Daniel L. SteinDaniel L. Stein

Professor of Physics and Mathematics
Ph.D., Princeton University, 1979

My Research

D.L. Stein: Research on Biophysics - for Physicists

In collaboration with Walter Nadler (University of Juelich, Germany), I have worked on the problem of ligand migration (e.g., CO or O2) in globular proteins like myoglobin. There is some beautiful physics associated with the problem: far from being a random walk of a point particle on a static lattice, the ligand deforms the protein, which in turn acts back on the ligand; and the protein is continually fluctuating while all this is happening. In fact, if the protein were frozen into its static, average conformation, no ligand diffusion could occur at all! The fluctuation of the protein at physiological temperatures (well above its glass transition) opens voids through which the ligand can travel.

There are many experimental studies of the time-, pressure-, and temperature-dependence of the diffusion process. Using these to guide our work, we have proposed and studied a reaction-diffusion model of the process. Our model explains the observed time-dependence of the ligand recombination following flash photolysis. More importantly, we proposed a sharp experimental test to resolve the problem (sometimes referred to as the single-channel hypothesis) of the dimensionality of the ligand path within the protein. Our work can also be used to study passive ion-channel fluctuations in a different class of proteins.

The problem of protein conformational fluctuations has led us to consider the problem of diffusion on a fluctuating lattice; that is, where the bonds open and close randomly in time. With David Levermore (Mathematics Department, University of Maryland), we proposed a renormalization-group treatment of this problem, whose applications also extend to problems in other ares: for example, ionic conduction in polymeric solid electrolytes and protonic diffusion in hydrogen-bonded networks.

For detailed information on our research, see Technical Publications. Most of my recent publications are downloadable from this page. (To save both time and paper, the link will take you to the abstract on the cond-mat archives page. If desired, the full paper can then be downloaded from there.)

	 aligned helium enables MRI scans of the air space in the lungs. Univ. of VA School of Medicine.

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