Surfactant–cobalt(III) complexes: Synthesis, critical micelle concentration (CMC) determination, DNA binding, antimicrobial and cytotoxicity studies R. Senthil Kumar a , S. Arunachalam a, * , V.S. Periasamy b , C.P. Preethy b , A. Riyasdeen b , M.A. Akbarsha b a Department of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India b Department of Animal Science, Bharathidasan University, Tiruchirappalli 620 024, India article info Article history: Received 4 June 2008 Received in revised form 17 September 2008 Accepted 18 September 2008 Available online 30 September 2008 Keywords: Surfactant–metal complexes DNA binding Antibacterial activity Antifungal activity Cytotoxic activity abstract A new class of surfactant–cobalt(III) complexes, cis-[Co(bpy) 2 (C 11 H 23 NH 2 )Cl] 2+ (1) and cis- [Co(phen) 2 (C 11 H 23 NH 2 )Cl] 2+ (2) (bpy = 2,2 0 -bipyridyl, phen = 1,10-phenanthroline), have been synthe- sized and characterized. The critical micelle concentration (CMC) values of these complexes in aqueous solution were obtained from conductance measurements. The specific conductivity data (at 298, 308, 318 and 328 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization ðDG 0 m ; DH 0 m and DS 0 m Þ. The interaction between these complexes and calf thymus DNA in aqueous solution was investigated adopting electronic absorption spectroscopy, emission spectros- copy and viscosity measurements. Results suggest that the two complexes can bind to DNA via groove binding, van der Waals interactions and/or electrostatic interactions. The complexes showed moderate antibacterial and antifungal activities against certain selected microorganisms. The cytotoxic activity of the complexes on HBL-100 human breast cancer cells was determined adopting MTT assay and specific staining techniques, which revealed that the viability of the cells thus treated was significantly decreased and the cells succumbed to apoptosis as seen in the changes in the nuclear morphology and cytoplasmic features. Furthermore, the influence of complexes on normal cell lines from green monkey kidney was also determined and the results indicate that the effect is small on inhibition of viability. Ó 2008 Elsevier Inc. All rights reserved. 1. Introduction The interaction of transition metal complexes with DNA has long been a subject of intensive investigation with the perspective of development of newer materials for application in biotechnol- ogy and medicine. These investigations have resulted in the syn- thesis of many new metal complexes, which bind to DNA by non-covalent interactions such as electrostatic binding, groove binding and intercalative binding [1,2]. The main goal of cancer therapy is to attain the maximum ther- apeutic damage to tumor cells with the minimum concentration of the drug. There have been a number of reports highlighting the use of transition metal complexes as anticancer agents [3–5]. Among the metal complexes that have been studied, cobalt complex con- taining 1,10-phenanthoroline/2,2 0 -bipyridine is of interest because of its biological activities and ability to bind to DNA [6,7]. Surfactants, sometimes called surface-active agents, are among the most versatile chemicals available. These are amphiphilic mol- ecules consisting of a hydrophilic head group and a hydrophobic (lipophilic) tail and are, thus, able to interact with both polar and non-polar compounds. Accordingly, surfactants are often classified as non-ionic and ionic (cationic, anionic or zwitterionic). Cationic surfactants offer a few additional advantages over the other classes of surfactants. These substances, besides their surface activity, show antibacterial properties and are used as cationic softeners, lubricants, antistatic agents, etc. [8]. In the past decades, the inter- actions between DNA and cationic surfactants have attracted im- mense interest in the context of separation and purification of DNA [9]. While a large number of studies have been dedicated to interac- tion between DNA and the conventional surfactants, no report on the interaction of DNA with metallosurfactants is available. Metal- losurfactant complexes represent a new class of materials in which the polar headgroup of the surfactant molecule contains a metal complex portion as an integral structural component. There are only a few reports [10–12] on the synthesis, isolation and charac- terization of surfactant transition metal complexes, whereas there are numerous reports on the formation and study of such surfac- tants in solution without isolation. We have been interested in the synthesis and micelle forming properties of cobalt(III) com- plexes containing lipophilic ligands [13–15]. In spite of the greatest effort and success in the study of metallosurfactants of cobalt(III) complexes, such complexes still attract much attention due to the relative simplicity of their synthesis and their interesting prop- erties. To the best of our knowledge no previous study to find the 0162-0134/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jinorgbio.2008.09.010 * Corresponding author. Tel.: +91 431 2407053; fax: +91 431 2407043. E-mail address: arunasurf@yahoo.com (S. Arunachalam). Journal of Inorganic Biochemistry 103 (2009) 117–127 Contents lists available at ScienceDirect Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio