Aggregation Of Macromolecules Research Articles

Asymptotic analysis of particle cluster formation in the presence of anchoring sites

The aggregation or clustering of proteins and other macromolecules plays an important role in the formation of large-scale molecular assemblies within cell membranes. Examples of such assemblies include lipid rafts, and postsynaptic domains (PSDs) at excitatory and inhibitory synapses in neurons. PSDs are rich in scaffolding proteins that can transiently trap transmembrane neurotransmitter receptors, thus localizing them at specific spatial positions. Hence, PSDs play a key role in determining the strength of synaptic connections and their regulation during learning and memory. Recently, a two-dimensional (2D) diffusion-mediated aggregation model of PSD formation has been developed in which the spatial locations of the clusters are determined by a set of fixed anchoring sites. The system is kept out of equilibrium by the recycling of particles between the cell membrane and interior. This results in a stationary distribution consisting of multiple clusters, whose average size can be determined using an effective mean-field description of the particle concentration around each anchored cluster. In this paper, we derive corrections to the mean-field approximation by applying the theory of diffusion in singularly perturbed domains. The latter is a powerful analytical method for solving two-dimensional (2D) and three-dimensional (3D) diffusion problems in domains where small holes or perforations have been removed from the interior. Applications range from modeling intracellular diffusion, where interior holes could represent subcellular structures such as organelles or biological condensates, to tracking the spread of chemical pollutants or heat from localized sources. In this paper, we take the bounded domain to be the cell membrane and the holes to represent anchored clusters. The analysis proceeds by partitioning the membrane into a set of inner regions around each cluster, and an outer region where mean-field interactions occur. Asymptotically matching the inner and outer stationary solutions generates an asymptotic expansion of the particle concentration, which includes higher-order corrections to mean-field theory that depend on the positions of the clusters and the boundary of the domain. Motivated by a recent study of light-activated protein oligomerization in cells, we also develop the analogous theory for cluster formation in a three-dimensional (3D) domain. The details of the asymptotic analysis differ from the 2D case due to the contrasting singularity structure of 2D and 3D Green’s functions.Graphical abstract2D model of diffusion-based protein cluster formation in the presence of anchoring cites and particle recycling. a A set of N anchoring sites at positions xj\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extbf{x}}_j$$\\end{document}, j=1,…,N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$j=1,\\ldots ,N$$\\end{document}, in a bounded domain Ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega $$\\end{document}. b Diffusing particles accumulate at the anchoring sites resulting in the formation of particle aggregates or clusters Uj\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal {U}}}_j$$\\end{document}. c The clusters are dynamically maintained by a combination of lateral diffusion outside the clusters and particle recycling

A molecular study of viscosity-causing mechanism and viscosity reduction through re-emulsification for Jimsar shale oil

The high viscosity caused by oil–water emulsification and the lack of clarity on the viscosity-causing mechanism have seriously affected the development of Jimsar shale oil. In this paper, the mechanism behind the increase in viscosity due to emulsification for Jimsar shale oil is revealed at the molecular level, using high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with Electrospray ionization (ESI) technique. The high amount of N1 compounds (carbazoles and indoles) in shale oil combine with water through the N–H bond with the pyridine ring adsorbing formation water, which enhances crude oil's emulsification and water-binding ability. A stable W/O emulsion was formed with water and significantly increased the viscosity of the formation fluid. DFT calculations showed that the interaction energy (Eint) of anionic surfactant AS-1 and AS-2 with polar macromolecules was −258.70 and −77.03 kcal/mol, respectively. The interaction energy of these two systems was much lower than that between H2O and polar macromolecules (-50.87 kcal/mol). It indicated that AS-1 and AS-2 could penetrate the oil–water interface and form stronger interactions with polar macromolecules. Thus, the W/O emulsion is in a reversed-phase, and the viscosity is reduced. The laboratory results showed that the viscosity reduction rates (VRR) of AS-1 and AS-2 due to re-emulsification were greater than 94% at 30℃. The O/AS-1/W and O/AS-2/W emulsions formed during re-emulsification have pseudoplastic fluid flow characteristics and are relatively stable. The emulsions also exhibit spontaneous destabilization and water separation properties, lowering the cost of oil–water separation of produced liquid. Through weak dipole–dipole interaction, CH-π type interaction, and some weak interactions (O∙∙∙N, O∙∙∙S, O∙∙∙H), AS-1 and AS-2 make the space between crude oil and emulsion components more open and inhibit the aggregation of polar macromolecules furthering the viscosity reduction effect.

