285 research outputs found
Marie Morelle, YaoundĂ© carcĂ©rale. GĂ©ographie dâune ville et de sa prison
Sâil se concentre sur un Ă©tablissement carcĂ©ral spĂ©cifique, lâouvrage de Marie Morelle nâest pas une monographie. DĂšs lâentame de lâintroduction, lâauteure souligne que cette enquĂȘte sur la prison centrale de YaoundĂ©, appelĂ©e Kondengui en rĂ©fĂ©rence au nom du quartier dans lequel elle se situe, est un prolongement des travaux quâelle a menĂ©s dans le cadre de ses recherches doctorales : des rues Ă la prison, elle a suivi la trajectoire de nombre des enfants Ă qui elle avait consacrĂ© sa thĂšse (M..
pH-sensitive liposomes as a carrier for oligonucleotides: a physico-chemical study of the interaction between DOPE and a 15-mer oligonucleotide in quasi-anhydrous samples
AbstractpH-sensitive liposomes made of dioleoylphosphatidylethanolamine (DOPE)/oleic acid (OA)/cholesterol (CHOL) mixtures were shown to be very promising carriers for oligonucleotides (ON). However, it appeared necessary to clarify the structural consequence of the interactions of ON with the liposome, and especially on DOPE, the lipid responsible for the pH sensitivity. The present study was carried out by differential scanning calorimetry and X-ray diffraction, at low hydration. In such a case, DOPE generally adopt a hexagonal phase. It could be shown that ON increased DOPE transition temperature and increased v/al, as a result of electrostatic interactions between ON and DOPE headgroups. OA was found to have exactly opposite effects, its presence between DOPE molecules inhibiting the formation of hydrogen bonds. The presence of both ON and OA allowed the system to organize in a lamellar phase below the solid/liquid transition, whereas above this temperature ON preferably interacted with DOPE in a hexagonal phase and led OA to separate
Ice Formation in Model Biological Membranes in the Presence of Cryoprotectors
Ice formation in model biological membranes is studied by SAXS and WAXS in
the presence of cryoprotectors: dimethyl sulfoxide and glycerol. Three types of
phospholipid membranes: DPPC, DMPC, DSPC are chosen for the investigation as
well-studied model biological membranes. A special cryostat is used for sample
cooling from 14.1C to -55.4C. The ice formation is only detected by WAXS in
binary phospholipid/water and ternary phospholipid/cryoprotector/water systems
in the condition of excess solvent. Ice formation in a binary
phospholipid/water system creates an abrupt decrease of the membrane repeat
distance by delta-d, so-called ice-induced dehydration of intermembrane space.
The value of delta-d decreases as the cryoprotector concentration increases.
The formation of ice does not influence the membrane structure (delta-d = 0)
for cryoprotector mole fractions higher than 0.05.Comment: PDF: 9 pages, 3 figures; sourse in MS Wor
A Sucrose Solution Application to the Study of Model Biological Membranes
The small-angle X-ray and neutron scattering, time resolved X-ray small-angle
and wide-angle diffraction coupled with differential scanning calorimetry have
been applied to the investigation of unilamellar and multilamellar
dimyristoylphosphatidylcholine (DMPC) vesicles in sucrose buffers with sucrose
concentrations from 0 to 60%. Sucrose buffer decreased vesicle size and
polydispersity and increased an X-ray contrast between phospholipid membrane
and bulk solvent sufficiently. No influence of sucrose on the membrane
thickness or mutual packing of hydrocarbon chains has been detected. The region
of sucrose concentrations 30%-40% created the best experimental conditions for
X-ray small-angle experiments with phospholipid vesicles.Comment: PDF: 10 pages, 6 figures. MS Word sours
Structural and Functional Hierarchy in Photosynthetic Energy Conversionâfrom Molecules to Nanostructures
Basic principles of structural and functional requirements of photosynthetic energy conversion in hierarchically organized machineries are reviewed. Blueprints of photosynthesis, the energetic basis of virtually all life on Earth, can serve the basis for constructing artificial light energy-converting molecular devices. In photosynthetic organisms, the conversion of light energy into chemical energy takes places in highly organized fine-tunable systems with structural and functional hierarchy. The incident photons are absorbed by light-harvesting complexes, which funnel the excitation energy into reaction centre (RC) protein complexes containing redox-active chlorophyll molecules; the primary charge separations in the RCs are followed by vectorial transport of charges (electrons and protons) in the photosynthetic membrane. RCs possess properties that make their use in solar energy-converting and integrated optoelectronic systems feasible. Therefore, there is a large interest in many laboratories and in the industry toward their use in molecular devices. RCs have been bound to different carrier matrices, with their photophysical and photochemical activities largely retained in the nano-systems and with electronic connection to conducting surfaces. We show examples of RCs bound to carbon-based materials (functionalized and non-functionalized single- and multiwalled carbon nanotubes), transitional metal oxides (ITO) and conducting polymers and porous silicon and characterize their photochemical activities. Recently, we adapted several physical and chemical methods for binding RCs to different nanomaterials. It is generally found that the P(+)(Q(A)Q(B))(â) charge pair, which is formed after single saturating light excitation is stabilized after the attachment of the RCs to the nanostructures, which is followed by slow reorganization of the protein structure. Measuring the electric conductivity in a direct contact mode or in electrochemical cell indicates that there is an electronic interaction between the protein and the inorganic carrier matrices. This can be a basis of sensing element of bio-hybrid device for biosensor and/or optoelectronic applications
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