Large-sized Aggregates Research Articles

Phospholipids influence the aggregation of recombinant ovine prions: From rapid extensive aggregation to amyloidogenic conversion

The transformation of prion protein (PrP) into its insoluble amyloid form correlates with neurodegeneration in transmissible spongiform encephalopathies. PrP is connected to the neuronal membrane by a covalently-linked glycosylphosphatidylinositol (GPI) anchor. The current study demonstrates that phosphatidylinositol and phosphatidylethanolamine in low concentrations (0.5–50 μM) stimulate rapid unlimited aggregation of PrP. At a higher concentration (500 μM), lipid particles prevent the formation of large PrP aggregates and induce an increase in the β-sheet structure content of PrP protein. Thus, the liberation of PrP from the membrane and its direct interaction with its own GPI moiety, as well as with membrane lipids, can promote the formation of aggregated structures of PrP. The phospholipids studied are also able to upregulate the aggregation of oligomeric PrP forms (12-mers and 36-mers), the neurotoxicity of which has been reported recently. Low phosphatidylinositol concentrations induce these oligomers to form aggregates of smaller size when compared with aggregates formed directly from monomers. The inhibition of extensive aggregation observed at a high concentration of phosphatidylinositol (500 μM) results in both the formation of amyloids from PrP monomers and the interaction of protein molecules with lipid micelles. Thus, phospholipids are not only involved in the aggregation of prion monomers and their amyloidogenic conversion, but also regulate the aggregative status of prion oligomers already formed. Consequently, depending on their micellar status, phospholipids can either promote amyloidogenic conversion and conserve neurotoxic oligomeric forms (lipid micelles) or mediate the formation of large-size amorphous aggregates (non-micellar phospholipids).

Pavement Reflective Cracking Control with Coarse-Aggregate Asphalt Mix Interlayer

A test road was constructed using different asphalt concrete overlay treatments. The field observations conducted after 3 years of the pavement being in service indicated that the coarse-aggregate asphalt mix interlayer worked exceptionally well in reflective crack control. A three-dimensional finite element analysis showed that the main stresses in the coarse-aggregate asphalt mix interlayer were lower than those in the normal asphalt concrete interlayer with the same thickness. It is believed that the large-size aggregates and high air voids in the mixture can block the paths of initial cracks to extend to the top of the interlayer.

Titanium Oxide Nanoparticles Precipitated from Low‐Temperature Aqueous Solutions: I. Nucleation, Growth, and Aggregation

Titanium oxide (TiO2) thin films can be prepared by controlled hydrolysis of a titanium tetrachloride (TiCl4) precursor in an aqueous solution at temperatures below 100°C. As part of an effort to understand the formation of such TiO2 films, the kinetics of the nucleation, growth, and aggregation of TiO2 nanoparticles in aqueous solutions of TiCl4 were studied using dynamic light scattering and a transmission electron microscope (TEM). A higher degree of supersaturation, produced by a higher solution temperature, a higher concentration of TiCl4, or a higher pH, results in a shorter nucleation induction time, a faster initial growth/aggregation rate, and a larger aggregate size. The interfacial energy of TiO2 nanoparticles was found to be 0.072 J/m2 from the homogeneous nucleation theory. Further investigations by a high‐resolution scanning electron microscope (SEM) and TEM for the as‐deposited films showed the structure hierarchy organized from nanocrystalline particles precipitated in the supersaturated solution. As a result, the effect of solution conditions on the nucleation, growth, and aggregation of TiO2 nanoparticles can provide useful guidance for tailoring of microstructures of the TiO2 films.