Protein phase separation disorder as a potentially pervasive pathogenic mechanism of male infertility

Male infertility is a complicated pathological state with high genetic susceptibility. Genetic defects and gene mutations may affect the structure and function of key molecules associated with fertility, and then clinically manifest as azoospermia, teratospermia, oligozoospermia, or asthenozoospermia. Most of the current research mainly focuses on the infertility phenotype and downstream pathways and clarifies the relevant mechanism by using molecular biology methods to construct knockout or overexpression models combined with omics and experimental verification, but how the mutation itself affects biomacromolecular functions remains poorly understood. As a special state of intracellular aggregation of biological macromolecules, phase separation (PS) is closely related to many important basic life activities. It has been reported to participate in the occurrence and development of various diseases, including neurodegenerative diseases, cardiovascular diseases and tumors, but only a few reports addressed the potential impact of protein PS on fertility. Given the physiological characteristics of PS, we hypothesize that abnormal PS may be a common pathological regulatory mechanism of male infertility, especially spermatogenesis and maturation disorders. PS can affect spermatogenesis and maturation by interfering with the phase transition of key molecules or molecular clusters, leading to gamete loss or dysfunction. Targeted modulation of PS may be a potentially powerful means to improve male fertility.

Impact of flexibility on the aggregation of polymeric macromolecules.

Dependence of the dimerization probability and the aggregation behavior of polymeric macromolecules on their flexibility is studied using Langevin dynamics simulations. It is found that the dimerization probability is a non-monotonic function of the polymers persistence length. For a given value of inter-polymer attraction strength, semiflexible polymers have lower dimerization probability relative to flexible and rigid polymers of the same length. The threshold temperature of the formation of aggregates in a many-polymer system and its dependence on the polymers persistence length is also investigated. The simulation results of two- and many-polymer systems are in good agreement and show how the amount of flexibility affects the dimerization and the aggregation behaviors of polymeric macromolecules.

Statistical mechanics of coil–rod structure in biopolymer gels

Due to the unique properties of biopolymer gels, they are extensively used in the food industry and biomedical applications such as drug delivery. Different from rubber-like materials, the constituting chains in many biopolymer gels randomly interlock with neighbouring chains by means of physical rather than covalent cross-linking. Such polymer networks are characterized by two principal regions: the disordered zone containing coiled chains and the ordered zone in the form of ion-mediated aggregation of macromolecules and/or helical structures. The ordered regions serve as junction zones between the disordered chains, and the size of these zones may alter as a result of zipping/unzipping phenomena. The entire polymer network can be envisaged as a collection of coil–rod structures serving as the building blocks, where the coil and rod are representative of the disordered and ordered zones, respectively. The present work aims to provide a rigorous formulation of coil–rod structure that can predict its mechanical behaviour including zipping/unzipping characteristics. The coil–rod structure is modelled by a rod attached to a freely jointed chain, where the length of the rod and the number of segments in the freely jointed chain are adjustable input parameters. The relationship between the force and end-to-end distance of the coil–rod structure is derived based on statistical mechanics. The formulation is extended to incorporate the zipping/unzipping mechanism with the aid of Boltzmann averaging. As an example of its applications, the model is implemented into the eight-chain model to describe the macroscopic mechanical response of the network. Another example is demonstrated where the zipping/unzipping mechanism is shown to be able to capture the unwinding of a double-stranded DNA under a tensile force. The formulation presented in this work paves the way for future studies that model biopolymer gel networks with potentially complex chain interactions.

Disrupted cellulose aggregation leads to the reduced mechanical performance of wood–adhesive interphase during freeze–thaw cycles

The mechanical performance of engineered wooden products facing the freeze–thaw cycles (FTCs) arises as an attention-worthy issue since the application of timber architectures in cold climates spreads. Here, we reported an investigation to reveal the losses of the mechanical performance of the wood-phenol formaldehyde (PF) adhesive interphase after the FTCs. Results revealed that PF adhesive was barely affected by the FTCs due to the low moisture content and rigid networks, whereas the mechanical properties of the cell wall in wood-PF interphase reduced significantly (more than 30%) after 5 FTCs at – 40 °C. Cracks were observed in the cell wall and compound middle lamella after FTCs. Further investigation into the crystal structure of the cell wall in the wood-PF interphase demonstrated that the FTCs disrupt the aggregations of cellulose macromolecules. The stresses caused by the phase transition of free water and the external hydrogen bonds formed between water and cellulose disrupted hydrogen bond networks in the cell wall. A plausible mechanism for the FTCs reducing the mechanical properties of the wood-PF bonds can be concluded as the cracks and weakened cell walls crippled the structural integrity of the wood-PF interphase, making it a fragile and stress-concentrated site when subjected to load.

