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生物电分析化学 Electroanalytical Chemsitry and Its Biological Applications 主讲人：刘宏 教授 2015 年秋

生物电分析化学 Electroanalytical Chemsitry and Its Biological Applications 主讲人：刘宏 教授 2015 年秋. Electrode Reactions with Coupled Homogenous Chemical Reactions. Stable Uptake of a 2 nd electron (EE) Rearrangement (EC) Dimerization (EC2)

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生物电分析化学 Electroanalytical Chemsitry and Its Biological Applications 主讲人：刘宏 教授 2015 年秋

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  1. 生物电分析化学Electroanalytical Chemsitry and Its Biological Applications主讲人：刘宏 教授2015年秋

  2. Electrode Reactions with Coupled Homogenous Chemical Reactions • Stable • Uptake of a 2nd electron (EE) • Rearrangement (EC) • Dimerization (EC2) • Reaction with a electrophile/nucleophile followed by an additional electron transfer and further reaction (ECEC) • Loss of X- followed by dimerization (ECC2) • Loss of X- followed by a 2nd electron transfer and protonation (ECEC) • Reaction with a redox species (EC’)

  3. Reactions with One E Step • CE reaction (preceding reaction): • EC reaction (following reaction):

  4. Reactions with One E Step • Catalytic reaction (EC’):

  5. Reactions with Two or More E Steps • EE reaction • Zn2+ + 2e Zn • b. ECE reaction

  6. Reactions with Two or More E Steps • ECE reaction Overall reaction: Also called electron-transfer-catalyzed substitution reaction

  7. Reactions with Two or More E Steps • Square scheme electrochemistry of cis-W(CO)2(DPE)2

  8. Time Constant For a first-order reaction: A B The time constant, t1 is 1/k For a second-order reaction : A+A B The time constant, t2 is1/kC C is the initial concentration of reactant. t1 is the time required for the reactant concentration to drop to 37% of its initial valuein a first-order process, and t2 is the time required for the concentration to drop toone-half of C in a second-order process. Each electrochemical method is also describedby a characteristic time, te , which is a measure of the period during which a stable electroactivespecies can communicate with the electrode. For a given method with a particular apparatus, a certain range of te (a time window) exists. To study a coupledreaction, one must be able to find conditions that place the reaction‘s characteristic lifetimewithin the time window of the chosen technique.

  9. Time Constant

  10. CrEr process

  11. CrEr process

  12. Following reaction ErCi

  13. Catalytic reaction ErCi’ Zis in large excess, the reaction is a pseudo-first-order reaction

  14. ErEr reaction

  15. ErEq reaction

  16. EqEr reaction

  17. ErCiEr reaction

  18. Assignments 1. In a CV experiment, which parameter is often changed for study coupled-homogeneous reaction. For a first-order homogeneous reaction, what is the time constant of the homogeneous reaction? How to calculate the estimated scan rate of CV based on the time constant? 2. How does the shape of CV changed due to a coupled following reaction in an EC process. Is the shape change also a function of scan rate. 3. What is EC’ process. In the EC’ process which species is the catalyst, does the amount of the catalyst change during the reaction process.

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