Spectroscopic study of interaction of styrylcyanine dye Sbt and its derivatives with bovine serum albumin Eldar N. Kurtaliev n Samarkand State University, University blvd. 15, Samarkand 140104, Uzbekistan article info Article history: Received 21 December 2011 Received in revised form 24 February 2012 Accepted 26 March 2012 Available online 4 April 2012 Keywords: Styrylcyanine dyes Fluorescence Electronic absorption spectra Bovine serum albumin Binding constant abstract The spectral-fluorescent characteristics of styrylcyanine dye Sbt ((E)-2-(4-(dimethylamino) styryl)-3- methylbenzo[d]thiazol-3-ium iodide) and homodimers, dyes conjugated with two chromophores in aqueous solutions without and in the presence of bovine serum albumin (BSA), are studied. It is established that in the presence of BSA for dyes Dbt-5 and Dbt-10, an increase of the absorptivity, a slight broadening and the emergence of new band on the short wavelength range with l max ¼410 nm is observed; also hypsochromic shift of the absorption and fluorescence at 30 nm and 7 nm, respectively for the dye D-183 is observed. The intensity of the fluorescence emission fundamental band in all the studied dyes in the presence of BSA increases by 3.5 to 55 times. The binding constant (K) and number of binding sites (N) of studied dyes with BSA are determined. The dependence of the binding constants with BSA from the dipole moment of dye molecules is identified, which shows that in addition to the electrostatic attraction forces between molecules of styrylcyanine dyes with BSA, hydrophobic interactions are essential. It is shown that the aggregation of dye affects the processes of interaction of the dyes with the BSA. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Organic dyes are widely used as a working medium in dye lasers [1], in analytical chemistry to determine the various trace elements [2], in photodynamic therapy [3], tissue optics [4], analysis of cells [5]etc. Depending on the sphere of application of fluorophores their various properties: quantum yield [6] and photostability [7], pH dependence [8], fluorescence lifetime [9] are essential. In order to extend the applications the need to search for and synthesis of new organic dyes implies. In particular the search for new fluorescent probes and taps due to the increasing volume of laboratory testing and diagnosis of various diseases [10]. As fluorescent probes and markers for in vivo measurements cyanine dyes have been widely used in recent years [11,12], as well as their related class of compounds–styrylcyanine dyes [13–15]. The study of spectral-fluorescent properties of organic dyes conju- gated with two chromophores — homodimers — is of great interest for various applications [16], in particular as fluorescent probes in biomedical research [17,18]. Results on the interaction between the styrylcyanine dye Sbt and its homodimers with BSA by methods of absorption and fluorescence spectroscopy are presented in this paper. 2. Materials and experimental method Structural formulas of the studied dyes are listed in Table 1. Synthesis of the studied dyes was implemented by the Institute of Molecular Biology NAS of Ukraine, according to the methods described in [19,20]. Electronic absorption spectra were measured on a Specord 50 SA (Analytikjena, Germany) which allows measurement with an accuracy ( þ /  0.003 D) and resolution (0.3 nm) in the range of 190–1100 nm. Fluorescence spectra were measured on a homemade fluorescence measurement setup, assembled on the basis of mono- chromator MDR-12 (LOMO, Russia) with photomultiplier tube FEU- 100 (Russia). High brightness LEDs were used as an excitation source. BSA (‘‘Medpreparat’’, Konotop, Ukraine) was used as the protein. The bidistilled water was used as a solvent. Preparation of initial solutions of dyes was done by a volume–weight method. Working concentra- tions of 10 5  10 6 M solutions were prepared by diluting the stock solution. The magnitude of systematic error associated with inaccu- rate calibration and reference distributions with different wettability of the walls of dimensional dish does not exceed 1%. The concentra- tion of BSA (p) is defined by formula: p ¼ 1:45  D 280 0:74  D 260 (in mg/ml), where D 280 and D 260 — optical density of BSA solution at the wavelengths of the absorption at 280 nm and 260 nm [21]. Fluorescence titration by the method of Scatchard was carried out to determine the binding constants (K) and the number of binding sites (N) of studied dyes with BSA [22]. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2012.03.054 n Tel.: þ998906064398; fax: þ998662311586. E-mail address: kurtaliev@rambler.ru Journal of Luminescence 132 (2012) 2281–2287