast?enhancing agent in magnetic resonance imaging (MRI), is characterised by the rates of the exchange reactions that take place with the endogenous ions Cu2+and Zn2+. The reactions predominantly occur through the direct attack of Cu2+and Zn2+on the complex (rate constants are 0.93?0.17?M?1s?1and (5.6?0.4)?10?2M?1s?1, respectively). The proton?assisted dissociation of [Gd(DTPA)]2?is relatively slow (k1=0.58?0.22?M?1s?1), and under physiological conditions the release of Gd3+predominantly occurs through the reactions of the complex with the Cu2+and Zn2+ions. To interpret the rate data, the rate?controlling role of a dinuclear intermediate was assumed in which a glycinate fragment of DTPA is coordinated to Cu2+or Zn2+. In the exchange reactions between [Gd(DTPA)]2?and Eu3+, smaller amounts of Cu2+and Zn2+and their complexes with the amino acids glycine and cysteine have a catalytic effect. In a model of the fate of the complex in the body fluids, the excretion and the "dissociation" of [Gd(DTPA)]2?are regarded as parallel first?order processes, and by 10 h after the intravenous administration the ratio of the amounts of "dissociated" and excreted [Gd(DTPA)]2?is constant. From about this time, 1.71?% of the injected dose of [Gd(DTPA)]2?is "dissociated". The results of equilibrium calculations indicate that the Gd3+released from the complex is in the form of Gd3+?citrate.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk chelates contrast agents exchange reactions gadolinium kinetics
Megjelenés:	Chemistry European Journal. - 6 : 4 (2000), p. 719-724. -
További szerzők:	Burai László Brücher Ernő (1935-) (vegyész)
Pályázati támogatás:	FKFP 0448/1997 Egyéb
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001-es BibID:	BIBFORM082453
Első szerző:	Sarka Lajos
Cím:	Studies on the kinetic stabilities of the Gd3+ complexes formed with the N-mono(methylamide), N'-mono(methylamide) and N,N"-bis(methylamide) derivatives of diethylenetriamine-N,N,N',N",N"-pentaacetic acid / Lajos Sarka, László Burai, Róbert Király, László Zékány, Ernő Brücher
Dátum:	2002
ISSN:	0162-0134
Megjegyzések:	High kinetic stability is an important requirement for the Gd3+ complexes used as contrast enhancement agents in magnetic resonance imaging. The kinetic stabilities of the Gd3+ complexes formed with DTPA-N-mono(methylamide) (L3), DTPA-N'-mono(methylamide) (L2) and DTPA-bis(methylamide) (L1) are characterized by the rates of the exchange reactions with Eu3+ and the endogenous Cu2+ and Zn2+. The exchange reactions occur via the proton-assisted dissociation of the complexes and direct attack of the exchanging metal ions on the complex. On the basis of the line-shape analysis of the 1H NMR spectra of the LaL2, obtained in the pH range 2.5-3.5, we assume that for the proton-assisted dissociation of the complexes the formation of an intermediate containing a free iminodiacetate group must be followed with the rupture of the metal-central nitrogen bond. At about pH>=5, the reactions between GdL2 or GdL3 and Cu2+ or Zn2+ proceed predominantly by direct reaction of the reactants, through the formation of dinuclear intermediates. The contribution of the proton-assisted dissociation is highly important for GdL1, but its reaction with Zn2+ is significantly slower than the reactions of GdL2 and GdL3. The overall rates of dissociation of GdL1, GdL2, GdL3 and Gd(DTPA)2- through H+ (pH 7.4), Cu2+ (1x10-6 M) and Zn2+ (1x10-5 M)-assisted reactions are surprisingly very similar. Replacement of one or two carboxylates with amide groups results in significantly decreased stability constants, but has practically no effect on the kinetic stability of the Gd3+ complexes, indicating the lower reactivity of the amide groups with Cu2+ and Zn2+.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk
Megjelenés:	Journal of Inorganic Biochemistry. - 91 : 1 (2002), p. 320-326. -
További szerzők:	Burai László Király Róbert (1947-) (vegyész) Zékány László (1948-) (vegyész) Brücher Ernő (1935-) (vegyész)
Pályázati támogatás:	OTKA T025462 OTKA
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