A Molecular receptor based on the 2,3,7,8,12,13,17,18-octaethyl-21,23- dimethylporphyrin for detection of fluoride ions: Synthesis, spectral and complexation properties

Article abstract of DOI:10.1134/S1070363212070158

2,3,7,8,12,13,17,18-Octaethyl-21-methylporphyrin and 2,3,7,8,12,13,17,18- octaethyl-22,23-dimethylporphyrin monotriflate based on the former were synthesized. Basic and complexing properties of these compounds were studied by the method of spectrophotometric titration in acetonitrile-perchloric acid and acetonitrile-tetrabutylammonium fluoride systems at 298 K. It was established that in the system of acetonitrile-perchloric acid the cationic forms of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin do not form complexes with fluoride ions, whereas 2,3,7, 8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate forms complexes of 1:1 composition with the fluoride ions. The protonation constant of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin and the stability constant of the complex of 2,3,7,8,12,13,17,18-octaethyl-22,23- dimethylporphyrin with fluoride ions in acetonitrile at the standard temperature were determined. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070363212070158

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 7, pp. 1272–1277. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © Yu.B. Ivanova, Dao Tkhe Nam, A.V. Glazunov, A.S. Semeikin, N.Zh. Mamardashvili, 2012, published in Zhurnal Obshchei Khimii,
2
012, Vol. 82, No. 7, pp. 1173–1178.
A Molecular Receptor Based on the 2,3,7,8,12,13,17,18-Octaethyl-
2
1,23-dimethylporphyrin for Detection of Fluoride Ions:
Synthesis, Spectral and Complexation Properties
a
b
b
Yu. B. Ivanova , Dao Tkhe Nam , A. V. Glazunov ,
b
a
A. S. Semeikin , and N. Zh. Mamardashvili
a
Institute of Solution Chemistry, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia
e-mail: ybi@isc-ras.ru
b
Ivanovo State University of Chemical Technology, Ivanovo, Russia
Received May 31, 2011
Abstract—2,3,7,8,12,13,17,18-Octaethyl-21-methylporphyrin and 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethyl-
porphyrin monotriflate based on the former were synthesized. Basic and complexing properties of these
compounds were studied by the method of spectrophotometric titration in acetonitrile–perchloric acid and aceto-
nitrile–tetrabutylammonium fluoride systems at 298 K. It was established that in the system of acetonitrile–
perchloric acid the cationic forms of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin do not form complexes
with fluoride ions, whereas 2,3,7, 8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate forms com-
plexes of 1:1 composition with the fluoride ions. The protonation constant of 2,3,7,8,12,13,17,18-octaethyl-21-
methylporphyrin and the stability constant of the complex of 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethyl-
porphyrin with fluoride ions in acetonitrile at the standard temperature were determined.
DOI: 10.1134/S1070363212070158
Tetrapyrrole macrocycles are known as amphoteric
compounds: the presence of NH groups imparts them
an opportunity to show weak acidic properties, while
tertiary nitrogen atoms provide the basic properties.
The loss of protons leads to restructuring and
shortening of the conjugation chain while apparent
aromaticity of the system is retained. Adding protons
to the tertiary nitrogen atoms does not affect the planar
structure of the molecule. Cationic and anionic forms
of tetrapyrrole macrocycles have the same isoelec-
tronic conjugation chains and similar electronic
spectra, differing only by a shift of the absorption
bands. Protonated forms of porphyrins are known as
excellent chromophores possessing conformationally
flexible complexing cavity that can selectively bind
anions of different nature [1–8]. This property of the
protonated forms is reflected in the change of optical
signals of the electronic spectrum. Dicationic forms of
tetrapyrrole macrocycles are capable of forming
associates of 1:1 and 1:2 composition with the
molecules and anions. Thus, the dication forms of
mezoporphyrin IX in acetonitrile form associates of
1:1 and 1:2 composition with water molecules [9] and
halide ions (iodide, bromide, and chloride) [1].
