Photoinduced Coupled Charge and Proton Transfers in Gradually Twisted Phenol−Pyridinium Biaryl Series

Selective, pH-Dependent Colorimetric and Fluorimetric Detection of Quadruplex DNA with 4-Dimethylamino(phenyl)-Substituted Berberine Derivatives

The 9- and 12-dimethylaminophenyl-substituted berberine derivatives 3 a and 3 b were readily synthesized by Suzuki-Miyaura reactions and shown to be useful fluorescent probes for the optical detection of quadruplex DNA (G4-DNA). Their association with the nucleic acids was investigated by spectrometric titrations, CD and LD spectroscopy, and with DNA-melting analysis. Both ligands bind to duplex DNA by intercalation and to G4-DNA by terminal π stacking. At neutral conditions, they bind with higher affinity (Kb =105 -106  M-1 ) to representative quadruplex forming oligonucleotides 22AG, c-myc, c-kit, and a2, than to duplex calf thymus (ct) DNA (Kb =5-7×104  M-1 ). At pH 5, however, the affinity of 3 a towards G4-DNA 22AG is higher (Kb =1.2×106  M-1 ), whereas the binding constant towards ct DNA is lower (Kb =3.9×103  M-1 ) than under neutral conditions. Notably, the association of the ligand with DNA results in characteristic changes of the absorption and emission properties under specific conditions, which may be used for optical DNA detection. Other than the parent berberine, the ligands do not show a noticeable increase of their very low intrinsic emission intensity upon association with DNA at neutral conditions. In contrast, a fluorescence light-up effect was observed upon association to duplex (Φfl =0.01) and quadruplex DNA (Φfl =0.04) at pH 5. This fluorimetric response to G4-DNA association in combination with the distinct, red-shifted absorption under these conditions provides a simple and conclusive optical detection of G4-DNA at lower pH.

Rotamerism-driven large magnitude host–guest binding change in a crown ether derivatized pyridinium-phenolate series

A large magnitude host–guest binding change driven by transducting rotamerism effects is demonstrated within a crown ether modified pyridinium-phenolate series.

Excited-state proton transfer in N-methyl-6-hydroxyquinolinium salts: solvent and temperature effects

The excited-state proton transfer (ESPT) reaction of the "super"photoacid N-methyl-6-hydroxyquinolinium (MHQ) was studied using both fluorescence upconversion and time-correlated single photon counting (TCSPC) techniques. The ultrafast ESPT kinetics were investigated in various alcohols and water and determined to be solvent-controlled. The ESPT temperature dependence of MHQ was also studied in various alcohols and compared to that observed for another "super"photoacid, 5,8-dicyano-2-naphthol (DCN2). A full set of kinetic and thermodynamic parameters describing the ESPT was obtained. The protolytic photodissociation rate constant for MHQ was higher than that for DCN2, while the ESPT activation energies of MHQ were smaller. These findings are attributed to the approximately 3 orders of magnitude differences in excited-state acidities of MHQ and DCN2.