Journal of Molecular Structure 936 (2009) 213–219

Contents lists available at ScienceDirect

Journal of Molecular Structure

journal homepage: www.elsevier .com/ locate /molst ruc

Mn(II), Co(II), Zn(II), Fe(III) and U (VI) complexes of 2-acetylpyridine 4N-(2-pyridyl)thiosemicarbazone (HAPT); structural, spectroscopic and biological studies

Usama El-Ayaan a,b,*, Magdy M. Youssef a,b, Shar Al-Shihry b

a Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egyptb Department of Chemistry, College of Science, King Faisal University, P.O. Box 380, Hofuf 31982, Saudi Arabia

a r t i c l e i n f o

Article history:Received 14 May 2009Received in revised form 28 July 2009Accepted 29 July 2009Available online 3 August 2009

Keywords:2-AcetylpyridineThiosemicarbazone complexesSpectroscopyAntibacterial

0022-2860/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.molstruc.2009.07.042

* Corresponding author. Present address: DepartmScience, King Faisal University, P.O. Box 380, Hofuf 31553901011; fax: +966 35886437.

E-mail address: uelayaan@kfu.edu.sa (U. El-Ayaan

a b s t r a c t

The present work carried out a study on transition metal ion complexes which have been synthesizedfrom 2-acetylpyridine 4N-(2-pyridyl) thiosemicarbazone (HAPT) 1. These complexes namely[Zn(HAPT)Cl2] 2, [Mn (HAPT)Cl2] 3, [Co (HAPT)Cl2] 4, [Fe(APT)Cl2(H2O)] 5 and [UO2(HAPT)(OAc)2] 6, werecharacterized by elemental analysis, spectral (IR, 1H NMR and UV–vis) and magnetic moment measure-ments. Thermal properties and decomposition kinetics of all compounds are investigated. The interpre-tation, mathematical analysis and evaluation of kinetic parameters (E, A, DH, DS and DG) of all thermaldecomposition stages have been evaluated using Coats–Redfern equation. The biochemical studiesshowed that, complexes 3 and 6 have powerful and complete degradation effect on the both DNA andprotein. The SOD-like activity exhibited that complex 3 has a strong antioxidative properties. The anti-bacterial screening demonstrated that, the free ligand (HAPT), complexes 2, 3 and 6 have the maximumand broad activities against Gram-positive and Gram-negative bacterial strains.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

Thiosemicarbazones and their metal complexes have beensubject of interest because of their chemical and biological proper-ties [1,2]. The well documented biological activities of several het-erocyclic thiosemicarbazones have been often attributed to theirability to form chelates with transition metal ions [3,4]. 2-Acetyl-pyridine thiosemicarbazones were the first thiosemicarbazonesin which antimalarial activity was detected, and the highest activ-ity is reported when the N(4) position is either disubstituted orpart of a ring system [5]. N,N,S-tridentate thiosemicarbazones de-rived from 2-acetylpyridine form an important class of compoundspossessing biological activity [6,7]. Metal complexes of 4N-alkyl[8], 4N-dialkyl-thiosemicarbazone [9] derived from 2-acetylpyri-dine have been spectrally characterized; with tridentate coordina-tion of neutral and anionic ligands being reported.

In this paper we prepared the new ligand 2-acetylpyridine 4N-(2-pyridyl) thiosemicarbazone (HAPT) (Fig. 1) and studied its ligan-tional behavior towards some transition metal ions namely, Mn2+,Co2+, Zn2+, Fe3+ and U6+.

This class of ligands are very versatile compounds; structural iso-mers (E-, E’-and Z-forms) are reported [10,11]. We apply geometry

ll rights reserved.

ent of Chemistry, College of982, Saudi Arabia. Tel.: +966

).

optimization and conformational analysis to the free ligand andstudied all possible structural isomers and have got the minimumenergy with E-isomer. 1H NMR measurements confirm the presenceof one tautomers (E-form) for the HAPT free ligand. Other studiesshows only one isomer in the solid state but three isomers are ex-isted in solution [12] which confirmed by our calculations (Fig. 2).

Spectroscopic and thermal degradation kinetics of the resultingcomplexes in addition to its antibacterial activities against Gram-positive and Gram-negative bacteria are discussed.

