METAL COMPLEXES OF 1-(o/p-CARBOXY PHENYL)-4, 4, 6 ... › pdfs › IJRESS › IJRESS_712_27389.pdf · chemistry. A wide range of applicability abounds [2-6] in the pharmaceutical

International Journal of Research in Engineering and Social Sciences

ISSN 2249-9482, Impact Factor: 5.343, Volume 5 Issue 4, April 2015

Website: www.indusedu.org

E-mail id:- [email protected] Page 133

METAL COMPLEXES OF 1-(o/p-CARBOXY PHENYL)-4, 4, 6-

TRIMETHYL PYRIMIDINE-2-THIONE: SYNTHESIS AND BIOLOGICAL

EVALUATION STUDY

Pooja Sethi, Rajshree Khare and Yogita Mehta

Department of Chemistry, Maharishi Markandeshwar University, Mullana, Ambala, Haryana,

India.

Sonia Bhalla

Department of Biotechnology, Maharishi Markandeshwar College of Biotechnology, Maharishi

Markandeshwar University, Mullana, Ambala, Haryana, India.

ABSTRACT

Synthesis of new complexes of 1-(o/p-carboxy phenyl)-4, 4, 6-trimethyl pyrimidine-2-thione (o/p-

HCPPT) with metals (M(II) = Cu, Mn, Ni, Co, Zn, Pd ), taking Cu and Ni metals common to

both ortho and para ligands for comparison and evaluation of their biological potential. The

antibacterial activity of synthesized metal complexes [M(o/p-CPPT)2] was evaluated by

microdilution method using DMSO as a solvent against non-pathogenic bacterial strain of E.coli

MTCC 9537. All the synthesized complexes were evaluated for their DNA nicking activity. These

metal complexes were characterized by 1H-NMR, FTIR, UV–Vis, ESI-mass spectrometry, molar

conductivity, magnetic moment measurements. 1H-NMR and IR results showed that coordination

occurs via N and S forming four-membered cyclic ring. Mass spectrum and Elemental analysis

showed the formation of 1:2 metals to ligand stoichiometry. Ligand with para substitution and its

complexes with Cu(II) and Ni(II) metal exhibited very good DNA photocleavage activities as

compared to the ligand with ortho substitution and its metal complexes.

Keywords: Synthesis, 2-pyrimidinethione, biological activity, magnetic moment.





INTRODUCTION

The universal distribution of heterocyclic compounds in nature indicates the pivotal and essential

[1] character of their relevance to life. They are organic compounds in which there is at least one

hetero-atom present, nitrogen, oxygen and sulphur being the most common hetero atom. These

compounds have attracted considerable attention in recent years, especially in medicinal

chemistry. A wide range of applicability abounds [2-6] in the pharmaceutical industry. The five

and six membered heterocyclic compounds containing sulphur and nitrogen have notable

preeminence as they have many biological [7-9] and industrial applications [10-12].

Pyrimidine and its derivative are remarkably important class of nitrogen-containing heterocycles

owing to the presence of the pyrimidine skeleton in many natural products, synthetic compounds,

important constituent of nucleic acids and thio-nucleated analogues, used in chemotherapeutic

treatment, central nervous system (CNS) depressant properties [13, 14] and also act as calcium channel

blockers [15].

As DNA is primary target for most of the anti-cancer drugs [16], the discovery of small

molecules which can interact, bind or cleave specifically and block DNA synthesis of cancer

cells are of prime importance. Many complexes of platinum such as cisplatin have been reported

to possess good level of anticancer activities in vitro studies [17], but being non essential metal

in biological systems, its use is limited due to the side effects in body. Therefore, the discovery

of the metal based drugs with biocompatibility, is the focused area of research. Transition metals

are most suitable candidates for the synthesis of cancer combating non radioactive tools for

chemotherapy and diagnosis [18-25]. The transition metals with well defined geometry are well

known to bind specifically with the DNA molecule [26,27]. These metals possess excellent

complexation abilities and are quite economical than ruthenium, gold and platinum and are

comparatively very less toxic as they are required in small amount for the normal functioning of

the biological systems. Among them, complexes of Cu(II) and Ni(II) are well known for their

potential DNA cleaving and binding abilities [26,27].

