Spectral, kinetics, and redox studies on the transients formed on pulse radiolysis of aqueous solution of (4-methylthiophenyl)methanol

Article abstract of DOI:10.1246/bcsj.74.1649

Pulse radiolysis technique has been employed to investigate the nature and the redox properties of the transient species generated on radiolysis of aqueous solution of (4-methylthiophenyl)methanol (MTPM). Pulse radiolysis in 1,2-dichloroethane, reaction with specific one-electron oxidants (Cl₂^-, SO₄^-, Tl²⁺, Br) and reaction of OH radicals in acidic solution showed absorption bands at 320 and 545 nm; these are assigned to solute radical cation with positive charge on the benzene ring. OH-adduct was observed in neutral solution. The oxidation potential for MTPM/MTPM⁺ couple is determined to be 1.55 ± 0.04 V vs NHE. e_aq^- reacts with a bimolecular rate constant of 1.5 × 10⁹ dm³ mol^-1 s^-1 and the transient absorption bands (λax = 320, 470 nm) are assigned to the solute radical anion. E⁰ value for MTPM/MTPM^- couple is determined to be -1.84 ± 0.04 V vs NHE. The redox properties of the transient species formed on reaction with OH, H, and O^- have been evaluated.

Full text of DOI:10.1246/bcsj.74.1649

c. Jpn.
© 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 1649–1659 (2001) 1649
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Spectral, Kinetics, and Redox Studies on the Transients Formed on Pulse
Radiolysis of Aqueous Solution of (4-Methylthiophenyl)methanol
Pulse Radiolysis of (4-Methylthiophenyl)methanol
H. Mohan et al.
Hari Mohan and Jai Pal Mittal*,#
01
49
59
Radiation Chemistry & Chemical Dynamics Division, Bhabha Atomic Research Centre,
Trombay Mumbai 400 085, India
SJA8
09-2673
365
(Received October 16, 2000)
Pulse radiolysis technique has been employed to investigate the nature and the redox properties of the transient spe-
cies generated on radiolysis of aqueous solution of (4-methylthiophenyl)methanol (MTPM). Pulse radiolysis in 1,2-
00
01
·
dichloroethane, reaction with specific one-electron oxidants (Cl2·−, SO4·−, Tl2+, Br·) and reaction of OH radicals in
acidic solution showed absorption bands at 320 and 545 nm; these are assigned to solute radical cation with positive
charge on the benzene ring. OH-adduct was observed in neutral solution. The oxidation potential for MTPM/MTPM·+
couple is determined to be 1.55 0.04 V vs NHE. eaq− reacts with a bimolecular rate constant of 1.5 × 109 dm3 mol−1
s−1 and the transient absorption bands (λmax = 320, 470 nm) are assigned to the solute radical anion. E0 value for
MTPM/MTPM·− couple is determined to be −1.84 0.04 V vs NHE. The redox properties of the transient species
formed on reaction with ·OH, ·H, and O·− have been evaluated.
The oxidation mechanism of the sulfur-containing organic
compounds has been the subject of recent radiation and photo-
chemical investigations.1–7 The studies on the radical and radi-
cal ions of organic sulfides have gained importance as sulfer-
centered radical species are the possible key intermediates in
the biological systems with sulfur-containing comounds.8–12
have Hammett parameters26 (σ*) of 0.56 and 0, respectively. It
would be of interest to study the sites of attack in the presence
of alkyl and aryl groups present in the same molecule and
compare the results with thioanisole and 2-(phenylthio)etha-
nol, which have a group in common. The present investiga-
tions are aimed in this direction and the properties of the tran-
sient species formed on radiolysis of (4-methylthiophen-
yl)methanol (MTPM) are discussed.
·
One-electron oxidation of dialkyl sulfides (R2S) by OH radi-
cal leads to the formation of sulfur-centered dimer radical cat-
ion, (R2S)2·+, via a complex sequence of reactions involving
OH-adduct, α-thio radicals, and monomer radical cation for
which no direct evidence exists in the literature.13 Some ex-
perimental evidence for the formation of these intermediates
could be obtained in functionalized dialkyl sulfides.14,15 The
nature of the functional group, chain length from sulfur, and
pH have been shown to play an important role in the final sta-
bilization of the oxidized sulfur. Oxidized sulfur has a high
tendency to stabilize with the free p-electron pair of another
heteroatom (S, N, P, halogen) forming a 3-electron bonded
species, except in the case of t-butyl sulfide in which solute
radical cation was observed to have an absorption band at 285
nm, stabilized mainly due to the steric hindrance provided by
the solute molecule.10,16–19 Two-center three-electron (2σ–
1σ*) bonding has been subject of both experimental and theo-
retical investigations.20,21 Aryl substitution is also expected en-
hance the stabilization of monomer radical cation due to delo-
calization of the positive charge on the benzene ring.22,25 The
effect of substituents on the nature and reactivity of transients
produced from alkyl sulfides has been reasonably well under-
stood and a large number of publications have come in recent
years. The effect of aryl substitution on the nature of the tran-
sients formed is still lacking.22–25 CH2OH and CH3 groups
Experimental
(4-methylthiophenyl)methanol (MTPM, scheme 1), obtained
from Aldrich Chemicals, was of high purity and was used without
any further purification. Freshly prepared solutions were used for
each experiment. The solutions were prepared in 1 × 10−3 mol
dm−3 phosphate buffer using “nanopure” water. The pH was ad-
justed with NaOH/HClO4. High purity gases (N2, N2O, O2) were
used for purging the solutions. All other chemicals used were also
of high purity. The optical adsorption studies in the ground state
were carried out with Hitachi 330 spectrophotometer. All other
experimental details are described elsewhere.15
Pulse radiolysis experiments were carried out with high energy
electron pulses (7 MeV, 50 ns) obtained from a linear electron ac-
celerator whose details are given elsewhere.27 The dose delivered
per pulse was determined with aerated aqueous solution of KSCN
(1 × 10−2 mol dm−3) with Gε = 21,520 dm3 mol−1 cm−1 per 100
eV at 500 nm for the transient (SCN)2·− species.28 The G denotes
the number of species per 100 eV of absorbed energy and ε is the
·−
molar absorptivity of (SCN)2 species at 500 nm. The dose per
pulse was close to 15 Gy except for kinetic experiments, which
were carried out at a lower dose of about 10 Gy.
Radiolysis of N2-saturated neutral aqueous solution leads to the
formation of three highly reactive species (·H, ·OH, eaq−) in addi-
tion to the formation of less reactive or inert molecular products
(H2, H2O2).29
# Also affiliated as Honorary Professor with the Jawaharlal Nehru
Centre for Advanced Scientific Research, Bangalore, India.

