New 3-hydroxyflavone derivatives for probing hydrophobic sites in microheterogeneous systems

Article abstract of DOI:10.1016/j.tet.2007.07.074

Nine new 3-hydroxyflavone derivatives as fluorescent molecular sensors having two well-separated emission bands were synthesized. These sensors can occupy well-determined locations and orientations in macromolecular ensembles, such as micelles due to their finely-tuned designs. These polarity-sensitive dyes can incorporate into the anhydrous hydrophobic core of aqueous micelles.

Full text of DOI:10.1016/j.tet.2007.07.074

Tetrahedron 63 (2007) 10290–10299
New 3-hydroxyflavone derivatives for probing hydrophobic
sites in microheterogeneous systems
b
a
c
a
Turan Ozturk,a, Andrey S. Klymchenko, Asli Capan, Sule Oncul, Simay Cikrikci,
*
Sule Taskiran,a Bahar Tasan,a F. Betul Kaynak,d Suheyla Ozbeyd and Alexander P. Demchenkoc,e
aDepartment of Chemistry, Science Faculty, Istanbul Technical University, Maslak, Istanbul, Turkey
b
´
Department de Pharmacologie et Physicochimie, Photophysique des Interactions Biomolecularies, UMR7175, Institut Gilbert
´
´
Laustriat, Universite Louis Pasteur (Strasbourg I), BP 60024, 76401 Illkirch, France
cTUBITAK Research Institute for Genetic Engineering & Biotechnology, Gebze-Kocaeli, Turkey
dDepartment of Engineering Physics, Hacettepe University, Beytepe, Ankara, Turkey
ePalladin Institute of Biochemistry, Kiev, Ukraine
Received 16 March 2007; revised 9 July 2007; accepted 20 July 2007
Available online 29 July 2007
Abstract—Nine new 3-hydroxyflavone derivatives as fluorescent molecular sensors having two well-separated emission bands were synthe-
sized. These sensors can occupy well-determined locations and orientations in macromolecular ensembles, such as micelles due to their
finely-tuned designs. These polarity-sensitive dyes can incorporate into the anhydrous hydrophobic core of aqueous micelles.
Ó 2007 Published by Elsevier Ltd.
Our recent investigations10 to understand the behaviour of
3HFs with regard to their interaction with living cells, indi-
1. Introduction
cated that 3HFs can enter into lipid bilayers.11 Their applica-
3-Hydroxyflavones (3HF) 1 are important candidates as
fluorescent molecular sensors since they have interesting
fluorescent properties, resulting from their excited state
intramolecular proton transfer (ESIPT) reaction.1 This
property leads to two well-separated, highly intense and
solvent-dependent emission bands, the ratio of the intensi-
ties of which is strongly sensitive to the polarity and hydro-
gen bonding perturbations1c in proteins,2 micelles3 and
polymers.4 These bands originate from the normal excited
form (N*) and the phototautomer (T*).1a,5 It has been dis-
closed that the introduction of an electron donor group to
the 40-position of the 3HF increases the sensitivity of fluores-
cence spectra of the molecule, which has attracted the inter-
est of research groups as two-band fluorescent dyes with
a ratiometric response to different perturbations.6 This re-
sulted in a variety of applications for substituted 3HFs as
ion sensors7 and probes in the studies of organized systems
such as micelles8 and phospholipid vesicles.3,9
tion has dramatically increased in recent years—from studies
on effects of solubilization of water in reverse micelles8b and
inclusion complexes with cyclodextrins12 to the studies of su-
percritical liquids.13 These results have stimulatednew efforts
to synthesize improved compounds with the ability to occupy
well-determined locations and orientations in macromolecu-
lar ensembles, such as micells andphospholipid bilayers. This
led us to design a series of finely-tuned compounds 21–29
with prospective application in the studies of living cells.
Development of such probes is very important since the fast
detection of bio-pollution in the environment is desirable.
Additionally, an X-ray structure of 3HF is disclosed in this
work, which gives insight into the planarity of the molecule.
2. Results and discussion
2.1. Synthesis
The synthesis of finely-tuned 3HFs was carried out through
the modified Algar–Flyn–Oyamada (AFO) reaction.6g,14
The aldehydes 6–8 were synthesized from aniline 2, which
was dialkylated with iodobutane, iodohexane and iodooctane
to obtain the dialkylanilines 3–5, respectively, and sub-
sequent formylation with phosphoryl trichloride–DMF re-
sulted in the production of the aldehydes (Scheme 1).
O
OH
O
1
* Corresponding author. E-mail: ozturktur@itu.edu.tr
0040–4020/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.tet.2007.07.074

T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
10291
NR2
NH2
NR2
A
1.0
a
b
5
0.8
13
CHO
2
3 R=C4H9
4 R=C8H17
5 R=C12H25
6 R=C4H9
12
11
0.6
7 R=C8H17
8 R=C12H25
0.4
Scheme 1. (a) R–I, K2CO3, acetone, reflux and (b) POCl3–DMF, 0/60 ꢀC.
0.2
While the acetophenones 9 and 10 are commercially avail-
able, the ketone, 4-octyloxyacetophenone 11 was prepared
following the reaction conditions applied for the synthesis
of the alkylanilines 3–5. Condensation of the aldehydes 6–
8 with the acetophenones 9–11, using sodium methoxide
as base in place of sodium hydroxide, which is the main
modification of AFO reaction, gave intermediates 12–20 in
5 h, rather than nearly one week in the AFO reaction
(Scheme 2). The ring closure reaction was performed on
the intermediate without any isolation. To the reaction mix-
ture was added excess sodium methoxide and hydrogen per-
oxide at 0 ꢀC, then it was heated to boiling and kept at that
temperature for around 5 min. Isolation was achieved using
column chromatography, which gave the fluorescent 3HFs
21–29.
340
360
380
400
420
440
1.4
1.2
1.0
0.8
0.6
0.4
0.2
12
B
14
13
5
2
0.0
1.0
8
11
C
0.8
0.6
0.4
0.2
0.0
R
OH
+
6 - 8
O
9 R=H
4
10 R=MeO
11 R=C8H17
O
a
400
450
500
550
600
650
700
Wavelength, nm
R
ONa
NR'2
Figure 1. Normalized absorption (A) and fluorescence emission spectra of
28 (B and C) in aprotic solvents (B) and in protic solvents (C). Solvents are
numbered according to Table 1.
