4 of 11
MAAREF ET AL.
2.4.4 | 2,20-((1E,10E)-
((Methylenebis(4,1-phenylene))bis
(azanylylidene))bis (methanylylidene)) bis
(naphthalen-1-ol) (3d)
126.2, 129.1, 130.7, 132.0, 133.3, 133.5, 134.2, 134.6, 138.2,
142.9, 145.5, 152.8, 158.8, 162.0, 176.1. Anal. calcd for
C34H24N2O4S (556.63): C, 73.36; H, 4.35; N, 5.03; S,
5.76%. Found: C, 73.00; H, 4.42; N, 5.29; S, 5.50%. MS:
m/z (%) = 556 (12, M+), 508 (15), 402 (100), 387 (23),
354 (8), 339 (18), 277 (11), 189 (14), 169 (23), 152 (11),
140 (22), 127 (22), 115 (46), 92 (22), 76 (13), 65 (31).
M.p. 238–242ꢁC. IR (KBr, cm−1): IR (KBr, cm−1): 1481,
1
1562, 1598, 1618, 3443. H-NMR (400 MHz, CDCl3) δ:
4.09 (s, 2H, CH2), 7.10 (d, J = 9.2 Hz, 2H, H-Ar),
7.31–7.37 (m, 10H, H-Ar), 7.54 (t, J = 7.6 Hz, 2H, H-Ar),
7.73 (d, J = 8.0 Hz, 2H, H-Ar), 7.82 (d, J = 9.2 Hz, 2H, H-
Ar), 8.10 (d, J = 8.4 Hz, 2H, H-Ar), 9.34 (s, 1H, HC=N),
9.35 (s, 1H, HC=N), 15.57 (s, 2H, OH). 13C-NMR
(100 MHz, CDCl3) δ: 40.9, 108.7, 118.8, 120.5, 122.4,
123.5, 127.3, 128.1, 129.4, 130.2, 133.2, 136.7, 139.4, 143.4,
154.3, 170.5. Anal. calcd for C35H26N2O2 (506.59): C,
82.98; H, 5.17; N, 5.53%. Found: C, 83.02; H, 5.12; N,
5.41%. MS: m/z (%) = 506 (69, M+), 367 (17), 352 (14),
337 (100), 252 (45), 190 (8), 180 (7), 165 (31), 152 (14),
140 (6), 127 (13), 115 (34), 106 (6), 90 (11), 77 (6).
2.5 | Anti-microbial assays
Based on the protocol of the study, the broth dilution
method has been used to assess antibacterial activities on
Escherichia coli (ATCC 25922), Klebsiella pneumoniae
(ATCC 10031), Salmonella typhi (ATCC 1609), Pseudo-
monas aeruginosa (ATCC 27853), Enterococcus faecium,
Enterococcus faecalis (ATCC 29212), methicillin-resistant
Staphylococcus aureus (MRSA), Acinetobacter and
vancomycin-resistant Enterococcus (VRE) separated from
hospital-attained infections. In addition, Mueller−Hinton
broth, complemented with 2% glucose, has been
employed as the bacterial growth media. Moreover, the
antibacterial spectrum of bis-Schiff bases has been
applied for calculating suppression zone diameter.
Furthermore, a swab has been used for performing a
standard inoculum of 107 colony-forming units (CFU)/ml
to examine the stains on Mueller–Hinton agar plate.
Additionally, antibacterial agent-impregnated filter paper
discs (6 mg/ml) have been inserted on the agar medium.
Then, they were incubated at 37ꢁC overnight to obtain
the suppression zone diameter.
With regard to the research design, minimum inhibi-
tory concentration (MIC) has been employed for quanti-
tative computation of antibacterial activity of bis-Schiff
bases via the broth dilution techniques. In this stage, the
study bacterial suspension (107 CFU/ml) has been added
into the test tubes consisting of 5 ml of Mueller−Hinton
broth with 10-fold dilutions of bis-Schiff bases, which
were in the range between 0.003 mg/l and 36 mg/l. Then,
incubating the tubes was performed at 37ꢁC for 24 hr aer-
obically. Afterwards, they were investigated for visible
turbidity with no stirring. It should be noted that MIC
represents the minimum bis-Schiff bases concentration
without bacterial growth. Notably, each experiment was
performed three times in order to achieve satisfactory
outcomes of the MIC (μg/ml) for the strain. When the
MIC value was specified, 0.1 ml of inoculum from the
contents of the tubes with no noticeable turbidity was
sub-cultured on the nutrient agar plate. Afterwards, it
was been incubated at 37ꢁC for 24 hr. Then, a compari-
son was made between the emerged colony counts on
this subculture and CFU/ml counts on the original
inoculum.
2.4.5 | 2,20-((1E,10E)-
((Oxybis(4,1-phenylene))bis
(azanylylidene))bis (methanylylidene)) bis
(naphthalen-1-ol) (3e)
M.p. 241–245ꢁC. IR (KBr, cm−1): 1326, 1496, 1621, 3449.
1H-NMR (400 MHz, CDCl3) δ: 7.14–7.18 (m, 6H, H-Ar),
7.36–7.42 (m, 6H, H-Ar), 7.56 (td, 2H, J = 8.4, 1.2 Hz, H-
Ar), 7.76 (d, J = 8.0 Hz, 2H, H-Ar), 7.84 (d, J = 9.2 Hz,
2H, H-Ar), 8.15 (d, J = 8.4 Hz, 2H, H-Ar), 9.40 (s, 2H,
HC=N), 15.53 (s, 2H, 2OH). 13C-NMR (100 MHz, CDCl3)
δ: 107.4, 118.9, 119.9, 121.6, 121.9, 123.6, 127.4, 128.1,
129.4, 133.1, 136.3, 141.7, 155.1, 155.8, 168.5. Anal. calcd
for C34H24N2O3 (508.57): C, 80.30; H, 4.76; N, 5.51%.
Found: C, 80.21; H, 4.70; N, 5.53%. MS: m/z (%) = 508
(100, M+), 365 (12), 354 (28), 339 (84), 253 (53), 244 (17),
217 (10), 170 (15), 152 (13), 140 (10), 127 (18), 115 (44),
77 (7), 65 (5).
2.4.6 | 2,20-((1E,10E)-
((Sulfonylbis(4,1-phenylene))bis
(azanylylidene))bis (methanylylidene)) bis
(naphthalen-1-ol) (3f)
M.p. 237–241ꢁC. IR (KBr, cm−1): 1498, 1588, 1624, 3437.
1H-NMR (400 MHz, CDCl3) δ: 11.74 (d, J = 9.2 Hz, 2H,
H-Ar), 12.11 (d, J = 7.6 Hz, 2H, H-Ar), 12.29 (d,
J = 7.6 Hz, 2H, H-Ar), 12.48–12.54 (m, 6H, H-Ar),
12.65–12.70 (m, 6H, H-Ar), 13.22 (s, H, CH=N), 13.24
(s, H, CH=N), 14.34 (s, 1H, OH), 14.38 (s, 1H, OH). 13C-
NMR (100 MHz, CDCl3) δ: 114.11, 118.2, 125.7, 126.4,