Intensive property reduction potential

Mavicyanin (Mj = 18,000) is obtained from green squash (Cucurbito pepo medullosa), where it occurs alongside ascorbate oxidase [64]. It has a peak at 600 nm (e 5000 M cm and reduction potential of 285 mV. Further studies on this and the mung bean and rice bran proteins [65, 66] would be of interest. All the above type 1 Cu proteins have an intense blue color and characteristic narrow hyperfine EPR spectrum for the Cu(II) state. Table 3 summarizes the properties of those most studied. There is some variation in reduction potential and position of the main visible absorbance peak. In the case of azurin, for example, the latter is shifted from 597 to 625 nm. Stellacyanin has no methionine and the identity of the fourth ligand is therefore different [75]. The possibility that this is the 0(amide) of Gln97 has been suggested [63b]. It now seems unlikely that the disulfide is involved in coordination. Stellacyanin has 107 amino acids, with carbohydrate attached at three points giving a 40% contribution to the M, of 20,000 [75]. 

Figure 2. Schematic representation of some relevant ground and excited-state properties of Ru(bpy)j. MLCT and MLCT are the spin-allowed and spin-forbidden metal-to-ligand charge transfer excited states, responsible for the high intensity absorption band with = 450 nm and the luminescence band with = 615 nm, respectively. The other quantities shown are intersystem crossing efficiency energy (E°°) and lifetime (x) of the MLCT state luminescence quantum yield ( ) quantum yield for ligand detachment (O,). The reduction potentials of couples involving the ground and the MLCT excited states are also indicated.

Electronic Structures Absorption Spectra Fluorescence Intensities Electrochemical Properties (Oxidation/Reduction Potentials) Electron Flow in Molecular Wires Magnetic Interactions... 

Blue copper proteins have a single Cu atom at the active site, and three characteristic properties (1) an intense blue color at —600 nm, with absorption coefficients of 2000-6000 M cm arising from S(Cys) ()u(II) charge transfer (b) an unusually narrow hyperfine coupling (A values of 0.0035-0.0063 cm ) in the EPR spectrum of the Cu(II) protein due to asymmetry at the metal and (3) high reduction potentials (range 184-680 mV) as compared to the aqua Cu(II/I)... 

Warning Since reduction potentials are intensive properties, we do not multiply the half reaction potential by the number of times it occurs. 

Since the number of electrons lost must equal the number gained, the half-reactions must be multiplied by integers as necessary to achieve the balanced equation. However, the value of%° is not changed when a half-reaction is multiplied by an integer. Since a standard reduction potential is an intensive property (it does not depend on how many times the reaction occurs), the potential is not multiplied by the integer required to balance the cell reaction. 

Because electrical potential measures potential energy per electrical charge, standard reduction potentials are intensive properties. <3=t (Section 1.3) In other words, if we increase the amount of substances in a redox reaction, we increase both the energy and the charges involved, but the ratio of energy (joules) to electrical charge (coulombs) remains constant (V = 1/C). Thus, changing the stoichiometric coefficient in a half-reaction does not affect die value of die standard reduction potential. For example, for... 

Although we must multiply the iodide half-reaction by 3 to obtain a balanced equation, we do not multiply the E° value by 3. As we have noted, the standard reduction potential is an intensive property and so is independent of the stoichiometric coefficients. 

AElectrons flow from the anode, where oxidation occurs, to the cathode, where reduction occurs. The electrons always flow from the anode to the cathode no matter what type of battery. 21.58 A D-sized alkaline battery is larger than an AAA-sized one, so it contains greater amounts of the cell components. The cell potential is an intensive property and does not depend on the amounts of the cell components. The total charge, however, does depend on the amount of cell components, so the D-sized battery produces more charge. 

It is important to understand that the standard reduction potential is an intensive property (like temperature and density), not an extensive property (like mass and volume) [ M4 Section 1.4]. This means that the value of the standard reduction potential does not depend on the amount of a substance involved. Therefore, when it is necessary to multiply one of the half-reactions by a coefficient in order to balance the overall equation, the value of for the half-reaction remains the same. Consider a galvanic cell made up of a Zn half-cell and an Ag half-cell ... 

Notice that the standard reduction potentials of the half-reactions are not multiplied by their coefficients in the balanced overall equation. Recall your study of properties of matter from Chapter 3. Standard potential is an intensive property that does not depend on the amount... 

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