Dimers cyclodextrins

The manganese is -bonded to the silane phenyl groups. Cyclodextrins are known to function as hosts for a variety of guest substrates. Monomeric and dimeric -cyclodextrins have been shown to bind CpMn(CO)3 as a guest, allowing water solubility and/or photosubstitution to be studied. 

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

Matsue et al. [43] attempted to study the molecular rocket reaction in a ruthenocene-/ -cyclodextrin inclusion compound using the I00Ru y, p) "raTc reaction. They noticed a parallel relationship between chemical processes and nuclear-recoil-induced processes in the non-included ruthenocene compound, as shown in Fig. 9. In the nuclear-recoil-induced processes no dimerization can be observed because of the extremely low concentration of the product, whereas in the chemical processes dimerization is possible, as demonstrated by Apostolidis et al. [48]. When ruthenocene included in /J-cyclodextrin is irradiated with y-rays, a part of the ruthenocene molecule is converted to [TcCp2-] which escapes from the jS-cyclodextrin cavity. The [TcCp2] rocket thus produced can attack neighboring inclusion compounds so as to extract the enclosed ruthenocene molecules and abstract H or Cp (Cp cyclopentadienyl radical). This process is shown schematically in Fig. 10. 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

Kasatani K, Ohashi M, Kawasaki M, Sato H (1987) Cyanine dye-cyclodextrin system. Enhanced dimerization of the dye. Chem Lett 16 1633-1636... 

In order to determine the mechanism of complex-formation, however, kinetic methods must be used. Consider one host-two guests complex-ation. The two possible mechanisms are dimerization of the guest outside the cyclodextrin cavity followed by inclusion, and dimerization within the cyclodextrin cavity. Equilibrium measurements alone cannot distinguish between these two possibilities. The same is the case for 2 2 complex-formation, where a larger number of possible mechanisms exist. 

The alternative mechanism, involving dimerization of the guest prior to inclusion, is unable to fit the observed data. Using the method of Bernas-coni or Czerlinski - the following equation can be derived, characterizing the variation of 1/t with cyclodextrin and guest concentrations for the aforementioned stepwise-inclusion mechanism,... 

All of the dyes studied also dimerize in aqueous solution in the absence of cyclodextrin thus. 

Thus, the formation of a one host-two guests inclusion-complex seems to proceed by way of the stepwise inclusion of two guest molecules, with the inclusion of the second guest molecule being rate-determining. The formation of a two hosts-two guests complex may then proceed by the rapid addition of a second cyclodextrin molecule. No evidence has been presented that supports dimerization of the guest prior to inclusion. 

An interesting equilibrium study was performed by Kasatani and coworkers on the interaction of a series of cyanine dyes with beta and gamma cyclodextrin, using u.v.-visible spectrophotometric measurements. The results were consistent with the enhancement of dimer formation by inclusion of the dye molecules within the cyclodextrin. As expected from the work of others, such geometrical factors " as the size of the aromatic groups and the lengths of the central methine chains strongly influence the occurrence of dimer formation within the cyclodextrin cavity. 

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

The radical site of the intermediates in the dimerization reaction is stabilised by resonance and examples have been noted where dimerization occurs by substitution onto the aromatic ring. This is the major reaction course for the reduction of 1-acetylnaphthalene [3 ] which yields 1 in alkaline solution by a radical-ion radical coupling. In the reduction of acetophenone, small amounts of related reaction products, 2 and two diastereomers of 3, can be detected. The yields of these compounds are increased by the reduction of acetophenone encapsulated in a cyclodextrin [32],... 

Figure 6.23 Schematic representation of the packing of cyclodextrin structures, (a) Head-to-head channel type (b) head-to-tail channel type (c) cage type (d) layer type and (e) layer type composed of /TCD dimers. (Reproduced from [24] with permission of Elsevier).

The hetero-dimerization behavior of dye-modified -cyclodextrins with native CDs was investigated by means of absorption and induced circular dichroism spectroscopy in aqueous solution [43], Three types of azo dye-modified /i-CDs show different association behavior, depending on the positional difference and the electronic character of substituent connected to the CD unit in the dye moiety. p-Methyl Red-modified fi-CD (1), which has a 4-(dimethylamino)azobenzene moiety connected to the CD unit at the 4 position by an amido linkage, forms an intramolecular self-complex, inserting the dye moiety in its / -CD cavity (Figure 13). 1 also associates with native a-CD by inserting the dye residue into the a-CD cavity. The association constants for such hetero-dimerization are 198 M"1 at pH 1.00 and 305 M 1 at pH 6.59, which are larger than the association constants of 1 for / -CD (43 M 1 at pH 1.00). 

Permethylated tosylated a-cyclodextrin was coupled with aminohydroxyazo-benzene. The product was dimerized to Janus [2]pseudorotaxane, which in turn was bis-azo coupled with 2-naphthol-3,6-disulfonic acid. The product undergoes selfassociation as shown in Figure 14 [44], Note that the final product has o-quinone hydrazone structure. 

Kuwabara, T. Aoyagi, T. Takamura, M. Matsushita, A. Nakamura, A. and Ueno, A. (2002) Hetero-Dimerization of Dye-Modified Cyclodextrins with Native Cyclodextrins J. Org. Chem. 67, 720-725. 

Kikuchi, T. Narita, M. and Hamada, F. (2002) Synthesis of bis dansyl-modified /f-cyclodextrin dimer linked with azobenzene and its fluorescent molecular recognition, J. Incl. Phenom. 44, 329-333. 

Jung, J.H., Takehisa, C., Sakata, Y., and Kaneda, T. (1996) p-(4-Nitrophenylazo)phenol Dye-bridged Permethylated a-Cyclodextrin Dimer Synthesis and Self-aggregation in Dilute Aqueous Solution, Chem. Lett. 147-148. 

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