Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 690–703

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Synthesis, biological and comparative DFT studies on Ni(II) complexes of NO and NOS donor ligands T.A. Yousef a,b, O.A. El-Gammal b, Sara F. Ahmed b, G.M. Abu El-Reash b,⇑ a b

Department of Toxic and Narcotic Drug, Forensic Medicine, Mansoura Laboratory, Medicolegal Organization, Ministry of Justice, Egypt Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Synthesis of H2PAPS, H2PAPT, H2PABT

Cytotoxic activity of ligands and their Ni(II) complexes against human tumor cells.

and their Ni(II) complexes.  Experimental IR spectra of ligands are compared with those obtained theoretically from DFT calculations.  The free ligands showed a higher antibacterial and antitumor effect than their Ni(II) complexes.

a r t i c l e

i n f o

Article history: Received 9 April 2014 Received in revised form 25 June 2014 Accepted 2 July 2014 Available online 19 July 2014 Keywords: Thiosemicarbazide Spectral characterization DFT Thermal degradation

a b s t r a c t Three new NOS donor ligands have been prepared by addition ethanolic suspension of 2-hydrazino-2-oxoN-phenyl-acetamide to phenyl isocyanate (H2PAPS), phenyl isothiocyanate (H2PAPT) and benzoyl isothiocyanate (H2PABT). The Ni(II) complexes prepared from the chloride salt and characterized by conventional techniques. The isolated complexes were assigned the formulaes, [Ni2(PAPS)(H2O)2](H2O)2, [Ni(H2PAPT)Cl2(H2O)](H2O)2 and [(Ni)2(HPABT)2Cl2(H2O)2], respectively. The IR spectra of complexes shows that H2PAPS behaves as a binegative pentadentate via both CO of hydrazide moiety in keto and enol form, enolized CO of cyanate moiety and the CN (azomethine) groups of enolization. H2PAPT behaves as neutral tridentate via both CO of hydrazide moiety and CN (azomethine) group due to SH formation and finally H2PABT behaves as mononegative tetradentate via CO and enolized CO of hydrazide moiety, CO of benzoyl moiety and C@S groups. The experimental IR spectra of ligands are compared with those obtained theoretically from DFT calculations. Also, the bond lengths, bond angles, HOMO (Highest Occupied Molecular Orbitals), LUMO (Lowest Unoccupied Molecular Orbital) and dipole moments have been calculated. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the molecule. The theoretical values of binding energies indicate the higher stability of complexes than of ligands. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats–Redfern and Horowitz–Metzger methods. The antibacterial activities were also tested against B. Subtilis and E. coli bacteria. The free ligands showed a higher antibacterial effect than their Ni(II) complexes. The antitumor activities of the Ligands and their Ni(II) complexes have been evaluated against

⇑ Corresponding author. Tel.: +20 1000373155; fax: +20 502219214. E-mail address: [email protected] (G.M. Abu El-Reash). http://dx.doi.org/10.1016/j.saa.2014.07.015 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

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liver (HePG2) and breast (MCF-7) cancer cells. All ligands were found to display cytotoxicity that are better than that of Fluorouracil (5-FU), while Ni(II) complexes show low activity. Ó 2014 Elsevier B.V. All rights reserved.

balance at 298 K. 1H and 13C NMR measurements at room temperature were obtained on a Jeol JNM LA 300 WB spectrometer at 500 MHz, using a 5 mm probe head in d6-DMSO. Thermogravimetric measurements (TGA, DTG, 20–800 °C) were recorded on a DTG-50 Shimadzu thermo gravimetric analyzer at a heating rate of 15 °C/ min and nitrogen flow rate of 20 ml/min.

Introduction Coordination chemistry of semicarbazides/thiosemicarbazides has been a subject of enthusiastic research since they are versatile ligands that can give rise to a great variety of coordination modes and show a wide range of biological properties ranging from anticancer, antitumor, antifungal antibacterial, antimalarial, antifilarial, antiviral and anti-HIV activities [1]. Moreover, the biological activities of their complexes are related to metal ion coordination [2]. This has resulted in a large number of papers and several reviews [3,4] that summarized various aspects of the chemistry of these compounds, such as methods of their synthesis, spectral, magnetic, stereochemical, structural and other characteristics. Metal complexes with an ONS donor set have engendered much research because of their potential applications in fundamental and applied sciences due to their diverse roles in metallo-enzymes [3,4]. S-ligated transition metal complexes may mimic the ligation of certain biomolecules in proteins [5]. Nickel complexes with tridentate ONS donor Schiff bases are found to be good catalysts for the Kumada– Tamao–Corriu coupling [6]. In continuation of our previous work [7], we report herein the synthesis of Ni(II) complexes derived from a new ligands namely, 2-oxo-2-(phenyl amino)acetyl)-4-phenylsemicarbazide (H2PAPS), 1-(2-oxo-2-(phenylamino)acetyl)-4-phenylthio-semicarbazide (H2PAPT) and (Z)-N-benzoyl-N0 -(2-oxo-2(phenylamino) acetyl)-carbamo-hydrazonothioic acid (H2PABT). The study includes the structural elucidation supported by molecular modeling and DFT calculations of both ligands and it is complexes as well as the thermal degradation kinetics of complexes by Coats–Redfern and Horowitz–Metzger methods. Finally, study their importance as antitumor and antibacterial agents in the biological system.

Synthesis of ligands 2-Hydrazino-2-oxo-N-phenyl-acetamide was synthesized as previously described [7]. Ligands was synthesized by heating under reflux for 10 h an ethanolic solution of 2-hydrazino-2-oxoN-phenylacetamide in a 1:1 M ratio with phenyl isocyanate, phenyl isothiocyanate and benzoyl isothiocyanate. The precipitate was filtered off, washed several times with ethanol and recrystallized from hot ethanol and finally dried in vacuum desiccator over anhydrous CaCl2. Synthesis of complexes Synthesis of Ni(II) complexes A hot ethanolic solution of Nickel (II) chloride (1.0 mmol) was added to ethanolic solution of H2PAPS, H2PAPT and H2PABT (1.0 mmol). The mixture was heated under reflux for 2–3 h and the precipitates formed were filtered off, washed with ethanol followed by diethyl ether and dried in a vacuum desiccator over anhydrous CaCl2. The physical and analytical data of the isolated complexes are listed in Table 1. The complexes have high melting points and insoluble in common organic solvents; partially soluble in DMSO and found to be non-electrolytes. Unfortunately, we could not get single crystals from the solid Ni(II) complexes.

Experimental

Biology

Instrumentation and materials

Antibacterial activity Chemical compounds were individually tested against a panel of gram positive Bacillus Subtilis and negative Escherichia coli bacterial. Each of the compounds was dissolved in DMSO and solution of the concentration 1 mg/ml were prepared separately paper discs of Whatman filter paper were prepared with standard size (5 cm) were cut and sterilized in an autoclave. The paper discs soaked in the desired concentration of the complex solution were places aseptically in the Petri dishes containing nutrient agar media (agar

All the chemicals were purchased from Aldrich and Fluka and used without further purification. Elemental analyses (C, H and N) were performed with a Perkin–Elmer 2400 series II analyzer. IR spectra (4000–400 cm1) for KBr discs were recorded on a Mattson 5000 FTIR spectrophotometer. Electronic spectra were recorded on a Unicam UV–Vis spectrophotometer UV2. Magnetic susceptibilities were measured with a Sherwood scientific magnetic susceptibility Table 1 Analytical and physical data of ligands and their Ni(II)complexes. Compound empirical formula, (F.Wt)

Color

M.p. (°C)

H2PAPS C15H14N4O3 (298.30)

White

[Ni2(PAPS)(H2O)2](H2O)2 C30H32N8Ni2O10 (782.01)

Pale green

H2PAPT C15H14N4O2S (314.36)

White

237

[Ni(H2PAPT)Cl2(H2O)](H2O)2 C15H20Cl2N4NiO5S (498.01) H2PABT C16H14N4O3S (342.37)

Green

>300

[(Ni)2(HPABT)2Cl2(H2O)2] C32H30Cl2N8Ni2O8S2 (907.05)

Pale yellow Pale green

280 >300

230 >300

% Found (Calcd.) M

Cl

C

H

N

–

–

14.84 (15.01) –

–

11.44 (11.79) –

13.92 (14.24) –

13.05 (12.94)

7.95 (7.82)

60.30 (60.40) 46.15 (46.08) 57.10 (57.31) 36.45 (36.18) 56.31 (56.13) 43.05 (42.37)

4.74 (4.73) 4.52 (4.12) 4.24 (4.49) 4.26 (4.05) 4.25 (4.12) 3.52 (3.33)

18.81 (18.78) 14.52 (14.33) 17.51 (17.82) 11.39 (11.25) 16.15 (16.36) 12.45 (12.35)

–

Yield (%) 80 80 83 78 90 81

m(CAS)

m(C@N)a

m(NAN)

Cell proliferation assay HePG2 and MCF-7 cells were seeds in a 96-well plate at a density of 1.0  104 cells/well at 37 °C for 24 h under 5% CO2 [8]. The drugs of different concentration were added to each well and cultured for 48 h. The treated cells were washed with PBS and 100 ll of MTT solution (5 mg/ml MTT stock in PBS diluted to 1 mg/ml with 10%RPMI-1640 medium) was added to each well and incubated for 4 h at 37 °C. Finally, 100 lL of DMSO was added and optical densities at 570 nm were measured using a plate reader (EXL 800). The relative cell viability in percentage was calculated as (A570 of treated samples/A570 of untreated sample)  100.

– – 437 – – 471 – – 444 – – 504 – – 503 – – 504 3448 3443 – – – – – – –

Zone of inhibition by test compound ðdiametreÞ  100 Zone of inhibition by standard ðdiametreÞ

m(OH)

¼

1055 1041 1048 1103 1105 1076 1025 1028 1028

% Activity Index

– – – – – 1626 – – 1568

m(MAO)

m(MAN)

m(MAS)

20 g + beef extract 3 g + peptone 5 g) seeded with B. Subtilis and E. coli. The Petri dishes were incubated at 36 °C and the inhibition zones were recorded after 24 h of incubation. Each treatment was replicated three times. The antibacterial activity of a common standard antibiotic ampicillin was also recorded using the same procedure as above at the same concentration and solvents. The % activity index for the complex was calculated by the formula as under:

– – – – – – – – 419

T.A. Yousef et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 690–703

– – – – – 633 674 673 –

692

1559 1562 1568 – – – 1581 1574 – – – – 1363,656 1362,652 – – – 1365,658 – – – – – 2363 2360 2241 – 3292 3325 3291 3288,3200 3336,3196 3268,3184 3298,3111 3340,3105 3257,3136 1719 1721 – 1717 1794 1626 1710 1663 – H2PAPS (exp.) H2PAPS (theo.) [Ni2(PAPS)(H2O)2](H2O)2 H2PAPT (exp.) H2PAPT (theo.) [Ni(H2PAPT)Cl2(H2O)](H2O)2 H2PABT (exp.) H2PABT (theo.) [(Ni)2(HPABT)2Cl2(H2O)2]

exp.: experimental. theo.: theoretical. a new azomethine.

m(C@O)1 Compound

The IR spectra of H2PAPS, H2PAPT and H2PABT and their Ni(II) complexes were displayed as KBr disc in the 4000–400 cm1 range. The most important IR bands with probable assignments are given in Table 2. The IR spectrum of H2PAPS (Structure 1) shows three bands at 1719, 1669 and 1651 cm1 assignable to m(C@O)1, m(C@O)2 and m(C@O)3 vibrations, respectively. The bands at 3448 and 3292 cm1 are due to m(OH) and m(NH) vibrations, respectively. The medium bands at 1559 and 1055 cm1 are attributed to m(C@N) (azomethine) and m(NAN) vibrations [7,15] respectively. The appearance of m(OH) and it is absence in the other two ligands confirmed that H2PAPS is present in keto enol form. The IR spectrum of H2PAPT (Structure 2) shows two bands at 1717 and 1672 assignable to m(C@O)1 and m(C@O)2 vibrations, respectively. The bands at 3288 and 3200 cm1 are due to m(NH) vibrations. The two bands assigned to m(C@S) and d(C@S) appear at the frequencies 1363, 656 cm1, respectively. The medium band observed at 1103 is due to m(NAN) vibration.

Table 2 Principle infrared bands of ligands and their Ni(II)complexes.

IR spectral studies

m(C@0)2

m(C@0)3

Results and discussion

1651 1636 – – – – 1681 1654 1637

m(NH)

SH

m/d (C@S)

We performed cluster calculations using DMOL3 program [9] in Materials Studio package [10], which is designed for the realization of large scale density functional theory (DFT) calculations. DFT semi-core pseudopods calculations (dspp) were performed with the double numerical basis sets plus polarization functional (DNP). The DNP basis sets are of comparable quality to 6–31G Gaussian basis sets [11]. Delley et al. showed that the DNP basis sets are more accurate than Gaussian basis sets of the same size [12]. The Revised Perdew–Burke–Erenzrhof (RPBE) functional [13] is so far the best exchange–correlation functional [14], based on the generalized gradient approximation (GGA), is employed to take account of the exchange and correlation effects of electrons. The geometric optimization is performed without any symmetry restriction.

1669 1667 1636 1672 1671 1626 1668 1616 1637

m(C@N)

Molecular modeling

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The IR spectrum of H2PABT (Structure 3) reveals four bands at 1710, 1668, 1681 and 1581 cm1 attributed to the m(C@O)1, m(C@O)2, m(C@O)3 and m(C@N) vibrations, respectively. The medium intensity at 1025 cm1 is assigned to m(NAN) vibration. The bands located at 3298 and 3111 cm1 is attributed to m(NH) vibrations. The m(SH) [16,17] stretching band appears as a strong band at 2360 cm1 . The appearance of m(SH) in H2PABT and it is absence in H2PAPT because the benzoyl group act as electron donating which increase the basicity of NH neighbors to CS and so facilitate the tautomerization while in H2PAPT , the phenyl group act as withdrawing electron which make the tautomerization is difficult [16,17]. Semiempirical PM3 calculations full corroborate the higher stability of thione form for H2PAPT and thiole form for H2PABT depending on the values of stabilization energy and heats of formations. An insight on the IR spectra of the investigated Ni(II) complexes shows that H2PAPS behaves as binegative pentadentate (Structure 4) via carbonyl oxygen (C@O)2, the deprotonated enolic oxygen atom (@CAOA)1, (@CAOA)3 and two new C@N*(azomethine) groups. This behavior is revealed by: (i) Shift of m(C@O)2 to lower wavenumber. (ii) The disappearance of m(C@O)1 and m(C@O)3 bands with simultaneous appearance of new bands assignable to two m(C@N)* vibrations. H2PAPT suggests the coordination as neutral tridentate (Structure 5) via carbonyl oxygen of (C@O)1, (C@O)2 and new C@N*(azomethine) groups. This behavior is supported by: (i) the shift of m(C@O)1 and m(C@O)2 to lower wavenumber (ii) the appearance of bands at 2363 and 1626 cm1 refer to the m(SAH) group and m(C@N)* of a new azomethine, respectively. [18,19]. H2PABT act as mononegative tetradentate (Structure 6) via carbonyl oxygen of (C@O)2, (C@O)3, the deprotonated enolic oxygen atom (@CAOA)1 and (C@S) groups. This behavior is supported by: (i) the shift of m(C@O)2 and m(C@O)3 to lower wavenumber and m(C@S) to higher wavenumber. (ii) The disappearance of m(C@O)1 band with simultaneous appearance of new band assignable to m(C@N)* vibrations. 1

H and

13

C NMR spectra of the ligand

The 1H NMR spectrum of H2PAPS in d6-DMSO shows four signals at d = 8.26, 8.79, 10.60 and 10.68 ppm relative to TMS that disappear upon adding D2O. These signals are attributed to N4H, N3H, N2H and N1H [20] protons, respectively. The multiplets at 6.93– 7.82 ppm are assigned to phenyl ring protons. The 1H NMR spectrum of the H2PAPT shows three signals at d = 9.77, 10.66 and

10.90 ppm relative to TMS which disappear upon adding D2O and can be assigned to (N3H, N4H), N2H and N1H protons, respectively. The multiplets at 7.10–7.86 ppm are assigned to the phenyl ring protons. The 1H NMR spectrum of the H2PABT shows four signals at d = 10.81, 11.33, 11.82 and 12.4 ppm relative to TMS which disappear upon adding D2O and can be assigned to N1H, N2H, N3H and N4H protons, respectively. The multiplets at 7.14–7.99 ppm are assigned to the phenyl ring protons. In the 13C NMR spectra, the carbon resonance signals of the C@O group appear at d = 156.6–176.8. The C@S signals observed at d = 180.06–185.0 are characteristic for the thiocarbonyl group present in all the ligands. For all ligands, the aromatic carbons were observed at d = 120.8–141.4, and these chemical shifts are in agreement with those found for other thiosemicarbazide ligands [21,22]. Electronic spectra and magnetic moments The tentative assignments of the significant spectral absorption bands, magnetic moments and ligand field parameters of metal complexes are given in Table 3. The electronic spectra of the ligands exhibit bands in the regions (31,347–31,645) and (26,385–29,069) cm1 assignable to p ? p* and n ? p* transitions respectively [23–26]. The spectra of [Ni2(PAPS)(H2O)2](H2O)2, [Ni(H2PAPT)Cl2(H2O)](H2O)2, and [Ni2(HPACH)2Cl2(H2O)2] complexes exhibited two bands in the regions (16,181–17,667) and (23,041–23,809 cm1), assignable to 3A2g ? 3T1g(F)(m2) and 3A2g ? 3T1g (P)(m3) transitions which are characteristic for octahedral Ni (II) complexes [27]. The calculated ligand field parameters, Dq, B and b in the regions (776–833, 823–580 and 0.79–0.81) can be taken as an additional evidence for the supposed geometry. Again, the subnormal magnetic moment value, leff (2.32–2.90 B.M.) per one Ni atom may be due to an antiferromagnetic nature or a strong MAS bond formation. Thermogravimetric studies Thermogravimetric analysis (TGA) data for Ni(II) complexes are presented in (Table 4). One of the features in the TGA data concerning the associated water molecules within the complexes supports the elemental analyses [28]. An inspection of the data represented in this Table shows that the complexes undergo thermal degradation through three main steps: (i) dehydration step: starting at about 63 °C for physically adsorbed water and continuing from about 110 °C to 270 °C for coordinate water. (ii) Decomposition

Table 3 Spectral absorption bands of ligands and their Ni(II) complexes and the magnetic moments of the complexes. Compound

Band position (cm1)

Assignment

leff (B.M.)

Ligand field parameters Dq (cm1)

B (cm1)

b

H2PAPS

31,645 26,385

p ? p* n ? p*

–

–

–

–

[Ni2(PAPS)(H2O)2](H2O)2

23,148 16,181 12,903

3

A2g ? 3T1g(P) A2g ? 3T1g(F) 3 A2g ? 3T2g

776

826

0.79

2.90

H2PAPT

31,347 29,069

p ? p* n ? p*

–

–

–

–

[Ni(H2PAPT)Cl2(H2O)](H2O)2

23,041 17,667 15,723

3

A2g ? 3T1g(P) A2g ? 3T1g(F) 3 A2g ? 3T2g

806

823

0.79

2.79

H2PABT

31,347 28,011

p ? p* n ? p*

–

–

–

–

[(Ni)2(HPABT)2Cl2(H2O)2]

23,809 17,361 13,513

3

833

850

0.81

2.32

3

3

A2g ? 3T1g(P) A2g ? 3T1g(F) 3 A2g ? 3T2g 3

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Table 4 Decomposition steps with the temperature range and weight loss for Ni(II) complexes. Complex

Temp. range (°C)

Removed species

Found

Calcd (%)

[Ni2(PAPS)(H2O)2](H2O)2

36–77 141–195 343–426 426–800

2H2O 2H2O 4C6H5 2NiO + C6H4N8O4

4.89 5.00 39.86 50.22

4.60 4.60 39.43 51.34

[Ni(H2PAPT)Cl2(H2O)](H2O)2

40–129 130–218 218–402 402–520 520–596 596–800

2H2O H2O 2C6H5 + 2Cl HCN + CHO N2 NiO + HCN + SH

7.45 3.45 44.98 11.02 5.80 27.26

7.23 3.61 45.20 11.22 5.64 27.06

[(Ni)2(HPABT)2Cl2(H2O)2]

276–376 376–466 466–800

2H2O + 2Cl 3C6H5 NiO + NiS + C10H8N4O2S + C4H3N4O3

11.45 25.73 62.81

11.79 25.50 62.70

-11.0

ln x n=1

-11.0

Wt. loss

ln x n=1 ln x n=0.66

ln x n=0.66

ln x n=0.33

ln x n=0.33 lnx n=0

ln x

ln x

-11.5

lnx n=0

-11.5

ln x n=0.5

ln x n=0.5

-12.0

-12.0 -12.5

(a)

(b)

-12.5 0.00303 0.00306 0.00309 0.00312 0.00315

-13.0 0.0025 0.0026 0.0027 0.0028 0.0029

1/T

1/T ln x n=1 ln x n=0.66 ln x n=0.33 lnx n=0 ln x n=0.5

-12.5

ln x

-13.0

-13.5

-14.0

(c) 0.00156

0.00159

0.00162

0.00165

0.00168

1/T Fig. 1. Coats–Redfern plots of 1st step of (a) [Ni2(PAPS)(H2O)2](H2O)2, (b) [Ni(H2PAPT)Cl2(H2O)](H2O)2 and (c) [(Ni)2(HPABT)2Cl2(H2O)2].

step: starting mostly from about 250 °C (depending on the nature of each complex) at which decomposition of the organic part of the complex takes place. The weight loss corresponds to this step is due to the evolution of gases such as CO2, SO2, H2S, N2, HCl or NO2 resulting from the degradation of the organic moiety. (iii) The final step: the formation of metal sulfide or metal oxide as the final product and the thermogram shows thermal stability up to 800 °C.

Kinetic data The linearization curves of Coats–Redfern and Horowitz–Metzger methods are shown in Figs. 1 and 2. Kinetic parameters for the first stages, calculated by employing the Coats–Redfern and Horowitz–Metzger equations, are summarized in Tables 5 and 6. The thermodynamic data obtained with the two methods are in harmony with each other. The correlation coefficients of the Arrhenius

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ln x n=1 ln x n=0.66

0.6

ln x n=0.66

ln x n=0

0.4

ln x n=0.33

ln x n=0.5

ln x n=0 ln x n=0.5

0.5

0.2

ln x

0.0

ln x

ln x n=1

1.0

ln x n=0.33

-0.2

0.0

-0.5

-0.4 -0.6

-1.0

-0.8

(a)

-1.0 -6

-4

-2

0

2

4

6

(b) -1.5

-30

-20

-10

0

10

20

30

T-Ts

T-Ts 0.6 ln x n=1

0.3

ln x n=0.66 ln x n=0.33

0.0

ln x n=0 ln x n=0.5

ln x

-0.3 -0.6 -0.9 -1.2

(c) -1.5 -20

-10

0

10

20

T-Ts Fig. 2. Horowitz–Metzger plots of 1st step of (a) [Ni2(PAPS)(H2O)2](H2O)2, (b) [Ni(H2PAPT)Cl2(H2O)](H2O)2 and (c) [(Ni)2(HPABT)2Cl2(H2O)2].

Table 5 Kinetic parameters evaluated by Coats–Redfern equation for Ni(II) complexes. Complex

Peak

Mid temp (K)

Ea (kJ/mol)

DH* (kJ/mol)

DS* (kJ/mol K)

DG* (kJ/mol)

14

A (S1)

[Ni2(PAPS)(H2O)2](H2O)2

1st 2nd 3rd

323.20 449.62 643.25

97.58 98.71 227.78

1.61  10 5.60  109 1.62  1016

94.89 94.97 222.43

0.0264 0.0617 0.0590

86.37 122.72 184.49

[Ni(H2PAPT)Cl2(H2O)](H2O)2

1st 2nd 3rd 4th 5th

373.13 458.54 600.94 737.89 830.86

36.61 67.05 39.61 93.95 254.77

1.14  103 3.13  105 1.82  105 1.95  104 1.26  1014

33.51 63.24 34.61 87.81 247.86

0.1882 0.1433 0.1501 0.1703 0.0165

103.74 128.94 130.79 213.48 234.17

[(Ni)2(HPABT)2Cl2(H2O)2]

1st 2nd

617.50 706.08

114.57 92.25

3.09  107 7.30  104

109.44 86.38

0.1076 0.1590

175.86 198.63

plots of the thermal decomposition steps were found to lie in the range 0.9820–0.9996, showing a good fit with linear function. In order to assess the influences of the structural properties of the chelating agent, the order (n) and the heat of activation Ea of the various decomposition stages were determined from the TG and DTG using the Coats–Redfern [29] and Horowitz–Metzger [30]. The rate of decomposition of a solid expressed by the Arrhenius equation has the following form:

  da Ea gðaÞ ¼ A exp  dt RT

ð1Þ

where Ea is the activation energy, A is the Arrhenius pre-exponential factor, R is the gas constant and g(a) is the differential conversion factor and equal (1a)n where n is the reaction order, assumed to remain constant during the reaction [31,32]. A large

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Table 6 Kinetic parameters evaluated by Horowitz–Metzger equation for Ni(II) complexes. Complex

Peak

Mid temp (K)

DH* (kJ/mol)

DS* (kJ/mol K)

DG* (kJ/mol)

15

A (S1)

Ea (kJ/mol)

[Ni2(PAPS)(H2O)2](H2O)2

1st 2nd 3rd

323.20 449.62 643.25

102.90 106.08 238.32

1.22  10 4.31  1010 1.21  1017

100.21 102.34 232.97

0.0432 0.0447 0.0757

86.24 122.44 184.22

[Ni(H2PAPT)Cl2(H2O)](H2O)2

1st 2nd 3rd 4th 5th

373.13 458.54 600.94 737.89 830.86

42.98 74.63 49.61 106.47 268.37

9.49  103 2.49  106 3.82  105 1.69  105 9.39  1014

39.88 70.81 39.61 100.34 261.46

0.1706 0.1260 0.2501 0.1524 0.0332

103.55 128.61 130.69 212.77 233.88

[(Ni)2(HPABT)2Cl2(H2O)2]

1st 2nd

617.50 706.08

124.68 104.33

2.39  108 6.41  105

119.55 98.46

0.0906 0.1409

175.48 197.95

v. The positive sign of DG* reveals that the free energy of the final residue is higher than that of the initial compound, and hence all the decomposition steps are nonspontaneous processes.

numbers of decomposition processes can be represented as first order reaction [33], particularly, the degradation of the investigated series of metal complexes. Under this assumption the integration of Eq. (1) leads to:

lnð1  aÞ ¼ 

A b

Z

T

To

  Ea dT Exp  RT

ð2Þ

Based on Eq. (2), it is possible to analyze experimental data by the integral method, in order to determine the degradation kinetic parameters A, Ea. The other thermodynamic parameters of activation can be calculated by Eyring equation [34,35]. From the results obtained, the following remarks can be pointed out: i. All decomposition steps show the best fit for n = 1. ii. The negative value of the entropy of activation, DS* of some decomposition steps indicates that the activated fragments have more ordered structure than the undecomposed ones and the later are slower than the normal [36,37]. iii. The positive sign of activation enthalpy change, DH* indicates that the decomposition stages are endothermic processes. iv. The high values Ea reveals the high stability of such chelates due to their covalent bond character [38]. The increase of Ea on going from Ni(II) complex [(Ni)2(HPABT)2Cl2(H2O)2] < [Ni 2 (PAPS)(H 2 O) 2 ](H 2 O) 2 < [Ni(H 2 PAPT)Cl 2 (H 2 O)](H 2 O) 2 reflects the greater thermal stability of [Ni(H 2 PAPT)Cl 2 (H 2 O)](H 2 O) 2 complex than the other complexes.

Molecular modeling IR In order to acquire the spectroscopic signature of ligands molecule, we performed a frequency calculation analysis. The calculations were made for free molecule in vacuum, while experiments were performed for solid sample, so there are small differences between theoretical and experimental vibrational wavenumbers as shown in Fig. 3, 1R, 2R (Supplementary materials) and Table 2. The modes of vibrations are very complex due to the low symmetry of the ligand. Especially, in plane, out of plane and torsion modes are the most difficult to assign due to mixing with the ring modes and also with the substituent modes. But there are some strong frequencies useful to characterize in the IR spectrum. Chemical reactivity Global reactivity descriptors. The determination of energies of the HOMO (p donor) and LUMO (p acceptor) are important parameters in quantum chemical calculations. The HOMO is the orbital that primarily acts as an electron donor and the LUMO is the orbital that

Fig. 3. Theoretical IR spectrum of H2PAPT.

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largely act as the electron acceptor. These molecular orbitals are also called the frontier molecular orbitals (FMOs).

v. The energy gap (EHOMO–ELUMO) is an important stability index helps to characterize the chemical reactivity and kinetic stability of the molecule [40]. A molecule with a small gap is more polarized and is known as soft molecule. Soft molecules are more reactive than hard ones because they easily offer electrons to an acceptor. The energy gap is small indicating that charge transfer easily occurs in it which influences the biological activity of the molecule. Low value of energy gap is also due to the groups that enter into conjugation. The high value of DE could be expected to indicate the ligands molecule has high inclination to bind with the metal ion. vi. From the calculations of the binding energy we notice that there is an increase of the value of the calculated binding energy of complexes compared to that of the ligand which indicates that the stability of the formed metal complexes is higher than that of ligand.

i. The EHOMO and ELUMO and their neighboring orbitals are all negative, which indicate that the prepared molecules are stable [18,19]. ii. The FMOs theory predicts sites of coordination (electrophilic attack) on aromatic compounds. An initial assumption is that the reaction takes place with maximum overlap between the HOMO on one molecule and the LUMO on the other. The overlap between the HOMO and the LUMO is a governing factor in many reactions. We can indicate that from the calculation by searching for the largest values of molecular orbital coefficients. So, orbitals of the ligand with the largest value of molecular orbital coefficients may be considered as the sites of coordination. This conclusion is confirmed by the data obtained from the calculation because the nitrogen of the C@N group, C@S group and oxygen of C@O have the largest values of molecular orbital coefficients. iii. Gutmann’s variation rules, ‘‘the bond strength increases as the adjacent bonds become weaker’’ such as found by Linert et al. [39]. This interpretation agrees well with the resultant as the increase of the EHOMO is accompanied by a weakness (elongation) of the metal–ligand bonds, which leads to a strengthening (shortness) of the sites adjacent to the metal ligand centers. iv. The HOMO level for H2PAPS is mostly localized on N(5), N(6) and O(16) atoms, for H2PAPT is mostly localized on N(10), N(11), S(17), O(15) and O(16) atoms and H2PABT is mostly localized on O(19), S(17), O(15) and O(16) atoms (Fig. 4), 3R, 4R (Supplementary materials) indicating they are the preferred sites for nucleophilic attack at the central metal ion.

DFT method concept the chemical reactivity and site selectivity of the molecular systems. The energies of frontier molecular orbitals (EHOMO, ELUMO), energy band gap which explains the eventual charge transfer interaction within the molecule, electronegativity (v), chemical potential (l), global hardness (g), global softness (S) and global electrophilicity index (x) [41,42] are listed in Table 7.

v ¼ 1=2 ðELUMO þ EHOMO Þ

ð3Þ

l ¼ v ¼ 1=2 ðELUMO þ EHOMO Þ

ð4Þ

g ¼ 1=2 ðELUMO  EHOMO Þ

ð5Þ

S ¼ 1=2g

ð6Þ

Fig. 4. 3D plots frontier orbital energies using DFT method for H2PAPT.

Table 7 The calculated quantum chemical parameters of the ligands and their Ni(II) complexes. Compound

HOMO

LUMO

v

N

r

Pi

DE

x

DNmax

H2PAPS Keto H2PAPS Enol [Ni2(PAPS)(H2O)2](H2O)2 H2PAPT Thione H2PAPT Thiol [Ni(H2PAPT)Cl2(H2O)](H2O)2 H2PABT Thiol H2PABT Thione [(Ni)2(HPABT)2Cl2(H2O)2]

4.937 4.915 3.829 5.165 4.948 4.630 5.196 5.021 4.218

2.094 2.037 2.826 2.319 2.413 3.108 2.653 2.784 2.776

3.517 3.476 3.327 3.742 3.680 3.869 3.924 3.902 3.497

1.421 1.439 0.501 1.423 1.267 0.761 1.271 1.118 0.721

0.703 0.694 1.996 0.702 0.788 1.314 0.786 0.894 1.386

3.517 3.476 3.327 3.742 3.680 3.869 3.924 3.902 3.497

2.843 2.878 1.003 2.846 2.535 1.522 2.543 2.237 1.442

4.352 4.198 11.045 4.919 5.344 9.835 6.057 6.809 8.480

2.475 2.415 6.726 2.629 2.904 5.084 3.087 3.490 4.850

T.A. Yousef et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 690–703

ð7Þ

The inverse value of the global hardness is designed as the softness r as follow:

r ¼ 1=g

2.094 2.037 2.826 2.319 2.413 3.108 2.653 2.784 2.776

x ¼ l2 =2g

LUMO (eV)

698

Fig. 6. Molecular electrostatic potential map for [Ni(H2PAPT)Cl2(H2O)](H2O)2.

1.32786 1.72347 1.37721 1.28825 1.23006 4.33600 1.28124 2.32371 1.17510 4.186  103 4.134  103 8.730  104 4.062  103 4.074  103 4.517  103 4.375  103 4.359  103 9.451  103 6.431  105 6.433  105 1.624  106 8.458  105 8.459  105 1.592  106 9.170  105 9.171  105 2.749  106 1.486  103 1.352  103 2.805  103 1.348  103 1.268  103 1.476  103 1.423  103 1.338  103 3.019  103 1.661  103 1.707  103 3.713  103 1.731  103 1.713  103 1.885  103 1.803  103 1.844  103 3.972  103

Spin polarization energy Exchange–correlation energy

7.144  103 6.220  103 8.596  103 6.196  103 5.618  103 5.869  103 5.636  103 6.251  103 9.063  103 H2PAPS Keto H2PAPS Enol [Ni2(PAPS)(H2O)2](H2O)2 H2PAPT Thione H2PAPT Thiol [Ni(H2PAPT)Cl2(H2O)](H2O)2 H2PABT Thiol H2PABT Thione [(Ni)2(HPABT)2Cl2(H2O)2]

6.391  105 6.391  105 1.615  106 8.418  105 8.418  105 1.588  106 9.127  105 9.127  105 2.740  106

Electrostatic energy Kinetic energy Sum of atomic energies

Energy components (kcal/mol) Compound

Table 8 Some energetic properties of ligands and their Ni(II) complexes calculated by DMOL3 using DFT-method.

Fig. 5. Molecular electrostatic potential map for H2PAPT.

Total energy

1. Absolute hardness g and softness r are important properties to measure the molecular stability and reactivity. A hard molecule has a large energy gap and a soft molecule has a small energy gap. Soft molecules are more reactive than hard ones because they could easily offer electrons to an acceptor. In a complex formation system, the ligand acts as a Lewis base while the metal ion acts as a Lewis acid. Metal ions are soft acids and thus soft base ligands are most effective for complex formation. Accordingly, it is concluded that ligands, with a proper r value has a good tendency to chelate metal ions effectively [43]. This is also confirmed from the calculated chemical potential Pi. 2. This reactivity index measures the stabilization in energy when the system acquires an additional electronic charge (DNmax) from the environment. The electrophilicity index (v) is a positive, definite quantity and the direction of the charge transfer

1.904  102 9.731  102 6.652  103 9.465  102 1.441  103 2.010  103 1.965  103 1.290  103 7.379  103

Binding energy (kcal/mol)

Dipole moment (D)

Electrophilicity index is one of the most important quantum chemical descriptors in describing toxicity of various pollutants in terms of their reactivity and site selectivity. Also the electrophilicity properly quantifies the biological activity of drug receptor interaction. This new reactivity index measures the stabilization in energy when the system acquires an additional electronic charge from the environment. The importance of g and r is to measure the molecular stability and reactivity. The concepts of the parameters v and Pi are related to each other. The inverse of the global hardness is designated as the softness r. From the obtained data we can deduced that:

4.937 4.915 3.829 5.165 4.948 4.630 5.196 5.021 4.218

HOMO (eV)

ð8Þ

699

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is completely determined by the electronic chemical potential (Pi) of the molecule because an electrophile is a chemical species capable of accepting electrons from the environment and its energy must decrease upon accepting electronic charge. Therefore, the electronic chemical potential must be negative, exactly as supported by the values in Table 7.

the C-point and multiple k-points. In the present study, 3D plots of molecular electrostatic potential (MEP) of ligands (Figs. 5 and 6), 5R–7R (Supplementary materials) have been drew. The maximum negative region which preferred site for electrophilic attack indications as red color, the maximum positive region which preferred site for nucleophilic attack symptoms as blue color. Potential increases in the order red < green < blue, where blue shows the strongest attraction and red shows the strongest repulsion. Regions having the negative potential are over the electronegative atoms while the regions having the positive potential are over the hydrogen atoms.

Molecular electrostatic potential (MEP) The MEP is a plot of electrostatic potential mapped onto the constant electron density surface. It is also very useful in research of molecular structure with its physiochemical property relationship as well as hydrogen bonding interactions [44–46]. The electrostatic potential V(r) at a given point r (x, y, z) is defined in terms of the interaction energy between the electrical charge generated from the molecule electrons, nuclei and proton located at r. Computation of electrostatic potential is possible for molecules using

Geometry optimization with DFT method Analysis of the data in Tables 1S–12S (Supplementary materials) calculated for the bond lengths and angles for the bond, one can conclude the following remarks:

Fig. 7. DOS diagram of H2PAPT.

Fig. 8. DOS diagram of [Ni(H2PAPT)Cl2(H2O)](H2O)2.

Table 9 antibacterial activity of ligands and their Ni(II) complexes. Compound

H2PAPS [Ni2(PAPS)(H2O)2](H2O)2 H2PAPT [Ni(H2PAPT)Cl2(H2O)](H2O)2 H2PABT [(Ni)2(HPABT)2Cl2(H2O)2] Ampicillin

E. coli (mg/ml)

B. Subtilis (mg/ml)

Diameter of inhibition zone (in mm)

% Activity index

Diameter of inhibition zone (in mm)

% Activity index

8 13 13 13 14 12 27

29.6 48.1 48.1 48.1 51.8 44.4 100

NA NA 7 NA 9 NA 25

NA NA 28 NA 36 NA 100

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Fig. 9. Cytotoxic activity of ligands and their Ni(II) complexes against human tumor cells.

1- There is an elongation in the coordination bonds after complexation, which correlates with the experimental IR frequencies. As there is an elongation in the bonds a lower

energy of the vibration frequency is needed and the lower frequency and is approved by the experimental IR frequency values. 2- For H2PAPS, the C(3)AO(15), N(6)AC(7)azomethene, C(4)AO(16), C(4)AN(5) and C(7)AO(17) bond lengths becomes slightly longer in complexes as the coordination takes place via N(6) of azomethene group, O(15), O(16) and O(17) atom of N@CAO group that is formed on deprotonation of OH group in [Ni2(PAPS)(H2O)2]2H2O. C(4)AO(16) and C(7)AO(17) ketone-type (AO@CANAN@CA) in [Ni2 (PAPS) (H2O)2](H2O)2 complex enolized leading to absence of double bond character over C(4)AO(16) and C(7)AO(17) and its appearance over N(6)AC(7) and C(4)AN(5). The C(3)AO(15) bond distance in [Ni2(PAPS)(H2O)2](H2O)2 complex becomes longer due to the formation of the MAO bond which makes the CAO bond weaker [7,15]. 3- For H2PAPT, the C(8)AO(15) and C(9)AO(16) bond lengths becomes slightly longer in complexes as the coordination takes place via O(15) and O(16) atom of C@O group. The

Structure 1. Molecular modeling of H2PAPS.

Structure 2. Molecular modeling of H2PAPT.

T.A. Yousef et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 690–703

C(8)AO(15) and C(9)AO(16) bond distance in [Ni(H2PAPT)Cl2(H2O)](H2O)2 complex becomes longer due to the formation of the MAO bond which makes the CAO bond weaker. 4- For H2PABT, the C(8)AO(15), C(12)AS(17) and C(9)AO(16) bond lengths becomes slightly longer in complexes as the coordination takes place via S(17), O(15) and O(16) atom of N@CAO group. C(9)AO(16) enolized leading to absence of double bond character over C(9)AO(16) and its appearance over N(10)AC(9). The C(8)AO(15) and C(9)AO(16) bond distance in [(Ni)2(HPABT)2Cl2(H2O)2] complex becomes longer due to the formation of the MAO bond which makes the CAO bond weaker. 5- The bond angles of the thiosemicarbazide moiety of the ligands are altered somewhat upon coordination; the largest change affects C(7)AN(6)AN(5), O(15)AC(3)AC(4), O(17)AC(7)AN(6), O(19)AC(14)AN(13), C(15)AC(8)AC(9), C(12)AN(11)AN(10), O(16)AC(9)AN(10) and S(17)AC(12)AN(11) angles which are reduced or increased on complex formation as a consequence of bonding. 6- The bond angles in all complexes lie in the range reported for octahedral geometry predicting SP3d2 or d2SP3 hybridization [7,15].

701

Structure 4. Molecular modeling of [Ni2(PAPS)(H2O)2](H2O)2.

Other molecular properties The calculations of the binding energy revealed that the increase of the value of the calculated binding energy of complexes compared to that of the ligand indicates that the stability of the formed metal complexes are higher than that of ligand. Also energy components were calculated by DFT method shown in Table 8. Density of state calculations The density of state (DOS) gives information on the number and character of molecular orbitals as a function of the energy to obtain a simple view of the character of the orbitals in a certain energy range by evaluating the accompanying joint density of states, which is related to the absorption spectrum. This was done by making DOS calculations theoretically for the Ni complex as an example of ligand complexation. Making a comparison between

Structure 5. Molecular modeling of [Ni(H2PAPT)Cl2(H2O)](H2O)2.

the resultant diagrams (Figs. 7 and 8), 9R–12R (Supplementary materials) we observed the following: 1. In the case of the Ni complex, there is an observed increase in the DOS, which mean higher possible probabilities of electrons transitions and this makes it high stable than the ligand.

Structure 3. Molecular modeling of H2PABT.

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were calculated have been compared with experimental FTIR spectra. The observed and the calculated frequencies are in good agreement. The difference between the corresponding wave numbers (observed and calculated) is very small, for most of the fundamentals. Finally, antibacterial and antitumor has been studied. The ligands showed higher biological activity than their corresponding Ni(II) complexes. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2014.07.015. References

Structure 6. Molecular modeling of [(Ni)2(HPABT)2Cl2(H2O)2].

Antibacterial activity The ligands and their Ni(II) complexes, standard drug Ampicillin and DMSO solvent control were screened separately for their antibacterial activity against E. coli and B. Subtilis at 1.0 mg/ml concentration. The activity of the complexes has been compared with the activity of a common standard antibiotic Ampicillin and % The antibacterial results suggest that the ligands and its complexes (Tables 9) show a moderate activity against both the bacteria [46,47] as compared to the standard drug (Ampicillin). The Ni(II) complexes show higher antibacterial activity than the ligands. The negative results can be attributed either to the inability of the complexes to diffuse into the Gram-negative bacteria cell membranes and hence unable to interfere with its biological activity or they can diffuse and inactivated by unknown cellular mechanism i.e. bacterial enzymes. The positive results suggested the very diffusion of the complexes into the bacterial cells and were able to kill the bacterium as indicated by the zones of inhibition of bacterial growth [47,48]. Cell proliferation assay In view of the biological activity of thiosemicarbazones, we firstly have evaluated the ability of the some 4-(2-pyridyl)-3-Thiosemicarbazides derivatives to inhibit cancer cell growth against hepatocellular carcinoma (HCC) [20]. In our experiments, IC50 values (compound concentration that produces 50% of cell death) in micro molar units were calculated. For comparison purposes the cytotoxicity of Fluorouracil (5-FU) and the free ligands as well as their Ni(II) complexes has been evaluated under the same experimental conditions. It is clearly observed that complexation with metal has no synergistic effect on the cytotoxicity (Fig. 9). These gratifying results are encouraging its further screening in vitro. Therefore, its further biological evaluation in vivo as well as studies of mechanism of action is necessary [49]. Conclusion In the present work, three mononuclear Ni(II) complexes have been synthesized and characterized by physicochemical and spectroscopic methods. Theoretical studies carried out to elucidate and confirm the prepared compounds. The MEP map shows that the negative potential sites are on electronegative atoms while the positive potential sites are around the hydrogen atoms. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules. As a result, all the vibrational frequencies

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