Structure changes reversible

This highlight offers an overview of CD-containing nanosystems of various complexity with photoresponsive behaviour mediated by structural changes (reversible isomerizations, reversible or irreversible cleavage of covalent bonds) or release of bioactive species. Representative examples of the last decade have been described as to structural features, functions and operating mechanisms. CD-based systems which respond to light with emission of photons only or act as microreactors for photochemical reactions have been left out. 

The cis-trans isomerism of azobenzene can be used as a photoresponsive "switch" to regulate binding ability of CD when an azobenzene moiety is attached to CD. The photoresponsive CD reported first is azobenzene-capped g-CD in which the cap structure changes reversibly enlarging the hydrophobic cavity around substrate in its cis form. ... 

To convert a molecule with two chirality centers to its enantiomer the configura tion at both centers must be changed Reversing the configuration at only one chirality center converts it to a diastereomeric structure... 

Then, for any reversible structural change at constant uniform temperature and pressure... 

As mentioned above, water structure in reversed micelles deviates considerably from the structure in the bulk-phase. Therefore, the hydration shell of macromolecules entrapped in reversed micellar systems should be changed and thus also their conformation. According to the results of several authors this is indeed the case. 

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

Didodecyldimethylammonium bromide forms in the dilute-phase cylindrical reversed micelles in the range 2 < / < 8, showing an abrupt structural change at/ = 10 and forming spherical aggregates at/ > 10 [17],... 

By IR spectroscopy it was emphasized that the solubilization of amino acids or ohgopeptides in water-containing lecithin-reversed micelles involves structural changes in the aqueous micellar core [159]. 

Another interesting characteristic about many responsive gels is that the mechanism causing the network structural changes can be entirely reversible in nature. This behavior is depicted in Fig. 3 for a pH- or... 

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