Studies of the fluorescence light-up effect of amino-substituted benzo[b]quinolizinium derivatives in the presence of biomacromolecules

Abstract

A comparative study of the ability of amino-substituted benzo[b]quinolizinium derivatives to act as DNA- or protein-sensitive fluorescent probes is presented. Spectrophotometric titrations, DNA denaturation studies and viscometric titrations showed that all tested aminobenzo[b]quinolizinium derivatives intercalate into DNA with binding constants K(b) = 10(4)-10(5) M(-1). The intense fluorescence of the 9-aminobenzo[b]quinolizinium (Φ(fl) = 0.41) as well as the intrinsically very weak emission of the 7-aminobenzo[b]quinolizinium (Φ(fl) < 0.005) are quenched by the addition of DNA, most likely caused by a photoinduced electron transfer (PET) between the excited intercalated ligand and the DNA bases. The 6-aminobenzo[b]quinolizinium (1b) and the 6-amino-9-bromobenzo[b]quinolizinium (1c) exhibit very low fluorescence intensity in water (Φ(fl) < 0.005). However, in water-glycerol mixtures the emission intensity increases by factors of 56 (1b) and 27 (1c) with increasing glycerol content of the solution (0-100 wt%), which indicates the radiationless deactivation of the excited state of 1b and 1c due to a torsional relaxation, i.e. rotation about the exocyclic C(ar)-NH(2) bond. In the case of the bromo-substituted derivative 1c, a viscosity-independent heavy-atom-effect of the bromo substituent leads to additional quenching. The association of 1b and 1c with ds DNA leads to a restricted conformational flexibility of the intercalated ligand and results in an increase of fluorescence intensity. This effect is particularly strong in the presence of poly[dA-dT]-poly[dA-dT]. Upon association with ct DNA or poly[dG-dC]-poly[dG-dC] only very small enhancement of emission intensity (1b) or even a slight quenching (1c) of the fluorescence was observed because of the interfering PET reaction with the guanine residues. Preliminary experiments reveal that the 6-aminobenzo[b]quinolizinium derivatives 1b and 1c may also be employed as protein-sensitive probes, because their emission intensity increases upon association with selected albumins.

Steady-State and Femtosecond Transient Absorption Spectroscopy of New Two-Photon Absorbing Fluorene-Containing Quinolizinium Cation Membrane Probes

“…It was reported that quinolizinium derivatives can bind with biomacromolecules such DNA and proteins, exhibiting a fluorescence turn-on effect, because of a restricted conformation flexibility. 59,60 Similar effects were observed with quinoliziniums 1 and 2.…”

8-Styryl-substituted coralyne derivatives as DNA binding fluorescent probes

“…The emission shift is likely the result of suppressed deactivation pathways in the excited state, namely torsional relaxation, because of the reduced conformational flexibility within the binding site. 38 In particular, this effect was observed for quinolizinium derivatives, 39 namely the 9-(4-dimethylaminophenyl)benzo[ b ]quinolizinium in the presence of ct DNA or 22AG , 11 and berberine and sanguarine in the presence of abasic site-containing DNA. 40 This explanation is consistent with the observation that the red-shifted emission band of 4b is also present in a highly viscous solvent such as glycerol, in which the conformational flexibility is reduced leading to two distinct emitting species (Fig.…”

Studies of the binding mode of TXNHCH 2 COOH with calf thymus DNA by spectroscopic methods

“…In the literature there are many fluorescent compounds e.g. Ethidium bromide, acridine orange and methylene blue and they are normally used to probe the DNA structure in drug-DNA interactions [1][2][3][4][5][6][7][8][9][10][11][12]. The visualization of DNA labelled with a fluorescent dye through optical microscopy was reported [13,14].…”