282 research outputs found
Relating induction time and metastable zone width
© 2017 The Royal Society of Chemistry. A relation between induction time and metastable zone width in cooling crystallization has been developed based on the correlation between temperature and supersaturation with the induction time in the classical nucleation theory. By this relation, the nucleation times in linear cooling experiments and the induction times at constant temperature can be estimated from each other, i.e. estimating metastable zone widths from experimental induction times or interfacial energy and the pre-exponential factor from metastable zone widths. Ascorbic-water system, with 120 induction times and 192 metastable zone widths determined, and several systems reported in the literature, have been investigated to compare the estimated values of metastable zone width/induction time with experimental values, respectively. The estimated metastable zone widths are fairly consistent with the experimental values. The differences between experimental literature values of metastable zone widths and the estimated values using the literature induction times range from 0.1 K to 10 K with an average of 2.5 K. For two systems (paracetamol in ethanol and salicylic acid in ethyl acetate), estimated and experimental results are of very good consistency with an average uncertainty of only about 5%. More accurate extrapolations of the induction times from metastable zone widths have been investigated. The potential utilities of this approach in crystallization research and process understanding are discussed
Crystal structure of the co-crystal butylparaben– isonicotinamide (1/1)
The title 1:1 co-crystal, C11H14O3·C6H6N2O [systematic name: butyl 4-hyÂdroxyÂbenzoate–isonicotinamide (1/1)], crystallizes with one molÂecule of butylÂparaben (BPN) and one molÂecule of isonicotinamide (ISN) in the asymmetric unit. In the crystal, BPN and ISN molÂecules form hydrogen-bonded (O—Hâ‹ŻN and N—Hâ‹ŻO) dimers of paired BPN and ISN molÂecules. These dimers are further connected to each other via N—Hâ‹ŻO=C hydrogen bonds, creating ribbons in [011] which further stack along the a axis to form a layered structure with short Câ‹ŻC contacts of 3.285 (3) Å. Packing interÂactions within the crystal structure were assessed using PIXEL calculations
Review on life cycle of parabens: synthesis, degradation, characterization and safety analysis
In this review, we show the life cycle of parabens, commonly used preservatives that exist in nature and commercial products. Typical synthetic methods to produce parabens, and a set of complimentary characterization techniques to monitor the composition of parabens are also highlighted. This includes solid state analysis using Scanning Electron Microscope (SEM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD), in-situ monitoring of crystallization process using Focused Beam Reflectance Measurement (FBRM), Particle Vision Measurement (PVM), quantitative detection via High Performance Liquid Chromatography (HPLC), and Gas Chromatography (GC). An improved understanding of the overall physical, biophysical and chemical properties of parabens and their life cycle, summarized in this article, are vital for the safety control and extensive applications of relevant products in food, cosmetic and pharmaceutical industries
Effect of oscillatory flow on nucleation kinetics of butyl paraben
More than 165 induction times of butyl paraben-ethanol solution in a batch moving fluid oscillation baffled crystallizer with various amplitudes (1-9 mm) and frequencies (1.0-9.0 Hz) have been determined to study the effect of COBR operating conditions on nucleation. The induction time decreases with increasing amplitude and frequency at power density below about 500 W/m3; however, a further increase of the frequency and amplitude leads to an increase of the induction time. The interfacial energies and pre-exponential factors in both homogeneous and heterogeneous nucleation are determined by classical nucleation theory at oscillatory frequency 2.0 Hz and amplitudes of 3 or 5 mm both with and without net flow. To capture the shear rate conditions in oscillatory flow crystallizers, a large eddy simulation approach in a computational fluid dynamics framework is applied. Under ideal conditions the shear rate distribution shows spatial and temporal periodicity and radial symmetry. The spatial distributions of the shear rate indicate an increase of average and maximum values of the shear rate with increasing amplitude and frequency. In continuous operation, net flow enhances the shear rate at most time points, promoting nucleation. The mechanism of the shear rate influence on nucleation is discussed
Distributed Learning over Networks with Graph-Attention-Based Personalization
In conventional distributed learning over a network, multiple agents
collaboratively build a common machine learning model. However, due to the
underlying non-i.i.d. data distribution among agents, the unified learning
model becomes inefficient for each agent to process its locally accessible
data. To address this problem, we propose a graph-attention-based personalized
training algorithm (GATTA) for distributed deep learning. The GATTA enables
each agent to train its local personalized model while exploiting its
correlation with neighboring nodes and utilizing their useful information for
aggregation. In particular, the personalized model in each agent is composed of
a global part and a node-specific part. By treating each agent as one node in a
graph and the node-specific parameters as its features, the benefits of the
graph attention mechanism can be inherited. Namely, instead of aggregation
based on averaging, it learns the specific weights for different neighboring
nodes without requiring prior knowledge about the graph structure or the
neighboring nodes' data distribution. Furthermore, relying on the
weight-learning procedure, we develop a communication-efficient GATTA by
skipping the transmission of information with small aggregation weights.
