Spectrochimica Acta Part A 75 (2010) 422–427

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

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Microwave assisted synthesis, characterization and biological evaluation ofpalladium and platinum complexes with azomethines

Krishna Sharma, Ritu Singh, Nighat Fahmi, R.V. Singh ∗

Department of Chemistry, University of Rajasthan, Jaipur 302004, India

a r t i c l e i n f o

Article history:Received 30 April 2009Received in revised form 15 October 2009Accepted 28 October 2009

Keywords:Pd(II) and Pt(II) complexesAntimicrobial and antiamoebic activityThiosemicarbazone and semicarbazone

a b s t r a c t

Reactions of 3-acetyl-2,5-dimethylthiophene with thiosemicarbazide and semicarbazide hydrochlorideresulted in the formation of new heterocyclic ketimines, 3-acetyl-2,5-dimethylthiophene thiosemicar-bazone (C9H13N3OS2 or L1H) and 3-acetyl-2,5- dimethylthiophene semicarbazone (C9H13N3OS or L2H),respectively. The Pd(II) and Pt(II) complexes have been synthesized by mixing metal salts in 1:2 molarratios with these ligands by using microwave as well as conventional heating method for comparisonpurposes. The authenticity of these ligands and their complexes has been established on the basis ofelemental analysis, melting point determinations, molecular weight determinations, IR, 1H NMR andUV spectral studies. These studies showed that the ligands coordinate to the metal atom in a monobasic

Spectral studies bidentate manner and square planar environment around the metal atoms has been proposed to the com-plexes. Both the ligands and their complexes have been screened for their antimicrobial activities. The

oth thbeen

1

awooaTaubbcarameccne

(

1d

antiamoebic activity of bEntamoeba histolytica has

. Introduction

Uses of metal ions in therapeutic agents are known to acceler-te drug action and their efficacy enhanced upon the coordinationith a metal ion [1,2]. The classical coordination complex, cis-DDP

r cisplatin (cis-diammine dichloroplatinum), has been the subjectf much recent attention towards the metal-based chemother-py, because of its beneficial effects in the treatment of cancer.hiosemicarbazones and semicarbazones are now well establisheds an important class of sulphur/nitrogen donor ligands partic-larly for transition metal ions [3,4]. This is due to remarkableiological activities observed for these compounds, which has sinceeen shown to be related to their metal complexing ability. Theseompounds present a great variety of biological activities, viz.ntitumour [5], antimicrobial [6], anti-inflammatory and antivi-al activities. The significant anti-trypanosomal and antiamoebicctivity of semicarbazones of thiophene derivatives and theiretal complexes have also been reported [7]. We have previously

xamined the chelating behaviour of some N, S/O donor thiosemi-

arbazones and semicarbazones having isatin ring in several metalomplexes with the object of gaining more information about theirature of coordination and related structural and spectral prop-rties [8,9]. The inherent biological potential of sulphur/nitrogen

∗ Corresponding author. Tel.: +91 141 2704677; fax: +91 141 2704677.E-mail addresses: nighat.fahmi@gmail.com (N. Fahmi), rvsjpr@hotmail.com

R.V. Singh).

386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2009.10.052

e ligands and their palladium compounds against the protozoan parasitetested.

© 2009 Elsevier B.V. All rights reserved.

donor ligands prompted us to undertake systematic studies withtransition metals. Platinum metal and its complexes are widelyused as catalysts [10,11].

Platinum(II) and palladium(II) complexes with thiosemicar-bazones [12], semicarbazones [13] and S-methyl/benzyl dithiocar-bazates [14] were reported, which showed significant biologicalactivities. Pd and Pt complexes also show antiamoebic activity[15]. In recent years antimicrobial aspects and antifertility activ-ity of coordination compounds of palladium(II) and platinum(II)have also been reported [16]. Due to long-term treatment toxic-ity and clinical resistance to drugs commonly used, new effectiveagents are urgently needed. A new amoebicide with at least equiva-lent efficacy to metronidazole, well tolerated, with no carcinogenicpotential, would provide a new dimension in therapy. In viewof the importance of palladium(II) and platinum(II) complexes inchemotherapy as well as in catalysis and as part of our contin-uing interest in metal-Schiff base complexes, we report hereinthe preparation, characterization and evaluation of antibacterial,antifungal and antiamoebic activities of some Pd(II) and Pt(II) com-plexes derived from the thiosemicarbazone and semicarbazone of3-acetyl-2,5-dimethylthiophene.

2. Experimental

2.1. Material and methods

Palladium and platinum salts, PdCl2 and PtCl2 as well as 3-acetyl-2,5-dimethylthiophene were purchased from Alfa aesar and

K. Sharma et al. / Spectrochimica Acta Part A 75 (2010) 422–427 423

esis o

upwegaetaFrT

2

l

2

d(1t2(aauto

ered from the microwave oven and dissolved in a few mL of dry

TC

Fig. 1. Synth

sed as such. Solvents of analytical grade were distilled from appro-riate drying agents immediately prior to use. Molecular weightsere determined by the Rast Camphor method [17]. Chlorine was

stimated by Volhard’s method. Pd(II) and Pt(II) were estimatedravimetrically. Nitrogen was estimated by the Kjeldahl’s methodnd sulphur was estimated by the Messenger’s method [18]. Thelectronic spectra were recorded on a Varian–Cary/5E spectropho-ometer at SAIF, IIT, Madras, Chennai. Infrared spectra of the ligandsnd their complexes were recorded with the help of Nicolet MegnaTIR-550 spectrophotometer on KBr pellets. 1H NMR spectra wereecorded on a JEOL-AL-300 FT NMR spectrometer in DMSO-d6 usingMS as the internal standard.

.2. Preparation of the ligands

Two different routes were employed for the synthesis of theigands.

.2.1. Microwave assisted synthesisThe ligands were prepared by the condensation of 3-acetyl-2,5-

imethylthiophene (2.68 g, 17.03 mmol) with thiosemicarbazide1.55 g, 17.02 mmol) or semicarbazide hydrochloride (1.90 g,7.03 mmol), in the presence of sodium acetate. The reaction mix-ure was irradiated by the conventional microwave oven by taking–3 mL solvent. The reactions were completed in a short period5–7 min). The resulting precipitate was then recrystallized with

lcohol and dried under vacuum. These were characterized andnalysed before use. Elemental analyses (N and S) were conductedsing the methods mentioned above and their results were foundo be in good agreement with the calculated values. The structuresf the ligands have been shown in Fig. 1.

able 1omparison between microwave and thermal method.

Compound Yield (%) Solvent (mL

Thermal Microwave Thermal

L1H 85 92 100L2H 84 90 100[Pd(L1)2] 70 82 45[Pd(L2)2] 72 86 40[Pt(L1)2] 65 80 35[Pt(L2)2] 75 79 30

f the ligands.

2.2.2. Conventional thermal methodFor comparison purposes, the above ligands were also synthe-

sized by the thermal method. In this method, instead of few drops ofethanol, 100 mL of ethanol, was used to dissolve the starting materi-als of the ligands and the contents were refluxed for nearly 4–3.5 h.The residue formed was separated out, filtered off, washed withwater, recrystallized from ethanol and finally dried in vacuum overfused calcium chloride. A comparison between thermal method andmicrowave method is given in Table 1.

2.3. Preparation of the metal complexes

2.3.1. [M(L)2] type of complexesThis type of complexes, where M = Pd(II)/Pt(II) and

L = deprotonated ligands, was also prepared by above two differentroutes.

2.3.1.1. Microwave method. In microwave assisted synthesis, thepalladium complexes of the type [Pd(L)2] were prepared by irra-diating the reaction mixture of PdCl2 and respective ligands in drymethanol. In case of the platinum complexes of the type [Pt(L)2],ethanolic solution of PtCl2 and of the respective ligand were used.These reactions were carried out in 1:2 (metal:ligand) propor-tions and in the presence of few drops of ammonium hydroxideto make the solution basic (pH ca. 8.0). The products were recov-

methanol and ethanol, respectively, and were dried under reducedpressure.

2.3.1.2. Conventional thermal method. These complexes were alsosynthesized by the thermal method where instead of 4–7 min, reac-

) Time

Microwave Thermal (h) Microwave (min)

3 4 72 3.5 53 2 74 2 63 2.5 72 3 4

424 K. Sharma et al. / Spectrochimica Ac

Tab

le2

An

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ical

dat

aan

dp

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ical

pro

per

ties

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Com

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Col

our

Mel

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un

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.)(%

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un

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.)

NS

Cl

M

L1H

Bro

wn

174–

180

17.7

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8.48

)27

.89

(28.

20)

––

209.

47(2

27.3

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ream

206–

210

15.9

9(1

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(12.

94)

––

233.

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d(L

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l 2B

row

n23

6–24

012

.96

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20.1

0(2

0.39

)10

.88

(11.

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16.2

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6.77

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2.09

(632

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]B

row

n15

8–16

214

.85

(15.

03)

22.4

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)–

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.79

(12.

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9.08

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06)

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124

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Bro

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138–

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ta Part A 75 (2010) 422–427

tions were completed in 2–3 h and the yield of the products was alsoless than that obtained by the microwave assisted synthesis.

2.3.2. [M(LH)2]Cl2 type of complexesThis type of complexes, where M = Pd(II)/Pt(II) and LH = ligands,

was prepared only by the conventional thermal method as follows.

2.3.3. [Pd(LH)2]Cl2 type of complexesTo obtain this type of complexes the methanolic solution of

PdCl2 was mixed with methanolic solution of the ligand in 1:2 (M:L)molar ratios. The mixture was stirred on a magnetic stirrer for 2–3 hin the presence of few drops of concentrated HCl. The resultingproducts were recovered by filtration, washed with methanol anddried in vacuum.

2.3.4. [Pt(LH)2]Cl2 type of complexesThe ethanolic solution of PtCl2 was mixed with an ethanolic

solution of the ligand in 1:2 (M:L) molar ratios. The mixture wasstirred on a magnetic stirrer for 2–3 h in the presence of few dropsof concentrated HCl. The resulting products were recovered by fil-tration, washed with ethanol and dried in vacuum.

The physico-chemical properties and analytical data of thesecomplexes are listed in Table 2.

2.4. Microbiological studies

2.4.1. Antifungal activityThe antifungal activity of the standard fungicide (Flucanazone),

ligands and complexes were tested for their effect on the growthof microbial cultures and studied for their interaction with Fusar-ium oxysporum and Rhizopus nigricans using Czapek’s agar mediumhaving the composition, glucose 20 g, starch 20 g, agar-agar 20 gand distilled water 1000 mL.To this medium was added requisiteamount of the compounds after being dissolved in dimethylfor-mamide so as to get the certain concentrations (50, 100 and200 ppm). The medium then was poured into petri plates andthe spores of fungi were placed on the medium with the helpof inoculum’s needle. These petri plates were wrapped in poly-thene bags containing a few drops of alcohol and were placed inan incubator at 30 ± 2 ◦C. The controls were also run and threereplicates were used in each case. The linear growth of the fun-gus was recorded by measuring the diameter of the fungal colonyafter 96 h and the percentage inhibition was calculated by theequation:

% Inhibition = C − T

C100

where C and T are the diameters of the fungal colony in the controland the test plates, respectively [19].

2.4.2. Antibacterial activityAntibacterial activity was tested against Escherichia coli and

Staphylococcus aureus using the paper disc plate method [20]. Eachof the compounds was dissolved in DMSO and solutions of the con-centrations (500 and 1000 ppm) were prepared separately. Paperdiscs of Whatman filter paper (No. 42) of uniform diameter (2 cm)were cut and sterilized in an autoclave. The paper discs soaked inthe desired concentration of the complex solutions were placedaseptically in the petri dishes containing nutrient agar media (agar20 g + beef extract 3 g + peptone 5 g) seeded with E. coli and S. aureusbacteria separately. The petri dishes were incubated at 37 ◦C and

the inhibition zones were recorded after 24 h of incubation. Theantibacterial activity of a common standard antibiotic tetracyclinwas also recorded using the same procedure as above at the sameconcentrations and solvent. The % Activity Index for the complexwas calculated by the formula as under:

K. Sharma et al. / Spectrochimica Acta Part A 75 (2010) 422–427 425

Table 3Electronic spectral data (cm−1) of the palladium(II) and platinum(II) complexes.

Complex Spectral bands (cm−1) Transitions �1 (cm−1) �2 (cm−1) �3 (cm−1) �2/�1

[Pd(L1H)2]Cl2 22,222 1A1g → 1A2g (�1) 24,322 3368 1976 1.0924,390 1A1g → 1B1g (�2)26,666 1A1g → 1E1g (�3)

[Pd(L1)2] 21,598 1A1g → 1A2g (�1) 23,698 3530 2653 1.1023,923 1A1g → 1B1g (�2)26,881 1A1g → 1E1g (�3)

[Pt(L2H)2]Cl2 19,230 1A1g → 1A2g (�1) 21,330 5779 4876 1.2323,809 1A1g → 1B1g (�2)28,985 1A1g → 1E1g (�3)

2 19,120 1A → 1A (� ) 21,220 5609 4906 1.23

2

vbtoDsaimtnasmcwcgoTicqvrwpthaiTclwI

3

w

[Pt(L )2] 1g 2g 1

23,529 1A1g → 1B1g (�2)28,735 1A1g → 1E1g (�3)

% Activity Index

= zone of inhibition by test compound (diameter)zone of inhibition by standard (diameter)

× 100

.4.3. In vitro testing against Entamoeba histolyticaBoth the ligands and their Pd(II) complexes were screened in

itro for antiamoebic activity against (HK-9) strain of E. histolyticay microdilution method [21]. E. histolytica trophozoites were cul-ured in TYIS-33 growth medium by standard method [22] in wellsf 96-well microtiter plate. All the compounds were dissolved inMSO at which level no inhibition of amoeba occurs [23,24] and the

tock solutions of the compounds were prepared freshly before uset a concentration of 1 mg/mL. Twofold serial dilutions were maden the wells of 96-well microtiter plate (Costar). Each test includes

etronidazole as a standard amoebicidal drug, control wells (cul-ure medium plus amoebae) and a blank (culture medium only). Theumber of amoeba per mL was estimated with a haemocytometernd trypan blue exclusion was used to confirm viability. The celluspension used was diluted to 105 organism/mL by adding freshedium and 170 �L of this suspension was added to the test and

ontrol wells in the plate. An inoculum of 1.7 × 104 organisms/wellas chosen so that confluent, but not excessive growth took place in

ontrol wells. Plates were sealed and gassed for 10 min with nitro-en before incubation at 37 ◦C for 72 h. After incubation, the growthf amoebae in the plate was checked with a low power microscope.he culture medium was removed by inverting the plate and shak-ng gently. Plate was then immediately washed once in sodiumhloride solution (0.9%) at 37 ◦C. This procedure was completeduickly, and the plate was not allowed to cool in order to pre-ent the detachment of amoebae. The plate was allowed to dry atoom temperature, and the amoebae were fixed with methanol and,hen dry, stained with (0.5%) aqueous eosin for 15 min. Stainedlate was washed once with tap water and then twice with dis-illed water and allowed to dry. A 200-�L portion of 0.1N sodiumydroxide solution was added to each well to dissolve the proteinnd release the dye. The optical density of the resulting solutionn each well was determined at 490 nm with a microplate reader.he % inhibition of amoebal growth was calculated from the opti-al densities of the control and test wells and plotted against theogarithm of the dose of the drug tested. Linear regression analysis

as used to determine the best-fitting straight line from which theC50 (inhibitory concentration, 50%) value was found.

. Results and discussion

The reactions of PdCl2 with ligands were carried out in methanolhile in case of PtCl2, water and ethanol solution (1:1) of PtCl2 and

ethanolic solution of the ligand have been used for the reactions.The reactions of metal chlorides with ligands have been shown bythe following general equation:

MCl2 + 2LH → [M(LH)2Cl2]

MCl2 + 2LH + NH4OH → [M(L)2] + 2NH4Cl + 2H2O

where M = Pd(II) and Pt(II) and LH is the ligand molecule.The reac-tions proceed easily and all the complexes are soluble in DMSO,DMF and CHCl3. The complexes are monomers as revealed by theirmolecular weight determinations.

3.1. Electronic spectra

The electronic spectra of the ligands and their complexes wererecorded in distilled DMSO. The spectra of both the ligands L1Hand L2H show a broad band at 380–382 nm which can be assignedto the n–�* transitions of the azomethine group which under-goes a blue shift in the complexes due to the polarization withinthe >C N chromophore caused by the metal–ligand interaction.The spectra of the complexes show three bands due to three d–dspin allowed transitions. These are corresponding to the transitionsfrom the three lower lying d orbitals to the empty dx2 − y2 orbital.The ground state is 1A1g and excited states corresponding to theabove transitions are 1A2g, 1B1g and 1E1g in the order of increasingenergy. The three orbital parameters were calculated using a valueof F2 = 10F4 = 600 cm−1 for Slater Condon interelectronic repulsion[24]. The �2/�1 were also calculated and are in close agreement withthe data reported by others for square planar complexes [25,26](Table 3).

3.2. IR spectra

The tentative absorption frequencies of the ligands and theirmetal complexes along with their assignments are listed in Table 4.The IR spectra of the free ligands L1H and L2H display absorptionbands at 2910–3000, 1610–1620 and 1030/1690 cm−1 are assignedto �(NH), �(C N), and �(C S)/�(C O), respectively. The broad banddue to �(NH) vibrations, disappears in the spectra of [M(L)2] typeof complexes, indicating the deprotonation of this group on coor-dination with the metal atom. The negative shift (10–20 cm−1) of�(C N) band observed in all complexes indicates the involvementof azomethine nitrogen upon complexation [27]. The bands due to

�(C S) and �(C O) are shifted towards lower frequencies in thecomplexes indicating coordination of sulphur and oxygen to thecentral metal atom. The spectra of the free ligands display two sharpbands at 3340–3500 and 3350–3490 cm−1 due to �asym and �sym

vibrations of NH2 group, respectively, which remain at almost the

426 K. Sharma et al. / Spectrochimica Acta Part A 75 (2010) 422–427

Table 4IR (cm−1) and 1H NMR (ı, ppm) spectral data of the ligands and their corresponding complexes.

Compound IR spectral data (cm−1) 1H NMR spectral data (ı, ppm)

�(C N) �(M → S) �(M → O) �(M → N) –NH (bs) >aCH3 –NH2 (bs) Aromatic protons (m)

L1H 1610 – – – 8.59 2.08 2.70 6.43–8.57L2H 1620 – – – 8.78 2.12 3.06 6.73–7.61[Pd(L1H)2]Cl2 1625 305 – 352 8.38 2.06 2.68 6.55–7.38[Pd(L1)2] 1620 308 – 356 – 2.07 2.60 6.23–8.16[Pt(L1H)2]Cl2 1632 306 – 442 8.55 2.05 2.62 6.72–8.07[Pt(L1)2] 1618 310 – 445 – 2.03 2.65 6.71–8.02[Pd(L2H)2]Cl2 1628 – 412 358 8.62 2.09 3.04 6.74–8.06[Pd(L2)2] 1635 – 410 360 – 2.10 3.02 6.78–8.09[Pt(L2H)2]Cl2 1633 – 422 446 8.64 2.11 3.06 6.25–7.46[Pd(L2) ] 1630 – 425 448 – 2.08 3.05 6.79–8.10

bm

sN(tei�oiba�

3

or–ccaspbf

i

FL

2

s = broad signal.= multiplet.a CH3 attached to azomethine carbon.

ame positions in the spectra of the complexes, suggesting that theH2 group is not involved in chelation. The band due to �(C–S–C)

ring) of thiophene moiety remains unaltered thereby indicatinghe non-involvement of ring sulphur in coordination. The prefer-ntial coordination of thiolic sulphur over sulphur of thiophenes due to more nucleophilic character of the former. However, no(M–Cl) band in the region 295–345 cm−1 is observed in the spectraf [M(LH)2]Cl2 type of complexes, suggesting that chloride is ionicn these complexes. The mode of coordination is further supportedy the presence of the new bands at 352–360, 442–448, 305–310nd 410–425 cm−1 assigned to �(Pd → N), �(Pt → N), �(M → S) and(M → O), respectively.

.3. 1H NMR spectra

Further evidence for the coordinating mode of the ligands wasbtained from 1H NMR spectra. The 1H NMR spectra of the ligandsecorded in DMSO-d6 exhibit a broad peak at ı 8.59–8.78 ppm due toNH proton. The –NH proton signal of the ligands disappears in theomplexes of the type [M(L)2]. The absence of this signal in theseomplexes suggest that this proton has been lost via thioenolizationnd ketoenolization of >C S and >C O groups and coordination ofulphur and oxygen to the metal atoms, respectively, has takenlace. Other protons, viz. CH3 protons, NH2 protons and aryl car-ons in complexes resonate nearly at the same position as that of

ree ligands (Table 4).

On the basis of the above discussion, following structures shownn Figs. 2 and 3 have been proposed for the complexes.

ig. 2. Addition Complex, [M(LH)2]Cl2 where M = Pd and Pt, X = S (C9H13N3OS2 or1H) and O (C9H13N3OS or L2H).

Fig. 3. Substitution Complex, [M(L)2] where M = Pd and Pt, X = S (C9H13N3OS2 orL1H) and O (C9H13N3OS or L2H).

3.4. Biological activity

Antimicrobial activity of the synthesized ligands and their cor-responding metal complexes on selected fungi, F. oxysporum andR. nigricans and two bacteria, E. coli and S. aureus was carriedout (Tables 5 and 6). The complexes show moderate activity ascompared to the standard fungicide and bactericide but all thecomplexes are more active than their respective ligands and thusindicated that the complexation to metal enhances the activity

of the ligand. This may be explained by chelation theory [28],according to which chelation reduces the polarity of the ligandand the central metal atom because of the delocalization of �-electrons over the whole chelate ring increases, which favours

Table 5Antifungal screening data for the ligands and their complexes.

Compound % Inhibition after 96 h (conc. in ppm)

Fusarium oxysporum Rhizopus nigricans

50 100 200 50 100 200

L1H 40 55 67 30 45 60L2H 33 37 48 27 32 53[Pd(L1H)2]Cl2 46 58 65 42 57 64[Pd(L1)2] 45 56 61 40 55 63[Pd(L2H)2]Cl2 42 45 56 35 39 60[Pd(L2)2] 40 43 52 42 45 58[Pt(L1H)2]Cl2 50 62 68 46 59 66[Pt(L1)2] 49 60 66 43 58 64[Pt(L2H)2]Cl2 46 48 58 38 46 65[Pt(L2H)2]Cl2 42 45 54 34 39 62Flucanazone 82 99 100 86 98 100

K. Sharma et al. / Spectrochimica Acta Part A 75 (2010) 422–427 427

Table 6Antibacterial screening data for the ligands and their complexes.

Compound Staphylococcus aureus Escherichia coli

Diameter of inhibition zone (mm) % Activity Index Diameter of inhibition zone (mm) % Activity Index

500 1000 500 1000 500 1000 500 1000

L1H 7 9 46 50 9 10 52 55L2H 6 9 40 50 8 9 47 50[Pd(L1H)2]Cl2 9 11 60 61 12 14 70 77[Pd(L1)2] 8 10 53 55 10 12 56 66[Pd(L2H)2]Cl2 8 10 53 55 11 13 64 72[Pd(L2)2] 7 11 46 61 9 12 59 66[Pt(L1H)2]Cl2 10 13 66 72 13 16 76 88[Pt(L1)2] 9 12 60 6[Pt(L2H)2]Cl2 10 13 66 7[Pt(L2)2] 9 11 60 6Tetracyclin 15 18 100 10

Table 7In vitro antiamoebic activities of the ligands and their Pd(II) complexes against (HK-9) strain of E. histolytica.

S. no. Compound IC50 (�M) S.D.a

1 L1H 3.75 0.542 [Pd(L1H)2] 0.96 0.273 [Pd(L1)2] 1.55 0.304 L2H 4.40 0.845 [Pd(L2H)2]Cl2 1.60 0.406 [Pd(L2) ] 1.85 0.32

pbvc[

ehbmiciAtettp

4

binape

[[

[

[[[

[

[[[[

[

[

[[[[

2

7 Metronidazole 2.05 0.33

a Standard deviation.

ermeation of the complexes through the lipid layer of cell mem-rane. The variation in the activity of different complexes againstarious organisms depends either on the impermeability of theells of the microbes or differences in ribosome in microbial cells29].

Both the ligands and their palladium compounds were alsovaluated for antiamoebic activity in vitro using HK-9 strain of E.istolytica. The IC50 values in micromolar are shown in Table 7. Theiological data suggests that all the Pd(II) complexes were foundore active than their respective ligands. The free ligands exhib-

ted antiamoebic activity with IC50 of 3.75–4.40 �M whereas Pd(II)omplexes exhibit a significant improvement in antiamoebic activ-ty towards HK-9 strain of E. histolytica (IC50 of 0.96–1.85 �M).

possible explanation is that, by coordination, the polarities ofhe ligand and the central metal ion are reduced through chargequilibration, which favours permeation of the complexes throughhe lipid layer of the cell membrane [30]. Detailed studies ofhe toxicity of these compounds and mechanism of action are inrogress.

. Conclusion

On the basis of the analytical data and spectral studies, it haseen observed that the ligands coordinated to the metal atoms

n a monobasic bidentate manner and thus possess square pla-ar geometry. The complexes showed better antimicrobial andntiamoebic activities as compared to the parent ligands. The com-ounds also inhibit the growth of fungi and bacteria to a greaterxtent as the concentration is increased.

[

[[

[

6 11 14 64 772 13 15 76 831 11 12 64 660 17 18 100 100

Acknowledgement

One of the authors Krishna Sharma is thankful to CSIR, New Delhifor financial assistance through Grant No. 09/149(0435)/2006-EMR-I.

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