DNA binding and antibacterial properties of ternary lanthanide complexes with salicylic acid and phenanthroline

Twelve ternary lanthanide complexes RE(sal)₃phen (RE³⁺ = La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Yb³⁺, Lu³⁺, sal = salicylic acid, phen = phenanthroline) were prepared. Interactions between the complexes and calf thymus DNA (ct‐DNA) were investigated using UV–visible spectrophotometry, fluorescence quench experiment and viscosity measurement. Hypochromicity and red shift of the absorption spectra of complexes were observed in the presence of DNA. The enhanced emission intensity of ethidium bromide (EB) in the presence of DNA was quenched by the addition of lanthanide complexes, which indicated that the lanthanide complexes displaced EB from its binding sites in DNA. Based on the systematic research of the binding constant (K_b) and the fluorescence quenching constant (K_q) of the 12 complexes, we found that the complexes with smaller lanthanide ion radius had stronger binding abilities with DNA. Viscosity measurement showed that the relative viscosity of the DNA solution was enhanced with increasing the amounts of the complexes. All these results suggested that the complexes could bind to DNA and the major binding mode was intercalative binding. Moreover, all these complexes exhibited excellent antibacterial abilities against Escherichia coli. Also, the antibacterial activities of complexes with heavy rare earth were higher than those of complexes with light rare earth. Copyright © 2014 John Wiley & Sons, Ltd.