Synthesis, characterization, and antimicrobial activity of 4-imidazolecarboxaldehyde thiosemicarbazone and its Pt(II) and Pd(II) complexes European Journal of Chemistry 12 (1) (2021) 56-59 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2021 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.12.1.56-59.2070 European Journal of Chemistry View Journal Online View Article Online Synthesis, characterization, and antimicrobial activity of 4-imidazolecarboxaldehyde thiosemicarbazone and its Pt(II) and Pd(II) complexes Mohammed Bahreldin Hussein 1,*, Muna Mahdi Mohammed 1, Abdalla Gobara 2, Asha Fadllallah Wady 1 and Awad Salim Ibrahim Holy 3 1 Department of Chemistry, Faculty of Science, University of Kordofan, Elobeid, 52211, Sudan mohammedbahr66@gmail.com (M.B.H.), munamahdi622@hotmail.com (M.M.M.), ashafadel200@gmail.com (A.F.W.) 2 Department of Chemistry, Faculty of Education, Dalanj University, Dalanj, 53312 Sudan wadgobara35@gmail.com (A.G.A.) 3 Department of Chemistry, Faculty of Education, West Kordofan University, El-Nuhud, 55511, Sudan awads09131@gmail.com (A.S.I.) * Corresponding author at: Department of Chemistry, Faculty of Science, University of Kordofan, Elobeid, 52211, Sudan. e-mail: mohammedbahr66@gmail.com (M.B. Hussein). 10.5155/eurjchem.12.1.56-59.2070 Received: 15 January 2021 Received in revised form: 14 February 2021 Accepted: 18 February 2021 Published online: 31 March 2021 Printed: 31 March 2021 Schiff bases are versatile ligands, synthesized via condensation of primary amines with carbonyl compounds. In this study, equimolar amounts of 4-imidazolecarboxaldehyde and thiosemicarbazide were combined and the Schiff base 4-imidazolecarboxaldehyde thiosemicarbazone was prepared as a new bidentate complexing agent. The synthesized ligand was reacted with palladium (II) and platinum (II) ions yielding air-stable complexes. For characterization purpose, infrared spectra, mass spectra, electronic spectra, thermal analysis, proton nuclear magnetic resonance and 13-carbon nuclear magnetic resonance spectra studies were carried out on the obtained complexes and ligand. The characterization data showed that the ligand acts as a bidentate coordinate to the metal ions through azomethine nitrogen and sulfur atoms. An in vitro antimicrobial investigation was also carried out for the free ligand and its metal complexes against four bacteria; Bacillus cereus, Staphylococcus aureus (Gram-positive), Escherichia coli and Salmonella typhimurium (Gram- negative) and one Fungi; Candida albicans, to assess their antimicrobial properties by disc diffusion technique. Antimicrobial activity of the prepared complexes showed higher activity than the free ligand. Synthesis Schiff base Antimicrobial activity Structural characterization Pd(II) and Pt(II) complexes Imidazole thiosemicarbazone Cite this: Eur. J. Chem. 2021, 12(1), 56-59 Journal website: www.eurjchem.com 1. Introduction Thiosemicarbazones, an important class of synthetic compounds, have a variety of applications due to their wide spectrum of biological activities which include antifungal, antibacterial, anti-inflammatory, antimalarial antiviral, anti- tumoral, anticancer and among others as well as parasiticidal activity [1-12]. Thiosemicarbazones are very active ligands, in particular, that contain an imidazole moiety which is known to play an important role in biological systems as a part of the histidine residue in peptides and proteins and it has been shown that their biological activities are related to their ability to coordinate to metal centers in enzymes [13-15]. There are some research groups work about imidazole thiosemicar- bazone derivatives and their metal complexes such as West et al., Casas et al. and Rodriguez-Arguelles et al. [16-18]. West et al. have reported the synthesis of the substituted imidazole-2- carbaldehydethiosemicarbazone derivatives and some of their copper(II) complexes [16]. Casas et al. synthesized