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首页> 外文期刊>Chemistry: A European journal >Complexation of Polyvalent Cyclodextrin Ions with Oppositely Charged Guests: Entropically Favorable Complexation Due to Dehydration
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Complexation of Polyvalent Cyclodextrin Ions with Oppositely Charged Guests: Entropically Favorable Complexation Due to Dehydration

机译：多价环糊精离子与带相反电荷的客人的络合：由于脱水的熵有利络合

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Thermodynamic parameters for complexation of polyvalent cyclodextrin (CD) cation and anion with oppositely charged guests have been determined in D_2O containing 0.02M NaCl by means of ~1H-NMR spectroscopy. Protonated heptakis (6-amino-6-deoxy)-#beta#-CD (per-NH_3~+-#beta#-CD) forms stable inclusion complexes with monovalent guest anions. The enthalpy (#DELTA#H) and entropy changes (#DELTA#S) for complexation of per-NH_3~+-#beta#-CD with p-methyl-benzoate anion (p-CH_3-Ph-CO_2~-) are 3.8 (+-)0.7 kJmol~(-1) and 88.6 (+-) 2.2 Jmol~(-1) K~(-1), respectively. The #DELTA#H and #DELTA#S values for the native #beta#-CD-p-CH_3Ph-CO_2~- system are -8.6 (+-).01 kJmol~(-1) and 15.3 (+-) 0.7 Jmol~(-1) K~(-1), respectively. The thermodynamic parameters clearly indicate that dehydration from both the host and guest ions accounts for the entropic gain in inclusion process of p-CH_3-Ph-CO_2~- into the per-NH_3~+-#beta#-CD cavity. The fact that the neutral guests such as 2,6-dihydroxynaphthalene and p-methylbenzyl alcohol hardly form the complexes with per-NH_3~+-#beta#-CD exhibits that van der Waals and/or hydorphobic interactions do not cause the complexation of the polyvalent CD cation with the monovalent anion. The acetate anion is not included into the perNH_3~+-#beta#_CD cavity, while the butanoate and hexanoate anions form the inclusion complexes. The complexation of the alkanoate anions is entropically dominated. Judging from these results, it may be concluded that Coulomb interactions cooperated with inclusion are required for realizing the large entropic gain due to extended dehydration. Entropically favorable complexation was also observed for the anoinic CD-cationic guest system. The present study might present a general mechanism for ion pairing in water.
机译：多聚环糊精（CD）阳离子和阴离子与带相反电荷的客体络合的热力学参数已通过〜1H-NMR光谱法在含有0.02M NaCl的D_2O中确定。质子化的七（6-氨基-6-脱氧）-β-β-CD（-NH_3〜+-β-β-CD）与单价客体阴离子形成稳定的包合物。全NH_3〜+-＃β＃-CD与对甲基苯甲酸阴离子（p-CH_3-Ph-CO_2〜-）络合的焓（＃DELTA＃H）和熵变（＃DELTA＃S）为分别为3.8（±）0.7 kJmol〜（-1）和88.6（±）2.2 Jmol〜（-1）K〜（-1）。天然＃beta＃-CD-p-CH_3Ph-CO_2〜-系统的＃DELTA＃H和＃DELTA＃S值为-8.6（+-）。01 kJmol〜（-1）和15.3（+-）0.7 Jmol〜（-1）K〜（-1）。热力学参数清楚地表明，在将p-CH_3-Ph-CO_2〜-引入到每个NH_3〜+-＃beta＃-CD腔中的过程中，主体离子和客体离子的脱水都是熵增加的原因。中性客体（例如2,6-二羟基萘和对甲基苄醇）几乎不与过NH_3〜+-＃β＃-CD形成络合物，这一事实表明范德华力和/或疏水性相互作用不会引起多价CD阳离子与单价阴离子。乙酸根阴离子不包含在perNH_3〜+-＃beta＃_CD腔中，而丁酸根和己酸根阴离子则形成包合物。链烷酸酯阴离子的络合在熵中占主导地位。从这些结果来看，可以得出结论，由于扩展的脱水作用，实现大的熵增需要库仑相互作用和包含。阴离子CD-阳离子客体系统也观察到熵有利的络合。本研究可能会提出水中离子配对的一般机制。

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