\n",
- " Preparation of CS Schiff Base Derivatives\n",
- "
\n",
- " Characterization of CSSBs\n",
- "
\n",
- " FT-IR\n",
- "Spectroscopy and
1H NMR\n",
- "and
13C NMR Analyses\n",
- "
\n",
- " The FT-IR spectra of CSSBs (CS-P1, CS-P2, and CS-P3) are shown in [Figures S10–S12](\"http://pubs.acs.org/doi/suppl/10.1021/acsomega.0c01342/suppl_file/ao0c01342_si_001.pdf\") in the SI, respectively.\n",
- " All spectra of the new derivatives displayed a vibration band at 1633–1655 cm –1 corresponding to the (−CN) group.\n",
- " The aromatic ring showed a stretching vibration band ranging from 1400 to 1500 cm –1 related to the C–C bond, while the absorption band at 1057 cm –1 corresponded to the aromatic in-plane C–H bending.\n",
- " \n",
- " [ No band was observed in the region 1660–1730 cm ](\"#ref34\")–1 , which proved the absence of the carbonyl group, which in turn indicated that no residue of free aldehydes remained.\n",
- " The vibration bands at 2921 and 2883 cm –1 were related to the C–H stretching of methyl and methylene groups, respectively.\n",
- " \n",
- " [ The glycosidic bonds showed bands at 1155 and 900 cm ](\"#ref34\")–1 .\n",
- " The vibration bands at 1205–975 cm –1 were related to the C–O, C–C, and C–O–C stretching of glycosidic bonds and the pyranose ring.\n",
- " \n",
- " [\n",
- " ](\"#ref35\")\n",
- "
\n",
- "
\n",
- " The structure of the prepared CSSBs was confirmed by 1 H and 13 C NMR.\n",
- " The 1 H NMR spectra of the synthesized derivatives CS-P1, CS-P2, and CS-P3 are shown in [Figures S13–S15](\"http://pubs.acs.org/doi/suppl/10.1021/acsomega.0c01342/suppl_file/ao0c01342_si_001.pdf\") in the SI, respectively.\n",
- " The 13 C NMR spectra for CS-P1, CS-P2, and CS-P3 are shown in [Figures S16–S18](\"http://pubs.acs.org/doi/suppl/10.1021/acsomega.0c01342/suppl_file/ao0c01342_si_001.pdf\") in the SI, respectively.\n",
- " The 1 H and 13 C NMR data of all SBs are shown below.\n",
- "
\n",
- "
\n",
- "
\n",
- " Compound\n",
- "CS-P1\n",
- "
\n",
- " δ H (500 MHz, d\n",
- " 6 -DMSO) 7.33 (1H, d, J 0.8), 6.84 (1H, dd, J 7.5, 1.4), 6.78 (1H, td, J 7.5, 1.4), 6.38 (1H, td, J 7.5, 1.4), 6.33 (1H, dd, J 7.5, 1.5), 6.12 (1H, s), 5.83 (1H, d, J 2.5), 5.04 (1H, d, J 0.8), 4.93 (1H, s), 4.25 (1H, s), 3.92 (1H, s), 3.62 (1H, td, J 7.7, 4.0), 3.46 (1H, dd, J 12.2, 6.0), 3.35 (1H, ddd, J 9.4, 5.9, 3.5), 3.21 (1H, dd, J 12.3, 5.9), 3.00 (1H, dd, J 4.0, 2.5), 1.80 (1H, ddd, J 12.3, 7.7, 3.5), 1.31 (1H, ddd, J 12.3, 7.7, 3.5).\n",
- "
\n",
- "
\n",
- " δ C (125 MHz, d\n",
- " 6 -DMSO)153.38,\n",
- " 143.12, 134.23, 131.24, 129.33, 127.75, 122.07, 120.77, 114.44, 95.68, 74.70, 73.70, 69.45, 66.03, 37.86.\n",
- "
\n",
- "
\n",
- "
\n",
- " Compound CS-P2\n",
- "
\n",
- " δ H (500 MHz, d\n",
- " 6 -DMSO) 7.84 (1H, s), 7.64 (1H, s), 7.30 (1H, s), 7.25 (1H, dd, J 7.5, 1.5), 6.45 (1H, d, J 7.5), 6.14 (1H, d, J 3.1), 5.67 (1H, s), 5.53 (1H, s), 5.26 (2H, s), 3.88 (1H, td, J 7.8, 5.0), 3.64 (1H, s), 3.37 (1H, dd, J 12.4, 1.3), 3.25 (1H, ddd, J 4.8, 3.4, 1.3), 3.11 (1H, dd, J 12.4, 1.3), 2.89 (1H, dd, J 5.0, 3.1), 1.70 (1H, ddd, J 12.3, 7.8, 3.5), 1.30 (1H, ddd, J 12.3, 7.8, 3.5).\n",
- "
\n",
- "
\n",
- " δ C (125 MHz, d\n",
- " 6 -DMSO) 164.71, 147.34, 147.27, 139.42, 132.73, 125.45, 121.55, 112.39, 96.94, 75.14, 74.96, 70.71, 67.29, 63.16, 39.52, 39.12.\n",
- "
\n",
- "
\n",
- "
\n",
- " Compound CS-P3\n",
- "
\n",
- " δ H (500 MHz, d\n",
- " 6 -DMSO) 7.36 (1H, d, J 0.8), 6.38 (1H, d, J 2.5), 5.72 (1H, s), 5.26 (1H, s), 4.56 (1H, d, J 0.8), 4.33 (1H, s), 4.18–3.99\n",
- " (2H, m), 3.89 (1H, s), 3.63 (1H, dd, J 12.4, 1.3), 3.52 (1H, ddd, J 4.9, 3.5, 1.3), 3.38 (1H, dd, J 12.4, 1.3), 3.16 (1H, dd, J 4.4, 2.5), 1.96 (1H, ddd, J 12.3, 7.8, 3.6), 1.54 (1H, ddd, J 12.3, 7.8, 3.6).\n",
- "
\n",
- "
\n",
- " δ C (125 MHz, d\n",
- " 6 -DMSO) 158.92, 152.49, 134.20, 97.34, 86.33, 75.36, 71.11, 67.70, 64.24, 39.52, 34.06.\n",
- "
\n",
- "
\n",
- " The synthesized new CSSBs presented typical peaks of the Cs and SB parts.\n",
- "
\n",
- "
\n",
- "
\n",
- " Solubility Study\n",
- "
\n",
- " Different organic solvents were used to test the solubility of the synthesized compounds.\n",
- " \n",
- " [Table ](\"#tbl1\")[\n",
- " ](\"#tbl1\") shows the results.\n",
- " The prepared compounds dissolve in dimethyl sulfoxide and mixtures of equal proportions of dimethyl sulfoxide and trifluoroacetic acid.\n",
- " Partial dissolution or swelling was observed in some solvents such as dilute hydrochloric acid and acetic acid at 70 °C.\n",
- " In contrast, the products are not soluble in most inorganic solvents.\n",
- "
\n",
- "
\n",
- " 1\n",
- " Solubility Characteristics of CSSBs\n",
- "in a Variety of Solvents[\n",
- " \n",
- " solvents CH3COOH CF3COOH DMSO HCl NaOH H2O KOH DMSO + CF3COOH comp. codes 25 °C 70 °C 25 °C 70 °C 25 °C 25 °C 25 °C 25 °C 25 °C 25 °C\n",
- " ](\"#t1fn1\")\n",
- " CS-P1 | \n",
- " S+ | \n",
- " S* | \n",
- " S** | \n",
- " S** | \n",
- " S | \n",
- " S* | \n",
- " S+ | \n",
- " S+ | \n",
- " S** | \n",
- " S | \n",
- "
\n",
- " \n",
- " CS-P2 | \n",
- " S+ | \n",
- " S* | \n",
- " S** | \n",
- " S** | \n",
- " S | \n",
- " S* | \n",
- " S+ | \n",
- " S+ | \n",
- " S** | \n",
- " S | \n",
- "
\n",
- " \n",
- " CS-P3 | \n",
- " S+ | \n",
- " S* | \n",
- " S** | \n",
- " S** | \n",
- " S | \n",
- " S* | \n",
- " S+ | \n",
- " S+ | \n",
- " S** | \n",
- " S | \n",
- "
\n",
- " \n",
- " \n",
- " [a]\n",
- " S = soluble, S+ = insoluble, S*\n",
- "= partially soluble and swelling, S** = partially soluble.
\n",
- " \n",
- " \n",
- "
\n",
- "
\n",
- "
\n",
- " In\n",
- "Vitro Cytotoxicity Study\n",
- "
\n",
- " The cytotoxicity assay for the synthesized compounds was carried out based on MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide].\n",
- " MTT assay is a colorimetric assay used for assessing cell viability and to measure cytotoxicity.\n",
- " As illustrated in [Table ](\"#tbl2\")[\n",
- " ](\"#tbl2\") , the results of the tested compounds CS-P1, CS-P2, and CS-P3 show a small variation between samples in comparison with the control.\n",
- " Several earlier research studies have demonstrated that CS and CSSB derivatives have little cellular toxicity.\n",
- " Consequently, CS has many applications in the medical field.\n",
- " \n",
- " \n",
- " [−](\"#ref36\")[\n",
- " ](\"#ref37\")[\n",
- " ](\"#ref38\") The assay revealed that using a higher amount of the sample (200 mg) showed a cell viability of 89, 90, 90.1, and 91% for CS, CS-P1, CS-P2, and CS-P3, respectively.\n",
- " Conversely, a smaller amount (25 mg) of the tested compound showed a slight cytotoxicity of up to 2.5% compared with high concentrations, which is extremely suitable in medical applications.\n",
- " According to reported studies, compounds with higher than 75% cell viability are considered noncytotoxic.\n",
- " \n",
- " [ The cell viability assessment proved that the selection of these compound may depend on the antibacterial activity for their use in medical applications.](\"#ref39\")\n",
- "
\n",
- "
\n",
- " 2\n",
- " Cytotoxicity Test of CS and Their\n",
- "SB Derivatives on the Viability of Mouse Fibroblast Cell Lines[\n",
- " \n",
- " comp. conc. (mg) viable\n",
- "cells in the presence of CS viable cells\n",
- "in the presence of CS-P1 viable cells\n",
- "in the presence of CS-P2 viable cells\n",
- "in the presence of CS-P3\n",
- " ](\"#t2fn1\")\n",
- " 25 | \n",
- " 99 ± 0.83 | \n",
- " 99 ± 0.73 | \n",
- " 99 ± 0.60 | \n",
- " 99 ± 0.75 | \n",
- "
\n",
- " \n",
- " 50 | \n",
- " 97 ± 0.73 | \n",
- " 99 ± 0.91 | \n",
- " 98.1 ± 1.3 | \n",
- " 99 ± 0.89 | \n",
- "
\n",
- " \n",
- " 100 | \n",
- " 94 ± 0.63 | \n",
- " 98 ± 0.74 | \n",
- " 98 ± 1.2 | \n",
- " 98 ± 0.50 | \n",
- "
\n",
- " \n",
- " 150 | \n",
- " 93 ± 0.88 | \n",
- " 97 ± 0.65 | \n",
- " 98 ± 0.62 | \n",
- " 96 ± 1.2 | \n",
- "
\n",
- " \n",
- " 200 | \n",
- " 89 ± 0.53 | \n",
- " 90 ± 0.72 | \n",
- " 90.1 ± 0.74 | \n",
- " 91 ± 1.2 | \n",
- "
\n",
- " \n",
- " \n",
- " [a]\n",
- " The experiment\n",
- "was repeated three\n",
- "times and the mean was calculated.
\n",
- " \n",
- " \n",
- "
\n",
- "
\n",
- " Antimicrobial Study\n",
- "
\n",
- " The inhibition zone technique was used to assess the antibacterial activity of the CSSB derivatives.\n",
- " The results are shown in [Table ](\"#tbl3\")[\n",
- " ](\"#tbl3\") .\n",
- " From the results, all of the CSSBs and CS have a similar impact on strains of both E. coli and K. pneumonia and is similar to that of Cs.\n",
- " The reported study demonstrated that CS could terminate the cell formation of S. aureus and E. coli .\n",
- " \n",
- " [ CSSBs showed antibacterial action against S. aureus with an inhibition zone of 22 ± 0.3, 20 ± 1.2, and 19 ± 0.62 mm for CS-P1, CS-P2, and CS-P3, respectively.](\"#ref40\")\n",
- " The results also revealed that CS-P1, CS-P2, and CS-P3 have antibacterial action against S. mutans with an inhibition zone of 15 ± 0.89, 17 ± 0.50, and 18 ± 1.20 mm, respectively.\n",
- " Antifungal activity tests against two strains of fungi were carried out, and all verified CSSBs presented good results.\n",
- " The difference in inhibition between the two strains may result from the variances in the cell wall structures.\n",
- " From the result, it may be confirmed that the antibacterial action is through the breakage of the cell wall rather than the mechanism of interaction of CS derivatives with the DNA in the microorganism.\n",
- " The reaction of the active group on the CSSBs with the cell wall reduces permeability, which causes a shortage of substances in the cell, for example, amino acids, proteins, electrolytes, and lactate dehydrogenase.\n",
- " Therefore, the synthesized compounds lead to the inhibition of the metabolism of the bacteria and cause death.\n",
- " \n",
- " [\n",
- " ](\"#ref41\")\n",
- "
\n",
- "
\n",
- " 3\n",
- " Antimicrobial\n",
- "and Antifungal Activity\n",
- "Results of CS and CSSB Derivatives[\n",
- " \n",
- " Gram-negative\n",
- "bacteria Gram-positive\n",
- "bacteria fungi comp. codes \n",
- " E. coli\n",
- " K. pneumonia\n",
- " S. aureus\n",
- " S. mutans\n",
- " C. albicans\n",
- " A. fumigatus\n",
- " \n",
- " ](\"#t3fn1\")\n",
- " CS | \n",
- " 24 ± 0.63 | \n",
- " 26 ± 0.73 | \n",
- " NA | \n",
- " NA | \n",
- " 26 ± 0.79 | \n",
- " 16 ± 0.83 | \n",
- "
\n",
- " \n",
- " CS-P1 | \n",
- " 22 ± 0.73 | \n",
- " 28 ± 0.91 | \n",
- " 22 ± 0.3 | \n",
- " 15 ± 0.89 | \n",
- " 34 ± 0.99 | \n",
- " 26 ± 0.91 | \n",
- "
\n",
- " \n",
- " CS-P2 | \n",
- " 27 ± 0.83 | \n",
- " 27 ± 0.72 | \n",
- " 20 ± 1.2 | \n",
- " 17 ± 0.50 | \n",
- " 31 ± 1.29 | \n",
- " 25 ± 0.72 | \n",
- "
\n",
- " \n",
- " CS-P3 | \n",
- " 22 ± 0.98 | \n",
- " 26 ± 0.65 | \n",
- " 19 ± 0.62 | \n",
- " 18 ± 1.20 | \n",
- " 26 ± 0.49 | \n",
- " 21 ± 0.65 | \n",
- "
\n",
- " \n",
- " \n",
- " [a]\n",
- " NA means not detected.
\n",
- " \n",
- " \n",
- "
\n",
- "
\n",
- " Based on reported research, [ many mechanisms are proposed to clarify the action path of CS on microorganisms, which differs depending on the metabolic procedure and the structure of the cell wall.](\"#ref42\")\n",
- " The first suggestion is the interruption of the cell wall of the organism because of the electrostatic attraction between the positively charged amine groups in CS and the negative residue group in the bacterial cell wall, such as −COO – or PO 4\n",
- " 3– .\n",
- " The second mechanism suggested is the interaction of bacterial DNA with CS, which causes the inhibition of protein synthesis and mRNA by permeation of CS into the bacterial cell and then the nuclei.\n",
- " Another suggestion is based on the ability of CS to form a complex with metals, for instance, Zn 2+ , Mg 2+ , and Ca 2+ ; these metals are important for bacterial metabolic processes and growth.\n",
- "
\n",
- "