Primary Nucleation Research Articles

Direct preparation of micro and nano antimony trioxide using antimony concentrate via microwave roasting: Mechanism and process

Antimony sulfide (Sb2S3) concentrate is the main source for the production of antimony oxides and metallic antimony. Few researches have focused on preparing Sb2O3 crystals and Sb2O3 nanomaterials from minerals directly. In this research, a clean, short, direct preparation of Sb2O3 crystals and nanomaterials via microwave oxidation roasting using antimony sulfide minerals is investigated. A thermodynamic analysis of oxidation and the dielectric properties of antimony sulfide minerals reveal the reaction trends and heating characteristics of microwave oxidation roasting. The experimental results show that the Sb content within the crystalline product is 97.05% under roasting conditions of 400 °C for 45 min under an air flow of 0.8 m3/h. During roasting, the phase transformation follows the order of Sb2S3→Sb2O3→Sb2O4. The oxidation mechanism shows that the microwave field enhances the molecular and Knudsen diffusion, increasing the reaction entropy. The rapid, selective microwave roasting favors rapid primary nucleation and the formation of Sb2O3 crystals. For volatile components, directional growth of Sb2O3 nanorods and microspheres with nanostructures is enhanced under the alternating electromagnetic field. This clean and innovative method gives a promising and feasible technology for efficient utilization of minerals to prepare micro and nanomaterials.

Regulating the Crystallization Morphology of Poly(vinylidene fluoride‐chlorotrifluoroethylene) Ultrathin Film by Changing Temperature and Substrate

AbstractThe crystalline component and crystallization morphology of poly(vinylidene fluoride‐chlorotrifluoroethylene) (P(VDF‐CTFE)) ultrathin film have been investigated. The CTFE segment has been characterized as the crystal composition of the film. For the film on the Si substrate, the nucleation behavior is dominated by homogeneous nucleation to form edge‐on lamellae in the initial stage of crystal nucleation growth. The edge‐on lamella will continue to grow at high crystallization temperature (Tc). However, it will be transformed into flat‐on lamellae at low Tc. For the film on Au substrate, the primary nucleation rate of the layer near the film surface has a competitive relationship when compared with the primary nucleation rate of the layer near the film/substrate interface. The nucleation behavior is preferentially dominated by heterogeneous nucleation to form flat‐on lamellae at high Tc. But it is conducive to homogeneous nucleation to form edge‐on lamellae at low Tc. Further investigation suggests that the different crystalline morphologies of P(VDF‐CTFE) ultrathin film obtained on Au and Si surfaces are closely related to the different interface effects between the film and the substrates. It is anticipated that this study will cast new light on the rational regulation of the morphologies of ultrathin films.

Primary Nucleation in Metastable Solutions of Poly(3-hexylthiophene)

Primary Nucleation in Metastable Solutions of Poly(3-hexylthiophene)

Molecular insights into the primary nucleation of polymorphic amyloid β dimers in DOPC lipid bilayer membrane.

Alzheimer's disease (AD) pathology is characterized by loss of memory cognitive and behavioral deterioration. One of the hallmarks of AD is amyloid β (Aβ) plaques in the brain that consists of Aβ oligomers and fibrils. It is accepted that oligomers, particularly dimers, are toxic species that are produced extracellularly and intracellularly in membranes. It is believed that the disruption of membranes by polymorphic Aβ oligomers is the key for the pathology of AD. This is a first study that investigate the effect of polymorphic “α‐helix/random coil” and “fibril‐like” Aβ dimers on 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) membrane. It has been found that the DOPC membrane promotes Aβ1–42 “fibril‐like” dimers and impedes Aβ1–42 “α‐helix/random coil” dimers. The N‐termini domains within Aβ1–42 dimers play a role in Aβ aggregation in membrane milieus. In addition, the aromatic π–π interactions (involving residues F19 and F20 in Aβ1–42) are the driving forces for the hydrophobic interactions that initiate the primary nucleation of polymorphic Aβ1–42 dimers within DOPC membrane. Finally, the DOPC bilayer membrane thickness is locally decreased, and it is disrupted by an embedded distinct Aβ1–42 dimer, due to relatively large contacts between Aβ1–42 monomers and the DOPC membrane. This study reveals insights into the molecular mechanisms by which polymorphic early‐stage Aβ1–42 dimers have distinct impacts on DOPC membrane.

