Salt-dependent binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and dipyrido[3,2-a: 2′,3′-c]phenazine to calf thymus DNA

Mudasir, Karna Wijaya, Endang Tri Wahyuni, Naoki Yoshioka, Hidenari Inoue

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The salt-dependent binding of racemic iron(II) mixed-ligand complex containing 1,10-phenanthroline (phen) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz), [Fe(phen)2(dppz)]2+ to calf thymus DNA (ct-DNA) has been characterized by UV-VIS spectrophotometric titration. The equilibrium binding constant (Kb) of the iron(II) complex to ct-DNA decreases with the salt concentration in the solution. The slope, SK = (δlog Kb / δlog [Na2+]) has been found to be 0.49, suggesting that, in addition to intercalation, considerable electrostatic interaction is also involved in the ct-DNA binding of [Fe(phen)2(dppz)]2+. The calculation of non-electrostatic binding constant (Kto) based on polyelectrolyte theory has revealed that the non-electrostatic contribution to the total binding constant (Kb) increases significantly with the increase in [Na+] and reaches 36% at 0.1 M NaCl. On the other hand, the contribution of the non-electrostatic binding free energy (ΔGto) to the total binding free energy change (ΔGo) is considerably large, i.e. 87% at [Na+] = 0.1 M, suggesting that the stabilization of the DNA binding is mostly due to the contribution of non-electrostatic process. Moreover, the effect of specific ligand substitutions on ΔGo has been rigorously evaluated using the quantity ΔΔGto, i.e. the difference in ΔGto relative to that of the parent iron(II) complex, [Fe(phen)3]2+, indicating that each substitution of phen by dip and dppz contributes 7.5 and 17.5 kJ mol- 1, respectively to more favorable ct-DNA binding.

Original languageEnglish
Pages (from-to)44-50
Number of pages7
JournalBiophysical Chemistry
Volume121
Issue number1
DOIs
Publication statusPublished - 2006 Apr 20

Fingerprint

calves
Phenanthrolines
Iron
deoxyribonucleic acid
Salts
Ligands
salts
iron
ligands
Free energy
Substitution reactions
Intercalation
Coulomb interactions
Polyelectrolytes
Static Electricity
Titration
Stabilization
free energy
substitutes
phenazine

Keywords

  • 1,10-phenanthroline
  • DNA-binding
  • dppz
  • Iron(II)
  • Salt-dependence

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Biophysics

Cite this

Salt-dependent binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline and dipyrido[3,2-a : 2′,3′-c]phenazine to calf thymus DNA. / Mudasir; Wijaya, Karna; Tri Wahyuni, Endang; Yoshioka, Naoki; Inoue, Hidenari.

In: Biophysical Chemistry, Vol. 121, No. 1, 20.04.2006, p. 44-50.

Research output: Contribution to journalArticle

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abstract = "The salt-dependent binding of racemic iron(II) mixed-ligand complex containing 1,10-phenanthroline (phen) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz), [Fe(phen)2(dppz)]2+ to calf thymus DNA (ct-DNA) has been characterized by UV-VIS spectrophotometric titration. The equilibrium binding constant (Kb) of the iron(II) complex to ct-DNA decreases with the salt concentration in the solution. The slope, SK = (δlog Kb / δlog [Na2+]) has been found to be 0.49, suggesting that, in addition to intercalation, considerable electrostatic interaction is also involved in the ct-DNA binding of [Fe(phen)2(dppz)]2+. The calculation of non-electrostatic binding constant (Kto) based on polyelectrolyte theory has revealed that the non-electrostatic contribution to the total binding constant (Kb) increases significantly with the increase in [Na+] and reaches 36{\%} at 0.1 M NaCl. On the other hand, the contribution of the non-electrostatic binding free energy (ΔGto) to the total binding free energy change (ΔGo) is considerably large, i.e. 87{\%} at [Na+] = 0.1 M, suggesting that the stabilization of the DNA binding is mostly due to the contribution of non-electrostatic process. Moreover, the effect of specific ligand substitutions on ΔGo has been rigorously evaluated using the quantity ΔΔGto, i.e. the difference in ΔGto relative to that of the parent iron(II) complex, [Fe(phen)3]2+, indicating that each substitution of phen by dip and dppz contributes 7.5 and 17.5 kJ mol- 1, respectively to more favorable ct-DNA binding.",
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