Aggregation Of Macromolecules Research Articles

А new factor effecting gel strength of pectin polysaccharides

Pectin polysaccharides obtained from various raw materials have a different component composition and form gels with water, sugar and acid or calcium. In this study, an experimental approach the gelation properties of different pectin samples, varied from different sources, using new methods of hydrolysis and purification. Samples were obtained by hydrolysis of accelerated extraction of pectin and purified by diaultrfiltration, have a high gel strength. The highest gel strength have been found in series of high methoxyl (HM-) pectin samples of apple, peach, orange and low methoxyl (LM-) pectin samples of commercial citrus pectin and apple pectin obtained by new method. It is shown that in addition to the basic parameters (the content of galacturonic acid, degree of esterification, molecular weight and hidrodinamic radius macromolecule) to affect gel strength pectins aggregation of macromolecules, which is determined by the z-average molecular weight. There were observed a clear pattern of the influence of the molecular weight on hydrodynamic parameters for both HM- and LM- pectin samples on the gel strength. It were shown that a high values of molecular weight, intrinsic viscosity, and radius of gyration of pectin samples can significantly increase gel strength, while the value of Mz oppositely influenced the gel strength. As a result, a systematic analysis of this parameter and its relationship to the average molecular weight found that indeed the ratio Mz/Mw for pectin’s is an crucial to assess the quality of pectin at the study of gel strength for pectin polysaccharides.

Promoting action of demethoxyviridin on Aβ42 oligomers to form insoluble macromolecule aggregates

Promoting action of demethoxyviridin on Aβ42 oligomers to form insoluble macromolecule aggregates

The structure and function of 'active zone material' at synapses.

The docking of synaptic vesicles on the presynaptic membrane and their priming for fusion with it to mediate synaptic transmission of nerve impulses typically occur at structurally specialized regions on the membrane called active zones. Stable components of active zones include aggregates of macromolecules, 'active zone material' (AZM), attached to the presynaptic membrane, and aggregates of Ca(2+)-channels in the membrane, through which Ca(2+) enters the cytosol to trigger impulse-evoked vesicle fusion with the presynaptic membrane by interacting with Ca(2+)-sensors on the vesicles. This laboratory has used electron tomography to study, at macromolecular spatial resolution, the structure and function of AZM at the simply arranged active zones of axon terminals at frog neuromuscular junctions. The results support the conclusion that AZM directs the docking and priming of synaptic vesicles and essential positioning of Ca(2+)-channels relative to the vesicles' Ca(2+)-sensors. Here we review the findings and comment on their applicability to understanding mechanisms of docking, priming and Ca(2+)-triggering at other synapses, where the arrangement of active zone components differs.

ChemInform Abstract: Direct Measurements of Particle—Surface Interactions in Aqueous Solutions with Total Internal Reflection Microscopy

AbstractReview: 89 refs.

Study of Self-Diffusion of Silicone MQ Resins in Chloroform Solutions by Pulsed Field-Gradient NMR Spectroscopy

The self-diffusion of silicone MQ copolymers in solutions with chloroform was studied by pulsed field-gradient nuclear magnetic resonance over a wide range of macromolecular concentrations. The highly branched structure of the molecules reveals some characteristic features of the translational mobility. The studies were performed with the initial MQ copolymer as well as with the narrow-dispersed fractions obtained from it. The data indicate the differences in dynamics between fractions. The appearance of the species with different self-diffusivity with increasing of the polymer concentration in solutions was observed. Such behavior was attributed to the formation of aggregates of macromolecules in solution. The results show that the molecular weight influences the diffusion behavior of the MQ resins in solutions. The diffusion of the MQ resins reveals features characteristic for rigid macromolecular structures rather than flexible polymers. Differences in translational dynamics of MQ copolymers, linear flexible polymers and particle-like macromolecules are discussed.