Measurement of Lens Protein Aggregation in Vivo Using Dynamic Light Scattering in a Guinea Pig/UVA Model for Nuclear Cataract

The role of UVA radiation in the formation of human nuclear cataract is not well understood. We have previously shown that exposing guinea pigs for 5 months to a chronic low level of UVA light produces increased lens nuclear light scattering and elevated levels of protein disulfide. Here we have used the technique of dynamic light scattering (DLS) to investigate lens protein aggregation in vivo in the guinea pig/UVA model. DLS size distribution analysis conducted at the same location in the lens nucleus of control and UVA-irradiated animals showed a 28% reduction in intensity of small diameter proteins in experimental lenses compared with controls (P < 0.05). In addition, large diameter proteins in UVA-exposed lens nuclei increased five-fold in intensity compared to controls (P < 0.05). The UVA-induced increase in apparent size of lens nuclear small diameter proteins was three-fold (P < 0.01), and the size of large diameter aggregates was more than four-fold in experimental lenses compared with controls. The diameter of crystallin aggregates in the UVA-irradiated lens nucleus was estimated to be 350 nm, a size able to scatter light. No significant changes in protein size were detected in the anterior cortex of UVA-irradiated lenses. It is presumed that the presence of a UVA chromophore in the guinea pig lens (NADPH bound to zeta crystallin), as well as traces of oxygen, contributed to UVA-induced crystallin aggregation. The results indicate a potentially harmful role for UVA light in the lens nucleus. A similar process of UVA-irradiated protein aggregation may take place in the older human lens nucleus, accelerating the formation of human nuclear cataract.

Synthesis and aggregate formation of poly(styrenesulfonate)-b-poly(ethylene glycol)-b-poly(styrenesulfonate) triblock copolymers in aqueous solution induced by binding with aluminum ions

Well-defined water-soluble poly(styrenesulfonate)-b-poly(ethylene glycol)-b- poly(styrenesulfonate) (PSS-b-PEG-b-PSS) triblock copolymers with narrow molecular weight distribution (1.29 < Mw/Mn < 1.36) were synthesized in aqueous solution at 70 oC via reversible addition-fragmentation chain transfer (RAFT) polymerization. The complex formed by the PSS-b-PEG-b-PSS triblock copolymer coordinated with aluminum ion was investigated with turbidimetry, dynamic light scattering (DSL), zeta-potential, and transmission electron microscopy (TEM). The aggregation formation was based on the neutralization of the SO3- groups in the PSS blocks with Al3+ ions. The appearance, size and stability of the PSS-b-PEG-b-PSS/Al3+ aggregates were controlled by varying the PSS block length and degree of neutralization (DN). At DN = 0.33, where the PSS-b-PEG-b-PSS copolymer was completely neutralized with Al3+, the aggregate size increased with increasing PSS block length. The transition from the shrinking coil of small size to the interchain aggregates of large size was found at DN of about 0.33.

Kupffer cell depletion in vivo results in clearance of large-sized IgA aggregates in rats by liver endothelial cells

We investigated the clearance kinetics and tissue distribution of different sized IgA in normal and macrophage-depleted rats. Rats were injected iv with liposomes containing dichloromethylene diphosphonate (DMDP). DMDP treatment resulted in complete depletion of liver macrophages 24-48 h after administration. Normal and macrophage depleted rats were injected intravenously with monomeric, dimeric, polymeric or aggregated polymeric IgA (AIgA) and assessed for blood clearance and tissue distribution. In normal rats, clearance of IgA was size dependent, i.e. a faster clearance with increasing size. No differences in clearance kinetics were observed of the different sized IgA between normal and DMDP-treated rats. TCA non-precipitable radioactivity, a measure for degradation of IgA, was found in the circulation of normal and DMDP-treated rats after AIgA administration. The liver was the main organ responsible for the clearance of IgA in normal and DMDP-treated rats. Immunofluorescence studies on liver biopsies indicated that AIgA was associated with Kupffer cells in normal rats. Electron microscopical studies revealed that the AIgA was internalized and located in vesicles in Kupffer cells. In DMDP-treated rats the AIgA was associated with endothelial cells and electron microscopy studies showed that this AIgA was taken up by endothelial cells. These data show that rat liver endothelial cells are able to bind, internalize and degrade AIgA in situations where Kupffer cells are absent, and that these cells may play an important role in the handling of AIgA and IgA-immune complexes.

