Syntheses and interfacial hydrogen-bonded network of hexaalkyl tris(melamine) amphiphiles

At the air-water interface N,N′-dialkylmelamine amphiphiles bind barbituric acid (BA) in the aqueous phase and produce a linearly extended supramolecular network (sometimes referred as supramolecular strand, ribbon, or tape) linked through complementary hydrogen bonds. An amphiphile with more than two hydrogen-bonding sites may produce cross-linked hydrogen-bonded networks on water with the aid of an appropriate aqueous binding counterpart. Thus, we synthesized new amphiphilic molecules, Δ(m,n), that bear three melamine (2,4,6-triamino-1,3,5-triazine) rings and six alkyl chains. The lengths of the inside three alkyl chains (C_mH_2m+1) and the outside three alkyl chains (C_nH_2n+1) were varied. The influence of alkyl chain length on the monolayer properties and the binding behavior to aqueous BA was examined for Δ(12,10), Δ(12,12), Δ(12,14), Δ(12,18), and Δ(18,12). From FT-IR and X-ray photoelectron spectroscopic measurements of Δ(m,n) LB films, BA was found to bind to one melamine moiety each of Δ(m,n) in a 1:1 ratio through complementary hydrogen bonds. Plausible network models were proposed on the basis of binding stoichiometry and conformational consideration of the tris(melamine) amphiphile.