Effect of Dipole Orientation in Mixed, Charge-Equilibrated Self-assembled Monolayers on Protein Adsorption and Marine Biofouling

Abstract

While zwitterionic interfaces are known for their excellent low-fouling properties, the underlying molecular principles are still under debate. In particular, the role of the zwitterion orientation at the interface has been discussed recently. To elucidate the effect of this parameter, self-assembled monolayers (SAMs) on gold were prepared from stoichiometric mixtures of oppositely charged alkyl thiols bearing either a quaternary ammonium or a carboxylate moiety. The alkyl chain length of the cationic component (11-mercaptoundecyl)-N,N,N-trimethylammonium (MUDTMA), which controls the distance of the positively charged end group from the substrate's surface, was kept constant. In contrast, the anionic component, and, correspondingly, the distance of the negatively charged carboxylate groups from the surface, was varied changing the alkyl chain length in the thiol molecules from seven (MOA) via 11 (MDDA) to 15 (MHDA). In this way, the charge neutrality of the coating was maintained, but the charged groups exposed at the interface to water were varied, and thus, the orientation of the dipoles in the SAMs was altered. In model biofouling studies, protein 3 adsorption, diatom accumulation and the settlement of zoospores were all affected by the altered charge distribution. This demonstrates the importance of the dipole orientation in mixed charged SAMs for their inertness to non-specific protein adsorption and the accumulation of marine organisms. Overall, biofouling was lowest when both the anionic and the cationic groups were placed at the same distance from the substrate's surface.

Effect of Multilayer Termination on Nonspecific Protein Adsorption and Antifouling Activity of Alginate-Based Layer-by-Layer Coatings

“…The exceptional resistance of our coatings toward diatoms is in good agreement with results obtained from studies with other polysaccharide-based LbL coatings. , While the influence of multilayer termination on the number of adhered diatoms was unnoticeable for AC8 (7%) and AC8.5 (7%), this was not the case for AA/PEI multilayers because PEI-terminated AP8 (11%) exhibited higher cell densities than AA-terminated AP8.5 (2%). This might be explained by the negative zeta potential of N. perminuta cells, which was found to be ξ = −11.5 mV . While the electrostatic argument is intriguing, the question remains as to why negatively charged proteins respond less to such electrostatic interactions.…”

“…This might be explained by the negative zeta potential of N. perminuta cells, which was found to be ξ = −11.5 mV. 124 While the electrostatic argument is intriguing, the question remains as to why negatively charged proteins respond less to such electrostatic interactions. Eventually, the larger mass of the diatoms creates higher inertia compared to proteins and thus a larger impact force when hitting the coating.…”

Control of Marine Bacteria and Diatom Biofouling by Constant and Alternating Potentials

“…This could be connected with the fact that most organisms have negative zeta potentials ζ. 34,35,45 In our case, C. marina was reported to have a zeta potential of ζ = −33 mV 34 and N. perminuta of ζ = −12 mV. 35 This could cause attractive electrostatic interactions between the negative charge of the microorganisms and the positive potential applied to the surfaces and explain the increased attachment of bacteria and diatoms (Table 1).…”

“…The zeta potential ζ of N. perminuta was previously determined to be −12 mV. 35 Electrochemical Cell To Study the Attachment of Marine Organisms. Figure 1 shows the setup used to test the attachment of marine fouling organisms to surfaces under controlled electrochemical conditions.…”

Sol–Gel-Based Hybrid Materials as Antifouling and Fouling-Release Coatings for Marine Applications

“…51,52 Carboxyl-groups, which are not present in CH, show intermediate WCAs of 29°. 53 To conclude, the absence of carboxyand the presence of amino-groups, seems to be the main factor for the high CA of CH. Thus, the use of sol-gel chemistry allowed the synthesis of stable hybrid material coatings in which the original properties of the polysaccharides are preserved.…”