| Nucleic acids molecular "light switches" are a kind of polypyridyl ruthenium(II) complexes that are not photoluminescent in water but emit either in nonaqueous solvents or in the presence of DNA. The optical properties of molecular "light switches" have been studied in this thesis. The interactions between "light switches" and DNA have also been studied by fluorescence and Rayleigh light scattering (RLS) spectra. Based on this, novel methods for DNA determination were proposed. The main work are summarized as follows:1. The emission spectra of molecular "light switch" complex Ru(bpy)2(dppx)2+ in different environments have been studied. It was found that the solvent polarity and the ability of donating and transfering proton are the important factors in predicting luminescence intensity of Ru(bpy)2(dppx)2+in different systems. The fluorescence intensity of Ru(bpy)2(dppx)2 + in organic solvents will decrease dramatically with the increasing concentrations of water in the solutions, which follow the Perrin sphere model. The effect of base content of DNA on the fluorescence spectra of Ru(bpy)2(dppx)2+ has also been studied. Based on this, a fluorometric method was developed for the determination of exocellular DNA in a bacteria culture using molecular "light switch" complex Ru(phen)2(dppz)2+.2. The interacting mode between adriamycin (ADM) and DNA has been studied using molecular "light switch" complex Ru(bpy)2dppx2+ as spectroscopic probe. The influence of ADM on the fluorescence and Scatchard equation of Ru(bpy)2dppx2+-DNA system indicate that ADM intercalate in the base pairs of DNA. Compared with normal DNA interacting mode spectroscopic probe Ethidium bromide, Ru(bpy)2dppx2+' has the advantages of higher sensitivity, lower toxicity, higher stability and simplicity.3. A novel method was developed for selective determination of DNA with quinoline sulphate. The fluorescence of quinoline sulphate was greatly quenched by DNA in the pH range of 2-4, and the decreased intensity of fluorescence was proportional to the concentration of DNA. The liner range of the calibration curve was 0-700 ng/ml with the detection limit of 5.9 ng/ml. The proposed method was successfully used to determine the plasmid DNA extracted from colibacillus, which was dealt with RNase before determination.4. Based on the enhancement effect of DNA on the RLS signals of molecular "light switches" under acidic condition, a sensitive and convenient method for DNAdetermination was proposed. The experiments indicated that, under optimum conditions, good linear relationships were obtained between the RLS intensity and the concentration of nucleic acids. The detect limits of calf thymus DNA were 13.0 ng/ml. 4.2 ng/ml, 51.5 ng/ml and 3.0 ng/ml for four different "light switches", respectively. Plasmid DNA extracted from the bacillus subtilis were determined by the proposed method with satisfactory results.5. The solution of Ru(phen)2dppz2+ and SDS has high RLS signals due to Ru(phen)2dppz2+ assemble on the surface of the SDS micelle. Because of the high affinity constant (Kel61 mol"1) between Ru(phen)2(dppz)2+and DNA, the adding of DNA in the solution of Ru(phen)2(dppz)2+-SDS makes the dissociation of Ru(phen)2(dppz)2+ - SDS, and results in decreasing of the RLS signals and increasing of the absorbance. Based on this, a novel method is proposed for DNA assay.6. The interactions between two novel polypyridyl ruthenium(II) complexes Ru(bpy)2PIP(V)2+ and Ru(bpy)2PIP(IV)2+ and DNA have been studied by the RLS spectra. Under optimum condition, good linear relationships were obtained between the RLS signals and the concentrations of DNA. The linear ranges for the determination of DNA are 16 - 5120 ng/ml and 16 ~ 4000 ng/ml, respectively. The detect limits are 5.02 ng/ml and 10.6 ng/ml, respectively.7. The interactions between metal ions and DNA have been studied by the RLS spectra. In the acidic condition, the RLS signals of metal ions were linear increased by DNA, especially the transition metal io...
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