[Study on the interaction of ofloxacin and levofloxacin with DNA].

The interaction of ofloxacin (OFLX) and levofloxacin (L-OFLX) with calf thymus DNA(ctDNA)was studied by absorption spectra, fluorescence spectra, fluorescence polarization, and K3Fe(CN)6 quenching tests to show the interaction differences and binding modes. The experimental results of absorption spectra indicated that when ctDNA was added to the solution of OFLX or L-OFLX and its concentration was increased, the hypochromic effects in the absorption spectra of OFLX or L-OFLX were observed, and no changes in its maximum absorption wavelengths were found. Fluorescence spectroscopy was an appropriate method to study the interactions between small molecule ligands and biomacromolecule. From the measurements of emission peaks, transfer efficiency of energy, lifetime and so on, a vast amount of information about the interaction will be given. The experimental results indicated that the fluorescence quenching effects of OFLX and L-OFLX were not initiated by the dynamic collision according to the Stern-Volmer equation, and caused by the static quenching of compounds formation. From the Scatchard equation, its association constants were obtained for OFLX and L-OFLX to be 1.15 x 10(5) and 3.75 x 10(5) L x mol(-1), respectively. On the basis of the absorption spectra and the association constants, it was showed that the interaction between L-OFLX and ctDNA was stronger than that of OFLX and ctDNA. There are three modes for the binding of small molecules to DNA double helix: electrostatic binding, groove binding and intercalative binding. The interaction modes between OFLX, L-OFLX and ctDNA were studied by fluorescence polarization, the K3Fe (CN)6 quenching tests and so on. The results showed that the interaction modes of OFLX and L-OFLX with ctDNA were both groove binding.

[Fluorescence characteristic of enro floxacin sensitized by rare earth ion and its analytical application].

The fluorescence characteristic of enrofloxacin-yttrium (III) (ENRX-Y3+) was investigated in the present paper. Experimental results indicated that Y3+ ion could greatly increase the fluorescence intensity of the system. From this, a simple and sensitive method of determining the ENRX was set up. The fluorescence intensity of the system was measured with a 1 cm quartz cell at the excitation wavelengths of 274 nm and the emission wavelengths of 424 nm. The optimal conditions were obtained as follows: pH = 5.5-6.2, 0.1 mol x L(-1) hexamethylenamine (HMA) buffer, the concentration of yttrium(III) was 1.0 x 10(-4) mol x L(-1). Under the optimal conditions, the fluorescence intensity of the system showed a good linear relationship with the concentration of ENRX in the range of 1.0 x 10(-9) - 5.0 x 10(-6) mol x L(-1), its correlation coefficient was 0.9981, and the detection limit (S/N=3) was 2.3 x 10(-10) mol x L(-1). Interferences of common metal ions and other pharmaceuticals usually used for the compatibility of medicines with the fluorescence intensity of the system were studied, and the results showed that most metal ions except Tb3+, Cu2+ and AP+ and the compatible medicines used together with ENRX did not interfere with its determination. The recovery tests in the compatible medicines were also performed, and the results showed that all the recoveries were in the range of 98.0%-107.0%, and RSDs were in the range of 0.9%-4.5%. The presented method was used to determine the ENRX in actual pharmaceutical samples which were used in the treatment for animals as compared with the reported method of terbium (III) luminescence probe, and the results were satisfactory. In addition, the luminescence mechanism of the ENRX-Y3+ system was also discussed.

[Determination of ascorbic acid by indirect fluorimetry].

Experiments indicated that cerium(IV) ion which could not emit fluorescence was deoxidized by ascorbic acid to cerium(III) ion which could emit its characteristic fluorescence in water solution, while sodium hexametaphosphate added could greatly enhance the fluorescence intensity of the system. From this, an indirect sensitive method for determining ascorbic acid was developed. The fluorescence intensity of the system was measured in a 1 cm quartz cell with the excitation and emission wavelengths of 303 and 340 nm, respectively. The results showed that the fluorescence intensity of the system presented a linear relationship with the concentration of ascorbic acid in the range of 1.0 x 10(-7)-8.0 x 10(-6) mol x L(-1), the correlation coefficient r was 0.9997, and the detection limit (S/N = 3) was 1.6 x 10(-8) mol x L(-1). The presented method was used to determine ascorbic acid sample and vitamin C tablet, and the results were satisfactory.

[Study on the determination of ciprofloxacin by the terbium (Ill) ion fluorescence probe sensitized by the surfactant].

The experiments indicated that terbium(III) ion could complex ciprofloxacin, then emitted the characteristic fluorescence of terbium(III) ion. When the surfactant of SDBS was added, the fluorescence intensity of the system was greatly increased. From this, a sensitive method of determining the ciprofloxacin was developted. The fluorescence intensity was determined by a 1 cm quartz cell with the excitation wavelength of 300 nm and the emission wavelength of 545 nm. The optimal conditions are as follows: pH 8.0-8.5, the concentration of terbium(III) is 5.0 x 10(-5) mol x L(-1), the surfactant concentration of SDBS is 8.0 x 10(-4) mol x L(-1). The linear range is 2.5 x 10(-6) mol x L(-1) -2.0 x 10(-8) mol x L(-1), and the detection limit (S/N = 3) is 4.0 x 10(-9) mol x L(-1). The presented method was applied to determine the real pharmaceuticals of ciprofloxacin.