265 research outputs found
Highly Confined Stacks of Graphene Oxide Sheets in Water
Since the discovery of graphene oxide (GO), the most accessible of the
precursors of graphene, this material has been widely studied for applications
in science and technology. In this work, we describe a procedure to obtain GO
dispersions in water at high concentrations, these highly dehydrated
dispersions being in addition fully redispersible by dilution. With the
availability of such concentrated samples, it was possible to investigate the
structure of hydrated GO sheets in a previously unexplored range of
concentrations, and to evidence a structural phase transition. Tentatively
applying models designed for describing the small-angle scattering curve in the
Smectic A (or L) phase of lyotropic systems, it was possible to
extract elastic parameters characterising the system on the dilute side of the
transition, thereby evidencing the relevance of both electrostatic and steric
(Helfrich) interactions in stabilising aqueous lamellar stacks of GO sheetsComment: 11 pages, 10 figure
Genomic organization of the KTX2 gene, encoding a `short' scorpion toxin active on K+ channels
AbstractA single intron of 87 bp, close to the region encoding the C-terminal part of the signal peptide, was found in the gene of the `short' scorpion toxin kaliotoxin 2 of Androctonus australis acting on various types of K+ channels. Its A+T content was particularly high (up to 86%). By walking and ligation-mediated PCR, the promoter sequences of the kaliotoxin 2 gene of Androctonus australis were studied. The transcription unit of the gene is 390 bp long. Consensus sequences were identified. The genes of `short' scorpion toxins active on K+ channels are organized similarly to those of the `long' scorpion toxins active on Na+ channels and not like those of structurally related insect defensins, which are intronless
Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited
Water activity and its relationship with interactions stabilising lamellar
stacks of mixed lipid bilayers in their fluid state are investigated by means
of osmotic pressure measurements coupled with small-angle x-ray scattering. The
(electrically-neutral) bilayers are composed of a mixture in various
proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic
cosurfactant with an ethoxylated polar head. For highly dehydrated samples the
osmotic pressure profile always exhibits the "classical" exponential decay as
hydration increases but, depending on Simulsol to lecithin ratio, it becomes
either of the "bound" or "unbound" types for more water-swollen systems. A
simple thermodynamic model is used for interpreting the results without
resorting to the celebrated but elusive "hydration forces"Comment: 24 pages, 12 figures. Accepted for publication in The European
Physical Journal
A new class of scorpion toxin binding sites related to an A-type K+ channel: pharmacological characterization and localization in rat brain
AbstractA new scorpion toxin (3751.8 Da) was isolated from the Buthus martensi venom, sequenced and chemically synthesized (sBmTX3). The A-type current of striatum neurons in culture completely disappeared when 1 ÎŒM sBmTX3 was applied (Kd=54 nM), whereas the sustained K+ current was unaffected. 125I-sBmTX3 specifically bound to rat brain synaptosomes (maximum binding=14 fmol mgâ1 of protein, Kd=0.21 nM). A panel of toxins yet described as specific ligands for K+ channels were unable to compete with 125I-sBmTX3. A high density of 125I-sBmTX3 binding sites was found in the striatum, hippocampus, superior colliculus, and cerebellum in the adult rat brain
Interactions of small polypeptides with dimyristoylphosphatidylcholine monolayers: effect of size and hydrophobicity
