Synthesis, characterization and the interaction of some new water- soluble metal Schiff base complexes with human serum albumin Mozaffar Asadi a,⇑ , Zahra Asadi a , Somaye Barzegar Sadi a , Leila Zarei a , Fatemeh Moosavi Baigi b , Zahra Amirghofran c a Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Islamic Republic of Iran b Department of Chemistry, Ferdowsi University of Mashhad, Mashhad 91779, Islamic Republic of Iran c Immunology Department, Shiraz University of Medical Sciences, Shiraz 71454, Islamic Republic of Iran highlights  The nature of the interaction of water soluble metal Schiff base complexes with HAS was investigated.  The complex binding did not induce any aggregation on HSA molecules.  The mechanism of binding of the complexes with HSA was dynamic.  The microenvironment around the tryptophan residues did not show obvious changes during the binding process.  Thermodynamic results indicated that the binding process was endothermic. graphical abstract Effect of water soluble Schiff base complex, [ZnL], on the fluorescence spectra of HSA (T = 298 K). c(HSA) = 1.0  10 5 mol dm 3 , investigated c[ZnL]) = 2.510 6  2.0  10 5 mol dm 3 . article info Article history: Received 14 August 2013 Received in revised form 13 October 2013 Accepted 17 October 2013 Available online 31 October 2013 Keywords: Schiff base Human serum albumin Fluorescence abstract Some new water-soluble Schiff base complexes of Na 2 [M(L)(H 2 O) n ]; (M = Zn, Cu, Ni, Mn) with a new water-soluble Schiff base ligand where L denotes an asymmetric N 2 O 2 Schiff base ligands; N,N 0 -bis(5-sul- fosalicyliden)-3,4-diaminobenzophenone (5-SO 3 -3,4-salbenz) were synthesized and characterized. The formation constants of the water soluble Schiff base complexes were calculated by Ketelaar’s equation. The theoretical molecular structure for the complexes was computed by using the HF method and the 6-311G basis set. The mechanism of binding of Na 2 [M(L)(H 2 O) n ] with human serum albumin (HSA) was studied by fluorescence spectroscopic technique. The results of fluorescence titration showed that the intrinsic fluorescence of HSA was quenched by the complexes; which was rationalized in terms of the dynamic quenching mechanism. The values of Stern–Volmer constants, quenching rate constants, binding constants, binding sites and average aggregation number of HSA have been determined. The ther- modynamic parameters, were calculated by van’t Hoff equation, indicate that the binding is entropy dri- ven and enthalpically disfavored. Based on the Förster theory of non-radiation energy transfer, the efficiency of energy transfer and the distance between the donor (Trp residues) and the acceptor (com- plex) were obtained. Finally, the growth inhibitory effects of the complexes toward the K562 cancer cell line were measured. Ó 2013 Elsevier B.V. All rights reserved. 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.070 ⇑ Corresponding author. Tel.: +98 711 613 7121; fax: +98 711 646 0788. E-mail addresses: asadi@susc.ac.ir, mozaffarasadi@yahoo.com (M. Asadi). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 118–129 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa