Received 25 April 2021; Accepted 08 May 2021.
Invitro Biological Studies and Characterisation of Schiff Base Complexes of Co(Ii), Cu(Ii), Ni(Ii) and Zr(Iv) Using Dfmpm and 2,2-Diphenylethanamine
V.S. Lekha, Jisha George, S. Aswathi, K. Rajesh*
Department of Chemistry, University College, Thiruvananthapuram, Kerala, India
*corresponding author e-mail: [email protected] ABSTRACT
This article evokes that cardanol, the important component obtained from cashewnut shell liquid (CNSL), plays a pivotal role in the synthesis and enactment of variety of novel compounds of futuristic application .Cardanol transfigures into an aldehyde, di - - formylmethoxybis(3-pentadecenylphenol) methane (DFMPM) as per earlier methods . The synthesised aldehyde was used to prepare Schiff base ligand by using 2,2-diphenylethanamine, which on treatment with Co(II), Ni(II), Cu(II) and Zr(IV) metal salt solutions forming complexes. The prepared complexes were characterised by UV- visible, IR and NMR spectroscopy. The surface morphology of the crystals were studied by SEM and XRD.
The studies such as elemental analysis, melting point, conductivity, metalion intake, antibacterial, antifungal, anticancer, DNA cleavage, larvicidal, anti-inflammatory and insecticidal were conducted.
The studies confirmed hexacoordination in the Co(II), Ni(II) and Cu(II) complexes and octacoordination inZr(IV) complex. Other studies indicated that the complexes were good biological agents and they showed a ray of hope in their usage as pharmaceutical agents.
Keywords:Cardanol, DFMPM, Biological agents, Spectroscopy, Anticancer agent.
INTRODUCTION
Schiff’s bases and their complexes possess versatile properties as catalysts in various biological systems, and are used as polymers, dyes, antimicrobial agents, antifungal agents and have antitumor and cytotoxic activities, plant growth regulating, enzymatic activity and pharmaceutical properties.1Cardanol is the main component obtained by vacuum distillation of roasted cashew nut shell liquid (CNSL) and was used for the preparation of bioactive transition Schiff base metal complexes using standard methods.2,3,4The ligand and complexes were characterised by UV-visible, FTIR,1HNMR, SEM, XRD and elemental analysis, melting point, conductivity, metal ion intake, anti bacterial, anti fungal, anti cancer, DNA cleavage, larvicidal,anti-inflammatory and insecticidal activity were studied. The result indicated that the complexes of Cu(II), Co(II) Ni(II) and Zr(IV) were bioactive and also used for the removal of such ions from water and the nano crystalline nature of complexes were confirmed by SEM and XRD studies.5,6.7
EXPERIMENTAL
Synthesis of Schiff base ligand with DFMPM and 2,2-diphenylethanamine
The Schiff base ligand was prepared by the reported methods8,9Equimolarethanolic solution of DFMPM and 2,2 diphenylethanamine were mixed and refluxed for about an hour. Poured the reaction product in ice, (1+2) Schiff base ligand was obtained.1 The precipitated yellow compound was filtered washed with water and dried over anhydrous calcium chloride. The crude sample was recrystalised from 60% absolute alcohol
Synthesis of Schiff base metal complexes
All the metal complexes were prepared by mixing ethanolic solution of Schiff base ligand with the corresponding aqueous metal salt solution of Cu(II) nitrate, Co(II) nitrate, Ni(II) nitrate and Zr(IV) nitrate in 2:1 molar ratio. The resulting mixture was refluxed for about twelve hours at 70-80oC,10,11,12 a
Received 25 April 2021; Accepted 08 May 2021.
Estimation of metal ion intake
The filtrates obtained in the above method were collected. The collections were used for the estimation of Cu(II), Co(II) , Ni(II) and Zr(IV) intake for complexation using standard methods. 13
RESULT AND DISCUSSION
The analytical data of the complexes, together with their physical properties are mentioned in Table 1.
