Aggregation Reaction Research Articles

High-Yield α-Synuclein Purification and Ionic Strength Modification Pivotal to Seed Amplification Assay Performance and Reproducibility.

Alpha-synuclein seed amplification assays (αSyn-SAAs) have emerged as promising diagnostic tools for Parkinson's disease (PD) by detecting misfolded αSyn and amplifying the signal through cyclic shaking and resting in vitro. Recently, our group and others have shown that multiple biospecimens, including CSF, skin, and submandibular glands (SMGs), can be used to seed the aggregation reaction and robustly distinguish between patients with PD and non-disease controls. The ultrasensitivity of the assay affords the ability to detect minute quantities of αSyn in peripheral tissues, but it also produces various technical challenges of variability. To address the problem of variability, we present a high-yield αSyn protein purification protocol for the efficient production of monomers with a low propensity for self-aggregation. We expressed wild-type αSyn in BL21 Escherichia coli, lysed the cells using osmotic shock, and isolated αSyn using acid precipitation and fast protein liquid chromatography (FPLC). Following purification, we optimized the ionic strength of the reaction buffer to distinguish the fluorescence maximum (Fmax) separation between disease and healthy control tissues for enhanced assay performance. Our protein purification protocol yielded high quantities of αSyn (average: 68.7 mg/mL per 1 L of culture) and showed highly precise and robust αSyn-SAA results using brain, skin, and SMGs with inter-lab validation.

EFhd2 co-aggregates with monomeric and filamentous tau in vitro.

Tauopathies are characterized by the abnormal buildup of tau protein, with early oligomeric forms associated with neurodegeneration and the later neurofibrillary tangles possibly conferring neuroprotection. The molecular mechanisms governing the formation of these tau species are unclear. Lately, there has been an increased focus on examining the interactions between tau and other proteins, along with their influence on the aggregation of tau. Our previous work revealed EFhd2's association with pathological tau in animal models and tauopathy brains. Herein, we examined the impact of EFhd2 on monomeric and filamentous tau in vitro. The results demonstrated that EFhd2 incubation with monomeric full length human tau (hTau40) formed amorphous aggregates, where both EFhd2 and hTau40 colocalized. Moreover, EFhd2 is entangled with arachidonic acid (ARA)-induced filamentous hTau40. Furthermore, EFhd2-induced aggregation with monomeric and filamentous hTau40 is EFhd2 concentration dependent. Using sandwich ELISA assays, we assessed the reactivity of TOC1 and Alz50-two conformation-specific tau antibodies-to EFhd2-hTau40 aggregates (in absence and presence of ARA). No TOC1 signal was detected in EFhd2 aggregates with monomeric hTau40 whereas EFhd2 aggregates with hTau in the presence of ARA showed a higher signal compared to hTau40 filaments. In contrast, EFhd2 aggregates with both monomeric and filamentous hTau40 reduced Alz50 reactivity. Taken together, our results illustrate for the first time that EFhd2, a tau-associated protein, interacts with monomeric and filamentous hTau40 to form large aggregates that are starkly different from tau oligomers and filaments. Given these findings and previous research, we hypothesize that EFhd2 may play a role in the formation of tau aggregates. Nevertheless, further in vivo studies are imperative to test this hypothesis.

Induction of Salmonella Enteritidis into a Viable but Nonculturable State by Cinnamaldehyde and Its Resuscitation.

Trans-cinnamaldehyde (TC), a typical plant-derived compound, has been widely used in the control of foodborne pathogen contamination. Nevertheless, the risk associated with the occurrence of viable but nonculturable (VBNC) bacteria induced by TC remains unclear. The results of this study showed that Salmonella Enteritidis (S. Enteritidis) entered the VBNC state after being induced by TC at a minimum inhibitory concentration of 312.5 μg/mL and survived for at least 22 days under TC treatment. Enhanced resistance was found against heat treatment (75°C, 30 s), antibiotics (i.e., ampicillin, ceftriaxone sodium, chloramphenicol), and hydrogen peroxide (3%) in VBNC S. Enteritidis. A synergistic effect against VBNC S. Enteritidis occurred when TC was combined with acid treatment, including lactic acid and acetic acid (pH = 3.5). VBNC and resuscitated S. Enteritidis by sodium pyruvate treatment (100 mM) were found to retain the infectious ability to Caco-2 cells. Relative expression levels of the stress-related genes relA, spoT, ppx, lon, katG, sodA, dnaK, and grpE were upregulated in VBNC S. Enteritidis. Accumulation of reactive oxygen species (ROS) and protein aggregates was observed in VBNC cells. Besides, the resuscitation of VBNC cells was accompanied with clearance of ROS and protein aggregates. In summary, this study presents a comprehensive characterization of stress tolerance and resuscitation of VBNC S. Enteritidis induced by cinnamaldehyde, and the results provide useful information for the development of effective control strategy against VBNC pathogenic bacteria in food production.

