Co-conformation

Pharmaceutical and cosmetic grades of HPC, as for example Klucel NP manufactured by Aqualon Co., conform to the requirements of the HPC monograph as Usted in the current edition of the National Formula. ... 

Du Pont Co. conformal coatings, photoresists, manufacturing aids, electronic functional coating compounds... 

The macrocydic polyether dibenzo[24]crown-8 (DB24C8, Scheme 3) binds124,251 dialkylammonium-containing guests in solution, as well as in the solid state, to generate complexes with pseudorotaxane co-conformations that are stabilized primarily by [0—H-N+] and [O —H-C] hydrogen bonds. The com-plexation and decomplexation kinetics of these recognition events are influenced by the size of the... 

Chemical, electrochemical and/or photochemical stimuli can be used, for instance, to effect co-conformational changes in molecular devices. 

Numerous papers on CDs complexation of azo dyes concern stability, thermodynamics and kinetics of complexation and co-conformation The studies are followed frequently by theoretical calculations. 

Mayer, B. Zhang, X. Nau, W.M. and Marconi, G. (2001) Co-conformational Variability of Cyclodextrin Complexes Studied by Induced Circular Dichroism of Azoalkanes, J. Am. Chem. Soc. 123, 5240-5248. 

In these systems, chirality and sub-molecular motion stem directly from each other, thus showing an even more intimate relationship. Many different kinds of stimuli have been used to provoke such changes in co-conformation including pH-change [41-47], redox processes [41,47-49], the nature of the environment [50], photochemistry [51,52], temperature (entropy-driven shuttling) [53] and reversible covalent chemistry [54]. 

Fig. 22 Design of a bistable catenane that performs as a molecular rotary motor controlled by two pairs of independent stimuli (Si and S2)- The working scheme is based on the potential energy changes expected for the chemical reactions and co-conformational rearrangements brought about by stimulation with independent inputs. A, B recognition sites A site A is switched on, K hindering group, X blocking group...

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. 

Figure 13. The two spatial arrangements (co-conformations) associated with a [2]rotaxane, incorporating two different recognitions sites within its dumbbell-shaped component, can be interchanged by appropriate stimuli.

The [2]catenane 19" + incorporates (Figure 31) a macrocyclic polyether containing two dioxybenzene units, and a tetracationic cyclophane comprising a bipyr-idinium and a ram-bis(pyridinium)ethylene unit [36a, 62]. The H NMR spectrum [(CD3)2C0, 213 K] of 19" + shows the signals for two distinct co-conformations in a ratio of 92 8. In the major isomer, the bipyridinium unit is located inside the cavity of the macrocyclic polyether and the ra 5-bis(pyridinium)ethylene unit is posi-... 

---