Amphiphilic Glycolipids Research Articles

Discovery of synthesis and secretion of polyol esters of fatty acids by four basidiomycetous yeast species in the order Sporidiobolales.

Polyol esters of fatty acids (PEFA) are amphiphilic glycolipids produced by yeast that could play a role as natural, environmentally friendly biosurfactants. We recently reported discovery of a new PEFA-secreting yeast species, Rhodotorula babjevae, a basidiomycetous yeast to display this behavior, in addition to a few other Rhodotorula yeasts reported on the 1960s. Additional yeast species within the taxonomic order Sporidiobolales were screened for secreted glycolipid production. PEFA production equal or above 1g L-1 were detected in 19 out of 65 strains of yeast screened, belonging to 6 out of 30 yeast species tested. Four of these species were not previously known to secrete glycolipids. These results significantly increase the number of yeast species known to secrete PEFA, holding promise for expanding knowledge of PEFA synthesis and secretion mechanisms, as well as setting the groundwork towards commercialization.

Synthesis and Characterization of Four Diastereomers of Monorhamnolipids

Rhamnolipids are amphiphilic glycolipids biosynthesized by bacteria that, due to their low toxicity and biodegradability, are potential replacements for synthetic surfactants. The previously limited access to pure materials at the gram scale has hindered extensive characterization of rhamnolipid structure-performance behavior. Here, we present an efficient and versatile synthetic methodology from which four diastereomers of the most common monorhamnolipid, α-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate, are prepared and subsequently characterized. Exploration of their behavior at the air-water interface is reported and analyzed in terms of the absolute configuration of the lipid tail carbinols at pH 4.0 and 8.0. All diastereomers exhibit a minimum surface tension of about 28 mN/m without a significant difference between the protonated (nonionic) or deprotonated (anionic) states. At pH 4.0 (nonionic), all diastereomers have a critical micelle concentration (CMC) in the micromolar range. At pH 8.0 (anionic), CMC values for the (R,R), (S,S), and (S,R) diastereomers are approximately an order of magnitude higher than in their nonionic states, whereas the (R,S) diastereomer exhibits a CMC about five times larger.

The in situ gas-phase formation of a C-glycoside ion obtained during electrospray ionization tandem mass spectrometry. A unique intramolecular mechanism involving an ion-molecule reaction.

This study examines the electrospray ionization mass spectrometry (ESI-MS), in-source collision-induced dissociation (CID) fragmentation and low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of a synthetic pair of β- and α-anomers of the amphiphilic cholesteryl polyethoxy neoglycolipids containing the 2-azido-2-deoxy-D-galactosyl-D-GalN3 moiety. We describe the novel and unique in situ gas-phase formation of a C-glycoside ion formed during all these gas-phase processes and propose a reasonable mechanism for its formation. The synthetic amphiphilic glycolipids were composed of the 2-deoxy-2-azido-D-galactosyl moiety (GalN3, the hydrophilic part) covalently attached to a polyethoxy spacer which is covalently linked to the cholesteryl moiety (hydrophobic part). The 2-azido-2-deoxy-α- and β-D-galactosyl-containing glycolipids were studied by in-time and in-space ESI-MS and CID-MS/MS in positive ion mode, with quadrupole ion trap (QIT), quadrupole-quadrupole-time-of-flight (QqTOF), and Fourier transform ion cyclotron resonance (FTICR) instruments. Conventional single-stage ESI-MS analysis showed the formation of the protonated molecule. During the single-stage ESI-MS analysis and the CID-MS/MS of the [M+H](+) and [M+NH4](+) adducts obtained from both glycolipid anomers, the presence of a series of specific product ions with different intensities was observed, consistent with the [C-glycoside+H-N2](+), [cholestadiene+H](+), 2-deoxy-2-D-azido-galactosyl [GalN3](+), [GalNH](+) and [sugar-Spacer+H](+) ions. The gas-phase formation of the [C-glycoside+H-N2](+) ion isolated from the glycolipid anomers was observed during both the ESI-MS of the glycolipids and the CID-MS/MS analyses of the [M+H](+) ions and it was found to occur by an intramolecular rearrangement involving an ion-molecule complex. CID-QqTOF-MS/MS and CID-FTICR-MS(2) analysis allowed the differentiation of the two glycolipid anomers and showed noticeable variation in the intensities of the product ions.

Supramolecular Hydrogels Based on Glycoamphiphiles: Effect of the Disaccharide Polar Head

Supramolecular hydrogelators based on amphiphilic glycolipids have been prepared by clicking different sugar polar heads to a hydrophobic linear chain by copper(I)-catalyzed azide–alkyne [3 + 2] cycloaddition. The influence of the sugar polar head on the gelation properties in water has been studied, and the liquid crystalline properties of the amphiphilic materials have also been characterized. Stable hydrogels at room temperature have been obtained and the fibrillar supramolecular structures formed by the self-assembly have been studied by different microscopic techniques on the dried gel (xerogel) and hydrated conditions in order to characterize the micro- and nanostructures. Self-assembly gives rise to supramolecular ribbons with a torsion that is related to a chiral supramolecular arrangement of amphiphiles. The formation of an opposite helical arrangement of the ribbons has been found to depend on the sugar polar head. This fact was confirmed by circular dichroism (CD).