an imidazole-2-carbaldehydethiosemicarbazone ligand and some of its diorganotin (IV) complexes [17]. Rodriguez-Arguelles et al. also prepared cobalt (II) and nickel (II) complexes from 2- carbaldehyde thiosemicarbazone ligands and compared their coordinative behavior besides their antimicrobial activities [18]. In this paper, the preparation and characterization of 4- imidazolecarboxaldehyde thiosemicarbazone ligand and its metal complexes were described. In addition, in vitro antimicrobial investigation was also carried out for the ligand and its metal complexes against four bacteria; Bacillus cereus, Staphylococcus aureus, Escherichia coli and Salmonella typhimurium and one Fungi; Candida albicans. 2. Experimental 2.1. Materials and measurements ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.12.1.56-59.2070 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.12.1.56-59.2070 mailto:mohammedbahr66@gmail.com mailto:munamahdi622@hotmail.com mailto:ashafadel200@gmail.com mailto:wadgobara35@gmail.com mailto:awads09131@gmail.com mailto:mohammedbahr66@gmail.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.12.1.56-59.2070&domain=pdf&date_stamp=2021-03-31 Hussein et al. / European Journal of Chemistry 12 (1) (2021) 56-59 57 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.1.56-59.2070 N NH O H2N N H S NH2 + Ethanol / Water 7 h / - H2O N HN N N H S NH2 1 2 5 8 6 10 9 7 3 4 Scheme 1. Preparation of 4-imidazolecarboxaldehyde thiosemicarbazone (4-ITSC). N HN N N H S NH2 2 Reflux / 7 h K2PdCl4 Cl2N HN N N H S NH2 N NH N H N S H2N Pd Reflux / 7 h K2PtCl4 Cl2N HN N N H S NH2 N NH N H N S H2N Pt Scheme 2. Preparation of Pd(II) and Pt(II) complexes of 4-ITSC. All chemicals and solvents of the highest analytical grade were used as received from Sigma-Aldrich and Alfa-Aesar. The melting points of the synthesized compounds were determined by a capillary method in a Thomas Hoover apparatus. Mass spectrum of the ligand was carried out on Esquire LC-00084 electronic spray ionization (ESI) Mass spectrometer. Infrared spectra of the ligand and its metal complexes were recorded on Vertex-183387000 FT-IR spectrometer by using KBr disk in the range 4000-400 cm-1. 1H and 13C NMR spectra of the ligand and its metal complexes were recorded on a Bruker AV-III 600 operating at 600 MHz for 1H and 150 MHz for 13C by using DMSO-d6 as a solvent. UV-Vis spectra in solid state were recorded on a Cary-EL05123055 4000 UV-Vis spectrophoto- meter in the range 200-800 nm. Thermal analysis was carried out using DTA/TG HIGH RG 2/S thermal analyser. All measurements were carried out at technical University of Dresden, Germany. 2.2. Synthesis of 4-imidazolecarboxaldehyde thiosemicarbazone (4-ITSC) Equimolar amounts of thiosemicarbazide (910 mg, 0.001 mol) and 4-imidazole carboxaldehyde (960 mg, 0.001 mol) were dissolved in 20 mL of ethanol:water (60:40, v:v) and refluxed for 7 h in an oil bath at 78 °C [18-21]. The solution was allowed to cool at room temperature and left for slow solvent evaporation. After several days pale yellow crystals were obtained. The crystals were separated, washed with cold ethanol, and dried under vacuum (Scheme 1). 4-Imidazolecarboxaldehyde thiosemicarbazone: Color: Pale yellow. Yield: 72%. M.p.: 205-207 °C. FT-IR (KBr, ν, cm-1): 3397, 3202 (NH2), 3011 (NH), 1606 (C=N), 1103 (N-N), 851 (C=S). 1H NMR (600 MHz, DMSO-d6, δ, ppm): 12.4 (s, 1H, HN8), 8.2 (s, 1H, HC5), 7.3 (s, 2H, HN1), 8.3 (s, 1H, HN3), 8.0 (s, 1H, HC7), 7.7 (s, 1H, HC9). 13C NMR (150 MHz, DMSO-d6, ppm): 177.88 (C2), 135.54 (C6), 136.60 (C5), 132.13 (C9), 121.60 (C7). Ms (ESI, m/z): 170.0 [M, C5H7N5S]+. UV-Vis (λmax, nm): 313. 2.3. Synthesis of complexes 2.3.1. Synthesis of [Pd(4-ITSC]Cl2 K2PdCl4 (16.32 mg, 5.0×10-5 mol) was dissolved in hot ethanol and then mixed with a hot ethanolic solution containing 16.9 mg (1.0×10-4 mol) of 4-ITSC. The mixture was refluxed for 7 h at 78 °C in an oil bath and then allowed to cool at room temperature and left for slow solvent evaporation for several days. The colored precipitate was filtered off, washed with cold ethanol, and dried in air and vacuum oven (Scheme 2) [18,21]. Color: Orange. Yield: 77%. M.p: 220-222 °C. FT-IR (KBr, ν, cm-1): 3400, 3298 (NH2), 3115 (NH), 1613 (C=N), 816 (C=S), 1116 (N- N). 1H NMR (600 MHz, DMSO-d6, δ, ppm): 11.8 (s, 2H, HN8), 8.1 (s, 2H, HC5), 7.4 (s, 4H, HN1), 8.5 (s, 2H, HN3), 8.4 (s, 2H, HC7), 7.8 (s, 2H, HC9). 13C NMR (150 MHz, DMSO-d6, δ, ppm): 179.21 (C2), 135.97 (C6), 141.13 (C5), 129.21 (C9), 120.58 (C7). UV-Vis (λmax, nm): 226, 313, 376. 2.3.2. Synthesis of [Pt(4-ITSC)2]Cl2 K2PtCl4 (20.75 mg, 5.0×10-5 mol) of was dissolved in hot ethanol and then mixed with a hot ethanolic solution containing 16.9 mg (1.0×10-4 mol) of 4-ITSC. The mixture was refluxed for 7 h at 78 °C in an oil bath and then allowed to cool at room temperature and left for slow solvent evaporation for several days. The colored precipitate was obtained, filtered off, washed with cold ethanol, and dried in air and vacuum oven (Scheme 2) [18,21]. Color: Orange. Yield: 82%. M.p: 230-232 °C. FT-IR (KBr, ν, cm-1): 3390, 3303 (NH2), 3098 (NH), 1618 (C=N), 853 (C=S), 1082 (N-N). 1H NMR (600 MHz, DMSO-d6, δ, ppm): 11.9 (s, 2H, HN8), 8.2 (s, 2H, HC5), 7.2 (s, 4H, HN1), 8.6 (s, 2H, HN3), 8.3 (s, 2H, HC7), 7.9 (s, 2H, HC9). 13C NMR (150 MHz, DMSO-d6, δ, ppm): 178.21 (C2), 135.82 (C6), 142.68 (C5), 129.06 (C9), 120.70 (C7). UV-Vis (λmax, nm): 210, 226,265. 2.4. Antimicrobial activity 2.4.1. Antifungal screening Preliminary antifungal screenings of the prepared compounds at different concentrations were performed. Potato dextrose agar medium was prepared by using potato, dextrose, agar-agar and distilled water. Appropriate amount of the compounds in DMSO was added to potato dextrose agar medium in order to get a concentration of 100 and 200 µg/mL of compound in the medium. 58 Hussein et al. / European Journal of Chemistry 12 (1) (2021) 56-59 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.1.56-59.2070 Table 1. Thermal analysis of the synthesized Pd (II) and Pt (II)complexes. Complex TG (°C) DTA (°C) * Total mass loss (%) * Metallic residue (%) * Pd(4-ITSC)2Cl2 30-1050 220 (-), 312 (-) 80.35 (79.37) Pd 19.65 (20.63) Pt(4-ITSC)2Cl2 30-1050 220 (-), 609 (-) 70.27 (67.72) Pt 29.73 (32.28) * DTA: (-) Exothermic; Mass loss: Found (Calculated). The medium was poured into a set of two Petri plates under aseptic conditions in a laminar flow hood. When the medium in the plates was solidified, a mycelial disc of 0.5 cm in diameter was cut from the periphery of the seven days old culture and it was aseptically inoculated upside down in the center of the Petri plates. These treated Petri plates were incubated at 26±1 °C until fungal growth in the control Petri plates was almost complete. The mycelial growth of fungi (mm) in each Petri plate was measured [22]. 2.4.2. Antibacterial screening The paper disc diffusion method was used to screen the antibacterial activity of the prepared compounds and perfor- med by using Mueller Hinton agar (MHA). The ligand and its complexes were carried out according to the National Committee for Clinical Laboratory Standards Guidelines. Bacterial suspension was diluted with sterile physiological solution to 108 cfu/mL (Turbidity = McFarland standard 0.5). One hundred microliters of bacterial suspension were swabbed uniformly on the surface of MHA and the inoculum was allowed to dry for 5 minutes. Sterilized filter paper discs (Whatman No. 1, 6 mm in diameter) were placed on the surface of the MHA and soaked with 20 µL of a solution of each sample. The inoculated plates were incubated at 37 °C for 24 h in the inverted position. The diameters (mm) of the inhibition zones were measured [23]. 3. Results and discussion 3.1. Synthesis The synthesis of ligand containing an imidazole ring is outlined in Scheme 1. The corresponding palladium (II) and platinum (II) complexes were obtained in two steps. In the first step, the ligand was synthesized by condensing equimolar quantities of thiosemicarbazide with 4-imidazole carbox- aldehyde in ethanol: water mixture. In the second step, the prepared ligand was refluxed with metal salt in 1:2 M ratio, to obtain the desired complexes. The obtained compounds were characterized by UV-Vis, FTIR, 1H NMR, 13C NMR, Mass spectrometry, and thermogravimetric analyses. Some physical characteristics of the ligand and its corresponding metal complexes are given in experimental section. The infrared absorption bands become very useful for determining the mode of coordination of the ligands to metal. In the IR spectra, the absorption peaks at 3397 and 3202 cm-1 are assigned to ν(NH2). The absorption peak at 3011 cm-1 is assigned to ν(N-H). In both complexes, the presence of a band in this region (3115 and 3098 cm-1) corresponds to NH vibration, which indicates that the ligand is coordinated in the neutral form. The strong band observed at 1606 cm-1 in the free ligand has been assigned to ν(C=N) stretching vibrations [18,24,25]. On complexation, this bands were observed to be shifted to higher frequencies (1613-1618 cm-1) [18,24,25]. These results indicate that the imine nitrogen is coordinated to the metal ion. The ligand showed a medium band at 851 cm-1 ascribed to ν(C=S) vibrations. These absorption bands shift to lower and higher frequencies on the coordination of the thiocarbonyl sulfur to palladium (II) or platinum (II) ions. These results agree with other thiosemicarbazone complexes. In addition, the vibrational frequencies of the NH2 groups remain unchanged for the ligand and metal complexes. This evidence indicates the noncoordination of the NH2 group on the metal ion [10,18,26,27]. The electronic spectra of 4-ITSC showed that a strong absorption band at 313 nm. This band assigned to the π → π* transition of the azomethine group [24,25]. The intra-ligand transitions for Pd (II) complex were observed 226, 313, 376 nm and for Pt (II) complex was observed in 210, 226, 265 nm and these bands are mainly due to π → π* and n → π* transitions [24,25]. The 1H and 13C NMR spectra and chemical shift values of the ligand and corresponding metal complexes were record in DMSO-d6 solvent. The 1H NMR of 4-ITSC ligand and its metal complexes show signal at δ 8.3, 8.5, and 8.6 ppm have been assigned to δ(NHCS)protons and the signals at δ 7.3, 7.4 and 7.2 ppm have been assigned to δ(CSNH2) protons. The signals at δ 8.2, 8.1, and 8.2 ppm assignable to azomethine protons (CH=N). The downfield chemical shift in the spectra of Pd (II) and Pt (II) complexes indicated the coordination through the azomethine nitrogen to the metal atom resulting in the formation of a coordinate N→M linkage and all imidazole ring protons were observed in the expected regions [18,24-28]. The 13C NMR spectra revealed the presence of an expected number of signals corresponding to different types of carbon atoms present in the compounds. The spectra of the Schiff base ligand exhibit a strong band at δ 177.88 ppm due to C=S group. In the complex formation, the position of this band undergoes an up-field shift [24-28] to δ 179.21 and 178.21 ppm. This indicates that sulphur is involved in coordination (S→M linkage). These results in agreement with a previously publis- hed paper [24-27]. Generally, not much is known about the thermal properties of transition metal complexes of imidazolecarboxaldehyde thiosemicarbazones. The thermal behavior of the palladium (II) and platinum (II) complexes of the synthesized imidazole- carboxaldehyde thiosemicarbazones were studied under argon atmosphere using thermal analyzer (DTA/TG) and the results shown in Table 1. The thermal decomposition of the complexes was recorded from ambient temperature to 1050 °C. The results showed that the complexes generally decomposed in several thermal events (Decomposition steps). The