Synthesis, Spectral Characterization, and Antimicrobial Activity of Two Novel Schiff Bases Derived from Thiosemicarbazide and Mononuclear 3d Transition Metal Complexes

Introduction

 Treatment modalities and strategies that utilize the latest antifungal medications are imperative [1]. Over a billion people are affected by fungi worldwide, killing more than 1.5 million. Since metallo- drugs can target multiple pathways to curb drug resistance,[2]. they seem worthy of consideration among the various methods being pursued [3]. Sometimes, ligands protect or stabilize the metal ion or the metal by undergoing redox events which enhances the overall efficacy of the complex, and sometimes the metal and the ligand(s) are mutually responsible for its biological activity [4]. Schiff bases are compounds containing the azomethine group (-HC=N-). They are condensation products of ketones or aldehydes with primary amines and were first reported by Hugo Schiff in 1864[5]. Formation of Schiff base generally takes place under acid or base catalysis or with heat. The common Schiff bases are crystalline solids, which are feebly basic but at least some form insoluble salts with strong acids. Schiff bases derived from Thiosemicarbazide were reported to possess antibacterial [6], antifungal [7], antiviral, antiprotozoal [8], and anthelmintic activities. They also exhibit significant anticonvulsant activity [9], apart from other pharmacological properties, and are used for the preparation of complex compounds [10].  Thiosemicarbazides are frequently used as intermediate compounds in the synthesis of bioactive heterocyclic compounds during several biological and clinical practices [11-12]. The importance of carbazides, carbazones, thiosemicarbazide, and their transition metal complexes has grown in a short period of time because of the discovery of their effects on flu, protozoa, variola (smallpox), certain types of tumors, and fungi [13-14] and their corresponding derivatives thiosemicarbazide are related to several essential antimicrobial activities [15]. Fungicidal, anthelmintic, anti-bacterial, activity [16]. Schiff bases derived from simple thiosemicarbazide and its derivatives are found to be very effective in the field of pharmacology and other imp medicinal fields [17].   Now a day fungal and bacterial infection is very common in every area of human and animal society, by using this simple base complexation makes it possible to overcome diseases induced to measure the biological activities of metal complexes [18], with different transition metals like Co (II), Ni (II), Cu(II), Zn (II), Pb(II), Cd (II), and, Ag (I). This type of tactic would conceivably give compounds [19]. With superior biological activity in biochemical research [20]. In prepared Schiff base, one sulfur-containing moiety, the base makes more effective towards microorganisms basically for bacterial and fungal infections [21-22]. We have synthesized a novel series of Schiff base results from thiosemicarbazide [23]. More specifically, in order to better understand the ligand-metal complexation, antimicrobial study studies [24], were used to assess the new molecules the findings demonstrated the important biological potential of these compounds.

Experimental

Materials and methods  

All the reagents and chemicals used for the synthesis were of analytical grade and were purchased from commercial sources. They were used as received without further purification both aldehydes and thiosemicarbazide were purchased from Fluka, Sigma Aldrich, and metal nitrates were purchased from Merck and Spectrochem. Microanalyses (C, and N) were carried out with melting point apparatus used to determine the melting point of the synthesized compounds.  The FT-IR IR spectra of the compounds were recorded using a BRUKER FT-IR Spectrophotometer, and all spectra of synthesized compounds were recorded as KBr pellets. The UV/vis spectra of synthesized Schiff bases and their metal complexes were detectedin Thermos Scientific (Multiskan Go) Spectrophotometer by using DMSO solvent under 200-800 nm wavelength.  1HNMR spectra were recorded on a Bruker (400 MHz) spectrometer. Chemical shifts were reported as δ in ppm relative to tetramethyl silane (TMS) (δ 0.00 singlet) in deuterated dimethyl sulfoxide (DMSOd6) for compounds and deuterated chloroform (CDCl3) for compound 1g. HRMS spectra were recorded. Solvents are used in analytical grades. For the preparation of metal complexes of corresponding Schiff bases, the nitrate salts of metals were used for the synthesis of metal complexes. By using silica-coated aluminum plates the progress of the reaction was monitored in the UV chamber. By using an open capillary, the melting point of all the compounds was resolute. Mass spectra were learned on Bruker Compass Data Analysis 4.0.

General synthetic procedure for ligands

By condensing 2Methoxybenzaldehyde and 3Methoxybenzaldehyde (2.0mmol) in ethanol (15 ml) with Thiosemicarbazide (1mmol) in ethanol (15ml) were dissolved separately and aldehyde was added to the amines under stirring. The resulting mixture was stirred for 30 minutes at room temperature. Additionally, for enhancing the rate of the reaction 2-3 drops of dilute acetic acid were added to the reaction mixture followed by refluxing at 70-80⁰C for 5-8 hr, and the completion of the reaction was observed by TLC, using hexane and ethyl acetate (9:1v/v) as eluent. Under scheme-1 after completion of the reaction, the reaction mixture was allowed to cool at room temperature, the remaining precipitate was filtered, then wash with diethyl ether/ethanol (2:1) then put under a vacuum. For the synthesis of metal complexes of the above Schiff bases, the condensation refluxing method was acquired in which 0.01 M of metal (nitrate) ofCo (II), Ni (II), Fe (II), Cu (II), Ag (I), with 0.02 M of synthesized Schiff base in methanol is allowed to react in magnetic stirrer for 2-4 h. 1 Equiv. For making a slight basic medium a catalytic amount of KOH [1-2 drops] was added.  Precipitation of complexes seemed which be filtered on, and washed with ethanol and petroleum ether.

Synthesis of KL-1: (NE)-N,2-bis(2-methoxybenzylidene) hydrazine- carbothioamide

MP;168 Yield (0. 024g) 76%; White powder, Chemical Formula C₁₇H₁₇N₃O₂S (MW, 327.40).; Elemental analyses: Calculated; C, 62.36; H, 5.32; N, 12.83;O,9.77; S,9.79 %; Observed; C, 63; H, 5.22; N, 12.78; S, 9.72; IR (selected vibrations; cm-¹); FT-IR Spectroscopy(cm^-1): 3402.21, 3283.77 , them obtained stretching frequency at 1684.38 which is basically responsible for the confirmation of Schiff base (stretch, -C=N- imino), lowing of this transition because of presence of Thio and methoxy electron-withdrawing groups,  The IR spectra of Schiff base ligand (KL-1)  exhibits strong band at 3402.21, 3283.77 , 1684.38  due to  (stretch, -C=N- imino), the C-H stretching and bending vibrations appear at 1455.34, 1281.64 (aromatic -C=C-),1007cm^-1(v (N-N) group,1234.86 (C-O-C stretch(E,E)-1,3-bis(2-methoxybenzylidene)thiourea. 1H NMR (DMSO- d6, δ, ppm) The 1HNMR spectra of ligand were recorded in DMSO. The ¹HNMR spectrum of KL-1 shows a signal at 8.31 δ indicating the presence of azomethine (HC=N) proton. However, the multiple in the region 7.10-7.6 δ indicates the presence of phenolic protons; 6.6 (s. 1H) 7.4-7.3 (d, 1H), the important bands were observed at ~3.9δ assigned for methyl (O-CH₃); Mass Spectroscopy(ESI-MS): 302 [M+ H2O+H] ⁺ anal for C15H12N2O3S. UV/vis; 301 nm, 270 nm.

Synthesis of KL-2: (2E)-N,2-bis(3methoxybenzylidene)hydrazine- carbothioamide

MP;158 ⁰C Yield 0.022g (84%); light yellow powder, Chemical Formula: C₁₇H₁₇N₃O₂S (MW,327.40)  Elemental analyses: 62.37; H, 5.28; N, 12.87;O,9.76; S,9.79 %; Observed; C, 63; H,5.22;N, 12.78; S, 9.72; IR (selected vibrations; cm^-1); FT-IR Spectroscopy(cm^-1): FT-IR spectrum of ligands showed a band at a region of 1587.78  which is due to (-C=N- stretching)  frequency is a key feature of Schiff base. Some strong IR peaks are 1529.31(C=C aromatic) 1453.46 (CH₃ bend), 1035.06 (C-O-C-Stretch) 1261.40. As the ligand shows particular bands at a particular region, the same band is obtained for complexes also, we can say generally, via coordination bonds ligand complex suggesting that ligands have combined with the metal through coordination. the bands in the region of 640-660 cm^-1and 418 cm^-1, are accredited to ν(M-O) and ν(M-N) stretching vibrations respectively, compatible coordination with Schiff bases.

Scheme 1: Synthesis of KL-1 Ligand and synthesis of metal complexes Click here to View figure

General synthetic procedure for [M (KL1)2]

By using metal (II) nitrates complexes of (NE)-N, 2-bis (2-methoxybenzylidene) hydrazinecarbothioamide have been synthesized. To a stirring methanolic solution of KL-1and KL-2(1.0 mmol, 0.287g/0.332g) and KOH (1.0 mmol, 0.056g), a methanolic solution of metal (II) nitrates (1.0 mmol) were added dropwise at room temperature, then the resulting reaction mixture was extra stirred for 30 minutes. The reaction mixture was refluxed at 50-60°C for 2-4 h and the accomplishment of reaction was observed by TLC. Cooling the reaction content resulted in a precipitate which was filtered, washed with methanol (10 mL) .and finally dried at room temperature or vacuum. [25].

(2E,NE)-N,2-bis(2-methoxybenzylidene)hydrazinecarbothioamide- nickel(II) salt nickel [Ni(KL1)2](1)

have been synthesis, Green powder, yield: 0.308g,(80%),MP-136 °C, Chemical formula; [Ni(C17H₁₇N₃O2S²⁺], (MW; 386.1),Exact Mass; 385.0 Elemental Analysis: C, 52.88; H, 4.44; N, 10.88; Ni, 15.20; O, 8.20; S, 8.30.32; Found; C, 52.82; H, 4.42; N, 10.12; Ni, 14.30; O;8.13; S, 8.10; IR (selected vibrations; cm-^­1 ); 1619.54 (C=N), 3325.09 (N-H), 1364.33 ,604.13 ,817-811.21 (C=S) .UV/vis (λ max); 250-255 nm, Mass spectrometry (ESI-MS): 624.3 [M]+ anal for [Ni(C17H₁₇N₃O2S²⁺].

 (2E, NE)-N, 2-bis (2-methoxybenzylidene)hydrazinecarbothioamid, copper(II) salt(2) [Cu(KL-1)2]

Dark green, Yield 0.504g, (78%) MP-160°C Chemical Formula;[C₁₇H₁₇CuN₃O₂S_{2; ]}Exact Mass: 390.03 (Molecular Weight): 390.95, Elemental Analysis: C, 52.23; H, 4.38; Cu, 16.25; N, 10.75; O, 8.18; S, 8.20; Found; C, 52.12; H, 4.27; Cu, 16.22; N, 10.69 O, 8.16 S, 8.17; IR (selected vibrations; cm^-1 ); UV/vis (λmax); 287 nm, Mass spectroscopy (ESI-MS):[M]+ anal for  ;[C₁₇H₁₇CuN₃O₂S_2;]m/z: 195.01 (100.0%), 196.01 (49.3%), 195.52 (18.7%), 196.52 (8.5%), 197.01 (2.2%), 196.02 (2.2%), 195.51 (1.9%), 196.51 (1.7%), 197.02 (1.0%)

(2E,NE)-N,2-bis (2-methoxybenzylidene) hydrazinecarbothioamide, cobalt(II) salt;[Co(KL-1)₂]

Colour; Pink Yield;(0.316g) 82％Molecular Weight: (386.3), MP-168 °C Chemical Formula:[ C₁₇H₁₇CoN₃O₂S²⁺] ; Exact Mass: 386.0; Elemental Analysis: Calculated; C, 52.85; H, 4.44; Co, 15.25; N, 100.88; O, 8.28; S, 8.30; Found: C, 52.84; H, 4.43; Co, 15.23; N, 10.86; O, 8.26; S, 8.37; IR (selected vibrations; in cm^-1) 3283, 2310.80, 1618.13, 1450.81, 1304.86, 1032.02 m/z: 193.0 (100.0%), 193.5 (20.6%), 194.0 (6.9%), 194.5 (1.1%).

 (2E, NE)-N, 2-bis (2-methoxybenzylidene) hydrazinecarbothioamide, zinc (II) salt [Zn (KL-1)2] (3)

White powder obtained, Yield: 0.456g, (71%), MP-178°C. Chemical Formula: [Zn (C17H₁₇N₃O2S)₂] (MW, 392). Elemental analyses: Calculated; C, 51.98; H, 4.36; N, 10.70; O, 8.15.; S, 8.16.; Zn, 16.65. Found; C, 5-1.90; H, 4.32; N, 10.55; O, 8.13; S, 8.15; Zn, 16.40.IR (selected vibrations; cm^–1); 3337, 1630, 1327, 547. ¹HNMR (DMSO- d6, δ, ppm); 8.59 (2H), 8.36 (2H), 8.18 (2H), 8.06 (2H), 7.91 (2H), 7.86 (2H), 7.61 (2H), 7.535(2H), 7.28 (2H); UV/vis (λmax); 279nm, Mass spectrometry (ESI-MS): m/z: 195.5 (100.0%), 196.5 (64.3%), 197.5 (44.4%), 197.0 (21.3%), 196.0 (20.6%), 198.0 (9.2%), 197.5 (4.1%)

(2E, NE)-N, 2-bis (2-methoxybenzylidene)hydrazinecarbothioamide, silver(I) salt(4)-[Ag(KL-1)]

Have been synthesis, Black colour; Yield (0.332g) 78％; MP-158°C. Chemical Formula: C₁₇H₁₇AgN₃O₂S₂ Exact Mass: 434.0 Molecular Weight: (435.3), m/z: 217.0 (100.0%), 218.0 (99.8%), 217.5 (20.6%), 218.5 (20.2%), 219.0 (6.6%), 219.5 (1.0%)Elemental Analysis: Calculated; C, 46.91; H, 3.94; Ag, 24.78; N, 9.65; O, 7.35; S, 7.37 , Found; C, 46.81; H, 3.74; Ag, 24.68; N, 9.63; O, 7.32; S, 7.375 ,IR (selected vibrations; cm¹); 2922.78, 1618.76 , 2851.23, 1524.20, 1777.64, 1034.07, 2366.76, 1361.50, 795.59, 547.24.

(2E,NE)-N,2-bis(2-methoxybenzylidene)hydrazinecarbothioamide,cadmium(II)Salt(5) salt(5)[Cd(KL-1)2]

Colour; White; Yield; (0.352g) 80％; MP-163°C Chemical Formula: [C₁₇H₁₇CdN₃O₂S²⁺]Molecular Weight:( 439.8); Exact Mass: 441.0; Elemental Analysis: calculated ;   C, 46.42; H, 3.90; Cd, 25.56; N, 9.55; O, 7.28; S, 7.29; Found; C, 46.40; H, 3.90; Cd, 25.52; N, 9.54; O, 7.26; S, 7.27,;IR (selected vibrations; 2921.46, 1359.20, 1591.42, 1040.77, 1121.23, 855.24, 545.87 m/z: 220.5 (100.0%), 219.5 (83.5%), 220.0 (55.1%), 219.0 (46.5%), 218.5 (38.0%), 221.5 (29.2%), 221.0 (21.3%), 222.0 (5.7%), 216.5 (3.8%), 217.5 (3.0%), 222.5 (1.7%)

(2E,NE)-N,2-bis(2-methoxybenzylidene)hydrazinecarbothioamide, lead(II) salt [Pb(KL1)2] (6)

Colour; Creamy white; Molecular Weight: 534.6; Yield; (0.406)76%; MP176°Chemical Formula:[C₁₇H₁₇N₃O₂PbS²⁺]; Exact Mass: 535.1; Elemental Analysis: Calculated; C, 38.19; H, 3.21; N, 7.86; O, 5.99; Pb, 38.76; S, 6.00; Found.;: C, 38.17; H, 3.20; N, 7.84; O, 5.97; Pb, 38.75; S, 6.00; IR (selected vibrations; in cm^-1)-3284, 1617,  1450,m/z: 267.5 (100.0%), 267.0 (46.2%), 266.5 (41.3%), 268.0 (21.5%), 268.5 (6.7%), 265.5 (2.4%), 269.0 (1.0%)

Figure 1: Proposed structure of KL-1 (ligand) and their metal complexes. Click here to View figure

Scheme-2 Synthesis of KL-2 Ligand

Scheme 2: Synthesis of KL-2 Ligand and synthesis of metal complexes. Click here to View scheme

Synthesis of (2E)-N,2-bis(3-methoxybenzylidene)hydrazine carbothioamide, nickel(II) salt (2)

Colour; Dark green (powder),; Yield; (0.03gm)78,; MP-158℃;Chemical Formula:C₁₇H₁₇N₃NiO₂S²⁺,Mass;385.0,; Molecular Weight: 386.1; Elemental Analysis: Calculated – C, 52.88; H, 4.44; N, 10.88; Ni, 15.20; O, 8.29; S, 8.30  Observed; C,52.83; H,4.42; N,10.85, Ni,  15.20;O, 8.25; S,8.28; IR (selected vibrations; in cm^-1)-m/z: 192.5 (100.0%), 193.5 (45.5%), 193.0 (20.6%), 194.0 (10.7%), 194.5 (8.5%), 195.5 (1.8%), 195.0 (1.7%)

Synthesisof(2E)-N,2-bis (3-methoxybenzylidene) hydrazinecarbothioamide, copper (II) salt-(1)

Colour; Green, (powder) Yield 80% (0.031gm),MP-145℃, Mass:390.0, Chemical Formula: C₁₇H₁₇CuN₃O₂S²⁺, Elemental Analysis: Calculated- C, 52.23; H, 4.38; Cu, 16.25; N, 10.75; O, 8.18; S, 8.20 Observed-C, 52.21; H, 4.37; Cu, 16.22, N, 10.72; O, 8.16; S, 8.18. m/z: 195.0 (100.0%), 196.0 (51.5%), 195.5 (20.6%), 196.5 (10.3%), 197.0 (3.2%)

(2E)-N,2-bis(3-methoxybenzylidene)hydrazinecarbothioamide, silver(I) salt(4)

Colour; dark black powder; Yield (0.036)85%, MP-190℃ Chemical Formula: C₁₇H₁₇AgN₃O₂S⁺² Molecular Weight: 435.3;Elemental Analysis:Calculated- C, 46.91; H, 3.94; Ag, 24.78; N, 9.65; O, 7.35; S, 7.37, Observed-Elemental Analysis: C, 46.90; H, 3.92; Ag, 24.75; N, 9.64; O, 7.32; S, 7.36m/z: 434.0 (100.0%), 436.0 (99.8%), 435.0 (20.6%), 437.0 (20.2%), 438.0 (6.6%), 439.0 (1.0%)   1584.05,1487.97 ,1338.45, 1258.49,, 759.86 683.24 525.01