The data suggested that the complexes were in ML2 composition. The metal complexes of Cu(II), Co(II) ,Ni(II) and Zr(IV) were coloured solids, stable towards air and had high melting points above (250oC). The complexes were insoluble in water and common organic solvents but soluble in DMF, CDCl3,and DMSO. Analytical data suggested the metal to ligand ratio in all the complexes to be 1:2.15 Conductivities of solutions of the complexes showed as non electrolytes because their conductivity value were in the range 14-18 ohm-1cm2 mol-1.
Elemental Analysis
The analytical data suggested that all the complexes were mononuclear with the ligand coordinated to the central metal atom and the metal to ligand ratio in all complexes was 1:2, and their empirical formulae have been computed and are given in Table 1.15
TABLE -1
PHYSICAL CHARACTERISTICS AND ANALYTICAL DATA OF COMPLEXES Complexes /Ligand Yiel
d
Colou r
Molecular
formula Mol.weight Meltingpoi nt
Elemental Analysis (found)
C H N
Ligand L 56 brown C75H98N2O2 1058 217 85.07 (84.94)
9.26 (9.42
)
2.65 (2.87
) [CuL2 (NO3)2] 60 brown C150H196N6O10
Cu 2303.55 >250 78.14
(77.91) 8.51 (9.0)
3.65 (3.52
) [CoL2 (NO3)2] 58 brown C150H196N6O10
Co 2298.93 >250 78.30
(78.1)
8.53 (8.91
)
3.65 (3.50
) [NiL2 (NO3)2] 62 grey C150H196N6O10
Ni 2298.69 >250 78.31
(79.1)
8.53 (9.1)
3.65 (3.82
) [ZrL2 (NO3)4] 61
Light brow
n
C150H200N8O18
Zr 2491.22 >250
72.25 (72.48
)
8.02 (7.9
8)
4.49 (4.2
0) Conductivity Measurements
The molar conductivity values are given in Table 2. The conductivity was in the range 14-18 ohm-1 cm2 mol-1. Complexes with conductance below 18 ohm-1 cm2 mol-1 are non electrolyte in nature. The slightly higher conductance values may be due to partial solvolysis of the complexes in DMSO medium.15
TABLE -2
MOLAR CONDUCTANCE DATA OF THE COMPLEXES
Compounds Molar conductance Ohm-1 cm2 mol-1 [CuL2 (NO3)2] 15 [CoL2 (NO3)2] 14
Received 25 April 2021; Accepted 08 May 2021.
[ZrL2 (NO3)4] 18 FT-IR spectrum analysis
The IR spectral data of the ligand and complexes are shown in the Table 3. Coordination of the ligand to the metal causes shift of infrared bands to higher or lower frequencies with different intensities.The mode of coordination has been assigned by comparing the spectra of the metal complexes with that of the ligand. The IR spectrum of the ligand (L) showed characteristic bands at 2850 cm-1, 2900 cm-1,1600 cm-1 due to the O-C, C-H, C=N respectively.16 ‘The IR spectra of the complexes exhibited bands with the appropriate shifts due to complex formation. The IR broad bands of metal complexes in the range of 3350 cm-1 to 3250cm-1indicate the presence of co-ordinated or lattice water molecule.17,18 The absorption of phenyl groups is seen in the region 1700 cm-1-1550cm-1. The C-O phenolic stretching frequency is observed around 2340 cm-1 to 2000cm-1 which get shifted to lower or higher frequency region indicating co-ordination of phenolic oxygen. The band at 2900 cm-1 to 2780cm-1 and 1681 cm-1 to 1620 cm-1 were assigned to C-H and respectively.19,20 The imine peaks in the metal complexes showed changes in the ligand indicating co-ordination of the imine nitrogen atom to the metal ion. Another absorption band at 800 cm-1 to 700 cm-1 is assigned to M-N bond and bands at 730cm1 to 700 cm-1 is assigned to M-O bond.21,22 Fig1- 5 show the IR spectrum of ligand and metal complexes.23
TABLE --3
FT-IR FREQUENCIES (CM-1) OF THE LIGAND AND COMPLEXES Ligand/
Complexes
O-H
cm-1
O-C
cm-1
C-H
cm-1
C=N
cm-1
C=O
cm-1
free - C6H5
M-N
cm-1
M-0
cm-1 Ligand L 3350 2850 2900 1600 1630 1700 760 710 [CuL2(NO3)2] 3350 2350 2905 1634 1490 1650 780 700 [CoL2(NO3)2 ] 3300 2200 2900 1623 1480 1500 750 720 [NiL2(NO3)2] 3250 2265 2900 1651 1501 1600 740 700 [ZrL2(NO3)4] 3300 2000 2792 1681 1500 1550 800 730
Fig. 1. FTIR Spectrum of ligand (L)
Fig. 2. FTIR Spectrum of Cu(II) complex
Received 25 April 2021; Accepted 08 May 2021.
