SYNTHESIS, CHARACTERIZATION, BIOLOGICAL ACTIVITY, MOLECULAR DOCKING AND THERMAL ANALYSIS OF BINUCLEAR COMPLEXES

Because of their potential medical applications as antimicrobial medicines, metal-ligand complexes have sparked a lot of attention. Synthesis and characterization of various metal-diamine complexes were the goals of the research detailed in this paper. As a result, synthesis of new binuclear ligand; N,N'-bis(3-carboxysalcylidene)4-chloro-1,2-phenylenediamine (H4fsacph) which is derivative from the condensation of 3-formyl-2hydroxybenzoic acid and 4-chlorobenzene-1,2-diamine has been performed. The new synthesized ligand has formed a mononuclear complex with Cu(II). The mononuclear Cu(II) complex was used to form binary nuclear complexes with some metal ions, like Cr(III), Mn(II), Fe(III), Ru(III), Pd(II) and La(III) ions. Elemental analysis, IR, UVVisible, and thermal analyzes have been used to characterize the complexes. The interaction of a ligand with the receptors of Candida albicans and SARS-CoV-2 was predicted using molecular docking. Toward bacteria and fungi showing predominant activity against all fungi verified antibacterial activity of the synthesized complexes, while they have almost no activity against all bacteria. All compounds have shown antibacterial and antifungal activities, but the metal complexes showed better activities as compared to the original ligands, especially all zinc(II) complexes. The above results suggest that both ligands and their metal complexes have the potential to be explored as active pharmaceutical agents.


INTRODUCTION
The presence of three extremely virulent coronaviruses that lead to human deadly pneumonia, namely SARS-CoV, SARS-CoV-2, and Middle East respiratory disease coronavirus, has thrown recent global events into disarray (MERS-CoV). The World Health Organization (WHO) announced on 30 January 2020 that the outbreak of COVID-19 is a worldwide healthiness concern [1,2].
The World Health Organization in 2018 reported, 18.1 million new cases of cancer globally, with 9.6 deaths annually, with one in five men and one in six women expected to develop cancer in infancy, One out of every eight men and one out of every eleven women succumbs to the cancer. Female lung and breast cancers are the bulk of recent cases globally; Lung cancer (1.8 million fatalities, or 18.4% of all deaths), which has a bad prognosis, and colon cancer (881,000 deaths, or 9.2% of all deaths), stomach cancer (783,000 deaths), 8.2%, and hepatic cancer (881,000 deaths, 9.2%) handle the highest annual death rate (782,000 deaths, 8.2%). Schiff bases have sparked a considerable attention in recent years, and they've been used in a lot of different sectors. In latest days, Schiff bases have gained a lot of attention and have been used in a variety of industries [3,4].
In recent years, Schiff bases have gained a lot of attention and have been used in a variety of industries [1,2]. Although there are many different types of complexing and chelating ligands, Schiff bases are particularly interesting because of their vast range of uses in industrial and biology [3].
Because of their facile preparation and wide range of chelating potential of numerous metal ions, Schiff bases have been used successfully as ligands in coordination chemistry. Also, because

Antimicrobial studies
Tests for microbiological screening directly towards bacteria and fungi were carried out using fungi such as Candida albicans, Aspergillus flavus, and Penicillium oxalicum. While tested bacteria were Escherichia coli (Gram -ve bacteria), Micrococcus luteus (Gram +ve bacteria), and Micrococcus roseus (Gram +ve bacteria). Nutrient agar (N.A.) media mixed with one gram yeast per liter served as the culture medium. Antibacterial and antifungal activities of each complex were each sample was pre-incubated in 10 mL of Difco Nutrient Broth for 20 hours at 37 °C before being tested for bacteria using the traditional filter paper method. The agar medium employed in this investigation was made up of 3 g beef extract, 5 g peptone, and 15 g/L agar. Before sterilization, the medium was adjusted to a pH of 7 15 min at 121°C, kept in a 50 °C water bath. Each Petri plate received 20 mL of medium (10 mL diameter). Difco Nutrient Broth bacterial samples were diluted 5 times with sterilized physiological saline before being scattered on the agar plate using a sterile loop. After a 6-hour inoculation period (at room temperature), on the surface of the medium, discs carrying the various complexes were inserted. At a concentration of 0.5 mg/disc, the complexes were applied (Whatman No. 3 filter paper, 0.5 µm diameter). The plates were incubated at 37 °C for 24 hours to determine the zones of inhibition of microbial growth induced by the various complexes (mm). All the tests were done three times [11][12][13][14].

RESULTS AND DISSCUSION
The physical appearance, analytical data, and molecular weight of the Schiff base H4fsacph and its mono copper complex Cu(H2fsacph).2H2O and binuclear copper complexes were determined and listed in Table 1 [15,16].

IR spectra
To confirm the chemical structure of the prepared ligand N,N'-bis(3-carboxysalicylidene)-4chloro-1,2-phenylenediamine (H4fsacph) and its complexes, IR spectra were collected. The Infrared spectral data of the H4fsacph, mono nuclear copper Cu(H2fsacph).3H2O and Cu(II) binuclear complexes are listed in Table 2. The infrared spectrum for the H4fsacph ligand and mono Cu complex Cu(H2fsacph).3H2O exhibit weak bands appearing at 3040-3010 cm -1 and 2962-2853 cm -1 which can be attributed to the νC-H aromatic and of νC-H conjugated to the aromatic system, respectively. The free carboxylic groups of the free H4fsacph and its Cu(H2fsacph).3H2O appeared at 1696 and 1681 cm -1 , respectively. The band appeared around 1582-1568 cm -1 in the copper binuclear complexes spectrum, can be attributed to the bonded carboxylate groups. The band at 1239 cm -1 at the spectrum of the free ligand H4fsacph is tasked with the ν C-O phenolic stretching vibration. This band was red shifted to appear at range 1272-1258 cm -1 in the spectra of the complexes (2-4) representative that; oxygen atoms have been bonded with the metal ions. The phenolic group that acts as a link νC-O is appearing in the region 1580-1560 cm -1 as a shoulder that appear at 1527 cm -1 in a ligand that is free and at 1550 cm -1 when only one metal ion is connected (non-bridging), but in the present complexes this band could not be recognize owing to the strong absorption of the carboxylate groups νCOO -. The band at 3400-3200 cm -1 when only one metal ion is connected (non-bridging). The band, which appears at 766-759 cm -1 , is assigned to tri-substitution of benzene rings; It can be found in the free ligand and copper mononuclear complex spectral Cu(H2fsacph).3H2O. The bands at 420-405 cm -1 can be credited to νCu-O bonds [17][18][19].
For the binuclear copper complexes, the aromatic νC-H Absorption in the area is usually caused by stretching vibrations 3075-3010 cm -1 . The νC-H the aromatic ring system's stretching vibration occurs at 2990 cm -1 . This mode of vibrations appears in the same region in the spectra of the Cu(II) binuclear complexes. The peak at 1629 cm -1 within the range of the free ligand as well as in the mononuclear spectrum complex Cu(H2fsacph).3H2O at 1614 cm -1 is given to the νC=N stretching vibration. This band is blue shifted to appear around 1616-1605 cm -1 in all Cu(II) binuclear complexes, indicating coordination with the ligand through the two nitrogen atoms of the azomethine groups [20]. The phenolic group that acts as a link νC-O is appearing in the region 1580-1560 cm -1 as a shoulder that appear around 1527 cm -1 in the free ligand while at 1550 cm -1 when a single metal ion is connected (non-bridging), but in the present complexes this band could not be recognize owing to the strong absorption of the carboxylate groups νCOO -. The band located at 1239 cm -1 in the spectrum of the free ligand is to be allocated to νC-O phenolic stretching vibration, this band was red moved to appear at a range of 1268-1249 cm -1 in Cu(II) spectral properties binuclear complexes (3)(4)(5)(6)(7)(8)(9)(10)(11) indicating that; oxygen atoms have been bonded with the ions of metal. The existence of coordinated H2O molecules in Cu(II) binuclear (3)(4)(5)(6)(7)(8)(9)(10)(11) complexes is evidenced based on the appearance of νHO band from the area 3412-3342 cm -1 . Band, which is present at 768-760 cm -1 , is assigned to tri-substitution at benzene rings. The bands located at 550-290 cm -1 may be ascribed to νM-N, νM-O and νM-Cl bonds. Table 2, Figure 1 and Figure 2 show infrared spectral data and plot of the H4fsacph, copper mononuclear complex Cu(H2fsacph).3H2O and copper binuclear complexes [21,22].