Effects of temperature and concentration on mechanism and kinetics of thermally induced deposition from coffee extracts

AbstractProduction of soluble (instant) coffee powders typically involves extraction of roasted coffee by water followed by evaporation in order to concentrate extracts before spray or freeze drying to produce dry coffee powder. In the course of evaporation, deposition of dissolved material from coffee extracts is a major cause of fouling at the heat exchange surfaces of evaporators. Therefore, in order to improve the design and optimization of evaporation processes of coffee extracts, better understanding of the deposition mechanism and kinetics is needed. In this study, optical waveguide lightmode spectroscopy (OWLS) was used to monitor the initial formation of nanometer scale deposits on surfaces exposed to coffee extracts. OWLS measurements were complemented by light scattering from extract solutions, gravimetry of macroscopic deposits, and scanning electron microscopy imaging of deposited layers. Primary molecular-scale layers of about 1 mg m−2 were rapidly formed in the first stage of deposition, even at ambient temperature, followed by the secondary deposition with kinetics strongly dependent on temperature. Secondary deposition rates were low and largely independent of the extract concentration at ambient temperature, but became strongly dependent on the extract concentration at elevated temperatures. In particular, activation energies for the deposition between 25°C and 70°C were much higher for the original extract (13.3 mass %, solids) than for diluted extracts (up to 1.3 mass %, solids). Furthermore, heating of the original extracts above 60°C resulted in rapid aggregation of suspended macromolecules into large clusters, while only gradual aggregation was observed in diluted extracts.

Dynamic surface properties of sodium N-acryloyl-11-amimoundecanoate and poly(sodium N-acryloyl-11-aminoundecanoate)

Adsorption layers of sodium N-acryloyl-11-amimoundecanoate and poly(sodium N-acryloyl-11-aminoundecanoate) (PAAU-Na) are studied using surface dilatational rheology measurements. It is established that the dynamic surface elasticity values of the studied systems are different, while their surface tension isotherms are almost the same. PAAU-Na solutions containing excess indifferent electrolyte (NaCl) exhibit a conformational transition in a surface layer due to the formation of loops and tails, which penetrate the bulk phase. Slow variations in the surface properties of PAAU-Na solutions with time seem to be caused by the aggregation of macromolecules in the bulk phase. The aggregation process is investigated by scanning probe microscopy.

Distribution of Counterions around Lignosulfonate Macromolecules in Different Polar Solvent Mixtures

Lignosulfonate is a colloidal polyelectrolyte that is obtained as a side product in sulfite pulping. In this work we wanted to study the noncovalent association of the colloids in different solvents, as well as to find out how the charged sulfonate groups are organized on the colloid surface. We studied sodium and rubidium lignosulfonate in water-methanol mixtures and in dimethyl formamide. The number average molecular weights of the Na- and Rb-lignosulfonate fractions were 7600 g/mol and 9100 g/mol, respectively, and the polydispersity index for both was 2. Anomalous small-angle X-ray scattering (ASAXS) was used for determining the distribution of counterions around the Rb-lignosulfonate macromolecules. The scattering curves were fitted with a model constructed from ellipsoids of revolution of different sizes. Counterions were taken into account by deriving an approximative formula for the scattering intensity of the Poisson-Boltzmann diffuse double layer model. The interaction term between the spheroidal particles was estimated using the local monodisperse approximation and the improved Hayter-Penfold structure factor given by the rescaled mean spherical approximation. Effective charge of the polyelectrolyte and the local dielectric constant of the solvent close to the globular polyelectrolyte were followed as a function of the methanol content in the solvent and lignosulfonate concentration. The lignosulfonate macromolecules were found to aggregate noncovalently in water-methanol mixtures with increasing methanol or lignosulfonate content in a specific directional manner. The flat macromolecule aggregates had a nearly constant thickness of 1-1.4 nm, while their diameter grew when counterion association onto the polyelectrolyte increased. These results indicate that the charged groups in lignosulfonate are mostly at the flat surfaces of the colloid, allowing the associated lignosulfonate complexes to grow further at the edges of the complex.

