New reagents for determination of the quantum efficiency of singlet oxygen generation in aqueous media

Article abstract of DOI:10.1023/A:1012369120376

Water-soluble anthracene derivatives containing carboxy, dihydroxyphosphinyl, or pyridinium fragments bound via methylene groups to 9- and 10-carbon atoms were prepared, and their spectra, solubility, and reactivity toward singlet oxygen were studied. Using sodium α,α¹-(anthracene-9,10-diyl)bis(methylmalonate) as acceptor, it is possible to determine the quantum efficiency of singlet oxygen generation in aqueous solutions and in microheterogeneous media in the presence of biomacromolecules.

Full text of DOI:10.1023/A:1012369120376

Russian Journal of General Chemistry, Vol. 71, No. 1, 2001, pp. 36 41. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 1, 2001,
pp. 39 45.
Original Russian Text Copyright
2001 by Kuznetsova, Gretsova, Yuzhakova, Negrimovskii, Kaliya, Luk’yanets.
New Reagents for Determination of the Quantum Efficiency
of Singlet Oxygen Generation in Aqueous Media
N. A. Kuznetsova, N. S. Gretsova, O. A. Yuzhakova, V. M. Negrimovskii,
O. L. Kaliya, and E. A. Luk’yanets
Research Institute of Organic Intermediates and Dyes, Moscow, Russia
Received December 1, 1999
Abstract Water-soluble anthracene derivatives containing carboxy, dihydroxyphosphinyl, or pyridinium
fragments bound via methylene groups to 9- and 10-carbon atoms were prepared, and their spectra, solubility,
and reactivity toward singlet oxygen were studied. Using sodium , -(anthracene-9,10-diyl)bis(methyl-
malonate) as acceptor, it is possible to determine the quantum efficiency of singlet oxygen generation in
aqueous solutions and in microheterogeneous media in the presence of biomacromolecules.
Singlet molecular oxygen (1O2), being an electro-
philic agent, oxidizes unsaturated double bonds, sul-
fide, phenolic, amino groups, and other electron-donor
groups in organic compounds [1]. It is believed that
specifically the high reactivity of 1O2 toward bio-
molecules largely determines the efficiency of photo-
dynamic cancer therapy [2]. It is also suggested to use
photooxidation with singlet oxygen for water treat-
ment to remove environmentally hazardous phenols
[3 5]. For these and other practical applications, it
is important to know the efficiency of 1O2 generation
with sensitizers in aqueous media. However, the life-
ing in the number of carboxy groups [sodium , -
(anthracene-9,10-diyl)bis(methylmalonate), II] or con-
taining phosphonate groups instead of carboxy groups
[9,10-bis(dihydroxyphosphinylmethyl)anthracene, III;
9,10-bis(hydroxyethoxyphosphinylmethyl)anthracene,
IV], and also a cationic analog, 9,10-bis(pyridinio-
methyl)anthracene dichloride (V). Compounds III V
were unknown previously. Tetrasodium salt II, which
is more readily accessible and more soluble than I,
was tested as a chemical acceptor of 1O2 for its detec-
tion and determination of the quantum efficiency
in water and in microheterogeneous aqueous media in
the presence of biomacromolecules.
1
time of O2 in water is as short as 2 s [6] (1 2 orders
of magnitude shorter than in other solvents), which
R
severely complicates detection of 1O2 in aqueous
solutions, including its direct detection by IR lumines-
cence [7].
1
The quantum efficiency
of O2 generation in
water can be determined using photochemical reac-
tions of 1O2 with appropriate substrates: sterically
hindered amines [8], furan derivatives [9, 10], imida-
zole or histidine (photodecolorization of p-nitrosodi-
methylaniline in the presence of imidazole or histi-
dine, RNO method [11]), etc. However, all the known
R
I V
R
= CH COONa (I), CH(COONa) (II), PO(OH) (III),
2 2 2
PO(OEt)OH (IV), NC H Cl (V).