Permittivity analysis of weathered concrete in a bridge based on open-ended probe and impedance measurements

Pathologies like corrosion of rebars or alkali aggregate reactions in a reinforced concrete (RC) bridge are usually accompanied by the existence of aqueous pore solutions with a high concentration of ions. The distribution of aqueous solutions in the concrete is inhomogeneous and depends on the RC’s location in the bridge and complex climate factors. Frequency-dependent complex permittivity is sensitive to aqueous pore solutions because the high conductivity caused by charge carriers can result in a large imaginary part of the permittivity, much higher than that caused by water. In this study, we used a non-destructive open-ended probe to measure the complex permittivity of the RC in a bridge’s pillar with different levels of pathologies. By measuring the impedance of core samples with various controlled water volumetric fractions in the laboratory, the water effect on the evolution of the loss tangent (the ratio between the imaginary part of the permittivity and the real part) can be calibrated. Comparing the loss tangent in the bridge with that of the core samples treated by water, we can map the areas with a high density of aqueous pore solution and cracks, and estimate the unhealthy area with partial damage in the pillar by an effective and non-destructive diagnosis.

The alkali–silica reaction of seawater-mixed mortar

The application of seawater concrete is receiving increasing attention due to the advantage of using seawater in alleviating water scarcity. One concern with seawater concrete applications is the potential for alkali–silica reaction (ASR) due to the elevated alkali concentration. In this paper, the ASR risk induced by mixed seawater in cement mortar incorporating non-reactive or reactive aggregates (RAs) was studied through short-term and long-term experiments. Experimental results indicate that seawater only increased ASR in the presence of RAs due to the high alkali concentration. Replacing cement with 70% ground granulated blast-furnace slag (GGBS) prevented expansion, although very few ASR products may be observed. SEM results indicated that seawater decreases the (Na + K)/Si ratio and increases the Ca/Si ratio of ASR products slightly. Compared with cement mortar, C–S–H in GGBS blended cement mortar has a higher (Na + K)/Si ratio, which indicates its higher alkali binding capacity.

Elucidating the intrinsic core-shell structure of carbon nanospheres from glucose hydrothermal carbonization

This study explores the core-shell structure formation mechanisms of primary carbon nanospheres (PCNs) through hydrothermal carbonization (HTC) of glucose at 200 °C, focusing on key phase-change polymerization reactions. Colloidal carbon nanoparticles in the aqueous phase filtrate self-assembled into secondary carbon nanospheres (SCNs) with intrinsic hollow structures during room temperature storage. FTIR results revealed similar functional groups on the surfaces of PCNs and SCNs due to esterification reactions during HTC cooling. XPS and 13 C NMR analyses identified HMF aldol condensation and etherification as dominant reactions for PCNs, while esterification and aldol condensation with levulinic acid were dominant for SCNs. The hypothesis suggests that PCNs initially formed hollow microframeworks but collapsed due to consumption of encapsulated organics, resulting in hydrophobic cores. These cores grew through aggregation (linear) and surface reactions (exponential), internalizing hydrophilic surfaces into hydrophobic cores, forming the final core-shell structure of PCNs.

