Synthesis, spectroscopic and voltammetric studies of a novel Schiff-base of cysteine and saccharin Semiha Çakır a, * , Mustafa Odabas ßog ˘lu b , Ender Biçer c , Zehra Yazar a a Department of Chemistry, Faculty of Arts and Sciences, Gazi University, 06500 Teknikokullar-Ankara, Turkey b Department of Chemistry, Faculty of Arts and Science, Mehmet Akif Ersoy University, 15030 Burdur, Turkey c Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit-Samsun, Turkey article info Article history: Received 19 March 2008 Received in revised form 8 July 2008 Accepted 15 July 2008 Available online 23 July 2008 Keywords: Schiff-base Cysteine Saccharin Voltammetry Spectroscopy abstract In this study, a novel Schiff-base of cysteine and saccharin [(2R)-2-(1, 1-dioxo-1, 2-dihydro-1k6- benzo[d]isothiazol-3-ylideneamino)-3-mercapto-propionic acid] was synthesized and characterized by UV–Vis, FT-IR, 1 H NMR and elemental analysis. The voltammetric behaviour of Schiff-base was investi- gated on the static mercury drop electrode (SMDE) by using Square-Wave voltammetry (SWV) and Cyclic voltammetry (CV). The voltammograms of the Schiff-base gave three reduction waves in Britton–Robin- son buffer (pH 5.0–9.0) for the potential range from 0.0 to 1.4 V. The first reversible cathodic peak is due to reduction of the mercury thiolate, produced by the thiol group of Schiff-base which adsorbs at Hg elec- trode surface, to metallic mercury and free thiol. The second reduction peak may be assigned to the reduction of azomethine center (>C@NA) in the Schiff-base and the last peak may be related to the cat- alytic hydrogen reduction. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Cysteine is known as an active site in the catalytic activity of en- zymes known as cysteine protease. Many cysteine-containing nat- ural products exhibit important biological activities. There are also some studies on the synthesis and application of chemically mod- ified cysteines, especially on b-substituted cysteines, that outline better activities in antibiotics than cysteine itself [1]. Cysteine has also several pharmaceutical applications; namely, it is used in some antibiotics for the treatment of skin damages [2] and as a radio-protective agent [3]. It is also involved in the structure of vasopressin, as anti-diuretic hormone [4]. The detection of low molecular weight biological thiols has a great importance for diag- nosing and understanding disease states. Therefore, interaction be- tween cysteine and biological ligands is very important from the biological and pharmacological point of view. Also, the interaction of cysteine has vital importance as a model system for reactions of biological molecules with protein. Saccharin, [C 7 H 5 NO 3 S, also named 1,2-benzoisothiazol-3(2H)- on-1,1-dioxide or o-benzosulfimide] has been used as a non caloric sweetener [5], which is five hundred times sweeter than sugar. Large quantities of saccharin can cause cancer in laboratory ani- mals, such as rats. In 2003, the National Cancer Institute noted some evidence of an increased risk of bladder cancer in heavy users, particularly for those who heavily ingested the sweetener as a table top sweetener or through diet sodas [6]. Thus, the salts and complexes of saccharin have been exten- sively studied over the last several decades. Saccharin has been widely incorporated with variety of biologically active compounds. The saccharin anion is also an interesting polyfunctional ligand has several potential donor atoms [7]. Also, saccharin complexes have been reported to have superoxide dismutase-like behaviour (SOD) [8]. On the other hand, metal complexes of saccharin play a role in understanding human metabolic processes [9,10]. Cysteine is ac- tive in many functions of mitochondrial membranes [11], in mem- brane transport [12] and especially in enzyme catalysis [13]. It is known that monosaccharide bind is covalent to amino acids [14]. Binding an amino acid to a monosaccharide forms S-, O- or N- glycosides [15]. Sulfur-containing volatile compounds, thermally generated from cysteine in the presence of glucose, have been re- ported [16,17]. On the other hand, water, alcohols, thiols and amines additives to the carbonyl group have been rather exten- sively studied [18,19]. Çakır et al. have reported the results of stud- ies on interaction of cysteine with saccharin at pH 7.4 [20] and monosaccharides [21] in aqueous solution by voltammetric meth- ods. The detailed information about the voltammetric behaviour of cysteine has been declared at previous studies [22–25]. Moreover, the electrochemical behaviour of cysteine in the presence of some compounds or metals has been previously studied in our labora- tory by voltammetry and polarography [26–29]. In our previous study [20], the voltammetric analysis of the copper–cysteine sys- tem in the presence and absence of saccharin in the aqueous solu- 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.07.015 * Corresponding author. Tel.: +90 312 2021122; fax: +90 312 2122279. E-mail address: scakir@gazi.edu.tr (S. Çakır). Journal of Molecular Structure 918 (2009) 81–87 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc