The Journal of Physical Chemistry, Vol. 83, No. 23, 1979 3011
I3C NMR of Micellar Solutions
an absorption band around 1500 nm.16 In addition to relaxation of the medium, tunneling or hopping of electrons to deeper traps has been proposed. According to the model described in this paper, part of the absorption decay between 600 and 1000 nm may be due to geminate recombinationa5
Conclusion The model described in this paper predicts that when a solvated electron is formed near a positive scavenger (geminate ion), there will be a red shift of the spectrum. The red shift increases as the solvated electron becomes closer to the positive scavenger. Below the glass temperature the solvated electron will tunnel to the positive scavenger, causing a decay of the absorption on the red side of the absorption maximum. Although several assumptions have been made, there is a quantitative connection between the calculation and the spectral red shift. Acknowledgment. We thank M. Hollander and S . M. McNab for helping us to produce the final version.
References and Notes (1) J. R. Miller. J. Phvs. Chem.. 79. 1070 11975). (2j N. V. Klassen, H. A. Gilles, G. G. Teathe;, andL. Kevan, J . Chem. Phys., 62, 2474 (1975). (3) J. H. Baxendale and P. H. G. Sharpe, Chem. Phys. Lett., 39, 401 (1976). (4) J. R. Miller, B. E. Cliff, J. J. Hines, R. F. Runowski, and K. W. Johnson, J . Phys. Chem., 80, 457 (1976). (5) R. S. Dixon, V. J. Lopata, and C. R. Roy, Int. J. Radiat. Phys. Chem., 6, 707 (1976). (6) H.Hase, M. Noda, and T. Higashimura, J . Chern. Phys., 54, 2975 (1971). (7) J. Kroh and P. Polevoi, Int. J. Radiat. Phys. Chem., 11, 111 (1978). (8) G. V. Buxton and K. G. Kemsley, J . Chem. SOC.,Faraday Trans. 1 , 72, 466 (1976). (9) S. A. Rice and M. J. Piliing, Prog. React. Klnet., 9, 92 (1978). (IO) L. Kevan, Adv. Radiat. Chem., 4, 181 (1973). (11) D. Huppert, Ph. Avouris, and P. M. Rentzepis, J. Phys. Chem., 82, 2282 (1978). (12) K. J. Zamaraev and R. F. Khairutdinov, Chem. Phys., 4. 181 (1994). (13) A. T. Pudzianowski and R. N. Schwartz, J . Phys. Chem., 83, 224 (1979). (14) T. B. Truong, J. Chem. Phys., 67, 1957 (1977). (15) H. Hase and L. Kevan, J . Chem. Phys., 54, 908 (1971). (16) J. H. Baxendale and P. H. G. Sharpe, Int. J. Radiat. Phys. Chem., 8, 621 (1976).
13C NMR of Micellar Solutions. Micellar Aggregation Number from the Concentration Dependence of the 13C Chemical Shifts Bert-Ove Persson, Torbjorn Drakenberg, and Bjorn Lindman” Division of Physical Chemistry, Chemical Center, University of Lund, S-22007 Lund 7, Sweden (Received January 11, 1979)
13C NMR chemical shifts were determined as a function of concentration for aqueous solutions of sodium hexanoate, sodium octanoate, and nonylammonium bromide. Using the mass action law model for micelle formation, we have estimated the aggregation numbers by fitting calculated chemical shifts as a function of amphiphile concentration to the experimental values. For sodium octanoate and sodium hexanoate the calculations indicate the formation of an appreciable amount of premicellar aggregates with an aggregation number of about 3 or 4. For nonylammonium bromide the results are explained by the formation of large aggregates only.
Introduction It has been clear for some time that NMR is a very powerful method in studies of micellar systems. (For reviews see ref 1-4.) Proton NMR has been used, for example, to study solubilization5 and counterion NMR has been utilized in a variety of way^.^^^ More recently, it has been realized that 13C NMR is a much more potent tool than proton NMR in studies of the amphiphile itselfOgl3As an example, in sodium octanoate solutions all eight carbons give rise to well-separated signals which may be unambiguously assigned,12 whereas in proton NMR only the methyl and a-methylene signals can be observed separated from the signal from the other protons. Previously we have shown that the chemical shifts of the aliphatic carbons in octanoate are concentration dependent and the critical micelle concentration (cmc) can therefore be obtained12 by assuming the pseudophase separation model for micelle formation. We have also shown, assuming the mass action law model for micelle formation, that it is possible to derive a linear equation by means of which the aggregation number can be obtained.13 We have now continued this work and derived a computer program which can be used to calculate the aggregation number directly from the observed chemical shifts by fitting, with an iterative routine, the calculated shifts to the experimental ones. 0022-3654/79/2083-3011$01.00/0
Experimental Section All 13C NMR experiments have been performed on a Varian XL 100 spectrometer, working at 25 MHz for 13C, and operating in the Fourier transform mode. A spectral width of 1000 Hz and 8000 data points in the time domain have been used, resulting in an optimum resolution of 0.25 Hz or 0.01 ppm. A flip angle of 70’ and a recycling time of 4 s were used and the number of transients varied from 100 to 5000. The deuterium lock signal was obtained from D20 of the solvent. In the tables the shifts are always given relative to the lowest measured shift for convenience. The total shift relative to MeQSimay be obtained from the given shifts of the low concentration solutions relative to Me4Si. The samples were prepared by weighing amphiphile and D20 in appropriate amounts. Concentrations are given on the molality scale (m)as moles of amphiphile per 55.5 mol of D20. Sodium hexanoate and sotL.lm octanoate were obtained from BDH (England) and 1 :? was obtained from CIBA (Switzerland), and they wert d without further purification. Nonylammonium broi :e was prepared by mixing equimolar amounts of nonyi m i n e and hydrogen bromide. The mixture was evaporated to dryness and recrystallized from acetone. The computer calculations were made on a Univac 1108 computer. 3
0 1979 American
Chemical Society
3012
The Journal of Physical Chemistry, Vol. 83, No. 23, 1979
TABLE I:
I
L O . Persson, T. Drakenberg, and 6.Lindman
'C Chemical Shifts for Solutions of Nonylammonium Bromidea 1-CH,
Ctot3
lowest obsd shift 0.0443 0.0565 0.0899 0.0997 0.1056 0.1112 0.1145 0.1164 0.1202 0.1224 0.1274 0.1340 0.1570 0.1777 0.1997 0.2220 0.2448 0.2800 0.3345 0.3836 0.4469 0.4981 0.5521 0.6713 0.7748 0.8919 0,9990 1.1130 1.4165 2.2174
41.22 i 0.00 io.00 0.03 0.04 0.04 0.04 0.05 0.05 0.06 0.04 0.07 0.08 0.06 0.08 0.10 0.10 0.12 0.12 0.14 0.14 0.16 0.16 0.16 0.17 0.17 0.19 0.19 0.21 0.20 0.21
2-CH2
3-CH2
4-CH,
5-CH,
6-CH,
7-CH,
B-CH,
CH,
28.35 0.01
27.17 io.00 io.00 0.03 0.04 0.05 0.07 0.08 0.09 0.12 0.13 0.18 0.22 0.30 0.40 0.48 0.54 0.58 0.65 0.72 0.76 0.80 0.83 0.86 0.90 0.93 0.95 0.96 1.01 1.00 1.04
