Function Of Aggregate Size Research Articles

Charge Detection Mass Spectrometry Reveals Conformational Heterogeneity in Megadalton-Sized Monoclonal Antibody Aggregates.

Aggregation of protein-based therapeutics can occur during development, production, or storage and can lead to loss of efficacy and potential toxicity. Native mass spectrometry of a covalently linked pentameric monoclonal antibody complex with a mass of ∼800 kDa reveals several distinct conformations, smaller complexes, and abundant higher-order aggregates of the pentameric species. Charge detection mass spectrometry (CDMS) reveals individual oligomers up to the pentamer mAb trimer (15 individual mAb molecules; ∼2.4 MDa) whereas intermediate aggregates composed of 6-9 mAb molecules and aggregates larger than the pentameric dimer (1.6 MDa) were not detected/resolved by standard mass spectrometry, size exclusion chromatography (SEC), capillary electrophoresis (CE-SDS), or by mass photometry. Conventional quadrupole time-of-flight mass spectrometry (QTOF MS), mass photometry, SEC, and CE-SDS did not resolve partially or more fully unfolded conformations of each oligomer that were readily identified using CDMS by their significantly higher extents of charging. Trends in the charge-state distributions of individual oligomers provides detailed insight into how the structures of compact and elongated mAb aggregates change as a function of aggregate size. These results demonstrate the advantages of CDMS for obtaining accurate masses and information about the conformations of large antibody aggregates despite extensive overlapping m/z values. These results open up the ability to investigate structural changes that occur in small, soluble oligomers during the earliest stages of aggregation for antibodies or other proteins.

Microplastics alter soil structure and microbial community composition

Microplastics (MPs), including conventional hard-to-biodegrade petroleum-based and faster biodegradable plant-based ones, impact soil structure and microbiota in turn affecting the biodiversity and functions of terrestrial ecosystems. Herein, we investigated the effects of conventional and biodegradable MPs on aggregate distribution and microbial community composition in microhabitats at the aggregate scale. Two MP types (polyethylene (PE) and polylactic acid (PLA) with increasing size (50, 150, and 300 μm)) were mixed with a silty loam soil (0–20 cm) at a ratio of 0.5 % (w/w) in a rice–wheat rotation system in a greenhouse under 25 °C for one year. The effects on aggregation, bacterial communities and their co-occurrence networks were investigated as a function of MP aggregate size. Conventional and biodegradable MPs generally had similar effects on soil aggregation and bacterial communities. They increased the proportion of microaggregates from 17 % to 32 %, while reducing the macroaggregates from 84 % to 68 %. The aggregate stability decreased from 1.4 mm to 1.0–1.1 mm independently of MP size due to the decline in the binding agents gluing soil particles (e.g., microbial byproducts and proteinaceous substances). MP type and amount strongly affected the bacterial community structure, accounting for 54 % of the variance. Due to less bioavailable organics, bacterial community composition within microaggregates was more sensitive to MPs addition compared to macroaggregates. Co-occurrence network analysis revealed that MPs exacerbated competition among bacteria and increased the complexity of bacterial networks. Such effects were stronger for PE than PLA MPs due to the higher persistence of PE in soils. Proteobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, and Gemmatimonadetes were the keystone taxa in macroaggregates, while Actinobacteria and Chloroflexi were the keystone taxa in microaggregates. Proteobacteria, Actinobacteria, and Chloroflexi were the most sensitive bacteria to MPs addition. Overall, both conventional and biodegradable MPs reduced the portion of large and stable aggregates, altering bacterial community structures and keystone taxa, and consequently, the functions.

Modeling soil aggregate fracture using the discrete element method

The Discrete Element Method (DEM) is a suitable approach for modeling and simulating arable soil and tillage processes. In this work, we focus on modeling soil fragmentation which is a vital element of many soil treatments. We present a method for computing the indirect tensile strength of soil aggregates through simulation. DEM aggregates are constructed as spherical clusters of smaller spherical particles. A number of indirect tensile tests are conducted using simulated aggregates from which the critical polar force and tensile strength are identified. We propose a method for introducing random voids such that the distribution of simulated tensile strength corresponds to a given Weibull distribution. We propose to scale the number of voids linearly with the measured porosity of the aggregates. This approach showed better performance than introducing a constant number of voids. We identified that the friction between the sub-spheres can be related to the characteristic strength and the number of voids is related to the spread of strengths in the Weibull distribution. The calibration and validation are performed on experimental data. Based on this approach, the synthetic DEM aggregates allow for deriving the aggregate strength as a function of aggregate size. The results are based on fracturing individual aggregates but can be extended to simulations involving multiple interacting aggregates.

