Dr. Kai Leonhard Postdoctoral Student co-advised by John Prausnitz University at Cologne, Germany Dipl. Chem., 1998 Ph.D. in chemistry in 2001, U. K. Deiters group Funding Sources: NATO/DAAD

kl@stthd0.pc.uni-koeln.de     Radke Lab Home Page

Current Research Interest:

We use 3D lattice MC simulations to study protein folding, aggregation and adsorption at the oil/water interface. A special emphasis is on the role of interaction energies.

Amino acid/solvent energy interaction parameters determine bulk aqueous protein aggregation and oil/water adsorption. A broad range of protein behavior emerges with small changes in the solvent interaction energies in the employed 20-letter alphabet: from nonaggregating, to reversibly aggregating, or to irreversibly aggregating into crystals or amyloid fibrils. A similar wide variety of fascinating behaviors occurs at the oil/water interface, ranging from nonadsorbing to reversibly to irreversibly adsorbing with different degrees of aggregation at the interface and penetration into one or both phases. The interaction-parameter set is systematically explored and optimized for representing realistic behavior typical of many aqueous globular proteins (fast folding; nonaggregating in the bulk, but irreversibly adsorbing to and aggregating at the interface). The proposed model for 3D-lattice dynamic MC simulations is useful for calculating the qualitative behavior of proteins in bulk solvents and at fluid/fluid interfaces as a function of protein size and composition.

Previous Research Interests:

Diploma thesis and Dissertation: Global simulations of the simple liquids Ne, Ar, N2 and CO

The goal of global simulations is to obtain thermodynamic data without any measurements or parameter fitting.  This can be acomplished by using quantum mechanics to calculate interaction potentials between atoms or molecules and then performing molecular simulations with these potentials.
The accuracy of MP2 through MP4(SDTQ) and coupled cluster methods in combination with correlation-consistent basis sets of different sizes and two exptrapolation schemes to the basis set limt for the calculation of the pairwise additive portion of the interaction energies has been investigated for the four compounds.  The accuracy of the 2-body potentials was checked by comparison to experimental second virial coefficients.  Then, Gibbs ensemble MC simulations have been performed with the ab initio 2-body potentials and 3-body potentials taken from the literature. It was found that an accurate 2-body potential in combination with the isotropic Axilrod-Teller potential yields accurate thermonymanic data, even for dense fluids.

Other research interest at the University at Cologne: An equation of state for the critical region and for modeling the solubility of low-volatile organic compounds in near- and supercritical fluids

A semiempirical equation of state is developed, which is able to model the p-rho-T behaviour of fluids in the critical region, in the low density limit and at high pressure. The equation is developed in the framework of a local mean field model describing density fluctuations in a fluid. A simplified form of this equation of state is combined with a fugacity approach in order to calculate the solubility of several low-volatile solid organic compounds, in particular of the globular molecule adamantane in CO2 and the natural dyestuff beta-carotene in three compressed gases, i.e., CO2, CClF3, and N2O. Solubility maxima, which have been found experimentally as a function of pressure or density at constant temperature, are considered in the correlations. The saturation pressure of the pure solute required for the fugacity approach has been described by a Clausius-Clapeyron equation with two adjustable parameters. We have compared the saturation pressures deduced from the sequence of solubility isotherms with those reported in the literature. The results from our model demonstrate a substantial agreement between measured and calculated solubility data, even for a large solvent density region in its entirety.

4-month postdoc at COSMOlogic: COSMOtherm and association

During my short stay at COSMOlogic I performed calculations with the COSMOtherm package and worked on a project to describe particle dimerization and oligomerization  in the the COSMOtherm framework.

Publications:

U. K. Deiters, M. Hloucha und K. Leonhard, 1999, ,,Experiments? -- No Thank You!``, in Chemical Thermodynamics -- A `Chemistry for the 21st Century' monograph, IUPAC Monograph Series, edited by T. M. Letcher, (Oxford: Blackwell Science), p. 187-195.

K. Leonhard und T. Kraska, An Equation of State Describing the Critical Region: Extension to High Pressure., J. Supercrit. Fluids 16, 1-10 (1999).

K. Leonhard und U. K. Deiters, Monte Carlo Simulations of Neon and Argon Using Ab Initio Potentials, Mol. Phys. 98, 1603-1616 (2000).

T. Kraska, K. Leonhard, D. Tuma und G. M. Schneider, Correlation of the Solubility of Low-Volatile Organic Compounds in Near- and Supercritical Fluids. Part I: Applications to Adamantane and Beta-carotene, J. Supercritical Fluids 23, 209-224 (2002).

T. Kraska, K. Leonhard, D. Tuma und G. M. Schneider, Correlation of the Solubility of Low-Volatile Organic Compounds in Near- and Supercritical Fluids. Part II: Applications to Disperse Red 60 and Two Disubstituted Anthraquinones, Fluid Phase Equilibria 194-197, 469-482 (2002).

K. Leonhard und U. K. Deiters, Monte Carlo Simulations of Nitrogen Using an Ab Initio Potential, Mol. Phys. 100, 2571-2585 (2002).