Thermochemistry of solution of some quaternized derivatives of tetra(4-pyridyl)porphine in water

Article abstract of DOI:10.1134/S1070363207110199

Quaternized tetra(4-pyridyl)porphine derivatives: tetra(N-carboxymethyl-4- pyridyl)porphine tetrachloride, tetra(N-carboxymethyl-4-pyridyl)porphine tetrabromide, tetra(N-methyl-4-pyridyl)porphine tetraiodide, and tetra(N-ethoxycarbonylmethyl-4-pyridyl)porphine tetrachloride, were synthesized, isolated, and purified. The enthalpies of solution of these compounds in water at 298.15 K were determined calorimetrically. The effect of functional substituents in porphyrin ligands on the enthalpies of solution is discussed.

Full text of DOI:10.1134/S1070363207110199

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 11, pp. 1955 1958.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
pp. 1905 1908.
M.B. Berezin, N.M. Berezina, A.S. Semeikin, A.I. V’yugin, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 11,
Thermochemistry of Solution of Some Quaternized Derivatives
of Tetra(4-pyridyl)porphine in Water
M. B. Berezina, N. M. Berezinab, A. S. Semeikinb, and A. I. V’yugina
a Institute of Solution Chemistry, Russian Academy of Sciences,
ul. Akademisheskaya 1, Ivanovo, 153045 Russia
e-mail: mbb@isc-ras.ru
b Ivanovo State University of Chemical Technology, Ivanovo, Russia
Received October 2, 2006
Abstract Quaternized tetra(4-pyridyl)porphine derivatives: tetra(N-carboxymethyl-4-pyridyl)porphine
tetrachloride, tetra(N-carboxymethyl-4-pyridyl)porphine tetrabromide, tetra(N-methyl-4-pyridyl)porphine
tetraiodide, and tetra(N-ethoxycarbonylmethyl-4-pyridyl)porphine tetrachloride, were synthesized, isolated,
and purified. The enthalpies of solution of these compounds in water at 298.15 K were determined calori-
metrically. The effect of functional substituents in porphyrin ligands on the enthalpies of solution is discussed.
DOI: 10.1134/S1070363207110199
Comprehensive studies of porphyrins and related
molecules are stimulated by a number of factors, one
of which is that this class of compounds includes
chlorophyll and blood heme, the most important life
complexes whose functioning in plant leaves and in
blood of humans and animals determines the possibil-
ity of their existence and development. Water-soluble
porphyrins are of particular importance.
Quaternized derivatives I IV of tetra(4-pyridyl)por-
phine are convenient model compounds for studying
the state and reactivity of porphyrins in aqueous
media. To evaluate the energy characteristics of inter-
particle interactions in solutions, which are deter-
mined most accurately by the calorimetric method, we
examined the dissolution of I IV in water.
R
N
NH
R
R
N
HN
R
+ Cl
N CH2COOH
+ Br
N CH2COOH
II, R =
I, R =
Tetra(N-carboxymethyl-4-pyridyl)porphine
Tetra(N-carboxymethyl-4-pyridyl)porphine
tetrabromide
tetrachloride
+ I
N CH3
+ Cl
III, R =
IV, R =
N CH2COOC2H5
Tetra(N-methyl-4-pyridyl)porphine
Tetra(N-ethoxycarbonylmethyl-4-pyridyl)porphine
tetraiodide
tetrachloride
1955

1956
BEREZIN et al.
Table 1. Positions and intensities ( , nm/log ) of absorption bands in the electronic spectra of porphyrins
Porphyrin
1/log
2/log
3/log
4/log
Soret/log
Tetra(4-pyridyl)porphine (in CHCl3)
643/3.43
640/3.31
642/3.81
641/3.33
642/3.42
589/3.82
585/3.85
585/4.32
585/3.92
586/3.76
546/3.79
554/3.80
554/4.31
554/3.86
554/3.77
514/4.30
518/4.21
519/4.72
518/4.28
519/4.07
417/5.62
422
422
421
423
I
II
III
IV
Table 2. Enthalpies of solution of tetrapyridylporphine
polarization of the molecule, resulting from functional
substitution, leads to a weak hypsochromic shift of the
first band and to a bathochromic shift of the Soret
band of the porphyrins in the electronic absorption
spectra relative to unsubstituted tetrapyridylporphine.
1
derivatives in water at 298.15 K ( solHm, kJ mol )
m 104,
solH,
solH0,
Porphyrin
1
1
1
mol kg
kJ mol
kJ mol
The solvation of the quaternized tetra(4-pyridyl)-
porphine derivatives should lead to the formation of
a complex solvation (hydration) shell. The complex
structure of this shell is determined by multifunctional
substitution of the macroring periphery. The solvation
shell will cover such fragments as (a) the macroring
core (sixteen-membered aromatic macroring including
a cyclic system of bonds of fractional multiplicity);
I
1.3796
1.3967
1.4091
1.5348
1.8298
0.795
0.895
0.987
1.30
1.64
62.22
57.89
55.69
60.11
53.59
75.31
79.89
78.59
73.28
72.55
77.15
73.09
79.29
123.69
117.31
121.83
116.17
119.71
113.29
123.24
113.97
120.89
20.89
23.31
24.49
18.91
25.33
19.65
57.9 4.3
II
76.2 3.6
(b) semiisolated
bonds C =C in pyrrole rings;
(c) pyridinium fragments bearing a positive charge;
(d) acetic acid residues CH2COOH, esterified with
ethyl alcohol in the case of IV, or (e) methyl groups
(in the case of III) at the pyridine nitrogen atoms;
and, finally, four counteranions (Cl , Br , or I ) com-
pensating the positive charge of the pyridinium frag-
ments. Universal interactions prevail around frag-
ments a, b, and e, and specific interactions, around
fragments c and d. As noted above, the specific inter-
actions are complexation and acid base interaction,
including its initial step, hydrogen bonding. Apparent-
ly, in this case the substituted pyridinium fragments
themselves and the acetic acid residues making con-
tact with the nitrogen atoms of the pyridinium frag-
ments will actively participate in hydrogen bonding
with water molecules.
1.67
2.28
2.75
III
0.4599
0.5655
0.5832
0.6486
0.6959
0.7011
0.7067
0.7557
0.9542
0.9591
1.0636
1.1936
1.3226
1.4245
1.4281
118.9 5.2
IV
22.1 3.2
The compounds under consideration differ in the
nature and size of functional groups and also in the
nature of counteranion. Therefore, the enthalpies of
1
solution range from 20 to 120 kJ mol (Table 2).
No definite concentration dependence of the enthal-
Compounds I IV are readily soluble in water over
the entire pH range owing to the presence of charges
on nitrogen atoms of pyridinium fragments and on
counteranions.
py of solution of porphyrins I IV in water, solHm
=
f(m), was observed in the examined concentration
range, and the scatter of the H values is caused by
experimental errors, probably those in weighing small
(4 12 mg) portions of the compounds. The averaged
results of five to eight measurements of solHm are
given in Table 2 as the standard enthalpies of solution
The electronic absorption spectra of compounds
I IV in water and of tetra(4-pyridyl)porphine in chlo-
roform are given in Table 1. It can be seen that the
(
solH0).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 11 2007

THERMOCHEMISTRY OF SOLUTION OF SOME QUATERNIZED DERIVATIVES
1957
In the general case, the enthalpy of solution of a
substance consists of two terms: energy of phase tran-
sition (crystal lattice energy) and enthalpy of solvation
(hydration). Thus, changes in the structure of func-
tional groups of the porphyrin will affect both the
crystal lattice strength and the solvation interactions in
solution:
Comparison of these data and our results shows that
the large hydrophobic porphyrin cation exerts a signif-
icant leveling effect.
The dissolution of IV is the least endothermic:
1
solH0 22.1 kJ mol . That is, replacement of carboxy-
methyl substituents at the pyridinium nitrogen atoms
by ethoxycarbonylmethyl groups leads to the energy
1
gain in dissolution of 35.8 kJ mol . This is apparent-
solH = crH + solvH.
ly due to additional loosening effect of four ethyl
groups on the porphyrin crystal lattice.
Table 2 shows that the dissolution of all the por-
phyrins in water is strongly endothermic. This is
primarily caused by large energy consumption for
breaking the water structure to accommodate large
porphyrin molecules. The dissolution of compound
III containing no functional substituents prone to
hydration is the most endothermic. Furthermore, this
compound should presumably have the strongest
crystal lattice, because the molecule of III is more
compact compared to I, II, and IV.
Thus, our results suggest of strong solvation inter-
actions in aqueous solutions of water-soluble por-
phyrins, more pronounced than in nonaqueous solu-
tions [2].
EXPERIMENTAL
Tetra(4-pyridyl)porphine was prepared as follows.
Freshly distilled pyrrole (1 mol) and 4-pyridinecarbal-
dehyde (1 mol) were refluxed with stirring for 30 min
in 2.5 l of propionic acid, after which the solution was
cooled and diluted with water (1 : 1). Sodium acetate
was added to adjust pH 4 at which unsubstituted tetra-
pyridylporphine precipitates. The precipitate was fil-
tered off, washed with hot DMF and water, and dried.
The porphyrin was dissolved in chloroform and chro-
matographed on alumina (Brockmann grade II). The
eluate was evaporated to dryness on a rotary evap-
orator. The electronic absorption spectrum in chloro-
form (Table 1) agreed with published data [3].
Introduction of four terminal carboxymethyl (I, II)
or ethoxycarbonylmethyl (IV) groups into the porphy-
rin molecule leads not only to loosening of the crystal
lattice, but also to enhancement of solvation interac-
tions due to hydrogen bonding of oxygen-containing
functional substituents with water molecules. The
1
total effect of these contributions is 43 97 kJ mol
depending on the molecular structure. The exo contri-
1
bution is 61 kJ mol for tetra(N-carboxymethylpyrid-
1
4-yl)porphine tetrachloride and only 42.7 kJ mol for
1
the related bromide. The difference ( 20 kJ mol ) is
apparently caused by the effect of the counteranion.
According to [1], the difference between the enthal-
pies of hydration of Cl and Br ions is 33.5 kJ mol .
Quaternized derivatives of tetra(4-pyridyl)porphine
were prepared by the following general scheme:
1
RA
+N
AR
N
N
N
+
N
H
N
H
DMF
N
+ RA
N
N
N
reflux
H
N
H
N
+
N
N+
AR
N
N
RA
Tetra(N-carboxymethyl-4-pyridyl)porphine
tetrachloride I. Chromatographically purified tetra(4-
pyridyl)porphine (0.5 g) and chloroacetic acid (3 g)
were dissolved in 30 ml of DMF, and the mixture was
refluxed for 1 h. Then the solution was cooled and
diluted with benzene in a 1 : 1 ratio. The precipitate
was filtered off, washed successively with benzene
and acetone, and dried. Yield 0.75 g (93%). Found, %:
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 11 2007