1650 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Pulse Radiolysis of (4-Methylthiophenyl)methanol
·
H2O → H, ·OH, eaq−, H2, H2O2, H3O+
(1)
·
The reaction with OH radicals was carried out in N2O-saturated
−
·
solution where eaq is quantitatively converted to OH radicals
with G(·OH) = 5.6 and ·OH radical is the main reactive species to
react with the solute. The reaction with O·− was carried out in
·
N2O-saturated solution at pH = 13, where OH is converted to
O·− with a pKa value of 11.9. The reaction with eaq− was carried
out in N2-saturated solution in presence of t-butyl alcohol to scav-
·
enge OH radical. The reactions with specific one-electron oxi-
dants (N3 , CCl3OO·, Br·, I2·−) were carried out under conditions
·
·
such that OH radicals do not react with the solute initially, and
only the one-electron oxidants react with the solute.30–32
The radiolysis of a solute in aqueous solution is carried out to
investigate the reaction of eaq−, ·H, and ·OH radicals, whereas in a
non-polar solvent such as aliphatic, alicyclic, and also halo-al-
kanes, such reactions yield parent and free ions which can be easi-
ly used for the time-resolved study of electron transfer process-
es.33–35 1,2-Dichloroethane (DCE) has been employed as a solvent
for the study of solute radical cations due to its high ionization po-
tential (11.1 eV).34 The yield of solvent cations is increased be-
cause the electrons produced by ionizing radiations are scavenged
by the parent molecule and undergo dissociative electron capture
reaction. The ionization potential of organic sulfur compounds is
in the range of 8–9 eV and the solvent cations can easily transfer
their charge to solute molecules. The rate constant values were
taken from that kinetic analysis, for which very good correlation
was obtained between the experimental and calculated results.36
The bimolecular rate constant were determined from the linear re-
gression plots of kobs vs solute concentration for at least three ex-
periments and the variation was within 10%.
Fig. 1. Transient optical absorption spectra obtained on
pulse radiolysis, 1.5 µs after the pulse, of aqueous solution
MTPM (1.5 × 10−3 mol dm−3, pH = 7) in N2O-saturated
(a), in presence of t-butyl alcohol (0.3 mol dm−3) (b), and
in aerated conditions in absence of t-butyl alcohol (c). In-
set shows absorption time-profiles for the spectrum (a) at
different wavelengths for decay (A), and formation (B).
lar decay of 545 nm band (k = 4.2 × 104 s−1) and accelerated
decay of 320 nm band. Since the bands at 320 and 360 nm are
close to each other, their true decay rates could not be deter-
mined. These studies suggest that (1) the reaction of ·OH rad-
ical with MTPM results in the formation of more than one
transient species immediately after the pulse and without any
transformation to another transient species, (2) the transient
species absorbing at 545 nm has absorption in 320 nm region,
and (3) the transient species formed on addition/abstraction by
·OH radical have absorption in 320/360 nm region without any
contribution in 545 nm region.
Identification of Transient Species. The hydroxyl radi-
cals are known to react with organic compounds by H· atom
abstraction, addition, and electron transfer mechanism. In or-
der to establish the nature of ·OH radical reaction, pulse radi-
olysis studies were carried out with a number of specific one-
Results and Discussion
The ground state optical absorption spectrum of aqueous so-
lution of MTPM showed an absorption band at 255 nm (ε =
1.2 × 104 dm3 mol−1 cm−1) with very little absorption at λ >
300 nm, suggesting that optical absorption detection technique
can be used for pulse radiolysis studies without any correction
for the ground state absorption. The absorption spectrum re-
mained independent of pH in 1–13, showing the absence of
any pKa in this region.
Reaction of ·OH Radical in Neutral Solution. Figure 1a
shows the transient absorption spectrum obtained on pulse ra-
diolysis of N2O-saturated neutral aqueous solution of MTPM
(1.5 × 10−3 mol dm−3), which exhibits absorption bands at
320, 360, and 545 nm. In the presence of t-butyl alcohol (0.3
mol dm−3), an efficient ·OH radical and weak ·H atom scaven-
ger, very little absorption was observed in 350–390 nm region
(Fig. 1b), indicating that the contribution of H· atom reaction
is negligible. The transient spectrum (Fig. 1b) should be due
to the reaction of H· atom with the solute (see text). The bimo-
lecular rate constant for the reaction of ·OH radical, measured
by formation kinetic studies at 320 and 545 nm (B, inset of
Fig. 1), gave similar results: (4.5 0.8) × 109 dm3 mol−1 s−1.
The band at 545 nm and the initial portion of the band at 320
nm showed first order decay with k = 3.8 × 104 s−1. (A, inset
of Fig. 1). The band at 360 nm and the latter portion of the
band at 320 nm showed mixed and different kinetics. The tran-
sient absorption spectrum, in aerated conditions, also showed
absorption bands at 320, 360, and 545 nm (Fig. 1c) with simi-
electron oxidants.
Reaction with Cl2
·−
. The transient absorption band of
Cl2·− (345 nm) was observed to decay faster in the presence of
low concentrations of MTPM (0.8–3) × 10−4 mol dm−3, indi-
cating electron transfer from MTPM to Cl2·− (reaction 2). The
time resolved studies showed the formation of transient ab-
sorption bands at 320 and 545 nm (Fig. 2).
Cl2·− + MTPM → MTPM·+ + 2Cl−
(2)
The biomolecular rate constant for reaction (2), determined
from the decay of Cl2·− band at 345 nm as a function of solute
concentration, gave a value of 3.1 × 109 dm3 mol−1 s−1, close
to that determined from the growth of the band at 545 nm (k =
4.2 × 109 dm3 mol−1 s−1). Since Cl2·− is a specific one-elec-
tron oxidant (E0 = 2.1 V vs NHE), the transient absorption
spectrum (Fig. 2b) should be due to solute radical cation
(MTPM·+). The entire spectrum decayed by first order kinet-

H. Mohan et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1651
Table 1. Kinetic and Spectral Parameters of the Transient Species Formed on Reaction of ·H, ·OH, O·−, eaq−, and
Specific One-electron Oxidants and Reductants with MTPM
Transient
species
Reaction
pH
7
λmax
k/dm3 mol−1 s−1 kd/s−1
ε/dm3 mol−1 cm−1
MTPM + ·OH
320
360
545
320
545
320
545
320
545
320
545
320
545
320
545
320
545
360
330
485
320
470
320
470
4.5 × 109
—
—
3.8 × 104
2.5 × 104
·−
MTPM + Cl2
MTPM + Tl2+
MTPM + Br·
MTPM + NO3
1
3.1 × 109
2.2 × 109
4.1 × 109
4.5 × 109
2.5 × 109
—
8.3 × 103
5.5 × 103
—
radical
cation
radical
cation
radical
cation
radical
cation
radical
cation
radical
cation
radical
cation
H-adduct
1
2.1 × 104
4.1 × 104
2.6 × 104
—
1
—
—
—
—
·
1
·−
MTPM + SO4
7
·−
MTPM + Br2
1
—
MTPM + ·OH + H+
—
—
2.3 × 104
2.5 × 104
4.3 × 105 a)
2.5 × 104 a)
MTPM + H·
1
13
2.2 × 109
3.1 × 109
5.8 × 103
26.3 × 103
1.9 × 103
11.5 × 103
—
MTPM + O·−
−
MTPM + eaq
7
7
1.5 × 109
1.4 × 104
2.2 × 104
anion
radical
radical
anion
MTPM + COO·−
—
—
a) Second order kinetics (2k/εl).
