A Velocity-Gradient Flow Cell for Raman and Emission Spectroscopy of a DNA-Drug Solution

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The purpose of this work is to construct a new instrument with which one can examine the geometry of a DNA-Drug complex in a solution.In ordinary solutions, the molecules are randomly oriented. In a spectroscopic measurement on such a solution, therefore, information on the anisotropic properties of the molecules in question is obscured. Thus it is desirable to have molecules oriented in solution. This is known to be possible for the DNA duplex by placing its solution in a flow with a velocity gradient of 10^3 cm s^<-1>/cm order of magnitude. Wada and Kozawa (J.Polymer Sci.,A2, 853 (1964)), for example, produced such a velocity gradient in the flow of solution placed in the gap between two coaxial cylinders, one of which was rapidly rotated. They examined the anisotropy of the 260 nm absorption of DNA In the present study, a similar technique has been applied to Raman and fluorescence spectroscopy.A DNA solution was placed in the gap (1 mm) between two coaxial cylinders; the inside diameter of the outer cylinder was 12 mm, and the outside diameter of the inner cylinder was 10 mm. When the inside cylinder was rotated at 2500 revolutions per minute, a sufficiently large velocity gradient of the liquid flow was produced across the gap so that the DNA molecules were oriented along the flow direction. Anisotropy of the Raman scatterings of the DNA molecule was examined by passing an exciting laser beam into the gap from the bottom of the cylinder in the direction parallel to the cylinder axis. An antitumor drug, aclacinomycin A (HCl salt), was added to the DNA solution, and the anisotropy of its emission and Raman spectra was also examined. It has been established that aclacinomycin binds to DNA with its chromophore oriented parallel to the base plane of the DNA duplex.Thus, the newly constructed instrument proved to be powerful for elucidating the geometry of a DNA-drug interaction.