Varying flow in linear dichroism cells

The usefulness of linear dichroism (LD) in structure identification depends strongly on the orientation of the molecule in the linear dichroism cell. Hence, the fluid flow inside the linear dichroism cell which performs this act of orientation is of great importance. As such, this paper records the steps taken to identify the varying flow states in the cell, with changing rotation speed, and the resulting effects on the orientation of the molecule, as deduced from the LD spectra obtained. The previously known stiffening effects of ethidium bromide (EB) on DNA are reproduced to a certain extent, the change appearing for high concentrations of EB, but, significantly, at the same point at which Taylor vortices appear in the flow. The inability to scale up the results obtained from the micro-volume LD cell to match those from the larger cell suggest a dependence of the orientation on the flow profile in the cell, which are different in the two cells.