Aggregates Of Different Sizes Research Articles

Bacterial Cohesion Predicts Spatial Distribution in the Larval Zebrafish Intestine

Are there general biophysical relationships governing the spatial organization of the gut microbiome? Despite growing realization that spatial structure is important for population stability, interbacterial competition, and host functions, it is unclear in any animal gut whether such structure is subject to predictive, unifying rules or if it results from contextual, species-specific behaviors. To explore this, we used light sheet fluorescence microscopy to conduct a high-resolution comparative study of bacterial distribution patterns throughout the entire intestinal volume of live, larval zebrafish. Fluorescently tagged strains of seven bacterial symbionts, representing six different species native to zebrafish, were each separately monoassociated with animals that had been raised initially germ-free. The strains showed large differences in both cohesion—the degree to which they auto-aggregate—and spatial distribution. We uncovered a striking correlation between each strain’s mean position and its cohesion, whether quantified as the fraction of cells existing as planktonic individuals, the average aggregate size, or the total number of aggregates. Moreover, these correlations held within species as well; aggregates of different sizes localized as predicted from the pan-species observations. Together, our findings indicate that bacteria within the zebrafish intestine are subject to generic processes that organize populations by their cohesive properties. The likely drivers of this relationship—peristaltic fluid flow, tubular anatomy, and bacterial growth and aggregation kinetics—are common throughout animals. We therefore suggest that the framework introduced here of biophysical links between bacterial cohesion and spatial organization should be useful for directing explorations in other host-microbe systems, formulating detailed models that can quantitatively map onto experimental data, and developing new tools that manipulate cohesion to engineer microbiome function.

Understanding the microscopic origin behind heterogeneous properties of water confined in and around Aβ17-42 protofilaments.

Aggregation of amyloid beta (Aβ) peptides in the brain is responsible for one of the most devastating neurodegenerative diseases, namely, Alzheimer's disease. In this study, we have carried out atomistic molecular dynamics simulations to explore the effects of non-uniform structural distortions of Aβ17-42 pre-fibrillar aggregates of different sizes on the microscopic structure and ordering of water molecules confined within their amphiphilic nanocores. The calculations revealed non-uniform peptide-water interactions resulting in simultaneous existence of both highly ordered and disordered water molecules within the spatially heterogeneous confined environment of the protofilament cores. It is found that the high degree of ordering originates from a sizable fraction of doubly coordinated core water molecules, while the randomly oriented ones are those that are coordinated with three neighbors in their first coordination shells. Furthermore, it is quantitatively demonstrated that relative fractions of these two types of water molecules are correlated with the protofilament core topology and the degree of confinement within that. It is proposed that the ordered core waters are likely to stabilize the Aβ protofilaments by screening the residue charges and favoring water-mediated salt bridge formations, while the randomly oriented ones can drive further growth of the protofilaments by being displaced easily during the docking of additional peptides. In that way, both types of core water molecules can play equally important roles in controlling the growth and stability of the Aβ-aggregates.

Remarkably Efficient Blood-Brain Barrier Crossing Polyfluorene-Chitosan Nanoparticle Selectively Tweaks Amyloid Oligomer in Cerebrospinal Fluid and Aβ1-40.

Amyloid oligomers have emerged as a key neurotoxin in Alzheimer’s dementia. Amyloid aggregation inhibitors and modulators have therefore offered potential applications in therapeutics and diagnosis. However, crossing the blood–brain barrier (BBB) and finding the toxic aggregates among aggregates of different sizes and shapes remain a challenge. The ability of identifying early aggregates can provide a new approach to find inhibitors of the initial nucleation events correlating presenile dementia. In this study, we have prepared polyfluorene nanoparticles using chitosan as an additive, which enables it to cross BBB efficiently and employed as a highly efficient amyloid oligomer modulator. The polymer conjugate, polyfluorene–chitosan (PC), shows no toxicity in MTT assay and precludes self-aggregation of Aβ1–40 and human cerebrospinal fluid oligomers to final fibril formation. This modulation strategy is supported by thioflavin T assay, circular dichroism studies, atomic force microscope images, and Fourier transform infrared analysis. The polymer–protein interface exhibits the presence of co-aggregates and responded with a stable optical response. The simple synthesis to get desired sizes and shapes with necessary photophysical behavior, biocompatibility, and most prominently BBB permeability makes this polymer conjugate very unique and highly attractive for modulation of amyloid oligomers selectively as well as for developing next generation nanotheranostic materials toward presenile dementia.

