Specific ions effect on aggregation behaviors and structural changes of amyloid fibrils from rice glutelin

Metal ions have been considered as an important factor on fibrils assembly. Herein, a comprehensive analysis of specific ions effect on fibril formation and structural changes was investigated. The addition of ions (except Zn2+) accelerated the aggregation kinetics of rice glutelin fibrils (RGFs) from 0.93 to 1.28-2.19 h-1. In addition, the fibrillization rate followed the order of NH4+ > Li+ > Na+ > K+ > Cu2+ > Mg2+ > Ca2+ > Zn2+. The highest yield and length of fibrils were observed with Ca2+, probably due to the ionic bridging effect and hydrated capacity of Ca2+. However, Cu2+ reduced the fibrils yield, which was attributable to the fact that Cu2+ disrupted β-sheet structure and inhibited the transition of monomer to fibrils. The polymorphism of fibrils was observed with different salts, and the light metals presented a superior effect on fibrils formation than heavy metals. Overall, this work will provide a further information into how to tune the structure of RGFs using various ions.

Effect of heat treatment on conformation and aggregation properties of wheat bran dietary fiber-gluten protein

To understand the heat mediated cross-linking mechanism of gluten in the presence of wheat bran dietary fiber (WBDF), the effect of heat treatment on conformation and aggregation properties of wheat bran dietary fiber-gluten protein was comparatively investigated in this study. The results showed G' and G" increased after adding WBDF, then decreased after heating. The SE-HPLC, chemical interaction and surface hydrophobicity analysis revealed the WBDF participated in the rearrangement of intermolecular interactions and induced depolymerization behavior behavior of gluten via disulfide and non-covalent bonds at low temperatures (25 °C and 60 °C), but heating (at 95 °C) promoted these interactions via disulfide bonds. Besides, changes in the secondary structure of gluten protein induced by WBDF during heating were correlated with the steric hindrance and hydroxyl groups on WBDF. These results suggested that WBDF impeded the cross-linking and aggregation of gluten through the rearrangement of chemical bonds and physical entanglements, then this effect was weakened at high temperatures, most likely by improving the disulfide bonds among gluten proteins. This study consummates the understanding of the cross-linking mechanisms of gluten with WBDF during heating, and provides the theoretical basis for improving the quality and acceptability of whole wheat-based products.

Gastric aggregation of micellar casein powders induced by high hydrostatic pressure: Effect of serum Ca2+ level

Micellar casein (MC) has a unique gastric colloidal behavior in response to Ca2+ cross-linking, and its aggregation properties are closely related to pepsin and gastric acid. In this study, MC with different levels of colloidal calcium phosphate (CCP) was obtained by high hydrostatic pressure (HHP) at different pressures, followed by spray drying to obtain the powders. Different amounts of calcium chloride (exogenous Ca2+) were added to MC powders prior to in vitro simulated digestion to investigate the effect of exogenous serum Ca2+ levels on the aggregation behavior and the structure change of curds generated in gastric tract. The results revealed that HHP induced the emergence of more Ca2+-binding sites, thus Ca2+ was more likely to bind to MC matrix with low CCP levels. Meanwhile, high serum Ca2+ level provided more opportunities to form aggregates. The Highest pressure (500 MPa) with the highest Ca2+ level (5 mM) caused the lowest solubility aggregates, which were only 30% at the end of gastric digestion (120 min), half of the control sample (0 MPa with 0.15 mM Ca2+). The results of wide-angle X-ray scattering / small-angle X-ray scattering suggested that both pepsin and gastric acid-induced aggregation via Ca2+ as a bridge. For pepsin, Ca2+ cross-linked between para-κ-casein; For gastric acid, Ca2+ recombined phosphorylation sites and caused cross-linking of casein subunits.