Aggregation and Toxicology of Titanium Dioxide Nanoparticles

In their study of inhalation exposure of titanium dioxide particles, Grassian et al. (2007) presented a transmission electron micrograph (TEM) (their Figure 2A) as an image of “dispersed” TiO2 nanoparticles. Yet, the TiO2 nanoparticles in this TEM do not appear to be dispersed. There is clear evidence of self-organization of the nanoparticles into distinct assemblages, separated by relatively large regions devoid of any particle. This spatial pattern, very unlikely to occur randomly, is even more apparent when Grassian et al.’s TEM is contrast-enhanced, sharpened, and thresholded (Figure 1A) to eliminate the initial grainy background. With this image, one can demonstrate quantitatively the extent of clustering by calculating the radial distribution function (Torquato 2002), defined as the probability of finding a nanoparticle, in any direction, at various distances away from the center of a given nanoparticle. We compared the values obtained for this function with those associated with an image in which the same nanoparticles have been artificially dispersed (with image processing software). In the dispersed case (Figure 1B), the probability of finding a black pixel drops precipitously when the distance exceeds the apparent radius of nanoparticles, and then stays close to zero thereafter. In the “original” case (Grassian et al.’s Figure 2A), there is also a drop, but the radial distribution function never gets to zero. It progressively increases again as the radial distance increases. This quantitative difference between the curves in Figure 1B leads to the conclusion that the nanoparticles in Figure 1A are clustered. Figure 1 (A) Contrast-enhanced, sharpened, and segmented version of a TEM of a TiO2 nanoparticle suspension (modified from Grassian et al. 2007). (B) Radial distribution function versus radial distance for a representative point in a nanoparticle in (A); the dashed ... However, this conclusion is intriguing in itself. Indeed, before obtaining their TEM, Grassian et al. (2007) suspended the TiO2 nanoparticles in methanol and sonicated the suspension for an unspecified, but presumably appreciable “period of time.” Given this strongly dispersive treatment, it is remarkable that aggregation still occurred to the extent it did. This observation suggests that the 2- to 5-nm size of the primary TiO2 “nano”-particles may be somewhat irrelevant to environmental and toxicologic concerns because in nature, under conditions far more conducive to aggregation than those imposed by Grassian et al. (2007), nanoparticles may never be found alone, but are part of significantly larger-sized aggregates. In a recent study, French et al. (French RA, Jacobson AR, Kim B, Isley SL, Penn RL, Baveye PC, unpublished data) observed that in aqueous suspensions under a range of environmentally relevant conditions of pH and ionic strength, TiO2 nanoparticles form aggregates of several hundred nanometers to several micrometers in diameter within minutes. This aggregation may have toxicologic implications. In any given system (e.g., aerosols), it is possible that even a slight change in pH or ionic strength may cause TiO2 nanoparticles to cluster differently, and therefore to have very dissimilar biological activity. In general, this might explain mixed results found in the literature on the toxicity of TiO2 nanoparticles to environmentally relevant species. Until now, these inconclusive results have been explained (Oberdorster et al. 2005) by arguing that the high biological activity of TiO2 nanoparticles, caused by their large specific surface area, creates a high potential for inflammatory, pro-oxidant, and antioxidant activity. Yet, conflicting observations may perhaps be imputable instead to compounding factors due to nanoparticle aggregation, which so far has not been given serious consideration.

