Polyelectrolyte-protein synergism: pH-responsive polyelectrolyte/insulin complexes as versatile carriers for targeted protein and drug delivery

The co-assembly of polyelectrolytes (PE) with proteins offers a promising approach for designing complex structures with customizable morphologies, charge distribution, and stability for targeted cargo delivery. However, the complexity of protein structure limits our ability to predict the properties of the formed nanoparticles, and our goal is to identify the key triggers of the morphological transition in protein/PE complexes and evaluate their ability to encapsulate multivalent ionic drugs. A positively charged PE can assemble with a protein at pH above isoelectric point due to the electrostatic attraction and disassemble at pH below isoelectric point due to the repulsion. The additional hydrophilic block of the polymer should stabilize the particles in solution and enable them to encapsulate a negatively charged drug in the presence of PE excess. We demonstrated that diblock copolymers, poly(ethylene oxide)-block-poly(N,N-dimethylaminoethyl methacrylate) and poly(ethylene oxide)-block-poly(N,N,N-trimethylammonioethyl methacrylate), consisting of a polycation block and a neutral hydrophilic block, reversibly co-assemble with insulin in pH range between 5 and 8. Using small-angle neutron and X-ray scattering (SANS, SAXS), we showed that insulin arrangement within formed particles is controlled by intermolecular electrostatic forces between protein molecules, and can be tuned by varying ionic strength. For the first time, we observed by fluorescence that formed protein/PE complexes with excess of positive charges exhibited potential for encapsulating and controlled release of negatively charged bivalent drugs, protoporphyrin-IX and zinc(II) protoporphyrin-IX, enabling the development of nanocarriers for combination therapies with adjustable charge, stability, internal structure, and size.

Advances in Small Angle Neutron Scattering on Polysaccharide Materials

Polysaccharide materials and biomaterials gain the focus of intense research owing to their great versatility in chemical structures and modification possibilities, as well as their biocompatibility, degradability, and sustainability features. This review focuses on the recent advances in the application of SANS on polysaccharide systems covering a broad range of materials such as nanoparticulate assemblies, hydrogels, nanocomposites, and plant-originating nanostructured systems. It motivates the use of SANS in its full potential by demonstrating the features of contrast variation and contrast matching methods and by reporting the methodologies for data analysis and interpretation. As these soft matter systems may be organized in multiple length scales depending on the interactions and chemical bonds between their components, SANS offers exceptional and unique opportunities for advanced characterization and optimization of new nanostructured polysaccharide materials.

Structure of Single-Chain Nanoparticles under Crowding Conditions: A Random Phase Approximation Approach

The conformation of poly(methyl methacrylate) (PMMA)-based single-chain nanoparticles (SCNPs) and their corresponding linear precursors in the presence of deuterated linear PMMA in deuterated dimethylformamide (DMF) solutions has been studied by small-angle neutron scattering (SANS). The SANS profiles were analyzed in terms of a three-component random phase approximation (RPA) model. The RPA approach described well the scattering profiles in dilute and crowded solutions. Considering all the contributions of the RPA leads to an accurate estimation of the single chain form factor parameters and the Flory-Huggins interaction parameter between PMMA and DMF. The value of the latter in the dilute regime indicates that the precursors and the SCNPs are in good solvent conditions, while in crowding conditions, the polymer becomes less soluble.

Simultaneous SANS/FTIR measurement system incorporating the ATR sampling method

Small-angle neutron scattering (SANS) is widely used as a powerful technique to study the higher-order structure of soft matter. To increase the reliability of SANS profile analysis for complex multi-component systems, combining different types of structural information obtained by other methods is desirable. A simultaneous measurement system combining SANS and Fourier transform infrared (FTIR) spectroscopy meets this objective. It is beneficial for targets where matching the timing of structural changes between experiments is difficult, but the issue is that samples suitable for SANS are too thick for the typical transmission FTIR method. To overcome this problem, a new simultaneous measurement system that employs the attenuated total reflectance (ART) sampling method for FTIR spectroscopy has been developed.

Interchain Hydrodynamic Interaction and Internal Friction of Polyelectrolytes

Polyelectrolytes (PE) are polymeric macromolecules in aqueous solutions characterized by their chain topology and intrinsic charge in a neutralizing fluid. Structure and dynamics are related to several characteristic screening length scales determined by electrostatic, excluded volume, and hydrodynamic interactions. We examine PE dynamics in dilute to semidilute conditions using dynamic light scattering, neutron spinecho spectroscopy, and pulse field gradient NMR spectroscopy. We connect macroscopic diffusion to segmental chain dynamics, revealing a decoupling of local chain dynamics from interchain interactions. Collective diffusion is described within a colloidal picture, including electrostatic and hydrodynamic interactions. Chain dynamics is characterized by the classical Zimm model of a neutral chain retarded by internal friction. We observe that hydrodynamic interactions are not fully screened between chains and that the internal friction within the chain increases with an increase in ion condensation on the chain.