2. Experimental

2.1. Instrumentation and materials

All starting materials were purchased from Fluka, Riedel andMerck and used as received. Elemental analyses (C, H and N) wereperformed on a Perkin–Elmer 2400 Series II Analyzer. Electronicspectra were recorded on a UV-UNICAM 2001 spectrophotometerusing 10 mm pass length quartz cells at room temperature. Mag-netic susceptibility was measured with a Sherwood Scientific mag-netic susceptibility balance at 297 K. Infrared spectra wererecorded on a Perkin–Elmer FTIR spectrometer 2000 as KBr pelletsand as Nujol mulls in the 4000–200 cm�1 spectral range. 1H and13C NMR measurements at room temperature were obtained on aJeol JNM LA 300 WB spectrometer at 250 MHz, using a 5 mm probehead in CDCl3. Thermogravimetric (TG) and differential (DTG)

N NH2

+ CS2Et3N

N NH

S

S

Et3NH

N NH

S

S

Et3NH

Step 1

Step 2+ CH3I

N NH

S

SMe

N NH

S

SMe

+ NH2NH2N N

HNH

NH2

SStep 3

Fig. 3. Preparation of 4-(2-pyridyl)-3-thiosemicarbazide.

Fig. 1. Structure of the free ligand (HAPT).

214 U. El-Ayaan et al. / Journal of Molecular Structure 936 (2009) 213–219

thermogravimetric analysis were performed on a DTG-50 Shimazuinstrument at heating rate of 10 �C/min.

2.2. Preparation of the free ligand HAPT and its complexes

2.2.1. Preparation of 4-(2-pyridyl)-3-thiosemicarbazide4-(2-pyridyl)-3-thiosemicarbazide is prepared in three steps as

follow (Fig. 3):Step 1: Preparation of triethylammonium N-2-Pyridyldithiocarba-

mate. 2-aminopyridine (0.2 mol, 19 g), carbon disulphide (0.2mol, 12 mL) and triethylamine (0.2 mol, 30 mL) were warmed togive a clear solution. Two phases separated rapidly and the wholemixture was shaken at room temperature for 24 h, the whole hadthen solidified. The product was filtered and then washed withether and air-dried. The lemon-yellow plates formed were triethyl-ammonium N-2-Pyridyldithiocarbamate, C12H21N3S2, m.p. 85 �C,yield 49.0 g (90.5%).

Step 2: Preparation of Methyl-2-pyridyldithiocarbamate. Methanol(100 ml) was added to triethylammonium N-2-Pyridyldithiocarba-mate (49.0 g, 0.18 mol), followed by methyl iodide (13 ml,0.2 mol). After 1 h, water was added into the solution and pale yel-low needles of Methyl-2-pyridyldithiocarbamate were formed,C7H8N2S2, m.p. 101 �C, yield 25.2 g (76%).

Step 3: Preparation of 4-(2-pyridyl)-3-thiosemicarbazide. A mix-ture of 0.13 mol (25.0 g) of methyl-2-pyridyldithiocarbamate and13 ml (0.40 mol) of hydrazine hydrate in 10 ml of absolute ethanolwas heated for 5 min. An abundant amount of crystalline precipi-tate of 4-(2-pyridyl)-3-thiosemicarbazide was formed, m.p.193 �C, yield 21.2 g (97%). C6H8N4S (168.22) calcd: C 42.8, H 4.79,N 33.3, S 19.1; found C 42.3, H 4.70, N 32.9, S 18.9% – 1H NMR(DMSO-d6, 250 MHz, 24 �C) d = 11.48 (s, 1H, 4NH), 9.47 (s, 1H,2NH), 4.14 (s, 2H, NH2), 5.8–7.2 (m, pyridyl protons).

2.2.2. Preparation of 2-acetylpyridine 4N-(2-pyridyl)thiosemicarbazone(HAPT)

The ligand was prepared by boiling an ethanolic solution of 4-(2-pyridyl)-3-thiosemicarbazide (1.68 g, 10 mmol) and 2-acetyl

Fig. 2. Structure of (E, E’ an

pyridine (1.21 g, 10 mmol). The yellow crystals of HAPT were re-moved by filtration, washed with ethanol and recrystallized fromhot ethanol, m.p. 190, yield 2.51 g (92.6%). C13H13N5S (271.13)calcd: C 57.5, H 4.83, N 25.8, S 11.8; found C 57.3, H 4.75, N 24.9,S 11.5% – 1H NMR (DMSO-d6, 250 MHz, 24 �C) d = 1.341 (s, 3H,CH3), 4.13 (br s, 2H, NH) 5.88–6.36 (m, 3H), 6.62–6.83 (m, 2H),7.1–7.54 (m, 3H).

2.2.3. Synthesis of metal complexesAll complexes were prepared by refluxing HAPT (0.35 g,

1.0 mmol) and the hydrated metal salts (1.0 mmol) e.g. chlorideor acetate, in 30 ml ethanol for 2–3 h. The resulting solid com-plexes were filtered while hot, washed with ethanol followed bydiethyl ether and dried in vacuo over CaCl2.

2.3. Biological studies

2.3.1. DNA and protein electrophoresesAgarose gels. The free (HAPT) ligand or its Mn(II), Co(II), Zn(II),

Fe(III) and UO2(II) complexes (10 lM or 100 lM) were added indi-vidually to 1 lg of the DNA isolated from Escherichia coli. These sam-ples were incubated for 1 h at 37 �C. The DNA was analysed by usinghorizontal agarose gels electrophoresis. The electrophoresis wasperformed using 0.7% (w/v) agarose gels in TAE buffer (5 lM sodiumacetate, 1 lM EDTA and 0.04 M Tris–HCl pH 7.9). The agarose gelswere stained with ethidium bromide (0.5 lg/mL) and the DNAwas visualized on a UV transilluminator [13].

2.3.2. Polyacrylamide gel electrophoresisBovine serum albumin (BSA) (3 mg) was treated with the free

(HAPT) ligand or its Mn(II), Co(II), Zn(II), Fe(III) and UO2(II) com-plexes (10 lM or 100 lM) individually. The reaction mixtures wereincubated for 1 h at 37 �C. The protein samples were analyzedusing vertical one dimensional SDS–polyacrylamide gel electro-phoresis according to the method of Laemmli [14].

The samples were prepared by adding 15 lL 2 � SDS-gel load-ing buffer (100 mM Tris–HCl pH 6.8, 4% (w/v) SDS, 0.2% (w/v) bro-mophenol blue, 20% (v/v) glycerol, 200 mM DTT) and 15 lL proteinsamples and boiled in a water bath for 3 min, 20 lL of denaturedprotein samples were loaded into the gel.

d Z) isomers of HAPT.

Fig. 4. Structure of [Zn(HAPT)Cl2].

Fig. 5. Structure of [Mn(HAPT)Cl2].

U. El-Ayaan et al. / Journal of Molecular Structure 936 (2009) 213–219 215

2.3.3. Determination of SOD-like activitySuperoxide dismutase (SOD)-like activity was investigated

using Bridges and Salin method [15]. This method is based onthe inhibitory effect of SOD on the reduction of nitrobluetetrazoli-um (NBT) by the superoxide anion generated by the xanthine/xan-thine oxidase system. The solutions of the free (HAPT) ligand or itsMn(II), Co(II), Zn(II), Fe(III) and UO2(II) complexes were prepared indimethylsulphoxide (DMSO). For comparative purposes, the activ-ity of native horseradish superoxide dismutase (HR SOD) has alsobeen determined.

2.3.4. Antibacterial effectThe antibacterial investigation of the free (HAPT) ligand or its

Mn(II), Co(II), Zn(II), Fe(III) and UO2(II) complexes was carried outusing cup diffusion technique [16]. The test was done against theGram-negative Pseudomonas aeruginosa (P. aeruginosa) and Esche-richia coli (E. coli) and the Gram-positive Bacillus subtilis (B. subtilis)and Staphylococcus saprophyticus (S. st).The tested free (HAPT) li-gand or its complexes were dissolved in DMSO at concentration1 mg/mL. The Luria–Bertani Agar (LBA) medium was used. An ali-quot of the solution of the tested complexes equivalent to 100 lgwas placed separately in each cup. The LBA plates were incubatedfor 24 h at 37 �C and the resulting inhibition zones were measured.Amoxicillin 1 mg/mL was used as a positive control while DMSO,which exhibited no antibacterial activity, was used as a negativecontrol.

2.4. Molecular modeling

An attempt to gain a better insight on the molecular structure ofligand and its complexes, geometry optimization and conforma-tional analysis has been performed by the use of MM+ [17] force-field as implemented in hyperchem 5.1 [18].

3. Results and discussion

3.1. IR spectra of complexes

Important IR bands for the ligand and complexes with their ten-tative assignments are presented in Table 1.

In [Zn(HAPT)Cl2] the ligand HAPT acts as a neutral NNS triden-tate ligand. This mode of complexation is confirmed by (i) the in-plane ring deformation mode of pyridine at 592 cm�1 in the spec-tra of HAPT shifts to higher frequency (621 cm�1) in the spectra ofcomplex and (ii) the ligand show m(C@N) (azomethine) and m(C@S)(thioamide VI) bands at 1604, 1149 cm�1 respectively; on com-plexation, the positions of these bands are shifted to higher valuesindicating the coordination of both azomethine nitrogen and sulfurof the C@S group. Minimum energy, geometry optimization and

Table 1Analytical and physical data and main IR spectral bands of HAPT ligand and its metal com

Compound Color %Calc. (Found)

