Studies of the DNA–Acridine Complexes. I. Fluorescence Depolarization

The motion of the DNA–acridine complexes in solution was studied by the fluorescence depolarization method. Five derivatives of 3,6-diaminoacridine were used in order to investigate the effect of amino substituion on the depolarization results. A linear relation between the reciprocal polarization (1/P) and T/η was obtained by varying the temperature of a native DNA–acridine solution. The limiting polarization (P0) and the mean rotational relaxation time (ρh) of the complex were evaluated from these data. The ρh value of the complex (30–50 nsec) was much larger than the value of free acridine in water, but it was much too small to correspond to the rotation of the whole DNA molecule. Further, it was found that the values of P0 and ρh for 3,6-bis(diethylamino)acridine are much smaller than those for other acridines. This may result from some steric hindrance of the binding by bulky diethylamino groups.