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Y. Liu et al. / Journal of Organometallic Chemistry 899 (2019) 120903
benzyl dithiocarbazate (1.2 mmol) and TsOH (1.2 mmol) were
ground at room temperature. The progress of the reaction was
monitored by TLC until completed. And the mixture was incubated
in an oven at 80 ꢂC for 1 h. Then, The products were washed with
water, filtered through buchner funnel, recrystallized from ethanol
and dried (Scheme 1).
incubated at 30 ꢂC for 48 h. The results were recorded as the
diameter of the inhibition zones and compared with the standard
drug Nystatin.
2.4.3. Minimum inhibitory concentration (MIC)
Compounds with the high antimicrobial activity (ꢃ20 mm)
were selected for minimal inhibitory concentration (MIC) studies.
The minimum inhibitory concentration was determined using disk
diffusion techniques, and compounds containing 10, 25, 50, and
2.3. Synthesis of the metal (II) complexes
Among all Schiff bases, L1, L6, L11 are representative compounds
containing electron withdrawing and electron donating sub-
stituents. They were selected to synthesize the novel metal (II)
complexes with M(OAc)2$2H2O.
100 mg/mL were prepared and applied.
3. Results and discussion
In a dry agate mortar, S-benzyl-N-(1-ferrocenyl -3-arylacrylic
acid ketone) dithiocarbazinate (2 mmol), M(OAc)2$2H2O (1 mmol)
and TsOH (1.2 mmol) were ground at room temperature, moni-
toring by TLC until completed. The mixture was washed with water,
filtered through buchner funnel, recrystallized from acetone and
dried (Scheme 1).
3.1. Optimization of reaction conditions
As is known to all, the liquid-phase method has the disadvan-
tages with the great environmental pollution, long reaction time
and so on. Instead, the solvent-free method is the green method
with mild conditions, shorter time, higher yield and so on. Taking
the reaction of S-benzyl-N-(1-ferrocenyl-3- propiophenone)
dithiocarba-zinate (L1) and Pb(OAc)2$2H2O as an example, opti-
mizing the reaction conditions (Scheme 2), the results were shown
in Table 1.
Under the solvent-free method, the catalysts were: SiO2$SO3H,
silica gel, neutral Al2O3, BSA (benzenesulfonic acid), TsOH and DBSA
(dodecyl-benzenesulfonic acid), no catalyst as a blank experiment
(Table 1). The yield of the catalyst used was higher than the blank
experiment. And the highest yield was up to 90.1% under the
catalyst of TsOH with the dosage 1:1.2 (Table 1, entry 8).
Schiff base was synthesized from S-benzyl dithiocarbazate and
different ferrocenl chalcone through the Nucleophilic addition-
elimination reaction. Extending the substrate of the reaction and
comparing the yields of compounds under the optimum conditions,
they were synthesized by liquid-phase and solvent-free method,
respectively. For different Schiff bases and metal complexes, the
yields by the solvent-free method were higher than the liquid-
phase method (Fig. 1, Fig. 2).
2.4. Biological activity
2.4.1. Antibacterial activity (in vitro)
To assess the biological potential of the synthesized compounds,
they were tested by different species of bacteria. The organisms
used in the present investigations included three Gram-positive
bacterium (S. aureus ATCC 9144, Streptococcus BNCC 1022637 and
Actinomycetes ATCC 55605) and two Gram-negative bacterium
(E. coli ATCC 25922 and P. aeruginosa ATCC 43288). The antimi-
crobial activities were evaluated at a concentration of 3 g/L. The
bacterial inoculum was coated on the surface of the nutrient agar
with the sterile cotton swab. Tetracycline was set as the standard
antibacterial drug, DMSO as a control solvent and the plates were
incubated overnight at 37 ꢂC. The results of the antimicrobial ac-
tivities were showed in Fig. 5.
2.4.2. Antifungal activity (in vitro)
The antifungal activities of compounds were tested against five
fungal strains (C. albicans, A. flavus, A. niger ATCC9092, A. fumigatus
ATCC 46645, S. cerevisiae ATCC 87358) in vitro. And it was cultured
on malt medium about 48 h, with filtering of the culture through a
thin layer of sterile sintered glass G2 to remove mycelia fragments
before the solution containing the spores was used for inoculation.
For preparation of plates and inoculation, 1.0 mL of inoculum was
added to 50 mL agar medium (50 ꢂC) and mixed. The agar was
poured into the 120 mm Petri dish and allowed to cool to room
temperature. Wells (6 mm in diameter) were cut in the agar plates
using a proper sterile tube. Then, fill wells were filled up to the
surface of agar with 0.1 mL of the tested compounds dissolved in
Among them, the yields of the Schiff bases having strong
DMSO (200
mmol/mL). The plates were left on a leveled surface, and
Scheme 2. Synthesis of H2.
Scheme 1. Synthesis of Schiff bases and their metal (II) complexes.
Dang, Yang