Recanalization and particle exclusion after embolization of uterine arteries in sheep: a long-term study

To compare the long-term evolution of uterine arteries after embolization with the two most commonly used embolic agents for fibroid embolization: nonspherical polyvinyl alcohol (PVA) particles and trisacryl gelatin microspheres (TGMS). Prospective study. University-based interventional radiology, pathology, and reproductive physiology units. Two groups of 10 sheep embolized in the uterine artery. Embolization of the uterine artery with either 600-1000 microm nonspherical polyvinyl alcohol (PVA) particles or with 700-900 microm trisacryl gelatin microspheres (TGMS). Animals were synchronized and naturally inseminated. Animals were killed at 26 months. Uteri were examined pathologically for vessel size, site of occlusion, recanalization rate of vessels, and particle location within the vascular wall. The PVA particles were more numerous in the vessels' lumen than the TGMS particles (13.3 +/- 20.8 vs. 2.5 +/- 2.7), were located more proximally than TGMS (97% vs. 68% in the trunk and first branches of the uterine artery), and were found almost exclusively in the intima (99.2%). In contrast, 54.4% of the TGMS particles were found in the intima, and 45.6% partially or totally excluded. The rate of recanalization was not statistically significantly different for PVA and TGMS (65.2% vs. 60.6%). The long-term evolution of uterine arteries was different after uterine artery embolization with PVA and TGMS because PVA particles formed large-sized aggregates that occluded proximal vessels and remained in the vessel intima. Microspheres occluded more distal vessels, and about 50% of them were partially or totally excluded from the vessel.

EXPERIMENT AND MODELING ON RELATIONSHIP BETWEEN COMPRESSIVE STRENGTH AND VOID RATIO OF POROUS CONCRETE

In the present study, firstly porous concrete with relatively large size aggregate grain (particle size : 20-40mm) was made, and the relationship between void ratio and compressive strength was examined. Next, simple geometrical models was examined to represent the relationship between void ratio and compressive strength of porous concrete.The results obtained from the present study are as follows.1) The influence of the aggregate particle size on the relationship between void ratio and compressive strength of the porous concrete was small.2) It is possible to predict the experimental results of the relationship between void ratio and compressive strength of the porous concrete by means of simple geometrical models with ideally spherical aggregates. Especially, in the case of orthorhombic lattice array, excellent presumption accuracy was obtained.

An ultrastructural study of Porphyromonas gingivalis-induced platelet aggregation

One of the major pathogens of periodontitis, Porphyromonas gingivalis ( P. gingivalis), has the ability to aggregate human platelets. To investigate the interaction between P. gingivalis and human platelets in platelet rich plasma (PRP), platelet aggregation was measured by an aggregometer based on laser light scattering (LS) methods, and an ultrastructural study was performed using electron microscopy. A sharp and rapid increase of small-sized platelet aggregates was observed immediately after the addition of P. gingivalis to PRP, followed by the formation of medium- and large-sized aggregates in 2–3 min. In contrast, when Staphylococcus aureus ( S. aureus) was used in the control experiment, only a slight increase in small-sized aggregates was detected. By electron microscopy, discoid-shaped platelets were observed prior to adding P. gingivalis. By 5 min after the addition of the bacteria, enormous platelet aggregates were observable. Most of the P. gingivalis were present between the adherent platelets, while some were internalized in platelet engulfment vacuoles. In contrast, when washed platelets were incubated with the bacteria under a non-stirring condition to prevent platelet aggregation, and stained with ruthenium red (RR) as an electron dense tracer of the cell surface including the open canalicular system (OCS), both RR-positive and -negative vacuoles containing P. gingivalis were identified in the activated platelets. Thus, this observation suggests that P. gingivalis residing in the RR-negative vacuoles is incorporated into the platelet cytoplasm by phagocytosis.

Mechanical properties of three-leaf stone masonry grouted with ternary or hydraulic lime-based grouts

Masonry made up of two exterior leaves of stone masonry with the space between them filled with poor quality mortar and large size aggregates is quite common in structures belonging to the built cultural heritage. Grouting of this type of vulnerable masonry with cement-based grouts (cement content: 50–75%wt.) was proven mechanically efficient. However, the need to protect frescoes, mosaics and decorative elements, as well as the need to avoid problems of durability encountered due to the high content of cement, led to the development of grouts with reduced cement content, as well as to hydraulic lime-based grouts. In this paper, the effect of ternary grouts (mixes of cement [∼30%], pozzolan and hydrated lime) and hydraulic lime-based grouts on the compressive and on the shear strength of three-leaf stone masonry is experimentally investigated. Although the mechanical properties of the applied grouts are substantially lower than those of grouts with higher cement content, homogenization of masonry is achieved leading to a substantial improvement of the mechanical properties of masonry.

Changes in some soil physical properties and plant growth as affected by again rotating the paper residue in soil

A field experiment in Haditha city (240 km west Baghdad) achieved, the objective of this research to test application levels from the residue paper when again rotating the residue paper in soil in some soil physical properties and its effect in growth and yield of Okra.. The residue paper applies to soil with 0%, 0.75%, 1.5% and 3% from weight dry soil. The treatment distributed on the experimental unites by randomized complete block design in three replicated. Mean weight diameter bulk density, resistance of soil penetration, water infiltration, seed emergence, and the space afforded for the okra plant, and the yield for green pods ware measured, the important results can be summarized as follows: 1- The residue paper increase in mean weight diameter that is increased with all application levels compared with control and on, and increasing a large size aggregate can be stability in water. Also resistance of soil penetration decreased with all levels. On the other hand .All treatments study increased accumulative infiltration as compared with control. 3- There was an increasing in seed emergence as compared with control and All treatments study increased the radius cover by vegetative for the okra plant. Whereas significant increasing the yield for green pods by 75.8%, 45.6% and 57.5% for levels 0.75%, 1.5% and 3% from the residue paper respectively.

Neutral aldoses as source indicators for marine snow

The chemical characteristics of aggregating material in the marine environment are largely unknown. We investigated neutral aldose (NA) abundance and composition in aggregation of marine snow and other organic matter (OM) size fractions in the field. Four sample sets were fractionated using membrane filtration and ultrafiltration into the following size fractions: particulate material, high-molecular-weight (HMW) material, and low-molecular-weight (LMW) material. We also collected three sample sets of marine-snow aggregates. Each sample set contained small, medium, and large aggregate size fractions and each size fraction consisted of 25–50 aggregates. For 7 marine-snow samples and for each water-sample size fraction, we determined monomeric and polymeric NA concentration, NA yield (amount of NA-C normalized to organic carbon), and composition; total organic carbon (TOC) concentration; transparent exopolymer particles (TEP) concentration, and TEP propensity (TEP concentration after inducing TEP formation in filtered samples). This is the first study to include compound-specific NA determinations on these four marine OM size fractions. The mass balances of organic carbon and NA indicated that there were no serious contamination or loss problems. Concentrations, yields, and NA mol fractions in water samples were similar to results from other studies. Glucose and galactose had the highest relative abundance in all size fractions. The NA yield increased with increasing molecular weight or particle size for all fractions except marine snow. The NA yield increased in the order: LMW< marine snow< HMW< particles. Marine snow had a higher average NA yield than the LMW fraction, but lower than particle and HMW-fractions. This indicates that OM in marine snow could have been diagenetically derived from particulate and HMW-fractions, that is, marine snow may include material from the particulate and the colloidal phase. TEP concentration or TEP propensity was positively correlated with concentrations of all individual NAs as well as the sum NA concentrations, indicating that TEP contains neutral sugars in addition to the acidic polysaccharides stained in the determination of TEP concentrations. Despite the relatively low NA yield in marine snow, marine snow was enriched in NA when compared with seawater, with enrichment factors of 34–225 (average 125). By combining data from this study with data from other studies, we estimate that < 10% of carbohydrates in marine snow comprise NAs. There was no clear correlation between marine-snow aggregate size and NA yield, that is, there appears to be no general age difference between small and large marine-snow aggregates. NA composition was similar among different marine-snow size fracions collected during the same day, indicating that aggregation/disaggregation reactions resulted in homogenizing NA composition in marine-snow aggregates of all sizes. The NA composition of marine snow was different from that of other OM size fractions, indicating either that bacterial degradation has modified the composition of marine snow to a larger extent than other OM size fractions or that marine snow is formed through the aggregation of selected subcomponents of OM.

