Synthesis, structure, DNA binding and cleavage properties of ternary amino acid Schiff base-phen/bipy Cu(II) complexes

Ternary Cu(II) complexes [Cu(II)(saltrp)(B)] (1,2), (saltrp = salicylidene tryptophan, B = 1,10 phenathroline (1) or 2,2′ bipyridine (2)) were synthesized and characterized. Complex 2 was structurally characterized by single crystal X-ray crystallography. The molecular structure shows a distorted square pyramidal coordination geometry (CuN3O2) in which the ONO donor Schiff base is bonded to the Cu(II) in the basal plane. The N,N donor heterocyclic base displays an axial-equatorial binding mode. CT-DNA binding studies revealed that the complexes show good binding propensity (Intrinsic binding constant, Kb = 3.32 × 105 M−1 for 1 and Kb = 3.10 × 105 M−1 for 2). The catalytic role of these complexes in the oxidative and hydrolytic cleavage of DNA was studied in detail. Complex 1 binds and cleaves DNA more efficiently as compared to 2. From the kinetic experiments, rate constants for the hydrolysis of phosphodiester bond of DNA backbone were determined as 1.94 h−1 and 1.05 h−1 for 1 and 2 respectively. It amounts to (2.93–5.41) × 107 fold rate enhancement compared to uncatalyzed double stranded DNA, which is impressive as compared to related Cu(II) Schiff base complexes.

Graphical abstractTernary [Cu(II)(saltrp)(phen)] (1) and [Cu(II)(saltrp)(bipy)] (2) were synthesized, characterized and crystal structure reported for 2. Their DNA binding and cleavage properties (oxidative and hydrolytic) were studied. The complexes bind to CT-DNA in an intercalative mode. Complex 1 cleaves pUC19 DNA efficiently as compared to 2.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Tryptophan Schiff base Cu(II) complexes i.e. [Cu(II)(saltrp)(phen)](1) and [Cu(II)(saltrp)(bipy)](2) were synthesized and characterized. ► Crystal structure of 2 shows a square pyramidal coordination geometry CuN3O2 around Cu(II). ► CT-DNA binding studies revealed that the complexes bind to DNA in an intercalative mode. ► Oxidative and hydrolytic DNA cleavage studies show that 1 and 2 cleave DNA. ► The rate constants indicate that 1 and 2 enhance the rates of hydrolysis of phosphodiester bond of DNA backbone to the extent of (2.93–5.41) × 107.