Iron oxides are extremely abundant in soil and are integral to the survival of most microorganisms.  To acquire iron for use in biological processes, some microorganisms secrete organic ligands called siderophores to chelate iron from soil.  However, the surface mechanism by which siderophores chelate is not well studied due to the difficulties of creating and analyzing aqueous surface interactions rather than bulk interactions.  To explore this mechanism, a heat deposition of hematite onto polycrystalline and monocrystalline substrates was conducted to create a sample representative of the environment in which the mechanism occurs.  To determine the best conditions to study the desired chelation, these hematite samples were then put in contact with NaCl solutions of varying pHs and siderophore solutions of varying concentrations and were then subjected to second harmonic generation (SHG) analysis. The deposited hematite samples were found to produce comparable SHG signal to professionally manufactured samples and produced the greatest amount at neutral pHs.  The chelation of the sample by the siderophore solution occurred in analyzable quantities at a wide range of concentrations, informing future experiments.  Preliminary spectroscopic results on organic ligand adsorption will be presented.

Polycrystalline and monocrystalline hematite deposition and its use in nonlinear spectroscopy of environmental interfaces

ACS Spring 2022

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