Extended Q-range small-angle neutron scattering to understand the morphology of proton-exchange membranes: the case of the functionalized syndiotactic-polystyrene model system

Semi-crystalline polymers exhibit microphase separation into crystalline and amorphous domains characterized by multiple structural levels with sizes ranging from ångströms to hundreds of nanometres. The combination of small-angle (SANS) and wide-angle (WANS) neutron scattering on the same beamline enables reliable in situ characterization of such materials under application-relevant conditions, with the unique advantage of contrast variation by controlled labelling, allowing the structure of such multi-component systems to be resolved in detail. This paper reports a structural analysis performed on deuterated polymer membranes based on syndiotactic polystyrene (sPS) using an extended Q-range SANS and WANS combination, always with the same neutron scattering instrument, either a pinhole SANS diffractometer installed at a research reactor or a 'small- and wide-angle' time-of-flight diffractometer installed at a neutron spallation source. sPS is a semi-crystalline material that becomes hydrophilic and proton conducting when suitable functionalization is achieved by thin film sulfonation, and can form various co-crystalline complexes (clathrates) with small organic molecules stored in the crystalline phase as guests in the vacancies between the polymer helices. Therefore, this material is interesting not only for its conducting properties but also for its versatility as a model system to evaluate the usefulness of extended Q-range neutron scattering in such studies. Variation of neutron contrast was achieved in the amorphous hydrophilic phase by using H2O or D2O to hydrate the membranes and in the crystalline phase by loading the clathrates with deuterated or protonated guest molecules. The experimental approach, the advantages and limitations of the two types of instrumentation used in such analyses, and the main results obtained with respect to the structural characterization of sulfonated sPS membranes under different hydration and temperature conditions are reported, and the potential of this method for similar structural studies on other semi-crystalline polymeric materials is discussed.

Stability of Nanopeptides: Structure and Molecular Exchange of Self-assembled Peptide Fibers

Often nanostructures formed by self-assembly of small molecules based on hydrophobic interactions are rather unstable, causing morphological changes or even dissolution when exposed to changes in aqueous media. In contrast, peptides offer precise control of the nanostructure through a range of molecular interactions where physical stability can be engineered in and, to a certain extent, decoupled from size via rational design. Here, we investigate a family of peptides that form beta-sheet nanofibers and demonstrate a remarkable physical stability even after attachment of poly(ethylene glycol). We employed small-angle neutron/X-ray scattering, circular dichroism spectroscopy, and molecular dynamics simulation techniques to investigate the detailed nanostructure, stability, and molecular exchange. The results for the most stable sequence did not reveal any structural alterations or unimer exchange for temperatures up to 85 °C in the biologically relevant pH range. Only under severe mechanical perturbation (i.e., tip sonication) would the fibers break up, which is reflected in a very high activation barrier for unimer exchange of ∼320 kJ/mol extracted from simulations. The results give important insight into the relation between molecular structure and stability of peptide nanostructure that is important for, e.g., biomedical applications.

Microscopic Determination of the Local Hydration Number of Polymer Electrolyte Membranes Using SANS Partial Scattering Function Analysis

The conventional hydration number, λ, of a polymer electrolyte membrane (PEM) is estimated by the gravimetric measurement of the total water uptake in the membrane. This is the overall water molecules divided by the number of ionic groups covering the water distribution from the macroscale to the molecular level. For a more precise evaluation of the local ion-water interactions and ion transport efficiency in hydrophilic channels, in contrast to λ, we here propose an index, local hydration number (λ_local), defined as the number of water molecules located adjacent to and interacting with ionic groups in a PEM, per ionic group in the hydrophilic channels. We introduce an experimental method using partial scattering function analysis through a contrast-variation small-angle neutron scattering technique to precisely determine λ_local at the micro- (nano-) scale to the molecular level for PEMs. When applied to the benchmark material Nafion and the well-studied radiation-grafted PEM, consisting of poly(styrene sulfonic acid) grafted onto poly(ethylene-co-tetrafluoroethylene) (ETFE-g-PSSA), the obtained λ_local was close to the conventional λ. This means all water molecules interacted with sulfonic acid groups, which is much different from the case of anion-type grafted PEMs. Comparing the λ_local value obtained in this study with the conventional λ value confirmed that water existed only in nanostructured hydrophilic channels in these PEMs. The result of this work provides a route to understand local molecular structures of high-performing PEMs for energy conversion applications.

Protein-induced transformation of unilamellar to multilamellar vesicles triggered by a polysaccharide

We report on the morphological transitions of didodecyldimethylammonium bromide (DDAB) cationic vesicles and hybrid DDAB/hyaluronic acid (HA) vesicles upon addition of BSA at pH 7 where BSA is overall negatively charged. Small angle neutron scattering (SANS) is used to extract the size distributions of the nanovesicles, the thickness of the DDAB bilayers and their lamellarity. Although the HA-decorated DDAB vesicles contain the negatively charged polysaccharide the interaction with BSA appears to be more intense in comparison to bare vesicles. Characteristic peaks in the SANS patterns indicate the presence of multilamellar interfaces while the formation of multilamellar vesicles induced by BSA depends on the amount of added HA. Consequently, higher lamellarities are observed at higher BSA contents. This work demonstrates a simple methodology to tune the encapsulation of globular proteins in vesicular nanoassemblies by affecting their lamellarity and has direct implications on the application of vesicles and liposomes in protein delivery.

Block Copolymer Adsorption on the Surface of Multi-Walled Carbon Nanotubes for Dispersion in N,N Dimethyl Formamide

This research aims to characterize the adsorption morphology of block copolymer dispersants of the styrene-block-4-vinylpyridine family (S4VP) on the surface of multi-walled carbon nanotubes (MWCNT) in a polar organic solvent, N,N-dimethyl formamide (DMF). Good, unagglomerated dispersion is important in several applications such as fabricating CNT nanocomposites in a polymer film for electronic or optical devices. Small-angle neutron scattering (SANS) measurements, using the contrast variation (CV) method, are used to evaluate the density and extension of the polymer chains adsorbed on the nanotube surface, which can yield insight into the means of successful dispersion. The results show that the block copolymers adsorb onto the MWCNT surface as a continuous coverage of low polymer concentration. Poly(styrene) (PS) blocks adsorb more tightly, forming a 20 Å layer containing about 6 wt.% PS, whereas poly(4-vinylpyridine) (P4VP) blocks emanate into the solvent, forming a thicker shell (totaling 110 Å in radius) but of very dilute (<1 wt.%) polymer concentration. This indicates strong chain extension. Increasing the PS molecular weight increases the thickness of the adsorbed layer but decreases the overall polymer concentration within it. These results are relevant for the ability of dispersed CNTs to form a strong interface with matrix polymers in composites, due to the extension of the 4VP chains allowing for entanglement with matrix chains. The sparse polymer coverage of the CNT surface may provide sufficient space to form CNT-CNT contacts in processed films and composites, which are important for electrical or thermal conductivity.

