Environmental Engineering Reference
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the cationic micelles via association of the reactive BH 4 species on the micellar
surface but was inhibited by anionic micelles due to electrostatic repulsion (Larson
et al. 2000). In addition to the photoreduction as above, the effect of micelles on
photooxidation by 1 O 2 was also examined. The oxidation of polychlorophenolate
ion by 1 O 2 was enhanced in the HDTMA Cl micelles (Bertolotti et al. 1989b). In
contrast, the oxidation of nitrophenolate ions by 1 O 2 was retarded in the HDTMA
Br micelles although both reactive species were solubilized near the micellar sur-
face (Luiz et al. 1992). Since oxidation proceeds via electron transfer from the
nitrophenols, association with the cationic micelles is considered to inhibit this
process. The reduced photooxidation of pyrene in the Brij 35 micelles was exam-
ined at 350 nm by Sigman et al. (1998). The reaction was likely to be initiated by
electron transfer from pyrene instead of its excited triplet as there was no inhibition
of the reaction by Hg 2+ . This process seemed to be affected by the association of
pyrene with the polyethoxy moiety of Brij 35 estimated from the resemblance of
the fine structure of fluorescence in triethylene glycol.
The Norrish type II reaction of valerophenone was examined in benzene,
t -BuOH, and HDTMA Br micelles (Turro et al. 1977). The regioselectivity and
quantum efficiency in intramolecular cycloaddition via abstraction of the
-proton
by the excited carbonyl oxygen was very similar in the micelles and t -BuOH with
no quenching of acetophenone formation by Eu 3+ , showing the solubilization of the
ketone in the Stern layer. The spin state of the ketyl radical produced from the
excited benzophenone in ionic micelles has been examined under a moderate mag-
netic field (Scaiano et al. 1982). The reduced intersystem crossing of the radical
pairs caused by Zeeman splitting of the triplet state caused less formation of the
para -coupling product, indicating the singlet pathway. The photoinduced decarbo-
nylation via a free radical mechanism has been studied extensively in relation to the
cage effect of micelle by using dibenzyl ketone derivatives (Turro and Cherry 1978;
Turro et al. 1987). When A-C(=O)-B (A, phenyl; B, tolyl) was photolyzed at lower
concentrations of HDTMA Br around its cmc, the distribution of 1,2-diarylethanes
followed the statistics of AA:AB:BB = 1:2:1. In contrast, at the higher surfactant
concentrations well above cmc with the small ketone/micelle ratio, the product ratio
became <1:98:<1, clearly indicating the cage effect. The similarly high production
of AB in the micelle system containing Cu 2+ implied the formation of AA and BB
in an aqueous phase from the released radicals. By using the steady-state chemically
induced dynamic nuclear polarization (CIDNP) technique, Turro et al. demon-
strated that the escape of the radical (A . or B . ) from the secondary geminate radical
pair (A . - . B) produced via decarbonylation from micelle controls the extent of
recombination to form AB, and therefore the micelle having a larger volume
showed more significant cage effect. Lei et al. (1991) have shown a higher cage
effect in HDTMA Br and SDBS micelles than nonionic Triton X-100 one and
concluded that the ionic micelles reduce the radical escape by the counterions in the
Stern layer. In the case of benzyl esters having one of the basic structures of pesticide
such as pyrethroid, a similar cage effect was reported for its photoinduced decarboxy-
lation (Turro et al. 1980; Anvir et al. 1981). The photo-Fries rearrangement of esters
and amides was also studied in the micelle system from the aspect of organic synthe-
γ
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