All material used in the investigation were of reagent grade and were purchased commercially from British Drug House (BDH) and used as received. They include amino acids (valine, leucine, and isoleucine), salicylaldehyde, Cobalt (II) chloride, absolute methanol and ethanol. Double distilled water was used during the experimental process.

Schiff base (1-valine, 2-leucine, and 3-isoleucine) under investigation were prepared according to the procedure previously described in the literature [11] , Thus, in a 50 ml conical flask, prepare a separate solution by dissolving (1.2 g) of salicylaldehyde (0.75 g) of amino acids (1 - 3) and (0.4 g) of sodium hydroxide, in 15 ml of ethanol. Mix the salicylaldehyde solution within the proper amino acid solution. The mixture was stirred for 8 hours on a water bath at 70˚C. The obtained precipitate was filtered off and washed with cold ethanol. The solid products were recrystallized from hot ethanol to give yellow crystals, dried in vacuo over silica gel. The purity of the prepared compounds was checked by elemental analysis, IR, ¹H NMR spectra.

The preparation of the metal complexes under study were prepared according to procedure previously described in the literature [12] , thus, the complex [CoL₂]nH₂O have been prepared by the reaction of (0.590 gm) (2 mmole) of ligands (1 - 3) with (1 mmole) of Cobalt(II) chloride CoCl₂∙6H₂O (0.238 gm) dissolved in (20 mls) absolute ethanol and stirring for 24 hours. The obtained complexes were collected after evaporation of ethanol and was left in the desiccator to be dried under P₂O₅.

The prepared Schiff base and their metal complexes were provide by elemental analysis (C%, H%, N%) which were performed at the microanalytical center, Cairo University, the analysis were performed twice to check the accuracy of the analysis data. The IR spectra were recorded on as 8001-PC FTIR Shimadzu spectrophotometer using KBr pellets. Mass spectra of the complexes were performed using GC-2010 Shimadzu at Microanalytical center, Cairo University, Giza, Egypt. The magnetic susceptibility measurements for the complexes were determined by the Gouy balance using Hg[Co(SCN)₄] as calibration. ¹H NMR and ¹³C NMR were recorded on a Bruker DPX-400 spectrometer using DMSO d₆, as the solvent and TMS as internal standard. Molar conductivity of 10⁻³ M solutions of the complexes in DMF was measured on the conductivity meter ORION model 150 of 0.6 cell constant.

The CHN elemental analysis data of the investigation Schiff base ligands (1 - 3) and its Cobalt(II) metal complexes as shown in Table 1, exhibit the metal complexes formation of [ML₂] ratio. It was found that the theoretical values are in a good agreement with the found data.

The characteristic IR absorption bands of the studied amino acid Schiff bases and their Cobalt(II) complexes are presented in Table 2. The IR spectra of Schiff bases under study illustrate the following stretching frequencies:

1) A broad stretching frequency range between (2959 - 2922 cm⁻¹) in case of the free ligands which confirm OH group with shifting effect in case of complexes indicating the coordination of “O” group in complexation. The spectra of the Co(II) complexes exhibit broad bands in the range of (3415 - 3354 cm⁻¹) which analogous to the presence of hydrated water molecules [13] .

2) A strong to medium intensities bands are assigned to carbon nitrogen double bond (H-C=N) with stretching frequencies range between (1633 - 1625 cm⁻¹). The shifting of these bands to low frequencies comparing to the Schiff base ligands confirmed the participation of this group in complexation through Nitrogen atom [14] .

3) A strong to medium intensity bands are assigned to carbonyl group in Schiff base γ (C=O). They have stretching frequencies range between (1610 - 1593 cm⁻¹)

4) Schiff base show a linkage for sodium of carboxyl acid, (O-Na) at stretching range between γ (755 - 753 cm⁻¹). These values confirm the existence of these compounds as a sodium salts for carboxylic acids. The bands appeared at stretching frequencies range between γ (1522 - 1462 cm⁻¹) are assigned for (C=C).

The appearance of new bands in the range γ (563 - 461 cm⁻¹) [15] , and (421 - 277 cm⁻¹) [16] can be assigned to γ (M-O) and v (M-N) stretching vibrations observed in the metal complexes and absent in the free Schiff base ligands provide evidence that (C=O) and (C=N) moiety could be bonded to the metal ion through the Oxygen and the Nitrogen atoms.