Small-Angle Neutron Scattering Reveals the Nanostructure of Liposomes with Embedded OprF Porins of Pseudomonas aeruginosa

The use of liposomes as drug delivery systems emerged in the last decades in view of their capacity and versatility to deliver a variety of therapeutic agents. By means of small-angle neutron scattering (SANS), we performed a detailed characterization of liposomes containing outer membrane protein F (OprF), the main porin of the Pseudomonas aeruginosa bacterium outer membrane. These OprF-liposomes are the basis of a novel vaccine against this antibiotic-resistant bacterium, which is one of the main hospital-acquired pathogens and causes each year a significant number of deaths. SANS data were analyzed by a specific model we created to quantify the crucial information about the structure of the liposome containing OprF, including the lipid bilayer structure, the amount of protein in the lipid bilayer, the average protein localization, and the effect of the protein incorporation on the lipid bilayer. Quantification of such structural information is important to enhance the design of liposomal delivery systems for therapeutic applications.

Maleimide-Decorated PEGylated Mucoadhesive Liposomes for Ocular Drug Delivery

Liposomes are promising spherical vesicles for topical drug delivery to the eye. Several types of vesicles were formulated in this study, including conventional, PEGylated, and maleimide-decorated PEGylated liposomes. The physicochemical characteristics of these liposomes, including their size, zeta potential, ciprofloxacin encapsulation efficiency, loading capacity, and release, were evaluated. The structure of these liposomes was examined using dynamic light scattering, transmission electron microscopy, and small angle neutron scattering. The ex vivo corneal and conjunctival retention of these liposomes were examined using the fluorescence flow-through method. Maleimide-decorated liposomes exhibited the best retention performance on bovine conjunctiva compared to other types of liposomes studied. Poor retention of all liposomal formulations was observed on bovine cornea.

Variation of Structural and Dynamical Flexibility of Myelin Basic Protein in Response to Guanidinium Chloride

Myelin basic protein (MBP) is intrinsically disordered in solution and is considered as a conformationally flexible biomacromolecule. Here, we present a study on perturbation of MBP structure and dynamics by the denaturant guanidinium chloride (GndCl) using small-angle scattering and neutron spin–echo spectroscopy (NSE). A concentration of 0.2 M GndCl causes charge screening in MBP resulting in a compact, but still disordered protein conformation, while GndCl concentrations above 1 M lead to structural expansion and swelling of MBP. NSE data of MBP were analyzed using the Zimm model with internal friction (ZIF) and normal mode (NM) analysis. A significant contribution of internal friction was found in compact states of MBP that approaches a non-vanishing internal friction relaxation time of approximately 40 ns at high GndCl concentrations. NM analysis demonstrates that the relaxation rates of internal modes of MBP remain unaffected by GndCl, while structural expansion due to GndCl results in increased amplitudes of internal motions. Within the model of the Brownian oscillator our observations can be rationalized by a loss of friction within the protein due to structural expansion. Our study highlights the intimate coupling of structural and dynamical plasticity of MBP, and its fundamental difference to the behavior of ideal polymers in solution.

Influence of Chain Length of Gradient and Block Copoly(2-oxazoline)s on Self-Assembly and Drug Encapsulation

Amphiphilic gradient copolymers represent a promising alternative to extensively used block copolymers due to their facile one-step synthesis by statistical copolymerization of monomers of different reactivity. Herein, an in-depth analysis is provided of micelles based on amphiphilic gradient poly(2-oxazoline)s with different chain lengths to evaluate their potential for micellar drug delivery systems and compare them to the analogous diblock copolymer micelles. Size, morphology, and stability of self-assembled nanoparticles, loading of hydrophobic drug curcumin, as well as cytotoxicities of the prepared nanoformulations are examined using copoly(2-oxazoline)s with varying chain lengths and comonomer ratios. In addition to several interesting differences between the two copolymer architecture classes, such as more compact self-assembled structures with faster exchange dynamics for the gradient copolymers, it is concluded that gradient copolymers provide stable curcumin nanoformulations with comparable drug loadings to block copolymer systems and benefit from more straightforward copolymer synthesis. The study demonstrates the potential of amphiphilic gradient copolymers as a versatile platform for the synthesis of new polymer therapeutics.

Bifractal structure of chromatin in rat lymphocyte nuclei

The small-angle neutron scattering (SANS) on the rat lymphocyte nuclei demonstrates the bifractal nature of the chromatin structural organization. The scattering intensity from rat lymphocyte nuclei is described by power law Q^{-D} with fractal dimension approximately 2.3 on smaller scales and 3 on larger scales. The crossover between two fractal structures is detected at momentum transfer near 10^{-1}nm^{-1}. The use of contrast variation (D_{2}O-H_{2}O) in SANS measurements reveals clear similarity in the structural organizations of nucleic acids (NA) and proteins. Both chromatin components show bifractal behavior with logarithmic fractal structure on the large scale and volume fractal with slightly smaller than 2.5 structure on the small scale. Scattering intensities from chromatin, protein component, and NA component demonstrate an extremely extensive range of logarithmic fractal behavior (from 10^{-3} to approximately 10^{-1}nm^{-1}). We compare the fractal arrangement of rat lymphocyte nuclei with that of chicken erythrocytes and the immortal HeLa cell line. We conclude that the bifractal nature of the chromatin arrangement is inherent in the nuclei of all these cells. The details of the fractal arrangement-its range and correlation/interaction between nuclear acids and proteins are specific for different cells and is related to their functionality.