Modification of Paper Surface by All-Lignin Coating Formulations.

All-lignin coating formulations were prepared while combining water-soluble cationic kraft lignin (quaternized LignoBoost®, CL) and anionic lignosulphonate (LS). The electrostatic attraction between positively charged CL and negatively charged LS led to the formation of insoluble self-organized macromolecule aggregates that align to films. The structures of the formed layers were evaluated by atomic force microscopy (AFM), firstly on glass lamina using dip-coating deposition and then on handsheets and industrial uncoated paper using roll-to-roll coating in a layer-by-layer mode. Coated samples were also characterized by optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (SEM/EDS), and contact angle measurements. It was suggested that the structure of all-lignin aggregates is the result of the interaction of amphiphilic water-soluble lignin molecules leading to their specifically ordered mutual arrangement depending on the order and the mode of their application on the surface. The all-lignin coating of cellulosic fiber imparts lower air permeability and lower free surface energy to paper, mainly due to a decrease in surface polarity, thus promoting the paper's hydrophobic properties. Moderate loading of lignin coating formulations (5-6 g m-2) did not affect the mechanical strength of the paper.

Polyelectrolyte coating of cryo-EM grids improves lateral distribution and prevents aggregation of macromolecules.

Cryo-electron microscopy (cryo-EM) is one of the primary methods used to determine the structures of macromolecules and their complexes. With the increased availability of cryo-electron microscopes, the preparation of high-quality samples has become a bottleneck in the cryo-EM structure-determination pipeline. Macromolecules can be damaged during the purification or preparation of vitrified samples for cryo-EM, making them prone to binding to the grid support, to aggregation or to the adoption of preferential orientations at the air-water interface. Here, it is shown that coating cryo-EM grids with a negatively charged polyelectrolyte, such as single-stranded DNA, before applying the sample reduces the aggregation of macromolecules and improves their distribution. The single-stranded DNA-coated grids enabled the determination of high-resolution structures from samples that aggregated on conventional grids. The polyelectrolyte coating reduces the diffusion of macromolecules and thus may limit the negative effects of the contact of macromolecules with the grid support and blotting paper, as well as of the shear forces on macromolecules during grid blotting. Coating grids with polyelectrolytes can readily be employed in any laboratory dealing with cryo-EM sample preparation, since it is fast, simple, inexpensive and does not require specialized equipment.

Defects and countermeasures in laboratory diagnosis of rare IgE multiple myeloma

BackgroundIgE multiple myeloma (MM) is a rare subtype of MM that is easily misdiagnosed. We report a rare case of IgE-MM and investigate the application of the SLiM-CRAB criteria to screen for high-risk smoldering MM (SMM) patients, so as to summarize the causes and methods used to prevent missed diagnosis or misdiagnosis in IgE-MM. MethodsThe serum monoclonal protein (M-protein) classification and IgE quantification was performed and sent to several individual institutions. The results were collected and the causes of IgE detection defects were analyzed. ResultsUpon admission to our hospital, the patient’s serum free kappa light chain was 1069.9 mg/L, free lambda light chain was 9.2 mg/L, and free kappa/lambda ratio was 115.9, which met the SLiM criteria, but without CRAB features. Immunofixation electrophoresis (IF) showed “M-like protein aggregation bands” in all lanes. After pretreatment with 1% β-mercaptoethanol to depolymerize the aggregation of monoclonal protein, the “M-like protein aggregation bands disappeared. The other five institutions did not provide the correct typing results. The quantification of serum IgE was as high as 2.06 × 107 IU/mL, whereas 7 other testing institutions reported IgE levels ranging from 1.0 to 1100 IU/mL. ConclusionHigh-risk biomarkers in SLiM criteria can achieve good therapeutic effects in rare IgE-MM patients. Serum immunofixation performed without antisera against IgE, insufficient identification of the lytic bands produced by high macromolecule aggregation in IF, and the absence of a prozone effect avoidance procedure during IgE quantitative detection are the primary causes of missed diagnosis or misdiagnosis in patients with IgE-MM.

