Synthesis, Characterization, DNA Binding and Antimicrobial Activity of Copper (II) Complexes with 4-Aminoantipyrine Schiff Bases

 

B. Anupama, M. Sunitha and C. Gyana Kumari*

Department of Chemistry, Osmania University, Hyderabad -500007, India

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

 

ABSTRACT:

The Schiff bases namely 5-Me SALAAP, 3-OMe SALAAP, 3-Br, 5-Cl SALAAP have been prepared by reacting 4-amino antipyrine with 5-methyl salicylaldehyde/3-methoxy salicylaldeyde /3-Br, 5-Cl salicylaldehyde. The Cu(II) complexes have been prepared by reacting copper(II) chloride with those of Schiff bases in alcoholic medium .The complexes are non electrolytes in DMSO. These have been characterized by using elemental analysis, IR, UV-VIs, 1H, 13C NMR, Mass spectra, ESR spectra, Magnetic susceptibility, conductance measurements and thermal (TGA and DTA) anaylsis. The complexes were found to have composition ML2.On basis of elemental and spectral studies, six coordinated geometry is assigned for these complexes. The Schiff bases act as tridentate and coordinate through the azomethine nitrogen, carbonyl oxygen and phenolic oxygen respectively. Binding of synthesized complexes with calf thymus DNA (CT DNA) was studied by spectroscopic methods. The synthesized ligands and their metal complexes were screened against bacteria. (E.coli  and Staphylococcus aureus). The activity data show that the metal complexes are more potent than Schiff bases.

 

KEYWORDS: Schiff bases, aminoantipyrine,  DNA binding , Cu (II)complexes, microbial activity.

 


 

INTRODUCTION:

The interactions of metal complexes with DNA are now well documented. 1-3 In recent years a considerable amount of work has been done on the coordination chemistry of copper(II) complexes with Schiff ligands to model the physical and chemical behaviour of biological copper systems4. Heterocyclic compounds are very widely distributed in nature and are essential to many biological processes. In this arena, metal complexes derived from N-heterocyclic ligands, largely based on pyrazolone derivatives of 4-aminoantipyrine play an important role in pharmaceutical, clinical and analytical applications.

 

Pyrazolone is an active moiety as a pharmaceutical ingredient, especially in the class of nonsteroidal anti inflammatory agents used in the treatment of arthritis and other musculoskeletal and joint disorders. Earlier work reported that some drugs showed increased activity when administered as metal chelates rather than as organic compounds. The coordinating 4-aminoantipyrine has been modified into a flexible ligand system by condensation with a variety of reagents like aldehydes, ketones etc.5-9

 

Schiff bases of 4-aminoantipyrine and its complexes are known for their variety of applications in the area of catalysis10,11, clinical applications12 and pharmacology13,14. New kinds of chemo –therapeutic agents containing Schiff bases have gained significant attention among biochemists10 and of those aminoantipyrine are commonly administered intravenously to detect liver disease 12 in clinical treatment.

 

A search through the literature reveals that no work has been done on the Cu(II) metal complexes of Schiff base formed by the condensation of 4-aminoantipyrine with 5-methyl/3-Methoxy/3-Br,5-Cl salicylaldehydes. In the present context, we synthesized tridentate ligands from 4-aminoantipyrine and substituted salicylaldehydes. The synthesized compounds and their ligation behaviour with Cu(II) metal ion was studied.

 

EXPERIMENTAL:

Materials:

CuCl2.2H2O, 4-aminoantipyrine, 5-Methyl/3-Methoxy/3-Br, 5-Cl  Salicylaldehydes were purchased from Sigma Aldrich. All these chemicals were used as received without further purification. Solvents were analytical grade and purified by standard procedures.

 

Synthesis of Ligands:

A mixture of 4-amino antipyrine (0.05 mol)  and  5-methylsalicylaldehyde/ 3-methoxy salicylaldehyde/ 3-bromo, 5-chloro salicylaldehyde(0.05mol) in ethanol and refluxing the reaction mixture for 2 hours with constant stirring. The dark yellow solid product formed was filtered and washed with petroleum ether and recrystallized from ethanol. Purity of the compounds was checked by TLC. Yield: 85-90%. (Fig 1)

 

4-Amino antipyrine   Sustituted salicylaldehyde   Schiff base (Ligands)

Figure 1:    Synthesis of ligands    ( Y =  5-Me, 3-OMe , 3-Br, 5-Cl)

 

Preparation of the complexes:

In the preparation of the metal complexes, the metal and the ligands were mixed in 1: 2 molar ratio using required quantities of ethanol. Hot ethanolic solution of ligand (0.02 mol) and hot ethanolic solution of corresponding metal salt CuCl2 (0.01) were mixed together, refluxed for 2-3 hrs and left for evaporation at room temperature for 3 days. Coloured solid metal complexes were obtained. The products were filtered, washed with cold ethanol and dried under vacuum over Calcium Chloride.

 

Physical measurements:

Elemental analysis of the ligands and their metal complexes was carried out using a Perkin-Elmer 240C (USA) elemental analyser. Molarconductances of the metal complexes were measured in a DMSO solution using Digisun Electronic conductivity meter. Magnetic susceptibilities of the complexes were determined on Guoy balance, model 7550 using Hg[Co(NCS)4] as standard. The diamagnetic corrections of the complexes were done  using pascal’s constants. TGA  studies were carried on Shimadzu DTG -60 H system in the temperature range of 0-1000 0C. Melting points of the ligands and m.p/ decomposition temperature of complexes were determined on Polmon instrument.(model No.MP -96)  IR spectra were recorded in KBr discs on  Brucker FTIR  spectrophotometer  from 400 to 4000 cm-1.  Electronic spectra were recorded with a Elico  SL 159  UV Visible spectrometer from 200 – 1100 nm. 1H NMR and 13C NMR spectra were recorded using  CDCl3 , at Brucker 400 MHZ spectrometer. The mass spectra were recorded by ESI technique on LCQ ion trap (thermo Finningan Sanjose CA (USA) Mass spectrometer instrument. The ESR spectra of the Cu(II) complexes was recorded on Jeol, JES –FA 200 ESR Spectrometer at room temperature.

 

DNA Binding Activity:

A concentrated CT –DNA stock solution was prepared in 5mM Tris- HCl / 50 mM aq NaCl buffer (pH 7.5) and its concentration ws determined by UV absorbance at 260 nm. The molar absorption coefficient was taken as 6600M-1 cm-1  15. A solution of CT-DNA in 5mM Tris –HCl /50mM aqueous NaCl gave a ratio of UV absorption at 260 nm and 280 nm.(A260/280)) of 1.8 – 1.9 indicating that the DNA was sufficiently free from protein.16 All stock solutions were stored at 40C and were used within a week.

 

Absorption spectra were recorded on a UV-Visible spectrophotometer using 1 cm quartz microcuvettes. Absorption titrations were performed by keeping the concentration of the complex constant (16µM) and by varying the concentration of CT –DNA from 0 –140µM. The binding constant (Kb) for the binding of the complex with DNA, has been determined from the spectroscopic titration data using the following equation.17,18

 

[DNA]/(ɛa-ɛf) = [DNA] /(ɛbf) + 1/Kbbf ).........1

Where [DNA] is the concentration per nucleotide, the apparent extinction coefficient ɛa ,was obtained by calculating Aobs / [Complex], The terms ɛf and ɛb correspond to the extinction coefficients of the free (unbound) and of the fully bound complex respectively. Kb the ratio of the slope to the intercept, was obtained from a plot of [DNA]/ (ɛaf) versus [DNA] , a slope 1/(ɛbf ). And an intercept 1/Kb (ɛbf ).

 

RESULTS AND DISCUSSIONS:

The synthesized ligands and its Cu(II) complexes were found to be air stable. The ligands and complexes are soluble in ethanol and DMSO. The ligands and its complexes were characterized by analytical and spectral techniques.

 

Characterization of Ligands:

1H NMR Spectra:

The 1HNMR spectrum of ligand (L1/5-MeSALAAP/2,3–dimethyl-1-phenyl-4-(5-Methyl-2-hydroxy benzylideneamino)-pyrazol-5-one.) is recorded in CDCl3. 1H NMR spectrum displays  the following signals: C6H5 as a multiplet at 6-8 δ . =C –CH3 at 2.35 δ  -N-CH3  at 3.2 δ and azomethine proton –CH=N- at 9.82 δ, intramolecular hydrogen bonded OH group at 13.4 δ

 

The 1H NMR spectrum of ligand (L2 / 3-OMe SALAAP/2,3–dimethyl-1-phenyl-4-(3-Methoxy-2-hydroxy benzylideneamino)-pyrazol-5-one.) is recorded in CDCl3. 1H NMR spectrum displays  the following signals: C6H5 as a multiplet at 6-8 δ. =C –CH3 at 2.4 δ  -N-CH3  at 3.3 δ,OCH3at 3.8δ and azomethine proton –CH=N- at 9.8 δ, intramolecular hydrogen bonded OH group at 13.9 δ (Fig 2)

 

This ligand (L3) reported earlier19. The following spectral data obtained are in good agreement with the literature data. The 1H NMR spectrum of ligand (L3 / 3-Br,5-Cl SALAAP/2,3 –dimethyl-1-phenyl-4-(3-Bromo,5-Chloro-2-hydroxy benzylideneamino)-pyrazol-5-one.) is recorded in CDCl3. 1H NMR spectrum displays the following signals: C6H5 as a multiplet at 6-8 δ . =C –CH3 at 2.4 δ -N-CH3 at 3.3 δ,OCH3 at 3.8δ and azomethine proton –CH=N- at 9.82 δ, intramolecular hydrogen bonded OH group at 14.5 δ

 

Figure 2 1H  NMR Spectrum of  3-OMeSALAAP

 

13C NMR Spectra:

The 13C NMR Spectra of the Schiff base ligands is recorded in CDCl3.The azomethine carbon gives a peak at 163.7-164.7 δ,  =C –CH3 at 10.14-10.25 δ  -N-CH3  at 35.21-35.61δ in all the three ligands .In ligand L - OCH3 gives a peak at 56.06 δ.(Fig 3)

 

Figure 3  13C  NMR Spectrum of  3-OMe SALAAP

 

Characterization of metal complexes :

The synthesized ligands and its Cu (II) complexes were found to be air stable. The ligands and their complexes were characterized by analytical and spectral techniques. Physical characterization, microanalytcal and molar conductivity data of the complexes are given in Table 1.  Analytical data of the the complexes correspond well with the general formula ML2.The observed low molar conductivity(15-20 Ohm-1cm-1mol-1) of the complexes in DMSO  at room temperature is consistent with the non electrolytic nature of complexes20. Elemental analysis results for the metal complexes agree with the calculated values showing that the complexes have the metal/ligand ratio of 1: 2.

 

IR Spectra:

The important absorption frequencies of Cu (II) complexes with all the ligands and their assignments are given in Table- 2. In order to study the binding mode of the Schiff base to the metal ion in complexes, the IR spectra of the free ligands are compared with the spectra of corresponding complexes.

 

IR spectra of all the ligands displayed a medium intensity band around 1578-1598 cm-1 due to ѵC=N shifted to lower or higher frequency region to the extent 8-10 cm-1 in complexes, indicating the nitrogen of azomethine is coordinated to the metal ion21,22. The IR broad bands of metal complexes in the range of 3381-3422 cm-1 indicate the presence of coordinated/lattice water molecules23. The ѵC-O(phenolic) stretching frequency of ligands is seen around 1364-1371 cm-1 which gets shifted to lower or higher frequency region by 13-41 cm-1 in the complexes indicating coordination of phenolic oxygen24.Band at 1650-1663 cm-1, ѵC=O stretching frequency of free Schiff bases which is also shifted to lower frequency ranging from(1604-1660cm-1)in all the metal complexes, suggests the coordination of ligands to the metal ion via the C=O group.25,26,27 The two new bands appeared in the low frequency region around 526-592 cm-1 and 431-465cm-1are due to  ѵM-O and ѵM-N respectively are observed.28

 

Magnetic moment and electronic absorption spectra:

The electronic absorption spectral data and magnetic moment values of Schiff base ligands and their Cu(II)   metal complexes are given in Table 3

 

The electronic spectra for these three ligands behave very similarly and show characteristic bands at 302 -347 nm  and 401 to 412 nm representing intra ligand charge transfer transitions.(π – π* transition of carbonyl and C=N groups)29,30The electronic absorption spectra of Cu(II) complexes compared with those of the free Schiff bases exhibit new bands around 676-758nm .which are due to d –d  transitions, assigned to the transition 2Eg2T2g  (D) in distorted octahedral geometry29,31. Another high intense bands in the range of 314-327nm,427-464nm  are due to ligand –metal charge transfer transitions32.The magnetic moment of 1.79.-1.89 B.M falls within the range of normally observed for octahedral complexes.33The electronic spectra and magnetic moment data for all Cu(II) complexes coupled with the analytical, conductance data obtained for them suggest the distorted octahedral geometry.

 

ESR Spectral studies:

The ESR spectra (Fig 4) of the Cu(II) complexes were recorded on  Jeol  , JES –FA 200 ESR Spectrometer at R.T. The present Cu (II) complexes exhibited well resolved anisotropic signals in the parallel and perpendicular regions. The observed data showed that gΠ = 2.04 –2.49and g= 2.07 –2.23.


Table 1     Physical characterization, analytical , molar conductance data for the ligand and  its  complexes.

Compound

color

Formula

Molecular Weight

Melting point in 0 C

Molar conductivity (Ohm-1cm-1mol-1)

Ligand(L1)

yellow

C19H19N3O2

321

204

--

Ligand(L2)

yellow

C19H19N3O3

337

189

--

Ligand(L3)

yellow

C18H15BrClN3O2

419.5

201

--

[Cu(II)(L1)2]

brown

[C38H36N6CuO4]

704

224

15.4

[Cu(II)(L2)2]

brown

[C38H36NCuO6]

736

213

17.2

[Cu(II)(L3)2]

brown

[C38H28N6 Br2Cl 2CuO4]

900.5

265

19.8

The C,H and N analysis of Schiff base ligands and complexes are in good agreement with the expected values.

 

Table 2              Characteristic IR stretching bands of Schiff bases and their Cu(II) complexes in cm-1

Compound

ΰO-H /H2O

ΰC=N

ΰC=O

ΰPh-O

ΰM-O

ΰM-N

Ligand L1

3442

1578

1650

1371

---

---

[Cu(L1)2]H2O

3419

1586

1604

1384

526

433

Ligand L2

2826

1598

1663

1364

---

---

[Cu(L2)]H2O

3381

1606

1660

1389

592

446

Ligand L3

2948

1592

1660

1365

---

---

[Cu(L3)]H2O

3422

1582

1611

1324

559

450

 

Table 3         UV-Vis Spectral data and magnetic moment values of Schiff base ligands and their  complexes

Compound

Absorption(λ) in nm

Band assignment

Mag. Moment µ   (B.M)

Geometry

Ligand L1

304

347

401

π – π* transition

 

----

 

----

Ligand L2

302

342

402

π – π* transition

 

----

 

----

Ligand L3

302

347

412

π – π* transition

 

----

 

----

[Cu(L1)2]H2O

347

464

698

ligand–metal charge transfer transitions

2Eg2T2g

1.79

Distorted octahedral

geometry

[Cu(L2)2]H2O

 

312

432

676

ligand–metal charge transfer transitions

2Eg2T2g

1.84

Distorted octahedral

geometry

[Cu(L3)2]H2O

 

314

427

758

ligand–metal charge transfer transitions

2Eg2T2g

1.89

Distorted octahedral

geometry

 


The g Π values are greater than g suggesting major distortion from octahedral symmetry in the Cu(II) complexes.34 Kivelson and Neiman have shown that gII is a moderately sensitive function for indicatig covalency. Relatively speaking gΠ > 2.3 is characteristic of anionic environment and gΠ<2.3 of covalent environment in M –L bonding35.The observed gΠ values for complexes  are less than 2.3 in agreement with the covalent character of the M—L bond. The trend gΠ > g> 2.0023 observed for the complexes indicates that unpaired electron is localised in dx2-y2 orbital of the Cu(II) ion. Thus a tetragonal geometry is proposed for the complexes. G =(gΠ-2) /(g-2) ,which measure the exchange interaction between the  metal centres in a polycrystalline solid has been calculated. Acc. to Hathaway 36 if G>4 the exchange interaction is negligible  if G< 4 indicates considerable exchange interaction in the solid complexes.

 

The above reported complexes showed G values < 4 indicating the exchange interaction in complexes. Furthr more , Masa cesi etal 37 reported that gΠ is 2.4 for copper-oxygen bonds and 2.3 for copper –nitrogen bonds .for the complexes reported here ,gΠ values between 2.3 –2.4 which further confirms ,the presence of mixed copper- nitrogen and copper –oxygen bonds in these  chelate complexes.

 

Figure 4    ESR Spectrum of Cu(II)-5-Me SALAAP

 

Thermal Analysis :

In the present investigation heating rates were suitably controlled at 100C min-1 under nitrogen atmosphere and the weight loss was measured from the ambient temperature upto 10000C.  Water molecules in complexes are generally of two types lattice water and coordinated water.38 The lattice water will be lost at low temperature (60-1200C) where as the loss of coordinated water molecule is observed at high temperatures(150-2000C). In the thermograms of  DTA  and TGA of complex [Cu(II)5-Me SALAAP]H2O (Fig 5) small weight loss in the range of  60- 1200C  is assigned to loss of lattice water, maximum and gradual weight loss in the range of 300- 10000C  is and attributable to decomposition of ligand moiety. The residue at 10000 C indicates the involatile metal component present in the complex.

 

Figure 5    TGA  OF  Cu (II) -5-Me SALAAP

 

Mass Spectra of the compounds:

The mass spectral data of Schiff base ligands and their metal chelates are given in table 3. Mass spectra of the ligand and metal complexes show molecular ion peaks ,which are in good agreement with the expected values.The mass spectrum of ligand (L1)(Fig 6) gives a peak at 322 m/z ,which is assigned for [M+1] peak. And its Cu(II) complex gives molecular ion peak at 704 m/z( Fig 7),which is assigned as [M] peak. The mass spectrum of  Ligand (L2) gives a peak at 338 m/z ,which is assigned for [M+1].Its Cu complex gives a molecular ion peak at 736 m/z,which is assigned as [M]. The mass spectrum of ligand (L3) gives  peaks at 420m/z,[M] 422m/z[M+2],424m/z[M+4].The M+2 ,M+4 peaks are due to isotopic chlorine and bromine atoms.and its complex gives a peak at 904m/z which is assigned as [M+4].

 

Antimicrobial Activity:

In the present investigation , biological activity of the ligands and their Cu(II) complexes have been screened for antimicrobial activity against bacteria (E.coli  and Staphylo coccus aureus) by paper disc method. The concentrationfor these  samples maintained as 200µg/ml,100µg/ml,50µg/ml in DMSO.  In the present study ,the zones of inhibition of antibacterial activity have been presented in Table 4 and Fig 8.The results indicate that Copper complexes of all the three ligands show  activity against  Staph at 200µg/ml.Cu(II) complex of 3-Br,5-Cl SALAAP also showing activity against E.Coli at 2000µg/ml.

 

Table 3     Mass spectral data of Schiff base ligands and its metal complexes

Compound

Calculated mass

Obtained mass m/z

Peak assigned

Ligand (L1)

321.18

322

M+1

[Cu(L1)2]H2O

703.86

704

M

Ligand L2

337

338

M+1

[Cu(L2)2]H2O

735.5

736

M

Ligand L3

419.5

420,422,424

M,M+2,M+4

[Cu(L3)2]H2O

900.5

904

M+4

 

Figure 6  Mass Spectrum of 5-Me SALAAP

 

Figure 7   Mass spectrum of Cu(II) -5-MeSALAAP


 

Table 4 Antimicrobial activity of binary complexes

Complex

E.Coli 200µg/ml

Staph 200µg/ml

E.Coli 100µg/ml

Staph 00µg/ml

E.Coli 50µg/ml

Staph 50µg/ml

5-Me SALAAP

--

--

--

--

--

--

Cu(II) complex

--

+

--

--

--

--

3-OMe SALAAP

--

--

--

--

--

--

Cu(II)  complex

--

+

--

+

--

+

3-Br,5-Cl SALAAP

--

--

--

--

--

--

Cu(II)  complex

+

+

--

+

--

+

DMSO Control

--

--

--

--

--

--

+ indicates inhibition of growth around the paper disc,   -- indicates no inhibition of growth.

 


 

Antibacterial activity against Staphylococcus aureus of   Cu -3-Br,5-Cl SALAAP(2 CB)

 

Antibacterial activity against Staphylococcus aureus of  Cu -3-Br,5-Cl SALAAP( 2 M )

Figure 8  Antibacterial activity

 

Figure 9: Absorption spectrum of complex [Cu(II)(3-Br-5-ClSALAAP)2] in  Tris HCl buffer at 250C in  the presence of increasing amounts of DNA.   Conditions : [Cu] =16µM    [DNA]  = 0- 140µM. The arrow indicates the change in absorbance upon increasing the DNA   concentration.Insert : Plot of [DNA]/(ɛa - ɛf) vs [DNA].

 

DNA Binding Activity:

In general, complexes with aromatic moieties which bind to DNA through intercalation usually results in hypochromism and bathochromism, due to the stacking interaction between aromatic  chromophore of the complexes and the base pairs of DNA. The absorption spectra of the complex Cu (II) 3-Br, 5-Cl-SALAAP in the absence and presence of calf thymus DNA are illustrated in Fig 9. In the presence of DNA, decreases of peak intensities were observed in the absorption spectra of complex. Hypochromism was suggested to be due to the interaction between the electronic state of the intercalating chromophore and that of the DNA bases.39-43 In addition to the decrease in intensity, a small red shift (bathochromism) was also observed in the spectra. These spectral changes are consistent with the intercalation of complexes into the DNA base stack.The plot of the absorption titration data according to equation 1 gave a linear plot and resulted in an intrinsic binding constant (Kb) 2 x105 for complex44.

 

PROPOSED STRUCTURES OF Cu(II) COMPLEXES

Y = 5-Me  , 3-OMe , 3-Br,5-Cl

 

CONCLUSIONS:

TheCu (II) metal chelates of Ligands (L1,L2andL3) have been structurally characterized. The complexes of the ligands are non electrolytes in DMSO. These ligands act as tridentate, coordinating through nitrogen of azomethine, phenolic oxygen and carbonyl of antipyrine ring respectively. Geometries of the metal complexes are assigned, based on analytical ,conductance, magnetic and electronic spectral data. Biological studies of these complexes reveal that they show better activity when compared to that of the ligands.

 

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Received on 03.08.2011        Modified on 18.08.2011

Accepted on 25.08.2011        © AJRC All right reserved

Asian J. Research Chem. 4(10): Oct., 2011; Page 1529-1535