Synthesis, spectroscopic characterization and study the effect of gamma irradiation on VO²⁺, Mn²⁺, Zn²⁺, Ru³⁺, Pd²⁺, Ag⁺ and Hg²⁺ complexes and antibacterial activities

2.1 Material and methods

All organic compounds and the solvents were purchased from Fluka or Merck, Naser City, Egypt. The metal salts VOSO₄·3H₂O, MnSO₄, ZnSO₄, RuCl₃·3H₂O, PdCl₂, AgNO₃ and HgCl₂ were obtained from Fluka and used for complex preparation without further purification.

2.2 Preparation of the metal complexes

The organic ligand 4-(4-chlorophenyl)-1-(2-(phenylamino) acetyl) thiosemicarbazone (B) was previously prepared and characterized (Samar and Ayman, 2017). Metal complexes were prepared by adding Stoichiometrical amount of MX₂·nH₂O, where M = VO²⁺, Mn²⁺, Zn²⁺, Ru³⁺, Pd²⁺, Ag⁺ and Hg²⁺ and X = SO₄²⁻_, Cl⁻, NO₃⁻ and n = 0–3 in absolute ethanol to hot solution of the ligand in (1:1) molar ratio leading to the complexes are represented in Scheme 1. The resulting mixture was magnetically stirred at 60 °C for 6–8 h. The formed precipitate was filtered off while hot, otherwise the solution was left at 35 °C to evaporate some of solvent to promote crystallization. The crystals were collected by vacuum filtrations, washed several times with anhydrous diethyl ether and dried under vacuum in presence of P₄O₁₀.

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Scheme 1

Suggested chemical structures of metal complexes (B₁–B₇).

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2.3 Physical measurement

Elemental analyses (C, H and N) were performed at Microanalytical unit, Cairo University. Metal content was estimated complexometric using EDTA following standard literature methods (Bassett et al., 1978). The Fourier Transform Infrared (FT-IR) measurements were performed (4000–400 cm⁻¹) in KBr discussing. Nenexeus-Nicolidite-640-MSAFT-IR, Thermo-Electronics Co. (Central Lab, Faculty of Science, Menoufia University, Egypt). ¹H NMR spectra was recorded in DMSO- d₆ using 300 MHz Varian NMR spectrometer (Micro Analytical Center). The UV–visible absorption spectra was measured in DMF solution (10⁻³ M) using 4802 UV/vis double beam spectrophotometer. The molar conductivity measurements were made in DMF solution (10⁻³ M) using a Tacussel conductometer type CD6N. The magnetic susceptibilities of the complexes were measured by the modified Gouy method at room temperature using Magnetic Susceptibility Johnson Matthey Balance. The effective magnetic moments were calculated using the relation µ_eff = 2.828(χ_mT)^1/2 B.M., where χ_m is the molar magnetic susceptibility corrected for diamagnetism of all atoms in the compounds using Selwood and Pascal’s constants.

Thermal analysis (TGA/DTG) was obtained out by using a Shimadzu DTG-50 Thermal analyzer with a heating rate of 10 °C/min in nitrogen atmosphere with a following rate 20 ml/min in the temperature range 25–800 °C using platinum crucibles at Central Lab, Faculty of Science, Menoufia University, Egypt.

X-ray powder diffraction analyses of unirradiated B₂, B₅, B₆ and irradiated A₂, A₅, A₆ of solid samples were measured using Rigku Model ROTAFLEX Ru-200 at The National Research Center, Cairo, Egypt. Morphology and structural analysis by x-ray diffractograms give computer control formally finished by PHILIPS®MPDX́PERT X-ray diffractometer ready with Cu radiation CuKα (λ = 1.540 56 Å). The x́pert diffractometer has the Bragg- Brentano geometry. The X-ray tube was used for a copper tube operating at 40 kV and 30 mA. The scanning range (2θ) was 20–80° with step size of 0.02° and counting time of 3 s/step. Quartz was used as the standard material to accurate for the instrumental expansion. This identification of the complexes was done by a known method (Uarikumaran and Appukuttan, 2012) from the fit identified Scherrer formula, the average crystallite size, L, is $$\text{L}=\left(\text{K}\lambda /\beta cos\theta \right)$$ where λ is the X-ray wavelength in the manometer, K (constant equal to 0.9) is related to crystallite shape, and ß is the peak width at half maximum height. The value of ß in the 2θ axis of diffraction shape must be in radians. The θ is the Bragg angle and be able to in radians since the Cos θ compatible with the same number.

2.4 Theoretical calculation (molecular modeling)

Molecular modeling was applied to investigate the three dimensional arrangements for atoms in the complexes by employing semi-empirical molecular orbital calculations at the PM3 level provided by the HyperChem program.

2.5 Antibacterial activity

The highly pathogenic bacterium Streptococcus pyogenes isolated from human sources which is classified into Lancefield’s group A bacteria and E. coli isolated from the soil of Menoufia governorate were used in this study. Brain heart infusion (BHI) broth medium (MP Bio) contained 27.5 g nutrient substrate (brain extract, heart extract and peptones), 2 g D(+) glucose, 5 g NaCl, and 2.5 g Na₂HPO₄ per liter. The pH was adjusted to 7.4 by the addition of diluted NaOH. Nutrient broth (NB) medium contained 1 g D(+)glucose, 15 g peptone, 6 g sodium chloride, 3 g yeast extract per liter was used to grow the bacterial strains and monitoring SK activity during growth curve of the microbes. The pH was adjusted to 7.4 by the addition of diluted NaOH.

The in vitro antibacterial activities of the tested complexes were assessed as described (Hanaa et al., 2016) with some modification. The inhibitory effects of synthesized ligand and its complexes before and after exposure to γ-irradiation were tested on the pathogenic Gram-positive organism Streptococcus pyogenes and the Gram–negative bacterium Escherichia coli. Brain Heart Infusion (BHI) broth was used to grow Streptococcus pyogenes cells and nutrient broth medium was used to grow E. coli cells. Compounds were dissolved in DMSO which has no inhibition activity on both microbes. Two different concentrations (1 μg/ml, 5 μg/ml, 7 μg/ml and 10 μg/ml) were prepared. Bacterial strains were prepared by activating them on the proper broth media with shaking. The bacteria were cultured for 24 h at 37 °C in an incubator. One milliliter of the standard bacterial culture was used as inoculation in a broth medium. For growth studies, S. pyogenes and E. coli cultures were inoculated and grown aerobically on BHI broth medium and NB medium respectively. Growth was calculated turbidometrically at 650 nm using conventional spectrophotometer. After growing bacterial cultures on media that contain the ligand, the complex and the control, absorption measurements were accomplished by spectrophotometer after 24 and 48 h of incubation to determine the number of viable cells count per milliliter of sample and were used to the calculated the inhibition percentage.

2.6 Irradiation studies

For irradiation studies of solid samples of complexes B₁–B₇ were subjected to γ-irradiation to a dose of 60 kGy using Indian ⁶⁰Co γ-ray cell type GE-4000 A (at room temperature at the Egyptian Atomic Energy Authority Nasr City, Egypt) at a dose rate of 2.2 kGy h⁻¹. After removing the samples from the radiation field the FT-IR, absorption spectra and thermal analysis (TG/DTG) XRD, antibacterial activities of the irradiated samples were investigated. X-ray powder diffraction analyses of unirradiated B₁–B₇ and irradiated A₁–A₇ samples of complexes were carried out at the National Research center, Dokki, Cairo, Egypt by using Rigku Model ROTAFLEX Ru-200. Divergence and receiving slits were 1 and 0.1, respectively.

3.1 Physical data

The data shows that the reactions of the ligand with oxovanadium, manganese, zinc sulfate, ruthenium, palladium, mercuric chloride and silver nitrate in 1 M:1L molar ratio are resulted in given metal complexes B₁–B₇ (Table 1). The molar conductivities in DMF (10⁻³ M) solution exhibited that all metal complexes are non-electrolytes in nature (Geary, 1971).

3.2 Spectroscopic analysis

3.2.1

3.2.1 Proton nuclear magnetic resonance spectra

Comparison of the proton nuclear magnetic resonance of B and A (ligand before and after γ-irradiation) were recorded in DMSO‑d₆ solution (Fig. 1). The ¹H NMR spectra of B and A in DMSO‑d₆ revealed a chemical shift (δ, ppm) = 2.5 ppm, the N(4)H signal appeared at 8.85, 8.07 ppm and the N(2)H signal appeared at 9.7, 9.04 ppm and the peak of N(1)H appeared at 9.04, 8.9 ppm. The singlet signal appeared at 3.3, 3.2 ppm that are attributed to the protons of CH₂, the multiplet signal appeared at 6.7–7.5, 6.8–7.4 ppm that are attributed to the aryl protons. The intensity of irradiated (A) is higher than unirradiated (B) (Samar and Ayman, 2017; Samar, 2017). Also, ¹H NMR spectrum of [Pd(H₂L)Cl₂]·½ ETOH complex (Fig. 2) was recorded in DMSO‑d₆. After γ-irradiation the spectrum of [Pd(H₂L)Cl₂]·½ ETOH complex showed new peaks at 8.07, 9.0, 9.2 and 9.09 ppm is attributed to N(4)H, N(2)H, N(1)H, but the signal of N(2)H in B₅ is downfield 9.09 ppm as a comparison of B at 9.7 ppm. By using gamma ray the intensity of bands is higher than unirradiated

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Fig. 1

¹H NMR spectra of ligand in DMSO‑d₆ solution before and after irradiation (B, A).

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Fig. 2

¹H NMR spectra of Pd(II) complexes in DMSO‑d₆ solution before irradiation and after irradiation (B₅, A₅).

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3.2.2

3.2.2 Mass spectroscopy

The mass spectrum of the ligand exhibited a molecular ion peak at m/z = 336 amu (Calc. m/z = 334.5). The important fragment ions appear at: m/z 77 for [C₆H₄-3H]⁺, 112 for [C₆H₅Cl-H]⁺, 127 for [C₆H₅NCl- 2H]⁺, 201 for [C₇H₉N₃SCl]⁺, 228.5 for [C₈H₉N₃SOCl-H]⁺, 259 for [C₉H₁₀N₄OSCl-2H]⁺, 336 for [C₁₅H₁₅N₄OSCl] (Fig. 3). Also, the spectrum of complex [Hg(H₂L)Cl₂]·½ H₂O proceed the suggested formula by appearing a molecular ion peak at m/z 590 amu in proportion to [Hg(H₂L)Cl₂]·½ H₂O](B₇) which agree with its formula weight (calculated m/z = 606.1 amu). The additional fragments of A₇ and B₇ provide the peaks with various intensities at diverse m/z values approximating at: Calc/Found 76/77 [C₆H₄]⁺,91/90 [C₆H₄NH]⁺, 126.5/127[C₆H₄NHCl]⁺, 327.1/327[C₆H₄NHClHg]⁺, 362.6/361[C₆H₄NHCl₂Hg]⁺, 398.1/398[C₆H₄NHCl₃Hg]⁺, 498.1/498[M-(C₉H₉N₃Cl₃HgS]⁺, 590.1/593 [M-(C₁₅H₁₅N₄Cl₃ HgOS)]⁺, 606.1/606 [M-½H₂O]⁺. After γ-irradiation, the molecular ions tend to be more stable and break into fragments with higher intensity than before γ-irradiation.

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Fig. 3

Mass spectra of ligand before and after irradiation (B, A).

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3.2.3

3.2.3 IR spectra

The most important assignments of the IR spectra of the free organic ligand and its metal complexes B₁–B₇ and A₁–A₇ are done in the range 4000–400 cm⁻¹. The comparison between the functional groups for unirradiated and irradiated ligand B and A is presented in Fig. 4 and Table 2. It was found that the functional groups of the ligand B appear at 3302; 3302 cm⁻¹, 3100; 3103 cm⁻¹, 1670; 1668 cm⁻¹ and 750; 751 cm⁻¹ respectively are attributed to the stretching frequencies of υ(N2—H), υ(N1—H), υ(C⚌O) and υ(C⚌S), respectively. After γ-irradiation their corresponding bands υ(N1—H) and υ(C⚌S) were shifted to higher wave numbers as compared to that of free B. While, the functional group of υ(C⚌O) shifted to lower wave number after γ-irradiation) (Morsy et al., 2011). After γ-irradiation the intensity of the peaks become more sharper than that of unirradiated ligand.

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Fig. 4

IR spectra of ligand and VO(II), Mn(II), Hg(II) complexes before and after irradiation (B, B₁, B₂, B₇ and A, A₁, A₂, A₇).

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Table 2 Infrared spectral bands (cm⁻¹) for ligand and its metal complexes.

	Compound	ν(N4—H)	ν(N2—H)	ν(N1—H)	ν(C⚌O)	ν(C⚌S)	ν(M—N)	ν(M—O)
B	H2L	3335	3302	3100	1670	750	–	–
A	H2L	3481	3302	3103	1668	751	–	–
B1	VO(HL)2	3430	3358	3301	–	758	509	634
A1	VO(HL)2	3422	3295	3233	–	757	467	636
B2	Mn(H2L)2SO4·2H2O	3502	3296	3101	1672	753	436	634.5
A2	Mn(H2L)2SO4·2H2O	3408	3296	2927	1672	755	508	633.5
B3	Zn(H2L)2SO4	3499	3296	3102	1631	725	467	635
A3	Zn(H2L)2SO4	3470	3296	3104	1632	756	468	635
B4	Ru(HL)3	3450	3296	3101	–	756	468	638
A4	Ru(HL)3	3480	3296	3101	–	755	465	638
B5	Pd(H2L)Cl2·½ETOH	3444	3296	3197	1602	760	457	601
A5	Pd(H2L)Cl2·½ETOH	3424	3296	3196	1603	761	465	603
B6	Ag(H2L)(HL)H2O·½ETOH	3428	3296	3100	1633	753	549	409
A6	Ag(H2L)(HL)H2O·½ETOH	3430	3295	3100	1633	753	507	413
B7	Hg (H2L)Cl2·½H2O	3465	3297(m)	3104	1632	755	509	550
A7	Hg (H2L)Cl2·½H2O	3420	3296	2926	1633	755	509	555

Where:

B = before γ-irradiation.

A = after γ-irradiation.

Coordination modes of respective unirradiated B₁–B₇ and irradiated metal complexes A₁–A₇ have been proven by comparing with ligand B. VO(II) and Ru(III) complexes B₁, B₄, and A₁, A₄ are shown significant changes showed significant changes compared to the spectrum of free B. The most important diagnostic spectral bands are exhibited at 3358–3296, 3233–3101 and 758–755 cm⁻¹ in B₁, B₄. Also, the IR spectra of A₁, A₄ are showed bands at 3233–3101 and 757–756 cm⁻¹, respectively_, which attributed to the stretching frequencies of υ(N2—H), υ(N1—H) and υ(C⚌S). The bands corresponding to υ(N2—H), υ(C⚌S) were shifted to lower frequency of complexes A₁ and A₄. However, the IR spectra of VO(II) and Ru(III) complexes before and after γ-irradiation were showed that υ(C⚌O) disappeared upon complexes formation, indicating the coordination of the ligand in enol-form and the ligand behaves as monobasic tetradentate. Also, coordination takes place via N(2)H and enolic oxygen (C—O). On the other side, IR spectra (Fig. 4) of complexes before B₂, B₃, B₅, B₆ and B₇ and after γ-irradiation A₂, A₃, A₅, A₆ and A₇ show four strong bands at 3296; 3100–3197; 1601–1672 and 725–760 respectively, also bands at 3101–3295; 3297–3196; 1601–1672 and 753–761 cm⁻¹, respectively that are attributed to υ(N4—H), υ(N2—H), υ(N1—H), υ(C⚌O) and υ(C⚌S). After γ- irradiation, the bands corresponding to υ(N1—H) was shifted to lower frequency as compared to those of complexes B₂, B₅ and B₇. However, the band attributed to υ(C⚌S) was shifted to higher wave number and higher intensity of band of irradiated. While, in complexes A₄ and A₆ the υ(C⚌O) is shifted to higher wave number as compared to that unirradiated complexes. The new bands appeared at 638–549; 638–507, 509–409 and 508–413 cm⁻¹ are assigned to υ(M—O) and υ(M—N) for B₁–B₇ and A₁–A₇ complexes, respectively (Krishnan et al., 2010; Seena and Kurup, 2007). The IR spectra of VO(II) complexes before and after γ-irradiation display new bands at 1012 and 1014 cm⁻¹ assigned to υ(V⚌O) (Maany et al., 2006).

3.3 X-ray diffraction patterns

XRD analysis was performed for the solid samples of Mn²⁺, Pd²⁺, Ag⁺ B₂, B₅, B₆ and A₂, A₅, A₆ to confirm the crystal structure of these complexes. The XRD patterns of the created complexes were approved in order to provide insight about the lattice parameters of the prepared complexes.

Figs. 5a–5c represents XRD patterns for complexes Mn²⁺, Pd²⁺, Ag⁺. The observed peak sharpness in the diffraction pattern indicates that Mn²⁺, Pd²⁺, Ag⁺ complexes are in the nanometer range. The diameter of particles are found in nanorange as fellow: Mn²⁺, 3–130 nm; Pd²⁺, 3–172 nm; Ag⁺, 3–151 nm. The nanoparticles size of complexes may serve strongly in different application fields in between the biological one (Uarikumaran and Appukuttan, 2012). The X-ray diffraction patterns of uniradiated and irradiated complexes demonstrate that:

1. The characteristics of the material is developed

2. Dislocation of longer interplanar spacing.

3. New peaks appeared

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Fig. 5a

XRD spectra of Mn(II) complexes before and after irradiation (B₂ and A₂).

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Fig. 5b

XRD spectra of Pd(II) complexes before and after irradiation (B₅ and A₅).

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Fig. 5c

XRD spectra of Ag(I) complexes before and after irradiation (B₆ and A₆).

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As shown in Figs. 5a–5c, complexes of Mn²⁺, Pd²⁺, Ag²⁺ showed new peaks and some of them displaced to longer interplanar spacings. After irradiation, the position of atoms in the lattice changes and consequently, the scattering power also changed, leading to changes in intensity which exhibited a high intensity (Jayashri et al., 2014). It is noted that the effect of γ-irradiation caused a noticeable transform in the intensity of the peaks. In fact, the intensity of the peaks of irradiated is sharper than unirradiated.

3.4 Thermal studies (TGA/DTG)

The thermal behavior of the B and its previously synthesized B₁–B₇ complexes and A₁–A₇ are listed in Table 3 and Figs. 6a–6d. The thermal behaviors of the ligands and their complexes B₁–B₇ and A₁–A₇ were investigated by thermogravimetric studies in temperature range 25–800 °C. The character of anticipated chemical change with temperature and percent of metal oxide achieved is summarized in Table 3.

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Fig. 6a

TGA/DTG curves of ligand before and after irradiation (B and A).

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Fig. 6b

TGA/DTG curves of unirradiated (B₃) and irradiated (A₃).

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Fig. 6c

TGA/DTG curves of unirradiated (B₅) and irradiated (A₅).

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Fig. 6d

TGA/DTG curves of unirradiated (B₇) and irradiated (A₇).

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The TG curve of B and A (Fig. 6a) showed a thermal stability till 150 °C and also showed two decomposition steps in the temperature range 150–633 °C; 155–680 °C with total weight loss of calc 99.9% (Found 100%); calc100% (Found 100%) before and after γ-irradiation, respectively. After γ-irradiation, the thermogravimetric analyses curves of the ligand revealed that γ-irradiation persuaded thermal stability to the substance than that of unirradiated. These results coincide well with the structure of the ligand resolute from elemental analysis and IR spectrum.

The TG curve of VO²⁺complexes B₁ and A₁ (Table 3) exhibited a gradual decomposition at a temperature range 195–570 °C, leaving VO as ending remainder at 570 °C. The TG curve after γ-irradiation is similar to that of before irradiation

TGA curve for B₂ and A₂ exhibited three degradation stages before and after γ-irradiation (Fig. 6b). TG curves of B₂ exhibited weight loss in the temperature range 30–100 °C (Calc./Found % 4.2/4.9 that was allocated to loss of two molecules of water. The TG curve showed gradual decomposition at a temperature range 279–490 °C, leaving MnO as final remainder at 798 °C. The TG curve after γ-irradiation is similar to that of before irradiation

As shown in Fig. 6c, TGA curve of Zn²⁺ complexes B₃ and A₃ illustrated the first stage at temperature range 233–719 °C and second stage ended with leaving ZnO as final residue at 798 °C. The TG curve after irradiation of complex A₃ reveals no change as compared to B₃ before irradiation.

The TG curve of Ru³⁺complexes exhibited two degradation stages before and after γ-irradiation (Table 3). For B₄, the first stage starts at temperature range 150–389 °C and the second stage ended with leaving RuO₂ as final residue at 688 °C. For A₄, the TG curve showed a gradual decomposition at a temperature range 180–493 °C, leaving Ru₂O₃ as ending remains at 680 °C.

Pd²⁺ complexes B₅ and A₅ demonstrated weight loss in the temperature range 30–196 °C (Calc./Found % 4.3/4.9) that was assigned to loss of half ethanol molecule. The TG curve revealed gradual decomposition at a temperature range 196–383 °C, leaving PdO as final residue at 561 °C. But in case of A₅, the TG curve of demonstrated weight loss in the temperature range 30–200 °C (Calc./Found% 4.3/4.9) that was assigned to loss of half molecule of ethanol (Figs. 6a–6d). The TG curve displayed steady rotting at a temperature range 200–332 °C, leaving Pd as final remainder at 699 °C.

The TG curve of Ag⁺ complexes before and after γ-irradiation B₆ and A₆ showed weight loss of (Calc./Found% 5.01/7.03) at temperature range 30–113 °C, that was assigned to loss of molecule of water and half molecule of ethanol (Table 3). On additional heating of B₆ and A₆ decomposed at 185–642 °C. The thermogram of complex illustrated one step of decomposition at 279 °C includes the completion of the decomposition process. The TG curve of A₆ after γ-irradiation is similar to that of B₆ before γ-irradiation.

Hg²⁺ complexes before and after γ-irradiation B₇ and A₇ displayed three degradation stages (Fig. 6d). The first stage of B₇ exhibited weight loss in the temperature range 30–100 °C (Calc./Found% 1.4/1.39) that was assigned to loss of half molecule of water. The second stage exhibited a gradual decomposition at a temperature range 255–615 °C. The final stage at 799 °C assigned to leave half molecule of HgO. After γ- irradiation, the TG curve of A₇ is similar to B₇ before γ-irradiation.

It is noted that the slightly higher value produced for the percentage of the remainder when relative to the theoretical value of pure metal oxide in B₁, A₁, B₂, A₂, B₃, A₃ and B₅ exhibited that the remains were impure with carbon. The character of the remains was accounted and recognized by infrared spectroscopy (Ahmed, 2006; Sanaa et al., 2015).

3.5 Molecular modeling

Molecular modeling was applied to investigate the three-‐dimensional arrangements of atoms in the chelates by employing semi‐empirical molecular orbital calculations at the PM3 level provided by the Hyperchem 8.03 program (HyperChem, 2007).

Several shots to develop suitable crystals for X-ray crystallography were ineffective. Using theoretical parameters helps to characterize the molecular structure of the investigated complexes. Thus, the geometries of the ligand, Mn²⁺, Pd²⁺ and Hg²⁺complexes were optimized by hyper chem. 8.03 Molecular Modeling and Analysis Program (Mohamed et al., 2015) using the molecular mechanics calculations (PM3). The calculated bond lengths and bond angles for the B, B₂, B₅ and B₇ complexes are listed in tables (S1–S4).

The energetic properties of these compounds are listed in Table 5. The optimized constructions of the ligand and B₂, B₅ and B₇ are shown in Figs. 7a, b and 8a, b. The main selected bond lengths demonstrated in Table 4 elicited the following:

• The obtained bond lengths of the N—N and C—OH groups for the ligand were 1.4320 and 1.2198 Å, respectively. The bond lengths of these groups appeared within the range 1.3246–1.5418 and 1.2056–1.3351 Å in the complexes which confirmed the coordination of these groups to the metal ions. The M—O bond length is found to be shorter than the M—N bond length, except for Pd complex.

• The values of bond angle confirmed the octahedral geometry for B₂ and square planer for B₅ and B₇ complexes (Mohamed et al., 2015). The compound with higher HOMO energy implies that the molecule is a superior electron donor.