complexes lost moisture around 100 °C, and then started to decompose at a temperature above this limit. The total weight loss around 1050 °C is nearly 70-80% and this mass loss equals the loss of two moles of 4-ITSC and chloride ligands in agreement with the proposed metal:ligand ratio of 1:2 of the complex [24]. The remaining weights correspond to the metallic residue as shown in Table 1. The coordinative mode of compounds studied here becomes plain in palladium (II) and platinum (II) complexes of 4-imidazolecarbaldehyde thiosemicarbazone in which the ligand behaves as NS donor giving square planar geometry. 3.2. Antimicrobial activity The synthesized compounds were screened in vitro for their antibacterial activity against four pathogenic bacteria; Bacillus cereus, Staphylococcus aureus, Escherichia coli, Salmonella typhimurium and one fungus; Candida albicans at a concentration of 100 and 200 µg/mL with DMSO as the solvent. The results showed that the tested compounds possess moderate antimicrobial activity against most of the tested organisms, as shown in Table 2. Hussein et al. / European Journal of Chemistry 12 (1) (2021) 56-59 59 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.1.56-59.2070 Table 2. Antimicrobial activity of synthesized thiosemicarbazone and its complexes. Compound Concentration (μg/mL) Diameter of inhibition zone (mm) Gram+ve bacteria Gram-ve bacteria Fungi B. cereus S. aureus E. coli S. typhi C. Albicans 4-ITSC 100 10 07 07 06 00 200 10 11 12 10 09 Pd(4-ITSC)2Cl2 100 11 09 16 11 09 200 12 12 19 14 10 Pt(4-ITSC)2Cl2 100 11 11 11 11 10 200 12 12 11 13 11 Gentamicin 200 20 14 17 16 - In similar previous studies, the evaluation of antibacterial activity of the synthesized compounds exhibit a moderate inhibitory effect on the microbial proliferation and only against some Gram-positive bacteria [18,20,21,23,25,28]. The palla- dium complex was more effective against E. coli than standard drug. 4. Conclusion In this study, condensation reaction was adopted for preparing a new Schiff base ligand; 4-imidazolecarboxaldehyde thiosemicarbazone. The ligand and its metal complexes were fully characterized by several techniques and the antibacterial and antifungal activities of the ligand and its metal complexes were also evaluated. Acknowledgements Authors are thankful to the Chairperson, Department of Inorganic Chemistry, Technical University of Dresden, Germany for providing research facilities and constant encouragement. Mohammed Bahreldin is thankful to German Academic Exchange Services DAAD for a research grant to Germany. Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors are contributed in this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Mohammed Bahreldin Hussein https://orcid.org/0000-0002-1919-6176 Muna Mahdi Mohammed https://orcid.org/0000-0001-7031-1128 Abdalla Gobara Habieballa https://orcid.org/0000-0002-8770-0936 Asha Fadllallah Wady https://orcid.org/0000-0001-9331-986X Awad Salim Ibrahim https://orcid.org/0000-0002-2948-7049 References [1]. Quiroga, A. G.; Perez, J. M.; Lopez-Solera, I.; Masaguer, J. 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Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). https://orcid.org/0000-0002-1919-6176 https://orcid.org/0000-0001-7031-1128 https://orcid.org/0000-0002-8770-0936 https://orcid.org/0000-0001-9331-986X https://orcid.org/0000-0002-2948-7049 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Materials and measurements 2.2. Synthesis of 4-imidazolecarboxaldehyde thiosemicarbazone (4-ITSC) 2.3. Synthesis of complexes 2.3.1. Synthesis of [Pd(4-ITSC]Cl2 2.3.2. Synthesis of [Pt(4-ITSC)2]Cl2 2.4. Antimicrobial activity 2.4.1. Antifungal screening 2.4.2. Antibacterial screening 3. Results and discussion 3.1. Synthesis 3.2. Antimicrobial activity 4. Conclusion Acknowledgements Disclosure statement ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField20: PrintField21: PrintField22: PrintField23: