3.1. Elemental analysis and molar conductance
The analytical and physical data of the prepared ligand and metal complexes are collected in Table (1). The chemical composition and stoichiometry of the prepared metal complexes were confirmed by the results of elemental analysis. The obtained data showed satisfactory agreement with the proposed molecular formulae. These data also indicated that the metal complexes have 1:1 (metal: ligand) stoichiometry.
The complexes are found to be air stable for a long time, insoluble in different organic solvents such as (ethanol, methanol, carbon tetrachloride, chloroform, dichloromethane and acetone) but soluble to great extent in DMF and DMSO. Conductivity measurements in non-aqueous solution have frequently been used in structural studies of the prepared metal complexes within the limits of their solubility. The molar conductance values of 10− 3 M solution of the complexes in DMF are listed in Table (1) show that copper complexes(B1 and B2) are non-electrolytes in nature [17]. However, complexes (B3, B4) show molar conductivity values of 72 and 65 ohm− 1 cm2 mol− 1 indicating 1:2 and 1:1 electrolytic nature in DMF(10− 3 mol L− 1) solution, respectively [18].
Table 1
Elemental analyses and physical properties of ligand (H2LB) and its metal complexes.
No.
|
Molecular formula
|
(Emperical formulae)
|
M.wt.
|
Colour
(Yield %)
|
|
C
|
H
|
N
|
M
|
Λm
|
|
H2LB
|
(C16H18N4OS)
|
314
|
Buff
75
|
61.1
(61.3)
|
5.73
(5.70)
|
17.8
(17.9)
|
-
|
-
|
B1
|
Cu(H2L)I
|
(C16H18N4OSICu)
|
504.5
|
Green
78
|
38.1
(38.4)
|
3.6
(4.2)
|
11.1
(11.4)
|
12.6
(12.3)
|
25
|
B2
|
Cu(H2L)2(ClO4)2
|
(C32H36N8O10S2Cl2 Cu)
|
889.5
|
Green
60
|
43.2
(43.8)
|
4.0
(3.78)
|
12.6
(12.9)
|
7.1
(7.6)
|
24
|
B3
|
[Zn (H2L)2(H2O)]SO4
|
(C32H38N8O7S2 Zn)
|
807.4
|
Yellow
65
|
47.5
(47.2)
|
4.7
(4.9)
|
13.8
(13.6)
|
8.1
(8.3)
|
72
|
B4
|
[Cd (H2L)Cl]Cl
|
(C16H18N4OSCl2Cd)
|
497.4
|
White
70
|
38.6
(39.2)
|
3.6
(4.3)
|
11.3
(11.5)
|
22.6
(23.0)
|
65
|
Ʌm = molar conductivity (ohm− 1 cm2 mol− 1) in 10− 3 M DMF solution |
3.2. Nuclear magnetic resonance spectroscopy
The 1H NMR is a helpful tool for the preparation of organic compounds in conjugation with other spectrometric information, nuclear magnetic resonance is a physical phenomenon based upon the magnetic properties of an atom's nucleus.. The most commonly used nuclei are hydrogenl and carbon13, although certain isotopes of many other elements nuclei can also be observed. Comparison of the proton nuclear magnetic resonance of 1-(p-(methylanilinocetyl-4-phenyl-thiosemicarbazide) ligand before and after γ- irradiation (H2LB and H2LA) recorded in DMSO-d6 solution is found in (Fig. 1). The 1H NMR spectrum of the ligand before γ - irradiation(H2LB) in DMSO-d6 exhibited a chemical shift (δ \ppm) = 2.5ppm for (DMSO) before and after γ- irradiation, the N(4)H signal appears with 9.44 ppm and the N(2)H signal appears with 9.51, 10.05 ppm indicating the involvement of these hydrogen through intra-molecular hydrogen bonding with the carbonyl oxygen, the peak of N(1)H appeared at 9.62 ppm for ligand after gamma irradiation .The singlet signal appears with 2.14, 3.9, 3.7 ppm attributed to the protons of methyl CH3, singlet signal appears with 3.7 ppm attributed to the protons of CH2, the multiplet signal appears with 5.85–7.1, 6.5–7.4 ppm attributed to the aryl protons. The intensity of the bands after irradiation are higher than before irradiation and some bands disappear upon irradiation [19, 20].Also 1H NMR spectra of [Zn(H2L)2 SO4] before and after γ-irradiation (B3,A3) displayed signals at 2.14(s, 6H, 2CH3), 3.76(s,4H,2CH2), 5.59(s,2H,2NH), 6.32–7.43(m, 18H, Ar-H), 9.55(s,1H, NH) and10.51(s, H, NH) as shown in (Fig. 2) and. While [Cd(H2L)Cl2] before and after γ-irradiation (B4, A4) complexes displayed signals at 2.16(s, H, CH3), 3.77(s,2H,2CH2), 5.56(s, H, NH), 6.51–7.52(m, 9H, Ar-H), 9.44 (s,1H, NH), 9.61 (s,1H, NH) and 10.05(s, H, NH) as shown in Fig. 3.
The effect of γ-irradiation on the chemical shift of [Zn(H2L)2]SO4 and [Cd(H2L)Cl]Cl after γ-irradiation are similar to before irradiation.
3.3. Mass spectroscopy
Mass spectral data confirm the structure of the ligand as indicated by the molecular ion peak (M+) corresponding to their molecular weight. MS of H2LB (Fig. 4) confirms the proposed formula, the observed peak at m/z = 313amu (M) corresponding to the ligand moiety (C16H18N4OS, atomic mass m/z = 314 molecular ion peak). The spectrum also shows important fragment ions in the range m/z = 51 for [C4H4-H]+, 77 for [C6H5]+, 107 for [C7H8N]+ base peak, 120 for [C7H6NO]+, 135 for [C8H7S]+, 280 for[C14H13N3SO-H]+ and 313 for[C16H18N4SO-H]+may be assigned to different fragments.
Also the spectrum of complex (B3) confirms the proposed formula by showing a molecular ion peak at m/z 807.4 amu corresponding to [Zn(H2L)2(H2O)SO4] (B3) (Fig. 5) which coincide with its formula weight (calculated m/z = 807.4 amu). The other fragments of the complex give the peak with various intensities at different m/z values like at Calc/Found: 77 [C6H5], 91 [C6H4NH], 120[C9H8NH], 255 [C13H13N5O], 535[C24H24N8O2], 715[C30H29N8O4S2], 783[C30H38N8O7S2Zn], 807.4/806 [C32H38N8O7S2 Zn].
3. 4. Ft-ir Spectra
3.4.1. FT- IR spectra of the ligand before and after γ-irradiation
The comparison between the functional groups of the ligand before and after irradiation (H2LB and H2LA) the infrared spectra are presented in Fig. 6 and Table 2. It has been found that the functional groups of the ligand before γ-irradiation and after presented at 3384,3336 cm− 1; 3263,3185cm− 1; 3150,3126cm− 1; 1672,1689 cm− 1 and 749,750 cm− 1 are attributed to the stretching frequencies of υ(N4-H), υ(N2-H) and υ(N1-H), υ(C = O) and υ(C = S) respectively. After γ-irradiation the bands corresponding to υ(C = O) shift to higher frequencies or slightly shift as compared with before γ-irradiation [21]. After γ-irradiation the intensity of the peaks are more sharper than before γ-irradiation.
Table 2
Infrared spectral bands (cm− 1) for ligand and its metal complexes before and after irradiation
No
|
Compound
|
υ (OH)/
υ (N4-H)
|
υ (N2-H)
|
υ (N1-H)
|
υ (C = O)
|
υ (C = S)
|
υ (M-O)
|
υ (M-N)
|
|
H2LB
|
3384
|
3263
|
3150
|
1672
|
749
|
-
|
-
|
|
H2LA
|
3336
|
3185
|
3126
|
1689
|
750
|
|
|
B1
|
Cu(H2L)I
|
3431
|
3293
|
3183
3150
|
1597
|
749
|
603
|
529
|
A1
|
Cu(H2L)I
|
3434
|
3295
|
3185
3151
|
1597
|
750
|
602
|
529
|
B2
|
Cu(H2L)2 (ClO4)2
|
3437
|
3295
3206
|
3153
3122
|
1595
|
754
|
614
|
545
|
A2
|
Cu(H2L)2(ClO4)2
|
3433
|
3297
3209
|
3154
|
1595
|
756
|
612
|
539
|
B3
|
[Zn (H2L)2(H2O)]SO4
|
3420
|
-
|
3170
|
1593
|
754
|
614
|
512
|
A3
|
[Zn (H2L)2(H2O)]SO4
|
3420
3277
|
-
|
3138
3164
|
1619
1593
|
755
|
618
|
512
|
B4
|
[Cd(H2L) Cl] Cl
|
3426
|
3268
|
3179
|
1685
1613
|
744
|
591
|
533
|
A4
|
[Cd(H2L)Cl] Cl
|
3433
|
3269
|
3179
|
1685
1617
|
744
|
591
|
532
|
Where: B = before γ-irradiation, A = after γ-irradiation |
3.4.2. FT-IR spectra of copper complexes before and after γ-irradiation
The FT-IR spectra of the Cu(I, II) complexes before and after γ-irradiation (B1, B2 and A1, A2) show significant changes compared to the spectrum of the free ligand (Figs. 7 and 8 ). The most important diagnostic spectral bands are summarized in Table 2. The IR spectra of copper complexes (B1, B2 and A1, A2) show strong bands at 3431; 3437; 3293; 3295; 1597; 1595 and 749; 754 cm− 1 for before irradiation, also at 3434; 3433; 3295; 3297; 1597; 1595 and 750;756 cm− 1 for after irradiation which assigned to the stretching frequencies of υ(N4-H), υ(N2-H), υ(C = O) and υ(C = S). The bands corresponding to υ(N4-H), υ(N2-H), υ(C = O) and υ(C = S) appear at the same frequency or slightly shift to higher frequency after gamma irradiation. The IR spectra of Cu complexes before irradiation show that υ(C = O) and υ(N2-H) shift to lower frequency upon complexation as compared of free ligand, indicating that coordination of the ligand in keto-form and the ligand behaves as neutral bidentate or tetradentate, coordination take place via (C = O) and N(2)H.
The IR spectra of Cu(I, II) complexes before and after γ- irradiation display new bands at 603, 614 and 529,545 cm− 1 assigned to υ(Cu-O) and υ(Cu-N) respectively [22, 23]. IR spectra of the complexes (A1 and A2) showed that the intensity of the IR bands became more intense than before γ- irradiation [24].
3.4.3. IR spectra of Zinc(II) complexes before and after γ-irradiation
The IR spectra of Zn(II) complexes (Fig. 9) show strong bands at 3420,3170, 3164, 1593, 1619 and 754,755 cm− 1 before irradiation and after γ-irradiation which attributed to the stretching frequencies of υ(N4-H) υ(N1-H), υ(N2-H), υ(C = O) and υ(C = S)wagging vibrations, respectively. The IR spectra of Zn(II) complex before and after γ- irradiation it is seen that the band corresponding to υ(C = O) was shifted to lower frequency upon complexation and the ligand behave as neutral tetradentate and coordination take place via two (C = O) and two (N2-H), the band corresponding to υ(N4-H) appears at the same frequency for before γ- irradiation and after γ-irradiation, high intensity of the bands of function groups after γ-irradiation. The new bands appeared at 614,618 and 512 cm− 1 are assigned to υ(Zn-O) and υ(Zn-N), respectively [25].
3.4.4. FT-IR spectra of Cd(II) complexes before and after γ-irradiation
The FT-IR spectra of Cd(II) complexes (Fig. 10) show strong bands at 3426, 3433; 3268, 3269; 3179; 1685 and 744 cm− 1 before irradiation and after γ-irradiation which attributed to the stretching frequencies of υ(N4-H) υ(N2-H), υ(N1-H) and υ(C = S)wagging vibrations, respectively. The IR spectra of Cd(II) complexes before and after γ- irradiation showed that the band corresponding to υ(C = O) is shifted to higher frequency upon complex formation and the ligand behave as neutral tridentate and coordination take place via (C = O), (N2-H) and (C = S), the band corresponding to υ(N4-H) shifts to higher frequency after γ-irradiation, high intensity of the bands of function groups after γ-irradiation. The new bands appeared at 591and 533, 532 cm− 1 assigned to υ(Cd-O) and υ(Cd-N) respectively [26].
3.5. UV- Vis spectra and magnetic moment properties
The electronic spectral bands of the ligand (H2LB) and Cu(I, II), Zn(II) and Cd(II) complexes in DMF solution within the range 200–800 nm are tabulated in Table 3 and depicted in Figs. (11–14). The electronic spectrum of the ligand exhibits bands at 314, 292 and 279 nm, respectively.
3.5.1. The electronic absorption spectra of copper complexes before and after γ- irradiation.
The electronic spectra of Cu(I) complexes before and after irradiation (B1 and A1) display bands at 300 and 409 nm, respectively. Cu(I) ions have the d10 configuration and therefor the Cu(I) complexes should not exhibit any d-d transition and have tetrahedral geometry [27].
While the electronic absorption spectra of Cu(II) (B2 and A2) before and after irradiation exhibited bands at 308, 398 and 653 nm in DMF refer to L→M charge transfer and d→d transitions, respectively in octahedral geometry [28]. Diamagnetic behavior of complex (B1) and the magnetic suitability value of complex (B2) is 1.78 B.M., which is an indicative of tetrahedral and octahedral geometry [27, 29].
3.5.2. Zinc(II) complexes before and after γ-irradiation
The electronic absorption spectra of Zn(II) complexes before and after γ-irradiation displayed bands at 300, 282; 448 and nm in DMF solution, octahedral structure of Zn(II) complex is suggested which is diamagnetic in nature [30].
4.5.3. Cadium(II) complexes before and after γ-irradiation
The electronic absorption spectra of Cd(II) complexes before and after γ-irradiation displayed three bands at 284,390, 610 nm ; 282,385and 608 nm in DMF solution attributed to charge transfer transition which assigned to tetrahedral geometry around Cd(II) ion [31, 32]. The Cd(II) complexes are diamagnetic because of d10 electronic configuration of Cd(II) ion [33].
Table (3). The electronic absorption spectral data in DMF solution of ligand and its magnetic moment and metal complexes before and after irradiation value
No
|
Compound
|
Assignment
|
DMF
|
µeff (B.M.)
|
Geometry
|
|
H2LB
|
314, 292, 279
|
-
|
L
|
B1
|
Cu(H2L)I
|
300
409
|
Dia
|
Tetrahedral
|
A1
|
Cu(H2L)I
|
300
408
|
Dia
|
Tetrahedral
|
B2
|
Cu(H2L)2(ClO4)2
|
653
398
308
|
1.74
|
Octahedral
|
A2
|
Cu(H2L)2(ClO4)2
|
653
398
308
|
-
|
Octahedral
|
B3
|
[Zn (H2L)2(H2O)]SO4
|
448
300
|
Dia
|
Octahedral
|
A3
|
[Zn (H2L)2(H2O)]SO4
|
445
282
|
Dia.
|
Octahedral
|
B4
|
[Cd (H2L)Cl]Cl
|
610
390
284
|
Dia.
|
Tetrahedral
|
A4
|
[Cd (H2L)Cl]Cl
|
608
385
282
|
Dia.
|
Tetrahedral
|
3.6. X-ray diffraction patterns
XRD analysis was performed to confirm the crystal phase of compound. Samples B1-B3 and A2,A3 (was just before and after the irradiation as shown in Figs. 15–17 and Table (4). The XRD patterns of the synthesized compounds were carried out in order to give an insight about the lattice dynamics of the compounds. The X-ray diffraction were recorded by using (CuKα) radiation (1.5406 Å). The intensity were collected over a 2h range of 5–90o. The average grain size of the samples was estimated using the diffraction intensity peak. The pattern found reflects a tracker on the fact that each solid describes a definite compound of a definite construction which is not contaminated with initial materials. This identification of the complexes was done by a known method [34].The mean grain size (D) of the particles was determined from the XRD line broadening measurement using the Scherrer equation: D = 0.89λ/β (Cosθ)
An observable peak sharpness in the diffraction pattern indicates that the Cu(I, II) and Zn(II) complexes before and after irradiation (Figs. 15–17 and Table (4) are in the nanometer range. The diameter of particles are found in nanorange scale as follows: Cu(I) complex before (B1) 4.83nm; Cu(II)complexes before and after irradiation(B2 and A2) 3.6, 5.79 nm; Zn(II) complexes before and after irradiation (B3 and A3) 5.97, 3.84 nm. The nanoparticles sized complexes may serve strongly in different application fields in between the biological one [35].
Figures (15–17) show that Cu(I,II), Zn(II) complexes new peaks appear and some peaks displaced to longer interplanar spacings. The major factors tending to influence the intensity of powder patterns are structure factor, polarization factor, atomic scattering factor, multiplicities and preferred orientations. Upon irradiation, the position of atoms in the lattice changes and consequently, the scattering power also changes, leading to changes in intensity which display high resistance [36]. It should be noted that the Zn(II) complex (A3) after irradiation increases the crystalline size than B3 before irradiation.
Table 4. XRD data of Cu(I, II) , Zn(II) complexes before (B1, B2, B3) and after irradiation(A2,A3)
3.7. Thermal behavior of ligand and metal complexes before and after γ-irradiation
The thermal behavior of the ligand and Cu(I, II), Zn(II) and Cd(II) complexes before and after γ-irradiation was investigated by thermogravimetric technique in temperature range 25–800°C. The thermal behavior data of the ligand and Cu(I,II), Zn(II) and Cd(II) complexes (B1, B2, B3, B4 and A1 ,A2, A3, A4) before and after γ-irradiation are tabulated in Table 5 and depicted in Figs. (18–20).
3.7.1. The ligand before and after γ –irradiation
The TG curves of the ligand before and after γ-irradiation show that it is thermally stable till 140°C,125°C, respectively. Also the TG curves show three decomposition steps in the temperature range 140–550 oC ;125–510°C with total weight loss of Calc.100% (Found 100%) before and after γ-irradiation, respectively.
3.7.2. Copper Complexes
The TG thermograms of copper complexes (B1 and A1) display three steps of decomposition as shown in Table 5 and Fig. (18). The first step of decomposition appeared within the temperature range 134–255 and 147–293 ºC with mass loss of 21% (calc. 21.2%) and 28.7% (calc. 28.3%) for complex (B1) and complex (A1), respectively, corresponding to loss of (CH3C6H5NH) and (HI + NH). The second step appeared at 258–410 and 294–385°C with mass loss of 19.0% (calc. 18.2%) and 11.0% (calc. 10.1%) for complexes (B1 and A1), respectively, corresponding to further decompositions of organic ligand. The third TG decomposition step appeared within the temperature ranges 410–753°C and 385–701°C with mass loss of 36.0% (calc. 36.5%) and 35.0% (calc.34.1%), respectively, corresponding to complete decomposition of the organic ligand. The final remained product appeared above 735°C with remain mass of 24.0% (calc. 22.9%) for complex (B1) and above 701 ºC with mass remain of 25.3% (calc. 25.3%) for complex(A1) represent the formation of (CuO + 3C) and (CuO + 4C) as a final product [37].
The TGA curve of copper complexes (B2 and A2) display successive steps of decomposition as shown in Table 5 and Fig.(S1). The decomposition starts within the temperature range 420–620 and 440–790°C with mass loss of 82.0% (calc. 83%) and 84.4% (calc. 84.6%) for complex (B2) and complex (A2), respectively. The final thermoproduct appeared at 620°C with mass loss 18.0% (calc. 17%) for complex (B2) and at 790 ºC with mass loss 15.6% (calc. 15.7%) for complex(A2) represents the formation of (CuO + 7C) and (CuO + 6 C) as a final product [37].
3.7.3. Zinc (II) Complex
The TG thermograms of Zn(II) complexes (B3,A3) showed several steps of decomposition. The first step of decomposition appeared at 180–332 and 170–354°C with mass loss 39% (calc. 39.3%) and 50% (calc. 50.3%) for complexes B3 and A3 which corresponded to decomposition of organic ligand. The second step of decomposition appeared at 332–749 and 354–705°C with mass loss 39% (calc. 38.8%) and 50% (Calc.50 %) ), respectively, for complexes (B3,A3) which attributed to complete decomposition of organic ligand. The remaining weigh for complex (B3) appeared above 704°C and above 660°C with mass remain of 22.1% (calc. 21%) and 21% (calc. 21.7%)corresponding to the formation of ZnO as final products in addition to 7C residue [37].
3.7.4. Cadmium (II) Complexes
The TG thermograms of Cd(II) complexes (B4, A4) display successive decomposition steps within the temperature range 134–789 and 139–718°C with mass loss 88.2% (calc. 88.5%), respectively for complexes (B4, A4), are assigned to the material decomposition. The final weight residue appeared at above 789 and 718°C corresponded to Cd and CdO for complexes (B4,A4) as thermo finial products in addition to carbon residue for complex (A4) [38].
Table 5
Thermal analysis data of ligand and Cu(I, II), Zn(II) and Cd(II) complexes before and after irradiaton
No.
|
Molecular formulae
|
Temp. range (°C)
DTG
|
Temp. range (°C)
|
Mass loss %
|
Assignment
|
TGA
|
Found
|
Calc.
|
|
H2LB
|
180,500
|
140
140–550
|
-
100
|
-
100
|
Melting Decomposition
|
|
H2LA
|
180,550
|
125
125–510
|
-
100
|
-
100
|
Melting Decomposition
|
B1
|
Cu(H2L)I
|
206
313
639
|
134–255
255–410
410–753
|
21
19.0
36.0
24
|
21.2
18.2
36.5
22.9
|
Loss of CH3C6H5NH
Further Decomposition
Completion of decomposition of organic ligand
CuO + 3C
|
A1
|
Cu(H2L)I
|
287
314
602
|
147–293
294–385
385–701
|
28.7
11
35
25.3
|
28.3
10.1
34.1
25.3
|
Loss of CH3C6H5NH + HI + NH
Further Decomposition
Complete Decomposition
of organic ligand
CuO + 4C
|
B2
|
Cu(H2L)2(ClO4)2
|
547, 637, 685
|
420–620
at 620
|
82
18
|
83
17
|
Decomposition
CuO + 7C as final product
|
A2
|
Cu(H2L)2(ClO4)2
|
429
|
440–790
at 790
|
84.4
15.6
|
84.3
15.7
|
Decomposition
CuO + 6C as final product
|
B3
|
Zn(H2L)2(H2O)SO4
|
216
384
646
|
180–332
332–499
499–704
|
39
39
22
|
39.3
38.8
21
|
decomposition
Complete decomposition of the organic ligand
ZnO2 + 7C
|
A3
|
Zn(H2L)2(H2O)SO4
|
220
599
|
170–374
374–660
At 660
|
50
29
21
|
50.3
28
21.7
|
Decomposition
Complete decomposition of the organic ligand
ZnO2 + 7C
|
B4
|
Cd(H2L)Cl2
|
186
257
335
701
|
134–789
At 789
|
88.2
11.8
|
88.4
11.6
|
decomposition
Complete decomposition of the organic ligand
Cd
|
A4
|
Cd(H2L)Cl2
|
186
331
644
|
139–718
at 718
|
82.7
17.3
|
82.3
46.6
17.7
|
decomposition
Complete decomposition proccess
CdO + 2C
|
From all of the above, the suggested chemical structure of metal complexes are shown in Scheme 1
3.8. Structure characterization with DFT study
The geometric structures of H2LB ligand and its metal complexes were optimized as shown in (Fig. 21). Upon coordination of H2LB to the metal atom, some bond lengths become slightly longer than in the free ligand accompanied with changes in angles that were clarified in Table 6 as (C5-O8), (N4-C5), (N7-C6) and (N3-C2). This finding is due to the formation of M-N & M-O bonds in all complexes that make the C-O (S. S. Hassan, 2017, S. S. Hassan, 2018) and C‐N bonds weaker (Safaa S. Hassan, 2020). It was observed from the energy values that the stability of ligand increases upon complexation with Zn (II) and Cu(II) ions in ratio (1 to 2) metal to ligand. The ionic complexes (Cd(II) & and Cu(I)) show higher energy values than the parent ligand. The polarity of ligand increased after complexation by its coordination to metal ions as it is evident from the magnitude of their dipole moments. The ionic complexes have higher polarity than the non-electrolytic complexes. The molecular properties are mentioned in Table 6 which can be calculated as follows: Hardness η = (I-A)/2, Softness (S) S = 1/ 2η, Chemical potential (µ), µ = -(I + A)/2 and Electronegativity (χ), χ = (I + A)/2η. From HOMO-LUMO gap (ΔE), one can detect whether the molecule is hard or soft. Larger ΔE corresponding to harder molecule and small one related to the softer molecule. The polarizability of the soft molecule is more than the hard one because it needs lower energy to excitation, thus softness (S) and hardness (η) are properties of molecule that measures the chemical reactivity. We found the ligand and Cu(I) complex were more harder than the remaining complexes. The generated molecular orbital energy diagrams HOMO and LUMO are presented in (Fig. 22).
The formal charge of cadmium, zinc and copper were Cd2+, Zn2+, Cu2+, Cu+ but the calculated charges on [Cd (H2L)Cl]Cl, Cu(H2L)2(ClO4)2, Cu(H2L)I and Zn(H2L)2(H2O) SO4were 0.856, 0.579, 0.413 and 0.884, respectively. It can be explained due to the charge transfer from the examined ligand to the central metal ions i.e. L→M. So, the theoretical calculations confirm the results that obtained from the analysis tools which were discussed in the previous characterization part.
Table 6
Ground state properties of H2L ligand using B3LYP/6-31G(++)d,p and its metal complexes using B3LYP/LANL2DZ
Parameter
|
H2LB
|
[Cu(H2L)I]
|
[Cu(H2L)2(ClO4)2]
|
[[Zn (H2L)2(H2O)]SO4
|
[Cd(H2L)Cl]Cl
|
ET, Hartree
|
-1312.9304
|
-1135.3041
|
-2676.2810
|
-1991.3548
|
-986.9751
|
EHOMO, eV
|
-5.22
|
-6.06
|
-6.04
|
-2.52
|
-9.06
|
ELUMO, eV
|
-1.38
|
-3.88
|
-4.91
|
-1.72
|
-8.46
|
ΔE, eV
|
3.84
|
2.18
|
1.13
|
0.80
|
0.6
|
I=- E HOMO, eV
|
5.22
|
6.06
|
6.04
|
2.52
|
9.06
|
A= - E LUMO, eV
|
1.38
|
3.88
|
4.91
|
1.72
|
8.46
|
χ, eV
|
3.30
|
4.97
|
5.47
|
2.12
|
8.76
|
η, eV
|
1.92
|
1.09
|
0.565
|
0.4
|
0.30
|
S, eV− 1
|
0.26
|
0.45
|
0.88
|
1.25
|
1.67
|
µ, eV
|
-3.30
|
-4.97
|
-5.47
|
-2.12
|
-8.76
|
Dipole Moment
|
3.2200
|
15.1634
|
3.2461
|
8.2389
|
15.7912
|
a E: the total energy (a.u.), b HOMO: highest occupied molecular orbital (eV) and c LUMO: lowest unoccupied molecular orbital (eV), ΔE = Elumo-EHomo |
Table 7
Some of the optimized bond lengths, Å and bond angles, degrees, for (H2L) and complexes using B3LYP/6-311G(++)d,p.
Bond length (Ao)
|
H2LB
|
[Cu(H2L)I]
|
[Cu(H2L)2(ClO4)2]
|
[Zn (H2L)2(H2O)]SO4
|
[Cd(H2L)Cl]Cl
|
R(M-Cl)
|
---
|
2.19937
|
---
|
---
|
2.37881
|
R(M-O8)
|
---
|
2.22007
|
1.93603
|
2.06440
|
2.36369
|
R(M-N3)
|
---
|
1.96135
|
2.65910
|
2.04013
|
1.94974
|
R(M-O-ClO3)
|
---
|
---
|
1.97195
|
---
|
3.04748
|
R(M-S1)
|
---
|
2.60876
|
---
|
2.37828
|
---
|
R(M-O-H2)
|
---
|
---
|
---
|
2.10239
|
---
|
R(C2-S1)
|
1.73273
|
1.80438
|
---
|
1.80719
|
1.46624
|
R(C5-O8)
|
1.25861
|
1.27510
|
1.27514
|
1.30843
|
1.45986
|
R(N4-C5)
|
1.35538
|
1.36229
|
1.34735
|
1.39788
|
1.32019
|
R(N3-C2)
|
1.36138
|
1.32646
|
1.46312
|
1.47620
|
1.35331
|
R(N7-C6)
|
1.44027
|
1.45935
|
1.45631
|
1.47188
|
1.45929
|
R(N9-C2)
|
1.37062
|
1.37303
|
1.34881
|
1.42723
|
1.36423
|
A(N3-M-Cl1)
|
---
|
175.483
|
---
|
---
|
68.909
|
A(Cl1-M-Cl2)
|
---
|
---
|
---
|
---
|
---
|
A(Cl1-M-O8)
|
---
|
108.139
|
---
|
---
|
118.508
|
A(O8-M-N3)
|
---
|
76.143
|
71.994
|
80.528
|
68.909
|
A(M-N3-N4)
|
---
|
118.525
|
98.360
|
103.377
|
118.280
|
A(M-O8-C2)
|
---
|
110.583
|
125.403
|
111.998
|
116.580
|
A(N3-M-O-ClO3)
|
---
|
---
|
98.448
|
---
|
---
|
A(O8-M- O-H2)
|
---
|
---
|
---
|
90.905
|
---
|
A(N3-M-S1)
|
---
|
66.774
|
---
|
81.522
|
---
|
3.9. Antibacterial Activity
The synthesized ligand and its metal complexes were separately exposed to gamma irradiation to test their improvement as active antibacterial drugs [39]. Results in Table (8), Figs. 23 and 24 showed antibacterial activity against the tested microbes. Generally, it was found that antibacterial activity of both the synthetic ligand and metal complexes before and after γ-irradiation was proportionally increased with increased concentration. The tested compounds before and after γ-irradiation are found to have remarkable biological activity. The results in Table (8) Figs. (23 and 24) indicate that in case of E.coli for 1µg/ml and 5µg\ml the corresponding Cu(II) and Zn(II) complexes showed much better antibacterial activity with respect to the individual ligand and complexes against the same microorganism under identical experimental conditions, the antibacterial activity of the tested compounds were found to follow the order: A2 > A3 > B1 > A1 > B3 >B2 >A4 >H2LA > H2LB > B4 for 1µg\ml before and after irradiation, Antibacterial activity of 5µg/ml concentration in case of E.coli follow the order A3 > B1 > A2 > B3 > A1 >H2LA >H2LB >A4 >B4 before and after irradiation. On the other hand, antibacterial activity was recorded when using the ligand and metal complexes with S.pyogenes follow the order: A3 > A2 > A1 > B3 > A4 >H2LA >H2LB >B4 >B2 >B1 for before and after irradiation with1µg/ml concentration [23]. Antibacterial activity of 5µg/ml concentration for both the free acyclic ligand and its complexes before and after irradiation followed the order: B2 = B3 > H2LA > A2 > A1 > A3 > H2LB >B1 when compounds were used with S. pyogenes [40]. Results suggested that in case of 1µg/ml and 5µg/ml Cu(II) and Zn(II) complexes have higher activity than other complexes The chelation could facilitate the ability to cross the cell membrane of E. coli and can be explained by Tweedy’s chelation theory. Chelation/complexation could enhance the lipophilic nature of the central metal atom which in turn, favors its permeation through the lipoid layer of the membrane thus causing the metal complex to cross the bacterial membrane more effectively thus increasing the activity of the complexes. Besides from this many other factors such as