Aggregate Radius Research Articles

Comparative Analysis of the Effects of α-Crystallin and GroEL on the Kinetics of Thermal Aggregation of Rabbit Muscle Glyceraldehyde-3-Phosphate Dehydrogenase

Effects of alpha-crystallin and GroEL on the kinetics of thermal aggregation of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been studied using dynamic light scattering and analytical ultracentrifugation. The analysis of the initial parts of the dependences of the hydrodynamic radius of protein aggregates on time shows that in the presence of alpha-crystallin or GroEL the kinetic regime of GAPDH aggregation is changed from the regime of diffusion-limited cluster-cluster aggregation to the regime of reaction-limited cluster-cluster aggregation, wherein the sticking probability for the colliding particles becomes lower the unity. In contrast to alpha-crystallin, GroEL does not interfere with formation of the start aggregates which include denatured GAPDH molecules. On the basis of the analytical ultracentrifugation data the conclusion has been made that the products of dissociation of GAPDH and alpha-crystallin or GroEL play an important role in the interactions of GAPDH and chaperones at elevated temperatures.

Magnetooptical studies of aggregates of nanoparticles in colloidal solutions of magnetite

The birefringence in a colloidal solution of nanosized magnetite particles in kerosene exposed to constant, alternating, and pulsed magnetic fields is studied. Data on the birefringence kinetics in nonstationary magnetic fields is used to determine the hydrodynamic radius of particle aggregates in solutions. The permanent dipole moment of aggregates and the anisotropy of the magnetic susceptibility are calculated based on the data of magnetooptical experiments. It is shown that the induced dipole moment plays a significant role in an orientation of aggregates of magnetic nanoparticles under the effect of a field.

Micelle Formation of Amphiphilic Polystyrene-b-poly(N-vinylpyrrolidone) Diblock Copolymer in Methanol and Water−Methanol Binary Mixtures

The micelle formation by the amphiphilic polystyrene-block-poly(N-vinylpyrrolidone) (PS48-b-PNVP99) copolymer is investigated in methanol and water-methanol binary mixtures of various compositions using 1H NMR, fluorescence spectroscopy, static/dynamic light scattering (SLS/DLS), and transmission electron microscopy (TEM). Critical micelle concentrations (cmc) are determined by employing fluorescence spectroscopy and DLS measurements. The cmc of the PS48-b-PNVP99 block copolymer increases with increasing methanol content in the water-methanol binary mixtures, suggesting that methanol is a better solvent for the PS48-b-PNVP99 block copolymer than water-methanol mixtures or pure water. The amphiphilic PS48-b-PNVP99 diblock copolymer forms spherical micelles of Rh approximately 16 nm in pure methanol solution as revealed by DLS measurements. In contrast, significantly larger micelles having higher aggregation numbers are formed in water-methanol binary mixtures. Temperature dependent data reveal an increase in aggregation number and radius of gyration (Rg) concomitantly with temperature (10-40 degrees C). In contrast, the overall size (Rh) of the micelles remains almost constant over the same temperature range. An explanation is tendered that PNVP coronas dehydrate/desolvate at higher temperatures counteracting the increase in micelle size (Rh) caused by increased aggregation numbers (Nagg).

Microstructural characterization of lysophosphatidylcholine micellar aggregates: The structural basis for their use as biomembrane mimics

Lysophosphatidylcholines are widely used as biomembrane mimics. In order to furnish a structural basis for this application, in this work the self-aggregation behaviour of n-acyl-lysophosphatidylcholines (C n lysoPC, n = 6,8,10,12), in aqueous solution has been investigated by the PGSTE-NMR and spin probing EPR techniques at 25 °C. The experimental data show that C n lysoPCs behave as zwitterionic surfactants, and permit evaluation of the influence of the acyl chain length on the phospholipid micellization. For all the C n lysoPCs considered, the phospholipid intradiffusion coefficient trend shows a slope change corresponding to the critical micelle concentration (CMC). In the micellar composition range, solubilized tetramethylsilane (TMS) molecules were used to determine the micelle intradiffusion coefficient, from which the aggregate radii and the aggregation numbers were obtained. The solvent intradiffusion coefficient in the C n lysoPC aqueous mixtures has been also measured. The results show that the C n lysoPC micelles present a thick external layer constituted by strongly hydrated glycerophosphocholine groups. The ability of this layer to embed either anionic or cationic guest molecules has been studied by EPR spectroscopy, employing 3-carboxy-PROXYL in its deprotonated form (CP −) or TEMPO-choline (TC) as spin probes. In all the considered systems, the nitrogen isotropic hyperfine coupling constant of the spin probe, A N, decreases and the correlation time, τ C, increases with increasing phospholipid molality. The results show that C n lysoPC micelles can establish a variety of interaction with different guests. In fact, CP − anions interact with the C n lysoPC choline groups adsorbing on the micelle surface, while TC cations interacting with the C n lysoPC phosphate groups are embedded in thick external layer of the micelles.

An ellipsometry study of silica nanoparticle layers at the water surface

We have studied silica nanoparticle layers spread at the air/water interface. The surface pressure of the layers has been determined in a Langmuir trough via two orthogonal Wilhelmy plates. We observed significant differences in surface pressure according to the preparation protocol: layers spread then compressed or layers obtained after successive spreading steps. We also studied the two types of layers by multiple angle of incidence ellipsometry. We introduce a two-layer model which enables us to evaluate the radius of interfacial aggregates and their contact angle with the air/water interface.

The P21/m- C2/m phase transition in synthetic amphiboles in the system Li2ONa2OMgOSiO2H2O: a high-T FTIR study

The P 2 1 / m ↔ C 2/ m phase-transition has been studied by high- T FTIR analysis on a series of synthetic amphiboles in the Li 2 O–Na 2 O–MgO–SiO 2 –H 2 O (LNMSH) system. Spectra were collected in the T range 25–450 °C on KBr disks. All examined amphiboles have P 2 1 / m symmetry at room T . Their OH-stretching FTIR spectrum consists of two main bands at ~3740 and 3715 cm −1 . At the transition temperature ( T c ), these bands merge into one single absorption centred at ~3720 cm −1 , and no further change is observed beyond this T . Significant modifications consisting in peak shifting and band broadening are also observed in the MIR (medium infrared) 1300–640 cm −1 region. T c values for the different compositions were estimated based on various methods; the most reliable procedure is considered to be the fit of Landau 2-4-6 potentials using band shifts observed in the MIR region. The T c values obtained for all samples are consistent with previous results obtained on two members of the series examined here by single-crystal or synchrotron powder H T -XRD (high- T X-ray diffraction). They correlate linearly with the aggregate cation radius at M (4) [ T c (°C) = 803–533 〈 r M (4) 〉; R 2 = 0.97]. This work thus provides a measure of the role played by the size of the M (4) polyhedron in determining the T c in simple chemical systems where the B-site occupancy (and geometry) is the only variable. The slope of the equation is far less steep in the LNMSH system than in cummingtonite; crystal-chemical reasons for this behaviour are discussed, and the local order between A and monovalent B cations is suggested to be the major constraint. In more complex systems, inspection of the available data shows that other factors such as the aggregate size of the strip of octahedra must be taken into account.

Effects of Caseins on Thermal Stability of Bovine β-Lactoglobulin

Casein fractions have been shown to act as molecular chaperones and inhibit aggregation of whey proteins in dilute solutions (< or =1% w/v). We evaluated if this approach would stabilize protein solutions at higher concentration and thermal processing temperatures desired for beverage applications. Mixtures of beta-lactoglobulin (BLG) (6% w/v) with either beta-casein (BCN) (0.01-2% w/v) or alpha s-casein (ACN) (2% w/v) were adjusted to pH 6.0 and heated (70-90 degrees C) for 20 min, cooled, and then analyzed to determine the degree of aggregation. Aggregation was determined by solution turbidity as optical density (OD) at 400 or 600 nm. The addition of 0.05% (w/v) BCN or greater caused a drop in turbidity for solutions heated at 70-90 degrees C. In contrast, inhibition was observed in BLG-ACN mixtures at 70 degrees C but not at > or =75 degrees C. Moreover, prolonged heating (90 min) of BLG with 2% (w/v) BCN (pH 6.0) at 90 degrees C produced a clear solution while BLG-ACN solutions formed translucent gels after heating for 15 min. The weight-averaged molar mass and root-mean-square (rms) radius of soluble aggregates were determined by size exclusion chromatography in conjunction with multiangle laser light scattering (SEC-MALS). SEC-MALS confirmed the turbidity results by showing that the BLG-BCN mixture (8% w/v protein) produced aggregates with lower molar mass and smaller rms radius (majority 20-40 nm). These results showed that BCN is a feasible component to stabilize higher concentrations of whey proteins in beverages.