A long-range order in a thermally driven system with temperature-dependent interactions.

Aggregation of macro-molecules under an external force is far from being understood. An important driving situation is achieved by temperature difference. Inter-particle interactions in metallic nanoparticles with ligand capping are reported to be sensitive to temperature and the zeta potential of the particles being reduced in the cold region. Such particles form aggregates in the cold region of the system in the presence of temperature difference. Here we study the aggregation of particles in the presence of temperature difference with temperature-dependent interaction parameters using Brownian dynamics simulation. The particle interaction and particle diffusion are considered to be sensitive to the local temperature. We identify a long-range structural order in the cold region of the system using the Avrami equation for crystal growth kinetics. Our observations might be useful in designing ordered structures with macro-molecules under non-equilibrium steady-state conditions.

Temperature Dependence of the Rayleigh Ratio for Toluene: Thermoresponsive Polymers Characterization

AbstractBenzene and toluene are commonly used reference substances for static light scattering (SLS) measurements. However, due to the appearance and wide availability of solid‐state lasers with various wavelengths, there is a need for data on the Rayleigh ratios for references at various wavelengths. Thermoresponsive polymers, which are widely researched now, can have lower critical solution temperature (LCST) values very close to the human body temperature (30–36 °C). Such polymers can be used to develop efficient means for targeted drug delivery. In this paper, we report how to accurately determine the absolute molecular weights of thermoresponsive polymers by the SLS method. This is especially important when the LCST value of a polymer is close to the room temperature (at which SLS measurements are usually taken), which can lead to overestimated results due to the aggregation of macromolecules. So, it is necessary to carefully select the measurement temperature and, accordingly, data are needed on the temperature dependence of the Rayleigh ratios for a reference sample. The Rayleigh ratios and depolarization factors, ρu and ρv, were first determined for toluene within a wide temperature range (10–50 °C). The temperature dependencies of these parameters were shown to be linear in the whole range investigated. Temperature coefficients for the calculation of the Rayleigh ratios at different scattering geometries were obtained. The particular importance of choosing the optimal measurement temperature when determining the molecular weights of thermoresponsive polymers with low values of LCST using the static light scattering method was demonstrated.

Impact of ethanol addition on the behaviour of xanthan gum in aqueous media

The effect of ethanol (EtOH) addition on the behaviour of xanthan gum (XG) chains in water (W) was investigated at 25 °C by using turbidimetry, zeta potential, refractometry and viscometry. The presence of EtOH (nonsolvent) in aqueous solution of XG reduces the thermodynamic quality of solvent and increases the polymer-polymer contacts (i.e., electrostatic, H-bonding or hydrophobic interactions). Thus, the transition from an expanded chain conformation to a more compact one was evidenced by viscometry, zeta potential masurements and refractometry while the aggregation of macromolecules or phase separation were observed by turbidimetry. A phase diagram for XG in solvent/nonsolvent mixtures was provided.For volumetric fractions of ethanol (ϕEtOH) higher than 0.3, zeta potential increases above −30 mV and the aggregation of xanthan chains takes place. Measurements of refractive indices were used to determine the preferential adsorption coefficient (λ1) for different volumetric fractions of ethanol. The parameter λ1 quantifies the polymer chain affinity for one component of the solvent/nonsolvent mixtures.The polyelectrolyte effect of XG chains in solution and the variable polarity as a function of W/EtOH composition influence the overall thermodynamic behaviour of XG assessed through the viscometric parameters determined by using the Wolf approach.

Morphology of chemically in situ precipitated films of polyaniline on the substrate of cellulose triacetate

Thin films of polyaniline were obtained by chemical oxidation of0,05 Maniline with ammonium peroxydisulfate on the substrate of cellulose triacetate in situ in an aqueous solution of0.5 Mcitric acid (CA).These films on flexible substrate of cellulose triacetate were characterized by UV/VIS, FTIR ATR spectroscopy as well as SEM and atomic force microscopy. With the assistance of scanning electron microscope (SEM) was found that the film of polyaniline on substrate of cellulose triacetate, formed predominantly of macromolecular aggregates of different sizes, which are mainly close in the shape to circle. Detailed analysis of 2D-images of atomic force microscope confirmed, that polyaniline aggregates are preferably in the shape to circle. However, analysis of 3D-images displayed that the aggregates obtained by polyaniline on the surface of cellulose triacetate have an irregular quasi cone-shaped appearance with smooth (polished) sides. Obviously, that the growth of these aggregates occurs from the surface into the solution and when the aniline is consumed, happens smoothing effect of surfaces of these formations. In the films of polyaniline were detected the large cone-shaped localized aggregates of macromolecules of polyaniline. The parameters of thin polyaniline films such as: roughness, root mean square, asymmetry, eccentricity, average maximum height of sample as well as average maximum height and depth of roughness were determined and calculated by atomic force microscopy. As we can see from comparison of the calculated results of determining the thickness of polyaniline film on the matrix substrate with different methods shows their good convergence. The established effective thickness by various methods of polyaniline film is 80 nm. Keywords : polyaniline, cellulose triacetate, films, structure, topology, morphology

