Daisies, preparing

Fig. 4.4. Layout of the integrated surface analysis and preparation system DAISY-MAT (Darmstadt integrated system for materials research). A photoelectron spectrometer is connected by a sample handling system to various deposition and surface treatment chambers. Preparation and analysis can be repeatedly performed under controlled ultrahigh vacuum conditions...

When supramolecular polymers are treated with bulky stopper groups, they may form poly[2]rotaxane daisy chains [32,60-68]. Cyclic tri[2]rotaxanes (daisy chain necklace) containing cyclodextrins have been prepared from the mixture of 6-(4-aminocinnamoyl)-Q -CD and 2,4,6-trinitrobenzene sulfonic acid sodium salt [50,59] in an agueous solution (Fig. 21). If the molecule changes its conformation (or co-conformation), the ring may expand or shrink by external conditions (temperature, solvents, photochemically, elec-trochemically). These compounds are important because the cycle can be used as a chemical valve as seen in ion channels in biological membranes. 

Echinacea, a genus including nine species that grow in the United States, is a member of the daisy (Asteraceae Compositae) family. Three of these species are commonly found in herbal preparations the dried rhizome and roots of E. angustifolia, the narrow-leaved echinacea pallida, the pale-flowered echinacea and A. purpurea, the cultivated variety. The latter is the species most commonly found in herbal preparations (Tyler, 1993). 

Pyrethroids represent a new class of highly selective insecticide. These preparations are almost completely non-toxic towards mammals. Pyrethroids are related to natural insecticide pyrethrin, which is obtained from Pyrethrum, a daisy-like flower grown in large quantities in Kenya, Africa (Figure 9). 

When supramolecular polymers are treated with bulky stopper groups, they may form poly[2]rotaxane daisy chains [45-53]. Harada et al. [31] treated 6-p-aminoCiO-a-CD (40 mM) with 2M excess 2,4,6-trinitrobenzenesulfonic acid sodium salt (TNBS) as bulky stoppers in aqueous solutions. The resulting precipitate was found to be mainly a cyclic trimer by H NMR and TOF mass spectra. After purification of the crude product, the 2D ROESY spectrum of the cyclic trimer shows cross-peaks between phenyl protons close to an amino group and secondary hydroxyl groups (0(2)H). A trinitrophenyl group is found at the secondary hydroxyl group side. A proposed structure of a cyclic trimer (cyclic daisy chain) is shown in Fig. 3.12. Kaneda et al. [38] reported the preparation of cyclic di[2]rota-xane fashion constructed tail-to-tail by azobenzene derivatives of permethylated a-CDs and showed its computer-generated supramolecular structures (Fig. 3.13). Easton et al. [39] also reported the preparation of cyclic di[2]rotaxane constructed by stilbene-appended a-CDs in tail-to-tail fashion (Fig. 3.14). Kaneda et al. [40]... 

Topologically linked poly[2]rotaxane is called daisy-chain-type polyrotaxane. Since Stoddart and coworkers attempted to construct a supramolecular poly[2]rotaxane (poly-pseudo[2]rotaxane) in 1998, many researchers have tried to prepare the daisy-chain-type polyrotaxane. However,... 

True daisy-chain-type poly[2]rotaxane was first prepared by Harada et al. in 2008 (Scheme 8). They utilized f-CD having p-aminocynnamoyl functionality as a monomer which underwent the thread-type self-assembly to yield polypseudo[2]rotaxane in water. Daisy-chain-type poly[2]rotaxane was formed via the end-capping reaction with adamantanecarboxylic acid at each end of the guest groups. The poly[2]rotaxane with molecular weight higher than 1.6 X 10" consisted of about 13 monomer units, as determined by MALDl-TOF mass spectra. 

One conceptually easy way to access polyrotaxane structures is to prepare a rotaxane monomer which has reactive groups on (or as) its stoppers and/or on its macrocyclic component and then subsequently carry out a conventional polymerization reaction. This potentially opens up access to a wide range of interlocked polymeric architectures from simple main-chain polyrotaxanes to molecular necklaces, the daisy-chain systems and even dendritic interlocked species. 

Figure 44 Schematic representation of the interlocked stmctures (a) molecular necklaces, (b) daisy-chains, and (c) interlocked dendrimers which have been prepared using the phosphonium stopper exchange methodology.

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