ics with k = 3.6 × 104 s−1, close to the value observed for the
decay of 545 nm band in N2O-saturated solutions. Under the
present experimental conditions, the molar absorptivity at 320
and 545 nm bands were determined to be 8.3 × 103 and 5.5 ×
103 dm3 mol−1 cm−1, respectively (Table 1).
Reaction with Other Oxidizing Agents. One-electron
oxidation of MTPM has also been investigated with a number
of oxidizing agents (Table 1) and the transient absorption spec-
trum obtained in each case was similar to that obtained on re-
action with Cl2·− in comparable yield. Br2·− was also able to
undergo electron transfer with MTPM, but with ~65% yield.
N3· radical (E0 = 1.3 V vs NHE) was not able to undergo elec-
tron transfer with MTPM. These studies suggest that the oxi-
dation potential of MTPM/MTPM·+ couple is in the range of
1.3 and 2.1 V.
Pulse Radiolysis in DCE. The transient absorption spec-
trum obtained on pulse radiolysis of N2-saturated solution of
MTPM (4 × 10−3 mol dm−3) in DCE showed the formation of
transient bands at 320 and 545 nm (Fig. 3), similar to those ob-
tained on reaction of specific one-electron oxidants (Table 1)
Fig. 2. Transient optical absorption spectrum obtained on
pulse radiolysis of aerated aqueous solution of Cl− (4 ×
10−2 mol dm−3, pH = 1) in presence of MTPM (3 × 10−4
mol dm−3), immediately (a), and 5.5 µs after the pulse (b).
Inset shows absorption time profiles at 345 nm in absence
(c), and presence of MTPM (d), and at 545 nm (e).
·
and OH radicals with MTPM in acidic solution (see text).
The transient absorption spectrum (Fig. 3) is assigned to solute
radical cation (reactions 3 and 4). Since the exact yield of sol-
vent radical cation (DCE·+) is not known, the molar absorptiv-
ity of solute radical cation (MTPM·+) in DCE could not be de-
termined.
DCE·+ + MTPM → MTPM·+ + DCE
(4)
DCE → DCE·+ + e−
(3)
Different Channels for Reaction of ·OH Radical. The
nature of the transient absorption band at 545 nm formed on

1652 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Pulse Radiolysis of (4-Methylthiophenyl)methanol
Fig. 3. Transient absorption spectrum obtained on pulse ra-
diolysis of N2-saturated solution of MTPM (4 × 10−3 mol
dm−3) in DCE 1.5 µs after the pulse.
Fig. 4. Transient absorption spectra obtained on pulse radiol-
ysis of MTPM (1 × 10−3 mol dm−3) 190 µs after the pulse
in N2O (a), and aerated conditions (b). Inset show absorp-
tion-time profiles at 320 nm in N2O (c), aerated (d), and
O2-saturated conditions (e).
·−
·
reaction of Cl2 and OH radicals with MTPM was similar,
and is assigned to the same species (MTPM·+). Using the mo-
lar absorptivity at 545 nm = 5.5 × 103 dm3 mol−1 cm−1, we
tion. The contribution of α-thio radicals may be negligible.
Lower yield (Fig. 4b) may be due to lower ·OH radical yield in
the aerated solution. The faster decay of the 320 nm band in
presence of oxygen (inset of Fig. 4) may be due to the addition
of oxygen to carbon centered radical (Scheme 1c) and the bio-
molecular rate constant was calculated to be ~4 × 108 dm3
mol−1 s−1. The contribution of individual reactions (Scheme
1b and 1c) could not be determined due to the close proximity
of these absorption bands.
·
observed that ~53% of OH radicals react with MTPM by
electron transfer mechanism and the remaining react by some
other mechanism (addition/abstraction). The ratio of the ab-
·−
sorbance at 320/545 nm bands formed on reaction of Cl2
with MTPM is 1.5 whereas that formed on reaction with ·OH
radicals in N2O-saturated solutions (Fig. 1a) is 2.8. These re-
·
sults suggest that OH radical is also reacting with MTPM to
form transient species with absorption in 320 nm regions.
The transient absorption spectrum (Fig. 4a), obtained on
pulse radiolysis of N2O-saturated neutral aqueous solution of
MTPM (1 × 10−3 mol dm−3), 190 µs after the pulse, exhibits
an absorption band at 320 nm with a shoulder in 350–370 nm
region. During this time, the transient absorption due to the
solute radical cation (λmax = 320 and 545 nm) has completely
decayed and this spectrum (Fig. 4a) should be due to some
transient species other than solute radical cation. The absorp-
tion at 320 nm decayed by second order kinetics with 2k/εl =
1.9 × 105 s−1. In aerated conditions, the absorption-time pro-
file showed accelerated decay (inset of Fig. 4), the initial por-
tion decaying by first order kinetics with k = 9 × 104 s−1 (Fig.
4d) but the nature of the absorption spectrum remained the
same (Fig. 4b).
