Styliani Constas Associate Professor B.Sc. (University of Athens, Greece) M.Sc. (Queen's University, Kingston, Canada) Ph.D. (University of Toronto) Marie Curie Fellow (AMOLF, Amsterdam, The Netherlands) Office: Room 071, Lab Room 068, Chemistry Building (519) 661-2111 ext. 86338
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Theoretical physical chemistry; Computer simulations in Condensed Phase
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Awards:
• Premier's Research Excellence Award
• Accelerator Grant for Exceptional New Opportunities (AGENO), NSERC
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Current Research Programs:
We study dynamics of activated processes such as chemical reactions in solution, conformational changes of macromolecules and disintegration mechanisms of charged nanodroplets. The studies are performed by molecular simulations where we focus on development and application of Molecular Dynamics and Monte Carlo techniques. Sizes of systems that are investigated range from clusters to bulk. The systems are modeled on atomic scale using different levels of description that range from quantum chemical to empirical in order to capture features defining the properties of the systems.
Charged nanodroplets and clusters
Charged droplets are ubiquitous in atmospheric aerosols and experimental techniques such as electrospray mass spectrometry. We study the mechanism and dynamics of disintegration of the charged nanodroplets with respect to volume to charge ratio. We also study proton transfer reactions in the unique environment of the droplet using Feynman's path integral representation of the protons. Examples of charged nanodroplets that we have studied contain:
• several alkali or alkaline earths ions in water or mixture of solvents
• highly charged peptides in water
• sodiated poly(ethylene glycol) polymers with and without water
Dynamics of chemical reactions in solution
Chemical reactions in solution and phase transitions are examples of processes of chemical interest that occur at long time scales. Such time scales cannot be simulated using straightforward Molecular Dynamics techniques even with the use of the fastest computers. In order to tackle these problems we employ theories of activated processes. The study involves the investigation of an appropriate reaction coordinate (or a set of such coordinates) that describes well the physical process. The phenomena that are studied are complex and the degrees of freedom of the environment, for example the solvent, has to be taken into account in the construction of the reaction coordinate. Reversible work profiles and sampling of trajectories initiated at the transition state reveal the reaction mechanism and allow for the computation of the rate. In addition to this approach for the study of reactions, transition path sampling methods [L. R. Pratt ``A statistical method for identifying transition states in high dimensional problems'', J. Chem. Phys. 85(9): 5045-5048 (1986)] are used. We apply the methods in the study of proton transfer in biological molecules where we use Feynman's path integral representation of the proton and other mixed quantum-classical methods.
"Recoil-growth" schemes for high density polymer systems
Polymers are ubiquitous in industrial and technological applications. Due to the extremely long relaxation times present in high density polymer systems such systems are impossible to model by conventional Molecular Dynamics and Monte Carlo methods. The first problem encountered in the computation of equilibrium and dynamic properties is the generation of equilibrated configurations. We develop biased Monte Carlo schemes that allow for rapid equilibration of these complex systems and we apply these schemes in the study of problems of biological interest.
Collaborative projects with chemical engineering
In collaboration with groups in chemical engineering, we simulate the "oiling-out" effect and develop efficient computational schemes that assist the experimental methods in separation of enantiomers with applications in drugs and agrochemicals.
Selected Publications:
S. Consta "Manifestation of Rayleigh instability in Droplets containing multiply charged macroions", J. Phys. Chem. B, 114(16):5263 (2010).
S. Consta "Detecting reaction pathways and computing reaction rates in condensed phase", Theoretical Chemistry Accounts, 116(1-3):373 (2006).
O. M. Braun, M. Paliy, S. Consta "Ordering of a thin lubricant film due to sliding", Phys. Rev. Lett. 92 (25): Art. No. 256103 (2004).
S. Consta, K. Mainer and W. Novak "Mechanisms of Fragmentation processes of droplets charged with ions", Journal of Chemical Physics 119(19):10125 (2003).
S. Consta, N.B. Wilding, D. Frenkel, and Z. Alexandrowitz. ``Recoil growth: an efficient simulation method for multi-polymer systems.'' Journal of Chemical Physics, 110 :3220--3228 (1999).
