An analytic structure factor for macroion solutions

Hayter, John B.; Penfold, J.

doi:10.1080/00268978100100091

Cited by 1,099 publications

(851 citation statements)

References 9 publications

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“…The value of S max (Table I) rose slowly with increasing ϕ, from 1.2 at ϕ ¼ 0.04, to 2.6 AE 0.1 at ϕ ¼ 0.16. Despite our polydispersity, which should lower S max slightly [32,33] and add a low-q incoherent scattering [33,34], these values agree well with the Hayter-Penfold mean spherical approximation (MSA) model [35] of monodisperse Yukawa spheres (Table I, using 8 nm particles with 5 mM salt and a surface charge of 170e).…”

supporting

confidence: 69%

Hiding in Plain View: Colloidal Self-Assembly from Polydisperse Populations

Cabane

Artzner

et al. 2016

Phys. Rev. Lett.

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We report small-angle x-ray scattering experiments on aqueous dispersions of colloidal silica with a broad monomodal size distribution (polydispersity, 14%; size, 8 nm). Over a range of volume fractions, the silica particles segregate to build first one, then two distinct sets of colloidal crystals. These dispersions thus demonstrate fractional crystallization and multiple-phase (bcc, Laves AB 2 , liquid) coexistence. Their remarkable ability to build complex crystal structures from a polydisperse population originates from the intermediate-range nature of interparticle forces, and it suggests routes for designing self-assembling colloidal crystals from the bottom up.

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supporting

confidence: 69%

Hiding in Plain View: Colloidal Self-Assembly from Polydisperse Populations

Cabane

Artzner

et al. 2016

Phys. Rev. Lett.

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“…We used a three-shell model for the bilayer cross-section and modeled the bilayer in terms of a central hydrophobic core, containing the hydrocarbon chains, sandwiched between inner and outer hydrophilic layers, composed by the hydrophilic head groups and hydration water. This approach, including its use of molecular constraints, was pioneered by Luzatti and Husson (41), later refined (42,43), and recently further modified and extensively applied to lipid bilayers by Kucerka et al (44,45). Our approach is similar in spirit to Kucerka's approach (see SI Text).…”

Section: Resultsmentioning

confidence: 56%

Reconciliation of opposing views on membrane–sugar interactions

Andersen

Wang

Arleth

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

134

177

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It is well established that small sugars exert different types of stabilization of biomembranes both in vivo and in vitro. However, the essential question of whether sugars are bound to or expelled from membrane surfaces, i.e., the sign and size of the free energy of the interaction, remains unresolved, and this prevents a molecular understanding of the stabilizing mechanism. We have used smallangle neutron scattering and thermodynamic measurements to show that sugars may be either bound or expelled depending on the concentration of sugar. At low concentration, small sugars bind quite strongly to a lipid bilayer, and the accumulation of sugar at the interface makes the membrane thinner and laterally expanded. Above ∼0.2 M the sugars gradually become expelled from the membrane surface, and this repulsive mode of interaction counteracts membrane thinning. The dual nature of sugar-membrane interactions offers a reconciliation of conflicting views in earlier reports on sugar-induced modulations of membrane properties.membrane interface | membrane structure | preferential binding | preferential exclusion | interaction free energy S mall sugars such as the disaccharides sucrose and trehalose are among the so-called osmolytes (1) or compensatory solutes (2), which are accumulated in response to environmental stress in virtually all taxa. Their function is to act as inert regulators of the osmotic pressure, but they also optimize the physical properties of the cytosol (3) and stabilize biomolecular conformations against cold, drought, and heat (4-7). The same small carbohydrates have also proven useful in vitro as protectants or excipients for biopreservation (8). Many reports have shown that membranous structures are particularly stabilized by small sugars (4, 6, 9), but the definition of stabilization covers a wide range of biological and physical parameters. Thus, studies on intact cells have documented improved survival following exposure to heat, cold, drought, or chemical stressors (6,10,11). Other works have analyzed stabilization on the basis of phenomenological properties of model membranes, for example, the leakage or intermixing of probes in liposomes (12, 13). Finally, stability has been discussed with respect to rigorous physical parameters such as the structure or mechanical properties of lipid bilayers (14, 15). The current work addresses membrane dimensions and the thermodynamics of interaction with the purpose of elucidating fundamental aspects of membrane-sugar interrelationships. The different observations of sugar stabilization have sparked a large number of studies on sugars and model membranes (usually phospholipid bilayers) over the past 30 y. Investigations of fully hydrated membranes show an interesting tendency to fall into two groups with mutually conflicting conclusions. Thus, many investigations have suggested direct (favorable) interaction of sugars and the phospholipid interface (16-23), and it is obvious that such interactions could be the origin of sugar effects, for example, through int...