Influence of Nickel on Niobium Nitride Formation in As-Cast Stainless Steels

The influence of the nickel content and cooling rate on niobium nitride precipitation in as-cast stainless steels were analysed. Niobium microalloying is important for mechanical properties and the prevention of intergranular corrosion in stainless steels. However, coarse precipitates can negatively affect steel properties. The precipitation of NbN depends on thermodynamic conditions, which are dictated by the chemical composition and temperature. The thermodynamic computations were used to estimate niobium nitride precipitation. Additionally, segregation models were used to predict precipitation. Three steel batches with different nickel contents (9 wt.%, 4.7 wt.%, and 0.16 wt.%) were prepared in an induction furnace and cast into sand moulds. The polished and etched samples were examined with an optical microscope, followed by a more detailed examination using a scanning electron microscope. An automatic scanning electron microscope analysis of the niobium particles was performed to obtain particle number and size distribution. Primary niobium carbonitrides, eutectic phases, and heterogenous nucleations on MnS inclusions were observed. As the proportion of nickel in the solution decreased, the solubility of nitrogen in the melt increased, which is manifested by a lower formation of primary and eutectic niobium carbonitrides, while MnS non-metallic inclusions played an important role in the heterogeneous nucleation.

Cross-Seeding Controls Aβ Fibril Populations and Resulting Functions.

Amyloid peptides nucleate from monomers to aggregate into fibrils through primary nucleation. Pre-existing fibrils can then act as seeds for additional monomers to fibrillize through secondary nucleation. Both nucleation processes occur simultaneously, yielding a distribution of fibril polymorphs that can generate a spectrum of neurodegenerative effects. Understanding the mechanisms driving polymorph structural distribution during both nucleation processes is important for uncovering fibril structure-function relationships, as well as for creating polymorph distributions in vitro that better match fibril structures found in vivo. Here, we explore how cross-seeding wild-type (WT) Aβ1-40 with Aβ1-40 mutants E22G (Arctic) and E22Δ (Osaka), as well as with WT Aβ1-42, affects the distribution of fibril structural polymorphs and how changes in structural distribution impact toxicity. Transmission electron microscopy analysis revealed that fibril seeds derived from mutants of Aβ1-40 imparted their structure to WT Aβ1-40 monomers during secondary nucleation, but WT Aβ1-40 fibril seeds do not affect the structure of fibrils assembled from mutant Aβ1-40 monomers, despite the kinetic data indicating accelerated aggregation when cross-seeding of any combination of mutants. Additionally, WT Aβ1-40 fibrils seeded with mutant fibrils produced similar structural distributions to the mutant seeds with similar cytotoxicity profiles. This indicates that mutant fibril seeds not only impart their structure to growing WT Aβ1-40 aggregates but also impart cytotoxic properties. Our findings establish a relationship between the fibril structure and the phenotype on a polymorph population level and that these properties can be passed on through secondary nucleation to the succeeding generations of fibrils.

Natural Seeder‐Feeder Process Originating From Mixed‐Phase Clouds Observed With Polarization Lidar and Radiosonde at a Mid‐Latitude Plain Site

AbstractNatural seeder‐feeder processes play an essential role in the formation and enhancement of precipitation. However, the cloud‐seeding process from mixed‐phase clouds is still not well understood due to the lack of sufficient observations. Natural seeder‐feeder processes from mixed‐phase clouds (seeder clouds) to lower‐lying liquid clouds (feeder clouds) were observed on 19 occasions using ground‐based polarization lidar and radiosonde measurements from June 2018 to June 2020 at a mid‐latitude plain observatory in Wuhan (30.5°N, 114.4°E), China. Ice crystals originating from seeder clouds fell into feeder clouds located 0.2–2.2 km below. During the sedimentation between seeder and feeder clouds, ice crystals partly underwent sublimation when passing through the in‐between dry air layers. The feeder clouds inhibited those ice crystals from complete sublimation and grew them larger by riming or vapor deposition from a favorable liquid water supply. Subsequently, ice crystals were observed afresh falling from feeder clouds, forming ice virgae descending toward the surface. Owing to cloud seeding, feeder clouds with cloud‐top temperatures (CTTs) as warm as −0.2°C to −14.5°C could produce ice virgae, although these CTTs are generally considered somewhat insufficient to initiate primary ice nucleation. The observed optically thin feeder clouds prolonged the survival time/distance of falling ice crystals, indicating that denser feeder clouds may induce enhanced precipitation.

