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

Matthew B Stewart; Darli T Myat; Michael Kuiper; Richard J Manning; Stephen R Gray; John D Orbell

doi:10.1016/j.carbpol.2017.01.072

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

Carbohydr Polym. 2017 May 15:164:162-169. doi: 10.1016/j.carbpol.2017.01.072. Epub 2017 Jan 22.

Authors

Matthew B Stewart¹, Darli T Myat², Michael Kuiper³, Richard J Manning², Stephen R Gray⁴, John D Orbell⁵

Affiliations

¹ Institute for Sustainability and Innovation (ISI), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia; College of Engineering and Science, Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia. Electronic address: Matthew.Stewart@vu.edu.au.
² Institute for Sustainability and Innovation (ISI), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia; College of Engineering and Science, Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia.
³ Victorian Life Sciences Computation Initiative, the University of Melbourne,Parkville Campus, 187 Grattan Street, Carlton, VIC 3010, Australia. Electronic address: mkuiper@unimelb.edu.au.
⁴ Institute for Sustainability and Innovation (ISI), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia; College of Engineering and Science, Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia. Electronic address: Stephen.Gray@vu.edu.au.
⁵ Institute for Sustainability and Innovation (ISI), Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia; College of Engineering and Science, Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia. Electronic address: John.Orbell@vu.edu.au.

PMID: 28325313
DOI: 10.1016/j.carbpol.2017.01.072

Abstract

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.

Keywords: Alginates; Alpha-l-guluronic acid; Beta-d-mannuronic acid; Membrane fouling; Molecular dynamics.