Rz 10 assume that a similar transition state is involved in methyl transfer from any methylsulfonium compound. In order to test this hypothesis, we are continuing the study of nonenzymic transmethylation on molecules which are more closely related to SAM in structure, but which are not so readily decomposed in basic media.
Registry No. -ZaDicationic detergents (I), R?J+MeZ(CHz),N +Me2R 2Br-(where R = cetyl and n = 4 and 6), readily micellize, and the micelles are effective catalysts of the reactions of hydroxide ions with chloro-and fluoro-2,4-dinitrobenzene and hydroxide and fluoride ions with p-nitrophenyl diphenyl phosphate. With n = 4 and 6, those detergents are two-to fivefold better catalysts than cetyltrimethylammonium bromide, CTABr. The dicationic detergent R N +Me2CH2C=CCHz?J +MeaRBrz-also micellizes, but it and I (n = 2 ) are not markedly better catalysts than CTABr.
The reactions between p-nitrophenyl diphenyl phosphate and hydroxide or fluoride ions in water a t 25" are catalyzed strongly by cationic micelles of cetyltrimethylammonium bromide, with the rate increasing to a maximum a t ca. 3 X 10-8 M detergent. The detergent increases the activation enthalpy, but makes the activation entropy less negative. Added salts inhibit the catalysis, and the inhibition is largest with anions of low charge density. Anionic micelles of sodium lauryl sulfate strongly inhibit the reaction, as does the uncharged detergent Igepal, but here there is marked inhibition at submicellar concentrations. The inhibition can be related to the extent of incorporation of the substrate into the micelles, or its association with the detergent.
Fig. 13.
J-Tk < 1 --1 major ordering in the following way. Given A' processors initially loaded with a data value, repeat N12 times: 01, "Expensive comparison-interchange" of processors #(2i + ]) with processors #(2J -t-2). 0 < i < Nj2 -1. Time: At^ + tc if processor array has more than two columns and more than one row; 0 if A' = 2: and 2t,, + tc otherwise. 02 "Cheap comparison-interchange"' of processors #(2/) with processors #(2/ + 1), 0 s / s N/2 -1. Time: 2i, + tf.
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