Observation of nucleic acid and protein correlation in chromatin of HeLa nuclei using small-angle neutron scattering with D_{2}O-H_{2}O contrast variation

The small-angle neutron scattering (SANS) on HeLa nuclei demonstrates the bifractal nature of the chromatin structural organization. The border line between two fractal structures is detected as a crossover point at Q_{c}≈4×10^{-2}nm^{-1} in the momentum transfer dependence Q^{-D}. The use of contrast variation (D_{2}O-H_{2}O) in SANS measurements reveals clear similarity in the large scale structural organizations of nucleic acids (NA) and proteins. Both NA and protein structures have a mass fractal arrangement with the fractal dimension of D≈2.5 at scales smaller than 150 nm down to 20 nm. Both NA and proteins show a logarithmic fractal behavior with D≈3 at scales larger than 150 nm up to 6000 nm. The combined analysis of the SANS and atomic force microscopy data allows one to conclude that chromatin and its constitutes (DNA and proteins) are characterized as soft, densely packed, logarithmic fractals on the large scale and as rigid, loosely packed, mass fractals on the smaller scale. The comparison of the partial cross sections from NA and proteins with one from chromatin as a whole demonstrates spatial correlation of two chromatin's components in the range up to 900 nm. Thus chromatin in HeLa nuclei is built as the unified structure of the NA and proteins entwined through each other. Correlation between two components is lost upon scale increases toward 6000 nm. The structural features at the large scale, probably, provide nuclei with the flexibility and chromatin-free space to build supercorrelations on the distance of 10^{3} nm resembling cycle cell activity, such as an appearance of nucleoli and a DNA replication.

Evidence of supercoolable nanoscale water clusters in an amorphous ionic liquid matrix

Nanoscale water clusters in an ionic liquid matrix, also called "water pockets," were previously found in some mixtures of water with ionic liquids containing hydrophilic anions. However, in these systems, at least partial crystallization occurs upon supercooling. In this work, we show for mixtures of 1-butyl-3-methylimidazolium dicyanamide with water that none of the components crystallizes up to a water content of 72 mol. %. The dynamics of the ionic liquid matrix is monitored from above room temperature down to the glass transition by combining depolarized dynamic light scattering with broadband dielectric and nuclear magnetic resonance spectroscopy, revealing that the matrix behaves like a common glass former and stays amorphous in the whole temperature range. Moreover, we demonstrate by a combination of Raman spectroscopy, small angle neutron scattering, and molecular dynamics simulation that, indeed, nanoscale water clusters exist in this mixture.

Separation of the inelastic and elastic scattering in time-of-flight mode on the pinhole small-angle neutron scattering diffractometer K-WS-2

To study and control the incoherent inelastic background in small-angle neutron scattering, which makes a significant contribution to the detected scattering from hydrocarbon systems, the KWS-2 small-angle neutron scattering diffractometer operated by the Jülich Centre for Neutron Science (JCNS) at Heinz-Maier Leibnitz Zentrum (MLZ), Garching, Germany, was equipped with a secondary single-disc chopper that is placed in front of the sample stage. This makes it possible to record in time-of-flight mode the scattered neutrons in the high-Q regime of the instrument (i.e. short incoming wavelengths and detection distances) and to discard the inelastic component from the measured data. Examples of measurements on different materials routinely used as standard samples, sample containers and solvents in the experiments at KWS-2 are presented. When only the elastic region of the spectrum is used in the data-reduction procedure, a decrease of up to two times in the incoherent background of the experimentally measured scattering cross section may be obtained. The proof of principle is demonstrated on a solution of bovine serum albumin in D2O.

Structural Organization of Cardiolipin-Containing Vesicles as Models of the Bacterial Cytoplasmic Membrane

The bacterial cytoplasmic membrane is the innermost bacterial membrane and is mainly composed of three different phospholipid species, i.e., phosphoethanolamine (PE), phosphoglycerol (PG), and cardiolipin (CL). In particular, PG and CL are responsible for the negative charge of the membrane and are often the targets of cationic antimicrobial agents. The growing resistance of bacteria toward the available antibiotics requires the development of new and more efficient antibacterial drugs. In this context, studying the physicochemical properties of the bacterial cytoplasmic membrane is pivotal for understanding drug-membrane interactions at the molecular level as well as for designing drug-testing platforms. Here, we discuss the preparation and characterization of PE/PG/CL vesicle suspensions, which contain all of the main lipid components of the bacterial cytoplasmic membrane. The vesicle suspensions were characterized by means of small-angle neutron scattering, dynamic light scattering, and electron paramagnetic spectroscopy. By combining solution scattering and spectroscopy techniques, we propose a detailed description of the impact of different CL concentrations on the structure and dynamics of the PE/PG bilayer. CL induces the formation of thicker bilayers, which exhibit higher curvature and are overall more fluid. The experimental results contribute to shed light on the structure and dynamics of relevant model systems of the bacterial cytoplasmic membrane.

Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers

In this work we present a fundamental analysis based on small-angle scattering, linear rheology and differential scanning calorimetry (DSC) experiments of the role of different hydrogen bonding (H-bonding) types on the structure and dynamics of chain-end modified poly(ethylene glycol) (PEG) in bulk. As such bifunctional PEG with a molar mass below the entanglement mass Me is symmetrically end-functionalized with three different hydrogen bonding (H-bonding) groups: thymine-1-acetic acid (thy), diamino-triazine (dat) and 2-ureido-4[1H]-pyrimidinone (upy). A linear block copolymer structure and a Newtonian-like dynamics is observed for PEG-thy/dat while results for PEG-upy structure and dynamics reveal a sphere and a network-like behavior, respectively. These observations are concomitant with an increase of the Flory-Huggins interaction parameter from PEG-thy/dat to PEG-upy that is used to quantify the difference between the H-bonding types. The upy association into spherical clusters is established by the Percus-Yevick approximation that models the inter-particle structure factor for PEG-upy. Moreover, the viscosity study reveals for PEG-upy a shear thickening behavior interpreted in terms of the free path model and related to the time for PEG-upy to dissociate from the upy clusters, seen as virtual crosslinks of the formed network. Moreover, a second relaxation time of different nature is also obtained from the complex shear modulus measurements of PEG-upy by the inverse of the angular frequency where G' and G'' crosses from the network-like to glass-like transition relaxation time, which is related to the segmental friction of PEG-upy polymeric network strands. In fact, not only do PEG-thy/dat and PEG-upy have different viscoelastic properties, but the relaxation times found for PEG-upy are much slower than the ones for PEG-thy/dat. However, the activation energy related to the association dynamics is very similar for both PEG-thy/dat and PEG-upy. Concerning the segmental dynamics, the glass transition temperature obtained from both rheological and calorimetric analysis is similar and increases for PEG-upy while for PEG-thy/dat is almost independent of association behavior. Our results show how supramolecular PEG properties vary by modifying the H-bonding association type and changing the molecular Flory-Huggins interaction parameter, which can be further explored for possible applications.

Adhesion Process of Biomimetic Myelin Membranes Triggered by Myelin Basic Protein

The myelin sheath-a multi-double-bilayer membrane wrapped around axons-is an essential part of the nervous system which enables rapid signal conduction. Damage of this complex membrane system results in demyelinating diseases such as multiple sclerosis (MS). The process in which myelin is generated in vivo is called myelination. In our study, we investigated the adhesion process of large unilamellar vesicles with a supported membrane bilayer that was coated with myelin basic protein (MBP) using time-resolved neutron reflectometry. Our aim was to mimic and to study the myelination process of membrane systems having either a lipid-composition resembling that of native myelin or that of the standard animal model for experimental autoimmune encephalomyelitis (EAE) which represents MS-like conditions. We were able to measure the kinetics of the partial formation of a double bilayer in those systems and to characterize the scattering length density profiles of the initial and final states of the membrane. The kinetics could be modeled using a random sequential adsorption simulation. By using a free energy minimization method, we were able to calculate the shape of the adhered vesicles and to determine the adhesion energy per MBP. For the native membrane the resulting adhesion energy per MBP is larger than that of the EAE modified membrane type. Our observations might help in understanding myelination and especially remyelination-a process in which damaged myelin is repaired-which is a promising candidate for treatment of the still mostly incurable demyelinating diseases such as MS.

Reversible multilayered vesicle-like structures with fluid hydrophobic and interpolyelectrolyte layers

Hydrophobic blocks of amphiphilic block copolymers often form glassy micellar cores at room temperature with a rigid structure that limits their applications as nanocapsules for targeted delivery. Nevertheless, we prepared and analyzed core/shell micelles with a soft core, formed by a self-assembled block copolymer consisting of a hydrophobic block and a polycation block, poly(lauryl acrylate)-block-poly(trimethyl-aminoethyl acrylate) (PLA-QPDMAEA), in aqueous solution. By light and small-angle neutron scattering, by transmission electron microscopy and by fluorescence spectroscopy, we showed that these core/shell micelles are spherical and cylindrical with a fluid-like PLA core and a positively charged outer shell and that they can encapsulate and release hydrophobic solutes. Moreover, after mixing these PLA-QPDMAEA core/shell micelles with another diblock copolymer, consisting of a hydrophilic block and a polyanion block, namely poly(ethylene oxide)-block-poly(methacrylic acid) (PEO-PMAA), we observed the formation of novel vesicle-like multicompartment structures containing both soft hydrophobic and interpolyelectrolyte (IPEC) layers. By combining small-angle neutron scattering with self-consistent field modeling, we confirmed the formation of these complex vesicle-like structures with a swollen PEO core, an IPEC inner layer, a PLA soft layer, an IPEC outer layer and a loose PEO corona. Thus, these multicompartment micelles with fluid and IPEC layers and a hydrophilic corona may be used as nanocapsules with several tunable properties, including the ability to control the thickness of each layer, the charge of the IPEC layers and the stability of the micelles, to deliver both hydrophobic and multivalent solutes.

Physicochemical Approach to Understanding the Structure, Conformation, and Activity of Mannan Polysaccharides

Extracellular polysaccharides are widely produced by bacteria, yeasts, and algae. These polymers are involved in several biological functions, such as bacteria adhesion to surface and biofilm formation, ion sequestering, protection from desiccation, and cryoprotection. The chemical characterization of these polymers is the starting point for obtaining relationships between their structures and their various functions. While this fundamental correlation is well reported and studied for the proteins, for the polysaccharides, this relationship is less intuitive. In this paper, we elucidate the chemical structure and conformational studies of a mannan exopolysaccharide from the permafrost isolated bacterium Psychrobacter arcticus strain 273-4. The mannan from the cold-adapted bacterium was compared with its dephosphorylated derivative and the commercial product from Saccharomyces cerevisiae. Starting from the chemical structure, we explored a new approach to deepen the study of the structure/activity relationship. A pool of physicochemical techniques, ranging from small-angle neutron scattering (SANS) and dynamic and static light scattering (DLS and SLS, respectively) to circular dichroism (CD) and cryo-transmission electron microscopy (cryo-TEM), have been used. Finally, the ice recrystallization inhibition activity of the polysaccharides was explored. The experimental evidence suggests that the mannan exopolysaccharide from P. arcticus bacterium has an efficient interaction with the water molecules, and it is structurally characterized by rigid-rod regions assuming a 14-helix-type conformation.