30.08
29.98 io.00
29.80 i 0.00 0.01 0.04 0.04 0.06 0.08 0.10 0.10 0.12 0.14 0.17 0.22 0.31 0.41 0.48 0.54 0.60 0.65 0.73 0.76 0.81 0.85 0.86 0.91 0.93 0.95 0.97 1.01 1.00 1.04
32.76 0.01 c 0.00 0.02 0.03 0.04 0.07 0.11 0.09 0.11 0.11 0.15 0.20 0.27 0.34 0.41 0.45 0.49 0.54 0.60 0.63 0.66 0.70 0.72 0.74 0.76 0.78 0.78 0.83 0.80 0.82
23.67 io.00 io.00 0.02 0.02 0.03 0.04 0.06 0.06 0.08 0.09 0.10 0.13 0.19 0.25 0.29 0.33 0.36 0.39 0.43 0.47 0.48 0.50 0.51 0.53 0.54 0.55 0.56 0.59 0.57 0.57
15.06 io.00 io.00 0.02 0.02 0.03 0.06 0.06 0.04 0.06 0.06 0.09 0.10 0.14 0.18 0.21 0.24 0.24 0.28 0.31 0.32 0.34 0.35 0.36 0.37 0.36 0.37 0.37 0.43 0.36 0.34
_____
:o.oo
i
0.01 0.03 0.04 0.04 0.06 0.05 0.08 0.08 0.10 0.12 0.16 0.21 0.25 0.28 0.32 0.35 0.39 0.41 0.44 0.45 0.46 0.48 0.49 0.50 0.50 0.53 0.51 0.52
0.01 io.00 0.04 0.04 0.06 0.09 0.10 0.12 0.14 0.15 0.20 0.25 0.36 0.46 0.54 0.61 0.67 0.73 0.81 0.87 0.91 0.95 0.97 1.01 1.04 1.07 1.09 1.13 1.11 1.14
50.00
0.03 0.04 0.05 0.08 0.09 0.10 0.12 0.14 0.18 0.23 0.31 0.41 0.48 0.54 0.59 0.65 0.73 0.77 0.81 0.83 0.87 0.89 0.92 0.95 0.95 1.01 0.99 1.01
The chemical shifts (in ppm) are given relative t o the lowest observed shift in relation to external Me,% This lowest observed shift is given on the t o p line. A positive shift is downfield. Carbons are numbered from the polar head group. The assignment of carbons 4-CH2,5-CH2,and 6-CH, is only tentative.
Calculations Using the mass action law model of micelle formation, assuming no effects from the counterions and also assuming one single micelle size with a well-defined aggregation number, N , we can write N(mon) + mic with an equilibrium constant based on concentration and not activity K = CmicCmo;N (1) Here C, and Cmicrepresent the monomer and micelle concentrations, respectively. The total amphiphile concentration is given by (2) C t o t = Cmm + NCmic and the observed chemical shift, bobsd, is given by (rapid exchange) 6obsd
= (CmonSmon + N C m i J m i c ) Ctot-'
(3)
where 6,, and gmic are the chemical shifts, for a given carbon, of the monomer and micelle, respectively. C,, and Cmichave to be calculated in an iterative way from assumed values of the equilibrium constant and aggregation number from c,,, = CtOt(l+ KNCmonN-l)-l (4) which can be obtained from eq 1 and 2. When C,, and Cmicare known, 6,, and amic can be found by use of eq 3 and the observed chemical shifts at various amphiphile concentrations in a least-squares treatment by finding the minimum of Cn(aobsd - 6ca1cd)2,where n is the number of concentrations used. The calculations have been performed in the following way: for each aggregation number within a preselected
I
I
0
\
5
,N=5
10
15
1fCtot
20
Figure 1. Theoretical curves illustrating the shape of plots of chemical shift against 1/C, for N = 5 (a), 10 (b), 20 (c), 50 (d), and (e). The chemical shift difference is held constant at 1.0 ppm.
range, the equilibrium constant which gives the lowest error square sum in the least-squares treatment by using eq 3 is searched for, just by changing that constant step by step. In these first calculations the simple program described above was used to test if it may be worth the effort to develop a more sophisticated program, which is now being done. In Figure 1 are shown some examples of calculated curves obtained by using a constant value of amic - 6,, and various aggregation numbers, showing that the shifts are very sensitive to N in the concentration interval around the cmc.
Results and Discussion In the present work we have chosen to study n-nonylammonium bromide (NAB) (Table I), sodium n-octanoate (Table 11), and sodium n-hexanoate (Table 111) since they have reasonably high critical micelle concentrations. In
13C NMR
The Journal of Physical Chemisfry, Vol. 83, No. 23, 7979 3013
of Micellar Solutions
TABLE 11:
'C Chemical Shifts for Solutions of Sodium Octanoatea
lowest obsd shift
1-CH, 39.34
2-CH2 27.59
3-CH, 30.38
0.0496 0.1004 0.2009 0.2495 0.3016 0.3218 0.3407 0.3615 0.3729 0.4026 0.4226 0.4434 0.4632 0.4800 0.4999 0.5520 0.6036 0.6530 0.6986 0.8054 0.9779 1.2559 1.5017 1.7546 2.0047
io.00 0.01 0.02 0.03 0.04 0.04 0.04 0.04 0.06 0.07 0.08 0.08 0.09 0.10 0.10 0.12 0.13 0.14 0.15 0.18 0.20 0.24 0.26 0.26 0.27
to.00 0.01 0.01 0.01 0.03 0.03 0.03 0.04 0.04 0.06
i
Ctot, m
0.09 0.10 0.11 0.11 0.14 0.16 0.18 0.19 0.24 0.27 0.33 0.36 0.37 0.39
0.00
4-CH2 29.92
5-CH2 32.70
6-CH2 23.66
CH 1 15.06
io.00
i 0.00
i 0.00
i 0.00
i 0.00
i 0.00
0.03 0.04 0.06 0.06 0.06 0.08 0.08 0.12 0.14 0.16 0.18 0.19 0.21 0.27 0.32 0.36 0.39 0.46 0.54 0.64 0.70 0.7 2 0.76
0.02 0.02 0.04 0.04 0.04 0.06 0.06 0.09 0.10 0.12 0.14 0.14 0.16 0.20 0.23 0.26 0.29 0.34 0.39 0.46 0.50 0.51 0.53
0.01
0.01 0.03 0.04 0.06 0.06 0.07 0.08 0.10 0.13 0.14 0.17 0.19 0.21 0.23 0.29 0.34 0.38 0.42 0.50 0.59 0.69 0.75 0.78 0.81
0.02 0.02 0.05 0.05 0.06 0.07 0.09 0.11 0.13 0.15 0.18 0.20 0.22 0.27 0.33 0.37 0.41 0.48 0.58 0.68 0.74 0.77 0.81
0.02 0.03 0.05 0.05 0.05 0.07 0.05 0.11 0.11 0.13 0.14 0.16 0.16 0.19 0.20 0.23 0.24 0.28 0.31 0.35 0.37 0.37 0.37
a The chemical shifts (in p p m ) are given relative to the lowest observed shift in relation t o external Me,Si. The lowest observed shift is given on the t o p line. A positive shift is downfield. Carbons are numbered from the polar head group.
TABLE 111: "C Chemical Shifts for Solutions of Sodium Hexanoatea
Ctot, m
COO-
1-CH, 2-CH, 3-CH, 4-CH2 CH,
lowest 189.98 39.32 obsd shift 0.0991 io.00 +o.oo i o . 0 0 0.2022 0.2999 0.01 0.3908 - 0.02 0.02 0.5016 -0.03 0.03 - 0.04 0.04 0.6038 0.6248 - 0.05 0.04 0.6418 -0.05 0.04 0.6646 - 0.05 0.04 0.6737 - 0.06 0.04 0.7048 -0.06 0.04 0.7247 - 0.06 0.05 0.7435 - 0.07 0.05 0.7633 - 0.07 0.05 0.05 0.7870 - 0.08 0.8061 -- 0.08 0.05 0.8546 - 0.08 0.05 - 0.09 0.9063 0.06 0.9561 --0.10 0.06 1.0099 -0.12 0.07 1.1092 - 0.14 0.07 1.2074 0.09 -0.17 1.4058 - 0.22 0.11 1.6107 -0.28 0.12 1.8152 -0.35 0.13 2.0132 - 0.42 0.14 2.5058 0.17 2.9927 0.20 3.5015 0.23 4.0067 0.23 4.5072 0.25
TABLE IV : Calculated Aggregation Number (A'), Equilibrium Constant ( K ) , Error Square Sum (I:), and Shift Difference between Monomer and Micelle for Nonylammonium Bromide Solutions
27.26 32.71 23.47 14.94
