BSA binding and antimicrobial studies of branched polyethyleneimine–copper(II)bipyridine/phenanthroline complexes Gopalaswamy Vignesh a , Sankaralingam Arunachalam a,⇑ , Sivanandham Vignesh b , Rathinam Arthur James b a School of Chemistry, Bharathidasan University, Tiruchirapalli 620 024, Tamil Nadu, India b Department of Marine Science, Bharathidasan University, Tiruchirapalli 620 024, Tamilnadu, India highlights " Binding of some polymer–copper(II) complexes with bovine serum albumin. " Hydrogen bonding attraction plays a major role in the binding process. " Binding induces considerable amount of conformational changes in the protein. " These polymer–copper(II) complexes show anti bacterial and antifungal activities. graphical abstract The binding constant for the binding between polymer–copper(II) complex and BSA depend on the degree of coordination (x) of the copper complex units in the polymer back bone chain. article info Article history: Received 10 February 2012 Received in revised form 21 April 2012 Accepted 3 May 2012 Available online 12 May 2012 Keywords: Polymer–copper(II)bipyridine/ phenanthroline Bovine serum albumin Fluorescence Circular dichroism Antimicrobial abstract The interaction of two water soluble branched polyethyleneimine–copper(II) complexes containing bipyr- idine/phenanthroline with bovine serum albumin (BSA) was studied by, UV–Visible absorption, fluores- cence, lifetime measurements and circular dichroism spectroscopic techniques. The polymer–copper(II) complexes strongly quench the intrinsic fluorescence of BSA is the static quenching mechanism through hydrogen bonds and van der Waal’s attraction. The distance r, between the BSA and the complexes seems to be less than 2 nm indicating that the energy transfer between the donor and acceptor occurs with high probability. Synchronous fluorescence studies indicate the binding of polymer–copper(II) complexes with BSA mostly changes the polarity around tryptophan residues rather than tyrosine residues. The circular dichroism studies indicate that the binding has induced considerable amount of conformational changes in the protein. The complexes also show some antibacterial and antifungal properties. Ó 2012 Elsevier B.V. All rights reserved. Introduction Proteins are important chemical substances in our life and the major targets of many types of medicines in the body. Serum albu- mins are most abundant proteins in the circulatory system of a wide variety of organisms. They have important role in bioregula- tory functions like maintenance of the colloidal osmotic blood pressure and blood pH, in addition to this they serve as depot pro- teins and as transport proteins for a variety of endogenous and exogenous substances such as fatty acids, hormones and drugs [1,2]. Among the serum albumins, bovine serum albumin (BSA) is an attractive macromolecule frequently used in biophysical and biochemical studies because of its structural homology with human serum albumin (HSA), its availability, low cost and unusual 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.05.009 ⇑ Corresponding author. Tel.: +91 431 2407053. E-mail address: arunasurf@yahoo.com (S. Arunachalam). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 108–116 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa