annual report annual report annual report annual report 2005

26
RADIATION CHEMISTRY AND PHYSICS, RADIATION TECHNOLOGIES
sible. Besides TP •– , also cation radical and triplet
excited state TP* are known to absorb in the same
region. TEA is a scavenger for cation radical and
excited states of TP. The occurrence of both species
were confirmed also by the experiments under O 2
and N 2 O. Kinetics of the absorption decay is quite
complicated and the best fitting to the experimental
results can be achieved taking an exponential
decay equation with three different constants. In
Figure 2, there are presented experimental traces
of absorbencies at 475 nm vs. time in logarithmic
scale for 14 mM TP in Ar-saturated samples in the
absence and presence of TEA.
Fig.2. Experimental absorbance vs. time trace at 475 nm in
14 mM TP deoxygenated R 4
NNTf 2
solution with and
without 3% TEA added. Decaying parts of traces
were fitted using equation: A(t)=A1*exp(-t*k1)+
A2*exp(-t*k2) + A3*exp(-t*k3) + A0. Dose – 15 Gy.
CO 2 saturation of 14 mM TP solution cut initial
absorbance by about 50% and eliminates additional
absorbance formation after the electron
pulse. Only in the sample with TEA added some
participation of TP •– in the spectra can be distinguished.
The effect can be explained by CO 2 reac-
tion with solvated and dry electrons thus eliminating
one path of TP •– formation. Some TP •– are
formed by reaction of excited TP* states with TEA.
Direct reactions involving TP, TP •– , CO 2 and CO 2
•–
are too slow to be observed in pulse radiolysis time
scale. The reactions involving metal complexes are
underway.
References
[1]. Welton T.: Chem. Rev., 99, 8, 2071-2083 (1999).
[2]. Wasserscheid P., Keim W.: Angew. Chem. Int. Ed.,
39, 21, 3772-3789 (2000).
[3]. Ionic liquids: Industrial application to green chemistry.
Eds. R.D. Rogers, K.R. Seddon. ACS Symp. Ser., 818
(2002).
[4]. Grodkowski J., Neta P.: J. Phys. Chem. A, 106, 22,
5468-5473 (2002).
[5]. Grodkowski J., Neta P.: J. Phys. Chem. A, 106, 39,
9030-9035 (2002).
[6]. Grodkowski J., Neta P.: J. Phys. Chem. A, 106, 46,
11130-11134 (2002).
[7]. Wishart J.F., Neta P.: J. Phys. Chem. B, 107, 30,
7261-7267 (2003).
[8]. Grodkowski J., Neta P., Wishart J.F.: J. Phys. Chem.
A, 107, 46, 9794-9799 (2003).
[9]. Grodkowski J., Płusa M., Mirkowski J.: Nukleonika,
50, Suppl.2, s35-s38 (2005).
[10]. Zimek Z., Dźwigalski Z.: Postępy Techniki Jądrowej,
42, 9-17 (1999), in Polish.
[11]. Grodkowski J., Mirkowski J., Płusa M., Getoff N.,
Popov P.: Rad. Phys. Chem., 69, 379-386 (2004).
[12]. Grodkowski J.: Radiacyjna i fotochemiczna redukcja
dwutlenku węgla w roztworach katalizowana przez
kompleksy metali przejściowych z wybranymi układami
makrocyklicznymi. Instytut Chemii i Techniki
Jądrowej, Warszawa 2004, 56 p. Raporty IChTJ. Seria
A nr 1/2004 (in Polish).
[13]. Shida T.: Electronic absorption spectra of radical ions.
Elsevier, Amsterdam 1988, p.446.
SINGLET OXYGEN-INDUCED OXIDATION
OF ALKYLTHIOCARBOXYLIC ACIDS
Monika Celuch 1/ , Mirela Enache 1,2/ , Dariusz Pogocki 1/
1/
Institute of Nuclear Chemistry and Technology, Warszawa, Poland
2/
Institute of Physical Chemistry “I.G. Murgulescu”, Romanian Academy, Bucharest, Romania
Singlet oxygen ( 1 O 2 ) could be generated in biological
systems by endogenous and exogenous processes
(e.g. enzymatic and chemical reactions, UV
or visible light in the presence of a sensitizer) [1].
Numerous data show that proteins are the major
targets of 1 O 2
-induced damage in the living cells.
The primarily reactions occur here preferentially
with residues of aromatic and sulphur containing
amino acids [1].
In particular, reaction of 1 O 2 with thioether sulphur
of methionine (Met) leads to the formation
of persulphoxide [2,3]:
1
O 2 + >S → >S (+) O-O (–) (1)
which is in equilibrium with superoxide radical-anion
(O 2
•–
) and respective sulphur-centered radical-
-cation:
>S (+) O-O (–) = >S •+ •–
+ O 2 (2)
However, the major pathway of persulphoxide decay
is bimolecular reaction with the second molecule
of thioether that leads to the formation of
respective methionine sulphoxide [2,3]:
>S (+) O-O (–) + >S → 2 >S=O (3)
In this work, we have investigated the mechanisms
of deprotonation and decarboxylation of sulphur-centered
radical-cation (>S •+ ) the irreversible
processes, which compete with the formation
of sulphoxide (reaction 3) by moving the equilibrium
(2) to the right hand side. Importantly, efficiency
of both decarboxylation and deprotonation
could be influenced by various factors such as
neighbouring group participation and environmental
effects. These phenomena may be studied using
thioethers diverse by the number and positions
of carboxylate groups. Therefore, the experiments