Biological target hydrogen bonds

Hydrogen bonds play a major role in the interactions of a substrate with its biological target. The latter is generally a protein which bears many possible sites for hydrogen bonds. 

The affinity of a substrate with its biological target is first connected to its complementarity with this macromolecule target. The molecular recognition and affinity depend on all the favorable interactions that exist in the supramolecular assembly formed between the substrate and the macromolecule. If the presence of fluorine atoms enhances the strength or the number of these favorable interactions, the affinity of the fluorinated substrate will be higher than that of the parent compound. The main parameters involved are the steric and conformational effects, the dipolar/hydrophobic interactions, and the hydrogen bonds. 

A hydrogen bond, involving an acidic hydrogen atom borne by a fluorine-substituted or halogen-substituted carbon, seems to contribute to the activity and selectivity of volatile fluorinated anesthetics (Table 3.2). These molecules, although nonfunctional, can bind stereoselectively with protein targets of the central nervous system. Different biological behaviors have been reported for both enantiomers of isoflurane (cf. Chapter 8). ... 

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