Soil aggregate size mediates the responses of microbial communities to crop rotation

Soil microorganisms play an essential role in the redistribution of soil aggregate sizes due to the microenvironmental changes. Yet, little is known regarding how individual microbial taxa within different-sized aggregates respond to agronomic practice. This study integrated physical, chemical, and molecular techniques (i.e., high-throughput DNA sequencing and qPCR) to assess the influence of corn-tobacco rotation on the soil microbial community at the soil microenvironment scale, i.e., within mega- (>2 mm), macro- (0.25–2 mm) and micro-aggregate (<0.25 mm) fractions. The soil samples (0–20 cm) analyzed in this study originated from corn and tobacco, which were cultivated under three different fertilization regimes. The results demonstrate that corn-tobacco rotation substantially impacted the distribution of aggregate sizes, and the shift in soil microbial communities associated with soil aggregates was related to changes in soil total carbon (TC), the C/N ratio and pH. The indicator microbial taxa (i.e., those were sensitive to crop rotation) varied with aggregate size. When compared with tobacco soil, the corn soil showed higher relative abundances of probably more copiotrophic taxa across large-sized aggregates, also with more bacteria in mega-aggregates and more fungi in macro-aggregates. Changes in total microbial communities associated with mega- and macro-aggregates in response to crop rotation were driven mainly by alterations in bacterial and fungal communities, respectively. Overall, the results of this study demonstrate that soil aggregate size strongly affected the microbial community composition on agricultural fields, promoting the differential responses between bacteria and fungi to crop rotation in specific size of aggregates.

Improved removal of dyes by [sodium alginate/4-methyl-2-(naphthalen-2-yl)-N-propylpentanamide-functionalized ethoxy-silica] composite gel beads

In this paper, the synthesis of [sodium alginate/4-methyl-2-(naphthalen-2-yl)-N-propylpentanamide-functionalized ethoxy-silica] composite gel beads is described. The characterizations were carried out using Fourier Transform InfraRed, Scanning Electron Microscopy, point zero charge and water content. The morphology of the alginate gel beads are changed after functionalization and are characterized by aggregates of different sizes and irregular shapes. The adsorption is checked for Methylene Blue and Acid Blue 25 in batch mode with reference to the change of pH, time, temperature, and adsorbate concentration. A reliance on the studied experimental conditions is observed. The sorption capacities were improved using composite gel beads compared to gel beads. A possible complex formation of composite gel beads and the studied adsorbates is proposed. The kinetic data complies well with the second order. The intra-particular Diffusion exhibits the existence of two successive adsorption stages of mass transport. The data fitted with Freundlich indicate that the adsorption might occur in the heterogeneous adsorption sites. The prepared beads are considered moderate for the removal of the dyes (n > 1). The negative value of enthalpy (−23.7 < ΔH* < −7.14) confirms that the process is exothermic which is, also, supported by the decrease of the adsorption energy constants (B) of Temkin model.

On Upscaling of Soil Microbial Processes and Biogeochemical Fluxes From Aggregates to Landscapes

