Alkyl and perfluoroalkyl glycolipid-based supramolecular assemblies

Approaches to the Synthesis of Perfluoroalkyl-Modified Carbohydrates and Derivatives: Thiosugars, Iminosugars, and Tetrahydro(thio)pyrans

Fluoroalkyl-substituted carbohydrates play relevant roles in diverse areas such as supramolecular chemistry, glycoconjugation, liquid crystals, and surfactants, with direct applications as wetting, antifreeze, and coating agents. In light of these promising applications, new methodologies for the late-stage incorporation of fluoroalkyl R_F groups into carbohydrates and derivatives are herein presented as they are relevant to the synthetic carbohydrate community. Previously reviewed protocols for the installation of R_F groups onto carbohydrates and derivatives will be succinctly summarized in the light of the new achievements. Fluoroalkyl-substituted iminosugars, on the other hand, are also interesting glycomimetic derivatives with prominent roles as glycosidases and glycosyltransferases inhibitors, as has recently been demonstrated. Also, they positively contribute to the study of sugar-protein interactions and enzyme mechanisms. New advances in the syntheses of fluoroalkyl-substituted iminosugars will also be presented here.

Non-Ionic Surfactant Vesicles (Niosomes) as New Drug Delivery Systems

Lipid vesicular systems composed of hydrated amphihiles with or without bilayer inducing agents such as cholesterol. On the basis of used amphiphilic molecule different nomenclature are used as liposomes, ufasomes and niosomes. Nonionic surfactants with mono-, di- or trialkyl chains form niosomes which are lipid vesicles with more chemical stability in comparison with phospholipids of liposomes. Both hydrophobic and hydrophilic chemicals can be encapsulated in niosomes as a new drug delivery system. This drug carrier system could have administered via injection, oral, pulmonary, vaginal, rectal, ophthalmic, nasal or transdermal routes with penetration enhancing potential. This chapter presents a detailed explain about niosome forming components, methods of preparation and routes of administration. Many examples for drug delivery potential of niosomes are also available in this review. Vaccine adjuvant and genetic substances vector capabilities are not given here.

Non-Ionic Surfactant Vesicles (Niosomes) as New Drug Delivery Systems

Lipid vesicular systems composed of hydrated amphihiles with or without bilayer inducing agents such as cholesterol. On the basis of used amphiphilic molecule different nomenclature are used as liposomes, ufasomes and niosomes. Nonionic surfactants with mono-, di- or trialkyl chains form niosomes which are lipid vesicles with more chemical stability in comparison with phospholipids of liposomes. Both hydrophobic and hydrophilic chemicals can be encapsulated in niosomes as a new drug delivery system. This drug carrier system could have administered via injection, oral, pulmonary, vaginal, rectal, ophthalmic, nasal or transdermal routes with penetration enhancing potential. This chapter presents a detailed explain about niosome forming components, methods of preparation and routes of administration. Many examples for drug delivery potential of niosomes are also available in this review. Vaccine adjuvant and genetic substances vector capabilities are not given here.

Tubular microstructures made from nonchiral single-chain fluorinated amphiphiles: impact of the structure of the hydrophobic chain on the rolling-up of bilayer membrane

The nonchiral, single-chain fluorinated amphiphiles derived from dimorpholinophosphate, C(n)F(2n+1)(CH(2))(m)OP(O)[N(CH(2)CH(2))(2)O](2) (FnCmDMPs), form hollow tubular bilayer-based self-assemblies when dispersed in water, ethanol/water mixtures, and dimethylformamide. The fluorinated tubules are highly stable and sturdy. Upon heating, they transform reversibly into giant multilamellar vesicles. Uncommon U-shaped and V-shaped coiled membranes were obtained from mixtures of FnCmDMPs. Depending on conditions, fluorinated tubules can evolve with time into collapsed flattened crystallized needles. The successive steps involved in the formation and evolution of these tubules were identified, and the specific features of fluorinated chains that are relevant to membrane coiling and tubule formation are discussed.