Synthesis and Characterization of Maltose-Based Amphiphiles as Supramolecular Hydrogelators

Low molecular mass amphiphilic glycolipids have been prepared by linking a maltose polar head and a hydrophobic linear chain either by amidation or copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition. The liquid crystalline properties of these amphiphilic materials have been characterized. The influence of the chemical structure of these glycolipids on the gelation properties in water has also been studied. Glycolipids obtained by the click coupling of the two components give rise to stable hydrogels at room temperature. The fibrillar structure of supramolecular hydrogels obtained by the self-assembly of these gelators have been characterized by electron microscopy. Fibers showed some torsion, which could be related with a chiral supramolecular arrangement of amphiphiles, as confirmed by circular dichroism (CD). The sol-gel transition temperature was also determined by differential scanning calorimetry (DSC) and NMR.

Purification of gangliosides by liquid-liquid partition chromatography

A liquid-liquid partition chromatographic technique was applied to separate amphiphilic glycolipids. A two-phase solvent system composed of n-butanol-t-butyl methyl ether-acetonitrile-water at a volume ratio of 3:1:1:5 was found to be suitable for separating the gangliosides from total lipids extracted from rat brain by liquid-liquid partition chromatographic systems, namely centrifugal partition chromatography (CPC) and high-speed counter-current chromatography. GM1 could be separated rapidly by using the upper phase as stationary phase for both systems. Moreover, various kinds of gangliosides (GM1, GD1a, GD1b, GT1b) could be separated individually by using the lower phase as stationary phase by CPC. The sample can be recovered without loss by these systems.

Purification by centrifugal partition chromatography of amphiphilic compounds, glycolipids and pseudo-glycolipids synthesized by using cells

Centrifugal partition chromatography (CPC) was applied to separate amphiphilic glycolipids and pseudo-glycolipids synthesized by using cells. Neutral and acidic lipid fractions were isolated by CPC under suitable conditions respectively. Separation of neutral lipid, Gb3-type and Gb4-type oligosaccharide synthesized by using cells, was performed with a two-phase solvent system composed of chloroform–methanol–water at a volume ratio of 5:6:4. On the other hand, separation of acidic lipid, GM3-type oligosaccharide synthesized by using cells, and ganglioside extracted from rat brain were performed with a two-phase solvent system composed of butanol–ethanol–1% acetic acid at a volume ratio of 4:1:5. 8.3 mg of Gb3 analogue, 5.1 mg of Gb4 analogue, and 19.5 mg of GM3 analogue were purified from 3.2 l of culture medium obtained by incubation of African green-monkey kidney (Vero) cells with 50 μM n-dodecyl β-lactoside using CPC.

Tilted supramolecular structures of amphiphilic glycolipids in straight‐core smectic C liquid crystals

Optical microscopic and the electric polarization studies show that amphiphilic glycolipids form tilted supramolecular structures in straight‐core tilted smectic liquid crystals. Glycolipid and chiral smectic C (SmC) structures show spontaneous polarization while glycolipid and non‐chiral SmC structures show no spontaneous polarization. We deduce from these observations that glycolipid molecules in chiral SmC structures nano‐segregate in tilted double layers sandwiched between layers of straight‐core liquid crystal molecules. In non‐chiral SmC structures, tilted glycolipid molecules are nano‐segregated in the layers of straight‐core liquid crystal molecules. This indicates that, in contrast to the currently accepted interdigitated model, amphiphilic glycolipids may already have a tilted structure.

Evidence for uncorrelated tilted layer structure and electrically polarized bilayers in amphiphilic glycolipids

A strong low-frequency dielectric relaxation mode spanning from below 100 Hz at low temperatures to 100 kHz at high temperature, x-ray diffraction studies, and optical microscopic observations show, contrary to the currently accepted models, that the glycolipid molecules are tilted with respect to the layer normal in the smectic phase but the tilt direction is not correlated between the bilayers. The tilted glycolipid bilayers are electrically polarized. The tilted structure and the electric polarization of amphiphilic glycolipids may play an important role in biological cell membrane.

Method for the OSO4-free preservation of brain tissue suitable for immunocytochemistry in TEM

Following conventional OsO4-fixation and embedding of brain tissue in Epoxide resins for ultrastructural investigations, on the one hand, the wellknown good depiction of structures is obtained, on the other hand, however, according to these procedures a considerable loss up to 80% of glycolipid-bound and up to 50% of glycoprotein-bound neuraminic acid of important native compounds has to be put up with. The fixation of brain tissue by 1% glutaraldehyde and 1% paraformaldehyde in 0.1 mol/l Na-K-phosphate-buffer, followed by dehydration in acetone or ethanol at--25 degrees C and embedding in Lowicryl K4M preserves for instance amphiphilic glycolipids (gangliosides) to a high degree (95%) and in addition provides a good depiction of neuronal structures. The incubation of ultrathin sections of carp brain, treated as described above, with the specific antibody Q211 against polar gangliosides gave first evidence for a specific labelling of these amphiphilic glycosphingolipids and their localization within the brain tissue.