PacSurf2016 Session BI-WeM: Biomolecule/Material Interactions

The lipid bilayer is the fundamental structure of cell membranes, at which the transportation of materials and signals in and out of cell membranes take place. Ion channels are one of representative membrane proteins promoting these reactions. They retain their proper structures and function only when they are incorporated in lipid bilayer membranes. It is necessary to reconstruct the membrane proteins into artificial lipid membranes to investigate the structure and function of membrane proteins out of cells. n this study we reconstructed the ion channels into solid-supported lipid bilayers (SLBs), which is an artificial lipid bilayer at solid-liquid interfaces, using proteoliposomes. We investigated the distribution and orientation of ion channels in the SLBs using fluorescence microscopy and atomic force microscopy (AFM).

Artificial neural networks (ANNs) form a class of powerful multivariate analysis techniques, yet their routine use in the surface analysis community is limited. Principal component analysis (PCA) is more commonly employed to reduce the dimensionality of large time-of-flight secondary ion mass spectrometry (ToF-SIMS) data sets and highlight key characteristics. The strengths and weaknesses of PCA and ANNs as methods for investigation and interpretation of a complex multivariate sample set will be considered. Using ToF-SIMS, spectra were acquired from an antibody and its proteolysis fragments with three primary-ion sources to obtain a panel of 72 spectra and a characteristic peak list of 775 fragment ions. The use of ANNs as a means to interpret the ToF-SIMS spectral data is explored, highlighting the optimal neural network design and computational parameters, and considering the technique limitations. Employing Bi₃⁺ as the primary-ion source, ANNs can accurately classify antibody fragments from the parent antibody based on ToF-SIMS spectra.

Adsorption, surface complexation and reactivity of biological molecules on inorganic surfaces and interfaces is pervasive throughout an enormous range of fields such as chemistry (geochemistry, biochemistry), biotechnology (medical implants, biosensors, tissue engineering, bioelectronics, biomimetics and artificial photosynthesis), radiation technology (radiation damage and detection), colloid chemistry, surface chemistry and physics. Hydrogen and its interaction at surfaces clearly plays a pivotal role in the ultimate functionality of many biologically-based surfaces. Through the hydrogen’s subtle interaction with the tethering surface, or interface, and the surrounding wet environment can and does lead to a multifaceted response to changes in temperature, pH, radiation etc.

Inelastic neutron spectroscopy is the domain of vibrational spectroscopic studies on bulk materials. At first sight, surface studies using such a method, with relatively low neutron flux rates and largish sample size, seems a totally hopeless task. There are, however, exceptions to this rather bullish view, where the surface dominates the scattered signal due to huge surface to volume ratios and large scattering cross-sections from adsorbate molecules, that incorporate for example, hydrogen, which neutrons are supremely sensitive to.

The deposition of amino acids and carbonyl-sulphide onto oxide surfaces is a fruitful area of discovery in the field of prebiotic formation of peptides and an example of how neutron spectroscopy makes significant contributions to the understanding of the subtle chemistry between adsorbate, substrate and surrounding environment. In this series of studies the deposition of amino-acids onto alumina from solution and in the presence of OCS is investigated by both inelastic neutron spectroscopy and high resolution photoemission which allows both the vibrational and electronic structure to be determined for these incredibly interesting systems. Studies focused on the extent of adsorption at various pH's, the character of each adsorbate (zwitterionic, basic, acidic), and the number of discrete surface sites of adsorption. Results show strong chemisorption of amino acids through an ester type bond with the alumina surface across a range of pH. Direct sorption of the amine group with alumina is observed only at pH 9. Formation of multilayers and/or peptides can also occur in conjunction with OCS absorption.