Electron-Spin-Resonance Studies of a Chlorpromazine Derivative Bound to DNA Fibres

Abstract
Solutions of DNA [from calf thymus], spin-labeled with the radical cation of chlorpromazine [a tranquilizer], were used to produce oriented species of fibers pulled from a gel obtained by ultracentrifugation. The ESR spectra, recorded at X and Q band frequencies, are given for both gel and fibers; 14N hyperfine coupling parameters were obtained by computer fitting. The spectra are explained in terms of a strongly immobilized label having one principal hyperfine tensor axis parallel to the axis of the DNA helix, and the preferential orientation of the chlorpromazine ions with their planes perpendicular to the DNA helical axis.