A MODULAR APPROACH TO POLYMER ARCHITECTURE CONTROL VIA CATENATION OF PREFABRICATED BIOMOLECULAR SEGMENTS - POLYMERS CONTAINING PARALLEL BETA-SHEETS TEMPLATED BY A PHENOXATHIIN-BASED REVERSE TURN MIMIC

A biomolecular Lego set modular method whereby prefabricated building blocks are linked block by block has been developed and applied to the synthesis of peptide-based polymers containing parallel beta-sheets i nduced by phenoxathiin derivatives acting as reverse turn mimics. Spec troscopic studies show that phenoxathiin is an effective template for beta-sheet formation allowing even weak hydrogen accepters such as est er amides to exist almost exclusively in intramolecularly hydrogen-ban ded conformations. Replacing the phenoxathiin derivative with flexible hydrocarbon chains results in substantial loss of intramolecular hydr ogen bonding. Solid state FTIR of the polymers revealed that the expec ted parallel beta-sheets were retained in the polymer solely due to th e presence of the rigid phenoxathiin template. Conformationally unrest ricted units incapable of inducing sheet formation provide mostly rand om coils and contribute to interchain and intersheet antiparallel hydr ogen bonding. The nature of the beta-sheet domains has been confirmed through study of model octapeptides. DSC and TGA studies reveal that a s the flexibility of the linkers decreases T-g and onset decomposition temperature also decrease. Powder X-ray diffraction of the unoriented polymers shows that they are semicrystalline.