Insight into the Binding Mechanisms of Quartz-Selective Peptides: Toward Greener Flotation Processes

Abstract

Mining practices, chiefly froth flotation, are being critically reassessed to replace their use of biohazardous chemical reagents in favor of biofriendly alternatives as a path toward green processes. In this regard, this study aimed at evaluating the interactions of peptides, as potential floatation collectors, with quartz using phage display and molecular dynamics (MD) simulations. Quartz-selective peptide sequences were initially identified by phage display at pH = 9 and further modeled by a robust simulation scheme combining classical MD, replica exchange MD, and steered MD calculations. Our residue-specific analyses of the peptides revealed that positively charged arginine and lysine residues were favorably attracted by the quartz surface at basic pH. The negatively charged residues at pH 9 (i.e., aspartic acid and glutamic acid) further showed affinity toward the quartz surface through electrostatic interactions with the positively charged surface-bound Na+ ions. The best-binding heptapeptide combinations, however, contained both positively and negatively charged residues in their composition. The flexibility of peptide chains was also shown to directly affect the adsorption behavior of the peptide. While attractive intrapeptide interactions were dominated by a weak peptide–quartz binding, the repulsive self-interactions in the peptides improved the binding propensity to the quartz surface. Our results showed that MD simulations are fully capable of revealing mechanistic details of peptide adsorption to inorganic surfaces and are an invaluable tool to accelerate the rational design of peptide sequences for mineral processing applications.

Emerging Trends of Computational Chemistry and Molecular Modeling in Froth Flotation: A Review

“…Very recently, a robust simulation scheme combining classical MD, replica exchange MD, and steered MD was synergized to characterize the quartz-selective peptide sequences initially identified by phage display at pH 9 as alternative reagents for direct flotation of quartz mineral. 186 The simulation results revealed that the simultaneous presence of positively and negatively charged residues in peptide sequences are favorable for stronger binding of peptides to the surface due to two main reasons. First, the negatively charged residues have strong affinities toward abundant positively charged moieties on quartz surface at basic pH, and second, the repulsive self-interactions in the peptide chain containing dissimilarly charged residues keep the extended conformation of the peptide, guaranteeing the accessibility of peptide side groups to the surface.…”

“…The consideration of protonation/deprotonation states of adsorbates with pH-sensitive functional groups at different pK a is not sufficient to model adsorption phenomena at different pHs. 186 For solid molecular modeling (particularly molecular dynamics simulations) at different pH, the mineral surface and solution must also be carefully constructed. The type and area density of surface groups upon solvation, the likely ionization degree as a function of pH, the ionic strength and type of cations, etc.…”

“…The amino acid acid–base speciation as a function of pH also plays a role in their level of interaction with the sulfide surfaces. Very recently, a robust simulation scheme combining classical MD, replica exchange MD, and steered MD was synergized to characterize the quartz-selective peptide sequences initially identified by phage display at pH 9 as alternative reagents for direct flotation of quartz mineral . The simulation results revealed that the simultaneous presence of positively and negatively charged residues in peptide sequences are favorable for stronger binding of peptides to the surface due to two main reasons.…”

“…At this stage, the value of these simulations of the pH and its impact on the speciation of the collector and, thus, on the reagent-mineral interactions is to be taken cum grano salis because all the criteria to account for the pH in the flotation are not there. The consideration of protonation/deprotonation states of adsorbates with pH-sensitive functional groups at different p K a is not sufficient to model adsorption phenomena at different pHs . For solid molecular modeling (particularly molecular dynamics simulations) at different pH, the mineral surface and solution must also be carefully constructed.…”