| Supramolecular chemistry is in the frontier of Chemistry. As an important supermolecular host, cyclodextrin (CD) is attracting more and more attention. Cyclodextrins are a class of cyclic oligosaccharide molecules normally comprised of six (α), seven (β) or eight (γ),α-1,4 linked D(+)-glucopyranose unite, in which the interior surface of the cavity is hydrophobic and the external surface is hydrophilic. They are well known for their ability to form inclusion complexes with a wide variety of guest molecules ranging from organic molecules to inorganic compounds and ions.This work include two parts: 1. Studied the inclusion behaviour between Costa-type complexes and cyclodextrins, and explored the molecular recognition properties. 2. Synthesized and characterized a new type of pseudorotaxane and rotaxane based on cyclodextrin.1. It has been widely accepted that the binding forces involved in the inclusion complex formation are van der Waals interactions, hydrophobic interactions, hydrogen bonding and so on. Regardless of what kind of stabilizing forces is involved, the geometric matching is an important factor for determining the stability of inclusion complex. Because of the various volume of the CD's cavity within the series (α: 0.174 nm~3,β: 0.262 nm~3 andγ-cyclodextrin: 0.427 nm~3 ), they are suitable to include guest with different dimensions. In our previous work, it has been established that cyclodextrin formed a kind of 1:1 inclusion complex with alkylcobaloxime, an organometallic complex which has aσ-type Co-C bond and is served as coenzyme B12 models.In order to further study the molecular recognition between alkylcobalt complexes and CDs, and explore the effect of electrostatic interactions on stability of the inclusion, we are encouraged to investigate the inclusion behavior of Costa-type organocobalt complexes with various CDs in aqueous solution. The Costa-type complex is a type of coenzyme B12 model. It has a mixed shiff base-oxime system with the equatorial ligand having the same charge (+1) as the B12 corrin and are typically ionic compounds with complex cation. We synthsized five Costa-type complexes and have abtained two crystal-structures. We studied the inclusion behavious between Costa-type complex and CDs, the 1H NMR spectra indicated that Costa-type complex and CD formed inclusion complex in aqueous solution, with the R group being included in the CD cavity and its planar ligand was placed near the wider opening of the CD.Furthermore the stability constants of inclusion complexes formed between Costa-type complex and various CDs were determined by the 1H NMR study. We can see from the result that:1) when Costa-type complexes have different alkyl groups as axial ligand, the stability constants was enhanced with length increase of R group. It probably revealed that the R group would insert into the cavity more deeply with the increase of the length of R groups, at the same time the hydrophobic and van der Waals interactions enhanced, thus the stability increase.2) When Costa-type complex formed inclusion complexes with different CDs, the sequence of the stability constants wasα-CD >β-CD >γ-CD. Because the diameter of the cavity ofα-CD is smaller ( 4.7~5.2 A ) than that ofβ-CD ( 6.0~6.4 A ) andγ-CD ( 7.5~8.3 A ),α-CD was suitable for including straight-chain alkyl and the stability ofα-CD adduct was enhanced.3) When negatively charged sulfatedβ-CD and Carboxylatedβ-CD formed inclusion complexes with Costa-type complex, stability constants are in acceptable agreement with that of naturalβ-CD. When the DFT-B3LYP method had been used to study the charge distributions of Costa-type complexes, the result showed that although Costa-type complexes have +1 cation, the positive charges disperse in the cobalt atom and C atoms of the equatorial ligand, while the R group is almost electro-neutralize. In the process of inclusion, it is the R group which acts as a recognition position and inserts into the cavities of CDs, so the stability constants were not effected when the CDs were modified with negatively charged functional groups. 2. Rotaxane is a type of supramolecule. In recent years, studies of pseudorotaxanes and rotaxanes have received much attention because of their interesting structures and properties as well as the potential applications for molecular devices. Pseudorotaxane is a type of complex that consists of a cyclic molecule acts as wheel and a threadlike molecule acts as axle, in which the wheel is host and the axle is guest. It is commonly used as precusor for the formation of permanently interlocked rotaxane by adding'stopper'components, which are bulky enough to prevent unthreading. Cyclodextrin is commonly used as host in rotaxane studies.Now we synthsized a type of bisimidazolyl compounds, i.e. bid (1,10-bis(imidazol-1-lyl)decane), bih (1,6-bis(imidazol-1-lyl)hexane) and bix (1,4-bis(imidazol-1-ylmethyl)benzene), which can be employed as guest to produce a new series of pseudorotaxanes with cyclodextrins. And we characterized the psuedorotaxanes with 1H NMR and element analysis. We found that with the length changing of guest molecules, [2] or [3] pseudorotaxanes can be formed. It is interested to note that bid which white longer alkyle chain can thread two CDs and form [3] pseudorotaxane, while bih and bix thread only one CD ring and form [2] pseudorotaxanes. Furthermore two crystal structures of bid/2β-CD and bih/β-CD pseudorotaxanes have been obtained.Based on this type of pseudorotaxanes, we synthsised metalo-rotaxanes by using Costa-type complex and cobaloxime as stoppers. When Costa-type complex with two bromines as axial ligand react with bid/β-CD pseudorotaxane, N atom of imidazole subtitute the Br ligand and bid coordinate with Costa-type complex, thus metalo-rotaxane been synthsized. Metalo-rotaxanes can also be synthesized from cobaloxime and bid/β-CD. Furthermore, the rotaxanes were characterized by 1H NMR and ESI-MS. The thermogravimetric analysis of this type of rotaxanes is also studied. The results indicate that through self-assembly and coordination a kind new metallo-rotaxane was fabricated. Their interested structures and properties will have potential application in the future. |
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