Biomimetics, possible applications

Many naturally occurring polyethers such as brevitoxin B (123) have been proposed to biosynthetically derive from the polyepoxidation of polyenes and subsequent cyclization of the resulting polyepoxides (Scheme 3.40) [79, 80]. Such a biomimetic polyene-polyepoxide-polycyclization approach would provide a potentially powerfid and versatile strategy for the synthesis of polyethers, with quick assembly of stereochemically complex molecules from relatively simple achiral polyalkene precursors. The epoxidation with ketone 42 should provide a valuable method to investigate this biosynthetic hypothesis and possible application of the proposed pathway in the synthesis of polyethers. 

Following the introduction of MCM-41 type materials [1], the synthesis of surfactant templated nanostructured materials has attracted the attention of the scientific community because it provides the possibility of tailoring pore size, geometry and surface chemistry through control of the synthesis conditions. Potential applications of these materials range from separations and catalysis [2] to the production of biomimetic materials [3] and devices for optical and electronic applications [4]. Several synthesis protocols have been developed in the last ten years and are the focus of many recent reviews [5]. Despite the enormous experimental effort to develop methods to control the structure and composition of templated nanoporous materials, modeling the different processes has remained elusive, mainly due to the overlapping kinetic and thermodynamic effects. The characterization of... 

The possibility that an electron-transfer path is involved in photo-sensitized oxygenation has been considered on several occasions. This is relevant in several fields of application, from the biomimetic oxygenation of indole and flavin derivatives [106] to pollutant control. With reference to latter, it has been suggested that SET occurs in heterogeneous photosensitized oxidation by solid semiconductors, in which the adsorbed substrate donates an electron to the photogenerated hole and... 

The macrocycle phthalocyanine contains 8 N atoms, but usually only the four N-atoms on the inner side of the cycle are able to coordinate. In fact, in most cases the synthesis of phthalocyanine is realized in the presence of a metal ion as the template. It is also possible to attach various substituents on the phthalocyanine macrocycle. As for porphyrin, when coordinating to a metal ion, the H-atoms of the two NH groups on the inner side of the phthalocyanine cycle are replaced. The incorporation of metal porphyrin and phthalocyanine complexes into porous crystals has been gaining increasing interest. The properties of the complexes located in zeolite channels or cages are usually different from those of the compounds in solution, and they may find applications in areas such as catalysis, photochemistry, electrochemistry, and biomimetics. 

An interesting possible further extension is the functionalization of bispidine ligands with hydrophobic groups, for example, for metal ion selective extractions (69, 339). biopolymers for nuclear medicinal applications (340), solids for heterogeneous catalysis and sensors, or additional coordination sites for the synthesis of heterodinuclear complexes with applications in biomimetic chemistry, catalysis, and as luminescence sensors. There is a variety of possible sites for ligand modification. Of particular interest is the C9 position, which has been selectively and stereospecifically reduced to an alcohol (190), and the two hydrolyzed C1,C5 ester groups (167). 

A limited improvement in this context may be possible by the use of more stable proteins, e.g. from thermophilic bacteria. However, many principles demonstrated by nature could be transposed to sensor development. For example, biomimetic channel and carrier molecules could be used in conjunction with stabilized lipid membranes to prepare sensitive and selective electrochemical transducers which embodied the principle of intrinsic amplification by depolarization. The use of artificial receptor sites would probably result in a substantial reduction of the desired selectivity coefficients, but this could easily be compensated by the application of array processing for background correction. 

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