EXCHANGE BETWEEN ALKYLAMMONIUM AND SODIUM-IONS AT THE SURFACE OF DODECYL-SULFATE MICELLES

被引:37
作者
BONILHA, JBS
MARY, R
GEORGETTO, Z
ABUIN, E
LISSI, E
QUINA, F
机构
[1] UNIV SANTIAGO CHILE,FAC CIENCIAS,DEPT QUIM,CASILLA 5659 CORREO 2,SANTIAGO,CHILE
[2] UNIV SAO PAULO,INST QUIM,SAO PAULO,SP,BRAZIL
[3] UNIV SAO PAULO,FAC FILOSOFIA CIENCIAS & LETRAS RIBERAO PRETO,DEPT QUIM,SAO PAULO,SP,BRAZIL
基金
巴西圣保罗研究基金会;
关键词
D O I
10.1016/0021-9797(90)90304-7
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The ion exchange between sodium and a series of alkylammonium cations of the general formula R4-YNHY + (with R = methyl, ethyl, propyl, butyl; Y = 0 to 4), at the surface of dodecylsulfate micelles, was studied using fluorescence techniques. The selectivity coefficients obtained indicate that all of the organic counterions considered bind more strongly to the micelles than do either sodium or ammonium ions. Replacement of hydrogen by methyl groups (Y = 1 to 3) in the ammonium ion increases the binding strength, the free energy increment for transfer of the counterion from water to the micelle, ΔμO, being -300 ± 30 cal/mole per methyl group. For alkylammonium ions, a ΔμO for transfer of -570 ± 50 cal/mole per methylene group, irrespective of the number of alkyl chains, was found. This indicates that the binding strength of alkylammonium ions is dominated by their hydrophobicity, independent of the spatial distribution of the alkyl groups attached to nitrogen. The possible use of these results to decide between "open" or "structured" micellar models is discussed. Tetraalkyl ions show considerably lower binding affinities than might be expected from the total hydrophobicity of their chains. This result is interpreted in terms of an unfavorable location of the fourth alkyl chain. © 1990.
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页码:238 / 245
页数:8
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