Recognition substrate

Side group capable of molecular recognition. Substrate to be recognized. 

P. Caliceti, O. Schiavon, EM. Veronese, I.M. Chaiken, Effects ofmonomethoxypoly(ethylene glycol) modification of ribonuclease on antibody recognition, substrate accessibihty and conformational stabihty. /. Mol. Recognit., 3 (2) 89-93,1990. 

According to these basic concepts, molecular recognition implies complementary lock-and-key type fit between molecules. The lock is the molecular receptor and the key is the substrate that is recognised and selected to give a defined receptor—substrate complex, a coordination compound or a supermolecule. Hence molecular recognition is one of the three main pillars, fixation, coordination, and recognition, that lay foundation of what is now called supramolecular chemistry (8—11). 

Information may be stored in the architecture of the receptor, in its binding sites, and in the ligand layer surrounding the bound substrate such as specified in Table 1. It is read out at the rate of formation and dissociation of the receptor—substrate complex (14). The success of this approach to molecular recognition ties in estabUshing a precise complementarity between the associating partners, ie, optimal information content of a receptor with respect to a given substrate. 

The weak intemiolecular forces that are principally involved in stabilizing receptor-substrate interactions and involved in molecular recognition processes (16) are summarized in Table 2. Examples are shown in Figure 1. 

Most effective differentiation of the receptor between substrates will occur when multiple interactions are involved in the recognition process. The more binding regions (contact area) present, the stronger and more selective will be the recognition (17). This is the case for receptor molecules that contain intramolecular cavities, clefts or pockets into which the substrate may fit (Fig. 1). 

Topology. This parameter may have reference to either the receptor as an individual molecular stmcture or to the receptor—substrate complex on a higher level of organization that is direcdy related to the mode and efficiency of molecular recognition (14,30). 

Substrates involved in molecular recognition may feature a particular shape, size, state of charge, chemical affinity or optical specification (19,30,33—36). In general most of these parameters share. Nevertheless there may be dominating features of a certain substrate molecule to be used by a complementary receptor in the recognition process (9). 

Fig. 10. Linear recognition diagrammatic representation of the recognition of linear dicationic (a) and dianionic (b) substrates (c, d) typical examples of...

Fig. 11) form very strong and selective complexes with Fe or actinide and lanthanide ions (63,64) while a similar receptor with hard endocarboxyhc acid groups is efficient for hard and ions showing again responsibility of a charge density effect in the receptor—substrate recognition (65). Thus,... 

Fig. 13. Hydrogen bond dominated substrate recognition of (a), (c) dicarboxylic acids (b) 2-anainopyrknidine and (d) urea.

Fig. 14. 71-Stacking and chaige-tiansfei dominated recognition of flat aromatic—heteioaromatic substrates (formation of intercalates).

While the previous receptors are typically used in organic solvents, except for the cyclodextrins, there are special cases of cyclophane receptors supphed with peripheral charges (ammonium units) (107—12) or ionizable groups (carboxylate functions) (113,114) (Fig. 17) to allow substrate recognition, as in nature, in an aqueous medium, profiting from the solvophobic effects of water (115). 

Multiple and Multisite, Coreceptor- and Coupled-System Substrate Recognition... 

Fig. 19. Multiple and multisite substrate recognition (a) a homo dinuclear (dicationic) and (b) a heterodinuclear (cation and anion) iaclusion complex (c) a...

Fig. 22. Principle of chiral receptor—substrate recognition (a) formation of diastereomeric inclusion complexes (b) three-point interaction model.

Fig. 23. Prototypical receptor molecules for chiral (enantioselective) substrate recognition.

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