Synthesis, characterization, molecular docking and

Journal of Photochemistry & Photobiology, B: Biology 160 (2016) 392–399

Contents lists available at ScienceDirect

Journal of Photochemistry & Photobiology, B: Biology journal homepage: www.elsevier.com/locate/jphotobiol

Synthesis, characterization, molecular docking and biological studies of self assembled transition metal dithiocarbamates of substituted pyrrole-2-carboxaldehyde Shahab A.A. Nami a,⁎, Irfan Ullah a, Mahboob Alam b, Dong-Ung Lee b, Nursabah Sarikavakli c a b c

Department of Kulliyat, Faculty of Unani Medicine, Aligarh Muslim University, Aligarh 202002, India Division of Bioscience, Dongguk University, Gyeongju 780-714, Republic of Korea Department of Chemistry, Faculty of Arts and Sciences, Adnan Menderes University, Turkey

a r t i c l e

i n f o

Article history: Received 6 March 2016 Accepted 9 May 2016 Available online 11 May 2016 Keywords: Self assembled dithiocarbamate Transition metal complexes Pyrrole-2-carboxaldehyde 1,4-phenylenediamine

a b s t r a c t A series of self assembled 3d transition metal dithiocarbamate, M(pdtc) [where M = Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)] have been synthesized and spectroscopically characterized. The bidentate dithiocarbamate ligand Na2pdtc (Disodium-1,4-phenyldiaminobis (pyrrole-1-sulfino)dithioate) was prepared by insertion reaction of carbondisulfide with Schiff base, N,N′-bis-(1H-pyrrol-2-ylmethylene)-benzene-1,4-diamine (L1) in basic medium. The simple substitution reaction between the metal halide and Na2pdtc yielded the title complexes in moderate yields. However, the in situ procedure gives high yield with the formation of single product as evident by TLC. Elemental analysis, IR, 1H and 13C NMR spectra, UV–vis., magnetic susceptibility and conductance measurements were done to characterize the complexes, M(pdtc). All the evidences suggest that the complexes have tetrahedral geometry excepting Cu(II) which is found to be square planar. A symmetrical bidentate coordination of the dithiocarbamato moiety has been observed in all the complexes. The conductivity data show that the complexes are non-electrolyte in nature. The anti-oxidant activity of the ligand, Na2pdtc and its transition metal complexes, M(pdtc) have been carried out using DPPH and Cu(pdtc) was found to be most effective. The antimicrobial activity of the Na2pdtc and M(pdtc) complexes have been carried out and on this basis the molecular docking study of the most effective complex, Cu(pdtc) has also been reported. © 2016 Elsevier B.V. All rights reserved.

1. Introduction The synthesis and characterization of metal complexes bearing sulfur donor ligands continues to increase at an unabated pace, because of their resemblance to several important biomolecules, such as amino acids and vitamins [1]. Dithiocarbamate ligands are organosulfur compounds having remarkable complexing ability. This may be due to the small bite angle of CSS group which can coordinate almost with all metal ions even in unusual oxidation states like Ni(IV) and Cu(III) [2]. In some of the metal dithiocarbamato complexes the spin-crossover behavior is also reported. The rich coordination chemistry of dithiocarbamate ligand is well documented and established [3]. Their complexes are finding newer applications in many areas of chemistry, biology and industry [4]. For instance, (CH3)2NCSS¯ is used for the separation of various metal ions as their metal chelates [5] while its Sn-complex is found to possess strong anti-cancer properties [6]. Similarly, several dialkyl dithiocarbamate salts have shown promising biological properties like anti-alkylation [7], cytotoxicity and antitumor [8] as well as anti-HIV properties [9]. Diethyldithiocarbamate has also been used to ⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (S.A.A. Nami).

http://dx.doi.org/10.1016/j.jphotobiol.2016.05.010 1011-1344/© 2016 Elsevier B.V. All rights reserved.

minimize the initiation of acquired immune deficiency syndrome (AIDS) in human immunodeficiency virus infected individuals via inhibition of NF-κB activation. Recently, Wang et al. have reported the cytotoxicity of Au(III) complexes with 5-aryl-3-(pyridin-2-yl)-4,5dihydropyrazole-1-carbothioamide derivatives, which showed higher cytotoxicity than the cisplatin against HeLa cell [10]. It was also reported that Au(III)-dithiocarbamato complexes displayed antitumor properties with almost no nephrotoxic side-effects [11]. Besides, being biologically robust, dithiocarbamates owe special attention as agrochemicals. The Manganese complex of dithiocarbamate (maneb), iron complex (ferbam), zinc complex (ziram or zineb) are well known pesticides with an estimated annual global consumption of 25,000–35,000 metric tons [12]. From the structural point of view dithiocarbamate ligands and their complexes are very interesting and intriguing. They have the ability to bind in a monodentate as well as bidentate fashion generating varied structures like macrocycles [13], capsules and cylinders [14], cages [15], cryptands [16], catenanes [17–18] and loops [19]. These structures are mainly constructed by exploiting the self-assembling nature of the dithiocarbamate ligand [20]. In continuation of our interest in the self-assembled dithiocarbamates [21–22] and their transition metal complexes, we, herein report the synthesis, characterization, spectral and antioxidant studies of a