Effect of aggregation behavior on microplastic removal by magnetic Fe3O4 nanoparticles

Magnetic nanotechnologies have been shown to be an efficient approach to the reduction of microplastic (MP) pollution in aquatic environments. However, uncertainties remain regarding the relationship between particle stability and MP removal under varying water conditions, hindering the practical application of magnetic nanotechnologies for MP removal. Herein, the influence of particle aggregation behavior on nano-scale MP removal by Fe3O4 nanoparticles (FNPs) was investigated, by monitoring dynamic light scattering parameters and analyzing the microstructures of particle aggregates. Results showed that 83.1 %-92.9 % of MPs could be removed by FNPs within 1 h, and MP removal exhibited a high degree of Pearson correlation (R = 0.95; P = 0.04) with particle aggregation behavior mediated by the FNPs dosage. Furthermore, pH-dependent electrostatic interactions significantly influenced particle aggregation behavior and the removal of MPs. Under pH <6.7 conditions, electrostatic attraction between electropositive FNPs and electronegative MPs led to charge neutralization-induced aggregation and efficient removal MP performance. Under increasingly saline conditions, compression of the electrical double layer enhanced the self-aggregation behavior of MPs, weakening the electrostatic repulsion between FNPs and MPs under alkaline conditions. Therefore, salinity improved the MP removal efficiency, especially under alkaline conditions, with MP removal increasing from 4.47 % to 55.1 % when the mass fraction of NaCl was increased from 0 % to 1 %. These findings further our understanding of the effect of aggregation behavior on MP removal by FNPs and highlight the potential for magnetic nanotechnology application in the removal of nano-scale MPs from aquatic environments, while also providing valuable insights for the design of FNP-based materials.

PHEROMONE COMMUNICATION IN FEATHER-FEEDING WING LICE (INSECTA: PHTHIRAPTERA)

Pheromone communication is central to the life history of insect parasites. Determining how pheromones affect parasite behavior can provide insights into host-parasite interactions and suggest novel avenues for parasite control. Lice infest thousands of bird and mammal species and feed on the host's feathers or blood. Despite the pervasiveness of lice in wild populations and the costs they exact on livestock and poultry industries, little is known about pheromone communication in this diverse group. Here, we test for pheromone communication in the wing lice (Columbicola columbae) of Rock Doves (Columba livia). Wing lice spend the majority of their lives on bird flight feathers where they hide from host preening by inserting their bodies between coarse feather barbs. To feed, wing lice must migrate to bird body regions where they consume the insulating barbs of contour feathers. We first show that wing lice readily form aggregations on flight feathers. Next, using a Y-tube olfactometer, we demonstrate that wing lice use pheromone communication to move toward groups of nearby conspecifics. This pheromone is likely an aggregation pheromone, as wing lice only produce the pheromone when placed on flight feathers. Finally, we found that when forced to choose between groups of male and female lice, male lice move toward male groups and females toward female groups, suggesting the use of multiple pheromones. Ongoing work aims to determine the chemical identity and function of these pheromones.

Coexistence of aggregates and flat states of hydrophobically modified sodium alginate at an oil/water interface: A molecular dynamics study

Hydrophobically modified sodium alginate stabilizes benzene in water emulsions. The stability of the emulsion is related to the interface properties at the mesoscopic scale, but the details of the polymer adsorption, conformation and organization at oil/water interfaces at the microscopic scale remain largely elusive. In this study, hydrophobically modified sodium alginate was used as a representative of amphiphilic polymers for prediction of distribution of HMSA at the oil/water interface by coarse-grained molecular dynamics simulation. The result showed that driven by the interaction energy between the hydrophobic segment and benzene, HMSA will actively accumulate at the oil/water interface. The HMSA molecules parallel to the oil/water interface prevent the hydrophobic segments in the micelles from approaching the oil/water interface, so that the micelles can exist stably by steric hindrance. This study would be helpful to understand the aggregation behavior of amphiphilic polymers at the oil/water interface, these results can have applications in diverse sectors such as drug, food industry, where polymers are used to stabilize emulsions.

The aggregation of natural inorganic colloids in aqueous environment: A review

Natural inorganic colloids (NICs) are the most common and dominant existence in the ecosystem, with high concentration and wide variety. In spite of the low toxicity, they can alter activity and mobility of hazardous engineered nanoparticles (ENPs) through different interactions, which warrants the necessity to understand and predict the fate and transport of NICs in aquatic ecosystems. Here, this review summarized NICs properties and behaviors, interaction mechanisms and environmental factors at the first time. Various representative NICs and their physicochemical properties were introduced across the board. Then, the aggregation and sedimentation behaviors were discussed systematically, mainly concerning the heteroaggregation between NICs and ENPs. To speculate their fate and elucidate the corresponding mechanisms, the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (X-DLVO) theories were focused. Furthermore, a range of intrinsic and extrinsic factors was presented in different perspective. Last but not the least, this paper pointed out theoretical and analytical gaps in current researches, and put forward suggestions for further research, aiming to provide a more comprehensive and original perspective in the fields of natural occurring colloids.