Empirical formula, (F.Wt) C H N

(HAPT) , 1 Pale-yellow 57.50 4.83 25.8C13H13N5S(271.34) (57.42) (4.75) (24.9)[Zn(HAPT)Cl2] , 2 Yellow 38.23 3.22 17.19C13H13Cl2N5SZn (407.64) (38.15) (3.19) (17.44)[Mn(HAPT)Cl2] , 3 Orange–yellow 39.31 3.29 17.63C13H13Cl2MnN5S (397.19) (38.86) (3.28) (17.88)[Co(HAPT)Cl2], 4 Green 42.8 3.31 19.21C13H12ClCoN5S (364.7) (42.8) (3.31) (19.23)[Fe(APT)Cl2(H2O)], 5 Gray–green 37.60 3.40 16.90C13H14Cl2FeN5OS (415.1) (37.40) (3.20) (15.90)[UO2(HAPT)(OAC)2], 6 Orange 30.96 2.90 10.60C17H19N5O6SU (659.5) (29.28) (2.47) (10.40)

conformational analysis has been performed and confirmed the5-coordinate zinc(II) complex through one HAPT ligand and twoCl� coordinated to the central metal (Fig. 4). Similar structurewas observed for [ZnCl2(HL)] where HL = 2-acetylpyridine 4N-eth-ylthiosemicarbazone [19].

In [Mn(HAPT)Cl2] and [Co(HAPT)Cl2] the ligand behaves as neu-tral bidentate ligand coordinating through the nitrogen of pyridylring and the nitrogen of azomethine group (see Table 1, Fig. 5).The tetrahedral structure of both complexes was confirmed byapplying minimum energy, geometry optimization and conforma-tional analysis by the use of MM + forcefield as implemented inhyperchem.

IR spectrum of [Fe(APT)Cl2(H2O)] (Fig. 6) shows that the ligandbehaves as a mononegative tridentate via the azomethine nitrogen,nitrogen of the pyridyl ring and the CS in the thiol form. This modeof complexation is suggested by (i) the shift of azomethine nitro-gen to higher wavenumber (1605 ? 1645 cm�1). (ii) Coordinationof the pyridine nitrogen is indicated by the positive shift of the ringdeformation band in the complex (there is an unshifted band ineach spectrum due to the second uncoordinated ring). (iii) the ab-sence of one m(NH) and the thioamide IV m(C@S) and the appear-ance of new band assigned to m(CAS) confirm the coordination of

plexes.

m(NH) m(C@N) m(C@S) H(py) m(CAS)

S

11.8 3222,3165 1604 1149 592, 600 �(11.5)7.86 3292,3198 1645 1157 621, 598 �(7.80)8.07 3219, 3186 1645 1149 635, 600 �(8.02)8.79 3215, 3184 1647 1157 625, 595 �(8.79)7.72 3219 1645 – 630, 595 700(7.28)4.86 3220, 3160 1593 1155 636, 595 �(4.80)

Fig. 6. Structure of [Fe(APT)Cl2(H2O)].

216 U. El-Ayaan et al. / Journal of Molecular Structure 936 (2009) 213–219

the thiol sulfur atom. In addition to the infrared band observed at3540 cm�1. Coordination of water molecule was confirmed bythermal anaylsis, the coordinated water molecule was removedat 186–220 �C temperature range.

The uranyl complex exhibits three bands at 918, 830 and270 cm�1 assigned to m3, m1 and m4 vibrations, respectively, of thedioxouranium ion [20,21]. The force constant (F) for the bondingsites of m(U@O) is calculated by the method of McGlynn et al.[22]. The FUO value is 6.96 m dynes �1, the UAO bond distanceis calculated with the help of the equation [23]. Shown below.

RU�O ¼ 1:08F�1=3 þ 1:17

The UAO bond distance (1.74 Å) falls in the usual region as re-ported earlier [24]. Peaks at 1444 and 1534 cm�1 are assigned tomsym(COO) and masym(COO), respectively [25,26], NMR spectra showtwo signals at 2.75 and 2.82 ppm, are assigned to methyl groupsindicating the presence of two acetate groups in the coordinationsphere of uranium.

3.2. Electronic spectra and magnetic moment measurements

Electronic spectra were measured in 10�3 M dimethyl sulfoxide(DMSO) solution of all studied complexes.

The magnetic moment of [Mn(HAPT)Cl2] complex, (5.9 B.M.)indicate the presence of five unpaired electrons, as expected forhigh spin 3d5 system [27]. The electronic spectra provide evidencefor tetrahedral structure in two ways. Firstly, the fact that the spec-tra at 24,814 cm�1 is clearly observed indicates tetrahedrally coor-dinated manganese(II) [28], and secondly tetrahedral complexeswhere the laporte restriction is not so rigid generally exhibit spec-tra with molar extinction coefficient in the 1–10 lmol�1 cm�1

range [29].The electronic spectrum of the green [Co(HAPT)Cl2] complex

exhibits one intense band at 14705 cm�1 attributed to 4A2 ?4T1

Fig. 7. TG and DTG of [HAPT], (

(P) transition in a tetrahedral structure. The shoulder at16863 cm�1 may be due to spin coupling [30]. The green color isan additional evidence for this structure.

