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001-es BibID:	BIBFORM016454
Első szerző:	Baranyai Zsolt (vegyész)
Cím:	Equilibrium Studies on the Gd3+, Cu2+ and Zn2+ Complexes of BOPTA, DTPA and DTPA-BMA Ligands: Kinetics of Metal-Exchange Reactions of Gd(BOPTA) (2-) / Zsolt Baranyai, Zoltán Pálinkás, Fulvio Uggeri, Ernő Brücher
Dátum:	2010
ISSN:	1434-1948
Megjegyzések:	The stability and protonation constants of the complexes formed between the ligand BOPTA [H(5)BOPTA: 4-carboxy-5,8,11-tris(carboxymethyl)-1-phenyl-2-oxa-5,8,11-triazatrideca n-13-oic acid] and Gd3+, Cu2+, and Zn2+ have been determined by pH potentiometry (Gd3+, Zn2+) and spectrophotometry (Cu2+) at 25 degrees C and at constant ionic strength maintained by 0.15 M NaCl. For comparison, the stability and protonation constants of the complexes of Gd3+, Cu2+, and Zn2+ formed with DTPA and DTPA-BMA {H(5)DTPA: diethylenetriamine-N,N,N',N '',N ''-pentaacetic acid, H(3)DTPA-BMA: 2,2'-[(carboxymethyl)imino]bis[ethylenebis(methylcarbamoyl-methyl)imino] diacetic acid} have also been determined under similar conditions. The stability constants (log K-ML) of the complexes of BOPTA and DTPA are very similar, but in 0.15 m NaCl the protonation constants of the ligands (log K-j(H)) and the log K-ML values are lower than those obtained in 0.1 M KCl or Me4NCl by 0.3-0.9 log K units. The order of selectivity of the ligands for Gd3+ over Zn2+ is BOPTA > DTPA > DTPA-BMA. The complex [Cu(DTPA-BMA)](-) deprotonates in the pH range 7-10 with the dissociation of an amide NH group and the coordination of the amide N atom. The kinetics of the exchange/transmetallation reactions between the complex [Gd(BOPTA)](2-) and the metal ions Cu2+, Zn2+, and Eu3+ have been studied by spectrophotometry (Cu2+, Eu3+) and relaxometry (Zn2+) in the pH range 3.3-6 at 25 degrees C in 0.15 m NaCl. The reactions with Cu2+ and Zn2+ occur predominantly with direct attack of the metal ions on the [Gd(BOPTA)](2-) complex. The kinetic activity of Eu3+ is lower, and in the exchange reactions with Eu3+ the proton-assisted dissociation of [Gd(BOPTA)](2-) (which is followed by fast reaction between the free ligand and Eu3+) could be also investigated. The rate constants, characterizing the proton-assisted dissociation of [Gd(BOPTA)](2-) and the exchange reactions occurring with the direct attack of Cu2+, Zn2+, and Eu3+ on the complex, are lower by about 30-90% than the rate constants obtained earlier for similar transmetallation reactions of [Gd(DTPA)](2-). The half-time for the dissociation of [Gd(BOPTA)](2-) at pH 7.4 and at 25 degrees C in the presence of 1 x 10(-5) m Zn2+ and 1 x 10(-5) M Cu2+ is 169 h.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban Lanthanides Thermodynamics Kinetics Reaction mechanisms mri contrast agents diethylenetriaminepentaacetic acid stability ions dissociation dimeglumine constants biodistribution thermodynamics gadopentetate
Megjelenés:	European Journal of Inorganic Chemistry. - 13 (2010), p. 1948-1956. -
További szerzők:	Pálinkás Zoltán (1984-) (vegyész) Uggeri, Fulvio Brücher Ernő (1935-) (vegyész)
Internet cím:	DOI Intézményi repozitóriumban (DEA) tárolt változat
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001-es BibID:	BIBFORM006209
Első szerző:	Mato-Iglesias, Marta
Cím:	Lanthanide complexes based on a 1,7-diaza-12-crown-4 platform containing picolinate pendants : a new structural entry for the design of magnetic resonance imaging contrast agents / Mato-Iglesias, M., Roca-Sabio, A., Palinkas, Z., Esteban-Gomez, D., Platas-Iglesias, C., Toth, E., de Blas, A., Rodriguez-Blas, T.
