Spectrochimica Acta Part A 93 (2012) 180–184 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy j our na l ho me p age: www.elsevier.com/locate/saa Binding interaction of 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole with bovine serum albumin J. Jayabharathi ∗ , V. Thanikachalam, K. Jayamoorthy, N. Srinivasan Department of Chemistry, Annamalai University, Annamalainagar, Tamilnadu 608002, India a r t i c l e i n f o Article history: Received 9 February 2012 Received in revised form 24 February 2012 Accepted 7 March 2012 Keywords: Benzimidazole BSA XRD Quenching FRET a b s t r a c t A promising benzimidazole derivative 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole (MBTBI) has been synthesized and characterized by single crystal XRD, NMR, mass and IR spectral techniques. The mutual interaction of this benzimidazole derivative (MBTBI) with bovine serum albumin (BSA) was investigated using solution spectral studies. The fluorescence quenching mechanism of BSA by MBTBI was analyzed and the binding constant has been calculated. The binding distance between these two was obtained based on the theory of Forester’s non-radiation energy transfer (FRET). The effect of some common ions on the binding constant was also examined. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In recent years, organic heterocyclic compounds such as pyri- dine, oxadiazole, pyrazine and imidazole have received immense attention owing to their potential use in molecular designs tar- geting biological and electronic applications. Imidazole is quite attractive due to their biological activities [1–3] and sensor appli- cations [4–8]. Fused imidazole derivatives such as benzoimidazoles and phenanthroimidazoles [9–13] have also been used in the fabrication of light-emitting devices, employing them as electron- transporting layer and as sensitizers in dye-sensitized solar cells [14–18]. Functional imidazoles have been mainly developed due to their wide optical absorption, bright luminescence and bipo- lar transport characteristics. There is a growing interest in the design and synthesis of imidazoles enriched with functional chro- mophores to enhance their optical and charge transport properties. BSA has been studied as a model protein due to its structural homology with human serum albumin [19]. There are three types of fluorophores in BSA, namely tryptophan residues (Trp), tyro- sine residues (Tyr), and phenylalanine residues. Although both Trp and Tyr residues can be excited at 280 nm, energy transfer effect at 280 nm mostly comes from Trp residues [20]. At the excitation wavelength of 280 nm, BSA exhibits a strong fluorescence emission with a peak at around 340 nm [21]. Serum albumins are the most abundant proteins in plasma [22]. As the major soluble protein con- stituents of the circulatory system, they have many physiological ∗ Corresponding author. Tel.: +91 9443940735. E-mail address: jtchalam2005@yahoo.co.in (J. Jayabharathi). functions [23]. Among them, BSA has a wide range of functions involving the binding, transport, and delivery of fatty acids, por- phyrins, bilirubin, steroids, etc. It is home to specific binding sites for metals, pharmaceuticals and dyes [24]. BSA has two tryptophan moieties at positions 134 and 212 as well as tyrosine and pheny- lalanine [25], the protein intrinsic fluorescence is due to aromatic amino-acid residues. Recently we have reported the interaction of imidazole with bovine serum albumins [26–30]. In the present work, the fluorescence quenching technique is applied to study the interaction between benzimidazole derivative [MBTBI] and BSA. 2. Experimental 2.1. Materials and methods All BSA solution was prepared in the Tris–HCl buffer solu- tion (0.05 mol L -1 Tris, 0.15 mol L -1 NaCl, pH 7.4) and it was kept in the dark at 303 K. Tris base (2-amino-2-(hydroxymethyl)-1,3- propanediol) had a purity of not less than 99.5% and NaCl, HCl and other starting materials were all of analytical purity and doubly distilled water was used throughout. 2.2. Optical measurements NMR spectra have been recorded for the benzimidazole derivative [MBTBI] on a Bruker 400 MHz instrument. The ultraviolet–visible (UV–vis) spectra have been measured on UV–vis spectrophotometer (Perkin Elmer, Lambda 35) and corrected for background due to solvent absorption. Photoluminescence (PL) spectra have been recorded on a (Perkin Elmer LS55) fluorescence 1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2012.03.018