pH- and Time-Resolved <i>in Situ</i> SAXS Study of Self-Assembled Twisted Ribbons Formed by Elaidic Acid Sophorolipids

Conditions that favor the helical structure formation in structurally similar sophorolipids (SLs), that is, elaidic acid SLs (having a <i>trans</i> double bond between the C9 and C10 positions of the alkyl chain) and stearic acid SLs (no double bond), are presented here. The helical self-assembled structures formed by elaidic acid SLs were independent of pH and also were mediated by a micellar intermediate. On the other hand, the stearic acid SLs formed helical structures under low pH condition only. Astonishingly, the formation routes were found to be different, albeit the molecular geometry of both SLs is similar. Even if a conclusive mechanistic understanding must await further work, our studies strongly point out that the noncovalent weak interactions in elaidic acid SLs are able to overcome the electrostatic repulsions of the sophorolipid carboxylate groups at basic pH and facilitating the formation of helical structures. On the other hand, the hydrophobic interactions in stearic acid SLs endow the helical structures with extra stability, making them less vulnerable to dissolution upon heating

Using Evaporation-Induced Self-Assembly for the Direct Drug Templating of Therapeutic Vectors with High Loading Fractions, Tunable Drug Release, and Controlled Degradation

A novel one-step approach for designing nonaggregated silica-based mesostructured therapeutic vectors is presented. Evaporation-induced self-assembly was used in combination with amphiphilic drugs for preparing already loaded class I and class II hybrid materials containing from 50 to 60 wt % (up to 75 vol %) of three drugs (glucosyl-resveratrol, stearoyl choline, sophorolipid). A good mesostructuration was able to promote an interfacial control of the drug release in PBS medium. The investigation of both release mechanisms and matrix dissolution was conducted via in situ ellipsometry and NMR. It proved that the nature of the drug/matrix interaction, the chemical composition of the drug/matrix interface, and the mesostructuration quality parameters must be taken into account at the same time for tuning the drug release rate, while maintaining the dissolution rate of silica at a reasonable level for limiting its toxicity. It proved also that noncalcined as-made silica-based class I hybrid materials can be efficiently used for tuning drug release kinetics from 1 h to day scale

One-Step Introduction of Broad-Band Mesoporosity in Silica Particles Using a Stimuli-Responsive Bioderived Glycolipid

Stimuli-responsive glycolipid biosurfactants belonging to the family of acidic sophorolipids (SL) have been used to introduce a broad range of pore size in the mesoscale regime (2–30 nm) in silica particles using a one-pot co-assembly sol–gel route in water. The pore size distribution is tailored by the sole interaction between an amino-modified silane, aminopropyltriethoxy silane (APTES), and SL. No additional compounds (e.g., block copolymers, polymers, organic solvents, pore-swelling agents) have been used to promote the formation of mesopores larger than 2 nm. Materials morphology and porosity have been characterized by high resolution TEM, SEM, and nitrogen physisorption, while the interaction between the glycolipid and silica is demonstrated by FT-IR and solid-state NMR

Hydrothermal Carbon from Biomass: Structural Differences between Hydrothermal and Pyrolyzed Carbons via ¹³C Solid State NMR

The objective of this paper is to better describe the structure of the hydrothermal carbon (HTC) process and put it in relationship with the more classical pyrolytic carbons. Indeed, despite the low energetic impact and the number of applications described so far for HTC, very little is known about the structure, reaction mechanism, and the way these materials relate to coals. Are HTC and calcination processes equivalent? Are the structures of the processed materials related to each other in any way? Which is the extent of polyaromatic hydrocarbons (PAH) inside HTC? In this work, the effect of hydrothermal treatment and pyrolysis are compared on glucose, a good model carbohydrate; a detailed single-quantum double-quantum (SQ-DQ) solid state ¹³C NMR study of the HTC and calcined HTC is used to interpret the spectral region corresponding to the signal of furanic and arene groups. These data are compared to the spectroscopic signatures of calcined glucose, starch, and xylose. A semiquantitative analysis of the ¹³C NMR spectra provides an estimation of the furanic-to-arene ratio which varies from 1:1 to 4:1 according to the processing conditions and carbohydrate employed. In addition, we formulate some hypothesis, validated by DFT (density functional theory) modeling associated with ¹³C NMR chemical shifts calculations, about the possible furan-rich structural intermediates that occur in the coalification process leading to condensed polyaromatic structures. In combination with a broad parallel study on the HTC processing conditions effect on glucose, cellulose, and raw biomass (Falco, C.; Baccile, N.; Titirici, M.-M. <i>Green Chem.</i>, <b>2011</b>, DOI: 10.1039/C1GC15742F), we propose a broad reaction scheme and in which we show that, through HTC, it is possible to tune the furan-to-arene ratio composing the aromatic core of the produced HTC carbons, which is not possible if calcination is used alone, in the temperature range below 350 °C

