A magnetic viscometer for shear-sensitive macromolecules.

This paper is a report about a rotation-viscometer with a submerged rotor which has been developed for measuring the viscosity of biological macromolecules. The device avoids the effects of surface disturbance. The rotor is centered and height-balanced electromagnetically and is controlled by a light barrier. The driving force is a rotating electromagnetic field and rotor revolution periods are measured by an electronic timer controlled by a second ligh barrier. Shearing effects are negligible if very slow revolutions are pre-selected; thus, intrinsic viscosity values for DNA can be obtained by merely extrapolating the concentration dependence. In contrast to DNA, chromatin has a very low viscosity with almost no dependence on concentration. If the ionic strength of a chromatin solution is decreased, the viscosity increases due to structural unfolding.