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2.3. Synthesis of (5,5-dimethylhydantoinyl)-3-ethyl dimethylamine
(DHEDA)
75 mL of bacterial suspensions containing 106–107 CFU/mL buf-
fered at pH 7 in a 250 mL conical flask. After concussion with
200 r/min at 37 °C for 1, 5, and 10 min, 0.5 mL of the various bac-
terial suspensions were placed in sterile test tubes, each containing
4.0 mL of sterile phosphate buffer and 0.5 mL of sterile 0.1 N
sodium thiosulfate to quench any oxidative free chlorine which
might have been present, and vortexed for several seconds. The
8. 91 g (0.10 mol) of N,N-dimethyl ethanolamine were added
dropwise to 12.83 g (0.11 mol) of 99% thionyl chloride in a
250 mL flask and the mixture was cooled in an ice bath. Then,
the reaction mixture was stirred at 35–50 °C for 1 h. Thereafter,
150 mL of ethanol were added, and the mixture was refluxed. After
the reaction mixture was cooled to room temperature, the inter-
mediate 2-dimethylaminoethyl chloride hydrochloride was re-
moved by filtration. After removing some solvent by vacuum
rotary evaporation, a second crop was collected to achieve a total
yield of 91–94% [28]. The obtained intermediate was mixed with
10.24 g (0.08 mol) of 5,5-dimethylhydantoin (DMH) and 12.76 g
(0.18 mol) of sodium ethoxide in 300 mL of ethanol and stirred at
60 °C for 12 h. Finally, the light yellow solid DHEDA product was
obtained after filtration of the produced NaCl and then removal
of solvent. The yield was about 80%, calculated from the mass per-
centage of DHEDA in the crude product obtained by a titration
method [29].
mixed bacterial suspensions were serially diluted, and 100 lL of
each dilution were placed onto a nutrient agar plate. Viable bacte-
rial colonies on the agar plates were counted after incubation at
37 °C for 24 h. Bacterial reduction is reported according to the
following equation:
Log reduction of bacteria ¼ logðN1=N2Þ
ð2Þ
where N1 is the number of bacteria counted from the original bac-
terial suspension, and N2 is the number of bacteria counted from
each sample.
Also, a column filled with this new porous Cl-PSQH resin was
used to test its antimicrobial effects for water disinfection.
10.00 g of the as-prepared porous Cl-PSQH resin with a chlorine
loading of about 5.49% was filled into a 50 mL acid burette. About
10 L of water containing 104 CFU/mL bacteria were flowed through
the burette continually for a period of 2 d by gravity feed (3.5 mL/
min). After 2 d, 0.5 mL of effluent was collected for the measure-
ment of viable bacterial colonies and then another 10 L of water
containing 104 CFU/mL bacteria were flowed through the burette.
The above procedure was repeated for 6 times.
2.4. Synthesis of poly(5,5-dimethylhydantoinyl-3-ethyl-p-
ethenylphenylmethyl dimethylammonium chloride) (PSQH)
4.28 g of DHEDA crude product were added to 30 mL of ethanol
in a 250 mL flask and stirred until completely dissolved at 70 °C.
Then 2.82 g of CMPS were added to the solution above. The mix-
ture was stirred slowly using a magnetic stirring apparatus at
70 °C for 8 h. The produced PSQH resin was removed by filtration
and washed with tap water for 6 times and then deionized water
once. After dried in a vacuum oven at 80 °C for 2 h, 5.18 g of PSQH
resin were obtained.
2.7. Regenerability, preliminary stability, and hygroscopicity testing
Cl-PSQH resin was tested for its regenerability. 5.00 g of
Cl-PSQH resin containing an oxidative chlorine loading of 5.63%
were subjected to 150 mL of 0.03 N Na2S2O3 solution for 1 h to
quench the oxidative chlorine completely, and then regenerated
by exposure to 17.09 g of 10% sodium hypochlorite for 2 h after
rinsing with distilled water to remove the adsorbed Na2S2O3. After
each cycle, the Cl+% of the sample was measured for the evaluation
of regenerability.
Cl-PSQH resin was also tested for its preliminary storage stabil-
ity under room temperature. Cl-PSQH resin initially containing
5.39% oxidative chlorine loading was stored at room temperature.
Periodically over a 20 d storage time, the Cl+% of the sample was
measured for the evaluation of its preliminary storage stability.
For hygroscopicity evaluation, 5.00 g of the dry resin was stored
in open-mouth container under room temperature for 24 h to ab-
sorb the moisture in the air completely. The hygroscopic rate
(HR%) could be calculated using the following equation:
2.5. Chlorination and titration
2.00 g of PSQH were suspended in 20 mL of deionized water. To
the stirred suspension were added dropwise 3.42 g of 10% sodium
hypochlorite solution at 0–5 °C over a period of 2 h. Meanwhile,
the pH was adjusted to 7 by the addition of 0.5 N HCl solution.
The chlorinated resin (Cl-PSQH) was then filtered, rinsed with
tap water, and then thoroughly rinsed with deionized water to re-
move free chlorine, and then dried at 45 °C for 2 h. Regeneration of
the antimicrobial function of the sample resin was performed un-
der the same conditions.
The percentage of oxidative chlorine (Cl+) covalently bonded to
the amide nitrogen atom of Cl-PSQH was determined by a modified
iodometric/thiosulfate titration procedure. About 0.04 g powder of
the chlorinated beads was suspended in 45 mL of ethanol. After
addition of 5 mL 0.04 N sulfuric acid solution and 0.20 g of KI, the
solution was titrated with 0.01 N of sodium thiosulfate solution
until the yellow color disappeared at the end point. The percentage
of Cl+ in the porous beads could then be calculated using the fol-
lowing equation:
HR% ¼ ðW2 ꢂ W1Þ=W1 ꢀ 100%
ð3Þ
where W1 is the weight of dry resin and W2 is the weight of the
hygroscopic resin.
3. Results and discussion
Clþ% ¼ ½N ꢀ V ꢀ 35:45=ð2 ꢀ WÞꢁ ꢀ 100%
ð1Þ
3.1. Synthesis of DHEDA
where N and V are the normality (eqv/L) and volume (L), respec-
tively, of the Na2S2O3 consumed in the titration, and W is the
weight in grams of the sample.
5,5-dimethylhydantoin is an important N-halamine precursor
containing both cyclic amide and imide groups. Its active imide
group can react with some organic halides to form derivatives of
5,5-dimethylhydantoin which can be grafted on the surfaces of
materials, and its amide group can be easily transferred to an
N-halamine functional group upon exposure to dilute sodium
hypochlorite solution. In this study 2-chloroethyl dimethylamine
was used to react with 5,5-dimethylhydantoin to form 5,5-dim-
ethylhydantoinyl-3-ethyl dimethylamine (DHEDA). It was found
2.6. Assessment of antimicrobial efficacy
The porous Cl-PSQH resin prepared as described above with a
chlorine loading of about 5.61% was tested for antimicrobial effi-
cacy against S. aureus ATCC 6538P and E. coli O157:H7 ATCC
11229. 0.75 g of resin (CMPS, PSQH, Cl-PSQH) was added to