Monday, November 8, 2010
Hall 1 (Salt Palace Convention Center)
Synthetic polypeptide analogues of adhesive mussel foot proteins (mfps) were used to study the role of DOPA in adhesion. The ‘mussel-inspired peptide' is a random co-polymer of 3, 4-dihydroxyphenyl-L-alanine (DOPA) and N-(2-hydroxyethyl)-L-glutamine synthesized with DOPA concentrations of 0, 3, 10, 18 and 27 mol% and molecular weights in the range of 5.9-7.1 kDa. Thin films (~3-5 nm thick) of the mussel-inspired peptide were used in the Surface Forces Apparatus (SFA) to measure the force-distance profile and adhesion energies of the films in a buffer consisting of 250 mM KNO3 and 10 mM acetic acid pH 5.5. The adhesion energy of the mussel-inspired peptide films to mica and TiO2 surfaces was measured as a function of the DOPA concentration in the peptides. Adhesion increased with DOPA concentration and was significantly stronger to TiO2 than mica. Additionally, adhesion to TiO2 increased two-fold if the contact time of the film with TiO2 increased from ~1 to ~60 minutes. At DOPA concentrations above 10 mol%, contact times of 60 minutes also appeared to allow for rearrangements of the DOPA residues within the film resulting in an apparent phase transition on decompression of the film. These effects were not observed upon interaction of the films with mica. Oxidation of DOPA to the quinone form, either by addition of periodate or by increasing the pH, is observed to increase the thickness and reduce the adhesion of the films. Adding thiol polymer between the oxidized films appears to recover some of the adhesion properties of the mussel-inspired films either by cross-linking or reducing the quinone back to DOPA. Comparison of the mussel-inspired peptide films to previous studies on mfp-3 thin films shows that the majority of the adhesion in the mfp-3 can be attributed to DOPA.