Fig.3. FTIR Spectrum of Co(II) complex
Fig. 4. FTIR Spectrum of Ni(II) complex
Fig. 5. FTIR Spectrum of Zr(IV) complex UV-visible spectrum analysis
The UV-visible spectra are often very helpful for structural identification. The ligand showed a broad band at 480 nm which is assigned to π-π* transition of the >C=N chromophore. This band was shifted to lower wave length suggesting the co-ordination of imine nitrogen with central metal ion. The UV- visible spectrum of Cu(II) complex showed three absorption bands at 398, 580 and 588nm giving an octahedral geometry with field transition 2B1g->2A1g,2B1g->2B2g and 2B1g->2E2g respectively.24 Co(II) and Ni(II) complexes, showed absorption bands at 598 to 398 nm and 598 to 395 nm respectively and suggested octahedral geometry.25 The spectrum of Zr(IV) complexes showed three absorption bands at 398, 568 and 606 nm respectively suggesting octacoordination, table 4 shows the UV-visible spectral data of complexes.26
TABLE - 4:
UV-VISIBLE SPECTRAL DATA OF COMPLEXES
Ligand/Complexes max(nm)
Ligand L 360, 480, 520 [CuL2(NO3)2] 398, 580, 588 [CoL2(NO3)2 ] 398, 512, 598 [NiL2(NO3)2] 395, 572, 598 [ZrL2(NO3)4] 398, 568, 606
Received 25 April 2021; Accepted 08 May 2021.
1H NMR Spectrum analysis
The 1HNMR spectrum of ligands and metal complexes in CDCl3 vividly gave high presence of – CH, ,–C6H5, – O – CH2 groups. On examining the 1HNMR spectrum of ligand (Fig.6) it exhibited a multiplet signal at δ=7.002 ppm –7.020 ppm is due to substituted aromatic ring protons. The presence of H – C = N- group is indicated by the singlet at δ = 7.022ppm. The multiplet at δ 6.537 ppm δ = 6.639 ppm and δ = 5.168 ppm – δ = 5.691 ppm were due to the olifinic protons of the side chain and – O-CH2 -group of the ligand respectively.12,27
Fig. 6. 1H NMR spectrum of ligand
In the 1H NMR spectrum of the Cu(II) complex (Fig.7), the presence of H – C = N- group is indicated by the singlet at δ = 7.120 ppm. A singlet at δ = 2.15 ppm is due to the substituted – CH2 -group. The signal at 2.736 is due to the presence of O – CH2 group. The signals at δ = 2.27 and 2.6 gave light on the presence of C6H5 - CH - group.28
Fig. 7.1H NMR spectrum of Cu(II) complex
In the 1HNMR spectrum of the Co(II) complex (Fig.8), the presence of H – C = N- group is indicated by the singlet at δ = 7.250 ppm. This also gave signals of– O-CH2 group at δ =2.56 ppm δ =1.238 ppm for
CH2 groups and δ =2.27 for C6H5-CH group.28,29
Fig.8. 1H NMR spectrum of Co(II)complex
Received 25 April 2021; Accepted 08 May 2021.