Dátum:	2008
ISSN:	0020-1669
Megjegyzések:	We have synthesized a new macrocyclic ligand, N,N'-Bis[(6-carboxy-2-pyridyl)methyl]-1,7-diaza-12-crown-4 (H(2)bp12c4), designed for complexation of lanthanide ions in aqueous solution. The X-ray crystal structure of the Gd-III complex shows that the metal ion is directly bound to the eight donor atoms of the bp12c4 ligand, the ninth coordination site being occupied by an oxygen atom of a carboxylate group of a neighboring [Gd(bp12c4)](+) unit, while the structure of the Lu-III analogue shows the metal ion being only eight-coordinate. The hydration numbers obtained from luminescence lifetime measurements in aqueous solution of the Eu-III and Tb-III complexes suggest an equilibrium in aqueous solution between a dihydrated (q = 2), ten-coordinate and a monohydrated (q = 1), nine-coordinate species. This has been confirmed by a variable temperature UV-vis spectrophotometric study on the Eu-III complex. The structure of the complexes in solution has been investigated by H-1 and C-13 NMR spectroscopy, as well as by theoretical calculations performed at the DFT (B3LYP) level. The results indicate that the change in hydration number occurring around the middle of the lanthanide series is accompanied by a change in the conformation adopted by the complexes in solution [Delta(lambda lambda lambda lambda) for q = 2 and Lambda(delta lambda delta lambda) for q = 1]. The structure calculated for the Yb-III complex (Lambda(delta lambda delta lambda)) is in good agreement with the experimental structure in solution, as demonstrated by the analysis of the Yb-III-induced paramagnetic H-1 shifts.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
Megjelenés:	Inorganic Chemistry. - 47 : 17 (2008), p. 7840-7851. -
További szerzők:	Roca-Sabio, Adrián Pálinkás Zoltán (1984-) (vegyész) Esteban-Gómez, David Platas-Iglesias, Carlos Tóth Éva (1967-) (koordinációs kémia) de Blas, Andrés Rodríguez-Blas, Teresa
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001-es BibID:	BIBFORM018851
Első szerző:	Pálinkás Zoltán (vegyész)
Cím:	Kinetics of the Exchange Reactions between Gd(DTPA), Gd(BOPTA), and Gd(DTPA-BMA) Complexes, Used As MRI Contrast Agents, and the Triethylenetetraamine-Hexaacetate Ligand / Zoltán Pálinkás, Zsolt Baranyai, Ernő Brücher, Béla Rózsa
Dátum:	2011
ISSN:	0020-1669
Megjegyzések:	The kinetics of ligand exchange reactions occurring between the Gd(DTPA), Gd(BOPTA), and Gd(DTPA-BMA) complexes, used as contrast agents in MRI, and the ligand TTHA, have been studied in the pH range 6.5?11.0 by measuring the water proton relaxation rates at 25 ?C in 0.15 M NaCl. The rates of the reactions are directly proportional to the concentration of TTHA, indicating that the reactions take place with the direct attack of the HiTTHA(6?i)? (i = 0, 1, 2 and 3) species on the Gd3+ complexes, through the formation of ternary intermediates. The rates of the exchange reactions of the neutral Gd(DTPA-BMA) increase when the pH is increased from 6.5 to 9, because the less protonated HiTTHA(6?i)? species can more efficiently attack the Gd3+ complex. The rates of the exchange reactions of [Gd(DTPA)]2? and [Gd(BOPTA)]2? also increase from pH 8.5 to 11, but from 6.5 to 8.5 an unexpected decrease was observed in the reaction rates. The decrease has been interpreted by assuming the validity of general acid catalysis. The protons from the HiTTHA(6?i)? species (i = 2 and 3) can be transferred to the coordinated DTPA or BOPTA in the ternary intermediates when the dissociation of the Gd3+ complexes occurs faster. The kinetic inertness of Gd(DTPA), Gd(BOPTA), and Gd(DTPA-BMA) differs very considerably; the rates of the ligand exchange reactions of Gd(DTPA-BMA), thus the rates of its dissociation, are 2 to 3 orders of magnitude higher than those of Gd(DTPA) and Gd(BOPTA). The rates of the ligand exchange reactions increase with increasing concentration of the endogenous citrate, phosphate, or carbonate ions at a pH of 7.4, but the effect of citrate and phosphate is negligible at their physiological concentrations. The increase in the reaction rates at the physiological concentration of the carbonate ion is significant (20?60%), and the effect is the largest for the Gd(DTPA-BMA) complex.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
