Hybrid Silica-Polypeptide Particles: Properties, Transitions and Superstructures

Louisiana State University, Baton Rouge LA

Investigators

Abstract

TECHNICAL: Submicron hybrid particles will be developed. Each particle will have a silica core and covalently attached polypeptide shell. The shell confers the interesting chemical properties; it can be tailored to respond to temperature, even in an organic solvent where powerful ionic forces are absent, or to pH in aqueous environments where those forces predominate. The size, surface density and surface thickness of the particles will be controlled, enabling a study of how these parameters affect conformational transitions. The limits of making the particles by an "attach to" mechanism (fully formed polymers are connected to the silica cores) will be explored. The particles feature a number of useful physical functions. Either core or shell may bear fluorescent moieties to facilitate visualization of magnetic alignment, equilibrium structures or phase separation. The polypeptides comprising the shell are capable of forming liquid crystals when not tethered to a core, raising the possibility that "local liquid crystals" will form where particles covered with these molecules touch, elevating the local concentration of mesogens. This will be explored by chaining together superparamagnetic variants of the particles using an applied magnetic field. While held in these chains, reactions on the particles or their precursor cores will be explored, possibly leading to particles wearing a polypeptide belt or to poly(colloids) that may be able to undergo muscle-like expansions and contractions, even in an organic solvent. NON-TECHNICAL: Polypeptide-coated particles provide an excellent platform for applied discovery because they merge the characteristics of proteins' chemical versatility, ability to recognize markers for disease, switchable size and shape with ease of manipulation using gravitational or magnetic fields. The particles look a bit like porcupines, with "prickles" coating a central core. It is hoped that variants built with magnetic inclusions can be connected, leading to artificial "cilia" that respond to stimuli such as acidity or temperature. Related materials in the future are anticipated to have optoelectronic uses, such as light harvesting or sensing of amino acids related to disease. Researchers associated with the project team will train for a long career, emphasizing technical skills, critical thinking, ethical awareness and communication. Team members are expected to be factual advocates for their craft and for science in general. An important venue for such expression will be the Chemical Education Foundation's You Be the Chemist Challenge competition, a "quiz bow" for middle school students. Graduate student and postdoctoral team members will assist with the competition and/or training of students. Selected young scholars who perform well in the competition will actively participate in the proposed research, erasing the major deficiency of a structured question-and-answer competition, i.e. that it provides no practical training. The Chemical Education Foundation attempts to follow the careers of its young challengers, which provides at no cost to NSF a way to track the efficacy of competition-based science training. It is hoped that additional middle school students will be engaged in active learning, using a technical hobby as a starting point.