In the 1H NMR spectrum of the Ni(II) complex (Fig.9), the presence of H – C = N- group is indicated by the singlet at δ = 7.220ppm. The spectrum gave signals for – O-CH2 -group at δ =2.582ppm and δ =1.26 ppm for -CH2 group.28,29
Fig.9 . 1H NMR spectrum of Ni(II) complex
In the 1H NMR spectrum of the Zr(IV) complex (Fig.10), the presence of H – C = N- group is indicated by the singlet at δ = 7.800ppm it is due to the olifinic protons of the side chain and a singlet at δ = 7.213 ppm is due to – O-CH2 -group. A singlet at δ =2.810 ppm is due to substituted H-C-C=O- group and a singlet at δ = 1.994ppm is due to substituted -CH2-NH group.28,29
Fig.10. 1H NMR spectrum of Zr(IV) complex
Based on the observations in elemental analysis, FT-IR, electronic and 1H NMR spectral studies, the proposed structure of ligand (L) and its metal complexes are given in Fig.11 - 13.
Fig.11.Structure of ligand
Received 25 April 2021; Accepted 08 May 2021.
Fig.12. Structure of Schiff base complexes, M = Cu(II),Co(II) and Ni(II)
Fig.13. Structure of Schiff base complex, M=Zr(IV) SEM analysis
The surface morphology of the complexes has been examined using scanning electron microscope. The SEM image of Ni(II) and Zr(IV) complexes are given in fig 14 and 15. The SEM image ofNi(II) complex showed sand grain like and rock piece like appearances. Also the SEM image ofZr(IV) complex showed crystal like appearance. Careful examination of the SEM images clearly indicate the nano scale size of the complexes.10
Fig.14.SEM images of Ni(II) complex
Received 25 April 2021; Accepted 08 May 2021.
Fig. 15. SEM images of Zr(IV) complex X-Ray Diffraction Analysis
The X-ray diffractogram of Cu(II) and Zr(IV) complexes are given in Fig.16 and 17and the grain size of the complexes are shown in table 5. The maximum peak recorded was at 3.504nm and 7.760 nm for [CuL2(NO3)2] and [ZrL2(NO3)4] respectively.30 It is evident that the strong and broad peaks confirm the complex formation and the appearance of large feeble peaks indicate micro crystalline nature. The grain size of the complexes was calculated using Scherrer`s formula. These values suggested that the complexes are in nano crystalline size.31,32
TABLE – 5: GRAIN SIZE OF THE COMPLEXES
Complex Grain size (nm) [CuL2(NO3)2] 3.5
[ZrL2(NO3)4] 7.7
Fig.16. X-Ray Diffraction analysis of Cu(II) complex
Fig.17. X-Ray Diffraction analysis ofZr(IV) complex
Received 25 April 2021; Accepted 08 May 2021.
Metal ion intake
The structural parameters play pivotal role in complex formation.33It can be understood by noting in the metal ion intake and is decreased in the order Ni(II), Co(II)>Zr(IV) > Cu(II) at their natural pH.According to Pearson, hard acid preferred to combine with hard base and soft acid preferred to combine with soft base. In the present study the interaction of Ni(II) is more intense than other divalent metal ions with the Schiff base ligand.Nature of the ligand and the chelate effect were other factors involved in the complex formation.34
TABLE - 6
METAL ION INTAKE MEQ/G OF COMPLEXES
Complexes Metal Ion intake meq/g [CuL2(NO3)2] 0.3890 [CoL2(NO3)2 ] 0.4942 [NiL2(NO3)2] 0.6012 [ZrL2(NO3)4] 0.4520 BIOLOGICAL SCREENING
Antibacterial activity
Ligand and metal complexes were screened against bacteria in order to determine their antibacterial property. The result obtained showed that the activity of Schiff bases are more pronounced when coordinated with the metal ion. Schiff bases are characterized by an imine group –N=CH-, which helps to clarify the mechanism of transamination and racemization reaction in biological system. The mode of action of the compounds may involve formation of a hydrogen bond through the azomethine group (>C=N–) with the active centres of various cellular constituents, resulting in interference with normal cellular processes.34
TABLE. -7
ANTIBACTERIAL ACTIVITY DATA OF METAL COMPLEXES
Organisms
Diameter of zone of inhibition (mm)
Name of the sample Identity H1 H2 H3 H4
E.coli
Positive 33 33 33 36 F1 9 6 13 4 F2 12 8 18 10
V.cholerae
Positive 35 35 33 32 F1 12 8 13 11 F2 14 12 16 11
S.typhi
Positive 35 36 36 39 F1 11 4 12 7 F2 12 6 16 8
S.aureus
Positive 39 37 39 38 F1 10 5 11 9
F 11 9 10 9
Received 25 April 2021; Accepted 08 May 2021.