In view of the above mentioned facts and our continued interest in the synthesis of novel metal

complexes based on pyrimidine-2-thione with first transition series in the present study, we

report the synthesis of 1-(o/p-carboxy phenyl)-4, 4, 6-trimethyl pyrimidine-2-thione (o/p-

HCPPT) and its complexation with metals of first transition series. All the synthesized





compounds were screened for DNA photocleavage study and anti-bacterial activities with an aim

and hope to find new class of biologically active agents.

EXPERIMENTAL SECTION

Materials and Methods

All reactions were monitored on Thin Layer Chromatography (TLC) using petroleum ether/ethyl

acetate (7.5:2.5) as the mobile phase. The spots were visualized using a UV lamp. The elemental

analyses (C, H, N, S) was obtained from a LECO 2400 analyzer. The 1H-NMR spectra of ligand

and complexes were recorded on Bruker 400 MHz instrument with CDCl3 as the solvent, using

Tetramethylsilane (TMS) as the internal standard. IR spectra were measured on Nicolet-iS50

FTIR Affinity in 4,000 –200 cm-1

range using Reflectance mode. The electronic spectra were

recorded using Shimadzu UV 1800 instrument in CHCl3 as solvent. Mass spectra were recorded

on Agilent mass spectrometer. All the melting points were determined using open capillary

method and are uncorrected. Molar conductivity measurements were conducted at room

temperature on a Labtronics Model LT-16 digital conductivity bridge.Gel electrophoresis

cleavage experiments were achieved with the help of by agarose gel electrophoresis.

Synthesis of 4-Isothiocynato-4-methylpentan-2-one (Scheme:1)

4-Isothiocynato-4-methylpentan-2-one was prepared by diluting the sulphuric acid (1.1mol) with

distilled ice cold water (100 ml) and was added over a period of 25 minutes to mesityl oxide (1

mol) at 15°C. Then ammonium thiocyanate (1.1mol) aqueous solution was added to the mixture

at 21°C in one lot. A reddish brown oily layer separated out after 15 min stirring, washed with

aqueous sodium carbonate solution and with distilled water. Finally, the oily layer was dried

over anhydrous sodium sulphate [28].

C CH

CH3

C

O

CH3

CH3

N

C

S

C

CH3

CH3

N C S

CH2 C CH3

O

Mesityl oxide Ammonium thiocyanate 2-Methyl-2-isothiocyano-4-pentanone

H+

Scheme : 1





Step-2

Synthesis of 1-(o/p-carboxy phenyl)-4, 4, 6-trimethyl pyrimidine-2-thione(o/p-HCPPT)

(4.71 g, 0.1 mol) 2-Methyl-2-isothiocyano-4-pentanone and o/p-Amino benzoic acid (4.11

g,0.1 mol) was dissolved in ethanol (30 ml) and added 0.1 ml conc.H2SO4.The solution was

refluxed on water bath for 10 hours. The contents were cooled and the solid was filtered,

washed with chilled alcohol and purified the solid via crystallization from acetic acid [29].

C

CH3

CH3

N C S

CH2 C CH3

O

H++

N

NH

Me Me

Me

R

o/p-Aminobenzoic acid 1-(o/p- carboxy phenyl)-4, 4, 6-trimethyl pyrimidine-2-thione

S

2-Methyl-2-isothiocyano-4-pentanone

RNH2

Where R= o/p-C6H5COOH Scheme : 2

Step 3

Synthesis of metal complexes of 1-(o/p-carboxy phenyl)-4, 4, 6-trimethyl pyrimidine-2-

thione with Cu(II), Mn(II), Ni(II), Zn(II), Co(II), Pd(II) metal ions

The metal complexes of the ligand (o/p-HCPPT) were prepared by taking ligand (0.1 mol) in 100

ml of round bottom flask to which 30 ml of methanol and excess NaOH solution was added and

stirred for 30 min-1 hour. Clear solution of the appropriate metal acetates (Cu(II), Ni(II), Co(II),

Mn(II) Zn(II) and Pd(II) ) (0.05mol) in 30 methanol was added to the ligand solution dropwise

with continuous stirring. The mixture was stirred further for 30 minutes at 70 °C. The reaction

mixture was refluxed for 4h. The metal complexes thus formed are filtered, washed with

methanol followed by the petroleum ether to remove any traces of metal salt impurities and dried

in hot air oven for 2h.

2+ M+2

.xH2O

N

N

S

H3C CH3

H3C

R

N

N

S

CH3H3C

CH3

R

M

N

N

S

H3C CH3

H3C

R





Where M+2 = Cu+2, Ni+2, Co+2,

Zn+2, Mn+2 and Pd+2 Complex with metal

Where R= o/p-C6H5COOH and M = Cu, Ni, Co, Zn, Mn, Pd

Scheme : 3

In Vitro Antibacterial Activity

The antibacterial activity of synthesized compounds i.e. metal complexes were evaluated by

microdilution method [30] using DMSO as a solvent against pathogenic bacterial strain of E.coli

MTCC#9537. Minimum inhibitory concentrations (MICs) was determined as the lowest

concentration of the compound synthesized that inhibited the visible growth of the bacteria under

study after overnight incubation. In the present investigation,chloramphenicol was used as

reference drug. To conclude the antibacterial activity, decline in the growth curve of bacteria was

also determined in the presence and absence of the known concentration of the compounds

synthesized. This was achieved using UV spectrophotometric readings taken at frequent and

equal interval of the incubating broth kept at shaking conditions of 100 RPM.

Plasmid DNA Photocleavage Studies

DNA photocleavage experiment was performed using plasmid pUC18 in TE (Tris 10mm, EDTA

0.01mm, pH 8.0) buffer in presence of 10-100μg of the synthesized compounds in different

autoclaved PCR tubes. These tubes were placed directly on the surface of a trans-illuminator

(8000 mW/cm) at 360 nm. The samples were irradiated for 30 min at room temperature. After

irradiation, samples were further incubated at 37 °C for 1 h and under visible light. Irradiated

samples were mixed with 6X loading dye containing 0.25% bromophenol blue and 30%

glycerol. The samples were then analyzed by electrophoresis on a 0.8% agarose horizontal slab

gel in Tris-Acetate EDTA buffer (40 mm Tris, 20 mm acetic acid, 1 mm EDTA, pH: 8.0).

Untreated plasmid DNA was maintained as a control in each run of gel electrophoresis, which

was carried out at 5V/cm for 2.0 h. Gel was stained with ethidium bromide (1 μg/ml) and

photographed under UV gel docking system.

RESULT AND DISCUSSION

Conductance and Elemental Analysis

The recorded conductance and elemental analysis data for the synthesized complexes are

presented in Table 1. The conductance of all the synthesized metal complexes was recorded in





10-4

M DMSO at room temperature in order to determine their electrolytic nature. The observed

low conductance values for all the metal complexes suggested their non electrolytic [31-33]

nature. The formation of metal complexes was ascertained by using technique like IR, 1H NMR,

Mass ,UV spectra, Elemental analysis and Magnetic moment.Table 1.

Table 1:Physical data of ligand and its metal complexes

IR Spectra

The tentative assignments for infrared spectral data of ligands and the complexes are presented

in Table 2. The IR spectrum of 1-(o/p- carboxy phenyl)-4, 4, 6-trimethyl pyrimidine-2-thione

(o/p-HCPPT) shows a band at 3151 cm-1

in o-HCPPT and at 3195cm-1

in p-HCPPT which is

attributed to υ(N-H) stretching vibrations. Band at 1604 cm-1

/ 1601cm-1

in o-HCPPT/ p-HCPPT

respectively is designated to δ(N-H) deformations [34]. Absence of υ(SH) at 2600 cm-1

in o/p

derivative indicates that free ligand exist in thione form [35].

On complexation, disappearance of υ(NH) stretching bands and appearance of strong bands in

the range 1543-1510 cm-1

which are assigned to combination of υ(C=C) and υ(C=N) skeletal

vibrations of pyrimidine-thione ring, shifted to low or high frequency suggesting N-coordination

through deprotonated ring nitrogen atom. Besides, these o/p- ligand bands at 1209, 1177 cm-

Ligand/

Complex

Color %Yield Molecular

wt.

Melting

point

Solubility Conductance

Ligand

o-HCPPT White 65.4% 276 207°C CHCl3 1.1

p-HCPPT White 57.9% 276 204°C DMSO 1.0

Complexes

[Co(o-CPPT)2] Light Pink 71.7% 609 172°C CHCl3,DMSO 2.1

[Ni(o/p-CPPT)2] Light Green 72.1% 609 174°C CHCl3,DMSO 1.7&1.8

[Cu(o/p-CPPT)2] Dark Green 88.3% 613 110°C CHCl3,DMSO 1.4&1.5

[Pb(p-CPPT)2] Cream 86.4% 656.42 98°C CHCl3 1.3

[Zn(p-CPPT)2] Cream 79.8% 615.38 160°C CHCl3,DMSO 1.5

[Mn(p-CPPT)2] Off White 75.6% 605 198⁰C CHCl3 1.2





1/1206, 1168 cm

-1 are assigned to a prevaling υ(C=S) contribution, shows lower intensity or

some times absence in spectra of metal complexes. This indicates the involvement of exocyclic

sulphur atom in coordination. The bands arising at or near 734-787 cm-1

due to C-S further

supports the involvement of sulphur in coordination [38-40].

Systematic shifts called ‘thioamide bands’ due to extensive coupling of δ(NH), υ(N-C=S),

υ(C=N) and υ(C=S) in the spectra of complexes implies that there is interaction between ring

N, exocyclic S atom and metal ions [35-37]. The presence of several new bands in far IR spectra

of complexes between 410 and 198 cm-1

are assignable to υ(M-N) and υ(M-S) stretches

respectively [41]. It is in accordance with N,S chelation through the deprotonated nitrogen atom

N-3 and the exocyclic sulphur atom [42-44].

Table 2:IR data of ligand and its metal complexes

Ligand/

Complexes

ʋ(OH) ʋ(NH) δ (NH) ʋ(C=O) ʋ(C=C)+

ʋ(C=N)

ʋ(N-C=S)

ʋ(C=N), ʋ(N-C=S),

ʋ(C=S)

ʋ(C-S) ʋ(M-N) ʋ(M-S)

Ligand

o-HCPPT 3350 3151 1604 1714 1535 1480 1386,1311,1177 - - -

p-HCPPT 3310 3195 1601 1679 1533 1422 1335,1284,1128 - - -

Complexes

[Co(o-CPPT)2] 3317,

3490

- - 1716 1517 - 1351,1235,1136 754 335 198

[Ni(o-CPPT)2] 3480 - - 1716 1510 1417 1321,1215,1170 750 312 202

[Cu(o-CPPT)2] 3403 - - 1716 1527 1406 1311,1225,1121 734 349 221

[Pb(p-CPPT)2] 3485 - - 1688 1532 - 1378,1255,1160 783 390 226

[Zn(p-CPPT)2] 3325 - - 1686 1529 1412 1318,1210,1110 781 410 270

[Mn(p-CPPT)2] 3490 - - 1680 1543 - 1385,1200,1158 787 361 228

1H NMR Spectra

The 1H NMR spectra of ligand HCPPT was recorded in CDCl3. The spectrum of o-HCPPT

exhibit singlest at δ 1.25, 1.30, 1.33, 4.88 and 9.5 ppm which are assigned to 2(CH3), 1(CH3),

C=C-H and N-H respectively. A multiplet at δ 7.0-7.2 ppm is due to ArC-H. The spectrum of p-

HCPPT exhibit singlet at δ 1.36, 1.40, 1.56, 4.9, 7.96 ppm, assigned to 2(CH3), 1(CH3), C=C-H

and N-H respectively and the appearance of two doublet of doublet at δ 7.3-7.9 ppm are due to

ArC-H.





The 1H NMR spectrum of free ligand displayed a signal at 8.81 ppm and 8.96 ppm due to N-H

proton which disappears in spectra of metal complexes. The deprotonation of N-H proton after

complexation also confirms the coordination of metal ion through the deprotonated N(3) atoms

[45-49] which is in agreement with IR discussion. Moreover, chemical shifting is observed in the

values of metal complexes as compared to free ligands(Table 3).

NMR spectrum of Ni and Co complex shows broad peaks due to the paramagnetic behavior of

the metal ion [50-51]. This observation is in full agreement with the reported results, which

further confirms the formation of metal complexes.

Table 3: 1H NMR data of ligand and its metal complexes

Mass spectra

The mass fragmentation of o/p-HCPPT and some selected metal complexes are presented in

Table 4. Appearance of an intense molecular ion peak at m/z 277.48 (M++1) in mass spectrum of

o/p-HCPPT corresponds to its molecular formula (calcd.276).

The mass spectrum Cu(II) complex show peak at m/z 615.20 corresponding to [Cu(o-CPPT)2]+,

Ni(II) complex shows peak at m/z 610 due to [Ni(o-CPPT)2]+ and that of Mn(II) complex shows

peak at m/z 606 corresponding to [Mn(p-CPPT)2]+complex. The spectrum of Co(II) complex

show peak at m/z 610 due to [Co(o-CPPT)2]+.

All the mass spectra also shows a peak at m/z 277 which is due to the formation of free ligand

during fragmentation process.

Table 4: (M++1) Mass fragmentation data of ligand and its metal complexes

Protons o-HCPPT p-HCPPT [Pb(p-CPPT)2] [Zn(p-CPPT)2]

1H(ppm)

1H(ppm)

1H(ppm)

1H(ppm)

3CH3 1.25,1.30,1.33 1.29,1.32,1.44 1.1,1.2,1.42 1.06-1.49

C=C-H 4.88 4.95 4.88 4.90

N-H 8.81 8.96 - -

ArC-H 7.0-7.2 7.3,7.9 7.1, 7.6 7.1,7.58

O-H - 10.19 10.7 10.6

o/p-HCPPT [Cu(o-CPPT)2] [Ni(o-CPPT)2] [Co(o-CPPT)2] [Mn(p-CPPT)2]





Elemental Analysis

Data of elemental analysis of ligand and metal complexes is given in Table 5. IR and NMR data

clearly indicates the coordination of the ligand (o/p-HCPPT) with metals. Mass spectra and

Elemental analysis also confirms that metal complexes are formed in 1:2 metal ligand ratio and

supports the following proposed structure of the complexes formed(Fig: 1).

Table 5: Elemental Analysis of ligand and metal complexes

Ligand/

Complex

C H N S O

Ligand

o-HCPPT 60.7%

(60.8%)

5.8%

(5.7%)

10.2%

(10.1%)

11.5%

(11.6%)

11.5%

(11.6%)

p-HCPPT 60.7%

(60.8%)

5.5%

(5.7%)

9.8%

(10.1%)

11.3%

(11.6%)

11.3%

(11.6%)

Complexes

[Co(o-CPPT)2] 55.1%

(55.8%)

4.8%

(4.9%)

9.1%

(9.0%)

10.3%

(10.4%)

10.3%

(10.4%)

[Ni(o-CPPT)2] 54.9%

(55.1%)

4.6%

(4.9%)

8.7%

(9.1%)

10.4%

(10.5%)

10.3%

(10.5%)

[Cu(o-CPPT)2] 54.6%

(54.7%)

4.76%

(4.8%)

9.1%

(9.0%)

10.3%

(10.4%)

10.3%

(10.2%)

[Pb(p-CPPT)2] 44.1%

(44.3%)

3.5%

(3.9%)

7.1%

(7.3%)

8.2%

(8.4%)

8.2%

(8.4%)

[Zn(p-CPPT)2] 53.9%

(54.3%)

3.9%

(4.8%)

9.0%

(9.1%)

10.3%

(10.4%)

10.3%

(10.4%)

127.5,179.4,

245.5,265.4,

277.4

m/z

163.48,243.52,

283.49,299.44,

329.49,277.48,

615.18

m/z

179.45,265.49,

277.48,299.43,

610.21 m/z

240.51,265.49,

277.49,299.43,

300.19,610.47

m/z

127.53,245.54,

277.49,299.45,

327.47,345.47,

373.49,606

m/z





[Mn(p-CPPT)2] 55.4%

(55.5%)

4.8%

(4.9%)

9.0%

(9.1%)

10.3%

(10.4%)

10.2%

(10.4%)

*Calculated in parenthesis

Proposed structure of Metal complexes:

N

N

S

H3C CH3

H3C

R

N

N

S

CH3H3C

CH3

R

M

Where R= o/p-C6H5COOH

Fig: 1

Magnetic Measurements and Electronic Spectra

The magnetic data pertaining to these complexes are given in table 5. The magnetic moment 1.79

BM of Cu(II) complexes for S = ½, as mostly to watched for Cu(II) complexes [52,53]. The

magnetic data of Ni(II) complexes show magnetic moments of 3.21 BM, which are close to that

of an octahectral d8

system with two unpaired electrons [54,55]. Co(II) complexe shows

magnetic moment values of 3.67 BM and this value complies with values reported for octahedral

complexes [56,57]. Mn(II) complexe shows magnetic moment values of 5.68 BM andas

expected for high spin distorted octahedral geometry around the central metal ion [58] while

Zn(II) and Pd (II) have no unpaired electrons, show diamagnetic behaviour.

UV visible Spectra

The UV visible spectral data of all complexes are presented in table 5. The electronic spectra of

o/p-HCPPT and its Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pd(II) complexes in CHCl3

exhibit absorption bands at 279-290 and 305-384 nm that can be assigned to π → π* and n →

π* intra-ligand charge transfer, respectively [59].

In addition to the above bands, for [Mn(o-CPPT)2] complex d-d transitions of t2g3 eg

2 are feeble

and spin forbidden, merely visible even in the concentrated solutions; a weak band at 510 may

be assigned to 6A1g →

4T1g(G) transitions respectively[60]. Absorptions at 427, 478, 530 for

[Co(o-CPPT)2] complexes were assigned to 4T1g →

4T2g(F),

4T1g →

4T1g(P),

4T1g →

4A2g(F)

transitions respectively [61].





The electronic spectra of d8 system show bands at 751,475 which are assigned to

3A2g →

3T2g,

3A2g →

3T1g (F),

3A2g →

3T1g (P) and CT transitions of [Ni(o/p-CPPT)2]. The electronic spectra

of [Cu(o/p-CPPT)2] complexes show CT bands at 712,547 which are assigned to 2B1g→

2B2g

and 2B2g →

2Eg transitions, respectively[62]. Hence, a distorted octahedral geometry was

proposed for the copper complexes [55,63]. The complexes with Zn(II), Pd (II) shows no band

in visible region as expected for d10

system and should be diamagnetic.

[Pd(CPPT)2] complex displayed two bands at 475 and 425 assigned to 1A1g →

1B1g and

1A1g →

1E2g transitions typical of four coordinate square planar geometry[64,65]. As the spectra of

[Zn(CPPT)2]complexes were not well resolved, they were not interpreted but their μeff values

showed that they are diamagnetic as expected.

Table 6: The electronic absorption and Magnetic moment data of o/p-HCPPT and its metal

complexes

Ligand/

Complex

Magnetic Moment(BM) Transitions λmax nm

o-HCPPT - 290

p-HCPPT - 310

[Co(o-CPPT)2] 3.68 (Ocahedral) 427,478,530

[Ni(o/p-CPPT)2] 3.11and 2.98 ( bothOcahedral) 751,475

[Cu(o/p-CPPT)2] 1.79 and 1.75 (bothOcahedral) 712,547

[Mn(p-CPPT)2]

5.77 (Ocahedral) 510

[Zn(p-CPPT)2]

Diamagnetic 350,410

[Pd (p-CPPT)2]

Diamagnetic 475, 425

Biological Activities

All the ligand and metal complexes synthesized were subjected to the biological activities that

they can exhibit. Major purpose of this study was to determine the potential of compounds to

inhibit the bacterial growth. All the complexes and ligand were subjected to the MIC test as

mentioned by Andrews 2001 using microdilution method for pathogenic bacteria i.e. Escherichia





coli (MTCC#9537). It was revealed that [Ni(p-CPPT)2] and [Cu(p-CPPT)2] exhibit antibacterial

activity to greater extent and was found to exhibit MIC at 40μg but rest of the compounds

exhibited the MIC at 80 μg. Ortho substituted complexes were not efficient in inhibiting the

growth of bacteria upto 80 μg and proved weaker than para substituted complexes. This fact was

also proved when the well diffusion method for the determination of inhibition zone was used for

the efficiency of the compounds under study. Larger zone of inhibition were obtained when para