Single-molecule observation of self-propagating amyloid fibrils.

The assembly of misfolded proteins into amyloid fibrils is associated with amyloidosis, including neurodegenerative diseases such as Alzheimer's, Parkinson's and prion diseases. The self-propagation of amyloid fibrils is widely observed in the aggregation pathways of numerous amyloidogenic proteins. This propensity with plasticity in primary nucleation allows amyloid fibril polymorphism, which is correlated with the pathology/phenotypes of patients. Because the interference with the nucleation and replication processes of amyloid fibrils can alter the amyloid structure and the outcome of the disease, these processes can be a target for developing clinical drugs. Single-molecule observations of amyloid fibril replication can be an experimental system to provide the kinetic parameters for simulation studies and confirm the effect of clinical drugs. Here, we review the single-molecule observation of the amyloid fibril replication process using fluorescence microscopy and time-lapse atomic force microscopy, including high-speed atomic force microscopy. We discussed the amyloid fibril replication process and combined single-molecule observation results with molecular dynamics simulations.

Tuning the rate of aggregation of hIAPP into amyloid using small-molecule modulators of assembly

Human islet amyloid polypeptide (hIAPP) self-assembles into amyloid fibrils which deposit in pancreatic islets of type 2 diabetes (T2D) patients. Here, we applied chemical kinetics to study the mechanism of amyloid assembly of wild-type hIAPP and its more amyloidogenic natural variant S20G. We show that the aggregation of both peptides involves primary nucleation, secondary nucleation and elongation. We also report the discovery of two structurally distinct small-molecule modulators of hIAPP assembly, one delaying the aggregation of wt hIAPP, but not S20G; while the other enhances the rate of aggregation of both variants at substoichiometric concentrations. Investigation into the inhibition mechanism(s) using chemical kinetics, native mass spectrometry, fluorescence titration, SPR and NMR revealed that the inhibitor retards primary nucleation, secondary nucleation and elongation, by binding peptide monomers. By contrast, the accelerator predominantly interacts with species formed in the lag phase. These compounds represent useful chemical tools to study hIAPP aggregation and may serve as promising starting-points for the development of therapeutics for T2D.

Enhancement of protein crystallization with the application of Taylor vortex and Poly(ionic liquid)s

With the increase demands for biopharmaceuticals, the development of efficient protein crystallization processes for manufacturing highly pure crystalline products has become critical for downstream biomanufacturing. This work focused on the combined effects of the uniform shear rate in a solution created by using the Taylor vortex and the macromolecular architecture of a solution developed using poly(ionic liquid)s during protein crystallization. The results were as follows: (1) the accelerated primary nucleation rate with a uniform shear force that was generated by the Taylor vortex; (2) the stability of the protein product prepared using the poly(ionic liquid)s was high in the crystallization solution; and (3) improved control of supersaturation of the polymer was achieved with the salting-out effect. The average crystal size in the control group was considerably lower than 1 μm with low quality (9.00 Å) and yield (56%) of crystals, but the average size of lysozyme crystals obtained using the Taylor vortex and poly(ionic liquid)s increased up to 5 μm with high quality (1.86 Å) of crystals and yield (86%). A higher diffraction resolution indicated a better ordered crystalline structure, demonstrating that the Taylor vortex and poly(ionic liquid)s are useful for improving the crystal quality.