Pronounced electron-acceptor properties of chemo-
receptors are largery determined by the medium
acidity function and the structure of the molecule. The
simplicity and accessibility of spectral analysis
techniques to determine anions in solutions using
protonated forms of porphyrins makes these studies
interesting and relevant.
In this study, we synthesized 2,3,7,8,12,13,17,18-
octaethyl-21-methylporphyrin (I) and converted it into
2
,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin
monotriflate (II) where the porphyrin is in the
protonated form stabilized by the triflate ion.
Basic properties of I were studied by the method of
spectrophotometric titration [5] in an acetonitrile–
perchloric acid system. Increasing concentration of acid
in the system of acetonitrile–perchloric acid leads to two
sets of spectral curves in the electron absorption spec-
tra (Fig. 1, the EAS parameters are listed in the table),
to each set corresponds its own set of isosbestic points.
1
272

A MOLECULAR RECEPTOR BASED ON THE 2,3,7,8,12,13,17,18-OCTAETHYL-...
1273
Et
NR
Et
Et
Et
NR
Et
Et
+
N
N
N
R
Et
Et
Et
Et
Et
Et
Et
Et
HN
HN
−
CF SO3
3
N
Et
Et
I
II
After determination of the inflection point in the titra-
tion curve (Fig. 2) we separated two electron absorp-
tion spectra in correspondence with the sequential
biprotonation (Scheme 1) and calculated the correspond-
ing protonation constants, log k = 6.1 and log k
=
b1
b2
5.2 (the standard technique is described in detail in [1, 5]).
A
(a)
A
λ, nm
λ, nm
A
(
b)
λ, nm
–
5
–6
Fig. 1. Variation of EAS (280–700 nm) of I in the system of CH
3
CN–HClO
4
. (a) c(HClO
4
) = (0–2.42)×10 M, cporph
=
.
6.39×10 M,
–5
–5
+
λ = 280–700 nm; (b) c(HClO
4
) (0–2.42)×10 M, cporph= 4.91×10 M, λ = 400–700 nm; N(CH
3
)Et , (1) H(CH )Et
8
3
8
P, (2) H
2
(CH
3
)Et
8
P ,
2
+
3 3 8
and (3) H (CH )Et P .
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012

1
274
IVANOVA et al.
Scheme 1.
k
b1
+
Н(СН
3
)Et
8
P + H ҙ Н
2
(CH
3
)Et P
8
k
b2
+
+
P++
Et
Н
2
(CH
3
)Et
8
P + H ҙ Н
3
(CH )Et
3 8
Et
+
N
N
H
Et
Et
Et
NR
HN
Et
Et
NR
Et
Et
kb1
N
N
Et
Et
Et
Et
Et
Et
Et
kb2
HN
Et
Et
N H+
Et
Et
Et
Et
NR
Et
HN
H+
N
Et
We revealed the region of concentrations of
tion cavity of the porphyrin. Previously obtained data
on similar systems have shown that there is a depen-
dence of receptor properties of tetrapyrrole macro-
cycles with quartenated methyl groups on the number
and nature of the substituents and counterions [8, 10, 11].
perchloric acid where the concentration of the dica-
tions of I in the system of acetonitrile–perchloric acid
is maximal, and carried out a direct titration of the
dication forms of porphyrin I with a solution of the
fluoride salt in the system of acetonitrile–tetrabutyl-
ammonium fluoride.The formation of stable complexes
Taking into account the basic properties of
2
+
–
2+.
–
H P Hal and H P 2Hal was not observed, which is
2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin
I
4
4
probably due to the screening effect of the methyl
group at the intracyclic nitrogen atom on the coordina-
we synthesized 2,3,7,8,12,13,17,18-octaethyl-22,23-di-
methylporphyn monotriflate II. Compound II has
Parameters of electron absorption spectra of porphyrin I and its mono- and diprotonated forms in the system of HClO –
4
CH
3
CN, and porphyrin II and its fluoride complex IIa in the system of (C
4
H
9
)
4
NF–CH
CNa
3
Porphyrin
Н(CH )Et
λ
1
(log ε)
λ
2
(log ε)
λ
3
(log ε)
λ
4
(log ε)
5
λ (log ε)
3
8
P
397 (5.42)
392 (5.51)
400 (5.49)
400 (5.08)
426 (4.76)
502 (4.43)
532 (4.21)
534 (4.54)
535 (4.52)
541 (4.19)
539 (4.03)
583 (4.09)
560 (4.58)
560 (4.61)
572 (4.25)
597 (3.97)
640 (3.92)
640 (3.86)
604 (4.19)
619 (3.72)
–
Н
2
3
(CH
3
3
)Et
)Et
8
P+
P++
503 (4.41)
Н
(CH
8
–
–
–
(
СН
3
3
)
)
2
2
Et
Et
8
8
P+Т–
P+F–
(СН
a
–3
–1
–1
λ
max, nm (ε×10 , l mol cm ).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012

A MOLECULAR RECEPTOR BASED ON THE 2,3,7,8,12,13,17,18-OCTAETHYL-...
1275
several advantages compared with compound I: The
tetrapyrrole macrocycle is initially in the protonated
form, and the obtaining of the porphyrin protonated
forms does not require performing additional
experiments with a careful selection of the conditions
of their existence (the determination of pH, solvent
nature, and the protonating agent with accounting for
the influence of its counterion on the cationic forms of
the macrocycle).
system we investigated the complexing properties of II
with fluoride ion. Synthetically modified macro-
heterocycle II forms the analtical signal due to
chemical interaction of the receptor molecules with the
substrate (fluoride) in the region of concentration of
the fluoride salts from 0 to 2.27×10 M. In the EAS of
the system of acetonitrile–tetrabutylammonium fluoride
a formation of a set of spectral curves with individual
isosbestic point was observed (Fig. 3).The titration
curve is of a single-stage character (Fig. 4). These
experimental data provided a possibility to express the
process by Scheme 2.
–
5
Using the method of spectrophotometric titration
[
5] in the acetonitrile–tetrabutylammonium fluoride
Scheme 2.
k
+
–
–
+
–
–
H(СН
3
)
Et
2 8
P Т + F ҙ H(СН
3
)
Et
2 8
P F + T
−
Et
Et
Et F Et
+
N
R
+
Et
Et
Et
N
NR
R
NR
k
Et
Et
Et
Et
Et
HN
N
HN
N
Et
II
Et
IIа
Et
Et
+
–
–5
Replacement of the triflate ion in H(CH ) Et T by
centration to 2.27×10 M also leads to a red shift (26 nm),
as well as to broadening of the Soret band and a de-
crease in its intensity. Simultaneously the intensity of
the band λ decreases and a`band at λ appears (Fig. 3).
3
2
8
+
–
the fluoride ion with the formation of H(CH ) Et F
3
2
8
leads to a strong red shift in the EAS, which is typical
for such processes [8]. The increase in the fluoride con-
572
597
A
A
c, M
λ, nm
+
–
Fig. 2. Spectrophotometric titration curve of the porphyrin
3 2 8
Fig. 3. Variation of EAS of the H(CH ) Et P T in the
–5
–
5
(
I) (cporph.= 4.91×10 M) in system of CH
3
CN–HClO
4
;
system of CH
3
CN–(C
4
H
9
)
4
4 9
NF, cporph = 1.08×10 M, c(C H ) =
–
5
–5
c(HClO
4
) = (0–2.42)×10 M, λ = 502 nm, 298 K.
(0–2.27)×10 M.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012

1
276
IVANOVA et al.
heterocyclic compounds for the detection and selective
A
binding anions of different nature.
EXPERIMENTAL
Acetonitrile from ALDRICH was not subjected to
further purification. The water content determined by
Fisher did not exceed 0.04%. The solution of
(
C H ) NF was prepared on the basis of acetonitrile.
4
9 4
The salt was purified in a Soxhlet apparatus with
acetonitrile and dried in a vacuum (1.33 Pa) at 393 K
to the constant weight. The spectrophotometric titra-
tion of I with a solution of (C H ) NF in acetonitrile
4
9 4
was carried out using a Varian Cary 100 spectro-
photometer.
c(Bu NF), M
4
A working solution of perchloric acid was prepared
using dried acetonitrile and perchloric acid (8.75 M
aqueous solution of chemically pure grade). The
experimental procedure and data processing are given
in [1, 5]. Error in the determination of the constants
was ±(3–5)%. Mass spectra were obtained on electron
impact mass spectrometer complex MX-1310 at the of
ionizing electrons energy 70 eV and ionization
+
–
Fig. 4. Spectrophotometric titration curve of H(CH
3
)
4
2
H
Et
9
8
)
P T ,
NF,
–5
c
porph = 1.5×10 M in the system of CH
3
CN–(C
4
–
5
c[(C
4
H
9
)
4
NF] = (0–2.27) ×10 M, λ = 400 nm, 298 K.
The complexation constant log k of the process
shown in the Scheme 2 in the system of acetonitrile–
tetrabutylammonium fluoride calculated with the
equation log k = log (Ind) – nlog S[(C N ) NF], where
4
9 4
1
chamber temperature 150–200°C. H NMR spectra
k is association constant of porphyrin molecules with
were recorded on a Bruker VC-200 spectrometer with
the operating frequency 200 MHz from solutions in
deuterochloroform, internal reference TMS.
+
fluoride ion, Ind is indicator ratio [H(CH ) Et F/
3
2
8
+
–
[
H(CH ) Et T ], c is analytical concentration of tetra-
3
2
8
butylammonium fluoride in solution in M, n = 1 (the
number of added fluoride ions formed at the
dissociation of tetrabutylammonium fluoride) gives the
value log k = 5.18.
2,3,7,8,12,13,17,18-Octaethyl-21-methylporphyrin.
To a solution of 3,7,8,12,13,17,18-octaethylporphyrin
(
250 mg, 0.47 mmol) in 30 ml of chloroform was
added 5 ml (2.2 g, 15.5 mmol) of methyl iodide and
excess of freshly dried sodium formate. The mixture
was refluxed for 24 h, then cooled to room tempe-
rature, filtered from the precipitate, evaporated to
minimum volume, and chromatographed on aluminum
oxide of III degree of activity by Brockmann, eluting
with chloroform–light petroleum ether. Eluate
containing 3,7,8,12,13,17,18-octaethyl-21-methylpor-
phyrin was evaporated to the minimum volume, the
product was precipitated with methanol, filtered off,
Comparing the parameters of the EAS for mono-
cationic forms obtained by different methods it is
possible to see that the absorption bands in the EAS of
monocationic forms of compound II suffer a red shift
(
8 nm of the Soret band, 7, 12, and 21 nm in the long-
wavelength region) compared with the monocationic
forms of compound I. At the replacement of triflate
ions by fluoride (formation of compound IIa) the red
shifts in the EAS significantly increase (up to 26 nm),
easily detecting the presence of fluoride in acetonitrile
solutions of compound II. The sensitivity of the
proposed macroheterocycle II covers a wide range of
the halogen concentration in solution {c[(C H ) NF] =
washed with methanol, and dried at 70ºC in air. Yield
1
0
.15 g (61%). H NMR spectrum, δ, ppm: 9.95 s, 9.89
s (2×2H, ms-H); 4.04 m, 3.97 m, 3.78 m (16H,
4
9 4
0–2.27×10–5 M), λ 400 nm, 298 K}, which shows a
CH
2
CH
3
), 1.93 t, 1.91 t, 1.1 t (24H, CH
2
CH
3
), –4,79 s
(
(
8
8
3H, CH ) (CDCl int. TMS). Found, %: C 80.97, H
3
3,
possibility to propose the tetrapyrrole chromophore as
an effective molecular receptor for the registration of
fluoride ions. The studies provide estimates of receptor
properties of the protonated forms of tetrapyrrole
compounds by different methods, which significantly
expands the possibilities of creating new macro-
.84, N 10.19. C H F N O S. Calculated, %: C
3
9
51
3
4
3
0.98, H 8.82, N 10.21.
2,3,7,8,12,13,17,18-Octaethyl-22,23-dimethylpor-
phyrin monotriflate. To a mixture of 250 mg
(0.46 mmol) of octaethyl porphin and 1,25 g (4.6 mmol)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012

A MOLECULAR RECEPTOR BASED ON THE 2,3,7,8,12,13,17,18-OCTAETHYL-...
1277
of potassium carbonate was added to 70 ml of dry
chloroform, and then 0.53 ml (4.6 mmol) of methyl
trifluoromethanesulfonate in 20 ml of chloroform. The
mixture was stirred at room temperature for several
hours. The reaction monitoring was carried out by
TLC every 2 h. After completion, the reaction mixture
was filtered of through a glass frit filter from inorganic
precipitate, evaporated to a half of its volume, and
chromatographed on aluminum oxide of III degree of
activity, eluting with chloroform. Porphyrin eluate was
evaporated to minimum volume, precipitated with
methanol, the precipitate was filtered off, washed with
methanol, and dried at 70ºC in air. Yield 0.32 g (96%).
2. Kruk, N.N., Starukhin, A.S., Ivanova, Yu.B., Shei-
nin, V.B., and Mamardashvili, N.Zh., Zh. Prikl. Spectr.,
2
007, vol. 74, no. 6, p. 750.
3. Kruk, N.N., Starukhin, A.S., Sheinin, V.B., Ivanova, Yu.B.,
and Mamardashvili, N.Zh., RF Patent 2345352, Byul.
Izobret., no. 3, 27.01.2009.
4. Ivanova, Yu.B., Kruk, N.N., Starukhin, A.S., and
Mamardashvili, N.Zh., Ross. Khim. Zh., 2009, vol. 53,
no. 2, p. 7
5. Ivanova, Yu.B., Churakhina, Yu.I., and Mamarda-
shvili, N.Zh., Zh. Obshch. Khim., 2008, vol. 78, no. 4,
p. 691.
6. Kruk, M.M., Starukhina, A.S., Mamardashvili, N.Zh.,
Mamardashvili, G.M., Ivanova, Yu.B., and Maltseva, O.,
J. Porphyrins Phthalocyanines, 2009, vol. 13, no. 11,
p. 1148.
1
H NMR spectrum (CDCl int. TMS), δ, ppm: 10.35 s,
3
,
1
0.22 s, 10.19 (2×2H, ms-H); 3.86 m, 4.13 m (16H,
CH CH ) 1.99 t, 1.93 t, 1.69 t, 1.50 t (24H, CH CH )
2
3 ;
2
3 ;
–
5.88 s (6H, 22,23-CH ). Found, %: C 65.73, H 7.25,
7. Toldina, O.V., Ivanova, Yu.B., Mamardashvili, G.M.,
and Mamardashvili, N.Zh., Tetrahedron Lett., 2008,
vol. 48, no. 43, p. 3752.
3
N 7.83, S 4.59. C H F N O S. Calculated, %: C
39
51
3
4
3
6
5.71, H 7.21, F 7.99, N 7.86, O 6.73, S 4.50.
ACKNOWLEGMENTS
8
. Ivanova, Yu.B. and Mamardashvili, N.Zh., Book of
Abstracts, Topics in Supramolecular Chemistry,
Leuven, Belgium, 2010, p. 27.
This work was supported by Rusian Foundation for
9
. Ivanova, Yu.B., Sheinin, V.B., and Berezin, B.D.,
Koord. Khim., 2002, vol. 28, no. 2, p. 158–160.
BASIC Research (grant no. 10-03-90000-Bel_a) and
the Seventh Framework Programme of the European
Community for Research, Technological Development
and Demonstration Activities, IRSES-GA-2009-247260.
10. Kulikova, O.M., Ivanova, Yu.B., Glazunov, A.V.,
Semeikin, A.S., and Mamardashvili, N.Zh., Zh. Obshch.
Khim., 2011, vol. 81, no. 10, p. 1741.
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1
. Ivanova, Yu.B., Sheinin, V.B., and Mamardashvili, N.Zh.,
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 7 2012