Metal complexes of ferrocenyl-substituted Schiff base: Preparation, characterization, molecular structure, molecular docking studies, and biological investigation

Journal Pre-proof Metal complexes of ferrocenyl-substituted Schiff base: Preparation, characterization, molecular structure, molecular docking studies, and biological investigation Walaa H. Mahmoud, Reem G. Deghadi, Gehad G. Mohamed PII:

S0022-328X(20)30014-0

DOI:

https://doi.org/10.1016/j.jorganchem.2020.121113

Reference:

JOM 121113

To appear in:

Journal of Organometallic Chemistry

Received Date: 10 November 2019 Revised Date:

8 January 2020

Accepted Date: 9 January 2020

Please cite this article as: W.H. Mahmoud, R.G. Deghadi, G.G. Mohamed, Metal complexes of ferrocenyl-substituted Schiff base: Preparation, characterization, molecular structure, molecular docking studies, and biological investigation, Journal of Organometallic Chemistry (2020), doi: https:// doi.org/10.1016/j.jorganchem.2020.121113. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Metal Complexes of Ferrocenyl-Substituted Schiff Base: Preparation, Characterization, Molecular Structure, Molecular Docking Studies, and Biological Investigation Walaa H. Mahmouda,b, Reem G. Deghadia,* and Gehad G. Mohameda,b a

Chemistry Department, Faculty of Science, Cairo University, Giza, 12613, Egypt

b

Egypt Nanotechnology Center, Cairo University, El-Sheikh Zayed, 6th October City, Giza, 12588, Egypt

* Corresponding Author-Email: [email protected]

Abbreviations FT-IR UV-Vis 1 H-NMR SEM DFT HOMO LUMO MCF-7 IC50 O.D. MOE EI-MS MEP TG DTG DMSO DMF

Fourier-transform infrared spectroscopy Ultraviolet–visible spectroscopy Proton nuclear magnetic resonance Scanning electron microscope Density function theory Highest occupied molecular orbital Lowest unoccupied molecular orbital Michigan cancer foundation-7 Half-maximal inhibitory concentration Optical density Molecular operating environment Electrospray ionization Mass Spectrometry Molecular electrostatic potential Thermo gravimetric analysis Differential thermogravimetric analysis Dimethyl sulfoxide N,N-dimethylformamide

Abstract The organometallic Schiff base ligand (L) was synthesized by reacting 2-acetylferrocene with 1,8-naphthalenediamine in 1:1 molar ratio. The reaction of Schiff base with some transition metal ions mains to mono-species of chelates. The ligand and its metal complexes were characterized using elemental analysis (C, H, N and M), molar conductivity, FT-IR, UV-Vis, 1HNMR, SEM and mass spectrometry. Also, their TG and DTG studies were investigated. All complexes had an octahedral geometry. From the spectral analyses data, the Schiff base ligand acted as NN-bidentate ligand. In addition, computational studies of the ligand (L) have been carried out by using the DFT method. From the optimized structure, the energy gap, HOMO, LUMO energy values, electronegativity and electrophilic index were calculated. The antibacterial and antifungal activities of the synthesized complexes have been screened in vitro against different bacteria and fungi species. The effect of these complexes on the proliferation of human breast cancer (MCF-7) cell line was studied and then compared with the parent free organometallic Schiff base. It was found that [Fe(L)(H2O)2Cl2]Cl.3H2O complex showed the lowest IC50 value (11.3 µM). Docking studies were used to investigate the interaction between ferrocene, Schiff base and its metal complexes with the active site of the 3HB5 receptor.

Key words: 2-acetylferrocene; Schiff base; DFT; antibacterial activities; MCF-7; Docking. 1. Introduction Cyclometalated complexes of a large variety of ligands that contain N, S or O as the heteroatom, have been widely investigated. The cyclometallated compounds containing a metal-carbon bond that stabilized by the intramolecular coordination of one or two neutral atoms are well known. These π-donor ligands and their metal complexes have great interest because of their important applications in many areas including homogeneous catalysis, design of new metallomesogens, organic synthesis, antitumoral medicines and resolution of racemic ligands [1]. The synthesis of half-sandwich metal-containing compounds is being investigated due to their crucial effect in the radiopharmaceutical industry. Some of these compounds are made from cyclopentadiene that attached to a targeting biomolecule such as a small molecule or a tumorspecific peptide that binds to a central nervous system receptor [2, 3]. The bio-organometallic chemistry is a new field that gaining a lot of research interest where cyclopentadiene ligated transition metal compounds give a link between organometallic chemistry with molecular biotechnology, biology and medicine [4]. Scientists utilized organometallic compounds that can be used in treating breast cancer, which is the most common cancer among women, affecting about one in eight females [5]. Many of metal-containing compounds can be used as good reducing

agents. For example, ferrocene, this is readily oxidized by hydroxyl radicals to stable ferrocenium. These hydroxyl radicals (•OH) are reduced to (–OH). This redox reaction can help in removing these deleterious compounds. This fact proposes that the ferrocene group may be useful in the therapeutic center if its pharmacokinetic response, solubility and distribution in the body could be suitably tailored [6]. The ferrocenyl group shows a special affinity towards proteins, amino acids, carbohydrates and DNA. So, it was widely used in the medicinal designs and biological researches. The ferrocene-related organometallic medicines have pharmacological functions of mainly ascribe to the effects of the cytotoxicity, redox property and lipophilicity of the ferrocene moiety on biological targets [7-9]. In continuation of our interest in organometallic ferrocene Schiff base ligands and their coordination chemistry [10], this article was interested in the synthesis of novel organometallic

Schiff

base

ligand

(L)

by

condensation

of

2-acetylferrocene

with

1,8-naphthalenediamine, then its coordination behavior with different transition metal ions was studied. The prepared ligand (L) and its metal complexes were characterized using different techniques. The biological and anticancer activities of these compounds were investigated. Also, the molecular and electronic structure of the organometallic Schiff base ligand was optimized theoretically and different quantum chemical parameters were calculated. Furthermore, molecular docking was studied to explain the mode of binding of the ferrocene, organometallic Schiff base (L) and its Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with the receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5).

