A6Mo2P4O19 (A = Rb, Cs) and Rb2MoP2O9: New molybdophosphates with distinct polyanionic configurations

The exploration in the A-Mo-P-O (A = Rb, Cs) systems has allowed several new Mo(V) phosphates, Rb2MoP2O9, Rb6Mo2P4O19 and Cs6Mo2P4O19 synthesized through the spontaneous nucleation method. Single-crystal X-ray diffraction analysis...

Potassium Sulfate: A New Candidate to Explore Non-Photochemical Laser-Induced Nucleation Mechanisms

In this paper, we report a study on the nucleation behavior of potassium sulfate (K2SO4) from aqueous solutions under the influence of unfocused nanosecond laser pulses. The objective is to contribute to the general understanding of the Non-Photochemical Laser-Induced Nucleation (NPLIN) mechanism. First, the influence of several parameters such as supersaturation as well as laser parameters (pulse energy, number of pulses, and laser polarization) on induction time, probability of nucleation and mean number of crystals in comparison with spontaneous nucleation was investigated. Then, we examined the influence of gas composition (i.e., degassing and gas bubbling (CO2 and N2)) of the supersaturated solutions on the NPLIN kinetics, showing no correlation between gas content (or nature) on the crystallization behavior. Our study questions the role of impurities within the solution regarding the mechanism of laser-induced nucleation.

Emergence and maintenance of different sized actin filaments in a common pool of building blocks

Actin is one of the key structural components of the eukaryotic cytoskeleton that regulates cellular architecture and mechanical properties. Dynamic regulation of actin filament length and organization is essential for the control of many physiological processes including cell adhesion, motility and division. While previous studies have mostly focused on the mechanisms controlling the mean length of individual actin filaments, it remains poorly understood how distinct actin filament populations in cells maintain different size using the same set of molecular building blocks. Here we develop a theoretical model for the length regulation of multiple actin filaments by nucleation and growth rate modulation by actin binding proteins in a limiting pool of monomers. We first show that spontaneous nucleation of actin filaments naturally leads to heterogeneities in filament length distribution. We then investigate the effects of filament growth inhibition by capping proteins and growth promotion by formin proteins on filament length distribution. We find that filament length heterogeneity can be increased by growth inhibition, whereas growth promoters do not significantly affect length heterogeneities. Interestingly, a competition between filament growth inhibitors and growth promoters can give rise to bimodal filament length distribution as well as a highly heterogeneous length distribution with large statistical dispersion. We quantitatively predict how heterogeneity in actin filament length can be modulated by tuning F-actin nucleation and growth rates in order to create distinct filament subpopulations with different lengths.

Investigation of the Freezing Phenomenon in Vials Using an Infrared Camera

The freezing phenomenon has a dramatic impact on the quality of freeze-dried products. Several freezing models applied to solutions in vials have been proposed to predict the resulting product morphology and describe heat transfer mechanisms. However, there is a lack of detailed experimental observations of the freezing phenomenon in vials in the literature. Thus, the present work offers new experimental observations of the freezing phenomenon in vials by infrared (IR) thermography. IR imaging allowed each vial’s whole axial temperature profile to be collected during freezing, providing significant insights into the process. Spontaneous nucleation and vacuum-induced surface freezing (VISF), as a controlled nucleation technique, are investigated. Batches having vials in direct contact with the shelf (exchanging heat mainly through conduction) as well as suspended (exchanging heat mainly through natural convection and radiation) were tested. The study used three solutions: sucrose 5%, mannitol 5%, and dextran 10%. SEM images coupled with an automated image segmentation technique were also performed to examine possible correlations between the freezing observations and the resulting pore size distributions. IR thermography was found to be a promising tool for experimentally predicting the resulting product morphology in-line.

Molecular Dynamics Simulation of Homogeneous Nucleation and Growth of Supercooled Al Liquid

Molecular dynamics simulation is used to study the spontaneous nucleation and solidification of Al liquid. According to the mean first-passage time (MFPT), the critical crystal nucleus size at 31.6% undercooling is 152 atoms, the nucleation rate is [Formula: see text][Formula: see text]m[Formula: see text][Formula: see text]s[Formula: see text]. The nucleation rate obtained by the survival probability (SP) is [Formula: see text][Formula: see text]m[Formula: see text][Formula: see text]s[Formula: see text], which is very consistent with the result obtained by MFPT. Using Johnson–Mehl–Avrami (JMA) law to analyze the growth of the two extreme conditions in the experiment, the system with the smallest average atomic volume (Run38) grows faster than the system with the largest volume (Run73). In terms of microstructure, Run38 is a lamellar (LAM) structure, and Run73 is a complex polycrystalline structure accompanied by five-fold twinning (FFT). The shapes of clusters in a given range (5–10,000 atoms) during solidification in 100 experiments were counted. The results show that no clusters are perfectly spherical, but ellipsoids are of different shapes, and the larger the ellipsoid size, the closer to a spherical shape.

