Intermolecular forces of marine adhesive molecules

To gain a better understanding of undesirable biofouling in marine systems, Atomic Force Microscopy (AFM) and light scattering were used to examine the adhesion and conformational behavior of two different model marine adhesive molecules under varying ionic and pH conditions and on various substrates. The first molecule was an extracellular polysaccharide (EPS) secreted by the marine bacteria Pseudomonas atlantica, possibly a key component of the initial conditioning layer of biofilm formation. The second was Mytilus edulis foot protein 1 (Mefp-1), which is secreted by the Eastern blue mussel as part of an active adhesion process involving the mussel foot or byssus.; Measurements of adhesion forces between two layers of adsorbed EPS on silica indicated that polymer bridging clearly occurred for layers of anionic EPS and for layers of an anionic model dextran, but was absent for neutral EPS. Light scattering measurements of the EPS in free solution confirmed a change from large to small dimensions with an increase in ionic strength. As the ionic strength was increased to marine salt concentrations, the adsorbed anionic EPS also changed from an extended to a contracted configuration, and collapsed onto the solid substrate surface forming a strongly adhered layer.; Measurements of adhesion forces between Mefp-1 and a silica substrate indicated that a high pH (8.5) and 3h of contact time was necessary to develop maximum adhesion. The addition of salts containing monovalent cations (NaCl, KCl, Na₂SO₄) increased adhesion only slightly, whereas salts containing divalent cations (MgCl₂, CaCl₂) induced multiple jump-outs in the decompression curve similar to those seen for other biological systems. Addition of FeCl₃ resulted in the highest adhesion observed. Measurements of Mefp-1 adhesion on seven polymeric surfaces with increasing surface energy indicated that the critical surface tension of Mefp-1 (29–33 mN/m) determined the thermodynamic criteria for which substrates exhibited low and invariant adhesive energy or high and increased adhesive energy. The Johnson-Kendall-Roberts (JKR) model correctly predicted the adhesion trend but overpredicted the magnitude of the adhesion energy. High adhesion observed for polyethersulfone (PES) may be due in part to chemically specific π-π interactions between the Mefp-1 and PES.