Firoozeh Malekzadeh - Department of Biochemistry and Biophysics, Faculty of Sciences, Mashhad Branch, Islamic AzadUniversity, Mashhad, Iran
Mehran Gholamin - Department of Biochemistry and Biophysics, Faculty of Sciences, Mashhad Branch, Islamic AzadUniversity, Mashhad, Iran
Jamshid Khan Chamani - Department of Biochemistry and Biophysics, Faculty of Sciences, Mashhad Branch, Islamic AzadUniversity, Mashhad, Iran

Due to the sensitivity of CD signal to subtle variation of DNA chiral conformation, CD is usefultechnique to follow the complex-DNA interaction via investigation the changes in the DNAMorphology[1].In particular B-DNA shows two CD bands:a positive band at 278 nm due to base-stackingand a negative band at 246 nm due to the right handed helicity[2]. Classical interaction tend to enhancethe intensities of bands due to strong base stacking interaction and stable DNA conformation ,whilesimple groove binding and electrostatic interaction show less perturbation or no perturbation on the basestacking and helicity bands[3]. The result indicate that in the present of two drugs both positive andnegative bands are increase and decrease respectively and this type of changes in the CD bands wasregarded that B-DNA changes conformation to A-DNA in intercalative binding mode .The enhancementof positive bands was due to drugs that stacked in to the base pairs of duplex DNA,which prevented theadjacent base pairs from close stacking[4].

Intercalation;Circular dichroism; B-DNA; right handed helicity; base-stacking