AbstractSoil microbial communities respond to spatial and temporal variations in environmental conditions (e.g., saturation and ambient temperatures) as reflected in the dynamics of microbially produced greenhouse gas (GHG) fluxes (primarily CO2, N2O, and CH4) emitted from soil surfaces. Despite considerable progress in resolving key soil microbial processes, their quantification remains largely empirical with limited predictability. We report a mechanistic and analytical modeling framework for integrating local environmental effects on GHG‐producing microbial processes primarily in soil aggregates (or other hot spots) and the upscaling of these to regional GHG fluxes. The mechanistic model enables systematic evaluation of how soil structural features (e.g., aggregation and layers), spatial variability, and dynamic ambient conditions (e.g., temperature and hydration) affect soil microbial functioning. The upscaling of microbial processes from aggregates of different sizes to soil profiles and landscapes implements mechanistically derived microbial response functions with spatial information on soil type, land cover, and resource distribution. The modeling framework was evaluated using reported field data for seasonal N2O emissions from subarctic regions resulting in reasonable agreement. The proposed analytical framework offers a practical compromise balancing a simplified representation of dynamic microbial processes that respond to local conditions with an upscalable representation of soil GHG fluxes over landscapes under changing environmental conditions.

Denitrification in Soil Aggregate Analogues-Effect of Aggregate Size and Oxygen Diffusion

Soil-borne nitrous oxide (N$_2$O) emissions have a high spatial and temporal variability which is commonly attributed to the occurrence of hotspots and hot moments for microbial activity in aggregated soil. Yet there is only limited information about the biophysical processes that regulate the production and consumption of N$_2$O on microscopic scales in undisturbed soil. In this study, we introduce an experimental framework relying on simplified porous media that circumvents some of the complexities occuring in natural soils while fully accounting for physical constraints believed to control microbial activity in general and denitrification in particular. We used this framework to explore the impact of aggregate size and external oxygen concentration on the kinetics of O$_2$ consumption, as well as CO$_2$ and N$_2$O production. Model aggregates of different sizes (3.5 vs. 7\,mm diameter) composed of porous, sintered glass were saturated with a defined growth medium containing roughly 10$^9$ cells ml$^{-1}$ of the facultative anaerobic, \textsl{nosZ}-deficient denitrifier \textsl{Agrobacterium tumefaciens} with N$_2$O as final denitrification product and incubated at five different oxygen levels (0-13\,vol-$\%$). We demonstrate that the onset of denitrification depends on the amount of external oxygen and the size of aggregates. Smaller aggregates were better supplied with oxygen due to a larger surface-to-volume ratio, which resulted in faster growth and an earlier onset of denitrification. In larger aggregates, the onset of denitrification was more gradual, but with comparably higher N$_2$O production rates once the anoxic aggregate centers were fully developed. The normalized electron flow from the reduced carbon substrate to N-oxyanions (e$^{-}_{\rm denit}$/e$^{-}_{\rm total}$ ratio) could be solely described as a function of initial oxygen concentration in the headspace with a simple, hyperbolic model, for which the two empirical parameters changed with aggregate size in a consistent way. These findings confirm the important role of soil structure on N$_2$O emissions from denitrification by shaping the spatial patterns of microbial activity and anoxia in aggregated soil. Our dataset may serve as a benchmark for constraining or validating spatially explicit, biophysical models of denitrification in aggregated soil.

Theoretical deposition of random walk-generated nanoaggregates in the lungs of healthy males and females

Background: Particle aggregates with different complexity and size represent an essential component of the ambient atmosphere. Therefore, theoretical knowledge on the effects of this particle group in the human respiratory tract is indispensable. In the present study an innovative model for the hypothetical generation of such aggregates is described in detail. In addition, lung deposition of the computed particles was predicted for both male and female subjects. Methods: The theoretical approach used in this contribution is based on a random-walk algorithm allowing the construction of aggregates with cluster-, chain- or disk-like geometry. Basic components of these complex particulate structures are represented by monodisperse spheres with a diameter of 1 nm. These spherical elements were sticked together by random walks consisting of 10, 100 or 1,000 steps, resulting in aggregates of different size and complexity. Deposition calculations were carried out by assuming (I) a stochastic structure of the human respiratory tract and (II) different physical mechanisms seizing the inhaled particles. Results: Under sitting breathing conditions total deposition of variably sized nanoaggregates ranges from 98.9% to 100% in males and from 98.6% to 100% in females. In the extrathoracic region particle accumulation amounts to 39.3–64.6% (males) and 40.4–64.1% (females), whereas bronchial deposition adopts values of 20.4–44.6% (males) and 20.9–43.2% (females). Alveolar deposition can be estimated at 1.68–14.9% in males and 1.58–18.4% in females. Gender-specific differences of generation-by-generation deposition of nanoaggregates are on the order of 0–0.5%. Conclusions: According to the results of the study deposition of nanoaggregates in the human respiratory tract strongly depends on the size of the inhaled particulate structures. In addition, partly significant differences of pulmonary particle accumulation between male and female subjects can be determined. All these circumstances have to be considered with regard to the formulation of respective health risk assessments.

