Modeling and synthesis of functionalized meta-poly(phenylene ethynylene) helical structures

The ability of meta-poly(phenylene ethynylene) (mPPE) materials to undergo random coil to helix conformational changes under select conditions affords many opportunities for their use in sensor, separation, catalysis, and bio-related applications. Thus, to advance the development of these materials, a modeling procedure based on replica exchange molecular dynamics (REMD) simulation was developed to reliably assess factors affecting the folding behaviors of functionalized mPPE variants in solution. A combinational modeling study of 20 functionalized mPPEs in five solvent conditions provided insight into how mPPE secondary structure is impacted by the complex relationship between mPPE functional groups and solvent moieties. Further, these simulation results predicted mPPE structures that exactly matched those experimentally observed with eight previously studied mPPE systems. Using this REMD procedure, a series of new mPPE structures having an alternating arrangement of exohelix functional groups were developed, so as to optimize both the functionality and structure of the polymer. Seven new functionalized mPPEs were synthesized based on this concept. The folding behaviors of these new polymers were characterized using UV absorbance and fluorescence emission spectroscopy, and these results showed that the observed behaviors matched those predicted from simulation. Additionally, two mPPEs having both ester and amine functional groups were found to be soluble and form stable helical structures in water. The imine functional groups of these helical mPPEs were also used as metal ligands for the synthesis of a polymer supported manganese(salen) complex. Formation of these catalytically active complexes demonstrated our ability to manipulate functional group interactions through the mPPE folding process. Additional modeling studies demonstrated that hydrogen bonds inside the helix cavity could be used as a highly effective stabilizer for mPPE helical structures. Finally, five mPPE helical structures having different endohelix functional groups were used as functionalized nanochannels in a modeling study that demonstrated how the through pore transmission of water can be controlled by the presence of specific endohelix functional groups. The ability to control this through channel flow is important for a variety of separation and bioactive species applications. The combined simulation and experimental efforts show that for the first time one can use computational methods to direct the synthesis of mPPE systems with specified folding behaviors.