INTERDIGITATED CHIRAL ACHITECTURES AT AIR/LIQUID INTERFACE Ivan Kuzmenko, Ronith Buller, Meir Lahav, Leslie Leiserowitz, Dept. of Materials&Interfaces, The Weizmann Inst. of Science, Israel. K.Kjær, Dept.of Solid State Physics, Risø National Laboratory, Denmark. J.Als-Nielsen, Niels Bohr Insitute, H.C.Orstead Laboratory, Denmark.

The design of supramolecular motifs requires complementarity and strong interactions between the molecules to "cement" the various building blocks. Among possible motifs, interdigitated bilayers are of importance since they constitute the walls of bio- and artificial membranes.(1)

A principal way for devising new materials involves the self-assembly of molecules at interfaces. Here we propose an approach for the design of crystalline interdigitated multilayers, composed of chiral molecules A and B, where A is a water-insoluble molecule composed of a long hydrocarbon chain and a hydrophilic headgroup of acid character and B is a water-soluble base. The acid-base complementarity should ensure alternating juxtaposition between the A and B units within each layer, whereas interdigitation of the hydrocarbon chains of the A molecules would promote multilayer arrangement. Molecular chirality of both components, yielding diastereomeric arrangements, is an additional variable. The phenylethylamine mandelates(2) were chosen as suitable templates satisfying the above criteria.

The chiral amphiphile, R-p-pentadecylmandelic acid, (R-C₁₅-MA), when compressed over a 0.008M aqueous solution of chiral R-phenylethylamine (R-PEA), formed an interdigitated trilayer film (R-C₁₅-MA, R-PEA), which is crystalline, but for the alkyl p-C₁₅H₃₁ chains at the top surface of the film. By comparison, the amphiphile R-C₁₅-MA over an S-PEA solution formed, on compression, a (R-C₁₅-MA, S-PEA) bilayer which is neither crystalline nor interdigitated. An analogous result was obtained for the bimolecular system in which the hydrocabon chain was attached to phenylethylamine only. The formation and packing arrangements of these multilayers will be discussed.(3)

The major tools applied for structure elucidation were grazing incidence X-ray diffraction and atomic force microscopy.

1.J. L. Slater, C. H. Huang, Prog.Lipid.Res. 27, 325 (1988).

2.M. C. Brianso, M. Leclercq, J. Jacques, Acta Cryst. B35, 2751

(1979); S. Larsen, H. L. Diego, Acta Cryst. B49, 303 (1993).

3.I. Kuzmenko, R. Buller, K. Kjaer, J. Als-Nielsen, M. Lahav, L.Leiserowitz, to be submitted for publication, (1996).