Functionalized lipid nanoparticles for subcutaneous administration of mRNA to achieve systemic exposures of a therapeutic protein

Lipid nanoparticles (LNPs) are the most clinically advanced delivery system for RNA-based drugs but have predominantly been investigated for intravenous and intramuscular administration. Subcutaneous administration opens the possibility of patient self-administration and hence long-term chronic treatment that could enable messenger RNA (mRNA) to be used as a novel modality for protein replacement or regenerative therapies. In this study, we show that subcutaneous administration of mRNA formulated within LNPs can result in measurable plasma exposure of a secreted protein. However, subcutaneous administration of mRNA formulated within LNPs was observed to be associated with dose-limiting inflammatory responses. To overcome this limitation, we investigated the concept of incorporating aliphatic ester prodrugs of anti-inflammatory steroids within LNPs, i.e., functionalized LNPs to suppress the inflammatory response. We show that the effectiveness of this approach depends on the alkyl chain length of the ester prodrug, which determines its retention at the site of administration. An unexpected additional benefit to this approach is the prolongation observed in the duration of protein expression. Our results demonstrate that subcutaneous administration of mRNA formulated in functionalized LNPs is a viable approach to achieving systemic levels of therapeutic proteins, which has the added benefits of being amenable to self-administration when chronic treatment is required.

Structure and Dynamics of Ribonuclease A during Thermal Unfolding: The Failure of the Zimm Model

Disordered regions as found in intrinsically disordered proteins (IDP) or during protein folding define response time to stimuli and protein folding times. Neutron spin-echo spectroscopy is a powerful tool to directly access the collective motions of the unfolded chain to enlighten the physical origin of basic conformational relaxation. During the thermal unfolding of native ribonuclease A, we examine the structure and dynamics of the disordered state within a two-state transition model using polymer models, including internal friction, to describe the chain dynamics. The presence of four disulfide bonds alters the disordered configuration to a more compact configuration compared to a Gaussian chain that is defined by the additional links, as demonstrated by coarse-grained simulation. The dynamics of the disordered chain is described by Zimm dynamics with internal friction (ZIF) between neighboring amino acids. Relaxation times are dominated by mode-independent internal friction. Internal friction relaxation times show an Arrhenius-like behavior with an activation energy of 33 kJ/mol. The Zimm dynamics is dominated by internal friction and suggest that the characteristic motions correspond to overdamped elastic modes similar to the motions observed for folded proteins but within a pool of disordered configurations spanning the configurational space. For IDP, internal friction dominates while solvent friction and hydrodynamic interactions are smaller corrections.

Lamellarity and size distributions in mixed DPPC/amphiphilic poly(2-oxazoline) gradient copolymer vesicles and their temperature response

Mixed liposomes of dipalmitoylphosphatidylcholine (DPPC) and gradient (pseudodiblock) poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) (MPOx) copolymers are investigated by small angle neutron scattering (SANS). All experimental data, from different phospholipid-copolymer compositions, concentrations and temperatures are fitted with one model. This model allows the determination of the separate contributions from vesicular populations of different lamellarity and size. MPOx copolymers are proved to modify both the size and lamellarity of DPPC liposomes. The gradient copolymer with higher hydrophilic content induces shrinkage of the uni- and bi-lamellar DPPC vesicles. The copolymer with lower hydrophilic content causes dramatic changes on the lamellarity of DPPC vesicles by the formation of hexa-lamellar vesicles. The tendency of multi-lamellar vesicles to transform into uni-lamellar ones as temperature increases is more pronounced in the presence of the copolymers. These findings may have direct implications on the drug loading and release properties of liposomes and their interactions with cells.

Phase behavior of ultrasoft spheres show stable bcc lattices

The phase behavior of supersoft spheres is explored using solutions of ultralow cross-linked poly(N-isopropylacrylamide)-based microgels as a model system. For these microgels, the effects of the electric charges on their surfaces can be neglected and therefore only the role of softness on the phase behavior is investigated. The samples show a liquid-to-crystal transition at higher volume fraction with respect to both hard spheres and stiffer microgels. Furthermore, stable body centered cubic (bcc) crystals are observed in addition to the expected face centered cubic (fcc) crystals. Small-angle x-ray and neutron scattering with contrast variation allow the characterization of both the microgel-to-microgel distance and the architecture of single microgels in crowded solutions. The measurements reveal that the stable bcc crystals depend on the interplay between the collapse and the interpenetration of the external shell of the ultralow cross-linked microgels.

Switch of fractal properties of DNA in chicken erythrocytes nuclei by mechanical stress

The small-angle neutron scattering (SANS) on the chicken erythrocyte nuclei demonstrates the bifractal nature of the chromatin structural organization. Use of the contrast variation (D_{2}O-H_{2}O) in SANS measurements reveals the differences in the DNA and protein arrangements inside the chromatin substance. It is the DNA that serves as a framework that constitutes the bifractal behavior showing the mass fractal properties with D=2.22 at a smaller scale and the logarithmic fractal behavior with D≈3 at a larger scale. The protein spatial organization shows the mass fractal properties with D≈2.34 throughout the whole nucleus. The borderline between two fractal levels can be significantly shifted toward smaller scales by centrifugation of the nuclei disposed on the dry substrate, since nuclei suffer from mechanical stress transforming them to a disklike shape. The height of this disk measured by atomic force microscopy (AFM) coincides closely with the fractal borderline, thus characterizing two types of the chromatin with the soft (at larger scale) and rigid (at smaller scale) properties. The combined SANS and AFM measurements demonstrate the stress induced switch of the DNA fractal properties from the rigid, but loosely packed, mass fractal to the soft, but densely packed, logarithmic fractal.