The absorbance of the transient band at 545 nm remained
independent of solute concentration, indicating it to be due to a
monomer species. Sulfur-centered monomer radical cations
have absorption in 300 nm region and are highly unstable, but
have a high tendency to coordinate with another solute mole-
cule, forming a 3-electron bonded sulfur-centered dimer radi-
cal cation.10 These dimer radical cations of dialkyl sulfides
have absorption in 400–500 nm region. Therefore the transient
absorption bands at 320 and 545 nm could not be due to a sul-
fur-centered cationic species. On the other hand, the reaction
α-Thio radical and sulfur-centered OH-adduct of dialkyl
sulfides have absorptions in 290–310 nm region and at 360 nm,
respectively.10 ·OH radical addition to the benzene ring results
in the formation of a transient absorption band in 310–330 nm
region.37 The fact that the nature of the transient absorption
spectrum remained the same in aerated conditions (Fig. 4),
suggests that it is not due to α-thio radical formed on abstrac-
tion of H· atom from CH3/CH2OH groups. Therefore the tran-
sient absorption band at 320 nm may be due to the addition of
·OH radicals to the benzene ring (Scheme 1c) and the shoulder
at 360 nm to sulfur-centered OH-adduct (Scheme 1b). The ad-
dition of ·OH radicals to the benzene ring could be at any posi-
Scheme 1.

H. Mohan et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1653
Scheme 2.
Fig. 6. Absorption-time profiles obtained on pulse radiolysis
of aerated acidic (HClO4 = 5.5 mol dm−3) aqueous solu-
tion of MTPM (1.5 × 10−3 mol dm−3) at 320 and 545 nm.
·
for the reaction of OH radical with MTPM. The other tran-
sient species, formed in neutral solution are converted to solute
radical cations in acidic solution. The overall reaction of ·OH
radical with MTPM in acidic solutions can be represented by
Scheme 2.
Oxidation Potential of MTPM/MTPM·+ Couple. The
·−
transient absorption band of Br2 (λ = 360 nm), formed on
Fig. 5. Transient absorption spectrum obtained on pulse ra-
diolysis of aerated acidic (HClO4 = 5.5 mol dm−3) aque-
ous solution of MTPM (1.5 × 10−3 mol dm−3), 2.5 µs after
the pulse (a). Inset show absorption-time profiles at 360
nm in aerated (b), acidic (HClO4 = 1 mol dm−3) (c), and
variation of absorbance at 545 nm as a function of [HClO4]
(d).
pulse radiolysis of N2O-saturated neutral aqueous solution of
Br− (4 × 10−2 mol dm−3) was observed to decay more quickly
on addition of low concentration of MTPM (1 × 10−4 mol
dm−3), indicating electron transfer from MTPM to Br2·−. The
·−
pseudo-first-order rate (kobs) of Br2 was observed to depend
on [Br−]. The transient band of MTPM·+ (λ = 545 nm),
formed on pulse radiolysis of aerated acidic (HClO4 = 5.5 mol
dm−3) aqueous solution of MTPM (1.5 × 10−3 mol dm−3) was
observed to decay faster on addition of low concentration of
Br−, indicating electron transfer from Br− to MTPM·+. These
studies and the fact that the yield of the 545 nm band, formed
on reactions of Br2·− with MTPM, was ~65%, suggest the ex-
istence of the following equilibrium. It is assumed that there is
no reversible nucleophilic addition of the bromide ion to the
ring of the solute radical cation, as time-resolved studies have
not shown the formation of any band other than that of solute
radical cation.
·
of OH radicals with aryl substituted sulfides have absorption
bands in 310 and 530 nm region and are assigned to solute rad-
ical cation with positive charge on the benzene ring.22,23,25
Therefore the transient absorption bands at 320 and 545 nm are
assigned to solute radical cations with positive charge on the
benzene ring (Scheme 1a). Under the present experimental
conditions, the contribution of sulfur-centered dimer radical
cations may be negligible and such cations may be formed
only at very high solute concentrations.
Reaction of ·OH Radical in Acidic Solution. The decay
of the transient absorption band at 360 nm (inset of Fig. 5) was
observed to increase from 9.5 × 103 s−1 to 1.5 × 105 s−1 when
the HClO4 concentration was increased from 0 to 1 mol dm−3.
Simultaneously, the absorbance of 545 nm band increased,
reaching a saturation value when [HClO4] was in the region of
5–6 mol dm−3 (Fig. 5d). The transient absorption spectrum
showed bands at 320 and 545 nm (Fig. 5a), similar to those ob-
tained on reaction of Cl2·− and other specific one-electron oxi-
dants with MTPM. The entire spectrum decayed by first order
kinetics with k = 2.4 × 104 s−1 (Fig. 6). The increase in the
absorbance may be due to the fact that the equilibrium
(Scheme 2) shifts towards the right in acidic solutions. Under
these conditions, only one channel (Scheme 1a) is being used
Br2·− + MTPM ꢀ MTPM·+ + 2Br−
[Br−]2
(5)
1
1
1
(6)
=
+
∆A Kε[R] [MTPM] ε[R]
·−
The transient absorption of MTPM·+ at 545 nm where Br2
has negligible absorption (path length = 1 cm), is related to
the equilibrium constant (K) in Eq. 6, where [R] is the radical
concentration, which was kept constant at a given dose, and ε
is the molar absorptivity of the transient at 545 nm. The satu-
ration value of the absorbance (∆A) was measured at 545 nm
and the plot of 1/∆A vs [Br−]2/[MTPM] was linear (Fig. 7A).
The absorbance was measured for low concentrations of

1654 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Pulse Radiolysis of (4-Methylthiophenyl)methanol
Fig. 8. Transient absorption spectra obtained on pulse radiol-
ysis of N2-saturated acidic (pH = 1) aqueous solution of
MTPM (1 × 10−3 mol dm−3) in presence of t-butyl alcohol
(0.3 mol dm−3) 1.5 µs after the pulse. Inset show absorp-
tion-time profiles at 360 nm.
Fig. 7. (A) Plot of 1/∆A (545 nm) as a function of [Br−]2/
[MTPM] and (B) kobs/[Br−]2 (360 nm) as a function of
[MTPM]/[Br−]2 obtained on pulse radiolysis of N2O-satu-
rated aqueous solution for various concentrationsof Br−
(0.4–2) × 10−4 mol dm−3 and MTPM (1–3) × 10−2 mol
dm−3
.
MTPM (0.4–2) × 10−4 mol dm−3, so that any depletion in the
absorbance due to the partial decay of MTPM·+ is negligible.
The equilibrium constant (K) = intercept/slope was deter-
mined to be 4.45. Under the present experimental conditions,
G(·OH) = 5.6 and [R] = 0.93 × 10−5 mol dm−3, the molar ab-
sorptivity at 545 nm was determined to be 5.5 × 103 dm3 mol−1
cm−1.
Scheme 3.
idation potential value for MTPM/MTPM·+ couple was deter-
mined to be 1.55 0.04 V vs NHE.