i o . 0 0 io.00 10.00 i o . 0 0 i o . 0 0 0.01 i o . 0 0 0.02 0.01 0.02 i o . 0 0 0.03 0.01 0.04 0.02 0.02 0.02 0.03 0.02 0.06 0.03 0.07 0.02 0.04 0.03 0.08 0.02 0.04 0.02 0.04 0.03 0.08 0.02 0.04 0.03 0.08 0.02 0.04 0.04 0.09 0.02 0.05 0.04 0.09 0.02 0.05 0.04 0.09 0.04 0.06 0.04 0.09 0.04 0.06 0.04 0.10 0.04 0.06 0.04 0.10 0.04 0.06 0.04 0.10 0.04 0.06 0.05 0.11 0.06 0.12 0.04 0.08 0.04 0.08 0.06 0.13 0.05 0.08 0.07 0.14 0.08 0.15 0.06 0.10 0.06 0.12 0.10 0.16 0.08 0.16 0.13 0.21 0.11 0.21 0.16 0.23 0.12 0.25 0.20 0.27 0.15 0.29 0.23 0.29 0.20 0.39 0.31 0.35 0.25 0.48 0.37 0.39 0.29 0.54 0.42 0.42 0.30 0.58 0.45 0.41 0.33 0 . 6 3 0.48 0.42 a The chemical shifts (in ppm) are given relative t o the lowest obseived shift in relation t o external Me,%. This lowest observed shift is given on the top line. A positive shift is downfield. Carbons are numbered from the polar head group.
a previous paper we have presented the results that we obtained for the aggregation number ( N = 37 f 5) for the
carbon no.a _______
1 2 3
4 5 6 7 8 9 a
6 mic ,
N
(10) (15) 37 33 33 33 33 35 28
log K (7.3) (11.5) 31.8 28.2 28.2 28.0 28.5 30.1 23.7
1042 -_-
(13) (7 1 12 6 10 8 14 3 11
stno,,
. .
PPm 0.2 0.6 1.1 1.2 1.1 1.1 0.9 0.6 0.4
Carbons are numbered starting with the a-CH, group.
NAB micelles by using a linearized e q ~ a t i 0 n . lWe ~ have found this treatment not to be completely satisfactory, and therefore, have now used the treatment delineated in the previous section. In Table IV is shown the data obtained for NAB. We can here see that there is a very good consistency in the aggregation numbers obtained by using various carbon signals when those having small chemical shift differences between monomers and micelles are excluded. (For these the precision is insufficient.) In Figure 2 is shown the agreement between experimental and calculated chemical shifts for carbon 4. (Carbons are numbered starting with the cu-CH2.) The actual calculation was performed by deleting the two data points a t the lowest amphiphile concentrations and also a few points for the very highest concentrations. When the two low concentration points were included in the calculation the error square sum was significantly higher than those in Table IV. (As the two data points at the lowest concentrations seem to be -0.02 ppm too low for all carbons, with values on hmiC - h,, ranging from 0.2 to 1.2 ppm, it is probable that this is due to a drift in the spectrometer.) If we concentrate on the five central carbon atoms in NAB, we can see that the distribution in the aggregation number obtained is much
3014
The Journal of Physical Chemistry, Vol. 83, No. 23, 1979
d
TABLE V: Calculated Aggregation Number (N), Error Square Sum ( 2 : ), and Chemical Shift Difference (6 mic -- 6 man) for Sodium Octanoate Solutions
ppm
c\\
car- 6 h c bon 8 mom no.b .ppm .
31.0
I 0
B.-0. Persson, T. Drakenberg, and B. Llndman
L 1
1
I
I
I
5
10
15
20
25
1’Ctot
Figure 2. Chemical shift of carbon 4 in NAB as a function of Cm-’[m-’]: solid line, calculated with N = 33, 6 , = 30.1, and 6,, = 31.3; +, experimental points.
less than what could be obtained by using the linearized equation reported previ0us1y.l~The mean values obtained by these two methods are, however, very similar. The error square sums (given in Table IV) obtained from the least-squares treatment on the basis of eq 3 are all within what can be expected with an accuracy of fO.O1 ppm. Very few points have a difference between experimental and calculated shifts by more than 0.01 ppm. One interesting observation here is that the error square sum is increasing much faster when the aggregation number is decreased from the optimum value than when it is increased from that value. This indicates that the distribution of micelle size is unsymmetrical around the optimum value found here, a fact that may be predicted on theoretical grounds4J4-17but for which it is difficult to obtain experimental support in the concentration region just above the cmc, where there is no change in micellar shape. By extending the presently used simplified model, we hope, in calculations in progress, to obtain quantitative information on the micelle size distribution curve. For sodium octanoate and sodium hexanoate systems, calculations have been performed on three different concentration intervals: (1)all data points up to 4.5 and 2.0 m for hexanoate and octanoate, respectively, (2) all data points up to concentrations of 0.8 and 0.4 rn for hexanoate and octanoate, respectively, and (3) all data points for the two lowest concentrations and those above interval 2. For hexanoate the aggregation number was found to be less than 5 in all calculations, indicating that there is no appreciable formation of micelles within the normal meaning of the word. The results for octanoate are gathered in Table V and, as can be seen by using carbons 3 to 5, very consistent data are obtained from either of the chosen intervals. However, it is interesting to note that the aggregation number obtained from intervals 2 and 3 are very different, 4-5 and 10-11, respectively. This is a good indication of the formation of premicellar aggregates with small aggregation numbers, 4-5 or less, in a narrow interval before the formation of larger aggregates. It is at present difficult to judge how relevant these aggregation numbers are, but at least the combined error square sum for intervals 2 and 3 is about half that of interval 1. This indicates that it might be worth while to extend the program to handle the case with two different aggregation numbers, which is now being done. Another change in the program that we are working on now is to use a distribution of aggregation numbers instead of a single one, which will approach the multiple equilibrium model for micelle formation, Regarding the results for octanoate, one can also observe that the minimum in the sum of squares of the error is both rather flat and asymmetric, pointing to a
1 2 3 4 5 6 7
0.4 0.6 1.1 1.1 1.0 0.7 0.5
interval l a N 6 8 9 9 9 10 18
interval 2a
--
1042: N 8 7 20 12 23 13 28
4 5 4 5 4 5 5
interval 3a
1042:
N
3.5 1.6 5.4 2.6 6.7 3.5 12.1
6 7 11 11 10 13 20
a The intervals are defined in the text. numbered starting with the a-CH, group.
10‘‘~ 3.9 4.3 4.7 3.9 5.1 5.0 8.8
Carbons are
rather broad and asymmetric micelle size distribution. The amphiphiles studied were chosen since it could be expected that they would represent rather different aggregation patterns and this, indeed, may clearly be seen to be the case. Summarizing the results, we can see that the data for nonylammonium bromide closely follow the mass action law model with a single aggregation number (35 f 2 for the five carbons with the largest shifts). For sodium hexanoate the mean aggregation number is small (5 or less) over the whole concentration range studied. Sodium octanoate displays both features depending on concentration: first, formation of spa11 aggregates (4-5 monomers) and then formation of larger ones (10-11 monomers). The aggregation of both sodium hexanoate and sodium octanoate has been extensively studied by Danielsson, Stenius, and co-workers18-22with several experimental techniques. Although these investigations were performed in the presence of high concentrations of added salt and, therefore, not directly comparable with the present conditions it is of interest to correlate the two sets of data. (An advantage of the present technique is that salt addition is not required.) For hexanoate, the group in Abo inferred the presence of small aggregates of about the same size as found here but with larger aggregates ( N N 17). However, the different conditions should be remembered; the added electrolyte certainly favors aggregation as is well known from the lowering of critical micelle concentrations on salt addition. For sodium octanoate, Stenius and coworkers2l found, in addition to small aggregates ( N N 5), micellar aggregates with an aggregation number between 9 and 17, thus in agreement with the present results. The study of I3 C chemical shifts offers a very direct way of monitoring the amphiphile aggregation process and of deducing micelle aggregation numbers which are difficult to obtain in an unambiguous way by other experimental appro ache^.^^ However, the present approach contains simplifying assumptions which it is desirable to eliminate as far as possible and to assess their influence on the results. For example, it is important to establish to what extent an asymmetry of the error square sum is due to the model adopted. It is also important to include the effect of counterion binding. In this respect it is significant to note that a number of experimental findingsz3 are consistent with an ion condensation behavior analogous to that found for cylindrical p~lyelectrolytes.~~ Theoretical studies by Wennerstrom and c o - w o r k e r ~give ~ ~ -strong ~ ~ support for the idea that counterion condensation should be a general feature of aggregates of ionic amphiphiles and it is hoped that these results can be incorporated into the analyses of 13C data at a later stage. References a n d Notes (1) G. J. T. Tiddy, Spec. Period. Rep.: Nucl. Magn. Reson., 4, 233 (1975); 6, 207 (1977).
