Redox and Electrochemistry

Enzymes that catalyze redox reactions are usually large molecules (molecular mass typically in the range 30-300 kDa), and the effects of the protein environment distant from the active site are not always well understood. However, the structures and reactions occurring at their active sites can be characterized by a combination of spectroscopic methods. X-ray crystallography, transient and steady-state solution kinetics, and electrochemistry. Catalytic states of enzyme active sites are usually better defined than active sites on metal surfaces. 

The determination of H202 is very important in many different fields, such as in clinical, food, pharmaceutical, and environmental analyses [202], Many techniques such as spectrophotometry, chemiluminesence, fluorimetry, acoustic emission, and electrochemistry methods have been employed to determine H202. Electrochemical methods are often used because of their advantages. Among these electrochemical methods, the construction of the mediator-free enzyme-based biosensors based on the direct electrochemistry of redox proteins has been reported over the past decade [203— 204], The enzyme-based biosensors, which use cyt c as biocatalyzer to catalyze H202, were widely studied. 

The band gap, determined as the onset of the absorption band in thin films is 2.95 eV (425 nm). Janietz et al. [252] used the onset of the redox waves in CV experiments to estimate the /P and Ea energies of the dialkyl-PFs (Figure 2.11). The gap between the obtained energy levels (5.8 eV for 7P and 2.12 eV for EA) IP—EA 3.8 eV is substantially higher than the optical band gap. Although optical absorption and electrochemistry test two physically different processes (vertical electron excitation and adiabatic ionization) and are not expected to be the same,... 

Number of electrons (n). There is one final divergence from standard lUPAC usage that may cause confusion. In normal thermodynamics, the symbol n is used for amount of substance . An older convention is followed in electroanalytical work, and electrochemistry in general, such that n means simply the number of electrons involved in a redox reaction. Normal lUPAC representation would use V for this latter parameter since the number of electrons is a stoichiometric quantity. The opposition from electrochemists has been so concerted that lUPAC now allows the use of n as a permissible deviation from its standard practice. 

Cobalt(II) hexacyanoferrate, formally similar to Prussian blue, exhibits a far more complex electrochemistry. Only recently, Lezna etal. [65] succeeded in elucidating this system by a combination of in situ infrared spectroscopy and electrochemistry, and ex situ X-ray photoelectron spectroscopy. Figure 8 shows the pathways of the three different phases involved in the electrochemistry, and their interconversion by electrochemical redox reactions and photochemical reactions. 

Abstract This chapter discusses the electronic absorption spectra and electrochemistry of phthalocyanine complexes which are redshifted to 730nm and beyond. These are mainly manganese phthalocyanine derivatives and phthalocya-nines containing sulfur substituents. The chapter concentrates mainly on the work done during the last 10 years. There are 96 references quoted and three detailed tables on the electronic absorption spectra, redox potentials, and analytes that are electrocatalyzed using manganese and titanium phthalocyanine complexes. 

L Her, M, Pondaven A (2003) Redox properties and electrochemistry of phthalocyanines In Kadish KM, Smith KM, Guilard R (eds) Porphyrin handbook, phthalocyanine properties and materials, vol 16, Chap 104. Academic Press, New York... 

Although oxidation-reduction potentials can be treated in a general way, (as in most textbooks of physical chemistry and electrochemistry), here we shall first classify redox systems and then deal separately with the potentials within each class. This not only suits the beginner but has been proved most useful for the study of inorganic qualitative and quantitative analysis. The four classes dealt with here are (a) metal electrodes, (b) simple redox systems, (c) combined redox and acid-base systems and (d) gas electrodes. 

Fig. 44. (a) Faradaic processes involving a redox couple dominated by a CB mechanism on an n-type semiconductor, (b) As (a) for a VB mechanism on a p-type semiconductor, (c) Redox couples and electrochemistry on Ge. 

Thus the pH-Eh-E32- measurements can be employed to characterize the state of reducing environments concerning sulfur chemistry and electrochemistry. The redox level deduced from the Eh measurements should be in agreement with the redox level estimated from the chemical analyses of the sulfur species as found in laboratory experiments. ... 

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