The effect of partial methylation of the glycine amino group on crystal structure inN,N-dimethylglycine and its hemihydrate

Abstract

N,N-Dimethylglycine, C(4)H(9)NO(2), and its hemihydrate, C(4)H(9)NO(2)·0.5H(2)O, are discussed in order to follow the effect of the methylation of the glycine amino group (and thus its ability to form several hydrogen bonds) on crystal structure, in particular on the possibility of the formation of hydrogen-bonded `head-to-tail' chains, which are typical for the crystal structures of amino acids and essential for considering amino acid crystals as mimics of peptide chains. Both compounds crystallize in centrosymmetric space groups (Pbca and C2/c, respectively) and have two N,N-dimethylglycine zwitterions in the asymmetric unit. In the anhydrous compound, there are no head-to-tail chains but the zwitterions form R(4)(4)(20) ring motifs, which are not bonded to each other by any hydrogen bonds. In contrast, in the crystal structure of N,N-dimethylglycinium hemihydrate, the zwitterions are linked to each other by N-H···O hydrogen bonds into infinite C(2)(2)(10) head-to-tail chains, while the water molecules outside the chains provide additional hydrogen bonds to the carboxylate groups.