Template biomimetic

Zhang, Y., Wu, H Li,)., U, L, )iang, Y Jiang, Y. and Jiang, Z. (2008) Protamine-templated biomimetic hybrid capsules efficient and stable carrier for enzyme encapsulation. Chemistry of Materials, 20, 1041-8. 

The size-exclusion and ion-exchange properties of zeoHtes have been exploited to cause electroactive species to align at a zeoHte—water interface (233—235). The zeoHte thus acts as a template for the self-organization of electron transfer (ET) chains that may find function as biomimetic photosynthetic systems, current rectifiers, and photodiodes. An example is the three subunit ET chain comprising Fe(CN)g anion (which is charge-excluded from the anionic zeoHte pore stmcture), Os(bipyridine)3 (which is an interfacial cation due to size exclusion of the bipyridine ligand), and an intrazeoHte cation (trimethylamino)methylferrocene (F J ). A cationic polymer bound to the (CN) anion holds the self-assembled stmcture at an... 

Addadi and Weiner (1999) have concisely and critically reviewed these various strategies and have added their own variant - the use of biological templates, for instance bacterium surfaces to assist self-assembly. Here, self-assembly and biomimetics join forces productively. 

Nickel complexes of this group are of interest in biomimetic work. By means of ligand (320) the complete reaction cycle of acteyl CoA synthase could be executed (Scheme 2). Ligand (320) can also be synthesized by a template reaction. Upon reduction of the Ni11 complex (321) with Na/Hg, the ligand backbone is cleaved, resulting in a thermally stable trinuclear Ni11 alkyl thiolato complex (322). 

Macrocyclic complexes of zinc have inspired interest in varied areas such as supramolecular and biomimetic chemistry including hydrolysis enzymes, such as phosphatases and esterases, and also for the fluorescent detection of zinc. The polyaza macrocycles and their A--functionalized derivatives are particularly well represented. An important aspect of macrocycle synthesis is the use of metal templates to form the ligand. Examples of zinc as a template ion will be discussed where relevant. 

As mentioned earlier, biological systems have developed optimized strategies to design materials with elaborate nanostructures [6]. A straightforward approach to obtaining nanoparticles with controlled size and organization should therefore rely on so-called biomimetic syntheses where one aims to reproduce in vitro the natural processes of biomineralization. In this context, a first possibility is to extract and analyze the biological (macro)-molecules that are involved in these processes and to use them as templates for the formation of the same materials. Such an approach has been widely developed for calcium carbonate biomimetic synthesis [13]. In the case of oxide nanomaterials, the most studied system so far is the silica shell formed by diatoms [14]. 

In fact, such biomimetic molecules demonstrate the ability to tailor the growth of silica nanoparticles in a way that is very similar to diatom-extracted species. However, they demonstrate the same limitations in terms of morphological control of nanoparticle assembly. This is because the diatom shell architecture results not only from interactions of silica precursors with templating molecules but also benefits from a cell-driven molding of the vesicular compartment where silicification occurs [29]. Thus, it is very likely that diatom-like synthetic silica will only be achieved when such confinement/molding effects are taken into account in the design of biomimetic experiments [30]. 

However, it has to be realized that biological templates remain inserted in the final nanoparticles and this is not acceptable for many applications. Nevertheless, some recent examples indicate that such biomimetic materials may be suitable for the design of biotechnological and medical devices [32]. For instance, it was shown that silica gels formed in the presence of p-R5 were excellent host matrices for enzyme encapsulation [33]. In parallel, biopolymer/silica hybrid macro-, micro- and nanocapsules were recently obtained via biomimetic routes and these exhibit promising properties for the design of drug delivery materials (see Section 3.1.1) [34,35],... 

Knecht, M.R. and Wright, D.W. (2004) Amine-terminated dendrimers as biomimetic templates for silica nanospheres formation. Langmuir, 20, 4728-4732. 

Capsules with high enzyme loading and activity prepared by templating BMS spheres can also be used as biomimetic reactors [89]. For example, PGA/ PLL capsules with pre-loaded urease (prepared via a BMS sacrificial template) are capable of catalyzing the hydrolysis of urea and have been shown to induce the exclusive formation of CaC03 particles inside the capsules [89]. 

Fig. 1. Preparation of configurational biomimetic imprinted networks for molecular recognition of biological substrates. A Solution mixture of template, functional monomer(s) (triangles and circles), crosslinking monomer, solvent, and initiator (I). B The prepolymerization complex is formed via covalent or noncovalent chemistry. C The formation of the network. D Wash step where original template is removed. E Rebinding of template. F In less crosslinked systems, movement of the macromolecular chains will produce areas of differing affinity and specificity (filled molecule is isomer of template).

Rather than using the protein molecule as a whole, the imprinting of selected protein epitopes may present a more practical approach. Imprints of such patches may then act as receptors for these parts of the protein. It could be shown that an MIP imprinted with a tetrapeptide was able to recognize not only the template but also a protein bearing the same 3-amino acid terminus as the peptide template [129]. If this approach proves to be successful in other cases as well, MI-based recognition will no longer be limited to small molecules. The result will be even more antibody like biomimetic polymers. 

AU the synthesized compounds, regarchess of their probe s size or charge, display microbial activity in P. putida similar to that of the biomimetic analogs lacking the probe. These results provide an indication that the epical site in the tetrahedral carbon-based templates is available for attachment of chemical moieties without hampering iron(in) coordination and receptor recognition. 

The second group of hydroxamate-based chelators consists of biomimetic ferrichrome analogs modified by introducing hydrophobic amino acids between the template and the hydroxamic acid binding sites 59, 60, 66, 68, 70, 199 and 200. Since they function to withhold iron from cells in contrast to their original function of iron delivery, they were named reversed siderophores (RSF) . ... 

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