Carbon as template

Baldwin, J.M., Schertler, G.F., Unger, V.M., 1997. An a-carbon template for the transmembrane helices in the rhodopsin family of G protein-coupled receptors. J. Mol. Biol. 272, 144-164. 

In addition, experiments of isobutane diffusion reveal that the effective diffusivity is three times higher over a carbon-templated hierarchical zeolite [143]. Similar conclusions were drawn by Groen et al. [144] with hierarchical zeolites synthesized using the desilication method, where a two-order-magnitude improvement was observed in the diffusion of neopentane inside desiUcated ZSM-5 because of the shorter diffusion path length and presence of an accessible network of mesopores. 

C02-expanded ethanol, porous hollow metal oxide nanoparticles have been prepared using a carbon template by Sun and co-workers.A metal salt, such as C0 j(NO3)3,(CO3)z(OH) , wHaO, can be prepared from the corresponding metal nitrate in COa-expanded ethanol and deposited on the surface of template carbon colloids. Thermal treatment in nitrogen affords CoO nanocrystals. When calcined in air, these can be transformed to C03O4. Electron microscopy images of these dense hollow porous nanostructures are shown in Fig. 9. The improved performance of this material as an anode in Li-02 battery has also been demonstrated, along with the capacity to generate FeO NiO and MnO, nanocomposites. 

This work focuses on tailoring the porous structure and the metal content of carbon materials using a carbonization-templating procedure. The objective of this research is to study the effects of the templates porosity and the type of metals in the carbon precursors on the surface features of template derived carbons. 

Aryl- and alkenylcarbene complexes are known to react with alkynes through a [3C+2S+1C0] cycloaddition reaction to produce benzannulated compounds. This reaction, known as the Dotz reaction , is widely reviewed in Chap. Chromium-Templated Benzannulation Reactions , p. 123 of this book. However, simple alkyl-substituted carbene complexes react with excess of an alkyne (or with diynes) to produce a different benzannulated product which incorporates in its structure two molecules of the alkyne, a carbon monoxide ligand and the carbene carbon [128]. As referred to before, this [2S+2SH-1C+1C0] cycloaddition reaction can be carried out with diyne derivatives, showing these reactions give better yields than the corresponding intermolecular version (Scheme 80). 

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

The pores of the silica template can be filled by carbon from a gas or a liquid phase. One may consider an insertion of pyrolytic carbon from the thermal decomposition of propylene or by an aqueous solution of sucrose, which after elimination of water requires a carbonization step at 900°C. The carbon infiltration is followed by the dissolution of silica by HF. The main attribute of template carbons is their well sized pores defined by the wall thickness of the silica matrix. Application of such highly ordered materials allows an exact screening of pores adapted for efficient charging of the electrical double layer. The electrochemical performance of capacitor electrodes prepared from the various template carbons have been determined and are tentatively correlated with their structural and microtextural characteristics. 

Fuertes A.B. Template synthesis of mesoporous carbons with a controlled particle size, J. Mater. Chem. 2003 13 3085-8. 

The synthesis of carbon templated mesoporous tin MFI catalysts with different Si/Sn was carried out using microwave and in typical synthesis methodology TEOS, TPAOH, [Sn(C5H70)2]2]Cl2, ethanol and water were employed where the molar composition of the reaction mixture was 0.06 TPAOH 0.67 H20 0.028 TEOS 1.3 g EtOH X mg of tin precursor (X = 85, 63, 42, 21 mg). This synthesis mixture was stirred for 90 min at room temperature and then Black pearl 2000 carbon (10% wt. of TEOS) was added and again stirred for 4 h vigorously. The crystallization of C-meso-Sn-Silicalite was performed in a Teflon cup placed in a microwave oven (MARS-5, CEM, maximum power of 1200 W). 

