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Coliman, Brauman, et al. / Reduction of ,ß-Unsaturated Carbonyl Compounds by NaHFe2(C0)% 1119 lack of knowledge of the subsequent reaction of pip radicals with excess pip (i.e., total consumption of pip), and the relatively low [pip]o''lTpPFeC]]o ratios used to keep the autoreduction rate slow enough to follow by FT NMR. The relatively low sensitivity of NMR also did not permit a significant variation in [TPPFeCI]o• (41) C. E. Castro, personal communication. (42) The experimental conditions were such that thermal effects from the light can be totally discounted. (43) No attempt was made to fit the reduction rates to a rate law. (44) L. A. Constant and D. G.

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Physiol., 4b, 989 I -1100 115 0 500 (nm) Figure 3. Electronic spectrum of a lecithin membrane: A, Hem. Mn(II1) membrane; B, treatment of A with NaOCl for 1 min; C, treatment of B with aqueous ascorbic acid for 1 min. concentration) containing KCl(1 .O M ) to adjust its ionic strength. After 1 min, most of the Mn(II1) in the membrane was effectively converted into Mn(1V) (more than 80%) as ascertained by electronic spectral changes as shown in Figure 3. Spectra were obtained after washing the membranes rapidly three times with aqueous alkaline solution ( p H 12) to remove traces of NaOCl absorbed on the surface.The Hm.Mn(IV) in the membrane was stable enough for spectroscopic measurements. The Mn(IV) membranes were then treated with aqueous ascorbic acid (0.01 M ) , containing KCl (1.0 M ) , for 1 min. After rapid washing with the aqueous solution of p H 12, Hm-Mn(1V) was estimated by electronic spectral changes, which showed that most of the Hm-Mn(1V) was converted to Hm.Mn(II1) (70-80%) (Figure 3).Spontaneous transport of ascorbic acid through the lecithin-Hm.Mn(II1)-n-decane membrane from B (0.01 M ascorbic acid and 1.0 M KC1) to A (1.0 M KC1) was measured by the spectroscopic determination of ascorbic acid (265 nm) in A. It was (3.8 f 0.3) X 10-I2 mol min-I, ca. 3000 times slower than the reduction of the Mn(1V) membrane by ascorbic acid. The continuous electron transfer through the lecithin-Hm-Mn membrane from the ascorbic acid solution (5.0 X M ) to the sodium hypochlorite solution (1.3 X 10-l M ) was also studied by use of a salt bridge. The amount of the ascorbic acid oxidized was 7.4 X mol rnin-l (ca. 2.3 turnover per M n in 25 min), 195 times faster than the rate of spontaneous transport. This strongly indicates that the oxidation-reduction did not result from material transport but from one-way electron transport as shown in Figure 1. Treatment of Mn(1V) membranes with an aqueous solution of p H 4 containing 1.0 M KCI instead of aqueous ascorbic acid again reduced Mn(1V) to Mn(II1) as in the homogeneous system,' but the rate was considerably slower than that of the ascorbic acid reduction.These electron translocating membranes are versatile, allowing the preparation of one-way oxidation-reduction electron transport systems or the effective separation of electrons from positive holes.