On the solution self-assembly of nanocolloidal brushes: insights from simulations

The synthesis of novel nanoparticles with exceptional properties continues to stimulate thesearch for advanced applications in fields as diverse as solar energy harvesting and polymerreinforcement. It is widely recognized that to practically exploit the promised benefits it isnecessary to guide the assembly of the various nanoparticles into well-definedsupra-molecular structures. Towards this goal, we report Monte Carlo simulation results forthe self-assembly of spherical nanoparticles in implicit solvent. The nanoparticles interactsolely via dispersive interactions, modeled as square-well potentials. To control themorphology of the self-assembled aggregates, side chains are grafted on specificlocations on the nanoparticle surface (i.e., on the equator, on the tropics, on theentire tropical region, or uniformly on the nanoparticle surface). The results arediscussed in terms of average cluster size, probability of observing aggregates ofgiven size, and aggregate radius of gyration and asphericity as a function of theaggregate size. The parameters of interest are the solution conditions and thenanoparticle volume fraction (always in the dilute regime). As shown in previous reports(e.g., Striolo 2007 Small 3 628), the nanoparticles form insoluble agglomeratesin the absence of the side chains. When the side chains are long and uniformlydistributed on the nanoparticles, these remain individually dispersed in solution.More importantly, when the side chains are grafted on selected locations on thenanoparticles, these self-assemble, yielding structures composed of up to 7–10nanoparticles. The number of grafted side chains is the parameter that predominantlydetermines the average aggregate size, while the aggregate morphology can betuned by appropriately controlling the distribution and length of the grafted sidechains.

Reconciling STEM and X-ray Scattering Data To Determine the Nanoscale Ionic Aggregate Morphology in Sulfonated Polystyrene Ionomers

This paper reports the first quantitative reconciliation of imaging and scattering data for poly(styrene-ran-styrenesulfonate) (P(S-SSx)) ionomers. We examined the morphology of solvent-cast and spin-cast P(S-SS0.019)-M ionomers using the combination of scanning transmission electron microscopy (STEM) and X-ray scattering, where the scattering data were fit with a liquidlike hard-sphere model. Both the ionic aggregate sizes (R1) and the sample volume per ionic aggregate (VP) as measured by both techniques were in good agreement. In addition, STEM found that P(S-SS0.019) ionomers prepared by spin-casting exhibit nanometer spherical ionic aggregates that are indistinguishable in size, shape, and spatial distribution from the bulk solvent-cast ionomers. Six P(S-SS0.019)-M ionomers fully neutralized with various cations have ionic aggregate compositions that are predominately ionic, and the ionic aggregate radius (R1) increases as the cation radii increases. Finally, the influence of copolymer type was studied by comparing P(S-SS0.070) and P(S-MAA0.072) ionomers. The ionic aggregates in P(S-SS0.070)-Cu are surrounded by a thicker region of limited mobility and are more ionic as compared with P(S-MAA0.072) ionomers. Although STEM and X-ray scattering have been reconciled for these P(S-SSx) ionomers, a broad application of the liquidlike hard-sphere scattering model is not recommended. However, when STEM and X-ray scattering are reconciled, detailed morphological information can be extracted from the scattering data, particularly regarding the composition of the ionic aggregates, which is important for understanding the mechanisms of ion transport.

