Selected hydrated electron

According to the Marcus theory [64] for outer-sphere reactions, there is good correlation between the heterogeneous (electrode) and homogeneous (solution) rate constants. This is the theoretical basis for the proposed use of hydrated-electron rate constants (ke) as a criterion for the reactivity of an electrolyte component towards lithium or any electrode at lithium potential. Table 1 shows rate-constant values for selected materials that are relevant to SE1 formation and to lithium batteries. Although many important materials are missing (such as PC, EC, diethyl carbonate (DEC), LiPF6, etc.), much can be learned from a careful study of this table (and its sources). 

Ross, A. B. (1975), Selected Specific Rates of Reactions of Transients from Water in Aqueous Solution. Hydrated Electron, Supplemental data, NSRDS-NBS 43, Supplement, National Bureau of Standards, Washington, D.C. 

With the aid of electron tunneling it appears possible to regulate the selectivity of redox conversions. For practically important reactions this has not been realized so far, but that this approach may prove to be useful is demonstrated, e.g. by the data presented in Table 6. In this table, a comparison is made between the rate constants for reactions of three different acceptors with hydrated electrons in liquid water at 298 K and the characteristic times, t, for reactions of the same acceptors with trapped electrons in solid water-alkaline glasses at 77 K. The values of x have been calculated using the values of ve and ae from Ref. [21]. It can be seen in the liquid, when due to diffusion the reagents can approach to within short distances of each other (direct collisions), that the rate constants for all three... 

Anbar M, Bambenek M, Ross AB. Selected specific rates of reactions of transients from water in aqueous solution. I. Hydrated electron. Natl Stand Ref Data Ser, Natl Bur Stand (US) 1973 43 1998 43(Suppl) 67 pp. 

Many of the results from the last decade were obtained by scavenging method but some of them were from direct detection with pulsed beam. We summarize here a selection of important papers concerning the hydrated electron, the hydroxyl radical, the superoxide radical, the molecular product, the hydrogen peroxide, and molecular hydrogen. 

A wealth of information on the reduction of metal ions in aqueous solutions has been obtained and a compilation was published in 1988 [20], However, alkali or alkaline earth metal ions such as Li Na or cannot be reduced by the hydrated electron in aqueous solution but can form an ion pair with the solvated electron in polar liquids. Among the various reactions of the solvated electron, the reduction of halogenated hydrocarbons is often used in radiation chemistry to produce well-defined radicals because of the selective cleavage of the carbon-halogen bond by the attack ofthe solvated electron. This reaction produces the halide ion and a carbon-centered radical, and is of great interest for environmental problems related to the destruction of halogenated organic contaminants in water and soil [21,22]. 

To study their properties, the easiest way is to form them by one-electron reduction of disulfide bonds. Among radicals from water radiolysis, hydrated electron is the most powerful reductant. It reacts with almost all amino acids and especially with the disulfide groups. Using less powerful reductants such as COO radicals, some selectivity in the attack appears. An example is displayed in Figure 3. 

Carbonate radical is generated by the reaction of OH radical with carbonate ion and bicarbonate ion [reaction (19)(20)], so this experiment was done under N20 saturation[reaction (9)]. Carbonate radical has an absorption peak at 600 nm. As well as hydrated electron and sulphate radical, the rate constant of the reaction of carbonate radical with polymer chains[reaction (21)] can be calculated from estimating the slope of the pseudo first-order decay rate of the absorbance at 600 nm against polymer concentration. Then, the rate constants with CM-chitin and CM-chitosan, CM-cellulose were determined as (3.9 6.4)x 105[MXs l](Figure 8). These values are lower than the value of OH radical and sulphate radical, and so this shows carbonate radical is less oxidative than OH radical and sulphate radical. Focusing the rate constants of CM-chitosan, the value at around pH 9.5 is lower than over pH 10. This is because of pKa of amino group, protonation and unprotonation. For a weak reactivity of carbonate radicals, it can be assumed that carbonate radical have a selectivity attacking polymer chains. 

The 2AP radical cations, 2AP +, formed together with hydrated electrons by the photoionization process, rapidly deprotonate to the neutral radicals, 2AP(-H)- [31]. The latter radicals selectively oxidize nearby G bases to form G(-H)" radicals - a process that is completed within 100gs after the actinic laser flash. Combination of the G(-H)" and "N02 radicals occurs on millisecond time scales with similar rate... 

The production of H2 in the radiolysis of water has been extensively re-examined in recent years [8], Previous studies had assumed that the main mechanism for H2 production was due to radical reactions of the hydrated electron and H atoms. Selected scavenger studies have shown that the precursor to the hydrated electron is also the precursor to H2. The majority of H2 production in the track of heavy ions is due to dissociative combination reactions between the precursor to the hydrated electron and the molecular water cation. Dissociative electron attachment reactions may also play some role in y-ray and fast electron radiolysis. The radiation chemical yield, G-value, of H2 is 0.45 molecule/100 eV at about 1 microsecond in the radiolysis of water with y-rays. This value may be different in the radiolysis of adsorbed water because of its dissociation at the surface, steric effects, or transport of energy through the interface. 

Manipulation of the Primary Radicals. In the radiolysis of aqueous solutions, the initially formed radicals can be manipulated via appropriate chemical additives to produce solutions that largely contain a single radical species. Solutions containing primarily the HO radical, the hydrated electron, or the hydrogen atom can be produced to study the reactions of individual radicals. As discussed in later sections, solutions of these selected radicals can then be converted to a variety of radical reactants with careful selection of reaction conditions. 

The radicals e-aq (hydrated electron) and H (hydrogen atom or hydrogen radical) are reducing species, whereas the OH is an oxidizing agent [112]. It is possible to select out a particular radical by alterations of pH and addition of various compounds [35]. One method of generating almost exclusively OH is irradiation of an aqueous solution, saturated with nitrous oxide gas (N20), converting e aq into extra OH (Eq. 12-13) [112]. 

Both of these paths can be studied by pulse radiolysis when selective reductants can be used to reduce the metal complex or the radical source. For example, one can use hydrated electrons to reduce RX (present in excess over M P) and C02 radicals to reduce M "P. On the other hand, if COj is the sole reducing radical in the system, since this does not react rapidly with RX, one can prepare M P and follow its subsequent reaction with RX. Of course, R- can be prepared also by reactions of various precursors other than RX. 

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