Soluble TREM2 inhibits secondary nucleation of Aβ fibrillization and enhances cellular uptake of fibrillar Aβ

Triggering receptor expressed on myeloid cells 2 (TREM2) is a single-pass transmembrane receptor of the immunoglobulin superfamily that is secreted in a soluble (sTREM2) form. Mutations in TREM2 have been linked to increased risk of Alzheimer's disease (AD). A prominent neuropathological component of AD is deposition of the amyloid-β (Aβ) into plaques, particularly Aβ40 and Aβ42. While the membrane-bound form of TREM2 is known to facilitate uptake of Aβ fibrils and the polarization of microglial processes toward amyloid plaques, the role of its soluble ectodomain, particularly in interactions with monomeric or fibrillar Aβ, has been less clear. Our results demonstrate that sTREM2 does not bind to monomeric Aβ40 and Aβ42, even at a high micromolar concentration, while it does bind to fibrillar Aβ42 and Aβ40 with equal affinities (2.6 ± 0.3 µM and 2.3 ± 0.4 µM). Kinetic analysis shows that sTREM2 inhibits the secondary nucleation step in the fibrillization of Aβ, while having little effect on the primary nucleation pathway. Furthermore, binding of sTREM2 to fibrils markedly enhanced uptake of fibrils into human microglial and neuroglioma derived cell lines. The disease-associated sTREM2 mutant, R47H, displayed little to no effect on fibril nucleation and binding, but it decreased uptake and functional responses markedly. We also probed the structure of the WT sTREM2-Aβ fibril complex using integrative molecular modeling based primarily on the cross-linking mass spectrometry data. The model shows that sTREM2 binds fibrils along one face of the structure, leaving a second, mutation-sensitive site free to mediate cellular binding and uptake.

Insights into the Interactions that Trigger the Primary Nucleation of Polymorphic α-Synuclein Dimers.

Parkinson's disease is associated with the accumulation of α-synuclein (AS) aggregates that include polymorphic AS oligomers and polymorphic fibrils. There have been advances in solving the polymorphic state of AS fibrils, both by experimental techniques and molecular modeling tools. Yet, the polymorphic AS oligomers are now considered as the neurotoxic species, thus current and future studies making efforts to solve their structures at the molecular level. Importantly, it is crucial to explore the specific interactions between AS monomers within the dimer that stabilize the dimer and yield nucleation. Herein, we present a first work that probes at the molecular level the specific interactions between monomers in polymorphic AS dimers are derived from AS fibrils by applying molecular modeling tools. Our work reveals that both N-terminal and the non-amyloidogenic component domains play a role in the dimerization of all polymorphic AS dimers. In addition, helices along the N-terminal of AS monomers impede the contacts between AS monomers, thus preventing the nucleation or the dimerization of AS. This work provides insights into several mechanisms of the production of polymorphic AS dimers. Thus, the findings obtained in this work may assist in developing new therapeutic strategies for inhibiting the formation of the early-stage neurotoxic AS dimers.

Xylitol used as phase change material: Nucleation mechanisms of the supercooling rupture by stirring

With a very high energy density, Xylitol is a promising phase change material for low temperature heat storage (< 100 °C). However, it has a high and persistent supercooling, which inhibits the latent heat restitution during thermal discharges. Bubbling in supercooled Xylitol has already been identified as an efficient crystallization triggering technique. This paper provides a detailed analysis of the nucleation mechanisms involved. A first conclusion is that primary nucleation has shown to be impossible to activate by stirring or shearing in reasonable timescales. This leads to a description of the crystallization based on secondary nucleation. A particular attention was paid to unintentional seeding, which showed to be likely the starting point of most of the Xylitol crystallizations observed in literature. Coupling seeding and bubbling was then identified as an improvement of the nucleation triggering technique. Adding a seeding step to the discharge protocol indeed leads to faster and reproducible crystallizations. In a second part, a parametric study, conducted for a mechanical and a bubbling agitation, showed that secondary nucleation in Xylitol is a thermally activated mechanism. Therefore, surface nucleation was proposed as the main source of secondary nuclei. Finally, a first model for the surface nucleation in supercooled Xylitol, emphasizing on the influence of Xylitol viscosity, was proposed.

A Protein Corona Modulates Interactions of α-Synuclein with Nanoparticles and Alters the Rates of the Microscopic Steps of Amyloid Formation.