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“…The interparticle structure factor S(q) was taken into account by using the mean spherical approximation (MSA) according to Hayter and Penfold. 44 A more detailed description of the model used is given in the next section. The fitting procedures were performed using the SASfit software which uses the least-squares fitting approach consisting of minimizing the squared chi (χ 2 ).…”

Section: Small Angle X-ray Scattering (Saxs)mentioning

confidence: 99%

“…44 It describes the structure factor of charged objects in a dielectric medium and combined with P(q) allows the inclusion of interparticle interference effects due to screened Coulomb repulsion between charged particles. The salt concentration used to compute the ionic strength of the solution, which in turn is used to compute the Debye screening length, was fixed as the molar concentration of surfactant monomers.…”

Section: Small Angle X-ray Scattering Measurementsmentioning

confidence: 99%

Supramolecular complexes formed by the association of poly(ethyleneimine) (PEI), sodium cholate (NaC) and sodium dodecyl sulfate (SDS)

Felippe

Bellettini

Eising

et al. 2011

J. Braz. Chem. Soc.

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A formação de complexos supramoleculares em solução aquosa pela associação do polieletrólito poli(etilenoimina) (PEI) com misturas do biossurfactante colato de sódio (NaC) e o surfactante aniônico dodecil sulfato de sódio (SDS) foi aqui investigado usando as técnicas de condutivimetria, tensiometria, fluorimetria, espalhamento de raios X a baixos ângulos (SAXS) e medidas de pH. Os resultados de fluorimetria, condutivimetria e medidas de pH levaram à conclusão de que os monômeros de NaC e SDS ligam-se primeiramente em sítios específicos das cadeias do polieletrólito PEI via interação eletrostática e posteriormente através de associação cooperativa. A interação do NaC com o PEI é mais fraca do que a interação do SDS com o PEI, porém, a adição de SDS ao sistema NaC-PEI levou à formação de micelas mistas SDS-NaC que interagiram fortemente com o polieletrólito PEI. Os resultados de SAXS sugeriram que o complexo supramolecular possui característica elipsoidal e essa forma não depende da concentração de surfactante nem da χ NaC .The formation of supramolecular complexes produced by association of poly(ethyleneimine) (PEI) and mixtures of sodium cholate (NaC) and sodium dodecyl sulfate (SDS) was investigated by pH, electrical conductivity, fluorescence spectroscopy and small angle X-ray scattering (SAXS) measurements. The fluorescence linked to previously measured values of pH and conductivity led to the conclusion that NaC and SDS molecules firstly bind to specific sites of the PEI chains via electrostatic interaction and secondly undergo self-assembly through regular cooperative association. The interaction of NaC with the polyelectrolyte PEI is weaker than that of SDS and the addition of SDS to the NaC-PEI system led to the formation of mixed NaC-SDS micelles which stronger interact with PEI. The SAXS results suggested that the micellar aggregates have a considerably ellipsoidal characteristic and the micellar shape is not affected by the surfactant concentration nor by χ NaC .Keywords: sodium cholate, sodium dodecyl sulfate, poly(ethyleneimine), polymer-surfactants interaction IntroductionBile salts are naturally-occurring amphiphilic molecules. They are physiologically important in the solubilization and transport of fats and lipids. The structure of bile salts in water has been extensively investigated. Although they are comparable to common surfactants, the general conclusion is that biosurfactants self-assemble in a different way than the standard surfactants. [1][2][3][4][5][6][7][8][9][10][11][12][13] Poly(ethyleneimine) (PEI) is a member of a large family of water-soluble polyamines having different molecular weights (M w ) and polymer architectures. Polyamines are weak bases and exhibit a cationic character depending on the degree of protonation. PEI has been extensively studied (particularly the branched form) due to its intense use in the formulation of drugs, thickeners, flocculating agents, personal care products, food products, detergents and adhesives. It has also been used for biological proposes to p...

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An analytic structure factor for macroion solutions

Cited by 1,099 publications

References 9 publications

Hiding in Plain View: Colloidal Self-Assembly from Polydisperse Populations

Hiding in Plain View: Colloidal Self-Assembly from Polydisperse Populations

Reconciliation of opposing views on membrane–sugar interactions

Supramolecular complexes formed by the association of poly(ethyleneimine) (PEI), sodium cholate (NaC) and sodium dodecyl sulfate (SDS)

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