Chemistry Reference
In-Depth Information
Fig. 1 Different duplex
conformation of DNA
Minor Groove
Msjor Groove
Msjor Groove
Minor Groove
A-form RNA
B-form DNA
Z-form DNA
bound and distinguish specific base sequences in single or double helices of nucleic
acids, a lot of natural molecules are able to recognize selectively sites on DNA
and RNA, and some of these can interfere with processes controlling the flow of
genetic information (replication, transcription, and transduction). The most signifi-
cant characteristic of all these molecules is the presence of (hetero-)aromatic
chromophores having the ability to intercalate with DNA basis by
interactions,
inhibiting the transcription process. Synthetic derivatives of natural compound have
been used as antibiotic (actinomycin D [
3
,
4
] and rifamycin [
4
]) or as antitumor
(daunomycin); however, other molecules such as proflavine, ethidium ion, and
porphyrinoids have been studied owing to the high efficiency in PDT [
5
-
8
].
Porphyrinoids are ideal compounds to be incorporated into DNA due to peculiar
characteristics: (1) high molar absorptivity coefficient of the main absorption band
(called Soret band) owing to the large aromatic structure, (2) the possibility to tune
the electronic properties of the molecules by implementing small variation in the
macrocycle ring or introducing metal ions in the core, (3) absorption spectrum in the
360-750 nm range, far from spectroscopic interference of nucleic acid absorption, and
(4) ability to act as photosensitizers in the presence of oxygen. This latter characteristic
promoted the interest of scientific community to study the binding of porphyrinoids
with DNA in order to use them in PDT. It has been demonstrated that a photosensitizer
needs to be bound to DNA in order to produce photodynamic damage [
9
], and
the efficiency of this process depends on the type of interaction of the photosensitizer
[
10
,
11
]. Thus, the understanding of mechanism involved in the binding of
porphyrinoids with DNA can help to find a porphyrinoid with specific base degrada-
tion activity. For these reasons several synthetic derivatives of porphyrinoids have
been proposed to improve the non-covalent interactions with DNA.
There are several spectroscopic techniques for the investigation and characteri-
zation of porphyrinoid-DNA systems such as UV-Vis, fluorescence, RLS, CD, and
NMR. As concerns the utility of the various techniques, it is, noteworthy, singularly
used to give fast, intuitive but not always detailed information about the type of
interaction. Only analyzing by more than one of those methods is possible to
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