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α-Alkoxyalkyl radicals with a leaving group L = Cl or OCOCH3 in β-position are produced by H-abstraction from the corresponding saturated substrates by ·OH, SO·4- or (CH3)3CO· radicals. From ESR spectroscopic observations it is concluded that in aqueous solution at pH 5 -9 the following fast hydrolysis reactions take place: The rate constants of these reactions and for the hydrolysis of CH3O-ĊH-CH2Cl are k ≥ 106 s-1, whereas the rate constant for CH3O-ĊH-CH2OCOCH3 was determined to be ≈ 2 × 103 s-1 at room temperature. The radicals with L = Cl cannot be scavenged by O2 which fact leads to a value of k ≥ 2 × 10-7 s-1. α-Alkoxyalkene radical cations are assumed as intermediates in the hydrolysis reactions. The radicals with L = OCOCH3 and the radical CH3O--ĊH-CH2Cl are observable in acetone solution ESR spectroscopically. In aqueous solution at pH below 3 proton catalyzed reactions are observed by ESR spectroscopy: Radicals resulting from H-abstraction at the CH3O-groups of the substrates or at the 5-positions of the cyclic ethers are also observed. The ESR parameters and the pH-ranges of existence of the above radicals are given. Support of the reported reactions comes from quantitative analysis of stable products such as H+, Cl- or CH3OH after 60Co-γ-irradiation of N2O saturated aqueous solutions of the substrates. The behaviour of the radicals is used as a model to describe a modified version of the degradation of DNA-4′ radicals in aqueous solution in the absence of oxygen.

The e.s.r. spectra of 1-yl, 2-yl and 3'-yl methoxyethyl phosphate radicals derived from CH3OCH2CH2-OPO3H2 by hydrogen abstraction have been measured in aqueous solutions and the hyperfine constants determined. The coupling constants vary strongly with protonation or alkylation of the phosphate group. The 2-yl radicals eliminate phosphate. The rate-constants for the elimination (ke) have been estimated by e.s.r. measurements and by product studies as a function of pH using 60Co gamma-radiolysis. The ke values vary from approximately 0.3 s(-1) for the CH3OCHCH2OPO3--radical and approximately 10(3) s-1 for CH3OCHCH2OPO3H-, to approximately 3 X 10(6) S-1 for CH3OCHCH2OPO3H2. Alkylation of the phosphate group increases the elimination rate-constant to a similar extent as protonation. The results support a recent mechanism which described the OH-radical-induced single-strand breaks of DNA in aqueous solution starting from the C-4' radical of the sugar moiety. It is further concluded the C-4' radical of DNA eliminates the 3'-phosphate group faster than the 5'-phosphate group.

acids, stearic acid having a C18 alkyl chain may fit more smoothly with SMC than arachidic acid having a C20 alkyl chain from a molecular model. Therefore, it is reasonable that the fluorescence decay time of SMC excited at 576 nm becomes shorter in the order stearic acid, arachidic acid, and tripalmitine; in other words, the reaction rate of SSP *-SMC becomes larger in the same order. This result indicates that the volume and rigidity of reaction cage surrounding chromophores is essential to determine the rate of photoisomerization of SSP •*-SMC.On the other hand, the fluorescence decay of SMC on excitation at 314 nm (Figure 9) is slightly faster in aliphatic acids than in tripalmitine. In the foregoing discussion, it is found that when SMC is irradiated with UV laser, the energy relaxation pathway in SMC is predominantly the excitation energy migration and trapping processes instead of the isomerization reaction. Since the excitation energy migration is sensitive to the interchromophore distance, the difference in the fluorescence decays can be interpreted as due to the slightly close average chromophore distance in aliphatic acids compared in tripalmitine.The time-resolved fluorescence spectra (Figure 8) show a large red-shift in the SMC fluorescence band with time; the maximum wavelength is 616 nm at 0 ps and 660 nm at 1 ns. Such a large time-dependent spectral shift is quite common in LB monolayer films containing organic dye chromophores such as rhodamine B.21 Excited singlet dye chromophores in LB films undergo energy migration among energetically different sites and energy trapping by higher aggregates as trap sites. It is recognized that the electronic energy level of dye chromophores is slightly different with each other due to different conformation and different interaction with environmental molecules. In the case of rhodamine B, site-energy distribution arises from different relative angles of the phenyl ring. This interpretation will be adapted to the excitation energy relaxation of merocyanine in LB films. It is possible that chromophores of merocyanine caused by the C-O bond cleavage of spiropyran have different conformations in LB films. This will result in the energy level distribution of merocyanine among different sites. The energy migration among different sites is responsible for the time-dependent red shift of the fluorescence of SMC.Acknowledgment. This work was supported by the Ministry of Education, Science and Culture, Grant-in-Aid for General Scientific Research No. 01470002. We acknowledge The Research Foundation for Opto-Science and Technology (Hamamatsu) and The Mitsubishi Foundation for their financial support.