H1 =[CuL2(NO3)2] , H2 = [CoL2(NO3)2], H3 =[NiL2(NO3)2] ,H4 = [ZrL2(NO3)4]
Fig.18. Graphical representation of antibacterial activity in metal complexes Antifungal Activity
Cu(II), Co(II), Ni(II) and Zr(IV) complexes are studied against Aspergillusniger and Aspergillusflavus. Antifungal activity data are shown in table 8 and graphical representation in fig.20.
It is found that the activity increased upon coordination. The increased activity of the metal chelates can be explained on the basis of chelation theory. The orbital of each metal ion is made so as tooverlap with the ligand orbital. Increased activity enhances the lipophilicity of complexes due to delocalization of pi-electrons in the chelate ring. In some cases increased lipophilicity leads to break down of the permeability barrier of the cell. Ni(II) complex showed more activity towards Aspergillusniger. These results may be due to the higher stability of complexes.35
TABLE -8
ANTI-FUNGAL ACTIVITY DATA OF SCHIFF BASE COMPLEXES
FUNGAI
[CuL2(N O3)2] (mm)
[CoL2( NO3)2]
(mm)
[NiL2(N O3)2] (mm)
[ZrL2
(NO3)4] (mm) Aspergill
usniger 19 7 12 10
Aspergill
usflavus 7 9 8 7
Fig. 19. Graphical representation of antifungal activity of complexes Anti-inflammatory activity
In vitro anti-inflammatory study, [NiL2(NO3)2] was performed to evaluate the effect of HRBC membrane stabilization. Diclofenac sodium was used as standard and distilled water was used as control. The percentage inhibition of haemolysis by Diclofenac sodium and [NiL2(NO3)2] samples
0 20 40 60 80 100 120 140 160 180
P o s itive F 1 F 2 P o s itive F 1 F 2 P o s itive F 1 F 2 P o s itive F 1 F 2
H1 H2 H3 H4
0 5 10 15 20 25 30
Cu(II) Co(II) Ni(II) Zr(IV)
Aspergillus niger Aspergillus flavus
Received 25 April 2021; Accepted 08 May 2021.
increased with increase in concentration. Diclofenac sodium and [NiL2(NO3)2] samples exhibited statistically significant anti-inflammatory activity (NCCLS- 1993). Table.9 depicts the anti inflammatory activity data of Ni(II) complex.34
TABLE- 9
ANTI-INFLAMMATORY ACTIVITY OF Ni(II) COMPLEX
Sl
No. Drug Concentration [µg]
%
Inhibition of
haemolysis 1 Diclofenac
100 80
300 97
500 98
2 [NiL2(NO3)2]
100 88.04
300 90.02
500 92.01
Larvicidal activity
The metal complex [NiL2(NO3)2] showed enhanced larvicidal activity. The result obtained is presented in table.10. The action of larvicides upset the normal behaviour and action of target organism.
Chelation increases the lipophilic nature of central metal atom, which in turn favours the molecule in crossing the cell membrane of the microorganism and enhancing larvacidal activity of complexes.
Brine shrimp cytotoxic assay of [NiL2(NO3)2] was performed to evaluate its cytotoxic activity. Sample exhibited very high cytotoxic activity, at 50μg, 200μg, 400μg and 600μg it showed 60%,70%,90% and 100% mortality respectively.36
TABLE --10
LARVICIDAL ACTIVITY DATA OF Ni(II) COMPLEX Concentration
(µg/ml)
50 μg
200
μg 400 μg 600
μg Control -ve control Number of
brine shrimp per test sample
10 10 10 10 10 10
Average number of
survivors
4 3 1 0 10 10
Average number of
deaths
6 7 9 10 0 0
Percentage
mortality 60 70 90 100 0 0
Anticancer activity
Determination of invitroantiproliferative effect of Ni(II) complex was done. The extracts developed were culturedin hela cells and it was done in 6,12 and 24(µl) volume. When concentration increased the number of dead cells increased and the complex is potential due to less number of live cells.
