Mono-, Bi-, and Trinuclear Bis-Hydrated Mn2+ Complexes as Potential MRI Contrast Agents

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• 作者：Attila Forg谩cs ; Mart铆n Regueiro-Figueroa ; Jos茅 Luis Barriada ; David Esteban-G贸mez ; Andr茅s de Blas ; Teresa Rodr铆guez-Blas ; Mauro Botta ; Carlos Platas-Iglesias
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 5, 2015
• 年：2015
• 卷：54
• 期：19
• 页码：9576-9587
• 全文大小：627K
• ISSN：1520-510X

文摘

We report a series of ligands containing pentadentate 6,6鈥?((methylazanediyl)bis(methylene))dipicolinic acid binding units that form mono- (H₂dpama), di- (mX(H₂dpama)₂), and trinuclear (mX(H₂dpama)₃) complexes with Mn²⁺ containing two coordinated water molecules per metal ion, which results in pentagonal bipyramidal coordination around the metal ions. In contrast, the hexadentate ligand 6,6鈥?((ethane-1,2-diylbis(azanediyl))bis(methylene))dipicolinic acid (H₂bcpe) forms a complex with distorted octahedral coordination around Mn²⁺ that lacks coordinated water molecules. The protonation constants of the ligands and the stability constants of the Mn²⁺, Cu²⁺, and Zn²⁺ complexes were determined using potentiometric and spectrophotometric titrations in 0.15 M NaCl. The pentadentate dpama^{2鈥?/sup> ligand and the di- and trinucleating mX(dpama)₂4鈥?/sup> and mX(dpama)₃6鈥?/sup> ligands provide metal complexes with stabilities that are very similar to that of the complex with the hexadentate ligand bcpe2鈥?/sup>, with log 尾₁₀₁ values in the range 10.1鈥?1.6. Cyclic voltammetry experiments on aqueous solutions of the [Mn(bcpe)] complex reveal a quasireversible system with a half-wave potential of +595 mV versus Ag/AgCl. However, [Mn(dpama)] did not suffer oxidation in the range 0.0鈥?.0 V, revealing a higher resistance toward oxidation. A detailed 1H NMRD and 17O NMR study provided insight into the parameters that govern the relaxivity for these systems. The exchange rate of the coordinated water molecules in [Mn(dpama)] is relatively fast, k_ex298 = (3.06 卤 0.16) 脳 108 s鈥?. The trinuclear [mX(Mn(dpama)(H₂O)₂)₃] complex was found to bind human serum albumin with an association constant of 1286 卤 55 M鈥? and a relaxivity of the adduct of 45.2 卤 0.6 mM鈥? s鈥? at 310 K and 20 MHz.}