O
12 R=H, R'=C4H9
13 R=H, R'=C8H17
14 R=H, R'=C12H25
17 R=MeO, R'=C12H25
18 R=C8H17O, R'=C4H9
19 R=C8H17O, R'=C8H17
shorter wavelengths exhibits dramatic change of its intensity
relative to the T* band located at longer wavelengths. A
spectral shift to longer wavelength accompanies an increase
of relative intensity of N* band. This shift is especially
strong in protic solvents such as butanol and ethanol so
that the T* band becomes poorly resolved and is observed
as shoulders. According to the commonly accepted model
of 3HF photophysics, the N* band belongs to the initially ex-
cited species and the T* band to the product of ESIPT reac-
tion. Strong solvent-dependent sensitivity of the spectrum
indicates the strong influence of solute–solvent interactions
in the ground and excited states. Since it is known that the
spectra of 3HFs are very sensitive to the hydrogen bonding
of proton–donor groups of solvents with 4-carbonyl func-
tionality, and that their dipole moments increase dramati-
cally on excitation favouring the strong effects of solvent
polarity, significant differences between fluorescence spec-
tra in aprotic and protic solvents and also in solvents of dif-
ferent polarities were expected and experimentally observed
(Fig. 1).
15 R=MeO, R'=C4H9 20 R=C8H17O, R'=C12H25
16 R=MeO, R'=C8H17
b
NR'2
R
O
O
OH
21 R=H, R'=C4H9
22 R=H, R'=C8H17
23 R=H, R'=C12H25
24 R=MeO, R'=C4H9 29 R=C8H17O, R'=C12H25
25 R=MeO, R'=C8H17
26 R=MeO, R'=C12H25
27 R=C8H17O, R'=C4H9
28 R=C8H17O, R'=C8H17
Scheme 2. (a) MeONa, EtOH, rt and (b) H2O2/MeONa, 0 ꢀC/reflux.
2.2. Solvent-dependent variations of spectra
The influence of solvent on the absorption and fluorescence
spectra is illustrated for one of the synthesized dyes, 28
(Fig. 1). A smooth absorption band located in the region of
400 nm exhibiting significant solvent-dependent shifts, and
in fluorescence spectra, two bands, typical feature of 3-
hydroxychromones were observed. The N* band located at
Solvent-dependent spectroscopic behaviours of three repre-
sentatives 22, 25 and 28, having equal lengths of hydrocar-
bon chains, of three synthesized 3HF families were studied

10292
T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
in detail (Table 1). A strong correlation of the position of ab-
sorption band maxima on electronic polarizability function
f(n) (where n is the refraction index) and of the position of
N* band on polarity function f(3) (where 3 is the dielectric
constant) was observed. These results were illustrated by
plotting corresponding graphs.
to be common behaviour among the studied compounds.
On the other hand, positions of the fluorescence spectra de-
pend more strongly on solvent polarity (Fig. 3). For both N*
and T* bands, the spectra shift to longer wavelengths with
the increase of f(3), but for N* band this dependence is
much stronger compare to the T* band. Such behaviour of
the three compounds, 22, 25 and 28, was noticed to be sim-
ilar. The band positions do not show a strong dependence on
the formation of intermolecular hydrogen bond by the
carbonyl groups of the studied probes that occur in protic
solvents. This observation is in line with the previous
results6h obtained for a similar 3HF derivative having a sim-
pler structure (40-diethylamino-3-hydroxyflavone) for which
the detailed spectroscopic data obtained in 21 solvents were
analyzed. Therefore, the major effect on the positions of the
spectral bands is the solvent polarity.
In Figure 2, the results were compared using the plots of po-
sition of fluorescence band maximum on energy scale (in
cmꢁ1) versus the function f(n). It was observed that all the
points corresponding to the solvents with proton–donor
and proton–acceptor properties lie below the lines drawn
for neutral solvents. This indicates that specific solute–
solvent interactions always shift the absorption spectra to
longer wavelengths. And, in general, this effect is stronger
than the effect of electronic polarizability, which is found
Table 1. Spectroscopic properties of the studied 3-hydroxyflavone derivatives in different solventsa
ꢂ
ꢂ
ꢂ
IN =IT
ꢂ
Solvent
Hexane
3HF
f(3)
f(n)
a
b
labs (nm)
lN ðnmÞ
lN ðnmÞ
1
22
25
28
0.1849
0.1862
0.00
0.00
406
397
397
428
415
431
556
563
566
0.01
0.01
0.01
2
Toluene
22
25
28
0.2387
0.3413
0.3563
0.3850
0.4074
0.4217
0.4574
0.4601
0.4647
0.4704
0.4798
0.4802
0.4842
0.2261
0.2324
0.2104
0.1853
0.1977
0.2032
1.1955
0.1862
0.1804
0.1812
0.2043
0.1747
0.2199
0.00
0.00
0.15
0.00
0.00
0.10
0.37
0.33
0.04
0.37
0.00
0.07
0.00
0.14
0.29
0.02
0.45
0.48
0.05
0.48
0.56
0.49
0.48
0.74
0.32
0.88
410
402
402
458
449
457
567
572
572
0.04
0.01
0.01
3
Anisole
22
25
28
412
406
403
477
460
468
574
578
578
0.02
0.07
0.04
4
Chloroform
22
25
28
417
409
409
485
474
476
565
568
568
0.68
0.26
0.26
5
Ethyl acetate
Tetrahydrofuran
Dichloromethane
n-Butanol
22
25
28
406
396
397
483
462
475
571
575
573
0.36
0.62
0.1
6
22
25
28
406
399
396
477
456
457
577
579
579
0.22
0.07
0.05
7
22
25
28
415
406
407
496
480
479
571
576
575
0.68
0.2
0.15
8
22
25
28
415
405
411
515
511
511
—
551
553
—
1.39
1.27
9
Isopropanol
Acetone
22
25
28
413
409
407
511
506
505
—
555
558
—
1.38
1.21
10
11
12
13
22
25
28
407
399
400
505
482
482
576
580
580
0.99
0.19
0.17
Ethanol
22
25
28
413
405
409
526
514
516
—
—
—
—
—
—
N,N-Dimethylformamide
Acetonitrile
Dimethyl sulfoxide
22
25
28
410
401
405
510
528
509
583
583
580
1.43
0.87
1.39
22
25
28
407
400
402
510
501
501
572
579
579
1.33
0.36
0.34
14
22
25
28
410
409
404
514
500
500
585
590
589
0.18
0.67
0.55
a and b: Abraham’s hydrogen bond acidity and basicity, respectively;1,2 labs is the position of absorption maximum, lN and lT are the positions of the fluo-
rescence maxima of the N* and T* states. The data in brackets refer to poorly resolved maximum (shoulder).
a
ꢂ
ꢂ

T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
10293
24800
24600
24400
24200
24000
1
A
A
23000
22000
21000
20000
19000
18000
N*
1
5
6
13 10
2
2
14
12
6
3
3
9
5
4
11
10
7
12
7
9
8
13
14
8
4
11
1
T*
23800
25400
4
7
5
2
6
10 13
3
B
14
12
17000
24000
1
N*
B
25200
25000
24800
24600
5
1
10
23000
22000
21000
20000
19000
6
13
2
12
2
5
3
6
4
10
13
11
7
7
3
8
14
9
11
12
8
14
4
9
24400
25400
8
C
9
18000 T*
17000
1
4
6
1
5
7
13
6
25200
25000
24800
24600
24400
24200
10
2
5
14
3
10
12
N*
23000
22000
21000
20000
19000
18000
17000
2
C
1
13
3
12
14
2
6
3
9
5
7
7
10
4
11
4
12
11
8
14
9
8
13
0.16
0.18
0.20
0.22
0.24
0.26
f(n)= (n2-1)/(2n2+1)
8
T*
9
1
4
5
Figure 2. Position of absorption band maxima of studied flavones as a func-
tion of solvent polarizability, f(n) in neutral (-), protic (B) and H-bond ac-
ceptor (6) solvents and also in chloroform (:) and dichloromethane (;).
The probes are A: 22, B: 25, C: 28. Solvents are numbered according to
Table 1.
7
13
3
6
12
14
2
10
0.45
0.15
0.20
0.25
0.30
0.35
f( )=( -1)/(2 +1)
0.40
0.50
Figure 3. Position of N* and T* band maxima in fluorescence spectra as
a function of polarity f(3) of different solvents. Symbols of the points corre-
spond to that in Figure 2. The probes are A: 22, B: 25, C: 28. Solvents are
numbered according to Table 1.
As was found earlier for other functional 3HFs,6a–g the most
significant solvent-dependent changes are observed for the
relative intensities of the N* and T* bands (Fig. 4). The mag-
nitude of these changes is so big that a logarithmic scale for
ꢂ
ꢂ
displaying the intensity ratios, logðIN =IT Þ; was applied. It
was observed that the ratio increases with increasing solvent
polarity f(3).
and the increase of N*/T* intensity ratio. This property can
be applied to detect penetration of polar and protic solvents
such as water into microscopic particles and nanocompo-
sites.
As was indicated earlier,6h intermolecular hydrogen bonding
effects may produce an additional increase of band intensity
ratio on the background of polarity effects. In the results of
the present study in which the deconvolution of the spectra
into individual components was not used, such dependence
was not clearly seen. Analysis of specific solvent effect
based on Abraham’s solvent acidity ‘a’ and basicity ‘b’ pa-
rameters indicated that the positions of the N* and T* bands,
particularly their intensity ratio, are strongly sensitive to hy-
drogen bonding. Increase of the solvent polarity and the for-
mation of hydrogen bonds produce spectral changes in the
same direction: the shift of N* band to a longer wavelength
2.3. Studies in micelles
Micelles formed by surfactant molecules are self-assembled
structures that are characterized by a strong gradient of po-
larity from polar interface exposed to aqueous solvent to hy-
drophobic core formed by hydrocarbon chains. In addition to
many industrial applications, such as micellar catalysis and
biocatalysis, micelles serve as simple models of biomem-
branes and test systems for probe development for biomem-
brane research. Probes that incorporate into the hydrophobic
core of micelles and biomembranes and report in a two-band

10294
T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
shown). Probes 21–23 exhibit the highest fluorescence inten-
A
B
C
14
13
12
sity with a variation of relative intensity of N* and T* fluo-
rescence bands (Fig. 5, A–C). There is an important
regularity: upon increase of chain length from 21 to 23,
the N* band compared to T* band (which is poorly resolved
in 21) changes dramatically; it decreases its relative intensity
and moves to shorter wavelengths. This is a strong indication
of changing the fluorophore environment—transition from
more polar and hydrated sites to hydrophobic sites in micelle
interior. The striking difference in response between the in-
corporated probes should be attributed to the effect of differ-
ent substituents that verify the location of the fluorophore in
the micelle structure. This interpretation is in line with the
results obtained in model solvents that are presented above.
It is logical to suggest that increase of the size of hydropho-
bic tail favours deeper location of fluorophore moiety into
the micelle.
0.0
-0.5
-1.0
-1.5
-2.0
7
10
4
5
3
6
2
1
9
8
13
14
12
0.0
-0.5
-1.0
-1.5
-2.0
0.0
4
Quite contrasting results were obtained from the study on
dyes of 24–26 and 27–29 series in the same, Triton X-100,
micelles. For 24, two bands of almost equal intensities
were observed, and for 27 the T* band is substantially
higher, which indicates a low polarity location of the dye.
The tendency to decrease the relative intensity of the N*
band on increasing the chain length is also observed for
them. In addition, except 27, these compounds exhibit sub-
stantially decreased relative intensity, which may be due to
some quenching effect or some parts of the dye becoming
aggregated in the micelle. However, this issue needs
a more detailed investigation.
7
10
5
6
3
2
1
8
12
9
13
14
11
-0.5
-1.0
-1.5
-2.0
4
7
10
5
A
1200
21
6
24
1000
3
27
800
2
TX
600
1
400
200
0
0.15
0.20
0.25
0.30
f(ε) = (ε-1)/(2ε+1)
0.35
0.40
0.45
0.50
1800
B
ꢂ
ꢂ
Figure 4. Logarithm of intensity ratio ðIN =IT Þ versus polarity f(3) for dif-
ferent solvents. Symbols of the points correspond to that in Figure 2. The
probes are A: 22, B: 25, C: 28. Solvents are numbered according to Table 1.
22
1500
25
1200
28
TX
900
600
300
wavelength-ratiometric manner on polarity and hydration at
their binding sites are in high demand. For this reason we un-
dertook a series of experiments on incorporation of synthe-
sized dyes into micelles formed by cationic surfactant
CTAB and neutral Triton X-100. Surprisingly, despite the
similarity of structures of these dyes, divergent and therefore
interesting results for their behaviour in these micelles were
obtained.
0
600
C
23
26
29
500
400
300
200
100
0
TX
In Triton X-100 micelles all the dyes incorporate well into
micelles and show an increase of intensity from almost
zero level observed in water (where most of them have
a very low solubility) to a certain level, which reaches a max-
imum at concentrations corresponding to surfactant critical
micelle concentrations (cmc). This level remains constant
on further increase of surfactant concentration (data not
450
500
550
600
650
Wavelength (nm)
Figure 5. Fluorescence spectra of new dyes in Triton X-100 micelles formed
in water.

T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
10295
Even more interesting results appear on the studies of new
dyes in cationic detergent CTAB (Fig. 6, A–C). In the line
of dyes 21–23 only a relatively intense N* band that is
strongly shifted to longer wavelengths was observed.
Thus, regardless of the length of the attached chain, the fluo-
rophore is exposed to polar micelle surface and is highly
hydrated (with 4-carbonyl group forming hydrogen bond
with water). This conclusion is supported by our recently ob-
tained data on the influence of hydrogen bonding with water
on the fluorescence spectra of compounds of the same
3-hydroxyflavone family.15
spectroscopic properties that are due to differences in their
location and orientation in the micelles. Probes 27 and 25
are the most interesting for different micellar, bilayer struc-
tures and also apolar interfaces due to the possibility of
hydrophobic location of their fluorophore unit. The low po-
larity of location of the probes is witnessed by the following
facts. (i) Position of the most polarity-sensitive N* band cor-
responds to that in low-polar aprotic solvents (see Table 1).
(ii) There is no evidence for the presence of the hydrogen-
bonded forms of the dyes (that should have the spectrum
strongly shifted to longer wavelengths). The micelle cores
do not contain the groups that could be hydrogen bond do-
nors, so the only expected partners for the formation of these
bonds could be hydration water. Thus the probes are com-
pletely inaccessible to contact with water molecules. (iii)
On the addition of iodide ions that are known as strong
water-solublecollisional fluorescence quenchers, thequench-
ing effect is not observed (data not shown). This fact is
especially demonstrative for CTAB micelles since Iꢁ ions
can substitute Brꢁ ions in the polar interface layer thus
increasing substantially their local concentration.
Regarding the other studied compounds 24–29, their relative
fluorescence intensity is comparatively low (with the excep-
tion of 25) or is dramatically quenched as for 26 and 29. It is
not excluded that these compounds incorporate into micelles
in such a way that their fluorescence is quenched by colli-
sions with bromide ions, which are known as a strong fluo-
rescence quencher.16 The dye 25 presents an exclusion due
to its intense fluorescence spectrum with two bands being
well resolved and of almost equal intensities, which indi-
cates a moderately polar unhydrated fluorophore environ-
ment. The relatively narrow widths of these bands indicate
the absence of heterogeneity of location of the studied
probes (the distribution between the sites of different polar-
ity and hydration), which in biomembrane studies was
not achieved with 3HF probes having more simple
structures.17,18
Thus, to our best knowledge this is the first example of
successful incorporation of polarity-sensitive dye into the
anhydrous hydrophobic core of an aqueous micelle. The pre-
viously applied more simple in structure 3HF derivatives did
not achieve that goal. It is also known that many other
applied probes of low polarity, such as aminonaphthalene,
coumarin and aminophthalimide derivatives, are known to
distribute in micelles between core and interface regions
with a significant extent of hydrogen bonding to hydration
water.19–22
Thus, the synthesized dyes despite the same fluorophore
incorporated into their structures display a variety of
1200
2.4. X-ray single crystal measurement
A
21
1000
24
800
X-ray study reveals that in the crystal structure of 24 the
asymmetric part of the unit cell contains two crystallograph-
ically independent molecules labelled A and B (Fig. 7). Both
molecules are chemically equivalent but differ essentially in
the conformation. As expected, the chromanone moiety of
both molecules is planar i.e., the mean deviations of the
atoms from the least-square squares planes are ꢁ0.048(5)
27
600
400
200
CTAB
0
200
0
˚
B
and ꢁ0.055(5) A for C4 and C3 in A and B, respectively.
22
25
28
150
100
50
The phenyl ring and the chromanone moiety make a dihedral
angle of 9.1(2)ꢀ in A, and the corresponding angle for B is
CTAB
0
C
2800
23
26
29
2100
1400
700
0
CTAB
450
500
550
600
650
Wavelength (nm)
Figure 7. Perspective views of the asymmetric unit. Displacement ellipsoids
are scaled to 30% probability level. Hydrogen atoms were not shown for
clarity.
Figure 6. Fluorescence spectra of new dyes in CTAB micelles formed in
water.

10296
T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
27.9(2)ꢀ, which reflects the major deviation from the planarity
of the molecule. The value given for A is comparable
withthose ofmikanin(7.9ꢀ intetragonal form23 and 9.2ꢀ intri-
clinicform24 of the same molecule), flavone-30-sulfonamide25
(8.3ꢀ) and diethyl 2-6-dimethyl-4-(2-phenyl-4-oxo-4H-
1-benzopyran-6-yl)-1,4-dihydropyridine-3,5-dicarboxylate26
(10.7ꢀ), while the corresponding value for B is comparable
with those of 3-hydroxy-30-methylflavone27 (23.1ꢀ) and 5-
hydroxy-7-methoxyflavone28 (24.8ꢀ). The coplanarity of the
phenyl ring and the chromanone has been attributed to short
intramolecular hydrogen contacts between H atoms of the
phenyl and oxo groups of the pyran-4-one group. In flavones,
generally, an increase of the dihedral angle means a decrease
inthedegreeofconjugationbetweentheC2–C12bondandthe
p electrons of the pyran-4-one ring.