The effects of size and hydrophobicity of small (molecular weights below 2,000) polypeptides on their predominantly hydrophobic interactions with a neutral phospholipid monolayer were studied. The changes in surface pressure were determined when various concentrations of Gly, Gly-Gly-Gly, -Ala, -Ala--Ala--Ala, -Ala-Gly-Gly-Gly-Gly, -Phe--Leu--Glu--Glu--Leu, adrenocorticotropic hormone fragments 1-10 (ACTH-(1-10)), porcine [beta]-lipotropin, [alpha]-endorphin and human fibrinopeptide A were injected under dimyristoylphosphatidylcholine (DMPC) monolayers at an initial surface pressure of 10 dyne/cm. In all cases, when peptides with the same number of residues are compared, the concentration needed to increase the surface pressure of the film by 1 dyne/cm was inversely related to its hydrophobicity. A reasonably good correlation was found to exist between the calculated free energy of transfer of a polypeptide from ethanol to water (a measure of its hydrophobicity) and its ability to increase the surface pressure of the DMPC film (a measure of the extent of its interaction with the neutral lipid monolayer).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28014/1/0000450.pd
Wheat germ in vitro translation to produce one of the most toxic sodium channel specific toxins
Envenoming following scorpion sting is a common emergency in many parts of the world. During scorpion envenoming, highly toxic small polypeptides of the venom diffuse rapidly within the victim causing serious medical problems. The exploration of toxin structure-function relationship would benefit from the generation of soluble recombinant scorpion toxins in Escherichia coli. We developed an in vitro wheat germ translation system for the expression of the highly toxic Aah (Androctonus australis hector)II protein that requires the proper formation of four disulphide bonds. Soluble, recombinant N-terminal GST (glutathione S-transferase)-tagged AahII toxin is obtained in this in vitro translation system. After proteolytic removal of the GST-tag, purified rAahII (recombinant AahII) toxin, which contains two extra amino acids at its N terminal relative to the native AahII, is highly toxic after i.c.v. (intracerebroventricular) injection in Swiss mice. An LD50 (median lethal dose)-value of 10 ng (or 1.33 pmol), close to that of the native toxin (LD50 of 3 ng) indicates that the wheat germ in vitro translation system produces properly folded and biological active rAahII. In addition, NbAahII10 (Androctonus australis hector nanobody 10), a camel single domain antibody fragment, raised against the native AahII toxin, recognizes its cognate conformational epitope on the recombinant toxin and neutralizes the toxicity of purified rAahII upon injection in mice
FlutuaçÔes e interaçÔes em situação de nano-confinamento anisotrópico
La structure et les interactions qui stabilisent des empilements lamellaires lyotropes de bicouches lipidiques "poilues" (et dĂ©pourvues de charge Ă©lectrique nette) dans leur Ă©tat fluide sont principalement Ă©tudiĂ©es par diffusion de rayons X aux petits angles. Les empilements lamellaires sont utilisĂ©s comme matrices hĂŽtes afin de confiner et dâencapsuler des nano-bĂątonnets dâADN qui sâauto-assemblent en diffĂ©rentes structures en fonction du confinement rĂ©alisĂ©. Lâobjectif fixĂ© est de comprendre lâorigine des mĂ©canismes qui sont responsables de la formation de tels assemblages supramolĂ©culaires. Dans ce but,on sâintĂ©resse aux mĂ©canismes entropiques et interfaciaux, sensibles expĂ©rimentalement Ă la physico-chimie du systĂšme, cette derniĂšre affectant notamment le caractĂšre "liĂ©"ou "non liĂ©" des systĂšmes lamellaires Ă haute dilution. Un modĂšle thermodynamique est utilisĂ© afin dâinterprĂ©ter la dĂ©croissance exponentielle "classique" observĂ©e dans les profils de pression osmotique en