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ABSTRACT. Spectroscopic and viscosity methods were applied to investigate the interaction between methylene blue (MB)-Sm(III) complex and herring sperm DNA by using acridine orange as a spectral probe in Tris-HCl buffer (pH 7.40). By means of molar ratio method, the binding ratios between MB-Sm(III) and DNA were determined as nSm(III):nMB =1:3, nMB-Sm(III) complex:n DNA = 8:1, and the apparent molar absorption coefficient of εMB-Sm(III)-DNA was found to be 7.01×10 5 M -1 ·cm -1 . The bonding constants at different temperatures K θ 292K = 7.35×10 5 M -1 , K θ 310K = 1.25×10 5 M -1 were obtained by double reciprocal method. Thermodynamic function computation demonstrates that ∆rSm Ө is the primary driving power of the interaction between MB-Sm(III) and herring sperm DNA. By combination analysis of the Scatchard method, circular dichroism spectroscopy and viscosity method, it suggests that the interaction mode between MB-Sm(III) complex and herring sperm DNA are a mixed binding, which contains partial intercalation and electrostatic interaction.

Spectroscopic and viscosity methods were applied to investigate the mechanism of interaction between Congo red (CR)-Sm(III) complex and herring sperm DNA by using acridine orange as a spectral probe in Tris-HCl buffer (pH 7.40). The binding ratio of Sm(III)(CR) 3 : DNA is 5 : 1, the apparent molar absorptivity of " Sm(III)(CR)3-DNA is 4.80 Â 10 5 L (mol cm) À1 and the bonding constant of Sm(III)(CR) 3 interacting with DNA is KThe results confirm that the interaction between Sm(III)(CR) 3 complex and DNA is a partial intercalation, and the reaction process is entropy favorable.

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