Here, we determine by neutron spin echo spectrometry (NSE) how the flexibility of egg lecithin vesicles depends on solvent composition in two protic ionic liquids (PILs) and their aqueous mixtures. ...In combination with small-angle neutron scattering (SANS), dynamic light scattering (DLS), and fluorescent probe microscopy, we show that the bending modulus is up to an order of magnitude lower than in water but with no change in bilayer thickness or nonpolar chain composition. This effect is attributed to the dynamic association and exchange of the IL cation between the membrane and bulk liquid, which has the same origin as the underlying amphiphilic nanostructure of the IL solvent itself. This provides a new mechanism by which to tune and control lipid membrane behavior.
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IJS, KILJ, NUK, PNG, UL, UM
We discuss the complex interplay between host and guest dynamics for a polymer in soft confinement by a droplet-phase microemulsion. Intermediate scattering functions obtained by neutron spin echo ...spectroscopy are first analysed by means of an effective diffusion coefficient. From its dependence on the absolute of the scattering vector
q
we concluded a sophisticated model for the systems dynamics taking both polymer and microemulsion contributions into account. Global fitting of this model to the intermediate scattering functions at all measured
q
-values and all investigated confinement sizes eventually allows for a precise disentangling of the pure polymer dynamics in confinement from the overlaying microemulsion dynamics. Validity of our approach is further supported by numerical random walk calculations.
PEG confined to the core of a droplet phase microemulsion is located at the water/surfactant interface. Neutron spin echo spectroscopy allows to disentangle polymer from droplet dynamics. Under large confinement sizes accelerated dynamics are found.
Apolar lipids within the membranes of archaea are thought to play a role in membrane regulation. In this work we explore the effect of the apolar lipid squalane on the dynamics of a model ...archaeal-like membrane, under pressure, using neutron spin echo spectroscopy. To the best of our knowledge, this is the first report on membrane dynamics at high pressure using NSE spectroscopy. Increasing pressure leads to an increase in membrane rigidity, in agreement with other techniques. The presence of squalane in the membrane results in a stiffer membrane supporting its role as a membrane regulator.
Apolar lipids within the membranes of archaea are thought to play a role in membrane regulation.
This paper investigates how the properties of multiblock copolypeptides can be tuned by their block architecture, defined by the size and distribution of blocks along the polymer chain. These ...parameters were explored by the precise, genetically encoded synthesis of recombinant elastin-like polypeptides (ELPs). A family of ELPs was synthesized in which the composition and length were conserved while the block length and distribution were varied, thus creating 11 ELPs with unique block architectures. To our knowledge, these polymers are unprecedented in their intricately and precisely varied architectures. ELPs exhibit lower critical solution temperature (LCST) behavior and micellar self-assembly, both of which impart easily measured physicochemical properties to the copolymers, providing insight into polymer hydrophobicity and self-assembly into higher order structures, as a function of solution temperature. Even subtle variation in block architecture changed the LCST phase behavior and morphology of these ELPs, measured by their temperature-triggered phase transition and nanoscale self-assembly. Size and morphology of polypeptide micelles could be tuned solely by controlling the block architecture, thus demonstrating that when sequence can be precisely controlled, nanoscale self-assembly of polypeptides can be modulated by block architecture.
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Polymeric nanocapsules have application in versatile fields, thus they have drawn much attention in the past decade. Preparing a homogeneous, uniform, small nanocapsule system is challenging and ...requires further improvement. A powerful way for realizing controlled synthesis of these submicron structures is by initiating them from a vesicular basis. Herein, we report the formation of highly monodisperse and rather small polymeric nanocapsules originating from a well-defined self-assembled surfactant-based system. In our approach, a monomer is initially dissolved in surfactant micelles, which are transformed spontaneously into well-defined vesicles upon mixing with a second surfactant solution. Subsequently, the monomer-loaded vesicles become polymerized via UV-initiated polymerization, where different amounts of monomers and cross-linkers are employed. The whole process is characterized in detail by light scattering and small-angle neutron scattering (SLS, DLS, and SANS) analyses. The final product of small, unilamellar, highly monodisperse polymeric nanocapsules has potential for applications with entrapping the cargo either in the aqueous core or in the hydrophobic membrane.
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By combining oppositely charged polydiallyldimethylammonium chloride (PDADMAC) and sodium polyacrylate (NaPA), interpolyelectrolyte complexes (IPECs) can be formed in aqueous solution. Such IPECs are ...studied for rather short NaPA and under variation of the Mw of PDADMAC. The focus is on elucidating the effect of having a hydrophobic modification of the NaPA, which is introduced by having 10 mol% of the monomeric units substituted by ones carrying a dodecyl alkyl chain. This modification renders the complexes more hydrophobic, which is seen in the fact that precipitation of the complexes occurs at a lower mixing ratio and the biphasic region is also wider. The structures of the soluble IPECs are studied by a combination of light and neutron scattering (SANS). It is observed that the complexes formed possess typical radii of gyration of ≈30–40 nm, which become somewhat smaller with increasing length of the PDADMAC chain. The SANS data can be described well with the Beaucage model for complexes, where locally small hydrophobic domains of cylindrical shape are formed, whose persistence length decreases with increasing content of NaPA in the complexes. In contrast no such structures are seen for NaPA without the hydrophobic modification. The cylindrical domains are then arranged within larger‐sized clusters of 30–40 nm, which become more compact with reduced length of the PDAMAC chains. The structure of the IPECs is largely determined by the presence of the hydrophobic modification of the NaPA and is further controlled by the length of the hydrophobic modification. Such IPECs of controlled structure, relatively small size, and containing hydrophobic domains are potentially interesting as delivery systems due to having domains of variable polarity.
