Study of equilibria between water-soluble cationic porphyrins
and nucleosides or nucleotides
Magdalena Makarska, Stanisław Radzki
Department of Inorganic Chemistry, Maria Curie-Skłodowska University
Pl. M. C. Skłodowskiej 2, 20-031 Lublin, Poland
e-mail:madzia@hermes.umcs.lublin.pl
Interactions of porphyrins and their complexes with nucleic acids building blocks, as
purines and pyrimidines, as well as their nucleoside and nucleotide derivatives, are interesting
and very popular subject for many scientists [1 – 8]. The reason of such popularity is
connected with potential usefulness of the interactions mentioned above, for example in
photodynamic therapy of cancer (PDT) [9]. Metal complexes of porphyrins can be also
utilized as cleavage agents using during study of nucleic acids tertiary structure, which is
helpful in better understanding of different drugs and enzymes functioning [4].
There are specific interactions between porphyrins and nucleic acids in water solution,
leading often to formation of new biological systems, or, depending on reaction conditions, to
cleavage or destruction of polynucleotide structure. The porphyrin molecule influences the
DNA chain by its particular elements, that is why the best manner for study of porphyrin –
DNA interactions is investigation of porphyrin interactions with nucleic bases and their
derivatives. Such procedure is the simplification of the real model of porphyrin – DNA
interactions, but easier to understand and study.
The main aim of our research was the analysis of interactions between free porphyrins
H2TTMePP (meso-tetrakis[4-(trimethylamino)phenyl]porphyrin) and H2TMePyP (mesotetrakis(1-methyl-4-pirydyl)porphyrin), as well as their copper complexes, CuTTMePP and
CuTMePyP, with 5 series of compounds: nucleic base – nucleoside – nucleotide, where the
starting compound was adenine, guanine, cytosine, thymine and uracil, respectively. The
titration experiments were carried at two values of ligand concentration, 10-3 and 10-2 M.
Higher concentrations of reagents were believed to give better picture of investigated
interactions. Most of the nucleic compounds is poor soluble in water, what implies the use of
big amounts of sodium hydroxide for their better solubility. The high pH value of such
obtained reagent solutions hinders the concluding, because the porphyrin can interact with
nucleic base and sodium base simultaneously. The measurements were carried in 0.025 M
TRIS buffer, at adequate for each series of compounds pH value to minimalize the measuring
error.
The good example of changes in the porphyrin spectrum during the titration by TRIS
and uracil at pH=12.69 are the Figures 1 and 2, respectively. The absorbance changes during
titration of porphyrin solution by different nucleic agents are shown in the function of
porphyrin concentration (Fig. 3, 4) and in the function of the changes of ligand concentration.
The experimental data obtained during measurements and association constants
calculated on the grounds of these data indicate that there are interactions between porphyrins
H2TMePyP and H2TTMePP, as well as their copper complexes, and nucleic bases and their
derivatives.
The big differences in the results for particular nucleic agents, and first of all for
different pH values indicate the diversification of interaction level of investigated systems.
1
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8
A
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1
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[
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=
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6
9
]
+
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2
Q
b
a
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d
1
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5
1
6
5
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0
4
2
2
3
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03
7
54
0
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2
54
5
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7
55
0
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2
55
5
05
7
56
0
06
2
56
5
06
7
57
0
0

[
n
m
]
Fig. 1. Evolution of H2TTMePP spectrum during titration by TRIS, in 0.025 M TRIS buffer, at pH=12.69.
2
.
0
A
1
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9
H
T
T
M
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=
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]
+
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1
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0
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7
56
0
06
2
56
5
06
7
57
0
0

[
n
m
]
Fig.2.
Evolution of H2TTMePP spectrum during titration by uracil, in 0.025 M TRIS buffer, at pH=12.69.
Interactions of H2TTMePP with nucleic bases are much stronger than interactions of
H2TMePyP. Such effect is caused by the aniline group, much bigger than pyridyl group –
“stacking” (specific interactions consisting in forming of associates by reacting molecules)
between porphyrin and nucleic ligands is much more stronger for bigger compounds.
The results show also that the more stable associates are formed at lower pH value.
Moreover, the strength of the obtained associates increases in series: nucleic base →
nucleoside → nucleotide, although many departures from the rule are observed, because of
high diversity and different pH values of investigated systems.
The association constants for interactions between porphyrins and nucleic agents let us
suppose that by means of adequate porphyrin substituent groups and metal ion in porphyrin
cave it would be possible to control the level of interactions between porphyrins and
complicated DNA systems and, probably, introduce metalloporphyrins to the desirable place
of DNA chain.
1
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8
A
1
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6
1
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4
1
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2
H
T
T
M
e
P
P
n
o
r
m
a
l
i
z
e
d
p
l
o
t
2
p
H
=
1
2
.
7
+
t
r
i
s
+
u
r
a
c
i
l
+
u
r
i
d
i
n
e
+
U
T
P
1
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0
0
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8
0
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6
0
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4
0
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2
0
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0
2
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5
3
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0
3
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5
4
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0
6
c
H
T
T
M
e
P
P
*
1
0
M
2
Fig. 3. The dependance of absorbance versus porphyrin concentration for titration series of H 2TTMePP, at
pH=12.69.
2
.
0
A
1
.
8
1
.
6
1
.
4
H
T
T
M
e
P
P
n
o
r
m
a
l
i
z
e
d
p
l
o
t
2
p
H
=
1
2
.
4
+
t
r
i
s
+
u
r
a
c
i
l
+
u
r
i
d
i
n
e
+
U
T
P
1
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2
1
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0
0
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8
0
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6
0
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4
0
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2
0
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0
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5
3
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0
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5
4
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0
4
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5
6
c
H
T
T
M
e
P
P
*
1
0
M
2
Fig. 4. The dependance of absorbance versus porphyrin concentration for titration series of H 2TTMePP, at
pH=12.4.
However, the substitution reactions proceeding on the metallic centres connected with
nucleic acids are much more complicated, what is caused by the interactions of ligands with
other groups, as well as conformational changes in a macromolecule. Therefore all data
obtained during study of porphyrin – DNA interactions should be particularly considered,
because some porphyrin systems can join and interact with DNA in different ways, depending
on neighbouring chemical compounds [10, 11]. Very often the manner of interactions
between reagents is determined by the kind of reaction buffer and ionic strength connected
with environment of investigated system [1].
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porphyrins and nucleotides or amides: buffer–dependent dramatic changes of binding
affinities and modes”; Chem. Commun., 2000, 23.
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dC)]2 and [Poly(dA–dT)]2”; J. Phys. Chem., 1996, 100, 12649.