Yield escape radical

In 1981, the author s group found large MFEs and MIEs on the radical pair lifetime (Trp) and the escape radical yield (Fe) under magnetic fields of 0 - 70 mT with an ns-laser photolysis at room temperature for the photoreduction reactions of benzophenone (BP), benzophenone-sodium dodecyl sulfate (SDS) solutions [1]. Here, micellar molecules act as hydrogen donors (RH). The scheme of such photoreduction reactions of the benzophenone isotopes (XCO) can be represented by the following reaction scheme ... 

Fig. 7-2. Plots of values proportional to the escape radical yield (Fe) against magnetic fields (S) observed at 525 nm for a micellar SDS solution of ( ) BP, (o) BP-dio, and ( ) BP- C. (Reproduced from Ref. [lb] by permission from The American Chemical Society)...

With an ns-laser photolysis apparatus, Steiner measured the escape radical yield (d>p) in the absence and presence of an external magnetic field below 0.414 T, exciting thionine (TH" ) at 500 nm and observing its semiquinone (TH2 ) absorption at 780 nm. He obtained the relative MFE (AR) defined as... 

The author s group [12] tried to find saturation behavior of the MFEs due to the AgM in fluid solutions with our pulsed magnet and found that the MFEs on the escape radical yield (1e(B)) observed for the photoreduction of 4-methoxybenzophenone with thiophenol (Reaction S-5 in Table 7-2) were almost saturated by the fields of -30 T. The isotropic g-values of the thiyl and ketyl radicals have been determined to 2.0082 and 2.0027 so Ag=0.0055 [12]. From ns-laser photolysis measurements with our electromagnet, superconducting magnet, and pulsed magnet, we observed the time profiles of the transient absorption (A(f) curves) of the ketyl radical and obtained the MFEs (A(B)=Ye(B)/1e(0 T)) on the )4eld. The R(B) values obtained at room temperature in 2-methyl-1-propanol are plotted... 

Delaire et al. [124] have reported that laser photolysis of an acidic solution (pH 2.8) containing PMAvDPA (23) and MV2 + allows the formation of surprisingly long-lived MV + - and DPA cation radicals with a very high charge escape quantum yield. The content of the DPA chromophores in PMAvDPA is as low as less than 1/1000 in the molar ratio DPA/MAA. Figure 20 shows a decay profile of the transient absorption due to MV + monitored at 610 nm [124]. The absorption persists for several milliseconds. As depicted in Fig. 20, the decay obeys second-order kinetics, which yields kb = 3.5 x 10s M 1 s. From the initial optical density measured at 610 nm, the quantum yield for charge escape was estimated to be 0.72 at 0.2 M MV2 +. ... 

During irradiation, the holes produced in the ice phase are sequestered by the ice. This is not strictly true for the excess electrons some escape the ice phase and are selectively scavenged by DNA. The degree to which this increases the yield of electrons trapped by DNA is considered to be relatively small and therefore when computing yields of direct damage in DNA, the mass of the ice phase is usually excluded from the target mass. While ice is a relatively passive component of the system, it does provide an important reference point with respect to product yields. Electrons and holes are quite mobile in ice [87,88] it is a decent conductor. Consequently, even at low temperatures, the free radical yields are quite low, e.g., the yield of HO in ice at 77 K is 0.037 gmol/J [83]. This is just one example of a... 

As shown in Fig. 3-1, some radicals in separated radical pairs re-encounter their partners within the solvent cages, but others escape from the cages, forming "escape radicals". Since the time scales for the secondary recombination and the S-To conversion rates are 10 " 10 and 10 10 s, [3] respectively, the change in the S-To conversion rate by an external magnetic field and/or the HFC term can influence the yield of cage and escape products. 

Eq. (6-6) shows that the yield of the cage product decreases with increasing B. It is noteworthy that the magnetically induced decrease in Eq. (6-6) is proportional to B. On the other hand, the yield (T/(B)) of the products from the triplet pair such as escape radicals, escape products, and the triplet state, if any, increases with increasing B. 

As shown in Chapter 7, we have found large MFEs on both the lifetimes of radical pairs and the yields of escape radicals in the above-mentioned reactions, measuring the transient absorption of intermediate radicals with an ns-laser photolysis method. Okazaki and Shiga [15] observed similar MFEs on the yield of R in the reaction of 2-methyl-1,4-naphthoquinone in a micellar SDS solution, measuring the yield of spin adducts with a conventional ESR method. Here, the escape radical reacts with a spin trap (TNO) and generates a spin adduct (T(R)NO ) as follows ... 

Okazaki et al. showed some examples for spin-manipulation [14] (1) Because the yield of spin adducts produced from escape radicals was found to be decreased by the resonance microwave irradiation, the yield of cage (escape) products was found to be increased (decreased) with a high pressure liquid chromatography (HPLC) technique. (2) Because the resonance microwave irradiation induces a transition between two definite nuclear spin-levels, the enrichment of this nuclear spin could be realized. Indeed, the ratio of was... 

After the decay of the a-b value, it attains a constant value at / = te as shown in Fig. 14-12(a). This value corresponds to the yield of the escape radical. Thus, the rate constant of the spin-relaxation and that of the escape of radicals from a radical pair ( r+Ar and e) can also be obtained with Eq. (14-12) and the following relations ... 

Fig. 15-5. A schematic representation of the experimentally observed yield of escape radical (y(5)-y(0mX)) in the pyrene/l,3-DCB system [12]. (Reproduced from Ref. [13] by permission from Taylor Francis Limited)...

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