Coordination compounds and Schiff base compounds in presence of coordination chemistry mechanism for Schiff base for mation explain the basicity character of the Schiff base ligands, biological important of Schiff base ligands and the biological revolution of transition metals using copper, for complexation of Schiff base ligands. Diversity applications of Schiff bases complexes due to catalytic biological application such anti bacterial, anti fungal, anti oxidant, anti inflammetry, anti-viral, anti tumor etc. In Cu(II) complex with the new Schiff bases of the type p-HABT and p-HBAMP were prepared by reaction of p-hydroxy benzaldehyde with 2 amino thiazole / 2 amino -6 methyl pyridine have been synthesized and characterized with the help of IR and electronic spectral data. Comparative bacterial behaviour of Schiff bases with their Cu(II) complexes have also been studied against E. coli and S Aureus.

Metal chelates of Schiff bases have played a central role in the development of coordination chemistry. They are also important components of every day products as varied as cleaning material, medicines, inks and paints. Several Schiff base are reported to be therapeutically active possessing cytotoxic, anti-inflammatory and antiviral activities. 

Schiff base metal complexes is their biological activity with the main aim being the discovery of safe and effective therapeutic agents for the treatment of bacterial infectious and cancers. A number of Schiff base metal complexes have a diverse spectrum of biological and pharmaceutical activities. For instance transition metal complexes of Schiff base ligands bearing "O" and "N" donor atoms are very important because of their biological proper lies such as antibacterial, antifungal, anti-inflammatory [2], analgesic [3,4] anticonvulsant [5], anti-tubercular [6], antioxidant [7] and anthelmintic [8]. The Schiff base-transition metal complexes have also been used as biological models to understand the structure of bimolecules and biological processes [9]. 

All the chemicals and solvents used were of analytical reagent grade. The metal salts (Cu⁺², Chlorides) Merck were used for the synthesis of metal complexes.

1.1 Physical measurements

Magnetic susceptibility measurements of the Synthesized complexes were carried out at room temperature by vibrant Sample Magneto meter (VSM) method at C.S.I.F. IIT, Chennai.

The Infrared spectra of the ligands and their metal complexes were recorded at Perkin-Elmer Spectrophotometer in the region 4000-200 cm^-1 from St. John's College Agra.

Mass Spectra of the ligands were recorded in the region 100-350 MHz at the C.S.I.F, C.D.R.I, Lucknow.

The ESR Spectra of Cu(II) complexes were recorded on a Varian X-band spectrophotometer E-112 at C.S.I.F., IIT, Chennai.

Elemental microanlyses of Carbon, hydrogen and nitrogen CHN micro analyzer were used the analysis were done at C.S.I.F., CDRI Lucknow.

The synthesized compounds were screened in vitro for their anti bacterial activities against E. coli and S. aureus using disc diffusion method[10].

1.2 Synthesis of Schiff Bases [L1]

(a) Schiff base derived from p-Hydroxy benzalidene with 2-aminothiazole (SB₁)

1.22 gm of p-hydroxy benzal dehyde and 1.0 gm of 2-amino thiazole were dissolved in 40ml dry ethanol and refluxed for 14 hours over a water bath using water condenser. The obtained solution was allowed to cool at room temperature and excess of ethanol was allowed to evaporate slowly. The concentrated solution was cooled in refrigerator and obtained product was filtered washed with ether and dried under reduced pressure over anhydrous calcium chloride.

i. Molecular formula = C₁₀H₈N₂OS

ii. Molecular weight = 204.15

iii. Melting Point =135⁰C,

iv. Colour = Brownish yellow.

v. Elemental analysis data (in %) C₁₀H₈N₂OS (204.15) found C-57.95% H=3.97% N=13.80%, S=15.75%

vi. Calculated : C = 58.82% H=3.92% N = 13.72% S = 15.70%.

vii. IR Frequencies : υ─OH = 3629 cm^-1, υ CH═N = 597cm^-1, υ C-S-C = 837 cm^-1

(b) Schiff base derived from p-Hydroxy benzaliden with 2-amino-6-methyl pyridine (SB₂)

The Schiff base was prepared by refluxing calculated quantities of 1.22gm of p-hydroxy benzaldehyde in ethanol was mixed with ethanolic solution of 1 ml of 2-amino-6-methyl pyridene (which is dissolved in ethanol). The mixture was refluxed for 12 hours over a water bath. The solution containing the product was allowed to cool at room temperature. The excess of ethanol was distilled off and the concentration solution was cooled in refrigerator for 24 hours the obtained product was filtered and washed with acetone several time and followed by ether. It was recrystallized with absolute  alcohol and dried under reduced pressure of CaCl₂.

i.Molecular formula = C₁₃H₁₂N₂O

ii.Molecular weight = 212.21

iii.Melting Point  = 170⁰C

iv.Colour = Light yellow

v.Elemental analysis (in %) found C = 72.45%, H = 5.52%, N = 13.25%

vi.Calculated C = 73.57, H = 45.69, N = 13.19%

vii.Important  IR frequencies – υ – OH = 3630cm^-1, υ-CH=N=1612 cm^-1, υ C-N-C = 1498cm^-1

1.3 Synthesis of metal complexes

(a) Preparation of metal complexes with p-HBAT (SB₁)

Where : M = Cu (II), X = Cl^–

Synthesis of the Schiff Base Metal (II) complexes

The Schiff base metal (II) complexes were prepared by reacting the Schiff base with the metal (II) ions a per the literature method (II)

The metal chloride (5m mol, 25ml) dissolved in ethanol or distilled water was added drop wise to a solution of SB₁ or SB₂ (10m ml, 25ml) in the solvent. The resulting mixture was stirred for 30 minutes and refluxed for 2-3 hours on a water bath. The contents were cooled and solvent was slowly evaporated and washed with ethanol, ether and dried in air.

Cu(C₁₀H₈N₂OS)₂Cl₂ : MP = 155⁰C, Formula weight = 542.74, colour = Dirty Black μ (B.H.) = 1.80% of element found C = 45.57%, H = 2.88%, N = 10.25%, S=11.75%, Cl = 13.25%, M = 11.76%

Calculated C = 44.26%, H=2.95%, N=10.32% S= 11.81%, Cl = 13.06%, M=11.71%

IR frequencies (cm^-1) υ_(CH=N)=1602, υ_C-S-C(thiazol) = 837, υ_(C=N) = 1512

Coordination Modes :  υ_M-O = 515, υ_M-N = 420, υ_M-Cl = 294.

Cu(C₁₃H₁₂N₂O)₂Cl₂ : MP = 160⁰C Formula weight = 558.86 colour = Dark brown, µ = 1.75 of element found C = 01.56%, H = 4.45%, N = 10.10%, Cl = 12.72%, M = 11.47%

Calculated : C = 0.558%, H = 4.33%, N = 10.02%, Cl = 12.68%, M = 11.36%

IR Frequencies : υ_(CH=N)=1600, υ_C-N-C(thiazol) = 1513, υ_(C=N) = 1512

Coordination Modes : υ_(M-O) = 525, υ_(M-N) Pyridine = 423.

1.4 Biological Assay

Schiff bases are characterized by an imine group-N=CH, which help to clarify the mechanism of transamination and racemization reaction in biological system [11].

The synthesized ligand and its transition metal (II) complexes were screened in vitro for their antibacterial activities against E. coli and Staphylococcus aureus bacterial strains using filter paper disc method [12, 13]. The disc diffusion method was used because of its convenience, efficiency and low cost.

The activity of newly synthesized Schiff base ligand is also lesser than that of its complexes. The comparative antimicrobial evaluation reveals that the Schiff base C₁₀H₈N₂OS is almost inactive against E. coli at the concentration of 250ppm and 500ppm, while it showed optimum at 750ppm. The activity of Cu(II) complexes increase with 750ppm and less active in 250ppm.

C₁₃H₁₂N₂O is almost in active against S. aureus at the cone of 250ppm and 500ppm while it showed optimum activity at 750ppm in less than E.coli. Cu(II) complexes of this ligand is less active.

Table-1

Antibacterial Activity Data  Against E.Coli

(inhibition of radial growth in mm)

Table-2

Antibacterial Activity Data  Against S. Aureus

(inhibition of radial growth in mm)

Antimicrobials-antibiotics, anti-virals anti-fungal and anti parasitics are substances widely used to prevent and treat infections in humans, aquaculture, livestock and crop production. Their effectiveness is now in jeopardy because a number of antimicrobial treatments that once worked no longer do so because microorganisms have become resistant to them.