Megjelenés:	Inorganic Chemistry. - 50 : 8 (2011), p. 3471-3478. -
További szerzők:	Baranyai Zsolt (1977-) (vegyész) Brücher Ernő (1935-) (vegyész) Rózsa Béla
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001-es BibID:	BIBFORM010530
Első szerző:	Pálinkás Zoltán (vegyész)
Cím:	Stability, Water Exchange, and Anion Binding Studies on Lanthanide(III) Complexes with a Macrocyclic Ligand Based on 1,7-Diaza-12-crown-4: Extremely Fast Water Exchange on the Gd3+ Complex / Zoltán Pálinkás, Adrián Roca-Sabio, Marta Mato-Iglesias, David Esteban-Gómez, Carlos Platas-Iglesias, Andrés de Blas, Teresa Rodríguez-Blas, Éva Tóth
Dátum:	2009
ISSN:	0020-1669
Megjegyzések:	The picolinate-derivative ligand based on the 1,7-diaza-12-crown-4 platform (bp12c4(2-)) forms stable Ln(3+) complexes with stability constants increasing from the early to the middle lanthanides, then being relatively constant for the rest of the series (logK(LnL) = 16.81(0.06), 18.82(0.01), and 18.08(0.05) for Ln = La, Gd, and Yb, respectively). The complex formation is fast, allowing for direct potentiometric titrations to assess the stability constants. In the presence of Zn2+, the dissociation of [Gd(bp12c4)](+) proceeds both via proton- and metal-assisted pathways, and in this respect, this system is intermediate between DTPA-type and macrocyclic, DOTA-type chelates, for which the dissociation is predominated by metal- or proton-assisted pathways, respectively. The Cu2+ exchange shows an unexpected pH dependency, with the observed rate constants decreasing with increasing proton concentration. The rate of water exchange, assessed by O-17 NMR, is extremely high on the [Gd(bp12c4)(H2O)(q)](+) complex (k(ex)(298) = (2.20 +/- 0.15) X 10(8) s(-1)), and is in the same order of magnitude as for the Gd3+ aqua ion (k(ex)(298) = 8.0 x 10(8) s(-1)). In aqueous solution, the [Gd(bp12c4)(H2O)(q)](+) complex is present in hydration equilibrium between nine-coordinate, monohydrated, and ten-coordinate, bishydrated species. We attribute the fast exchange to the hydration equilibrium and to the flexible nature of the inner coordination sphere. The large negative value of the activation entropy (Delta S-double dagger = -35 +/- 8 J mol(-1) K-1) points to an associative character for the water exchange and suggests that water exchange on the nine-coordinate, monohydrated species is predominant in the overall exchange. Relaxometric and luminescence measurements on the Gd3+ and Eu3+ analogues, respectively, indicate strong binding of endogenous anions such as citrate, hydrogencarbonate, or phosphate to [Ln(bp12c4)](+) complexes (K-aff = 280 +/- 20 M-1, 630 +/- 50 M-1, and 250 +/- 20 M-1, respectively). In the ternary complexes, the inner sphere water molecules are fully replaced by the corresponding anion. Anion binding is favored by the positive charge of the [Ln(bp12c4)](+) complexes and the adjacent position of the two innersphere water molecules. To obtain information about the structure of the ternary complexes, the [Gd(bp12c4)(HCO3)] and [Gd(bp12c4)(H2PO4)] systems were investigated by means of density functional theory calculations (B3LYP model). They show that anion coordination provokes an important lengthening of the distances between the donor atoms and the lanthanide ion. The coordination of phosphate induces a more important distortion of the metal coordination environment than the coordination of hydrogencarbonate, in accordance with a higher binding constant for HCO3- and a more important steric demand of phosphate.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
Megjelenés:	Inorganic Chemistry. - 48 : 18 (2009), p. 8878-8889. -
További szerzők:	Roca-Sabio, Adrián Mato-Iglesias, Marta Esteban-Gómez, David Platas-Iglesias, Carlos de Blas, Andrés Rodríguez-Blas, Teresa Tóth Éva (1967-) (koordinációs kémia)
Internet cím:	DOI Intézményi repozitóriumban (DEA) tárolt változat
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