A tripodal Schiff base ligand, 2,4,6-Tris(4-carboxybenzimino)-1,3,5-triazine (MT) and its trinuclear Dy(III), Er(III), and Gd(III) complexes were synthesized. These were characterized using UV-visible, IR, 1H, and 13C NMR spectroscopies, elemental analysis, and molar conductivity measurements. The spectral studies indicate that the ligand is hexadentate and coordinates to the Ln(III) ions through the oxygen atoms of the carboxylic group. The trinuclear complexes were characterized as being bridged by carboxylate anions to the Dy(III), Er(III), and Gd(III) salen centers and displaying a coordination number of six. Biological studies revealed that MT is more active against the test micro-organisms relative to the trinuclear complexes. Acute toxicity studies revealed that MT is safe and has a wide range of effective doses (ED50). In vivo antimalarial studies indicate that MT could serve as an effective antimalarial agent since it has parasitemia inhibition of 84.02% at 50 mg/kg and 65.81% at 25 mg/kg, close to the value (87.22%) of the standard drug—Artesunate. Molecular docking simulation studies on the compounds against SARS-CoV-2 (6Y84) and E. coli DNA gyrase (5MMN) revealed effective binding interactions through multiple bonding modes. The binding energy calculated for Er(III)MT-6Y84 and Er(III)MT-5MMN complexes showed active molecules with the ability to inhibit SARS-CoV-2 and E. coli DNA gyrase.

N-(Benzothiazol-2-yl)-4-chlorobenzenesulphonamide (NBTCS) was synthesized by condensation reaction of 4-chlorobenzenesulphonyl chloride and 2-aminobenzothiazole in acetone under reflux. Neodymium(III) and thallium(III) complexes of the ligand were also synthesized. Both ligand and metal complexes were characterized using UV-Vis, IR, 1H- and 13C-NMR spectroscopies, elemental analysis and molar conductance measurement. IR studies revealed that the ligand is tridentate and coordinates to the metal ions through nitrogen and oxygen atoms of the sulphonamide group and nitrogen atom attached to benzothiazole ring. The neodymium(III) complex displays a coordination number of eight while thallium(III) complex displays a coordination number of six. The ligand and its complexes were screened in vitro for their antibacterial activities against Escherichia coli strains (E. coli 6 and E. coli 13), Proteus species, Staphylococcus aureus and Pseudomonas aeruginosa using the agar well diffusion technique. The synthesized compounds were found to be more active against the microorganisms screened relative to ciprofloxacin, gentamicin and co-trimoxazole.

S-1,3-Benzothiazol-2-ylthiophene-2-carbothioate (SBC) was synthesized by the S-acylation of 2-mercaptobenzothiazole with thiophene-2-carbonylchloride in the presence of pyridine. Its Ce(IV) and Nd(III) complexes were also synthesized. The ligand and its Ce(IV) and Nd(III) complexes were characterized by UV-visible, IR and GC-MS spectroscopy. In addition, the ligand was characterized based on its 1 H and 13 C NMR data and the metal complexes based on conductivity measurement and stoichiometric ratio of combination. The infrared spectral study of S-1,3-benzothiazol-2-ylthiophene-2-carbothioate and its Ce(IV) and Nd(III) complexes gave evidence for coordination through the nitrogen of the benzothiazole ring and carbonyl oxygen. All the complexes were found to contain coordinated water and were assigned octahedral geometry. Antibacterial screening of the compounds were carried out in vitro on Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The compounds showed significant activities against Gram-positive bacteria than Gram-negative bacteria. However, the ligand showed more chemotherapeutic efficacy than the complexes. The compounds were not active against Pseudomonas aeruginosa. Synthesis of S-1,3-benzothiazol-2-ylthiophene-2carbothioate:The ligand was prepared by S-acylation of 2mercaptobenzothiazole with thiophene-2-carbonylchloride in the presence of pyridine which acts as a catalyst 11 . To a solution of 2-mercaptobenzothiazole (2.51 g, 0.015 mole), thiophene-2-carbonylchloride (1.60 mL, 0.015 mole) was added followed by 5 mL of pyridine. The mixture was heated with stirring over a water bath until fumes of hydrogen chloride ceased to appear. About 2 mL of distilled water was added, followed by 2 mL of pyridine to eliminate the excess reagent. The product solidified upon stirring with a glass rod into a white coloured solid. Water (10 mL) was added, the product filtered and recrystallized from dilute ethanoic acid. The yield was 40.38 % and the melting point 162 °C. The spectral results are as follows: UV (λmax nm, cm -1 ) (ethanol): (256, 271, 336); (13, 845,14,657,18,172). IR (KBr, νmax, cm -1 ): 3054 (s), 2985 (m), 1670 (m), 1560 (m), 1497 (m), 1420 (s), 1077 (s), 896 (s), 738 (sh), 706 (w). 1 H NMR (CDCl3) (δ, ppm): 7.15 (1H, d), 7.20 (2H, t), 7.23 (1H, d), 7.25-7.40 (4H, m). 13 C NMR (δ, ppm): 112. 551, 121.412, 124.622, 127.232, 130.365, 141.002, 191.212. Syntheses of Ce(IV) and Nd(III) complexes:The complexes were synthesized by refluxing ethanol solutions of Ce(SO4)2 and Nd(NO3)3·5H2O with the ligand, respectively in amounts equal to metal: ligand molar ratio of 1:2 to ensure complete reaction 6,7 . To ethanolic solution (20 mL) of cerium(IV) sulphate (0.32 g, 0.004 mole) was added a solution of S-1,3benzothiazol-2-ylthiophene-2-carbothioate (2.22 g, 0.008 mole) in ethanol (40 mL). The mixture was refluxed for 1 h under constant stirring at 80 °C. On cooling, milk coloured precipitate formed. They were filtere...

No abstract

No abstract