International Journal of Scientific and Research Publications, Volume 4, Issue 4, April 2014 1 ISSN 2250-3153 www.ijsrp.org Binding of Natural Antioxidant, Curcumin with Metal- Salen Complexes T. Rajendran 1,2 , K. Senthil Murugan 3 , G. Balakrishnan 3 , C. Karthikeyan 3 , S. Thanaraj 4 , G. Arunkumar 4 , V. K. Sivasubramanian 5 , M. Ganesan 5 , K. Vijaya 1 1 Professor, Department of Chemistry, PSNA College of Engineering & Technology, Dindigul-624 622, India. 2 Associate Professor and Head (Rtd), Department of Chemistry, Vivekananda College, Tiruvedakam West, Madurai 625 234, India 3 Research Scholar, Department of Chemistry, Vivekananda College, Tiruvedakam West, Madurai 625 234, India. 4 P.G. Student, Department of Chemistry, Vivekananda College, Tiruvedakam West, Madurai, 625 234, India. 5 Associate Professor, Department of Chemistry, Vivekananda College, Tiruvedakam West, Madurai 625 234, India Abstract- Six transition metal-salen complexes (metal = Fe, Mn and Cr) 1-6 have been synthesized and characterized using different spectroscopic and electrochemical techniques. The binding studies of natural antioxidant, curcumin with the complexes (1-6) have been carried out by electronic absorption spectroscopic technique. The substantial shift in the absorption maximum of complexes (1-6) when they bind to curcumin indicated that there was a strong binding between them. The binding constant calculated ranges from 20 to 2.46 X 10 4 M -1 s -1 . To the best of our knowledge, this is the first report for studying binding nature of curcumin, the natural antioxidant with these biologicallly relevant metal-salen complexes. Index Terms- metal-salen complexes; anti-oxidant; binding constant; curcumin; UV-vis titration. I. INTRODUCTION alicylidene-ethylenediamines, commonly known as salens, can stabilize the high oxidation states of most of the transition metals and even some p-block metals in various oxidation states and their complexes are capable of oxidizing a variety of organic compounds [1,2]. Because of their easily tunable chiral environment, metal-salen derivatives are efficient asymmetric catalysts for sulfoxidation [3-5], epoxidation [6], epoxide ring opening [7], hydrolytic kinetic resolution [8], hetero Diels-Alder reactions [9] etc., Mn(salen) complexes are widely utilized as highly reactive epoxidation catalysts [10-13]. Fe(salen) complexes serve as nonheme enzyme models to explore the oxidizing intermediates when activated by chemicals [14]. Recently Mellah et al. reported the efficient electropolymerized chromium–salen complexes for heterogeneous asymmetric catalysis [15]. Fujii et al. have made a detailed mechanistic study using sterically hindered manganese- salen complex as a model system to explore the structure– reactivity relationships for the high catalytic activity of the epoxidation catalyst, Mn(III)-salen [16]. As a principal curcuminoid, curcumin derived from the plant Curcuma longa, is a gold-colored spice commonly used for hundreds of years in Asian countries, not only for health care but also for the preservation of food and as a yellow dye for textiles [17]. Since the time of Ayurveda (1900 bc) turmeric has been used as chemotherapeutic agent for a wide variety of diseases including those of the skin, pulmonary, and gastrointestinal systems, aches, pains, wounds, sprains, and liver disorders. From the past five decades, extensive research has come to a conclusion that most of these activities associated with turmeric, are due to curcumin. Because of antioxidant nature of curcumin [18-19], it serves as anticancer drugs [20-23], anti-inflammatory [24,25], anti HIV [26], antibacterial and antifungal activities and thus has a potential against various malignant diseases, diabetes, allergies, arthritis, Alzheimer’s disease [27-29], and other chronic illnesses. These effects are mediated through the regulation of various transcription factors, growth factors, inflammatory cytokines, protein kinases, and other enzymes. From a chemical stand point, the biological activities of curcumin are derived from the antioxidant property of the methoxyphenol group and the action of the aryl group in diketone [30-32]. β-diketones are present as the enol form, and form chelates with different transition metal ions, for example, Fe 2+ , Fe 3+ , Cu 2+ and Zn 2+ etc., [33-39]. It is desirable to study the nature of interaction between catalytic metal – salen complexes with curcumin. As far as we know, there is no literature available on the catalytic role of biologically relevant metal-salen complexes for the binding of biologically important curcumin (polyphenols). To accomplish this we have synthesized various metal– salen complexes (1-6). II. EXPERIMENTAL METHODS 2.1 Materials and Methods All the chemicals were purchased from Aldrich and used as received. Some of them were from Merck. All the solvents and reagents, if necessary, were purified before use as per the standard procedures [40]. Complexes 1-6 were prepared from the previously published reports [41-43]. Electronic absorption spectra were measured with a JASCO V-530 UV-vis. Spectrophotometer. Thermostated temperature bath was used to maintain the required temperature. The infrared spectra of the complexes were recorded in a JASCO FT/IR-430 spectrophotometer in KBr pellet medium. Electrochemical measurements were carried out on a potentiostat-galvanostat (CH Instruments Electrochemical Analyzer) using a 3 mm 2 surface glassy carbon electrode as the working electrode, a platinum wire as the counter electrode, and a standard calomel electrode as the reference electrode. The acetonitrile solution of complexes (1 mM) along with the electrolyte (0.10 M of sodium S