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Organic & Biomolecular Chemistry
Journal Name
COMMUNICATION
of the caged compounds (5a, 5b, 6 andDFOAI:E1E0.1a0t391/5C9OMB0)0a0f9t0eAr
photolysis using the agar well diffusion technique on E.cloacae
cells (MTCC 509) by incubating a Nutrient Agar (NA) plate at 37
°C. Results showed that donor 5a has better inhibition against
E.cloacae cells (MTCC 509), as indicated by greater zone of
inhibition by dual release of SO2 and FAEE in comparison to
other donors 5b, 6 and FAEE (see Fig. S22 in the SI).
Conclusions
Fig. 6 (a) Emission spectra of 5a (1 x 10-4 M) recorded during photolysis by 1PE at
regular interval of time (0-60 min) and (b) % of emission intensity upon photolysis of 5a
by 1PE at different time intervals (0-60 min). Excitation wavelength: 330 nm.
In conclusion, we have demonstrated one and two-photon
activated SO2 donor based on DMNB phototrigger. The
designed system not only releases SO2 but also active drug
FAEE and the fluorescent nature of FAEE helped in self-
monitoring of the uncaging process by an increase in the
fluorescent intensity. Further, the in vitro studies reveal that
the designed SO2 donor was able to release SO2 gas within the
cells. Finally, the SO2 donor 5a exhibited an enhanced
antibacterial activity which is due to the synergistic effect of
the released SO2 along with the active drug (FAEE) in
comparison to the individual release of SO2 and FAEE from 5b
and 6, respectively.
To check the self-reporting ability of dual (SO2 and FAEE)
uncaging process in vitro, the E.cloacae (MTCC 509) cells were
incubated with sulfonate 5a independently for 3 h and
fluorescence microscopy images were recorded before (0 min)
and after (60 min) irradiation (Fig. S19 in the ESI). At 0 min,
cells emitted blue fluorescence reveal that the compound 5a
was readily internalized by the cells. After irradiation for 60
min, we noted an increase in the intensity of blue
fluorescence, suggesting that the release of the active drug
(FAEE). The release of active drug FAEE also determines the
SO2 generation capability in the cells. Fig. S20 in the ESI shows
fluorescence enhancement data for the cellular experiment
upon 1PE and 2 PE.
Acknowledgements
Lastly, the antibacterial activity of the caged compounds 5a,
5b, and 6 (100 M) were evaluated before and after photolysis
by a broth dilution method against E.cloacae cells (MTCC 509).
The percentage of cell viability was plotted against the
concentration of 5a, 5b, and 6 before and after irradiation.
We thank DST SERB (Grant No. EMR/2016/005885) for
financial support and DST (SR/FST/CSII-026/2013) for 500 MHz
NMR. Yarra Venkatesh is thankful to the Indian Institute of
Technology Kharagpur for the fellowship. We are grateful to S.
Bhattacharya (Physics Department, IIT Kharagpur) for helping
us to perform the two-photon uncaging experiments.
Table 1. Antibacterial Activity of 5a, 5b, 6 and FAEE after Photolysis
entry
compound
MIC
(M)a
2.6
6.3
10.8
12.3
Notes and references
1
2
3
4
5a
5b
6
1
2
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FAEE
aMinimum inhibitory concentration (MIC) is the minimum concentration of the
compound required to inhibit 99% of bacterial growth. Data are the mean of
triplicate experiments ± S.E.
3
4
5
(a) Z. Meng, G. Qin, B. Zhang, J. Bai, Mutagenesis 2004, 19,
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It was observed that before photolysis there is no
remarkable inhibitory activity at the studied concentration of
5a, 5b, and 6 (see Fig. S21 in the ESI). After photolysis for 60
min, sulfonate 5a found to have greater inhibitory activity (MIC
at 2.6 μM) by the dual release of SO2 and FAEE compared to
carbonate 6 and sulfonate 5b having the MIC at 10.8 μM, MIC
at 6.3 μM by releasing FAEE and SO2, respectively (Table 1).
Further, we also evaluated the antibacterial activity of FAEE
alone after photolysis and it was found to be 12.3 μM. From
these results, it is evident that the enhanced antibacterial
activity of 5a could be attributed to the synergetic effect of
released SO2 and FAEE.
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