Studies On Different Assembilies Of Chemical Modified Cyclodextrin Isomers In Aqueous Solution

During the past decades, researches on molecular recognition based on crown ether, cyclodextrin (CD), calixarene and porphyrin have attracted tremendous attention. Among them, CDs serve as the second generation of supramolecular assembilies. In order to understand the mutual recognition of biological molecules from the viewpoint of chemistry, it is important to study the molecular recognition processes of CDs with their guest molecules. And for application purposes, it is necessary to chemically modify CDs. Chemical modification can not only improve the inherent physical and chemical properties of CDs, but also render them extra functions.CDs and their derivatives have been popular candidates for enzyme simulation systems for many years. In recent years, much attention has been paid to the functionlization of CDs, where the signal response and transduction of aritifical systems are under construction. In this thesis, we intend to use the unique pâ†'Ï€*electron transition of dithiolate as probe to analyse the changes of dynamic spatial information between dithiolate moiety and CD moiety. Our experiment is based on the site-specific modification of CDs. We use the reversible conversion of different CDs assembilies as chemical signal to detect the occurrence of external metal ions.Our studies cover the following three points:1. Chemical modification of CDsA convenient and efficient method was developed to singly modify the hydroxyl group at the primary or secondary rim of p-CD to give mono [6-deoxy-6-(o-p-toluensulfonyl)]-β-CD (6-Ots-β-CD) and mono[2-deoxy-2-(o-p-toluensulfonyl)]-β-CD (2-Ots-β-CD). The crude products were then converted to the final products mono[6-deoxy-6-(2-butenedinitrile-2,3-dimercapto sodium salt)]-β-CD (6-Mnt-β-CD) and mono[2-deoxy-2-(2-butene dinitrile-2,3-dimercapto sodium salt)]-β-CD (2-Mnt-β-CD). The four compounds were characterized by induced circular dichroism (ICD) spectroscopy, IR spectroscopy, UV spectroscopy, thermogravimetry,1H-and13C-NMR spectroscopy.2. Studies on the Head-to-Head mutual penetrating model of6-Mnt-β-CDDifferent from its isomer2-Mnt-β-CD exhibiting the absence of circular dichroism signal in solution,6-Mnt-β-CD showed splitting Cotton effects via forming a head-to-head mutual penetrating model in aqueous solution. We used Co2+and Cu2+to bond with the Mnt group to disrupt the mutual penetrating model of6-Mnt-β-CD. The ITC measurements of Ada upon complexation with β-CD,2-Mnt-β-CD and6-Mnt-β-CD showed different assembilies of the host molecules. Then we covalently linked a second CD moiety with Mnt-modified CDs. Because of the steric effect of two CD cavities, Mnt group was thus pulled out of the cavity of CD. After the reaction, there was only one negative cotton peak in ICD spectrum. Considering Harata and Kodaka’s rules, the two CD cavities might strongly interact with each other and adopt certain dominant co-conformation in solution, which makes the transition moment of Mnt group almost parallel to CD symmetry axis. Therefore only negative Cotton effect was observed. 3. Studies on the plannar transition metal ion-pair compoundCharge transfer complexes with dithiolene ligands show unusual optical, electrical, magnetic and electrochemical properties, which lead to potential applications in the fields of semiconductor, superconductor, and photoelectric conductor. We used Zn(dmit)2(Et4N+)2as the structural unit to synthesize a plannar ion-pair complex and characterized it by IR spectroscopy, XPS,1H-and13C-NMR spectroscopy.