The Spectroscopic And Electrochemical Study Of Langmuir-Blodgett Films Of Heme

Heme (iron porphyrin in nature) is a very important biologic compound. It has lots of function in life. Langmuir-Blodgett (LB) technique is an efficient way to simulate biologic films. The study on the LB films of heme is significant.This thesis includes three parts. First, studies on the characteristics of the LB films of heme. Second, studies of the electrochemical behaviors of the LB films of heme and the electrocatalytic effects of oxygen reduction. Last, studies of the electrochemical behaviors of catechol and ascorbic acid on the Heme LB/GC electrode. The main contents are as follow:1. Heme can form stable monolayer on pure water (subphase). The effects of pH on the surface pressure-area (Ï€-A) isotherms were discussed. When the pH is between 3-7, the ability of forming monolayer of heme is better. Some information about the orientation of heme in LB films were obtained from the UV-visible and polarized UV-visible spectra, low angle X-ray diffraction, and fluorescent spectra. Since the ordered arrangement of heme molecules increases, the absorbance of the LB films of heme is greatly increased with the increase of deposition pressure of heme.2. The electrochemical behaviors of Heme LB films on glass carbon electrode (Heme LB/GC electrode) were investigated with cyclic voltammetry. It's shown that Heme LB/GC electrode has a good ability to electro-catalyze the oxygen reduction. Some affairs influencing the signal on the Heme LB/GC electrode were studied and the optimum condition was given. The affairs mainly include the effects of molar ratio of heme to cephalin, the number of LB layers, the pH of the solution and other variables. The results indicate that the peak current (ip) of reduction increases with the increasing of scan rate and a plot of ip vs v1/2 is linear. Then the difference of the electrochemical behavior of the heme in ordered LB films was compared with those in cast film and aqueous solution. The electro-catalyzed kinetics of Oxygen reduction on Heme LB films was studied using potential step and rotating disk electrode. The transference number of electrons was calculated to be 4, based on the slope of Q-t1/2curve and I-lim-w1/2 curve. The catalytic mechanism belongs to the ECE process.3. The new Heme LB/GC electrode cannot promote the oxidation of catechol and ascorbic acid, but the Polyheme LB/GC electrode can do.