2.1. Chemicals
4-Chlorobenzaldehyde, 4-Bromobenzaldehyde, 4-Methoxybenzaldehyde, 4-Hydroxy-3-methoxy benzaldehyde, and Piperidine were purchased from (BDH, England). 4-Dimethylaminobenzaldehyde and Dimethyl sulfoxide from (MERCK, Germany). 2,4-Dihydroxybenzaldehyde and 3-Amino-1,2,4-triazole-5-thiole from (Sigma). 4-Methylbenzaldehyde (Fluka); 2,4-Dichlorobenzaldehyde (CDH, India); 4-Nitrobenzaldehyde and 2-Bromobenzaldehyde (Alfa Aesar, USA). Absolute ethanol (QRëC).TLC silica gel 60 F254, aluminium sheet, 20cm x 20cm (Merck, Germany).
2.2. Instruments
Except for a Bruker Avance, all of the devices or instruments used to determine the structure of produced chemicals are located at the College of Applied Sciences, Samarra University. Infrared spectra were recorded using a Shimadzu Japanese Company-supplied Fourier Transform Infrared Spectrophotometer/FTIR-8400S device: samples were created as (KBr) discs. The nuclear magnetic resonance (1H-NMR) spectra were measured using a Bruker Advance (400 MHz) at Basra University's College of Education, Department of Chemistry. Using DMSO-d6 as an internal reference [1H (DMSO-d6) = 2.51 ppm and 13C (DMSO-d6) = 39.9 ppm]. Shimadzu GC-MS-QP 2010 Ultra mass spectrometer recorded mass spectra: solvent, MeOH.
2.3. Biological assay
2.3.1. Compounds and cells
Before being serially diluted for utilization in a culture medium, all test compounds were dissolved in DMSO at an initial concentration of 0.032 mg/mL. Pathogenic microorganisms of four types were utilized, including klebsiella Pneumoniae and Pseudomonas aeruginosa (Gr-ve), examples of Gram-negative bacteria. Gram-positive (Gr+ve) microorganisms include Staphylococcus aureus and Streptococcus mutans. The four bacterial species were examined at Samarra University's Microbiology Laboratory, Pathological Analysis Department, and College of Applied Sciences.
2.3.2. Antibacterial assay
The organic solvent DMSO was used to create test solutions for the substances (T1–T10) at varying concentrations (0.032, 0.016, 0.008, 0.004, 0.002, 0.001, and 0.0005 mg/ml, respectively). Then, the modified agar diffusion method (Dahham et al., 2014 Nalawade et al., 2016), also known as the Kerby-Bauer method, was used to produce and sterilise the nutritional medium, after which the dishes were infected with bacterial isolates using the diffusion method. The seven concentrations were distributed across two plates dug at a rate of 3–4 holes with a diameter of 5 mm in the vicinity of each dish. Finally, 50–70 µL of each of the seven concentrations prepared were added to each pit. The dishes were then incubated at 37 °C for 24 hours. All the results were read the next day to determine the sensitivity of the used derivatives, which depend on the diameter of inhibition. An increase in the diameter of inhibition means an increase in the biological activity of the prepared compounds.
2.4. Synthesis method
2.4.1 General procedure for properties of the new Schiff bases series (T1-T10)
The compounds (T1-T10) were synthesized by combining 70 µL of morpholine with 2-amino-4,2,1-triazole-5-thiol (0.5 g, 0.004 mol) and stirring at 15 minutes before adding equivalent moles of the respective aldehydes (0.004 mol) in 100mL of absolute ethanol and refluxing while stirring for 6 hours.
Yield: (1.33g, 74.2%), Light Orange crystals; mp: (159-162) °C. UV ?max (MeOH):324 nm. IR (KBr, cm-1):3263 (N-H); 3040 (C-H aromatic); 2966 (C-H aliphatic); 1604 (C=N); 1560 and 1456 (C=C aromatic); 1355 (-NO2 asymmetrical stretching); 702 (C-S). 1H-NMR (400 MHz, DMSO-d6) d, ppm: 8.48 (1H, s, -CH=N-)imine; 8.03 (2H, d, J=8.2 Hz, H-3, H-5)ph; 8.28 (2H, d, J=8.0 Hz, H-2, H-6)ph; 3.11 (4H, t, J=4.0 Hz, H-2’, H-6’)mor; 3.81 (4H, t, J=4.0 Hz, H-3’, H-5’)mor (Fig.2).
Yield: (1.34g, 53.8%), Red; mp: sticky°C. UV ?max (MeOH):318 nm. IR (KBr, cm-1):3329(O-H); 3267 (N-H); 3035 (C-H aromatic); 2933 (C-H aliphatic); 1662 (C=N); 1604 and 1529 (C=C aromatic); 1168 (C-O)(Fig.3).
Yield: (1.47g, 75.7%), Light Yellow crystals; mp:( 173-175) C°. UV ?max (MeOH):308 nm. IR (KBr, cm-1): 3448 (N-H); 3150(C-H aromatic); 2966 (C-H aliphatic); 1643 (C=N); 1595 and 1544 (C=C aromatic); 657 (C-Br). 1H-NMR (400 MHz, DMSO-d6) d, ppm: 8.35 (1H, s, -CH=N-)imine; 7.79 (2H, d, J=8.0 Hz, H-3, H-5)ph; 7.48 (2H, d, J=8.2 Hz, H-2, H-6)ph; 3.13 (4H, t, J=4.0 Hz, H-2’, H-6’)mor; 3.82 (4H, t, J=4.0 Hz, H-3’, H-5’)mor (Fig.4).
Yield: (1.29g, 63.5%), Off White crystals; mp: (225-227) C°. UV ?max (MeOH):302 nm. IR (KBr, cm-1):3250 (N-H); 3080(C-H aromatic); 2962 (C-H aliphatic); 1640 (C=N); 1597 and 1473 (C=C aromatic); 700(C-Cl). GC-MS: [m/z, (%)]: 326 ([M]+,15%), 102 (85%), 74 (60%), 43 (100%)(Fig.5).
Yield: (1.27g, 61.4%), Light Yellow crystals; mp: (164-166) C°. UV ?max (MeOH):304 nm. IR (KBr, cm-1):3394 (N-H); 3040(C-H aromatic); 2970 (C-H aliphatic); 1645 (C=N); 1604 and 1516 (C=C aromatic); 2854 and 1456(O-CH3).GC-MS: [m/z, (%)]: 322([M]+, 10%), 158 (48%), 113 (43%), 71(100%) (Fig.6).
Yield: (1.21g, 42.5%), Off White crystals; mp: (190-192) C°. UV ?max (MeOH):302 nm. IR (KBr, cm-1):3253 (N-H); 3120(C-H aromatic); 2966 (C-H aliphatic); 1651(C=N); 1598 and 1550 (C=C aromatic); 2912 and 1463(-CH3). 1H-NMR (400 MHz, DMSO-d6) d, ppm: 8.29 (1H, s, -CH=N-)imine; 7.70 (2H, d, J=8.0 Hz, H-3, H-5)ph; 6.97 (2H, d, J=8.0 Hz, H-2, H-6)ph; 3.08 (4H, t, J=4.0 Hz, H-2’, H-6’)mor; 3.79 (4H, t, J=4.0 Hz, H-3’, H-5’)mor. GC-MS: [m/z, (%)]: 306 ([M]+,25%), 117 (65%), 56 (65%), 44 (100%)(Fig.7).
Yield: (1.34g, 81.5%), Light Orange crystals; mp: (175-177) C°. UV ?max (MeOH):348 nm. IR (KBr, cm-1):3421 (N-H); 3025(C-H aromatic); 2958(C-H aliphatic); 1633(C=N); 1604 and 1527 (C=C aromatic); 1357(C-N); 2856(CH3-N). GC-MS: [m/z, (%)]: 335 ([M]+,7%), 122 (14%), 106 (35%), 91 (100%)(Fig.8).
Yield: (1.28g, 75.0%), Dark Brown; mp: sticky C°. UV ?max (MeOH):328 nm. IR (KBr, cm-1):3442 (N-H); 3038(C-H aromatic); 2970 (C-H aliphatic); 1647 (C=N); 1587 and 1506 (C=C aromatic); 1336(C-O). GC-MS: [m/z, (%)]: 324 ([M]+,11%), 247 (10%), 168 (13%), 108 (100%) (Fig.9).
Yield: (1.43g, 72.0%), Light Brown crystals; mp: (251-253) C°. UV ?max (MeOH):312 nm. IR (KBr, cm-1):3259 (N-H); 3044(C-H aromatic); 2962 (C-H aliphatic); 1591(C=N); 1564 and 1463 (C=C aromatic); 773(C-Cl). 1H-NMR (400 MHz, DMSO-d6) d, ppm: 8.63 (1H, s, -CH=N-)imine; 8.02 (1H, d, J=8.0 Hz, H-6)ph; 7.57 (1H, dd, J=8.0 Hz, H-5)ph; 7.60 (1H, s, Hz, H-3)ph; 3.13 (4H, t, J=4.0 Hz, H-2’, H-6’)mor; 3.82 (4H, t, J=4.0 Hz, H-3’, H-5’)mor(Fig.10).
Yield: (1.47g, 63.9%), Yellow crystals; mp: (277-279) C°. UV ?max (MeOH):314 nm. IR (KBr, cm-1):3251 (N-H); 3078(C-H aromatic); 2962 (C-H aliphatic); 1597 (C=N); 1560 and 1473 (C=C aromatic); 600(C-Br)(Fig.11).