Elongated supramolecular assemblies in drug delivery

This review presents different lipid-based elongated microstructures: tubules, cochleate cylinders and ribbons. Their composition, process of preparation and the mechanism behind their formation is discussed as well as their use as a drug delivery system.

Carbohydrate- and related polyol-derived fluorosurfactants: an update

A short review of recent literature is presented on the synthesis, biological properties, colloid and surface chemistry, and applications of carbohydrate- and related polyol-derived amphiphiles with perfluoroalkyl hydrophobes.

Synthesis and supramolecular characterization of a novel class of glycopyranosyl-containing amphiphiles

A novel class of glycopeptidolipids is described, which potentially can be used as a novel antigen-delivery system. The compounds have been prepared by a combination of solid-supported and solution-based methods. The use of the orthogonally protected FmocLysDde derivative provided an opportunity to incorporate two different types lipids. It was found that the model compound 1 forms aggregates in aqueous media which can be described as rod or tubelike structures. The aggregates can be stabilized by topotactic photopolymerization. Studies on the structural analogues 2-5 revealed the effect of the carbohydrate, peptide, and lipid moiety on the aggregation properties. It is concluded that none of the structure elements can lay claim to be exclusively important for the formation of highly organized aggregates such as tubes, fibers, or helical ribbons from 1, but the presence of all of these structural elements afforded the most uniformly shaped extended structures.

Small-Angle Scattering and Electron Microscopy Investigation of Nanotubules Made from a Perfluoroalkylated Glucophospholipid

Anionic glucophospholipids were recently reported as a new family of tubule-forming lipids. We report here investigations on the structure of nanotubules made from a glucophospholipid with a mixed fluorocarbon-hydrocarbon hydrophobe, using freeze fracture and cryo-transmission electron microscopy (TEM) and X-ray and neutron small angle scattering (SAXS, SANS). The hollow and regularly shaped tubules are very thin: they have an external radius of 140 Å and an internal radius of 35 Å on the average. Their 105 Å-thick wall appears to consist in three bilayers in which the glucophospholipid molecules are probably in a tilted and/or interdigitated configuration. Upon heating these nanotubes convert reversibly into vesicles; transformation is complete at 60 degrees C. Copyright 1999 Academic Press.

Highly fluorinated amphiphiles and colloidal systems, and their applications in the biomedical field. A contribution

Fluorocarbons and fluorocarbon moieties are uniquely characterized by very strong intramolecular bonds and very weak intermolecular interactions. This results in a combination of exceptional thermal, chemical and biological inertness, low surface tension, high fluidity, excellent spreading characteristics, low solubility in water, and high gas dissolving capacities, which are the basis for innovative applications in the biomedical field. Perfluoroalkyl chains are larger and more rigid than their hydrogenated counterparts. They are considerably more hydrophobic, and are lipophobic as well. A large variety of well-defined, modular fluorinated surfactants whose polar head groups consist of polyols, sugars, sugar phosphates, amino acids, amine oxides, phosphocholine, phosphatidylcholine, etc, has recently been synthesized. Fluorinated surfactants are significantly more surface active than their hydrocarbon counterparts, both in terms of effectiveness and of efficiency. Despite this, they are less hemolytic and less detergent. Fluorosurfactants appear unable to extract membrane proteins. Fluorinated chains confer to surfactants a powerful driving force for collecting and organizing at interfaces. As compared to non-fluorinated analogs, fluorosurfactants have also a much stronger capacity to self-aggregate into discrete molecular assemblies when dispersed in water and other solvents. Even very short, single-chain fluorinated amphiphiles can form highly stable, heat-sterilizable vesicles, without the need for supplementary associative interactions. Sturdy microtubules were obtained from non-chiral, non-hydrogen bonding single-chain fluorosurfactants. Fluorinated amphiphiles can be used to engineer a variety of colloidal systems and manipulate their morphology, structure and properties. Stable fluorinated films, membranes and vesicles can also be prepared from combinations of standard surfactants with fluorocarbon/hydrocarbon diblock molecules. In bilayer membranes made from fluorinated amphiphiles the fluorinated tails segregate to form an internal teflon-like hydrophobic and lipophobic film that increases the stability of the membrane and reduces its permeability. This fluorinated film can also influence the behavior of fluorinated vesicles in a biological milieu. For example, it can affect the in vivo recognition and fate of particles, or the enzymatic hydrolysis of phospholipid components. Major applications of fluorocarbons currently in advanced clinical trials include injectable emulsions for delivering oxygen to tissues at risk of hypoxia; a neat fluorocarbon for treatment of acute respiratory failure by liquid ventilation; and gaseous fluorocarbon-stabilized microbubbles for use as contrast agents for ultrasound imaging. Fluorosurfactants also allow the preparation of a range of stable direct and reverse emulsions, microemulsions, multiple emulsions, and gels, some of which may include fluorocarbon and hydrocarbon and aqueous phases simultaneously. Highly fluorinated systems have potential for the delivery of drugs, prodrugs, vaccines, genes, markers, contrast agents and other materials.

