Publications by authors named "Cristelle Mériadec"

21 Publications

  • Page 1 of 1

In vitro solubilization of fat-soluble vitamins in structurally defined mixed intestinal assemblies.

J Colloid Interface Sci 2021 May 5;589:229-241. Epub 2021 Jan 5.

INRAE, BIA, F-44316 Nantes, France. Electronic address:

The structures of fed state intestinal assemblies containing bile components, dietary fat, and fat-soluble vitamins are not well known, although they are involved in lipid transport. In this study, several methods were used to investigate structural transitions upon various dietary lipids or various fat-soluble vitamins incorporation in bile intestinal assemblies. In particular, DLS and turbidimetry were used to study transition points as a function of component concentration, and cryo-TEM and SAXS were used to resolve assembly structures at microscopic and supramolecular scales, respectively. Results showed that increasing the concentration of dietary lipids in bile assembly induced a transition from core-shell micelles to unilamellar vesicles (except with caprylate lipids, always yielding micelles). In these specific assemblies, increasing the concentration of a fat-soluble vitamin either induced a systematic structural transition, defining a solubilization capacity (α-tocopherol or phylloquinone), or induced a structural transition only in micelles (retinol), or did not induce any structural transition up to very high concentrations (cholecalciferol). Using SAXS data, ideal molecular organizations are proposed for assemblies in the absence or presence of α-tocopherol.
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http://dx.doi.org/10.1016/j.jcis.2021.01.002DOI Listing
May 2021

Loading of lutein in egg-sphingomyelin vesicles as lipid carriers: Thermotropic phase behaviour, structure of sphingosome membranes and lutein crystals.

Food Res Int 2020 12 7;138(Pt A):109770. Epub 2020 Oct 7.

INRAE, BIA, 44316 Nantes, France.

Lutein is a xanthophyll carotenoid provided exclusively by the diet, that has protective functions and beneficial effects on human health. Supplementation in lutein is necessary to reach the recommended daily dietary intake. However, the introduction of lutein into foods and beverages is a real challenge since this lipophilic nutrient has a poor aqueous solubility and a low bioavailability. In this study, we investigated the capacity of egg-sphingomyelin (ESM) vesicles called sphingosomes to solubilise lutein into the bilayers. The thermal and structural properties of ESM bilayers were examined in presence of various amounts of lutein by differential scanning calorimetry (DSC) and temperature-controlled X-ray diffraction (XRD), the structures of sphingosomes and lutein crystals were observed by microscopic techniques. ESM bilayers were in the fluid L phase above the phase transition temperature T = 39.6 °C and in the lamellar ripple P phase below T where ESM sphingosomes exhibited ondulations and were facetted. Lutein molecules were successfully incorporated into the ESM bilayers where they induced a structural disorganisation. For ESM/lutein 90/10 %mol (91.8/8.2 %wt; 89 mg lutein / g ESM), lutein partitioning occured with the formation of lutein crystals in the aqueous phase together with lutein-loaded ESM vesicles. This study highlighted the capacity of new lipid carriers such as egg-sphingosomes to solubilise lutein and opens perspectives for the formulation of effective lutein-fortified functionnal foods and beverages providing health benefits.
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http://dx.doi.org/10.1016/j.foodres.2020.109770DOI Listing
December 2020

Boron Effect on Sugar-Based Organogelators.

Chemistry 2020 Nov 29;26(61):13927-13934. Epub 2020 Sep 29.

Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR6226, Université de Rennes, 35000, Rennes, France.

The reaction of several alkylglucosides with phenyl boronic acid permitted easy access to a series of alkylglucoside phenyl boronate derivatives. This type of compound has structures similar to those of known benzylidene glucoside organogelators except for the presence of a boronate function in place of the acetal one. Low to very low concentrations of these amphiphilic molecules produced gelation of several organic solvents. The rheological properties of the corresponding soft materials characterized them as elastic solids. They were further characterized by SEM to obtain more information on their morphologies and by SAXS to determine the type of self-assembly involved within the gels. The sensitivity of the boronate function towards hydrolysis was also investigated. We demonstrated that a small amount of water (5 % v/v) was sufficient to disrupt the organogels leading to the original alkylglucoside and phenyl boronic acid; an important difference with the stable benzylidene-based organogelators. Such water-sensitive boronated organogelators could be suitable substances for the preparation of smart soft material for topical drug delivery.
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http://dx.doi.org/10.1002/chem.202001970DOI Listing
November 2020

Hybrid gold nanoparticle-quantum dot self-assembled nanostructures driven by complementary artificial proteins.

Nanoscale 2020 Feb;12(7):4612-4621

University Rennes 1, Institute of Chemical Sciences, UMR 6226 CNRS, Campus Beaulieu, F-35042 Rennes, France.

Hybrid nanostructures are constructed by the direct coupling of fluorescent quantum dots and plasmonic gold nanoparticles. Self-assembly is directed by the strong affinity between two artificial α-repeat proteins that are introduced in the capping layers of the nanoparticles at a controlled surface density. The proteins have been engineered to exhibit a high mutual affinity, corresponding to a dissociation constant in the nanomolar range, towards the protein-functionalized quantum dots and gold nanoparticles. Protein-mediated self-assembly is evidenced by surface plasmon resonance and gel electrophoresis. The size and the structure of colloidal superstructures of complementary nanoparticles are analyzed by transmission electron microscopy and small angle X-ray scattering. The size of the superstructures is determined by the number of proteins per nanoparticle. The well-defined geometry of the rigid protein complex sets a highly uniform interparticle distance of 8 nm that affects the emission properties of the quantum dots in the hybrid ensembles. Our results open the route to the design of hybrid emitter-plasmon colloidal assemblies with controlled near-field coupling and better optical response.
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http://dx.doi.org/10.1039/c9nr09987eDOI Listing
February 2020

Polyoxothiometalate-Derivatized Silicon Photocathodes for Sunlight-Driven Hydrogen Evolution Reaction.

ACS Omega 2018 Oct 22;3(10):13837-13849. Epub 2018 Oct 22.

Institut Lavoisier de Versailles (UMR-CNRS 8180), UVSQ, Université Paris-Saclay, 45 Avenue de Etats-Unis, 78000 Versailles, France.

Silicon photocathodes coated with drop-casted {MoS}-based polyoxothiometalate assemblies are demonstrated to be effective for sunlight-driven hydrogen evolution reaction (HER) in acid conditions. These photocathodes are catalytically more efficient than that coated with the parent thiomolybdate incorporating an organic ligand, as supported by a higher onset potential and a lower overvoltage at 10 mA cm. At pH 7.3, the trend is inversed and the beneficial effect of the polyoxometalate for the HER is not observed. Moreover, the polyoxothiometalate-modified photocathode is found to be also more stable under acid conditions and can be operated at the light-limited catalytic current for more than 40 h. Furthermore, X-ray photoelectron spectroscopy and atomic force microscopy measurements indicate that the cathodic polarization of both photocathodes leads to the release of a large amount of the deposited material into the electrolyte solution concomitantly with the formation of mixed valence species {Mo(IV) Mo(III) O S } resulting from the replacement of S sulfido ligands in the cluster by oxo O groups; these combined effects are shown to be beneficial for the photoelectrocatalysis.
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http://dx.doi.org/10.1021/acsomega.8b01734DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6645094PMC
October 2018

Organic Nanoscrolls from Electrostatic Interactions between Peptides and Lipids: Assembly Steps and Structure.

Langmuir 2019 08 2;35(32):10648-10657. Epub 2019 Aug 2.

I2BC, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay , 91198 , Gif-sur-Yvette cedex , France.

An important aspect of cells is their shape flexibility that gives them motion but also a high adaptation versatility to their environment. This shape versatility is mediated by different types of protein-membrane interactions among which electrostatic plays an important role. In the present work we examined the interaction between a small dicationic peptide, that possesses self-assembly properties, and lipid model membranes. The peptide, lanreotide, spontaneously forms nanotubes in water that have a strictly uniform diameter. In the current work, we show that the interaction between the cationic peptide and negatively charged bilayers of lipids induces the formation of myelin sheath-like structures that we call nanoscrolls. By deciphering the different steps of formation and the molecular structure of the self-assembly, we show how electrostatics modify the spontaneous peptide and lipid way of packing.
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http://dx.doi.org/10.1021/acs.langmuir.9b01542DOI Listing
August 2019

Molecular and Material Engineering of Photocathodes Derivatized with Polyoxometalate-Supported {MoS} HER Catalysts.

J Am Chem Soc 2019 Jul 10;141(30):11954-11962. Epub 2019 Jul 10.

Université Reims Champagne Ardenne , Institut de Chimie Moléculaire de Reims (ICMR), UMR7312 CNRS-URCA, Moulin de la Housse, BP 1039, 51687 Reims Cedex 2 , France.

Molecular engineering of efficient HER catalysts is an attractive approach for controlling the spatial environment of specific building units selected for their intrinsic functionality required within the multistep HER process. As the {MoS} core derived as various coordination complexes has been identified as one as the most promising MoS-based HER electrocatalysts, we demonstrate that the covalent association between the {MoS} core and the redox-active macrocyclic {PW} polyoxometalate (POM) produces a striking synergistic effect featured by high HER performance. Various experiments carried out in homogeneous conditions showed that this synergistic effect arises from the direct connection between the {MoS} cluster and the toroidal {PW} units featured by a stoichiometry that can be tuned from two to four {MoS} cores per {PW} unit. In addition, we report that this effect is preserved within heterogeneous photoelectrochemical devices where the {MoS}-{PW} (thio-POM) assembly was used as cocatalyst () onto a microstructured p-type silicon. Using a drop-casting procedure to immobilize onto the silicon interface led to high initial HER performance under simulated sunlight, achieving a photocurrent density of 10 mA cm at +0.13 V vs RHE. Furthermore, electrostatic incorporation of the thio-POM anion into a poly(3,4-ethylenedioxythiophene) (PEDOT) film is demonstrated to be efficient and straightforward to durably retain the at the interface of a micropyramidal silicon () photocathode. The thio-POM/PEDOT-modified photocathode is able to produce H under 1 Sun illumination at a rate of ca. 100 μmol cm h at 0 V vs RHE, highlighting the excellent performance of this photoelectrochemical system.
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http://dx.doi.org/10.1021/jacs.9b03950DOI Listing
July 2019

Casein interaction with lipid membranes: Are the phase state or charge density of the phospholipids affecting protein adsorption?

Biochim Biophys Acta Biomembr 2018 12 28;1860(12):2588-2598. Epub 2018 Sep 28.

Science and Technology of Milk and Egg (STLO), INRA, Agrocampus Ouest, 35000 Rennes, France. Electronic address:

Casein micelles are ~200 nm electronegative particles that constitute 80 wt% of the milk proteins. During synthesis in the lactating mammary cells, caseins are thought to interact in the form of ~20 nm assemblies, directly with the biological membranes of the endoplasmic reticulum and/or the Golgi apparatus. However, conditions that drive this interaction are not yet known. Atomic force microscopy imaging and force spectroscopy were used to directly observe the adsorption of casein particles on supported phospholipid bilayers with controlled compositions to vary their phase state and surface charge density, as verified by X-ray diffraction and zetametry. At pH 6.7, the casein particles adsorbed onto bilayer phases with zwitterionic and liquid-disordered phospholipid molecules, but not on phases with anionic or ordered phospholipids. Furthermore, the presence of adsorbed caseins altered the stability of the yet exposed bilayer. Considering their respective compositions and symmetry/asymmetry, these results cast light on the possible interactions of casein assemblies with the organelles' membranes of the lactating mammary cells.
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http://dx.doi.org/10.1016/j.bbamem.2018.09.016DOI Listing
December 2018

Mechanical Properties of Membranes Composed of Gel-Phase or Fluid-Phase Phospholipids Probed on Liposomes by Atomic Force Spectroscopy.

Langmuir 2017 05 16;33(21):5117-5126. Epub 2017 May 16.

STLO, INRA, Agrocampus Ouest, 35000 Rennes, France.

In many liposome applications, the nanomechanical properties of the membrane envelope are essential to ensure, e.g., physical stability, protection, or penetration into tissues. Of all factors, the lipid composition and its phase behavior are susceptible to tune the mechanical properties of membranes. To investigate this, small unilamellar vesicles (SUV; diameter < 200 nm), referred to as liposomes, were produced using either unsaturated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in aqueous buffer at pH 6.7. The respective melting temperatures of these phospholipids were -20 and 41 °C. X-ray diffraction analysis confirmed that at 20 °C DOPC was in the fluid phase and DPPC was in the gel phase. After adsorption of the liposomes onto flat silicon substrates, atomic force microscopy (AFM) was used to image and probe the mechanical properties of the liposome membrane. The resulting force-distance curves were treated using an analytical model based on the shell theory to yield the Young's modulus (E) and the bending rigidity (k) of the curved membranes. The mechanical investigation showed that DPPC membranes were much stiffer (E = 116 ± 45 MPa) than those of DOPC (E = 13 ± 9 MPa) at 20 °C. The study demonstrates that the employed methodology allows discrimination of the respective properties of gel- or fluid-phase membranes when in the shape of liposomes. It opens perspectives to map the mechanical properties of liposomes containing both fluid and gel phases or of biological systems.
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http://dx.doi.org/10.1021/acs.langmuir.7b00363DOI Listing
May 2017

Atomic view of the histidine environment stabilizing higher-pH conformations of pH-dependent proteins.

Nat Commun 2015 Jul 20;6:7771. Epub 2015 Jul 20.

CNRS, UMR 6251, Institut de Physique de Rennes, 263 av. Général Leclerc, Université Rennes I, 35042 Rennes Cedex, France.

External stimuli are powerful tools that naturally control protein assemblies and functions. For example, during viral entry and exit changes in pH are known to trigger large protein conformational changes. However, the molecular features stabilizing the higher pH structures remain unclear. Here we elucidate the conformational change of a self-assembling peptide that forms either small or large nanotubes dependent on the pH. The sub-angstrom high-pH peptide structure reveals a globular conformation stabilized through a strong histidine-serine H-bond and a tight histidine-aromatic packing. Lowering the pH induces histidine protonation, disrupts these interactions and triggers a large change to an extended β-sheet-based conformation. Re-visiting available structures of proteins with pH-dependent conformations reveals both histidine-containing aromatic pockets and histidine-serine proximity as key motifs in higher pH structures. The mechanism discovered in this study may thus be generally used by pH-dependent proteins and opens new prospects in the field of nanomaterials.
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http://dx.doi.org/10.1038/ncomms8771DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4518280PMC
July 2015

Effects of a novel archaeal tetraether-based colipid on the in vivo gene transfer activity of two cationic amphiphiles.

Mol Pharm 2014 Sep 30;11(9):2973-88. Epub 2014 Jul 30.

Unité INSERM 1078, SFR ScInBioS; Université de Bretagne Occidentale, Université Européenne de Bretagne , 46 rue Félix Le Dantec, CS51819, 29218 Brest Cedex 02, France.

Gene therapy for treating inherited diseases like cystic fibrosis might be achieved using multimodular nonviral lipid-based systems. To date, most optimizations have concerned cationic lipids rather than colipids. In this study, an original archaeal tetraether derivative was used as a colipid in combination with one or the other of two monocationic amphiphiles. The liposomes obtained, termed archaeosomes, were characterized regarding lipid self-assembling properties, macroscopic/microscopic structures, DNA condensation/neutralization/relaxation abilities, and colloidal stability in the presence of serum. In addition, gene transfer experiments were conducted in mice with lipid/DNA complexes being administered via systemic or local delivery routes. Altogether, the results showed that the tetraether colipid can provide complexes with different in vivo transfection abilities depending on the lipid combination, the lipid/colipid molar ratio, and the administration route. This original colipid appears thus as an innovative modular platform endowed with properties possibly beneficial for fine-tuning of in vivo lipofection and other biomedical applications.
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http://dx.doi.org/10.1021/mp4006276DOI Listing
September 2014

Directing peptide crystallization through curvature control of nanotubes.

J Pept Sci 2014 Jul 11;20(7):508-16. Epub 2014 Jun 11.

iBiTec-S, SB2SM, UMR 8221, CEA/CNRS, CEA-Saclay, 91191, Gif-sur-Yvette, France; Institut de Physique de Rennes, UMR 6251 CNRS/Université Rennes 1, Campus Beaulieu, 35042, Rennes Cedex, France; Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire (LIONS), IRAMIS, NIMBE, UMR 3299 CEA/CNRS CEA-Saclay, 91191, Gif-sur-Yvette Cedex, France.