Alkali-silica reaction of ferronickel slag fine aggregate in Portland cement and alkali-activated slag mortars: Pessimum effect investigation

Ferronickel slag (FNS) with dense and hard nature exhibits great potential to be utilized as recycled aggregate in concrete production. This study investigated the alkali-silica reaction (ASR) and the pessimum proportion of FNS fine aggregate in Portland cement (PC) and alkali-activated ground granulated bast furnace slag (AAS) mortars as a substitute for river sand. Over a 120-day period, the accelerated mortar bar test revealed that the addition of FNS fine aggregate in both cases resulted in harmless ASR expansion. In PC mortars, the ASR expansion consistently decreased from 0.569 % to 0.114 % as the FNS content increased. In comparison, AAS mortars with higher pore solution alkalinity had the pessimum proportion of 30 % FNS. The ASR expansion values initially increased from 0.472 % to 0.554 % with an increase in FNS content from 0 % to 30 %, but then decreased to 0.146 % as the FNS content was further raised to 100 %. The amorphous ASR gel was identified as a hydrated alkali silicate gel and present within the existing veins in the river sand grain. The ASR reaction of FNS fine aggregate exhibited a self-mitigating effect on the deleterious expansion through its pessimum behavior. Additionally, the addition of FNS fine aggregate yielded a beneficial outcome by reducing the cumulative pore volume in the mortars, and thus enhanced the compressive strengths.

Adiabatic Potential for Conformational Change of VGa–VN Complex Defects in GaN

Focusing on a VGa–VN complex vacancy defect in GaN, the adiabatic potential for conformational changes of the VGa–VN is investigated using the density functional theory. There are two types of configurations due to the symmetry of the crystal, it is confirmed that there is almost no difference in their stability or electronic state. Using these configurations as the initial and final states, the defect reaction is analyzed when VGa–VN moves using the climbing‐image nudged elastic band method. The reaction barrier for the migration of VGa (VN) is found to be 2.2 (3.3) eV. It is concluded that these reactions occur frequently as GaN is annealed since the atomic diffusion potential barrier is similar to that in other semiconductors. These results suggest that VGa–VN in GaN moves through the crystal as a pair of vacancies by alternately repeating the VGa and the VN migration. These results provide important knowledge for elucidating the microscopic mechanism of the experimentally observed VGa–VN aggregation reaction.

From risk study to field evidence: an unprecedented and isolated case of delayed ettringite formation in Brazil

This paper describes the first ever reported case in Brazil where delayed ettringite formation (DEF) has been confirmed as the sole cause of deterioration in field concrete. Still under construction and less than 2 years old, numerous cracks were observed in the foundation structures of a building located in Recife, a city known for its history of alkali–aggregate reaction (AAR) cases. In addition to a field survey of cracks, microstructural analyses, tests for residual expansion and compressive strength, a review of the structural design, determination of sulfate content in the groundwater and simplified thermal analysis were carried out. The results confirmed that DEF was the sole cause of the damage present in cast-in-place concrete structures, with no evidence of AAR or any other deterioration process. This work corroborates previously published studies on the high risk of the occurrence of DEF in the region, demonstrating the urgent need for a preventive technical standard in the country, considering the chemical composition of cements and prior thermal analyses to adopt possible preventive measures to limit the maximum internal temperature of concrete.

Copper ion incorporation in α-synuclein amyloids.

Copper ion dys-homeostasis is linked to neurodegenerative diseases involving amyloid formation. Even if many amyloidogenic proteins can bind copper ions as monomers, little is known about copper interactions with the resulting amyloid fibers. Here, we investigate copper interactions with α-synuclein, the amyloid-forming protein in Parkinson's disease. Copper (Cu(II)) binds tightly to monomeric α-synuclein in vitro involving the N-terminal amine and the side chain of His50. Using purified protein and biophysical methods in vitro, we reveal that copper ions are readily incorporated into the formed amyloid fibers when present at the start of aggregation reactions, and the metal ions also bind if added to pre-formed amyloids. Efficient incorporation is observed for α-synuclein variants with perturbation of either one of the high-affinity monomer copper-binding residues (i.e., N-terminus or His50) whereas a variant with both N-terminal acetylation and His50 substituted with Ala does not incorporate any copper into the amyloids. Both the morphology of the resulting α-synuclein amyloids (amyloid fiber pitch, secondary structure, proteinase sensitivity) and the copper chemical properties (redox activity, chemical potential) are altered when copper is incorporated into amyloids. We speculate that copper chelation by α-synuclein amyloids contributes to the observed copper dys-homeostasis (e.g., reduced bioavailable levels) in Parkinson's disease patients. At the same time, amyloid-copper interactions may be protective to neuronal cells as they will shield aberrantly free copper ions from promotion of toxic reactive oxygen species.

