Amino acids zwitterions, favored conformations

Fig. 8.—Favored Conformation of Some o-Amino Acid Zwitterions as Indicated by Molecular-orbital Calculations. ...

In contrast, Nagy pointed out [13] that the zwitterionic P-alanine ( H3N-CH2-CH2-C00 ), which forms an intramolecular hydrogen bond in its favorable NCCC gauche conformation in aqueous solution (note the difference with GABA upon one less CH2 group in the linker), transforms to the intramolecularly hydrogen-bonded neutral species in chloroform with an anti -COOH group. This is an important consequence of the solvent effect on the amino acid tautomeric forms in different media. 

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