126-44-3Relevant articles and documents
Kinetics of Ga(NOTA) formation from weak Ga-citrate complexes
Morfin, Jean-Francois,Toth, Eva
, p. 10371 - 10378 (2011)
Gallium complexes are gaining increasing importance in biomedical imaging thanks to the practical advantages of the 68Ga isotope in Positron Emission Tomography (PET) applications. 68Ga has a short half-time (t1/2 = 68 min); thus the 68Ga complexes have to be prepared in a limited time frame. The acceleration of the formation reaction of gallium complexes with macrocyclic ligands for application in PET imaging represents a significant coordination chemistry challenge. Here we report a detailed kinetic study of the formation reaction of the highly stable Ga(NOTA) from the weak citrate complex (H3NOTA = 1,4,7-triazacyclononane-1,4, 7- triacetic acid). The transmetalation has been studied using 71Ga NMR over a large pH range (pH = 2.01-6.00). The formation of Ga(NOTA) is a two-step process. First, a monoprotonated intermediate containing coordinated citrate, GaHNOTA(citrate), forms in a rapid equilibrium step. The rate-determining step of the reaction is the deprotonation and slow rearrangement of the intermediate accompanied by the citrate release. The observed reaction rate shows an unusual pH dependency with a minimum at pH 5.17. In contrast to the typical formation reactions of poly(amino carboxylate) complexes, the Ga(NOTA) formation from the weak citrate complex becomes considerably faster with increasing proton concentration below pH 5.17. We explain this unexpected tendency by the role of protons in the decomposition of the GaHNOTA(citrate)* intermediate which proceeds via the protonation of the coordinated citrate ion and its subsequent decoordination to yield the final product Ga(NOTA). The stability constant of this intermediate, log K GaHNOTA(citrate) = 15.6, is remarkably high compared to the corresponding values reported for the formation of macrocyclic lanthanide(III)-poly(amino carboxylates). These kinetic data do not only give mechanistic insight into the formation reaction of Ga(NOTA), but might also contribute to establish optimal experimental conditions for the rapid preparation of Ga(NOTA)-based radiopharmaceuticals for PET applications.
Enzyme-assisted matrix isolation of novel quinoxaline-2,3-dithiol nickel(II) complexes
Mikhailov, Oleg V.,Polovnyak, Valentin K.
, p. 807 - 809 (2007/10/02)
The complexation reaction occurring on the nickel(II) hexacyanoferrate(II), Ni2, matrix immobilized in the gelatin layer, containing an alkaline solution of quinoxaline-2,3-dithiol has been studied.It has been shown that three different complex forms can be obtained: (Ni2L)2 (I), NiL(H2O)2 (II) and Ni(HL)2 (III) (where HL and L are partially and fully deprotonated forms of ligand respectively), while the reaction carried out in solution produces only one compound, Ni(HL)2.Chelate I (of an orange-yellow colour) is formed at ligand concentration CL) less than 10-3 mol.dm-3, hexacyanoferrate(II) nickel(II) concentration (CF) above 3.0 * 10-2 mol.m-2 and a short (1-2 min) contact time of an immobilized matrix with ligand solution.Chelate II (of a pink-red colour) is formed at CL above 5.0 * 10-3 mol.dm-3 and CF less than 2.0 * 10-2 mol.m-2 and chelate III (blue-green colour) is formed upon the reaction of acid solutions (ρH 5) and the gelatin layer containing chelate II.Chelate I has only a wing of an electron transfer intensive band, the maximum of which is in the near UV region, and an indistinct shoulder at 430-440 nm, chelate II has λmax = 535 nm and chelate III has λmax = 630 nm and λmax = 700 nm.It has also been pointed out that complexation on the immobilized Ni2 matrix in the Ni(II)-quinoxaline-2,3-dithiol system enables one to obtain more complex forms than with complexation in the same system in aqueous solutions.