(2E)-N,2-bis(3methoxybenzylidene)hydrazinecarbothioamide, cadmium(II)salt-(5)

Colour; white powder; Yield (0.352gm) 80%,MP- 196 ℃;  Mass: 441.0 Chemical Formula: C₁₇H₁₇CdN₃O₂ S²⁺, Elemental Analysis: (Calculated) C, 46.42; H, 3.90; Cd, 25.56; N, 9.55; O, 7.28; S, 7.29; Observed; C, 46.42; H, 3.82; Cd, 25.53; N, 9.54; O, 7.27; S, 7.27; IR (selected vibrations; in cm^-1)- m/z: 220.5 (100.0%), 219.5 (83.5%), 220.0 (55.1%), 219.0 (46.5%), 218.5 (38.0%), 221.5 (29.2%), 221.0 (21.3%), 222.0 (5.7%), 216.5 (3.8%), 217.5 (3.0%), 222.5 (1.7%)

Synthesis of (2E)-N, 2-bis (3methoxybenzylidene) hydrazine- carbothioamide, lead (II) salt-(3)

Colour; Creamy white; Yield (0.041 gm.) MP- 200℃ 78,Chemical Formula: C₁₇H₁₇N₃O₂PbS²⁺, Mass: 535.1; Elemental Analysis: Calculated – C, 38.19; H, 3.21; N, 7.86; O, 5.99; Pb, 38.76; S, 6.00; Observed -C, 38.18; H, 3.19; N, 7.84; O, 5.94; Pb, 38.74; S, 6.00; IR (selected vibrations; in cm^-1)- 1401.82,667.19, 505.91 m/z: 267.5 (100.0%), 267.0 (46.2%), 266.5 (41.3%), 268.0 (21.5%), 268.5 (6.7%), 265.5 (2.4%), 269.0 (1.0%)

Scheme 3: The proposed structure of KL-2(ligand) and their metal complexes. Click here to View Scheme

Results and Discussion

 Mixed ligand Complexes (Schiff bases) KL-1 and KL-2 were synthesized by reaction of 2-methoxy benzaldehyde and 3- methoxy benzaldehyde with thiosemicarbazide in a 2:1 ratio in Ethanol in the presence of the catalytic amount of dilute acetic acid (Scheme 1).   Metal complexes of corresponding Schiff bases were prepared by using nitrate salt. The resulting metal complexes were neutral, colored, air-stable, and remarkably soluble in DMF and DMSO Table- 1    Summarize the Physicochemical properties of ligands and their metal complexes, and Table -2 and Table -3 summarize the antibacterial and anti-fungal activity of the ligands and corresponding metal complexes. By using the Spectroscopic technique and elemental analysis all synthesized compounds were characterized. i.e., IR, UV/Vis, ¹HNMR, and mass spectrometry. FT-IR Spectroscopy (cm^-1); 3402.21, 3283.77 they obtained stretching frequency at 1684.38 which is basically responsible for the conformation of Schiff base (stretching -C=N- imino), lowing of this transition because of the presence of Thio and methoxy electron-withdrawing groups.The IR spectra of Schiff base ligand (KL-1)  shows strong band at 3402.21, 3283.77 , 1684.38  due to  (stretch, -C=N- imino),1455.34 (CH₃ bend) ,1281.64 (aromatic -C=C-), 1234.86 (C-O-C stretch)3402.21 (strong N-H stretch) ,3283.77(=CH-H stretch)  ¹H NMR: of KL-1 in (DMSO-d6, δ, ppm) 8.2-7.5 (m, 4H, J = 1.36 Hz), 6.6 (s. 1H) 7.4-7.3 (d, 1H), 3.68 (m, 5H), 2.54 (s, 3H), 2.48 (m, 4H)  Mass Spectroscopy (ESI-MS): 302 [M+H₂O+H]  anal for C₁₅H₁₂N₂O₃S. UV/vis; 301 nm, 270 nm. Reaction progress was determined by using the thin-layer chromatographic technique [26]. Here we are using a conventional method which is to report an effectual practical technique (reflux) for the synthesis of a Schiff base (Scheme 1).

