Lipid-bilayer-mimicking solid-state structures of Cu(ii) and Ni(ii) with l-tryptophan and l-tyrosine Schiff base derivatives

Abstract

New metal-amino acid Schiff bases resembling lipid bilayers have been isolated and established by single-crystal X-ray crystallography. Hydrogen bonding between the solvate and coordination sphere and aromatic stacking of the Schiff base ligands lead to discrete hydrophilic and hydrophobic regions. [Cu2(WNap)2(H2O)2]·2H 2O, 1 (WNap = N-(2-hydroxy-1-naphthalidene)-l-tryptophan), gives bilayer sheets with width ratio of ca. 3 Å: 5 Å (hydrophilic: hydrophobic). Replacement of Cu2+ by octahedral Ni2+ gives [Ni(WNap)(H2O)2(MeOH)]·H2O, 2, with a slight increase of hydrophilic layer width (by ca. 2 Å). The additional hydroxyl group in [Ni(YNap)(H2O)2(MeOH)]·1.5H 2O, 3 (YNap = N-(2-hydroxy-1-naphthalidene)-l-tyrosine), successfully introduces a separate amphiphilic layer, originated from the hydrogen bond interaction of tyrosine side chain. The coordination environments of 2 and 3 are isostructural whereas 1 is dinuclear with the Cu(ii) metal centers showing different geometries (square planar and square pyramid). © 2011 The Royal Society of Chemistry.