Synthesis and Characterization of Bioactive Transition Metal Complexes from Cardanol

C. Isac Sobana Raj¹*, C.M. Sofia¹ and M. Antilin Princela²

¹Department of Chemistry and Research centre N. M. Christian College,Marthandam-629165 India.

²Department of Chemistry, Annai Velankanni College, Tholayavattam-629157 India.

*Corresponding Author E-mail: isacsobanaraj@yahoo.co.in

ABSTRACT:

Cardanol 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 with p-toluidine. This preparation involves (i)Conversion of cardanol into bis(3-pentadecenylphenol) methane (BPPM) using formaldehyde. (ii) bis(3-pentadecenylphenol) methane into di-α-formylmethoxy bis(3-pentadecenylphenyl)methane (DFMPM) on treatment with epichlorohydrin followed by the action of sodium periodate. (iii)DFMPM undergo condensationwith p-toluidine to form (1+2)  Schiff base ligand and finally (iv) Schiff base complexes with transition metal salts. The ligand and complexes were characterized by UV-visible, IR, 1H NMR and elemental analysis, melting point, conductivity, metal ion intake and the antibacterial activity were studied.  The results indicate that the complexes of Cu(II), Ni(II) and Co(II) were bioactive and also used for the removal of such ions from water. The nanocrystalline nature of the complexes were confirmed by SEM studies.

KEYWORDS: Cardanol, Formaldehyde, Epichlorohydrin, p-toluidine, Schiff base.

INTRODUCTION:

Cardanol, a phenolic compound obtained from the vacuum distillation of Cashew nut shell liquid (CNSL)  with a long carbon chain in the metaposition. Cardanol finds many applications in the form of phenol-formaldehyde resin in varnishes, paints, printing inks, lacquers, brake linings, friction materials and adhesives[1].A new compound of cardanol, bis(3-pentadecenylphenol)methane(BPPM) was prepared by treating cardanol and formaldehyde in the molar ratio 2:1 along with hydrochloric acid at 90-95^oC for 2 hours[2-7].Diglycidyl ether of BPPM(DEBPPM) was synthesized with epichlorohydrin in the presence of sodium hydroxide at 75^oC for 2 hours. In addition, DEBPPM on treatment with sodium periodate, di-a-formylmethoxy bis(3-pentadecenyl phenyl)methane was obtained. DFMPM undergoes condensation reaction  with p-toludine,a (1+2) schiff base ligand was obtained. Schiff base ligand formed bioactive Schiff metal complexes with transition metal salt solutions. The present investigation involves the Synthesis  and Characterisation of schiff base ligand(L) and the complexes of Cu(II), Ni(II) and Co(II) ions.

The ligand and complexes were characterised by Elemental analysis, Melting point, conductance measurementsUV-Visible,IR,₁H NMR, Metal ion intake, Antibacterial and Antifungal activity were studied. The result indicates all the complexes of Cu(II),Ni(II) and Co(II) are hexa co-ordinated having moderate antibacterial and antifungal activity. The particle size of these complexes were analysed by SEM  studies and also the metal ion intake indicates the ligand can be used for the extraction of these metals from water.

MATERIALS AND PHYSICAL MEASUREMENTS:

Cardanol was obtained from M/S.Satya Cashew, Chennai, India. Formaldehyde (37% solution), hydrochloric acid, epichlorohydrin, Para toludine, sodium hydroxide and other chemicals used were of GR/AR grade quality obtained from Merck chemicals. All the solvent used were purified by standard methods[8].

The micro analytical data(C,H,N) were collected using Perkin Elmer 2400 instrument. The metal ion intakes were estimated by standard methods[8].IR spectra were obtained using PE IR spectrum, Instrument model: System 2000.1H  NMR  spectrum was obtained using AMX-300MHz,FT NMR spectrometer. Conductance measurements were obtained using systronics-305 conductivity meter. Electronic spectra of the ligands and its complexes was obtained using Perkins Elmer Lamda-25 UV-Visible spectrometer in the range of 200-1100 nm. Surface morphological studies was obtained using JSM-5610 scanning electron microscope.

Synthesis

Synthesis of bis (3-pentadecenylphenyl) methane (BPPM), diglycidylether of bis (3-pentadecenylphenyl) methane (DEBPPM), di-a-formylmethoxybis (3pentadecenylphenyl) methane (DFMPM) were prepared as per the earlier methods[9-11].

Preparation of Schiff base metal complexes

The metal complexes were prepared by adding aqueous solution of Cu(II) nitrate, Ni (II) nitrate, Co (II) nitrate to the ligand in ethanol in 1:2 molar ratio and refluxed for about twelve hours at 80^oC[12].  The precipitated solids were filtered, washed with ethanol, diethyl ether and hot water, and finally dried under vacuum at 90^oC. Yield =55-59%.

Estimation of metal ion intake

The filtrate obtained in the above methods were collected and the collections were used for the estimation of the transition metal ions used for complexation by using standard methods[8].

RESULTS AND DISCUSSION

All the metal complexes are coloured solids, stable towards air and have high melting points(above 230^oC).The complexes are insoluble in water and common organic solvents, but are soluble in DMF,CDCl₃  and  DMSO.

Elemental analysis

The analytical data suggest that all the complexes are mononuclear with the ligand coordinated to the central metal atom and the metal to ligand ratio in all complexes was 1:2, and their formulae have been computed  and given in table 1.

IR Spectra

Selected IR spectral bands for the ligands and its complexes are given in table2. The IR spectrum of the free ligand is characterized mainly by the strong bands at 2926.22 cm^-1, 2854.38 cm^-1 and 1601.7cm^-1 which are attributed the stretching frequencies of O-C, C-H, and C=N (azomethine) respectively[13]. The IR Spectrum of the free ligand was compared with the spectra of metal complexes. The characteristic absorption bands 3425.58 cm^-1, 3402.43 cm^-1 range were attributed to –OH group of the coordinated or lattice water[14]. The absorption bands in the range 2854.65-2854.3 cm^-1, 2924.09 cm^-1 and 1651-1658.78 cm^-1 were assigned to O-C, C-H, and C=N respectively[15,16]. The imine peak in the metal complexes showed change in shifts compared to the ligand indicating coordination of the imine nitrogen atom to the metal ion due to coordination. Another absorption bands at 991.41cm^-1-1050.9cm^-1 is assigned to the coordinated nitro group with the central metal atom and 432.05 cm^-1-470.63 cm^-1 is assigned to M-N bond and 459cm^-1-462cm^-1 is assigned to M-O bond[17,18]

Table 1:Physical characteristics  and analytical data of the complexes

Compound	Yield %	Colour	Mol. formula	M.W.	m.p. ^oC	Elemental analysis found (Calcd)%			Molar conductance Ohm^-1 cm^2mol^-1	Metal ion intake meq/g
						C	H	N
Ligand(L)	60	Brown	C61H86N2O2	878	217	83.38 (83.37)	9.81  (9.79)	3.17  (3.18)	-	-
[CuL2(NO3)2]	57	Light green	C122H172N6O10Cu	1943.54	>230	75.34  (75.32)	8.87  (8.84)	4.33  (4.32)	18	0.82
[CoL2(NO3)2]	59	Brown	C122H172N6O10Co	1938.93	>230	75.53  (75.50)	8.89 (8.87)	4.31  (4.33)	15	0.6245
[NiL2(NO3)2]	55	Brown	C122H172N6O10Ni	1938.71.	>230	75.49  (75.52)	8.86  (8.87)	4.34  (4.33)	14	0.3890

Table 2:Selected FT IR frequencies(cm^-1) and UV-Visible spectral data(nm) of the ligand and complexes

Ligand/Complex	nO-H (H2O)	nO-C	nC-H	nC=N	nM-N	nM-O
C61H86N2O2(L)	3398.1	2926.2	2854.3	1601.7	-	-
[CuL2(NO3)2]	3425.58	2924.09	2854.65	1651.07	509.21	432.05
[CoL2(NO3)2]	3402.43	2924.09	2854.65	1581.63	779.24	424.34
[NiL2(NO3)2]	3400	2485.46	2921.09	1626.21	725.23	432.05

Figure : 1FTIR Spectrum of the Ligand

Structure of  ligand

General structure of Schiff base metal complex of ligand(L)

M = Cu(II), Ni(II) and Co(II)

Figure : 2 FTIR Spectrum of Cu (II) complex

Figure : 3 FTIR Spectrum of  Co (II) complex

Figure : 4 FTIR Spectrum of Ni (II) complex

UV Visible Spectra

The absorption region assignment and geometry of the ligand and complexes are given in Table 3. The ligand showed a broad band at 360 nm which is assigned to p-p^* transition of the C=N chromophore[19]. On complexation this bond was shifted to the lower wave length suggesting the coordination of imine nitrogen with central metal ion. The UV spectra of the Cu(II) complexes showed three absorption bands at 895nm giving an octahedral geometry with field transitions.²B_1g²A_1g, ²B_1g²B_2g and ²B_1g²E_2g respectively. The broadness and position of the band favours distorted octahetral geometry for copper(II) complex due to Jahn Teller effect. The UV spectra of Co(II) and Ni(II) complexex showed absorption bands at 760 nm and 772nm, 590nm and 402nm respectively suggesting octahedral geometry for the complexes.

Table 3: UV Visible Spectra of the ligand (L) and its complexes

Complex	lmax(nm)
[CuL2(NO3)2	895
[CoL2(NO3)2	760
[NiL2(NO3)2	540

Magnetic susceptibility and magnetic measurements (BM)

The magnetic susceptibility values of the complexes are shown in table 4. The Cu(II) complex exhibited magnetic moment of 1.8 BM indicating distorted octahedral nature of the complex. Co(II) complex showed magnetic moment of 4.6 BM indicated the formation of high spin complex and having octahedral geometry. The Ni(II) complex exhibited the magnetic moment value of 3.3 BM indicating octahetral coordination of the complex

Table 4: Magnetic Susceptibility values of the complexes

Complex	Magnetic Susceptibility(BM)
[CuL2(NO3)2]	1.8
[CoL2(NO3)2]	4.6
[NiL2(NO3)2]	3.3

Metal ion intake

The complexation behavior of Cardanol based Schiff base was affected by structural parameters[20]. This study indicated that the metal ion intake decreased from Cu(II)Co(II)Ni(II).(Table 1). This order can be explained by Pearson’s proposal[21-23], hard acids prefer to combine with hard base and soft acids prefer to combine with soft  base. It was found that the interaction of Cu(II) is normally more intence than any other divalent metal ions with Schiff base ligands[24]. Nature of the ligand and the chelate effect were the factors involved in complexation hence the ligand have been used as metal ion acceptor in the environmental chemistry  and technological interest[24]. The ligand can be also used for the removal of Cu(II), Ni(II),Co(II), ions from water.

Antibacterial activity

Antibacterial activities of the ligand, complexes and standard drugs were screened by disc diffusion method in DMSO solvent. The results of antibacterial study are given in table 5.The  antibacterial activity was estimated based on the size of inhibition zone in the discs[25-28]. Under identical conditions the Schiff base complexes of copper(II),cobalt(II), and nickel(II) had moderate antibacterial activities against these bacteria.

