Electrochemical Analysis in a Liposome Suspension Using Lapachol as a Hydrophobic Electro Active Species

Abstract

This study demonstrated that the electro-chemical analysis of hydrophobic quinones can be performed in liposome suspension systems. We prepared and analyzed liposome suspensions containing lapachol, which is a quinone-based anti-tumor activity compound. In this suspension system, a simple one redox couple of lapachol is observed. These results are quite different from those obtained in organic solvents. In addition, the pH dependence of redox behaviors of lapachol could be observed in multilamellar vesicle (MLV) suspension system. This MLV suspension system method may approximate the electrochemical behavior of hydrophobic compounds in aqueous conditions. A benefit of this liposome suspension system for electrochemical analysis is that it enables to observe water-insoluble compounds without using organic solvents.Key words cyclic voltammogram; lapachol; liposome; multilamellar vesicle (MLV) Electrochemical analyses of organic compounds with cyclic voltammetry or pulse voltammetry provide us general information about the redox property of those compounds. Commonly, organic solvents are used for the analysis of organic compounds with an excessive amount of supporting electrolytes such as tetraalkyl ammonium salts. The combination of an organic solvent with an electrolyte enables it to analyze electrochemical behaviors of organic compounds. However, the results highly depend on the stabilization energy from organic solvents and electrolytes, especially redox potentials are very sensitive to electrolyte concentrations.1,2) This mutual dependence sometimes causes problems in understanding the meaning of the potentials.On the other hand, quinones play an important role in biological systems and serve as active sites for quinoenzymes in biological functions. It is presumed that the redox properties of quinones are controlled by hydrogen bonding with surrounding proteins or solvents. As a result, hydrogen-bonding interactions have been the primary focused of most studies. [3][4][5] Most studies are performed using quinone compounds and proton donors in coexistence with organic solvents, so as to increase the solubility. However, it is unclear whether the results of an electrochemical measurement using organic solvents reflect real in vivo behavior.We propose that liposome suspensions might serve as a substitute for organic solvents. Liposomes have been studied as an artificial biomembranes and also play important roles as drug delivery systems. The possibility of liposomal use diverges into many scientific branches. Recently, an interesting study reported that electrochemical measurements were performed using a liposome-modified electrode.6,7) On the basis of these studies, we attempted to perform electrochemical measurements using a liposome suspension in place of organic solvents. Results and DiscussionPreparation of a Liposome Suspension Using a Hydrophobic Electro-Active Compound First, we tried to prepare electro-active liposome suspensions. A chloroform solution containing soy lecithin (200 mg) is taken in a round...

Study on Redox Properties and Cytotoxicity of Anthraquinone Derivatives to Understand Antitumor Active Anthracycline Substances

“…Many studies on the redox properties of this anthraquinone derivative have been reported. [4][5][6][7][8] Most of these relate to anion radicals and include changes in reduction potential because of intramolecular and intermolecular hydrogen bonds, 5) and disproportionation/comproportionation reactions of reductants and dianions of anthraquinone 7) ; there are no reports on the properties of oxidized radicals.…”