Burai L, Tóth E, Seibig S, Scopelliti R, Merbach A E
Institut de Chimie Minérale et Analytique, Université de Lausanne-BCH, Switzerland.
Chemistry. 2000 Oct 16;6(20):3761-70. doi: 10.1002/1521-3765(20001016)6:20<3761::aid-chem3761>3.0.co;2-6.
We report the first solid state X-ray crystal structure for a Eu(II) chelate, [C(NH2)3]3[Eu(II)(DTPA)(H2O)].8H2O, in comparison with those for the corresponding Sr analogue, [C(NH2)3]3[Sr(DTPA)(H2O).8H2O and for [Sr(ODDA)].8H2O (DTPA5 = diethylenetriamine-N,N,N',N",N"-pentaacetate, ODDA2- =1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diacetate ). The two DTPA complexes are isostructural due to the similar ionic size and charge of Sr(2+) and Eu(2+). The redox stability of [Eu(II)(ODDA)(H2O)] and [Eu(II)(ODDM)]2- complexes has been investigated by cyclovoltammetry and UV/Vis spectrophotometry (ODDM4- =1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane-7,16-++ +dimalonate). The macrocyclic complexes are much more stable against oxidation than [Eu(II)(DTPA)(H2O)]3- (the redox potentials are E1/2 =-0.82 V, -0.92 V, and -1.35 V versus Ag/AgCl electrode for [Eu(III/II)(ODDA)(H2O)],[Eu(III/II)(ODDM)], and [Eu(III/II)(DTPA)(H2O)], respectively, compared with -0.63 V for Eu(III/II) aqua). The thermodynamic stability constants of [Eu(II)(ODDA)(H2O)], [Eu(II)(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2- were also determined by pH potentiometry. They are slightly higher for the EuII complexes than those for the corresponding Sr analogues (logK(ML)=9.85, 13.07, 8.66, and 11.34 for [Eu(II)(ODDA)(H2O)], [Eu(II)(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2-, respectively, 0.1M (CH3)4NCl). The increased thermodynamic and redox stability of the Eu(II) complex formed with ODDA as compared with the traditional ligand DTPA can be of importance when biomedical application is concerned. A variable-temperature 17O-NMR and 1H-nuclear magnetic relaxation dispersion (NMRD) study has been performed on [Eu(II)(ODDA)(H2O)] and [Eu(II)(ODDM)]2- in aqueous solution. [Eu(II)(ODDM)]2- has no inner-sphere water molecule which allowed us to use it as an outer-sphere model for [Eu(II)(ODDA)(H2O)]. The water exchange rate (k298(ex)= 0.43 x 10(9)s(-1)) is one third of that obtained for [Eu(II)(DTPA)(H2O)]3-. The variable pressure 17O-NMR study yielded a negative activation volume, deltaV (not=) = -3.9cm3mol(-1); this indicates associatively activated water exchange. This water exchange rate is in the optimal range to attain maximum proton relaxivities, which are, however, strongly limited by the fast rotation of the small molecular weight complex.
我们报道了铕（II）螯合物[C(NH2)3]3[Eu(II)(DTPA)(H2O)].8H2O的首个固态X射线晶体结构，并将其与相应的锶类似物[C(NH2)3]3[Sr(DTPA)(H2O).8H2O以及[Sr(ODDA)].8H2O（DTPA5 = 二亚乙基三胺-N,N,N',N",N"-五乙酸，ODDA2- = 1,4,10,13-四氧杂-7,16-二氮杂环十八烷-7,16-二乙酸）的结构进行了比较。由于Sr(2+)和Eu(2+)的离子大小和电荷相似，这两种DTPA配合物具有同构结构。通过循环伏安法和紫外/可见分光光度法研究了[Eu(II)(ODDA)(H2O)]和[Eu(II)(ODDM)]2-配合物的氧化还原稳定性（ODDM4- = 1,4,10,13-四氧杂-7,16-二氮杂环十八烷-7,16-二丙二酸根）。大环配合物比[Eu(II)(DTPA)(H2O)]3-对氧化更稳定（相对于Ag/AgCl电极，[Eu(III/II)(ODDA)(H2O)]、[Eu(III/II)(ODDM)]和[Eu(III/II)(DTPA)(H2O)]的氧化还原电位分别为E1/ = -0.82 V、-0.92 V和-1.35 V，而Eu(III/II)水合离子的氧化还原电位为-0.63 V）。还通过pH电位滴定法测定了[Eu(II)(ODDA)(H2O)]、[Eu(II)(ODDM)]2-、[Sr(ODDA)(H2O)]和[Sr(ODDM)]2-的热力学稳定性常数。对于EuII配合物，其稳定性常数略高于相应的Sr类似物（在0.1M (CH3)4NCl中，[Eu(II)(ODDA)(H2O)]、[Eu(II)(ODDM)]2-、[Sr(ODDA)(H2O)]和[Sr(ODDM)]2-的logK(ML)分别为9.85、13.07、8.66和11.34）。与传统配体DTPA相比，由ODDA形成的Eu(II)配合物热力学和氧化还原稳定性的提高在生物医学应用方面可能具有重要意义。对水溶液中的[Eu(II)(ODDA)(H2O)]和[Eu(II)(ODDM)]2-进行了变温17O-核磁共振和1H-核磁共振弛豫分散（NMRD）研究。[Eu(II)(ODDM)]2-没有内球水分子，这使我们能够将其用作[Eu(II)(ODDA)(H2O)]的外球模型。水交换速率（k298(ex)= 0.43 x 10(9)s(-1)）是[Eu(II)(DTPA)(H2O)]3-的三分之一。变压17O-核磁共振研究得到了一个负的活化体积，ΔV (not=) = -3.9cm3mol(-1)；这表明水交换是缔合活化的。这种水交换速率处于获得最大质子弛豫率的最佳范围内，然而，这受到小分子配合物快速旋转的强烈限制。