Effect of curdlan on the aggregation behavior and structure of gluten in frozen-cooked noodles during frozen storage

Due to the crucial role of gluten network in maintaining the tensile properties of frozen-cooked noodles (FCNs), the underlying mechanism of protective effect of curdlan on FCNs quality during frozen storage was explored from the perspective of aggregation behavior and structure of gluten in this study. The results showed that curdlan weakened the depolymerization behavior of gluten proteins through inhibiting the disruption of disulfide bonds; Curdlan stabilized the secondary structure of gluten proteins by restraining the transformation of compact α-helices to other secondary structures; Atomic force microscope results implied that curdlan inhibited the aggregation of gluten chains; Confocal laser scanning microscopy observation analyzed by AngioTool software indicated that the connectivity and uniformity of gluten network were enhanced because of curdlan. This study may provide more comprehensive theories for the strengthening effect of curdlan on FCNs quality from the perspective of gluten structure and contribute to the quality improvement of FCN in the food technology field.

Synthesis, Aggregation Behavior and Drug-binding Interactions of Fatty acid-imidazolium-based Surface-active Ionic Liquids

The renewable fatty acid-based surface-active ionic liquids (SAILs) containing ethyl-substituted imidazolium head groups were prepared and structurally analyzed by Fourier transform infrared spectroscopy (FTIR), ¹HNMR and ¹³CNMR spectroscopy. The products were named as; 3-ethyl-1-(2-dodecanoyl oxy) ethylimidazolium bromide [C₁₂Eeim]Br, 3-ethyl-1-(2-tetradecanoyl oxy) ethylimidazolium bromide [C₁₄Eeim]Br and 3-ethyl-1-(2-hexadecanoyl oxy) ethylimidazolium bromide [C₁₆Eeim]Br. The critical micelle concentration (cmc) values of the three SAILs have been evaluated using conductivity measurements, probe-less UV-visible spectroscopy and fluorescence spectroscopy. The obtained cmc values were compared with the earlier reported non-functionalized SAILs such as [C_nmim]Br and [C_neim]Br where n= 12, 14, 16. The values were found to be 3 to 9 times lower mainly due to the presence of ester chain and also ethyl substituted imidazole ring. Thermodynamic parameters were evaluated by conductivity data at three different temperatures. Further, the aggregation behavior of SAILs with anesthetic drug, lidocaine hydrochloride (LC) has been studied using fluorescence. The fluorescence and UV-visible studies showed strong synergistic interactions operating between SAILs and drug molecules involving H bonding and cation-π interactions. The interactions grew stronger with the elongation of SAIL-chain length (12C-16C). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements suggested the formation of vesicles in SAIL-LC mixtures. These studies may thus offer an effective candidate which would serve as vectors for drug molecules in terms of their enhanced solubilization, permeability and target-specific delivery.

Dynamic interactive self organizing aggregation method in swarm robots

The present study aims to propose a dynamic interactive self-organizing aggregation (DISA) method for swarm robots. The proposed method was determined by way of the movement of swarm robots, obstacle, and robot sensors. The controller used in the DISA method helps the state selector decide through the utilization of these sensors. Systematic simulations were conducted a different number of robots {10, 25, 50}, different detection radii {3, 4} and different arena sizes {40 × 40, 50 × 50, 60 × 60}. The performance of aggregation behavior was compared with other aggregation methods recommended in literature using Total Distance (TD) between robots, Cluster Metrics (CM), Expected Cluster Size (ECS) metric and aggregation completion time. Moreover, noise at different intensities was applied to sensor inputs of the robots. The robustness of the effect of increasing noise on aggregation behavior was examined comparatively. Consequently, the simulation results based on the other compared methods indicated that the utilization of the proposed DISA method led to a higher performance by 88% in the ECS and CM metric as well as in all TD metric measurements and aggregation completion time results.