The electronic spectral results of the studied Schiff bases (1 - 3) with Cobalt(II) complexes are presented in Table 2. The electronic spectra studies were carried out in DMF solvent. The electronic spectra of the Schiff bases (1 - 3) show a low energy bands at (413 - 410 nm) which assigned to NH form, while (314 - 312 nm) which assigned to the OH form are in agreement with the NMR results Table 3. For electronic spectra of the Schiff bases with Cobalt(II) complexes, both NH and OH peaks are not assigned with agreement to the occurrence of Schiff bases (1 - 3) metal complexes, as it is illustrated in Table 2. The electronic spectra of the Schiff base exihibit Π to Π* (phenyl ring) and n to Π* (H-C=N) transition [17] . Whereas, for Co(II) metal complexes, the electronic spectral results display two bands for Val-Co at 360 nm (27777 cm⁻¹), and 727 nm

(13755 cm⁻¹), assigned to ⁴T_1g(F) to ⁴T_2g(F), and ⁴T_1g(F) to ⁴T_1g(p), transition in octahedral field [13] , indicating an octahedral geometry around Co(II) ion. Their magnetic moments at room temperature (μeff = ~4.4 μ_B), corroborate with high-spin octahedral coordination of the Co(II)ion [15] [18] .

The ¹H NMR spectra of the investigated Schiff base ligands (1 - 3) presented in Table 3, and the assignment clearly presented as it numbered in Figure 1, which showed the following frequencies.

・ A singlet at (14.50 - 14.30 ppm) corresponds to phenolic -OH proton [19]

・ A sharp singlet frequency at (8.43 - 8.35 ppm) was observed and attributed to the α-H, for CH=N group Table 3.

・ The multiplets observed in the region (7.35 - 6.70 ppm) are ascribed to the aromatic hydrogen.

・ The triplet observed in the region (3.65 - 3.52 ppm) are assigned for (HC-R) group as illustrated in Table 3.

The ¹³C NMR spectra of the investigated Schiff base ligands (1 - 3) presented in Table 3, and the assignment clearly presented as it numbered in Figure 1, which showed the following frequencies:

・ The chemical shift values for C₁, C₃, C₅ of the aromatic carbons observed symmetrically in the range (118.05 - 116.15 ppm), where the chemical shift values for the other carbon atoms of the aromatic ring C₄, C₆ are observed at the range of (131.93 - 131.24 ppm) and the C₂ have the chemical shift values in the range (164.76 - 163.26 ppm) influenced by the phenolic group.

・ The chemical shift value for α-C (H-C=N) is observed at (163.45 ppm) influenced by imine group.

・ The chemical shift value for δC1⁻ (R-CH) for valine, leucine, and Isoleucine are observed at (78.05, 70.45, and 75.43 ppm) respectively as in Table 3.

・ The carboxylic carbon δC2⁻ have the chemical shift value in the range (173.72 - 173.00 ppm) influenced by the oxygen atoms of the carboxylic acid group.

¹³C NMR spectrum of the Schiff base ligands were recorded in DMSO d₆, all assignments of the carbon atoms were founds on the expected regions [19] .

The mass spectral fragmentation of the Schiff base ligands (1 - 3) and Co(II) metal complexes are shown in Table 4, as follows:

1) Valine Schiff base ligand is represented by the peak at m/e⁺ = 243 analogous to [C₁₂H₁₄NO₃Na] structure. Another peak at m/e⁺ = 221 is equal to the formula [C₁₂H₁₄NO₃]. The structure [C₁₂H₁₄NO] is analogous to peak at m/e⁺ = 176. Meanwhile, the peak at m/e⁺ = 132 is equal to the formula [C₉H₉NO], where the last peak at m/e⁺ = 107 is attributing to [C₇H₆O].

2) Leucine Schiff base ligand is represented by peak at m/e⁺ = 257 analogous to [C₁₃H₁₆NO₃Na]. The peak at m/e⁺ = 242 is analogous to the loss of methyl molecule from the ligand, where the loss of another methyl molecule give a peak at m/e⁺ = 227. The peak at m/e⁺ = 202 is analogous to the loss of sodium atom. Meanwhile, the last peak at m/e⁺ = 132 is attributing to formula [C₈H₇NO].