+
5
5
methods for determining
have certain drawbacks,
Compounds I, II, and V were isolated and charac-
terized as salts, and phosphonates III and IV, as acids;
therefore, these two groups of compounds significant-
ly differed in properties, primarily in solubility. It
should be noted that sodium salts I and II at pH > 7
e.g., poor accuracy (RNO method according to our
experience) and the need in special equipment [8 10].
From the viewpoint of experimental convenience, it is
desirable to use a singlet oxygen acceptor whose con-
sumption can be monitored spectrophotometrically.
Previously suggested as such an acceptor was 9,10-
anthracenediyldipropionic acid (I) [12, 13]. To extend
2
1
dissolve to concentrations of 10 and 10 M, respec-
tively, whereas in acid media the solubility of these
4
compounds is limited ( 10 M). Phosphonates III
1
the scope of O2-sensitive agents, we studied in this
and IV are difficultly soluble in water, whereas in
alkaline solutions the concentrations of 10 and
2
work a series of anionic structural analogs of I differ-
1070-3632/01/7101-0036$25.00 2001 MAIK Nauka/Interperiodica

NEW REAGENTS FOR DETERMINATION OF THE QUANTUM EFFICIENCY
37
4
10 M, respectively, are attainable. 9,10-Bis(pyri-
diniomethyl)anthracene dichloride readily dissolves
in water.
The electronic absorption spectra of I V in the
range 350 400 nm show an absorption with a fine
structure, characterstic of the anthracene
(Fig. 1). The spectral characteristics of I V in aqueous
buffer solution (pH 7.4), namely, the and
system
max
values for the most intense components of the long-
wave multiplet, are given in the table.
The reactivity of I V toward singlet oxygen was
1
studied using Bengal Rose (BR) dye as O2 sensitizer.
We found that irradiation ( > 500 nm) of an aque-
ous buffer solution of Bengal Rose containing V does
not result in consumption of V, which shows that
the reactivity of V toward singlet oxygen is low. In
the case of I IV under conditions of photolysis we
observed a gradual (following the first-order kinetics)
decrease in the intensity of the substrate absorption
(Fig. 1; Fig. 2, curve 1). The reaction is inhibited by
1
Fig. 1. Variation of the electronic absorption spectrum of II
sodium azide, which is a well-known O2 quenching
in aqueous buffer solution (pH 7.4) under conditions of
photolysis sensitized with Bengal Rose: (1) before irradia-
tion and (2 6) after irradiation for 1.5, 3, 5, 7, and 9 min,
respectively.
agent, and is sharply accelerated on replacement of
H2O by D2O in which the lifetime of singlet oxygen
is considerably longer (Fig. 2). These tests confirm
that photolytic transformations of anthracenes I IV
involve 1O2. The processes can be represented by
a scheme generally accepted for sensitized photooxi-
dation with singlet oxygen:
3BR*
+
3O2
BR + 1O2,
AO2,
kr
A + 1O2
kq
kd
A + 1O2
1O2
A + 3O2,
3O2.
Here kr and kq are the rate constants of chemical and
physical quenching of 1O2 with acceptor A, and kd is
the rate constant of O2 deactivation with the solvent.
1
Fig. 2. Kinetic curves of photooxidation of II, sensitized
2
with Bengal Rose. Medium: (1) H O, (2) 2 10 M NaN
solution, and (3) D O.
2
3
For the above scheme, the following relations are
valid [6]:
2
kr[A]
,
=
(1)
1/[A]. Figure 3 shows such a dependence for the
case of photooxidation of II using Bengal Rose
as sensitizer; from the slope of this plot we obtain
AO2
kd + kr[A] + kq[A]
kq + kr
kd
kr
1
1
1
[A]
1
.
kr = (0.7 0.1) 107 l mol 1 s . Note that, according
=
+
(2)
kr
AO2
to published data, singlet oxygen reacts with struc-
turally related 9,10-dimethylanthracene with the rate
constant of the same order of magnitude:
Here
is the quantum efficiency of photoox-
idation of AaOs2inglet oxygen acceptor; for Bengal Rose
1
(0.7 2.7) 107 l mol 1 s depending on the solvent
5
1
= 0.75 [14], kd = 1/ = 3.2 10
s
in H2O [7].
