Interaction of porphyrins with adenine and adenosine complexes. Effect of a metal nature

Article abstract of DOI:10.1134/S1070328406040087

Reactions of complex formation of 5,10,15,20-tetraphenylporphine (H ₂TPP) and tetra-tert-butylphthalocyanine (H₂(t-Bu) ₄Pc) with adenine and adenosine complexes of d-metals in DMSO and ethanol are studied. It was found that H₂TPP reacts with Cu(II) and Hg(II) adeninates and adenosinates in DMSO, but does not react with Zn(II), Co(II), and Cd(II) adeninates and adenosinates (with both bridging and monodentate type of the ligand coordination). H₂(t-Bu)₄Pc enters the complex formation reaction with adeninates and adenosinates of all studied metals in DMSO at almost equal rates. The states of adenine and adenosine complexes of different d-metals in DMSO and ethanol are proposed on the basis of kinetic data obtained. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S1070328406040087

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2006, Vol. 32, No. 4, pp. 276–281. © Pleiades Publishing, Inc., 2006.
Original Russian Text © G.M. Mamardashvili, B.D. Berezin, 2006, published in Koordinatsionnaya Khimiya, 2006, Vol. 32, No. 4, pp. 288–293.
Interaction of Porphyrins with Adenine
and Adenosine Complexes.
Effect of a Metal Nature
G. M. Mamardashvili and B. D. Berezin
Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
Received June 14, 2005
Abstract—Reactions of complex formation of 5,10,15,20-tetraphenylporphine (ç2íêê) and tetra-tert-
butylphthalocyanine (ç2(t-Bu)4êÒ) with adenine and adenosine complexes of d-metals in DMSO and ethanol
are studied. It was found that ç2íêê reacts with Cu(II) and Hg(II) adeninates and adenosinates in DMSO, but
does not react with Zn(II), Co(II), and Cd(II) adeninates and adenosinates (with both bridging and monodentate
type of the ligand coordination). ç2(t-Bu)4êÒ enters the complex formation reaction with adeninates and ade-
nosinates of all studied metals in DMSO at almost equal rates. The states of adenine and adenosine complexes
of different d-metals in DMSO and ethanol are proposed on the basis of kinetic data obtained.
DOI: 10.1134/S1070328406040087
Previously [1–5], we studied the reaction of some
porphyrins with amino acid and peptide complexes
being chelate salts with bi- and tridentate ligands.
This reaction can be regarded as a particular case of a
chelate-macrocyclic interaction considered in detail in
[6, 7].
The reaction of formation of metalloporphyrins is
peculiar in that it can be used as a model reaction when
studying a series of problems in general, organic, and
physical chemistries, including determination of states
of the metal salts MXm(Solv)n – m (M is the transition
metal, Solv is a solvent) in solutions [11–13]. The pos-
sibility of using reaction (1) (see below) as indicator
Adenine (Äd, C5H5N5) and adenosine (Adz,
C10H13N5O4) form with d-metals two types of com- reaction when studying the states of salts in solutions
plexes, i.e., complexes with the bridging and mono-
dentate ligands. Neither the amino group in adenine
nor the hydroxyl group in adenosine act as the coordi-
nation center in complexes, and these bases do not
form chelate salts. The presence in complexes of che-
late salts or monodentate ligands, charged or
uncharged species, is determined, first of all, by the
conditions of synthesis of these complexes: reacting
species, pH of a medium, the concentration ratio of the
metal ions and adenine [8–10].
stems from unique coordinating properties of porphy-
rins (ç2ê). These properties specify constant composi-
tion of complexes (with a ratio of metal : porphyrin =
1 : 1); high stability of complexes, which nevertheless
strongly depends on the electronic structure and charge
of a cation; low rates of complexation reactions
between porphyrin and a metal salt that are easily mea-
sured by spectrophotometric method.
The reactions of complex formation of porphyrins
with different metal salts in polar solvents are classified
as follows [14]: 1) reactions between inner-sphere com-
plexes; 2) reactions of replacement of the ligands
The structures of solid adenine and adenosine com-
plexes are studied well today, whereas the states of
monodentate and bridging adenine and adenosine com-
plexes in solutions are studied poorly. The following directly bonded to a metal ion by other ligands; 3) reac-
questions are still to be answered: which species are
formed during dissociation of monodentate and bridg-
ing metal adeninates and adenosinates, for example, in
DMSO and how deep is this process; what is the differ-
ence between dissociation of the complexes in DMSO
and in aqueous or alcohol media, and how the metal
nature affects the dissociation reaction.
tions proceeding in one stage, when the porphyrin
ligand provides to a metal ion the electron pairs suffi-
cient to fill in its valence orbitals.
When reacting with the cis-solvate of porphyrin, the
MX2(Solv)n salt looses two molecules of a solvent to give
the polar transition state [(Solv)2H2ê · MX2(Solv)n – 4]# [12]:
276

INTERACTION OF PORPHYRINS WITH ADENINE AND ADENOSINE COMPLEXES
277
H
N
Solv
#
N
M
N
Solv
Solv
H
H
N
N
X
M
X
Solv
M
Solv
Solv
Solv
Solv
N
X
X
N
(1)
+
+ 2HX
N
N
N
N
Solv
N
H
Solv
In general, the choice of DMSO solvent when increases as compared to other solvents, since DMSO
studying reaction (1) is not adequate. The rate of this favors the formation of macrocyclic structure with a
more polar bond N–H. Therefore, in DMSO,
ç2(t-Bu)4êÒ is more reactive in reaction (1) as com-
pared to porphyrin itself, i.e., 1,10,15,20-tetraphen-
ylporphine (ç2íêê).
reaction substantially depends on the coordinating
capability of a solvent. The stronger complex solvates
are formed by the M2+ cations or the metal acido salts
åï2 with a solvent, the lower the reaction rate is. In its
capability of solvation, DMSO is only inferior to pyri-
dine and hexamethylphosphortriamide. Therefore, the
rate of reaction between porphyrins and metal salts in
DMSO is considerably lower than in ethanol, methan-
ol, acetic acid, or in many other solvents. However, in
the case of biocomplexes, such as amino acid, peptide,
or nucleoside complexes, DMSO is just about the sole
organic solvent in which these complexes dissolve. The
solubility of biocomplexes in DMSO is low, as a rule,
but is sufficient to study the reaction of porphyrin coor-
dination by spectrophotometric method. Almost the
same solubility in ethanol is shown only by adeninates
and adenosinates of Hg(II) and Cd(II).
The aim of this work was to study the reaction of
complex formation of porphyrin molecules with ade-
nine and adenosine complexes of different d-metals.
The data obtained make it possible to study peculiari-
ties of complexation of porphyrins with monodentate
and bridging biological ligands on the basis of general
principles of coordination chemistry of solutions and to
consider the possibility of using the reaction of forma-
tion of metallophophyrins as a model reaction in the
study of states of different biological complexes, for
example, metal adeninates and adenosinates, in solu-
tions.
EXPERIMENTAL
On the contrary, for porphyrins with more delocal-
ized bonds, for example, tetra-tert-butylphthalocyanine
(ç2(t-Bu)4êÒ), the rate of reaction (1) in DMSO sized and purified by the known procedures [15, 16].
Porphyrins, ç2Têê and ç2(t-Bu)4êÒ, were synthe-
t-Bu
t-Bu
N
NH
N
NH
N
N
N
N
N
HN
HN
N
t-Bu
t-Bu
(H2TPP)
(H2(t-Bu)4Pc)
Also, analytical grade ëuCl2 · 2H2O, ZnCl2 · H2O, complexes with adenine and adenosine (I–XV) were
CoCl2 · H2O, and CdCl2 · H2O were used in the syn- prepared according to [9] from metal chlorides and
thesis. The Cu(II), Cd(II), Co(II), Zn(II), and Hg(II) adenine or adenosine, respectively, in ethanol. The
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 4 2006

278
MAMARDASHVILI, BEREZIN
Table 1. The results of elemental analysis and color of Cu(II), Cd(II), Co(II), Zn(II), and Hg(II) complexes with adenine and
adenosine
Content (found/calcd.), %
Complex
Cu(Ad)Cl2 (I)
Color
C
H
N
Pale green
Pale blue
Pale green
Green
21.60/22.39
29.19/29.78
28.90/29.87
35.40/35.90
22.41/22.64
29.50/29.98
35.51/36.14
21.70/22.14
28.80/29.50
35.49/35.78
25.96/26.51
26.66/26.66
33.53/33.47
22.16/22.14
30.80/29.81
2.03/1.87
2.68/2.48
3.67/3.23
4.14/3.89
1.84/1.89
2.46/2.49
3.86/3.91
1.94/1.84
2.70/2.45
4.10/3.87
2.45/2.21
3.03/2.88
3.82/3.62
1.91/1.84
3.43/3.23
26.10/25.50
34.74/33.42
17.42/16.42
20.93/20.41
26.41/26.35
34.98/34.80
21.08/20.91
25.83/25.78
34.42/34.17
20.87/20.56
30.92/30.39
15.55/15.58
19.52/19.80
25.83/25.22
17.39/17.79
Cu(Ad)2Cl2 (II)
Cu(Adz)Cl2 (III)
Cu(Adz)2Cl2 (IV)
Co(Ad)Cl2 (V)
Blue
Co(Adz)2Cl2 (VI)
Co(Ad)2Cl2 (VII)
Zn(Ad)Cl2 (VIII)
Zn(Ad)2Cl2 (IX)
Zn(Adz)2Cl2 (X)
Cd(Ad)2Cl2 (XI)
Cd(Adz)Cl2 (XII)
Cd(Adz)2Cl2 (XIII)
Hg(Ad)2Cl2 (XIV)
Hg(Adz)2Cl2 (XV)
Blue
Blue
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
Colorless
results of elemental analysis of the obtained metal
adeninates and adenosinates are given in Table 1; the
complexes have the following structures
The kinetics of complex formation reaction of por-
phyrins with metal adeninates and adenosinates was
studied by spectrophotometric method [13]. The reac-
tion had pseudofirst order in porphyrin, which was con-
firmed by a linear character of the function ln(c0/cτ) =
f(τ) (where c0 and cτ are the initial and current concen-
trations of porphyrin, respectively). The effective rate
constants (keff) of pseudofirst-order reaction were deter-
NH2
R
NH2
N
N
NR
N
N
N
N
Cl
Cl
Cl
N
N
D
1
M
Cl M
M Cl
Cl
5
1
N
N
N
4
N
NR
N
N
R
NH2
H2N
2
3
MAdCl2: R = H;
MAdzCl2: R =
H
O
H
H
H
CH2 OH
OH
0
OH
400
900
λ, nm
The electronic absorption spectra of Cu(II) complexes in
DMSO: (1) CuCl , (2) Cu(Ad) Cl (λ = 674 nm), (3)
The electronic absorption spectra of Cu(II) adenine
and adenosine complexes in DMSO are presented in
figure.
2
2
2
Cu(Ad)Cl (λ = 667, 699 nm), (4) ëu(Adz) Cl (λ =
2
2
2
844 nm), and (5) Cu(Adz)Cl (λ = 888 nm).
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 4 2006

INTERACTION OF PORPHYRINS WITH ADENINE AND ADENOSINE COMPLEXES
279
Table 2. The kinetic parameters of reaction (1) of porphyrins with CuCl2 and I–XV complexes in DMSO and ethanol
(cporph ≈ 5 × 10–6 mol/l, ccompl ≈ 3 × 10–4 mol/l)*
H2TPP
keff × 104, s–1
T = 343 K T = 353 K T = 363 K
H2(t-Bu)4Pc
keff × 104, s–1
T = 288 K T = 298 K T = 313 K
Salt
Ea, kJ/mol
Ea, kJ/mol
DMSO
66
CuCl2
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
XIII
XIV
XV
2.63
0.78
0.36
1.05
2.42
5.08
1.40
0.60
2.10
4.20
9.43
2.40
0.94
3.98
7.14
1.87
11.0
0.58
10.4
2.10
12.8
0.72
12.3
2.47
15.8
0.98
15.6
8.3
10.8
15.7
12.2
8.8
34
58
49
68
56
2.12
1.72
1.60
1.60
2.04
2.00
1.78
2.40
2.20
2.19
0.77
7.50
2.40
2.76
2.60
2.57
3.38
3.30
2.90
3.66
3.50
3.43
0.94
8.40
3.27
5.33
5.12
4.96
6.80
6.60
5.71
6.55
6.60
6.37
1.24
9.94
No reaction
″
″
″
″
″
″
″
″
″
35
34
36
36
35
30
33
32
14.3
8.6
0.12
0.21
0.32
48
Ethanol
19
XI
10.0
14.5
20.3
120
150
38.0
42.0
XII
XIII
XIV
XV
13.8
37.9
23.3
10.5
40.8
77.5
30.0
21.5
56
37
13
1.05
0.24
1.62
0.53
2.97
1.67
31
59
37
* The error of determination of k —3–4%; E —7–10%.
eff
a
mined from the change in optical density of a solution
at certain time intervals at wavelengths corresponding
to maxima of the absorption bands of metalloporphy-
rins and calculated from the following equation
RESULTS AND DISCUSSION
The study of the reaction of chlorides, adeninates,
and adenosinates of d metals with ç2TPP and
ç2(t-Bu)4êÒ showed that the reaction rate depends con-
siderably on the porphyrin and solvent nature (Table 2).
The reaction of complex formation of ç2TPP with
d-metal adeninates and adenosinates (Table 2) in
DMSO occurs only with Cu(II) and Hg(II) salts.
ç2TPP does not react with adeninates or adenosinates
of Zn(II), Co(II), and Cd(II), both bridging and mono-
D0 – D∞
-- -------------------
,
c0
cτ
1
--
τ
1
τ
keff
=
ln---- = ln
Dτ – D∞
where τ is the reaction time, D0, Dτ, and D∞ are optical
densities at the initial time, current moment, and final
time, respectively. The error in determination of keff was
3%. The calculated reaction order in salt (found from dentate. At the same time, ç2(t-Bu)4êÒ reacts with
the slope of logkeff = f( logcsalt ) was close to 1 in all
cases. The activation energy (Ea) was calculated form
the Arrhenius equation from the temperature depen-
dences of keff, obtained for ç2TPP at 338–363 K and for
ç2(t-Bu)4êÒ at 288–313 K. Spectrophotometric mea-
surements were performed using Specord M40 spectro-
photometer. Freshly prepared solutions of porphyrins
and salts in DMSO were used in experiments.
adeninates and adenosinates of all metals under study
(I–XV) in DMSO at almost equal rates.
In DMSO, metal chlorides, including CuCl2,
undergo solvolytic dissociation according to the fol-
lowing equation [12, 17]
2[MCl2(DMSO)2] + 5DMSO
(2)
[MCl(DMSO)3]+ + [M(DMSO)6]2+ + 3Cl–.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 4 2006

280
MAMARDASHVILI, BEREZIN
The analysis of kinetic data on reaction (1) per- M−DMSO bonds, which determine the kinetics of
formed in [11, 12] indicates that in the case of Cu(II) reaction (1).
chloride, in reaction (1), the most reactive are complex
NH2
solvates [Cuël2(DMSO)2] and [CuCl(DMSO)3]+ hav-
ing a lower effective charge and a lower coordination
number of the Cu2+ ion. As was noted above, the rate of
this reaction is determined to a great extent by the
M−Solv bond strength. The presence in the complex
solvate of stronger Cu–Cl bonds brings about weaken-
ing of the Cu–DMSO bonds and, on the contrary, in the
case of the lacking stronger Cu–Cl bonds in the com-
plex and with the positive charge, all Cu–DMSO bonds
in [Cu(DMSO)6]2+ become stronger.
+
NR
ÑDåMëSOé
ÑDåMëSéO
2+
Cu
Cl–
Cl–
N
Ñåëé
DMSO
Ñåëé
DMSO
N
N
Inner coordination
sphere
Outer coordination
sphere
Although the mechanism of complexation of phtha-
locyanines does not differ, in principle, from that of
complexation of porphyrins proper [11, 12], of the two
factors determining the rate of this reaction (the
strength of two M–Solv bonds and the degree of polar-
ity of the porphyrin N–H bond), the predominant factor
in phthalocyanines in DMSO is high polarity of the
N−H bond. Therefore, in the case of complex formation
reaction with ç2(t-Bu)4êÒ, an increase in the strength
of the M–DMSO bonds due to the presence of purine
bases in the outer coordination sphere of a metal does
not affect the rate of reaction (1). On the contrary, as
with amino acid complexes [1, 3], the rate of complex-
ation reaction with ç2(t-Bu)4êÒ (with bulky ligands in
complex solvate) increases.
Both bridging and monodentate Zn(II), Co(II), and
Cd(II) adeninates and adenosinates (V–XIII) do not
react with H2íêê in DMSO. Obviously, the inhibiting
effect of the purine bases contained in the outer coordi-
nation sphere of Zn(II), Co(II), and Cd(II) prevents the
formation of transition state in reaction (1).
In ethanol, the rates of complexation of porphyrins
themselves with metal chlorides are higher than in
DMSO. The same regularity is observed also for Cd(II)
adeninates and adenosinates (the Zn(II), Co(II), and
Cu(II) adeninate and adenosinate complexes are insol-
uble in ethanol). In DMSO, these complexes do not
react with ç2íêê, whereas in ethanol, this reaction
occurs at measurable rates. As complexes V–XIII do
not dissociate in DMSO with detachment of adenine
and adenosine ligands, in ethanol, these complexes
(soluble complexes) are likely to undergo partial disso-
ciation with the formation of species kinetically active
in reaction (1). The main reason for which reaction (1)
does not take place for complexes V–XIII in DMSO is
strong inhibiting effect of purine bases in the outer
coordination sphere of a metal. This inhibiting effect is
also observed in ethanol (the rates of complex forma-
tion of porphyrins with Cd(Ad)2Cl2, Cd(Adz)Cl2, and
Cd(Adz)2Cl2 are lower than that with CdCl2). However,
the strength of the M–EtOH bonds, other conditions
being equal, is significantly lower than that of the
M−DMSO bonds. Therefore, although the inhibiting
effect of purine bases in ethanol decreases the reaction
rate, it does not lead to complete suppression of the
reaction.
Almost equal rates of complexation of both porphy-
rins with CuCl2(DMSO)2 and Cu(Adz)2Cl2 suggest that
adenosine complex (IV) dissociates in DMSO with
detachment of two adenosine molecules to give
CuCl2(DMSO)2 (i.e., both adenosine ligands in this
complex are replaced by the solvent molecules):
CuCl2(Adz)2 + 2DMSO
(3)
CuCl2(DMSO)2 + 2Adz.
Low rates of reactions of porphyrins with
ëu(Ad)2Cl2 suggest that this salt is also transformed to
ëuCl2(DMSO)2 according to Eq. (3), but thermody-
namic equilibrium is shifted substantially toward the
initial compound (in DMSO, ëu(Ad)2Cl2 has its char-
acteristic absorption spectrum), and the number of
reactive species in reaction (1), (ëuCl2(DMSO)2 and
[CuCl(DMSO)3]+) is very low.
The state of the complexes ëuAdCl2 and CuAdzCl2
(which in a solid phase are regarded as binuclear com-
plexes) in DMSO solutions can be determined from the
following considerations. As the rates of interaction of
both porphyrins with “bridging” Cu(II) adeninate and
adenosinate are almost equal, it is obvious that in both
cases, solvolytic dissociation (dissociation under the
action of the solvent molecules) of these complexes
results in the same species, which are kinetically active
in reaction (1). The species that can form in dissocia-
tion of both complexes are likely to be
[CuCl(DMSO)3]+. In the case of bridging Cu adeninate,
the solution contains, in addition to [CuCl(DMSO)3]+,
also species with adenine molecules in the inner coor-
dination sphere of a metal, which is confirmed by the
electronic absorption spectrum of “bridging” Cu aden-
inate in DMSO that differs from that of Cu chloride.
At the same time, it should be noted that the rate of
ç2íêê complexation with ëu(Ad)Cl2 and ëu(Adz)Cl2
is three to four times as low as that with CuCl2. This
fact can be explained as follows. Bridging molecules of
Cu(II) adeninate and adenosinate can dissociate in
DMSO with detachment of the adenine and adenosine
ligands. The later ligands remain in the outer coordina-
tion sphere of the complex and slow down reaction (1)
(possibly, due to the presence of purine bases in the
outer sphere of a metal thus creating steric hindrances
The solvent nature also influences the reaction of
to reaction (1)) and increase the strength of the porphyrins with Hg(II) complexes. Whereas the rates
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 4 2006

INTERACTION OF PORPHYRINS WITH ADENINE AND ADENOSINE COMPLEXES
281
of ç2íêê interaction with Hg(II) complexes in ethanol
are higher then in DMSO, in the case of ç2(t-Bu)4êÒ,
when going from DMSO to ethanol, the rates of com-
plex formation decrease, as was expected.
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A conclusion was made in [18] that in the case of
amino acid chelate salts of Hg(II), porphyrin molecules
(particularly, phthalocyanine molecules) can be suc-
cessfully used as competing chelating agents for
“decomplexing” of amino acids (in prospect, for
removing from organism of Hg2+ ions bonded by pro-
tein components). It is obvious that the efficiency of
porphyrin molecules as competing chelating agents
will be substantially higher in the case when the Hg2+
ions are bonded by adenine or adenosine molecules.
17. Gutman, V., Coordination Chemistry in Nonaqueous
Solvents, Berlin: Springer, 1968.
18. Mamardashvili, G.M. and Berezin, B.D., Koord. Khim.,
2005, vol. 31, no. 2, p. 93.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 4 2006