The present experimental
study attempts to elucidate the binding interaction between two types of
acridone derivative, 8-choloro acridone
(CA) and nitrile cyanide acridone (NCA), and calf thymus DNA (ctDNA). To perform
this study, several spectroscopic
techniques were employed. The obtained result revealed that CA and NCA can bind
to ctDNA by a quenching constant of 2.949×103 and 7.063×103 M-1
respectively. Further analysis pointed out that the
interaction between CA and ctDNA was controlled by a dynamic quenching
mechanism while the dominant quenching process in ctDNA-NCA interaction was static. Calculating and analyzing the
thermodynamic parameters allows an estimation of the forces that drives the
complex formation. In present study, the thermodynamic properties of the binding process indicated that the resulting ctDNA-CA and
ctDNA-NCA complexes were stabilized by hydrophobic and van der Waals intercations
respectively. The fluorescence
displacement experiments were conducted by using ethidium bromide (EB) and
acridone orang (AO) as fluorescence probes and showed that CA and NCA compete
against intercalator probes and thereby they probably interact with ctDNA
through intercalation. Given that the melting temperature of ctDNA went up by 6-8 C
in the presence of CA and NCA, it can be thus inferred that these two compound probably
intercalated into ctDNA and brought greater stability in ctDNA. A closer insight into the modes of binding was achieved by measuring and comparing ctDNA
viscosity in the absence and presence of CA and NCA. The results displayed that
the presence of CA resulted in a decrease in the relative viscosity of ctDNA
which is a characteristic of non-classical intercalation bindings. In contrast,
the ctDNA relative viscosity increased through binding on NCA which reflect the
fact that NCA bound ctDNA intercalately. The
effect of ionic strength on the interactions indicated that the ctDNA-NCA and
ctDNA-CA interactions were relatively dependent and independent on the salt
concentration respectively.


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