AN INVESTIGATION OF THE IMPACT OF MOLECULAR-GEOMETRY UPON MICROCAPSULE SELF-ASSEMBLY

Bis-amide dicarboxylic acids derived from the condensation of malonic acid, 1,1-dimethylmalonic acid, 1,1-cyclopropane dicarboxylic acid, or maleic acid with L-phenylalanine, (L-Phe), are shown to supramolecula rly self-assemble in aqueous solution. When basic solutions of these d iacids are taken to pH 2.4, microcapsules are formed. Scanning and tra nsmission electron micrographs confirm that microcapsules and not soli d microspheres are generated. The ability of these assemblies to encap sulate other materials present during their formation in water was dem onstrated with a tannic acid marker. Structure-activity studies clearl y demonstrate the importance of a cis geometry between L-Phe fragments for self-assembly. Molecular modeling revealed that the cis geometry of 1a, 5a, and 14 imparts a helical structure to these systems. The su bsequent self-association via hydrogen bonds of these hydrophobic heli cal diacids is postulated as the mechanism for their self-assembly, No nmicrocapsule forming scaffolds (predicated on oxalic, fumaric, and su ccinic acid backbones) favored ''cuplike'' or pocket geometries which were not conducive to intermolecular aggregation.