A long side chain imidazolium-based graft-type anion-exchange membrane: novel electrolyte and alkaline-durable properties and structural elucidation using SANS contrast variation

Newly designed styrylimidazolium-based grafted anion-exchange membranes (StIm-AEMs), in which imidazolium ionic groups are attached to styrene at the far side from the graft chains, were prepared by radiation-induced graft polymerization of p-(2-imidazoliumyl) styrene onto poly(ethylene-co-tetrafluoloethylene) (ETFE) films, followed by N-alkylation and ion-exchange reactions. StIm-AEM having an ion exchange capacity (IEC) of 0.54 mmol g-1 with a grafting degree (GD) of ∼18%, possesses practical conductivity (>50 mS cm-1) even with a very low water uptake (∼10%) and high stability over 600 h in a 1 M KOH solution at 80 °C. There exists a critical IEC (IECc) in the range of 0.7-0.8 mmol g-1 over which the membrane showed high water uptake, which resulted in pronounced susceptibility to hydrolysis. Using small-angle neutron scattering technique with a contrast variation method, we found the hydrophilic phase in StIm-AEMs with IECs lower and higher than IECc shows "reverse-micelles" with water domains dispersed in the polymer matrix and "micelles" with graft polymer aggregates dispersed in the water matrix, respectively. The further analysis of micelle structures using the hard-sphere liquid model and Porod limit analysis reveals that the interfacial structures of ionic groups are essential for the electrochemical properties and durability of StIm-AEMs. In addition, StIm-AEM with an IEC of 0.95 mmol g-1 and the maximum power density of 80 mW cm-2 in the hydrazine hydrate fuel cell test, exhibited long-term durability under constant current (8.0 mA) up to 455 h, which, thus far, is the best durability at 80 °C for platinum-free alkaline-type liquid fuel cells.

The Effects of Temperature and Humidity on the Microstructure of Sulfonated Syndiotactic-polystyrene Ionic Membranes

Polymeric membranes based on the semi-crystalline syndiotactic-polystyrene (sPS) become hydrophilic, and therefore conductive, following the functionalization of the amorphous phase by the solid-state sulfonation procedure. Because the crystallinity of the material, and thus the mechanical strength of the membranes, is maintained and the resistance to oxidation decomposition can be improved by doping the membranes with fullerenes, the sPS becomes attractive for proton-exchange membranes fuel cells (PEMFC) and energy storage applications. In the current work we report the micro-structural characterization by small-angle neutron scattering (SANS) method of sulfonated sPS films and sPS-fullerene composite membranes at different temperatures between 20 °C and 80 °C, under the relative humidity (RH) level from 10% to 70%. Complementary characterization of membranes was carried out by FTIR, UV-Vis spectroscopy and prompt-γ neutron activation analysis in terms of composition, following the specific preparation and functionalization procedure, and by XRD with respect to crystallinity. The hydrated ionic clusters are formed in the hydrated membrane and shrink slightly with the increasing temperature, which leads to a slight desorption of water at high temperatures. However, it seems that the conductive properties of the membranes do not deteriorate with the increasing temperature and that all membranes equilibrated in liquid water show an increased conductivity at 80 °C compared to the room temperature. The presence of fullerenes in the composite membrane induces a tremendous increase in the conductivity at high temperatures compared to fullerenes-free membranes. Apparently, the observed effects may be related to the formation of additional hydrated pathways in the composite membrane in conjunction with changes in the dynamics of water and polymer.

Morphology, gelation and cytotoxicity evaluation of D-α-Tocopheryl polyethylene glycol succinate (TPGS) - Tetronic mixed micelles

HYPOTHESIS

The combination of polymeric surfactants into mixed micelles is expected to improve properties relevant to their use in drug delivery, such as micellar size, gelation, and toxicity. We investigated synergistic effects in mixtures of D-α-Tocopheryl polyethylene glycol succinate (TPGS), an FDA-approved PEGylated derivative of vitamin E, and Tetronic surfactants, pH-responsive and thermogelling polyethylene oxide (PEO)-polypropylene oxide (PPO) 4-arm block copolymers. We hypothesized that mixed micelles would form under specific conditions and provide a handle to tune formulation characteristics.

EXPERIMENTS

We examined the morphology of the self-assembled structures in mixtures of TPGS with two Tetronic: T1107 and T908, using a combination of dynamic light scattering (DLS), small-angle neutron scattering (SANS), NMR spectroscopy (NOESY and diffusion NMR) and oscillatory rheology, over a range of compositions, temperatures and pH. Cell viability was assessed in NIH/3T3 fibroblasts.

FINDINGS

The combination of TPGS with either of the two Tetronic produces spherical core-shell micelles that comprise both surfactants in their structure (mixed micelles). T1107 unimers incorporate into TPGS aggregates below the critical micelle temperature of the poloxamine, while mixed micelles only form under limited conditions with T908. At high concentration/temperature, small proportions of TPGS extend the gel phase, more markedly with T1107, with similar elastic moduli (30-50 kPa) and a BCC crystalline structure. Cell viability of NIH/3T3 fibroblasts grown in the hydrogels increases significantly when the poloxamine gels are doped with TPGS, making the combination of poloxamines and TPGS a promising platform for drug delivery.