1958
BEREZIN et al.
C 57.26; H 4.14; N 11.03; O 12.41. C48H38N8O8Cl4.
Calculated, %: C 57.85; H 3.84; N 11.24; O 12.84.
tivity of freshly distilled water did not exceed 1.8
10
6
1
1 cm .
The thermal effects of solution were measured with
Tetra(N-carboxymethyl-4-pyridyl)porphine
tetrabromide II. Tetra(4-pyridyl)porphine (0.5 g) and
bromoacetic acid (3 g) were dissolved in 30 ml of
DMF, and the mixture was refluxed for 1 h. Porphyrin
II was isolated similarly to I. Yield 0.9 g (94.8%).
Found, %: C 48.53; H 3.89; N 9.57; O 10.01. C48H38
N8O8Br4. Calculated, %: C 49.08; H 3.26; N 9.54;
O 10.89.
a isoperibolic calorimeter with automatic data acquisi-
tion and processing [5]. The temperature in the ther-
mostat was maintained with an accuracy better than
0.001 C. The sensitivity of the measurement circuit
was 0.00001 C. The electronic absorption spectra
were recorded on a Cary-300 spectrophotometer.
ACKNOWLEDGMENTS
Tetra(N-ethoxycarbonylmethyl-4-pyridyl)por-
phine tetrachloride IV. Purified tetra(4-pyridyl)-
porphine (0.5 g) and ethyl chloroacetate (3 ml) were
dissolved in 30 ml of DMF, and the mixture was re-
fluxed for 1 h. Then the solution was cooled and di-
luted with benzene in 1 : 1 ratio. Porphyrin IV was
isolated similarly to I. Yield 0.82 g (92%). Found,
%: C 61.89; H 4.10; 10.65; O 10.97. C56H54N8O8Cl4.
Calculated, %: C 60.66; H 4.91; N 10.11; O 11.54.
The study was financially supported by the Russian
Foundation for Basic Research (project no. 04-03-
32653).
REFERENCES
1. Yatsimirskii, K.B., Termokhimiya kompleksnykh soe-
dinenii (Thermochemistry of Coordination Compounds),
Moscow: Akad. Nauk SSSR, 1951, p. 51.
Tetra(N-methyl-4-pyridyl)porphine tetraiodide
III. Chromatographically purified tetra(4-pyridyl)por-
phine (1 g) and methyl iodide (6 ml) were dissolved
in 80 ml of DMF, and the mixture was refluxed for
1 h. Then the solution was cooled and diluted with
100 ml of acetone. The precipitate was filtered off,
washed with acetone, and dried. Yield 1.78 g (98%).
Found, %: C 44.41; H 3.06; N 9.53. C44H38N8I4.
Calculated, C 44.53; H 3.23; N 9.44.
2. V’yugin, A.I. and Krestov, G.A., Rastvory neelektroli-
tov v zhidkostyakh (Solutions of Nonelectrolytes in
Liquids), Moscow: Nauka, 1989, p. 137.
3. Hambright, P. and Fleischer, E.Y.B., Inorg. Chem.,
1970, vol. 9, no. 7, p. 1757.
4. Karyakin, Yu.V. and Angelov, I.I., Chistye khimiches-
kie veshchestva (Pure Chemicals), Moscow: Khimiya,
1974.
5. Kustov, A.V., Emel’yanov, A.A., Syshchenko, A.F.,
Krest’yaninov, M.A., Zheleznyak, N.I., and Koro-
lev, V.P., Zh. Fiz. Khim., 2006, vol. 80, no. 9, p. 1724.
Water used in the studies was purified by the
standard procedure [4]. The specific electrical conduc-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 11 2007