In vitro DNA binding studies of the sweetening agent saccharin and its copper(II) and zinc(II) complexes

Abstract

The interactions of fish sperm DNA (FS-DNA) with the sodium salt of sweetener saccharin (sacH) and its copper and zinc complexes, namely [M(sac)(2)(H2O)(4)]center dot 2H(2)O (M = Cu-II or Zn-II) were studied by using UV-Vis titration, fluorometric competition, thermal denaturation, viscosity and gel electrophoresis measurements. The intrinsic binding constants (K-b) obtained from absorption titrations were estimated to be 2.86 (+/-0.06) x 10(4) M-1 for Na(sac), 6.67 (+/-0.12) x 10(4) M-1 for Cu-sac and 4.01 (+/-0.08) x 10(4)M(-1) for Zn-sac. The Cu-sac complex binds to FS-DNA via intercalation with a K-A value of 50.12 (+/-0.22) x 10(4) M-1 as evidenced by competitive binding studies with ethidium bromide. Moreover, competition experiments with Hoechst 33258 are indicative of a groove binding mode of Na(sac) and Zn-sac with binding constants of 3.13 (+/-0.16) x 10(4) M-1 and 5.25 (0.22) x 10(4) M-1, respectively. The spectroscopic measurements indicate a moderate DNA binding affinity of Na(sac) and its metal complexes. The suggested binding modes are further confirmed by the thermal denaturation and viscosity measurements. In addition, Cu-sac and Zn-sac show weak ability to damage to pBR322 supercoiled plasmid DNA.