Measuring the bending rigidity of microbial glucolipid (biosurfactant) bioamphiphile self-assembled structures by neutron spin-echo (NSE): interdigitated vesicles, lamellae and fibers

Bending rigidity, k, is classically measured for lipid membranes to characterize their nanoscale mechanical properties as a function of composition. Widely employed as a comparative tool, it helps understanding the relationship between the lipid's molecular structure and the elastic properties of its corresponding bilayer. Widely measured for phospholipid membranes in the shape of giant unilamellar vesicles (GUVs), bending rigidity is determined here for three self-assembled structures formed by a new biobased glucolipid bioamphiphile, rather associated to the family of glycolipid biosurfactants than phospholipids. In its oleyl form, glucolipid G-C18:1 can assemble into vesicles or crystalline fibers, while in its stearyl form, glucolipid G-C18:0 can assemble into lamellar gels. Neutron spin-echo (NSE) is employed in the q-range between 0.3 nm-1 (21 nm) and 1.5 nm-1 (4.1 nm) with a spin-echo time in the range of up to 500 ns to characterize the bending rigidity of three different structures (Vesicle suspension, Lamellar gel, Fiber gel) solely composed of a single glucolipid. The low (k= 0.30 $\pm$ 0.04 kbT) values found for the Vesicle suspension and high values found for the Lamellar (k= 130 $\pm$ 40 kbT) and Fiber gels (k= 900 $\pm$ 500 kbT) are unusual when compared to most phospholipid membranes. By attempting to quantify for the first time the bending rigidity of self-assembled bioamphiphiles, this work not only contributes to the fundamental understanding of these new molecular systems, but it also opens new perspectives in their integration in the field of soft materials

Myelin figures from microbial glycolipid biosurfactant amphiphiles

Myelin figures (MFs) -- cylindrical lyotropic liquid crystalline structures consisting of concentric arrays of bilayers and aqueous media -- arise from the hydration of the bulk lamellar phase of many common amphiphiles. Prior efforts have concentrated on the formation, structure, and dynamics of myelin produced by phosphatidylcholine (PC)-based amphiphiles. Here, we study the myelinization of glycolipid microbial amphiphiles, commonly addressed as biosurfactants, produced through the process of fermentation. The hydration characteristics (and phase diagrams) of these biological amphiphiles are atypical (and thus their capacity to form myelin) because unlike typical amphiphiles, their molecular structure is characterized by two hydrophilic groups (sugar, carboxylic acid) on both ends with a hydrophobic moiety in the middle. We tested three different glycolipid molecules: C18:1 sophorolipids and single-glucose C18:1 and C18:0 glucolipids, all in their nonacetylated acidic form. Neither sophorolipids (too soluble) nor C18:0 glucolipids (too insoluble) displayed myelin growth at room temperature (RT, 25 C). The glucolipid C18:1 (G-C18:1), on the other hand, showed dense myelin growth at RT below pH 7.0. Examining their growth rates, we find that they display a linear L $\alpha$ t (L, myelin length; t, time) growth rate, suggesting ballistic growth, distinctly different from the L $\alpha$ t^(1/2) dependence, characterizing diffusive growth such as what occurs in more conventional phospholipids. These results offer some insight into lipidic mesophases arising from a previously unexplored class of amphiphiles with potential applications in the field of drug delivery

Chemical Modification of Xylan

Our study is part of the general context of valuing by-products from the wood industry, which consists of the chemical modification of xylan by synthesis of branched copolymers such as xylan-g-PLLA. The used xylan is extracted from chestnut and 4-dimethylaminopyridine (DMAP) is the catalyst. In fact, the synthesis of xylan-graft-poly (L-lactide) copolymer starting from natural and renewable resource products xylan and L-lactide is performed under different conditions. The results of the grafting reaction are unfavorable due to longer time because of depolymerization reactions. Another result is the solubility and insolubility of the copolymers synthesized in water. This first result indicates that there is a change in the properties of xylan. Moreover, the solubility of the xylan-g-PLLA copolymers is different from one study to another. Grafting of PLLA onto xylan was confirmed by Fourier transform infrared (FT-IR) and 1HNMR analyzes. The dynamic mechanical analysis showed that the xylan-g-PLLA plastic materials have interesting thermomechanical properties

Design and synthesis of triphenylphosphonium-porphyrin@xylan nanoparticles for anticancer photodynamic therapy