2. Results and discussion 2.1.

Characterization of the organometallic Schiff base ligand (L) The organometallic Schiff base ligand (L) was synthesized by the reaction between

2-acetylferrocene and 1,8-naphthalenediamine in 1:1 molar ratio. The results of an elemental analysis for the ligand were in good agreement with the calculated values that confirmed its molecular formula as C22H20FeN2. The synthesized ligand was stable in air and soluble in DMF and DMSO. The IR spectral analysis provides some important information concerning the skeleton of the synthesized ligand. The most significant peak to identify the synthesis of the Schiff base ligand was the presence of imine bond ν(C=N) which showed vibration at 1593 cm-1 [11, 12]. Also, the IR spectrum of the ligand (L) showed two bands at 3408 and 3375 cm-1 due to νasy(NH2) and νsym(NH2) [13]. Furthermore, a band at 640 cm-1 was observed in the spectrum corresponding to the ν(NH2)bending [14]. The formation of the new organometallic Schiff base ligand (L) was also supported by the 1H-NMR spectral study. This spectrum was recorded in DMSO-d6 solution using (TMS) tetramethylsilane as an internal standard. The 1H-NMR spectrum of the free ligand showed singlet signal at 5.41 ppm which correspond to NH2 proton [15]. Also, the substituted ferrocenyl

ring indicated the characteristic multiplet signals due to the presence of nonequivalent nine protons in the range of 4.09-4.75 ppm [16]. Multiplets signals were appeared at 6.39-7.07 ppm which corresponding to naphthalene protons [17]. From the spectrum, the methyl protons also appeared at 1.76 ppm [18]. These proton signals were very important in expecting the good preparation of the Schiff base ligand. In order to give more structural information for synthesis of the organometallic Schiff base ligand (L), the EI-MS spectrum of this prepared ligand was recorded. The proposed molecular formula of this ligand was confirmed by comparing its molecular formula weight with m/z value. The spectrum of the ligand indicated a molecular ion peak at m/z = 368.75 a.u, which coincides with the formula weight of the ligand C22H20N2Fe with molecular weight of 368 g/mol.

2.1.1. Geometrical optimization of the organometallic Schiff base ligand The optimized structure of the organometallic Schiff base ligand (L) with atomic numbering has been given in Figure (1). All the bond lengths and bond angles of the synthesized Schiff base ligand were calculated and then were listed in Supplementary Table (1). Furthermore, the optimized factors calculations were performed with Gaussian 09 software package program [19], and calculated by using the optimized structure of the ligand with density functional theory (DFT) method [20]. These optimized factors such as ∆E, absolute electronegativities, χ, absolute hardness, η, chemical potentials, Pi, absolute softness, σ, global softness, S, global electrophilicity, ω, and additional electronic charge, ∆Nmax, were calculated using the equations in the supplementary information S1 [21, 22]. Finally, these factors are listed in Table (2). Chemical hardness (η) is correlated with the reactivity and the stability of a chemical system. In accordance with frontier molecular orbitals, chemical hardness relates to the energy gap between HOMO and LUMO orbitals. The energy gap was 3.30 eV. When this gap increases, the compound becomes more stable. Furthermore, the value of electrophilicity index (χ) is positive, while the chemical potential (Pi) showed a negative value. These results indicated that the Schiff base ligand can donate electrons to metal ions [23]. (Figure 1) (Supplementary Information S1) (Supplementary Table 1) (Table 2)

2.1.2. Molecular electrostatic potential (MEP) In order to study the mechanism of the reactions, electrostatic potential maps were studied. These maps are used for expecting sites available for the reactions and to occur identification of the electronic charge distribution around molecular surface [24]. Also, it was used for exploring the

sites available for nucleophilic reactions, electrophilic attack, and H-bonding interaction. This information can be used to detect how molecules interact with one another. As a result, the map of the organometallic Schiff base ligand was calculated by using the same basis set for optimization [25]. 3D plot of MEP was showed at Figure (2). The values of the electrostatic potential are performed by different colors: green characterizes regions of zero potential, blue characterizes regions of most positive electrostatic potential and red characterizes regions of most electronegative electrostatic potential. The colors order as red < orange < yellow < green < blue, when the potential increases [26, 27]. MEP of organometallic Schiff base ligand showed that the most negative regions located around the nitrogens of the naphthalene group so they were surrounded by red color and acted as a site for nucleophilic attack. While the ferrocene rings surrounded by greenish blue and blue colors. This detected the zero potential around them. Compared to FQ (Ferroquine) and Me-FQ (Methylferroquine), the bulky ferrocenyl group is twisted around the bond between N11 and C4 to minimize the steric and electronic interactions with the quinoline ring. Shape analysis was achieved also by computing the molecular electrostatic potential (MEP) surfaces. By comparison between FQ, Me-FQ and the prepared ferrocenyl ligand, it was showed that nitrogen atoms surrounded by red color. While the ferrocene rings in all compounds were surrounded by greenish blue color. The polar surface areas (PSA) were estimated at 14 Å2 for FQ and only 10 Å2 for Me-FQ. Thus, computational analysis suggests that FQ and RQ are likely to exhibit an intramolecular hydrogen bond [28]. (Figure 2)

2.1.3. Vibrational properties The experimentally observed infrared (FT-IR) peaks of the organometallic Schiff base ligand are compared with the intensely vibrational frequencies that can be calculated from DFT/ B3LYP method. These peaks were shown in Figure (3). The IR vibrational peaks were often overrated by DFT method. These may be due to the errors that arise from the incomplete treatment of electron correlation and vibrational anharmonicity. For overcoming this problem, the computed vibrational frequencies were often multiplied by a scaling factor (0.9648) [29, 30]. The data showed that the imine (C=N) group appeared experimentally at 1593 cm-1 while the (NH2)bending band appeared at 640 cm-1. These bands indicated by DFT method at 1616 and 699 cm-1, respectively. From these results, it was revealed that there is an excellent agreement between the experimental/theoretical IR stretching frequencies and the ligand was successfully prepared. (Figure 3)

2.1.4. UV-Visible analysis The experimental UV-Vis absorption spectrum of the organometallic Schiff base ligand showed two bands which congruent to π-π* transitions in the naphthalene group at 266 nm and the higher band represented at 339 nm was related to π-π* transitions due to the -C=N- group [31]. DFT calculations can theoretically confirm the UV transitions that occurred in the Schiff base ligand. The DFT data showed two absorption bands at 268 and 341 nm. The theoretical absorption bands and the excitation energies along with their oscillator strengths that were calculated using DFT method for the ligand were given in Table (3). The theoretical and experimental bands were shown in Figure (4). The band appeared at 268 nm with an oscillator strength of f = 0.15 congruent to the transition of HOMO-4 to LUMO. The band appeared at 341 nm with an oscillator strength of f = 0.04 was arisen from the transition of HOMO-1 → LUMO or HOMO → LUMO+2. These results were observed in Figure (5) [22, 32]. (Figure 4) (Figure 5) (Table 3)

2.2.

Characterization of Schiff base metal complexes

2.2.1. Elemental analysis The metal complexes were prepared by the reaction of equimolar amounts of the bidentate Schiff base ligand (L) with different transition metal ions in appropriate solvents. The isolated colored solid Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes are stable in air, having high melting points and insoluble in water, ethanol but readily soluble in DMF. From these data, it was obvious that complexes had 1:1 stoichiometry (metal: Schiff base ligand).

2.2.2. Molar conductivity measurements The molar conductivities measurements of the organometallic Schiff base complexes were measured in DMF solvent with 1.0 × 10-3 M concentration at 25 °C. The molar conductance values of the Cr(III), Fe(III) and Ni(II) complexes were 62, 58 and 58 Ω-1 mol-1 cm2, respectively, indicated that they had electrolytic nature. While the Mn(II), Co(II), Cu(II), Zn(II) and Cd(II) complexes have molar conductance values lower than 50 Ω-1 mol-1 cm2 in the range of 6-27 Ω-1 mol-1 cm2. It was concluded from these results that they were non-electrolytes.

2.2.3. IR spectra In order to study the binding mode of the organometallic Schiff base ligand to the M(II)/M(III) ions in the complexes, the IR spectrum of the free Schiff base ligand was compared

with the spectra of the complexes. From the data, it was concluded that all complexes showed a significant change of ν(C=N) (azomethine) band which was shifted from lower (1593 cm-1) to higher (1643–1653 cm-1) frequencies [20, 33]. The IR spectra of all complexes showed a broad band around 3407-3437 cm-1 assigned to ν(OH) of coordinated or crystalline water molecules that were associated with the complex. The IR spectrum of the ligand showed two bands at 3408 and 3375 cm-1 due to ν(NH2)asy and ν(NH2)sym. The appearance of OH band in all complexes may be overlapped with these two bands that corresponding to the ν(NH2) stretching vibrations [13]. So, it should detect the ν(NH2)bending band of all complexes. The ν(NH2)bending band has appeared at 640 cm-1 in the free organometallic Schiff base ligand. This band was shifted to appear in the range of 600-695 cm−1, while disappeared in the Fe(III) complex [14]. This indicated that the Schiff base ligand coordinated to the metal ions via the amino group. All complexes indicated two weaker bands in the region of 824–934 and 805–870 cm-1. These bands corresponding to ν(OH) rocking and wagging modes of vibrations of coordinated water molecules, respectively [33]. In addition, new two bands have appeared in the regions of 527-593 and 456-491 cm-1 which were assigned to the formation of M-O of coordinated water and M-N bonds, respectively [34]. Therefore, from the results of IR spectra of the Schiff base and its metal complexes, it was indicated that the prepared Schiff base ligand behaved as neutral bidentate ligand and form coordination bonds with metal ions through azomethine-N and amino group-N.

2.2.4. Scanning Electron Microscope (SEM) One of the most important functions of SEM analysis is to check the surface morphology of the selected compounds. So, the micrographs of the organometallic Schiff base and its Cd(II) complex were studied and showed in Figure (6). The micrograph of the ligand gave a sponge-like an appearance with a numerous rock parts. These facts discovered the amorphous nature of the ligand with complicated interpretation because it’s unclear appearance. On the other hand, the micrograph of [Cd(L)(H2O)2Cl2] complex indicated the presence of well-defined platelets. The average particle size of nanostructures can be also detected by SEM analysis. The particle size of the ligand was 32 nm, while the Cd(II) complex was 15 nm. From the SEM study, it is evident that the synthesized nanostructure particle size of Cd(II) complex was found to grow up from just a single molecule to several molecules in the nanoscale [35, 36]. (Figure 6)

2.2.5. UV-Visible spectra of the ligand and its metal complexes The UV-Vis absorption spectrum of the Schiff base ligand within the range of 200-700 nm was scanned and assigned in DMF. In the spectrum of the free ligand, it was shown that there were

two bands which congruent to π-π* transitions of the naphthalene group at 266 nm and the higher band situated at 339 nm was related to π-π* transitions of the -C=N- group [31, 37]. The nature of the Schiff base ligand field around the metal ions and also the geometry of the metal complexes can be detected. From UV-Vis spectra, they were showed that 266 nm band that present in the ligand is shifted in all complexes to lower or higher values in the range of 262-292 nm. This band assigned to π-π* transitions of the naphthalene group. Also, the band of azomethine group was shown at 339 nm in the ligand, also was shifted to lower values at 307-330 nm that assigned to π-π* transition [38]. This data confirmed the coordination of the azomethine nitrogen to the metal ions. Additionally, a strong band appeared at 537 nm in Cu(II) complex, can be assigned to d-d transition [39].

2.2.6. Thermal analysis of Schiff base ligand and its metal complexes The thermogravimetric analysis TG and differential thermogravimetric analysis DTG of the prepared Schiff base ligand and its metal complexes were studied. The stages of decomposition, number of stages, temperature ranges, decomposition product loss, the found and calculated weight loss percentage and the residues of all compounds were given in Supplementary Table (4) and also were shown in Supplementary Figure (7). The thermal decomposition process of the organometallic Schiff base ligand involved one decomposition step. The decomposition of the ligand started at 95 °C and finished at 855 °C, which involved the removal of C22H20N2 molecule and is accompanied by a weight loss of 84.98% (calc. = 84.78%). Finally Fe metal remains as residue. The overall weight loss amounted to 84.98% (calc. = 84.78%). The thermal decomposition of [Cr(L)(H2O)2Cl2]Cl.3H2O and [Zn(L)(H2O)2Cl2]H2O complexes occurred via five degradation steps. The first and second steps of decomposition occurred within the temperature range 30-360 °C, which congruent to the loss of two water molecules of hydration, Cl2 gas and C3H4 molecule (found 23.86% and calc. = 23.84%) in first complex, while in Zn(II) complex lost Cl2 gas and water molecule of hydration in the first and second steps of decomposition within the range of 30–335 °C (found 15.39% and calc. = 15.95%). The third step of decomposition in Cr(III) complex occurred in the range of 360–595 °C and congruent to the elimination of C4H8N molecule (found 11.29% and calc. = 11.35%). While, loss of C2H6 molecule within the temperature range of 335–500 °C (found 5.86% and calc. = 5.38%) in Zn(II) complex. The last two steps of Cr(III) complex occurred within the temperature range of 595–1000 °C (found 25.01% and calc. = 25.22%) and congruent to the loss of C7H14O0.5NCl molecule and the ferric and chromic oxides contaminated with carbon presented as residues. While in Zn(II) complex, the fourth step congruent to a loss of C8H14 molecule within the temperature

