untitled European Journal of Chemistry 4 (2) (2013) 157‐161 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2013 EURJCHEM DOI:10.5155/eurjchem.4.2.157‐161.752 European Journal of Chemistry Journal homepage: www.eurjchem.com Synthesis, characterization and catalytic activity of Cu(II), Co(II), Ni(II), Mn(II) and Fe(III) complexes of 4‐((3‐formyl‐4‐hydroxyphenyl)diazenyl)‐N‐(4‐ methyloxazol‐2‐yl) benzenesulfonamide Ahmed Imam Hanafy a,b,*, Ali Mostafa Ali Hassan b, Sayed Ahmed Shama c, Hamdy Khamees Thabet b,d, Hany Mohammad Zaky El‐alfy c a Chemistry Department, Faculty of Science, Taif University, 21985, Taif, Saudi Arabia b Chemistry Department, Faculty of Science, Al‐Azhar University, Nasr City, 11884, Cairo, Egypt c Chemistry Department, Faculty of Science Benha University, 13518, Benha, Egypt d Chemistry Department, Faculty of Science and Arts, Northern Border University, 91911, Rafha, Saudi Arabia *Corresponding author at: Chemistry Department, Faculty of Science, Taif University, 21985, Taif, Saudi Arabia. Tel.: +966.2.8322143; fax: +966.2.8322143. E‐mail address: ahmedih@yahoo.com (A.I. Hanafy). ARTICLE INFORMATION ABSTRACT Received: 17 February 2013 Received in revised form: 12 March 2013 Accepted: 20 March 2013 Online: 30 June 2013 KEYWORDS The sulfonamide derivative, 4‐((3‐formyl‐4‐hydroxyphenyl)diazenyl)‐N‐(4‐methyloxazol‐2‐ yl) benzenesulfonamide (FDMB), was synthesized and characterized. Additionally, its Cu(II), Co(II), Ni(II), Mn(II) and Fe(III) complexes were prepared and their structures were investigated by elemental analysis, thermal analysis and (IR, electronic and EPR) spectroscopy. The mode of binding indicates that the ligand binds to the metal ion through carbonyl oxygen and OH phenolic with displacement of its proton. The Co(II) complex was applied for the hydrolysis of nerve agent‐like compound, bis‐(p‐nitrophenyl) phosphate (BNPP). The results showed a significant rate enhancement of 2.5 million fold with respect to the auto‐hydrolysis of BNPP under the same conditions. EPR Hydrolysis Nitrophenol Sulfonamide Methyloxazol Phosphoester 1. Introduction Sulfonamide moiety has a vital functionality because of its wide varieties of reported biological [1,2] and pharmacological activities such as anticancer [3,4], carbonic anhydrase inhibitory [5,6], antibacterial [7,8], antimalarial [9], antitumor [10], antihypertensive [11], and anti‐inflammatory [12]. Sulfonamide has been also reported to possess good herbicidal [13] and corrosion inhibitory properties [14,15]. At the same time, N‐salicylideneamino acidato metal complexes with different organic ligands have been prepared, characterized [16‐18] then the chemical nuclease property of these metal complexes that intercalates into the DNA grooves [19] have been introduced. Some ternary salicylaldehyde‐amino acid Schiff base complexes of Cu(II) with 1,10‐phenanthroline and 2,2ʹ‐bipyridine exhibit antitumor activity as tumor chemo‐ therapeutic agents and tumor radio‐imaging [20]. It is well known that the phosphoester bond is considered as backbone of the pesticides and nerve agents. Hydrolytic chemistry can play very important role in degradation of phosphoester pesticides and nerve agents, including the G‐agents (Sarin and Salman) and the VX‐agent [21]. Recent efforts to design synthetic metalloenzymes and elucidate the mechanisms by which metal ions promote hydrolysis have focused primarily on metal complexes [22]. A large number of metal complexes have been synthesized in recent years as models of metallohydrolases, for the purpose of effective hydrolysis of phosphoesters such as DNA and nerve agent‐like compounds [23,24]. In this study, we prepared and characterized 4‐((3‐formyl‐ 4‐hydroxyphenyl)diazenyl)‐N‐(4‐methyloxazol‐2‐yl) benzene sulfonamide and its metal complexes. The Co(II) complex has been used as heterogeneous catalyst on the hydrolysis of phosphodiesters bis‐(p‐nitrophenyl)phosphate as a nerve agent like compound. 