[15]. It is also known that the acidic form of I in D2O
1
In accordance with Eq. (2), kr is determined
from the slope of the dependence of 1/ vs.
quenches O2 with the total rate constant kq + kr =
1
(8.2 0.5) 107 l mol 1 s [12].
AO2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 1 2001

38
KUZNETSOVA et al.
wA[II]
wII[A]
Spectral characteristics and rate constants of chemical
reaction with singlet oxygen of meso-substituted anthra-
cenes in aqueous buffer solutions (pH 7.4)
krA = krII
(3)
.
The resulting values of kr are given in the table;
it is seen that, among the examined compounds, sodi-
um salt I reacts with O2 most efficiently. For com-
pounds II and III, the rate constants of oxidation with
singlet oxygen are by a factor of about 2.5 lower than
for I, and compound IV is still less reactive. Cationic
derivative V shows virtually no reactivity toward elec-
trophilic singlet oxygen.
7
1
Comp.
no.
,
kr 10
max
nm
1
l mol 1 s
I
380
380
380
9000
9800
8200
9800
9000
1.7 0.3
0.7 0.1
0.7 0.1
0.45 0.1
<0.01
II
III
IV
V
382.5
377
Despite a lower, compared to I, reactivity toward
1O2, compound II, nevertheless, has certain advan-
tages: It is by an order of magnitude more soluble
in water and is more accessible [16]. Therefore, we
studied the state of II in aqueous solution and in het-
erogeneous systems in the presence of biomacromole-
cules (albumin) and examined the possibility of using
The contribution of physical quenching to the over-
all process is estimated from the portion intercepted
on the ordinate by the plot of 1/
vs. 1/[A]; ac-
cording to Eq. (1), this portion iAsO2equal to (kq +
kr)/ kr. However, in our case it was impossible to
estimate the ratio of the physical and chemical routes
1
II as a chemical acceptor of O2 for determining
in aqueous solutions.
Spectrophotometric studies were performed in
aqueous buffer solution with physiological pH (phos-
phate buffer, pH 7.4). We found that in the range of
concentrations of II from 10 4 to 10 2 M the Lambert
Bouguer Beer law is obeyed, indicating the absence
of spectroscopically detectable aggregation of II un-
der the experimental conditions. Taking into account
the fact that for certain scientific and practical pur-
poses (including photodynamic therapy) the sensitizer
activity should be estimated in a microheterogeneous
biological medium, we examined the effect of albu-
min as a model biomacromolecule on the state of II
in an aqueous buffer solution. We found that albimun
1
of O2 quenching with II, because of the small size of
this portion and poor accuracy of its determination
(Fig. 3).
For sodium salt I and also for phosphonates III and
IV we estimated kr in H2O relative to II from the rates
of their reaction with O2 under identical sensitization
conditions. At kd >> ( k q + k r )[A] addition of A does
not cause significant deviation of the O2 concentra-
tion from the photochemical steady-state level, and
acceptor A is consumed according to a first-order
kinetic equation
1
1
5
in a concentration of 10 M causes no changes in
wA = d[A]/dt = kr[1O2]st[A].
the electronic absorption spectrum of II (working
3
concentration 1 10 M). Hence, interaction of II
Hence follows Eq. (3) from which we calculated
with the protein is weak, at least at the above concen-
tration ratio.
the absolute values of kr :
Thus, the properties of II make it promising as
acceptor for detection and quantitative determination
1
of O2.
Consider the kinetic principles of
determination.