Electronic spectra
The electronic absorption spectra of the free ligand N,N'-bis(3-carboxysalicylidene)-4-chloro-1,2phenylenediamine H4fsacph (1) and its mononuclear copper complex Cu(H2fsacph).3H2O (2) are recorded in the ultraviolet and visible region in the range 200-900 nm. The measured absorption spectral data are given in Table 3.
The absorption spectra of the mononuclear copper complex Cu(H2fsacph).3H2O are not the same as the spectrum of the free ligand. The shoulder that developed at 345 nm and the two peaks that occurred at 329 and 385 nm vanished, and a new peak for copper appeared at 343 nm (H2fsacph).3H2O. The charge exchange between the ligand and the metal is responsible for this new peak. The absorption peak in the ultraviolet region due to intraligand transitions appearing at λmax= 259 nm with molar absorptivity ε =1155 mol -1 cm -1 still visible in the spectra of mononuclear complex is the spectrum of the free ligand, but red shifted by 2.0 nm with increasing in molar absorptivity by 1030 mol -1 cm -1 for Cu(H2fsacph).3H2O. This is as a result of the combination of copper metal ions that formed. The alteration in the ligand's electronic conformation is what is responsible for the redshift and enhanced intensity of this band. The band due to intraligand charge transfer appearing at λmax= 308 nm with molar absorptivity ε = 1575 mol -1 cm -1 . The peaks in the nujol mulls depict the complex of Cu's square planar structure (II) [25].
Generally, all Cu(II) binuclear complexes exhibited three strong peaks, the first peak appeared at 258-262 nm, that stands for intraligand π-π* transition [26]. The intraligand n-π* charge transfer was represented by the second peak, which emerged in the 306-309 nm region. L→Cu charge transfer is responsible for the third peak, which emerged in the region of 339.5-343.5 nm. The peaks, which appear at range 750-775 nm in nujol mull, can be attributed to d-d transition for square planar Cu(II) structure [27].  Table 3. The electronic absorption spectral data of the free ligand, mono nuclear copper Cu(H2fsacph).3H2O and Cu(II) binuclear complexes, either in solution or as (nujol mulls).
, we obtain the following results: All of the Cu(II) ions that are located in the outer coordination site have been determined to have square planar configurations with dsp 2 hybrid. Square-planar divalent metal ions including Pd(II), Cu(II), Ni(II), Co(II), and Mn(II) are found inside the coordination site. La(III), Ru(III), Fe(III), and Cr(III) are examples of trivalent metal ions that are octahedral. The La(III) ion lacks an observable magnetic moment because the unpaired 4f electrons in La(III), which are known to be the cause of the paramagnetism, are relatively significantly screened from environmental influences by the overlaying and p electrons. This is consistent with the experimental value that was measured. Due to the antiferromagnetic spin exchange process involving Cu2+ and the other metal ions, the complexes 4, 7, and 8 have rather low magnetic moment values. But complexes 5, 6, 9, 10 and 11 exhibit slightly larger magnetic moment values than that calculated, this is arising from the presence of ferromagnetic spin coupling interaction between Cu 2+ and the metal ions.  Thermal studies Table 5 shows the thermal data for each step of the thermal decomposition of them. The TGA of free ligand N,N'-bis(3-carboxysalcylidene)-4-chloro-1,2-phenylenediamine show thermal stability up to 210 °C which indicates a lack of water molecules. Thermal breakdown takes place above this temperature. There are two fundamental processes; the first is the first step in the 210-350 °C temperature range and corresponds to the loss of two carboxylic groups, two phenolic groups, and an atom of chlorine. The reduction of all organic moieties, including three benzene rings and two azomethine groups, is taking place in the second stage, which is now occurring at 350-680 °C. The loss of water lattice molecules, chlorine atoms, azomethine groups, benzene rings, oxygen atoms, hydroxyl groups, CO groups, CO2, and the production of metal oxides are all part of the overall thermal disintegration process for complexes 2-11. The process of fragmentation varies depending on the compound and the temperature.  2, 3, 6, 8, and 9, in the temperature range 220-500 °C for complexes 7, 10, and 11, and in the temperature range 390-460 °C for complexes 4 and 5. In the temperature range of 180-660 °C, the loss of benzene rings occurs in two stages [23]. When the temperature drops below a certain threshold 250-700 °C for complexes 2-11), CO2 is released.