2. Experimental 2.1. Physical measurements Cu(II), Co(II), Ni(II), Mn(II) and Fe(III) ions were determined by complexometric titration using xylenol orange as indicator [25,26]. Carbon, hydrogen and nitrogen contents were determined at the Microanalytical Unit, Cairo University, Egypt. IR spectra of the ligand and its solid complexes were recorded in KBr disc on a Mattson 5000 FT‐IR spectrometer. The electronic spectra of the ligand and its solid complexes were recorded in DMSO in UV/Vis range (195‐1100) nm using Perkin Elmer Lambda 35 UV/Vis Spectrometer. Magnetic moments were determined using a Johnson Matthey balance at room temperature (25 °C) with Hg[Co(NCS)4] as a calibrant. The diamagnetic corrections for the ligand and the metal atoms were computed using Pascal's constants [27]. Thermal analysis measurements TGA were recorded on a Shimadzu thermo‐ gravimetric analyser model TGA‐50H, using 20 mg samples. The flow rate of nitrogen gas and heating rate was 20 mL/min and 10 °C/min, respectively. 158 Hanafy et al. / European Journal of Chemistry 4 (2) (2013) 157‐161 Table 1. Physical properties and elemental analysis of the synthesized metal complexes. Complex M.wt, g Color Yield, % Melting point, oC %C Calcd./Found %H Calcd./Found %N Calcd./Found %M Calcd./Found Cu(L‐H)2(H2O)3 887 Bluff 72 >300 45.9/45.9 3.6/4.3 12.6/12.2 7.1/7.5 Mn(L‐H)2 (H2O)6 931 Brown 65 >300 43.8/43.6 4.1/3.3 12.0/11.4 5.9/6.3 CoL‐H (Ac)MeOH.3H2O 589 Brown 75 >300 40.7/41.5 4.4/4.0 9.5/10.3 10.0/10.5 NiL‐H (Ac)MeOH.1.5H2O 562 Brown 73 >300 42.7/42.7 4.1/4.2 9.9/10.2 10.5/10.0 FeL‐H (OH)2(H2O)2 511 Black 70 176 39.9/40.1 3.7/3.8 10.9/10.9 10.9/11.0 The 1H NMR spectra were recorded in DMSO‐d6 using ovarian FT‐300 MHz spectrometer using TMS as internal standard. The mass spectrum of the ligand was recorded on a Shimadzu GC‐S‐QP 1000 EX spectrometer using a direct inlet system. The kinetic measurements for hydrolysis of phosphodiester were performed using Perkin Elmer Lambda 35 UV/Vis Spectrometer. 2.2. Synthesis of 4‐((3‐formyl‐4‐hydroxyphenyl)diazenyl)‐N‐ (4‐methyloxazol‐2‐yl)benzenesulfonamide (FDMB) Sulfamethoxazole (0.01 mol) was mixed with HCl (10 mL) and water (16 mL) and then digested on a water bath for 30 min. The sulfamethoxazole hydrochloride was cooled to 5 oC and diazotized with ice‐cold aqueous NaNO2 solution (5 g, 20 mL). A cold solution of salicylaldehyde (0.01 mol) dissolved in 10% NaOH solution (50 mL) was added to the cold diazonium salt solution with vigorous stirring. A red colour developed immediately and the stirring was continued for 1 h. The reaction mixture was kept overnight in a refrigerator, followed by 3 h at room temperature, and then acidified with dilute acetic acid. The yellow orange precipitate separated out. The precipitate was filtered, washed several times with water to remove excess acetic acid and water‐soluble materials, and finally dried in air. The crude product was washed with hexane to remove any tarry materials, dried in vacuum and recrystallized from methanol to yield yellow prismatic crystals of Ligand FDMB. 4‐((3‐Formyl‐4‐hydroxyphenyl)diazenyl)‐N‐(4‐methyloxazol‐ 2‐yl)benzenesulfonamide (FDMB): Color: Light brown. Yield: 70%. M.p.: 204 oC. FT‐IR (KBr, , cm‐1): 3072 (OH), 1658 (C=O), 1614 (C=N), 1401 (SO2), 3420 (NH), 1476 (N=N). 