Synthesis, Photophysical Properties and Antioxidant Activity of Novel Quinoline Derivatives.

Novel quinoline derivatives were synthesized based on 6-amino-substituted quinoline, and antioxidant activity of these compounds is studied by p-nitroso-N,N-dimethylaniline assay. The rate of the reaction between OH radicals and quinoline derivatives is determined by photometric method and the obtained results are compared with that of well-known antioxidant vitamin C. Quinoline derivatives exhibit pronounced antioxidant activity, which strongly depends on the structural features of compounds. Photophysical properties such as UV-Vis absorption and fluorescence maxima, and Stokes shift are also reported. To reveal the potential application of novel quinoline derivatives as fluorescence probes the values of quantum yields are determined and the obtained results are explained in terms of structural features of compounds.

The Study of the Effect of Dimethylsulfoxide (or Diethylsulfoxide) on Quinine Sulfate-DNA Binding by UV-Vis and Steady-State Fluorescence Spectroscopies.

The effect of dimethylsulfoxide (DMSO) and diethylsulfoxide (DESO) on binding between quinine sulfate (QS) and DNA was studied by virtue of UV-Vis absorption, steady-state fluorescence spectroscopies, and fluorescence polarization measurements. The binding constant was determined at three different temperatures and the values of standard Gibbs energy change, enthalpy and entropy of binding were determined. The mechanism of binding and the effect of sulfoxides on this process was revealed. The values of binding constant, fluorescence polarization and iodide quenching studies confirmed that the main binding mode in QS-DNA system is groove binding. Addition of sulfoxides does not change the binding mechanism. Moreover, with addition of sulfoxides binding constant increases due to the removal of water molecules from DNA grooves making them more available for QS molecules. To explain the effect of DMSO and DESO on QS-DNA binding the photophysical properties of QS in aqueous solutions of DMSO and DESO were also studied. On the basis of quantum yield of QS in water, DMSO and DESO the types of intermolecular interactions were discussed. The obtained results show that quantum yield of QS in sulfoxides is lower compared with that in water and aqueous solution of 0.1 M H2SO4. QS forms ground state complexes with both DMSO and DESO that are stronger fluorophores compared with free QS molecules.

Fluorescence anisotropy studies on the Hoechst 33258-DNA interaction: the solvent effect.

Fluorescence anisotropy method was applied to characterize the interactions of DNA minor groove binder Hoechst 33258 with different solvents without and in the presence of DNA. It is important to study the interaction of small molecules with DNA for the purpose of better understanding the mechanism of their action, as well as to design novel and more effective compounds. Spectroscopic study of the ligand in different binary mixed solvents containing DMSO, alcohols and buffer was carried out. Studies were performed without and in the presence of DNA. Fluorescence anisotropy studies reveal the characteristics of Hoechst 33258 in different mixed solvents. The results show the strong dependence of the anisotropy of Hoechst 33258 on solvent content, viscosity and intermolecular interactions. Communicated by Ramaswamy H. Sarma.

Study of the Interaction of Novel Nonprotein Amino Acids with Trypsin by Steady-State Fluorescence Spectroscopy.

The interaction of (2R, 3S)-hydroxyleucine (trypsin inhibitor) and ß-hydroxyvaline with trypsin has been studied by the steady-state fluorescence spectroscopy. The analysis of fluorescence spectra has revealed the mechanism of binding of these nonprotein amino acids to trypsin. According to the docking (2R, 3S)-hydroxyleucine form hydrogen bonds with trypsin having little effect on tryptophan and tyrosine residues in enzyme molecule. The results obtained in this study indicate that fluorescence of trypsin is quenched at high concentrations of amino acids. Thus fluorescence spectra analysis confirms data obtained by molecular docking.

Photophysical properties of methylene blue in water and in aqueous solutions of dimethylsulfoxide.

A detailed study of the effect of aprotic polar solvents such as dimethylsulfoxide on methylene blue (MB) was carried out through a combination of UV-vis absorption and steady-state fluorescence spectroscopy techniques at 293.15 K. In aqueous solutions MB tends to exhibit strong tendency to aggregate. The dimerization behavior of MB in water was analyzed in terms of monomer-dimer equilibrium. The addition of dimethylsulfoxide prevents dimerization of dye molecules. From absorption spectra the dimerization constants and changes of standard Gibbs energy were calculated. From the steady-state fluorescence spectra the quantum yields and Stokes shifts were determined. To explain the effect of dimethylsulfoxide properly the other polar aprotic solvents such as N, N-dimethylformamide, acetonitrile and acetone were used. It is suggested that water structural effect is the major factor in aggregation phenomenon. Moreover the quantum yield increases drastically in dimethylsulfoxide compared with water assuming that MB may be characterized as viscosity probe.

The effect of dimethylsulfoxide on absorption and fluorescence spectra of aqueous solutions of acridine orange base.

The photophysical properties of aqueous solutions of acridine orange base (AOB) in wide concentration range of dimethylsulfoxide (DMSO) were studied by using absorption and steady-state fluorescence spectroscopy techniques at room temperature. The absorption spectrum of acridine orange in water shows two bands at 468 and 490 nm which were attributed to the dimer ((AOBH)2(2+)) and monomer (AOBH(+)) species respectively. In DMSO solution for the same AOB concentration only the basic form was detected with the band at 428 nm. The addition of DMSO to AOB aqueous solution leads to the decrease of absorption band at 490 nm and the new absorption band increases at 428 nm due to deprotonated (basic) form of AO and the first isosbestic point occurs at 450 nm. The evolution of isosbestic point reveals that an other equilibrium, due to the self-association of DMSO molecules takes place. From the steady-state fluorescence spectra Stokes shifts were calculated for AOB in aqueous and DMSO solutions. The addition of DMSO into the aqueous solution induced the enhancement in the fluorescence intensity of the dye compared to those in water.