INTERACTIONS BETWEEN DNA AND PSORALENAMINES STUDIED WITH DICHROISM TECHNIQUES

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Abstract
The interaction of a series of water‐soluble mono‐ and bis‐psoralenamines with calf thymus DNA has been studied with flow UV linear dichroism (LD), circular dichroism (CD) and equilibrium techniques. The positive charge of a protonated amino group strongly enhances the DNA affinity compared to that of the parent compound, 8‐methoxypsoralen. The orientation of the psoralen when bound to DNA, depends on the position of the amino substituent. With amino substituents in the 5‐position (on the‘hydrophobic edge’of psoralen) psoralenamines tend to bind with a considerable tilt relative to the average orientation of the DNA base‐pairs. The tilt generally increases with an increased psoralen: base‐pair ratio, indicating a more random, nonintercalated binding. With the amino substituents in the 8‐position the psoralen binds with its plane parallel to that of the DNA bases as expected for intercalation. The DNA CD supports that these psoralenamines induce a considerable perturbation of the DNA structure, and the CD induced in the psoralen chromophore is in qualitative agreement with intercalation. The study also includes a theoretical and an experimental determination of the UV transition moments of the psoralen chromophore.

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