| Polycyclic aromatic hydrocarbons(PAHs)are a group of persistent organic pollutants(POPs)with carcinogenic,teratogenic and mutagenic properties.They have been frequently found in contaminated soil,water and air.The PAH contamination has become a worldwide environmental problem in the last decades.PAHs can be absorbed and distributed into the organisms,and more and more studies focus on the interactions of PAHs with biological materials.One hot issue drawing researchers' attentions is how to explore the combinations of PAHs with biological materials through physically weak interactions.Florescence technology has been commonly utilized to clarify the interactions among chemicals.However,little information is hitherto available on the utilization of the florescence technology to explore the physical interaction between PAHs and genetic materials.In the present work,the interactions between PAHs,phenanthrene(Phen)and pyrene(Pyre)as representatives,and DNA in aqueous solution were elucidated using a fluorescence spectroscopy.The effects of different acidity of aqueous solution on the combination of PAHs and DNA were determined using multi-way modeling techniques.Major findings are presented as follows.(1)The interactions between two DNA complexing agents(Phen and Pyre)and DNA were examined using a fluorescence spectroscopy.Phen and Pyre were separately titrated with the DNA in aqueous solution,and then solutions containing the complexing agent were examined following the generation of EEM plots.The binary system titrations provided clear evidence that both Phen and Pyre combined with DNA genetic units;however,the nature of interactions were different,depending on the molecular size of test PAHs.DNA decreased significantly the fluorescence emission intensity of Phen,while a slight decrease was observed in Pyre fluorescence emission intensity due to DNA addition.One binding site was found for Phen-to-DNA combination,but the binding site number of Pyre-to-DNA combination cannot be calculated because there are multiply and very weak attractions between Pyre and DNA.Blue shifts in the wavelength of maximum Phen or Pyre fluorescence emission when adding DNA to Phen and Pyre solution,which is consistent with the idea that a "complex"(PAH-DNA)is being formed.Results of this study provide a new technique for exploring the physical interaction between molecular DNA and PAHs.(2)The effects of different acidity of aqueous solution on the combination of PAHs and DNA were determined using multi-way modeling techniques.Static quenching was obviously observed as a consequence of the ?-stacked non-covalent and non-fluorescent complexes formation between the water-soluble Phen and DNA,and the specific binding interactions of Phen with DNA was found at different acidity in the solution.The heavily acidic condition(pH 3.0)is unfavored of the fluorescence quenching of Phen caused by DNA.This suggests that protonation of phosphate group in extra DNA impedes the combination of Phen with genetic bases in intra DNA.Calculated values of fluorescence quenching constants(Ksv)are in the descending order of pH 9.0(0.34)? pH 7.0(0.36)>pH 3.0(0.26).The binding sites for different acidic treatments are all approximately equal to one,suggesting a major binding site between genetic base and Phen.The interactions of PAHs with DNA exists predominantly blue shift of fluorescence emission wavelengths corresponding to maximal emission intensity.These results prove that the formation of?-stacked complexes inhibits the DNA deprotonation,and a notable finding is the deprotonation against interactions of DNA bases with Phen in aqueous solution.Results of this work would be valuable for searching the PAH fluorescence quenchers,determining their fluorescence decay kinetics,designing the new fluorescent chemosensors and tracing the PAHs in aqueous environments.The results provide insights into the interactions of the water-soluble PAHs with biological active substances,which might benefit our understandings of the DNA pharmacology. |
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