An Electrochemical Study On The Behavior Of Mimic Biomembrane

Nowadays it is taken for granted that the lipid bilayer comprises the fundamental structure of all biomembranes. The recognition of the lipid bilayer as a model for biomembranes dates back only about 75 years or so. The origin of the lipid bilayer concept, however, is much older and traceable for more than three centuries! It all began with the physicist and inventor Robert Hooke of Hooke's Law fame, who in 1665 coined the term 'cell' to describe the unit structure of a cork slice he observed with his primitive microscope. Some three decades later, Isaac Newton estimated the thickness of 'blackest' soap films. Newton's value of 3/8×10⁶ in. when converted into modern units is equal to 9.5nm, which is in excellent agreement with modern measurements. The early observation of 'black holes' in soap films had a profound influence in the development of the lipid bilayer concept of biomembranes and its subsequent experimental realization in bilayer lipid membranes (planar lipid bilayers and spherical liposomes). Without question, the inspiration for these exciting developments come from the biological world, where, for example, Nature uses self-assembly as a strategy to create complex, functional structures such as viral protein coatings, and DNA. Thermodynamics favors self-assembly, if the molecules of an amphipathic phospholipid (e.g. phosphatidylcholine, PC) are in water, the hydrocarbon chains will want to be 'away' from the aqueous solution. They could all go to the top (like oil on water), or they could have the hydrocarbon chains point toward each other. With the hydrocarbon chains pointing toward each other, amphiphilic molecules of phospholipids could form two different configurations. One is a micelle that may be depicted as a ball with the lipid polar groups on the outside and the hydrocarbon chains pointing together, the other a lipid bilayer.Rudin and his coworkers showed in early 1960 that a soap film in its final stages of thinning has a structure comprised of two lipid monolayers sandwiching an aqueous solution. They also showed that, an under water 'lipid film', or a BLM formed from brain extracts was self-sealing to puncture with many physical and chemical properties similar to those of biomembranes. Upon modification with a certain protein (called EIM, excitability-inducing molecule), this otherwise electrically 'inert' structure of about 5 nm thick became excitable, displaying characteristic features similar to those of action potentials of the nerve membrane. The BLM system, as evidenced by the cited references, has since been widely used for investigations into avariety of physical, chemical and biological phenomena including membrane reconstitution, molecularbiology, bio/medical research, solar energy transduction, and biosens or development.The bilayer leaflet model for the structure of biomembranes may be simply state as follows: the basic construct of all biological membranes consists of a bimolecular lipid leaflet (i.e.a lipid bilayer for short) with sorbed non-lipid layers (mostly proteins). In the interior of the bilayer, hydrocarbon chains are held together by London-van der Waals forces and are in a liquid-crystalline state, in physiological conditions. An important evidence in support of the bimolecular leaflet model was the formation of a 'black' lipid membrane of planar configuration discovered inl960. Suffice it here to state that later investigations carried out by many groups have demonstrated that BLMs are excellent experimental models for biological membranes. Lipid vesicles of spherical configuration soon followed this, namely liposomes, described by Bangham. With the availability of planar BLMs and spherical liposomes, it was possible to investigate electrical properties and transport phenomena across an ultrathin (～5nm) bilayer lipid membrane separating two aqueous solutions. Since membrane function and structure are the 'two sides' of the same lipid bilayer, the general ultrastructure of the biomembrane emerging from current work is that the lipids in the form of a bilayer provide the framework for proteins and other constituents, which are immersed to varying degrees in the lipid bilayer. The lipid bilayer of the membrane is actually fluid and has the consistency of olive oil (viscosity～ 1cP). The lipids, proteins, and other constituents are thus perceived to be able to extend freely within the confine of the lipid bilayer. However, the picture is a dynamic one, in that phospholipids and cholesterol form a hydrophobic, fluid bilayer in which functional entities such as receptors, ionchannels, pigments, proteins, etc can be embedded. At the molecula level, both lipids and proteins exhibit asymmetry; the composition of the inside of a membrane is different from the outside. This must be so in order to explain the active transport of species across the membrane. Also active sites of membrane-bound enzymes or immunological determinants are found only on oneside of a lipid bilayer. It is also able to provide us with insights into the mechanism by which energies of various forms (electromagnetic, chemical, electrical, etc.) can be transduced in membrane systems as well as permitting inter- and intracellular exchange of solutes, information and signal transduction.In this thesis, the composition, structure and basic property of biomembrane was simply introduced. The construction method of all kinds of mimetic biomembrane was detailed described. The progress of mimetic biomembrane was simply reviewed. Electrochemistry, biosensor, patch clapm, pattern study of mimetic biomembrane were paid much attention. Electrochemistry, all kinds of spectroscopy and atomic force microscopy were used to study different mimetic biomembrane system, such as supported bilayer lipid membrane, cast lipid film etc. The main results are as follows:1. The article examines membrane permeability and reassembled behavior due to the surfactant hexadecyl trimethyl ammonium bromide (HTABr) addition. The influence of HTABr on s-BLMs was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experimental results show that the HTABr appeared to be an effective ion carrier to facilitate the transmembrane transportation of ferrocyanide/ferricyanide. The permeability of s-BLMs changes with time and concentration of surfactant addition. At the same time, it is interesting to note that phosphatidylcholine molecules can self-assemble again on the surface of Pt electrode within limitative time and/or concentration of surfactant addition. The phenomenon of transmembran etransportation of ferrocyanide/ferricyanide disappeared in the absence of the surfactant hexadecyl trimethyl ammonium bromide.2. Self-assembled monolayer of 1-dodecanethiol was prepared on gold electrode. The different kinds of probes such as ferrocyanide/ferricyanide, dopamine, ascorbic acid and hydroquinone were used to investigate the electron-transfer process in the presence of surfactant hexadecyl trimethyl ammonium bromide. Cyclic voltammetry and electrochemical impedance spectroscopy studies showed the selective electrochemical recognition of probe molecules in solution on self-assembled monolayer of thiol, and the possible mechanism was also discussed.3. The electrochemical behavior of bilayer lipid membranes (l- α -phosphatidylcholine PC) on Pt electrode interacted with heteropolyoxotungstate (K₇[PTi₂W₁₀O₄₀] · 6H₂O, PM-19) was investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). Experiments showed that PM-19 could interact with lipid membranes and lead to the marker ions Fe(CN)₆^3-/ Fe(CN)₆^4- crossing the s-BLMs. It was found that some kinds of micropores had been formed on the film by AFM. This may be helpful to understand biological activity and medical chemistry of polyoxometalates in vivo.4. The free radicals scavenging activity of polysaccharides, which was extracted from Se-enriched corelyceps links, was examined by cyclic voltammetry and UV-vis spectroscopy. The results indicated that the polysaccharides exhibited higher activites of scavenging hydroxyl radicals than metal Se or glucose. Moreover, the presence of polysaccharides can influence the free radicals scavenging activity of catalase, and the possible mechanism of the free radicals scavenging activity of polysaccharides was also discussed.5. The influence of chlorpromazine hydrochloride on bilayer lipid membranes and monolayer of 1-dodecanethiol was investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). Experiments showed that chlorpromazine hydrochloride could interact with lipid membranes and lead to the marker ions Fe(CN)₆^3-/Fe(CN)₆^4- crossing the s-BLMs. changing the structure and properties of thiol monolayer. It was found that some kinds of micropores had been formed on the film, and the possible mechanism was also discussed.