Microorganisms that develop resistance to commonly used antimicrobials are referred to as super bugs. UNEP released in 2023 the flag ship report Bracing for Super bugs, strengthening environmental action in the 'One Health' response to antimicrobials resistance.

Microscope creatures, which have been around for and over 3.8 billion years, have the greatest genetic and metabolic variety. They play crucial function in ensuring.

1.5 Electron spin resonance values of Cu(II) complexes (cm^-1)

1.6 IR spectral Analysis

(a)) The IR ligand band at 1597cm^-1 shifted to higher side in the complexes (1597±20cm^-1) suggesting participation of azomethine group in complexation [14] Medium intensity band at ~ 410-424 cm^-1 in these complexes are assignable to υ M-N stretching vibration[15] which confirm the involvement of Nitrogen atom of azomethine group in the coordination. In the spectrum of Ligand a broad band of υ-OH stretching vibration appear at 3629cm^-1, which disappeared in complexes thus indicating deprotonation of phenolic oxygen. The involvement of Phenolate oxygen in the coordination is also supported by the band appearing at 513-520cm^-1 due to M-O[16]

The characteristic infra-red bands in the spectra of the ligand are observed at ~1512 (C=N cyclic) ~1377(C-N) and ~837 cm^-1 (C-S-C) of the thiazole moiety [17]. In halogen bands were identified in the region 300-200 cm^-1 with certainty.

(b) The strong absorption band for the pyridine ring occurring at 1498 cm^-1 (υ-pyridine) is shifted to higher frequency region by 15-20cm^-1 in the complexes, indicating the participation of nitrogen atom of pyridine in the coordination [18]. In the far infrared region 410-425cm^-1 due to M-N bond [19, 20].

In the infrared spectra of the ligand, the broad band at 3630 cm^-1 phenolic (OH) [21] disappears in the spectra of all the complexes indicating the disappears in the spectra of all the complexes indicating the deprotonation of phenolic–OH group and coordination to the metal in through the oxygen atom which is further substantiated by hypso chromatic shift of the phenolic ν_c-o modes around 1480 cm^-1 of free ligand by 10-20cm^-1 in the spectra of the complexes. The coordination through  phenolate oxygen of the ligand is further confirmed by the occurrence of new bands at 520-512 cm^-1 in the spectra of the complexes which may be assigned to M-O [22] stretching vibration respectively. The infrared spectra of Schiff base ligand exhibits a sharp band at 1612cm^-1 due to the prensence of azomethine group [23] which is shifted to lower furequency region by 20-40 cm^-1 in the complexes, indicating the coordination of
(-C=N), nitrogen in complexation. The is further confirmed by the appearance of new bands at 520-510cm-1 due to M-N bond respectively.

(ii)  Mass spectral studies

The main characteristic of a molecule when exposed to high energy electrons is the initial formation of molecular ion with a high degree of vibrational and probably electronic excitation. The majority of M⁺ ions would fragment is such away that the distribution of smaller amount of energy would occur more rapidly.

The mass spectra of the two Schiff base derived from p-hydroxy benzaldehyde with 20aminothiazole / 2-amino-6-methyl pyridine were recorded at room temperature. A graphic presentation of spectrum is used for determination of molecular mass of Schiff bases.

1. Schif, H. " Mithelilunges aus dem Universitäts laboratorium in Pisa : Eine neue Reihe organischer Basen," Annalender Chemie und Pharmacie, 131(1), 118-119, (1864).

2. Sathe, B.S., Jaya Chandran, E., Jaglap, V.A. and Sreenivasa, G.M. "Synthesis and anti bacterial, anti fungal activity of novel analogs of fluoro benzothiazole Schiff bases", Journal of chemical and Pharmaceutical Sciences, 3(4), 216-217 (2010).

3. Sandhi, S.M., Singh, N. A. Kumar, N., Lozach, O. and Meijer, L. "Synthesis, anti inflammatory analysis and Kinase (CDK – 1, CDK-5 and GSK-3) inhibition activity evaluation of  benzoimedazole / benzoizole derivatives and some Schiff's bases". Bioorganic & Medicinal Chemistry, 14(11), 3758-3765 (2006).

