Electrochemistry And Surface-Enhanced Raman Spectroscopy Of Azopurine

Electrochemical method is an important tool to characterize the electrochemical interfacal system,and thermodynamic data of electrode reactions.It also can be used to detect unstable intermediates in an electrochemical reaction,and then deduce the kinetic constant of the reaction.As one of the most widely used electrochemical methods,cyclic voltammetry(CV)has been developed for half a century since its emergence in the 1960s and has become a standard test method for electrochemistry.It is a transient measurement method,which is the case of continuous linear change of electric potential,widely applied in the initial electrochemical research of the new system,and also can be used to obtain relevant information of complex electrode reactions.In order to obtain the electrochemical information varying with potential and current and molecular fingerprint information at the same time,we used the electrochemical surface-enhanced Raman spectroscopy(EC-SERS)on in-situ spectroscopic technology.In the EC-SERS experiment,the laser is focused on the local area of the electrode surface.The molecules adsorbed on the nanostructured surface of the electrode can get amplification Raman signals with million times under the enhancement effect of SPR.This makes the EC-SERS to detect the signals of the adsorbed molecules significantly stronger than species in the solution of phase.Simutaneously,for surface species adsorbed on the electrodes,the EC-SERS effectively avoid the interference of other species in the electrolytic solution phase.In the previous work of our group,it has been found that the SERS spectra of azopurine adsorbed on silver nanoparticles changes with the pH values.This is preliminarily considered that changing the pH value causes a spontaneously chemical reaction of azopurine.In this work,we will focus on a deeper understanding on the chemical reaction process of azopurine with pH values,and discuss the chemical properties of azopurine from the electrochemical point of view.The research of the thesis is mainly divided into two parts:The first is to study the electrochemical properties of azopurine by CV curves on polished gold and silver electrodes.Firstly,the CV of different concentrations and different scanning rates were tested in the PBS buffer and HAc-NaAc buffer containing azopurine.A pair of redox peaks were found on the voltammetry.Secondly,it is found that this is a two-electron two-proton reaction controlled by adsorption species under the present experimental conditions.Thirdly,the apparent transfer coefficient and the apparent rate constant k,of the electrochemical process were determined by fast-scan cyclic voltammetry(FCV).Furthermore,the electrochemical behavior of silver nanoparticles was also studied by cyclic voltammetry.The second is to use the EC-SERS technique to characterize the azopurine reactants and products in the electrochemical redox process.Firstly,it was found that azopurine was reduced to 1,1'-dihydroazopurine under acidic conditions on the basis of comparing normal Raman spectra of azopurine with EC-SERS on silver nanoparticles modified electrode and gold nanoparticles modified electrode.This reaction can spontaneously occur on gold and silver nanoparticle modified electrodes.Secondly,the reaction of azopurine on different nanoparticle modified electrodes is different in alkaline solution.Our results show that azopurine can be reduced to 1,1'-dihydroaza-adenine on gold nanoparticles,but it is reduced to adenine on silver nanoparticles at more negative potentials.By combining the electrochemical characterization and in-situ EC-SERS of azopurine adsorbed on metal nanoparticles modified electrodes under different experimental conditions,on the one hand,we can understand the system more deeply.The intrinsic mechanism of the electrode reaction process leads to a further understanding of the chemical properties of azo derivatives.On the other hand,we can carefully explore the electrochemical reaction under various conditions,such as electrolytes,pH values,applied potential,and excitation wavelength,etc.,so that the nature of the electrochemical process was reavealed.