According to relation (1), there can be two limiting
cases of sensitized photooxidation. If kr[A] >> kd +
kq[A], the reaction is zero-order with respect to A, and
=
. If kr[A] + kq[A] << kd, the reaction is
AO2
first-order with respect to A, and << . Because
AO2
1
of fast decay of O2 in aqueous solutions, we failed
to provide with compound I and II the conditions
1
for complete binding of O2 and for zero order of
the reaction with respect to A. Consumption of the ac-
3
4
ceptor in the range of its concentrations 10 10
M
Fig. 3. Plot of 1/
in aqueous buffer solution (pH 7.4), sensitized with
Bengal Rose.
vs. 1/[A] for photooxidation of II
AO2
followed a first-order kinetic equation, which suggests
that kr[A] + kq[A] << kd. Under these conditions,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 1 2001

NEW REAGENTS FOR DETERMINATION OF THE QUANTUM EFFICIENCY
39
Eq. (1) transforms into formula (4) from which we
obtained relation (5) used for determination of by
the relative procedure, with Bengal Rose as reference:
the excited dye molecule with oxygen and formation
1
of O2; secondly, they show that compound II effi-
1
ciently competes with albumin for O2.
kd
kr[A]
Thus, our results demonstrate the feasibility of
,
(4)
(5)
=
AO2
using II to determine
not only in aqueous solutions
but also in microheterogeneous biological media.
w IBR
BR
AO2
BR
AO2
BR
.
=
=
wBR
I
EXPERIMENTAL
Here w and wBR are the rates of consumption of
The electronic absorption spectra were recorded
with an SF-26 spectrophotometer.
1
the O2 acceptor in the presence of the compound
being tested and Bengal Rose, respectively; I and IBR
Rate constants of chemical reactions of anthra-
are the numbers of light quanta taken up in unit time
1
cenes I V with O2. The dependence of the quan-
by the sensitizer being tested and Bengal Rose, re-
1
BR
tum efficiency of photooxidation of II with O2 on
spectively;
= 0.75 [14].
the concentration of II was studied in a buffer solution
5
The choice of sensitizers for testing compound II
was governed by the following criteria: high solubility
in water, absence of aggregation, and availability of
data on the quantum efficiency of singlet oxygen
generation. Among common sensitizers, these criteria
are met by Bengal Rose and sulfonated aluminum
phthalocyanine containing more than three sulfo
groups per molecule [17]; Bengal Rose was already
chosen as reference.
(PBS, pH 7.4, Sigma) with Bengal Rose (2 10 M)
1
as O2 sensitizer. The irradiation was performed in
the long-wave absorption band of the sensitizer with
a DKSSh-150 lamp through a ZhS-18 color filter and
an interference color filter with the transmission at
549 5 nm. Irradiation was performed in a standard
1-cm cell; the acceptor consumption was monitored
by a decrease in its optical density at 400 nm (layer
thickness 0.05 1 cm depending on concentration).
The light flux intensity was measured with a Spectra
Physics-404 power meter. The least-squares process-
ing of the experimental data gives for the slope of
The sample of sulfonated aluminum phthalocya-
nine was a mixture of sulfonic acids with different
degrees of sulfonation. The electronic absorption spec-
trum of the dye in aqueous buffer solution (pH 7.4)
was characteristic of the monomer, with a strong Q
band (maximum at 675 nm). Addition of Triton X-100
detergent did not affect the spectrum, which con-
firmed the absence of aggregates in the sensitizer
solution. Using the above-described procedure, with
the 1/
vs. 1/[A] dependence (Fig. 3) the value
AO2
of 0.067 0.006 M (correlation coefficient r 0.98).
Calculation of kr for II from the slope gives the value
1
of (0.7 0.1) 107 l mol 1 s .
For acceptors I, III V the values of kr were deter-
5
mined relative to II. An air-saturated 2 10
M
II as a scavenger, we determined
for sulfonated
solution of Bengal Rose (1O2 sensitizer) containing
10 M anthracene derivative was irradiated in a 1-cm
aluminum phthalocyanine in a phosphate buffer solu-
tion containing 1 wt % Triton X-100 (conditions of
[18]) and obtained the value of 0.39 0.06, which,
within the measurement error, coincided with pub-
4
cell with a 300-W incandescent lamp through a ZhS-18
1
color filter. Photooxidation of the O2 acceptor was
monitored spectrophotometrically by a decrease in
the optical density in the absorption maximum (for
lished data (
0.38 [18], 0.34 [19], 0.34 [20]).
