FORMATION OF SPECIFIC HYDROPHOBIC SITES FOR INCORPORATION OF METHYLENE-BLUE BY LATERALLY ARRANGED L-GLUTAMATE RESIDUES IN ANIONIC, CRYSTALLINE BILAYER AGGREGATES

Bilayer membranes, formed from dioctadecyl L-glutamate-derived anionic amphiphiles, incorporated the cationic dye, methylene blue (MB), into their crystalline, hydrophobic region. The incorporated, monomeric MB was extraordinarily converted into a dimeric species during the gel-t o-liquid crystalline phase transition by binding to carboxylates. A fu rther increase in temperature upon the phase transition temperature le d to the ordinary dimer-to-monomer transition of the bound, aggregated MB as well as the conventional various dye-polyion systems including micellar systems. However, such extraordinary behaviour strongly depen ds on the chemical structure of the bilayer-forming component amphiphi les. The molecular structure requirements of anionic amphiphiles for s uch incorporation has been investigated by varying the alkyl chain len gth, the average degree of polymerization (x), and the kind of amino a cid residue in the connector moiety. Specific incorporation of MB into the crystalline, hydrophobic region is peculiar to molecular assembli es formed from L-glutamate amphiphiles with long alkyl chains and low x values. Corresponding DL-glutamate derivatives showed ambiguous tran sitions and L-aspartate derivatives did not show such specific incorpo ration, indicating that the specific behaviour is peculiar to the L-gl utamate derivatives. The same conclusion that the monomeric dye specie s in the crystalline bilayer state is incorporated in the hydrophobic region of the bilayer aggregates could be confirmed by using the solva tochromic dye, 4-[4-(dimethylamino)styryl]-N-methylpyridinium iodide ( St-4C1), as a micro-environmental probe instead of MB.