Changes in Hydration of Lanthanide Ions on Binding to DNA in Aqueous Solution

Abstract

The interaction of the trivalent lanthanides Ce(III), Eu(III), and Tb(III) with sodium deoxyribonucleic acid (DNA) in aqueous solution has been studied using their luminescence spectra and decays. Complexation with DNA is indicated by changes in luminescence intensity. In the system terbium(III)-DNA, changes in luminescence with pH are suggested to be due to the protonation of phosphate groups. The degree of hydration of Tb(III) on binding to DNA is followed by luminescence lifetime measurements in water and deuterium oxide solutions, and it is found that the lanthanide ion loses at least one hydration water on binding to long double stranded DNA at pH 4.7 and pH 7. Rather different behavior is observed on binding to long or short single stranded DNA, where six water molecules are lost, independent of pH. It is suggested that in this case the lanthanide probably binds to the bases of the DNA backbone. The DNA conformation seems to be an important factor in the binding. In addition, the isotopic effect on terbium luminescence lifetime may provide a useful method to distinguish between single and double stranded DNA. DSC results are consistent with cleavage of the double helix of DNA at pH 9 in the presence of terbium.

Using lanthanides as probes for polyelectrolyte–metal ion interactions. Hydration changes on binding of trivalent cations to nucleotides and nucleic acids

“…DNA was thermally denatured to produce ss-DNA by heating at 90°C for 10 min and then cooling rapidly by injecting the sample into a beaker that is cooled by immersion into a mixture of cold ice and ethanol. Following this treatment, the DNA in aqueous solution for the EPR experiments was shown to be single stranded by differential scanning calorimetry (DSC) [32]. DNA concentration was measured by its absorbance at 260 nm, e 260 = 6600 M À1 cm À1 .…”

“…In previous studies with DNA [32], we have shown that the binding of lanthanides is strongly dependent upon pH, and that at high pH both phosphate groups and bases may be involved. Such two-site binding has previously been suggested from both luminescence [65] and 1 H NMR spectroscopy [66] Phosphorous-31 NMR spectroscopy has proved to be a powerful technique here for studying the conformation, dynamics and binding of nucleic acids in aqueous solutions [67][68][69].…”

“…Trivalent lanthanide ions form a relatively homogeneous group of 15 elements having attractive, spectroscopic and magnetic properties [31], and have been used as probes of the interactions of metal ions with nucleic acids [32] and other polyelectrolytes [33].…”

“…Replacement of OH oscillators by the OD ones causes the vibronic deexcitation pathway to become exceedingly inefficient, and the resultant isotope effect on luminescence lifetimes permits the determination of the number of water molecules in the first coordination sphere of metal ion [54][55][56][57][58][59][60][61][62], in addition to the changes in hydration on lanthanide ion binding. This technique has been applied to study lanthanide ion dehydration on binding to DNA [32], polyvinylsulfonate [33] and sodium dodecyl sulfate [63] in aqueous solutions as well as to AOT/water/isooctane microemulsions [64]. We extend this study to the behavior of lanthanide ions on binding to RNA.…”

Novel materials based on DNA‐CTMA and lanthanide (Ce3+, Pr3+)

“…Because of their spectroscopic and magnetic properties, trivalent lanthanide ions can be used as probes of the metal ions interaction with DNA. Costa et al 19 ). The fluorescence studies of these compounds were also performed to see the influence of DNA matrix.…”