Influence of Sodium Chloride and Glucose on Acid‐Induced Gelation of Heat‐Denatured Ovalbumin

We examined the effects of NaCl and glucose on cold-set ovalbumin gelation. Cold-set gels were prepared by adding glucono-delta-lactone (GDL) to a 2% heated ovalbumin solution. For the gel prepared from ovalbumin heat-denatured with NaCl and glucose, the gel with 10 mM NaCl was most transparent and had high gel strength. Its maximum complex shear modulus (G*) and turbidity were 2.5 times greater and 3 times lower, respectively, than those of the gel without NaCl. The turbidity of the gel with the higher NaCl content increased steeply after the addition of GDL and did not change during the experimental period. The maximum G* of the gel exhibited positive correlations with the molar mass, radius, and surface hydrophobicity of soluble aggregates and the NaCl content, but the turbidity exhibited negative correlations with these factors. The presence of glucose did not significantly affect the turbidity or rheological properties of the gel. For the gel prepared by adding NaCl and glucose with GDL, the presence of glucose did not affect the turbidity, but the maximum G* decreased in inverse proportion to the glucose content. The turbidity of the gel with higher NaCl content (>or= 50 mM) was the greatest among all samples, and the increased turbidity was maintained throughout the measurements. The gels with 50 and 100 mM NaCl exhibited thixotropy during shearing at a constant shear rate. Therefore, the presence of NaCl and glucose during cold gelation could facilitate the preparation of cold-set gels having various properties for food applications.

Numerical Simulation of Dust Aggregate Collisions. II. Compression and Disruption of Three‐Dimensional Aggregates in Head‐on Collisions

We study collisions between dust aggregates to construct a model of their structural evolution in protoplanetary disks. We carry out three-dimensional simulations of aggregate collisions and examine their compression and disruption processes following our previous two-dimensional simulations. We take clusters of ballistic cluster-cluster aggregation(BCCA)formedbyahit-and-stickprocessasinitialstructuresandstudytheirhead-oncollisionswiththe use of realistic binding forces. Our numerical results indicate that the energy criteria for compression and disruption of BCCA clusters are consistent with previous two-dimensional simulations. For aggregate compression at a collision, we succeed in obtaining a scaling law in which the gyration radius of the resultant aggregate is proportional to E � 0:10 imp , where Eimp is the impact energy. Furthermore, we derive an ‘‘equation of state’’ of aggregates which reproduces the scaling law for compression. The equation of state is useful for describing the density evolution of dust aggregates during their growth. Subject headingg circumstellar matter — dust, extinction — methods: n-body simulations — planetary systems: formation — planetary systems: protoplanetary disks

Simultaneous estimation of attenuation and structure parameters of aggregated red blood cells from backscatter measurements

The analysis of the ultrasonic frequency-dependent backscatter coefficient of aggregating red blood cells reveals information about blood structural properties. The difficulty in applying this technique in vivo is due to the frequency-dependent attenuation caused by intervening tissue layers that distorts the spectral content of backscattering properties from blood microstructures. An optimization method is proposed to simultaneously estimate tissue attenuation and blood structure factor. With in vitro experiments, the method gave satisfactory estimates with relative errors below 22% for attenuations between 0.101 and 0.317dB∕cm∕MHz, signal-to-noise ratios&amp;gt;28dB and kR&amp;lt;2.7 (k being the wave number and R the aggregate radius).

Salt Effect on Polymerizable Vesicles of Allyl Dodecyl Dimethylammonium Bromide and Sodium Dodecyl Sulfonate in Aqueous Solution

AbstractPolymerization reactions in vesicles are known to fix the vesicular structure to provide stabilized hollow colloidal nanoparticles used as biological membrane models, drug delivery vehicles, or templates for the synthesis of nanostructures. As a precursive work of polymerization directly from vesicles, a polymerizable surfactant, allyl dodecyl dimethylammonium bromide (ADDB) was synthesized, and spontaneous stable vesicles were formed from aqueous solutions of ADDB and sodium dodecyl sulfonate (SDS) in equimolar composition. The aqueous mixture of ADDB/SDS could form homogeneous solutions even at a high surfactant or sodium bromide (NaBr) concentration. Before polymerization, salt effect on the polymerizable vesicles was investigated by using dynamic light scattering (DLS) and freeze‐fracture transmission electron microscopy (FF‐TEM) measurements. It was interestingly revealed by the DLS method that the vesicle size increased from 83 nm in a salt‐free solution to 250 nm with increasing the salt concentration to 250 mmol/L, but decreased from 250 to 180 nm with increasing the salt concentration to 1000 mmol/L. The same meaningful trend was disclosed by the FF‐TEM measurements that when NaBr concentration was below 150 mmol/L the dispersed individual vesicle size was about 70 nm but it decreased to 20 nm while the NaBr concentration was above 400 mmol/L. The causation of increment of average aggregate radius can be attributed to the fusion and flocculation of vesicles observed clearly under a TEM imagine. The decrease of vesicle size results from the fact that, at a high salt concentration, electrolyte screens the interaction between the charged head groups, thus entropic increase drives big vesicles to decrease to small ones.

