Meso-trans-diaryldihexadecyltetrabenzoporphyrins and their zinc complexes: Synthesis and spectra

Article abstract of DOI:10.1134/S1070363207080257

3-[(1-Oxo-1H-isoindol-3-yl)(phenyl)methylidene]-2,3-dihydro-1H-isoindol-1- one, 3-[(1-oxo-1H-isoindol-3-yl)(1-naphthyl)methylidene]-2,3-dihydro-1H- isoindol-1-one, and 3-[(1-oxo-1H-isoindol-3-yl)(9-anthryl)methylidene]-2,3- dihydro-1H-isoindol-1-one were prepared by the reactions of phthalimide with phenylacetic, 1-naphthylacetic, and 9-anthrylacetic acids, respectively. Heating of these precursors with stearic acid in the presence of zinc oxide yielded zinc complexes of meso-trans-diphenyldihexadecyltetrabenzoporphyrin, meso-trans-di(1-naphthyl)dihexadecyltetrabenzoporphyrin, and meso-trans-di(9-anthryl)dihexadecyltetrabenzoporphyrin, respectively. Treatment of the metal complexes with HCl yielded the porphyrin bases. The spectral properties of the compounds were studied.

Full text of DOI:10.1134/S1070363207080257

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 8, pp. 1448 1454.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
pp. 1370 1376.
N.E. Galanin, L.A. Yakubov, G.P. Shaposhnikov, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 8,
meso-trans-Diaryldihexadecyltetrabenzoporphyrins
and Their Zinc Complexes: Synthesis and Spectra
N. E. Galanin, L. A. Yakubov, and G. P. Shaposhnikov
Ivanovo State University of Chemical Technology,
Pr. F. Engel’sa 7, Ivanovo, 153000 Russia
e-mail: ttoc@isuct.ru
Received February 6, 2007
Abstract 3-[(1-Oxo-1H-isoindol-3-yl)(phenyl)methylidene]-2,3-dihydro-1H-isoindol-1-one, 3-[(1-oxo-1H-
isoindol-3-yl)(1-naphthyl)methylidene]-2,3-dihydro-1H-isoindol-1-one, and 3-[(1-oxo-1H-isoindol-3-yl)(9-
anthryl)methylidene]-2,3-dihydro-1H-isoindol-1-one were prepared by the reactions of phthalimide with
phenylacetic, 1-naphthylacetic, and 9-anthrylacetic acids, respectively. Heating of these precursors with stearic
acid in the presence of zinc oxide yielded zinc complexes of meso-trans-diphenyldihexadecyltetrabenzopor-
phyrin, meso-trans-di(1-naphthyl)dihexadecyltetrabenzoporphyrin, and meso-trans-di(9-anthryl)dihexadecyl-
tetrabenzoporphyrin, respectively. Treatment of the metal complexes with HCl yielded the porphyrin bases.
The spectral properties of the compounds were studied.
DOI: 10.1134/S1070363207080257
meso-Substituted tetrabenzoporphyrins are import-
ant synthetic analogs of natural porphyrins. Unique
electron-optical properties of these compounds allow
their use, e.g., in photodynamic therapy of tumor
diseases [1 5]. In addition, meso-substituted tetraben-
zoporphyrins exhibit interesting acid base [6] and
electrochemical [7] properties, which makes promis-
ing their use as sensors for small molecules and ions.
(very low yield of the desired porphyrin). At the same
time, with an increase in the length of alkyl substitu-
ents, the lipophilicity of meso-alkyl-substituted tetra-
benzoporphyrins increases, which is important for
their potential use in photodynamic therapy and makes
them more soluble in nonpolar organic solvents. The
solubility becomes still higher if a molecule of tetra-
benzoporphyrin contains alkyl and aryl substituents
simultaneously.
meso-Aryl-substituted tetrabenzoporphyrins have
been studied to a greater extent. Data on meso-alkyl-
substituted derivatives of tetrabenzoporphyrins are
scarce [8], although such compounds may also be of
large interest.
Unsymmetrically substituted tetrabenzoporphyrins
are often prepared by stepwise condensation of phthal-
imide I with various carboxylic acids [9, 10]. We also
applied this method to the synthesis of zinc meso-
trans-diaryldihexadecyltetrabenzoporphyrinates.
One of synthetic routes to metal complexes of
meso-substituted tetrabenzoporphyrins is template
condensation of phthalimide I with alkyl- and arylace-
tic acids in the presence of a complexing metal. In the
synthesis of meso-tetraalkyltetrabenzoporphyrins, the
condensation occurs with a yield of up to 15% only
with lower aliphatic carboxylic acids (from propionic
to enanthic) [8]. As the length of the alkyl chain of
carboxylic acids is increased to seven and more car-
bon atoms, the yield of meso-tetraalkyltetrabenzopor-
phyrins drastically decreases, and our attempts to pre-
pare zinc meso-tetrahexadecyltetrabenzoporphyrinate
by the reaction of phthalimide I with excess stearic
acid II in the presence of zinc oxide gave poor results
3-[(1-Oxo-1H-isoindol-3-yl)(phenyl)methylidene]-
2,3-dihydro-1H-isoindol-1-one III was prepared by
heating phthalimide I with phenylacetic acid IV in the
presence of zinc oxide at 240 C, as described in [10].
The similar reactions of I with 1-naphthylacetic (V)
and 9-anthrylacetic (VI) acids in the presence of zinc
oxide at 250 C for 40 min yielded the naphthyl- and
anthryl-substituted analogs of III, respectively: 3-[(1-
oxo-1H-isoindol-3-yl)(1-naphthyl)methylidene]-2,3-
dihydro-1H-isoindol-1-one VII and 3-[(1-Oxo-1H-
isoindol-3-yl)(9-anthryl)methylidene]-2,3-dihydro-1H-
isoindol-1-one VIII.
1448

meso-trans-DIARYLDIHEXADECYLTETRABENZOPORPHYRINS
1449
CH2CO2H
O
V
N
NH
O
VII
O
ZnO
NH
CH2CO2H
O
I
O
VI
N
NH
O
VIII
9-Anthrylacetic acid VI required for the synthesis
of VIII was prepared by the reaction of anthracene
with acetic anhydride in the presence of potassium
permanganate in accordance with the scheme
ously indicates that the CH2COOH group appears at
the 9-position of anthracene.
Compounds VII and VIII after chromatographic
purification on alumina are purple and brown pow-
ders, respectively, readily soluble in various organic
solvents. Their structure was confirmed by elemental
analysis, electronic spectroscopy, and mass spectrom-
etry.
CH2CO2H
(CH3CO)2O, KMnO4
In the electronic absorption spectrum of VII (Fig. 3,
curve 2), there are two bands in the visible range with
maxima at 517 and 481 nm. Comparison of this spec-
VI
Its structure was confirmed by elemental analysis
and by vibrational and H NMR spectroscopy.
1
T, %
The IR spectrum of VI (Fig. 1) contains a strong
1
band at 1697 cm characteristic of C=O stretching
50
1
vibrations. The bands at 1418 and 1301 cm corre-
40
30
20
10
spond to the C=C stretching vibrations in the aromatic
1
core, and strong bands at 728 and 889 cm , to
1
CH(arom.). The band at 1228 cm characterizes the
O H bending vibrations.
1
In the H NMR spectrum of VI (Fig. 2), the low-
est-field signal is that of 10-H (a singlet at 8.56 ppm).
The signal of two protons 4-H and 5-H is a doublet
at 8.19 8.28 ppm; that of two protons 1-H and 8-H,
a multiplet at 7.95 8.07 ppm; and the 2-H, 3-H, 6-H,
and 7-H protons give a multiplet at 7.45 7.65 ppm.
A higher-field singlet at 4.63 ppm belongs to two
methylene protons. The observed pattern unambigu-
1500
1000
500
, cm
1
Fig. 1. IR spectrum of 9-anthrylacetic acid VI.
(T) Transmission.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 8 2007

1450
GALANIN et al.
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
, ppm
1
Fig. 2. H NMR spectrum of acid VI in DMSO-d .
6
trum with that of III [10] (Fig. 3, curve 1) shows that
replacement of the phenyl substituent by the 1-naph-
thyl group leads to a hypsochromic shift of the ab-
sorption bands by 7 nm, which is apparently due to
stronger distortion of the planar structure of VII as
a result of the steric effect of the bulkier naphthyl
substituent. Furthermore, the short-wave absorption
band at 458 nm, present in the electronic absorption
spectrum of III, is not manifested in the spectrum of
VII, which is apparently caused by stronger associa-
tion of VII in solution. Replacement of the naphthyl
substituent by the anthryl group (compound VIII)
leads to a still stronger ( 60 nm) hypsochromic shift
of the absorption bands compared to VII, without sig-
nificant changes in the overall spectrum shape (Fig. 3,
curve 3). This pattern can be accounted for to still
stronger distortion of the structure of VIII under the
influence of the anthryl substituent and, as a conse-
quence, to disturbance of the conjugation system.
D
1.0
1
2
0.5
0.0
3
450
500
550
, nm
Fig. 3. Electronic absorption spectra in acetone: (1) III,
(2) VII, and (3) VIII. (D) Optical density.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 8 2007

meso-trans-DIARYLDIHEXADECYLTETRABENZOPORPHYRINS
1451
In the mass spectra of VII and VIII (electron im-
pact), we detected the signals of protonated molecular
ions [M + H]+, m/z 401 and 451, respectively.
By heating compounds III, VII, and VIII with
excess acid II in the presence of zinc oxide at 350 C
for 30 min, we prepared zinc complexes of meso-
trans-diaryldihexadecyltetrabenzoporphyrins (IX XI).
C16H33
Ar
Ar
O
N
N
H35C17CO2H (II), ZnO
Zn N
N
N
NH
O
Ar
H33C16
III, VII, VIII
IX XI
Ar = C6H5 (III, IX), 1-C10H7 (VII, X), 9-C14H9 (VIII, XI).
Complexes IX XI were isolated from the reaction
visible range: Soret band and Q band. An increase in
the volume of the meso-aryl substituents (going from
IX to XI) is accompanied by successive hypsochromic
shift of the absorption bands. In the spectra of IX XI,
the Q band maximum is at 634, 628, and 622 nm,
respectively. The shift of the Soret band is still more
significant: from 441 nm in IX to 435 nm in X and
421 nm in XI.
mixture and purified by column chromatography.
Treatment of their chloroform solutions with concen-
trated HCl gave the corresponding meso-trans-diaryl-
dihexadecyltetrabenzoporphyrins XII XIV, which
were also purified chromatographically.
Compounds IX and XII are waxy substances, and
X, XI, XIII, and XIV, powder-like solids. All these
compounds are dark green and are readily soluble in
polar and nonpolar organic solvents. Their structure
was determined by elemental analysis and by electron-
Comparison of the electronic absorption spectrum
of IX with that of zinc meso-trans-diphenyltetraben-
zoporphyrinate [11] shows that introduction of two
long alkyl substituents leads to a bathochromic shift
of the major absorption bands, with the Soret band
1
ic, vibration, and H NMR spectroscopy.
1
In the H NMR spectrum of IX in the range 7.65
8.25 ppm, there is a multiplet corresponding to ten
protons of two phenyl substituents, and a multiplet at
6.85 7.25 ppm belongs to 16 protons of the benzene
rings of the isoindole fragments. The signals of pro-
tons of two meso-alkyl substituents are observed in
the higher field. A triplet at 2.41 ppm corresponds to
four protons of the -methylene groups, and a singlet
at 1.23 ppm, to the resonance of 56 protons of the
other CH2 groups. Finally, six protons of the terminal
D
2.0
2
3
1
1.5
1.0
1
methyl groups give a singlet at 0.87 ppm. The H
NMR spectra of complexes X and XI resemble that of
IX and also contain low-field signals of protons of
aryl substituents and benzene rings of isoindole frag-
ments and high-field signals of alkyl protons, with
their position only slightly depending on the structure
of alkyl substituents.
0.5
0.0
400
500
600
700
, nm
In the electronic absorption spectra of complexes
IX XI (Fig. 4), there are two strong bands in the
Fig. 4. Electronic absorption spectra in CCl : (1) IX,
(2) X, and (3) XI. (D) Optical density.
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 8 2007

1452
GALANIN et al.
semiempirical (AM1) quantum-chemical calculations
of the geometric structure of porphyrins XII XIV.
As the calculations showed, the meso-phenyl substitu-
ents in XII form an angle of 35 with the macroring
plane; the meso-naphthyl substituents in XIII, an
angle of 51 ; and the meso-anthryl substituents in
XIV, an angle of 70 . Thus, the results of quantum-
chemical calculations are consistent with the observed
spectral pattern.
D
2
1
3
1.5
1.0
0.5
0.0
EXPERIMENTAL
The electronic absorption spectra of the compounds
obtained were measured on a Hitachi UV-2001 spec-
trophotometer; the 1H NMR spectra (CDCl3, 200 MHz,
internal reference TMS), on an AMD-200 spectrom-
eter; the IR spectra, on an Avatar 360 FT-IR spectro-
400
500
600
700
, nm
Fig. 5. Electronic absorption spectra in CCl : (1) XII,
(2) XIII, and (3) XIV. (D) Optical density.
4
1
photometer in the range 400 4000 cm from thin
films; and the mass spectra, on a Varian Saturn 2000R
chromatograph mass spectrometer. The elemental
analysis was performed with a FlashEA 1112 CHNS-
O analyzer.
shifted by 8 nm and the Q band, by only 1 nm.
Apparently, the meso-alkyl substituents only slightly
affect the macroring geometry, and slight bathochrom-
ic shift of the bands is determined only by their posi-
tive I effect. At the same time, two phenyl substitu-
ents in IX form a relatively small dihedral angle with
the macroring and to some extent participate in the
formation of the overall conjugation system. This
results in a bathochromic shift of the bands (by 10 nm
on the average) relative to their position in the elec-
tronic absorption spectrum of zinc tetrabenzopor-
phyrinate [12]. An increase in the geometric size of
meso-naphthyl substituents in X leads, as we believe,
to their larger dihedral angle with the macroring plane
and hence to smaller extent of conjugation compared
to IX. Therefore, the bathochromic shift of bands in
the spectrum of X relative to that of zinc tetrabenzo-
porphyrinate is as small as 5 nm. As for XI, the meso-
anthryl substituents in its molecule are essentially
noncoplanar with the macroring, the conjugation is
fully broken, and the bands in the electronic absorp-
tion spectrum occur at approximately the same posi-
tions as in that of zinc tetrabenzoporphyrinate.
3-[(1-Oxo-1H-isoindol-3-yl)(phenyl)methylidene]-
2,3-dihydro-1H-isoindol-1-one III was prepared as
described in [10], and 1-naphthylacetic acid V, as
described in [13].
9-Anthrylacetic acid VI. In a 250-ml two-necked
flask equipped with a stirrer and a reflux condenser,
18 g of anthracene was dissolved in 100 ml of acetic
anhydride, the solution was heated to reflux, and 4 g
of KMnO4 was added over a period of 1 h, after
which the mixture was refluxed for an additional 1 h.
After the reaction completion, excess acetic anhydride
was distilled off, the residue was mixed with 100 ml
of a 10% NaOH solution, and the unchanged anthra-
cene was filtered off. The filtrate was acidified with
HCl to pH 4 5, and the precipitate of acid VI was
filtered off. Yield 1.35 g (70% based on converted
anthracene). Pale yellow powder insoluble in water
but readily soluble in aqueous alkalis, DMF, DMSO,
1
and acetone. IR spectrum (thin film), , cm :
2920 (C H), 1697 (C=O), 1418, 1301 (C=C), 1228
(O H), 889, 728 ( CH(arom.)). 1H NMR spectrum
(DMSO-d6), , ppm: 8.56 s (1H), 8.28 8.19 d (2H),
8.07 7.95 m (2H), 7.65 7.45 m (4H), 4.63 s (2H).
Found, %: C 80.24; H 4.88. C16H12O2. Calculated, %:
C81.34; H 5.12.
The electronic absorption spectra of metal-free
porphyrins XII XIV show the same trend (Fig. 5).
An increase in the volume of the substituents also
leads to a successive hypsochromic shift of the ab-
sorption bands, and, whereas in the spectrum of XII
the bands are shifted bathochromically relative to
tetrabenzoporphyrin [12] by 16 nm on the average, in
the spectrum of XIV they occur at virtually the same
positions as in that of tetrabenzoporphyrin. As in the
case of the zinc complexes, this trend should be attri-
buted to an increase in the extent of nonplanarity of
the system. To confirm this assumption, we performed
Reaction of phthalimide with arylacetic acids in
the presence of zinc oxide (general procedure). A
mixture of 0.02 mol of imide I, 0.02 mol of acid V or
VI, and 0.6 g of ZnO was heated at 350 C for 40 min,
after which the reaction mixture was cooled, ground,
and refluxed in 100 ml of 10% HCl for 10 min. Then
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 8 2007

meso-trans-DIARYLDIHEXADECYLTETRABENZOPORPHYRINS
1453
the precipitate was filtered off and washed on the filter
with 200 ml of hot water. After drying, the precipitate
was dissolved in chloroform and chromatographed on
a column packed with alumina (Brockmann grade II,
eluent chloroform); the main red-brown band was
collected, and the solvent was removed.
trum (CCl4), max, nm (log ): 628 (4.49), 582 (4.00),
459 (4.51), 435 (5.14). 1H NMR spectrum (CDCl3), ,
ppm: 8.27 7.24 m (30H), 2.45 t (4H), 1.22 s (56H),
0.84 s (6H). Found, %: C 82.94; H 7.98; N 4.15.
C88H96N4Zn. Calculated, %: C 82.89; H 7.59; N 4.39.
Zinc meso-trans-di(9-anthryl)dihexadecyltetra-
benzoporphyrinate XI was prepared by the general
procedure from compound VIII. Yield 0.10 g (14%).
Dark green powder readily soluble in benzene, chloro-
form, CCl4, hexane. Electronic absorption spectrum
(CCl4), max, nm (log ): 622 (4.51), 574 (4.00), 421
3-[(1-Oxo-1H-isoindol-3-yl)(1-naphthyl)methyli-
dene]-2,3-dihydro-1H-isoindol-1-one VII was pre-
pared by the general procedure with acid V. Yield
0.81 g (20%). A purple powder readily soluble in
acetone, DMF, and chloroform. Electronic absorption
spectrum (acetone), max, nm (D/Dmax): 517 (0.80),
481 (1.00). Mass spectrum (electron impact, 80 eV),
m/z (%): 401 [M + H]+ (70), 262 (100). Found, %: C
79.77; H 4.55; N 6.73. C27H16N2O2. Calculated, %:
C 80.99; H 4.03; N 7.00.
1
(5.03). H NMR spectrum (CDCl3), , ppm: 8.67
7.33 m (34H), 2.45 t (4H), 1.27 s (56H), 0.86 s (6H).
Found, %: C 80.94; H 7.95; N 4.36. C96H100N4Zn.
Calculated, %: C 83.76; H 7.60; N 3.99.
meso-trans-Diaryldihexadecyltetrabenzopor-
phyrins XII XIV (general procedure). A 0.1-g por-
tion of IX XI was dissolved in 20 ml of chloroform,
10 ml of concentrated HCl was added, and the mix-
ture was stirred at 20 C for 2 h, after which the or-
ganic phase was separated and washed successively
with water, 10% ammonia, and again water to pH 7.
The solvent was removed, and the residue was dis-
solved in chloroform and chromatographed on a
column packed with alumina (Brockmann grade II,
eluent chloroform). The major green band was
collected.
3-[(1-Oxo-1H-isoindol-3-yl)(9-anthryl)methyli-
dene]-2,3-dihydro-1H-isoindol-1-one VIII was pre-
pared by the general procedure with acid VI. Yield
0.90 g (19%). A brown powder readily soluble in
acetone, DMF, and chloroform. Electronic absorption
spectrum (acetone), max, nm (D/Dmax): 454 (0.55),
424 (1.00). Mass spectrum (electron impact, 80 eV),
m/z (%): 451 [M + H]+ (50), 221 (100). Found, %:
C 82.40; H 4.75; N 5.67. C31H18N2O2. Calculated, %:
C 82.65; H 4.03; N 6.22.
