Flow dichroism of deoxyribonucleic acid solutions

The flow dichroism of dilute DNA solutions (A 260 ≈ 0.1) has been studied in a Couette‐type apparatus with the outer cylinder rotating and with the light path parallel to the cylinder axis. Shear gradients in the range of 5–160 sec. −1 were studied. The DNA samples were whole, “half,” and “quarter” molecules of T4 bacteriophage DNA, and linear and circular λb 2 b 5 c, DNA. For the linear molecules, the fractional flow dichroism is a linear function of molecular weight. The dichroism for linear λ DNA is about 1.8 that of the circular molecule. For a given DNA, the dichroism is an approximately linear function of shear gradient, but with a slight upward curvature at low values of G , and some trend toward saturation at larger values of G . The fractional dichroism increases as the supporting electrolyte concentration decreases.