Dynamic Light Scattering for the Characterization of Polydisperse Fractal Systems: II. Relation between Structure and DLS Results

AbstractDynamic light scattering (DLS) is frequently used to characterize suspensions of pyrogenic silica which consists of polydisperse fractal aggregates of sintered spherical primary particles. As the method primarily measures temporal fluctuations of scattered light caused by the translational and rotational diffusive motion of the aggregates it is an important prerequisite to identify those structural properties that are measurable with DLS and to quantify the method's sensitivity to changes in these properties. In a recent paper [1] we have investigated the structure‐hydrodynamics relationship via simulations. Here, the validation of the simulation results by experimental data is presented. Therefore, the structure of different pyrogenic silica grades has been characterized by static light and X‐ray scattering and the diffusional properties were obtained by multi‐angle DLS measurements. It is shown that the hydrodynamic radii determined with DLS scale well with the mean aggregate radius of gyration but that the influence of rotational diffusion has to be accounted for in the measurements.

Kinetics of thermal aggregation of glycogen phosphorylase b from rabbit skeletal muscle: Mechanism of protective action of α‐crystallin

The kinetics of thermal aggregation of glycogen phosphorylase b (Phb) from rabbit skeletal muscle have been studied by dynamic light scattering (0.08M Hepes, pH 6.8, containing 0.1M NaCl; 48 degrees C). The hydrodynamic radius of the start aggregates determined from the initial linear parts of the dependences of the hydrodynamic radius (R(h)) on time was found to be 16.7 +/- 1.0 nm. At rather high values of time, the R(h) value for the protein aggregates becomes proportional to t(1/1.8) = t(0.56) suggesting that the aggregation process proceeds in the regime of diffusion-limited cluster-cluster aggregation. In the presence of alpha-crystallin, a protein possessing the chaperone-like activity, the process of protein aggregation switches to the regime of reaction-limited cluster-cluster aggregation as indicated by the exponential dependence of the R(h) value on time. It was shown that the addition of alpha-crystallin raises the rate of thermal inactivation of Phb. These data in combination with the results of the study of interaction of Phb with alpha-crystallin by analytical ultracentrifugation suggest that alpha-crystallin interacts with the intermediates of unfolding of the Phb molecule.

Quantifying the Adhesion and Interaction Forces Between Pseudomonas aeruginosa and Natural Organic Matter

Atomic force microscopy (AFM) was used to characterize interactions between natural organic matter (NOM), and glass or bacteria. Poly(methacrylic acid) (PMA), soil humic Acid (SHA), and Suwannee River humic Acid (SRHA), were adsorbed to silica AFM probes. Adhesion forces (Fadh) for the interaction of organic-probes and glass slides correlated with organic molecular weight (MW), but not with radius of the organic aggregate (R), charge density (Q), or zeta potential (zeta). Two Pseudomonas aeruginosa strains with different lipopolysaccharides (LPS) were chosen: PAO1 (A+B+), whose LPS have common antigen (A-band) + O-antigen (B-band); and mutant AK1401 (A+B-). Fadh between bacteria and organics correlated with organic MW, R, and Q, but not zeta. PAO1 had lower Fadh with silica than NOM, which was attributed to negative charges from the B-band polymers causing electrostatic repulsion. AK1401 adhered stronger to silica than to the organics, perhaps because the absence of the B-band exposed underlying positively charged proteins. DLVO calculations could not explain the differences in the two bacteria or predict qualitative or quantitative trends in interaction forces in these systems. Molecular-level information from AFM studies can bring us closer to understanding the complex nature of bacterial-NOM interactions.

