Ni 2+ , Pt 4+ , Pd 2+ , and Mn 2+ Metal ions Complexes with Azo Derived from Quinolin-2-ol and 3-amino-N-(5-methylisoxazol-3-yl) Benzenesulfonamide: Synthesis, Characterization, Thermal Study ,and Antioxidant Activity

: Diazotization reaction between quinolin-2-ol and (2-chloro-1-(4-(N-(5-methylisoxazol-3-yl)sulfamoyl)phenyl)-2l4-diazyn-1-ium was carried out resulting in ligand-HL, this in turn reacted with the next metal ions (Ni 2+ , Pt 4+ , Pd 2+ , and Mn 2+ ) forming stable complexes with unique geometries such as (tetrahedral for both Ni 2+ and Mn 2+ , octahedral for Pt 4+ and square planer for Pd 2+ ). The creation of such complexes was detected by employing spectroscopic means involving ultraviolet-visible which proved the obtained geometries, fourier transfer proved the formation of azo group and the coordination with metal ion through it. Pyrolysis (TGA & DSC) studies proved the coordination of water residues with metal ions inside the coordination sphere as well as chlorine atoms. Moreover, element micro-analysis and AAS that gave corresponding outcome with theoretically counting outcome. ( 1 H & 13 C-NMR) and magnetic quantifications can also indicate the formation of ligand-HL and occurrence of coordination. Antioxidant activities of these compounds were evaluated against (DPPH) radical and were compared to the standard natural antioxidant, ascorbic acid. The findings showed that these compounds exhibit excellent radical scavenging activities


Introduction:
Azo dyes derived from aromatic amines and their mineral complexes are characterized by applicability in multi usages.Furthermore, such compounds have special interest in many researches, this contributes to their applications as textile dyes, pharmaceutical materials and indicators. 1 Azo-dyes have biological activities such as antibacterial, antifungal, anti-HIV and antitumor, so they have immense importance in medicinal chemistry. 2Furthermore, they have important roles in food and analytical chemistry. 3mong these compounds, heterocyclic azo-dyes and their metal complexes can be involved in biological reactions like nitrogen fixation and RNA inhibition, in cosmetics as well as in non-linear optics protein synthesis. 4,5Sulfa compounds are well known as useful antibiotics in the assorted microbial contagion treatment [6][7][8] Nevertheless, the high applications of these compounds stimulate allergic side effects to many body organs 9,10 as well as lymphadenopathy, hepatotoxicity, and haematological disorders 11 .In order to beat such quandaries and to make efficient drugs, new functionalized sulfonamide derivatives and their transition metal complexes [12][13][14][15] were employed in clinical trials.Metal sulfonamide complexes were more effective than the drugs from which they come.Also, the azo dyes have been testified to display diversity in bio-vitality, involving antiinflammatory, antibacterial, and antiviral 15 activities.Sulfamethoxazole (SMX), a sulfonamide drug has a structural analoque of p-aminobenzoic acid that inhibits the synthesis of intermediary di hydro folic acid from its precursors.It is a bacteriostatic antibiotic, used in synergistic combination therapy with Trimethoprim for the treatment of urinary tract infections, respiratory tract pathogens, skin pathogens, certain enteric pathogens; and as a substitute to amoxicillin-based antibiotics in treating sinusitis and prophylaxis of pneumonia in patients living with AIDS.The clinical importance of sulfamethoxazole and trimethoprim-sulfamethoxazole combination has slowly declined in the most recent decades, largely as a result of the development and rapid spread of resistance to these agents among all major bacterial pathogens 16 .Moreover, for this reason, we aimed to prepare a new class of sulfamethaxazole-based drugs, by making a chemical combination with 2hydroxy quinolone (quinolin-2-ol).Then investigate the formation of such combination using spectroscopic methods, then allowing this azoligand to react with a series of metal salts including (Pt 4+ , Pd 2 +, Ni 2+ and Mn 2+ ), then investigating the formation of the complexes using the same methods that used with ligand.

Synthesis of Azo Dye Ligand
The ligand in Scheme 1 was synthesized according to the suggested method at which an amount of (2.05 g, 0.005 mol) 17 from Sulfamethoxazole (3-amino-N-(5-methylisoxazol-3yl)benzenesulfonamide) is dissolved in a mixture consisting of 4 mL of 37% HCl and 35 mL distilled water DW.Then this mixture is allowed to be cooled in a temperature starts at 0⁰C up to 5⁰C followed by discontinuously addition of (0.375 g, 0.005 mol) NaNO2 solution which in turn is dissolved in 30 mL DW, with continuous stirring and under controlling the range of temperature, which must be kept around 5⁰C for 30 minutes.After 15 minutes, diazotization-coupling operation occurs resulting in diazonium salt, which in turn added through filtered funnel containing cube of ice of DW onto 0.726 g, 0.005 mol solution of 2hydroxy quinolin (quinolin-2-ol) dissolved in 50ml of absolute EtOH and 15 ml of 10% NaOH solution with cooling and continuous stirring.We can clearly observe the creation of reddish-brown precipitate scheme 1, this precipitate is left for one hour under 5 ⁰C, then filtered and washed several periods with distilled water.Finally, recrystallization process by absolute ethanol is carried out, followed by drying in oven at 50 ⁰C.yielding in 68% product having (133-135) ⁰C m. p.

General Approach for Metal Complexes Synthesis
A specific amount of azo-ligand, which dissolved in absolute ethanol, is added discontinuously with continuous stirring onto a specific amount for each of the next metal salts: (Pt 4+ , Pd 2+ , Ni 2+ and Mn 2+ ) solutions.The resultant mixture is heated and refluxed for one hour up to 80 ⁰C, followed by cooling at room temperature.After 24 hours, a completely precipitation occurs, scheme 1.Then, solution containing-precipitate is filtered, washed several times with distilled water and washed with little amount of cold ethanol.Finally, recrystallization process using absolute ethanol is carried out for the synthesized complexes.The molar ratio of the synthesized complexes has been found to be 1:1 M: L.

Physical and Chemical Properties
Reactions of metal salts with ligand gave the synthetic complexes (Scheme 1).The results of elemental analysis demonstrates 1:1 M:L stoichiometry for all complexes.The elemental analysis results were compatible with theoretical calculated results as denoted in Table 1.

Magnetic Nuclear Resonance Spectrum of Ligand ( 1 H-NMR & 13 C-NMR)
Magnetic nuclear resonance spectrum of the new azo ligand was studied using dimethyl sulfoxide DMSO-d6 as solvent and TMS as standard reference.Fig. 1 demonstrates the chemical shifts of these spectra. 1 H-NMR spectrum of the ligand demonstrates several chemical shifts, those as follows: singlet signals: 1H of Ar-OH group, 1H of N-H amino group, 2H of both (aromatic C-H which nearby to CH3 and 3-quinoline of C-H group which nearby to OH), and 3H of CH3 group these signals were observed at : 1.08 ppm, 10.51 ppm, (6.72-6.79)ppm and 2.60 ppm respectively.We also observed only one multiplet signal at (7.68-7.95)ppm attributed to 8H of Ar-H in addition to solvents signal (DMSO) which observed at (2.41-2.51)ppm. 13C-NMR spectrum in Fig. 1

UV-Vis Studies of the Ligand (HL) and Its Complexes:
Figure 2 and Table 2 illustrate the electronic transitions of the ligand at ultra violet region in the range 296 nm, 33783 cm -1 and 328 nm, 30487 cm -1 those absorption bands belong to (π →π*) and (n→π*) electronic transitions respectively.The presence of non-bonding electrons or heteroatoms causes (n→π*) transition, while the presence of unsaturated bonds and aromatic rings causes (π →π*) transition 20 .We can apparently observe in Fig. 3, the occurrence of coordination in [Mn(L)Cl(H2O)2], is because of the observed shifting in absorption range of detected transitions at ultra violet region compared to the range of the same transitions in free (HL) to appear at 296 nm, 33783 cm -1 and 322 nm , 31055 cm -1 .Other indication supports the coordination is clear of the d-d transitions in the metal itself, those transitions denoted as 6 A1→ 4 T1(G) at (493 nm, 20283 cm -1 ) and 6 A1→ 4 T2(G) at (703 nm, 14224 cm -1 ) and the magnetic moment (3.71 B.M) can definitely support tetrahedral geometry 21,22 .Figure 4 of [Pd(L)(H2O)Cl] complex shows electronic transitions in ultra violet region resemble those in ligand in its free form with some modifications including shifting and intensity changes because of the coordination with metal ion, those are (π→ π*) and (n→ π*)+(C.T) at 298 nm, 33557 cm -1 and 339 nm, 29498 cm -1 respectively.Additionally, 1 A1g→ 1 B1g and 1 A1g→ 1 A2g (d-d transitions) can clearly be observed at 582 nm, 17182 cm -1 and 721nm, 13869 cm -1 respectively.Those transitions can definitely support square planer geometry 23 .
[Pt(L)(H2O)Cl] complex shows the following transitions : π→ π* at nm, 32679 cm -1 , n→ π* at 333 nm, 30030 cm -1 and C.T(M→L) transition at 398 nm, 25125 cm -1 those belong to ligand with some shifting that supports the coordination.Other transitions are (d-d) transitions that referred to as 1 A1g→ 1 T2g at 659 nm, 15174 cm -1 and 1 A1g→ 1 T1g at 768 nm, 13020 cm -1 ; the mentioned transitions can definitely support octahedral geometry of the complex 23 .All the electronic transitions information for the ligand (HL) & products are displayed in Table 2 in addition to the information of [Ni(L)Cl(H2O)] complex and other complexes 23 .LC-Mass spectrum. of ligand (HL) & some products were tested using LC-Mass device, this approach is one of the most important approaches in characterization and complementary for the rest approaches by which the molecular weight of the compound is estimated according to the relation (m/z).Mass information of the ligand in Scheme 2 shows the fragmentation pattern and the extract mass for each pattern.We can clearly observe the molecular ion peak [M] + for the fragment C10H9N2O3S + and its relative abundance about 45% in Fig. 5, in addition to other abundances for the rest of peaks including C9H6N3O + , C6H6NO2S + , C7H7 + , C2H6N3O + and C4H4NO + mentioned in Table .3 and corresponded the next abundances : 43% , 15% , 13% , 33% and 42% respectively 19 .For [Pt(L) (H2O)Cl], Fig. 6 and Scheme 3, we can also detect the molecular ion peak (M + ) at 727 m/z with relative abundance 20% and next patterns: C19H14Cl3PtN5O3S + , C9H5PdN2O + , C10H10N3O3S + , C3H4PdNO + , C6H6NO2S + , C4H5N2O + and C6H6N + , which corresponded to 709 m/z, 387 m/z , 265 m/z, 252 m/z, 156 m/z , 97 m/z and 92 m/z respectively 19 .Additionally, [Ni(L)Cl(H2O)] complex in Fig. 7 and Scheme 4, illustrate the next fragments: (M + ) at 520 m/z with relative abundance 12%, C19H14N5NiO4S + , C10H10N3O3S + , C9H5N2NiO + , C6H6NO2S + , C3H4NiNO + , C4H5N2O + and C6H6N + that correspond to 467 m/z, 252 m/z, 215 m/z, 156 m/z, 128 m/z, 97 m/z and 92 m/z respectively 24 .Finally, Fig. 8 and Scheme 5 of [Pd(L)(H2O)Cl] complex illustrate the next fragments: (M + ) at 568 m/z with relative abundance 10%, C19H14N5O4PdS + , C9H5PdN2O + , C10H10N3O3S + , C3H4PdNO + , C6H6NO2S + , C4H5N2O + and C6H6N + corresponded to 514 m/z, 263 m/z , 252 m/z, 176 m/z, 156 m/z , 97 m/z and 92 m/z respectively 24 .FT-IR spectrum of ligand in Fig. 9, displays unique absorption band attributed to azo group formation.Synthesis of such group causes the appearance of N=N stretching absorption band in the range (1448 -1403) cm -1 , this band is a strong evidence which supports the formation of ligand.In addition to the disappearing of asymmetric stretching vibrational mode of NH2 group because of diazotization coupling reaction through this group with 2-hydroxyquinolin.Other absorption bands were clearly observed at 3381 cm -1 , 3091 cm - 1 , 2977 cm -1 and (1160 -1086) cm -1 for each of the following groups : (NH) amine, (C-H) aromatic, (C-H) aliphatic and (SO2) respectively 25 .For Pdcomplex in Fig. 10, we can clearly notice the occurrence of coordination depending on the shifting in the ranges of absorption bands for azogroup by the range (32-13) cm -1 to be observed at (1480-1390) cm -1 . 26For Mn-complex, the absorption of azo band was shifted by 60 cm -1 compared to free ligand to be observed at 1388 cm -1 . 27and Ni-complex by the range (21-34) cm -1 and observed at (1469-1369) cm -1 . 28This can strongly proves the occurrence of coordination.Table 4 demonstrates all FT-IR spectral data of the ligand and some of its complexes.

Study of Thermogravimetric Analysis for Compounds:
Pyrolysis studies for the ligand and some of its complexes were carried out depending on thermogravimetric analysis curve (TGA) by measuring the changes in masses of the substances under study relative to temperature when these substances obey controlled thermal program in a specific time.The result curve is considered as thermogravimetric curve, which indicates thermal stability, reaction rates, chemical structure and the thermal stability of the products as denoted in Table 6 in addition to each pyrolysis step occurred.DSC differential scanning calorimetry technique, defined as pyrolysis technique, was employed for estimating the amount of absorbed and released heat and for the thermal changes that happened for tested substance.Table 7, shows Ti/⁰C, Tf/⁰C, heat amount (ΔH) in J/g unit if it was exothermic or endothermic.TGA technique demonstrates that, the ligand (HL) is analyzed in three steps as illustrated in Fig. 11 that displays the mechanism of its degradation, the critical temperature at which the maximal transformation of ligand occurs and the percentage of theoretical and calculated mass loss.It was found that, the estimated mass loss is 92.5393 % and the remnant is 7.4607 % whereas the calculated mass loss is 94.0353 % and the remnant is 5.9647 %. 29 Figure 12 of [Pt(L)(H2O)Cl3] complex, displays four steps degradation of the complex, the critical temperature at which the maximum mutation of complex is carried out and the percentage of theoretical is 30.2886% and the remnant is 69.7114 %, and calculated mass loss 29.04 % and the remnant is 70.96 % as PtO. 30And about [Mn(L)Cl(H2O)2] in Fig. 13, by the same approach we can investigate two pyrolysis steps ends with 14.3013 % and 13.7999 % as MnO which are the values of estimated and calculated remnants respectively. 31,32n addition to 85.6987 % and 86.2001% which are the values ofestimated and calculated mass loss respectively.By the same way, we can also determine the pyrolysis steps of [Ni(L)(H2O)Cl] complex that mentioned in Fig. 14 and in Table 5 and 6 .Scheme 6, clearly explains the pyrolysis steps of the ligand and complexes.

Investigation of Antioxidant Activity
The DPPH method was used to investigate antioxidant activity of the ligand and its metal complexes.Gallic acid was employed as a phenol containing reference.To provide a series of standards, five normal solutions of different concentrations (0.2, 0.4, 0.6, 0.8, and 1 mmol.l-1) of 10 mmol were prepared.An amount of 1-liter solution of Gallic acid, using ethanol as a diluent.6 mL of 45 g of DPPH solution was added to 100 µL of each of normal Gallic acid solution.After 30 minutes of incubation at room temperature in the dark, the absorbance of the reaction mixture was measured using a UV-vis spectrophotometer at 517 nm.The following equation was used to calculate percentage of root scavenger DPPH.Because of its simplicity and reliability, the majority of studies to evaluate the antioxidant activity of their targets uses the DPPH test, and Table 5 introduces the incomes of the radical scavenging activity of DPPH compounds.A lower IC 50 value referrers to higher DPPH radical scavenging activity and according to the IC50 values the order of oxidation activity is followed as (GA> [Pd(L)(H2O)Cl]> [Ni(L)(H2O)Cl]> [Mn(L)Cl (H2O)2]> [Pt(L)(H2O)Cl]> L).The table showed that almost all of the compounds had radical scavenging activities in the DPPH assay.It was important to observe that azo complex showed better antioxidant activity than azo ligand [33][34][35][36] , as shown in Table 7.

Table 3 . LC-Mass spectral data of ligand L and its complexes
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Table 7 . Antioxidant activity of Azo dye and its complexes
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