Unified modeling of contrasting basin-scale dissolved Al distributions using dissolution kinetics of diatom aggregates: Implication for upwelling intensity as a primary factor to control opal burial rate

Distribution of dissolved aluminum is strongly coupled with dissolution of diatom frustules, since opal is the main scavenger of dissolved oceanic Al. Given Al has a much shorter residence time compared with silicic acid, vertical processes affecting Al must be much more important. It may therefore be possible to understand dissolution behavior of diatom frustules indirectly via Al distribution.In this paper, we explore the features that dissolution kinetics of diatom frustule aggregates would provide with respect to vertical profiles of silicic acid, opal and dissolved Al. This dissolution kinetics has merits to understand 1) the elemental composition of siliceous fraction of settling particles and 2) limited occurrence of opal deposition. The dissolution kinetics of diatom frustule aggregates describes dissolution as a function of aggregate size, which depends on diatom productivity. To heighten our understanding, a unidimensional model has been developed incorporating the dissolution kinetics. This model reproduces basin-scale Al vertical profiles in the Atlantic and Pacific Oceans and Arctic and Mediterranean Seas with the identical parameter of Al absorption by opal as well as maximum Si concentration and minimum Al concentration at increasing depths with increasing Si concentrations.The distribution of opal predicted by this model may be useful and may explain discrepancies between the observed and previously-modeled depth profiles for dissolved Al. This model predicts the effective dissolution/burial of frustules during periods of smaller/greater production. Because upwelling triggers the production of diatoms, we propose that increase in upwelling intensity may be most important parameters to reduce the oceanic silicic acid inventory.

Water Migration and Swelling in Engineered Barrier Materials for Radioactive Waste Disposal

Deep, underground repositories are needed to isolate radioactive waste from the biosphere. Because bentonite is an integral component of many multibarrier repository systems, information on the hydraulic behavior of bentonite is crucial for modeling the long-term viability of such systems. In this paper the hydraulic behavior of bentonite samples was analyzed as a function of aggregate size, and samples were subjected to hydrothermal treatments involving contact with NaCl, KCl, and deionized water. Neutron and X-ray imaging were used to quantify water sorption into packed bentonite samples and bentonite swelling into the water column. The distance between the original clay-water interface and the wetting front was determined as a function of time. Average water uptake exhibited a square-root-of-time dependence in freshly prepared samples, but more variable rates were observed for samples previously in contact with water. The radiography was supported by small-angle neutron scattering analysis and ultra-small-angle neutron scattering analysis of aggregate size distributions and by inelastic neutron scattering to understand the physicochemical environment of the sorbed water. Results showed that hydrothermal treatment with KCl had the greatest effect of increased water transport in the bentonite, possibly as a result of the interaction of K+ with smectite layers in the clay.

Scale effect of aggregate rupture: Using the relationship between friability and fractal dimension to parameterise discrete element models

Accurate modelling of porous aggregate rupture is critical when simulating natural phenomena involving material fragmentation and seeking to improve technological processes. For this, numerical models based on the discrete element method must be parameterised, which is a challenging task. It is even more challenging in the case of scale-variant materials, e.g. agricultural soils. In numerical simulations based on theoretical considerations, we identified a linear correlation between friability and fractal dimension for porous aggregates, with particle bond strength defining the rate at which friability coefficient diminished with fractal increment. By combining numerical simulation results with laboratory measurements, we established a unique use for friability as a material macro property to determine particle bond strength and density for different aggregate sizes. This allows parameterisation of discrete element models to simulate how tensile strength varies as a function of aggregate size.

Using a Numerical Method for Designing an Asphalt Mix with Specific Aggregate Material Properties