In the absence of efficient crystallization methods, the molecular structures of fibrous assemblies have so far remained rather elusive. In this paper, we present a rational method to crystallize the lanreotide octapeptide by modification of a residue involved in a close contact. Indeed, we show that it is possible to modify the curvature of the lanreotide nanotubes and hence their diameter. This fine tuning leads to crystallization because the radius of curvature of the initially bidimensional peptide wall can be increased up to a point where the wall is essentially flat and a crystal is allowed to grow along a third dimension. By comparing X-ray diffraction data and Fourier transform Raman spectra, we show that the nanotubes and the crystals share similar cell parameters and molecular conformations, proving that there is indeed a structural continuum between these two morphologies. These results illustrate a novel approach to crystallization and represent the first step towards the acquisition of an Å-resolution structure of the lanreotide nanotubes β-sheet assembly.
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http://dx.doi.org/10.1002/psc.2647DOI Listing
July 2014

Thermotropic luminescent clustomesogen showing a nematic phase: a combination of experimental and molecular simulation studies.

Chemistry 2014 Jul 4;20(28):8561-5. Epub 2014 Jun 4.

Université de Rennes 1 - ENSC Rennes - CNRS UMR 6226 "Institut des Sciences Chimiques de Rennes", Campus de Beaulieu, CS 74205, 35042 Rennes Cedex (France).

Octahedral Mo6 nanoclusters are functionalized with two organic ligands containing cyanobiphenyl (CB) units, giving luminescent hybrid liquid crystals (LC). Although the mesogenic density around the bulky inorganic core is constant, the two hybrids show different LC properties. Interestingly, one of them shows a nematic phase, which is particularly rare for this kind of supermolecular system. This surprising result is explained by using large-scale molecular dynamic simulations.
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http://dx.doi.org/10.1002/chem.201402466DOI Listing
July 2014

Experimental observation of double-walled peptide nanotubes and monodispersity modeling of the number of walls.

Langmuir 2013 Feb 12;29(8):2739-45. Epub 2013 Feb 12.

Institut de Biologie et de Technologies de Saclay/Service de Bioénergétique, Biologie Structurale et Mécanismes, UMR 8221 CNRS and CEA, CEA-Saclay, 91191 Gif-sur-Yvette, France.

Self-assembled nanoarchitectures based on biological molecules are attractive because of the simplicity and versatility of the building blocks. However, size control is still a challenge. This control is only possible when a given system is deeply understood. Such is the case with the lanreotide acetate, an octapeptide salt that spontaneously forms monodisperse nanotubes when dissolved into pure water. Following a structural approach, we have in the past demonstrated the possibility to tune the diameter of these nanotubes while keeping a strict monodispersity, either by chemical modification of one precise amino acid on the peptide sequence or by changing the size of the counterions. On the basis of these previous studies, we replaced monovalent counterions by divalent ones to vary the number of walls. Indeed, in the present work, we show that lanreotide associated with a divalent counterion forms double-walled nanotubes while keeping the average diameter constant. However, the strict monodispersity of the number of walls was unexpected. We propose that the divalent counterions create an adhesion force that can drive the wall packing. This adhesion force is counterbalanced by a mechanical one that is related to the stiffness of the peptide wall. By taking into account these two opposite forces, we have built a general model that fully explains why the lanreotide nanotubes formed with divalent counterions possess two walls and not more.
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http://dx.doi.org/10.1021/la304862fDOI Listing
February 2013

Electroless patterned assembly of metal nanoparticles on hydrogen-terminated silicon surfaces for applications in photoelectrocatalysis.

ACS Appl Mater Interfaces 2013 Jan 11;5(2):338-43. Epub 2013 Jan 11.

Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS/Université de Rennes 1, Matière Condensée et Systèmes Electroactifs (MaCSE), Campus de Beaulieu, 35042 Rennes Cedex, France.

The deposition of gold and platinum nanoparticles (NPs) on hydrogen-terminated Si(100) (Si(100)-H) surfaces has been performed by galvanic displacement using fluoride-free sub-millimolar metallic salt solutions. The scanning electron microscopy (SEM) images showed the formation of oblate hemispherical NPs, with an average diameter of ca. 40 nm and an average height of 20 ± 10 and 10 ± 5 nm for Au and Pt, respectively. Furthermore, the calculated number density was (6.0 ± 0.8) × 10(9) Au NPs cm(-2) and (6.6 ± 1.3) × 10(9) Pt NPs cm(-2) with a larger size distribution measured for Au NPs. The Au 4f and Pt 4f X-ray photoelectron spectra of the metallized surfaces were characterized by a principal component corresponding to either the metallic gold or platinum. However, two other components located at higher binding energies were also visible and ascribed to gold or platinum silicides. Using this fluoride-free deposition process and a "reagentless" UV photolithography technique, we have also demonstrated that it was possible to prepare metallic NP micropatterns. Following this approach, single metal (Au) and two metals (Au and Pt) patterns have been produced and characterized by energy-dispersive X-ray spectroscopy (EDS) which revealed the presence of the expected metal(s). Such metallic NP micropatterned surfaces were used as photocathodes for H(2) evolution from water as a proof-of-concept experiment. These electrodes exhibited much higher electrocatalytic performance than that of nonmetallized Si(100)-H, both in the absence of light and under illumination. The overpotential for hydrogen evolution was significantly decreased by ca. 450 mV with respect to Si(100)-H (measured for a current density of 0.1 mA cm(-2)) under identical illumination conditions.
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http://dx.doi.org/10.1021/am302226qDOI Listing
January 2013

Stereochemical effect revealed in self-assemblies based on archaeal lipid analogues bearing a central five-membered carbocycle: a SAXS study.

Langmuir 2012 May 8;28(20):7591-7. Epub 2012 May 8.

Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France.

The relative stereochemistry (cis or trans) of a 1,3-disubstituted cyclopentane unit in the middle of tetraether archaeal bipolar lipid analogues was found to have a dramatic influence on their supramolecular self-assembly properties. SAXS studies of two synthetic diastereomeric archaeal lipids bearing two lactosyl polar head groups at opposite ends revealed different lyotropic behaviors. The cis isomer led to L(c)-L(α)-Q(II) transitions whereas the trans isomer retained an L(α) phase from 20 to 100 °C. These main differences originate from the conformational equilibrium (pseudorotation) of 1,3-disubstituted cyclopentanes. Indeed, this pseudorotation exhibits quite similar orientations of the two substituents in a trans isomer whereas several orientations of the two alkyl chains are expected in a cis-1,3-dialkyl cyclopentane, thus authorizing more conformational flexibility in the lipid packing.
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http://dx.doi.org/10.1021/la2045948DOI Listing
May 2012

Near-infrared chiro-optical effects in metallogels.

Chem Commun (Camb) 2012 Feb 7;48(17):2283-5. Epub 2011 Dec 7.

Sciences Chimiques de Rennes, UMR UR1-CNRS 6226, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes, France.

A series of novel metallogelators containing near-IR nickel-bis(dithiolene) absorbers were rationally designed and synthesized. Robust gel networks are formed by right handed helical 1D-nanofibers which generate strong and remarkable chiro-optical effects in the near-infrared region.
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http://dx.doi.org/10.1039/c2cc16549jDOI Listing
February 2012

Structural role of counterions adsorbed on self-assembled peptide nanotubes.

J Am Chem Soc 2012 Jan 22;134(1):723-33. Epub 2011 Dec 22.

Institut de Biologie et de Technologies de Saclay/Service de Bioénergétique, Biologie Structurale et Mécanismes, Commissariat à l'Énergie Atomique et aux Énergies Alternatives-Saclay, 91191 Gif-sur-Yvette, France.

Among noncovalent forces, electrostatic ones are the strongest and possess a rather long-range action. For these reasons, charges and counterions play a prominent role in self-assembly processes in water and therefore in many biological systems. However, the complexity of the biological media often hinders a detailed understanding of all the electrostatic-related events. In this context, we have studied the role of charges and counterions in the self-assembly of lanreotide, a cationic octapeptide. This peptide spontaneously forms monodisperse nanotubes (NTs) above a critical concentration when solubilized in pure water. Free from any screening buffer, we assessed the interactions between the different peptide oligomers and counterions in solutions, above and below the critical assembly concentration. Our results provide explanations for the selection of a dimeric building block instead of a monomeric one. Indeed, the apparent charge of the dimers is lower than that of the monomers because of strong chemisorption. This phenomenon has two consequences: (i) the dimer-dimer interaction is less repulsive than the monomer-monomer one and (ii) the lowered charge of the dimeric building block weakens the electrostatic repulsion from the positively charged NT walls. Moreover, additional counterion condensation (physisorption) occurs on the NT wall. We furthermore show that the counterions interacting with the NTs play a structural role as they tune the NTs diameter. We demonstrate by a simple model that counterions adsorption sites located on the inner face of the NT walls are responsible for this size control.
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http://dx.doi.org/10.1021/ja210299gDOI Listing
January 2012

Control of peptide nanotube diameter by chemical modifications of an aromatic residue involved in a single close contact.

Proc Natl Acad Sci U S A 2011 May 25;108(19):7679-84. Epub 2011 Apr 25.

Unité Mixte de Recherche 6251, Centre National de la Recherche Scientifique and Université Rennes 1, F-35 Rennes, France.

Supramolecular self-assembly is an attractive pathway for bottom-up synthesis of novel nanomaterials. In particular, this approach allows the spontaneous formation of structures of well-defined shapes and monodisperse characteristic sizes. Because nanotechnology mainly relies on size-dependent physical phenomena, the control of monodispersity is required, but the possibility of tuning the size is also essential. For self-assembling systems, shape, size, and monodispersity are mainly settled by the chemical structure of the building block. Attempts to change the size notably by chemical modification usually end up with the loss of self-assembly. Here, we generated a library of 17 peptides forming nanotubes of monodisperse diameter ranging from 10 to 36 nm. A structural model taking into account close contacts explains how a modification of a few Å of a single aromatic residue induces a fourfold increase in nanotube diameter. The application of such a strategy is demonstrated by the formation of silica nanotubes of various diameters.
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http://dx.doi.org/10.1073/pnas.1017343108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3093526PMC
May 2011

Supramolecular structures based on new bolaamphiphile molecules investigated by small angle and wide angle X-ray scattering and polarized optical microscopy.

J Phys Chem B 2009 Nov;113(47):15433-44

UMR CNRS 6226, Sciences Chimiques de Rennes, Equipe Chimie Organique et Supramoléculaire, Ecole Nationale Supérieure de Chimie de Rennes, 35708 Rennes cedex 7, France.

In this paper, we present a study of the structural and self-assembling properties of a new family of bolaamphiphiles. These bolaamphiphiles are unsymmetrical, having one sugar polar head at one side and one glycine betaine polar head at the other side. The variations that we introduced concern the length of the main bridging chain that connects the two polar heads as well as the length of the side chain linked at the anomeric position of the sugar moiety. Another variation concerns the introduction of a diacetylenic unit into the main chain in order to rigidify it. We have performed small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) on the dry compounds as a function of temperature and observed the lamellar structures. We also measured the SAXS and WAXS spectra of aqueous solutions of these compounds that have shown various lamellar structures. The hydrocarbon chain fluidity and, as a consequence, the interlamellar distance varied as a function of temperature. The obtained SAXS and WAXS results are compared with the polarized optical microscopy measurements.
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http://dx.doi.org/10.1021/jp905747rDOI Listing
November 2009

Structure of liquid films of an ordered foam confined in a narrow channel.

Langmuir 2007 Nov 19;23(24):12055-60. Epub 2007 Oct 19.

Groupe Matière Condensée et Matériaux, UMR CNRS 6626, Université de Rennes I, Campus de Beaulieu, Rennes Cedex, France.

A bamboo foam is the simplest case of an ordered foam confined in a narrow channel. It is made of a regular film distribution, arranged perpendicularly to the channel. Our work consists of studying the structural properties of several films taken in a drained foam. X-ray experiments highlighted the equality of the equilibrium thickness for each film within a foam. The same thickness was found as by measurements of disjoining pressure isotherms, proving as well that films of a bamboo foam behave like isolated ones. The refinement of X-ray data by a simple model of specular reflectivity showed a significant variation of the electronic distribution of the surfactant layer for a common black film forwarding from one equilibrium state to another. A discussion on the organization of the surfactant molecules to the gas/liquid interface and film is proposed.
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http://dx.doi.org/10.1021/la701738zDOI Listing
November 2007