Anticancer activity of the complex is shown in table.11 and in fig.20. From this it was found that as thevolume of the samples increases the percentage viability of the assay decreases. Reduction of MTT can only occur in metabolically active cells and the level of activity is a measure of the viability of the cells.37
Received 25 April 2021; Accepted 08 May 2021.
TABLE - 11
ANTICANCER ACTIVITY DATA OF Ni(II) COMPLEX
Sample volume (µl)
Average Absorbance
@ 540nm
Percentage Viability
CONTROL 0.5149 _
[NiL2(NO3)2] 6 0.4703 91.33812 [NiL2(NO3)2] 12 0.3163 57.05962 [NiL2(NO3)2] 24 0.2938 54.80676
Fig. 20.MTT assay of Ni(II) Complex Nuclease Activity
The nuclease activities of metal complexes of ligand were studied using gel electrophoresis and the respective photograph is shown in Fig.21. The cleavage efficiency of the complexes were compared with the control DNA to study the binding ability. The presence of smear in the gel diagram indicates the radical cleavageby the abstraction of hydrogen from sugar units of DNA. The metal complexes were able to convert super coiled DNA into opencircular DNA (Yano, S, Inoue, S 1998). The reaction is modulated by the metallo complexes bound hydroxyl or peroxide radical generated from the oxidant H2O2. Complexes of Zr(IV) showed enhanced nuclease activity.38
Fig.21. Gel electrophoresis diagram of complexes Lane 1-Control DNA
Lane 2-DNA treated with H2O2
Lane3-DNA+Cu(II) complex + H2O2 Lane4-DNA + Co(II) complex + H2O2 Lane5-DNA+Ni(II) complex + H2O2
Lane6-DNA+Zr (IV) complex + H2O2
Insecticidal activity
The eggs of C. cephalonica were collected and these eggs were inoculated in clean and sterile plastic tubs (35 x 10 cm; 5 L capacity), which contained mixture of partially ground Bajra grains (2.5 kg) and groundnut powder (100 g) in the laboratory at 28±2º C. This was kept as the mother colony and sub cultured for further generations. The complexes were found to be inactive towards the medium and reaction did not occur.
CONCLUSION
The Schiff base metal complexes were synthesized from cardanol using 2,2-diphenylethanamine. The ligands and complexes were insoluble in water and common organic solvents, but soluble in DMF,
Received 25 April 2021; Accepted 08 May 2021.
analytical data. From the spectral and stoichiometric analysis, a hexacoordinated nature was assigned for the Cu(II),Ni(II) and Co(II) complexesand octacoordinated nature for the Zr(IV) complex. FT-IR, UV-visible and NMR studies showed the presence of nitrate group inside the coordination sphere.
Careful examination of XRD and SEM studies clearly indicated that the complexes were nano crystalline and lower magnification showed grain like appearance. Metal ion intake explained that the ligand can be effectively used for extraction of metal ions from waters. All complexes were found to be more potent towards E.coli and V.choleraebacteria.Ni(II) complex showed more activity towards Aspergillusniger. Anticancer and larvicidal activity has been done in [NiL2(NO3)2] complex.
[ZrL2(NO3)4] complex showed enhanced nuclease activity.Compounds show bright path towards pharmaceutical as well as chemical sciences.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interestsregarding the publication of this article.
ACKNOWLEDGEMENT
The authors are thankful to the authorities of SAIF centres, IIT Madras, Chennai, CUSAT, Cochin and NIIST, Trivandrum for the instrumental analysis. We are also grateful to Department of Chemistry, Government College for Women and University College, Thiruvananthapuram for providing analytical facilities procured under FIST. We thank UGC (FIP/XII PLAN/ KLKE029/ TF 35) for providing financial support as Teacher Fellowship to one of the authors under the Faculty Development Programme.
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