INTRODUCTION:
Theimportanceofmetalcomplexesasdrugs,theirroleinthebiologicalsystemsandinthebiologicalactionofcertaindrugshasbeenrealized.Theyarebaseduponcertainphysicalproperties,e.g.,lowdissociationconstantsresultingintightlyheldmetalions,specialoxidation-reductionpotentials,solubilityandelectrondistribution.Themajorityoftheimportantmetalcomplexesarechelates1.Studiesontherelationshipofmetalcomplexesandbiologicalresponsehavebeenreported2,3.TheSchiffbasesandtheirmetalcomplexesareofbiologicalimportance.
TheSchiffbasespossessvariousactivitiessuchasantibacterialactivity,antifugalactivity,anticanceractivity,antitumoractivityandantitubercularactivity4.MetalcomplexesoftheSchiffbasesalsoshowtheseactivities.Thesecomplexesareoftenmoreactivethantheligandsduetocomplexationwithlesssideeffects.
PresentworkdealswithsynthesisofSchiffbaseligand(Fig1)2-[(1-Naphthalen-1-yl-ethylimino)-methyl]-phenolanditstransitionmetalcomplexes(Fig2)bycondensingwithmetalsaltsofNi(II),Cu(II),Co(II),Mn(II)andZn(II).FurtherSchiffbaseanditscomplexeshavebeenscreenedfortheirantibacterialactivity.
Fig1.StructureofLigand2-[(1-Naphthalen-1-yl-ethylimino)-methyl]-phenol
Fig:2Structureofmetalcomplex(M=Ni,Cu,Co,Mn,Zn)
MATERIAL AND METHODS:
Chemicals and reagents:
The chemicals used are 1-Naphthalen-1-yl-ethylamine (Merck,AR grade) and Salicyldehyde (Merck, AR grade),Ethyl alcohol (Merck,AR grade), Cobalt (II) chloride dihydrate (Sigma Aldrich), Nickel(II) chloride hexahydrate (Sigma Aldrich), Copper(II) chloride dihydrate (Sigma Aldrich), Zinc (II) chloride (Sigma Aldrich), Manganese (II) chloride tetrahydrate (Sigma Aldrich)
Synthesis of Ligand:
The Schiff Base ligand 2-[(1-Naphthalen-1-yl-ethylimino)-methyl]-phenol (Fig 1) was synthesized by condensing amine 1-Naphthalen-1-yl-ethylamine with Salicyldehyde in equimolar proportions. To an ethanolic solution (10 ml) of the amine (0.01 mole) was added salicyldehyde (0.01 mole) in ethanol (10 mL) with stirring. The mixture was then refluxed for 30 mins. The reaction mixture was then cooled which immediately gave a precipitated product. The product then obtained was filtered, washed with ethanol and then dried. The crude product was then crystallized from aqueous ethanol to give a yield of 80%.
Synthesisofmetalcomplexes:
Theligandandmetalsaltinthemolarratioof2:1weredissolvedinethanolandthereactionmixturewasheatedonwaterbathforaboutonehour.Itwasthencooledwhencolouredsolidseparatedoutwhichwaswashedwithethanolanddried.ThisisthegeneralmethodemployedforthesynthesisofmetalcomplexesofligandwithmetalchloridesvizNi(II),Cu(II),Co(II),Mn(II)andZn(II).
Antimicrobial studies:
The various screening studies carried out include the in vitro study against Gram-positive and Gram-negative bacteria viz. Staphylococcus aureus and E. coli
RESULTS AND DISCUSSION:
Formation of the complex was indicated by color change and melting point. Physical characteristics of Schiff base and metal complexes are given in Table 1.
Table 1: Physical characteristics
|
Compound |
Color |
Yield % |
M.P (oC) |
|
Ligand (SB1) |
Bright Yellow |
80 |
91 |
|
SB1-Ni complex |
Greenish yellow |
75 |
291 |
|
SB1-Cu complex |
Brown |
68 |
269 |
|
SB1-Co complex |
Buff |
59 |
270 |
|
SB1-Mn complex |
Blackish Green |
72 |
240 |
|
SB1-Zn complex |
Light yellow |
78 |
253 |
NMR and IR spectra:
From the NMR spectral data, formation of ligand was confirmed by presence of CH=N peak at d 8.8 and OH at d 5.6. In the present investigation the Infra red values for major peaks are assigned. The IR spectrum of ligand gave a strong band at 1625.07 cm-1 and 3039.33 cm-1 which are attributed to the stretching frequencies of C=N (azomethine) and OH respectively. Complexes showed a lower shift of wave numbers for C=N. Also IR bands were observed for M-O and M-N. All complexes showed bands at 3300 cm-1 to 3400 cm-1 indicating co-ordinated H2O moiety in the complexes. Complex of SB1-Ni showed IR bands at 1610.98 cm-1 and 3350.34 cm-1 corresponding to C=N and H2O, IR values of 455.80 cm-1and 541.15 cm-1 were assigned to M-O and M-N respectively. Similarly complex of SB1-Zn complex showed bands at ʋ(C=N) 1607.66 cm-1, ʋ(H2O) 3494.99 cm-1, ʋ (M-O) 579.94 cm-1 and ʋ (M-N) 424.00 cm-1. Similarly bands were observed for Cu complex at ʋ(C=N) 1610.58 cm-1, ʋ(H2O) 3397.49 cm-1, ʋ (M-O) 468.96 cm-1 and ʋ (M-N) 507.83 cm-1. Co complex ʋ(C=N) 1615.47 cm-1, ʋ(H2O) 3412.64 cm-1,ʋ (M-O) 436.58 cm-1and ʋ (M-N) 570.22 cm-1. Mn complex ʋ(C=N) 1614.70 cm-1, ʋ(H2O) 3338.33 cm-1, ʋ (M-O) 436.74 cm-1 and ʋ (M-N) 570.45 cm-1.
Electronic absorption spectra:
In the electronic spectra, the Co(II) complexes exhibited two energy peak at 28735 cm–1 and 28985 cm–1, which can be assigned5 to the transitions 4T1g(F) → 4T2g(F), 4T1g(F) → 4A2g(F) and 4T1g (F) → 4T2g (P) for a high spin octahedral geometry respectively while Mn complexes showed peaks at 29411 cm–1 and 28571 cm–1. The electronic spectra of the Ni(II) complexes showed d–d transition at 28571 cm–1, 25125 cm–1 and 21052 cm–1 5. These are assigned to 3A2g(F) → 3T2g(F), 3A2g(F) → 3T1g(F) and 3A2g (F) → 3T2g(P) transitions, respectively. These are consistent with a well- -defined octahedral geometry. The Zn(II) complexes exhibited only a high intensity band at 28011 cm–1 and 26881cm–1, which is assigned to ligand–metal charge transfer. In case of the Cu(II) complexes, a broad band at 30565cm–1, and 22259 cm–1 5was observed that is assigned to the 2Eg → 2T2g transition, which confirms its octahedral geometry.
Thermo Gravimetric Analysis:
TGA analysis is carried out to explain the thermal stability of complexes. TGA study of complex showed weight loss in the temperature range of 110oC-200oC is due to elimination of coordinated water molecule. Also gradual decrease in mass is seen up to 300oC due to loss of volatile matter. And a plateau observed above 350oC respectively which corresponds to the formation of stable metal oxide.
Table 2: ESR values for copper complex
|
Complex |
gll value |
g⊥ value |
gavg |
G |
|
SB1-Cu complex |
2.4077 |
2.0605 |
2.1762 |
7.001 |
Table 3: Antibacterial activity for Organism-Staphylococcus aureus
|
Sample |
Concentration |
Zone of Inhibition in mm |
|
Ligand - SB1 |
20 |
10 |
|
40 |
- |
|
|
60 |
12 |
|
|
80 |
10 |
|
|
100 |
11 |
|
|
Control |
0 |
|
|
SB1-Ni complex |
20 |
- |
|
40 |
10 |
|
|
60 |
12 |
|
|
80 |
12 |
|
|
100 |
09 |
|
|
Control |
0 |
|
|
SB1-Cu complex |
20 |
- |
|
40 |
10 |
|
|
60 |
11 |
|
|
80 |
12 |
|
|
100 |
10 |
|
|
Control |
0 |
|
|
SB1-Co complex |
20 |
- |
|
40 |
09 |
|
|
60 |
11 |
|
|
80 |
11 |
|
|
100 |
10 |
|
|
Control |
0 |
|
|
SB1-Mn complex |
20 |
- |
|
40 |
10 |
|
|
60 |
12 |
|
|
80 |
12 |
|
|
100 |
10 |
|
|
Control |
0 |
|
|
SB1-Zn complex |
20 |
09 |
|
40 |
10 |
|
|
60 |
11 |
|
|
80 |
13 |
|
|
100 |
11 |
|
|
Control |
0 |
ESR:
The gll and g⊥ values for Copper complex is
reported in the following Table 2. The spectrum showed asymmetric bands with
two g values. The trend gll> g⊥ > 2.00277, indicates that the
unpaired electron lay predominately in the dx2-y2 orbital
with possibly mixing of dz2 orbital because of the low symmetry. The
axial symmetry parameter ‘G’ is determined as G =
. G values found to be more than 4
suggesting very weak or no interaction in the solid state.
Table 4: Antibacterial activity for Organism-E.coli
|
Sample |
Concentration |
Zone of Inhibition in mm |
|
Ligand - SB1 |
20 |
08 |
|
40 |
11 |
|
|
60 |
11 |
|
|
80 |
13 |
|
|
100 |
12 |
|
|
Control |
0 |
|
|
SB1-Ni complex |
20 |
- |
|
40 |
- |
|
|
60 |
09 |
|
|
80 |
12 |
|
|
100 |
11 |
|
|
Control |
0 |
|
|
SB1-Cu complex |
20 |
- |
|
40 |
- |
|
|
60 |
10 |
|
|
80 |
12 |
|
|
100 |
10 |
|
|
Control |
0 |
|
|
SB1-Co complex |
20 |
- |
|
40 |
- |
|
|
60 |
11 |
|
|
80 |
12 |
|
|
100 |
11 |
|
|
Control |
0 |
|
|
SB1-Mn complex |
20 |
08 |
|
40 |
- |
|
|
60 |
11 |
|
|
80 |
11 |
|
|
100 |
10 |
|
|
Control |
0 |
|
|
SB1-Zn complex |
20 |
- |
|
40 |
- |
|
|
60 |
12 |
|
|
80 |
12 |
|
|
100 |
10 |
|
|
Control |
0 |
Magnetic susceptibility measurements:
The effective magnetic moment values for the complexes were determined. The magnetic moment value 3.9 B.M for Co(II) complex suggests an octahedral environment6,7. The magnetic moment value of the Cu (II) complexes of 1.57 B.M suggests distorted octahedral geometry8,9. The magnetic moment value of the Ni(II) complexes 2.89 B.M suggests an octahedral geometry. Mn (II) complexes with the value of 5.5 B.M indicate octahedral geometry10. The Zn(II) complexes were found to be diamagnetic, as expected for d10 configuration.
Antimicrobial activity:
In the present work the Schiff bases have been screened for their antibacterial and antifungal activity. The test compounds have been subjected to screening against Gram-positive and Gram-negative bacteria viz Staphylococcus aureus and E. coli using nutrient broth as the culture medium by agar cup diffusion method. The activity was compared with that of erythromycin and tetracycline. Erythromycin showed a zone of inhibition of 19mm (intermediate range) and 16mm (intermediate range) for E.coli andS.aureus respectively. Similarly Tetracycline showed a zone of inhibition of 15mm (intermediate range) and 18mm (intermediate range) for E.coli andS.aureus respectively. The results of the studies for Schiff base and its complexes are summarized in Table 3 and Table 4.
The evaluation of the antimicrobial activity was carried out after the incubation period by the measurement of the diameter of the inhibition zones. The different concentrations of ligand and metal complexes were found to inhibit the E.coli andS.aureus which can be seen from zone of inhibition in the above tables. However the activity of complexes was found to be less than that of the ligand. All the above results were compared with two standard antibiotics Erythromycin and Tetracycline. Hence it was concluded that the synthesized compounds exhibited weak antimicrobial activity on the microbes under study. The order of the activity can be summarized as follows: Standard > Ligands > Complexes.
ACKNOWLEDGEMENT:
The authors are grateful to the authorities of NES, Science CollegeNanded for the facilities.
CONFLICT OF INTEREST:
The authors declare no conflict of interest.
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Received on 23.08.2017 Modified on 13.09.2017
Accepted on 20.11.2017 © AJRC All right reserved
Asian J. Research Chem. 2018; 11(1):19-22.
DOI:10.5958/0974-4150.2018.00005.6