A new series of optoelectronic nanocomposites: CMI-1 mesoporous core/ZnS shell

The conception of a totally new optoelectronic composite with a highly organized mesoporous silica core and a uniform ZnS shell (200 nm in thickness) with new optical properties is reported. The starting CMI-1 material was firstly functionalized with ethylenediamine groups and then the growth of the ZnS shell was targeted by the immersion of the functionalized CMI-1 material in a Zn(CH 3COO) 2 solution followed by a reaction with sodium sulfide. The new optoelectronic nanocomposite has been characterized by a series of techniques such as SEM, TEM and nitrogen adsorption–desorption. The optical properties of the new nanocomposite have been evaluated by photoluminescent spectroscopy. No quantum size effect has been observed due to the large size aggregates in ZnS later.

Cadherin Conformations Associated with Dimerization and Adhesion

To investigate conformations of C-cadherin associated with functional activity and physiological regulation, we generated monoclonal antibodies (mAbs) that bind differentially to monomeric or dimeric forms. These mAbs recognize conformational epitopes at multiple sites along the C-cadherin ectodomain aside from the well known Trp-2-mediated dimer interface in the N-terminal EC1 domain. Group 1 mAbs, which bind monomer better than dimer and the Trp-2-mutated protein (W2A) better than wild type, recognize epitopes in EC4 or EC5. Dimerization of the W2A mutant protein via a C-terminal immunoglobulin Fc domain restored the dimeric mAb-binding properties to EC4-5 and partial homophilic binding activity but did not restore full cell adhesion activity. Group 2 and Group 3 mAbs, which bind dimer better than monomer and wild type better than W2A, recognize epitopes in EC1 and the interface between EC1 and EC2, respectively. None of the mAbs could distinguish between different physiological states of C-cadherin at the cell surface of either Xenopus embryonic cells or Colo 205 cultured cells, demonstrating that changes in dimerization do not underlie regulation of adhesion activity. On the cell surface the EC3-EC5 domains are much less accessible to mAb binding than EC1-EC2, suggesting that they are masked by the state of cadherin organization or by other molecules. Thus, the EC2-EC5 domains either reflect, or are involved in, cadherin dimerization and organization at the cell surface.

Micro- to Nanoscale Structure of Biocompatible PLA−PEO−PLA Hydrogels

We observe large-scale structures in hydrogels of poly(l-lactide)-poly(ethylene oxide)-poly(l-lactide) (PLLA-PEO-PLLA) ranging in size from a few hundred nanometers to several micrometers. These structures are apparent through both ultra-small angle scattering (USAS) techniques and confocal microscopy. The hydrogels showed power law scattering in the USAS regime, which is indicative of scattering from fractal structures. The fractal dimension of the scattering from hydrogels revealed that the gels have large size aggregates with a mass fractal structure over the nanometer-to-micrometer length scales. The aggregates also seem to become more "dense" with an increase in the molecular weight of crystalline PLLA domains. Visualization through confocal microscopy confirms that the gels have a microstructure of interspersed micrometer-sized polymer inhomogeneities with water channels running between them. The presence of micrometer-sized water channels in the hydrogels has very important implications for biomedical applications.

Mechanism of Formation of Amyloid Protofibrils of Barstar from Soluble Oligomers: Evidence for Multiple Steps and Lateral Association Coupled to Conformational Conversion