Table 1: Physico-chemical properties of ligand (L) and complexes 

Comp.no.	Colour	Molecular formula	Mo. Weight	Yield %	MP 0C
KL-1	White powder	[C17H17N3O2S]	327.40	76%	168
1-	Green	[Ni(C17H17N3O2S2+].	386.1	80	136
2-	Dark green	[CuC17H17N3O2S2;]	390.95	78	160
3-	Pink	[CoC17H17N3O2S2+]	386.3	82	169
4-	White	[Zn(C17H17N3O2S)]	392	71	178
5-	Black	[AgC17H17N3O2S2]	435.3	78	158
6-	White	[CdC17H17N3O2S2+]	439.8	80	163
7-	Creamy-white	[PbC17H17N3O2S2+]	534.6	76	176
KL-2   Light yellow	Light yellow	[C17H17N3O2S]	327.40	84	158

Antimicrobial Activity

Antifungal Activity (in vitro)  

Aspergillus Niger was obtained from the Department of Microbiology, Dr. Harisingh Gour University, Sagar, MP, and maintained on a Czapek dox medium at 28°C. Antifungal activity [27]. of all compounds was conducted on a solid Czapek dox medium using a well diffusion method against A. Niger. Spores of A. Niger was collected using a wet cotton swab followed by spreading these on the Czapek dox medium. Wells (6 mm in diameter) were formed in the solid agar plates containing Czapek dox medium using a sterilized cork borer. 100 µL test sample was poured into a well and plates were transferred to incubate at 30°C for 48 h. [28-29].

Antibacterial activity

Similarly, the antibacterial activity was assessed against Bacillus subtilis. B. Subtilis was grown and maintained on a nutrient agar medium. In vitro antibacterial activity was evaluated by the well diffusion method as described by Mukherjee et al. The overnight old bacterial culture ws centrifuged at 10000 g for 10 min. The bacterial pellet was washed by suspended in sterile distilled water (20 mL) followed by centrifugation at 10000 g then resuspended in sterilized distilled water and used for the assay. The suspension containing bacterial cells was spread on a solid agar plate and wells (6 mm in diameter) were formed in the solid nutrient agar plates using a sterilized cork borer. 100 µL test sample was poured into a well and plates were transferred to an incubator at 37°C for 24h. [30] After incubation, the zones of inhibition were recorded as the total diameter of the zone of inhibition minus the diameter of the well. All test runs were conducted in triplicate and the average value of inhibition was presented as activity.

Figure 2: Anti-bacteria activity of KL-1 and KL-2 Click here to View figure

Figure 3: Representation of antimicrobial activity of KL-1 and KL-2 and their metal complexes. Click here to View figure

Figure 4: Anti-fungal activity of KL-1 and KL-2 Click here to View figure

 Table 2: Antimicrobial data of [zone of inhibition] of KL-1

S. No.	Dilution coding	Zone of inhibition (in mm)
		Bacillus subtilis	Aspergillus Niger
1.	KL-1	7	8
2.	KL-1 Cu	9	7
3.	KL-1 Ni	8	11
4.	KL-1Ag	10	14
5.	KL-1 Pb	9	9
6.	KL-1 Cd	11	15
7.	Standard drug	16	17

 

Figure 5: Graphical representation of KL-1 and their metal complexes Click here to View figure

Table 3: Antimicrobial data of [Zone of inhibition] of KL-2

S. No.	Dilution coding	Zone of inhibition (in mm)
		Bacillus subtilis	Aspergillus Niger
1.	KL-2	8	8
2.	KL-2 Cu	9	7
3.	KL-2 Ni	8	11
4.	KL-2 Ag	10	14
5.	KL-2 Pb	9	9
6.	KL-2 Cd	11	15
7.	Standard drug	16	17

Figure 6: Graphical representation   of KL-2 and their metal complexes Click here to View figure

Order of antimicrobial activity in used different metal complexes –   Cd>Pb>Ag>Ni >Cu

Conclusion

An antifungal and anti-bacterial evaluation of a series of metal complexes formed from Schiff base tetradentate ligands was performed. Two novel Schiff base derivatives were synthesized from different aldehydes and thiosemicarbazide. The structures of Schiff base ligands and metal complexes were supported by different spectroscopic techniques such as FT-IR, 1H-NMR, and high-resolution mass spectrometry (HRMS).    By using the conventional method [3]. We have synthesized some thiosemicarbazide-derived Schiff base and their metal complexes by the green conventional method [Reflux method].  Preparation of Schiff base by using reflux method was completed within 5-7 h, high yields and all the product obtained were moderate to moral yields, and such type of methodology condensed the time and creation of by-products. Synthesis is simple and eco-friendly and can be used as an alternative to the existing conventional heating method [31]. From the results of anti-bacterial and anti-fungal studies, [32]. It was concluded that the tested compounds exhibited significant antibacterial activities against both Bacillus subtilis fungi and Aspergillus Niger organisms. Among the tested compounds, compounds with Ag (I), Pb (II), and Cd (II) display promising antibacterial and antifungal activities [33]. Such analysis ascribed the greater electronic attractiveness which favors greater diffusion through the microbial membrane.The results of this study revealed that these complexes have a targeted activity, although, other modes of action cannot be ruled out because metal complexes are known to target multiple pathways to evade drug resistance.[34].

