Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2011_2012/HUTTER%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 31st May 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 22
Dr. Jeff Hutter
Department of Physics & Astronomy
Western University
“Examining the role of crystallization inhibitors using atomic-force microscopy”
ABSTRACT
Kinetic inhibitors are additives that affect crystallization kinetics without altering thermodynamic properties, such as the melting point. Based on their effectiveness at exceedingly small concentrations, models for the mechanism by which such additives operate have assumed adsorption to crystal growth faces. A well-known model proposed in 1958 by Cabrera and Vermilyea (the C-V model) suggests that impurities adsorb to growth faces and pin growth steps, forcing them to curve, and thus decreasing the effective supersaturation via the Gibbs-Thomson effect. Despite considerable effort, direct evidence for this mechanism has only been offered for a few systems, while significant objections have been raised: How can the irreversible adsorption required to pin growth steps be reconciled with the observed dependence on inhibitor concentration? How can growth proceed at all in the presence of strongly adsorbed inhibitor molecules?
The main example of kinetic inhibition that will be discussed here involves the crystallization of calcium oxalate monohydrate (COM), which is the main mineral component of kidney stones. Certain proteins, such as osteopontin (OPN), are known to inhibit stone formation, but the details of the process are not well understood. In order to determine the role of such inhibitors, we have examined the growth of COM at the molecular level and in real time using the atomic force microscope (AFM). We find that the presence of OPN, as well as synthesized peptides corresponding to portions of the OPN molecule, results in clear changes in the morphology and propagation speed of growth steps. By observing the subsequent recovery of COM growth when the inhibitor is flushed from solution, we can test the validity of the assumptions of the C-V model. An improved understanding of this inhibitor mechanism may result in the design of therapeutic agents for the prevention of kidney stones, as well as an improved ability to tailor additives for a variety of commercial processes.