Synthesis templates

Ordered nanostructured materials were prepare by the template technique. This method consists of a thermal decomposition of the sol—gel precursor within the pores of a membrane. The template is dipped into the sol for 10 min and taken out for heating at r 400 °C resulting in the formatimi of nanomaterial within the template pores. Different types of template have been widely investigated such as anodic alununum oxides (AAO), porous polymer and nano-channel glass templates. The final nano-specimens are obtained by dissolutimi the template composites in 6 mol NaOH solutimi. The template method with porous membranes of AAO has 

The template method involves using the pores in a microporous solid as nanoscopic beakers for the synthesis of nanoparticles of the desired material [1,3,10]. A wide variety of materials are available for use as template materials [1,10,14-19]. Pore diameter sizes range from Angstroms to many p,m. Several of the more common materials used as templates are reviewed below. 

Possin, in 1970, was the first to use the pores in track-etched mica membranes as templates to make nanomaterials [23]. This was accom- 

Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

There has been extensive recent use of track-etched membranes as templates. As will be discussed in detail below, these membranes are ideal for producing parallel arrays of metal nanowires or nanotubules. This is usually done via electroless metal deposition [25], but many metals have also been deposited electrochemically [26]. For example, several groups have used track-etched templates for deposition of nanowires and segmented nanowires, which they then examined for giant magnetoresistance [27-29]. Other materials templated in the pores of track etch membranes include conducting polymers [30] and polymer-metal composites [31]. 

Anodically grown aluminum oxide (AI2O3) has also been used extensively as a template [3,32-37]. When grown on high-purity aluminum, this material has a hexagonal pattern of cylindrical pores, which extend through the thickness of the alumina (Fig. 1C and ID). These microporous alumina films can be removed from the substrate A1 metal and collected as a freestanding membrane [37,38]. 

The deposition or confined crystalHzation of metal atoms may be conducted within the pores in anodic aluminum oxide (AAO) membranes [92, 101, 103, 164, 165], mesoporous siHca [96, 102, 106, 166, 167], or micelles in solution [55, 56, 139]. The crystallization of metal atoms within templates can be achieved through a 

Gel fiber oxide precursors on self-aesembled Gel liber 

Metal oxide nanotubes containing bundles of gel fiber 

Nakamura and Matsui [71] prepared silica nanotubes as a spin-off product of sol-gel synthesis wherein tetraethylorthosilicate (TEOS) was hydrolyzed in the presence of ammonia and D, L-tartaric acid. Ono et al. [72] showed that certain cholesterol derivatives can gelate tetraethyl orthosilicate (TEOS) to obtain tubular silica structures. Using cholesterol based gelators nanotubes of transition metal (Ti, V and Ta) oxides can also be prepared. The organogelators used in these processes are chiral diamino 

The advantage of template synthesis is that organo or hydrogelator templates can direct the shape-controlled synthesis of oxide nanotubes. Recent reports describe the use of carbon nanofibers as a template for the shape-controlled synthesis of zirconia, alumina and silica nanotubes [78]. The shape of vapor grown carbon nanofiber 

A few synthetic methodologies have been reported for ID-nanostructured a-Fe203 materials. For example, Mann et al. [84] 

---

Regioselective and stereoselective template synthesis in chemistry of fullerenes annelated with heterocycles or linked with heterocyclic fragments 99ACR537. 

Template synthesis and chirality of catenanes, rotaxanes, and pretzelanes including N-macroheterocyclic lactams and related compounds as structure components 99PAC247. 

Nonionic template synthesis of amide-linked catenanes and rotaxanes with macroheterocyclic fragments 97AG(E)930. 

Figure 4.24 Template synthesis of a gold(lll) macrocycle complex.

Keywords Fischer carbenes Template synthesis Cocyclization Cycloaddition Cyclopentadienes Cyclopentenones Domino reactions... 

Complexes containing encapsulated metal ions (clathrochelates ) with the formula [M(dioxime)3(BR)2] are known with iron(II) 135, cobalt(ll) 136, cobalt(III) 137, and ruthenium(ll) 138 (Fig. 37) [205-220]. Generally, these macrobicyclic complexes are prepared by template synthesis from a mixture of... 

Schalley CA, WeUandt T, Briiggemann J,V6gtle F (2004) Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes. 248 141-200 Scheer M,see Balazs G (2003) 232 1-23... 

Reverse transcriptase j Synthesizes DNA from RNA template. Synthesis of cDNA from mRNA RNA (S end) mapping studies. 

Template effects have been used in rotaxane synthesis to direct threading of the axle through the wheel. Since macrocycHc compounds such as cyclodextrins, crown ethers, cyclophanes, and cucurbiturils form stable complexes with specific guest molecules, they have been widely used in the templated synthesis of rotax-anes as ring (wheel) components. Here, we briefly discuss macrocycles used in the synthesis of rotaxane dendrimers and their important features. 

In this review, we tried to cover all the supramolecular species that maybe classified as rotaxane dendrimers. We classified them by their structures - where in dendrimer rotaxane-hke features are introduced. Several different types of macrocycles have been employed as a ring component in the templated synthesis of rotaxane dendrimers. While the synthesis of Type I and II rotaxanes dendrimers is relatively straightforward, that of well-defined Type III rotaxane dendrimers, particularly those of second and higher generations, is still challenging. 

According to Ref. [12], template for synthesis of nanomaterials is defined as a central structure within which a network forms in such a way that removal of this template creates a filled cavity with morphological or stereochemical features related to those of the template. The template synthesis was applied for preparation of various nanostructures inside different three-dimensional nanoporous structures. Chemically, these materials are presented by polymers, metals, oxides, carbides and other substances. Synthetic methods include electrochemical deposition, electroless deposition, chemical polymerization, sol-gel deposition and chemical vapor deposition. These works were reviewed in Refs. [12,20]. An essential feature of this... 

Template Synthesis and Catalysis of Metal Nanoclusters in Ordered Mesoporous Silicas... 

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

A tandem enzymatic aldol-intramolecular Homer-Wadsworth-Emmons reaction has been used in the synthesis of a cyclitol.310 The key steps are illustrated in Scheme 8.33. The phosphonate aldehyde was condensed with dihydroxyacetone phosphate (DHAP) in water with FDP aldolase to give the aldol adduct, which cyclizes with an intramolecular Horner-Wadsworth-Emmons reaction to give the cyclo-pentene product. The one-pot reaction takes place in aqueous solution at slightly acidic (pH 6.1-6.8) conditions. The aqueous Wittig-type reaction has also been investigated in DNA-templated synthesis.311... 

A template synthesis employing Ni(OAc)2, 2,5-dihydroxy-2,5-dimethyl-1,4-dithiane, and 3,3 -iminobis(propylamine) gave the water-soluble five-coordinate complex [Ni(495)], the crystal structure of which shows trigonal bipyramidal coordination of Ni11 with the central amine and terminal thiolates in plane and the two imino nitrogens in axial positions. Solvatochromism of the complex is interpreted in terms of S" H bonding, which may be of relevance to the catalytic cycle in hydrogenases.1341... 

---