Reversible Responsibility Study Of The Novel Cyclodextrin Supramolecular System

As a functional supermolecular host compound, cyclodextrins (CD) have attracted more and more attention in material, pharmacology, catalysis and analysis for their unique bucket-shape structure, good biocompatibility and modifiable molecular structure. One of the most important properties of CD is its ability to form the inclusion complexes with the guest molecules. There are two modes of the actions between cyclodextrins and the guest molecules:One is endo-recognition (the guest molecules are included by cyclodextrins and form the inclusion compounds), and the acting forces accounted for the endo-recognition are hydrophobic interaction, release of "high-energy" water from the CDs cavity, relief of conformational strain energy possessed by the uncomplexed CDs, induction forces and the London dispersion force. The other mode is exo-recognition (the guest molecules are combined at the external surface with protuberances and depressions rather than an internal cavity, and the acting forces between CDs and the guest molecules in exo-recognition is mainly hydrogen bound. More than one acting forces would contribute to the CDs supermolecular interactions. Contribution of each acting force about the CDs supermolecular interactions relates to the solvents, temperature and the shape, volume, polarity and amount of the substituent groups. Among these factors, solvent and temperature must be addressed. It is important to study the affections of the solvent and temperature in the CDs supermolecular interactions, and helpful for us to study the mechanism of CDs supermolecular interactions and choose the most favorable reaction conditions.The main content of the paper showed as follows:1. Temperature dependent reversible supramolecular assemble ofβ-CD in N,N-dimethylformamide(a) One reversible supramolecular assemble behavior of P-CD in DMF was reported.β-CD could sedimentate with temperature increasing while dissolve again with temperature decreasing in DMF was reported. The sedimentation temperature (Ts) varies with changing of P-CD concentration, as well as introducing of extra organic molecules in the solution. Variable temperature IR shows that the intramolecular H-bond by C2-OH and C3'-OH on the secondary side of P-CD would break at about 65℃, and the intermolecular H-bond betweenβ-CD and a-naphthol would break at approximate 95℃. The breaking of the H-bond on the secondary side ofβ-CD, as well as between P-CD and the guest molecules, may bring in the intermolecular H-bond formation betweenβ-CD molecules, and a consequent sedimentation of p-CD in DMF.(b)'H NMR, ROESY, variable temperature IR (VT-IR), variable temperature NMR (VT-NMR), VT-ICD and XRD discovered that the guest molecules were combined at the external surface of CDs and formed the exo-complex rather than included in the CDs cavity. VT-IR showed that the exo-complex which formed between CDs and a-naphthol, the guest molecule, would dissociate when the system was heated. In the system of CDs/DMF/organic molecules, hydrogen bond is the mainly acting force.2. The affection of the Salt Effect to the system ofβ-CD/DMF/organic molecules(a) The affection of the Salt Effect to the system ofβ-CD/DMF/organic molecules was discussed. The sedimentation temperature would rise as a consequence of the addition of LiCl, and the system ofβ-CD/DMF/organic molecules could gel when LiCI was added at the specific conditions.(b) The affections of both the ratio of P-CD and organic molecules and quantity of LiCl were also discussed. 3. Structure analysis of the new native P-CD crystal form(a) A new crystal Forms of native P-CD were obtained.(b) The hydrates carry common features:the crystal structures are isomorphous, belonging to the same group P21; the conformation of theβ-CD macrocycle is stabilized by systematic intramolecular O-2...O-3 hydrogen bonds between neighboring glucose units, existing in an open, round state, with the heptagon formed by seven O-4 atoms being very regular; in the crystal lattice, theβ-CD molecules are stacked in a herringbone pattern, different numbers of water molecules are located as space-filler between the macrocycles.In the new form, only one water molecule is included in the cavity. The number of the crystal water is less than FormⅠand FormⅡwhich had been reported.4. Temperature dependent in-out isomerism of the mono-β-CD derivative(a) A newβ-CD derivative mono-(6-deoxy-2-benzoyl-ethylamino)-β-cyclodextrin was prepared.(b) VT-NMR, VT-IR and VT-ICD were employed to detect the structure changing of mono-(6-deoxy-2-benzoyl-ethylamino)-β-cyclodextrin during the heating process. Detection discovered that the aromatic ring substituent group would move out from the cavity of CDs at about 650C, and self-inclusion of theβ-CD derivative dissociate subsequently.5. The Beirut reaction catalyzed byβ-CDThe Beirut reaction was carried out with the presence ofβ-CD. The experiments tested thatβ-CD could catalyze the Beirut reaction remarkably. The reaction catalyzed byβ-CD could take place at room temperature and in water, and a higher yield could be obtained.