Effect of sodium tripolyphosphate on the interaction and aggregation behavior of ovalbumin-lysozyme complex

The mechanism by which sodium tripolyphosphate affected the aggregation behavior of ovalbumin-lysozyme complexes was investigated in this work. The highest stability coefficients were detected for natural ovalbumin and lysozyme at pH 9.0 and pH 5.0, with values of 0.981 and 0.931, respectively. The turbidity of the phosphorylated ovalbumin-lysozyme complexes was 1.71-fold to the natural complexes at pH 7.0. This result was related to the fact that the phosphorylated sample had a lower isoelectric point. Besides, both intermolecular forces and SDS-PAGE analysis indicated that the disulfide bond was the most important interaction in the complex. Circular dichroism analysis showed that phosphorylation weakened the unfolding and stretching of the structure caused by heat treatment. Moreover, transmission electron microscopy pictures confirmed that the network structure of phosphorylated ovalbumin-lysozyme complex was broader than natural protein. This study provides information for further understanding the effect of phosphorylation on protein aggregation behavior.

Unraveling the interaction mechanism between collagen and alcohols with different chain lengths and hydroxyl positions

The present study systematically investigated the effects of alcohols, including methanol, ethanol, n-butanol, and propanol with different hydroxyl group numbers and locations on the thermal stability and molecular aggregation behavior of collagen. The results of ultra-sensitive differential scanning calorimetry (US-DSC), dynamic light scattering (DLS) and intrinsic fluorescence showed that with the increase of carbon chain length, alcohols can denature collagen, accompanied by transition in triple helical structure, promoted aggregation behavior, and altered molecular interactions. However, with the number of hydroxyl groups in alcohol molecules increased, the thermal stability of collagen increased and the molecules tended to disperse. Furthermore, radial distribution function (RDF) results showed that alcohols can change the structure of the hydration layer around collagen, thus altering the aggregation morphology of collagen molecules in solution. The results of the interaction between components in different alcohol systems demonstrated that with the decrease of alcohol polarity, bridge bond networks were formed between collagen molecules. Specifically, it was found that because the hydroxyl groups in 1,3-propanediol are located at both ends of the carbon chain, the reticular bridge bond structure formed between the collagen molecules changed into chain-like bridge structure. The bridge bonds between collagen molecules were considered to be weak cross-linking, which was an important reason for the destruction of collagen structure. In this study, the mechanism of interaction between different alcohols and collagen was elucidated, which will be helpful for further development of complex alcohol and collagen products.

Interactions between gluten and water-unextractable arabinoxylan during the thermal treatment

This study aimed to investigate the interactions between gluten and water-unextractable arabinoxylan (WUAX), which changed the conformation and aggregation of gluten during the thermal treatment. In this work, the interactions between water-unextractable arabinoxylan and wheat gluten during thermal treatment were extensively evaluated by different techniques. The results showed that the extra WUAX could impair the viscoelasticity as well as weaken the thermal properties of gluten. The fluorescence spectra revealed the extra WUAX changed the conformation of gluten molecules. Besides, chemical interaction measurement indicated that the extra WUAX prevented the formation of partial disulfide bonds and had a major effect on the hydrophobic interaction of gluten. In summary, these results indicated that WUAX disrupted the covalent crosslinking by affecting disulfide bonds between gluten proteins, and dominated the folding/unfolding process of gluten via the competition with gluten for water, resulting in the poor quality of whole wheat-based foods.

Predicting the aggregation tendency of oxidized nanoscale zero-valent iron in aquatic environments

Predicting the aggregation tendency of nanoscale zero-valent iron (nZVI), oxidized nZVI, in particular, is crucial for the risk assessment of nZVI in aquatic environments. In this study, the comprehensive effects of the pH and ionic strength (IS) on the aggregation behaviors of two highly oxidized nZVIs (HO-nZVI) were examined. Compared with hematite nanoparticles, HO-nZVI presented a sudden acceleration in aggregation under critical conditions; moreover, the morphology of the HO-nZVI aggregates at pH and IS values higher or lower than the critical conditions was significantly different. Furthermore, owing to the differences in magnetization between the two prepared HO-nZVI samples, their critical coagulation conditions were significantly different. The significant changes in the aggregation behavior of the HO-nZVI samples were analyzed using colloidal theories, and the aggregation tendency of HO-nZVI under specific conditions could be simulated by calculating the theoretical critical conditions of aggregation via a method that takes into account the hydrochemical properties, magnetization, and surface charge of HO-nZVI. To examine the correctness of the method, we compared the experimentally determined colloidal stability of HO-nZVI in water samples collected from nearby rivers with the theoretically predicted value. The results indicated that the method was adequate for most situations, except for those in which the hydrochemical properties of the water samples were close to the critical coagulation conditions. Our study proposes a theoretical approach that is viable for simulating the colloidal stability of magnetic nanoparticles in aquatic environments; we anticipate that it will further facilitate the risk assessment of nanoparticles.

Gel properties of salty liquid whole egg as affected by preheat treatment

Heat treatment is an indispensable processing step of seasoned liquid egg. The effects of preheat treatment (60-75 °C) on gel properties of liquid whole egg (LWE) at different NaCl concentrations (0-3%, w/w) were investigated to provide guidance for the production of salty LWE. Results showed that LWE exhibited higher particle size after heating, with coincidental increases in surface hydrophobicity and decreases in protein solubility. While LWE with NaCl added exhibited increase in protein solubility and decrease in particle size of aggregates. Electrophoresis and optical microscopy showed that NaCl would induce the transformation of egg granules from insoluble form to soluble form, inhibiting the aggregation of LWE proteins during preheat treatment, reflected by the reduced particle size. The analysis of gel aggregated force and texture indicated that NaCl addition and preheat treatment can improve gelling properties of LWE synergistically by strengthening the hydrophobic interaction and hydrogen bonds.

Environmental and physiological determinants of huddling behavior of molting female southern elephant seals (Mirounga leonina)

While endotherms can rely on their insulation to reduce heat loss to adapt to cold environments, renewing of fur during molt impairs insulation while they have to perfuse the periphery to support epidermal tissues. The southern elephant seal Mirounga leonina undertakes an annual catastrophic molt while fasting on land in a wet, windy and cold environment. However, southern elephant seals show characteristic aggregation patterns that are predicted to reduce high metabolic costs during the molt. Between 2012 and 2016, 59 female elephant seals were tracked on land during their molt to study their aggregation behavior in relation to molt stage, habitat type and local weather conditions. Infrared thermography and stomach temperature loggers were used to observe variation in body surface and internal temperature in relation to molt stage and aggregation behavior. We found that thermal constraints varied during the molt, with a peak in surface temperature during the mid-stage of the molt. Wallows (mud pools) appear as favorable habitat to aggregate while molting. Indeed, wallows offered a warmer microclimate with greater ground temperature and lower wind speed. Moreover, there was a greater proportion of aggregated seals and larger group size in wallows. These aggregation patterns in wallows were influenced by local weather such that a greater proportion of seals were located in the center of the aggregation, and larger group size occurred during days of unfavorable meteorological conditions. We also observed a higher proportion of seals at mid-stage of molt amongst aggregated seals compared to isolated individuals. This aggregation behavior may reduce the cost of thermogenesis as surface body temperature and stomach temperature were cooler by 1.0 °C and 1.5 °C, respectively, in aggregated compared to isolated seals. As a consequence, huddling behavior may be thermally advantageous for female southern elephant seals during the molt.

Characterization, origin and aggregation behavior of colloids in eutrophic shallow lake

Stability of colloidal particles contributes to the turbidity in the water column, which significantly influences water quality and ecological functions in aquatic environments especially shallow lakes. Here we report characterization, origin and aggregation behavior of aquatic colloids, including natural colloidal particles (NCPs) and total inorganic colloidal particles (TICPs), in a highly turbid shallow lake, via field observations, simulation experiments, ultrafiltration, spectral and microscopic, and light scattering techniques. The colloidal particles were characterized with various shapes (spherical, polygonal and elliptical) and aluminum-, silicon-, and ferric-containing mineralogical structures, with a size range of 20-200 nm. The process of sediment re-suspension under environmentally relevant conditions contributed 78-80% of TICPs and 54-55% of NCPs in Lake Taihu, representing an important source of colloids in the water column. Both mono- and divalent electrolytes enhanced colloidal aggregation, while a reverse trend was observed in the presence of natural organic matter (NOM). The influence of NOM on colloidal stability was highly related to molecular weight (MW) properties with the high MW fraction exhibiting higher stability efficiency than the low MW counterparts. However, the MW-dependent aggregation behavior for NCPs was less significant than that for TICPs, implying that previous results on colloidal behavior using model inorganic colloids alone should be reevaluated. Further studies are needed to better understand the mobility/stability and transformation of aquatic colloids and their role in governing the fate and transport of pollutants in natural waters.

