Farshid Hajibabaei, - Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
Fatemeh Hedayati, - Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
Sadegh Salehzadeh - Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran

Methylene Blue (MB) is one of the sensitive fluorescent probes that bind to DNA via intercalation. On the other hand, Hoechst 33258 (HO) binds strongly to the minor grooves of ct-DNA [1]. Figure 1 shows the emission spectra of the MB with adding different amounts of the Zn(II) complex to DNA–MB system. As can be seen, upon the addition of Zn(II) complex the fluorescence intensity of MB increases, which is due to the intercalation of this complex to ct-DNA base pairs and displacing some MB from the DNA– MB system. Also, the effect of Zn(II) complex on DNA–HO system fluorescence intensity or the position of the emission of the DNA–HO system was negligible, indicating that Zn(II) complex cannot displace HO from the DNA–HO system [2].