Optical Properties of Oriented Dye‐LiDNA Complexes Prepared with the Wet Spinning Method

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Abstract
For the study of the spatial arrangement of dyes bound to DNA a recently developed wet spinning method for DNA has been modified in order to prepare highly oriented dye‐DNA complexes. After bathing in alcoholic solutions containing LiCl and either acridine orange, proflavin or chrysazin, spun LiDNA deposits were dried and thereby coalesced into films of highly oriented dye‐LiDNA complexes. The method is reproducible and it is possible to obtain samples of practically any desired dimensions.The maxima of absorption and emission spectra were characteristic for these dyes when bound to DNA. The films exhibited a strong negative dichroism. The dichroic ratios indicated that the absorption vectors of these dyes would be inclined more than 65° to the DNA helix axis. Preliminary polarized fluorescence measurements have been performed using the recently developed method of Nishijima and coworkers. To analyze the fluorescence intensity curves the recent theoretical study of Desper and Kimura has been extended for uniaxial orientation (The Appendix) to account for the occurrence of non‐coinciding absorption and emission vectors of the single chromophoric group. The application of this extended theory to simple models indicated that the angles of inclination to the DNA helix axis of the absorption and emission vectors of acridine orange and proflavin would be confined to the interval 65°–90°. The angles between the absorption and emission vectors in these dyes were estimated to lie within an interval of 20°–30°. It is concluded that improved experimental conditions and use of a computer to analyze the polarized fluorescence curves would give more precise information.Wide‐angle X‐ray diffraction photographs of the specimens showed the undistorted crystalline B form pattern which might indicate that the dye molecules have not penetrated the DNA crystallites in the present modification of the wet spinning method. Other methods for introducing the complexing agents in the wet spinning method are discussed and the wide applicability of these samples of oriented DNA complexes for physico‐chemical studies is stressed.