Langmuir 1997, 13, 3247-3250
3247
Notes Cationic Surfactants with Counterions of Glucuronate Glycosides
Chart 1
F. M. Menger,* W. H. Binder, and J. S. Keiper Department of Chemistry, Emory University, Atlanta, Georgia 30322 Received February 3, 1997. In Final Form: March 28, 1997X
Introduction The past 100 years has seen new surfactants synthesized mainly from petroleum-based starting materials. Strong arguments could be made, however, for enhanced emphasis in the future on surfactants with at least a partial “natural product” component: (a) They are obtainable from renewable resources. (b) They are likely to be biodegradable. (c) “Natural” surfactants have a wealth of structural diversity that has yet to be explored. Consider, for example, surfactants made from glucose esterified with fatty acids. One could, in principle, selectively attach the fatty acids to any of the five hydroxyls of the sugar. How such structural variations would influence the properties of the resulting surfactant (e.g. detergency, foaming, rheology, biocompatibility, etc.) is not known. Clearly, a vast opportunity in colloid chemistry is available to anyone willing to carry out the synthetic work. We do not mean to imply that significant inroads into natural-product surfactants have not already taken place. A few arbitrarily selected papers will illustrate the current interest in the topic: Krafft, Riess, et al.1 have made new anionic glucophospholipids (1 in Chart 1 where R ) a double tail) that form hollow tubules. Schmidt and Jankowski2 reported a variety of surfactants with sugar head-groups including those with two sugars and one lipophilic tail (2). The Lattes group3 prepared new doublechain surfactants from glucose and lactose (3) as an alternative to AOT, an “unnatural” commercial surfactant. And we ourselves4 synthesized a variety of polyhydroxylated surfactants (4) with D-glucamine head-groups. The approach taken in the present note is different from that seen in Chart 1. Instead of incorporating a sugar into the head-group per se, our compounds combine an ordinary cationic amphiphile with an anionic sugar counterion. Structural modifications were then focused on the counterion as opposed to the primary amphiphilic entity. Compounds 5-7 illustrate the idea. Thus, hexa-
decyltrimethylammonium ion was provided with glucuX
Abstract published in Advance ACS Abstracts, June 1, 1997.
(1) Giulieri, F.; Guillod, F.; Greiner, J.; Krafft, M.-P.; Riess, J. G. Chem. Eur. J. 1996, 2, 1335. (2) Schmidt, R. R.; Jankowski, K. Liebigs Ann. 1996, 867. (3) Andre´-Barre`s, C.; Madelaine-Dupuich, C.; Rico-Lattes, I. New J. Chem. 1995, 19, 345. (4) Menger, F. M.; Catlin, K. K.; Chen, X. Y. Langmuir 1996, 12, 1471.
S0743-7463(97)00111-X CCC: $14.00
ronate counterions. Since the latter possess glycosidic tails of varying length (4, 8, and 12 carbons), the hydrophobicity of the counterions themselves was controlled. The question, therefore, was how these unusual hybrids of petroleum-based and natural-product-based components would behave. There was reasonable certainty that the glucuronate glycoside counterions would tightly associate with the hexadecyltrimethylammonium micelles. For one thing, even simple counterions such as chloride and bromide normally bind to cationic micelles to the extent of 6080% (the remainder residing in the diffuse double layer and beyond). The glucuronate glycoside counterions should be even more prone to reside at the micelle surface, owing to their hydrophobic moieties. When the counterion chain becomes long, as in 7, there would, of course, exist the elements of a mixed micelle. The amphiphilic properties of surfactants 5-7 were investigated using three different methods: (a) tensiometric determination of the critical micelle concentration (cmc); (b) dynamic light scattering of small vesicles; and (c) light microscopy of giant vesicles. Results and Discussion Several syntheses of glucopyranuronic acid glycosides, either by direct oxidation of alkyl glucosides or by glycosylation of an appropriately protected glucuronic acid, have been described.5 Since direct oxidation of the 6-hydroxyl in alkyl glucopyranosides is complicated by competing cleavage of the glycosidic bond and subsequent difficulties in product purification, we decided upon the latter approach. Thus, direct glycosidation was performed on methyl β-D-1,2,3,4-tetra-O-acetylglycopyranosiduronate (9; Scheme 1). This latter compound was obtained from D-glucurono-6,3-lactone (8) in two steps.6 Glycosylation of 9 with alcohols of varying chain length proved to be more difficult than expected. Attempted glycosylation via the 1-bromide (plus Hg2(CN)2 or silver triflate)6 and the 1-(phenylthio)glycoside (plus (dicollidine) iodonium perchlorate) failed to give any product. On the other hand, slow addition of SnCl4 to a solution of glycosyl donor (5) (a) Matsunaga, I.; Nagataki, S.; Tamura, Z. Chem. Pharm. Bull. 1984, 32, 2832. (b) Nakano, T.; Ito, Y.; Ogawa, T. Carbohydr. Res. 1993, 243, 43. (c) Bertho, J.-N.; Ferrie`res, V.; Plusquellec, D. J. Chem. Soc., Chem. Commun. 1995, 1391. (d) Timell, T. E.; Enterman, W.; Spencer, F.; Soltes, E. J. Can. J. Chem. 1965, 43, 2296. (e) Fabre, J.; Betbeder, D.; Paul, F.; Monsan, P. Synth. Commun. 1993, 23 (10), 1357. (6) Bollenback, G. N.; Long, J. W.; Benjamin, D. G.; Lindquist, J. A. J. Am. Chem. Soc. 1955, 77, 3310.
© 1997 American Chemical Society
3248 Langmuir, Vol. 13, No. 12, 1997
Notes
Scheme 1
Table 1. Cmc Values for Surfactants 5-7 plus Several Others entry
compound
1 2 3 4 5 6 7
5 6 7 HTAB HTAH HTAG
a
cationic chain length
counterion chain length
cmc, mM
16 16 16 16 16 16 0 (NMe4+)
4 8 12 0 (Br-) 0 (OH-) 0 (glucuronate) 12 (glucuronate)
1.0 0.22 0.04a 0.9 1.0 3.0 9.5
Vesicles are observed at 3.0 mM.
Figure 1. Plot of surface tension as a funciton of concentration: ∆, 5; O, 6; ], 7.
9 and alcohol in dichloromethane gave fair yields of the corresponding methyl 1-O-alkyl-2,3,4-tri-O-acetylglucopyranosiduronates 10-12. The configuration at the anomeric center was assigned as R owing to the small coupling constant (