The results of antibacterial activity substantiate the findings of earlier researcher that biologically inactive compounds become active and less biologically active compounds become active upon coordination. Such enhancement in biological activity of metal complexes can be explained on the basis of Overtone’s concept and chelation theory. According to Overtone concept of cell permeability, the lipid membrane that surrounds the cell favour the passage as only lipid soluble materials due to which liposolubility is an important factor that controls antimicrobial activity. On chelation, the polarity of the metal ion is reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of the positive charge of the metal ion with donar group. Further it increases the delocalisation of π- electron over the whole chelate ring and enhanced lipophlicity of the complex. This enhanced the lipophilicity in turn enhances the penetration of the complexes into lipid membrane and blocking of metal binding sites on the enzyme of the micro organisms.the  metal  complexes may also be a vehicle for activation of the ligandas the cytotoxic agent. Moreover, coordination may lead to significant reduction of drug resistance also other factors such as solubility, conductivity and dipole moment may also be amongst the possible reasons causing enhancement of bacterial activity of the metal complexes as compared to the uncomplexed Schiff base compound.

The present investigation suggest that all the metal complexes of the ligand bearing metal ion, phenolic moiety, unsaturated side chain, benzene ring,-N=CH- group have comparatively more biological activity. This study serve as a basis for the chemical modifications directed towards the development of new class of antibacterial agents.

Table 5: Antibacterial activity data of  complexes

Complex	Klebsiella	S. aureus	E. coli	P. aueginosa	B. cereus
[CuL(NO3)2]	10mm	++	++	++	++
[Co(NO3)2]	++	++	++	++	10mm
[NiL(NO3)2]	10mm	14mm	++	++	++

1-5 mm (++) = less active

Antifungal activity

The Schiff base transition metal complexes derived from cardanol   possess effective antifungal activity. Presence of methoxy, Nitrogroup, C₆H₄ – CH₃ groups, metal atom enhance fungicidal activity towards Candida albicans. [29]. Schiff bases and their metal complexes[30] formed between furan or furylglycoxal with various amines show antifungal activity against Helminthosporium gramineum, Syncephalostrum recemouses and C. capsici. Tridentate Schiff base [31] and their metal complexes show biocidal activities. Ruthenium (II) complexes [32] with Schiff base salicyladmine, thalium (I) complexes [33] with benzothiazolines, copper (II) complexes [34] of benzoylpyridines, copper (II) complexes of benzoylpyridine Schiff base show antifungal activities. Oxovanadium (IV) complexes [35] with triazole shows antifungal activity.

Schiff bases [36] derived from salicyladehydes and boronate esters show antifungal  activities against A. niger and A. flaves. Schiff base [37] of salicylaldehyde and O, O-di-methyl thiophosphoramide and their complexes with Cu(II), Ni(II) and Zn(II) are effective chemicals to kill Tetranychus bimaculatus. The present study substantiate the findings of earlier researches and were potent antifungal agents.

Table 6:Antifungal activity data of complexes

Complex	Candida albicans
[CuL2(NO3)2]	14mm
[CoL2(NO3)2]	18mm
[NiL2(NO3)2]	12mm

SEM Analysis

The surface morphology of the complexes have been examined using scanning electron microscope. The SEM images of  Cu(II), Ni(II), are given below. The SEM images showed that all the complexes are nano crystalline in nature showed rough and pitted surface

SEM  image of Schiff base complex of Cu (II)

SEM image of Schiff base complex of Ni (II)

CONCLUSION:

Schiff base metal complexes of Cu(II),Ni(II), and Co(II) were synthesized from cardanol using para toulidine were clearly described and characterized on the basis of analytical and spectral data. Metal ion intake explained that the complexes can be effectively used for extraction of metal ion from waters. Antibacterial and antifungal studies showed that the Cu(II),Ni(II) and Co(II) complexes have moderate antibacterial and antifungal activity.

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Received on 12.07.2014         Modified on 22.07.2014

Accepted on 08.08.2014         © AJRC All right reserved

Asian J. Research Chem. 7(8): August 2014; Page 711-716