Most photosensitizers (PS) suffer from a lack of water solubility and from a low selectivity toward tumor cells. Delivery systems using nanoparticles make it possible to improve PS water solubility, and also tumor targeting via the enhanced permeability and retention (EPR) effect. Among the organelles, mitochondria are attractive target sites for drug-delivery strategies since they perform a variety of key cellular processes. Our study was aimed at synthesizing nanoparticles consisting of xylan-carrying porphyrins attached to a triphenylphosphonium moiety, in order to enhance the PDT effect through mitochondrial targeting. Hybrid nanoparticles were designed that consisted of a silica core coated with xylan substituted with porphyrin derivatives carrying a triphenylphosphonium moiety. These hybrid nanoparticles have been constructed, along with their counterparts devoid of silica core, taking into consideration the controversy surrounding the use of silica nanoparticles. Phototoxicity experiments, conducted against the HCT-116 and HT-29 colorectal cancer cell lines, showed that nanoparticles with porphyrins bearing a triphenylphosphonium moiety exhibited an enhanced photocytotoxic effect in comparison with free porphyrin or nanoparticles with porphyrins without the triphenylphosphonium moiety

Design and synthesis of triphenylphosphonium-porphyrin@xylan nanoparticles for anticancer photodynamic therapy

Most photosensitizers (PS) suffer from a lack of water solubility and from a low selectivity toward tumor cells. Delivery systems using nanoparticles make it possible to improve PS water solubility, and also tumor targeting via the enhanced permeability and retention (EPR) effect. Among the organelles, mitochondria are attractive target sites for drug-delivery strategies since they perform a variety of key cellular processes. Our study was aimed at synthesizing nanoparticles consisting of xylan-carrying porphyrins attached to a triphenylphosphonium moiety, in order to enhance the PDT effect through mitochondrial targeting. Hybrid nanoparticles were designed that consisted of a silica core coated with xylan substituted with porphyrin derivatives carrying a triphenylphosphonium moiety. These hybrid nanoparticles have been constructed, along with their counterparts devoid of silica core, taking into consideration the controversy surrounding the use of silica nanoparticles. Phototoxicity experiments, conducted against the HCT-116 and HT-29 colorectal cancer cell lines, showed that nanoparticles with porphyrins bearing a triphenylphosphonium moiety exhibited an enhanced photocytotoxic effect in comparison with free porphyrin or nanoparticles with porphyrins without the triphenylphosphonium moiety

The origins and development of Zuwīla, Libyan Sahara: an archaeological and historical overview of an ancient oasis town and caravan centre

Zuwīla in southwestern Libya (Fazzān) was one of the most important early Islamic centres in the Central Sahara, but the archaeological correlates of the written sources for it have been little explored. This paper brings together for the first time a detailed consideration of the relevant historical and archaeological data, together with new AMS radiocarbon dates from several key monuments. The origins of the settlement at Zuwīla were pre-Islamic, but the town gained greater prominence in the early centuries of Arab rule of the Maghrib, culminating with the establishment of an Ibāḍī state ruled by the dynasty of the Banū Khaṭṭāb, with Zuwīla its capital. The historical sources and the accounts of early European travellers are discussed and archaeological work at Zuwīla is described (including the new radiocarbon dates). A short gazetteer of archaeological monuments is provided as an appendix. Comparisons and contrasts are also drawn between Zuwīla and other oases of the ash-Sharqiyāt region of Fazzān. The final section of the paper presents a series of models based on the available evidence, tracing the evolution and decline of this remarkable site

Erwin Panofsky. Tomb sculpture, Us Changing Aspects from Ancient Egypt to Bernini

Chaleix P. Erwin Panofsky. Tomb sculpture, Us Changing Aspects from Ancient Egypt to Bernini. In: Bulletin Monumental, tome 131, n°2, année 1973. pp. 188-191

Sahara. Revue internationale de préhistoire et histoire du Sahara

Robert-Chaleix Denise. Sahara. Revue internationale de préhistoire et histoire du Sahara. In: Revue française d'histoire d'outre-mer, tome 82, n°307, 2e trimestre 1995. p. 218

Erwin Panofsky. Tomb sculpture, Us Changing Aspects from Ancient Egypt to Bernini

Chaleix P. Erwin Panofsky. Tomb sculpture, Us Changing Aspects from Ancient Egypt to Bernini. In: Bulletin Monumental, tome 131, n°2, année 1973. pp. 188-191

Mester de Paradj Corinne & Mester. - Regards sur l'habitat traditionnel au Niger

Robert-Chaleix Denise. Mester de Paradj Corinne & Mester. - Regards sur l'habitat traditionnel au Niger. In: Cahiers d'études africaines, vol. 30, n°118, 1990. p. 218