range of 500–720 °C (found 19.96% and calc. = 19.71%). And he last step congruent to a loss of C3H4N2 molecule within the temperature range of 720–1000 °C (found 12.60% and calc. = 12.19%), leaving FeO and ZnO contaminated with carbon as residues. [Mn(L)(H2O)2Cl2].3H2O, [Fe(L)(H2O)2Cl2]Cl.3H2O and [Co(L)(H2O)2Cl2]H2O complexes showed two decomposition stages. The first stage is one step in the temperature range of 30-115 °C, 30-285 °C and 35-215 °C in the three complexes, respectively. Which congruent to the loss of three water molecules of hydration and C2H4 molecule (Found = 14.43% and calc. = 14.04%), loss of C6H5Cl molecule, Cl2 gas and 2H2O (Found = 34.99% and calc. = 35.37%) and loss of one hydrated water molecule, 2HCl and C6H7N molecule (found = 33.43%; calc. = 33.33%), respectively. The second stage is one step in all complexes except Mn(II) complex which corresponding to two steps of decomposition. It is in the temperature range of 115-475 °C represented the loss of C18H20N2 molecule and Cl2 gas (Found = 57.01% and calc. = 57.36%), at the temperature range of 285-1000 °C with losing of C16H21N2O0.5 molecule (Found = 40.76% and calc. = 40.13%) and at the temperature range of 215-900 °C which related to loss of C16H15N molecule (found = 40.23%; calc. = 40.04%) in Mn(II), Fe(III) and Co(II) complexes respectively. Finally, the FeO remained with Fe2O3 oxides as residues while with MnO or CoO contaminated with carbon as residues. [Ni(L)(H2O)3Cl]Cl.3H2O, [Cu(L)(H2O)2Cl2]H2O and [Cd(L)(H2O)2Cl2] complexes were thermally decomposed in three stages. The first stage is one step of decomposition. Occurred in the temperature range of 30–135 °C, 30-150 °C and 70–265 °C, respectively. Representing the loss of three water molecules of hydration (found 8.30% and calc. 8.91%), the loss of hydrated water molecule and ½ Cl2 (found 9.46% and calc. 9.61%) and the loss of 2HCl and C6H4N molecules (found 27.61% and calc. = 27.77%), respectively. The second stage corresponded to also one step of decomposition within the temperature range of 135–295 °C, 150–325 °C and 265–675 °C, respectively. Which congruent to loss of H2O and ½ Cl2 gas (found 8.24% and calc. 8.83%), loss of C5H10N molecule (found 15.17% and calc. = 15.09%) and loss of C10H6N molecule (found 23.61% and calc. = 23.85%) in Ni(II), Cu(II) and Cd(II) complexes. The final stage was one step in all complexes except in Ni(II) complex which corresponded to two steps. Within the temperature range of 295–995 °C, 325–965 °C and 675–900 °C, respectively. That attributed to the loss of C18H24N2Cl molecule leaving FeO and NiO contaminated with carbon as residues (found 50.73% and calc. 50.08%), the loss of C9H14NCl molecule (found 30.92% and calc. 30.82%), leaving FeO and CuO contaminated with carbon as residues and the loss of C6H12 fragment (found 14.58% and calc. = 14.31%) leaving ferric and cadmium oxides as the product of decomposition. The ferrocenyl organometallic Schiff base contains iron atom. When forms complexes with various transition metal ions, the complexes then contain two metal atoms. As a result, the

complexes became very stable and the residues were oxides of iron mixed with another oxide due to their high stability up to 1000 °C. So, the residues of the complexes were contaminated with carbon atoms. (Supplementary Figure 7) (Supplementary Table 4)

2.2.7. Structural interpretation After condensation of the organometallic Schiff base ligand with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal chlorides, they were characterized using different spectroscopic techniques. Accordingly, the structure of the metal complexes was given in Figure (8). (Figure 8)

2.2.8. Antimicrobial activities The effectiveness of an antimicrobial agent is based on the zones of inhibition; based on their respective zones of inhibition, the data obtained showed that the synthesized complexes have got the capacity to inhibit the metabolic growth of the investigated bacteria [40, 41]. The prepared compounds screened against different Gram-positive bacteria: Bacillus subtilis and Staphylococcus aureus, Gram-negative bacteria: Escherichia coli and Salmonella typhimurium and two strains of fungi (Aspergillus fumigatus and Candida albicans). The data of the in vitro antimicrobial activity of the ligand (L) and its metal complexes are given in Supplementary Table (5) and are represented in Figure (9). Also, DMSO is used as control [40]. The results of bacterial and fungal activities were varied in all prepared metal complexes. These variations depend on the difference in the ribosome of the microbial cells or on their impermeability of the microbial cells [42]. When the antimicrobial activities of the metal chelates are increased, these may be due to the effect of metal ion on normal cell process. These higher activity values of the metal chelates can be discussed by the basis of Overtone’s concept and Chelation theory [43, 44]. Furthermore, the activities of the prepared organometallic ligand and its metal complexes were confirmed by calculating the activity index according to equation in Supplementary Information S2 [45, 46], and then were shown in Figure (10). From the data of activity index, it showed that Cr(III), Mn(II), Fe(III) and Ni(II) complexes had no activity index, while the [Cu(L)(H2O)2Cl2]H2O complex showed higher activity index than the others. The data of biological activities of the synthesized ligand and its metal complexes against different bacteria and fungi species indicated that Cr(III), Mn(II), Fe(III) and Ni(II) complexes had no activity against all different species, while the ligand had no activity against all the bacterial

species except E-coli species. Co(II), Cu(II), Zn(II) and Cd(II) complexes have higher activity than the parent organometallic Schiff base ligand. Cu(II) complex can be used as the most important and effective drug against Staphylococcus aureus. Also, the activity of these compounds against two fungal species showed that ligand and its metal complexes had no fungal activities against the two different species except the ligand and Cu(II) complexes which had activity values 12 and 13 mm/mg, respectively, against Candida albicans. (Figure 9) (Figure 10) (Supplementary Table 5) (Supplementary Information S2)

2.2.9. Anticancer activities For arbitrating the efficiency of any new compound used as an anticancer drug, it must be improving the hematological, biochemical profile, clinical and reduction in viable tumor cell count in the host and also prolongation of lifespan [47]. In order to evaluate the anticancer activity of the synthesized organometallic Schiff base and its metal complexes, these compounds used to treat MCF-7 (breast carcinoma cells) at concentration 100 µM. It was found that the ligand and its Cr(III), Fe(III), Cu(II) and Cd(II) complexes have inhibition fraction higher than 70%. Furthermore, the half-inhibitory concentration (IC50) values for these active compounds were calculated by using different concentrations (5, 12.5, 25 and 50 µM). The data were summarized in Table (6) and also were offered in Figure (11). From these data, it illustrated that the IC50 values of the investigated compounds were 11.3, 16.6, 20.2, 35 and 37.7 µM for Fe(III)-L, Cd(II)-L, Ligand, Cr(III)-L and Cu(II)-L, respectively. So, it is concluded that Fe(III) and Cd(II) complexes are higher active than the Schiff base ligand but Cr(III) and Cu(II) complexes are less active than ligand against MCF-7 cell line. Consequentially, the Fe(III) complex with the lowest IC50 value may be indicated its magnificent activity against breast cancer cell line than the other compounds. It demonstrates that changing the complexation locations and the nature of the metal ion has a clear effect on the biological way. Cytotoxicity potency of the synthesized compounds may be due to the central metal atom which was presented by Tweedy’s chelation theory [44, 48]. This indicated improving the antitumor potency upon coordination. The improvement of cytotoxic potency may be specified due to that positive charge of the metal increased the acidity of the coordinated ligand that bears protons, this causing more potent hydrogen bonds [49, 50]. (Figure 11) (Table 6)

2.2.10. Molecular modeling of ferrocene, Schiff base (L) and its metal complexes: Docking study

The molecular docking studies aid to describe the inhibitory potential and also can be expected the binding mode or mechanism of chemical moieties in the pocket of the enzyme. This method is considered as a very helpful key tool in computer drug design [51]. Furthermore, it is a well-established computational technique that used to expect the interactions between prepared compounds and enzyme receptors. It is useful to shed light on the optimized orientations and binding characteristics of a molecule that results in a new complex with overall minimum energy [52]. Xanthine oxidoreductase (XOR) is a key enzyme in the degradation of DNA, RNA and highenergy phosphates and also plays a role in milk lipid globule secretion. XOR may be differentially expressed in breast cancer [53]. Due to the importance of docking studies nowadays, we interested to dock the ferrocene, prepared Schiff base and its metal complexes with the receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5). Three-dimensional structures of docking are shown in Figure (12). Also, the binding energies of these compounds were calculated using computational docking studies [54, 55]. These energy values were listed in Supplementary Table (7). From these data, it is showed that there are interactions between all compounds and the 3HB5 receptor. The main interaction forces between the compounds and the active sites were H-donor, Hacceptor, ionic, π-H, π-π* and cation-π. The lowest binding energies of the ferrocene, ligand (L) and its metal complexes with 3HB5 receptor were calculated and showed in Supplementary Figure (13). The results indicated the minimum binding energy was -12.5 kcal mol−1 for Fe(III) complex. This result was in good agreement with the experimental one for Fe(III) complex against breast cancer cell line, which has the lowest IC50 value. Also, it showed that the binding energy decreases upon coordination. So, the complexes are more active with lower BE than the ligand and the starting material ferrocene which means that the formation of Schiff base ligand and its complexes enhance the activity. From the earlier data, it is concluded that prepared Schiff base and its metal complexes had lower binding energies than the parent ferrocene compound. Therefore, the activity of these prepared compounds became better against breast cancer and also, improves the properties of anticancer medicines especially when they prepared in nanostructures. (Figure 12) (Supplementary Figure 13) (Supplementary Table 7)

3. CONCLUSION This paper represented a simple method for synthesis of a new organometallic Schiff base ligand (L) and its Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes. Both the Schiff base ligand (L) and its metal complexes were characterized by using different spectroscopic techniques for determination of their geometry. •

From IR spectral analysis: the prepared Schiff base ligand behaved as a neutral bidentate ligand in all metal complexes. It formed coordinate bonds with the transition metal ions through the two nitrogen atoms of azomethine and amino groups.

•

From elemental analysis and conductivity: the reaction between Schiff base ligand and metal ions occurred as 1:1 molar ratio. All the prepared complexes had octahedral structures. Also, the data showed that all complexes were non-electrolytes except Cr(III), Fe(III) and Ni(II) complexes which were 1:1 electrolytes.

•

By screening all compounds against breast cancer cell line (MCF-7) and then determine the IC50 values for the active compounds with inhibition fraction higher than 70%, it indicated that the Fe(III) complex has the lowest IC50 value (11.3 µM) than the ligand and the other complexes.

•

The biological activity of the synthesized ligand and its metal complexes was studied against Gram-positive bacteria: Bacillus subtilis and Staphylococcus aureus, Gram-negative bacteria: Escherichia coli and Salmonella typhimurium and two strains of fungi (Aspergillus fumigatus and Candida albicans). It was found that the Co(II), Cu(II), Zn(II) and Cd(II) complexes had higher activities against all different bacterial species than the other complexes. Cu(II) complex can be used as the most important and effective drug against Staphylococcus aureus species. But, each of Cr(III), Mn(II), Fe(III) and Ni(II) complexes had no activity against any species. Also, the ligand and Cu(II) complexes are biologically active against the fungus, Candida albicans. While other complexes are biologically inactive.

•

The DFT calculations and computational results were applied successfully to determine the binding energies, bond length, dipole moment and other parameters for the ligand (L). Furthermore, it confirmed the experimental IR and UV-Vis data by comparing it with the theoretical values.

•

Molecular docking studies of the ferrocene, free organometallic Schiff base and its Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with receptor of (PDB ID: 3HB5) showed that the binding energy decreased upon coordination.

4. Experimental 4.1.

Materials and reagents Chemicals of the highest purity were used in the preparation and in all analyses. The

chemicals used included 2-acetylferrocene, 1,8-naphthalenediamine, hexahydrate of Cr(III), Fe(III), Co(II) and Ni(II) chlorides, di-hydrate of Mn(II) and Cu(II) chlorides and anhydrous Zn(II) and Cd(II) chlorides and they were supplied from Strem Chemicals Inc., Sigma-Aldrich, SigmaAldrich, Sigma-Aldrich, Sigma-Aldrich, BDH, BDH, BDH, BDH, and Merck, respectively. Solvents that used were ethanol (95%), methanol and N,N-dimethylformamide (DMF). Deionized water was usually used in all preparations.

4.2.

Solutions Preparation of stock solutions with concentration 1 X 10-3 M for the organometallic Schiff

base ligand and its metal complexes by dissolving an accurately weighed amount in N,N-dimethylformamide solvent. Then the conductivity of these metal complexes solutions was measured. By dilution of the earlier solutions of the Schiff base ligand and its metal complexes to concentration 1 X 10-4 M, their UV–Vis spectra could be measured.

4.3.

Solution of anticancer study A stock solution with concentration (1 × 10-3 M) of Schiff base ligand (0.12 X 10-2 g L-1)

was prepared in the appropriate volume of DMF (90%). DMSO was used in cryopreservation of cells. The medium used in the experiment was RPMI-1640. This medium was used for maintenance and culturing of the human tumor cell line. The medium was used in a powder form. Then it could be prepared as follows: mixed 2 g of sodium bicarbonate with 10.40 g of the medium, completed the solution to 1000 mL by using distilled water as a solvent and shaken carefully until complete dissolution. After that, the medium was sterilized by filtration in a Millipore bacterial filter (0.22 mL) and kept in a refrigerator with temperature 4 °C and checked at regular intervals for contamination. The medium was warmed in a water bath at 37 °C before using and supplemented with FBS and penicillin-streptomycin. Sodium bicarbonate was used in the preparation of RPMI1640 medium. Preparing isotonic trypan blue solution (0.05%) in normal saline and was used for viability counting. FBS (10%, heat inactivated for 30 min at 56 °C), 2 µM streptomycin and 100 units/mL penicillin were used for the supplementation of RPMI-1640 medium prior to use. For the harvesting of cells, trypsin (0.25 X 10-1 % w/v) was used. To dissolve unbound SRB dye, acetic acid (1% v/v) was used. The protein-dye used was SRB (0.40%) dissolved in 1% acetic acid. A stock solution of trichloroacetic acid (50%) was prepared and stored. 50 µL of the prepared stock

solution was added to 200 µL of RPMI-1640 medium per well to yield a final concentration of 10% used for protein precipitation. Ethanol (70%) and isopropanol (100%) were used. For solubilization of the SRB dye, tris base (pH = 10.50, 10 mM) was used. Tris base (121.10 g) was dissolved in 1000 mL of distilled water and then the pH was adjusted using hydrochloric acid (2 M).

4.4.

Instrumentation Microanalyses of carbon, hydrogen and nitrogen were carried out at the Microanalytical

Center, Cairo University, Egypt, using a CHNS-932 (LECO) Vario elemental analyzer. Analyses of the metals were conducted by dissolving the solid complexes in concentrated HNO3 and dissolving the residue in deionized water. The metal content was carried out using inductively coupled plasma atomic absorption spectrometry (ICP-AES), Egyptian Petroleum Research Institute. 1H-NMR spectra, as solutions in DMSO-d6, were recorded with a 300 MHz Varian-Oxford Mercury at room temperature using tetramethylsilane as an internal standard. Fourier transform infrared (FT-IR) spectra were recorded with a PerkinElmer 1650 spectrometer (400-4000 cm-1) as KBr pellets. Mass spectra were recorded using the electron ionization technique at 70 eV with an MS-5988 GS-MS Hewlett-Packard instrument at the Microanalytical Center, National Center for Research, Egypt. Molar conductivities of 10-3 M solutions of the solid complexes in DMF were measured using a Jenway 4010 conductivity meter. UV–visible spectra were obtained with a Shimadzu UVmini-1240 spectrophotometer. The scanning electron microscope (SEM) image of the complexes was recorded by using SEM Model Quanta 250 FEG (Field Emission Gun) attached with EDX unit (Energy Dispersive X-ray Analyses), with accelerating voltage 30 K.V., magnification 14X up to 1000000 and resolution for Gun.1n, National Research Center, Egypt). Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses of the solid complexes were carried out from room temperature to 1000 °C using a Shimadzu TG-50H thermal analyzer. Anticancer activity experiments were performed at the National Cancer Institute, Cancer Biology Department, Pharmacology Department, Cairo University. The optical density (OD) of each well was calculated spectrophotometrically at 564 nm with an ELIZA microplate reader (Meter tech. R960, USA). Antimicrobial measurements were carried out at the Microanalytical Center, Cairo University, Egypt.

4.5.

Synthesis of organometallic Schiff base ligand (L) Preparation of novel organometallic Schiff base (L) by condensation between

a methanolic solution of 1,8-naphthalenediamine (0.03 mol, 4.74 g) with a methanolic solution of 2-acetylferrocene (0.03 mol, 7 g) as shown in Scheme (1). The resulting mixture was stirred under

reflux at 100–150 °C for about 3 h, during which a brown solid compound was separated. The brown solid then filtered, recrystallized, washed by diethyl ether and finally dried in vacuum. (Scheme 1)

(2-(1-((8-aminonaphthalen-1-yl)imino)ethyl)cyclopenta-2,4-dien-1-yl)(cyclopenta-2,4-dien1-yl)iron (L). Yield 95%; m.p. 79 °C; brown solid. Anal. Calc. for C22H20N2Fe (%): C, 71.74; H, 5.44; N, 7.61; Fe, 15.22. Found (%): C, 71.30; H, 4.95; N, 7.55; Fe, 14.80. FT-IR (ν, cm-1): azomethine (C=N) 1593sh, ν(NH2)bending 640m. 1H-NMR (300 MHz, DMSO-d6, δ, ppm): 4.09-4.75 (m, 9H, ferrocene ring), 6.39-7.07 (m, 6H, naphthalene ring), 5.41 (s, 2H, NH2-bending), 1.76 (s, 3H, methyl group of ferrocene). UV-Vis (λmax, nm): 266 (π–π* of naphthalene ring) and 339 (π–π* of C=N group).

4.6.

Synthesis of Schiff base metal complexes Some transition metal complexes were prepared by reaction of ethanolic solution (60 °C) of

Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) chlorides (1.09 X 10-3 mol) with the DMF solution of the Schiff base ligand (L) (0.4 g, 1.09 X 10-3 mol). All complexes were precipitated by stirring the resulting mixture under refluxing for 1-2 h. Then the complexes were collected by filtration and then purified by using diethyl ether as a washing solution several times. The solid complexes dried in a desiccator over anhydrous calcium chloride.

[Cr(L)(H2O)2Cl2]Cl.3H2O Yield 75%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H30Cl3FeCrN2O5 (%): C, 42.82; H, 4.87; N, 4.54; Fe, 9.08; Cr, 8.44. Found (%): C, 42.51; H, 4.63; N, 4.21; Fe, 9.01; Cr, 8.21. Λm (Ω-1mol-1cm2) = 62; FT-IR (ν, cm-1): azomethine (C=N) 1643sh, H2O stretching of coordinated water 829s and 805w, (NH2)bending 674w, (M-O) 579s, (M-N) 478w. UV-Vis (λmax, nm): 292 (π–π*).

[Mn(L)(H2O)2Cl2]3H2O Yield 80%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H30Cl2FeMnN2O5 (%): C, 45.21; H, 5.14; N, 4.80; Fe, 9.59; Mn, 9.42. Found (%): C, 44.98; H, 5.05; N, 4.40; Fe, 9.32; Mn, 9.11. Λm (Ω-1mol-1cm2) = 27; FT-IR (ν, cm-1): azomethine (C=N) 1652sh, H2O stretching of coordinated water 924s and 870w, (NH2)bending 600w, (M-O) 565w, (M-N) 478w. UV-Vis (λmax, nm): 265 (π–π*).

[Fe(L)(H2O)2Cl2]Cl.3H2O Yield 82%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H30Cl3Fe2N2O5 (%): C, 42.55; H, 4.84; N, 4.51; Fe, 18.05. Found (%): C, 42.05; H, 4.52; N, 4.19; Fe, 17.85. Λm (Ω-1 mol-1cm2) = 58; FT-IR (ν, cm-1): azomethine (C=N) 1647sh, H2O stretching of coordinated water 878s and 823s, (NH2)bending disappear, (M-O) 566m, (M-N) 476w. UV-Vis (λmax, nm): 263 (π–π* of naphthalene) and 307 (π–π* C=N group).

[Co(L)(H2O)2Cl2]H2O Yield 91%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H26Cl2FeCoN2O3 (%): C, 47.83; H, 4.71; N, 5.07; Fe, 10.15; Co, 10.69. Found (%): C, 47.62; H, 4.41; N, 4.77; Fe, 10.02; Co, 10.12. Λm (Ω-1mol-1cm2) = 21; FT-IR (ν, cm-1): azomethine (C=N) 1648sh, H2O stretching of coordinated water 934w and 828s, (NH2)bending 695w, (M-O) 593w, (M-N) 478w. UV-Vis (λmax, nm): 262 (π–π*).

[Ni(L)(H2O)3Cl]Cl.3H2O Yield 89%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H32Cl2FeNiN2O6 (%): C, 43.56; H, 5.28; N, 4.62; Fe, 9.24; Ni, 9.74. Found (%): C, 43.19; H, 4.85; N, 4.42; Fe, 9.04; Ni, 9.35. Λm (Ω-1mol-1cm2) = 58; FT-IR (ν, cm-1): azomethine (C=N) 1647sh, H2O stretching of coordinated water 880s and 825s, (NH2)bending 600w, (M-O) 531w, (M-N) 491w. UV-Vis (λmax, nm): 271 (π–π*).

[Cu(L)(H2O)2Cl2]H2O Yield 79%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H26Cl2FeCuN2O3 (%): C, 47.44; H, 4.67; N, 5.03; Fe, 10.06; Cu, 11.41. Found (%): C, 47.02; H, 4.30; N, 4.93; Fe, 10.00; Cu, 11.94. Λm (Ω-1mol-1cm2) = 3; FT-IR (ν, cm-1): azomethine (C=N) 1653sh, H2O stretching of coordinated water 883w and 860w, (NH2)bending 659w, (M-O) 527w, (M-N) 456w. UV-Vis (λmax, nm): 269 (π–π* of naphthalene), 313 (π–π* C=N group) and 537 (d-d transition).