Topological Connection between Vesicles and Nanotubes in Single-Molecule Lipid Membranes Driven by Head–Tail Interactions

Lipid nanotube–vesicle networks are important channels for intercellular communication and transport of matter. Experimentally observed in neighboring mammalian cells but also reproduced in model membrane systems, a broad consensus exists on their formation and stability. Lipid membranes must be composed of at least two molecular components, each stabilizing low (generally a phospholipid) and high curvatures. Strong anisotropy or enhanced conical shape of the second amphiphile is crucial for the formation of nanotunnels. Anisotropic driving forces generally favor nanotube protrusions from vesicles. In this work, we report the unique case of topologically connected nanotubes–vesicles obtained in the absence of directional forces, in single-molecule membranes, composed of an anisotropic bolaform glucolipid, above its melting temperature, Tm. Cryo-TEM and fluorescence confocal microscopy show the interconnection between vesicles and nanotubes in a single-phase region, between 60 and 90 °C under diluted conditions. Solid-state NMR demonstrates that the glucolipid can assume two distinct configurations, head–head and head–tail. These arrangements, seemingly of comparable energy above the Tm, could explain the existence and stability of the topologically connected vesicles and nanotubes, which are generally not observed for classical single-molecule phospholipid-based membranes above their Tm

In Situ Time-Resolved SAXS Study of the Formation of Mesostructured Organically Modified Silica through Modeling of Micelles Evolution during Surfactant-Templated Self-Assembly

The mechanisms of formation of organically modified (phenyl, vinyl, and methyl) silica materials with cubic <i>Pm</i>3̅<i>n</i> and hexagonal <i>p</i>6<i>m</i> periodic mesostructures obtained in one step in the presence of the cetyltrimethylammonium bromide (CTA⁺B) surfactant are reported in this study. Understanding the way these complex materials form is difficult but undoubtedly necessary for controlling the material structure and its properties because of the combined presence of surface organic groups and large surface areas. Here, the mechanism of formation is clarified on the basis of the modeling of time-resolved in situ small angle X-ray scattering (SAXS) experiments, with a specific focus on the micelle evolution during material formation. Their fast self-assembly is followed for the first time with a quick temporal resolution of a few seconds using a third-generation synchrotron radiation source. To better understand the behavior of the complex organic-containing mesostructure, we perform a comparative study with the corresponding organo-free, isostructural materials obtained from three different surfactants (CTA⁺, CTEA⁺, and CTPA⁺) having a constant chain length (C₁₆) and an increasing polar head volume (met-, et-, and prop-). Numerical modeling of SAXS data was crucial to highlighting a systematic sphere-to-rod micellar transition, otherwise undetected, before the formation of the 2D hexagonal phase in both organo-free and organo-containing systems. Then, two different pathways were found in the formation of the cubic <i>Pm</i>3̅<i>n</i> mesostructure: either an ordering transition from concentrated flocs of spherical micelles (from CTEA⁺ or CTPA⁺) for pure TEOS systems or a structural transformation from an intermediate 2D hexagonal mesophase in organosilane systems (from CTA⁺). Combining the comparison between organo-free and organo-containing systems with numerical modeling, we find that the hexagonal-to-cubic phase transition in the organically modified materials seems to be strongly influenced not only by the obvious presence of the organic group but also by the quicker and more massive condensation kinetics of silicate oligomers on the CTA⁺ micellar surface. Finally, quite unexpectedly, we find a wormlike-to-sphere micellar transition in the CTPA⁺ system