Abstract Common approaches for designing asphalt mixes mainly deal with the determination of the optimal percentage of the binder content, which is performed according to the volumetric properties, durability index, and strength of the produced asphalt. In this regard, laboratory results of asphalt mix designs, considering the changes in physical properties of the aggregates from production to the distribution of hot mix asphalt, highlight the need for fabrication of cyclic control specimens. The approach presented in this study allows the reduction of human mistakes during samples preparation, easy control of optimum binder content with respect to the probable changes in the aggregate sizes in each step of fabrication, transportation and implementation of the hot asphalt mix, and provide a uniform ultimate surface of the distributed asphalt. By adjusting the numerical values of the factors effective on the optimum binder percentage and constructing some statistical regression models in statistical package for the social sciences (SPSS), we obtained a set of linear equations that give the optimum binder percentage as a function of aggregate size, binder absorption, specific gravity of the mix, and specific surface of the materials. According to the results of the SPSS 23 analysis, the optimum binder content of the aggregates from 30 different mines was evaluated with respect to their grain size. Based on the obtained results and Marshall Laboratory test data, we extracted some relations for estimating the optimum binder content for hot mix asphalt. Using this method, the optimal binder content is determined using the results of the sieve analysis of the aggregates without the need for repetitive fabrication of asphalt specimens or spending a long time. Consequently, the optimal binder content for the 0–19-mm binder and 0–13-mm topcoat asphalts was determined with high accuracy.

Soil macroaggregates and organic-matter content regulate microbial communities and enzymatic activity in a Chinese Mollisol

The formation and turnover of macroaggregates are critical processes influencing the dynamics and stabilization of soil organic carbon (SOC). Soil aggregate size distribution is directly related to the makeup and activity of microbial communities. We incubated soils managed for >30 years as restored grassland (GL), farmland (FL) and bare fallow (BF) for 60 days using both intact and reduced aggregate size distributions (intact aggregate distribution (IAD)<6 mm; reduced aggregate distribution (RAD)<1 mm), in treatments with added glucose, alanine or inorganic N, to reveal activity and microbial community structure as a function of aggregate size and makeup. Over a 60-day incubation period, the highest phospholipid fatty acid (PLFA) abundance was on day 7 for bacteria and fungi, on day 15 for actinomycete. The majority of the variation in enzymatic activities was likely related to PLFA abundance. GL had higher microbial abundance and enzyme activity. Mechanically reducing macroaggregates (>0.25 mm) by 34.7% in GL soil with no substrate additions increased the abundance of PLFAs (average increase of 15.7%) and activities of β-glucosidase (increase of 17.4%) and N-acetyl-β-glucosaminidase (increase of 7.6%). The addition of C substrates increased PLFA abundance in FL and BF by averages of 18.8 and 33.4%, respectively, but not in GL soil. The results show that the effect of habitat destruction on microorganisms depends on the soil aggregates, due to a release of bioavailable C, and the addition of substrates for soils with limited nutrient availability. The protection of SOC is promoted by larger size soil aggregate structures that are important to different aggregate size classes in affecting soil C stabilization and microbial community structure and activity.

Highly Anisotropic Conjugated Polymer Aggregates: Preparation and Quantification of Physical and Optical Anisotropy

Controlling morphological order of conjugated polymers over mesoscopic and microscopic scales could yield critical improvements in the performance of organic electronics. Here, we utilize a multimodal apparatus allowing for controlled solvent vapor annealing and simultaneous wide-field epifluorescence microscopy to demonstrate bottom-up growth of morphologically ordered anisotropic aggregates prepared from single poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) chains, with length scales controllable from tens of nanometers to several micrometers. Preparation of micrometer-scale fiber aggregates that interconnect to form spanning networks is also demonstrated. We quantify aggregate physical and optical anisotropy, degree of quenching, and exciton diffusion characteristics as a function of aggregate size. The demonstration of controlled preparation of highly anisotropic aggregates provides a path for controlled postprocessing of organic thin films at length scales relevant to the operati...

A new adsorption model to quantify the net contribution of minerals to butachlor sorption in natural soils with various degrees of organo-mineral aggregation

The effect of interactions between soil minerals and organic matter as a function of aggregate size on butachlor sorption was quantified in natural soils with various degrees of organo-mineral aggregation. The smallest size clay microaggregates sorbed most butachlor (58% to 71%) and the fine sand fraction sorbed the least (less than 4.3%). When normalized to organic carbon, butachlor sorption to the clay microaggregates was even smaller than to the silt and sand fractions under specific soil conditions. The sum of sorption to the different fractions was, on average, above 78% greater than sorption to the bulk soils, with the greatest differences in the soils with relatively higher ratios of clay to soil organic carbon (RCO). This suggests that minerals can physically protect favorable sorption sites within soil organic matter (SOM), and inhibit butachlor sorption by influencing SOM physical conformation. Comparisons of changes in butachlor sorption coefficients (both Kd and Koc) in two different series of soils, with the same mineral components but gradients of total organic carbon (TOC) and RCO values also showed that minerals can directly contribute to soil butachlor sorption processes, which may be even more pronounced in soils with relative higher RCOs. A new adsorption model was proposed and verified to quantify the net contribution of minerals to butachlor sorption, based upon 38 different soils. This study has increased our ability to quantify the positive direct contribution of soil minerals and their negative indirect contribution through associated effects on SOM physical conformation during butachlor sorption in natural soils.