1H NMR (300 MHz, DMSO‐d6, δ, ppm): 2.31 (s, 3H, CH3), 6.19 (s, 1H, CH‐ oxazole), 7.20‐8.03 (m, 7H, Ar‐H), 8.22 (s, 1H, CHO), 10.37 (s,1H, NH), 11.64 (s, 1H, OH). MS (EI, m/z (%)): 386 (M+, 12). 2.3. Preparation of metal complexes Metal chlorides (Fe(III) and Mn(II)) or metal acetates (Cu(II), Co(II), Ni(II)) (1.0 mmol) were dissolved in ~60 mL methanol. This solution was added dropwise to (0.2 mmol) of the ligand dissolved in ~40 mL methanol with continues stirring. The mixture was heated under reflux for 2.0 hrs. The precipitate was formed and filtered off, washed with diethyl ether and finally dried in an open air. The physical properties of the metal complexes are listed in Table 1. 2.4. Kinetic reactions for phosphoester hydrolysis The hydrolytic reaction was performed using solid complexes as heterogeneous catalysts in 50 mL of N‐2‐ hydroxyethylpiperazine‐N’‐2‐ethanesulfonic acid (HEPES) buffer solution (50 mmol, pH = 8.0). The substrate bis‐(p‐ nitrophenyl) phosphate (BNPP), dissolved in 50 mmol of HEPES buffer solution (pH = 8.0) was added to the previous solution. The heterogeneous mixture has been stirred using a magnetic stirrer. The mixture was centrifuged and the absorbance of the supernatant has been measured using spectrophotometer at 405 nm. The increase in absorbance at 405 nm was followed with time. The reference cell contains substrate without the complex has been used to correct the background hydrolysis. Experiments were repeated three times to ensure accuracy. 3. Results and discussion The structure of the organic ligand FDMB was elucidated on the basis of its analytical and spectral data. The infrared spectrum of FDMB reveals absorption bands at 1658, 1476, 1401 and 1614 cm‐1 corresponding to νC=O, νN=N, νSO2, and νC=N, respectively. The 1H NMR of this compound showed signal at δ 2.31 (s, 3H, CH3), 6.19 (s, 1H, CH‐oxazole), 7.20‐8.03 (m, 7H, Ar‐ H), 8.22 (s, 1H, CHO), 10.37 (s, 1H, NH) and 11.64 (s, 1H, OH). All these data together with the mass spectrum which showed a molecular ion peak at m/z = 386, and base peak at m/z = 121 suggest the proposed structure of the ligand FDMB (Scheme 1). S O ON H O N N N OH O 4‐((3‐Formyl‐4‐hydroxyphenyl)diazenyl)‐N‐(4‐methyloxazol‐2‐yl)benzene sulfonamide (FDMB). Scheme 1 3.1. IR spectra By comparing the IR spectral data of the ligand and their metal ion complexes, one finds that the whole metal ions bind to the organic ligand through phenolic OH group with the liberation of its hydrogen atom and the oxygen atom of the aldehydic group. This assumption is supported by disappearance of the νOH band which was appeared at 3072 cm‐ 1. At the same time the carbonyl band νCO was shifted to higher wavenumber. Both Co and Ni complexes have two bands at (1320‐1340) and (1515‐1520) cm‐1 corresponding to acetate group νsymCOO and νasymCOO. On the other hand the negative test for the chloride ion in the iron complex indicates the liberation of two chloride ions with the formation of two hydroxo Fe3+ compound due to a partial hydrolysis of FeCl3. The band observed at 950 cm‐1 which is obscured in the spectra of the ligand and the above mentioned complexes may attribute to OH hydroxo [28]. The proposed structures also were supported by existence of C=N, SO2, NH and N=N bands at their positions in