J . Am. Chem. SOC.1989, 111, 3001-3006
300 1
Preparation and Characterization of Glycerol-Based Cleavable Surfactants and Derived Vesicles David A. Jaeger,* Janusz Jamrozik,' Timothy G. Golich, Malgorzata Wegrzyn Clennan, and Jamshid Mohebalian Contribution from the Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071. Received May 2, 1988. Revised Manuscript Received November 26, 1988
Abstract: Four cleavable double-chain surfactants were synthesized: [(2,2-diheptadecyl- 1,3-dioxolan-4-yl)methyl] trimethylammonium methanesulfonate ( l a ) , the analogous bromide (1 b), [ (2,2-diheptadecyl-1,3-dioxolan-4-yl)methyl]dimethyl(3-sulfopropyl)ammoniumhydroxide inner salt (IC), and sodium 3-[(2,2-diheptadecyl-1,3-dioxolan-4-yl)methoxy]1propanesulfonate (Id). Vesicles of la, lb, and Id prepared by sonication were characterized by 'H NMR line width narrowing, dynamic laser light scattering, differential scanning calorimetry, and dye entrapment and leakage studies. In vesicular form, the hydrolytic lability of Id was greater than that of l a / l b , due to a combination of electrostatic effects resulting from the different subtituents on the dioxolane ring. Neutral organic compounds can be readily isolated from vesicular solutions of Id after its hydrolysis. Thus Id is appropriate for the application of vesicular media to preparative chemistry.
Vesicles a r e closed bilayer structures formed by double-chain surfactants in water.2 Numerous organic reactions have been performed in vesicular media,* and in several instances impressive selectivity has been realized that is unobtainable in conventional solvent^.^ In general, such selectivity derives from the ability of vesicles to solubilize, orient, and compartmentalize reactants. Before vesicular media can be used on a practical level in preparative chemistry, however, a major obstacle must be overcome, namely, the difficulty inherent in the isolation of products from surfactant-based solutions. As presented herein, we have addressed this problem by the preparation and characterization of cleavable double-chain surfactants 1 and their derived vesicles. After their fl-Cl7H35
Scheme I' C17H35
HOCH2
\C=O / C17H35
f
-
-
HOCH l
b
a
I
2
CHzOH
3
C
O-CHz
\,.I
la
I
I
CH20SOzMe 4 HOCH2
-
CHzX
2
+
la, X N'MeaMeSOf b , X = N+MesBrc, X =N*M~z(CHZ)~SO~ d , X = O(CH2)aSOJNa'
use in vesicular form, 1 can be converted to nonsurfactant compounds to facilitate product isolation by standard procedures. Several other cleavable double-chain surfactant^,^ a s well as a variety of single-chain analogue^,^ have been described recently.