[Zn(L)(H2O)2Cl2]H2O Yield 85%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H26Cl2FeZnN2O3 (%): C, 47.31; H, 4.66; N, 5.02; Fe, 10.04; Zn, 11.65. Found (%): C, 47.11; H, 4.38; N, 4.98; Fe, 9.97; Zn, 11.43. Λm (Ω-1mol-1cm2) = 24; FT-IR (ν, cm-1): azomethine (C=N) 1648sh, H2O stretching of coordinated water 824s and 822m, (NH2)bending 630w, (M-O) 544w, (M-N) 487s. UV-Vis (λmax, nm): 273 (π–π*).

[Cd(L)(H2O)2Cl2] Yield 78%; m.p. >300 °C; dark brown solid. Anal. Calc. for C22H24Cl2FeCdN2O2 (%): C, 44.97; H, 4.09; N, 4.77; Fe, 9.54; Cd, 19.08. Found (%): C, 44.53; H, 3.95; N, 4.43; Fe, 9.36; Cd, 18.89. Λm (Ω-1mol-1cm2) = 6; FT-IR (ν, cm-1): azomethine (C=N) 1644m, H2O stretching of coordinated water 891s and 820m, (NH2)bending 617sh, (M-O) 536w, (M-N) 490s. UV-Vis (λmax, nm): 268 (π–π* of naphthalene) and 330 (π–π* C=N group).

4.7.

Spectrophotometric studies All prepared DMF solutions with concentration (1 X 10-4 M) of organometallic Schiff base

and its metal complexes were used for measuring their absorption spectra. These spectra were scanned within the wavelength range from 200 to 700 nm.

4.8.

Antimicrobial activity A filter paper disk with size 5 mm was put into 250 mL flasks which containing 20 mL of

the working volume of tested solution (100 mg mL-1). All prepared flasks were autoclaved at 121 °C for 20 min. LB agar media surfaces were inoculated with different four investigated bacteria (Gram-negative bacteria: Salmonella typhimurium and Escherichia coli, Gram-positive bacteria: Staphylococcus aureus and Bacillus subtilis, and two strains of fungi (Candida albicans and Aspergillus fumigatus) by diffusion agar technique [56]. Then these surfaces with different species were transferred to a saturated disk with a tested solution in the center of Petri dish (agar plates). The newly prepared Schiff base ligand and its metal complexes were placed at 4 equidistant places at a distance of 2 cm from the center in the inoculated Petri plates by using DMSO as the control. Finally, all these prepared Petri dishes were incubated for 48 hr at 25 °C where clear or inhibition zones were detected around each disk. The flask which used as control one of the experiments was designed to perform under the same condition described previously for each microorganism but with DMF solution only and by subtracting the diameter of inhibition zone resulting with DMF from that found in each case, as a result, antibacterial activity could be calculated. Ketokonazole and gentamycin were used as reference compounds for antifungal and antibacterial activities, respectively. All experiments were performed as triplicate and data plotted were the mean value.

4.9.

Anticancer activity Potential cytotoxicity of the prepared novel Schiff base ligand and its metal complexes were

investigated using the method of Storeng and Skehan [57]. Before treatment with the newly prepared Schiff base ligand and its metal complexes for allowing attachment of the cell to the wall

of the plate, cells were plated in 96-multiwell plate (104 cells well-1) for 24 h. The tested compounds under-investigated were prepared in different concentrations (0, 5, 12.5, 25, 50 and 100 µM) which were then added to the cell monolayer triplicate wells were prepared for each individual dose. These monolayer cells were incubated for 48 h at 37 °C and in 5 % CO2 atmosphere with the compounds. The monolayer cells were fixed after 48 h, then washed and finally stained with SRB stain. Excess stain was removed by washing with acetic acid, and the attached stain was recovered with

Tris–EDTA

buffer.

The

optical

density (O.D.)

of

each

well

was

measured

spectrophotometrically at 564 nm by using an ELIZA microplate reader. Then the mean background absorbance was automatically subtracted and the mean values of each drug concentration were calculated. The survival curve of breast tumor cell line for each compound was obtained by drawing a relation between surviving fraction and drug concentration. Calculation: The percentage of cell survival was calculated as follows: Survival fraction = O.D. (treated cells) / O.D. (control cells). Also, the concentrations of the Schiff base ligand or its metal complexes required to produce 50 % inhibition of cell growth (IC50 values) were calculated. The experiment was repeated three times for MCF-7 cell line.

4.10. Computational methodology Molecular modeling theoretical calculations and DFT studies for the prepared organometallic Schiff base ligand (L) was carried out on the Gaussian03 package [58], by using density functional theory (DFT) level of theory. The molecular geometry for the prepared ligand was fully optimized by using density functional theory (DFT) which based on the B3LYP method along with the LANL2DZ basis set. The structure of the ligand (L) was firstly optimized by using Chemcraft version 1.6 package [59], and GaussView version 5.0.9 [60]. Also, quantum chemical factors such as the lowest unoccupied molecular orbital energy (ELUMO), the highest occupied molecular orbital energy (EHOMO), HOMO–LUMO energy gap (∆E) and dipole moment for the investigated ligand were calculated.

4.11. Molecular docking Molecular docking studies were done by using MOE 2008 software and it is rigid molecular docking software. The function of this study is to expect the possible binding modes and the lowest binding energies of the ferrocene, novel ferrocenyl Schiff base ligand and its metal complexes against the receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5) which may be considered as an interactive molecular graphics program [61]. The structure of ferrocene, Schiff

base ligand, its metal complexes, and the receptor were used as input in PDB format. The structure of these compounds in PDB file format was created by using Gaussian03 software. The crystal structure of the receptor breast cancer mutant oxidoreductase (PDB ID: 3HB5) was downloaded from the protein data bank (http://www.rcsb.org./pdb). In Docking studies some ligands were removed as water molecules, co-crystallized ligands, counter ions (Cl) and other unsupported elements (e.g., K, Na, Hg, etc.,) but the amino acid chain was kept [62].

Acknowledgements The research did not receive any specific funding

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List of Scheme′s Captions Scheme 1. Preparation of organometallic Schiff base ligand (L).