4. Mishra, R.M., Pandey, S. and Saxena, R. "Homozygous hemoglobin D with alpha thalassemea : case report," The Open Hematology Journal, 2, 1-4 (2011).

5. Ajit, C. Kumar and Pandeya, S.N. Synthesis and anticonvulsant activity (chemoshock) of Schiffe and mannich bases of esalin derivatives with 2-amino pyridine (mechanism of action)," International Journal of Pharm Tech Research, 4(2), 590-598 (2012).

6. About-Fadl, T., Mohammed, F.A.H. and Hassan, E.A.-S. "Syntheses, anti tubercular activity and pharmacokinetic studies of some Schiff bases derived from 1-alkylisatin and isonicotinic acid hydrazid (unh), "Archives of Pharmacal Research, 26(10), 778-784 (2003).

7. Wei, D., Li, N., Lu, G. and Yao, K. Syntheses, catalytic and biological activity of novel di nuclear copper complex with Schiff Base, "Science in China Series B, 49(3), 225-229 (2006).

8. Avaji, P.G., Vinod Kumar, C.H., Paul, S.A., Shivananda, K.N. and Nagaraju, C. "Synthesis, spectral characterization, in vitro microbiological evaluation and cytotoxic activities of novel macrocyclic bis hydra zone," European Journal of Medicinal Chemistry, 44(9), 3552-3559 (2009).

9. Chohan, Z.H., Wardell, J.L., Low, J.N., Meehan, P.R. and Ferguson, G. "Tetra ethyl ammonium bromo (1, 3-ditheol - 2-one -4, 5-dithiolato) diethyl stannate (-1-)," Acta Crystallo graphical Section C Crystal, Structure communications, 54(10) (1998).

10. Zaidan, M.R.S., Noor Rain, A., Badrul, A.R., Adlin, A., Norazah, A. and Zakeah, I. "In vitro screening of five local medicinal plants for anti-bacterial activity using diffusion method antibacterial actively wing disc diffusion method, "Tropical Biomedicine, 2, 165-170 (2006).

11. Ashraf, M.A., Mohmmad, K.W. : Synthesis, characterization and Biological Activity of Schiff Bases. IPCBEE, 10, 1-7 (2011).

12. Raman, N., Kulandaisamy, A. and Jeyasubra Manean, K., Synthesis, spectral, redox and biological studies of some Schiff base copper(II), Nickel(II), cobalt(II), Manganese(II), Zinc(II) and oxovanadium complexes derived from 1-phenyl-2,3dimethyl-4(4 iminopentan-2- one)pyrazole-5-one and 2-amino phenol/ 2-amino-thiophenol. Indian J. Chem., 41(A), 942 (2002).

13. Murray, P.R., Baron, E.J., faller, M.A.P., Tenover, F.C. and Volke, R.H. In-Manual of clinical microbiology, ASM Washington, D C, USA (1995).

14. Mishra, A.P., Srivastava, S.K. and Srivastava, V., J. Indian Chem. Soc., 73, 261 (1996).

15. Percy, G.C. and Thornton, D.A., J. Inorg. Nucl. Chem., 34, 3357 (1972).

16. Palenik, G.J. and Wester, D.W., Inorg. Chem., 17, 864 (1978).

17. Mishra, R.P., Mohapatra, B.B. and Guru, S., J. Indian Chem. Soc., 56, 832 (1973).

18. Bailer, J.C., "Comprehensive Inorganic Chemistry" Pergmann Press, New York, 3, 325 (1978).

19. Kumar, M. and Sinha, A.K., Asian J. Chem., 6(4), 782 (1994).

20. Mekami, M., Nakagawa, I. and Shimanounchi, T., Spectro Chim, Acta, 25A, 365 (1969).

21. Singh, R.V. and Tandon, J.P., Indian. J. Chem., Sect. A, 19, 602 (1988).

22. Nakamato, K., "Infrared Spectra of Inorganic and Coordination Compound," Willey, New York, 152, 167 (1963).
23. Bhaskare, C.K. and Hankara, P.P., J. Indian Chem. Soc., 72, 585 (1995).