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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Complexation of Eu(III) with Cucurbit[n]uril, n=5 and 7: A Thermodynamic and Structural Study
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Complexation of Eu(III) with Cucurbit[n]uril, n=5 and 7: A Thermodynamic and Structural Study

机译：Eu（III）与葫芦[n] uril，n = 5和7的络合：热力学和结构研究

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摘要

Cucurbit[n]urils (CBn) are a new class of macrocyclic cage compounds capable of binding organic and inorganic species, owing to their unique pumpkin like structure comprising of both a hydrophobic cavity and a hydrophilic portal. The thermodynamics of the complexation of Eu(III) with CBn of a different cavity size viz. cucurbit[5]uril (CB5) and cucurbit[7]uril (CB7) has been studied by UV-Vis spectroscopy and calorimetry at 25 degrees C whereas the structure of the complexes was investigated using time resolved fluorescence spectroscopy (TRFS) and extended X-ray absorption fine structure spectroscopy (EXAFS) in a formic acid-water mixture (50 wt%). This is the first report on the structural investigation of Eu-CBn complexes in solution. The thermodynamic data (Delta G, Delta H and Delta S) for Eu(III) complexation with CBn reveal the formation of a 1:1 complex with CB5, while both 1:1 and 1:2 complexes are observed with CB7. The signatures of these species are observed in ESI-MS measurements, which corroborates with the species postulated in thermodynamic studies. The complexation reactions are found to be driven by Delta S as Delta H is either small negative or positive indicating the formation of inner sphere complexes, which is in line with TRFS and EXAFS results. These studies show that Eu(III) caps one of the CB5 portals by binding with all the carbonyl groups in the 1:1 Eu-CB5 complex, whereas in the 1:1 Eu-CB7 complex, Eu(III) interacts with only a few of the carbonyl groups of CB7. The computational studies (DFT calculations) on Eu-CB5 and Eu-CB7 complexes further support the experimental data.
机译：葫芦（CBn）是一类新型的能结合有机和无机物种的大环笼化合物，由于它们独特的南瓜状结构，既包含疏水腔又包含亲水门户。 Eu（III）与不同腔尺寸的CBn络合的热力学。葫芦[5] uril（CB5）和葫芦[7] uril（CB7）已在25°C下通过紫外可见光谱和量热法进行了研究，而复合物的结构则使用时间分辨荧光光谱（TRFS）和扩展X进行了研究-甲酸-水混合物（50 wt％）中的X射线吸收精细结构光谱法（EXAFS）。这是关于溶液中Eu-CBn配合物结构研究的第一份报告。 Eu（III）与CBn络合的热力学数据（δG，δH和δS）显示与CB5形成1：1的络合物，而对CB7观察到1：1和1：2的络合物。在ESI-MS测量中观察到了这些物种的特征，这与热力学研究中假设的物种相符。发现络合反应是由Delta S驱动的，因为Delta H为小负值或正值，表明形成了内球络合物，这与TRFS和EXAFS结果一致。这些研究表明，Eu（III）通过与1：1 Eu-CB5络合物中的所有羰基结合来封盖CB5门户之一，而在1：1 Eu-CB7络合物中，Eu（III）仅与一个CB5门户相互作用。 CB7的羰基很少。 Eu-CB5和Eu-CB7配合物的计算研究（DFT计算）进一步支持了实验数据。

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