values, see table). In the absence of the sensitiz-
The procedure was tested in a microheterogeneous
medium in the presence of albumin (sensitizer to
albumin concentration ratio 1 : 1). It is known that at
this concentration ratio sulfonated aluminum phthalo-
cyanine occurs virtually completely on the protein sur-
face [21]. Proteins quench 1O2 [7], and therefore,
competing with the scavenger, they can decrease
max
er, no consumption of I V was observed. The photo-
oxidation rate was determined from the initial portion
of the kinetic curve of decolorization, corresponding
to the pseudo-first order of the reaction. The quantity
kr was calculated by Eq. (3).
The 1O2 quantum efficiency
for sulfonated
the accuracy of
determination by the suggested
aluminum phthalocyanine was determined in an aque-
ous buffer solution (pH 7.4) in the presence of 1 wt %
Triton X-100. The sensitizer concentration was about
procedure. We found that, under conditions of photo-
oxidation sensitized with sulfonated aluminum phtha-
locyanine, salt II in the absence and in the presence
5
3
10 M. The dye solution containing 1 10 M II
was placed in a standard 1-cm cell and irradiated with
a DKSSh-150 lamp in the long-wave absorption band
through a ZhS-18 glass color filter and an interference
5
(10 M) of albumin is consumed with the same rate.
Firstly, these results confirm the conclusion made
in [21] that the protein does not prevent reaction of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 1 2001

40
KUZNETSOVA et al.
filter with the transmission maximum at 550 nm for
Bengal Rose (reference) and 700 nm for sulfonated
aluminum phthalocyanine. The intensity of light
fluxes was measured with a Spectra Physics-404
power meter; the fraction of light absorbed by
the sample was calculated by integrating the overlap
of the transmission spectra of the color filters and
the absorption spectrum of the dyes. Sensitized oxida-
tion of II was monitored spectrophotometrically by
a decrease in absorption in the maximum ( = 400 nm,
layer thickness 0.05 cm). The results are well re-
producible; the accuracy, 15%, is determined by
Tetrasodium , -(anthracene-9,10-diyl)bis(meth-
ylmalonate) (II). A solution of 2.15 g of NaOH in
10 ml of water was added to a suspension of , -
(anthracene-9,10-diyl)bis(methylmalonic) acid (5.5 g)
in 10 ml of water. To this mixture, 100 ml of toluene
was added, and water was removed by azeotropic
distillation with a Dean Stark trap. Then the solvent
was distilled off, 100 ml of anhydrous ethanol was
added, 50 ml was distilled off, and the precipitate was
filtered off and washed with anhydrous ethanol. Yield
1
of II 6.31 g (95%). H NMR spectrum (D2O), , ppm:
3.51 t (2H, CH=), 4.10 d (4H, ArCH2), 7.56 q (4H,
H ), 8.40 q (4H, H ). Found, %: C 53.15; H 2.75.
C22H14Na4O8. Calculated, %: C 53.02; H 51.17.
the error of
of Bengal Rose taken as reference.
Bengal Rose and Triton X-100 were purchased
from Aldrich. Sodium salt of sulfonated hydroxyalu-
minum phthalocyanine was a mixture of sulfonates
consisting (according to HPLC) of tetra-, tri-, and
disulfonic acid salts (41, 46, and 6%, respectively),
with the average content of sulfo groups of 3.14 per
molecule.
Disodium 9,10-anthracenediyldipropionate (I) was
prepared from , -(anthracene-9,10-diyl)bis(methyl-
malonic) acid as described in [16].
9,10-Bis(pyridiniomethyl)anthracene dichloride
(III). 9,10-Bis(chloromethyl)anthracene (0.508 g) was
refluxed for 1 h in 5 ml of pyridine. The mixture was
cooled, and the product was filtered off, washed with
toluene, and crystallized from ethanol toluene (1 : 5).
