Preparation Of Zinc-tetraarylporphyrins And Investigation Of The Electron Transfer At The Liquid/liquid Interface

Porphyrins and their derivatives are natural macrocyclic compounds,which are paid an increasing attention because of their excellent optical and electric properties.It is reported that the varied coordinated metal ions and substituents have great effect on the physical and chemical properties of porphyrins.Hence,investigation of the effect of the structure variation on the property of porphyrin facilitates our understanding the biological activity and mechanism of porphyrin compound in organism.Porphyrins play important roles in organisms.They participate in several important physiological processes,such as photosynthesis and respiratory chain reaction in mitochondria.These reactions occur at the biological membrane interface.Liquid/liquid interface is regarded as the simplest simulated biological membrane model because of its soft and free characteristics and close-packed arrays of immiscible ions.The charge transfer process at the liquid/liquid interface is one of the most fundamental and important physicochemical processes,which also is the essential and nuclear content of the interfacial electrochemistry.Investigation of the charge transfer at the liquid/liquid interface and corresponding chemical reactions is in favor of our understanding of the biochemical processes at the membrane interface in organisms.A series of zinc-tetraarylporphyrins are designed and synthesized in this thesis in order to investigate the effects of systematic meso-π-extension on the physical and chemical properties of zinc porphyrins.The single step and consecutive two step electron transfer of a series of zinc-tetraarylporphyrins are investigated by scanning electrochemical microscopy and thin-layer cyclic voltammetry.This thesis includes the following five parts:Chapter One:ReviewThe investigation progress of porphyrin compounds was reviewed.The synthetic methods of porphyrins and corresponding merits and demerits were summarized.The progress and theoretical basis of the interfacial electrochemistry at liquid/liquid interface were stated.The research methods for study of interfacial electrochemistry at liquid/liquid interface and corresponding principles were introduced.Chapter Two:Synthesis and characterization of zinc-tetraarylporphyrinsThe Adler-Longo method was adopted to synthesize three kinds of tetraarylporphyrins and their zinc complexes（zinc-tetraarylporphyrins,ZnTArPs）.The meso-π-extension of ZnTArPs increased at a 2ⁿ pattern,where 2ⁿ was the benzene ring number in an aryl group and the aryl group represented phenyl,naphthyl and pyrenyl group,respectively.The structures and properties of tetraarylporphyrins and their zinc complexes are characterized by nuclear magnetic resonance（NMR）,high resolution mass spectrometer（HR-MS）,UV-vis spectrometry,fluorescence spectrometry,infrared spectroscopy.The UV-vis spectra,infrared spectra and fluorescence spectra of ZnTArPs were compared in order to study the effects of meso-π-extension on the physical and chemical properties.Chapter Three:Investigation of the interfacial electron transfer of zinc-tetraarylporphyrins by using scanning electrochemical microscopyThe scanning electrochemical microscopy（SECM）and conventional cyclic voltammetry were employed to investigate the bimolecular electron transfer reaction between ZnTArPs and hydroquinone（HQ）at the liquid/liquid interface.The effects of meso-π-extension on the interfacial electrochemical properties were also studied.The experimental results showed that the constant composition approximation model was still suitable for the three ZnTArPs-HQ reaction systems.Electron transfer rate constant increased with the increase of K_r.The correlation between the overall driving force and electron transfer rate constant was examined by two ways.One way was to adopt different zinc porphyrins as the reactant in organic phase.The other way was to adjust Galvani potential difference by adjusting the concentration of ClO₄^-in aqueous phase.As a result,the electron transfer kinetics of each ZnTArP-HQ reaction system obeyed the Butler-Volmer theory when the overall driving force was small.Chapter Four:Investigation of the redox properties and interfacial consecutive electron transfer behaviors of zinc-tetraarylporphyrins by using thin-layer cyclic voltammetryThe thin-layer cyclic voltammetry and conventional cyclic voltammetry were adopted to study the effects of meso-π-extension on the interfacial consecutive electron transfer behaviors of zinc-tetraarylporphyrins and redox properties in homogeneous solution.The correlation between the overall driving force and electron transfer rate constant was examined by adopting different zinc porphyrins as the reactant in organic phase.The experimental results showed that the two-step electron transfer rate constants were insensitive to the change of overall driving force in a wide potential range.The structure optimization data of neutral zinc prophyrins showed that zinc-tetraphenylporphyrin was the most active species among neutral zinc porphyrins.In contrast,zinc-tetrapyrenylporphyrin cation was the most active species among tree ZnTArP cations at a fixed valence state.Chapter Five:Investigation of the electron transfer behavior of levodopa at the simulated biological membraneThe nitrobenzene/water interface was used as the simulated biological membrane in order to investigate the interfacial electron transfer behavior of levodopa.Three different zinc-tetraarylporphyrins with systematic meso-π-extension were used as the reactants in organic phase.These zinc-tetraarylporphyrins reacted with levodopa at the liquid/liquid interface.The thin-layer cyclic voltammetry was used to monitor ZnTArPs-levodopa electron transfer reaction systems and to calculate the two-step electron transfer constants.The effects of meso-π-extension on the electron transfer constant of ZnTArPs-levodopa reaction systems were also investigated.The experimental results showed that levodopa was oxidized to generate levodopaquinone under the experimental conditions.With the increasing meso-π-extension,the electron transfer rate constant for the first step slightly increased while that for the second step decreased successively.Hence,the interfacial electron transfer behavior of levodopa was influenced remarkably by the surroundings.