Acknowledgment

All The authors gratefully acknowledge the economic and financial support for Dr. Harisingh Gour [A Central University] Vishwavidyalaya Sagar, Department of Chemistry Sagar (MP) for laboratories facilities to carry out the work. We are thankful to the Head, Department of Chemistry, SIC of Dr. H. S. Gour University, for providing a laboratory and another facility, IISER Bhopal for spectral analysis [mass spectrometry].  We are also grateful to the Department of Microbiology for carrying out antimicrobial studies.

 Conflict of Interest

Authors have no conflict of interest

References

1. Wiederhold N., Infect. Drug Resist., 2017, 10, 249–259.
2. Fisher M. C . Hawkins N. J, Sanglard D., and Gurr S. J., Science, 2018, 360, 739–742.
3. 3 – Denning D. W., Philos. Trans. Soc R.., B, 2016, 371, 20150468.
4. Pfaller M. A., Diekema D. J, Gibbs D. L, Newell V. A, J. F. Meis, I. M. Gould, W. Fu, A. L. Colombo and E. Rodriguez-Noriega, J. Clin. Microbiol., 2007, 45, 1735– 1745.
5. O’Conner, MJ.:  West BO (1967) Metal Complexes of Hydrogenated Schiff Bases. Aust J Chem 20:2077–2085. https://doi.org/10.1071/CH9672077
6. Parham, S.; Kharazi AZ, Bakhsheshi-Rad HR, et al (2020) Antioxidant, antimicrobial and antiviral properties of herbal materials. Antioxidants 9:1–36. https://doi.org/10.3390/antiox9121309
7. Mishra, N,.: Kumar K, Pandey .:H, et al (2020) Synthesis, characterization, optical and anti-bacterial properties of benzothiazole Schiff bases and their lanthanide (III) complexes. J Saudi Chem Soc 24:925–933. https://doi.org/10.1016/j.jscs.2020.09.009
8. Josephus, RS; Nair MS (2008) Antibacterial and Antifungal Studies on Some Schiff Base Complexes of Zinc (II). Mycobiology 36:93. https://doi.org/10.4489/myco.2008.36.2.093
9. Mishra, N; Gound, SS; Mondal, R; et al (2019) Synthesis, characterization and antimicrobial activities of benzothiazole-imino-benzoic acid ligands and their Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes. Results Chem 1:100006. https://doi.org/10.1016/j.rechem.2019.100006
10. Mishra, AP; Sharma, N.; Jain RK (2013) Microwave Synthesis, Spectral, Thermal and Antimicrobial Studies of Some Ni (II) and Cu (II) Schiff Base Complexes. Open J Synth Theory Appl 02:56–62. https://doi.org/10.4236/ojsta.2013.22007
11. 11-Tokalı, FS.; Taslimi, P.; Usanmaz, H.; et al (2021) Synthesis, characterization, biological activity, and molecular docking studies of novel Schiff bases derived from thiosemicarbazide: Biochemical and computational approach. J Mol Struct 1231 https://doi.org/10.1016/j.molstruc.2020.129666
12. 12- Avasthi, K; Yadav.; Khan, T.; (2018) Greener and Efficient Synthesis of Some Novel substituted Azitidinones With 4- Amino Pyridine via Heterogenous catalyst
13. 13-Govindula, A.;(2020) of Biomedical AND Pharmaceutical sciences. 7:174–190
14. 14- Sahu, M; Manna AK, Rout K, et al (2020) Inorganica Chimica Acta A highly selective thiosemicarbazone based Schiff base chemo sensor for colorimetric detection of Cu 2 + and Ag + ions and turn-on fluorometric detection of Ag + ions. Inorganica Chim Acta 508:119633. https://doi.org/10.1016/j.ica.2020.119633
15. 15-Mishra, N.; Kumar, K.; Pandey, H.; et al (2020) Synthesis, characterization, optical and anti-bacterial properties of benzothiazole Schiff bases and their lanthanide (III) complexes. J Saudi Chem Soc 24:925–933. https://doi.org/10.1016/j.jscs.2020.09.009
16. 16- Patil, S.; Jadhav, SD.; Shinde, SK.; (2012) CES as an Efficient Natural Catalyst for Synthesis of Schiff Bases under Solvent-Free Conditions: An Innovative Green Approach. Org Chem Int 2012:1–5. https://doi.org/10.1155/2012/153159
17. 17- Synthesis, SB.; Antioxidant I(2018) Cu (II) Complexes https://doi.org/10.3390/molecules23071581.
18. 18- Raju, VV.; Balasubramanian, KP. ;(2011) Synthesis, spectral characterization, catalytic and biological studies of new Ru (II) carbonyl Schiff base complexes of active amines. 3:542–550
