Bioinspired models

The cationic complex [CpFe(CO)2(THF)]BF4 (23) can also catalyze the proton reduction from trichloroacetic acid by formation of Fe-hydride species and may be considered as a bioinspired model of hydrogenases Fe-H Complexes in Catalysis ) [44]. This catalyst shows a low overvoltage (350 mV) for H2 evolution, but it is inactivated by dimerization to [CpFe(CO)2l2-... 

The first examples of the so-called supramolecular catalysis are based on bioinspired molecular recognition, which is an essential attribute of biochemical systems. Structures such as receptors, antibodies, and enzymes can all recognize a feature that is important for their specific functions, often in the presence of species of quite similar structure. The ability to discriminate depends exclusively on the structural properties of these biological macromolecules. Recent progress in bioor-ganic chemistry has shown that many of these functions can be incorporated into smaller, synthetically more accessible structures as model systems [27]. 

Fig. 49 (a) Examples of Janus-type bis-dendrons and (b) model of the self-assembly in a core-shell columnar LC structure [154]. Reproduced with permission [154, Bioinspired supra-molecular liquid crystals, Fig. 3], copyright 2006, The Royal Society... 

The catalytic properties of Mn enzyme structural models are not limited to the natural substrates of the enzymes they mimic. One could classify this catalysis based upon the substrates as biological mimetic catalysis or biomimetic catalysis [175] and biologically inspired catalysis or bioinspired catalysis [176], Unlike biomimetic catalysis, its bioinspired counterpart capitalizes on nature s findings to change nonnatural substrates chemically and, perhaps, unravel novel chemistry. 

Apart from the catalytic properties of the Mn-porphyrin and Mn-phthalo-cyanine complexes, there is a rich catalytic chemistry of Mn with other ligands. This chemistry is largely bioinspired, and it involves mononuclear as well as bi- or oligonuclear complexes. For instance, in Photosystem II, a nonheme coordinated multinuclear Mn redox center oxidizes water the active center of catalase is a dinuclear manganese complex (75, 76). Models for these biological redox centers include ligands such as 2,2 -bipyridine (BPY), triaza- and tetraazacycloalkanes, and Schiff bases. Many Mn complexes are capable of heterolytically activating peroxides, with oxidations such as Mn(II) -> Mn(IV) or Mn(III) -> Mn(V). This chemistry opens some perspectives for alkene epoxidation. 

Photochemistry and Photophysics in Bioinspired Systems Studies and Modelling... 

Biomimetic and bioinspired synthetic model complexes were very useful in providing information about basic functional principles and mechanistic aspects... 

Without doubt, ligands based on bridging alkoxide or phenolate groups are most prominent in biomimetic or bioinspired chemistry with bimetallic sites. Even before the X-ray crystal structure of urease became known, first model compounds using this ligand type were developed. Complex 3, reported in 1989 by Buchanan,... 

Despite the obvious versatility of light-activated key steps and their numerous advantages for the biomimetic modeling of natural systems, up to now, only very few examples are known, where such types of photosensitized processes have been successfully combined to complete reaction cycles with reasonable catalytic turnovers 6). In the last section, we are therefore briefly presenting two case studies which describe some recent work performed in our own group focusing on bioinspired catalytic systems that can be controlled and driven by visible light. 

Next to the rich oxygenation chemistry of Mn in Mn-Pc and Mn-POR complexes, there exists catalytic chemistry of Mn with non-heme-type ligands, mostly bioinspired. In Photosystem II, a non-heme multinuclear Mn redox center allows to oxidize water, while in catalase the active center is a dinuclear Mn species [34], Biomimctic models for these biological redox centers use ligands such as 2,2 -bipyridine (BPY), triaza- and tetraazacycloalkanes and Schiff bases such as Me(Salen) and Mc(saloph) (structure sec below) [23J. Usually, the complexes activate heterolytically peroxides, with Mn valency changes such as ... 

Chemists have devised an extensive range of synthetic replicating system, both bioinspired and completely artificial, which have demonstrated that molecules can replicate themselves through minimal kinetic models. It is clear, therefore. 

Koh LB, Merrett K, Elizondo RA, Griffith, M, 2014. Biomimetic Regeneration of Comeal Tissue. In Handbook of Biomimetics and Bioinspiration 3 Tissue Models pp. 1069-1088. 

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