solubility, dipole moment, conductivity influenced by metal ion may be possible reasons for remarkable antibacterial activities of these complexes [41]. Exposure to gamma 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 other factors such as solubility, dipole moment, and conductivity influenced by metal ion. Additionally, exposure to gamma irradiation increased the antibacterial activity of both the free a cyclic ligand and their complexes when used with both concentrations (1µg/ml and 5µg/ml) in case of the Gram positive S. pyogenes bacterium. It also has been observed that some moieties such as N(2)H linkage introduced into such compounds exhibits extensive biological that may be responsible for increase in hydrophobic character and liposolubility of the molecules in crossing the cell membrane of the microorganism and enhance biological utilization ratio and activity of complexes activity [42]. The antibacterial studies of the prepared compounds screened against both Gram positive and Gram negative bacteria proved that these compounds exhibit remarkable antibacterial activity and can be used in the future as therapeutic drugs for pathogenic bacterial diseases.
Table 8
Antibacterial activity of ligand and their metal complexes
No.
|
Compound
|
Inhibition %
|
S. pyogenes
|
E.coli
|
1µg/ml
|
5µg/ml
|
1µg/ml
|
5µg/ml
|
|
H2LB
|
75.32
|
91.24
|
48.76
|
56.23
|
|
H2LA
|
74.40
|
95.32
|
52.11
|
66.76
|
B1
|
Cu(H2L)I
|
57.66
|
88.3
|
86.44
|
92.13
|
A1
|
Cu(H2L)I
|
88.41
|
94.31
|
82.8
|
86.50
|
B2
|
Cu(H2L)2(ClO4)2
|
64.5
|
96.16
|
70.55
|
54.92
|
A2
|
Cu(H2L)2(ClO4)2
|
90.34
|
94.82
|
97.63
|
89.34
|
B3
|
[Zn (H2L)2(H2O)]SO4
|
8.16
|
96.16
|
82.16
|
87.3
|
A3
|
[Zn (H2L)2(H2O)]SO4
|
91.42
|
93.23
|
92.6
|
96.83
|
B4
|
[Cd (H2L)Cl]Cl
|
48.23
|
58.31
|
43.66
|
32.8
|
A4
|
[Cd (H2L)Cl]Cl
|
74.42
|
65.03
|
56.63
|
46.43
|
The molecular docking
To understand the interaction of all the synthesized molecules with topoisomerase II DNA gyrase enzymes, the crystal structure of topoisomerase II was downloaded from Protein Data Bank (PDB ID: 2XCT) and the molecular docking studies were performed using the Moe program. The protein ligand interaction plays a significant role in structural based drug designing. The different types of interactions are mentioned in Table 9 and seen in Fig. 25. The preferred compounds Cd(II) Cu(II) and Zn(II) complexes had a scoring value of − 5.02, − 9.41 and − 10.87 ,respectively. The Zn(II) complex showed the highest binding affinity and interaction with topoisomerase II DNA gyrase enzymes (2XCT) by using most types of protein binding interactions. The binding affinity of our compounds achieved higher or the same values numerous previous works against the same type of protein [43, 44]. The molecular docking of our work supported that the chelates are more active than their parent ligand against the same microorganism as mentioned also in many of our previous works [45–48].
Table 9
Comparison of binding affinity of complexes against topoisomerase II DNA gyrase enzymes (PDB Code: 2XCT)
Antitumor docking 4jsv
|
Compound
|
Involved amino acids(scoring energy)
|
Type of interaction
|
H2LB
|
Lys-1270(-2.99)
|
Side chain donor
|
[Cu(H2L)I]
|
Asp-1114(-3.30)
|
Side chain acceptor
|
[Cu(H2L)2(ClO4)2]
|
Arg-1299 (-9.41)
|
Arene-cation interaction
|
[Zn(H2L)2]SO4
|
Glu-585, Pro-1080, Tyr-1150 and His-1081(-10.87)
|
Side chain acceptor, Backbone acceptor, Arene-arene and Arene-cation
|
[Cd(H2L)Cl]Cl
|
Ser1584(-5.02)
|
Solvent contact
|