The use of computed tomography and scanning microscopy methods for assessing the alkaline reactivity of aggregate

The reaction of alkalis with aggregate containing reactive forms of silica (ASR) plays a significant role in shaping the durability of concrete, as the strongly hygroscopic reaction products generated lead to internal stress, causing its expansion and cracking. This study presents an extended analysis of corrosive processes occurring in mortars with reactive natural aggregate from Poland, using computed tomography and scanning microscopy methods. Numerous cracks in the grains and the surrounding cementitious matrix were observed, indicating a high degree of advancement of corrosive processes. Over time, the proportion of pores with reduced sphericity increased, indicating ongoing degradation of the mortars. The usefulness of computed tomography in studying the progress of ASR was demonstrated. Scanning microscopy confirmed that the cause of mortar degradation is the formed ASR gel with a typical composition, located within the volume of reactive grains, cracks propagating into the cementitious matrix, and accumulated in air voids.

Mitigation mechanisms of alkali silica reaction through the incorporation of colloidal nanoSiO2 in accelerated mortar bar testing

Alkali Silica Reactivity (ASR) is a prominent issue concerning the durability of concrete structures. To mitigate this deleterious reaction, a widely accepted practice involves replacing significant cement portions with supplementary cementitious materials (SCMs). Given the scarcity of high-quality SCMs, nanoSiO2 exhibits considerable promise, given its minimal dosage requirement for ASR mitigation, whether applied independently or in conjunction with other SCMs. This research investigates the efficacy and underlying mechanisms of colloidal nanoSiO2 (CNS) in accelerated mortar bar tests according to the ASTM C1260 method. The experimental methodology incorporated two distinct forms of CNSes, CNS1 and CNS2, with average particle sizes of 14 and 67 nanometers, respectively. The outcomes are subsequently compared to the ASR performance of a sample containing silica fume (SF). The results demonstrate that the CNS size is pivotal in governing the pozzolanic reaction rate. The CNS2 and SF exhibited analogous pozzolanic reactions, displaying superior effectiveness in promoting pozzolanic activity compared to the CNS1. At a 4.75% cement replacement level, the CNS2 achieved a 78% reduction in mortar expansion over the control sample. The CNS1, when utilized at 4.75% and 7% cement replacement levels, yielded expansion reductions of 38% and 43%, respectively. It was found that the inclusion of the CNS can increase the porosity of mortar and contribute to silica dissolution from the reactive aggregates. Meanwhile, the addition of CNS improved the bulk resistivity of mortar by 200%-600% and flexural strength by 25%-62% based on the replacement levels and the CNS types. Moreover, improvements in calcium hydroxide consumption and alkali binding in the ASR gel were observed during the test, indicating the underlying mechanisms for expansion mitigation. These research outcomes can accelerate the CNS utilization to mitigate the ASR in practical field applications.

Resilience in a noisy urban system

The ability of cities to recuperate from disturbances and return to their evolutionary pathways depends, first and foremost, on the type of damage that the shock created. But in addition, it depends on how information is transmitted in the urban system and on how noise filters distort the information that reaches economic agents. So long as the transmission of information does not disturb the functioning of the urban economy, shocks do not prevent the return to the long‐run evolutionary paths. We study the migration decisions of agents, following information that they receive using an agent‐based model of endogenous growth in a closed urban system. These decisions affect the spread of innovative ideas, of innovations, and the birth rate of new firms. The aggregate reactions of agents to shocks can affect the resilience of the entire urban system and of individual cities, sometimes allowing a return to the same domain, and sometimes driving the system and parts of its constituents to another regime of behavior. We analyze the repercussion of shocks on the resilience of urban systems by considering how noise in the transmission of information affects the decisions of agents at various times and locations. The conclusions are that, while information noise is a burden that constantly and systematically hinders the economic potential of the system, financial shocks reshuffle resources causing a fundamental change in the urban system trajectories.

