Supramolecular “gates

FIGURE 2.2.3 Control of drug release from mesopore channel by coumarin supramolecular gate. 

Modification of the release rate of the loaded mesoporous silica can for instance be achieved by surface functionalization of the mesoporous silica (Song et al. 2005). This can be achieved either by applying polyelectrolyte multilayer coatings (Zhu et al. 2005), or by ionic interaction of oppositely charged polycations and anionic SBA-15 (Yang et al. 2005) or by anchoring suitable polyamines on the external surface to obtain a pH and anion-controlled nano-supramolecular gate-like ensemble (Bernardos et al. 2008). 

Supramolecular architectures capable of self-inclusion of compounds through supramolecular gates are very attractive research objects. In such systems, the gates can be either open or closed, providing control over the guest release or binding. Analysis of literature data shows that controlled release/binding properties can be realized on surfaces [92], in the membranes [93], and in porous systems [94]. 

Xu H, Xu X, Dabestani R et al (2002) Supramolecular fluorescent probes for the detection of mixed alkali metal ions that mimic the function of integrated logic gates. J Chem Soc Perkin Trans 2 636... 

In the light of promising applications offered by these supramolecular glycoconju-gate structures, notably for the intrinsic optical and electrochemical properties of metal complexes, this underexploited research area is undoubtedly in its infancy and holds promise for such systems as biomarkers or sensitive biosensors. 

Keywords Luminescence m Fluorescence m Phosphorescence a Sensors a Switches a Logic Gates a Supramolecular Systems a Truth Tables a Photoinduced Electron Transfer a Molecular-Level Devices... 

Figure 3. A supramolecular arrangement of a helices of voltage-gated Na" channel proposed by Numa [Noda et al. (1984)). Four helix bundles of segment 2 from each repeat unit constitute the wall of hydrophilic pore through which ions pass. All the other helices 1, 3-6, cover the pore and stabilize it in bilayer membranes. The ion pair 1 is a mimic from oligoether carboxylate and dioctadecyidimethylammonium representing hydrophilic helix 2 and all the other hydrophobic helices 1 and 3-6, respectively.

One of the most promising bottom-up approaches in nanoelectronics is to assemble 7i-conjugated molecules to build nano-sized electronic and opto-electronic devices in the 5-100 nm length scale. This field of research, called supramolecular electronics, bridges the gap between molecular electronics and bulk plastic electronics. In this contest, the design and preparation of nanowires are of considerable interest for the development of nano-electronic devices such as nanosized transistors, sensors, logic gates, LEDs, and photovoltaic devices. 

Another way of designing NOT logic gates is to arrange PET involving the input guest species (Figure 3). Examples from the supramolecular era can be illustrated from publications by Czarnik and Fabbrizzi, with 3 32,33 and 4, 34 35 respectively. 

A diverse number of approaches to the design of artificial ion channels and the study of their transport has been described. The ability of these systems to be effective as ion channels varies considerably, but taken together they show that the activity of structurally simple ionophores can mimic those of their more illustrious natural counterparts. The challenge of controlling selectivity and the phenomenon of gating or rectification remains to be overcome in artificial systems but the expansion of knowledge in the field of supramolecular chemistry promises to resolve many of the outstanding questions in the near future. 

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