The structural characterization and DNA binding of pyridyl-azo-acetylacetonato complexes of zinc(II), cadmium(II) and mercury(II) Paramita Dutta a , Sudipa Mondal a , Suman Roy a , Elena Lopez-Torres b , Chittaranjan Sinha a,⇑ a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India b Departamento de Química Inorgánica, c/Francisco Tomás y Valiente, 7, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain article info Article history: Received 7 July 2014 Accepted 1 January 2015 Available online 22 January 2015 Keywords: Pyridyl-azo-acetylacetonato Zinc triad Structure and spectra DNA binding DFT computation Molecular docking abstract 3-(2-(Pyridin-3-yl)hydrazono)pentane-2,4-dione (L) has been reacted with MX 2 (M = Zn(II), Cd(II), Hg(II) and X = Cl  ,I  , OAc  , NO 3  ,N 3  ) and the complexes [ML 2 X 2 ] have been spectroscopically characterized. The distorted tetrahedral structure of [ZnL 2 Cl 2 ] has been confirmed by single crystal X-ray crystallogra- phy where L serves as monodentate pyridyl-N donor ligand. The ligand, L and the complexes, [ML 2 X 2 ], are emissive and life time close to nano second. The DNA binding of L and [ML 2 X 2 ] has been considered and shows that the binding constant (K b ) lies 6.15  10 4 M 1 to 4.55  10 5 M 1 . Due to solubility problem and appearance of colloidal feature with DNA solution at experimental condition some of the complexes could not be studied and the binding efficiency decreases following the order [ZnL 2 X 2 ] > [CdL 2 X 2 ]> [HgL 2 X 2 ]. [ML 2 (N 3 ) 2 ] shows highest binding efficiency. Molecular docking of DNA with L and [ZnL 2 Cl 2 ] suggest partly intercalated and hydrogen bonded interaction with heterocyclic bases (adenine, cytosine, thymine). Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Metal complexes may bind DNA both by coordination and through intercalation of the attached aromatic ligand. This field has received attention in the research of chemistry and biology [1–5]. The binding of the metal complexes affects the replication and transcription of DNA and ultimately leads to the cell death. The toxicity of metal ions mainly heavy/soft metals is of intense interest in this respect. Metal induced toxicity is well reported in the literature [6]. Over the past few years, an intensive effort has been focused to develop metal-based drugs with improved clinical effectiveness, reduced toxicity and broader spectrum of activity than that of cisplatin [7,8]. Heterocyclic compounds have valuable properties such as chemotherapeutic agents [3], dyestuffs [9,10], co-polymer [11] etc. Metallo-heterocycles (metal complexes of heterocycles) develop exciting chemistry and have been used in catalysis, redox reactions, photoactivity, organic synthesis, drugs etc. [12–16]. Pyridine and its derivatives are functionalized so that the ligands may be coordinated to the metal ions that may influ- ence the optical, electrochemical, catalytic, biological properties of each other. 3-Aminopyridine derivatives show biomedical activity and one of the derivatives, 3-aminopyridine-2-carboxalde- hyde thiosemicarbazone is a ribonucleotide reductase inhibitor [17,18]. This has encouraged us to synthesize a new compound, 3-(2-(pyridin-3-yl)hydrazono)pentane-2,4-dione (L), which reacts with MX 2 (M = Zn(II), (1); Cd(II), (2); Hg(II), (3) and X = Cl  (a), I  (b), NO 3  (c), OAc  (d), N 3  (e)) in methanol to synthesize [ML 2 X 2 ] complexes. All these compounds are characterized by spectro- scopic data. The structure has been confirmed by X-ray crystallog- raphy for [ZnL 2 Cl 2 ]. The binding efficiency of metal complexes with DNA has been investigated by electronic absorption spectral tech- nique. DFT computation of an optimized geometry of a complex, [ZnL 2 Cl 2 ] has been used to explain the spectral properties and has been extended to other isoelectronic and isostructural com- plexes. The molecular docking trial has been carried out to exam- ine the binding of ligand and one of the complexes, [ZnL 2 Cl 2 ], with DNA and supports the experimental observation. 2. Experimental 2.1. Materials 3-Aminopyridine, MCl 2 , M(NO 3 ) 2 , M(OAc) 2 (M = Zn(II), Cd(II), Hg(II)); NaN 3 were purchased from Merck, India. Hepes buffer and ZnI 2 were purchased from Himedia; CdI 2 and HgI 2 were http://dx.doi.org/10.1016/j.poly.2015.01.001 0277-5387/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Fax: +91 33 2414 6584. E-mail address: c_r_sinha@yahoo.com (C. Sinha). Polyhedron 89 (2015) 203–212 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly