The present experimentalstudy attempts to elucidate the binding interaction between two types ofacridone derivative, 8-choloro acridone(CA) and nitrile cyanide acridone (NCA), and calf thymus DNA (ctDNA). To performthis study, several spectroscopictechniques were employed.
The obtained result revealed that CA and NCA can bindto ctDNA by a quenching constant of 2.949×103 and 7.063×103 M-1respectively. Further analysis pointed out that theinteraction between CA and ctDNA was controlled by a dynamic quenchingmechanism while the dominant quenching process in ctDNA-NCA interaction was static. Calculating and analyzing thethermodynamic parameters allows an estimation of the forces that drives thecomplex formation. In present study, the thermodynamic properties of the binding process indicated that the resulting ctDNA-CA andctDNA-NCA complexes were stabilized by hydrophobic and van der Waals intercationsrespectively. The fluorescencedisplacement experiments were conducted by using ethidium bromide (EB) andacridone orang (AO) as fluorescence probes and showed that CA and NCA competeagainst intercalator probes and thereby they probably interact with ctDNAthrough intercalation.
Given that the melting temperature of ctDNA went up by 6-8 Cin the presence of CA and NCA, it can be thus inferred that these two compound probablyintercalated into ctDNA and brought greater stability in ctDNA. A closer insight into the modes of binding was achieved by measuring and comparing ctDNAviscosity in the absence and presence of CA and NCA. The results displayed thatthe presence of CA resulted in a decrease in the relative viscosity of ctDNAwhich is a characteristic of non-classical intercalation bindings.
In contrast,the ctDNA relative viscosity increased through binding on NCA which reflect thefact that NCA bound ctDNA intercalately. Theeffect of ionic strength on the interactions indicated that the ctDNA-NCA andctDNA-CA interactions were relatively dependent and independent on the saltconcentration respectively.