COMMUNICATIONS TO THE EDITOR
1961
10.0
0
300
400
500
600
suggests the worthiness of investigations of the kinetics of reactions in or at the surfaces of micelles and the possible design of micelle catalysts. Though a few noteworthy contributions to the study of reactions in micelles have been made6 the employment of an amphiphile as a nucleophile or general catalyst has yet to be investigated. To this end we have investigated in detail the reactions of esters of type I with micelleforming agents of type 11, 111, and IV and with the nucleophilic agents V.
T,OK.
Figure 1. The variation with temperature of the rate of formation of l,%difluoroethyleneto 1, l-difluoroethylene.
&3-&CO~H~,,CH3
(n = 0, 416, 8)
e
OaSO[CHz111CH3
based on reaction path degeneracy alone. However, it should be pointed out that there are many more reaction possibilities in the chloro system and that the three isomeric chloroethylenes are also formed by a pathway not involving the “hot” trichloroethane intermediate. A number of experimental and theoretical studies are now being undertaken to characterize the alaand alp transition states and to determine the relative significance of each elimination. In order to explain the proportion of 1,l- product it may very well be necessary to take into account the alaelimination from -CFH2 in CFH&F2H*.
(1)’ (11
8
[CH~]~N[CHZIISCH~ HOCH2CHz [OCHzCHzI 170CeHd[CHz1i&Ha
(IIIY (IVY
The hydrolyses of esters I were followed spectrophotometrically at 410 mp or autotitrjmetrically. In the absence of agents 11, 111, IV, and V the hydrolyses of esters I were found to be first order in [OH-] and first order in ester between pH 8.0 and 10.5 ( p = 0.1 and 0.5). The rate constants for alkaline hydrolysis at 30” and p = 0.1 (kOH in liters per mole per minute) were 2651 (at 5 X to 1.7 X M ) for n = 0; 1165 Acknowledgment. This work was supported by a (at 5 X low5to 1.7 X M ) for n = 4; 953 (at grant from the National Science Foundation. 2.08 X to 8.33 X M ) for n = 6; and 340 (at 5 X t o 1.7 X loe4 M ) for n = 8. All the DEPARTMENT OF CHEMISTRY JAMES T. BRYANT
UNIVERSITY OF CALIFORNIA BERNARD KIRTMAN SANTABARBARA, CALIFORNIA 93106 GLYN0. PRITCHARD (1) A. L. Berger and K. LinderstrZm-Lang, Arch. Biochem. Biophys., 69, 106 (1957). RECEIVED FEBRUARY 10, 1967
Nucleophilic Micelles. I
Sir: The study of micelles has provided much of the basis for the understanding of lyophobic bonding, a factor of paramount importance in the stabilization of the tertiary structure of proteins.’l2 The similarity in micelle and protein structure is seen from the X-ray determined tertiary structure of myoglobin3 and lysozyme4 from which it is evident that the nonpolar side chains are, in the main, located in the interior in lyophobic regions while the polar amino acid side chains are generally located a t the periphery of the protein. Much the same information is obtained from chemical and physical studies of other proteins.s This resemblance between the structure of micelles and enzymes
(2) G. NBmethy and H. A. Scheraga, J . Phys. Chem., 66, 1773 (1962). (3) J. C. Kendrew, et al., Nature, 185, 422 (1960). (4) D. C. Phillips, Sci. Am., 215, 78 (1966). (5) G. G. Hammes and H. A. Scheraga, Biochemistry, 5,3690 (1966). ( 6 ) E. F. J. Duynstee and E. Grunwald, J. Am. Chem. SOC.,81, 4540, 4542 (1959); J. L. Kurz, J. Phys. Chem., 66, 2239 (1962); D. G. Herries, W. Bishop, and F. M. Richards, ibid., 68, 1842 (1964); L. J. Winters and E. Grunwald, J . Am. Chem. Soc., 87, 4608 (1965); M. T. A. Behme, J. G. Fullington, R.Noel, and E. H. Cordes, ibid., 87, 266 (1965). (7) For n = 0 , Anal. Calcd for CsHsNO7NaS: C, 33.93; H, 2.14; N, 4.95. Found: C, 33.81; H, 2.28; N , 4.93. For n = 4, Anal. Calcd for C I ~ H ~ ~ N O I SC, N ~42.50; : H, 4.15; N, 4.13. Found: C, 42.11; H, 4.39; N, 4.32. For n = 6, Anal. Calcd for C1dHlsNOrSNa: C, 45.77; H, 4.94; N, 3.81. Found: C, 45.50; H, 5.24; N, 3.74. (8) City Chemical Corp. (9) Courtesy of Professor E. H. Cordes (originally obtained from General Aniline and Film Corp.). (10) For n = 3, Anal. Calcd for ClrHzaNzClz: C, 57.30; H, 8.94; N, 9.55. Found: C, 56.62; H, 9.14; N, 8.89. For n = 9, Anal. Calcd for CioHasNaCla: C, 63.66; H, 10.15; N , 7.43. Found: C, 63.01; H, 10.17; N , 7.42.