Nanoparticles (NPs) can modulate protein aggregation and fibril formation in the context of amyloid diseases. Understanding the mechanism of this action remains a critical next step in developing nanomedicines for the treatment or prevention of Parkinson's disease. α-Synuclein (α-Syn) can undergo interactions of different strength with nanoparticles, and these interactions can be prevented by the presence of a protein corona (PC) acquired during the exposure of NPs to serum proteins. Here, we develop a method to attach the PC irreversibly to the NPs, which enables us to study in detail the interaction of α-Syn and polyethylenimine-coated carboxyl-modified polystyrene NPs (PsNPs-PEI) and the role of the dynamics of the interactions. Analysis of the kinetics of fibril formation reveals that the NPs surface promotes the primary nucleation step of amyloid fibril formation without significantly affecting the elongation and fragmentation steps or the final equilibrium. Furthermore, the results show that even though α-Syn can access the surface of NPs that are precoated with a PC, due to the dynamic nature of the PC proteins, the PC nevertheless reduces the acceleratoring effect of the NPs. This effect is likely to be caused by reducing the overall amount of weakly interacting α-Syn molecules on the NP surface and the access of further α-Syn required for fibril elongation. Our experimental approach provides microscopic insight into how serum proteins can modulate the complex interplay between NPs and amyloid proteins.

Production of Sucrose Crystals of Uni-Modal Size Distribution by Seeded Batch Cooling Crystallization

From sucrose aqueous solution of high viscosity, sucrose was crystallized by seeded cooling in a batch crystallizer. At low seed loadings, the product crystal size distribution (CSD) was wide-spread because of enormous secondary and primary nucleation. However, at high seed loadings, it became uni-modal, where the crystallization was dominated by seed growth with practically no secondary nucleation. Enough seeding was thus effective in suppressing nucleation even during batch crystallization with high viscosity solution. The volume mean size of the product crystals obtained at high seed loadings agreed with that calculated by a simple mass balance assuming growth-dominated crystallization with no change in the number of crystals.

The unexpected dominance of secondary over primary nucleation.

It is still a challenge to control the formation of particles in industrial crystallization processes. In such processes, new crystals can be generated either by primary or secondary nucleation. While in continuous stirred tank crystallization processes, secondary nucleation is thought to occur due to the shear or attrition of already present larger crystals; in antisolvent crystallization processes, where mixing at the inlets locally causes high supersaturations, primary nucleation is understood to be the main mechanism. We aim to show here that secondary nucleation is the dominant nucleation mechanism, even under conditions that are generally considered to be dominated by primary nucleation mechanisms. Measurements of primary and secondary nucleation rates under similar industrial crystallization conditions of sodium bromate in water, sodium chloride in water, glycine in water and isonicotinamide in ethanol show that the secondary nucleation rate is at least 6 orders of magnitude larger in all these systems. Furthermore, seeded fed-batch and continuous antisolvent crystallizations of sodium bromate under high local supersaturation, seeded with crystals of a specific handedness, result in a close to chirally pure crystalline product with the same handedness. This shows that indeed, enantioselective secondary nucleation is the dominant mechanism in these antisolvent crystallizations. It is even possible to use the enantioselective secondary nucleation mechanism to control the product chirality in such a process, making antisolvent crystallization a viable crystallization-enhanced deracemization technique, having a superior productivity compared to other crystallization-enhanced deracemization methods. Our finding of a dominant secondary nucleation mechanism, rather than primary nucleation, will have a strong impact on nucleation control strategies in industrial crystallization processes.

Chaperones mainly suppress primary nucleation during formation of functional amyloid required for bacterial biofilm formation.

Unlike misfolding in neurodegenerative diseases, aggregation of functional amyloids involved in bacterial biofilm, e.g. CsgA (E. coli) and FapC (Pseudomonas), is carefully regulated. However, it is unclear whether functional aggregation is inhibited by chaperones targeting pathological misfolding and if so by what mechanism. Here we analyze how four entirely different human chaperones or protein modulators (transthyretin, S100A9, Bri2 BRICHOS and DNAJB6) and bacterial CsgC affect CsgA and FapC fibrillation. CsgA is more susceptible to inhibition than FapC and the chaperones vary considerably in the efficiency of their inhibition. However, mechanistic analysis reveals that all predominantly target primary nucleation rather than elongation or secondary nucleation, while stoichiometric considerations suggest that DNAJB6 and CsgC target nuclei rather than monomers. Inhibition efficiency broadly scales with the chaperones' affinity for monomeric CsgA and FapC. The chaperones tend to target the most aggregation-prone regions of CsgA, but do not display such tendencies towards the more complex FapC sequence. Importantly, the most efficient inhibitors (Bri2 BRICHOS and DNAJB6) significantly reduce bacterial biofilm formation. This commonality of chaperone action may reflect the simplicity of functional amyloid formation, driven largely by primary nucleation, as well as the ability of non-bacterial chaperones to deploy their proteostatic capacities across biological kingdoms.

Data mining crystallization kinetics

The database contains information on crystallization kinetics that describes crystal growth and primary nucleation for small molecules. In total, there are more than 336 datapoints distributed in more than 90 different chemical entities.

Bulk and surface exsolution produces a variety of Fe-rich and Fe-depleted ellipsoidal nanostructures in La0.6Sr0.4FeO3 thin films.

The past several years have seen a resurgence in the popularity of metal exsolution as an approach to synthesize advanced materials proposed for novel catalytic, magnetic, optical, and electrochemical properties. Whereas most studies to-date have focused on surface exsolution (motivated by catalysis), we instead report on the diversity of nanostructures formed in La0.6Sr0.4FeO3 thin films during sub-surface or so-called 'bulk' exsolution, in addition to surface exsolution. Bulk exsolution is a promising approach to tuning the functionality of materials, yet there is little understanding of the nanostructures exsolved within the bulk and how they compare to those exsolved at gas-solid interfaces. This work combines atomic- and nano-scale imaging and spectroscopy techniques applied using a state-of-the-art aberration-corrected scanning transmission electron microscope (STEM). In doing so, we present a detailed atomic-resolution study of a range of Fe-rich and Fe-depleted nanostructures possible via exsolution, along with qualitative and quantitative chemical analysis of the exsolved nanostructures and oxide phases formed throughout the film. Local structural changes in the perovskite matrix, coinciding with nanostructure exsolution, are also characterized with atomic-resolution STEM imaging. Fe exsolution is shown to create local A-site rich domains of Ruddlesden-Popper phase, and some stages of this phase formation have been demonstrated in this work. In particular, phase boundaries are found to be the primary nucleation sites for bulk and surface exsolution, and the exsolved particles observed here tend to be ellipsoidal with shape factor of 1.4. We report a range of nanostructure types (core-shell, bulk core-shell, adjacent, and independent particles), revealing several possible avenues of future exploration aimed to understand the formation mechanism of each exsolution type and to develop their functionality. This work is thus relevant to materials scientists and engineers motivated to understand and utilize exsolution to synthesize materials with predictable nanostructures.

Towards an enhanced control of protein crystallization: Seeded batch lysozyme crystallization in a meso oscillatory flow reactor

Protein crystallization has been shown as a viable alternative to conventional protein purification methods. However, the stochastic and spontaneous nature of the primary nucleation process makes protein crystallization difficult to control. An approach often used in the crystallization of small organic and inorganic molecules to improve the reproducibility of the process and better control the crystallization outcome is seeding. This study presents for the first time the investigation of seeding on batch protein crystallization in a meso oscillatory flow reactor (meso-OFR). Seeded and unseeded lysozyme batch crystallization experiments were carried out, where the influence of the initial lysozyme concentration (initial supersaturation) and the seed quantity on the onset of nucleation, crystal properties and yield was assessed. No major influence of the seed quantity on the product crystal size was verified for the initial lysozyme concentration of 20 mg·mL−1 (below the secondary nucleation threshold - SNT), while for the initial lysozyme concentration of 25 mg·mL−1 (above the SNT) the onset of nucleation and mean crystal size significantly decrease with increasing seed quantity. Further, crystal yield increases with both the initial lysozyme concentration and seed quantity. Overall, the results highlight seeding as a promising technique to improve control over the crystallization time and product crystal size.