Research Interests
Research Interests by Douglas J. Henderson.
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Recently, my interests have centered on two projects. Firstly, using
our computer simulations as a guide, I am interested in the development
of better theories of electrochemical interfaces. Our simulations have
shown that the venerable Gouy-Chapman theory is not very accurate. We
have obtained excellent agreement with the simulation results using
density functional theory, where the properties of the electrolyte are
assumed to be a nonlocal function of the electrolyte density in the
interface. As can be seen in the figure, the Gouy-Chapman theory is in
rather poor agreement with our simulation results. We expect our work
to lead to a better understanding electrochemical reactions. Secondly, I have been studying the selectivity and conductance of channels in physiological membranes. Channels are proteins with a hole that allows the passage of selected ions that convey messages to the interior of a cell. For example, the calcium channel passes the signal for the heart to beat. My colleagues and I have modeled the calcium channel as a smooth cylinder. The important structural elements of the calcium channel are the four glutamate side chains that are attached to the side of the channel cylinder. For simplicity, we model each glutamate as a pair of half charged oxygen ions that are constrained to remain within the channel. This simple model accounts for the selectivity of the calcium channel. We have studied this model channel by simulations and by a simple theory. If this model calcium channel is placed in a Na Cl solution, the sodium ions in the channel are replaced by calcium ions when a very small amount of calcium ions are added to the solution. The mechanism appears to be a competition between electrostatics and the limited space of the channel. A calcium ion delivers twice the charge of a sodium ion while occupying about the same space. We have called this mechanism "space charge competition".
 Density profiles of ions near a charged semipermeable membrane. The curves give our theoretical results, and the points are computer simulation results. The membrane is impermeable to the ions represented by the solid curve. Diffuse layer potential of an aqueous NaCl solution as a function of the electrode charge density. The three sets of curves are, from bottom to top, for 1M, 0.1M, and 0.01M. The points are the simulation results and the solid and dash-dot curves give the density functional and Gouy-Chapman theory results. Physical Review Letter - Molecular Dynamics Simulation of Continuous Current Flow through a Model Biological Membrane Channel Physical Review Letter - Ion Accumulation in a Biological Calcium Channel: Effects of Solvent and Confining Pressure Other research interests:
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