CLONING AND EXPRESSION OF MCE1A GENE FROM MYCOBACTERIUM TUBERCULOSIS BEIJING AND H37RV STRAIN FOR VACCINE CANDIDATE DEVELOPMENT.

Background:Tuberculosis remains the leading cause of death in the world, especially wherever poverty, malnutrition and poor housing prevail. Mycobacterium tuberculosis Beijing strain is the most common strain that causes tuberculosis in Indonesia. The wide spread of tuberculosis has been further aggravated by HIV-AIDS and drug resistance. Unfortunately, Bacille Calmette-Guerin (BCG) as the current vaccine has different protection function and efficacy. According to function analysis, mce1A gene was predicted to have a role in host invasion and survival of Mycobacterium tuberculosis in human macrophages.Materials and Methods:We performed cloning and protein expression of Mce1A gene of Mycobacterium tuberculosis Beijing strain as local isolate and standard strain H37Rv as a comparison on the expression system Escherichia coli BL21(DE3). Mce1A gene from the strains were amplified by PCR and inserted into the vector pET28a. Each resulting recombinant plasmid was subsequently transformed into E. coli BL21(DE3) and Mce1A protein was expressed with IPTG induction.Results:E. coli BL21(DE3) was succesfully transformed with a recombinant plasmid that contains the Mce1A gene insert with correct orientation and reading frame. There was no mutation found in the amino acids sequence for B and T cell epitope. Mce1A expression in E. coli BL21(DE3) showed a protein band that was higher than expected. The protein was confirmed with Western blotting using anti-His detector.Conclusion:We assumed that Mce1A recombinant protein that has been expressed in E. coli BL21(DE3) is in their dimeric form or alternatively formed aggregates of different sizes.

Increasing temperature of cooling granular gases

The kinetic energy of a force-free granular gas decays monotonously due to inelastic collisions of the particles. For a homogeneous granular gas of identical particles, the corresponding decay of granular temperature is quantified by Haff’s law. Here, we report that for a granular gas of aggregating particles, the granular temperature does not necessarily decay but may even increase. Surprisingly, the increase of temperature is accompanied by the continuous loss of total gas energy. This stunning effect arises from a subtle interplay between decaying kinetic energy and gradual reduction of the number of degrees of freedom associated with the particles’ dynamics. We derive a set of kinetic equations of Smoluchowski type for the concentrations of aggregates of different sizes and their energies. We find scaling solutions to these equations and a condition for the aggregation mechanism predicting growth of temperature. Numerical direct simulation Monte Carlo results confirm the theoretical predictions.

Laboratory investigation on use of quarry waste in open graded friction course

•Gainful utilization of limestone mining waste in open graded friction course has been explored.•Quarry waste processed into aggregates of different sizes and then evaluated for physical parameters.•Five mixes were prepared replacing conventional aggregate with recycled aggregates at an interval of 25% by weight.•Each mix was evaluated for strength, durability, permeability, drain down, moisture susceptibility, and rutting behavior.•Use of limestone quarry waste in open graded friction course is feasible.

