Synthesis, Physico-Chemical investigations of Co(II), Ni(II) and Cu(II) complexes and their in vitro microbial, cytotoxic, DNA cleavage studies

Figures & data

Scheme 1.  Synthesized metal complexes.

Table 1.  Elemental analysis of Schiff base and its Co(II), Ni(II), and Cu(II) complexes with magnetic and molar conductance data.

Empirical formula	M (%)		C (%)		H (%)		N (%)		Molar conductance (ohm^−1 cm^−2 mol^−1)	Mag. moment (µeff, BM)
	Obsd.	Calcd.	Obsd.	Calcd.	Obsd.	Calcd.	Obsd.	Calcd.
C20H14N2O3S	—	—	66.23	66.29	3.81	3.86	7.69	7.73	—	—
Co(C20H14N2O3S)2.2H2O	7.19	7.21	58.72	58.75	3.17	3.20	6.82	6.85	26	4.92
Ni(C20H14N2O3S)2.2H2O	7.14	7.18	58.74	58.77	3.14	3.18	6.84	6.86	30	3.38
Cu(C20H14N2O3S)2.2H2O	7.69	7.73	58.39	58.43	3.13	3.16	6.78	6.82	20	1.74

Table 2.  Important infrared frequencies (in cm⁻¹) of Schiff base and its Co(II), Ni(II), and Cu(II) complexes.

Empirical formula	Coordinated water ν(OH)	ν(C-S-C)	ν(C=N)	ν(C=O)	H-bonded -OH stretching	M-N	M-O
C20H14N2O3S	—	865	1645	1740	2674	—	—
[Co(C20H14N2O3S)2].2H2O	3440	862	1630	1738	—	455	530
[Ni(C20H14N2O3S)2].2H2O	3420	861	1625	1736	—	435	540
[Cu(C20H14N2O3S)2].2H2O	3435	860	1627	1739	—	430	545

Table 3.  Ligand field parameters of Co(II) and Ni(II) complexes.

Empirical formula	Transition (cm^−1)			ν2 calcd. (cm^−1)	Dq (cm^−1)	B^1 (cm^−1)	% Distortion	ν2/ν1	LFSE	µeff calcd. (BM)	β	β° (%)
	ν1	ν2	ν3
[Co(C20H14N2O3S)2].2H2O	9680	—	19,845	20,530	1085.0	755.70	—	2.12	24.80	—	0.781	21.85
[Ni(C20H14N2O3S)2].2H2O	10,416	16,459	26,452	16,495	1041.6	779.96	0.220	1.58	35.71	3.17	0.739	26.14

Figure 1.  FAB-mass spectrum of Schiff base.

Figure 2.  FAB-mass spectrum of Co(II) complex.

Figure 3.  Thermogravimetric (TGA/DTG) curves of Cu(II) complex.

Figure 4.  Thermogravimetric (TGA/DTG) curves of Ni(II) complex.

Table 4.  Thermogravimetric data of Co(II), Ni(II), and Cu(II) complexes.

Empirical formula	Decomposition temperature (°C)	%Weight loss		Inference
		Obsd.	Calcd.
[Co(C20H14N2O3S)2].2H2O	175–198	4.38	4.41	Loss of water molecule
	250–270	42.54	42.59	Loss of 2-amino-4-phenyl-1,3-thiazole
	365–420	45.75	45.78	Loss of aldehyde moieties
[Ni(C20H14N2O3S)2].2H2O	170–195	4.37	4.40	Loss of water molecule
	245–260	42.58	42.61	Loss of 2-amino-4-phenyl-1,3-thiazole
	370–415	45.74	45.79	Loss of aldehyde moieties
[Cu(C20H14N2O3S)2].2H2O	205–230	4.35	4.39	Loss of water molecule
	310–340	42.31	42.35	Loss of 2-amino-4-phenyl-1,3-thiazole
	570–605	45.47	45.52	Loss of aldehyde moieties

Figure 5.  Cyclic voltammogram of Cu(II) complex.

Table 5.  Antibacterial results for Schiff base and its Co(II), Ni(II), and Cu(II) complexes.

Compound	Conc. (μg/mL)	Antibacterial activity (zone of inhibition in %)				Antifungal activity (zone of inhibition in %)
		E. coli	S. aureus	S. pyogenes	P. aeruginosa	A. flavus	Cladosporium	A. niger
C23H18N4O6S	100	67	64	59	69	84	74	79
[Co(C23H16N4O6S)].2H2O	100	80	77	65	87	85	78	77
[Ni(C23H16N4O6S)].2H2O	100	78	74	68	71	98	97	82
[Cu(C23H16N4O6S)].2H2O	100	89	82	71	85	75	70	88
Gentamicin/fluconazole	100	100	100	100	100	100	100	100

Figure 6.  Antibacterial study of Schiff base and its Co(II), Ni(II), and Cu(II) complexes.

Figure 7.  Antifungal study of Schiff base and its Co(II), Ni(II), and Cu(II) complexes.

Table 6.  Minimum inhibitory concentration (MIC, μg/mL) results for Schiff base and its Co(II), Ni(II), and Cu(II) complexes.

Compound	MIC				MIC
	E. coli	S. aureus	S. pyogenes	P.aeruginosa	A. flavus	Cladosporium	A. niger
C23H18N4O6S	5	15	10	5	15	5	5
[Co(C23H16N4O6S)].2H2O	5	5	5	5	5	10	5
[Ni(C23H16N4O6S)].2H2O	10	15	10	10	10	15	10
[Cu(C23H16N4O6S)].2H2O	5	5	10	5	5	10	10

Table 7.  Brine shrimp bioassay data for Schiff base and its Co(II), Ni(II), and Cu(II) complexes.

Compound	LD50 (M/mL)
C23H18N4O6S	6.3916 × 10^−3
[Co(C23H16N4O6S)].2H2O	8.4389 × 10^−4
[Ni(C23H16N4O6S)].2H2O	2.6917 × 10^−3
[Cu(C23H16N4O6S)].2H2O	9.5638 × 10^−4

Figure 8.  Agarose gel electrophoresis. M, standard molecular weight marker; C-E.coli, control DNA of E. coli; lanes 1–4, E. coli DNA treated with Schiff base, Cu(II), Co(II), and Ni(II) complexes, respectively; lanes 5–8, A. niger DNA treated with Schiff base, Cu(II), Co(II), and Ni(II) complexes, respectively; C-niger, control DNA of A. niger.

Figure 9.  Octahedral structure of metal(II) complexes.