Claude Desruisseaux

Diffusion coefficient of DNA molecules during free solution electrophoresis.

The free‐draining properties of DNA normally make it impossible to separate nucleic acids by free‐flow electrophoresis. However, little is known, either theoretically or experimentally, about the diffusion coefficient of DNA molecules during free‐flow electrophoresis. In fact, many authors simply assume that the Nernst‐Einstein relation between the mobility and the diffusion coefficient still holds under such conditions. In this paper, we present an experimental study of the diffusion coefficient of both ssDNA and dsDNA molecules during free‐flow electrophoresis. Our results unequivocally show that a simplistic use of Nernst‐Einsteins relation fails, and that the electric field actually has no effect on the thermal diffusion process. Finally, we compare the dependence of the diffusion coefficient upon DNA molecular size to results obtained previously by other groups and to Zimms theory.

Theory of DNA electrophoresis: a look at some current challenges.

Although electrophoresis is one of the basic methods of the modern molecular biology laboratory, new ideas are being suggested at an accelerated rate, in large part because of the pressing demands of the biomedical community. Although we now have, at least for some methods, a fairly good theoretical understanding of the physical mechanisms that lead to the observed peak spacings, widths and shapes, this knowledge is often too qualitative to be used to guide further technical developments and improvements. In this article, we review some selected elements of the current state of our theoretical ignorance, focusing mostly on DNA electrophoresis, and we offer several suggestions for further theoretical investigations.

Capillary electrophoretic separation of uncharged polymers using polyelectrolyte engines. Theoretical model.

We recently demonstrated that the molecular mass distribution of an uncharged polymer sample can be analyzed using free-solution capillary electrophoresis of DNA-polymer conjugates. In these conjugates, the DNA is providing the electromotive force while the uncharged polydisperse polymer chains of the sample retard the DNA engine with different amounts of hydrodynamic drag. Here we present a theoretical model of this new analytical method. We show that for the most favourable, diffusion-limited electrophoresis conditions, there is actually an optimal DNA size to achieve the separation of a given polymer sample. Moreover, we demonstrate that the effective friction coefficient of the polymer chains is related to the stiffness of the two polymers of the conjugate, thus offering a method to estimate the persistence length of the uncharged polymer through mobility measurements. Finally, we compare some of our predictions with available experimental results.

Trapping Electrophoresis and Ratchets: A Theoretical Study forDNA-Protein Complexes

Recently, Griess and Serwer (1998. Biophys. J. 74:A71) showed that it was possible to use trapping electrophoresis and unbiased but asymmetrical electric field pulses to build a correlation ratchet that would allow the efficient separation of naked DNAs from identical DNAs that form a complex with a bulky object such as a protein. Here we present a theoretical investigation of this novel macromolecular separation process. We start by looking at the general features of this electrophoretic ratchet mechanism in the zero-frequency limit. We then examine the effects of finite frequencies on velocity and diffusion. Finally, we use the biased reptation model and computer simulations to understand the band-broadening processes. Our study establishes the main experimental regimes that can provide good resolution for specific applications.

DNA separation mechanisms during electrophoresis.

This chapter describes the separation mechanisms used for DNA electrophoresis. The focus is on the concepts that may help the researcher understand the methodology, read the theoretical literature, analyze experimental data, identify the relevant separation regimes, and/or design optimization strategies. But first, let’s look at some key definitions. Since capillary electrophoresis (CE) is a “finish line” technique, the mobility μ(M) and the velocity v(M) of a molecule of size M (in bases or base pairs) in an electric field E are generally defined as: