DNA cleavage and in vitro antimicrobial studies of Co(II), Ni(II), and Cu(II) complexes with ONNO donor Schiff bases: Synthesis, spectral characterization, and electrochemical studies

Figures & data

Scheme 1.  Synthesis of Schiff bases H₂L^I and H₂L^II.

Table 1.  Elemental analysis of Schiff bases and their Co(II), Ni(II), and Cu(II) complexes along with molar conductance and magnetic moment data.

Comp. no.	Empirical formula	Color/yield (%)	M%		C%		H%		N%		Molar conductance (ohm^−1 cm^2 mol^−1)	μeff (BM)
			Obsd	Calcd	Obsd	Calcd	Obsd	Calcd	Obsd	Calcd
H2L^I	C28H20N2O6	84	—	—	69.99	70.0	4.16	4.16	5.84	5.83	—	—
H2L^II	C24H20N2O6	82	—	—	66.74	66.66	4.63	4.63	6.47	6.48	—	—
1	Co(C28H18N2O6).2H2O	Brown/68	10.29	10.29	58.63	58.63	3.14	3.14	4.88	4.88	19	4.9
2	Co(C24H18N2O6).2H2O	Brown/67	11.18	11.19	54.65	54.64	3.42	3.41	5.32	5.31	18	4.75
3	Ni(C28H18N2O6).2H2O	Yellowish green/71	10.13	10.14	58.73	58.74	3.15	3.14	4.88	4.89	22.5	3.3
4	Ni(C24H18N2O6).2H2O	Yellowish green/73	11.01	11.02	54.74	54.75	3.42	3.42	5.33	5.32	23	3.1
5	Cu(C28H18N2O6).2H2O	Dark green/69	10.91	10.92	58.23	58.23	3.12	3.11	4.86	4.85	29.7	1.74
6	Cu(C24H18N2O6).2H2O	Dark green/68	11.85	11.86	54.24	54.23	3.41	3.38	5.27	5.27	27	1.75

Table 2.  The important infrared frequencies (in cm⁻¹) of Schiff bases and their metal complexes.

Compound	Co-ordinated waterν(OH)	Lactonylν(C=O)	ν(C=N)	H-bonded–OHstretching	ν(C=C)	Phenolicν(C-O)	ν(M-N)	ν(M-O)
C28H20N2O6	—	1735	1613	3072	1585	1306	—	—
C24H20N2O6	—	1720	1632	3062	1585	1305	—	—
Co(C28H18N2O6).2H2O	3439	1737	1602	—	1578	1355	524	381
Co(C24H18N2O6).2H2O	3433	1721	1618	—	1579	1335	506	376
Ni(C28H18N2O6).2H2O	3449	1736	1603	—	1580	1358	499	380
Ni(C24H18N2O6).2H2O	3435	1721	1622	—	1580	1340	510	375
Cu(C28H18N2O6).2H2O	3446	1735	1598	—	1582	1356	480	378
Cu(C24H18N2O6).2H2O	3438	1720	1617	—	1581	1331	496	380

Table 3.  The important ¹H NMR and ¹³C NMR data for Schiff bases.

Schiff base no.	^1H NMR (CDCl3) (ppm)	^13C NMR (CDCl3) (ppm)
H2L^I	14.7 (s, 2H, OH), 9.42 (s, 2H, HC=N), 6.1–7.6 (m, 10H, Ar-H), 2.4 (s, 6H, Ar-CH3)	111.3, 113.1, 118.6, 123.6, 125.5, 126.7, 131.5, 133.6, 138.2, 148.6, 152.2, 158.6, (aromatic carbon), 144.3 (C=N), 172.8 (C=O), 38.4 (CH3)
H2L^II	14.3 (s, 2H, OH), 9.1 (s, 2H, HC=N), 6.1–7.7 (m, 6H, Ar-H), 2.5 (s, 6H, Ar-CH3), 2.1 (t, 4H, CH2-CH2)	113.1, 118.6, 123.6, 125.5, 126.7, 131.5, 133.6, 138.2, 148.6, (aromatic carbon), 142.3 (C=N), 165.6 (C=O), 36.8 (CH3), 21.4 (CH2)

Table 4.  Biological results for Schiff bases and their metal complexes.

Compound	Conc. (μg/mL)	% Inhibition against bacteria				% Inhibition against fungi
		E. coli	S. aureus	P. aeruginosa	S. typhi	A. flavus	Cladosporium	A. niger
C28H20N2O6	25	6.97	17.14	2.63	26.19	84.31	53.84	47.61
	50	23.25	23.52	44.73	45.23	92.15	76.92	76.19
	100	95.34	38.2	50.00	59.52	96.07	87.17	88.09
C24H20N2O6	25	8.26	16.35	6.35	28.96	82.64	52.86	54.36
	50	25.36	25.36	41.98	44.96	88.96	71.56	75.93
	100	92.55	44.26	52.63	61.59	94.56	82.94	83.67
Co(C28H18N2O6).2H2O	25	—	—	—	—	76.47	5.12	57.14
	50	13.95	4.41	15.7	33.33	80.39	28.2	69.04
	100	62.79	8.82	26.31	59.52	84.31	46.15	73.8
Co(C24H18N2O6).2H2O	25	—	—	14.69	26.76	78.96	6.94	61.73
	50	16.35	15.63	16.98	44.96	88.56	36.57	75.91
	100	71.56	26.35	24.86	66.93	92.57	49.382	81.09
Ni(C28H18N2O6).2H2O	25	—	30.88	—	30.95	5.88	66.66	—
	50	18.6	36.76	—	73.8	23.52	76.92	28.57
	100	37.2	47.05	7.89	83.33	41.17	79.48	50.00
Ni(C24H18N2O6).2H2O	25	—	15.63	—	42.59	9.68	64.91	25.39
	50	36.35	22.65	15.63	76.91	36.86	78.35	44.86
	100	59.63	29.63	19.86	87.33	49.76	81.94	65.92
Cu(C28H18N2O6).2H2O	25	55.81	7.35	52.63	—	56.86	41.02	35.17
	50	65.11	13.23	60.52	14.28	64.7	53.84	57.14
	100	83.72	22.05	71.05	42.85	78.43	92.36	83.33
Cu(C24H18N2O6).2H2O	25	88.37	20.88	26.31	57.14	86.27	33.33	61.9
	50	90.69	20.58	26.31	64.28	92.11	66.66	66.66
	100	93.02	36.76	76.84	69.04	94.11	74.35	80.95
Gentamicin	25	86.04	5.88	81.57	61.9
	50	88.37	7.35	86.84	71.4	—	—	—
	100	88.37	14.7	89.47	80.95
Fluconazole	25					84.31	92.3	88.09
	50	—	—	—	—	94.1	94.87	92.85
	100					96.08	97.43	97.61
Control	100	100	100	100	100	100	100	100

Table 5.  Minimum inhibitory concentration (μg/mL) of selected compounds against selected bacteria.

Compound	E. coli	P. aeruginosa	S. typhi	A. flavus	Cladosporium	A. niger
C28H20N2O6	10	10	25	10	10	10
C24H20N2O6	10	10	25	10	10	10
Co(C28H18N2O6).2H2O	10	10	10	10	10	25
Co(C24H18N2O6).2H2O	10	10	25	10	10	10
Ni(C28H18N2O6).2H2O	25	10	10	25	10	10
Ni(C24H18N2O6).2H2O	10	25	10	25	10	25
Cu(C28H18N2O6).2H2O	10	10	25	10	10	10
Cu(C24H18N2O6).2H2O	10	10	25	10	25	10
Gentamicin	10	10	10	—	—	—
Fluconazole	—	—	—	10	10	10

Figure 1.  DNA cleavage study of Co(II) (2) and Cu(II) (6) complexes on genomic DNA. M, standard molecular weight marker; C- E.coli, control DNA of E. coli; lane 1, E. coli DNA treated with Co(C₂₄H₁₈N₂O₆).2H₂O; lane 2, E. coli DNA treated with Cu(C₂₄H₁₈N₂O₆).2H₂O; lane 3, A. niger DNA treated with Co(C₂₄H₁₈N₂O₆).2H₂O; lane 4, A. niger DNA treated with Cu(C₂₄H₁₈N₂O₆).2H₂O; C- niger: control DNA of A. niger.

Figure 2.  Structure of metal complexes 1, 3, and 5.

Figure 3.  Structure of metal complexes 2, 4, and 6.