substituted complexes were poured in the wells agar plates swabbed with the bacteria however

smaller zone of inhibition were obtained when equivalent amount of ortho substituted complexes

were used in the same study. All the compounds were also subjected to the spectrophotometric

analysis which revealed that [Ni(o-CPPT)2] in the dose of 200 µg per 15 ml of inoculated broth

resulted in a decline of 30% in log phase. It is noteworthy here that the reference drug

chloramphenicol proved less efficient than [Ni(o-CPPT)2] as the drug revealed MIC at 70 µg. It

was found that metal complexes have good antibacterial activity than a free ligand under

identical experimental conditions for one kind of microorganism (Table 5). It was evident from

the data that this activity increases significantly on coordination. Moreover, coordination reduces

the polarity of the metal ion mainly because of the partial sharing of its positive charge with the

donor groups [66,67] with in the chelate ring system formed during coordination. This process,

in turn, leads to increase in the lipophilic character of metal chelates so as to make it more

permeable through the lipid layer of microorganisms thus destroying them more aggressively.

Once the compound enters into the microbial cell, it restricts the growth of microorganism by

binding at the active site of enzymes which involves in various essential biochemical processes

including cell respiration and proteins synthesis in the cell. The mode of action of complexes

involves the formation of hydrogen bonds with imino group by the active sites leading to

interference with the cell wall synthesis. The hydrogen bond formation damages the cytoplasmic

membrane and the cell permeability may also be altered leading to cell death. The higher activity

of Cu(II) and Ni(II) complexes of para ligand may be explained as, on chelation the polarity of

Cu(II) and Ni(II) ion is reduced to a greater extent due to overlap of the ligand orbital and partial

sharing of the positive charge of the copper ion with donor groups. Therefore, Cu(II) and

Ni(II)ions are easily adsorbed on the surface of the cell wall of microorganisms The adsorbed





Cu(II) and Ni(II) ions disturb the respiratory process of the cells and blocks the synthesis of

proteins. This, in turn, restricts further growth of the organisms [68].

DNA Photocleavage Study

There has been a great interest in the discovery of chemical nuclease to overcome the most

threatening danger to the humans, which is cancer. Transition metal complexes are known to

bind specifically with DNA and possess good nuclease activities. They were investigated well in

recent years for the same purpose[66]. These complexes were also studied for antimicrobial

activity and possible photo cleavage activity using pUC18 plasmid in present study. The

complexes were dissolved in DMSO such that each µl of the solution mix had 10-100 µg of the

compound in separate reaction mixtures. 4 µg of the plasmid was subjected to the concerned

activity at various concentrations of all the compounds. It was surprising to note that p-HCPPT -

ligand, [Ni(p-CPPT)2] and [Cu(p-CPPT)2] showed nicking at 20μg to reveal Form I and II DNA

however Form III DNA was also visualized at 45μg, however rest of the compounds revealed

FORM II DNA at 40μg but failed to reveal Form III structure upto 80μg. In addition to these

results, it was also observed that H2O2 had no additional effect on the nicking activity of the

complexes. The enhanced nuclease activity in case of metal complexes may be due to better

binding ability with plasmid DNA as compared to free ligand and the difference in the nuclease

activity among the metal complexes might be due to different degree of binding ability of

different pyrimidine based metal complexes with the plasmid DNA.

Fig:2 Lane C has the control plasmid and lane 1 para ligand, 2 and 5 has the complexes

containing p-nickel and p-copper respectively. The upper arrow displays the form II structure

and the lower arrow points toward the form III structure of DNA resulting from the nicking

activity of the complexes.

CONCLUSION





In search of some biologically active agents, a bidentate pyrimidine-2-thione was synthesized

under solvent free conditions and its metal complexes have been proposed. All compounds

were evaluated for their DNA photocleavage ability and antibacterial agents. It has been

observed that p-substituted ligand and its complexes with Cu(II) and Ni(II) were found to exhibit

good DNA fragmentation and antibacterial potential as compared to ortho substituted ligand and

other complexes. Some structural modifications in the ligand may lead to development of better

DNA nicking agents in future.

ACKNOWLEDGEMENT

Financial support from Management of Maharishi Markandeshwar University Education Trust

is highly acknowledged.

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