engleski

Hydrogen bonding organization in crystal structures of (S, S)-N, N'-PHTHALOYL-BIS(amino acid) derivatives

Understanding the role of hydrogen bonding and its overall topology in the formation of supramolecular assemblies is of great importance, both, in the theoretical and practical aspects. The organization of organic molecules into nano- or micro-dimensional assemblies can lead to design of new materials of versatile applications. Predicting the gelation on the basis of the constitutional and conformational characteristics of an organic molecule and the properties of liquid to be gelled is a challenge. Recently we have shown that chiral bis(amino acid) oxalamides represent a rare group of gelators capable to gel water and various lipophilic organic solvents (Makarević et al., Chem. Eur. J. 2001, 7, 3328), whereas our new results are related to chiral bis(leucinol)oxalamides exhibiting gelating properties (Makarević et al., Chem. Eur. J. 2003, 9, 5567). In continuation of this work the gelation properties of the series of (S, S)-N, N'-phthaloyl-bis(amino acid methyl ester) (ten compounds) and their free acids in connection to their hydrogen bonding pattern have been studied. To influence topology of hydrogen bond network the phtaloyl spacer with ortho-, meta- and para-substitutions was used. Modifications at the terminal side of the molecule by esterification reduce the number of donor sites. The derivative with ortho-substitution in the crystal packing develops one-dimensional hydrogen bond network. However, terephthaloly derivatives organize in two-dimensional zigzag-networks (see figure). A bulky terephthaloyl spacer forces molecules to be oriented in perpendicular fashion. In such an arrangement CH... π interactions are favoured. Due to the strong donor-acceptor abilities of carboxyl groups of amino acids they exhibit much more intricate hydrogen bonded networks in the crystal structure.

Hydrogen_Bonding; Assembling; Gels

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