Photo-electrochemical Properties Of Interactions Of Polypyridyl Ruthenium Complexes With DNA And Their Electrochemical Assembly

Ruthenium possesses 4d⁷5s¹ electronic structure and its ions haveforms of Ru(â… ), Ru(â…¡) and Ru(â…¢). Ru(â…¡) can form easily octahedralruthenium (â…¡) complex with chelating atoms. The redox potentials ofruthenium center ion and DNA binding of the complexes are affected byconjugated intensity and spacial structure of ligands. We choose fourpolypyridine ruthenium (â…¡) complexes with different ligands such as A[Ru(bpy)₂tatp(ClO₄)₂], B [Ru(bpy)₂dmt(ClO₄)₂], C [Ru(phen)₂dmt(ClO₄)₂],D [Ru(dmp)₂dmt(ClO₄)₂], and E [Ru(bpy)₃Cl₂] (where bpy=2,2′-bi-pyridine, tatp=1,4,8,9-tetra-aza-triphenylene, dmt=2,3-dimethyl-1,4,8,9-tetraazatriphenylene, phen=1,10-phenanthroline and dmp= 2,9-di-methyl-1,10-phenanthroline) as our researchful object. The effects of theligands on the electronic absorption spectra, fluorescence spectra,electrochemical behavior, electrochemiluminescence properties of thesecomplexes have been investigated. Based on these results, the interactionof these compounds with DNA and their electrochemical assembly in theabsence and presence of DNA are also been studied.In chapter 1, the basic properties of DNA and polypyridyl rutheniumcomplexes are first introduced. Then, the progresses on assembly of DNAand/or polypyridyl ruthenium complexes are also reviewed. Theimmobilization for them on the substrates is fulfilled by using the methodsincluding chemical adsorption, self-assembly monolayer, electrochemicalmethod, Langmuir-Biodgett technique, Biotin-Avidin system, and covalentbinding. In chapter 2, all chemicals, instruments and experimental methodsused in this thesis are briefly described.In chapter 3, the electronic absorption spectra of polypyridylruthenium complexes A, B, C, D and E have been studied in thc absenceand presence of DNA. The results show that the presence of DNA canresult in obvious hypochromism, red shift. According to the hypochromism,bathochromism phenomena, and the binding constants, the interactivestrength of these complexes with DNA conforms the order A＞C＞B＞D. TheDNA binding of the complexes A, B and C is suggested to be intercalativemodes. Furthermore, the effects of ion strength on the interaction of thesecomplexes with DNA have been studied. NaCl concentration of 0.22 molL^-1 is a turning point. When the concentration of NaCl is higher than theturning point, the interaction of complex with DNA becomes extremelyweak.In chapter 4, the fluorescence properties of these complexes A, B, Cand D in buffer solution have been studied. The complexes A, B, C exhibitstrong fluorescence properties at about 590 nm, but D indicates weakfluorescence. The results show that the presence of DNA can enhance thefluorescence strength of these ruthenium complexes at 450 nm excitedlight. At the low ion strength (＜0.25 mol L^-1), fluorescence strengthbecomes stronger with the increasing concentration of DNA. Theconcentration of NaC1 is proved to have an obvious effect on theDNA-binding of these complexes.In chapter 5, the electrochemical properties of these complexes havebeen studied by using the methods such as cyclic voltammetry, differentialpulse voltammetry, the fluorescence microscope imaging. Moreover, theassembly mechanism of these complexes on ITO electrode is explored. Inthe potential range from 0.2 to 1.5 V, a couple of well-defined redox wavesare observed in pH=7.2 buffer solution, the oxidize wave is ascribedRu(â…¢)] from Ru(â…¡). The formal E^o′ of these complexes conforms thefollowing A＞C≈D＞B＞E. The order matches with the conjugated intensity of ligands. When continuous voltammetric sweeping is carriedout in the potential range from 0.2 V to 1.5 V a new wave appears,representing the oxidation of dissolved reactant Ru(â…¡)to form a layer ofproduct Ru(â…¢)adsorbed strongly on the ITO clectrode. Through thefluorescence microscope observation assembled layer on ITO electrode,the orange-red light is discovered at 490 nm excited wavelength. Theelectrochemical properties and assembly of these complexes on theelectrode are affected by the ion strength. High ion strength is discoveredto influence the assembly of these complexes on the electrode.In chapter 6, the electrochemical properties and assembly of thesecomplexes A, B, C, and D on the ITO electrode in the buffer solutioncontaining 0.224 mmol L^-1 DNA have been investigated. The resultsindicate that the redox reaction at more positive potential exhibits a quasi-reversible process. The effects of ion strength on the electrochemicalproperties of the interactive products between these complexes and DNAare discovered. Compared with the in absence of DNA, DNA can promotethe assembly of the complexes on the ITO electrode. The fluorescencestrength of the assembly layer is stronger than the complexes themselves.The electrochemical assembly of these complexes on the electrode isaffected by the ion strength. The high ion strength may be hindered theassembly of the complexes in the presence of DNA. The of the assembledlayer is applied in the determination of the DNA-binding for thesecomplexes. The assembled layer obtained from 0.2 mmol L^-1[Ru(bpy)₂tatp]²⁺/0.224 mmol L^-1DNA in buffer solution is used as theprobe of DNA-binding mode for [Ru(bpy)₂L]²⁺ (L: tatp, bpy, dmt).In chapter 7, the Electrochemiluminescence (ECL) properties of five kinds ofruthenium complexes A, B, C, D and E have been studied. The results show that thesecomplexes exhibit an excellence ECL signals in the absence and presence of DNA,but complexes D has weak ECL intensity. The influence of ion strength on ECLproperties of the ruthenium complexes in buffer solution containing DNA is largercompared with that in absence of DNA.