Interpolyelectrolyte complexes (IPECs) of PDADMAC are formed with normal and hydrophobically modified PAA. This modification leads to the formation of much larger complexes with an internal substructuring. SANS yields a detailed structural description of the aggregates, which on a nm‐level are cylindrical. Hydrophobic polyelectrolyte modification is therefore an elegant way to control structure and properties of IPECs.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Aqueous mixtures of polyelectrolytes and oppositely charged surfactants form clear and homogeneous solutions if either the polyelectrolyte or the surfactant is present in excess. Around charge ...equilibrium, macroscopic precipitates are formed. Near the phase boundary on the polyelectrolyte-rich side, nanometric polyelectrolyte/surfactant complexes can greatly increase the viscosity of aqueous solutions. This behavior is governed by the composition and chemical nature of the polyelectrolyte and surfactant. Here, we investigate complexes consisting of the polycation JR 400 and two different surfactants, namely, sodium octyl sulfate (SOS) and sodium tetradecyl sulfate (STS), which only differ in the length of their alkyl tail. Using small-angle neutron scattering and neutron spin-echo spectroscopy, we find that STS forms mixed aggregates with JR 400 which results in a pronounced increase in viscosity. Such an increase is not observed for SOS where no mixed aggregates are formed. Comparison with atomistic molecular dynamics simulations shows good qualitative agreement.
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Low-molecular weight gelators (LMWGs) are small molecules (
< ∼1 kDa), which form self-assembled fibrillar network (SAFiN) hydrogels in water when triggered by an external stimulus. A great majority ...of SAFiN gels involve an entangled network of self-assembled fibers, in analogy to a polymer in a good solvent. In some rare cases, a combination of attractive van der Waals and repulsive electrostatic forces drives the formation of bundles with a suprafibrillar hexagonal order. In this work, an unexpected micelle-to-fiber transition is triggered by Ca
or Ag
ions added to a micellar solution of a novel glycolipid surfactant, whereas salt-induced fibrillation is not common for surfactants. The resulting SAFiN, which forms a hydrogel above 0.5 wt%, has a "nano-fishnet" structure, characterized by a fibrous network of both entangled fibers and β-sheet-like rafts, generally observed for silk fibroin, actin hydrogels or mineral imogolite nanotubes, but not known for SAFiNs. The β-sheet-like raft domains are characterized by a combination of cryo-TEM and SAXS and seem to contribute to the stability of glycolipid gels. Furthermore, glycolipid is obtained by fermentation from natural resources (glucose, rapeseed oil), thus showing that naturally engineered compounds can have unprecedented properties, when compared to the wide range of chemically derived amphiphiles.
Interactions of polyelectrolytes with oppositely charged surfactants can give rise to a large variety of self-assembled structures. Some of these systems cause a drastic increase in solution ...viscosity, which is related to the surfactant forming aggregates interconnecting several polyelectrolyte chains. For these aggregates to form, the surfactant needs to be sufficiently hydrophobic. Here, we present a system consisting of the anionic surfactant sodium monododecyl phosphate and the cationic cellulose-based polyelectrolyte JR 400. The hydrophobicity of the surfactant can be controlled by the solution's pH. At pH > 12, the surfactant headgroup bears two charges. As a consequence, the solution viscosity decreases drastically by up to two orders of magnitude, while it can be as high as 10 Pa s at lower pH. In this paper, we investigate the changes of the mesoscopic structure of the system which lead to such drastic changes in viscosity using small angle neutron scattering and neutron spin-echo spectroscopy. Such systems are potentially interesting as they allow for a modular design where stimuli responsiveness is introduced by relatively small amounts of surfactant reusing the same simple polyelectrolyte.
A pH sensitive surfactant with an oppositely charged polyelectrolyte allows the reversible control of solution viscosity through aggregate formation.
Low-molecular weight gelators (LMWGs) are small molecules (Mw < ∼1 kDa), which form self-assembled fibrillar network (SAFiN) hydrogels in water when triggered by an external stimulus. A great ...majority of SAFiN gels involve an entangled network of self-assembled fibers, in analogy to a polymer in a good solvent. In some rare cases, a combination of attractive van der Waals and repulsive electrostatic forces drives the formation of bundles with a suprafibrillar hexagonal order. In this work, an unexpected micelle-to-fiber transition is triggered by Ca2+ or Ag+ ions added to a micellar solution of a novel glycolipid surfactant, whereas salt-induced fibrillation is not common for surfactants. The resulting SAFiN, which forms a hydrogel above 0.5 wt%, has a “nano-fishnet” structure, characterized by a fibrous network of both entangled fibers and β-sheet-like rafts, generally observed for silk fibroin, actin hydrogels or mineral imogolite nanotubes, but not known for SAFiNs. The β-sheet-like raft domains are characterized by a combination of cryo-TEM and SAXS and seem to contribute to the stability of glycolipid gels. Furthermore, glycolipid is obtained by fermentation from natural resources (glucose, rapeseed oil), thus showing that naturally engineered compounds can have unprecedented properties, when compared to the wide range of chemically derived amphiphiles.
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