The electronic spectrum of [Fe(APT)Cl2(H2O)] complex showsseveral bands at 14,705 and 23,980 cm�1 assigned to 4T1g ?

6T1g

(G) and 4T1g ?4Eg(G) transitions, respectively. Although d–d tran-

sitions are forbidden in high spin iron(III) complexes, the highintensity band at 27,397 cm�1 may be ascribed to borrowing ofintensity from a low lying charge transfer band .

The electronic spectrum of [UO2(HAPT)(OAc)2] shows twobands at 20,700 and 27,397 cm�1 assignable to 1R+

g ?2g4 and

charge transfer n ! p� respectively.

3.3. Thermal analysis

Thermogravimetric (TG) and differential thermogravimetric(DTG) analysis of studied complexes are observed in Fig. 7.

In this study, we use the integral method of Coats & Redfern toevaluate the kinetic parameters and study the thermal behavior ofcomplexes using the following equations:

ln1� ð1� aÞ1�n

ð1� nÞT2

" #¼ � E

RTþ ln

ARuE

� �for n –1 ð1Þ

ln� lnð1� aÞ

T2

� �¼ � E

RTþ ln

ARuE

� �for n ¼ 1 ð2Þ

where A, is the pre-exponential factor.The correlation coefficient, r, was computed using the least

square method for different values of n, by plotting the left-handside of Eqs. (1) or (2) versus 1000/T, Fig. 8(a) and (b). The n valuewhich gave the best fit (r ffi 1) was chosen as the order parameterfor the decomposition stage of interest. From the intercept and lin-ear slope of such stage, the A and E values were determined. Theother kinetic parameters, DH, DS and DG were computed usingthe relationships; DH = E–RT, DS = R[ln(Ah/kT)] and DG = DH–TDS,where k is the Boltzmann’s constant and h is the Planck’s constant.The kinetic parameters are listed in Table 2. The following remarkscan be pointed out: (i) all complexes decomposition stages show abest fit for (n = 1) indicating a first order decomposition in all cases.Other n values (e.g. 0, 0.33, and 0.66) did not lead to better corre-lations. (ii) The value of DG increases significantly for the subse-quently decomposition stages of a given complex. This is due toincreasing the values of TDS significantly from one stage to anotherwhich overrides the values of DH. Increasing the values of DG of agiven complex as going from one decomposition step subsequently

a) and [Mn(HAPT)Cl2], (b).

Fig. 8. (a) Coats–Redfern Plots for (HAPT) free ligand, where Y = [�ln(1-a)/T2]. (b) Coats–Redfern Plots for [Mn(HAPT)Cl2] complex, where Y = [�ln(1�a)/T2].

Table 2Temperature of decomposition, and the kinetic parameters of free ligand and its metal complexes.

Compound Step T (K) A (S�1) E (kJ mol�1) DH (kJ mol�1) DS (kJ mol�1 K�1) DG (kJ mol�1)

(HAPT) 1st 445 8.90 � 1015 140.17 136.47 0.049 114.752nd 533 4.65 � 1018 177.86 173.43 0.099 120.49

[Mn(HAPT)Cl2] 1st 578 2.1 � 105 85.30 80.49 �0.156 171.142nd 888 9.3 � 104 135.50 128.12 �0.167 276.56

[Co(HAPT)Cl2] 1st 616 6.46 � 1011 166.65 161.53 �0.033 181.962nd 847 5.71 � 1012 245.0 238.0 �0.018 253.0

[UO2(HAPT)(OAC)2] 1st 546 2.8 � 106 92.20 87.66 �0.135 161.282nd 682 2.0 � 105 94.35 88.68 �0.158 196.803rd 728 1.3 � 104 94.34 88.28 �0.182 220.63

[Fe(APT)Cl2(H2O)] 1st 459 5.58 30.42 26.61 �0.243 137.932nd 533 52.49 44.84 40.41 �0.225 160.413rd 645 1.92 � 1010 156.47 151.11 �0.063 191.594th 760 1.20 � 1018 293.2 286.9 0.085 222.2

U. El-Ayaan et al. / Journal of Molecular Structure 936 (2009) 213–219 217

to another reflects that the rate of removal of the subsequent li-gand will be lower than that of the precedent ligand [31,32]. Thismay be attributed to the structural rigidity of the remaining com-plex after the expulsion of one and more ligands, as compared withthe precedent complex, which require more energy, TDS, for itsrearrangement before undergoing any compositional change. (iii)The negative values of activation entropies DS indicate a more or-dered activated complex than the reactants and/or the reactionsare slow [33]. (iv) The positive values of DH mean that the decom-position processes are endothermic.

Fig. 9. Effect of 10 lM of the HAPT free ligand and its metal complexes on the DNAin vitro.

3.4. Biochemical effect of HAPT ligand and its metal complexes on theDNA in vitro

The degradation effect of 10 lM and 100 lM of the free (HAPT)ligand, 1 and its (2–6) complexes on the DNA in vitro is illustratedin Figs. 9 and 10 respectively. Both the �ve control (only DNA) an-d +ve control (DNA in DMSO) does not exhibit any degradationthrough the incubation period as illustrated in Fig. 9 lanes 1 & 2and Fig. 10 lanes 1 & 2, respectively.

At concentration of 10 lM the ligand (HAPT), 1 and its Zn(II)complex, 2 does not degrade the DNA as illustrated in Fig. 9 lanes3 and 8, respectively. However, the higher concentration (100 lM)of 1 exhibit a considerable degradation effect on the DNA as

Fig. 10. Effect of 100 lM of the HAPT free ligand and its metal complexes on theDNA in vitro. Fig. 12. Effect of 100 lM of the metal complex on the BSA protein in vitro.

218 U. El-Ayaan et al. / Journal of Molecular Structure 936 (2009) 213–219

illustrated in Fig. 10 lane 3. Zn(II) complex, 2 in the higher concen-tration (100 lM) degrade completely the DNA as illustrated inFig. 10 lane 8. On the other hand, 10 lM of 4 completely degradethe DNA as illustrated in Fig. 9 lane 5 but the higher concentration(100 lM) exhibit a partial degradation effect on the DNA as illus-trated in Fig. 10 lane 5.

Fe(III) complex, 5 exhibits a partial degradation effect on theDNA in both lower concentration (10 lM) and higher concentra-tion (100 lM) as illustrated in Figs. 9 and 10 lanes 7 and 7,respectively.

Complexes 3 and 6 exhibit a complete degradation effect of theDNA in both low concentration (10 lM) as illustrated in Fig. 9 lanes4 and 6 and high concentration (100 lM) as illustrated in Fig. 10lanes 4 and 6, respectively.

It is clear that both 4 in lower concentration (10 lM) and 2 inthe higher concentration (100 lM) have a complete degradationeffect on the DNA in vitro and this effect is more than the degrada-tion effect which recorded with the parent ligand (HAPT).

Complexes 3 and 6 have powerful and complete degradation ef-fect on the DNA in both low (10 lm) and high (100 lm) concentra-tions. Therefore, 3, 6 and 4 complexes in low concentrations can beused as a promising anti-tumor agent in vivo to inhibit the DNAreplication in the cancer cells and not allow the tumor for furthergrowth. More work in vivo need to be carried out to understand theexact pathway of 3, 6 and 4 complexes in vivo.

Further biochemical studies to illustrate the exact role of thepromising degradation effect by 3, 4 and 6 complexes on tumorcells were carried out. Therefore, we decided to study the effectof the free (HAPT) ligand and its studied metal complexes on theBSA and the results were illustrated in Figs. 11 and 12.

Fig. 11. Effect of 10 lM of the HAPT free ligand and its metal complexes on the BSAprotein in vitro.

The free ligand (HAPT), 1 and its Fe(III) complex, 5 have noapparent degradation effect on the BSA at concentrations of10 lM as illustrated in Fig. 11 lanes 3 and 8, respectively, or at con-centration of 100 lM as illustrated in Fig. 12 lanes 3 and 8,respectively.

Zn(II) complex, 2 at concentration 10 lM has more degradationeffect on the BSA (Fig. 11 lane 9) than that observed for the samecomplex at 100 lM as (Fig. 12 lane 9). On the other hand, Co(II)complex, 4 at concentration 10 lM has less degradation on theBSA (Fig. 11 lane 6) than the degradation observed with it at con-centration 100 lM (Fig. 12 lane 6) as compared with the controls.

At concentration 10 lM Mn(II) complex, 3 has little cleavage ef-fect on the BSA than UO2(II) complex, 6 as illustrated in Fig. 11lanes 5 and 7 respectively. Both 3 and 6 complexes at concentra-tion 100 lM degrade completely the BSA as illustrated in Fig. 12lanes 5 and 7, respectively.

It is clear that the parent ligand (HAPT) has apparent effect onDNA at high concentration 100 lM but has no apparent effect onthe BSA. The complexes 3 and 6 have a strong degradation effecton both DNA and BSA While, the Co(II) complex, 4 has strong deg-radation effect on DNA but less effect on the BSA.

The free ligand (HAPT) show low SOD-like activity as repre-sented in Table 3 as inhibition percent 15.5%. In addition, 6 and 2complexes exhibited low SOD-like activity as well as representedin Table 3 as inhibition percent of 12% and 13%, respectively.

Complexes 4 and 5 show moderate SOD-like activity as repre-sented in Table 3 as inhibition percent of 35% and 41.8%,respectively.