Cold and distant: structural features of the nucleoprotein complex of a cold-adapted influenza A virus strain

Two influenza A nucleoprotein variants (wild-type: G102R; and mutant: G102R and E292G) were studied with regard to macro-molecular interactions in oligomeric form (24-mers). The E292G mutation has been previously shown to provide cold adaptation. Molecular dynamics simulations of these complexes and trajectory analysis showed that the most significant difference between the obtained models was distance between nucleoprotein complex strands. The isolated complexes of two ribonucleoprotein variants were characterized by transmission electron microscopy and differential scanning fluorimetry (DSF). Presence of the E292G substitution was shown by DSF to affect nucleoprotein complex melting temperature. In the filament interface peptide model, it was shown that the peptide corresponding in primary structure to the wild-type NP (SGYDFEREGYS) is prone to temperature-dependent self-association, unlike the peptide corresponding to E292G substitution (SGYDFGREGYS). It was also shown that the SGYDFEREGYS peptide is capable of interacting with a monomeric nucleoprotein (wild type); this interaction's equilibrium dissociation constant is five orders of magnitude lower than for the SGYDFGREGYS peptide. Using small-angle neutron scattering (SANS), the supramolecular structures of isolated complexes of these proteins were studied at temperatures of 15, 32, and 37 °C. SANS data show that the structures of the studied complexes at elevated temperature differ from the rod-like particle model and react differently to temperature changes. The data suggest that the mechanism behind cold adaptation with E292G is associated with a weakening of the interaction between strands of the ribonucleoprotein complex and, as a result, the appearance of inter-chain interface flexibility necessary for complex function at low temperature.Communicated by Ramaswamy H. Sarma.

A new simultaneous measurement system of wide Q-range small angle neutron scattering combined with polarized Fourier transform infrared spectroscopy

Small angle neutron scattering (SANS) is a versatile and convenient method to investigate the higher order structure of molecular assembly systems. However, the more complicated a system of interest, the more difficult the interpretation in the SANS profile. In order to increase the reliability of structural analysis on a complicated system, it is desirable to obtain different kinds of structural information from the same sample simultaneously. Polarized infrared spectroscopy is able to provide information about the molecular structure, concentration, and orientation of each chemical species in a system. In order to utilize these advantages of polarized infrared spectroscopy, a simultaneous measurement system was built by incorporating a Fourier transform infrared (FTIR) spectrometer into a time-of-flight small angle neutron scattering instrument covering a wide Q range. Using this system, simultaneous measurements of wide- and small-angle neutron scattering and polarized FTIR spectroscopy was realized for the first time.

Hierarchical Morphology of Poly(ether ether ketone) Aerogels

The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in 4-chlorophenol (4CP) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in both 4CP and dichloroacetic acid (DCA) up to a concentration of 25 wt %. Highly porous aerogels of PEEK were prepared through simple solvent exchange followed by one of two drying methods of solvent removal from the wet gel: freeze-drying or supercritical CO₂ fluid extraction (SC-drying). The field-emission scanning electron microscopy analysis showed that gelation of PEEK in 4CP, followed by SC-drying, produced aerogels with well-defined lamellar aggregates as compared to less ordered aggregates formed from DCA. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density, regardless of the preparation method (gelation solvent selection, concentration variation, or drying method). Nitrogen adsorption-desorption isotherms indicate that PEEK aerogels are comprised of mesopores (2-50 nm diameter pores) formed from stacked crystalline lamella. PEEK aerogels prepared using SC-drying exhibit higher Brunauer-Emmett-Teller surface areas than freeze-dried aerogels of comparable density. The ultra-small-angle X-ray scattering/small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering analysis revealed a hierarchical morphology of the PEEK aerogels with structural features from PEEK crystallites to agglomerates of stacked lamella that spanned a wide range of length scales. SANS contrast-matching confirmed that the morphological origin of the principle scattering feature in PEEK aerogels is stacked crystalline lamella. Nitrogen sorption measurements of porosity and the specific surface area of the PEEK aerogels were correlated with the SAXS analysis to reveal a remarkably high surface area attributed to the platelet-like, lamellar morphology. Contact angle and contact angle hysteresis (CAH) revealed that low-density PEEK aerogels (ρ < 0.15 g/cm³) have water contact angles above the superhydrophobicity cutoff angle (>150°) and a very low CAH near 1°.

Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach

The preparation of poly(N-isopropylacrylamide) microgels via classical precipitation polymerization (batch method) and a continuous monomer feeding approach (feeding method) leads to different internal crosslinker distributions, i.e., from core-shell-like to a more homogeneous one. The internal structure and dynamics of these microgels with low and medium crosslinker concentrations are studied with dynamic light scattering and small-angle neutron scattering in a wide q-range below and above the volume phase transition temperature. The influence of the preparation method, and crosslinker and initiator concentration on the internal structure of the microgels is investigated. In contrast to the classical conception where polymer microgels possess a core-shell structure with the averaged internal polymer density distribution within the core part, a detailed view of the internal inhomogeneities of the PNIPAM microgels and the presence of internal domains even above the volume phase transition temperature, when polymer microgels are in the deswollen state, are presented. The correlation between initiator concentration and the size of internal domains that appear inside the microgel with temperature increase is demonstrated. Moreover, the influence of internal inhomogeneities on the dynamics of the batch- and feeding-microgels studied with neutron spin-echo spectroscopy is reported.

Soft particles in an electric field - a zero average contrast study

We report on the structural properties of ionic microgel particles subjected to alternating electric fields, using small-angle neutron scattering. The experiments were performed under so-called zero average contrast conditions, which cancel the structure factor contribution to the scattered intensity, allowing us to obtain direct information on the single particle size and structure as particles align in field-induced strings. Our results reveal only a marginal compression of the particles as they align in strings, and indicate considerable particle overlap at higher field strengths. These findings provide further insight into the origins of the previously reported unusual path dependent field-induced crystal-crystal transition found for these systems (P. S. Mohanty et al., Phys. Rev. X, 2015, 5, 011030).