the ligand spectrum without changes (Table 2) which indicate that these functional groups are not participating in the binding. The band appears at (3480‐3490) cm‐1 was attributed to water molecules in all metal complexes. The mode of binding in these metal complexes reveals that the copper and manganese coordinate to the ligand FDMB in the ratio of 1:2 (M:L) where M = Cu or Mn and L = FDMB. Whereas the coordination of the cobalt, nickel and iron complexes are founded to be in the mole ration of 1:1 (M:L). Hanafy et al. / European Journal of Chemistry 4 (2) (2013) 157‐161 159 Table 2. IR bands of the ligand and its metal complexes. Compound νC=O νC=N νN=N νC‐O νSO2 νNH Ligand 1658 1614 1476 1092 1401 3420 Cu(L‐H)2(H2O)3 1795 1611 1471 1103 1398 3423 Mn(L‐H)2 (H2O)6 1795 1618 1467 1109 1396 3424 CoL‐H (Ac)MeOH. 3H2O 1791 1620 1468 1101 1398 3423 NiL‐H (Ac)MeOH. 1.5H2O 1865 1616 1474 1101 1397 3421 FeL‐H (OH)2(H2O)2 1796 1618 1468 1109 1397 3419 3.2. Electronic and EPR spectra The electronic spectrum of [CoL‐H (Ac)MeOH].3H2O complex shows two bands at 380 and 453 nm assignable to 4T1g(f) → 4A2g(f) transitions The magnetic moment value 4.5 B.M. is in conformity with tetrahedral structure. The magnetic moment measurement of the Ni(II) complex [NiL‐H (Ac)MeOH].1.5H2O at room temperature shows that the nickel complex is a diamagnetic. The band appears at 450 nm with the diamagnetic nature corresponding to a square planar geometry around the Ni(II) ion. The manganese complex [Mn(L‐ H)2](H2O)6 shows intense absorption band at 340 nm assigned to ligand centered transition while two weak transitions are observed at 375 nm and 460 nm may be referred to a combination of MLCT and d‐d transition (4A1→4T1), suggesting tetrahedral geometry of the complex. The magnetic moment value of the manganese(II) complex 5.6 BM may also support a high spin tetrahedral complex [29]. The magnetic moment (1.9 BM) of the Cu(II) complex [Cu(L‐H)2](H2O)3 at room temperature corresponds to one unpaired electron [30]. The electronic spectrum of the copper (II) complex recorded in ethanol reveals an absorption band at 495 nm. This band can be attributed to d‐d transition (2B1g→2A1g), which supports square‐planar geometry around the metal ion [31]. The bands at 280 and 370 nm can be assigned to a CT band from filled orbitals Cu(II) to the anti‐bonding π* orbitals of the ligand [32]. The EPR spectrum of the complex [Cu(L‐H)2](H2O)3 was recorded as a polycrystalline sample at room temperature. The spectrum of the complex exhibits a single anisotropic broad signal. The analysis of the spectrum (Figure 1) gives the g|| = 2.1212 and g = 2.0811. These values indicate that the ground state of Cu(II) is predominately dx2‐y2, which supports a square planar structure [33,34]. The observed g|| value for the copper(II) complex is less than 2.3, thus, indicating that the bonds between the organic ligand and copper ion have a covalent character more than the ionic one. According to Hathaway and Billing [35,36] the G = (g|| − 2)/(g − 2), which measures the exchange interaction between the copper centers in a polycrystalline solid has been calculated and found to be less than 4.0. This value indicates to a considerable exchange interaction in solid complex. Figure 1. EPR spectrum of Cu(II) complex. 