Volume 7 1 , Klzimhcr
rj
May 1967
COMMUNICATIONS TO THE EDITOR
1962
esters were found to provide Beer plots without change of slope across the range of concentrations for which the value of k m was found to be independent of ester concentration. Thus, no evidence exists for the formation of micelles in the concentration range of I employed in this study. Similar results were obtained a t p = 0.5. With 1.74 X M anionic ester I (n = 4; 1.1 = 0.5) the value of k O H remains unaffected on increase of the anionic amphiphile I1 to a concentration a t which a precipitate is formed. When the anionic amphiphile [I is replaced by the cationic I11 or neutral IV, however, the value of kOH is found to decrease as the concentration of amphiphile is increased to the critical M for I11 and 2 X micelle concentration (cmc) of M for IV and then to reach a constant value above the cmc. The decrease in rate is 4.5-5.8-fold (independent of n) for I11 and 12.7-fold for IV (n = 4). It may be concluded, therefore, that I is incorporated into cationic and neutral micelles and thus protected from hydroxide ion catalyzed hydrolysis. That esters of type I are not incorporated into micelles of like charge is shown by the fact that the value of koH for VI is not affected by I11 until a concentration of amphi-
phile is reached which is 10 times that of the crnc concentration and then the rate is only depressed by a factor of 1.7. That the values of k0H are not reduced ester must be incorporated into to zero' even when the micelles, indicates either that hydroxide ions can penetrate into the micelle or that the hydrolytic reactions occur only at the surface of the micelle. If I (n = 6) is allowed to react with V ( m = 3) in the presence of 111, above and below the crnc concentration of 111, it is found that the incorporation of I into micelles of I11 almost or completely abolishes the second-order reaction of 1 and V. To assess the feasibility of synthesizing micelleforming reagents with catalytic groups the reaction of I with V was investigated. The reagents V were designed to attract I via both electrostatic and lyophobic bonding involving the oppositely charged head groups, the phenyl rings and the aliphatic chains, respectively, so that amine and ester would be juxtaposed for an aminolysis reaction within the micelle. When n = 0 or 6 and m := 3 the reactions of I and V were found to be second order (ie., first order in the basic form of V and first order in I ; ko = 15.8 1. mole-' min-l and ka = 2.4 1. mole-' min-l). However, when n = 0, 4, 6 and m = 9, I was found to be incorporated into the micelles of V and :Its rate of disappearance a t constant pH The Journal of Physical Chemistry
greatly enhanced. Thus, increase in the concentration of V (I a t 5 X M ; I.( = 0.1) was accompanied by a rapid increase in the pseudo-first-order rate constant (kobsd) for disappearance of I in the vicinity of the cmc (ca. 7 X 10-8 M ) , the value of kobsd becoming invariant above the cmc. The increase in kobsd in the vicinity of the cmc was found to be dependent on approximately the second power of the amphiphile. The best fit of the
kinetic data to eq 1was a t a pH (8.65) approximating the pK, of the amphiphile where for n = 0, V , = 1.85 min-' and K = 1.18 X M 2 ; n = 4, V , = 0.19 min-' and K = 1.0 X M 2 ; and for n = 6, V , = 0.17 min-' and K = 3.0 X M 2 . The similarity of eq 1 and the Michaelis-Menten equation is obvious. From studies between pH 7.05 and 10.2 it was possible to show that the rate of the reactions was dependent on the mole fraction of V present as free amine and by the hydroxamate method" it could be shown that I plus V provided, in each case, an almost quantitative yield of acylated V. These results point out the interesting possibility of preparing catalytic amphiphiles which are effective at very low concentrations. Studies of this nature are now in progress in this laboratory.
Acknowledgment. This work was supported by a grant from the National Institutes of Health. (11) T. C. Bruice and F. H. Marquardt, J. Am. Chem. SOC.,84, 365 (1962).
DEPARTMENT OF CHEMISTRY UNIVERSITY OF CALIFORNIA AT SANTA BARBARA SANTABARBARA, CALIFORNIA
THOMAS C. BRUICE J. KATZHENDLER LEOR. FEDOR
RECEIVED MARCH 3, 1967
Revised Values of Integral Diffusion Coefficients
of Potassium Chloride Solutions for the Calibration of Diaphragm Cells
Sir: The diaphragm cell method of determining diffusion coefficients is a relative one whose accuracy is largely determined by the precision of the calibration experiments used to obtain the cell constant. In 1951, for Stokes' published integral diffusion coefficients boo KC1 for the calculation of diaphragm cell integral (1)
R.H.Stokes, J . Am. Chem. SOC.,7 3 , 3527 (1951).