食酢における高分子凝集物の発生予測方法

食酢製造企業にとって, 夏場に長期間, 無色透明ビンに入った食酢製品の透明度を維持することは重要であるため, 小売店で陳列されるまでに凝集物の発生をより正確に速やかに予測する必要がある。これまでの伝統的な手法は, 高温で高分子凝集を促進させることを意図した60°Cでの加速試験であり, 凝集物の発生を肉眼で観察するものだが, 1～2日以内での判定は難しかった。そこで, 加速試験で60°Cよりも高温化する手法, 加熱による各分子量領域の高分子濃度の変化を解析する手法, 色素結合性高分子の濃度を解析する手法を試みたが, 信頼性は不十分であった。一方, 膜濃縮後の濁度を測定する手法では, かなり好ましい結果が得られた。すなわち, 各食酢製品や凝集物を発生しやすくする物質を添加した食酢などを用いて調べた結果, 食酢原料の種類や製法にかかわらず, 37°Cでの凝集物発生速度は, 食酢の膜濃縮液の濁度によって比較的高い確率で予測できることがわかった。食酢の60°C加速試験の問題点も最後に指摘した。

Ammonia gas-sensing characteristics of fluorescence-based poly(2-(acetoacetoxy)ethyl methacrylate) thin films

Novel fluorescent poly(2-(acetoacetoxy)ethyl methacrylate)(PAAEMA) latexes have been synthesized by miniemulsion polymerization employing a polymeric costabilizer. Nanoscale aggregates of macromolecules bearing β-dicarbonyl are formed in the prepared latex particles. Ammonia and the β-dicarbonyl aggregates assemble a supramolecular complex, which exhibits strong visible fluorescence under UV light. The formation of the complex is confirmed by the characteristic absorption peak located at about 275nm in UV–Vis spectra. The absorption spectrum has been found to be applicable for ammonia detection. Atomic Force Microscopy (AFM) studies of surface morphology reveal that gas-sensing properties of the PAAEMA thin films involve the reversible absorption and desorption of ammonia. PAAEMA thin films are sensitive to ammonia gas and have a short response time of 80s when exposed to 54ppm of ammonia gas concentration.

Data handling for interactive metabolomics: tools for studying the dynamics of metabolome-macromolecule interactions

All published metabolomics studies investigate changes in either absolute or relative quantities of metabolites. However, blood plasma, one of the most commonly studied biofluids for metabolomics applications, is a complex, heterogeneous mixture of lipoproteins, proteins, small organic molecules and ions which together undergo a variety of possible molecular interactions including metal complexation, chemical exchange processes, micellular compartmentation of metabolites, enzyme-mediated biotransformations and small-molecule-macromolecule binding. In particular, many low molecular weight (MW) compounds (including drugs) can exist both ‘free’ in solution and bound to proteins or within organised aggregates of macromolecules. To study the effects of e.g. disease on these interactions we suggest that new approaches are needed. We have developed a technique termed ‘interactive metabolomics’ or i-metabolomics. i-metabolomics can be defined as: “The study of interactions between low MW biochemicals and macromolecules in heterogeneous biosamples such as blood plasma, without pre-selection of the components of interest”. Standard 1D NMR experiments commonly used in metabolomics allow metabolite concentration differences between samples to be investigated because the intensity of each peak depends on the concentration of the compound in question. On the other hand, the instrument can be set-up to measure molecular interactions by monitoring the diffusion coefficients of molecules. According to the Stokes–Einstein equation, the diffusion coefficient of a molecule is inversely proportional to its effective size, as represented by the hydrodynamic radius. Therefore, when low MW compounds are non-covalently bound to proteins, the observed diffusion coefficient for the compound will be intermediate between those of its free and bound forms. By measuring diffusion by NMR, the degree of protein binding can be estimated for either low MW endogenous biochemicals or xenobiotics. This type of experiment is referred to as either Diffusion-Ordered Spectroscopy (DOSY) or Diffusion-Edited Spectroscopy, depending on the type of post-acquisition data processing applied to the spectra. Results presented in this paper demonstrate approaches for the non-selective modelling of metabolite-macromolecule interactions (i-metabolomics), whilst additionally highlighting some of the all too frequently ignored issues associated with interpretation of data derived from profiling of blood plasma.

