Structural studies and patterning of self-assembling peptide amphiphiles and tripeptide lipids

One dimensional nanostructures formed by the self-assembly of synthetic molecules have been extensively studied in the author's laboratory recently. These structures have been shown to have promising potentials in fields ranging from tissue engineering to nanoelectronics. This thesis describes contributions towards understanding the structure and developing patterning techniques for two kinds of self-assembling systems: peptide amphiphiles (PA) and tripeptide lipids (PL). To explore the structure-property-function relationship of PA nanofibers, microscopy (AFM/SEM) and spectroscopic (FT-IR/PM-IRRAS) methods were used to characterize the external morphologies and the internal organization of secondary structures of the self-assembled nanofibers. The experimental results verified the beta-sheets were packed parallel to the long-axis of the nanofibers, and the peptide sequence was found to affect the packing order of both the peptide and alkyl segments. In another approach, differential chemical force microscopy (DCFM) was developed to study the co-assembly of nanofibers from a mixture of PA molecules, which has been demonstrated to differentiate and identify morphologically similar nanofibers of different chemical compositions with the resolution of AFM. A desire to improve surface organization of PA nanofibers led to efforts to pattern and align these nanofiber arrays on solid substrates. Patterning with direct and indirect dip-pen techniques yielded ordered arrays with positive and negative features with micro- and nano-scale resolution. Molecular combing techniques were also applied to the PA system to create aligned monolayers of PA nanofibers over macroscopic areas. The exploration of various parameters in these methods could provide effective techniques to control the morphology of PA nanostructures for future biomedical applications. In other work, structural studies of PL revealed the formation of nanohelices in organic solvents with their pitches controlled by the bulkiness of PL's head groups and the handedness of the peptide segments. By incorporating photo-switchable azobenzene groups in PL's structure, the pitch of those nanohelices could be decreased by the trans- to cis-transformation of the head group upon UV radiation, possibly as a result of the change in bulkiness of the azobenzene groups. The ability to fine-tune the nanostructures with molecular design strategies made PL an interesting candidate for chiral catalysis and templated mineralization.