2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
Absorbance
0.8
0.6
0.4
0.2
0.0
300 400 500 600 700
Wavelength, nm
7-COOEt-SeQ
7-COOH-SeQ
7-Ac-SeQ
7-CN-SeQ
Fig. 1. uV/VIS spectra of 7-substituted 6-oxo-6,9-dihydro[1,2,
5]selenadiazolo[3,4-h]quinoline derivatives measured in DMSO
(concentration 40 μM; cell length 1 cm)
a H γ = 0.135 mT and g-value = 2.0058). Additionally, Fig. 2.
b illustrates the formation of typical three-line EPR signal of
Tempol (a n = 1.575 mT; g = 2.0060) produced from TMP via
singlet oxygen. However, photogenerated paramagnetic Tempol
is upon prolonged irradiation decomposed to diamagnetic
products, most probably by the termination of its nitroxyl
group with super-oxide anion radicals ( > nO • + O 2 •– ).
a)
b)
0 44 88 132 176 220
Irradiation time, s
Fig. 2. The time-course of EPR spectra monitored upon photoexcitation
of aerated DMSO solutions of 7-COOEt-SeQ
(c 0 = 3.2 mM) in the presence of: a) DMPO spin trap (magnetic
field sweep, SW = 10 mT); b) TMP (SW = 6 mT)
The EPR experiments confirmed that the photoexcitation
of selenadiazoloquinolones in the presence of molecular
oxygen resulted in the formation of O 2 •– and 1 O2 , and
s522
these processes perform simultaneously. The photoactivity
of 7-sub-stituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,
4-h]quinoline derivatives upon irradiation of polychromatic
UV source was evaluated using (i) quantum efficiency
of spin-adduct formation of superoxide radical with DMPO
spin trap ( • DMPO-O 2 – ), and (ii) quantum efficiency of Tempol
generation from TMP by singlet oxygen. The values of
quantum efficiencies reflect the donor/acceptor properties of
substituents; the highest value of • DMPO-O 2 – quantum efficiency
was found for 7-acetyl 6-oxo-6,9-dihydro[1,2,5]selen
adiazolo[3,4-h]quinoline (7-Ac-SeQ).
The in vitro cytotoxic effect of six 7-substituted 6-oxo-
6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinoline derivatives
was investigated on cell proliferation of human leukemia
HL60 cells. Derivatives demonstrated different cytotoxic effects,
which were time- and concentration- dependent, and
the highest impact was found for 7-Ac-SeQ. The application
of UVA irradiation caused an escalation of 7-Ac-SeQ effects
on cell proliferation; the percentage of growth inhibition was
increased in the range of 10–50 %.
Conclusions
EPR and UV/Vis experiments confirmed UVA-induced
excitation of 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinoline
derivatives, which is coupled with electron
or energy transfer to molecular oxygen via Type I and
Type II photooxidation mechanisms producing super-oxide
anion radical and singlet oxygen.
Dedicated to Prof. Andrej Staško on the occasion of his
70 th birthday.
This study was financially supported by Scientific Grant
Agency of the Ministry of Education of the Slovak Republic
(Projects VEGA 1/4305/07, 1/0225/08 and VEGA 1/3579/06)
and Research and Development Agency of the Slovak Republic
(contract No. APVV 0055-07).
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