FULL PAPER z Anionic Glucophospholipids-A New Family of Tubule-Forming Amphiphiles Franqoise Giulieri, Friidiiric Guillod, Jacques Greiner, Marie-Pierre Krafft,* and Jean G. Riess* Abstract: zyxwvutsrqpon A new family of amphiphiles that form tubules (i.e.. hollow cylindrical bilayer-based microstructures) by self- aggregation has been identified, namely, anionic glucophospholipids of type 1, in which a double-tailed hydrophobe is grafted through a phosphate linkage to the 0-6 position of a polar glucose head group. Compounds 1 a-c self-assemble into stable, hollow tubular microstruc- tures when dispersed in water and cooled below the temperature at which the transi- tion between crystal and liquid-crystal phases takes place (estimated from change in turbidity). The diameter of the mi- crostructures appears to depend on the nature of the hydrophobic tail, signifi- cantly smaller diameters being obtained for fluorinated tails. No tubules were ob- tained when galactose (2a-c, pH zyxwv < 11) or mannose (3a-c) derivatives were used in- stead of glucose derivatives. or when glu- cose was derivatized at the 0 - 3 zyxwv (4b) rather than 0-6 position; in these cases only vesi- cles were formed. Tubules made of 1 con- verted rapidly into giant vesicles when Keywords amphiphiles * glucophospholipids * self-assembly * tubules - vesicles Introduction Glycolipids are important naturally occurring compounds.['] Almost all living cells have, for example, a surface glycocalyx consisting of glycoproteins and glycolipids, often terminated by sialic acid residues. The carbohydrates present on the cell sur- face are involved in a variety of receptor and signaling phenom- ena. Phosphorylated lipopolysaccharides are major components of gram-negative bacteria such as zyxwvutsrq E. Coli and Salmonella zyxwvut fy- phimuriurn.[21 They constitute the prime targets of the antibodies produced by the immune system in response to bacterial infec- tion. In drug delivery and targeting, oligosaccharides constitute potential recognition sites for carbohydrate-mediated interac- tions between cells and drug carriers (such as liposomes) which bear such site-directing molecules.[31 Sugar derivatives can be present as co-amphiphiles in vesicles made of phospholipids (monosialoganglioside GM 1. for example),14* '1 or can be cova- lently linked onto vesicles.[61 The formation of vesicles (lipo- somes) from various glyc~lipids,[~~ including fluorinated glyco- lipids['] and phosphoglycolipids.~g~ has been reported. Microtubules fulfill essential functions in eukaryotic cells.[101 Tubules, together with microfilaments and intermediate fila- ments, are the major constituents of the cytoskeleton. They are ['I Prof. 1. G. Riess. Dr. M. P. KraTTt. Dr. F. Giulieri. Dr. F. Guillod. Dr. 1. Greiner Unite de Chimie Molkulaire. associk au CNRS Universite de Nice-Sophia Antipolis. Faculte des Sciences Parc Valrose. 06108 Nice, Cedex 02 (France) Fax: Inl. code +(92)07-6144 e-mail: mpkw naxos.unice.fr heated; they spontaneously formed again upon cooling. The presence of a fluorinat- ed chain, as in 1 b and 1 c, increased the temperature at which the tubule-vesicle interconversion occurred to above room temperature. Because the amphiphiles are negatively charged, the formation of tubules is pH-dependent and is favored at higher pH. These findings support the view that hydration of and hydrogen bonds between polar heads play a major role in tubule formation. Hydration of the sugar-derived head groups decreases as the number of intermolecular hydrogen bonds increases; this favors membrane crystallization and tubule formation. the main components of stable assemblies such as the axoneme, centrosome, and other complex structures found in protozoa. They participate actively in various processes at the cellular level, notably in cell division, cell motility and intracellular transport. They also interact with a large number of proteins, including kinesin and dynein, the motor proteins, and cross- linking proteins such as nexin.1' '-''] Other naturally occurring lipid tubules are present on the surface of pine needle stomata responsible for C0,/02 exchange.[l4] These tubules are mainly composed of lO-nona~osanol[~~] and their purpose is to filter off dust particles, which would otherwise clog the transpiration pores on the leafs surface. It has also been shown that wax filaments consisting of tubular crystals are secreted by in- SeCtS.1161 Synthetic nanotubes have been obtained from novel forms of carbon, discovered since the mid-1 980's. They include tubular fullerenes," 7* Is] and graphitic and single-layer carbon nano- tubes.[1g* ' ' I Other tubules result from the self-assembly of am- phiphiles. With very few exceptions, the latter are chiral and/or can bind by means of hydrogen bonds between polar heads. These tubules usually consist of coiled single or multiple bilayer sheets; the volume of their aqueous core ranges from more to less significant. Tubules are generally considered to be quasi- crystalline assemblies, more ordered than The num- ber of tubule-forming molecules identified so far is still relatively small and principally includes certain alkylaldonamides,[221 amin~acids,'~'. 241 glut am ate^.[*^^ gIycolipids,['] phospholipid - nucleoside conjugates,'26. 271 diacetylenic lipid- biotin conjugates,[291 and porphyrin derivatives.1301 zy Cliem. On. J. 19%. 2. No. 10 lp VCH ~erlagsgesellsrhafr mbH. 0-69451 Weinhcim. 1996 0947-6539/96/02/0-133S B IS.O0+._75iO 1335