Size and Shape of Detergent Micelles Determined by Small-Angle X-ray Scattering

We present a systematic analysis of the aggregation number and shape of micelles formed by nine detergents commonly used in the study of membrane proteins. Small-angle X-ray scattering measurements are reported for glucosides with 8 and 9 alkyl carbons (OG/NG), maltosides and phosphocholines with 10 and 12 alkyl carbons (DM/DDM and FC-10/FC-12), 1,2-dihexanoyl-sn-glycero-phosphocholine (DHPC), 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] (LPPG), and 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS). The SAXS intensities are well described by two-component ellipsoid models, with a dense outer shell corresponding to the detergent head groups and a less electron dense hydrophobic core. These models provide an intermediate resolution view of micelle size and shape. In addition, we show that Guinier analysis of the forward scattering intensity can be used to obtain an independent and model-free measurement of the micelle aggregation number and radius of gyration. This approach has the advantage of being easily generalizable to protein-detergent complexes, where simple geometric models are inapplicable. Furthermore, we have discovered that the position of the second maximum in the scattering intensity provides a direct measurement of the characteristic head group-head group spacing across the micelle core. Our results for the micellar aggregation numbers and dimensions agree favorably with literature values as far as they are available. We de novo determine the shape of FC-10, FC-12, DM, LPPG, and CHAPS micelles and the aggregation numbers of FC-10 and OG to be ca. 50 and 250, respectively. Combined, these data provide a comprehensive view of the determinants of micelle formation and serve as a starting point to correlate detergent properties with detergent-protein interactions.

Chaperone-like activity of immunophilin FKBP12 from bovine brain, a cytoplasmic receptor of immunosuppressor FK506

The chaperone-like activity of brain immunophilin—a cytoplasmic receptor of immunosuppressor FK506 (FK506-binding protein, FKBP12) was evaluated in a test-system in vitro based on suppression of insulin aggregation as a result of A-and B-chain dissociation induced by disulfide bond reduction by dithiotreitol. Using dynamic light scattering technique we have demonstrated the concentration dependent suppression of light scattering intensity and the decrease of the hydrodynamic radius of insulin B-chain amorphous aggregates upon addition of FKBP12 to the incubation medium, a significant effect being revealed even in the substoichiometric concentration range. The results provide evidence that FKBP12 possesses chaperone-like activity preventing insulin aggregation.

Evidence for the formation of start aggregates as an initial stage of protein aggregation

The kinetics of thermal aggregation of glycogen phosphorylase b and glyceraldehyde 3-phosphate dehydrogenase from rabbit skeletal muscles were studied using dynamic light scattering. Use of high concentrations of the enzymes (1–3mg/ml) provided a simultaneous registration of the native enzyme forms and protein aggregates. It was shown that initially registered aggregates (start aggregates) were large-sized particles. The hydrodynamic radius of the start aggregates was about 100nm. The intermediate states between the native enzyme forms and start aggregates were not detected. The initial increase in the light scattering intensity is connected with accumulation of the start aggregates, the size of the latter remaining unchanged. From a certain moment in time aggregates of higher order, formed as a result of sticking of the start aggregates, make a major contribution to the enhancement of the light scattering intensity.

Investigation of the effect of dimethyl sulfoxide and diethyl sulfoxide on sodium dodecyl sulfate micellization in aqueous solutions by fluorescence method

The effect of dimethyl sulfoxide (DMSO) and diethyl sulfoxide (DESO) on micellization of sodium dodecyl sulfate in aqueous solutions is studied by fluorescence method using pyrene as a luminescence probe. The critical micellization concentration of the surfactant is found to increase upon the addition of DMSO and DESO. The aggregation numbers and radii of micelles, the hydrophilic group area, and the parameters of critical compaction of micelles are calculated from the data on fluorescence quenching by hexadecylpyridinium bromide. It is shown that the dependence of the aforementioned parameters on the content of DMSO, unlike DESO, is linear throughout the studied concentration range. It is assumed that, in DMSO solutions, polarization effects always prevail, whereas, at low concentrations of DESO, changes in water structure and the interactions of ethyl groups with hydrocarbon chains of sodium dodecyl sulfate also play a significant role.