Influence of primary particle polydispersity and overlapping on soot morphological parameters derived from numerical TEM images

Experimental studies of soot morphology based on analysis of transmission electron microscopy (TEM) images usually neglect the potential effects of primary particle polydispersity and overlapping. In this study, fractal aggregates of different sizes consisting of polydisperse and overlapping primary particles were numerically generated using typical fractal dimension and prefactor relevant to soot. A total of 3600 simulated two-dimensional projections for each primary particle size distribution and level of overlapping considered was produced and analyzed using two TEM image analysis methods commonly used in the literature to evaluate the effects of primary particle polydispersity and overlapping on the recovered morphological parameters of soot. Fairly large deviations in the recovered number of primary particles in aggregates were obtained by both methods considered using the procedure commonly used in the literature. A recommendation was proposed to improve the accuracy of the retrieved number of polydisperse primary particles in an aggregate. We show that the results obtained by using both the Tian et al. (2006) and Brasil et al. (1999) methods can be significantly improved by using the recommended modification for primary particle polydispersity levels commonly encountered in flame soot. Finally, we recommend to use the modified Tian et al. 2006 method for recovering the number of primary particles of aggregates consisting of both polydisperse and overlapped primary particles.

Flow Cytometric Analysis of Protein Aggregates.

Misfolding of proteins often leads to aggregation. Accumulation of diverse protein aggregates in various cells, tissue and organs is the hallmark of many diseases, such as Alzheimer's disease and Parkinson's disease. The main objective of this study was to present a novel method of characterization of protein aggregates, associated with differential toxicity with different size and composition in vitro using flow cytometry. A Beckman Coulter Epics XL flow cytometer with argon ion laser operating at 488 nm was used for flow cytometry analysis. The voltage and the gain settings for individual channels were set at high voltage and gain for the detections of autofluorescence, fluorescence of adsorbed Congo red, forward scattering (FSC) and side scattering (SSC) intensities from the aggregates of proteins and nanoparticles. Each sample was analyzed to characterize and quantify the number of aggregates with a limit of maximum 20,000 events. The flow cytometry data were analyzed using Flowing software version 2.5.1 and Origin 8.0. Autofluorescence and scattering intensities could distinguish between amyloid and nonamyloid aggregates. Dot plots of both side scattering (SSC) and forward scattering (FSC) intensities also showed characteristic fingerprint of both the types of aggregates when compared with those of well known nanoparticles of oxides of Fe and Cu. This work reports a novel, simple and robust flow cytometric method of characterization of protein aggregates of different size and composition which would find wider application in characterization of biomolecular aggregates, in general.

Electrochemical Characterization and Electrocatalytic Application of Gold Nanoparticles Synthesized with Different Stabilizing Agents

AbstractGold nanoparticles (AuNPs) have unique properties, making them attractive for electronic and energy‐conversion devices and as (electro)catalysts for electrochemical sensors. In addition to the size and shape of AuNPs, the electrocatalytic properties of AuNP‐sensors are also determined by the stabilizing agent used in their synthesis. Here, AuNPs were synthesized with citrate, alginate and quercetin, obtaining spherical and negatively charged nanoparticles. The AuNPs were used to modify glassy carbon electrodes (AuNPs/GCE), which were characterized by scanning electron microscopy and electrochemical techniques. The AuNPs/GCE showed aggregates of different sizes and degrees of dispersion on the electrode surface depending on the stabilizing agent. The AuNP's aggregates affect the homogeneity of the film, the reproducibility of the electrodes and their response in buffer solution. Finally, to evaluate the electrocatalytic ability of the AuNPs/GCE, we studied the oxidation of two analytes with opposite charges: (1) sunset yellow (negative) and (2) hydrazine (positive). Compared with GCE, the AuNPs/GCE showed good electrocatalytic properties for hydrazine, increasing the current up to 50 % and shifting the potential by almost 400 mV, depending on the AuNP used. For the negatively charged analyte, the current decreased up to 50 % and no shift in potential was observed. Thus, the electrocatalytic properties of the AuNPs showed to be highly dependent on the nature of the analyte.

