Studies on Metal Complexes of Pyrazole Bearing Ligand with Their Antimicrobial Screening

Introduction

Nowadays Metals complexes become very important in the field of medicinal chemistry^1,2. The divalent transition metals show various biochemical reactions ³. The researchers synthesised number of metal complexes having organic ligands due to their various biological activities ^4-6. 8-Hydroxy quinoline (8-HQ) is a significant heterocyclic compound in metal complexation due to their medicinal properties like antibacterial, anti-fungal, anti-malaria, anti-HIV anti-cancer^7-11. By chelation process 8- Hydroxy quinoline form metal complexes with divalent transition metal ions¹². 8-HQ shows potential therapeutic effect for the treatment in metabolism problem occurs due to of irregularity of metal and/or imbalance in metal ion problem in human body ^13,14. Hence, we synthesis metal complexes based on heterocyclic ligand and screened them for their antimicrobial activity. 

Scheme 1: Whole research work Click here to View Scheme

Experimental

1-(1H-benzimidazol-1-yl) propan-2-one (BIP) was synthesised from reported method^13,14.Laboratory grade chemicals were usd. The present element were analysed by titrimertically method ¹⁵. For IR and NMR spectra study Nicolet 760 FT-IR spectrometer and 60 MHz NMR spectrophotometer were used. The electronic spectra studied carried out using MgO. The evaluation of antimicrobial screening was analysed by Broth Dlution method^16,17. The whole reaction work is summarized in following scheme-1.

Synthesis of 1-(1H-benzimidazol-1-yl)-4-phenyl but-3-en-2-one (BIPB)^18,19

A mixture of 1-(1H-benzimidazol-1-yl) propan-2-one (BIP) (1m mol) andbenzaldehyde (1m mol) in C₂H₅OH (20 ml), was added dropwise to alkali solution of KOH, and stirred for 1day at 25°C. The reaction mixture added into ice cold water containing beaker with stirring. The resultant solid separated out and crystallized by R-sprit. The Yield was 76% and m.p was 123-124°C. The elemental analysis for C₁₇H₁₄N₂O (262 gm/mol),Cal.(Found) %C-77.84(77.8);%H-5.38(5.3) and %N-10.68(10.6). 

IR spectra (cm^-1,KBr): 3021 (Aromatic C-H Str.), 2900, 2820, 1500, 1380(C-H Str.), 1660 (CO), 1600 (N=C), 1580 (C=C). ¹HNMR(δ,ppm): 7.02-8.12 (m, 10H,benzimidazole, Aromatic-H), 4.96 (s, 2H, -N-CH₂-CO-), 6.47, 8.51(d, 2H, ethylene); 13C NMR (ppm): 196.51(CO), 112.31-138.25(Ar-C),58.34(CH₂), 148.88, 154.06 (C=C). Mass (m/z) : 263 (M+1)⁺. 

Synthesis of 1-((5-phenyl-1H-pyrazol-3-yl) methyl)-1H-benzimidazole (BIPP) ^19,20: 

Reflux a mixture of 1-(1H-benzimidazol-1-yl)-4-phenyl but-3-en-2-one (BIPB)  ( 0.5 m mol) in ethanol (5 ml), hydrazine hydrate(1.5 m mol)  for 4-5hrs. Aftyer completion of reaction, it was cooled at 0°C for overnight. The formed product was filtered, washed, dried and recrystallized from C₂H₅OH. 82% yield and  m.p. 160–161°C. The elemental analysis for C₁₇H₁₄N₄(274 gm/mol),Cal.(Found) %C-74.43(74.4);%H-5.14(5.1) and %N-20.42(20.4). IR spectra KBr (cm^-1):IR (KBr): ν 3425 (NH), 3020 (Aromatic C-H Str.), 2900, 2820, 1530, 1370(C-H Str.),1600 (C=N). 1HNMR (δ,CDCl₃,TMS): 7.29-7.87 (m,10H,Ar-H), 6.09 (s, 1H, NH), 4.82(s,2H,CH2), 5.15 (s, 1H, Hpyraz). 13C NMR : δ 113.7-148.8 (Ar-C), 57.8 (CH2),103.2(pyraz C-H), Mass (m/z) : 275 (M+1)⁺. 

Synthesis of 5-((3-((1H-benzimidazol-1-yl)methyl)-5-phenyl-1H-pyrazol-1-yl) methyl) -8-hydroxy quinoline (BIPPHQ)¹⁹: 

A mixture of triethyl amine (0.5 m mol) and 5-chloromethyl-8-hydroxy quinoline (0.5 mmol) was added with stirring to a cold mixture of 1-((5-phenyl-1H-pyrazol-3-yl) methyl)-1H-benzimidazole (BIPP) ( 0.5 m mol) in dry acetone (5 ml) at 0°C. Whole mixture was continuous stirred for 2 hrs 25°C. The solid product was separated out , it was filtered and  recrystallized from C₂H₅OH. yield was 70% and m.p. was 178–1789°C. The elemental analysis for C₂₇H₂₁N₅O (431 gm/mol),Cal.(Found) %C-75.16(75.1);%H-4.91(4.9) and %N-16.23(16.2). IR spectra (KBr, cm^-1) 3298(-OH),2932(CH2), 3028 (Aromatic C-H Str.), 2932, 2840,1508(C-H Str.),1619,1576,1508,1456(8-HQ moiety), 1508 (C=C),1456(C-C),1576 (C=N),1275-1298(C-N). 1HNMR (δ,CDCl₃,TMS): δ 7.29-7.98 (m,15H,Ar-H), 4.77-4.42 (s,4H,CH2), 5.11 (s, 1H, Hpyraz),9.51(s,1H,-OH). 13C NMR: δ 116.1-152.2(Ar-C), 51.9,58.7 (CH2),105.6 (pyraz C-H). Mass (m/z) : 432 (M+1)⁺. 

Synthesis of Metal complexes of 5-((3-((1H-benzimidazol-1-yl)methyl)-5-phenyl-1H-pyrazol-1-yl)methyl)-8-hydroxy quinoline (BIPPHQ)

The metal complexes of  BIPPHQ (i.e. of  Ni (II), Zn (II) , Cu (II), Mn (II) and Co (II) ions) were prepared by similar manner. The method as follow,

A preheated solution of salt of M(II) (2.5mmol) in aqueous formic acid (1:1,2.5ml) was added to the preheated  aqueous formic acid solution (20%,20ml) of BIPPHQ (5mmol) with stirring. Adjust the pH with NH₄OH (50%) solution and digested for 4hrs. The resultant product was filtered, washed and air-dried. All complexes were prepared and isolated in amorphous shape.

Table 1: Analysis of BIPPHQ and Its Metal Complex

Ligand and  Metal complexes	Elemental analysis (%)
	Mol. Wt.	Color	Yield %	%C	% H	% N	%M
				Calc. Found	Calc. Found	Calc. Found	Calc. Found
C27H21N5O	431	White	70	75.16 75.1	4.91 4.9	16.23 16.2	– –
C54H40N10O2Cu(II).2H2O	960.54	Pale white	67	67.52 67.5	4.62 4.6	14.58 14.5	6.62 6.6
C54H40N10O2Ni(II).2H2O	955.71	Greenish white	64	67.87 67.8	4.64 4.6	14.66 14.6	6.14 6.1
C54H40N10O2Co(II).2H2O	955.94	Off white	68	67.85 67.8	4.64 4.6	14.65 14.6	6.17 6.1
C54H40N10O2Zn(II).2H2O	962.38	Pale yellow	62	67.39 67.3	4.61 4.6	14.55 14.5	6.79 6.7
C54H40N10O2Mn(II).2H2O	951.94	Off  white	65	68.13 68.1	4.66 4.6	14.71 14.7	5.77 5.7

 

Table 2: Electronic spectral data and magnetic properties of metal  complexes of BIPPHQ

Metal  complexes	µeff (B.M.)	Electronic spectral  data (cm-1)	Transition
BIPPHQ-Cu(II)	1.92	23985 15763	CT 2B1g🡪 2A1g
BIPPHQ-Ni(II)	3.23	22239 15790	3A2g🡪 3T1g (P) 3A2g🡪 3T1g (F)
BIPPHQ-Co(II)	4.82	23955 18118 8742	4T1g(F) 🡪6T2g(õ1) 4T1g(F) 🡪 4A2g(õ2) 4T1g(F) 🡪 4A2g(υ2)
BIPPHQ-Mn(II)	5.52	23887 18340 16845	6A1g🡪6A1g(4Eg) 6A1g🡪4T2g(4G) 6A1g🡪4T1g(4G)
BIPPHQ-Zn(II)	Diamagnetic	–	–

 

Thermogravimetric analysis of synthesised BIPPHQ and metal complexes were carried out by Du point Thermo-gravimetric analyzer.