Cs+-H,O
Interaction in Lamellar Systems
(2) T. Nakagawa and F. Tokiwa in "Surface anc. Golloid Science", Vol 9, E. Matijevic, Ed., Wiiey, New York, 1976, p 69. (3) C. L. Khetrapal, A. C. Kunwar, A. C. Tracey, and P. Diehl, "Lyotropic Liquid Crystals", Springer-Verlag, Heidelberg, 1975. (4) H. Wennerstrom and B. Lindman, Phys. Rep., 52, 1 (1979). (5) J. C. Eriksson and G. Gillberg, Acta Chem. Scand., 20, 2019 (1966). (6) 8. Lindman and S. ForsBn, "Chlorine, Bromine and Iodine NMR. Physico-Chemical and Biological Applications", Springer-Verlag, Heidelberg, 1976. (7) B. Lindman, G. Lindblom, H. Wennerstrom, and H. Gustavsson, "Mlcellization, Solubilization and Microemulsions", K. L. Mittal, Ed., Plenum Press, New York, 1977, p 195. (8) J. B. Rosenholm, T. Drakenberg, and B. Lindman, J. Colloid Interface Sci., 63, 538 (1978). (9) E. Williams, 8. Sears, A. Allerhand, and E. H. Cordes, J. Am. Chem. SOC.,95, 4871 (1973). (10) U. Henriksson and L. Odberg, CoiioidPolym. Sci., 254, 35 (1976). (11) M.Alexandre, C. Fouchet, and P. Rigny, J . Chim. Phys., 70, 1073 (1973). (12) T. Drakenberg and 8. Lindman, J . Colloid Inferface Sci., 44, 184 (1973).
The Journal of Physical Chemistry, Vol. 83, No. 23, 1979 3015
(13) B.-0. Persson, T. Drakenberg, and 8. Lindman, J. Phys. Chem., 80, 2124 (1976). (14) J. N. Israelachvili, D. J. Mitchell, and B. N. Ninham, J . Chem. Soc., Faraday Trans. 2, 72, 1525 (1976). (15) P. Mukerjee, J. Phys. Chem., 76, 565 (1972). (16) P. Mukerjee in "Micellization, Solubilization and Microemulsions", Vol. 1, K. L. Mittal, Ed., Plenum Press, New York, 1977, p 171. (17) R. J. Tausk and J. Th. G. Overbeek, Biophys. Chem., 2, 175 (1974). (18) I . Danielsson, Fin. Kemistsarmf. Medd., 75, 65 (1966). (19) I.Danielssonand P. Stenius, J. Colbidlnterface Sci., 37, 264 (1971). (20) P. Stenius and C.-H. Zilliacus, Acta Chem. Scand., 25, 2232 (1971). (21) R. Friman, K. Pettersson, and P. Stenius, J . Colloid Interface Sci., 53, 90 (1975). (22) I.Danieisson, J. B. Rosenholm, P. Stenius, and S. Backlund, Progr. Colloid Polym. Sci., 61, 1 (1976). (23) B. Lindman and H. Wennerstrom, "Topics in Current Chemistry", Springer-Verlag, Heidelberg, in press. (24) G. S. Manning, Annu. Rev. Phys. Chem., 23, 117 (1972). (25) S. Engstrom and H. Wennerstrom, J. Phys. Chem., 82, 2711 (1978). (26) B. Jonsson and H. Wennerstrom, Chem. Scripf., in press. (27) G. Gunnarsson and H. Wennerstrom, J. Phys. Chem., in press.
