Enhancement of protein flocculant properties through carboxyl group methylation and the relationship with protein structural changes

Authors: Garcia, Rafael; Qi, Phoebe; ESSANDOH, MATTHEW - Oak Ridge Institute For Science And Education (ORISE); Bumanlag, Lorelie

Submitted to: Journal of Dispersion Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2020
Publication Date: 6/16/2020
Citation: Garcia, R.A., Qi, P.X., Essandoh, M., Bumanlag, L.P. 2020. Enhancement of protein flocculant properties through carboxyl group methylation and the relationship with protein structural changes. Journal of Dispersion Science and Technology. 0(0):1-12. https://doi.org/10.1080/01932691.2020.1793163.
DOI: https://doi.org/10.1080/01932691.2020.1793163

Interpretive Summary: Flocculants are substances that aid in clearing water of suspended particles. Many flocculants are synthetic polymers, but our past work has shown that some proteins from agricultural by-products can serve as bio-based alternatives. The performance of protein flocculants can be improved by using a chemical reaction that blocks the negative charges on the protein. In this paper we show that the conventional reaction duration of 24 hours is greatly excessive, and that much of the benefit occurs within the first minutes of reaction. By examining the changes in protein structure during the reaction, we are able to better understand the mechanisms behind the enhanced flocculant activity. These results show that methylated protein flocculant can be produced at much less expense than previously believed, improving the competitiveness of protein flocculants with their conventional counterparts.

Technical Abstract: Some proteins will function as flocculants to clear water of suspended particles. Prior work has shown that covalent methylation of a protein’s carboxyl groups can enhance that protein’s flocculant activity; this effect is usually attributed to the reduction in negative charges on the protein. We present results generated using four proteins which show that much of the flocculant activity enhancement occurs in a very short time at the beginning of the methylation reaction, before most of the carboxyl groups have been methylated. A variety of techniques are used to show that the methylation reaction has unintended effects on protein structure, and that these effects may play an important role in enhancing protein flocculant activity.