Divide and Rule: Phase Separation in Eukaryotic Genome Functioning.

The functioning of a cell at various organizational levels is determined by the interactions between macromolecules that promote cellular organelle formation and orchestrate metabolic pathways via the control of enzymatic activities. Although highly specific and relatively stable protein-protein, protein-DNA, and protein-RNA interactions are traditionally suggested as the drivers for cellular function realization, recent advances in the discovery of weak multivalent interactions have uncovered the role of so-called macromolecule condensates. These structures, which are highly divergent in size, composition, function, and cellular localization are predominantly formed by liquid-liquid phase separation (LLPS): a physical-chemical process where an initially homogenous solution turns into two distinct phases, one of which contains the major portion of the dissolved macromolecules and the other one containing the solvent. In a living cell, LLPS drives the formation of membrane-less organelles such as the nucleolus, nuclear bodies, and viral replication factories and facilitates the assembly of complex macromolecule aggregates possessing regulatory, structural, and enzymatic functions. Here, we discuss the role of LLPS in the spatial organization of eukaryotic chromatin and regulation of gene expression in normal and pathological conditions.

Characterization of polyaniline thin films prepared on polyethylene terephthalate substrate

The polyaniline thin films were prepared by in situ chemical polymerization of aniline on polyethylene terephthalate substrate in the aqueous solutions of citric acid with ammonium peroxydisulfate as oxidant. Using ultraviolet–visible and Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron with energy-dispersive X-ray microscopy, atomic force microscopy, and four-point probe resistivity measurements, pure polyethylene terephthalate and polyaniline thin films were thoroughly characterized. Chemical analysis confirmed the formation of polyaniline with a high degree of oxidation in the form of a smooth thin film (with a thickness of ~ 80 ± 10 nm) on polyethylene terephthalate surface. However, delocalized polyaniline macromolecule aggregates in the spherical shape (with the diameter of ~ 30–40 nm) as well as in the irregular shape (the maximum size of ~ 300 nm) were found on the substrate. The values of average arithmetic roughness, average square roughness, asymmetry, kurtosis, average maximal profile height as well as average maximal height, and depth of roughness were calculated based on the atomic force microscopy data for pure polyethylene terephthalate and polyaniline thin films.

Эффекты микрофазового разделения и корреляции типа плотность-плотность в аморфных полимерных пленках

The topology of density fluctuations on the surface of amorphous films obtained from solutions of some flexible-chain polymers has been studied using electron microscopy data in the submicron and micron scale ranges. It is shown that as the initial concentration of solutions increases, the effects of microphase separation in films increase due to the self-organization of aggregates (clusters) of macromolecules: anisotropy, long-range order, and correlation length of density fluctuations increase. Self-organization ends with the formation of an infinite cluster of particles, periodically-inhomogeneous in density and occupying ~ 30% of the surface of the films. The density – density correlation function of such a cluster on the ~ ξ scale has a universal form that does not depend on the composition and molecular weight of the polymer.

An In-Vitro Cell Model of Intracellular Protein Aggregation Provides Insights into RPE Stress Associated with Retinopathy.

Impaired cargo trafficking and the aggregation of intracellular macromolecules are key features of neurodegeneration, and a hallmark of aged as well as diseased retinal pigment epithelial (RPE) cells in the eye. Here, photoreceptor outer segments (POS), which are internalized daily by RPE cells, were modified by UV-irradiation to create oxidatively modified POS (OxPOS). Oxidative modification was quantified by a protein carbonyl content assay. Human ARPE-19 cells were synchronously pulsed with POS or OxPOS to study whether oxidatively modified cargos can recapitulate features of RPE pathology associated with blinding diseases. Confocal immunofluorescence microscopy analysis showed that OxPOS was trafficked to LAMP1, LAMP2 lysosomes and to LC3b autophagy vacuoles. Whilst POS were eventually degraded, OxPOS cargos were sequestered in late compartments. Co-localization of OxPOS was also associated with swollen autolysosomes. Ultrastructural analysis revealed the presence of electron-dense OxPOS aggregates in RPE cells, which appeared to be largely resistant to degradation. Measurement of cellular autofluorescence, using parameters used to assess fundus autofluorescence (FAF) in age-related macular disease (AMD) patients, revealed that OxPOS contributed significantly to a key feature of aged and diseased RPE. This in vitro cell model therefore represents a versatile tool to study disease pathways linked with RPE damage and sight-loss.