Vesicles made of glycophospholipids with homogeneous (two fluorocarbon or two hydrocarbon) or heterogeneous (one fluorocarbon and one hydrocarbon) hydrophobic double chains

The vesicle-forming ability of the new anionic double chain glycophospholipids 1-4, with either two hydrocarbon or two perfluorocarbon chains, or a mixed double chain (one fluorinated, one hydrogenated), was investigated. When dispersed in water, 1a-c,e, 2b,c and 4b,c readily gave heat-sterilizable vesicles, 30-70 nm in diameter. The galactose and mannose-based fluorinated vesicles were also highly stable on aging. The 6-substituted glucose derivatives 3 formed tubules that reversibly interconverted into vesicles, depending on temperature. The leakage rate in buffer of carboxyfluorescein or calcein from vesicles made from 1a-c,e 2b,c and 4b,c depended on the sugar (t1/2 galactose > mannose > glucose). It decreased significantly with increasing fluorination and length of the hydrophobic tails. The mixed perfluorocarbon/hydrocarbon-tailed amphiphiles were found to be miscible with both the two fluorocarbon chains and the two hydrocarbon chains derivatives. Such admixing tended, however, to increase the small unilamellar vesicles' permeability. In buffered serum, all the vesicles investigated were highly permeable, but incorporation of cholesterol or DSPC in vesicles made of 1e significantly reduced their permeability in serum. The new vesicle and membrane components have i.v. maximum tolerated doses as high as 500 mg/kg body weight in mice; hemolytic activity sharply decreases with increasing degree of fluorination.

Fluorinated vesicles

Stable fluorinated vesicles--i.e. vesicles with a hydrophobic and lipophobic fluorinated film within their bilayer membranes--have been obtained from a variety of neutral, zwitterionic or anionic fluorinated amphiphiles, including single chain phosphocholine derivatives, double-chain phospholipids, glycolipids and glycophospholipids, as well as from combinations of standard phospholipids with amphiphilic mixed fluorocarbon/hydrocarbon compounds. The strong hydrophobic interactions developed by perfluoroalkyl chains result in increased membrane stability, as strikingly illustrated by the fact that even short single-chain fluorinated amphiphiles can form stable, heat-sterilizable vesicles without the need for any additive. They also result in increased versatility in the aggregation behavior of fluorinated surfactants, as shown by the formation, depending on molecular structure and experimental conditions, of a range of supramolecular assemblies other than vesicles, including disks, helical tubules and fibers, for example from fluorinated glycolipids. The more impermeable, adjustable fluorinated core within the liposomal membrane confers to liposomes added drug and probe encapsulation stability as compared to their hydrogenated analogs, whether in buffer or in serum. Fluorinated vesicles made from perfluoroalkylated phospholipids were also found to have 3 to 6 times longer circulation half-lives in mice than similarly sized conventional DSPC/cholesterol liposomes. Finally, the incorporation of mixed fluorocarbon/hydrocarbon alkanes or alkenes into standard liposomes may provide an alternative, straightforward and cost efficient approach to fluorinated vesicles.