Self-aggregation of bio-surfactants within ionic liquid 1-ethyl-3-methylimidazolium bromide: A comparative study and potential application in antidepressants drug aggregation

Aggregation behavior of bio-surfactants (BS) sodium cholate (NaC) and sodium deoxycholate (NaDC) within aqueous solution of ionic liquid (IL) 1-ethyl-3-methylimidazolium bromide [Emim][Br] has been investigated using surface tension, conductivity, steady state fluorescence, FT-IR and dynamic light scattering (DLS) techniques. Various interfacial and thermodynamic parameters are determined in the presence of different wt% of IL [Emim][Br]. Information regarding the local microenvironment and size of the aggregates is obtained from fluorescence and DLS, respectively. FT-IR spectral response is used to reveal the interactions taking place within aqueous NaC/NaDC micellar solutions. It is noteworthy to mention that increasing wt% of [Emim][Br] results in an increase in the spontaneity of micelle formation and the hydrophilic IL shows more affinity for NaC as compared to NaDC. Further, the micellar solutions of BS-[Emim][Br] are utilized for studying the aggregation of antidepressants drug promazine hydrochloride (pH). UV-vis spectroscopic investigation reveals interesting outcomes and the results show changes in spectral absorbance of PH drug on the addition of micellar solution (BS-[Emim][Br]). Highest binding affinity and most promising activity are shown for NaC as compared to NaDC.

Towards a better understanding on aggregation behavior of CeO2 nanoparticles in different natural waters under flow disturbance

The fate of nanoparticles in natural waters is affected by the combination of various factors, especially the flow disturbance which plays a decisive role in the transport of nanoparticles. This study investigated the aggregation behavior of CeO₂ nanoparticles (NPs) in natural waters by using a unique instrument to simulate flow disturbance. The results indicated that, in the absence of a shear force, the CeO₂ NPs formed linear, chain-like aggregates in seawater, owing to the high IS, which compressed the electrical double layer of particles. On the other hand, the NPs formed more compact aggregates in lake water, owing to an ion bridge effect between the NPs and the dissolved organic matter (DOM). It was also found that shear forces affected the aggregation behavior of the NPs. A low shear force promoted the aggregation of the NPs by increasing the collision efficiency while the aggregates were broken by a high shear force. Remarkably, the NPs maintained their potential for continuous aggregation when the slow stirring was reintroduced, suggesting that the aggregates began to grow again under renewed stirring. The results of this study could help in predicting the fate and transport behavior of CeO₂ NPs in actual aquatic environments.

Tuning magnetic relaxation properties of "hard cores" in core-shell colloids by modification of "soft shell"

The present work introduces an impact of polyelectrolyte-based hydrophilic shell on magnetic relaxivity and luminescence of hard cores built from isostructural complexes of Tb(III) and Gd(III) in the core-shell aqueous colloids. Microscopic and scattering techniques reveal "plum pudding" morphology of the colloids, where polyelectrolyte-coated ultrasmall (<5nm) hard cores form aggregates in aqueous solutions. Interaction of bovine serum albumin (BSA) with the colloids provides a tool to modify the polyelectrolyte-based shell, which is the reason for the improvement in both aggregation behavior of the colloids and their relaxivity. The modification of the hydrophilic polyelectrolyte-based shell enables to tune the longitudinal relaxivity from 5.9 to 23.3mM^-1s^-1 at 0.47T. This tendency is the reason for significant improvement of contrasting effect of the colloids in T₁- and T₂-weighted images obtained by whole body scanner at 1.5T. High contrasting effect of the colloids, together with low cytotoxicity towards Wi-38 diploid human cells makes them promising MRI contrast agents.

Aggregation and rheological behavior of soluble dietary fibers from wheat bran

The present study assesses the aggregation behavior of wheat bran arabinoxylan-rich soluble dietary fiber (SDF) fractions with diverse molecular weight and substitution in order to provide useful information to prevent the formation of a block network. In the present work, dynamic and static light scattering, diffusing wave spectroscopy, small amplitude dynamic rheology, atomic force microscopy, and the water-holding and swelling capacities were evaluated to assess the SDF aggregation behavior induced by intrinsic and extrinsic factors. Furthermore, the rheological behavior was explained by the physically cross-linked or interpenetrating hydrocolloid network established during SDF self-aggregation, dependent on its molecular structure. The results indicated that the SDF fractions exhibiting a high molecular weight and a lower substitution degree and di-substituted ratio led to more significant aggregation due to the formation of disordered tangles coupled with a more solid-like behavior. The obtained information will prove useful for the development of more stable and compatible SDF fractions.

