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首页> 外文期刊>Chemistry: A European journal >Supramolecular assembly of an amphiphilic Gd-III chelate: Tuning the reorientational correlation time and the water exchange rate
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Supramolecular assembly of an amphiphilic Gd-III chelate: Tuning the reorientational correlation time and the water exchange rate

机译：两亲性Gd-III螯合物的超分子组装：调整方向相关时间和水交换速率

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摘要

We report the synthesis and characterization of the novel ligand H(5)EPTPA-C-16 ((hydroxymethylhexade-canoyl ester) ethylenepropylenetriami-nepentaacetic acid). This ligand was designed to chelate the Gd-III ion in a kinetically and thermodynamically stable way while ensuring an increased water exchange rate (k(ex)) on the Gd-III complex owing to steric compression around the water-binding site. The attachment of a palmitic ester unit to the pendant hydroxymethyl group on the ethylenediamine bridge yields an amphiphilic conjugate that form s micelles with a long tumbling time (pi(R)) in aqueous solution. ne critical micelle concentration (cmc = 0.34 mm) of the amphiphilic [Gd(eptpa-C-16)(H2O)](2-) chelate was determined by variable-concentration proton relaxivity measurements. A global analysis of the data obtained in variable-temperature and multiple-field O-17 NMR and H-1 NMRD measurements allowed for the determination of parameters governing relaxivity for [Gd(eptpa-C-16)(H2O)](2-); this is the first time that paramagnetic micelles with optimized water exchange have been investigated. The water exchange rate was found to be K-ex(298) = 1.7 x 10(8) s(-1), very similar to that previously reported for the nitrobenzyl derivative [Gd(eptpa-bz-NO2)(H2O)(2-)(k (298)(ex) = 1.5 x 10(8) s(-1)). The rotational dy namics of the micelles were analysed by using the Lipari-Szabo approach. ne micelles formed in aqueous solution show considerable flexibility, with a local rotational correlation time of tau(10)(298) = 330 ps for the Gd-III segments, which is much shorter than the global rotational correlation time of the supramolecular aggregates, tau(g0)(298) = 2100 ps. This internal flexibility of the micelles is responsible for the limited increase of the proton relaxivity observed on micelle formation (r(1) = 22.59 mm(-1) s(-1) for the micelles versus 9.11 mm(-1) s(-1) for the monomer chelate (20 MHz; 25 degrees C).
机译：我们报告了新型配体H（5）EPTPA-C-16（（（羟甲基己基-canoylester）乙烯丙烯三酰胺-nepentaacetic乙酸）的合成和表征。设计该配体以动力学和热力学稳定的方式螯合Gd-III离子，同时由于水结合位点周围的空间压缩，确保Gd-III配合物上的水交换速率（k（ex））增加。棕榈酸酯单元与乙二胺桥上的羟基甲基侧基的连接产生两亲性共轭物，在水溶液中形成具有长翻滚时间（pi）的胶束。通过可变浓度的质子弛豫度测量来确定两亲性[Gd（eptpa-C-16）（H2O）]（2-）螯合物的临界胶束浓度（cmc = 0.34 mm）。对在可变温度和多场O-17 NMR和H-1 NMRD测量中获得的数据进行全局分析，可以确定控制[Gd（eptpa-C-16）（H2O）]（2- ）;这是首次研究了具有最佳水交换性能的顺磁性胶束。发现水交换率为K-ex（298）= 1.7 x 10（8）s（-1），与先前报道的硝基苄基衍生物[Gd（eptpa-bz-NO2）（H2O）（ 2-）（k（298）（ex）= 1.5 x 10（8）s（-1））。使用Lipari-Szabo方法分析了胶束的旋转动力学。在水溶液中形成的微团胶显示出相当大的柔韧性，Gd-III片段的局部旋转相关时间为tau（10）（298）= 330 ps，比超分子聚集体tau的整体旋转相关时间短得多（g0）（298）= 2100 ps胶束的这种内部柔韧性是在胶束形成时观察到的质子弛豫度有限增加的原因（胶束的r（1）= 22.59 mm（-1）s（-1）与9.11 mm（-1）s（- 1）对于单体螯合物（20 MHz; 25摄氏度）。

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