Fluorescence Quenching Of Ofloxacin By Metals And Dissolved Organic Matter

In recent years,antibiotics have been widely detected in the environment.Once the antibiotics entered the environment,they could be hardly removed completely.If they presence in the environment,they will promote the generation of antibodies in microorganisms?such as virus?.These microorganisms will transport and transformation in the environment,showing drug-resistance to antibiotics.This process can bring serious health threat to human,animals and plants.Heavy metal pollution has been a hot research topic for a long time.As we all know that excessive amount of heavy metals will cause biological toxic effects to organisms in the environment.Heavy metal pollution will also bring food security problmes.Heavy metal pollution in the farmland has become an important environmental issue.In fact,in the next 30-40 years,the growing heavy metals in the soil will cause great threat to the land which we can use,so in order to relieve the problem effectively,the study of heavy metals in environmental behavior is urgently.An increasing attention has been on the dissolved organic matter?DOM?due to the complexity of its structure and its migration in the environment changeful.Coexistence of antibiotics and other contaminants?e.g.,heavy metals,DOM?is ubiquitous in the environment,their interaction will change their behavior and risk in the environment,only to find out their interaction mechanism can predict their risks and laws during migration in the environment reasonably,so we can establish a reasonable and reliable pollution control measures effectively.In this study,the mechanism analysis of ofloxacin?OFL,as a representative of antibiotics?with metal ions,DOM interaction using the method of fluorescence quenching,which can provide a theoretical basis for the environmental risk assessment of antibiotics.In this thesis,the major findings and conclusion of the study were as follows:?1?This study suggests that the data of the interaction between OFL and metal ions?DOM using fluorescence quenching method is reliable.The study conducted the fluorescence quenching data for the correction of inner filter effect?IFE?and temperature correction,so that the data is reliable and comparable.?2?According to Stern-Volmer curve under different temperatures,we know that the quenching between OFL and Cu?II?was static quenching,R² of the linear fit were all above 0.99,which meant that the fitting was good;according to the exclusion of anion in the copper nitrate and the degradation of OFL under the presence of Cu?II?,which proved that OFL fluorescence quenching came from the interaction between OFL and Cu?II?.?3?The OFL-Cu???interaction was quantitatively described using a stoichiometry equation.The calculation suggested that OFL-Cu?II?interaction was the mixture of 1:1 and 1:2 complexes.The negative ?G values and the negative ?H values suggested that the complexation is a spontaneous and exothermic process.Cation-? binding was excluded and the complexation of Cu???with OFL ketonic and carboxyl groups was proposed through UV-visible spectrum characterization,pH dependent complexation,and thermodynamic analysis.?4?The interaction between OFL with different batches of extraction DOM?DOM-4-DOM-7?in the ultra pure water is disorder from DOM-4 to DOM-7,which maybe because there was not a single mechanism between OFL and DOM,but the results of a variety of mechanisms were involved;also maybe for the degradation of OFL or DOM,and the degradation products were so complex that affecting the interaction between OFL and DOM.?5?The binding of OFL-DOM in the background water successively weakened from DOM-4 to DOM-7,from the lower n value of fitting data can be seen that not only the binding of OFL and DOM is non-linear,but also in a plurality combined louses.The combined was more and more weaken,according the elemental analysis and IR spectra,we made an conclusion like that:the hydrophobic effect may contribute to the OFL-DOM interaction.?6?According to the effect of K⁺ on the OFL-DOM system,we can conclude that whether K⁺ was in the background water or ultra pure water,it is not affected the interaction of OFL-DOM system,for the phenomenon of background water,we can explain like that K⁺ neither has the ability of complexation,nor has the function like the bridge,also could be a simple interaction between OFL and DOM,so cation has no effect on their interaction.?7?According to the effect of Cu²⁺ on the OFL-DOM system,we can have a verdict that Cu²⁺ in the OFL-DOM system,regardless of background water or ultra pure water,Cu²⁺ both has a promoting role on the interaction of the OFL-DOM,also the interaction of ultra-pure water significantly stronger than the background water.This possible because the addition of Cu²⁺ may first complex with OFL or DOM,then the formation of complex macromolecules may expose more binding sites,so the combination had been enhanced;background water ions occupied the binding sites on OFL or DOM,which made the binding in the background water weaker than that of ultra pure water.