Original article Antibacterial and DNA interaction studies of zinc(II) complexes with quinolone family member, ciprofloxacin Mohan Patel * , Mehul Chhasatia, Pradhuman Parmar Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, 388 120 Gujarat, India article info Article history: Received 13 March 2009 Received in revised form 23 July 2009 Accepted 15 October 2009 Available online 29 October 2009 Keywords: Zn(II) complexes Ciprofloxacin DNA interaction Intrinsic binding constant (K b ) MIC abstract DNA binding and cleavage characteristics of Zn(II) complexes have been investigated. The DNA inter- action property of the complexes has been investigated using absorption spectra, viscosity measure- ments, as well as gel electrophoresis studies. Intrinsic binding constant (K b ) has been estimated under similar set of experimental conditions. Absorption spectral study indicate that the Zn(II) complexes intercalate between the base pairs of the DNA tightly with intrinsic binding constant in the range of 1.0  10 4 –4.0  10 4 M 1 in phosphate buffer. The proposed DNA binding mode supports the large enhancement in the relative viscosity of DNA on binding. The antimicrobial activity of all the ligands and metal complexes has been examined by minimum inhibitory concentration method (MIC). Ó 2009 Elsevier Masson SAS. All rights reserved. 1. Introduction Fluoroquinolones represent an important group of chemother- apeutic compounds, which exhibit high antibacterial activities. An efficient representative of this group, ciprofloxacin (Cip ¼ C 17 H 18 FN 3 O 3 , 1-cyclopropyl-6-fluoro-4-oxo-7-(1-piperazinyl)-1,4- dihydroquinoline-3-carboxylic acid) [1] is widely used in clinical practice as a broad spectrum antimicrobial agent [2]. Quinolones comprise a group of well-known antibacterial agents and the first members being in clinical practice over 40 years [3,4]. They can act as antibacterial drugs that effectively inhibit DNA replication and are commonly used in treatment of many infections [5,6]. Studies on the biological properties of quinolone-metal complexes have been focused on the interaction with DNA, antibacterial activity tests on diverse microorganisms, cytotoxicity and poten- tial antitumor activity [7–15]. In this context, we have studied the interaction of Zn(II) with ciprofloxacin, in the presence of nitrogen-donor ligands such as bpdmed(A 1 )/mtma(A 2 )/apq(A 3 )/ bpeed(A 4 )/dcnd(A 5 )/dpeda(A 6 ). The coordination behaviors of the ligands towards transition metal salts have been investigated and the data have been correlated with their elemental analysis, thermal properties, magnetic measurements, IR and their DNA binding and cleavage behavior were also being examined using spectroscopic techniques (UV spectroscopy), viscosity measure- ments and gel electrophoresis technique. The antimicrobial effi- ciency (MIC) of the compounds has been screened against five different microorganisms. 2. Results and discussion 2.1. 1 H NMR and 13 C NMR spectra of Schiff bases The 1 H and 13 C NMR spectra of the ligands were carried out in CDCl 3 /MeOD and reported along with the possible assignment. The 1 H NMR spectra of ligands exhibiting peaks at about 6.5–8.19 ppm were assigned to the aromatic protons. The singlet peak which appeared at 7.5 ppm was assigned to the azomethine proton (–CH]N–). In the 13 C NMR spectra, the peaks observed at about 105.9–135.4 and 128.5–143.0 ppm were assigned to aromatic and thiophene carbons respectively. Peaks observed at about 140.0– 150.9, 165.3–167.3ppm were assigned to C–N and C]N carbons respectively. 2.2. Spectroscopic studies of the mixed-ligand complexes 2.2.1. Infrared spectroscopy The prominent IR spectral data of the complexes are shown in Table 1 . The n(C]O) stretching vibration band appears at 1708 cm 1 for ciprofloxacin, where as for complexes it appear at 1615–1629 cm 1 ; this shift towards lower energy suggests that * Corresponding author. Tel.: þ91 2692226858x220. E-mail address: jeenen@gmail.com (M. Patel). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech 0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmech.2009.10.024 European Journal of Medicinal Chemistry 45 (2010) 439–446