List of Figure′s Captions Fig. 1. The optimized structure of organometallic Schiff base ligand (L). Fig. 2. Molecular electrostatic potential map of organometallic Schiff base ligand (L), the electron density isosurface is 0.004 a.u. Fig. 3. IR spectra of organometallic Schiff base ligand (L) (a) experimental spectrum and (b) theoretical spectrum. Fig. 4. UV-Visible spectra of Schiff base ligand (L) (a) experimental spectrum and (b) theoretical spectrum. Fig. 5. Theoretical electronic absorption transitions for organometallic Schiff base ligand (L) in DMF solvent. Fig. 6. The SEM images of the nanoparticles produced a) organometallic Schiff base ligand (L) and b) [Cd(L)(H2O)2Cl2] complex. Supplementary Fig. 7. Thermal analyses (TG and DTG) of (a) Ligand (L), (b) Cr(III), (c) Mn(II), (d) Fe(III), (e) Co(II), (f) Ni(II), (g) Cu(II), (h) Zn(II) and (i) Cd(II) complexes. Fig. 8. The proposed structure of organometallic Schiff base metal complexes. Fig. 9. Biological activity of organometallic Schiff base ligand (L) and its metal complexes. Fig. 10. Activity index of Schiff base ligand (L) and its metal complexes against (a) different Gram-positive bacteria (b) different Gram-negative bacteria. Fig. 11. Antibreastic cancer activity of the Schiff bases ligand (L) and its metal complexes. Fig. 12. 3D structure of the interaction between a) ferrocene, b) organometallic Schiff base ligand, c) Cr(III)-L, d) Mn(II)-L, e) Fe(III)-L, f) Co(II)-L, g) Ni(II)-L, h) Cu(II)-L, i) Zn(II)-L and j) Cd(II)-L complexes with receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5). Supplementary Fig. 13. The relation between the lowest binding energy of ferrocene, organometallic Schiff base and its metal complexes with receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5).

List of Table′s Captions Supplementary Table 1. The different optimized parameters (bond lengths and bond angles) of organometallic Schiff base ligand (L). Table 2. The different quantum chemical parameters of organometallic Schiff base ligand (L). Table 3. Main calculated optical transitions with composite ion in terms of molecular orbitals. Supplementary Table 4. Thermoanalytical results (TG and DTG) of organometallic Schiff base ligand (L) and its metal complexes. Supplementary Table 5. Biological activity of organometallic Schiff base ligand (L) and its metal complexes. Table 6. Antibreastic cancer activity of organometallic Schiff base ligand (L) and its metal complexes. Supplementary Table 7. Energy values obtained in docking calculations of ferrocene, organometallic Schiff base (L) and its metal complexes with receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5).

Figure 1. The optimized structure of organometallic Schiff base ligand (L).

Figure 2. Molecular electrostatic potential map of organometallic Schiff base ligand (L), the electron density isosurface is 0.004 a.u.

(a)

(b)

Figure 3. IR spectra of organometallic Schiff base ligand (L) (a) experimental spectrum and (b) theoretical spectrum.

(a)

(b)

Figure 4. UV-Visible spectra of Schiff base ligand (L) (a) experimental spectrum and (b) theoretical spectrum.

Figure 5. Theoretical electronic absorption transitions for organometallic Schiff base ligand (L) in DMF solvent.

(a)

(b)

Figure 6. The SEM images of the nanoparticles produced a) organometallic Schiff base ligand (L) and b) [Cd(L)(H2O)2Cl2] complex.

OH2 NH2

OH2 Ni Cl

N

OH2 C H3C Fe

.Cl.3H2O

Figure 8. The proposed structure of organometallic Schiff base metal complexes.

Inhibition zone diameter(mm/mg sample) 35

30

25

20

15

10

5

0 [Cr(L)(H2O)2Cl2]Cl.3H2O [Mn(L)(H2O)2Cl2]3H2O [Fe(L)(H2O)2Cl2]Cl.3H2O [Co(L)(H2O)2Cl2]H2O compounds

[Ni(L)(H2O)3Cl]Cl.3H2O [Cu(L)(H2O)2Cl2]H2O [Zn(L)(H2O)2Cl2]H2O [Cd(L)(H2O)2Cl2] Gentamycin ketokonazole

Bacillus subtilis

Staphylococcus aureus

Escherichia coli

Salmonella typhimurium

Aspergillus fumigatus

Candida albicans

Figure 9. Biological activity of organometallic Schiff base ligand (L) and its metal complexes.

Schiff base ligand (L)

(a)

(b)

Figure 10. Activity index of Schiff base ligand (L) and its metal complexes against (a) different Gram-positive bacteria (b) different Gram-negative bacteria.

C=0 1.2 C=5 C = 12.5 1 C = 25 C = 50 Surviving fraction

0.8

0.6

0.4

0.2

Cd(II)-L

Cu(II)-L

Fe(III)-L

Cr(III)-L

Ligand L

0

compound

Figure 11. Antibreastic cancer activity of the Schiff bases ligand (L) and its metal complexes.

(a)

(c)

(e)

(b)

(d)

(f)

(g)

(i)

(h)

(j)

Figure 12. 3D structure of the interaction between a) ferrocene, b) organometallic Schiff base ligand, c) Cr(III)-L, d) Mn(II)-L, e) Fe(III)-L, f) Co(II)-L, g) Ni(II)-L, h) Cu(II)-L, i) Zn(II)-L and j) Cd(II)-L complexes with receptor of breast cancer mutant oxidoreductase (PDB ID: 3HB5).

Table 2. The different quantum chemical parameters of organometallic Schiff base ligand (L). The calculated quantum chemical parameters E (a.u)

-1083.17

Dipole moment (Debye)

3.72

EHOMO (eV)

-5.02

ELUMO (eV)

-1.72

∆E (eV)

3.30

χ (eV)

3.37

η (eV)

1.65

σ (eV)-1

0.61

Pi (eV)

-3.37

S (eV)-1

0.30

ω (eV)

3.44

∆Nmax

2.04

Table 3. Main calculated optical transitions with composite ion in terms of molecular orbitals. Compound

Transition

Excitation

λmax calc.

λmax exp.

Oscillator

energy

nm (eV)

nm (eV)

strength

341 (3.64)

339 (3.65)

0.04

268 (4.62)

266 (4.65)

0.15

(eV)

Ligand (L)

HOMO-1

LUMO

(36%)

4.08

HOMO

LUMO+2 (42%)

4.19

HOMO-4

LUMO

5.11

(60%)

Table 6 Antibreastic cancer activity of organometallic Schiff base ligand (L) and its metal complexes. Surviving fraction (MCF-7) Complex

IC50

Concn. 0.0

5.0

12.5

25.0

50.0

(µ µM)

Schiff base ligand (L)

1.0

0.978

0.626

0.423

0.410

20.2

[Cr(L)(H2O)2Cl2]Cl.3H2O

1.0

0.969

0.793

0.559

0.414

35

[Fe(L)(H2O)2Cl2]Cl.3H2O

1.0

0.779

0.455

0.428

0.317

11.3

[Cu(L)(H2O)2Cl2]H2O

1.0

0.815

0.753

0.612

0.392

37.7

[Cd(L)(H2O)2Cl2]

1.0

0.736

0.571

0.350

0.314

16.6

(µ µM)

38

Scheme 1. Preparation of organometallic Schiff base ligand (L).

39

•

Organometallic Schiff base ligand (L) and its metal complexes were synthesized and characterized using different tools.

•

Molecular docking studies of the ferrocene, Schiff base and its metal complexes with the active site of the 3HB5 receptor showed that Fe(III) complex had the highest binding ability and the minimum binding energy.

•

The results of biological activity assay of ligand and the complexes suggested that Cu(II) complex exhibited the highest activity against Staphylococcus aureus species.

Declaration of interests ☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

There is no conflict of interest