S.A.A. Nami et al. / Journal of Photochemistry & Photobiology, B: Biology 160 (2016) 392–399

393

Fig. 1. Synthesis of the Schiff base ligand (L1).

bidentate ligand Na2pdtc and its complexes. Moreover, the molecular docking studies of Cu(pdtc) has also been reported. However, due to the poor yield of the ligand and its successive metal complexes, we have employed the in situ strategy to obtain the metal complexes in appreciably high yields. 2. Experimental Hydrated metal (II) dichloride, MX2 ⋅ nH2O, pyrrole-2carboxaldehyde (Merck India), p-phenylenediamine (Acros), dimethyl sulfoxide (DMSO) and carbon disulfide (S. D. finechem India) were used as received. Methanol was distilled prior to use. Elemental analyses (C, H, N and S) were carried out with Elemental Vario EL III (Carlo Erba 1108) analyzer. The metal contents were estimated by complexometric titration [23]. IR spectra (4000–400 cm−1) were recorded with a Perkin Elmer RXI FT-IR spectrometer as KBr disc while the 600–200 cm− 1 range was scanned with CsI on a Nexus FT-IR Thermo Nicolet, Wisconsin. The Electronic spectra were recorded on a Lab India spectrophotometer in DMSO. The NMR spectra were recorded with a BRUKER AV-500 in DMSO. The conductivity measurements were done with a CM-82T Elico conductivity bridge in DMSO. Room temperature magnetic susceptibility measurements were done with a 155 Allied Research vibrating sample magnetometer. 2.1. Synthesis of the Schiff Base Ligand, N,N′-Bis-(1H-Pyrrol-2ylmethylene)-Benzene-1,4-Diamine (L1) In a pre-dissolved methanolic solution of p-phenylenediamine (10 mmol, 1.08 g), pyrrole-2-carboxaldehyde (20 mmol, 1.90 g) was added dropwise over a period of 30 min with continuous stirring. It was precipitated as yellow solid by adding 4 to 6 drops of concentrated HCl. The reaction mixture was stirred for 4 h in order to ascertain complete precipitation. The product was filtered, washed successively with methanol, diethyl ether and dried in vacuo over CaCl2. A single spot was obtained in ethyl acetate. M.p. 203 °C (decomp.). The reaction scheme is shown in fig. 1.

2.2. Synthesis of Na2pdtc (Disodium-1,4-phenyldiaminobis(Pyrrole-1sulfino)Dithioate) (L2) The Schiff base ligand, L1 (5 mmol, 1.31 g) was dissolved in double distilled water by vigorous shaking and mounted on an ice bath. Sodium hydroxide (16 mmol, 0.06 g) dissolved in minimum amount of water was added followed by drop wise addition of carbon disulfide (12 mmol, 0.72 mL) to obtain a light green color solution. The reaction mixture was stirred overnight and left in an open to obtain powdery stable product. It was washed with water and absolute ethanol and dried in vacuo over CaCl2. The probable structure of Na2pdtc is depicted in Fig. 2.

2.3. Conventional Synthesis of Transition Metal Complexes, M(pdtc) In well dissolved aqueous solution of Na2pdtc (5 mmol, 2.29 g), hydrated transition metal halide, MCl2 ⋅nH2O (5 mmol) dissolved in 10 mL distilled water was added drop-wise to obtain an immediate precipitation excepting ZnCl2 (5 mmol, 0.68 g) which was dissolved in 10 mL methanol. All the complexes were filtered, washed with absolute ethanol and dried in in vacuo over CaCl2 (Fig. 3). The complexes give a single dark spot in DMSO-water system.

2.4. In situ Synthesis of the Transition Metal Complexes, M(pdtc) The Schiff base ligand, L1 (5 mmol, 1.31 g) was dissolved in double distilled water by vigorous shaking and mounted on an ice bath. Sodium hydroxide (16 mmol, 0.06 g) dissolved in minimum amount of water is added to the reaction mixture. Carbon disulfide (12 mmol, 0.75 mL) was added drop-wise to obtain a light green solution. In this reaction mixture hydrated metal chlorides, MCl2 ⋅ nH2O (5 mmol) where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) dissolved in 10 mL MeOH was added to obtain successive precipitation of transition metal complexes. The compound was separated by filtration and washed several times by MeOH and dried in vacuo over CaCl2.

Fig. 2. Synthesis of Na2pdtc (Disodium-1,4-phenyldiaminobis (pyrrole-1-sulfino)dithioate).

394


Fig. 3. Synthesis of the complexes M(pdtc) where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II).

