PROTEIN ADSORPTION FROM SEAWATER ONTO SOLID SUBSTRATA .2. BEHAVIOR OFBOUND PROTEIN AND ITS INFLUENCE ON INTERFACIAL PROPERTIES

Modification of solid surfaces (e.g. minerals, biogenic debris, engine ered materials, etc.) and exchanges across their interfaces in seawate r can be influenced by the composition and behavior of adsorbed solute s, such as proteins. The present study illustrates that the degrees to which extracellular proteins adsorb from seawater solutions, denature in the bound state, alter the wettability of the interface, and imped e dissolution and oxidation of the substratum strongly depend on prote in concentration and substratum type. For all variables measured, a tr ansition in state of the interface is evident within the surface conce ntration range required to establish a monomolecular layer. The plant enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO), was used to examine the behavior of protein adsorbed to well-defined tita nium and copper surfaces in seawater. Secondary structure of proteins in thin films on Ti were most altered while those in thicker films and in Cu-bound films more closely resembled native protein as indicated by relative intensities of amide II and I, vibrational frequency shift s, and amide III features in spectra obtained by Fourier Transform Inf rared Reflectance-Absorbance Spectrometry (FT-IRAS). Critical surface tension (CST) of Ti oxides was significantly reduced in the presence o f very thin films, but was enhanced on coated Cu oxide surfaces. Diffe rences in interfacial CST reflect a higher degree of denaturation upon adsorption onto Ti oxides than onto Cu oxides, i.e. greater exposure of hydrophobic protein residues on less wettable substrata. Potential substratum oxidation rates and surface oxide accumulation derived from Electrochemical Impedance Spectroscopy (EIS) and ellipsometric measur ements, respectively, were inversely related to protein surface concen tration. Results consistently illustrate that substratum composition a nd protein concentration control film organization, protein denaturati on and interfacial attributes which are manifested as interfaces with varying wetting properties and as solid phases with varying susceptibi lity to oxidation and dissolution.