Advances and Pitfalls in the Capillary Electrophoresis Analysis of Aggregates of Beta Amyloid Peptides

Alzheimer’s disease is characterized by the accumulation of brain amyloid plaques composed of aggregates of amyloid β (Aβ) peptides. The present paper describes a novel and easy-to-run capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) method for the specific analysis of fibrillar forms of Aβ aggregates obtained after in vitro incubation of Aβ 1-40 monomer. For that purpose, an affinity CE-LIF approach in which the ligand thioflavine T was added to the running buffer has been used, leading to the separation and detection of various fibrillar aggregates which migrated as spikes. The procedure has been optimized to get spikes only corresponding to Aβ aggregates, through the careful elimination of interfering factors and the electrophoretic validation of the link between spikes and particulate material. This method exhibited semi-quantification capabilities, led to the separation of Aβ fibrillar aggregates of different sizes and showed that highly concentrated solutions of Aβ peptides led to the formation of aggregates of larger size than lower-concentrated solution did. Advances brought by this method as well as future development needed to overcome its present limitations are discussed.

Aging shapes the distribution of copper in soil aggregate size fractions.

Soil aggregates are often considered the basic structural elements of soils. Aggregates of different size vary in their ability to retain or transfer heavy metals in the environment. Here, after incubation of a sieved (<2mm) topsoil with copper, bulk soil was separated into four aggregate-size fractions and their adsorption characteristics for Cu were determined. By combining nano-scale secondary ion mass spectrometry and C-1s Near Edge X-ray Absorption Fine Structure Spectroscopy, we found that copper tends to bind onto organic matter in the <2μm and 20-63μm aggregates. Surprisingly, Cu correlated with carboxyl-C in the <2μm aggregates but with alkyl-C in the 20-63μm aggregates. This is the first attempt to visualize the spatial distribution of copper in aggregate size fractions. These direct observations can help improve the understanding of interactions between heavy metals and various soil components.

Soil aggregate and organic carbon distribution at dry land soil and paddy soil: the role of different straws returning.

Agriculture wastes returning to soil is one of common ways to reuse crop straws in China. The returned straws are expected to improve the fertility and structural stability of soil during the degradation of straw it selves. The in situ effect of different straw (wheat, rice, maize, rape, and broad bean) applications for soil aggregate stability and soil organic carbon (SOC) distribution were studied at both dry land soil and paddy soil in this study. Wet sieving procedures were used to separate soil aggregate sizes. Aggregate stability indicators including mean weight diameter, geometric mean diameter, mean weight of specific surface area, and the fractal dimension were used to evaluate soil aggregate stability after the incubation of straws returning. Meanwhile, the variation and distribution of SOC in different-sized aggregates were further studied. Results showed that the application of straws, especially rape straw at dry land soil and rice straw at paddy soil, increased the fractions of macro-aggregate (>0.25mm) and micro-aggregate (0.25-0.053mm). Suggesting the nutrients released from straw degradation promotes the growing of soil aggregates directly and indirectly. The application of different straws increased the SOC content at both soils and the SOC mainly distributed at <0.53mm aggregates. However, the contribution of SOC in macro- and micro-aggregates increased. Straw-applied paddy soil have a higher total SOC content but lower SOC contents at >0.25 and 0.25-0.053mm aggregates with dry land soil. Rape straw in dry land and rice straw in paddy field could stabilize soil aggregates and increasing SOC contents best.

Effect of Silver Particles Electrodeposited on Reticulated Vitreous Carbon for Nitrate Reduction

