Acid/base control

Figure 9. Acid/base controlled plug in/plug out of (9-anthracenyl)benzylammonium ion with a...

Fig. 26 The acid/base-controllable XOR gate based on the [2]pseudorotaxane [40-41]2+.

The threading of the dibenzylammonium cation into dibenzo[24]crown[8] has been exploited to assemble pseudorotaxanes at the surface of a nanocrystal96 and to induce and control formation of nanoparticle aggregates.97 However, the possibility of pH-triggered aggregation, related to the acid-base controlled dethreading of hydrogen-bonded pseudorotaxanes, was not explored. 

We also devised a system that uses acid/base control of expansion and contraction of the capsules and their guests. A number of studies with the cylindrical capsule defined its application as a reaction vessel [77,78] but the conformational flexibility [79] of normal alkanes as guests (which adopt shapes complementary to their hosts) offered an opportunity to create what we termed a spring-loaded device. 

Fig. 15. The acid/base-controllable switching of the [2]rotaxane 22-4PF6.

Figure 10.7. The acid/base-controlled switching of the [2]pseudorotaxane [1 12] 4PF6 and the change in the absorbance (A) of the charge transfer band (Amax = 490 nm) associated with [1 12] 4PF6 upon addition of CF3C02H and of /-PpNEt is shown.

Figure 10.15. The acid/base-controlled switching of the [2]rotaxane 20 4PF6 and the absorption spectra (MeCN, 25°C) of 20 4PF6 (a) before the addition of CF3C02H, (b) after the addition of CF3C02H and shuttling, and (c) after the addition of C5H5N and...

Fig. 17 (a) Seif-assembly of the triply threaded supramolecular system 14 j13H36+ and the subsequent synthesis of the triply interlocked species 15H39+. (b, c) Operation of I5H39+ as an acid-base controlled molecular elevator [78-80]... 

Buda, A. B. Wang, Y. Houk, K. N. Acid-base-controlled torquoselectivity theoretical predictions of the stoeochanical course of the electrocycUc reactions of cyclobutene-3-carboxyUc acid and the conjugate base and acid, J. Org. Chem. 1989, 54, 2264-2266. 

Further examples of hybrid pseudorotaxanes containing a linear component incorporating two dialkylammonium centres and a 4,4 -bipyridinium unit associated with an assortment of macrocyclic polyethers have been reported. Both multi-component rotaxanes and polyrotaxanes based on the above tetracationic thread were observed to form. The reversible acid-base-controlled dethreading/rethread-ing of such [n]-rotaxanes has been demonstrated using a combination of NMR, absorption and fluorescence spectroscopies. ... 

Figure 32. Acid/base-controlled plug-in/plug-out of (9-anthraccnyl) benzylammonium ion 34H, obtained by protonation of the corresponding amine 34, with ( )-binaphthocrown ether 33 [42]. The occurrence of photoinduced energy transfer in the plug-in state is schematized.

A Stock solution of the drug substance at the appropriate concentration using water and co-solvent (if necessary) is prepared for the set of acid/base hydrolysis studies. This solution is used to prepare the acid and base solutions as well as the drug substance as is control. Different co-solvents can be used in the acid and base degradation studies. If the co-solvent is not the same, drug substance as is and acid/base control (no drug substance) samples will need to be prepared in each of the solvent systems. For a summary of suggested samples and kinetic points see Table 1. 

The development of an acid-base-controllable XOR logic gate based upon a pseudorotaxane geometry relied upon a very strict set of guidelines being... 

Z6. Zweymiiller, E., Renal aspects of acid-base control in the newly bom. II. The organic acids. Acta Paediat. 49, 591 (1960). 

Proton-Transfer Polymerization. Proton-transfer polymerization (PTP) (Fig. 11) has been reported as a versatile route to hyperbranched polymers (56). Conceptnally, PTP is an acid-base controlled reaction where the nucleophilicity and basicity of monomer and intermediates play important roles. 

Figure 3 An acid-base controllable [c2]daisy chain.

Figure 22 (a) The acid-base controlled threading-dethreading of pseudorotaxane [34 D 35-H] +. (b) The acid-base and light... 

While one might have expected a reinforcement of the anion binding with the protonation of the receptors XCU, XCTU, XCUE and XCA, the addition of a stoichiometric amount of a strong acid (e.g. picric acid) leads to a complete release of the anion and the further addition of a base restores cleanly the host-guest complex. This acid-base control of the binding properties is highly reminiscent of allosteric processes encountered in natural systems. Finally, the more flexible XtubeU and XtubeTU are unable to bind efficiently anions in chloroform... 

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