Covalent recognition

When two or more reactants first approach one another, non-covalent recognition and attraction of the molecules or of parts of the molecules takes place and permits system aggregation, which may be of importance in obtaining the reaction products. For instance, the approach of a carbocation to a n system of olefins starts by forming a charge-transfer (CT) complex which precedes the formation of the C—C bond6. 

The chapter is split into two major sections, ionic recognition and molecular covalent recognition. Ionic recognition discusses synthetic receptor molecules designed to bind cations (metal, ammonium, bipyridinium ions) and anions (halide, azide, sulphate, phosphate, dicarboxylate ions etc.). The section on molecular covalent recognition describes the complexation of neutral (un-... 

In most cases, the proteia is immobilized onto y-aminopropyl sUica and covalently attached usiag a cross-linking reagent such as -carbonyl diimidazole. The tertiary stmcture or three dimensional organization of proteias are thought to be important for their activity and chiral recognition. Therefore, mobile phase conditions that cause proteia "deaaturatioa" or loss of tertiary stmcture must be avoided. 

A 1 1 mixture of thiols (7 and 2), on treatment with oxygen in the presence of a catalytic amount of Et3N, gives one unsymmetrical (4) and two symmetrical disulfides (3 and 5) (Eq. 4). As a measure of the degree of the recognition between 7 and 2 in the oxidation, the selectivity (r) is employed which is represented by the logarithmic ratio of the yield of 4 to twice that of 3 (Eq. 5). The r is so defined as to become zero when oxidation yields the three disulfides in a 1 2 1 ratio. In the present case, the recognition process is followed by covalent bond formation. 

N. T., Lhomme J., Helene C. Sequence-specific recognition, photocrosslinking and cleavage of the DNA double helix by an oligo-[alpha]-thymidylate covalently linked to an azidoproflavine derivative. Nucleic Acids Res. 1987 15 7749-7760. 

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