Tanaka, S. Katayama, Y. Tate, M. R Hillhouse, H. W. Miyake, Y. 2007. Fabrication of continuous mesoporous carbon films with face-centered orthorhombic symmetry through a soft templating pathway. J. Mater. Chem. 17 3639-3645. 

Thiophene-containing molecules can be found in both natural products and synthetic chemotherapeutics. Bithiophene 1, a naturally occurring nematocide, is isolated from the roots of Echinops spaerocephalus, whereas tiaprofenic acid, an anti-inflammatory agent, is a synthetic thiophene derivative. Moreover, thiophene is a useful template for four-carbon homologation via reduction [1], as well as a bioisostere of the benzene ring and other heterocycles in medicinal chemistry. 

Graphite and carbon fibers have been used at templates. Thus, nylon 6 has been polymerized on a graphite matrix. Such syntheses of polymers in the presence of a solid template, where the solid acts as a template have been described as polymerization-induced epitaxy (PIE). The monomer and resulting film is adsorbed on the template surface through only van der Waals forces. After polymerization, the polymer is washed from the template. The recovered polymer retains special structural features introduced by the template. 

Thiophenes have served as important four-carbon templates for molecular elaboration. Both functionalized cyclic and acyclic chains can be generated by carrying out conventional reactions on the thiophene nucleus and then performing a Raney nickel desulfurization at or near the very end of the scheme. Thus, the major constituent (279) of the Panamanian ant, Atta columbica, was made by Friedel-Crafts acylation of the thiophene derivative (277), followed by Grignard addition to the carbonyl group of (278), dehydration, and reductive desulfurization (Scheme 57) (60JOC1754). 

The synthesis of type II branched-chain sugars should seem a more difficult task because it needs activation of a carbon atom on the sugar template and a control of the stereochemical course of the carbon-carbon bond formation. Probably because of this apparent difficulty several methods have been devised in the last decade, in particular, in the field of organo-metallic and free radical reactions. 

Finally, this free radical approach is a good way to form carbocycles on the carbohydrate templates, provided the tether between the radical center and the olefin is a carbon chain [93,99-101], see also other contributions of this book describing the carbohydrate to carbocycle transformations. 

Carbon-based material on a silica template has been pioneered by Knox (34). It can be used at any pH. However, the mechanism of retention on this support is quite different from that for the average alkyl-bonded silica (35). Further information on reversed-phase retention can be found in Ref. 36. 

A molecularly imprinted polypyrrole film coating a quartz resonator of a QCM transducer was used for determination of sodium dodecyl sulphate (SDS) [147], Preparation of this film involved galvanostatic polymerization of pyrrole, in the presence of SDS, on the platinum-film-sputtered electrode of a quartz resonator. Typically, a 1-mA current was passed for 1 min through the solution, which was 0.1 mM in pyrrole, 1 mM in SDS and 0.1 M in the TRIS buffer (pH = 9.0). A carbon rod and the Pt-film electrode was used as the cathode and anode, respectively. The SDS template was then removed by rinsing the MlP-film coated Pt electrode with water. The chemosensor response was measured in a differential flow mode, at a flow rate of 1.2 mL min-1, with the TRIS buffer (pH = 9.0) as the reference solution. This response was affected by electropolymerization parameters, such as solution pH, electropolymerization time and monomer concentration. Apparently, electropolymerization of pyrrole at pH = 9.0 resulted in an MIP film featuring high sensitivity of 283.78 Hz per log(conc.) and a very wide linear concentration range of 10 pM to 0.1 mM SDS. 

The imprinting was accomplished by electrochemical co-polymerization of aniline with 1,2-phenylenediamine, in the presence of DNOC, which led to deposition of the resulting MIP film onto a carbon fibre microelectrode. After removing the DNOC template, the DNOC analyte was selectively determined, with the linear concentration range of 8 x 10 7 to 10 1 M and LOD of 0.2 mM, in the presence of interfering dinitrophenolic pesticides such as binapacryl, and dinobuton. 

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