Anticovid-19
By using MOE.2015.10 software, we can operate the molecular docking calculation. The key SARS-CoV-2 protease was found in the database of proteins (PDB ID: 6YB7, chain A). Following the model's verification, coordinated protein sequences. Following that, molecular docking was utilized to evaluate the antiviral activity of the formerly described medications, and SARS-CoV-2 protease from natural origin. In each case, the constants of energy and inhibition are given all of the chemicals were optimized in their active physiological settings. Before ensuring that the evaluated medicines and the ligand N,N'-bis(3-carboxysalcylidene)-4-chloro-1,2-phenylenediamine (H4fsacph) were in the optimal active state. SARS-CoV-2 protease H4fsacph was screened against. Last, the ligands used were chosen based on studies of the expected modes of binding and their ratings [33][34][35][36]. Lower docking molecular scores indicate that compounds have a stronger affinity for the 6YB7 protein. The direction of a ligand is determined using a form scoring characteristic that estimates the energies of the ligand-binding receptor. The analytical value of form scoring is related to van der van der Waals' appealing power. Energy minimizing once the initial orientation has been completed, as well as score reviews to identify the closest energy evaluation within the receptor-binding locations, minimization sites. Since then, the complex produced between the ligands screened with greater binding energies has been extremely stable, and SARS-primary CoV-2's protease has been identified. The ligand's capacity to bind the receptors that bind to the virus is revealed by the formation of inappropriate hydrogen bonding with the main protease chain. The docking value was -6.7, and the binding involving H4fsacph and 6YB7 by one hydrogen bond with Arg 4 is shown in Table 7.

Molecular structure
The 3-21G base set of the HF method has optimized the molecular structure of the N,N'-bis(3carboxysalcylidene)-4-chloro-1,2-phenylenediamine (H4fsacph). Using the programmed Gauss View was used to create the molecule and optimized [39].  The crucial traits are HOMO and LUMO, which are frequently used to chemically characterise the responsiveness of a system. EHOMO, ELUMO, and Egap of H4fsacph are shown in Figure 1. Table 8 represented the EHOMO, ELUMO, and Egap of H4fsacph. In fact, theoretically, the Egap is a crucial indicator of the chemical acuteness of a ligand, with a small gap signifying strong chemical reactivity (low steady) and a large gap signifying reduced chemical reactivity (high stable) (highly steady).
The theoretical elements, HOMO (π-donor) and LUMO (π-acceptor), are crucial to the architecture of molecules. The EHOMO and ELUMO principles, EHOMO-LUMO is distinguished from all other compounds by its energy difference Table 8. It is possible to assess the stability of molecules and the softness of compounds using the difference in energy. The molecule's lesser polarizability results from its lower energy volume (more reactive) [40].

Active sites
A technique for assessing the reactive groups in the evaluated adsorbate/adsorbents system and understanding the areas of electrophilic/nucleophilic attack and electrostatic potential zero regions is molecular electrostatic potential (MEP). Utilizing molecular electrostatic potentials (MEP), the whole N,N'-bis(3-carboxysalcylidene)-4-chloro-1,2-phenylenediamine (H4fsacph) electron density region was found in this work ( Figure 2). The different values of the MEP were shown on these maps using a range of colors (blue, light blue, green, yellow, and red). Likewise, the negative values of the MEP were represented by red and yellow colors, which are associated with electrophilic assault; the qualities were represented by blue colors, which are associated with nucleophilic attack; and the MEP zero area was represented by green [41].

Microbiological screening
Using fungi like Aspergillus flavus, Candida albicans, and Penicillium oxalicum, tests for microbiological screening directly towards bacteria and fungi were conducted. Escherichia coli (Gram -ve bacteria), Micrococcus luteus (Gram +ve bacteria), and Micrococcus roseus (Gram +ve bacteria) were the tested bacteria. Nutrient agar (N.A.) media supplemented with one gram of yeast per liter served as the culture medium. Each complex's antibacterial and antifungal properties were assessed using the traditional filter paper method previously described [37,42]. The produced complexes (1-11) clearly display dominating activity against all fungi, but essentially negligible activity against all bacteria [38].

CONCLUSION
The production of the new ligand (H4fsacph) and its mono-and binuclear complexes are discussed in this paper. The composition of the produced compounds and their activity were confirmed using characterization techniques and biological activities. These compounds are stable according to spectroscopic, magnetic, thermal, theoretical data, and the low energies of the HOMO and LUMO orbitals in the IR spectrum. The thermogravimetric study of the complexes reveals that the breakdown processes involve more than two phases. By attaching to the primary protease of SARS-CoV-2, H4fsacph was employed in molecular docking to evaluate its activity against COVID-19, which has antifungal properties with the Candida albicans 1zap receptor and was retrieved from the RCSB protein data library using PDB (ID: 6YB7).