In molecule A, the methoxy group at C7 is nearly coplanar
with the phenyl ring by the torsion angle C6–C7–O4–C11
176.7(4)ꢀ, whereas the methoxy group in B is slightly
twisted out of the phenyl ring with the torsion angle of
167.7(4)ꢀ. The butyl groups at N1 are nearly orthogonal to
the phenyl ring plane as indicated by the torsion angles
C19–C18–N1–C15 82.8(5)ꢀ and C23–C22–N1–C15
101.0(5)ꢀ (90.4(4)ꢀ and 93.6(4)ꢀ in B).
The crystal structure of 24 is stabilized by intra- and inter-
molecular hydrogen bonds (Table 2). The packing of the
molecules and the hydrogen bonding in the structure are
shown in Figure 8. The two independent molecules exhibit
the same pattern of hydrogen bonds except C17A–
H17A/O1A intramolecular interaction in A, which contrib-
utes to the coplanarity of the phenyl ring with the rest of the
molecule A. Chains of the molecules linked through O–H/
O hydrogen bonds, which extend along the b axis, are joined
by means of C11A–H11A/O2B bonds (Fig. 8).
3. Conclusion
With the aim of extending the possibilities of two-colour
ratiometric environment-sensitive probes to localize
selectively and to probe low-polar microenvironments we
synthesized a number of 3-hydroxyflavone derivatives.
They retain the major spectroscopic properties of parent
compounds and, in addition, are able to incorporate selec-
tively into low-polar environments. This is demonstrated in
the studies of neutral and cationic micelles. However, the
site and length of the hydrophobic substituent in the dye mol-
ecule, which has virtually no influence on spectroscopic
properties in neat solvents can modulate significantly these
properties in microheterogeneous systems such as micelles.
Figure 8. Compound 24 is viewed down the a axis and c face showing the
packing layers. Dotted lines show the intra- and intermolecular interactions.
4. Experimental
4.1. General
ꢀ
˚
Table 2. Hydrogen-bonding geometry (A, ) for 24
D–H/A
DꢁH
H/A
D/A
D–H/A
O2A–H2A/O3A
O2A–H2A/O3B(i)
O2B–H2B/O3B
0.82
0.82
0.82
0.82
0.96
0.93
0.93
0.93
2.27
2.01
2.30
1.94
2.59
2.17
2.28
2.36
2.704(4)
2.729(4)
2.736(4)
2.665(3)
3.443(6)
2.826(4)
2.850(4)
2.702(4)
114
146
114
148
148
127
119
102
Melting points are uncorrected. NMR spectra were recorded
in CDCl3 with tetramethylsilane as the internal standard for
1H (250 MHz) unless otherwise stated. Mass spectra were
recorded at an ionizing voltage of 70 eV. Chromatography
was performed on flash silica gel (Merck) and TLC was
carried out on 0.2-mm silica gel plates. All reagents and
solvents were of commercial grade (Aldrich) and purified
according to established convention.
O2B–H2B/O3A(i)
C11A–H11A/O2B(ii)
C13A–H13A/O2A
C13B–H13B/O2B
C17A–H17A/O1A
Symmetry codes: (i) ꢁx,ꢁy,ꢁz and (ii) ꢁx+1/2, yꢁ1/2,ꢁz+1/2.

T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
10297
4.1.1. 2-Hydroxy-4-octyloxyacetophenone (11).29 A mix-
ture of 2,4-dihydroxyacetophenone (5.00 g, 0.033 mol),
octyliodide (5.6 ml, 0.033 mol) and K2CO3 (5.00 g) was
refluxed in acetone (20 ml) for 3 h. To the reaction mixture
was added water (20 ml) and extracted with ethyl acetate
(3ꢃ30 ml). The organic layer was dried over MgSO4, fil-
tered and the solvent was evaporated under reduced pres-
sure. The crude product was chromatographed using
CH2Cl2 as eluting solvent to give the title compound 11
(Rf¼0.13) as a light brown viscous liquid (6.88 g, 79%).
1H NMR (CDCl3, 250 MHz) d 12.74 (s, 1H, OH), 7.6 (d,
J¼8.7 Hz, 1H), 6.5 (dd, J¼8.7 Hz, J¼2.4 Hz, 1H), 6.4 (s,
1H), 3.9 (t, J¼6.6 Hz, 2H), 2.53 (s, 3H), 1.4 (m, 12H), 0.9
(t, J¼5.59 Hz, 3H); C16H24O3; EIMS (m/z) 264 (M+).
4.1.2. N,N-Dibutylaminobenzene (3).30 To the mixture of
aniline 2 (0.008 mol, 0.72 ml), K2CO3 (2.18 g) and DMF
(dry, 5 ml) heated at 120 ꢀC was added butyliodide
(3.05 g, 0.03 mol). It was heated at the same temperature
for 10 h then the mixture was extracted with CH2Cl2, dried
over MgSO4, filtered and the solvent was evaporated under
reduced pressure. The crude product was chromatographed
using hexane/CH2Cl2 (4/1) as eluting solvent to give the title
compound 3 as a light brown viscous liquid, (1.029 g, 82%).
1H NMR (CDCl3, 250 MHz) d 7.17 (t, J¼5.3 Hz, 2H), 6.6
(m, 3H), 3.25 (t, J¼7.06 Hz, 4H), 1.6 (m, 4H), 1.3 (m,
4H), 0.9 (t, J¼6.2 Hz, 6H); C14H23N; EIMS (m/z) 205 (M+).
4.1.6. N,N-Dioctylaminobenzaldehyde (7). The crude
product was chromatographed using hexane/CH2Cl2 (2/1)
as eluting solvent to give the title compound 7 (Rf¼0.08)
1
as a brown viscous liquid (4.5 g, 65%). H NMR (CDCl3,
250 MHz) d 9.68 (s, 1H), 7.65 (d, J¼8.5 Hz, 2H), 6.62 (d,
J¼8.5 Hz, 2H), 3.28 (t, J¼7.2 Hz, 4H), 1.57 (m, 4H), 1.28
(m, 20H), 0.87 (t, J¼6.30 Hz, 6H); C23H39NO; EIMS
(m/z) 345 (M+).
4.1.7. N,N-Didodecylaminobenzaldehyde (8). The crude
product was chromatographed using hexane/CH2Cl2 (2/1)
as eluting solvent to give the title compound 8 (Rf¼0.11)
as a brown viscous liquid (6.23 g, 67%). 1H NMR (CDCl3,
250 MHz) d 9.75 (s, 1H), 7.60 (d, J¼8.2 Hz, 2H), 6.59 (d,
J¼8.2 Hz, 2H), 3.30 (t, J¼7.29 Hz, 4H), 1.50 (m, 4H),
1.21 (m, 36H), 0.84 (t, J¼6.27 Hz, 6H); C31H55NO; EIMS
(m/z) 458 (M+).
4.1.8. 2-(4-Dibutylamino)phenyl-3-hydroxy-4H-chro-
men-4-one (21). To the solution of dibutylaminobenzalde-
hyde 6 (3.33 g, 0.0143 mol) and 2-hydroxyacetophenone 9
(1.95 g, 0.0143 mol) dissolved in DMF (dry, 5 ml) was
added NaOMe (3.1 g, 0.057 mol) and the mixture was stirred
at room temperature until a deep red colour was obtained
(w5–8 h). Ethanol (20 ml) and NaOMe (0.7 g, 0.013 mol)
were added, then the mixture was cooled to 0 ꢀC, H2O2
(0.8 mol, 0.027 mol) was added carefully and heated at
120 ꢀC for 10 min. The yellow mixture was then poured
into water (50–100 ml) and neutralized with acetic acid. It
was extracted with CH2Cl2, dried over Na2SO4, filtered
and the solvent was evaporated under reduced pressure.
The crude product was chromatographed using hexane/ethyl
acetate (5/1) as eluting solvent to give the title compound 21
(Rf¼0.53) as a yellow powder (0.97 g, 21%), mp 130–
131.5 ꢀC. [Found: C, 75.42, H, 7.12, N, 3.55. C23H27NO3
C, 75.61, H, 7.39, N, 3.83%]; 1H NMR (CDCl3, 250 MHz)
d 8.21 (d, J¼6.4 Hz, 1H), 8.15 (d, J¼9.23 Hz, 2H), 7.63
(m, 1H), 7.53 (d, J¼8.2 Hz, 1H), 7.38 (m, 1H), 6.72 (d,
J¼9.2 Hz, 2H), 3.34 (t, J¼7.4 Hz, 4H), 1.60 (m, 4H), 1.35
(m, 4H), 0.96 (t, J¼7.3 Hz, 6H); C23H27NO3; EIMS (m/z)
366 (M++1).
The following were similarly prepared.
4.1.3. N,N-Dioctylaminobenzene (4).31 The crude product
was chromatographed using hexane/CH2Cl2 (4/1) as eluting
solvent to give the title compound 4 (Rf¼0.48) as a brown
1
viscous liquid (2.13 g, 84%). H NMR (CDCl3, 250 MHz)
d 7.18 (t, J¼5.20 Hz, 2H), 6.67 (m, 3H), 3.20 (t,
J¼7.3 Hz, 4H), 1.7 (m, 4H), 1.35 (20H, m), 0.9 (t,
J¼6.1 Hz, 6H); C22H39N; EIMS (m/z) 317 (M+).
4.1.4. N,N-Didodecylbenzamine (5). The crude product
was chromatographed using hexane/CH2Cl2 (4/1) as eluting
solvent to give the title compound 5 as a brown viscous liq-
1
uid (2.77 g, 78%). H NMR (CDCl3, 250 MHz) d 7.12 (t,
J¼5.25 Hz, 2H), 6.63 (m, 3H), 3.20 (t, J¼7.25 Hz, 4H),
1.68 (m, 4H), 1.33 (m, 36H), 0.89 (t, J¼6.19 Hz, 6H);
C30H55N; EIMS (m/z) 430 (M++1).
The following were similarly prepared.
4.1.9. 2-(4-Dioctylamino)phenyl-3-hydroxy-4H-chro-
men-4-one (22). The crude product was chromatographed
using hexane/ethyl acetate (5/1) as eluting solvent to give
the title compound 22 (Rf¼0.65) as a light brown viscous
liquid (1.2 g, 19%). [Found: C, 78.20, H, 8.79, N, 3.20.
C31H43NO3 C, 77.98, H, 9.01, N, 2.93%]; 1H NMR
(250 MHz, CDCl3) d 8.22 (d, J¼7.9 Hz, 1H), 8.15 (d,
J¼9.2 Hz, 2H), 7.64 (m, 1H), 7.52 (d, J¼7.6 Hz, 1H), 7.36
(m, 1H), 6.73 (d, J¼9.2 Hz, 2H), 3.33 (t, J¼7.4, 4H), 1.56
(m, 4H), 1.32 (m, 20H), 0.87 (t, J¼6.6 Hz, 6H);
C31H43NO3; EIMS (m/z) 478 (M++1).
4.1.5. N,N-Dibutylamino benzaldehyde (6).32 To an ice-
cooled round-bottom flask containing POCl3 (3.06 ml,
0.037 mol) was carefully added DMF (10 ml). The solution
was warmed to room temperature and added 3 (3.3 g,
0.021 mol). The mixture was stirred for 4 h at 60 ꢀC, then
cooled to room temperature and ice was added to terminate
the reaction. The mixture was extracted with CH2Cl2, dried
over Na2SO4, filtered and the solvent was evaporated under
reduced pressure. The crude product was chromatographed
using hexane/CH2Cl2 (2/1) as eluting solvent to give the title
compound 6 (Rf¼0.34) as a brown viscous liquid (3.33 g,
1
4.1.10. 2-(4-Didodecylamino)phenyl-3-hydroxy-4H-
chromen-4-one (23). The crude product was chromato-
graphed using hexane/ethyl acetate (5/2) as eluting solvent
to give the title compound 23 (Rf¼0.75) as a light brown vis-
cous liquid (1.6 g, 20%). [Found: C, 79.62, H, 9.85, N, 2.29.
C39H59NO3 C, 79.45, H, 10.01, N, 2.37%]; 1H NMR
68%). H NMR (CDCl3, 250 MHz) d 9.67 (s, 1H), 7.7 (d,
J¼8.9 Hz, 2H), 6.6 (d, J¼8.9 Hz, 2H), 3.35 (t, J¼7.6 Hz,
4H), 1.56 (m, 4H), 1.37 (m, 4H), 0.95 (t, 7.24 Hz, 6H);
C15H23NO; EIMS (m/z) 233 (M+).
The following were similarly prepared.

