Syn-Anti Competition in Carboxylate

The carboxylate anion is of particular importance to enzymatic activity as it serves as the functional portion of the Asp and Glu residues in proteins. As described above, there are a number of geometrical di.spositions in which the carboxylate can form H-bonds with other groups. Of particular interest is the question as to whether this group will form a stronger H-bond on its syn or anti side, with these terms defined in Fig. 6.16, with respect to the two O lone pairs. 

It is important to note the possibility of a smooth transition from one configuration to the next, with only small motions of the water molecule necessary. In other words, the sys- 

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