3) Isoleucine Schiff base ligand of the formula [C₁₃H₁₆NO₃Na] is represented by a base peak at m/e⁺ = 257, due to original molecular weight. The peak at m/e⁺ = 242 is analogous to the loss of the methyl molecule ( CH 3 − ) from the original ligand. The loss of another ( CH 3 − ) gives a peak at m/e⁺ = 227. Where the loss of sodium atom gives a peak at m/e⁺ = 202. The same spectrum shows a peak at m/e⁺ = 132 corresponding to the loss of (C₃H₃-O₂), from the free ligand.

4) Valine Schiff base Co(II) metal complex:

The spectrum of Schiff base Co metal complex shows a molecular ion peak at m/e⁺ = 497, corresponding to [(C₁₂H₁₄NO₃)₂Co]. Whereas, the peak at m/e⁺ = 414 analogous to [(C₉H₇NO₂)₂Co] as a result of a loss of (C₃H₇)₂. The peak at m/e⁺ = 384 due to [(C₉H₆NO₂)₂Co]. Whereas, the peak at m/e⁺ = 369 analogous to [(C₈H₆NO₂)₂Co] as result of loss of ( CH 3 − ). Another loss of (C₂H₄) gives a peak at m/e⁺ = 339. The peak appeared at m/e⁺ = 313 attributed to [(C₇H₅NO₂)₂Co].

5) Leucine Schiff base Co(II) metal complex:

The spectrum shows a molecular ion peak at m/e⁺ = 525 corresponding to [(C₁₃H₁₆NO₃)₂Co]. The peak at m/e⁺ = 468 is analogous to [(C₉H₈NO₃)Co] as a loss of (C₄H₉). Whereas, the peak at m/e⁺ = 412 is a result of a loss of another

(C₄H₉). The peak at m/e⁺ = 380 is due to loss of two oxygen atoms. Whereas, the peak at m/e⁺ = 355 is a result of loss of (C₂H₄) from the original complex.

6) Isoleucine Schiff base Co(II) metal complex:

The spectrum shows a molecular ion peak at m/e⁺ = 597 corresponding to [(C₁₃H₁₆NO₃)₂Co∙4H₂O]. The loss of 4 water molecules resulting a peak at m/e⁺ = 525, due to the original complex [(C₁₃H₁₆NO₃)₂Co]. The peak at m/e⁺ = 468 is a result of a loss of (C₄H₉) from the original peak. Whereas, a loss of another (C₄H₉) resulting a peak m/e⁺ = 412, due to the molecular formula [(C₉H₈NO₃)₂Co]. The peak at m/e⁺ = 380 is analogous to the loss of two oxygen atoms which is attributed to formula [(C₉H₈NO₂)₂Co]. the last peak at m/e⁺ = 355 corresponding to a loss of (C₂H₄) from the complex.

Antibacterial and antifungal activity of the synthesized ligands and their cobalt complexes are listed in Table 5. The results, displayed in Figure 2, are summarized in the following:

1) The all free ligands are biologically active against gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) and gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa), their Co(II) complexes show more bacterial activity against most bacterial species.

2) The three ligands are inactive against fungi (Candida albicans and Aspergillus flavus) but their complexes show activity against Candida albicans.

These results may be explained onthe bases that the metal complexes penetrate more easily through the bacterial cell wall, due to the proteic denaturation of the sulphydrile group [20] , destroying the bacterial cell wall.

The molecular docking approach can be used to model the interaction between a small molecule and a protein at the atomic level, which allow us to characterize the behavior of small molecules in the binding site of target proteins as well as to elucidate fundamental biochemical processes [18] . The docking process involves two basic steps: prediction of the ligand conformation as well as its position and

orientation within these sites (usually referred to as pose) and assessment of the binding affinity. These two steps are related to sampling methods and scoring schemes, respectively, which will be discussed in the theory section [21] Mol format file was used for docking process. Docking of these compounds into ATP binding sites of 3GEY transferase enzyme was performed using Moe 2009 program to stimulate the binding model and the protein crystal structure was obtained from the Protein Data Bank (PDB).

Molecular docking investigation proved that, ligands and their Co²⁺ complexes have shown interesting interaction with active site amino acids of ribosyltransferase (code: 3GEY). All ligands have many interactions as pointed in (Figure 3). For L₁, the presence of side chain acceptor interaction from the Tyr 582 to the carbonyl carboxylic group of the igand. For L₂ and L₃ the presence of metal contact receptor interaction between the nitrogen of His A537 and the sodium carboxylate. For Co (II) complexes the presence of polar and arene-arene type of bonding with Tyr A582.