Cesium Ion and Water Interaction in the Lamellar Phase of the I-Monooctanoin-Water-CsCI System. NMR Quadrupole Splittings and Chemical Shift Anisotropies Nils-Ola Persson and Goran Lindblom" Division of Physical Chemistry 2, Chemical Centre, University of Lund, S-220 07 Lund 7, Sweden (Received May 11, 1979) Publication costs assisted by the University of Lund
133Csand 2H magnetic resonance measurements on lamellar phases consisting of 1-monooctanoin, DzO, and CsCl are reported. The spectral parameters measured are 13Wsquadrupole splittings, shift anisotropies and isotropic chemical shifts, and deuteron quadrupole splittings. The dependencies of these parameters on amphiphile and salt concentration are discussed. The deuteron results indicate that a model assuming two kinds of water molecules, bound and free water, can be adapted. The cesium quadrupole splittings and shift anisotropies are in accordance with formerly obtained results for 23Naions. Evidence that the isotropic shifts of the cesium ion give a measure of the ion interactionwith the amphiphile polar group is presented. The splittings and chemical shift anisotropies are found to be almost temperature independent. It is shown that changes in the 133Cssplitting and chemical shift anisotropy are both due to changes in the fraction of bound ions and the order parameter for the 1-monooctanoin-water-CsC1system. When a second electrolyte is added changes also in the quadrupole coupling constant and/or the chemical shift tensor occur.
Introduction Lamellar liquid crystals have for a long time received much attention because of their suitability as models for biological membranes.' NMR provides a nondestructive and nonperturbative technique2i3to study molecular dynamics and molecular order in such systems. The ordering of the hydrocarbon chains in the interior of the amphiphile aggregates has been investigated mainly by means of deuteron magnetic resonance on deuterated hydrocarbon
nuclear quadrupole coupling constant or chemical shift tensors, r e ~ p e c t i v e l y ~ (see ~ ' ~ Jbelow). ~ However, often an estimate of the fraction of bound ions can be made from other studies,17 but the order parameter or quadrupole coupling constant are generally not obtained. Here an attempt has been made to improve the ion binding method by studying both quadrupole splittings and chemical shift anisotropies of cesium ions in a welldefined lamellar liquid crystalline system containing 1monooctanoin. A comparison between these NMR paramchain^.^^^ eters, considering the effect of temperature, water, and Information on water and counterion binding in lyoelectrolyte concentration, has then been made to extract tropic liquid crystals has been obtained from studies of information about the factors determining the splittings heavy wateP9 and counterion magnetic resonance methand shift anisotropies. Water orientation has also been o d ~ . ' ~ - The ' ~ NMR parameters measured have been relaxation times" (or line widths), quadrupole ~plittings,~-'~ studied by using 2H NMR on heavy water. or chemical shift anisotropies of both alkali16 (133Cs)and Method halide ions (19F-).'5Unfortunately, these experimental NMR parameters are often difficult to interpret in terms Extensive discussions of quadrupole splittings of quadof molecular interactions since the quadrupole splittings rupolar nuclei in different amphiphile systems have been or shift anisotropies are given by a product of the fraction given previously.'J4 Here only the relevant expressions of bound ions or molecules, the order parameter, and the for the splittings and chemical shift anisotropies for liquid 0022-3654/79/2083-30 15$0 1.OO/O
0 1979 American Chemical Society