Toward waste glass upcycling: Preparation and characterization of high-volume waste glass geopolymer composites

Portland cement-free high-volume waste glass geopolymer composite is proposed for the upcycling of glass waste. The “high-volume” is achieved by utilizing GP as the geopolymer precursor and glass cullet as the aggregate. Our observations show decent strength and durability can be obtained by the composites with up to ∼83 wt% waste glass by the mass of solid components. GP and common geopolymer precursors (class C and class F fly ash and slag) have synergistic effects on forming calcium-(sodium-)aluminosilicate hydrate (C-(N-)A-S-H) and sodium-aluminosilicate hydrate (N-A-S-H). A higher Ca content and dosage of Na2O, however, lead to a larger drying shrinkage. Although glass aggregate can reduce the shrinkage to some extent, the highly reactive aggregate may cause the progressive ASR in the Ca-rich mixtures. The ASR expansion decreases with the increasing dosage of Na2O possibly because an overly high pH in pore solution thermodynamically hindered the precipitation of ASR gels and/or a higher alkaline concentration favors the dissolution of aggregate surfaces at curing stage, and the dissolved Si participates in the hydration process.

Using Autoclave Concrete Prism Testing to Evaluate ASR Reactivity in Concrete Using Laboratory Tests and Outdoor Exposure Blocks as Benchmark Data

Abstract The alkali–silica reaction (ASR) occurs in concrete that contains silica in a reactive aggregate, sufficient alkalis, and sufficient moisture. Although the most widely accepted tests for evaluating ASR potential are the concrete prism test (CPT) and the accelerated mortar bar test, each test has limitations. Because of the need to test concrete mixes within a short period of time, an accelerated autoclave test method (autoclaved CPT [ACPT]) was investigated using concrete prism samples boosted to 3.0 % total alkali content subjected to an exposure temperature of 271°F (133°C) with a corresponding pressure of 29 psi (0.2 MPa) for 24 hours. A suite of aggregates was evaluated by concrete prism specimens using both the ACPT and CPT methods. The ACPT was able to classify individual aggregate fractions for ASR reactivity with 97.2 % accuracy for the proposed limit of 0.09 % expansion for 36 tested mixtures and approximately 130 specimens. Data from this test suggest that a week-long test could be considered an effective screening tool for the alkali reactivity of coarse or fine aggregate fractions. In addition, miniature CPT (AASHTO T 380, Standard Method of Test for Potential Alkali Reactivity of Aggregates and Effectiveness of ASR Mitigation Measures (Miniature Concrete Prism Test, MCPT) and 12-year outdoor exposure block results are evaluated and compared with both CPT and ACPT results. Although the data suggest a general agreement between these methods, further testing is warranted along with multi-laboratory precision evaluation.

Avaliação do pó de vidro na mitigação da reação álcali-sílica (RAS)

Abstract The alkali-silica reaction (ASR) is one of the problems that can compromise concrete durability, as the chemical reactions between the reactive aggregate and concrete pore solution, specifically sodium (Na+), potassium (K+), calcium (Ca2+) and hydroxyl (OH-) in the presence of moisture, trigger expansion and cracking of concrete elements. The use of pozzolanic materials, such as finely ground glass powder (particles smaller than 75μm), to partially replace cement has been widely studied and has demonstrated beneficial results. However, because the behavior of pozzolans towards ASR is not completely understood yet, this work evaluates the effect of incorporating ground glass powder into cementitious composites against ASR. To this end, 8% silica fume was used as a control admixture, and four levels of glass powder (10, 20, 30, and 50%) were incorporated into the cementitious mixture to partially replace cement. Expansion tests were carried out in accordance with NBR15577-4 (ABNT, 2018) on mortar bars using the accelerated test method to assess the mitigation of expansions. The results show that the expansions caused by ASR decreased with the increasing content of glass powder in the cement mixtures. Furthermore, only the 50% level reduced the expansions to a safe value according to the Brazilian standard.

Damage Generated and Propagated by the AAR Reactive Aggregate from Kingston, Ontario, Canada.

It remains unclear in the literature what the cause of the so-called alkali-carbonate reaction (ACR) damage to concrete is. However, expansion and cracks as distress features are often attributed to the alkali-silica reaction (ASR). Therefore, this work aims to assess the damage to concrete generated and propagated by the so-called ACR-susceptible reactive aggregate through mechanical testing (i.e., the direct shear test), microscopy (the damage rating index-DRI), and other techniques. Distinct induced expansion levels (i.e., 0%, 0.05%, 0.12%, and 0.20%) were selected to compare the distress caused by ACR to concrete affected by ASR. The results show that the behavior of ACR, namely, as captured through the DRI, is inconsistent with that of ASR, thus attesting to ACR being a distinct distress mechanism. The damage captured through mechanical testing does not distinguish ACR from ASR; however, microscopy reveals that cracks in the cement paste are the main damage mechanism. The proportions of cracks in the cement paste are 40-50% of the total number of cracks, whereas open cracks in the aggregates normally characterizing ASR represent only up to 20% of the total cracks.

DFT investigation of the regioselective allylation of pyrimidine 2′-deoxynucleosides

To understand the regioselectivity observed in the allylation of pyrimidine nucleosides and to identify the factors directing the reaction, a theoretical study of the regioselective allylation was carried out. Several key points were considered such as: the structure of the deprotonated nucleobase in the presence of Na+; the effect of the solvent on the dissociation and aggregation reactions of thymidine/Na+ ion pair; and the likely allylation reaction mechanisms involved. The results showed that the regioselectivity observed experimentally can be attributed to a greater stability of a dimeric form coupled to an increase of the reaction barrier in THF due to larger Na+ binding to the nucleobase.

Molecular insights into the bonding mechanisms between selenium and dissolved organic matter

Natural organic matter (NOM) plays a critical role in the mobilization and bioavailability of metals and metalloids in the aquatic environment. Selenium (Se), an environmental contaminant of aquatic systems, has drawn increasing attention over the years. While Se is a vital micronutrient to human beings, animals and plants, excess Se intake may pose serious long-term risks. However, the interaction between Se and dissolved organic matter (DOM) remains relatively unexplored, especially the reaction mechanisms and interactions of specific NOM components of certain molecular weight and the corresponding functional group change. Herein, we report an investigation on the interactions between Se and DOM by focusing on the mass distribution profile change of operationally defined molecular weight fractions of humic acid (HA) and fulvic acid (FA). The results showed that across all molecular weights studied, HA fractions were more prone to enhanced aggregation upon introduction of Se into the system. For FA, the presence of Se species results in aggregation, dissociation, and redox reactions with the first two being the major mechanisms. Total organic carbon analysis (TOC), UV–vis spectroscopy (UV–vis), and Orbitrap MS data showed that [10, 30] kDa MW fraction had the largest aromatic decrease (CRAM-like, lignin-like and tannin-like) upon addition of SeO2 via dissociation as the dominant mechanism. Fourier transform infrared spectroscopy (FT-IR) revealed that Se based bridging or chelation of functional groups from individual DOM components through hydrogen bonding in the form of SeO⋯H and possibly Se⋯H and/or attractive electrostatic interactions lead to aggregated DOM1⋯Se⋯DOM2. It was concluded from two-dimensional correlation analyses of excitation emission matrix (EEM) and FT-IR that the preferred Se-binding follows lipid ➔ peptide ➔ tannin ➔ aromatic functionalities. These results provide new understanding of Se interactions with various NOM components in aquatic environments and provide insight for Se assessing health risk and/or treatment of Se contaminated water.

Mechanisms for removing impurities in a single crystal superalloy by electron beam drip melting

The development of clean and green manufacturing of superalloys has attracted widespread attention. The returned scrap of superalloys, however, contains a significant amount of oxygen (O), nitrogen (N), and inclusions, which cannot be used effectively, and thus resulting in substantial waste generation. In this study, the electron beam drip melting (EBDM) is used to deeply remove the O, N and inclusions in a single crystal superalloy. The concentration of O and N can be reduced to 0.57 and 0.55 ppmw after drip melting, with removal rates of 97.9 % and 83.8 % respectively. The number density of inclusions experienced a significant decrease, dropping from 12.90 to 0.18 mm−2, representing a reduction of 98.6 %. The intense Marangoni convection will gather the surface inclusions in the central area of the electron beam spot. The inclusions get close to each other to form cavities, and thus the aggregation reaction occurs to form inclusion clusters. Due to the dissolution and decomposition reactions caused by the local overheating and bombardment of electron beam, the inclusions can be removed effectively. The generated O and N are eliminated through mass transfer and evaporation reactions, while the remaining inclusions on the surface can be artificially removed. The electron beam drip melting can be used for the preparation of superalloys with extremely low levels of O, N and inclusions.