Adsorption of Superparamagnetic Iron Oxide Nanoparticles on Silica and Calcium Carbonate Sand

Superparamagnetic iron oxide (SPIO) nanoparticles have the potential to be used in the characterization of porous rock formations in oil fields as a contrast agent for NMR logging because they are small enough to traverse through nanopores and enhance contrast by shortening NMR T2 relaxation time. However, successful development and application require detailed knowledge of particle stability and mobility in reservoir rocks. Because nanoparticle adsorption to sand (SiO2) and rock (often CaCO3) affects their mobility, we investigated the thermodynamic equilibrium adsorption behavior of citric acid-coated SPIO nanoparticles (CA SPIO NPs) and poly(ethylene glycol)-grafted SPIO nanoparticles (PEG SPIO NPs) on SiO2 (silica) and CaCO3 (calcium carbonate). Adsorption behavior was determined at various pH and salt conditions via chemical analysis and NMR, and the results were compared with molecular theory predictions. Most of the NPs were recovered from silica, whereas far fewer NPs were recovered from calcium carbonate because of differences in the mineral surface properties. NP adsorption increased with increasing salt concentration: this trend was qualitatively explained by molecular theory, as was the role of the PEG grafting in preventing NPs adsorption. Quantitative disagreement between the theoretical predictions and the data was due to NP aggregation, especially at high salt concentration and in the presence of calcium carbonate. Upon aggregation, NP concentrations as determined by NMR T2 were initially overestimated and subsequently corrected using the relaxation rate 1/T2, which is a function of aggregate size and fractal dimension of the aggregate. Our experimental validation of the theoretical predictions of NP adsorption to minerals in the absence of aggregation at various pH and salt conditions demonstrates that molecular theory can be used to determine interactions between NPs and relevant reservoir surfaces. Importantly, this integrated experimental and theoretical approach can be used to gain insight into NP mobility in the reservoir.

A population balance equation model to predict regimes of controlled nanoparticle aggregation

Forming stable clusters or aggregates of nanoparticles is of interest in a number of emerging applications. While formation of unstable fractal aggregates and flocs has been well-studied with both experiments and theory, the conditions that lead to stable, finite-sized clusters is not as well understood. Here, we present an integrated experimental and modeling study to explore aggregation in concentrated attractive colloidal suspensions. A population balance equation (PBE) model is used to predict the aggregation dynamics of quiescent colloidal suspensions. A DLVO (Derjaguin–Landau–Verwey–Overbeek) type potential is used to describe the interparticle potential, with attractive interactions arising from van der Waals forces and long-range repulsive interactions caused by electrostatics. The PBE model includes a full calculation of stability ratio variations as a function of aggregate size, such that the energy barrier increases with increasing size. As the ionic strength is decreased, the model predicts three regimes of behavior: uncontrolled aggregation into large flocs, controlled aggregation into stable clusters, and no aggregation. The model is tested experimentally using latex particles at different salt concentrations and particle concentrations. When the Hamaker constant and surface potential are fit to aggregate size measurements collected at one salt concentration, the model accurately predicts the final mean aggregate size and regimes of aggregation at other salt concentrations and the same particle concentration. This result suggests that van der Waals and electrostatic forces are the dominant particle interactions in determining the final aggregate state. The mean aggregate size and aggregation regimes at different particle concentrations could be accurately predicted by adjusting the surface potential. This parameter adjustment is consistent with the expectation that increasing colloid weight fractions cause aggregates to have a more fractal nature and hence have a lower effective repulsion. However, the model predicts much faster aggregation rates than what are observed experimentally. This discrepancy may be due to hydrodynamic effects or another slow dynamical process which is not accounted for in the model. Nevertheless, this study presents the first PBE model that can successfully predict stable aggregate size and aggregation regimes of charged colloidal particles over a range of salt concentrations and particle concentrations.