10298
T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
(250 MHz, CDCl3) d 8.1 (d, J¼7.0 Hz, 1H), 8.12 (d,
J¼9.2 Hz, 2H), 7.59 (m, 1H), 7.5 (d, J¼7.5 Hz, 1H), 7.32
(m, 1H), 6.68 (d, J¼9.2 Hz, 2H), 3.35 (t, J¼7.2 Hz, 4H),
1.58 (m, 4H), 1.30 (m, 36H), 0.83 (t, J¼6.5 Hz, 6H);
C39H59NO3; EIMS (m/z) 590 (M++1).
1.55 (m, 6H), 1.31 (m, 30H), 0.88 (m, 9H); C47H75NO4;
EIMS (m/z) 606 (M++1).
4.1.16. 2-(4-Didodecylamino)phenyl-3-hydroxy-7-octyl-
oxy-4H-chromen-4-one (29). The crude product was chro-
matographed using hexane/ethyl acetate (5/2) as eluting
solvent to give the title compound 29 (Rf¼0.85) as a brown
viscous liquid (1.47 g, 15%). [Found: C, 78.53, H, 10.71, N,
4.1.11. 2-(4-Dibutylamino)phenyl-3-hydroxy-7-methoxy-
4H-chromen-4-one (24). The crude product was chromato-
graphed using hexane/ethyl acetate (5/2) as eluting solvent
to give the title compound 24 (Rf¼0.5) as a yellow powder
(0.76 g, 15%), mp 147–149 ꢀC. [Found: C, 72.53, H, 7.52,
N, 3.45. C24H29NO4 C, 72.91, H, 7.34, N, 3.53%]; 1H
NMR (250 MHz, CDCl3) d 8.10 (d, J¼9.1 Hz, 2H), 8.09
(d, J¼8.8 Hz, 1H), 6.94 (m, 2H), 6.72 (d, J¼9.1 Hz, 2H),
3.9 (s, 3H), 3.33 (t, J¼7.3 Hz, 4H), 1.6 (m, 4H), 1.38 (m,
4H), 0.96 (t, J¼7.3 Hz, 6H); C24H29NO4; EIMS (m/z) 396
(M++1).
1
2.13. C47H75NO4 C, 78.66, H, 10.46, N, 1.95%]; H NMR
(250 MHz, CDCl3) d 8.09 (d, J¼9.1 Hz, 2H), 8.0 (d,
J¼8.8 Hz, 2H), 6.89 (m, 2H), 6.68 (d, J¼9.1 Hz, 2H), 3.98
(t, J¼6.3 Hz, 2H), 3.31 (t, J¼7.5 Hz, 4H), 2.11 (m, 6H),
1.53 (m, 6H), 1.29 (m, 40H), 0.77 (m, 9H); C47H75NO4;
EIMS (m/z) 718 (M++1).
4.2. X-ray analysis of 24
Single crystal measurements were performed on an Enraf–
Nonius CAD4 four circle diffractometer equipped with
graphite monochromator Cu Ka radiation. Semi-empirical
(c scan) absorption corrections were applied. Structure
was solved by direct methods (SHELXS97)33 and refined
by least-squares procedures on Fsqd (SHELXL97).34 Non-
hydrogen atom parameters were refined anisotropically.
All hydrogen atoms were geometrically located and in-
cluded using a riding model. The geometric calculations
were carried out with the program Platon.35 The crystal
data and final parameters of the results of refinement are
listed in Table 3. The molecular structure with numbering
scheme and the packing arrangement of the molecules are
presented in Figures 7 and 8. Selected bond lengths,
bond angles and torsion angles are listed in Table 4.
Fractional atomic coordinates, anisotropic displacement pa-
rameters and molecular dimensions have been deposited
with the Cambridge Crystallographic data centre (CCDC
651344).
4.1.12. 2-(4-Dioctylamino)phenyl-3-hydroxy-7-methoxy-
4H-chromen-4-one (25). The crude product was chromato-
graphed using hexane/ethyl acetate (5/2) as eluting solvent
to give the title compound 25 (Rf¼0.52) as a light brown vis-
cous liquid (1.3 g, 19%). [Found: C, 75.43, H, 8.45, N, 2.82.
C32H45NO4 C, 75.73, H, 8.87, N, 2.76%]; 1H NMR
(250 MHz, CDCl3) d 8.12 (d, J¼9.1 Hz, 2H), 8.09 (d,
J¼8.8 Hz, 1H), 6.93 (m, 2H), 6.9 (m, 2H), 6.42 (d,
J¼9.1 Hz, 2H), 3.91 (s, 3H), 3.32 (t, J¼7.1 Hz, 4H), 1.61
(m, 4H), 1.28 (m, 20H), 0.88 (t, J¼6.7 Hz, 6H);
C32H45NO4; EIMS (m/z) 508 (M++1).
4.1.13. 2-(4-Didodecylamino)phenyl-3-hydroxy-7-
methoxy-4H-chromen-4-one (26). The crude product was
chromatographed using hexane/ethyl acetate (5/2) as eluting
solvent to give the title compound 26 (Rf¼0.47) as a light
brown viscous liquid (1.51 g, 18%). [Found: C, 77.42, H,
9.53, N, 2.35. C40H61NO4 C, 77.54, H, 9.85, N, 2.26%];
1H NMR (250 MHz, CDCl3) d 8.11 (d, J¼9.1 Hz, 2H),
8.08 (d, J¼8.8 Hz, 1H), 6.91 (m, 2H), 6.89 (m, 2H), 6.38
(d, J¼9.1 Hz, 2H), 4.01 (s, 3H), 3.30 (t, J¼7.1 Hz, 4H),
1.60 (m, 4H), 1.30 (m, 36H), 0.85 (t, J¼6.6 Hz, 6H);
C40H61NO4; EIMS (m/z) 620 (M++1).
Table 3. Crystal data and structure refinement parameters for 24
Crystal data
Formula
C24H29NO4
Crystal habit
Crystal size (mm)
Symmetry
Brown, prism
0.30ꢃ0.33ꢃ0.48
Monoclinic, P21/n
a¼15.7075(17)
b¼15.3951(14)
c¼18.458(2)
4.1.14. 2-(4-Dibutylamino)phenyl-3-hydroxy-7-octyloxy-
4H-chromen-4-one (27). The crude product was chromato-
graphed using hexane/ethyl acetate (5/2) as eluting solvent
to give the title compound 27 (Rf¼0.8) as a light brown vis-
cous liquid (1.1 g, 19%). [Found: C, 75.31, H, 8.54, N, 3.12.
C31H43NO4 C, 75.45, H, 8.72, N, 2.83%]; 1H NMR
(250 MHz, CDCl3) d 8.13 (d, J¼9.1 Hz, 2H), 8.05 (d,
J¼8.7 Hz, 2H), 6.90 (m, 2H), 6.73 (d, J¼9.1 Hz, 2H), 4.02
(t, J¼6.2 Hz, 2H), 3.30 (t, J¼7.3 Hz, 4H), 2.10 (m, 6H),
1.52 (m, 6H), 1.28 (m, 8H), 0.84 (m, 9H); C31H43NO4;
EIMS (m/z) 494 (M++1).
Unit cell
ꢀ
˚
dimensions (A, )
b¼105.633(9)
3
V (A ), Z
˚
4298.4(8), 8
1.222, 395.48
1.54184, uꢁ2q
Dcalcd (g cmꢁ3), M
l (Cu Ka)
˚
(A), Scan type
m (Cu Ka) (mmꢁ1
Tmin, Tmax (%)
)
0.664
78.2, 81.9
Experimental data
2qmax (ꢀ)
Index ranges
Reflections collected
Reflections independent/used
in refinement
4.1.15. 2-(4-Dioctylamino)phenyl-3-hydroxy-7-octyloxy-
4H-chromen-4-one (28). The crude product was chromato-
graphed using hexane/ethyl acetate (5/2) as eluting solvent
to give the title compound 28 (Rf¼0.9) as a brown viscous
liquid (1.39 g, 17%). [Found: C, 77.53, H, 9.36, N, 2.44.
C39H59NO4 C, 77.35, H, 9.75, N, 2.31%]; 1H NMR
(250 MHz, CDCl3) d 8.1 (d, J¼9.0 Hz, 2H), 8.08 (d,
J¼8.8 Hz, 2H), 6.92 (m, 2H), 6.70 (d, J¼9.0 Hz, 2H), 4.04
(t, J¼6.3 Hz, 2H), 3.35 (t, J¼7.5 Hz, 4H), 2.13 (m, 6H),
141.58
ꢁ18ꢄhꢄ19; 0ꢄkꢄ18; ꢁ22ꢄlꢄ0
7330
7330/7112
No. of refined parameters
R/Rw values
524
0.0803/0.2234
1.02
0.00
ꢁ0.553, 0.761
GOF on F2
Final shift
ꢁ3
˚
(Dr)min, (Dr)max (e A
)

T. Ozturk et al. / Tetrahedron 63 (2007) 10290–10299
10299
ꢀ
˚
Table 4. Selected geometrical parameters ( , A) of 24
8. (a) Pivovarenko, V. G.; Tuganova, A. V.; Klymchenko, A. S.;
Demchenko, A. P. Cell. Mol. Biol. Lett. 1997, 2, 355–364;
(b) Klymchenko, A. S.; Demchenko, A. P. Langmuir 2002,
18, 5637–5639.
9. (a) Bondar, O. P.; Pivovarenko, V. G.; Rowe, E. S. Biochem.
Biophys. Acta 1998, 1369, 119–130; (b) Duportail, G.;
Klymchenko, A. S.; Mely, Y.; Demchenko, A. P. FEBS Lett.
2001, 508, 196–200; (c) Duportail, G.; Klymchenko, A. S.;
Mely, Y.; Demchenko, A. P. J. Fluorescence 2002, 12, 181–
185.
10. (a) Chattopadhyay, A.; London, E. Biochemistry 1987, 26, 39–
45; (b) Abrams, F. S.; London, E. Biochemistry 1993, 32,
10826–10831.
11. Klymchenko, A. S.; Duportail, G.; Ozturk, T.; Pivovarenko,
V. G. Chem. Biol. 2002, 9, 1199–1206.
12. Banerjee, A.; Sengupta, P. K. Chem. Phys. Lett. 2006, 424,
379–386.
13. Barroso, M.; Chattopadhyay, N.; Klymchenko, A. S.;
Demchenko, A. P.; Arnaut, L. G.; Formosinho, S. J. J. Phys.
Chem. A 2006, 110, 13419–13424.
14. Algar, J.; Flynn, J. Proc. R. Irish Acad. 1934, B42, 1–5.
15. Shynkar, V. V.; Klymchenko, A. S.; Piemont, E.; Demchenko,
A. P.; Mely, Y. J. Phys. Chem. A 2004, 108, 8151–8159.
16. Lakowics, J. R. Principles of Fluorescence Spectroscopy;
Kluwer: New York, NY, 1999.
Molecule A
Molecule B
C11–O4
C7–O4
C4–C10
C4–O3
C3–O2
C2–C12
C15–N1
C18–N1
C22–N1
C3–C2–C12
C2–C3–O2
O3–C4–C10
O4–C7–C8
N1–C15–C16
C18–N1–C22
C7–O4–C11
C8–C7–O4–C11
O1–C2–C12–C17
C14–C15–N1–C18
C19–C18–N1–C22
C23–C22–N1–C18
1.423(4)
1.352(4)
1.440(5)
1.241(4)
1.360(4)
1.468(4)
1.384(4)
1.445(5)
1.468(5)
128.4(3)
120.2(3)
123.5(4)
124.9(4)
122.4(3)
115.1(3)
118.9(3)
ꢁ3.7(6)
ꢁ7.4(5)
ꢁ3.2(6)
ꢁ89.2(4)
ꢁ87.2(5)
1.423(4)
1.359(4)
1.444(5)
1.242(4)
1.358(4)
1.454(5)
1.373(4)
1.457(4)
1.456(4)
128.2(3)
119.6(3)
123.2(4)
124.3(4)
123.2(3)
116.8(3)
118.7(3)
ꢁ12.5(6)
ꢁ24.2(5)
ꢁ12.4(5)
ꢁ93.0(4)
ꢁ82.9(4)
Acknowledgements
We thank TUBITAK for supporting this work (TBAG 2378-
103T122).
17. Klymchenko, A. S.; Duportail, G.; Demchenko, A. P.; Mely, Y.
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18. Klymchenko, A. S.; Mely, Y.; Demchenko, A. P.; Duportail, G.
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