19. 19- Jeewoth, T.; Bhowon, MG.; Li H.; Wah K (1999) Synthesis, characterization and antibacterial properties of Schiff bases and Schiff base metal complexes derived from 2, 3-diamino- pyridine. 448:445–448
20. 20- Khan, T.;(2018) An Efficient Synthesis and Antibacterial Activity of Some Novel 2- Azetidinone Derivatives of 4H-1,2,4-Triazoles Under Mild Conditions. 2–7. https://doi.org/10.1002/jhet.3136
21. 21-Sunil, K.; Kumara, TPP.; Kumar, BA.; Patel, SB.;(2021) Synthesis, Characterization and Antioxidant Activity of Schiff Base Compounds Obtained Using Green Chemistry Techniques. Pharm Chem J 55:46–53. https://doi.org/10.1007/s11094-021-02370-8
22. 22- Manjula, SN.; Malleshappa Noolvi N, Vipan Parihar K, et al (2009) Synthesis and antitumor activity of optically active thiourea and their 2-aminobenzothiazole derivatives: A novel class of anticancer agents. European J Med Chem 44:2923–2929. https://doi.org/10.1016/j.ejmech.2008.12.002
23. 23- Chetana, PR..; Somashekar, MN.; Srinatha, BS.; et al (2013) Synthesis, Crystal Structure, Antioxidant, Antimicrobial, and Mutagenic Activities and DNA Interaction Studies of Ni(II) Schiff Base 4-Methoxy-3-benzyloxybenzaldehyde Thiosemicarbazide Complexes. ISRN Inorg Chem 2013:1–11. https://doi.org/10.1155/2013/250791
24. 24- Abdel-Rahman, LH.; Abu-dief, AM.; El-khatib, RM..; Abdel-Fatah, SM .;(2016) Bioorganic Chemistry Some new nano-sized Fe ( II ), Cd ( II ), and Zn ( II ) Schiff base complexes as a precursor for metal oxides : Sonochemical synthesis, characterization, DNA interaction, in vitro antimicrobial and anticancer activities. Bioorg Chem 69:140–152. https://doi.org/10.1016/j.bioorg.2016.10.009
25. 25- Luo, Y.; Zhang, S.; Liu ZJ, et al (2013) Synthesis and antimicrobial evaluation of a novel class of 1,3,4-thiadiazole: Derivatives bearing 1,2,4-triazolo[1,5-a] pyrimidine moiety. Eur J Med Chem 64:54–61. https://doi.org/10.1016/j.ejmech.2013.04.014
26. 26- Kosti, P.; Ahmad, G.; Ratnesh, N.; et al (2021) and ­ Cd 2 + metal complexes of Schiff base ligand derived from 4 ‑ amino benzoic acid and isonicotinic hydrazide. J Iran Chem Soc 18:1773–1780. https://doi.org/10.1007/s13738-020-02148-x
27. 27- Al-Hamdani, AAS.; Al Zoubi, W.; (2015) New metal complexes of N3 tridentate ligand: Synthesis, spectral studies, and biological activity. Spectrochim Acta – Part A Mol Biomol Spectrosc 137:75–89. https://doi.org/10.1016/j.saa.2014.07.057
28. 28- AM A-D ;(2019) Azomethine Metal Chelates as an Efficient Catalyst for Oxidation of Organic Compounds. Ann Chem Sci Res 1:2–4. https://doi.org/10.31031/acsr.2019.01.000515
29. 29- Kasare, MS.; Dhavan, PP.; Jadhav, BL.; Pawar SD (2019) Synthesis of Azo Schiff Base Ligands and Their Ni (II), Cu ( II ) and Zn ( II ) Metal Complexes as Highly-Active Antibacterial Agents. 10792–10797. https://doi.org/10.1002/slct.201901605
30. 30- Magaldi, S.; Capriles, CH De.; Deibis L, et al (2001) “In vitro” Antifungal activity of protease inhibitors. 135–142
31. 31- Luo Y, Zhang S, Liu ZJ, et al (2013) Synthesis and antimicrobial evaluation of a novel class of 1,3,4-thiadiazole: Derivatives bearing 1,2,4-triazole [1,5-pyrimidine moiety. Eur J Med Chem 64:54–61. https://doi.org/10.1016/j.ejmech.2013.04.014
32. 32- Chetana PR, Somashekar MN, Srinatha BS, et al (2013) Synthesis, Crystal Structure, Antioxidant, Antimicrobial, and Mutagenic Activities and DNA Interaction Studies of Ni (II) Schiff Base 4-Methoxy-3-benzyloxybenzaldehyde Thiosemicarbazide Complexes. ISRN Inorg Chem 2013:1–11. https://doi.org/10.1155/2013/250791
33. 33- K, SDR.; Sudhakumari. ;(2020) Synthesis, Characterization and Antimicrobial studies of Schiff base Ligand from the amino acid L-arginine and its Cu ( II ), Ni ( II ), Co ( II ) complexes. 13:1–8
34. 34-Parikh, KS.; Vyas, SP.; (2012) Synthesis and spectral studies of some novel Schiff base derived with pyrimidines. Der Pharm Lett 4:638–640

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