Mn(II) complex, 3 exhibit a strong SOD-like activity comparedto the ligand, 1 as illustrated in Table 3 with inhibition percentof 58.5%.

There are three general classes of SODs which differ in theirmetal cofactors. The manganese-containing (MnSOD) and iron-containing (FeSOD) enzymes are cytoplasmic, while the copper-plus-zinc (CuZnSOD) enzyme is periplasmic. In addition, a new

Table 3Superoxide (SOD)-like activity of the metal complex as antioxidative enzyme.

Compound D Through 4 min % Inhibition

Control 0.620 �HR SOD 0.180 70.9HAPT, 1 0.465 15.5[Zn(HAPT)Cl2], 2 0.539 13[Mn(HAPT)Cl2], 3 0.257 58.5[Co(HAPT)Cl2], 4 0.403 35[Fe(APT)Cl2(H2O)], 5 0.361 41.8[UO2(HAPT)(OAC)2], 6 0.545 12

% inhibition = (DControl–DTest/DControl) � 100.

Table 4Effect of metal complex on some microorganisms the results expressed as zoneinhibition in millimeter diameter.

Compound E. coli P. aeruginosa B. subtilis S. st.

DMSO �ve �ve �ve �veAmoxicillin 14 25 19 17HAPT, 1 �ve 23 23 20[Zn(HAPT)Cl2], 2 �ve 23 31 19[Mn(HAPT)Cl2], 3 �ve 20 20 18[Co(HAPT)Cl2], 4 12 19 15 15[Fe(APT)Cl2(H2O)], 5 19 14 17 19[UO2(HAPT)(OAC)2], 6 10 22 25 19

U. El-Ayaan et al. / Journal of Molecular Structure 936 (2009) 213–219 219

class of nickel-containing SODs has been recently discovered inStreptomyces griseus and S. coelicolor [34]. A significant SOD-likeactivity was observed with complex 5. The highest SOD-like activ-ity was recorded with complex 3. The MnSODs and FeSODs havevery similar sequences and structures [35]. Usually FeSODs andMnSODs require specific metal for activity and can be distin-guished on the basis of amino acid sequence [36] and sensitivityto H2O2. Complexes 3 and 5 can be used as antioxidants to protectthe cells from the deleterious effect of super oxide radicals.

The parent (HAPT) ligand and its (2–6) complexes are waterinsoluble, therefore, the antimicrobial test was carried out inDMSO. The Amoxicillin was used a positive control and The DMSOwas used as a negative control for this test. The results of the anti-microbial test of the parent ligand and its metal complexes againstGram-negative Pseudomonas aeruginosa and Escherichia coli andGram-positive Bacillus subtilis and Staphylococcus saprophyticusare illustrated in Table 4.

The parent ligand has maximal antimicrobial activity regardingwith inhibition zone diameter against B. subtilis. 23 mm, S. st20 mm, moderate effect against P. aeruginosa 23 mm and has no ef-fect against E. coli (Table 4). Complexes 2 and 3 have no antimicro-bial activity against E. coli. In contrast, Zn and Mn complexes have astrong antimicrobial activity regarding with inhibition zone diam-eter against B. subtilis 23 and 20 mm respectively. Zn and Mn com-plexes express a remarkable antimicrobial activity against S. st. 19and 18 mm, respectively.

Complexes 5, 4 and 6 showed a wide spectrum of antimicrobialactivity regarding with the inhibition zone diameter against E. coli19, 12 and 10 mm respectively, against B. subtilis 14, 19 and 22 mmrespectively, against P. aeruginosa 17, 15 and 25 mm respectivelyand against S. st. 19, 15 and 19 mm, respectively.

4. Conclusion

A new series of complexes (2–6) were prepared from the novel li-gand 2-acetylpyridine 4N-(2-pyridyl)thiosemicarbazone (HAPT).Geometry optimization and conformational analysis have been per-formed and the perfect agreement with spectral studies allow forsuggesting the exact structure of all studied complexes. The stabilityof complexes was explained and kinetic parameters (E, A, DH, DSand DG) of all thermal decomposition stages have been evaluated

using Coats–Redfern method. The biochemical studies showed that;complexes 3 and 6 in both low (10 lM) and high (100 lM) concen-trations; have powerful and complete degradation effect on the DNA‘‘which maybe a sign for anti-tumor activity”. Moreover, complex 3exhibit antimicrobial effect against Gram-positive B. subtilis and S.St. bacterial strains and an antioxidative effect as SOD-like activity.

Acknowledgement

The financial support by the Deanship of Scientific Research(Project Number 90072) King faisal University, Saudi Arabia isgratefully acknowledged.

