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首页> 外文期刊>Chemistry: A European journal >Unexpected aggregation of neutral, xylene-cored dinuclear Gd-III chelates in aqueous solution
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Unexpected aggregation of neutral, xylene-cored dinuclear Gd-III chelates in aqueous solution

机译：中性二甲苯芯双核Gd-III螯合物在水溶液中的意外聚集

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摘要

We have synthesized ditopic ligands L-1, L-2, and L-3 that contain two DO3A(3-) metal-chelating units with a xylene core as a noncoordinating linker (DO3A(3-) = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate; L-1 = 1,4-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10- tetraazacyclododecane-1-yl]methyl}-2 benzene; L-2 = 1,3-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L 3 = 3,5bis{[4,7,10-tris(carboxymethyl)-1,4,7,10- tetra azacyclododecane-1-yl]methyl}benzoic acid). Aqueous solutions of the dinuclear Gd-III complexes formed with the three ligands have been investigated in a variable-temperature, multiple-field O-17 NMR and H-1 relaxivity study. The O-17 longitudinal relaxation rates measured for the [Gd2L1-3(H2O)(2)] complexes show strong field dependence (2.35-9.4 T): which unambiguously proves the presence of slowly tumbling entities in solution. The proton relaxivities of the complexes, which are unexpectedly high for their molecular weight, and in particular the relaxivity peaks observed at 40-50 MHz also constitute experimental evidences of slow rotational motion. This was explained in terms of self-aggregation related to hydrophobic interactions, pi stacking between the aromatic linkers, or possible hydrogen bonding between the chelates. The longitudinal O-17 relaxation rates of the [Gd2L1-3(H2O)(2)] complexes have been analysed with the Lipari-Szabo approach, leading to local rotational correlation times tau(298)(l) of 150250 ps and global rotational correlation times T-g(298) of 1.6-3.4 ns (c(Gd): 20-50 mm), 9 where tau(298)(l) is attributed to local motions of the Gd segments, while tau(298)(g) describes the overall motion of the aggregates. The aggregates can be partially disrupted by phosphate addition; however, at high concentrations phosphate interferes in the first coordination sphere by replacing the coordinated water. In contrast to the parent [Gd(DO3A)(H2O)(1.9)], which presents a hydration equilibrium between mono- and dihydrated species, a hydration number of q = 1 was established for the [Ln(2)L(1-3)-(H2O)(2)] chelates by O-17 chemical shift measurements on Ln = Gd and UV/Vis spectrophotometry for Ln = Eu. The exchange rate of the coordinated water is higher for [Gd2L1-3(H2O)(2)] complexes (k(ex)(291) = 7.5-12.0 x 10(6)s(-1)) than for [Gd(DOTA)(H2O)](-). The proton relaxivity of the [Gd2L1-3(H2O)(2)] complexes strongly decreases with increasing pH. This is related to the deprotonation of the inner-sphere water, which has also been characterized by pH potentiometry. The protonation constants determined for this process are logK(OH) = 9.50 and 10.37 for [Gd2L1(H2O)(2)] and [Gd2L3(H2O)(2)], respectively.
机译：我们合成了对位配体L-1，L-2和L-3，它们包含两个带有二甲苯核作为非配位连接子的DO3A（3-）金属螯合单元（DO3A（3-）= 1,4,7， 10-四氮杂环十二烷-1,4,7-三乙酸酯; L-1 = 1,4-双{[4,7,10-三（羧甲基）-1,4,7,10-四氮杂环十二烷-1-基]甲基} -2苯; L-2 = 1,3-双{[4,7,10-三（羧甲基）-1,4,7,10-四氮杂环十二烷-1-基]甲基}苯; L 3 = 3,5bis {[4,7,10-三（羧甲基）-1,4,7,10-四氮杂环十二烷-1-基]甲基}苯甲酸）。在可变温度，多场O-17 NMR和H-1弛豫研究中，研究了由三种配体形成的双核Gd-III配合物的水溶液。 [Gd2L1-3（H2O）（2）]配合物的O-17纵向弛豫速率显示出很强的电场依赖性（2.35-9.4 T）：明确证明了溶液中缓慢翻滚的实体的存在。配合物的质子弛豫性（其分子量出乎意料地高），特别是在40-50 MHz处观察到的弛豫性峰也构成了慢旋转运动的实验证据。用与疏水相互作用有关的自聚集，芳族连接基之间的pi堆积或螯合物之间可能的氢键进行了解释。 [Gd2L1-3（H2O）（2）]配合物的纵向O-17弛豫速率已通过Lipari-Szabo方法进行了分析，从而导致150250 ps的局部旋转相关时间tau（298）（l）和整体旋转相关时间Tg（298）为1.6-3.4 ns（c（Gd）：20-50 mm），9其中tau（298）（l）归因于Gd片段的局部运动，而tau（298）（g）描述骨料的整体运动。加入磷酸盐会部分破坏聚集体;但是，在高浓度下，磷酸盐会通过替换配位水而干扰第一配位领域。与母体[Gd（DO3A）（H2O）（1.9）]表现出一水合和二水合物种之间的水合平衡相反，对于[Ln（2）L（1- 3）-（（H2O）（2）]通过在Ln = Gd上进行O-17化学位移测量和Ln = Eu的UV / Vis分光光度法进行螯合。 [Gd2L1-3（H2O）（2）]配合物（k（ex）（291）= 7.5-12.0 x 10（6）s（-1））的配位水交换率比[Gd（ DOTA）（H2O）]（-）。 [Gd2L1-3（H2O）（2）]配合物的质子弛豫度随pH值的增加而大大降低。这与内层水的去质子化有关，内层水也已通过pH电位法表征。对于[Gd2L1（H2O）（2）]和[Gd2L3（H2O）（2）]，为此过程确定的质子化常数分别为logK（OH）= 9.50和10.37。

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