Template substrate interactions

The similarities of above experimental results inspired us to investigate the role of SE in heterogeneous catalytic enantioselective hydrogenation reactions. In heterogeneous catalytic reaction the SE means that a given template molecule interacts with the prochiral substrate in the liquid phase in such a way that one of the prochiral sites is preferentially shielded. If the substrate is shielded then its adsorption onto the metal can take place with its unshielded site resulting in ED. 

Lewis DF, Lake BG, Dickins M, et al. Homology modelling of CYP2A6 based on the CYP2C5 crystallographic template enzyme-substrate interactions and QSARs for binding affinity and inhibition. Toxicol In Vitro 2003 17 179-190. 

Figure 2 Modes of hemozoin inhibition. On a neutrai iipid dropiet tempiate (T), heme can aggregate to form the biomineral HZ. Antimalarials may inhibit this aggregation by binding heme substrate, interacting with the iipid tempiate or trapping heme bound to the template. All actions serve to prevent the formation of HZ.

It has been demonstrated that the first monolayer forms the crucial template for the growth of further moleeular layers [16, 17], and the strength of the adsorbate-substrate interaction, the orientation of the molecules, their bonding distances to the topmost substrate layer determine to some extent the properties of the multilayer film. The bonding distanee of the monolayer (Figure 9.2) is one of the central quantities in this eontext and can be determined, e.g., by... 

Poly(ferrocenylsilane) polyions are readily processed to novel, fully organometallic multilayer thin films. Furthermore, these organometaUic polyions, featuring a hydrophobic backbone, enable one to make use of both electrostatic and hydrophobic interactions to fabricate self-organized patterns on templated substrates, with potential applications as aqueous pro-cessable ultrathin etch resists. 

The LbL assembly of polymers to afford individiral nano-objects represents a imique synthetic methodology that combines features of solution- and solid-state assembly processes via selective interactions between polymers and preestablished templating substrates and, therefore, includes aspects of each of the typies of synthetic methods described in this chapter. The LbL terminology originates from the process, which involves alternating deposition of polymers and other components, having complementary functionalities to facilitate their attraction/adhesion, from solution onto a substrate to produce stable thin films. 

If we consider natural synthetic processes, enzymes are seen to exert complete control over the enantiomeric purity of biomolecules (see Figure 8.2). They are able to achieve this because they are made of single enantiomers of amino adds. The resulting enantiomer of the enzymes functions as a template for the synthesis of only one enantiomer of the product Moreover, the interaction of an enzyme with the two enantiomers of a given substrate molecule will be different. Biologically important molecules often show effective activity as one enantiomer, the other is at best ineffective or at worst detrimental. 

The latter method, the template method, involves a reaction to produce a transition state similar to the desired product using a template. The template should have a shape similar to the space of the product. The template interacts with the substrate by forming noncovalent bonds such as coordination bonds (Fig. 3). The representative and most successful examples are found in crown ether chemistry. In the chemistry, alkali metals act as templates to create a crown-ether-like transition state with an ethylene glycol substrate by using metal-oxygen coordination bonds. 

In this work a new approach is desribed, which can help to understand ED over heterogeneous catalysts We also hope that this approach can be used to find new modifiers for enantioselective heterogeneous catalytic reactions. The basis for this approach is the steric shielding known in organic chemistry [7,8]. A chiral template molecule can induce shielding effect (SE) in such a way that it preferentially interacts with one of the prochiral sites of the substrate. If a substrate is preferentially shielded its further reaction can take place only fi"om its unshielded site resulting in ED. 

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