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The use of templates

Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... [Pg.94]

As we have shown in this example, the use of templates and chemical descriptors allows RACHEL to generate chemically diverse ligand derivatives within specific user constraints. In addition, building structures from enriched corporate database fragments... [Pg.217]

As previously stated, the use of templates such as DBSA, HDTMAB, and PEOPE allows the formation of well-defined micellar structures in aqueous solution when the template concentration is above its CMC. In a recent publication [38], the polymerization with a bifunctional sodium dodecyl diphenyloxide disulfonate (DODD) as template was proposed to proceed by a micellar mechanism in the same way (Scheme 2). In an aqueous acid solution of DODD and aniline, anilium ions locate at the micellar interface, with benzene parts penetrating into the hydrophobic core of the DODD micelle to form the complex (as illustrated in Scheme 3b). At the concentration of 0.055 mol a slight turbidity was observed in solution, indicating micellar aggregation. Once the micellar structure is formed and the enzyme is added to the aqueous medium, addition of H2O2 triggers the polymerization of anilinium ions around micelles (Scheme 3). [Pg.5]

The formation of novel silicon-rich synthetic zeolites has been facilitated by the use of templates, such as large quaternary ammonium cations instead of Na+. For instance, the tetramethylammonium cation, [(CH3)4N], is used in the synthesis of ZK-4. The aluminosilicate framework condenses around this large cation, which can subsequently be removed by chemical or thermal decomposition. ZSM-5 is produced in a similar way using the tetra-.n-propyl ammonium ion. Only a limited number of large cations can fit into the zeolite framework, and this severely reduces the number of [AIO4] tetrahedra that can be present, producing a silicon-rich structure. [Pg.318]

Gold nanoparticle assembly can be induced in several ways such as binding of nanoparticles to other nanoparticles or nanomaterials, deposition of nanoparticles on functionalized surfaces, or the use of templates. This subsection presents some examples of the different types of assemblies of Au NPs. [Pg.165]

The use of templates that can nucleate secondary structures has also been studied [23], The fundamental idea is to attach one or more conformationally flexible peptides to a rigid template that is designed to initiate either a /f-sheet or an a-helix by forming the first crucial hydrogen bonds. These interactions compensate for the loss of entropy associated with the folding process and in particular in the initiation step. This strategy has been used to develop stable helices, sheets, and artificial proteins. [Pg.13]

During the preparation of this chapter, a review on the use of templates to induce peptide secondary structures appeared Scheiner JP, Kelly JW (1995) Chem Rev 95 2169... [Pg.36]

There are also potential disadvantages associated with the use of template methodology for the formation of macrocyclic ligands. Perhaps the most important is the observation that not all metal ions can act as templates for the specific cyclisation reactions of interest. In many cases it may not be trivial to find an appropriate template ion (if indeed... [Pg.141]

The use of templates to control the porosity of solids is not limited to small organic molecules. Alternative templates include dendrimers [16, 17], polymers [18], hard templates such as nanoparticle colloidal suspensions [19] and latex spheres [20] or even biological materials like butterfly wings [21], DNA [22] or viruses [23]. [Pg.50]

An attractive way to overcome the problem described above is the use of templates [26]. According to Bush, a template organizes an assembly of atoms, with respect to their loci, in order to achieve a particular linking of atoms [27]. [Pg.238]

Other examples of external input include the use of a scaffold or template to order the assembly process, and the necessity for the information already stored in a structure to be used in the formation of a new copy. Examples of these include the assembly of the bacteriophage T4 virus, which involves the use of template proteins, and the formation of new mitochondria which arise from the growth and division of preexisting mitochondria. [Pg.110]

The earliest syntheses of rotaxanes were largely based on the statistical or directed methods.2,3 Statistical methods require very precise reaction conditions, and directed methods involve numerous chemicals steps. However, the use of templates allows high control of these synthetic methods resulting in efficient and precise assemblies of rotaxanes that incorporate a wide range of chemical functionalities. Two types of interactions occur in synthetic template methods (1) purely organic and (2) transition-metal-templated. In this latter case, the template can easily be removed at the end of the synthesis, whereas in the former, the interactions between the template and the components of the final rotaxane will often be maintained. Selected examples will now illustrate the statistical, the directed, and templated strategies outlined above. The transition-metal-templated route will be developed separately. [Pg.132]

Novel methods of preparation of vanadium phosphate catalysts have been explored by several groups these methods include hydrothermal synthesis, gas-phase s)mthesis, supercritical antisolvent precipitation, and the use of templates and structure-directing agents to modify the bulk... [Pg.203]

In the search for zeolites with new pore dimensions and channel structure, researchers employed the use of templating molecules to direct the growth of the aluminosilicates. Tetramethylammonium was the first of these templates used to prepare sodalite and others soon followed [61]. Recently, spectroscopic studies have... [Pg.239]

In the use of templates, Sanders and co-workers [47] differentiate between two modes of action that are complementary a positive template directs the approach of two reactive end groups in a molecule, thereby generally supporting the desired intramolecular cyclization. In contrast, a negative template effect holds the reactive groups apart, thereby suppressing the intramolecular cyclization and leading preferentially to the (undesired) intermolecular reaction. [Pg.928]

Fig. 2 Different paths to obtain hybrid materials from molecular sources. Path A Sol-gel routes (Al conventional route for hybrid nanocomposites, A2 molecularly homogenous hybrids). Path B Assembly of nanobuilding blocks (ANBB), of prefunctionalized or postfunctionalized clusters or nanoparticles. Route C or D involve the use of templates capable of self-assembly, giving rise to organized phases. Path E involves integrative synthesis combining precedent paths from A to D and other processes, such as the use of lithography, casting, organogels or latex beads as templates, controlled phase separations, or external fields. (From Ref. l) (View this art in color at www.dekker.com.)... Fig. 2 Different paths to obtain hybrid materials from molecular sources. Path A Sol-gel routes (Al conventional route for hybrid nanocomposites, A2 molecularly homogenous hybrids). Path B Assembly of nanobuilding blocks (ANBB), of prefunctionalized or postfunctionalized clusters or nanoparticles. Route C or D involve the use of templates capable of self-assembly, giving rise to organized phases. Path E involves integrative synthesis combining precedent paths from A to D and other processes, such as the use of lithography, casting, organogels or latex beads as templates, controlled phase separations, or external fields. (From Ref. l) (View this art in color at www.dekker.com.)...
The PCM model can, as shown, also be used to describe the effect of other anions, surfactants, or chelates, e.g., with fatty acid templates. If 5(RH) < 0 (e.g., for an acetate group), it will remain in the gel produced and must be removed by pyrolysis, extraction, or some other means. We shall return to this matter when discussing the use of templates in the sol-gel processing of porous particles and gels. [Pg.473]

The Use of Templates in Combinatorial Chemistry for the Solid-Phase Synthesis of Multiple Core Structure Libraries... [Pg.229]


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Patterning of Alkanethiols Using the Nanotrench Template

The Use of 3-Hydroxy-2-Methylidene Propionic Acids as Templates

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