UC Santa Barbara

The rich structure and function of many biological systems relies on the dynamic conformations and assemblies of biomolecules. These dynamic structures are often governed by inter- and intramolecular forces, such as hydrogen bonding, Van der Waals forces, and/or Coulombic interactions. Among these, Coulombic interactions that are governed by protonation level are the most tunable in vitro, and have been demonstrated to trigger structural evolution of biomolecules in various pH titration experiments. This thesis presents a novel approach that leverages site-selective deprotonation electrochemistry to manipulate the dynamic structures of biomolecules. Using cyclic and differential pulse voltammetry, a linear correlation was found between proton dissociation constant (pKa) and redox potential of molecular moieties in various biomolecules, leading to the hypothesis that site-selective proton reduction could be used to manipulate the dynamic evolution of biomolecular structures. This hypothesis was tested using site-selective electrochemistry coupled with in situ optical spectroscopies to trigger and analyze the structural transitions of two biomolecular systems representing transitions of different hierarchical structures, namely the coil-to-helix transition of polylysine and assembly of reflectin (the unique protein that enables structural color changes in squid skin).

Evidence from voltammetry, optical spectroscopy, and microscopy indicates that site-selective deprotonation electrochemistry indeed occurred in sidechain moieties of amino acid residues of biomolecules, and could trigger structural conversion of biomolecules at multiple structural hierarchies. The methods developed in this thesis provide new ways to induce localized structural transition on demand, which, in contrast to conventional pH titration or genetic engineering, may provide unpredicted access to the kinetics and thermodynamics of biomolecules that are challenging to assess by other means. Furthermore, being able to actively actuate biomolecular structures may inspire the design and/or discovery of advanced, bio-functional materials that leverage nanoscopic mechanics to achieve unprecedented chemical and physical functions.