fonction de lâhydratation, sans faire appel Ă la force"dâhydratation". Une transition structurale est mise en Ă©vidence, Ă faible hydratation,entre deux phases lamellaires "liĂ©es". Le changement structural de la bicouche est discutĂ© en termes de couplage entre confinements vertical et latĂ©ral. La caractĂ©risation de la matrice lamellaire hĂŽte autorise finalement une description des organisations des bĂątonnets dâADN qui semblent directement corrĂ©lĂ©es aux propriĂ©tĂ©s physiques des bicouches, faisant ainsi apparaĂźtre quelques perspectives pour leur encapsulation au sein "dâognons".Structure and interactions stabilizing the lyotropic lamellar stack of (electrically-neutral)mixed "hairy" lipid bilayers in their fluid state are mainly investigated by means of small angleX-ray scattering. The lamellar stacks are used as hosts to confine and encapsulate DNA nanorods which organize themselves into different structures depending on the confinement.The challenge here is to understand the mechanisms responsible for the formation of these supramolecular assemblies. In this aim, we are interested in entropic and interfacial mechanisms which are both experimentally sensitive to the physical-chemistry of the system, changing in particular the âboundâ or âunboundâ character of the waters wollen systems. A thermodynamic model is then used for interpreting the âclassicalâexponential decay obtained in osmotic profiles as a function of hydration, without resorting to âhydration forcesâ. A structural transition between two different âboundâ lamellar phases is brought out at low hydration. The bilayer structural changes are discussed as resulting from a coupling between lateral and vertical confinements. The lamellar host characterization finally allows a description of the DNA nanorods organizations which seem to be directly correlated to the physical properties of the bilayers, leaving some perspectives for the encapsulation inside âonionsâ.A estrutura e as interaçÔes, que estabilizam os empilhamentos lamelares liotrĂłpicos dasmembranas lipĂdicas em seu estado fluido, sĂŁo estudadas principalmente por espalhamento de raios-x a baixos Ăąngulos. As membranas âpeludasâ (eletricamente neutras) sĂŁo compostas de uma mistura em diversas proporçÔes de lecitina, um fosfolipĂdio zwiteriĂŽnico, ede simulsol, um cotensoativo etoxilado nĂŁo iĂŽnico similar a um copolĂmero dibloco (curto). Esses empilhamentos lamelares sĂŁo utilizados como matrizes hospedeiras, com o intuito deconfinar e de encapsular nanobastĂ”es de DNA que se auto organizam em diferentes estruturas,em função do confinamento aplicado. O objetivo fixado Ă© de compreender aorigem dos mecanismos responsĂĄveis pela formação dessas organizaçÔes supramoleculares,nĂŁo regidas pelas interaçÔes eletrostĂĄticas. Dessa forma, nos interessamos aos mecanismos entrĂłpicos e interfaciais, que sĂŁo ligados Ă elasticidade membranar e Ă s interaçÔes mais especĂficas que intervĂȘm nas interfaces membrana-membrana ou DNA-membrana. Aabordagem experimental consiste em modificar os diferentes parĂąmetros fĂsico-quĂmicosda matriz hospedeira, como a hidratação do sistema, a natureza quĂmica do cotensoativo (blocos hidrofĂłbicos e/ou hidrofĂlicos) e a proporção de cotensoativo no interior da membrana.O cotensoativo tem entĂŁo uma função chave para modificar os dois mecanismos,perturbando o estado âligadoâ ou ânĂŁo-ligadoâ em sistemas lamelares altamente diluĂdos.Um modelo termodinĂąmico Ă© utilizado para interpretar o decrĂ©scimo exponencial âclĂĄssicoâobservado para os perfis de pressĂŁo osmĂłtica, quando se aumenta a hidratação, semutilizar a âforça de hidrataçãoâ. Uma transição estrutural Ă© evidenciada, Ă baixahidratação, entre duas fases lamelares âligadasâ. A mudança estrutural da membranaĂ© discutida graças ao acoplamento entre confinamento lateral e vertical, em analogia Ă conhecida transição âescova-cogumeloâ induzida pelo confinamento lateral, relevante paralongos polĂmeros lineares funcionalizados em superfĂcies rĂgidas [10]. A caracterizaçãoda matriz lamelar hospedeira permite, finalmente, uma descrição das organizaçÔes dosbastĂ”es de DNA que parecem diretamente correlacionados com as propriedades fĂsicasdas membranas, deixando, entĂŁo, algumas perspectivas para sua encapsulação no interiorde estruturas semelhantes a âcebolasâ
FlutuaçÔes e interaçÔes em situação de nano-confinamento anisotrópico
La structure et les interactions qui stabilisent des empilements lamellaires lyotropes de bicouches lipidiques "poilues" (et dĂ©pourvues de charge Ă©lectrique nette) dans leur Ă©tat fluide sont principalement Ă©tudiĂ©es par diffusion de rayons X aux petits angles. Les empilements lamellaires sont utilisĂ©s comme matrices hĂŽtes afin de confiner et dâencapsuler des nano-bĂątonnets dâADN qui sâauto-assemblent en diffĂ©rentes structures en fonction du confinement rĂ©alisĂ©. Lâobjectif fixĂ© est de comprendre lâorigine des mĂ©canismes qui sont responsables de la formation de tels assemblages supramolĂ©culaires. Dans ce but,on sâintĂ©resse aux mĂ©canismes entropiques et interfaciaux, sensibles expĂ©rimentalement Ă la physico-chimie du systĂšme, cette derniĂšre affectant notamment le caractĂšre "liĂ©"ou "non liĂ©" des systĂšmes lamellaires Ă haute dilution. Un modĂšle thermodynamique est utilisĂ© afin dâinterprĂ©ter la dĂ©croissance exponentielle "classique" observĂ©e dans les profils de pression osmotique en fonction de lâhydratation, sans faire appel Ă la force"dâhydratation". Une transition structurale est mise en Ă©vidence, Ă faible hydratation,entre deux phases lamellaires "liĂ©es". Le changement structural de la bicouche est discutĂ© en termes de couplage entre confinements vertical et latĂ©ral. La caractĂ©risation de la matrice lamellaire hĂŽte autorise finalement une description des organisations des bĂątonnets dâADN qui semblent directement corrĂ©lĂ©es aux propriĂ©tĂ©s physiques des bicouches, faisant ainsi apparaĂźtre quelques perspectives pour leur encapsulation au sein "dâognons".Structure and interactions stabilizing the lyotropic lamellar stack of (electrically-neutral)mixed "hairy" lipid bilayers in their fluid state are mainly investigated by means of small angleX-ray scattering. The lamellar stacks are used as hosts to confine and encapsulate DNA nanorods which organize themselves into different structures depending on the confinement.The challenge here is to understand the mechanisms responsible for the formation of these supramolecular assemblies. In this aim, we are interested in entropic and interfacial mechanisms which are both experimentally sensitive to the physical-chemistry of the system, changing in particular the âboundâ or âunboundâ character of the waters wollen systems. A thermodynamic model is then used for interpreting the âclassicalâexponential decay obtained in osmotic profiles as a function of hydration, without resorting to âhydration forcesâ. A structural transition between two different âboundâ lamellar phases is brought out at low hydration. The bilayer structural changes are discussed as resulting from a coupling between lateral and vertical confinements. The lamellar host characterization finally allows a description of the DNA nanorods organizations which seem to be directly correlated to the physical properties of the bilayers, leaving some perspectives for the encapsulation inside âonionsâ.A estrutura e as interaçÔes, que estabilizam os empilhamentos lamelares liotrĂłpicos dasmembranas lipĂdicas em seu estado fluido, sĂŁo estudadas principalmente por espalhamento de raios-x a baixos Ăąngulos. As membranas âpeludasâ (eletricamente neutras) sĂŁo compostas de uma mistura em diversas proporçÔes de lecitina, um fosfolipĂdio zwiteriĂŽnico, ede simulsol, um cotensoativo etoxilado nĂŁo iĂŽnico similar a um copolĂmero dibloco (curto). Esses empilhamentos lamelares sĂŁo utilizados como matrizes hospedeiras, com o intuito deconfinar e de encapsular nanobastĂ”es de DNA que se auto organizam em diferentes estruturas,em função do confinamento aplicado. O objetivo fixado Ă© de compreender aorigem dos mecanismos responsĂĄveis pela formação dessas organizaçÔes supramoleculares,nĂŁo regidas pelas interaçÔes eletrostĂĄticas. Dessa forma, nos interessamos aos mecanismos entrĂłpicos e interfaciais, que sĂŁo ligados Ă elasticidade membranar e Ă s interaçÔes mais especĂficas que intervĂȘm nas interfaces membrana-membrana ou DNA-membrana. Aabordagem experimental consiste em modificar os diferentes parĂąmetros fĂsico-quĂmicosda matriz hospedeira, como a hidratação do sistema, a natureza quĂmica do cotensoativo (blocos hidrofĂłbicos e/ou hidrofĂlicos) e a proporção de cotensoativo no interior da membrana.O cotensoativo tem entĂŁo uma função chave para modificar os dois mecanismos,perturbando o estado âligadoâ ou ânĂŁo-ligadoâ em sistemas lamelares altamente diluĂdos.Um modelo termodinĂąmico Ă© utilizado para interpretar o decrĂ©scimo exponencial âclĂĄssicoâobservado para os perfis de pressĂŁo osmĂłtica, quando se aumenta a hidratação, semutilizar a âforça de hidrataçãoâ. Uma transição estrutural Ă© evidenciada, Ă baixahidratação, entre duas fases lamelares âligadasâ. A mudança estrutural da membranaĂ© discutida graças ao acoplamento entre confinamento lateral e vertical, em analogia Ă conhecida transição âescova-cogumeloâ induzida pelo confinamento lateral, relevante paralongos polĂmeros lineares funcionalizados em superfĂcies rĂgidas [10]. A caracterizaçãoda matriz lamelar hospedeira permite, finalmente, uma descrição das organizaçÔes dosbastĂ”es de DNA que parecem diretamente correlacionados com as propriedades fĂsicasdas membranas, deixando, entĂŁo, algumas perspectivas para sua encapsulação no interiorde estruturas semelhantes a âcebolasâ
FlutuaçÔes e interaçÔes em situação de nano-confinamento anisotrópico
Structure and interactions stabilizing the lyotropic lamellar stack of (electrically-neutral)mixed "hairy" lipid bilayers in their fluid state are mainly investigated by means of small angleX-ray scattering. The lamellar stacks are used as hosts to confine and encapsulate DNA nanorods which organize themselves into different structures depending on the confinement.The challenge here is to understand the mechanisms responsible for the formation of these supramolecular assemblies. In this aim, we are interested in entropic and interfacial mechanisms which are both experimentally sensitive to the physical-chemistry of the system, changing in particular the âboundâ or âunboundâ character of the waters wollen systems. A thermodynamic model is then used for interpreting the âclassicalâexponential decay obtained in osmotic profiles as a function of hydration, without resorting to âhydration forcesâ. A structural transition between two different âboundâ lamellar phases is brought out at low hydration. The bilayer structural changes are discussed as resulting from a coupling between lateral and vertical confinements. The lamellar host characterization finally allows a description of the DNA nanorods organizations which seem to be directly correlated to the physical properties of the bilayers, leaving some perspectives for the encapsulation inside âonionsâ.La structure et les interactions qui stabilisent des empilements lamellaires lyotropes de bicouches lipidiques "poilues" (et dĂ©pourvues de charge Ă©lectrique nette) dans leur Ă©tat fluide sont principalement Ă©tudiĂ©es par diffusion de rayons X aux petits angles. Les empilements lamellaires sont utilisĂ©s comme matrices hĂŽtes afin de confiner et dâencapsuler des nano-bĂątonnets dâADN qui sâauto-assemblent en diffĂ©rentes structures en fonction du confinement rĂ©alisĂ©. Lâobjectif fixĂ© est de comprendre lâorigine des mĂ©canismes qui sont responsables de la formation de tels assemblages supramolĂ©culaires. Dans ce but,on sâintĂ©resse aux mĂ©canismes entropiques et interfaciaux, sensibles expĂ©rimentalement Ă la physico-chimie du systĂšme, cette derniĂšre affectant notamment le caractĂšre "liĂ©"ou "non liĂ©" des systĂšmes lamellaires Ă haute dilution. Un modĂšle thermodynamique est utilisĂ© afin dâinterprĂ©ter la dĂ©croissance exponentielle "classique" observĂ©e dans les profils de pression osmotique en fonction de lâhydratation, sans faire appel Ă la force"dâhydratation". Une transition structurale est mise en Ă©vidence, Ă faible hydratation,entre deux phases lamellaires "liĂ©es". Le changement structural de la bicouche est discutĂ© en termes de couplage entre confinements vertical et latĂ©ral. La caractĂ©risation de la matrice lamellaire hĂŽte autorise finalement une description des organisations des bĂątonnets dâADN qui semblent directement corrĂ©lĂ©es aux propriĂ©tĂ©s physiques des bicouches, faisant ainsi apparaĂźtre quelques perspectives pour leur encapsulation au sein "dâognons".A estrutura e as interaçÔes, que estabilizam os empilhamentos lamelares liotrĂłpicos dasmembranas lipĂdicas em seu estado fluido, sĂŁo estudadas principalmente por espalhamento de raios-x a baixos Ăąngulos. As membranas âpeludasâ (eletricamente neutras) sĂŁo compostas de uma mistura em diversas proporçÔes de lecitina, um fosfolipĂdio zwiteriĂŽnico, ede simulsol, um cotensoativo etoxilado nĂŁo iĂŽnico similar a um copolĂmero dibloco (curto). Esses empilhamentos lamelares sĂŁo utilizados como matrizes hospedeiras, com o intuito deconfinar e de encapsular nanobastĂ”es de DNA que se auto organizam em diferentes estruturas,em função do confinamento aplicado. O objetivo fixado Ă© de compreender aorigem dos mecanismos responsĂĄveis pela formação dessas organizaçÔes supramoleculares,nĂŁo regidas pelas interaçÔes eletrostĂĄticas. Dessa forma, nos interessamos aos mecanismos entrĂłpicos e interfaciais, que sĂŁo ligados Ă elasticidade membranar e Ă s interaçÔes mais especĂficas que intervĂȘm nas interfaces membrana-membrana ou DNA-membrana. Aabordagem experimental consiste em modificar os diferentes parĂąmetros fĂsico-quĂmicosda matriz hospedeira, como a hidratação do sistema, a natureza quĂmica do cotensoativo (blocos hidrofĂłbicos e/ou hidrofĂlicos) e a proporção de cotensoativo no interior da membrana.O cotensoativo tem entĂŁo uma função chave para modificar os dois mecanismos,perturbando o estado âligadoâ ou ânĂŁo-ligadoâ em sistemas lamelares altamente diluĂdos.Um modelo termodinĂąmico Ă© utilizado para interpretar o decrĂ©scimo exponencial âclĂĄssicoâobservado para os perfis de pressĂŁo osmĂłtica, quando se aumenta a hidratação, semutilizar a âforça de hidrataçãoâ. Uma transição estrutural Ă© evidenciada, Ă baixahidratação, entre duas fases lamelares âligadasâ. A mudança estrutural da membranaĂ© discutida graças ao acoplamento entre confinamento lateral e vertical, em analogia Ă conhecida transição âescova-cogumeloâ induzida pelo confinamento lateral, relevante paralongos polĂmeros lineares funcionalizados em superfĂcies rĂgidas [10]. A caracterizaçãoda matriz lamelar hospedeira permite, finalmente, uma descrição das organizaçÔes dosbastĂ”es de DNA que parecem diretamente correlacionados com as propriedades fĂsicasdas membranas, deixando, entĂŁo, algumas perspectivas para sua encapsulação no interiorde estruturas semelhantes a âcebolasâ
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