References

[1] S. Padhye, G.B. Kauffmann, Coord. Chem. Rev. 63 (1985) 127.[2] D.X. West, S.B. Padhye, P.B. Sonawane, Struct. Bonding 76 (1991) 1.[3] A.E. Liberta, D.X. West, Biometals 5 (1992) 121.[4] U. Abram, K. Ortner, K. Sommer, J. Chem. Soc. Dalton Trans. (1999) 735.[5] D.L. Klayman, J.F. Bartoserich, T.S. Griffin, C.J. Mason, J.P. Scovill, J. Med. Chem.

22 (1979) 885.[6] D.X. West, J.S. Billeh, J.P. Jasinski, J.M. Jasinski, R.J. Butcher, Trans. Met. Chem.

23 (1998) 209.[7] L. Labib, T.E. Khall, M.F. Iskander, L.S. Refaat, Polyhedron 15 (1996) 349.[8] (a) D.X. West, C.S. Carlson, A.C. Whyte, A.E. Liberta, Trans. Met. Chem. 15

(1990) 43;(b) D.X. West, R.D. Profilet, J.L. Hines, Trans. Met. Chem. 13 (1988) 467.

[9] (a) D.X. West, C.S. Carlson, C.P. Galloway, A.E. Liberta, C.R. Daniel, Trans. Met.Chem. 15 (1990) 91;(b) D.X. West, C.S. Carlson, A.E. Liberta, J.N. Albert, C.R. Daniel, Trans. Met.Chem. 15 (1990) 341.

[10] D.X. West, G.A. Bain, R.J. Butcher, J.P. Jasinski, Y. Li, R.Y. Pozdniakiv, J. Valdes-Martinez, R.A. Toscano, S. Hernandes-Ortega, Polyhedron 15 (1996) 665.

[11] D. Kovala-Demertzi, A. Domopouluo, M. Demetzis, C.P. Paptopoulou, A. Terzis,Polyhedron 12 (1994) 1917.

[12] K. Nomiya, K. Sekino, M. Ishikawa, A. Honda, M. Yokpyama, N.C. Kasuga, H.Yokoyama, S. Nakano, K. Onodera, J. Inorg. Biochem. 98 (2004) 601.

[13] J. Sambrook, E.F. Fritsch, T. Maniatis, Molecular Cloning: A Laboratory Manual,Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989.

[14] U.K. Laemmli, Nature 227 (1970) 689.[15] S.M. Bridges, M.L. Salin, Plant Physiol. 68 (1981) 275.[16] A.W. Bauer, W.M. Kirby, J.C. Sherris, M. Turck, Am. J. Clin. Pathol. 45 (1966)

493.[17] N.L. Allinger, J. Am. Chem. Soc. 99 (1977) 8127.[18] HyperChem version 5.1 Hypercube, Inc.[19] J.M. Perez, A.I. Matesanz, A. Martin-Ambite, P. Navarro, C. Alonso, P. Souza, J.

Inorg. Biochem. 75 (1999) 255.[20] F. Quilés, Vib. Spectro. 18 (1998) 61.[21] U. El-Ayaan, G.A. El-Reach, I.M. Kenawy, Synth. React. Inorg. Met.-Org. Chem.

33 (2003) 327.[22] S.P. McGlynn, J.K. Smith, W.C. Neely, J. Chem. Phys. 35 (1961) 105.[23] L.H. Jones, Spectrochem. Acta 11 (1959) 409.[24] T.H. Rakha, N. Nawar, G.M. Abu Reash, Synth. React. Inorg. Met.-Org. Chem. 26

(1996) 1705.[25] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination

Compounds, Wiley, New York, 1986, p. 231.[26] N.W. Alcok, V.M. Tracy, T.C. Waddington, J. Chem. Soc. Dalton (1976) 2243.[27] B.N. Figgis, J. Lewis, Prog. Inorg. Chem. 6 (1964) 37.[28] C.K. Jorgensen, Inorg. Chim. Acta. Rev. 2 (1962) 65.[29] A.P.B. Lever, Inorganic Electronic Spectroscope, Elsevier, Amsterdam, 1968.[30] P.K. Panda, S.B. Mishra, B.K. Mohapatka, J. Inorg. Nucl. Chem. 42 (1980) 497.[31] P.B. Maravalli, T.R. Goudar, Thermochim. Acta 325 (1999) 35.[32] K.K.M. Yusuff, R. Sreekala, Thermochim. Acta 159 (1990) 357.[33] A.A. Frost, R.G. Pearson, Kinetics and Mechanism, Wiley, New York, 1961.[34] E.J. Kim, H.J. Chung, B. Suh, Y.C. Hah, J.H. Roe, Mol. Microbiol. 27 (1998) 187.[35] W.F. Berer, I. Fridovich, Biol. Chem. 266 (1991) 303.[36] M.W. Parker, C.C.F. Blake, FEBS Lett. 229 (1988) 377.