Photoinduced Disaggregation of TiO2 Nanoparticles Enables Transdermal Penetration

Under many aqueous conditions, metal oxide nanoparticles attract other nanoparticles and grow into fractal aggregates as the result of a balance between electrostatic and Van Der Waals interactions. Although particle coagulation has been studied for over a century, the effect of light on the state of aggregation is not well understood. Since nanoparticle mobility and toxicity have been shown to be a function of aggregate size, and generally increase as size decreases, photo-induced disaggregation may have significant effects. We show that ambient light and other light sources can partially disaggregate nanoparticles from the aggregates and increase the dermal transport of nanoparticles, such that small nanoparticle clusters can readily diffuse into and through the dermal profile, likely via the interstitial spaces. The discovery of photoinduced disaggregation presents a new phenomenon that has not been previously reported or considered in coagulation theory or transdermal toxicological paradigms. Our results show that after just a few minutes of light, the hydrodynamic diameter of TiO2 aggregates is reduced from ∼280 nm to ∼230 nm. We exposed pigskin to the nanoparticle suspension and found 200 mg kg−1 of TiO2 for skin that was exposed to nanoparticles in the presence of natural sunlight and only 75 mg kg−1 for skin exposed to dark conditions, indicating the influence of light on NP penetration. These results suggest that photoinduced disaggregation may have important health implications.

Impact of Virus Aggregation on Inactivation by Peracetic Acid and Implications for Other Disinfectants

Viruses in wastewater and natural environments are often present as aggregates. The disinfectant dose required for their inactivation, however, is typically determined with dispersed viruses. This study investigates how aggregation affects virus inactivation by chemical disinfectants. Bacteriophage MS2 was aggregated by lowering the solution pH, and aggregates were inactivated by peracetic acid (PAA). Aggregates were redispersed before enumeration to obtain the residual number of individual infectious viruses. In contrast to enumerating whole aggregates, this approach allowed an assessment of disinfection efficiency which remains applicable even if the aggregates disperse in post-treatment environments. Inactivation kinetics were determined as a function of aggregate size (dispersed, 0.55 and 0.90 μm radius) and PAA concentration (5-103 mg/L). Aggregation reduced the apparent inactivation rate constants 2-6 fold. The larger the aggregate and the higher the PAA concentration, the more pronounced the inhibitory effect of aggregation on disinfection. A reaction-diffusion based model was developed to interpret the experimental results, and to predict inactivation rates for additional aggregate sizes and disinfectants. The model showed that the inhibitory effect of aggregation arises from consumption of the disinfectant within the aggregate, but that diffusion of the disinfectant into the aggregates is not a rate-limiting factor. Aggregation therefore has a large inhibitory effect if highly reactive disinfectants are used, whereas inactivation by mild disinfectants is less affected. Our results suggest that mild disinfectants should be used for the treatment of water containing viral aggregates.

Size-selective uptake of colloidal low density lipoprotein aggregates by cultured white blood cells

This paper illustrates how principles of colloid science are useful in studying atherosclerosis. Accumulation of foam cells in the arterial intima is a key step in atherogenesis. The extent of foam cell formation is enhanced by low density lipoprotein (LDL) aggregates, and we have previously shown that the size of sphingomyelinase (Smase)-hydrolysis-induced aggregates depends directly on the concentration of ceramide generated in the LDL phospholipid monolayer, mediated by the hydrophobic effect. Here, we focus on the effect of LDL aggregate particle sizes on their subsequent uptake by macrophages. Our data show the first direct measurement of uptake as a function of aggregate size and the first direct comparison of uptake after Smase-catalyzed and vortex-mixing-mediated aggregation. Vortex-mixed aggregates with radii 20–77 nm showed maximal uptake ∼118 μg sterol/mg protein at a 53 nm intermediate size, consistent with a mathematical model describing competition between aggregate surface area and volume. Smase-treated aggregates with radii 25–211 nm also showed maximal uptake at an intermediate size, ∼58 μg sterol/mg protein for 132 nm particles, and fit a modified model that incorporated ceramide concentration expressed as aggregate size. This study shows that particle size is significant and composition may also be a factor in LDL uptake.

Load Transfer Characteristics of Aggregate Interlocking in Concrete Pavement

This paper presents a finite-element model of a jointed concrete pavement with aggregate interlocking load transfer system. Interlocking mechanism has been modeled by a set of discrete springs. A new parameter “modulus of interlocking joint ( Kj ) ” has been introduced to represent the load transfer characteristics of the interlocked joint. Guidelines have been proposed for the selection of the modulus of interlocking joint as a function of aggregate size and joint opening. Stiffness values for the linear springs can be selected using the modulus value Kj . The numerical model, with the joint spring stiffness values selected from the present guidelines, has been validated with experimental results available in literature.