Reaction with H· Atoms. Figure 8 shows the transient
absorption spectrum obtained on pulse radiolysis of N2-satu-
rated acidic (pH = 1) aquesous solution of MTPM (1 × 10−3
mol dm−3) in the presence of t-butyl alcohol (0.3 mol dm−3),
which exhibits a band at 360 nm. Since the position of this
The equilibrium constant can also be determined from the
following kinetic equations:
kobs = kf[MTPM] + kr[Br−]2
(7)
(8)
·
band matched with that obtained on reaction of OH radical
kobs
[MTPM]
[Br−]2
= kf
+ kr
with MTPM and assigned to the sulfur-centered OH-adduct,
the transient species (Fig. 8) is therefore assigned to the sulfur-
centered H-adduct (Scheme 3). The rate constant for the reac-
tion of H· atom with the solute was determined by formation
kinetic studies and is shown in Table 1. In the absence of
knowledge about the nature of stable products formed, the ex-
act decay mechanism could not be given at this stage.
[Br−]2
The pseudo-first-order rate (kobs) was determined on monitor-
ing the decay of the transient band of Br2·− (λ = 360 nm) for
various concentrations of Br− = (2–4) × 10−2 mol dm−3 and
MTPM = (0–2) × 10−4 mol dm−3. The plot of kobs/[Br−]2 vs
[MTPM]/[Br−]2 gave a straight line (Fig. 7B) with slope (kf) =
16.7 × 108 and intercept (kf) = 0.465 × 108. The equilibrium
constant (K = kf/kr) was determined to be 35.9. It is related to
the difference (∆E0) of the oxidation potential of two couples
by the following relationship:
Reaction with O·−. Pulse radiolysis on N2O-saturated ba-
sic (pH = 13) aqueous solution of MTPM (1 × 10−3 mol
dm−3) showed the formation of transient absorption bands at
330 and 485 nm (Fig. 9). The kinetic parameters are shown in
Table 1. The adducts formed on addition of O·− and ·OH rad-
icals to the benzene ring are expected to give similar spectra.
But the nature of the spectra in the two cases was different.
Therefore, the transient species (Fig. 9) may not be due to O·−
-adduct but to a radical species formed on abstraction of H·
0.059 log K = E0 (Br2·−/2Br−) − E0 (MTPM/MTPM·+) (9)
Using the average value of equibrium constant (K) = 20.2 and
the value of 1.63 V vs NHE for E0 (Br2·−/2Br−) couple, the ox-

H. Mohan et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1655
Table 2. Second Order Rate Constants and Yields of MV·+ and TMPD·+ Formed on Reaction of Transient
Species Generated from MTPM under Different Conditions
Reaction
pH
MV·+
TMPD·+
k/109 dm3 mol−1 s−1 G(TMPD·+
)
k/109 dm3 mol−1 s−1 G(MV·+
)
MTPM/N2O
MTPM/N2/t-butyl alcohol
MTPM/N2O
13
1
7
8.9
—
4.1
4.8
0.5
1.9
—
—
4.2
0.2
< 0.1
2.2
Fig. 11. Absorption-time profiles obtained on pulse radioly-
sis of N2O-saturated aqueous solution of MTPM (1.7 ×
10−3 mol dm−3) containing TMPD (4 × 10−5 mol dm−3), λ
= 610 nm, pH = 6 (a), and MV2+ (4 × 10−5 mol dm−3), λ
= 605 nm, pH = 13 (b).
Fig. 9. Transient absorption spectra obtained on pulse radiol-
ysis of N2O-saturated aqueous (pH = 13) solution of
MTPM (1 × 10−3 mol dm−3) ꢀ 1 µs, and ꢁ 8 µs after the
pulse. Inset shows formation and decay of transient ab-
sorption bands at 335 and 485 nm.
The band at 485 and the initial portion of the band at 330 nm
decayed by first order kinetics with k = 4.8 × 10−5 s−1 match-
ing with the formation of the band at 310 nm. The transient
absorption spectrum (Fig. 10a), matched with that formed un-
der N2O-saturated conditions (Fig. 9). The accelerated decay
should be due to the reaction of the radical species with oxy-
gen; the bimolecular rate constant was determined to be 2.4 ×
109 dm3 mol−1 s−1. The transient absorption spectrum ob-
tained 8 µs after the pulse (Fig. 10b) should be due to a tran-
sient species formed on addition of oxygen to the radical spe-
cies and assigned to a peroxyl radical decaying by second or-
der kinetics with 2k/εl = 1.5 × 104 s−1.
Redox Reactions of Transient Adducts. The
oxidant
methylviologen (MV2+) and the reductant N,N,Nꢀ,Nꢀ-tetrame-
thyl-p-phenylenediamine (TMPD) were used to evaluate the
·
·
nature of radicals produced in reactions of OH, H, and O·−
with MTPM. The reaction rate was monitored at 605 nm (ε =
12 800 dm3 mol−1 cm−1) in the case of MV2+ and at 610 nm (ε
= 12 000 dm3 mol−1 cm−1) for TMPD. These redox experi-
ments were carried out at a lower dose 10 Gy per pulse, to min-
imize the effect of biomolecular radical recombination reac-
tions. The concentrations of TMPD and MV2+ were kept con-
stant at 4 × 10−5 mol dm−3 and of MTPM at 1.7 × 10−3 mol
dm−3. The bimolecular rate constants and G value obtained
under different experimental conditions are given in Table 2.
The typical absorption-time profiles obtained with MV2+ and
Fig. 10. Transient absorption spectra obtained on pulse radi-
olysis of aerated aqueous (pH = 13) solution of MTPM (1
× 10−3 mol dm−3), 1 µs (a), and 8 µs (b), after the pulse.
Inset show absorption-time profiles at 330, 485 and 290
nm.
atom by O·−. In aerated solutions, time-resolved studies
showed the formation of a transient band at 310 nm (Fig. 10b).

1656 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Pulse Radiolysis of (4-Methylthiophenyl)methanol
transient absorption band in 300–600 nm region, showing that
the reduction potential of MTPM/MTPM·− couple is quite
high. COO·− radical anion (E0 = −1.9 V) formed on pulse ra-
diolysis of N2O-saturated aqueous solution of sodium formate
(4 × 10−2 mol dm−3) in the presence of a low concentration of
MTPM (1 × 10−3 mol dm−3) showed the formation of tran-
sient absorption bands at 320 and 470 nm, similar to that ob-
tained on reaction with eaq−. Therefore, the COO·− radical an-
ion is able to transfer electron (reaction 11).
