Molecular and Supramolecular Ionic Devices

Selective ion receptors represent basic units for ionic transmitters or detectors selective ion carriers correspond to ionic transducers. These units may be fitted with triggers and switches sensitive to external physical (light, electricity, heat, pressure) or chemical (other binding species, regulating sites) stimuli for connection and activation. 

Approaches to artificial ion channels have, for instance, made use of macrocyclic units [6.72,6.74] (see also below), of peptide [8.183-8.185] and cyclic peptide [8.186] components, of non-peptidic polymers [8.187] and of various amphiphilic molecules [6.11, 8.188, 8.189]. The properties of such molecules incorporated in bilayer membranes may be studied by techniques such as ion conductance [6.69], patch-clamp [8.190] or NMR [8.191, 8.192] measurements. However, the nature of the superstructure formed and the mechanism of ion passage (carrier, channel, pore, defect) are difficult to determine and often remain a matter of conjecture. 

In addition to attempts at constructing ion channels on the basis of multicon-nected polyether macrocycles [8.193], we have investigated mainly two approaches 

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Molecular devices have been defined as structurally organized and functionally integrated chemical systems they are based on specific components arranged in a suitable manner, and may be built into supramolecular architectures [1.7,1.9]. The function performed by a device results from the integration of the elementary operations executed by the components. One may speak of photonic, electronic or ionic devices depending on whether the components are respectively photoactive electroactive or ionoactive, i.e., whether they operate with (accept or donate) photons, electrons, or ions. This defines fields of molecular and supramolecular photonics, electronics and ionics. 

Fig. 50. Chemionics as the chemistry of recognition-directed and self-organised photonic, electronic and ionic molecular and supramolecular devices generated by means of functional programmed chemical systems.

Heferocycles are a class of compoxmds especially relevanf in the life processes through their enzymatic fxmctions and the hereditary information transfer they also find applications in medicine, agriculture and industry, and in different areas of the chemistry. Heterocyclic compounds are often used in nanochemistry, molecular devices and sensors, combinatorial and supramolecular chemistry, and also in catalysis [8]. Furthermore, an important type of ionic liquids (ILs) useful in the pharmaceutical industry, which can act both as green solvents and catalysts, are composed of heterocyclic compoxmds [9,10]. 

Successive H-bond urea self-assembly of 4 and sol-gel transcription steps yield preferential conduction pathways within the hybrid membrane materials. Crystallographic, microscopic and transport data confirm the formation of self-organized molecular channels transcribed in solid dense thin-layer membranes. The ionic transport across the organized domains illustrates the power of the supramolecular approach for the design of continual hydrophilic transport devices in hybrid membrane materials by self-organization (Figure 10.8) [42-44]. 

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