Zinc meso-trans-diaryldialkyltetrabenzopor-
phyrinates IX XI (general procedure). A mixture of
0.001 mol of compound III, VII, or VIII, 0.003 mol
of acid II, and 0.5 g of zinc oxide was heated to
350 C and kept at this temperature for 30 min, after
which the mixture was cooled, dissolved in chloro-
form, and chromatographed on a column packed with
alumina (Brockmann grade II, eluent chloroform). The
major green band was collected.
meso-trans-Diphenyldihexadecyltetrabenzopor-
phyrin XII. Yield 0.07 g (78%). A dark green waxy
substance readily soluble in benzene, chloroform,
1
CCl4, and hexane. IR spectrum (thin film), , cm :
3268 (N H), 3062 (CAr H) 2926, 2860 (CAlk H),
1731 (C=C), 1499 (C=C), 1468 (C N). Electronic ab-
sorption spectrum (CCl4), max, nm (D/Dmax): 679
(0.09), 620 (0.24), 575 (0.08), 449 (0.97), 440 (1.00),
426 sh. Found, %: C 85.31; H 8.92; N 4.98. C80H94
N4. Calculated, %: C86.44; H 8.52; N 5.04.
Zinc meso-trans-diphenyldihexadecyltetraben-
zoporphyrinate IX was prepared by the general proce-
dure from compound III. Yield 0.20 g (34%). A dark
green waxy substance readily soluble in benzene,
chloroform, CCl4, and hexane. IR spectrum (thin
meso-trans-Di(1-naphthyl)dihexadecyltetraben-
zoporphyrin XIII. Yield 0.05 g (53%). A dark green
powder readily soluble in benzene, chloroform, CCl4,
1
film), , cm : 3061 (CAr H) 2923, 2852 (CAlk H),
hexane. Electronic absorption spectrum (CCl4),
,
max
1738 (C=C), 1495 (C=C), 1464 (C N). Electronic
absorption spectrum (CCl4), ma1x, nm (log ): 634
nm (D/Dmax): 667 (0.17), 601 (0.26), 564 (0.08), 465
(0.22), 435 (1.00), 422 (0.89). Found, %: C 86.11;
H 8.75; N 4.12. C88H98N4. Calculated, %: C 87.22;
H 8.15; N4.63.
(4.52), 586 (4.01), 441 (5.02). H NMR spectrum
(CDCl3), , ppm: 8.25 7.65 m (10H), 7.25 6.85 m
(16H), 2.41 t (4H), 1.23 s (56H), 0.87 s (6H). Found,
%: C 80.94; H 7.95; N 4.36. C80H92N4Zn. Calculated,
%: C 81.78; H 7.89; N 4.77.
meso-trans-Di(9-anthryl)dihexadecyltetrabenzo-
porphyrin XIV. Yield 0.06 g (64%). A dark green
powder readily soluble in benzene, chloroform, CCl4,
hexane. Electronic absorption spectrum (CCl4),
,
Zinc meso-trans-di(1-naphthyl)dihexadecyl-
tetrabenzoporphyrinate X was prepared by the
general procedure from compound VII. Yield 0.15 g
(23%). Dark gree powder readily soluble in benzene,
chloroform, CCl4, hexane. Electronic absorption spec-
max
nm (D/Dmax): 658 (0.17), 602 (0.25), 556 (0.14), 428
(1.00), 416 (0.96). Found, %: C 87.90; H 8.02; N
3.99. C96H102N4. Calculated, %: C 87.89; H 7.84;
N 4.27.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 8 2007

1454
GALANIN et al.
Nachamkin, I., J. Antimicrob. Chemother., 2001,
ACKNOWLEDGMENTS
vol. 48, no. 1, p. 105.
The study was financially supported by the Russian
Foundation for Basic Research (project no. 07-03-
00427a).
6. Kral, V., Furuta, H., Shreder, K., Lynch, V., and
Sessler, J.L., J. Am. Chem. Soc., 1996, vol. 118, no. 7,
p. 1595.
7. Kobayashi, N., Bull. Chem. Soc. Jpn., 2002, vol. 75,
no. 1, p. 1.
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