Discrimination between lineage-specific shelters by bat- and human-associated bed bugs does not constitute a stable reproductive barrier

The common bed bug Cimex lectularius, has been recently shown to constitute two host races, which are likely in the course of incipient speciation. The human-associated lineage splits from the ancestral bat-associated species deep in the history of modern humans, likely even prior to the Neolithic Period and establishment of the first permanent human settlements. Hybridization experiments between these two lineages show that post-mating reproductive barriers are incomplete due to local variation. As mating takes place in off-host refugia marked by aggregation semiochemicals, the present investigation tested the hypothesis that bed bugs use these semiochemicals to differentiate between refugia marked by bat- and human-associated bed bugs; this would constitute a pre-copulation isolation mechanism. The preference for lineage-specific odors was tested using artificial shelters conditioned by a group of either male or female bed bugs. Adult males were assayed individually in four-choice assays that included two clean unconditioned control shelters. In most assays, bed bugs preferred to rest in conditioned shelters, with no apparent fidelity to shelters conditioned by their specific lineage. However, 51 % of the bat-associated males preferred unconditioned shelters over female-conditioned shelters of either lineage. Thus, bed bugs show no preferences for lineage-specific shelters, strongly suggesting that semiochemicals associated with shelters alone do not function in reproductive isolation.

Micelle co-assembly in surfactant/ionic liquid mixtures

HYPOTHESIS

The phase behavior of amphiphiles is known to depend on their solvent environment. The organic character of ionic liquids suggested the possibility to tune surfactant aggregation, even in the absence of water, by selection of appropriate ionic liquid chemistry. To that end the behavior of the surfactant sodium dodecylsulfate in a chemically similar imidazolium ionic liquid, 1-ethyl-3-methyl imidazolium ethylsulfate, was explored.

EXPERIMENTS

The solubility of sodium dodecylsulfate in 1-ethyl-3-methyl imidazolium ethylsulfate was determined, establishing the Krafft temperature. Tensiometry was performed to obtain interfacial properties such as the surface excess and area per molecule. Pulsed-field gradient spin-echo NMR was used to determine the diffusion coefficients of all the major species, including micelles, as a function of surfactant concentration. Importantly, all three methods provided consistent values for the critical micelle concentration.

FINDINGS

Analysis of tensiometry data suggests, and is confirmed by NMR results, that the ionic liquid ions are incorporated along with surfactants into micelles, revealing a complex micellization behavior. In light of these findings past studies with ternary mixtures of surfactants, ionic liquids, and water may merit additional scrutiny. Given the large number of ionic liquids, this work suggests opportunities to further control micelle formation and properties.

Identification of a self-regulatory pheromone system that controls nymph aggregation behavior of rice spittlebug Callitettix versicolor

BACKGROUND

Nymphs of many spittlebug species are known to aggregate in one spittle mass, a behavior which greatly benefits the survival of the developing nymphs. Little is known, however, about the precise mechanisms that induce and regulate aggregation. Here, we investigated the aggregation behavior of nymphs of the rice spittlebug Callitettix versicolor, and analyzed the chemical composition of spittle masses.

RESULTS

We identified six n-alkane compounds, namely un-, do-, tri-, tetra-, penta- and hexadecane in the spittle mass. Importantly, we showed that solitary spittle mass (SSM) and aggregation spittle mass (ASM) differed significantly in the amounts and composition of these compounds. While un-, do-, tri-, tetra-and hexadecane were overrepresented in SSM, pentadecane was found at significantly higher levels in ASM. Electrophysiological experiments showed that antennae responses to these six compounds were significantly higher than to both the hexane and the docosane control, which suggests a specific role of the six volatile alkanes as pheromones. In agreement with this hypothesis, behavioral tests revealed that five of the six compounds (e.g. un-, do-, tri-, tetra-, and hexadecane) acted as attractants across a wide concentration range. Thus, these five compounds allow recruitment of additional nymphs to a growing spittle mass. The sixth compound, pentadecane, attracted nymphs at low doses, whereas at higher doses, this effect vanished, suggesting that this alkane functioned as a repellent, thus preventing recruitment of additional individuals to a full aggregation in a spittle mass.