Yield of III 0.57 g (71%); yellow crystals. Found, %:
C 72.41; H 5.12; Cl 15.82; N 6.54. C26H22Cl2N2.
Calculated, %: C 72.06; H 5.12; Cl 16.36; N 6.46.
Sodium 9,10-anthracenediyldiproponate (I) and
sodium , -(anthracene-9,10-diyl)bis(methylmalonate)
(II) were prepared by a modified procedure in [16],
starting from 9,10-bis(chloromethyl)anthracene.
Tetraethyl , -(anthracene-9,10-diyl)bis(methyl-
malonate). Metallic sodium (5 g) was added to 120 ml
of o-xylene and finely divided by vigorous stirring at
120 C. Then, with the vigorous stirring continued,
the mixture was cooled to 40 C, 67 ml of diethyl
malonate was added, and the mixture was heated at
100 C for 20 min. After that, 28.3 g of 9,10-bis(chlo-
romethyl)anthracene was added, the mixture was
refluxed for 4 h, cooled to room temperature, diluted
with 200 ml of hexane, filtered, and washed with
water; 30.2 g (56%) of chromatographically pure
tetraethyl , -(anthracene-9,10-diyl)bis(methylmalo-
nate) was obtained, mp 169 171 C (from o-xylene).
1H NMR spectrum (DMSO-d6), , ppm: 0.91 t (12H,
CH3), 3.80 t (2H, CH=), 3.92 m (8H, OCH2), 4.18 d
(4H, ArCH2), 7.57 q (4H, H ), 8.31 q (4H, H ).
Found, %: C 69.17; H 6.70. C30H34O8. Calculated,
%: C 68.95; H 6.56.
9,10-Bis(dihydroxyphosphinylmethyl)anthracene
(IV). To 0.08 g of 9,10-di(chloromethyl)anthracene
we added 0.3 ml of triisopropyl phosphite and heated
the mixture for 4 h at 160 C. The resulting 9,10-bis-
(diisopropoxyphosphinylmethyl)anthracene was pre-
cipitated with hexane and recrystallized from ben-
zene hexane. Yield 0.09 g (60%), mp 163 C. 1H
NMR spectrum (DMSO-d6), , ppm: 0.86 d (12H,
CH3); 1.16 d (12H, CH3), 4.27 d (4H, CH2P), 4.4 m
(4H, OCH), 7.56 m (4H, ArH), 8.35 m (4H, ArH).
A mixture of 9,10-bis(diisopropoxyphosphinyl-
methyl)anthracene (0.08 g) and 1 ml of concd. HCl
was heated for 2 h on a boiling water bath. The prod-
uct (IV) was reprecipitated from alkaline solution.
Yield 0.038 g (71%), mp >350 C (dec.).
, -(Anthracene-9,10-diyl)bis(methylmalonic)
acid. A solution of 12.0 g of NaOH in 40 ml of water
was added to a suspension of 9.6 g of the tetraester
in 80 ml of ethanol. The mixture was refluxed for 2 h,
cooled, diluted with 120 ml of water to complete dis-
solution of the precipitate, and filtered. The solution
was acidified, and the resulting precipitate was filtered
off and washed with hot water and alcohol. Yield of
the tetraacid 7.56 g (100%); the acid was practically
pure and was used without additional purification.
9,10-Bis(hydroxyethoxyphosphinylmethyl)anthra-
cene (V). To 0.3 g of 9,10-bis(chloromethyl)anthra-
cene we added 0.5 ml of triethyl phosphite and heated
the mixture for 2 h at 200 C. The mixture was
washed with chloroform, and the precipitate was re-
precipitated from aqueous alkali. Yield 0.076 g
(11%). H NMR spectrum (D2O + NaOD), , ppm:
0.86 t (6H, CH3), 3.3 q (4H, OCH2), 3.9 d (4H,
CH2P), 7.8 m (4H, ArH), 8.15 m (4H, ArH).
1
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NEW REAGENTS FOR DETERMINATION OF THE QUANTUM EFFICIENCY
41
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