Understanding the heterogeneity of the soluble oligomers and protofibrillar structures that form initially during the process of amyloid fibril formation is a critical aspect of elucidating the mechanism of amyloid fibril formation by proteins. The small protein barstar offers itself as a good model protein for understanding this aspect of amyloid fibril formation, because it forms a stable soluble oligomer, the A form, at low pH, which can transform into protofibrils. The mechanism of formation of protofibrils from soluble oligomer has been studied by multiple structural probes, including binding to the fluorescent dye thioflavin T, circular dichroism and dynamic light scattering, and at different temperatures and different protein concentrations. The kinetics of the increase in any probe signal are single exponential, and the rate measured depends on the structural probe used to monitor the reaction. Fastest is the rate of increase in the mean hydrodynamic radius, which grows from a value of 6 nm for the A form to 20 nm for the protofibril. Slower is the rate of increase in thioflavin T binding capacity, and slowest is the rate of increase in circular dichroism at 216 nm, which occurs at about the same rate as that of the increase in light scattering intensity. The dynamic light scattering measurements suggest that the A form transforms completely into larger size aggregates at an early stage during the aggregation process. It appears that structural changes within the aggregates occur at the late stages of assembly into protofibrils. For all probes, and at all temperatures, no initial lag phase in protofibril growth is observed for protein concentrations in the range of 1 μM to 50 μM. The absence of a lag phase in the increase of any probe signal suggests that aggregation of the A form to protofibrils is not nucleation dependent. In addition, the absence of a lag phase in the increase of light scattering intensity, which changes the slowest, suggests that protofibril formation occurs through more than one pathway. The rate of aggregation increases with increasing protein concentration, but saturates at high concentrations. An analysis of the dependence of the apparent rates of protofibril formation, determined by the four structural probes, indicates that the slowest step during protofibil formation is lateral association of linear aggregates. Conformational conversion occurs concurrently with lateral association, and does so in two steps leading to the creation of thioflavin T binding sites and then to an increase in β-sheet structure. Overall, the study indicates that growth during protofibril formation occurs step-wise through progressively larger and larger aggregates, via multiple pathways, and finally through lateral association of critical aggregates.

Chiral recognition of dipeptides in phosphatidylcholine aggregates

Enantiodiscrimination of ditryptophan enantiomers ( l-Trp- l-Trp and d-Trp- d-Trp, l-Trp- d-Trp and d-Trp- l-Trp) was observed in bio-membrane models, such as micellar aggregates of 1,2-diheptanoyl- sn-glycero-3-phospatidylcholine (DHPC) and multilamellar vesicles of either 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) or 1,2-dimyristoyl- sn-glycero-3-phospatidylcholine (DMPC) by solution 1H NMR and HR-MAS 1H NMR, respectively. The attainment of resolved signals, allowed the first detection of enantiodiscrimination at a molecular level, and the identification of the site of chiral recognition and of the interactions and conformations of homo- and heterochiral dipeptides in large-sized aggregates formed by a common component of bio-membranes.

Spinning wheel powder feeding device — fundamentals and applications

A spinning wheel powder feeding system has been developed as a conveying mechanism to feed fine particle aggregates on a laboratory scale. An example of a use of this conveying mechanism is with a transport tube reactor, since the reactor only provides a few seconds residence time to react the powder. Methods to shear the powder mechanically, as opposed to using a high gas velocity, are developed as to not reduce the available residence time in the reactor. The objective is to feed a powder at the smallest particle aggregate size possible rather than a large particle aggregate size generated by an upstream feeding device, and to achieve such dispersion using minimized gas flow. Statistical results show that the spinning wheel alone is able to reduce the mean aggregate size of the Particle Size Distribution (PSD) and when a minimal amount of gas is added to the system the PSD is reduced further. In addition, a fundamental model employing a discrete particle aggregate breakage equation combined with a Monte Carlo method has shown that the spinning wheel feeding system is able to consistently reduce particle aggregate size.

Kinetics of Insulin Aggregation: Disentanglement of Amyloid Fibrillation from Large-Size Cluster Formation

Kinetics of human insulin aggregation has been studied at pH 1.6 and 60°C, when amyloid fibrils are formed. We developed a novel approach based on the analysis of scattered light intensity distribution, which allows distinguishing between small and large size aggregates. By this method, we observed an exponential growth of fibrillar aggregates implying a heterogeneous aggregation mechanism. Also, the apparent lag time observed, correlated with the major increase of thioflavin T fluorescence, has been assigned to the onset of large size cluster formation.