THANKS STAN FOR HELPING MAKING THIS HAPPEN!
We used dynamic force spectroscopy to directly probe binding between complex, model and natural microbial polysaccharides and common iron (oxyhydr)oxides. Applying nucleation theory to our results demonstrates that if there is a strong attractive interaction between biopolymers and iron (oxyhydr)oxides, the biopolymers decrease the nucleation barriers, thus promoting mineral nucleation. These results are also supported by nucleation studies and density functional theory. Spectroscopic and thermogravimetric data provide insight into the subsequent growth dynamics and show that the degree and strength of water association with the polymers can explain the influence on iron (oxyhydr)oxides transformation rates.
Figure 1. a) Polysaccharide stalks from Gallionella and b) EPS produced by Shewanella are both associated with iron (oxyhydr)oxide formation. c) We covalently attached alginate and EPS to an AFM tip and brought the polymers in contact with ferrihydrite and hematite and obtained dynamic force spectra. d) Force curves typical for interaction between polymer brushes and minerals. Distance along the y-axis is the length between the surface and the tip pulling away from the surface. To derive single polymer binding events, we applied worm-like chain fits (black curve) for the last rupture event for each force curve.
Combined, our results provide a mechanistic basis for understanding how polymer-mineral-water interactions alter iron (oxyhydr)oxides nucleation and growth dynamics. Our work pave the way for an improved understanding of the consequences of polymer induced mineralization in natural systems and have implications for the global iron cycle and as well as understanding formation of banded iron formations (https://eartharxiv.org/pd73x/)