Spin trapping simulated spectra

Spin trapping with PMNB was applied to the radicals derived from initiator decomposition (formula 3) and their subsequent reactions with the model compounds (formula 5). Both initiator radicals could be trapped and identified. When model compounds were present during UV-irradiation, new radicals were identified from the ESR spectra. For dihydrocyclopentadiene (DHCPD) only one trapped radical was found and for ethylidene norbornane (ENB) two radicals. By comparison with computer simulated ESR spectra, it is concluded that the radicals of these model compounds are all allyl radicals (formula 8 and 9) formed by hydrogen abstraction from the models. Radical (8 a) has two stereoisomers but they have closely the same ESR spectra when trapped and cannot be separated. Radical (8 b) has two resonance structures (shift of double bond in the ethylidene group) but only one radical (8 b) is trapped, probably due to steric hinderance for trapping the methin radical. The DHCPD radical (formula 9) has two steric forms because the two allylic hydrogens are not identical. Once they are formed, the spin trap can only approach from one side and only one of the steric forms is trapped as shown in the ESR spectrum. 

FIGURE 5 Electron spin resonance spectra of degassed 1 1 acetone water solutions containing 0.15 M DMPO as a spin trap (a) 2.% H2O2 photolysed for 8 min (b) computer simulation on a assuming the prescence of DMPO OH, DMP0 00H and DMPO acetone species (a) dark spectrum of a l.T x 10 M Chi a solution (B) spectrum in A after white light photolysis. 

Figure 27 (a) Time evolution of ESR spectra of DMPO adducts at the cathode side, CCV operation in the in situ FC, with H2 at the anode. In the top spectrum 0 min indicates that the spin trap was added just before FC operation, as in Figure 2. Note the dominant DMPO/H adduct when the spin trap was added after 120 min of FC operation together with weak signals from the DMPO/OH adduct (circles) and the appearance of the CCR adduct (downward arrow points to the low-field signal) when the spin trap was added after 240 min of operation, (b) Experimental and simulated ESR spectra of adducts when the spin trap was added after 360 min of operation. The relative intensity of each adduct is shown on the left.

Figure 3. MOssbauer spectra of the reduced Rieske protein Thermus Thermophilus. (A) Spectrum taken at 230 K. The brackets indicate the doublets of the trapped-valence Fe2+ and Fe3+ sites. (B) 4.2 K spectrum of the same sample. The solid line is a spectral simulation based on an S = 1/2 spin Hamiltonian. S = 1/2 is the system spin resulting from coupling S = Sa + Sb according to H = JSa-Sb for J > 0 Sa = 5/2 and Sb = 2.

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