Reduction Potential of MTPM/MTPM·−. The yield of
the transient bands, formed on reaction of COO·− with MTPM
was only about 50%, indicating that complete electron transfer
is not taking place. The yield and the pseudo-first-order rate
(kobs), was found to depend on the concentrations of MTPM
and formate ion, indicating the existence of the following equi-
librium:
COO·− + MTPM ꢁ MTPM·− + CO2
(11)
Fig. 12. Transient absorption spectrum obtained on pulse ra-
The transient absorbance of MTPM·− at 320 nm (optical path
length = 1 cm), where COO·− has negligible absorption, was
determined for various concentrations of formate ions (2–6) ×
10−2 mol dm−3 and MTPM (0.6–3) × 10−3 mol dm−3 under
conditions such that ·H/·OH radicals would initially react with
formate ions and COO·− formed would then react with
MTPM. The transient absorption of MTPM·− is related to the
equilibrium constant K by the following relationship:
diolysis of N2-saturated aqueous solution of MTPM (1 ×
10−3 mol dm−3) containing t-butyl alcohol (0.3 mol dm−3
)
3 µs after the pulse. Inset shows absorption-time profile at
700 nm in the absence (a), and presence of MTPM (b).
·
TMPD are shown in Fig. 11. The reactions of OH radicals
with MTPM produce radical cations and neutral radicals
(Scheme 1). The radical cations would be able to oxidize
TMPD to TMPD·+ because the oxidation potential of solute
radical cations (1.55 V) is higher than that of TMPD·+/TMPD
couple. The neutral radicals are reducing MV2+ to MV·+. The
pulse radiolysis of N2O-saturated aqueous solution of MTPM
(1 × 10−3 mol dm−3) in presence of [Fe(CN)6]3− (1 × 10−3
mol dm−3), did not show any bleaching at 420 nm, indicating
1
1
[Formate−]
[MTPM]
1
(12)
=
+
∆A Kε[R]
ε[R]
where [R] is the radical concentration, which was maintained
constant at a given dose, and ε is the molar absorptivity at 320
nm. The saturation value of the absorbance was measured at
320 nm. The plot of 1/∆A vs [Formate−]/[MTPM] was linear
(Fig. 13A), with slope = 3.63 and intercept = 8.7. The equi-
librium constant (K) = intercept/slope was determined to be
2.4. Under the present experimental conditions with [R] =
0.95 × 10−5 mol dm−3, the molar absorptivity was determined
to be 1.2 × 104 dm3 mol−1 cm−1.
that the OH-adduct is not able to oxidize [Fe(CN)6]3−.38,39
−
Reaction with eaq
.
The decay of eaq− (inset of Fig. 12) at
700 nm was observed to become faster in the presence of low
concentrations of MTPM (0.8 × 10−3 mol dm−3). The rate
constant for reaction (10) was investigated on monitoring its
decay at 700 nm as a function of MPTM concentration (0–1)
× 10−3 mol dm−3 and the biomolecular rate constant was de-
termined to be 1.5 × 109 dm3 mol−1 s−1. The time-resolved
studies showed the formation of transient absorption bands at
320 and 470 nm (Fig. 12). The entire spectrum decayed by
first order with k = 1.5 × 104 s−1.
The equilibrium can also be determined from the following
kinetic equation:
kobs = kf[MTPM] + kf[Formate−]
(13)
(14)
−
MTPM + eaq → (MTPM)·−
(10)
kobs
[MTPM]
[Formate−]
= kf
+ kr
[Formate−]
The nature of the transient absorption spectrum, its decay and
formation kinetics remained the same at pH = 11, suggesting
the absence of any acid-base equilibrium. Therefore, the tran-
sient absorption spectrum obtained at pH 7 (Fig. 12) should be
due to an anion radical (MTPM)·− and not due to a H-adduct
formed on protonation of radical anion. The differences of the
transient absorption spectrum (Fig. 12) from that of H-adduct
(Fig. 8) also support these results.
Reaction with Other Reducing Agents. Isopropyl ketyl
radical, formed on pulse radiolysis of N2-saturated acidic (pH
= 1) aqueous solution of 2-propanol (1 mol dm−3) in the pres-
ence of a low concentration of MTPM, failed to produce any
The pseudo-first-order rate (kobs) was determined on monitor-
ing the formation of the transient absorption band of MTPM·−
at 320 nm for various concentrations of [MTPM] = (0.7–3) ×
10−3 mol dm−3 and formate ion (2–6) × 10−2 mol dm−3. The
plot (Fig. 13B) of kobs/[Formate−] vs [MTPM]/[Formate−]
gave a straight line with slope (kf) = 1.66 × 109 and intercept
(kr) = 0.84 × 108. The equilibrium constant was determined
to be 19.8. The equilibrium constant is related to the differ-
ence (∆E0) of the redox potential value of both the couples by
the following relationship:

H. Mohan et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1657
Table 3. Bimolecular Rate Constant for the Reaction of Sol-
ute Radical Anion with Organic Compounds
Compound
MV2+
Rate constant/dm3 mol−1 s−1
E0/V
4.6 × 109
−0.44
−1.45
−1.36
−1.50
C6H5CN
5.3 × 108
C6H5COCH3 5.2 × 108
CH3COCH3
2.8 × 108
Table 4. Bimolecular Rate Constant for the Reaction of
Solute Radical Cation with Inorganic Ions
Rate constant/
Reaction
E0/V ηCH3I/eV
dm3 mol−1 s−1
MTPM·+ + I−
MTPM·+ + N3
9 × 109
1.03
1.33
1.04
1.63
2.05
7.42
5.78
5.35
6.70
4.37
−
7 × 109
−
MTPM·+ + NO2
7.8 × 109
5 × 108
MTPM·+ + SCN−
MTPM·+ + Cl−
< 3 × 106
in Table 4. The rate constant values are observed to decrease
with increase in the oxidation potential value of the inorganic
ion. Based on the rate constant of a number of nucleophiles
with CH3I in methanol at 25 °C, the relative nucleophilic reac-
tivity parameter (ηCH3I) is available in the literature.42 The
rate constants obtained were observed to remain insensitive to
the relative nucleophilicity of the anion. The bimolecular rate
Fig. 13. (A) Plot of 1/∆A at 320 nm as a function of [For-
mate−]/[MTPM]. (B) Plot of kobs/[Formate−] as a function
of [MTPM]/[Formate−] obtained on pulse radiolysis of N2-
saturated aqueous solution containing different concentra-
tions of MTPM (0.7–3) × 10−3 mol dm−3 and formate−
−
constant for the reaction of radical cation with NO2 (7.8 ×
109 dm3 mol−1 s−1) was comparable with that of I− (9 × 109
dm3 mol−1 s−1) although the nucleophilicity increased from
5.35 to 7.42 eV. Therefore the reaction of solute radical cation
is mainly by electron transfer mechanism and not by the nu-
cleophilic addition and could be accounted for by the differ-
ence in their redox potential values.