2.5. In-vitro Antioxidant Activity 2.5.1. Free–Radical Scavenging Assay The free radical scavenging activity of the complexes was measured using modified protocol of Brand–Williams [24]. The Stock solution (1 mg/mL) of ligand and its transition metal complexes were diluted to final concentration 2, 4, 6, 8, 10, and 12 in DMSO. The ethanolic of DPPH (1 mL, 0.3 mmol) solution was mixed thoroughly with 3.0 mL of sample solution of different concentration. Meanwhile, ethanol (1 mL) was added to the samples (3.0 mL) to make the blank solution. The negative control consisted of DPPH solution (1 mL) and DMSO (3.0 mL). The tube was kept at an ambient temperature for 30 min and absorbance was measured at 517 nm using the UV–VIS. spectrophotometer. The scavenging activity is calculated by the following equation:

times (1, 2, 3, 4 and 5 days) and absorbance was measured at 532 nm using the spectrophotometer. BHT (1 mg/mL) was also assayed for comparison. A blank sample was prepared under the same conditions as described above, without adding any additive. The rate of antioxidant of peanut oil was estimated according to the increase of 2–thiobarbituric acid–reactive intermediate (TBARS) using the classical TBA procedure. The TBARS values of untreated and treated samples were used to calculate the inhibition of lipid oxidation by the following mathematical equation. Inhibition ð%Þ ¼ ðcontrol−treatmentÞ=control 100 All the tests were conducted in triplicate and the results are reported as the average. 2.6. Antibacterial Activity

%inhibition ¼ ½ðAB−AAÞ=AB 100: where AB is absorption of blank sample, AA: absorption of tested samples. The kinetics of DPPH scavenging activity was evaluated and the IC50 values were calculated using ascorbic acid as a positive control. 2.5.2. Scavenger Measurements of Hydroxyl Radical (•OH) The ability of the ligand and its complexes to effectively scavenge hydrogen peroxide was determined in accordance with the literature [25]. The hydroxyl radical (•OH) was generated in aqueous medium through the Fenton system [26]. The solution of the ligand and its complexes was prepared in DMSO. The assay mixture (5 mL) consisted of safranin (28.5 mmol), EDTA–Fe(II) (100 mmol), H2O2 (44.0 mmol), the tested ligand and complexes at various concentrations (2– 12 mmol) and a phosphate buffer (67 mmol, pH = 7.4). The assay mixtures were incubated at 37 °C for 30 min on water bath and the absorbance was recorded at 520 nm against a blank. Mannitol was used as standard for suppression of hydroxyl radical using the same procedure as described above. All the tests were run in triplicate and expressed as the mean. The scavenging ratio for •OH was calculated from the following equation. Scavenging ratio ð%Þ ¼ ½ðAi −A0 Þ=½ðAc −A0 Þ 100 where Ai is the absorbance in the presence of the tested ligand or its complexes; A0 is the absorbance of the tested compound; and Ac is the absorbance in the absence of the tested compound, EDTA–Fe(II) and H2O2. 2.5.3. Antioxidant Potential of Ligand and its Metal Complex in Peanut Oil Calculated amounts of ligand, Na2pdtc and its complex in DMSO were added to 50 mL of peanut oil. The mixture was mixed into the oil with a magnetic stirrer. The oxidative deterioration of samples was studied using Schaal oven test method as described in literature [27]. The oil samples (50 mL each) were placed in 100 mL beakers and kept in an oven maintained at 60 ± 0.5 °C for 24 h. The sample (1 mg/mL) was prepared under the same condition treated with different reaction

Screening for antibacterial activity was carried out in sterilized antibiotic discs (8 mm), following the standards for Antimicrobial Disc Susceptibility Tests, outlined by the National Committee for Clinical Laboratory Standards-NCCLS [28–29]. The density of the bacterial suspension was standardized by using a McFarland standard method. According to this standard protocol all the assays were carried out at 28 ± 3 °C. Bioassay of the ligand and its complexes, M(pdtc) were evaluated using the bacterial cultures of the gram negative bacteria Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumonia and the gram positive bacteria Bacillus subtilis, Streptococcus pyogenes, and Staphylococcus aureus by the disc diffusion method [30]. Standard reference antibiotic, Chloramphenicol, was used as a positive control for the tested bacteria, whereas DMSO was used as a negative control. In this method, liquefied agar medium having uniform thickness were poured in petri-plates. After solidification plates were inoculated with test micro-organisms, after which filter paper discs dipped in the solution of complexes dissolved in DMSO and standard drug solution dissolve in DMSO (each 10 μg/mL) were placed in each quadrant of the plate. The drug diffused into the agar medium prevented the growth of microbes and produced a clear zone of inhibition. Plates were first kept at 4 °C for 2 h to allow for diffusion of chemicals, followed by incubation at 28 °C. Antibacterial activity was evaluated by measuring the diameters (mm) of the zones of inhibition as depicted in Table 4 against the test bacteria after 24 h of incubation. Each assay was in triplicate with SD. 2.6.1. Docking Studies For macromolecular docking studies, the chemical structure of most effective metal complex, Cu(pdtc) was drawn using ChemDraw ultra. The 3D optimization was done in ChemDraw 3D ultra software and stored as .pdb file. The crystal structure of E. coli IDH (PDB ID: 4AJA) was downloaded from the protein data bank (http://www.rcsb.org./ pdb). All the heteroatoms associated with proteins including water molecules, bound ligands and any co-crystallized solvent were removed from the PDB file and the missing assignments like proper bonds, bond orders, visualization, hybridization and charges were assigned


using the Molegro Virtual Viewer [31]. PATCHDOCK [32–33] was employed for molecular docking of Cu(pdtc) complex. The atomic contact energy (ACE) was calculated and found to be negative. 3. Results and Discussion The Schiff base reaction of p-phenylenediamine and pyrrole-2carboxaldehyde in 1:2 molar ratio was carried out to obtain N,N′-bis(1H-pyrrol-2-ylmethylene)-benzene-1,4-diamine (L1) (Fig. 1). It was subsequently reacted with carbon disulfide in basic medium to generate disodium-1,4-phenyldiaminobis(pyrrole-1-sulfino)dithioate, Na2pdtc. The 3d mononuclear transition metal complexes, M(pdtc) where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), pdtc = 1,4phenyldiaminobis(pyrrole-1-sulfino)dithioate are obtained by the simple replacement of two chlorine atoms from MCl2 ⋅ nH2O by Na2pdtc (Fig. 1) in moderate yields. The amorphous complexes soluble in DMSO, DMF and are stable to light. MCl2 ⋅nH2O + Na2pdtc → M(pdtc) + 2NaCl. However, the complexes can also be obtained in higher yields by the in situ procedure. Herein, the Schiff base was reacted with carbondisulfide in presence of strong base and the metal halide was added in the reaction mixture to obtain the title complexes as depicted in the reaction below:

395

Table 2 Diagnostic IR bands of the ligand and its complexes. Complex

ν(M\ \S)

ν(C S)

ν(C N)

ν(C_N)

Na2(pdtc) Mn(pdtc) Fe(pdtc) Co(pdtc) Ni(pdtc) Cu(pdtc) Zn(pdtc)

– 412 w 421 w 407 w 425 w 416 w 398 w

1000 s 1035 s 1066 s 1037 s 1074 s 1038 s 1047 s

1509 m 1505 s 1505 s 1510 s 1508 s 1509 m 1510 s

1620 s 1614 s 1615 s 1606 s 1610 s 1613 s 1607 s

coordination of the dithiocarbamato group. Similarly, a strong band lying in between C\\N and C_N termed as thioureide band is observed in the 1505–1510 cm−1. This band results due to the delocalization of electron over the

group. However, for a symmetrical

The molar conductivity of 10−3 M solution of the complexes measured in DMSO indicated their non-electrolytic nature (Table 1) [34].

bidentate coordination this band normally appears at higher wave numbers as compared to its unsymmetrical analog [36]. The insertion of carbon disulfide with L1 also stems from the absence of strong split peak around 3480 cm−1 corresponding to secondary amine of pyrrole-2-carboxaldehyde and appearance of weak bands in the far IR region between 425 and 398 cm−1 due to M\\S bonds [37]. These weak bands are sensitive with the nature of metal ion [37]. On a similar basis, the formation of Schiff base is ascertained with the disappearance of strong carbonyl band (≈1665–1710 cm−1) and appearance of strong C_N band in the 1620–1606 cm−1. These peaks ascertain the formation of L1, Na2pdtc and the title complexes.

3.1. IR Spectra

3.2. 1H and 13C NMR Spectra

The IR spectra of dithiocarbamato complexes is quite conclusive, particularly the regions 930 to 1070 and 1450 to 1550 cm−1 [35]. The important IR bands are enlisted in Table 2. There are many reports regarding the distinction of monodentate and bidentate coordination of dithiocarbamate moiety with the metal ion. A single peak in the range 930 to 1070 cm−1 corresponds to the symmetrical bidentate bonding of dithiocarbamate moiety with the metal ion while splitting of this solitary peak within 20 cm− 1 is attributable to unsymmetrical monodentate coordination with the metal ion as depicted below:

The 1H NMR spectrum of L1 shows a single peak at 8.2 ppm corresponding to two C\\H protons of the azomethine groups. This peak provides a strong evidence for the Schiff base formation (Fig. 1). The single upfield peak appearing at 12.9 may be ascribed to N\\H groups. A bunch of peaks due to aromatic protons of the phenylenediamine moiety were found to appear in the 7.19–6.98 ppm range. The pyrrole ring contains three types of protons which appear as a multiplet centered at 6.46 ppm [38]. On a similar basis the 1H NMR spectrum of Na2L and M(pdtc) may be assigned and it does not show appreciable shift excepting the complete disappearance of N\\H peak which evidently supports the formation of dithiocarbamate group. Another feature is the small shift in the pyrrole protons due to the formation of CSS group and presence of transition metal ion. In case of Na2L and M(pdtc) the pyrrole ring was found to contain three different type of protons designated as Ha, Hb and Hc due to the presence of different electronic environments (Fig. 3).

L1 þ CS2 þ MC12 nH2 O → MðpdtcÞ þ 2HC1

In the present finding, we have observed a single strong band in the range of 1066–1000 cm− 1 corresponding to bidentate symmetrical

Table 1 Physicochemical properties of the ligand and its complexes. Complexes

Yield (%)

Molar conductance (ohm−1 mol−1 cm2)

Na2pdtc

48

–

Mn(pdtc)

69

11

Fe(pdtc)

68

35

Co(pdtc)

73

12

Ni(pdtc)

81

37

Cu(pdtc)

68

18

Zn(pdtc)

72

17

Analysis, (%) found (calcd.) C

H

N

S

M

47.09 (47.15) 45.91 (46.24) 44.93 (46.15) 45.51 (45.85) 45.68 (45.87) 45.19 (45.40) 45.01 (45.23)

2.69 (2.64) 2.39 (2.59) 2.41 (2.58) 2.39 (2.56) 2.37 (2.56) 2.42 (2.54) 2.31 (2.53)

12.55 (12.22) 12.09 (11.98) 12.06 (11.96) 11.89 (11.88) 11.93 (11.89) 11.46 (11.77) 11.42 (11.72)

27.64 (27.97) 27.48 (27.43) 27.48 (27.38) 27.57 (27.20) 27.48 (27.22) 27.12 (26.94) 27.07 (26.83)

– 12.04 (11.75) 12.08 (11.92) 12.19 (12.49) 12.51 (12.45) 13.09 (13.35) 12.35 (13.68)

396


Table 3 Antioxidant activity (IC50 values) and LOI of complexes.

Complexes

Na2(pdtc) Mn(pdtc) Fe(pdtc) Co(pdtc) Ni(pdtc) Cu(pdtc) Standard

IC50 (μg/mL) (Mean ± S.D.) (%) DPPH

OH

4.47 3.08 2.56 2.44 2.90 0.52 0.34

5.56 4.01 3.45 3.40 3.60 0.22 3.84

Lipid oxidation inhibition (LOI)

22 33 47 32 39 72 65

These protons are found to appear in the vicinity of 6.4, 6.2 and 7.7 ppm corresponding to Ha, Hb and Hc protons respectively (Fig. 3). In the 13C NMR spectrum of L1, Na2pdtc and M(pdtc) the most important feature is the absence of CSS band in L1, presence of CSS band at 208 ppm in case of Na2pdtc and an upfield shift in case of complexes ranging from 215 to 221 ppm due to the coordination of metal ion [39]. 3.3. Electronic Spectra and Magnetic Moment The electronic spectral bands along with the magnetic moment value are suggestive of tetrahedral configuration for Mn(pdtc), Fe(pdtc), Co(pdtc), Ni(pdtc) complexes while the Cu(pdtc) complex was found to be square planar. The Mn(II) complexes can easily be categorized into tetrahedral as well as octahedral on the basis of their electronic spectra [40]. The Mn(pdtc) exhibits two intense d-d absorption bands and one charge transfer band. The absorption bands appearing at 22,740 and 20,060 cm−1 correspond to 4T2 ← 6A1 and 4T1 ← 6A1 transitions, respectively while the band appearing at 35,400 cm− 1 may be ascribed to charge transfer. The tetrahedral Mn(II) complex gives magnetic moment of 5.9 B.M which is temperature independent. We have obtained a value of 5.7 B.M which is close to the spin only value for five unpaired electrons. The high-spin tetrahedral Fe(II) complexes show a weak spin allowed d-d transition in the visible region. The tetrahedral ferrous ions are easily oxidized in solution, hence, report of such complexes are not common. The magnetic moment of tetrahedral Fe(II) complexes lies in 5.0–5.5 B.M. range [41]. In the present study we have also observed a single broad band centered at 18,850 cm− 1 owing to 5 E ← 5T2 transition while the magnetic moment value is found to be 5.2 B.M. which is well within the limits ascribed for tetrahedral geometry. Besides, two charge transfer bands are also observed at 27,800 and 34,500 cm−1. The tetrahedral Co(II) complexes show three spin allowed d-d absorptions arising from the 4A2(F) ground term [42]. In tetrahedral Co(II) complexes due to absence of symmetry , mixing of d and p orbitals takes place generating intense d-d absorption bands. Sometimes, these bands are 200 times intense than those observed for octahedral analogs [43]. Moreover, in tetrahedral Co(II) complexes μeff lies in 4.2

to 4.7 B.M. range [44]. For Co(pdtc) two strong bands are observed at 15,504 and 21,882 cm− 1 corresponding to 4T2(F) ← 4A2(F) and 4 T1(F) ← 4A2(F) transitions, respectively. However, for Co(pdtc) we have observed a magnetic moment value of 4.3 which further supports the tetrahedral arrangement around Co(II) ion. Ideally three d-d bands along with a magnetic moment value ranging from 3.2–3.5 B.M. is characteristic of Ni(II) in tetrahedral coordination mode but deviation occurs both in terms of spectra as well as magnetic moment value depending upon the nature of ligands attached to the Ni(II) ion [45]. We have observed two d-d bands at 14,400 and 20,250 cm− 1 corresponding to 3T2(F) ← 3T1(F) and 3A2(P) ← 3T1(F) transitions, respectively for Ni(pdtc). The magnetic moment value was found to be 3.16 B.M. slightly lower than those generally observed for tetrahedral Ni(II) complexes. This lowering may be associated with slight deviation in the tetrahedral geometry around the Ni(II) ion in Ni(pdtc). The electronic spectra of Cu(pdtc) displays two prominent broad bands centered at 13,050 and 18,400 cm−1 corresponding to 2 Eg ← 2B1 and 2A1 ← 2B1 transitions, respectively. In addition, two strong charge transfer bands are also observed at 29,450 and 31,200 cm−1. On the basis of electronic spectra alone it is difficult to differentiate between square-planar and a tetrahedral arrangement as the d-d transitions occurs in the same region for both the geometries. In the present case the experimental magnetic moment (1.77 B.M) is in the range for a square-planar Cu(II) ion in Cu(pdtc) [46]. 3.4. Antioxidant Activity Transition metal ions are a vital part of many biological system because of their involvement in a number of enzymatic reactions like ceruloplasmin, cytochrome–c oxidase, Cu, and Zn-superoxide dismutase. These transition metal ions catalyze the oxidation and reduction linked with antioxidant system of the concerned organism. The varied behavior of transition metals relies upon the chemical environment, ionization potential and nature of ligands attached. The potent antioxidant activity of dithiocarbamate ligand and its metal complexes may be explained on the basis of electron donating capability of sulfur and the transition metals ion in their respective complexes which lead to the stabilization of free radicals or scavenging of hydroxyl ions. The dithiocarbamato complexes also utilize their loosely held electrons to check the propagation of free radicals of the stable radical 2,2– Diphenyl–1–picrylhydrazyl (DPPH) and lipid rancidity (Table 3). The complexes show inhibitory activity due to their ability to act as free radical acceptor and their activity increases with increasing complex concentration. Ascorbic acid, mannitol, and BHT are used as the standard antioxidants for comparison. Table 3 also indicates the scavenging capability of ligand and complexes on DPPH, •OH and lipid oxidation inhibition. The antioxidant activity of the compounds is expressed as 50% inhibitory concentration (IC50 in μg/mL) for DPPH, •OH and highest level in percentage for lipid oxidation inhibition. The table shows IC50 values for ligand, and their complexes against DPPH and •OH radical respectively. On comparison

Table 4 Antimicrobial activities of ligand and its complexes using disc diffusion method. Complexes

B. subtilis

S. pyogenes

S. aureus

P. aeruginosa

K. pneumonia

E. coli

Na2(pdtc) Mn(pdtc) Fe(pdtc) Co(pdtc) Ni(pdtc) Cu(pdtc) Zn(pdtc) CP

16.3 ± 0.31 21.9 ± 0.63 20.3 ± 0.15 20.4 ± 0.33 21.1 ± 0.75 23.6 ± 0.33 20.3 ± 0.43 24.8 ± 0.45

15.3 ± 0.25 20.6 ± 0.75 18.1 ± 0.55 20.4 ± 0.35 18.9 ± 0.37 22.3 ± 0.32 19.9 ± 0.45 23.1 ± 0.67

16.2 ± 1.1 20.9 ± 1.2 18.6 ± 1.1 20.7 ± 1.4 19.1 ± 1.3 21.3 ± 0.35 19.5 ± 1.4 22.3 ± 1.1

21.3 ± 0.37 28.1 ± 0.63 26.3 ± 1.4 27.1 ± 0.37 26.1 ± 0.67 30.1 ± 0.75 27.3 ± 0.36 31.9 ± 1.34

14.1 ± 0.22 17.5 ± 0.23 16.7 ± 0.44 18.5 ± 0.13 17.9 ± 1.1 19.0 ± 0.25 18.1 ± 0.23 20.1 ± 0.77

17.1 ± 0.25 23.6 ± 0.24 21.5 ± 0.64 23.1 ± 0.14 22.1 ± 0.34 26.5 ± 0.47 23.1 ± 0.44 27.9 ± 0.64

Each value represents the diameter of the zone of inhibition (mm). CP: Chloramphenicol (standard drug). Values are expressed in mean ± SD of three assays.


with ligand and its synthesized complexes the Cu(II) complex was found to exhibit highest antioxidant activity in both cases i.e. DPPH and •OH. The IC50 values of the ligand and its transition metal complexes are far less than those of ascorbic acid and mannitol suggesting that the synthesized metal complexes are more effective antioxidants for a particular radical (•OH). Antioxidant potential of the ligand and its complexes were measured by Schaal oven test as described in literature [27]. The initial observation clearly indicates that neither ligand nor complexes shown considerable inhibition power on lipid peroxidation as shown in Fig. 5. However, only Cu(pdtc) complex have some effect, the highest level reached being 72% attained after three days. The lipid oxidation inhibition of ligand and other metal complexes followed the same trend but at much lower rate. The lower antioxidant power of ligand as compared to the ascorbic acid and BHT may be due to the absence of free electrons unlike that of BHT. The free electrons are easily migrated to reactive center of free radical to produce stable species [47]. It is clear from ongoing discussion that the metal complexes exhibit strong antioxidant competence in the place where electron transfer are important criteria, thus, the greater antioxidant ability may be regarded due the neutralization of reactive oxygen species [48] as in case of hydroxyl radical etc.

397

Fig. 5. Hydrophobic groove binding of Cu(pdtc) where red color signifies hydrophilic residues while the blue color shows hydrophobic residues.

3.6. Docking Studies 3.5. Antibacterial Studies The ligand and its complexes were screened against few gram positive and gram negative bacteria notably Bacillus subtilis, Streptococcus pyogenes, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli by disc diffusion method at a concentration of 10 μg/mL. The growth inhibitory potentials of the tested compounds were compared with that of standard drug, Chloramphenicol (CP). Compounds were found to inhibit growth of B. subtilis, S. pyogenes, S. aureus, P. aeruginosa, K. pneumoniae and E. coli (Table 4). The antimicrobial activity of compound Cu(pdtc) was found to be comparable with CP. This behavior may be attributed to the effective interactions between the Cu(pdtc) and the receptor molecule (amino acids).

Molecular docking techniques are an attractive scaffold to understand the metal complex and protein receptor interactions which are quite helpful in rational drug designing, as well as in predicting the mechanistic pathways. The Cu(pdtc) shows hydrogen bonding as well as vander Walls interactions with the amino acid moieties of the receptor molecule (Fig. 4). The complex occupies hydrophobic groove (Fig. 5) implying appreciable vander Walls contact with the hydrophobic surface having side chain residues, namely Arg-365, Arg-132, Arg-222, Tyr-216, Met-362 and the Asp-148 attached to the Cu(II) ion (Fig. 4). However, the hydrogen bonding interactions were found to be Tyr216 and Arg-222 which indicates the high activity of Cu(pdtc) as antimicrobial agent. Its high negative ACE value, (−195.24 KJ/mol) suggests strong interaction between the complex and the receptor molecule. The

Fig. 4. Ligand map of Cu(pdtc) showing Hydrogen bonding and vander Walls interactions.

398


Fig. 6. (a) Dock pose view of Cu(pdtc) in the active site of protein receptor (PDB ID: 4AJA) showing various interactions. (b). Energy map visualization of Cu(pdtc) where green color represents favorable site for non-polar atoms, red color depicts the negative electrostatic charge in the region while the blue color corresponds to the positive charge in the protein. The yellow color signifies the atoms capable of formation of Hydrogen bonds.

Cu-complex can thus be considered as a model for anti-microbial activity (Fig. 6a and 6b). Acknowledgements The authors (SAAN and IU) are grateful to the University Grants CommissionIndia (Research scheme No. 40-54/2011 (SR)) for the financial support. References [1] L.A. Komarnisky, R.J. Christopherson, Nutrition 19 (2003) 54–61. [2] J.P. Barbier, R.P. Hugel, C. Kappenstein, Inorg. Chim. Acta 77 (1983) 117–118; B.B. Caul, K.B. Pandeya, J. Inorg. Nucl. Chem. 43 (1981) 1942–1944. [3] G. Hogarth, Prog. Inorg. Chem. 53 (2005) 71–561.

[4] G.D. Thorn, R.A. Ludwig, The dithiocarbamates and related compounds, Elsevier, Amsterdam, 1962; A.M. Bond, R.L. Martin, Coord. Chem. Rev. 54 (1984) 23–98. [5] M.L. Riekkola, O. Makitie, M. Sundberg, Kem. Kemi. 6 (1979) 525–529. [6] S. Khan, S.A.A. Nami, K.S. Siddiqi, J. Organomet. Chem. 693 (2008) 1049–1057. [7] Z.M. Hua, L. Hong, H.U. Ruixiang, L. Xuhong, D. Yecheng, H. Shequn, Chin. J. Appl. Chem. 10 (2001) 837–839. [8] G.C. Wang, Y.N. Lua, J. Xiao, L. Yu, H.B. Song, J.S. Li, J.R. Cui, R.Q. Wang, F.X. Ran, J. Organomet. Chem. 690 (2005) 51–56; S. Takahashi, H. Sato, Y. Kubota, H. Utsumi, J.S. Bedford, R. Okayasu, Toxicology 180 (2002) 249–256. [9] T.L. Sheng, X.T. Wu, P. Lin, Polyhedron 18 (1999) 1049–1054; L.J. Farrugia, F.J. Lawlor, N.C. Norman, J. Chem. Soc. Dalton Trans. (1995) 1163–1171. [10] S.X. Wang, W.Q. Shao, H.D. Li, C. Liu, K. Wang, J.C. Zhang, Eur. J. Med. Chem. 46 (2011) 1914–1918. [11] M.N. Kouodom, L. Ronconi, M. Celegato, C. Nardon, L. Marchio, Q.P. Dou, D. Aldinucci, F. Formaggio, D. Fregona, J. Med. Chem. 55 (2012) 2212–2216. [12] B. Cvek, Z. Dvorak, Curr. Pharm. Des. 13 (2007) 238–242.

