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Preparation of Supramolecular Complexes with Cyclodextrin |
Poly[2]rotaxane and supramolecular assembly have been prepared by modified cyclodextrins bearing an adamantyl group in an aqueous medium.
Proposed supramolecular structures formed by cinnamamide a-CD bearing an adamantyl group
Atsuhisa Miyawaki, Masahiko Miyauchi, Yoshinori Takashima, Hiroyasu Yamaguchi and Akira Harada "Formation of supramolecular isomers; poly[2]rotaxane and supramolecular assembly"
Chem. Commun., 2008,(4), 456 - 458,
a-CD with a 3-p-tert-Boc-cinnammoylamino group forms a supramolecular polymer. The existence of substitution/substitution interactions among the adjacent monomers of supramolecular polymer has been proved by the observation of positive and negative Cotton bands in the circular dichroism spectra. The supramolecular polymer was found to form a left handed helical conformation. The formation of helical supramolecular polymer with some cooperativity is shown by the CD spectra.
A proposed structure of a supramolecular polymer formed by 3-p-tBocCiNH-a-CD in aqueous solution.
Miyauchi, M.; Takashima, Y.; Yamaguchi, H.; Harada, A.
"Chiral Supramolecular Polymers Formed by Host-Guest Interactions"
J. Am. Chem. Soc. 2005, 127(9), 2984-2989.
6-p-tert-BocCiNH-b-CD formed intramolecular complexes. When adamantane carboxylic acid is added in the solution of 6-p-tert-BocCiNH-b-CD, the adamantane group is included in the b-CD cavity and the cinnamoyl group is kicked out of the cavity. When adamantane carboxylic acid was attached to a-CD at the 3-position (3-AdHexNH-a-CD) and the 3-AdHexNH-a-CD was mixed with 6-p-tert-BocCiNH-b-CD in D2O in a one-to-one ratio, they formed a heterodimer, which lines up end-to-end in longitudinal rows to form supramolecular oligomers in alternating manner.
Miyauchi, M.; Harada, A.
"Construction of Supramolecular Polymers with Alternating a-, b-Cyclodextrin Units Using Conformational Change Induced by Competitive Guests"
J. Am. Chem. Soc. 2004, 126(37), 11418-11419.
First, p-aminohydrocinnamoyl b-CD was prepared. This compound forms an intramolecular complex with cinnamoyl group being inside its own cavity, When adamantane carboxylic acid (AdCax) was added to this aqueous solution, AdCax was included in an b-CD cavity in place of the amino-cinnamoyl group. The aminocinnamoyl group was released from the b-CD cavity to be exposed in water. When a-CD was added to the solution, cinnamoyl group was found to be included into a-CD to give a pseudo-[2]rotaxane. Then another stopper group (TNB) was attached to the aminocinnamoyl group. The [2]rotaxane with a host(b-CD) and a guest (TNB) has been obtained.41 Although the [2]rotaxane exists as a monomer in organic solvents(DMSO), the rotaxane formed supramolecular [2]rotaxane polymers in water as proved by 1H-NMR spectra (Fig.15). The linear supramolecular polymers were observed by AFM techniques.
Proposed structures of supramolecular oligomer incorporating
3-AdHexNH-a-CD and 6-p-tBocCiNH-b-CD.
Miyauchi, M.; Hoshino, T.; Yamaguchi, H.; Kamitori, S.; Harada, A.
"A [2]Rotaxane Capped by a Cyclodextrin and a Guest: Formation of Supramolecular [2]Rotaxane Polymer"
J. Am. Chem. Soc. 2005, 127(7), 2034-2035.
Cyclic tri[2]rotaxanes (daisy chain necklace) containing cyclodextrins have been obtained by closing a tri[2]rotaxane containing a-CD and 6-(4-aminocinnamate) with 2,4,6-trinitrobenzene sulfonic acid sodium salt. If the molecule changes its conformation (or co-conformation), the ring may expand or shrink by external conditions (temperature, solvents, photochemically, electrochemically). These compounds are important because the cycle can be used as a chemical valve as can be seen in ion channels in biological membranes.
Daisy chain necklace: cyclic tri[2]rotaxane containing a-CD
Hoshino, T.; Miyauchi, M.; Kawaguchi, Y.; Yamaguchi, H.; Harada, A.
"Daisy Chain Necklace: Tri[2]rotaxane Containing Cyclodextrins. "
J. Am. Chem. Soc., 2000 , 122(40), 9876-9877.
CD-based supramolecular polymers have been prepared using a b-CD dimer and ditopic guest dimers having adamantyl groups.692,693 The ditopic guest dimers with varying flexibility and adamantyl moieties were prepared to investigate the conformation of the supramolecular cpmplexes. The ROESY spectra of the b-CD dimer with the ditopic adamantane guest dimers showed NOE between the protons of adamantyl substituents and the inner protons of CD. The b-CD dimer forms supramolecular polymers with stiff guest molecules to give high molecular weight supramolecular polymers, and the b-CD dimer gives cyclic supramolecular oligomers with flexible ditopic guest dimers. A 1:1 mixture of the b-CD-PEG dimer and the adamantane-PEG dime forms of the self-organized intermolecular supramolecular polymers.
Proposed structures of supramolecular oligomer incorporating b-CD dimer and adamanane dimer.
Ohga, K.; Takashima, Y.; Takahashi, H.; Kawaguchi, Y.; Yamaguchi, H.; Harada, A.
"Preparation of Supramolecular Polymers from a Cyclodextrin Dimer and Ditopic Guest Molecules: Control of Structure by Linker Flexibility"
Macromolecules 2005, 38 (14), 5897-5904.