(2–6) × 10−2 mol dm−3
.
0.059 log K = ∆E0
= E0 COO·−/COO − E0 MTPM/MTPM·− (15)
·
Effect of Substituents. The reaction of OH radical with
substituted aryl sulfides is observed to depend on the nature of
the substituents. Monomer radical cations with positive charge
on the benzene ring have been observed with diaryl sulfides.23
Taking the average of K = 11.1 and using the value of −1.9 V
for E0 COO·−/COO couple, the reduction potential value for
MTPM/MTPM·− couple was determined to be −1.84 0.04
V.
·
The reaction of OH radical with thioanisole showed the for-
mation of OH-adduct and monomer radical cations with posi-
tive charge on the benzene ring. In acidic solutions, the OH-
adduct is converted to monomer radical cation and a small
fraction to sulfur-centered dimer radical cations.25 The reac-
tion of ·OH radicals with 2-(phenylthio)ethanol has shown the
formation of α-thio radicals, OH-adduct and benzene centered
monomer radical cations. In highly acidic solutions, only
monomer radical cations are observed. The presence of CH3
and CH2OH groups (in thioanisole and 2-(phenylthio)ethanol)
have resulted in the formation of OH-adduct and α-thio radical
respectively. On the other hand, the presence of CH2OH group
on the benzene ring (in MTPM) has not shown any effect.
Only OH-adduct is observed, which should be due to the pres-
ence of CH3 group. The -OH group on the benzene ring as in
the case of 4,4ꢂ-thiodiphenol, resulted in the formation of phe-
noxyl radicals on fast deprotonation of solute radical cation.
Due to high electron density at sulfur in dialkyl sulfides, the bi-
Electron Transfer Reactions with Organic Compounds.
The transient species formed on reaction of eaq with MTPM
−
was able to transfer electrons to MV2+, as investigated by
monitoring the formation of MV·+ at 605 nm. The biomolecu-
lar rate constant was determined to be 4.6 × 109 dm3 mol−1
s−1 and G(MV·+) was 2.5, close to G(eaq−), showing complete
electron transfer from anion radical of MTPM to MV2+. The
reaction with other organic compounds was also investigated
and the rate constant values determined from the decay of the
radical anion at 320 nm are summarized in Table 3. The rate
constant values decreased with increase in the reduction poten-
tial value of the organic compound.
Reaction with Inorganic Ions. The radical cation can re-
act with an anionic nucleophile by addition and/or electron
transfer.40,41 Solvent polarity and redox potential of the nu-
cleophile have a strong effect on the relative contributions of
these two pathways. In order to estimate the relative contribu-
tions of these processes, we have determined the bimolecular
rate constant values for the reaction of solute radical cation
with a number of inorganic ions. The values are summarized
−
molecular rate constant for the reaction of eaq is quite low.
The aryl-substituted sulfides have shown higher reactivity with
eaq−. These results clearly demonstrate that the substituents

1658 Bull. Chem. Soc. Jpn., 74, No. 9 (2001)
Pulse Radiolysis of (4-Methylthiophenyl)methanol
New York (1988), p. 43.
13 a) M. Bonifacic, H. Möckel, D. Bahnemann, and K.-D.
Asmus, J. Chem. Soc., Perkin Trans. 2, 1975, 675. b) J. Mönig,
M. Göbl, and K.-D. Asmus, J. Chem. Soc., Perkin Trans. 2, 1985,
647. c) M. Göbl and K.-D. Asmus, J. Chem. Soc., Perkin Trans. 2,
1984, 691.
and their relative position with reespect to sulfur plays an im-
portant role on the nature of the transient species formed on re-
·
−
action fo OH radical and eaq with substituted sulfur com-
pounds.
Conclusions
·OH radical in neutral aqueous solution of (4-methylth-
iophenyl)methanol is observed to react by electron transfer
mechanism (53%) and by addition at sulfur and benzene ring.
In highly acidic solutions, only solute radical cation with posi-
tive charge on the benzene ring is observed. The oxidation po-
tential for the formation of solute radical cation is determined
to be 1.55 V. The transient species formed on reaction of ·OH
radicals by addition at sulfur and benzene ring have reducing
nature. eaq− has high reactivity and forms radical anions with
negative charge on the benzene ring. The reduction potenttial
is determined to be −1.84 V.
14 a) K. Bobrowski, D. Pogocki, and C. Schöneich, J. Phys.
Chem., 97, 13667 (1993). b) C. Schöneich and K. Bobrowski, J.
Phys. Chem., 98, 12613 (1994). c) K. Bobrowski and J. Holcman,
J. Phys. Chem., 93, 6381 (1989). d) K. Bobrowski, G. L. Hug, B.
Marciniak, B. Miller, and C. Schöneich, J. Am. Chem. Soc., 119,
8000 (1997). e) K. Bobrowski and C. Schöneich, J. Chem. Soc.,
Chem. Commun., 1993, 795.
15 a) D. K. Maity, H. Mohan, and J. P. Mittal., J. Chem. Soc.,
Faraday Trans., 90, 703 (1994). b) V. B. Gawandi, H. Mohan and
J. P. Mittal, J. Chem. Soc. Perkin Trans. 2, 1999, 1425. c) H.
Mohan, J. Chem. Soc. Perkin Trans. 2, 1821 (1990). d) V. B.
Gawandi, H. Mohan, and J. P. Mittal, Chem. Phys. Lett., 314, 451
(1999).
16 K. Bobrowski and J. Holcman, J. Phys. Chem., 93, 6381
(1981).
References
1
P. S. Mariano and J. L. Stavinoha, in “Synthetic Organic
17 H. Hungerbühler, S. N. Guha, and K.-D. Asmus, J. Chem.
Soc., Chem. Commun., 1991, 999.
18 E. Anklam, H. Mohan, and K.-D. Asmus, J. Chem. Soc.,
Perkin Trans. 2, 1988, 1297.
Photochemistry,” ed by W. M. Horspoel, Plenum Press, N.Y.
(1984), p. 145.
2
F. D. Lewis, in “Photoinduced Electron Transfer,” ed by M.
A. Fox and M. Chanon, Elsevier, Amsterdam (1988).
19 a) K.-D. Asmus, M. Göbl, K.-O. Hiller, S. Mahling, and J.
Mönig, J. Chem. Soc., Perkin Trans. 2, 1985, 641. b) K.-D.
