Tuning of Intercalation and Electron-Transfer Processes between DNA and Acridinium Derivatives through Steric Effects

Abstract

A series of acridinium derivatives 1-6, wherein steric factors have been varied systematically through substitution at the 9 position of the acridine ring, have been synthesized and their DNA interactions have been investigated by various biophysical techniques. The unsubstituted and methylacridinium derivatives 1 and 2 and the o-tolylacridinium derivative 6 exhibited high fluorescence quantum yields (Phi(f)() congruent with 1) and lifetimes (tau = 35, 34, and 25 ns, respectively), when compared with the arylacridinium derivatives 3-5. The acridinium derivatives 1 and 2 showed high DNA binding affinity (K = 7.3-7.7 x 10(5) M(-)(1)), when compared to the arylacridinium derivatives 3-5 (K = 6.9-10 x 10(4) M(-)(1)). DNA melting and viscosity studies establish that in the case of the aryl-substituted systems, the efficiency of DNA binding is in the order, phenyl > p-tolyl > m-tolyl >>>> o-tolyl derivative. The increase in steric crowding around the acridine ring hinders the DNA binding interactions and thereby leads to negligible binding as observed in the case of 6 (o-tolyl derivative). These results indicate that a subtle variation in the substitution pattern has a profound influence on the photophysical and DNA interactions. Further, they demonstrate that pi-stacking interactions of the ligands with DNA are essential for efficient electron transfer between the DNA bases and the ligands. These water soluble and highly fluorescent molecules which differ in their DNA binding mode can act as models to study various DNA-ligand interactions.

Determination of the binding affinities of plasmid DNA using fluorescent intercalators possessing an acridine skeleton

“…This finding implies that the changes in the binding constants of all studied ATA compounds cannot simply be represented by the dihedral angle ϕ [13]. From our AM1 calculations, follow that structure A is energetically most favored in comparison with B and C.…”

“…Recently it was found [13] that the intercalation affinity of 9-substituted acridinium derivatives with sterically insignificant substituents (methyl, phenyl, tolyl) depended also on the changes of the dihedral angle ϕ (AM1 calculation). In our case, we took in question, the three most probable tautomeric forms for ATA, illustrated for compound 1 (Fig.…”

Efficient Increase of DNA Cleavage Activity of a Diiron(III) Complex by a Conjugating Acridine Group

“…The moderate binding for this complex is comparable to those observed for many other acridine derivatives. [33] As a means for further clarifying the binding of the binuclear complex, viscosity measurements were carried out on calf thymus DNA by varying the concentration of the complex. Acridine, a classical intercalator, causes a moderated increase in the viscosity of the DNA solution due to the separation of base pairs at intercalation sites and hence an increase in overall DNA length ( Figure 5).…”

Carbon Nanotube–Acridine Nanohybrids: Spectroscopic Characterization of Photoinduced Electron Transfer

“…[39] Indeed, an exciplex always emits at longer wavelength compared with the corresponding monomers. As acridinium ions are already known to behave as electron acceptors in catalytic reactions and in photoinduced DNA cleavage via electron transfer, [40][41][42] we suggest here that the strong fluorescence quenching of acridinium is the result of a fast electron transfer from the nanotube (Scheme 3). Similarly with the discussion on exciplex formation between NT and PhA, the electron transfer could also occur "intermolecularly" between one nanotube and one excited PhMeA + linked to another nanotube in a bundle.…”