A reaction–diffusion model to predict the influence of neo-matrix on the subsequent development of tissue-engineered cartilage

Extracellular matrix (ECM) in chondrocytes-seeded agarose aggregates to form islands of matrix. These islands need to coalesce to develop functional cartilage. Hence, macroscopic properties are determined by transport and aggregation of macromolecules at the microscale, which varies temporally and spatially. This study evaluates the importance of the mutual interaction between matrix components and matrix development. Fluorescence recovery after photobleaching measurements demonstrates that diffusivity depends on the presence and density of ECM. A reaction–diffusion model describing synthesis, transport and immobilisation of ECM predicts steep gradients in ECM around chondrocytes, resembling histology. Steric hindrance of diffusion by ECM is essential for the formation of these gradients. Finally, microscopic ECM concentration is linked with macroscopic mechanical properties. Construct softening is predicted when temporal and spatial variations in diffusivity are considered. In conclusion, non-constant diffusion renders significant effects on both the microscopic ECM development and the macroscopic mechanical properties of developing tissue-engineered cartilage.

Self-assembly of an amphiphilic diblock copolymer in aqueous solutions: Effect of linear charge density of an ionogenic block

The effect of linear charge density of the ionogenic block on the selfassembly of the amphiphilic diblock copolymer based on polystyrene and poly(4�vin ylpyridine) partially alkylated by ethyl bromide in aqueous solutions at pH 9 is studied by UV spectrophotometry and dynamic and static light scattering. Dur� ing dispersion in water, the diblock copolymer forms micelles composed of the hydrophobic polystyrene core and the amphiphilic lyophilizing corona consisting of Nethyl�4�vinylpyridinium bromide ionic units and uncharged units of 4�vinylpyridine. It is shown that with a change in the fraction of charged units in the lyo� philizing block from 30 to 90 mol %, the thermodynamic quality of the solvent with respect to micelles is slightly monotonically improved and the hydrodynamic sizes of micelles in 0.05 M NaCl are increased. At the same time, such properties as the weightaverage deg ree of aggregation of macromolecules in a micelle, the dimensions of the corona in 0.05 M NaCl, and the dispersion stability of micelles in aqueous-saline solution abruptly change when the content of charged units in the lyophilizing block is 60-70 mol %. After addition of oppositely charged polyelectrolytes or lowmolecu larmass surfactants into the micellar solution, poly� electrolyte complexes form and the solubility of these complexes in an excess oppositely charged component likewise changes abruptly with variation in the fraction of charged units in the range from 60 to 70 mol %. A qualitative description is advanced to explain the effect of linear charged density of the lyophilizing block on the selfassembly and complexing behavior of diblock copolymers in aqueous solutions.

Connections of Synaptic Vesicles to Active Zone Material Before and after Docking on the Presynaptic

The active zones of axon terminals, which are where the initial events in synaptic transmission occur, are characterized in part by dense aggregates of macromolecules, called active zone material (AZM), attached to the cytoplasmic surface of the presynaptic plasma membrane and by synaptic vesicles docked on the presynaptic membrane, which contain neurotransmitter and fuse with the presynaptic membrane to release their neurotransmitter during synaptic transmission. Previous electron tomography (ET) studies on the 15nm of AZM next to the presynaptic membrane of axon terminals at resting frog and mouse neuromuscular junctions (NMJs) showed that it is composed of an organized network of elongate macromolecules that fall into several classes, one of which, ribs, connects to each docked vesicle.We used ET to study in axon terminals at resting frog NMJs the remaining 45nm of the AZM network deep to the presynaptic membrane. Like that in the initial 15nm, it is a highly organized network containing several classes of elongate macromolecules. Some of these, spars and booms, also connect to docked vesicles. Thus, each docked vesicle is connected to 3-4 ribs, 2-3 spars and 4-8 booms. For NMJs that had been fixed during electrical stimulation, we found that at those active zones where the docked vesicles had fused with and flattened into the presynaptic membrane, the vesicles moving from the reserve pool to replace them at the docking sites on the presynaptic membrane are connected to the ribs, spars and booms when 20-30 nm from the membrane. Altogether the findings support the hypothesis (Harlow et al., Nature 409: 479-484, 2001; Nagwaney et al., J. Comp. Neurol. 513: 457-468, 2009) that AZM helps regulate the docking of synaptic vesicles on the presynaptic membrane.

Physical Changes in Macromolecules of Active Zone Material that Regulate the Docking and Fusion of Synaptic Vesicles on the Presynaptic Membrane

The active zones of axon terminals are where the initial events in synaptic transmission occur. They are characterized by dense aggregates of macromolecules attached to the cytoplasmic surface of the presynaptic plasma membrane, called active zone material (AZM); synaptic vesicles docked on the presynaptic membrane, which contain neurotransmitter; and aggregates of cation channels in the presynaptic membrane that help regulate the fusion of the docked vesicles with the membrane leading to the exocytosis of their neurotransmitter during synaptic transmission.

Mechanistic insight of the photodynamic inactivation of Escherichia coli by a tetracationic zinc(II) phthalocyanine derivative

Photodynamic inactivation (PDI) of Escherichia coli has been studied in cultures treated with zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc(+4)) to obtain insight about the mechanism of damage. This phthalocyanine is rapidly bound to cells, reaching a value of approximately 0.8 nmol/10(6) cells when the cultures were incubated with 2 microM sensitizer. After 30 min of irradiation, a 4 log decrease of E. coli survival was observed. The photocytotoxic action was investigated in plasmid and genomic DNA by electrophoretic analysis. Absorption spectroscopic studies showed that this cationic phthalocyanine interacts strongly with DNA (K(DNA)=4.7 x 10(6)M(-1)). Photocleavage of calf thymus DNA sensitized by ZnPPc(+)4 was not found even after long irradiation periods. Similar results were also observed in genomic DNA extracted from E. coli cells after PDI treatment. Modifications of plasmid DNA isolated from bacteria were only observed after long irradiation periods. However, under these conditions transmission electron microscopy of the PDI bacteria revealed an aggregation of cytoplasmic macromolecules and irregularities in cell barriers. Also, scanning electron microscopy showed a shrunken appearance in cells after PDI. Even so, release of intracellular biopolymers was not detected by absorption. On the other hand, outer and inner membranes permeabilization assays showed an increase in the permeability. Consequently, alterations in the cell membrane functionality induced by ZnPPc(+4) appear to be the major cause of E. coli inactivation upon PDI.

The influence of the solveny medium on the aggregation of asphaltene macromolecules and determination of their molar mass

The formation of aggregates of a fraction of asphaltenes extracted from Brazilian crude oil was investigated by measuring the interfacial tension and kinematic viscosity of their solutions prepared in different solvents. The interfacial tension results indicate the existence of critical micelle concentration (CMC) levels of the asphaltenes in solvents with solubility parameters sufficiently different from those of the asphaltene tested. The kinematic viscosity measures revealed the formation of aggregates at concentrations above the CMC. The interfacial tension measures of asphaltenes in organic solutions, although infrequently mentioned in the literature, were used to calculate the molar mass, permitting the comparison of various molar masses attributed to the asphaltenes in the form of aggregates.