Load Transfer Characteristics of Aggregate Interlocking in Concrete Pavement

This paper presents a finite-element model of a jointed concrete pavement with aggregate interlocking load transfer system. Interlocking mechanism has been modeled by a set of discrete springs. A new parameter “modulus of interlocking joint (Kj)” has been introduced to represent the load transfer characteristics of the interlocked joint. Guidelines have been proposed for the selection of the modulus of interlocking joint as a function of aggregate size and joint opening. Stiffness values for the linear springs can be selected using the modulus value Kj. The numerical model, with the joint spring stiffness values selected from the present guidelines, has been validated with experimental results available in literature.

Combined ab initio and classical molecular dynamics simulations of alkyl-lithium aggregates in ethereal solutions

Molecular dynamics simulations of organolithium aggregates in solution are reported for the first time. We use a combined quantum/classical force field (the so-called QM/MM approach) and study ethyl-lithium aggregates in dimethyl ether (DME) solvent. The solutes are described at the Density Functional Theory level while solvent molecules are described using molecular mechanics. NVT Molecular Dynamics simulations at 200 K are carried out in the Born–Oppenheimer approximation. After equilibration, the production phase was run for 80 ps (monomer), 40 ps (dimer) and 26 ps (tetramer). The analysis of the results focuses on Li coordination as a function of aggregate size and we show that the total Li coordination number is always 4. No decoordination has been observed along the simulations. Fluctuations of the structures are predicted to be large in some cases and possible implications on reactivity are discussed.

Morphology, lacunarity and entropy of intra-aggregate pores: Aggregate size and soil management effects

In a hierarchical model of soil structure, small size aggregates are less porous and contain smaller pores than larger aggregates. Fractal dimensions obtained from aggregate mass-ratio data seem to confirm a hierarchical organization of intra-aggregate pores that may be altered by tillage. The objective of this study was to use image analysis to directly characterize the morphology and spatial arrangement of intra-aggregate pores as a function of aggregate size and soil management. The surfaces of wooded and cultivated sites of a Typic Hapludults, an Aquic Hapludults and an Ultic Hapludalfs were sampled. Hand-picked aggregates from each site were separated in three size groups having masses of 5–6 g ( M 5), 2 g ( M 2) and 0.5 g ( M 0.5) and 6 aggregates per size group were resin-impregnated and imaged. Measurements on the 108 images included pore shape (planar, irregular and rounded), the geometric mean of the Feret (longest) pore diameter (GMFD) for each shape group and pores greater than 300 μm 2, and properties of the spatial arrangement of pores characterized with a normalized entropy and a lacunarity function. Distributions of GMFD by shape were quantified with the Kullback–Leibler Divergence and a chi-square test. Planar pores had greater GMFD values than irregular and rounded pores and their distributions were significantly different ( P < 0.05) across aggregate sizes. Parameters from the normalized entropy and lacunarity functions were significantly ( P < 0.05): 1) different in cultivated than in wooded sites and in the M 0.5 than in the M 5 and M 2 size groups (entropy function only) and 2) correlated to the porosity, pore number and to GMFD (entropy function only) values of each pore shape group. The lacunarity function revealed a fractal or multifractal structure of pores within aggregates, while the normalized entropy function detected significantly lower entropy in aggregates of the M 0.5 size group. The GMFD of planar pores showed well defined trends with fractal parameters obtained from data (reported elsewhere) on aggregate mass-ratio. These results are evidence of differences in the organization and distribution of pores within aggregates of different sizes that may be of a hierarchical (fractal) type.

Curved single-bilayers in the region of the anomalous swelling: Effect of curvature and chain length

We have carried out density and DSC measurements on large unilamellar vesicles (LUVs) of different phosphocholines in the temperature range corresponding to the anomalous swelling regime of multibilayer systems, adjacent to the chain melting transition region. Experiments were performed for DPPC, DMPC and DC 13PC, as a function of aggregate size. The steep drop in density occurring around the main transition gets broader as the vesicle radius decreases and a two-step process is clearly observed for DMPC and DC 13PC vesicles smaller than 200 nm. No similar effect is observed for DPPC vesicles, whatever the aggregate dimension. DSC measurements corroborate density results, showing a splitting of the main peak that becomes more evident as the chain length decreases and as the curvature of the aggregate increases.