Spontaneous nucleation and fast aggregate-dependent proliferation of α-synuclein aggregates within liquid condensates at physiological pH

It is well-established that α-synuclein aggregation may proceed through an initial lipid-dependent aggregate formation and, if at acidic pH, a subsequent aggregate-dependent proliferation. It has also been recently reported that the aggregation of α-synuclein may also take place through an alternative pathway, which takes place within dense liquid condensates produced through liquid-liquid phase separation. The microscopic mechanism of this process, however, remains to be clarified. Here, we developed a fluorescence-based assay to perform a kinetic analysis of the aggregation process of α-synuclein within liquid condensates, and applied it to determine the corresponding mechanism of aggregation. Our analysis shows that at pH 7.4 the aggregation process of α-synuclein within dense condensates starts with spontaneous primary nucleation followed by rapid aggregate-dependent proliferation. Taken together, these results reveal a highly efficient pathway for the appearance and proliferation of α-synuclein aggregates at physiological pH.

Research on homogeneous nucleation and microstructure evolution of aluminium alloy melt

In this paper, based on the embedded atom method (EAM) potential, molecular dynamics simulations of the solidification process of Al–4 at.%Cu alloy is carried out. The Al–Cu alloy melt is placed at different temperatures for isothermal solidification, and each stage of the entire solidification process is tracked, including homogeneous nucleation, nucleus growth, grain coarsening and microstructure evolution. In the nucleation stage, the transition from high temperature to low temperature manifests a change from spontaneous nucleation mode to divergent nucleation mode. The critical nucleation temperature of the Al–Cu alloy is determined to be about 0.42 T m ( T m is the melting point of Al–4 at.%Cu) by calculating the nucleation rate and the crystal nucleus density. In the nucleus growth stage, two ways of growing up are observed, that is, a large crystal nucleus will absorb a smaller heterogeneous crystal nucleus, and two very close crystal nuclei will merge. In the microstructure evolution of the isothermally solidified Al–Cu alloy, it is emerged that the interior of all nanocrystalline grains are long-period stacking structure composed of face centred cubic (FCC) and hexagonal close-packed (HCP). These details provide important information for the production of Al–Cu binary alloy nano-polycrystalline products.

General nucleation-growth type kinetic models of nanoparticle formation: possibilities of finding analytical solutions

In this work, analytical solutions for the time dependences for the concentration of each chemical species are determined in a class of nucleation-growth type kinetic models of nanoparticle formation. These models have an infinitely large number of dependent variables and describe the studied process without approximations. Symbolic solutions are found for the mass kernel (where reactivity is directly proportional to the mass of a nanoparticle) and the diffusion kernel (where reactivity is independent of the size of the nanoparticle). The results show that the average particle size is primarily determined by the type of the kernel function and the ratio of the rate constants of spontaneous nucleation and particle growth. The final distribution of nanoparticle sizes is a continuously decreasing function in each studied case. Furthermore, the time dependences of the concentrations of monomeric units show the induction behavior that has already been observed in many experimental studies.

Oriented arrangement of simple monomers enabled by confinement: towards living supramolecular polymerization

The living supramolecular polymerization technique provides an exciting research avenue. However, in comparison with the thermodynamic spontaneous nucleation, using simple monomers to realize living supramolecular polymerization is hardly possible from an energy principle. This is because the activation barrier of kinetically trapped simple monomer (nucleation step) is insufficiently high to control the kinetics of subsequent elongation. Here, with the benefit of the confinement from the layered double hydroxide (LDH) nanomaterial, various simple monomers, (such as benzene, naphthalene and pyrene derivatives) successfully form living supramolecular polymer (LSP) with length control and narrow dispersity. The degree of polymerization can reach ~6000. Kinetics studies reveal LDH overcomes a huge energy barrier to inhibit undesired spontaneous nucleation of monomers and disassembly of metastable states. The universality of this strategy will usher exploration into other multifunctional molecules and promote the development of functional LSP.