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Exploratory Analysis of Glycine Peptide Sorption on Ferrihydrite using Calorimetric Techniques and Molecular Dynamics Simulations

EMSL Project ID


Ferrihydrite-organic matter associations are ubiquitous in the environment and can control the kinetics and favorability of biogeochemical processes. However, the dynamics and energetics of organic matter sorption, and the interplay between bonding mechanisms are not well understood and are difficult to examine due to the complexity in these systems. Addressing these uncertainties requires a more integrated approach that utilizes a combination of fine-scale experimental surface data and advanced computer-simulated models. We used a highly sensitive in-tandem flow adsorption microcalorimetry-ultraviolet-visible spectroscopy method to assess the effects of molecular size and conformation on the energetics, binding dynamics, and kinetics of glycine, α-alanine and β-alanine onto NO3-saturated ferrihydrite. Reactions were exothermic and exhibited three energetically distinct steps (contact zone, bridging zone and outer region) with enthalpic contributions ranging from 0-8.3 kJ mol-1. For a given amino acid, sorption during the second step had the highest net energy release (~7.5 kJ mol-1) followed by the first (~2.5 kJ mol-1) then the third step (<< 1 kJ mol-1). An increase in size from glycine to beta-alanine by an additional methyl group resulted in an outer region; a reduced sorbed fraction and faster reaction rate at the contact zone. Switching the position of the amine group in beta-alanine from the beta-carbon to the alpha-carbon, as observed in alpha-alanine, increased the reaction rate at the contact zone and resulted in a higher sorbed fraction in the outer region due to intermolecular interactions. Interestingly, the higher sorbed fraction for α-alanine was associated with a net-zero energy release which was consistent with this latter phase being entropy-driven. Further analyses are needed to validate the evolution and extent of bond formation as pertains to molecular size and conformation. We plan to conduct a systematic examination of the the sorption characteristics of a glycine peptide series (1-5 monomers) on ferrihydrite and compare the experimental data to theoretical model simulations to better inform our understanding of organic-mineral associations and its dynamics in response to environmental perturbations.

Project Details

Project type
Exploratory Research
Start Date
End Date


Principal Investigator

Omar Harvey
Texas Christian University


Burke Leonce
Texas Christian University

Team Members

Amity Andersen
Environmental Molecular Sciences Laboratory

Odeta Qafoku
Environmental Molecular Sciences Laboratory