Additionally, we theoretically analyze the convergence properties of GATTA for
non-convex loss functions. Numerical results validate the excellent
performances of the proposed algorithms in terms of convergence and
communication cost.Comment: Accepted for publication in IEEE TSP; with supplementary details for
the derivation
Oiling-out Crystallization of Beta-Alanine onSolid Surfaces Controlled by Solvent Exchange
Droplet formation in oiling-out crystallization has important implication for
separation and purification of pharmaceutical active ingredients by using an
antisolvent. In this work, we report the crystallization processes of
oiling-out droplets on surfaces during solvent exchange. Our model ternary
solution is beta-alanine dissolved in isopropanol and water mixture. As the
antisolvent isopropanol displaced the alanine solution pre-filled in a
microchamber, liquid-liquid phase separation occurred at the mixing front. The
alanine-rich subphase formed surface microdroplets that subsequently
crystallized with progression of solvent exchange. We find that the flow rates
have significant influence on the droplet size, crystallization process, and
growth rate, and final morphology of the crystals. At fast flow rates the
droplets solidified rapidly and formed spherical-cap structures resembling the
shape of droplets, in contrast to crystal microdomains or thin films formed at
slow flow rates. On a highly hydrophilic surface, the crystals formed thin film
without droplets formed on the surface. We further demonstrated that by the
solvent exchange crystals can be formed by using a stock solution with a very
low concentration of the precursor, and the as-prepared crystals can be used as
seeds to trigger crystallization in bulk solution. Our results suggest that the
solvent exchange has the potential to be an effective approach for controlling
oiling-out crystallization, which can be applied in wide areas, such as
separation and purification of many food, medical, and therapeutic ingredients.Comment: Advanced Materials Interfaces (2020
H+-Independent Glutamine Transport in Plant Root Tips
BACKGROUND: Glutamine is one of the primary amino acids in nitrogen assimilation and often the most abundant amino acid in plant roots. To monitor this important metabolite, a novel genetically encoded fluorescent FRET-reporter was constructed and expressed in Arabidopsis thaliana. As a candidate for the glutamine fluxes, the root tip localized, putative amino acid transporter CAT8 was analyzed and heterologously expressed in yeast and oocytes. PRINCIPAL FINDINGS: Rapid and reversible in vivo fluorescence changes were observed in reporter-expressing root tips upon exposure and removal of glutamine. FRET changes were detected at acid and neutral pH and in the presence of a protonophore, suggesting that part of the glutamine fluxes were independent of the pH. The putative amino acid transporter CAT8 transported glutamine, had a half maximal activity at approximately 100 microM and the transport was independent of external pH. CAT8 localized not only to the plasma membrane, but additionally to the tonoplast, when tagged with GFP. Ultrastructural analysis confirmed this dual localization and additionally identified CAT8 in membranes of autophagosomes. Loss-of function of CAT8 did not affect growth in various conditions, but over-expressor plants had increased sensitivity to a structural substrate analog, the glutamine synthetase inhibitor L-methionine sulfoximine. CONCLUSIONS: The combined data suggest that proton-independent glutamine facilitators exist in root tips
Jumping into metastable 1:1 urea-succinic acid cocrystal zone by freeze-drying
Aqueous solutions with molar ratios between urea and succinic acid from 0.3:1 to 3:1 were evaporated at room temperature, and products were pure or mixtures of stable 2:1 urea-succinic acid cocrystals, urea or succinic acid. By freeze-drying, metastable 1:1 urea-succinic acid cocrystal formed. The different mixtures of the 1:1 cocrystals reveal several "hidden" metastable zones in a ternary phase diagram of the 2:1 cocrystal. The formation of the 1:1 cocrystal indicated that the solution composition points in the phase diagram "jump" over the stable zone into the metastable zones
Development and workflow of a continuous protein crystallization process: A case of lysozyme
In the present work, a workflow on the development of a continuous protein crystallization is introduced, with lysozyme as a model protein, from microliter screening experiments, to small scale batch crystallization experiments in a shaking crystallization platform, and to batch and continuous crystallization experiments in an oscillatory flow platform. The lysozyme crystallizations investigated were for a concentration range from 30 to 100 mg/mL, shaking conditions from 100 to 200 rpm in the batch shaking crystallization platform, and oscillatory conditions with amplitude (x 0 ) from 5 to 30 mm and frequency (f) from 0.1 to 1.0 Hz in the batch oscillatory flow crystallization platform. We propose the use of the Reynold's number (R e ) for scaling up of the process from the shaking batch to the continuous oscillatory flow platform. Additionally, it is shown that the nucleation rate increased with increase in concentration of initial lysozyme solution, or increase in shear rate, inducing smaller size of lysozyme crystals. The properties and qualities of the crystal products indicate that continuous crystallization platforms may offer advantages to the downstream bioprocessing of proteins
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