Controlling Self-Assembly of Alpha Helix Coiled-Coil Bundlemers into Liquid Crystal Nanostructures

• Alicia Wexler, Biochemistry, Brandeis University

• Darrin Pochan, Materials Science and Engineering, University of Delaware

Liquid crystals are important technological materials, flowing like liquids but maintaining long-range order like solid crystals. However, because traditional liquid crystals are polymer-based materials, most of them are not biodegradable. Biomolecules, like peptides, are decomposable and self-assembling, making them an ideal sustainable soft material. This project focuses on the synthesis and study of the coiled coil bundlemer assembly of an alpha helical peptide, single charge positive 6, exploring how it changes based on peptide concentration, temperature, and NaCl concentration to maximize formation and function. Its bundlemers form via physical interactions resulting in a hydrophobic core. In these bundlemers, at high concentrations, a reflective lattice structure can be observed, known as liquid crystals. These are a key component of screens and biosensors, microscopically exemplifying their potential as optical responsive materials for biodegradable materials applications. After examining the peptide with CD, SAXS, and UV-Vis spectroscopy alongside POM and TEM microscopy, it can be concluded that SC+6 alpha helical secondary structures become more stable at moderate concentrations of NaCl but begin to denature after 0.5 molar concentrations and at 80 degrees Celsius regardless of salt concentration. Liquid crystals form at 10 weight percent in MilliQ deionized water. However, when introduced to NaCl at room temperature concentrations of 0.2 M and 1M, these crystals denature, but after heating, crystals reform at lower intensities in water and 0.2M NaCl. This indicates that the ideal production of liquid crystals for room-temperature electro-optical use occurs at 10 weight percent in water. Additionally, using these conclusions as a baseline for future characterization, this project may be used to explore an opposite sequence, single charge negative 6, as well as mixtures of the two obverse sequences.