Surface spectroscopy and microscopy studies of functional molecular films at electrified interfaces

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The general objective of this research program is to study the structure and reactivity of phospholipid bilayers deposited onto a metal electrode at the metal-solution interface. The functionality of these films will be determined by the presence of peptides and proteins. We will build asymmetric bilayer that mimics outer membrane (OM) of a gram-negative bacterium and will investigate interactions of the large antibacterial peptides with lipopolysaccharides (LPS) that constitute the outer leaflet of the outer bacteria membrane. Our goal is to learn how the peptides bound to the LPS and how they cause a poration of the membrane. We will investigate how the electric field affects the stability of the asymmetric bilayers in which top leaflet consisting of LPS and the bottom leaflet of phospholipids and incorporation of antibiotics into such membrane. We will use Langmuir-Schaeffer technique to assemble the asymmetric bilayer. We will employ electrochemical impedance spectroscopy (EIS) to provide information about the membrane barrier properties for the transport of ions (resistivity). The scanning probe microscopies such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) will be used to provide molecular level images of the monolayer of lipopolysaccharides (LPS) and the asymmetric bilayer. In situ photon polarization modulation Fourier transform infrared reflection absorption spectroscopy (PM-IRRAS), surface enhanced infrared (SEIRAS) and surface enhanced Raman spectroscopy (SERS) will be used to investigate conformation, orientation, interactions, and penetration of the peptides with and through the bilayer. The spectroscopic techniques are complementary; PM-IRRAS will provide information about steady state properties of the bilayer with and without the peptides. SEIRAS will be used to investigate kinetics of the structural changes induced by antibiotic peptides and their insertion or transport across the bilayer. SERS has unique potential for studies of polysaccharides. Its spectral range is extended down to very low wavenumbers and its signal is not affected by the spectral interferences caused by the presence of water. We will employ several platforms to obtain high quality SERS spectra of polysaccharides such as shell isolated gold nanoparticles, array of pure gold nanoparticles and array of gold nanocavities. In another theme we will apply spectroscopic tools to investigate the mechanism of bonding of CO2 reducing enzymes such as formate dehydrogenase, (FDH) without and with metal centers to conductive supports and their performance to convert CO2 to useful chemicals.  Our task will be to apply spectroscopic methods to provide information about the nature of the bond formed with conductive support, and structural changes of the enzyme accompanying changes of the redox state of its redox center.