c17
/\
CH2Br
C17H35
"-TH
CH2Br
5
Scheme IIa C17H35
(1) On leave from Jagiellonian University, Krak6w, Poland. (2) Fendler, J. H. Membrane Mimetic Chemistry; Wiley-Interscience: New York, 1982; Chapters 6 and 12. (3) For example, see: (a) Porter, N. A,; Ok,D.; Huff, J. B.; Adams, C. M.; McPhail, A. T.; Kim, K. J . A m . Chem. SOC.1988,110, 1896. (b) Ueoka,
0002-7863/89/1511-3001$01.50/0
5 lb
L
HOCH
Results Syntheses. T h e preparations of l a and l b a r e outlined in Scheme I. Ketalization of glycerol with ketone 2 gave hydroxy
R.; Matsumoto, Y . ;Moss, R. A.; Swarup, S.; Sugii, A,; Harada, K.; Kikuchi, J.; Murakami, Y. J . A m . Cbem. SOC.1988, 110, 1588. (c) Groves, J. T.; Newmann, R. J . Org. Chem. 1988, 53, 3891. (d) Mitzutani, T.; Whitten, D. G. J . A m . Cbem. SOC.1985, 107, 3621 and references therein. (4) (a) Jaeger, D. A,; Chou, P. K.; Bolikal, D.; Ok, D.; Kim, K. Y.; Huff, J. B.; Yi, E.; Porter, N. A. J . A m . Cbem. SOC.1988, 110, 5123. (b) Jaeger, D. A.; Golich, T. G. J . A m . Oil Chem. SOC.1987, 64, 1550. (c) Nuhn, P.; Dobner, B.; Kertscher, P.; Weissflog, W.; Brezesinski, G. Pbarmazie 1981, 36, 537. (d) Eibl, H.; Nicksch, A. Cbem. Pbys. Lipids 1978, 22, 1. ( 5 ) (a) Jaeger, D. A.; Ward, M. D.; Dutta, A. K. J . Org. Cbem. 1988,53, 1557. (b) Jaeger, D. A.; Finley, C. T.; Walter, M. R.; Martin, C. A. J . Org. Chem. 1986,51, 3956. (c) Jaeger, D. A.; Martin, C. A.; Golich, T. G. J . Org. Chem. 1984, 49, 4545. (d) Jaeger, D. A,; Frey, M. R. J . Org. Cbem. 1982, 47, 31 I . (e) Cuomo, J.; Merrifield, J. H.; Keana, J. F. W. J. Org. Chem. 1980, 45, 4216. (f) Epstein, W. W.; Jones, D. S.; Bruenger, D.; Rilling, H. C. Anal. Biochem. 1982, 119, 304. (9) Hayashi, Y.; Shirai, F.; Shimizu, T.; Nagano, Y.; Teramura, K. J . Am. Oil Cbem. SOC.1985, 62, 555.
H35c,0 ,-H ]z
O-CHZ
I
CH2NMe2
6 CHz-CHZ
6
+
\/so2
1
-
1C
CH2-0 7
3
b. c
ld
"(a) Me3N, MeOH; (b) NaH, C6H&(c) 7. ketal 3, which was converted to methanesulfonate 4. The reaction of 4 with M e , N in M e O H a t 7 5 OC yielded la. Ketalization of 3-bromo- 1,2-propanediol with 2 gave 5, which was converted to l b with the procedure for la. Alternatively, 5 was prepared from the reaction of 4 with LiBr in 3-pentanone.
0 1989 American Chemical Society
3002
J. Am. Chem. SOC.,Vol. 111, No. 8, 1989
I
Jaeger et al.
I Relative Mass
Figure 1. DLLS histograms for vesicular la, lb, and Id. The percent mass values for the populations are given in parentheses.
T h e syntheses of IC and Id are outlined in Scheme 11. A t 105 OC, 5 and M e 3 N in M e O H gave 6, which was converted to I C with sultone 7. Amine 6 likely derived from its S N 2 displacement by Br- from a n N-methyl group of initially formed lb. T h e reaction of t h e alkoxide ion derived from 3 with 7 gave Id. Vesicle Preparation and Characterization. Vesicles were prepared by sonication (150 W, bath, 50-55 "C) of surfactant in water/buffer solution and were characterized by 'H N M R line width narrowing, dynamic laser light scattering ( D L L S ) , differential scanning calorimetry ( D S C ) , and dye entrapment and leakage studies. Surfactant IC did not readily disperse in water on sonication and therefore was not included in these studies. The labilities of l a / l b and Id in vesicular form with respect to acid-catalyzed hydrolysis to 2 and 8 (eq 1) were also determined. Compounds 8b, 8c, and 8d were independently prepared and characterized (see Experimental Section).
-
HOFHZ
H30'
1
W
2
+
I
HOCH I
(1)
CHzX
0 a , X = N'Me3MeSO3c , X = NtMe2(CH2)3S0c
b , X = N'Me3Brd , X = O(CH2)3S03Nat
'H NMR Line Width Narrowing. T o a thin film of surfactant formed in a n N M R tube DzO was added. T h e system was sonicated for a given time (see Experimental Section) and its 'H N M R spectrum recorded. After a n additional sonication period, another 'H N M R spectrum was obtained. For la, lb, and Id, the line widths of the signals narrowed and their intensities increased in the second relative to the first spectrum. For example, for Id after 4 h the intensity of the methylene envelope a t 6 1.3 increased by a factor of 4 and its width a t half-height decreased by a factor of 0.7 relative t o the spectrum after 15 min of sonication. These observations are consistent with, but do not demand, the formation of vesicles.6 DLLS. A thin film of surfactant in a p H 7.4 phosphate buffer was sonicated for 1h, and the vesicular solution was filtered through a 0.45-wm Durapore filter. T h e filtrate was analyzed a t 23 OC by DLLS, and the resultant histograms of relative mass (6) (a) Finer, E. G.; Flook, A. G.; Hauser, H. Biochim. Biophys. Acra 1972, 260, 49. (b) Finer, E. G.; Flook, A. G.; Hauser, H. Biochim. Biophys. Acta 1972, 260, 59. (c) Browning, J. L. In Liposomes: From Physical Structure to Therapeutic Applications; Knight, C . G., Ed.; Elsevier/North Holland: New York, 1981; p 189.
(volume) vs hydrodynamic diameter for la, l b , and Id are given in Figure 1. For both la and lb, two, and for Id, three populations of particles were observed. DSC. T h e thermotropic properties of la, Ib, and Id were determined by D S C using two methods. In the first,' measurements were made on hydrated surfactant pellets resulting from the concentration of p H 7.4 vesicular solutions with a 3 0 0 0 0 molecular weight cut-off filter. The phase transition temperatures (T,) for la, l b , and Id were 37, 40, and 44 i 2 OC, respectively. A t T,, a bilayer undergoes a transition from the gel to the lessordered liquid crystalline state, corresponding to conformational changes of the n-alkyl groups.* In the second method, measurements were made on the vesicular solutions themselves, and the resultant thermograms a r e given in Figure 2. Single transitions were observed for l a and lb with T,'s of 38.0 and 39.3 f 0.5 OC and calorimetric enthalpies, AHHcal, of 43 and 41 kJ/mol, respectively. Several transitions were observed for Id: a t least two a t ca. 29 OC and one a t 44.2 f 0.5 "C. Micelles would not be expected to display phase transitions. Dye Entrapment and Leakage. Surfactant was sonicated in a p H 7.4 solution containing 0.050 M calcein, a fluorescent dye.' A t 25 "C, the resultant solution was first filtered through 0.4and 0.2-wm polycarbonate filtersi0 and then subjected to gel filtration chromatography" on Sephadex G-25-80 with a p H 7.4 phosphate buffer as eluant. For each surfactant, a portion of the dye eluted a t the void volume of the column. As described below, the fluorescence intensity of the eluant a t the void volume increased with time, consistent with the incorporation of dye in vesicles, but not micelles. For the latter, the fluorescence intensity would be invariant with time. T h e leakage of calcein from vesicles a t the void volume was determined by following the fluorescence intensity of the vesicular solution. T h e fluorescence quantum yield of this dye is concentration dependent and is relatively low a t 0.05 M calcein.' As calcein escapes from the vesicles into the bulk aqueous phase and is thus diluted, the fluorescence intensity of the solution increases. T h e course of calcein release from vesicles of l a , lb, and Id a t p H 7.4 and 20 OC over a n 8-h period is given in Figure 3. A t 8 h, the extents of release were 34%, 21%, and 21%, respectively. T h e enhancement of release a t lower p H s will be the subject of future study. Hydrolytic Lability. Vesicular solutions of l a , Ib, and Id in D,O were prepared by 4 h of sonication and then held a t 25 O C . In each case, there was no hydrolysis after 24 h as evidenced by 'H N M R analysis (absence of 2 and 8). Also, the line shapes and relative intensities of the signals did not change appreciably over the same period. A set of vesicular solutions identical with t h a t above was prepared, and after the sonication period, each solution a t 25 O C was adjusted to pD 1.4 with DCI-D,O after its ' H N M R spectrum was recorded. After 24 h, there were no signs of hydrolysis for l a and l b by ' H N M R analysis. However, the signals were substantially broader and less intense than those in the initial spectra. By 'H N M R analysis, Id completely hydrolyzed within 40 min. Complete hydrolysis of l a occurred during 2 h a t 50 "C in a sonicated 1:l:l (v/v/v) mixture of 1.0 M HCI-H20, CHC13, and E t O H . The organic solvents served to disrupt the vesicles and thus facilitated hydrolysis. A study of the kinetics of the hydrolysis of Id a t 25 O C and p H 3.0 in HC1-H20 gave a one-point, pseudo-first-order r a t e constant, k,, of 0.0123 f 0.0005 min-' over the first 30% of hydrolysis. This value corresponds to a half-life of 56 min. Since the nature of the system changed over the course of the hydrolysis, if for no other reason than the formation of hydrolysis products (7) Jacobson, K.; Papahadjopoulos, D. Biochemistry 1975, 14, 152. (8) Wilkinson, D. A,; Nagle, J. F. In ref 6c; p 273. (9) Allen, T. M. In Liposome Technology; Gregoriadis, G., Ed.; CRC Press: Boca Raton, FL, 1984; Vol. 3, p 177. (10) Szoka, F.; Olsen, F.; Heath, T.; Vail, W.; Mayhew, E.; Papahadjopoulos, D. Biochim. Biophys. Acta 1980, 601, 559. (1 1) Weinstein, J. N.; Yoshikami, S.; Henkart, P.; Blumenthal, R.; Hagins, W. A. Science (Washington, D.C.)1977, 195,489.
J . A m . Chem. Soc., Vol. 1 11, No. 8, 1989 3003
Glycerol-Based Cleauable Surfactants
1
I
15
25
35
45
55
65
15
I
,
25
35
45
1
I
55
65
10
I
I
eo
40
30
50
EO
Temoerature. ‘C
Figure 2. DSC thermograms for vesicular l a , lb, and Id.
cleavable surfactant would be extremely difficult if not impossible.
Discussion Two features of the above syntheses are noteworthy. First, the total lack of reaction a t 25 OC of 4/5 with M e 3 N in M e O H to give la/lb was surprising, since 9 can be converted to 10 under the same conditions (eq 2).13 The limited solubility of 4/5 cannot MeL
0-CH,
Me,
M e/
\0-CH 1
Me’
time, h
The hydrolytic labilities of the surfactants were also investigated by two F T - I R methods. In the first, a vesicular solution was concentrated a s above, and the resultant surfactant pellet was analyzed by the attenuated total reflectance ( A T R ) method. Specifically, vesicular solutions of la and lb in D 2 0 were adjusted to pD 1.4 with DCI-D,O a t 25 “ C . After 24 h, they were concentrated and analyzed. In each case, no absorption was detected in the 1700-cm-’ region, indicating the absence of 2 and thus the lack of hydrolysis, consistent with the ‘ H N M R results above. In a control, a mixture of lb and 13 mol % 2 in D 2 0 was sonicated for 4 h, followed by concentration and F T - I R analysis. Two absorption bands corresponding to 2 were clearly evident a t 1698 and 1704 cm-I. T h e observation of two bands suggests t h a t the carbonyl group of 2 resided in two different environments, which is not unreasonable given the heterogeneous nature of the sample. In the second F T - I R method, vesicular solutions identical with those above were analyzed without concentration using a cell with CaF, windows. However, this method was abandoned since ketone 2 could not be detected in control samples prepared from 5 mol % 2 and la or l b , presumably due to its insolubifity. Indeed, by visual inspection 2 did not dissolve during sonication of the control samples. A striking example of the potential for straightforward isolation of neutral organic products from vesicular I d was obtained in a study of the regiochemistry and relative rates of monohalogenation of n-alkyl phenyl ethers in vesicular media.12 In a control, 1.00 m L of 0.020 M vesicular Id containing 1.1 X IO4 M pentyl phenyl ether was subjected to a workup procedure involving the acidcatalyzed hydrolysis of I d to 2 and 8d. By H P L C analysis [25 cm X 4.6 m m i.d. column of IO-ym Econosil C 1 8 (Alltech); M e C N - H 2 0 elution; UV detection (210 nm)] of the resultant M e C N solution of pentyl phenyl ether (devoid of 2) with nonyl phenyl ether as an internal standard, the recovery of the former was 100% T h u s 0.018 mg of pentyl phenyl ether was isolated from a solution containing 14.5 mg of Id. In general, such an isolation from a vesicular solution based on a conventional non(12) Jaeger, D. A.; Clennan, M. W., to be published
‘0-CH
CH,Br
Figure 3. Calcein release from vesicular l a (O), l b (O),and Id (0).
2 and 8d, k , represents an average value.
0-CH2
C!H2N+Me3Br
9
10
be the sole reason for its lesser reactivity because 11, which should have a comparable solubility, yielded 12 in M e 3 N - M e O H a t 25 OC (eq 3).4a Perhaps the heptadecyl chains are coiled/aggregated
\’ j
Me
O-CHC16H33
Me3N+(CH2)3C
0- CHC16H33 11
Br-
\
(3)
O-CHCI~H~~
12
in M e O H with consequent steric hindrance of Me3N’s attack a t the primary carbon atom of 4/5. R a t e retardations due to the coiling/aggregation of long-chain alkyl groups have been reported previously for other systems.14 Second, the demethylation of N-methyl quaternary ammonium compounds by SN2 displacement with Br-/I- in a n alcohol solvent generally requires more drastic conditions than used to prepare 6 from 5.” T h e proposed displacement of 6 from a n N-methyl group of lb was perhaps facilitated by the latter’s aggregation. Such aggregation would concentrate Br- and the quaternary ammonium head groups a t the aggregate-MeOH interface, with a resultant greater S N 2 reactivity than expected for monomeric lb. However, it is generally believed that surfactants do not aggregate in MeOH.I6 But the aggregation of n-C,H2,+lNfMe3Br- ( n = 10, 12, 14, 16, and 18) in M e O H containing > 2 wt % C 6 H 6 has been reported.” In the D L L S histograms of Figure 1, the smaller particles grouped a t 64 nm for l a and lb are assigned to small unilamellar vesicles (SUV’s). For Id, the population grouped a t 26 nm is assigned to SUV’s, and that a t 105 nm to multilamellar vesicles (MLV’s). These assignments a r e generally consistent with the ranges of sizes for SUV’s and MLV’S., Micelles are not reasonable (13) Jaeger, D. A.; Mohebalian, J., to be published. (14) For example, see: Fan, W.-Q.; Jiang, X.-K. J.A m . Chem. Sor. 1985, 107, 7680 and references therein. (15) For example, see: (a) House, H. 0.; Muller, H. C.; Pitt, C. G.; Wickham, P. P. J . Org. Chem. 1963, 28, 2407. (b) Saito, S.; May, E. L. J. Org. Chem. 1962, 26, 4536. (16) Magid, L. In Solution Chemistry of Surfactants; Mittal, K. L., Ed.; Plenum Press: New York, 1979; Vol. 1, p 427. ( 1 7) Chattopadhyay, A. K.; Drifford, M.; Treiner, C. J . Phys. Chem. 1985, 89, 1537.
3004 J . A m . Chem. SOC.,Vol. 111, No. 8,1989 possibilities for these particles because they would likely have hydrodynamic diameters