Asmus, D. Bahnemann, C.-H. Fischer, and D. Veltwisch, J. Am.
Chem. Soc., 101, 5322 (1979). c) M. Bonifacic and K.-D. Asmus,
J. Chem. Soc.,Perkin Trans. 2, 1980, 758.
20 T. Clark, J. Am. Chem. Soc., 110, 1672 (1988).
21 M. L. McKee, J. Phys. Chem., 96, 1675 (1992).
22 M. Ioele, S. Steenken, and E. Baciocchi, J. Phys. Chem., A,
101, 2979 (1997).
23 L. Engman, J. Lind, and G. Merenyi, J. Phys. Chem., 98,
3174 (1994).
24 Y. Yagci, W. Schnabel, A. Wilpert, and J. Bending, J.
Chem. Soc., Faraday Trans., 90, 287 (1994).
3
(1994).
4
K. Mizuno and Y. Otsuji, Top. Curr. Chem., 169, 302
a) K. Bobrowski, B. Marciniak, and G. L. Hug, J. Am.
Chem. Soc., 114, 10279 (1992). b) B. Marciniak, G. L. Hug, J.
Rozwadowski, and K. Bobrowski, J. Am. Chem. Soc., 117, 127
(1995).
5
G. Cilento, in “Chemical and Biological Generation of Ex-
cited States,” ed by W. Adam and G. Cilento, Academic Press,
New York (1982).
6
C. von Sonntag, in “The Chemical Basis of Radiation Biol-
ogy,” Taylor and Francis, New York (1987).
G. V. Buxton, C. L. Greenstock, W. P. Helman, and A. B.
Ross, J. Phys. Chem. Ref. Data, 17, 513 (1988).
W. A. Prutz, in “Sulfur Centered Reactive Intermediates in
7
25 a) H. Mohan and J. P. Mittal, J. Phys. Chem. A, 101, 10012
(1997). b) V. B. Gawandi, H. Mohan, and J. P. Mittal, Phys.
Chem. Chem. Phys., 1, 1919 (1999). c) H. Mohan and J. P. Mittal,
Int. J. Chem. Kinetics, 31, 603 (1999).
8
Chemistry and Biology,” ed by C. Chatglilialogu and K.-D.
Asmus, NATO ASI Series A, Life Sciences, Plenum Press, New
York (1990), Vol. 197, 389.
26 R. W. Taft, J. Chem. Phys., 26, 93 (1957).
9
Yu. M. Torchinsky, in “Sulfur in Proteins,” ed by D.
27 a) S. N. Guha, P. N. Moorthy, K. Kishore, D. B. Naik, and
K. N. Rao, Proc. Indian Acad. Sci., (Chem. Sci.), 99, 261 (1987).
b) K. I. Priyadarsini, D. B. Naik, P. N. Moorthy, and J. P. Mittal,
Proc. 7th Tihany Symp. on Radiation Chemistry, Hungarian
Chem. Soc., Budapest, 105 (1991).
28 F. M. Fielden, in “The study of Fast Processes and Tran-
sient Species by Electron Pulse Radiolysis,” ed by J. H. Baxendale
and P. Busi, Reidel, Boston, (1982), p. 59.
29 J. W. T. Spinks and R. J. Woods, in “An Introduction to Ra-
diation Chemistry,” Wiley, New York (1990), p. 243.
30 P. Neta and R. E. Huie, J. Phys. Chem., 90, 4644 (1986).
31 G. L. Hug, NSRDS-NBS, 1981, 69.
32 P. Wardman, J. Phys. Chem. Ref. Data, 17, 513 (1988).
33 O. Brede, H. Orthner, V. E. Zubarev, and R. Hermann, J.
Phys. Chem., 100, 7097 (1996).
Metzer, Pergamon Press, Oxford, U. K. (1979).
10 a) K.-D. Asmus, D. Bahnemann, M. Bonifacic, and H. A.
Gillis, Discuss. Faraday Soc., 63, 1748 (1977). b) M. Göbl, M.
Bonofacic, and K.-D. Asmus, J. Am. Chem. Soc., 106, 5984
(1984). c) K.-D. Asmus, in “Sulfur Centered Reactive Intermedi-
ates in Chemistry and Biology,” ed by C. Chatgilialogu and K.-D.
Asmus, NATO ASI Series A, Life Sciences, Plenum Press, New
York (1990), Vol. 197, 155. d) K.-D. Asmus, Acc. Chem. Res., 12,
435 (1974).
11 R. S. Glass, in “Sulfur Centered Reactive Intermediates in
Chemistry and Biology,” ed by C. Chatgilialogu and K.-D.
Asmus, NATO ASI Series A, Life Sciences, Plenum Press, New
York (1990), Vol. 197, 213.
12 a) P. Wardman, in “Sulfur Centered Reactive Intermediates
in Chemistry and Biology,” ed by C. Chatgilialogu and K.-D.
Asmus, NATO ASI Series A: Life Sciences, Plenum Press, New
York (1990), Vol. 197, p. 415. b) P. Wardman, in “Glutathiene
Conjugation,” ed by, H. Sies and B. Ketterer, Academic Press,
34 N. E. Shank and L. M. Dorfman, J. Chem. Phys., 52, 4441
(1970).
35 E. J. Land, R. V. Bensasson, and T. G. Truscott, in “Flash
Photolysis and Pulse Radiolysis, Contribution to Chemistry, Biol-

H. Mohan et al.
Bull. Chem. Soc. Jpn., 74, No. 9 (2001) 1659
ogy and Medicine,” Pergamon Press, Oxford (1983).
36 M. S. Panajkar, P. N. Moorthy, and N. D. Shirke, BARC
Report, No. 1410, (1988).
37 H. C. Christensen, K. Sehested, and E. J. Hart, J. Phys.
Chem., 77, 983 (1973).
38 a) R. H. Schuler, Radiat. Phys. Chem., 39, 105 (1992). b)
X. Chen, R. H. Schuler, J. Phys. Chem., 97, 421 (1993).
39 a) M. K. Eberhardt, J. Phys. Chem., 81, 1051 (1977). b) G.
W. Klein, K. Bhatia, V. Madhavan, and R. H. Schuler, J. Phys.
Chem., 79, 1767 (1975).
40 L. J. Johnson and N. P. Schepp, J. Am. Chem. Soc., 116,
8279 (1994).
41 K. Koike and J. K. Thomas, J. Chem. Soc., Faraday Trans.,
88, 195 (1992).
42 R. G. Pearson, H. Sobel, and J. Songacad, J. Am. Chem.
Soc., 90, 319 (1968).