Electrostatic and Steric Effect of Peptides Functionalized on Self-Assembled Rosette Nanotubes
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Electrostatic and Steric Effect of Peptides Functionalized on Self-Assembled Rosette Nanotubes Mounir El-Bakkari, Rachel L. Beingessner, Aws Alshamsan, Jae-Young Cho and Hicham Fenniri* National Institute for Nanotechnology, Department of Chemistry, University of Alberta, 11421 Saskatchewan Drive, Edmonton, Alberta, T6G 2M9, Canada. ABSTRACT Discrete nanoscale tubular architectures have received significant attention during the past decade because of their potential role in electronic and photonic devices, sensors, liquid crystals, artificial channel systems and biomedical engineering [1-2]. Our research group has reported the synthesis and characterization of the bicyclic G∧C motif, a self complementary DNA base analogue, which undergoes hierarchical self-assembly to form Rosette Nanotubes (RNTs) [3]. The stability of this system depends however, on functional group density (sterics) and net charge (electrostatics) on the RNT surface [5c]. To this end, we have synthesized several G∧C modules bearing oligopeptides with different lengths and net charge and investigated their selfassembling properties. INTRODUCTION Building well-defined higher-order architectures through supramolecular chemistry is one of the challenges in nanotechnology and is critical for our understanding of biological selfassembly. Moreover, the organization of functional molecules into supramolecular architectures provides a powerful approach to create new nanoscale materials and devices [4]. Our group has been studying the self-assembly of functionalized self-complementary guanine-cytosine (G∧C) hybrid molecules into six-membered supermacrocycles (rosettes) maintained by 36 H-bonds [5]. These rosettes then stack to form a tubular structure called a rosette nanotube (RNT) that has an inner diameter of 1.1 nm. The RNTs are stabilized by a complex network of hydrogen bonds, electrostatic, hydrophobic and stacking interactions. Because the RNTs can be functionalized with many different types of groups, it is possible to tailor their properties for various applications. For instance, we have demonstrated that biocompatible hydrogels incorporating RNTs functionalized with lysine or short peptide (RGDSK) sequences, display dramatically enhanced osteoblast (bone-forming cells) adhesion properties [2b,c]. Given the complications that often arise from the materials currently used in orthopaedic implant surgeries such as insufficient osseointegration, these RNTs show great promise for tissue engineering applications. In this work, we wanted to explore how the chemical (electrostatics) and physical (sterics) factors affect the G∧C motif self-assembly process and use that knowledge to tune the stability and hierarchical organization of these materials. To this end, we have synthesized, by using solid-phase synthesis techniques [6], several mono (Kn.M) and twin (Kn.T) G∧C modules bearing oligopeptides with different lengths and net charge. The self-assembly of these motifs into RNTs in various pH environments were then investigated by scanning electron micros
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