S.A.A. Nami et al. / Journal of Photochemistry & Photobiology, B: Biology 160 (2016) 392–399 [13] L.H. Uppadine, J.M. Weeks, P.D.J. Beer, Chem. Soc. Dalton Trans. (2001) 3367–3372. [14] A. Husain, S.A.A. Nami, K.S. Siddiqi, Spectrochim. Acta A 73 (2009) 89–94. [15] P.D. Beer, A.G. Cheetham, M.G.B. Drew, O.D. Fox, E.J. Hayes, T.D. Rolls, Dalton Trans. (2003) 603–611. [16] P.D. Beer, N. Berry, A.R. Cowley, E.J. Hayes, E.C. Oates, W.W.W.H. Wong, Chem. Commun. (2003) 2408–2409. [17] M.E. Padilla-Tosta, O.D. Fox, M.G.B. Drew, P.D. Beer, Angew. Chem. Int. Ed. 40 (2001) 4235–4239. [18] W.W.H. Wong, J. Cookson, E.A.L. Evans, E.J.L. McInnes, J. Wolowska, J.P. Maher, P. Bishop, P.D. Beer, Chem. Commun. (2005) 2214–2216. [19] O.D. Fox, M.G.B. Drew, P.D. Beer, Angew. Chem., Int. Ed. 39 (2000) 136–140; O.D. Fox, E.J.S. Wilkinson, P.D. Beer, M.G.B. Drew, Chem. Commun. (2000) 391–392. [20] O.D. Fox, J. Cookson, E.J.S. Wilkinson, M.G.B. Drew, E.J. MacLean, S.J. Teat, P.D. Beer, J. Am. Chem. Soc. 128 (2006) 6990–7002. [21] S.A.A. Nami, A. Husain, Irfan Ullah, Spectrochim. Acta A 118 (2014) 380–388. [22] S.A.A. Nami, K.S. Siddiqi, Synth. React. Inorg. Met.-Org. Chem. 34 (2004) 1581–1590. [23] C.N. Reilly, R.W. Schmid, F.S. Sadek, J. Chem. Ed. 36 (1959) 619–625. [24] W. Brand-Williams, M.E. Cuvelier, C. Berset, Lebensm. Wiss. Technol. 28 (1995) 25–30. [25] Z.C. Liu, B.D. Wang, Z.Y. Yang, Y. Li, D.D. Qin, T.R. Li, Eur. J. Med. Chem. 44 (2009) 4477–4484. [26] C.C. Winterbourn, Biochem. J. 198 (1981) 125–131. [27] K.D. Economou, V. Oreopoulou, C.D. Thomopoulos, J. Am. Oil Chem. Soc. 68 (1991) 109–113. [28] C.H. Collins, P.M. Lyre, J.M. Grange, Microbiological Methods, sixth ed. Butterworths Co. Ltd., London, 1989. [29] NCCLS, Performance standards for antimicrobial disc susceptibility tests (M2-A5132), Approved Standards, NCCLS publication, Villanova, PA, USA, 1993. [30] R.E. White, M.J. Coon, Annu. Rev. Biochem. 49 (1980) 315–356.

399

[31] R. Thomsen, M.H. Christensen, J. Med. Chem. 49 (11) (2006) 3315–3321. [32] D. Duhovny, R. Nussinov, H.J. Wolfson, Efficient unbound docking of rigid molecules, in: Gusfield, et al., (Eds.), Proceedings of the 2'nd Workshop on Algorithms in Bioinformatics(WABI) Rome, Italy, Lecture Notes in Computer Science, 2452, Springer, Verlag 2002, pp. 185–200. [33] D.S. Duhovny, Y. Inbar, R. Nussinov, H.J. Wolfson, Nucl. Acids Res. 33 (2005) W363–W367. [34] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122. [35] H.C. Brinkhoff, A.M. Grottens, Recueil 111 (1971) 252–257. [36] C. O'Connor, J.D. Gilbert, G. Wilkinson, J. Chem. Soc. (A) (1969) 84–87. [37] K.S. Siddiqi, S.A.A. Nami, Y. Chebude, A. Marzotto, J. Chem. Res. (2006) 67–71. [38] B.K. Singh, A. Prakash, H.K. Rajour, N. Bhojak, D. Adhikari, Spectrochim. Acta A 76 (2010) 376–383. [39] S.M. Mamba, A.K. Mishraa, B.B. Mamba, P.B. Njobeh, M.F. Dutton, E.F. Kankeu, Spectrochim. Acta A 77 (2010) 579–587. [40] F.A. Cotton, D.M.L. Goodgame, M. Goodgame, J. Am. Chem. Soc. 84 (1962) 167–172. [41] B.N. Figgis, Introduction to Ligand Fields, Wiley Eastern Limited, New Delhi, 1976 285–319. [42] D.A. Clemente, A. Marzotto, G. Valle, C.J. Visona, Polyhedron 18 (1999) 2749–2757. [43] J.P. Jesson, S. Trofimenko, D.R. Eaton, J. Am. Chem. Soc. 89 (1967) 3148–3158. [44] I. Kuzniarska-Biernacka, A. Bartecki, K. Kurzak, Polyhedron 22 (2003) 997–1007. [45] A. Christensen, H.S. Jensen, V. McKee, C.J. McKenzie, M. Munch, Inorg. Chem. 36 (1997) 6080–6085. [46] R.G. McDonald, M.J. Riley, M.A. Hitchman, Inorg. Chem. 28 (1989) 752–758. [47] P. Molyneux, Songklanakarin J. Sci. Technol. 26 (2004) 211–219. [48] G.I. Giles, K.M. Tasker, R.J.K. Johnson, C. Jacob, C. Peers, K.N. Green, Chem. Commun. (2001) 2490; G.I. Giles, F.H. Fry, K.M. Tasker, A.L. Holme, C. Peers, K.N. Green, L.O. Klotz, H. Sies, C. Jacob, Org. Biomol. Chem. 1 (2003) 4317–4322.