CONCLUSIONS

In summary, our study identified a simple, yet fully functional feedback mechanism which allows aggregation at low nymph numbers, while preventing over-crowding beyond a set number of nymphs within one spittle mass. In conclusion, our study provides new insights into C. versicolor development and behavior that should greatly facilitate the identification of new approaches for pheromonal control of this pest.

Heterologous expression of a fungal sterol esterase/lipase in different hosts: Effect on solubility, glycosylation and production

Ophiostoma piceae secretes a versatile sterol-esterase (OPE) that shows high efficiency in both hydrolysis and synthesis of triglycerides and sterol esters. This enzyme produces aggregates in aqueous solutions, but the recombinant protein, expressed in Komagataella (synonym Pichia) pastoris, showed higher catalytic efficiency because of its higher solubility. This fact owes to a modification in the N-terminal sequence of the protein expressed in Pichia pastoris, which incorporated 4-8 additional amino acids, affecting its aggregation behavior. In this study we present a newly engineered P. pastoris strain with improved protein production. We also produced the recombinant protein in the yeast Saccharomyces cerevisiae and in the prokaryotic host Escherichia coli, corroborating that the presence of these N-terminal extra amino acids affected the protein's solubility. The OPE produced in the new P. pastoris strain presented the same physicochemical properties than the old one. An inactive form of the enzyme was produced by the bacterium, but the recombinant esterase from both yeasts was active even after its enzymatic deglycosylation, suggesting that the presence of N-linked carbohydrates in the mature protein is not essential for enzyme activity. Although the yield in S. cerevisiae was lower than that obtained in P. pastoris, this work demonstrates the importance of the choice of the heterologous host for successful production of soluble and active recombinant protein. In addition, S. cerevisiae constitutes a good engineering platform for improving the properties of this biocatalyst.

Oxidation of nanoscale zero-valent iron under sufficient and limited dissolved oxygen: Influences on aggregation behaviors

Oxidations of nanoscale zero-valent iron (nZVI) under aerobic (dissolved oxygen≈8mgL(-1)) and anaerobic (dissolved oxygen <3mgL(-1)) conditions were simulated, and their influences on aggregation behaviors of nZVI were investigated. The two oxidation products were noted as HO-nZVI (nZVI oxidized in highly oxygenated water) and LO-nZVI (nZVI oxidized in lowly oxygenated water) respectively. The metallic iron of the oxidized nZVI was almost exhausted (Fe(0)≈8±5%), thus magnetization mainly depended on magnetite content. Since sufficient dissolved oxygen led to the much less magnetite (∼15%) in HO-nZVI than that in LO-nZVI (>90%), HO-nZVI was far less magnetic (Ms=88kAm(-1)) than LO-nZVI (Ms=365kAm(-1)). Consequently, HO-nZVI formed small agglomerates (228±10nm), while LO-nZVI tended to form chain-like aggregations (>1μm) which precipitated rapidly. Based on the EDLVO theory, we suggested that dissolved oxygen level determined aggregation morphologies by controlling the degree of oxidation and the magnitude of magnetization. Then the chain-like alignment of LO-nZVI would promote further aggregation, but the agglomerate morphology of HO-nZVI would eliminate magnetic forces and inhibit the aggregation while HO-nZVI remained magnetic. Our results indicated the fine colloidal stability of HO-nZVI, which might lead to the great mobility in the environment.

Self-assembly of different single-chain bolaphospholipids and their miscibility with phospholipids or classical amphiphiles

A variety of bolalipids with a single long alkyl chain and two identical headgroups self-assemble in aqueous solutions into helical entangled nanofibers leading to the formation of a hydrogel. An increase in temperature usually leads to the break-up of the fiber structure into micellar aggregates. In this paper the question is addressed whether bolalipids of different lengths or different headgroup structures can form mixed fibers. Also, the stability of the fiber aggregation of bolalipids in mixtures with phospholipids forming lamellar bilayers is discussed. Here, the question whether single-chain bolalipids can be incorporated into phospholipid bilayers to stabilize bilayer membranes is important, as possibly lipid vesicles used for drug delivery can be improved. Finally, the stability of the fiber aggregate against solubilisation by common surfactants was studied. The paper addresses the question which type of aggregate structure dominates the self-assembly of bipolar and monopolar amphiphiles in aqueous suspension.