3.3. Thermal analysis The thermograms TGA confirms the amount of solvent inside and outside the coordination sphere and gives some information about the stability of this compound. The thermograms of all metal complexes (Figure 2) have two or three decomposition stages from 25 to 1000 °C. These stages involved mass loss of ~75 %. TGA of the all prepared complexes show first stages from 25‐95 °C corresponds to removal of water molecules outside the coordination sphere with weight loss calc. = 4.8‐11.6%, found = 5.2‐11.0 % indicating to 1.5‐6.0 molecules of water. The second inflection point stars at around 400 °C with starting the decomposition of the metal complexes with weight loss of about 68‐70% of the whole complex leaving the metallic residue for metal oxide or metal carbide. The elemental analysis, IR and electronic spectra with thermal analysis suggest the complexes structures given in Scheme 2‐4. Figure 2. TGA for Cu(II) (dark brown), Co(II) (reddish brown), Ni(II) (orange), Mn(II) (green) and Fe(III) (buff) complexes. M = Co, X = 3 and M= Ni, X = 1.5 Scheme 2 3.4. Hydrolysis of phosphodiester by Co(II) complex Since phosphate diesters are generally highly resistant toward the hydrolysis cleavage, therefore, catalysts reactive enough to hydrolyze the target bonds rapidly under physiological conditions represent a major challenge. 160 Hanafy et al. / European Journal of Chemistry 4 (2) (2013) 157‐161 M = Mn, X = 6 and M = Cu, X = 3. Scheme 3 The prepared complexes in this study have been used to investigate the hydrolysis of phosphoester bis‐(p‐nitrophenyl) phosphate (BNPP) in an aqueous medium and under normal conditions. The Co(II) complex showed a significant activity while the other metal complexes showed negligible activities. In order to establish the rate law for the heterogeneous bis‐(p‐ nitrophenyl)phosphate hydrolysis by the Co(II) complex [CoL‐ H(Ac)MeOH].3H2O, the rate is further determined at various BNPP concentration values (Figure 3) at pH = 8.0 and 25 °C. The rate of BNPP hydrolysis is found to be linear in the beginning and reaching saturation at high concentration of the substrate BNPP, suggesting the possibility of a pre‐equilibrium kinetics. This kinetic can be described as the binding of the substrate BNPP (S) to the metal center in the Co(II) complex to form the intermediate Co(II) complex‐S, followed by the conversion of the bound BNPP into products. The first order rate constant kcat and the maximal velocity Vmax were found to be 3.1×10‐4 s‐1 and 0.4 mM/min, respectively. The hydrolysis of BNPP with different concentrations of the catalyst [CoL‐H (Ac)MeOH].3H2O (Figure 4) showed linear trend with first order rate constant 3.1×10‐5 s‐1. The auto‐hydrolysis of BNPP is extremely slow with rate constant Ko of 1.1×10‐11 s‐1 at pH = 7.0 and 25 °C [37] Thus, the hydrolysis of BNPP here shows a significant rate enhancement of 2.8 million fold with respect to the autohydrolysis of BNPP under the same conditions. Scheme 4 Figure 3. Hydrolysis of BNPP using Co(II) complex in aqueous medium at pH = 8 and 25 °C. Figure 4. Hydrolysis of BNPP using different concentration of Co(II) complex in aqueous medium at pH = 8 and 25 °C. 4. Conclusions The antibacterial sulfonamide was used in the preparation of the novel ligand FDMB. The metal complexes of this new ligand were also prepared and fully characterized by different tools to investigate their chemical structures. The electronic spectral data showed that all metal complexes are either tetrahedral or square planner. The catalytic activity of the prepared complexes was investigated towards the hydrolysis of BNPP and the Co(II) complex showed the highest activity. 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