Nitrate is a serious contaminant of ground and surface water, which cause high concern in the field of health and environmental protection. Many processes have been used for nitrate removal and the electrochemical treatment is one of the most efficient due to its advantages regarding low cost effectiveness and ability to treat highly concentrated nitrate effluents. The cathode material is an important variable for the nitrate electroreduction process and the development of new electrodes to improve their catalytic activity is a challenge. Modification of electrodes by electrodeposition of metals has been frequently used for electrocatalysis of various reactions in solution and carbon materials are often used as supports for electrocatalysts. In this work, the reticulated vitreous carbon (RVC) was used as support for silver eletrodeposition and the effect of different parameters (applied potential, AgNO3 concentration and deposition time) on the morphology and electrocatalytic activity for nitrate reduction was studied. RVC was processed using poly(furfuryl alcohol) (PFA) resin synthesized according to the best condition established previously. Polyurethane foams with 70 ppi (pores per inch) were used as matrix for the PFA anchorage and after curing, they were heat treated at 1000 °C. All electrochemical experiments were performed in a conventional three electrode cell, using the RVC with electrodeposited Ag as working electrode, a Pt screen and Ag/AgCl as the counter and reference electrodes, respectively. The deposition potentials were chosen through cyclic voltammetry at 0.1, -0.3 and -0.7 V vs Ag/AgCl that can be related to the following regions, respectively: onset of Ag deposition, massive deposition and diffusion controlled deposition. The AgNO3 concentrations solutions used were 5, 10 and 20 mmol L-1, and the deposition times applied were 10, 60 and 180 s. The morphologies obtained by field emission scanning electron microscopy (FESEM) showed that Ag deposition is not uniform due to the RVC three-dimensional structure. Ag dendrites were formed on the highest RVC stems as shown in Figure 1. Ag aggregates of different sizes and shapes dispersed on the entire electrode surface could be observed depending on the experimental condition employed and sample depth. Difference in electrocatalytic activity of the Ag/RVC electrodes for nitrate reduction was confirmed by cyclic voltammetry in 0.1 mol L-1 K2SO4 solution containing 0.01 mol L-1 KNO3 and varied with the Ag amount on electrode surface in addition to its morphology. Figure 1 - FESEM micrograph of Ag electrodeposited on RVC at -0.3 V (vs Ag/AgCl), with a duration time of 60 s and AgNO3 concentration solution of 10 mmol L-1. Figure 1

Prediction of self-assemblies of sodium dodecyl sulfate and fragrance additives using coarse-grained force fields.

Coarse-grained force field (CGFF) methods were applied to study the self-assembly of sodium dodecyl sulfate with fragrance additives. The CGFF parameters were parameterized and validated using experimental and all-atom simulation data. Direct molecular dynamics simulations were carried out to characterize the initial aggregation, partitioning of fragrances, and chemical potentials of the surfactant and fragrance molecules in aggregates of different sizes. The equilibrium critical micelle concentrations (CMCs) and micelle size distributions, which could not be obtained by direct simulation, were predicted using the calculated chemical potentials in combination with a thermodynamic model. The predicted partitioning of fragrances, CMCs, micelle sizes, and micelle structures agree well with previously reported experimental data. Graphical abstract Enhancement of micelle size distribution using thermodynamic model.

Synthesis, characterization of hydroxyapatite‐lambda carrageenan, and evaluation of its performance for the adsorption of methylene blue from aqueous suspension

ABSTRACTThe present work describes the synthesis of hydroxyapatite‐lambda carrageenan CaHAp‐(λ‐Carr) using an aqueous co‐precipitation method. The characterization of the prepared hybrid compounds was achieved using chemical analysis, Fourier Transform Infrared spectroscopy, powder X‐ray diffraction, scanning electron microscopy, and specific surface area. The results gleaned from X‐ray powder analysis proved the presence of (λ‐Carr) and revealed that the increase of its concentration leads to the decrease of the CaHAp crystallinity. Fourier transform Infrared spectra show the presence of (λ‐Carr) and CaHAp characteristic vibrations in the resulting product. Scanning electron microscopy analyses reveal that the morphology of particles was changed by grafting and they are characterized by aggregates of different sizes and irregular shapes. After grafting BET measurements yielded particle specific surface areas ranging from 93 to 260 m2 g−1 depending on the grafted biopolymer. The prepared products were, further, applied for the adsorption of methylene blue (a cationic dye) from aqueous suspension. The adsorption capacity was determined with respect to pH value, the initial dye concentration, time contact, and temperature. The kinetic, thermodynamic, and adsorption isotherm models were assessed for the description of the dye adsorption process. The experimental resulting data show that the prepared hybrid compound CaHAp‐(λ‐Carr) is an efficient adsorbent for the removal of dyes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45385.