Template effect components

The s)mthesis of zeolites is traditionally performed by crystallisation from a sol-gel mixture comprising reagents such as silica, sodium aluminate, sodium hydroxide and water. Another key component of the sol-gel mixture is a base whose main role is to regulate the pH of the mixture. If an organic base is used then a templating effect may also be observed... 

These CD studies confirmed the binding stoichiometries of our aPNA-DNA complexes and provided further support for our binding model. Comparisons between the CD spectra of the individual components and the aPNA DNA complex suggest a template effect (not unhke that observed with certain DNA-binding proteins) where the components induce mutual conformational changes upon their interaction with each other. 

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 a 1 2 ratio these compounds yield a mixture of (Z/Z), (EIE) and (E/Z) isomers plus a substantial amount of the (E) and (Z) isomers of the monohydrazone monoketone. The complexity of the mixture (due to several equilibria that are established between its components) was illustrated by its complex H NMR spectrum. However, addition of one equivalent of barbiturate to the mixture led to a dramatic simplification of the NMR spectrum with the disappearance of the different products and the emergence of a single new species. This remarkable simplification of the spectrum is a consequence of the templating effect played by the barbiturate that amplifies the formation of only one of the receptors - in this case the ZyZ isomer. Interestingly, the addition of other species to the mixture such as acetate or 1-benzyluracil (with similar pKa values to barbiturate but different hydrogen bonding patterns) did not lead to the amplification of any specific species. 

These results represent the most spectacular example of the dramatic role of template effects as the main factors affecting the assemblage of complex three-dimensional structures with a high degree of pre-organization in the multi-component reaction complex. 

The ability of a transition metal atom to assemble and/or to orient within the framework of its coordination shell several components of a reaction (template effect). Some examples of reactions in which this effect is probably important are ... 

Rotaxanes and catenanes are supramolecular (multicomponent) species [1, 15] strictly related to, but also very different from, pseudorotaxanes (Fig. 2). Whereas pseudorotaxanes can undergo dissociation into their wirelike and macro-cyclic components, rotaxanes and catenanes are interlocked species, whose dissociation requires breaking of a covalent bond. The general strategy to prepare rotaxanes and catenanes with high yields is based on the template effect [44], which relies on the presence of molecular recognition sites in the components to be assembled. 

Ability to assemble and orient various reactive components within the coordination sphere (the template effect). 

The second concept inherent in the template effect is that cations of different sizes favor the formation of different ring sizes. In the cyclooligomerization of ethylene oxide reported by Dale et al. relatively more 15-crown-5 was formed in the presence of Na and more 18-crown-6 was formed when was added to the reaction mixture. When the reacting components are triethylene glycol and triethylene glycol dichloride, the possibilities are the formation of rings having sizes of 9. 

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