Template steric component

Figure 4. Pictorial representation of 3D-QSAR models. The color code is as follows sterically favourable and unfavourable interactions, green and red regions, respectively favourable and unfavourable influence of high electron density, cyan and yellow zones respectively. To aid interpretation the template 26, idazoxan compounds 35 and 40 have been added to the electrostatic map, whereas clonidine, compounds 5, 8 and 34 are shown in the steric map. n, number of data points q and r, cross-validated and non-cross-validated correlation coefficient, respectively s, standard deviation one, optimal number of components.

Protein segments adopt only a finite number of conformations in folded proteins.This limited dictionary of templates may be due to the inherent steric constraints of the backbone and other packing and electrostatic interactions in protein folding. This was most graphically demonstrated by Jones and Thirup. They showed that the majority of the polypeptide backbone of a new structure can be built up from component pieces of other structures, whether or not they are related. Unger et al. showed, in fact, that 76% of the main chain structure of an 82 protein data set can be constructed using only 100 unique hexapeptide templates. Amino acid side chains are also found in a restricted set of conformers. Recent work in our laboratory has shown that a set of four tetrapeptide templates is sufficient to define almost all loop conformations. 

The structure of such metallopolymers can be regulated by varying the ratio of sizes of block-copolymer (general molecular weight, composition) and micelle parameters (size of nucleus/cover, form, polydispersion), and this enables us to use block-copolymers as nanoreactors or templates. The ratio between the molecular weights of the first (polar) and the second (hydrocarbon) components Mi and M2) is important to provide steric stabilization M = nM2 (where n is the number of the second component chains). As a rule, M is 10 -10 andM2 = 10 -10. ... 

The template centre plays the key role in matrix reactions. If the steric course of macrocyclisation, or other multistep reaction, is directed and facilitated by the ligsons spatial structures, and their activation by coordination to the metal ion or another centre, then the process is controlled by the kinetic coordination template effect. If the metal ion (or another centre) sequesters one of the components from an equilibrium mixture (starting ligsons and oilier competing molecular species) and, as a consequence, shifts the position of the equihbriiun towards the formation of the desired product in the form of its metal complex, then the thennodynamic (or equilibrium) coordination template effect is considered to be operative for the reaction. 

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