6 research outputs found
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 (2ā30 nm) in silica particles using a one-pot co-assembly
solāgel 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 <sup>13</sup>C 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 <sup>13</sup>C 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 <sup>13</sup>C 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 <sup>13</sup>C 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 Ā°C
Topological Connection between Vesicles and Nanotubes in Single-Molecule Lipid Membranes Driven by HeadāTail Interactions
Lipid
nanotubeāvesicle 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
nanotubesāvesicles 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 Ā°C under diluted conditions. Solid-state NMR demonstrates
that the glucolipid can assume two distinct configurations, headāhead
and headātail. 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>3Ģ
<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<sup>+</sup>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<sup>+</sup>, CTEA<sup>+</sup>, and CTPA<sup>+</sup>) having a constant chain length (C<sub>16</sub>) 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>3Ģ
<i>n</i> mesostructure: either an ordering
transition from concentrated flocs of spherical micelles (from CTEA<sup>+</sup> or CTPA<sup>+</sup>) for pure TEOS systems or a structural
transformation from an intermediate 2D hexagonal mesophase in organosilane
systems (from CTA<sup>+</sup>). 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<sup>+</sup> micellar surface. Finally, quite unexpectedly, we find a wormlike-to-sphere
micellar transition in the CTPA<sup>+</sup> system