Template-directed Synthetic Approach

Finally some experiments are carried out based on the predicted reaction conditions. 7.3.2 Template-directed Synthetic Approach 

Designing Templates for the Synthesis of Microporous Solids Using de novo Molecular Design Method 

Predicting the Templating Ability of Organic Amines in the Formation of2-D Layered Aluminophosphates with Al3P4Oi Stoichiometry 

This method is based on the Burchart 1.01-Dreiding 2.21 force field in the Cerius2 package.1451 The Burchart force field is used to treat the frameworks, and the Dreiding II force field is used to treat the intra- and inter-molecular interactions. On the basis of known structure parameters, some parameters which are not addressed in the force field are added. 

In fact, the host-guest electrostatic energy is very similar for the compounds with specified AI3P40163 stoichiometry. The Coulombic interactions between the framework and template are ignored in the calculation. 

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The template-assisted synthetic strategies outlined above produce micro- or mesoporous stmetures in which amorphous or crystalline polymers can form around the organic template ligands (174). Another approach is the use of restricted spaces (eg, pores of membranes, cavities in zeolites, etc.) which direct the formation of functional nanomaterials within thek cavities, resulting in the production of ultrasmaU particles (or dots) and one-dimensional stmetures (or wkes) (178). For example, in the case of polypyrrole and poly(3-methylthiophene), a solution of monomer is separated from a ferric salt polymerization agent by a Nucleopore membrane (linear cylindrical pores with diameter as small as 30 nm) (179—181). Nascent polymer chains adsorb on the pore walls, yielding a thin polymer film which thickens with time to eventually yield a completely filled pore. De-encapsulation by dissolving the membrane in yields wkes wherein the polymer chains in the narrowest fibrils are preferentially oriented parallel to the cjlinder axes of the fibrils. 

An alternative synthetic approach that appears to demonstrate the importance of a template effect involves the formation of crowns directly from ethylene oxide in the presence of a Lewis acid such as BF3 <81CC684>. Cyclic products of the type (CH2CH20) are formed in which n = 4, 5, or 6. The product composition is altered by addition of M BF4 salts where M is Li, Na, or K. In all cases, the bulk of the product appears to be dioxane, (CH2CH20)2, but the proportion of 12-crown-4, 15-crown-5, and 18-crown-6 produced shifts to larger ring sizes when larger cations, rather than smaller ones, are added. 

This section has discussed a diverse range of self-assembled synthetic macromolecules such as block copolymers and elastm-like polymers for template-directed assembly of different types of inorganic nanoparticles into anisotropic ID nanostructures. In the next section, we introduce a simple and cost-effective approach for directing the assembly of gold nanoparticles into ID structures via self-assembly of a short commercially available surfactant. 

The size of synthetic molecules that can be synthesized using template-directed strategies seems more limited by the preparation of the precursors than by the final template-directed route in the present day. This observation forces one to reflect that perhaps sequential templating strategies are necessary, in which different templates are employed at each step of a one-pot linear or convergent route to a desired molecule. This kind of system or factory line approach to templated molecules would constitute a considerable... 

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