Structure and stability analyses of collagen hydrolysate coacervates triggered by ethanol in aqueous solution

AbstractThe coacervation of collagen hydrolysate (CH) in aqueous solution was triggered by ethanol as poor solvent which has a significant effect on the aggregation and rearrangement of CH macromolecules. In this work, the static coacervation was performed to investigate the influences on coacervates morphology. CH concentration and ethanol temperature had significant influences on coacervates morphology. Treatment for the CH solution of high concentration by lower temperature ethanol (<25°C) tended to form the microspheres morphology. High temperature ethanol was not conducive to CH coacervation, while enhanced the CH solubilization in water‐ethanol. By directly mixing CH solution and ethanol under agitation, dispersed nanospheres could be successfully obtained in suspension. The turbidity and absorbance tests were carried out to further study the CH coacervation behaviors. The stability of milky suspension induced by ethanol was evaluated by a self‐built light transmittance measurement. The result showed that the absorbance and turbidity of CH suspension increased with increasing the VEtOH ratio and CH concentration. The milky suspension with high VEtOH would turn clear gradually due to the CH solubilization in water–alcohol. The maximum absorbance presented at pH around 7 where the charges of CH molecules were negative. The coacervation behaviors of CH were very different from that of collagen and gelatin, owing to its lower molecular weight.

Self-assembly in amphiphilic spherical brushes.

The structure of amphiphilic spherical brushes, consisting of the nano-SiO2 core, the hyperbranched polyamidoamine subshell, and a grafted layer of long hydrophobically modified polyacrylamide (HMPAM) chains, in aqueous solution was analyzed and described in the framework of the original mean-field approach. The scaling estimations of the hydrodynamic radius of such polymer brushes as a function of the number of grafted macromolecules allow concluding that the HMPAM shells are in a globular state and that the region of the stretched chains adjacent to the grafting surface is a minor part of the grafted macromolecules and does not have a significant impact on the self-assembly of the HMPAM shell caused by the complex hydrophobic-hydrophilic composition of their monomer units. In mean-field theory, the amphiphilic nature of HMPAM was taken into account by attaching the hydrophobic side group H to some fraction of monomer units of the hydrophilic P backbone. The strong attraction of H groups causes the aggregation of macromolecules, whereas the affinity of hydrophilic P groups to solvent forces the aggregates to increase their surface. Due to such effective surface activity, in poor solvent, the grafted amphiphilic macromolecules could form a spherical compacted structure around the nanoparticle or self-assemble into a "hedgehog" structure with several "spines" having hydrophobic core and hydrophilic shell. State diagrams, obtained theoretically, reveal that the "hedgehog" structure is preferable for a wide range of energetic parameters.

Shaking-Induced Aggregation and Flotation in Immunoglobulin Dispersions: Differences between Water and Water-Ethanol Mixtures.

Structural characterization by three complementary methods of laser diagnostics (dynamic light scattering, laser phase microscopy, and laser polarimetric scatterometry) has established that shaking of immunoglobulin G (IgG) dispersions in water and ethanol–water mixtures (36.7 vol %) results in two effects. First, it intensifies the aggregation of IgG macromolecules. Second, it generates bubbles with a size range that is different in each solvent. The aggregation is enhanced in ethanol–water mixtures because of IgG denaturation. IgG aggregates have a size of ∼300 nm in water and ∼900 nm in ethanol–water mixtures. The flotation of IgG is much more efficient in water. This can be explained by a better adsorption of IgG particles (molecules and aggregates) on bubbles in water as compared to ethanol–water mixtures. Bulk nanobubbles and their association with IgG aggregates were visualized by laser phase microscopy in water but were not detected in ethanol–water mixtures. Therefore, the nanobubble flotation mechanism for IgG aggregates acting in water is not feasible for ethanol–water mixtures.