NDLI: Dissociation kinetics of $Mn^{2+}$ complexes of NOTA and DOTA

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Lukes, Ivan Kubícek, Vojtech Bonnet, Célia S. Drahos, Bohuslav Hermann, Petr Tóth, Éva
Description	Author Affiliation: Drahos B ( Department of Inorganic Chemistry, Faculty of Science, Universita Karlova (Charles University), Hlavova, 2030, 128 43 Prague 2, Czech Republic.)
Abstract	The kinetics of transmetallation of $[Mn(nota)]^{−}$ and $[Mn(dota)]^{2−}$ was investigated in the presence of $Zn^{2+}$ (5–50-fold excess) at variable pH (3.5–5.6) by $^{1}H$ relaxometry . The dissociation is much faster for $[Mn(nota)]^{−}$ than for $[Mn(dota)]^{2−}$ under both experimental and physiologically relevant conditions $(t_{½}$ = 74 h and 1037 h for $[Mn(nota)]^{−}$ and $[Mn(dota)]^{2−},$ respectively, at pH 7.4, $c(Zn^{2+})$ = $10^{−5}$ M, 25 °C). The dissociation of the complexes proceeds mainly via spontaneous $([Mn(nota)]^{−}k_{0}$ = (2.6 ± 0.5) × $10^{−6}s^{−1};$ $[Mn(dota)]^{2−}k_{0}$ = (1.8 ± 0.6) × $10^{−7}s^{−1})$ and proton -assisted pathways $([Mn(nota)]^{−}k_{1}$ = (7.8 ± 0.1) × $10^{−1}$ $M^{−1}s^{−1};$ $[Mn(dota)]^{2−}k_{1}$ = (4.0 ± 0.6) × $10^{−2}$ $M^{−1}s^{−1},$ $k_{2}$ = (1.6 ± 0.1) × $10^{3}M^{−2}$ $s^{−1}).$ The observed suppression of the reaction rates with increasing $Zn^{2+}$ concentration is explained by the formation of a dinuclear $Mn^{2+}–L–Zn^{2+}$ complex which is about 20-times more stable for $[Mn(dota)]^{2−}$ than for $[Mn(nota)]^{−}$ $(K_{MnLZn}$ = 68 and 3.6, respectively), and which dissociates very slowly $(k_{3}$ $∼10^{−5}$ $M^{−1}s^{−1}).$ These data provide the first experimental proof that not all $Mn^{2+}$ complexes are kinetically labile. The absence of coordinated water makes both $[Mn(nota)]^{−}$ and $[Mn(dota)]^{2−}$ complexes inefficient for MRI applications. Nevertheless, the higher kinetic inertness of $[Mn(dota)]^{2−}$ indicates a promising direction in designing ligands for $Mn^{2+}$ complexation.
ISSN	14779226
Issue Number	9
Volume Number	40
e-ISSN	13645447
Journal	Dalton Trans.
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2011-03-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Coordination Complexes Chemical Synthesis Heterocyclic Compounds Chemistry Manganese Compounds Models, Molecular Chlorides Crystallography, X-Ray Methods Hydrogen-Ion Concentration Kinetics Ligands Magnetic Resonance Spectroscopy Relaxation Water Zinc Compounds Journal Article Research Support, Non-U.S. Gov't
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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