A structural basis for the amphiphilic character of alginates – Implications for membrane fouling

• Published in: Carbohydrate polymers Vol. 164; pp. 162 - 169
• Main Authors: Stewart, Matthew B., Myat, Darli T., Kuiper, Michael, Manning, Richard J., Gray, Stephen R., Orbell, John D.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15.05.2017
• Subjects: Alginates; Alpha-l-guluronic acid; Beta-d-mannuronic acid; Membrane fouling; Molecular dynamics; Molecular dynamics; Alginates; Alpha-l-guluronic acid; Beta-d-mannuronic acid; Membrane fouling
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2017.01.072

•Alginates with high M content foul (bind to) hydrophobic membranes at low and neutral pH.•M has been shown by quantum chemical calculations to be to be uniquely amphiphilic.•A hydrophobic patch on M allows alginate polymers containing M to bind to a hydrophobic surface.•The mechanism of alginate binding to a hydrophobic membrane (polypropylene) has been demonstrated by MD simulations.•The hydrophobic patch of M is essential for the functioning of the enzyme mannuronan C-5 epimerase AlgE4. Ostensibly hydrophilic alginates are known to foul hydrophobic membranes, under various conditions. Here, controlled experiments have been conducted at high and low pH on the fouling of a polypropylene membrane by alginate and the results suggest that the observed fouling is due to an intrinsic property of the alginate. Thus quantum chemical calculations on the M and G monomers of alginate reveal that M adopts an equilibrium geometry that is hydrophilic on one face and hydrophobic on the other, i.e. is potentially amphiphilic. Molecular dynamics simulations on short alginate chains of different sequences interacting with a modelled polypropylene surface, show that this characteristic is carried over to the polymer and results in hydrophobic patches along the chain that facilitate attractive interactions with the polypropylene surface. This concept is buttressed by an analysis of the binding characteristics of a previously reported X-ray structure of the mannuronan C-5 epimerase AlgE4 enzyme.