Dr. Jan Sefcik (Strathclyde University)
Department of Chemical and Process Engineering, University of Strathclyde
Populations and size distributions of solute-rich mesoscale structures in aqueous amino acid solutions and their role in crystal nucleation.
Aqueous solutions of highly soluble substances such as small amino acids are usually assumed to be essentially homogenous systems with some degree of short range local structuring due to specific interactions on the sub-nanometre scale (e.g. molecular clusters, hydration shells), usually not exceeding several solute molecules. However, recent theoretical and experimental studies have indicated the presence of much larger supramolecular assemblies or mesospecies in solutions of small organic and inorganic molecules as well as proteins. We investigated both supersaturated and undersaturated aqueous solutions of simple amino acids using Dynamic Light Scattering (DLS), Brownian Microscopy/Nanoparticles Tracking Analysis (NTA) and Cryogenic Transmission Electron Microscopy (Cryo-TEM). Colloidal scale mesospecies (nanodroplets) were previously reported in supersaturated solutions of amino acids and were implicated as intermediate species on non-classical crystallization pathways. Surprisingly, we have found that the mesospecies are also present in significant numbers in undersaturated solutions even when the solute concentration is well below the solid-liquid equilibrium concentration (saturation limit). Thus, mesopecies can be observed with mean diameters ranging from 100 to 300 nm and a size distribution that broadens towards larger size with increasing solute concentration. Supersaturated solutions will be of course metastable with respect to the crystalline state and crystals can be expected to nucleate with higher likelihood within solute-rich mesospecies. We note that the mesospecies observed are not a separate phase and the system is better described as a thermodynamically stable mesostructured liquid containing solute-rich domains dispersed within bulk solute solution. At a given temperature, solute molecules in such a mesostructured liquid phase are subject to equilibrium distribution between solute-rich mesospecies and the surrounding bulk solution.
More about Professor Jan Sefcik
Jan Sefcik is a Professor in the Department of Chemical and Process Engineering at the University of Strathclyde and an Academic Director of the Doctoral Training Centre in Continuous Manufacturing and Crystallisation. He graduated with an IngChem degree in Chemical Engineering from the Slovak Technical University in Bratislava. After a PhD in Chemical Engineering from the University Minnesota in Minneapolis he was a Postdoctoral Scholar at the California Institute of Technology in Pasadena and a Senior Research Associate and Lecturer at the Swiss Federal Institute of Technology (ETH) in Zurich before joining Strathclyde in 2005.
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