Size Distribution of Linear and Helical Polymers in Actin Solution Analyzed by Photon Counting Histogram

Actin is a ubiquitous protein that is a major component of the cytoskeleton, playing an important role in muscle contraction and cell motility. At steady state, actin monomers and filaments (F-actin) coexist, and actin subunits continuously attach and detach at the filament ends. However, the size distribution of actin oligomers in F-actin solution has never been clarified. In this study, we investigated the size distribution of actin oligomers using photon-counting histograms. For this purpose, actin was labeled with a fluorescent dye, and the emitted photons were detected by confocal optics (the detection volume was of femtoliter (fL) order). Photon-counting histograms were analyzed to obtain the number distribution of actin oligomers in the detection area from their brightness, assuming that the brightness of an oligomer was proportional to the number of protomers. We found that the major populations at physiological ionic strength were 1–5mers. For data analysis, we successfully applied the theory of linear and helical aggregations of macromolecules. The model postulates three states of actin, i.e., monomers, linear polymers, and helical polymers. Here we obtained three parameters: the equilibrium constants for polymerization of linear polymers, K l = (5.2 ± 1.1) × 10 6 M −1, and helical polymers, K h = (1.6 ± 0.5) × 10 7 M −1; and the ratio of helical to linear trimers, γ = (3.6 ± 2.3) × 10 −2. The excess free energy of transforming a linear trimer to a helical trimer, which is assumed to be a nucleus for helical polymers, was calculated to be 2.0 kcal/mol. These analyses demonstrate that the oligomeric phase at steady state is predominantly composed of linear 1–5mers, and the transition from linear to helical polymers occurs on the level of 5–7mers.

Comparison of curdlan and its carboxymethylated derivative by means of Rheology, DSC, and AFM

Curdlan was carboxymethylated in an aqueous alkaline medium using monochloroacetic acid as the etherifying agent. The structure of carboxymethylated curdlan (CMc) was analyzed by FT-IR and NMR spectroscopy, which revealed that the carboxymethyl group was introduced mainly at the C-6 position as well as at the C-2 and C-4 positions. Furthermore, CMc was compared with the native curdlan by using rheology and DSC methods. It was found that in water, both polysaccharides behaved as pseudoplastic fluids and fit the power law and Herschel–Bulkley rheological models well. Both the storage shear modulus G′ and the loss shear modulus G″ of CMc aqueous solutions decreased and became more frequency dependent with decreasing concentration in comparison with the curdlan aqueous suspensions. The modulus–temperature curve also suggested that the gel characteristic of curdlan has been lost after chemical modification, which is consistent with the DSC results. AFM images revealed differences in the conformation of native and carboxymethylated curdlan, which changed from the aggregation of macromolecules to triple helices. All the experimental results suggest that the hydrogen bonds that bind curdlan with interstitial water to form the micelles have been destroyed completely and that the hydrophobic interactions related to the methylene groups at C-6 formed above 55 °C disappeared due to the introduction of the hydrophilic carboxymethyl group.

Rheological properties of starch and kaolin mixtures in water during and after heating

Gelatinization characteristics of the starch and kaolin mixtures were investigated with the Brabender viscograph at starch concentration of 40 g/l and different kaolin concentrations from 0 to 60 g/l. The properties of starch gelatinization were affected by the addition of kaolin. Above a kaolin concentration of 12 g/l had, an additional viscosity peak was seen at 73 °C. Further increase of kaolin concentration up to 60g/l led to an increase is the additional peak at 73 °C, while the value of maximum viscosity peak decreased. The rheological features of gelatinized starch and kaolin mixtures were also investigated. Dependence of shear stress on shear rate was obtained with the use of Haake RS 100 rheometer with Z 38 AL sensor. Shear rate was first increased from zero to 200 s −1 and then decreased from 200 s −1 to zero within 400 s period. Those measurements were obtained at the 20, 40, 60 and 70 °C for the mixtures containing 10 or 20 g/l of starch and for kaolin concentrations ranging from 0 to 15 g/l. The results showed the independence between final viscosity and kaolin concentration in the mixtures. Viscosity was affected only by the temperature of the measurment and the starch concentration (10 or 20 g/l). A mathematical model for the rheological behavior of gelatinized starch, was developed which contains the number and volume of macromolecule aggregates as well as the number of bonds between aggregates. According to this model, the bonds energy between the aggregates reached the value of 2–8 kJ/mol, which seemed to be close to the Van der Waals bonds energy.