Table 3: Thermogravimetric analysis of BIPPHQ and metal complexes

Ligand/ Metal chelates	% Weight loss at various temperature(°C)
	100	200	300	400	500	600	700
BIPPHQ	–	8.90	10.46	24.60	29.80	32.09	35.25
BIPPHQ-Cu(II).2H2O	0.04	5.73	12.33	27.88	33.59	37.14	39.9
BIPPHQ-Ni(II).2H2O	3.21	16.45	20.12	37.77	53.95	66.35	69.57
BIPPHQ-Co(II).2H2O	2.53	13.70	25.36	39.83	53.63	65.32	68.86
BIPPHQ-Zn(II).2H2O	7.46	16.05	32.20	37.49	56.26	67.35	70.12
BIPPHQ-Mn(II).2H2O	3.26	10.56	14.66	35.85	54.44	67.04	69.56

Results And Discussion

The synthesis of 5-((3-((1H-benzimidazol-1-yl)methyl)-5-phenyl-1H-pyrazol-1-yl)methyl)-8-hydroxy quinoline (BIPPHQ) synthesisd from 1-(1H-benzimidazol-1-yl) propan-2-one (BIP) and benzaldehyde. Table-1 data consist with the structure of synthesised compounds (Scheme-1). The most unique IR bands of BIPPHQ  shows which may be  due to 8-hydroxy quinoline, which are presented at 3298 (-OH), 2932(CH₂), 1576 (C=N) cm^-1.

BIPPHQ shows NMR peak at 9.51 for OH. The methylene proton shows singlet at 4.77-4.41 δ. It confirmed the structure of BIPPHQ.

Figure 1: 1H NMR of BIPPHQ Click here to View Figure

The elemental ananalysis (Table-I) are confirmed that the all metal complexed are divalent.

Figure 2: LC-MS of BIPPHQ Click here to View Figure

The significant differnece in IR of Ligand and metal complexes is the band of hydroxyl  group at 3298cm^-1 , which is absent in metal complexe may be due to complextion loos of hydrogen of hgydroxyol group^21,22. 

Table-2 shows the electronic spectral data and magnetic properties of metal complexes of BIPPHQ, which are shows the octahedral geometry of metal complexes^21-23. 

Table 4: Antibacterial activity of BIPPHQ and metal complexes

Compounds	MIC,μgmL-1
	Gram positive		Gram negative
	B.megaterium	S.Aureus	E.Coli	Ps.Aeruginosa
BIPPHQ	150	125	150	150
BIPPHQ -Cu(II)	25	50	25	50
BIPPHQ -Ni(II)	75	100	100	75
BIPPHQ -Co(II)	50	50	75	75
BIPPHQ -Zn(II)	75	100	100	100
BIPPHQ -Mn(II)	100	125	125	125
Amoxillin	250	150	250	200

 

Antibacterial and antifungal screening of BIPPHQ and metal complexes (Table-3 and 4) shows that  the metal complexes are more toxic than BIPPHQ, out of them metal complexes of Cu(II) is most toxic.

Table 5: Antifungal activity of BIPPHQ and metal complexes.

Compounds	Minimum Inhibitory Concentration (MIC, μgmL-1)
	Penicillium Expansum	Botrydepladia Thiobromine	Nigrospora Sp.	Fusarium oxyporium
BIPPHQ	150	150	125	150
BIPPHQ -Cu(II)	25	50	25	50
BIPPHQ-Ni(II)	125	100	100	125
BIPPHQ-Co(II)	100	125	100	125
BIPPHQ-Zn(II)	75	50	75	75
BIPPHQ-Mn(II)	150	125	100	125
Nystatin	300	200	250	200

 

Conclusion

The novel hetertocyclic ligand containing metal complxes of 5-((3-((1H-benzeimidazol-1-yl) methyl) -5-phenyl -1H-pyrazol-1-yl) methyl)-8-hydroxy quinoline (BIPPHQ) were sythsised.  All the characterization method predicted the structure of synthesised compounds. Antimicrobial screening of BIPPHQ and metal complexes were shows good effectiveness.

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest

The author(s) do not have any conflict of interest.

Data Availability Statement

This statement does not apply to this article.

Ethics Statement

This research did not involve human participants, animal subjects, or any material that requires ethical approval.

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