• The lower HOMO energy values illustrate that molecule donating electron aptitude is the weaker. On contrary, the LUMO energy presents the ability of a molecule receiving electron (Yousef et al., 2012; Seda et al., 2009). The energies of the HOMO and LUMO are negative which showed that the compounds under investigation were stable.

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Fig. 7a

Optimized molecular structure of ligand (B).

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Fig. 7b

Optimized molecular structure Mn complex (B₂).

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Fig. 8a

Optimized molecular structure of Pdomplex (B₅).

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Fig. 8b

Optimized molecular structure of Hg complex (B₇).

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3.6 Antibacterial activity

The synthesized ligand and its metal complexes before and after γ-irradiation were tested for their potential antibacterial activities (Tweedy, 1964). Results in Tables 6 and 7 and Figs. 9 and 10 illustrated antibacterial activities against the experienced bacteria. It was established that antibacterial activities of the artificial compounds before and after γ-irradiation were proportionally increased with concentration. The tested compounds before and after γ-irradiation are found to have remarkable biological activities. The results indicated that Ru³⁺complexes exhibited a potent antibacterial activity. The antibacterial activities of the experienced ligand and complexes against E. coli were found to follow the order: Ru³⁺ > Pd²⁺ > Ag⁺ > Zn²⁺ > VO²⁺ > Hg²⁺ > Mn²⁺ > H₂L for 1 µg before γ-irradiation. While, antibacterial activities of 5 μg/ml, 7 μg/ml and 10 μg/ml followed the order Ru³⁺ > Hg²⁺ > Pd²⁺ > H₂L > VO²⁺ > Mn²⁺ > Zn²⁺ > Ag⁺ before γ-irradiation. Alternatively, antibacterial activity was evidenced when using the compound and metal complexes with S. pyogenes followed the order: Ag⁺ > H₂L > Hg²⁺ > Zn²⁺ > Pd²⁺ > Ru³⁺ > Mn²⁺ > VO²⁺ with 1 μg/ml concentration (Hanaa et al., 2016). While, antibacterial activities of 5 μg/ml, 7 μg/ml and 10 μg/ml concentrations of compounds was in the following order: Hg(II) > Ru³⁺ > Ag⁺ > H₂L > Mn²⁺ > Zn²⁺ > Pd²⁺ > VO²⁺ (Mehmet et al., 2010). The complexes formation could make the penetration across the cell membrane of E. coli easier and can be elucidated by Tweedy’s chelation theory (Tweedy, 1964). Chelation could improve the lipophilic character of the central metal atom which in rotate, which improved its penetration through the lipoid layer of the membrane thus causing the metal complex to cross the bacterial membrane more successfully thus increasing the activity of the complexes. In addition, many other reasons for instance solubility, dipole moment, conductivity influenced by metal ion may be probable causes for amazing antibacterial activities of these complexes (Chohan et al., 2006). Exposure to γ-irradiation remarkably enhanced the antibacterial activity for both the ligand and its complexes when it was used in case of E. coli. The activity also increased after irradiation in case of S. pyogenes. This may be attributed to the different nature of the cell wall for both microbes which may be correlated with the above factors (Mehmet et al., 2010). Additionally, exposure to γ-irradiation increased the antibacterial activity of both the free a cyclic ligand and their complexes when used with both concentrations (1 μg/ml, 5 μg/ml, 7 μg/ml and 10 μg/ml) in case of the Gram positive S. pyogenes bacterium. It was also observed that some moieties for instance N(2)H linkage introduced into such compounds exhibits widespread biological that may be accountable for raise in hydrophobic nature and lipo-solubility of the molecules in crossing the cell membrane of the bacteria and augment biological consumption ratio and activity of complexes activity (Har et al., 2016; Huang et al., 2018, 2019; Zhenzhen et al., 2017). It is concluded that these compounds have antibacterial activities and can be used in the future as therapeutic drugs for bacterial diseases.

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Fig. 9

Antibacterial activity for the ligand and its metal complexes before and after irradiation against S. pyogenes.

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Fig. 10

Antibacterial activity for the ligand and its metal complexes before and after irradiation against E. coli.

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