Synthesis, growth and characterization of L-Leucine Magnesium Nitrate Hexahydrate crystal

L-Leucine Magnesium Nitrate HexaHydrate ([Formula: see text]) crystal is a nonlinear optical (NLO) material of semiorganic type. It has grown using a slow evaporation solution growth (SEST) technique at elevated temperature (40∘C) by dissolving LL+MNHH in double distilled water. It was crystalized and recrystalized from a supersaturated solution by stirring it for several hours to get high optical perfection. The X-ray diffraction studies confirmed the presence of the intermixed compound in the [Formula: see text] crystal and possess monoclinic structure. Fourier transform infrared spectroscopy (FTIR) spectrum identified the functional groups of the grown crystal. The crystal has very good optical absorption and transparency in the UV–Vis region. The thermal analysis revealed the thermal stability of the crystal. The dielectric study shows that dielectric constant and dielectric loss decrease at higher frequencies. The crystal showed nonlinear property by second-harmonic generation (SHG) study. This type of material with fair nonlinearity is useful in optoelectronics application devices.

Comparison of selected mathematical functions for the analysis of growth behavior of items and physical interpretation of AvramiWeibull function

Empirical data of sigmoidal-shaped y(t) growth behavior of different types of items, such as papers and citations earned by individual and all successively published papers of selected top-cited authors, germination of tomato seeds and three different bacteria, are analyzed and compared by Avrami-Weibull, Verhulst (logistic) and Gompertz functions. It was found that: (1) Avrami-Weibull function describes different types of the data better than Gompertz and Verhulst funtions, and (2), in comparison with Verhulst and Gompertz functions, Avrami-Weibull function, expressed in the form: y(t)/ymax = 1-exp[(t/Q)q] (where ymax is the maximum value of y(t) when t ® ¥, and Q and q are constants), is equally very versatile in explaining the generation rate dy(t)/dt of items in terms of its parameters Q and q. Using the basic concepts involved in the derivation of Avrami-Weibull function for overall crystallization from melt and supersaturated solution, the growth behavior of cumulative number y(t) of items produced at time t by individual (simple) sources and collectives or groups of simple sources (i.e. complex or composite sources) is presented. Comparison of the process of receiving of citations by papers with the processes of occurrence of chemical reactions and crystallization of solid phases from melts and supersaturated solutions shows that this process is similar to that of overall crystallization of solid phases from melts and solutions. Analysis of growth of citations using Avrami-Weibull function to individual papers published by different authors shows that 1 < q < 4 for most cases. This suggests that the process of citations to individual articles is mainly determined by progressive nucleation mode involving both diffusion and integration of published knowledge.

ASSESSMENT OF THE INFLUENCE OF THE THERMODYNAMIC FACTOR ON THE CRYSTALLIZATION PROCESS IN A VACUUM APPARATUS

Особенность состояния системы жидкость–твердое тело в метастабильном растворе вещества состоит в том, что она (система) претерпевает два фазовых превращения в вакуум-аппарате (ВА) – кристаллообразование и растворение, требующие экспериментального изучения и описания в силу их важности при совершенствовании технологии производства кристаллического сахара. Однако и теоретическое обоснование фазовых превращений в метастабильном растворе разработано недостаточно. В статье предпринята попытка количественно поставить и решить проблему учета возникающего при проведении обработки метастабильного сахарсодержащего раствора повышения температуры в результате конденсации молекул на центре концентрации при пересыщении в ВА. В качестве основы численного моделирования поставленной задачи использовали программные продукты информационной среды Mathcad. С использованием модели диффузионного массопереноса сахарозы в пересыщенном растворе к затравке был разработан алгоритм расчета зависимости массы сахарозы от времени проведения процесса кристаллизации. На примере сахарозы дана оценка влияния физического фактора – выделяющейся при кристаллообразовании теплоты на расчет теплового баланса и производительности ВА. The peculiarity of the state of the liquid-solid system in a metastable solution of a substance is that it (the system) undergoes two phase transformations in a vacuum apparatus (VA) – crystal formation and dissolution, requiring experimental study and description due to their importance in improving the technology of production of crystalline sugar. However the theoretical justification of phase transformations in a metastable solution has not been sufficiently developed. The article attempts to quantify and solve the problem of taking into account the temperature increase that occurs during the processing of a metastable sugar-containing solution as a result of condensation of molecules at the concentration center during supersaturation in VA. Software products of the Mathcad information environment were used as the basis for numerical modeling of the task. Using a model of diffusive mass transfer of sucrose in a supersaturated solution to the seed, an algorithm was developed for calculating the dependence of the sucrose mass on the time of the crystallization process. On the example of sucrose, an assessment of the influence of a physical factor – the heat released during crystallization on the calculation of the thermal balance and the productivity of the VA is given.

Phytoliths: Persistence & Release of Silicon in Soil and Plants – A Review

Phytoliths are formed from silica carried up from groundwater and some plants. The weathering of silicate minerals at the Earth’s surface provides large amounts of soluble silica, some of which is absorbed by growing plants. In solution, silica exists as mono silicic acid Si (OH4) with pH values of 2–9. It is carried upward in the vascular system and becomes concentrated during transpiration around the leaf stomata. The supersaturated solution begins to polymerize or gel then solidifies and forms solid opaline silica (SiO2:nH2O) bodies (phytoliths) within and between some of the plant cells. Phytoliths were extracted from the 7.4 meter loess core and analyzed morphologically and isotopically from the occluded carbon. Rates of isotopic fractionation between plant and phytolith were determined by measurements from many modern tree, fern, and grass species. The use of phytolith biochar as a Si fertilizer offers the undeniable potential to mitigate desilication and to enhance Si ecological services due to soil weathering and biomass removal. Silicon is accumulated at levels equal to or greater than essential nutrients in plant species belonging to the families Poaceae, Equisetaceae, and Cyperaceae. However, the abundance of silicon in soils is not an indication that sufficient supplies of soluble silicon are available for plant uptake.

A model of the growth of hydrogen bubbles in the electrolysis of water

The growth of attached bubbles during the electrochemical evolution of hydrogen at a horizontal cathode at the base of a quiescent, dilute aqueous solution is analysed using a simple model of the process that includes the Butler–Volmer reaction model, the diffusion and migration of electroactive species and a symmetry condition that approximately accounts for the presence of periodically spaced bubbles on the electrode surface. The diffusion controlled growth of a bubble approximately follows a $t^{1/2}$ law when the spacing of the bubbles on the electrode is large, departing slightly from it due to the non-uniformity of the concentration of dissolved hydrogen in the supersaturated solution into which the bubble grows, and approaches a $t^{1/3}$ law when the spacing decreases. The space- and time-averaged current density increases exponentially with the applied voltage for an alkaline solution when the consumption of water in the reaction is not taken into account. For an acidic solution, the average current density saturates to a transport limited value that depends on bubble spacing. For a given voltage, the presence of attached bubbles increases the average current density due to the decrease of the concentration overpotential caused by the bubbles. The spacing of the bubbles on the electrode surface decreases when the voltage increases if the maximum supersaturation at the electrode is imposed to be constant. The result suggests that coalescence of attached bubbles will occur above a certain voltage.

Frustrated peptide chains at the fibril tip control the kinetics of growth of amyloid-β fibrils

Amyloid fibrillization is an exceedingly complex process in which incoming peptide chains bind to the fibril while concertedly folding. The coupling between folding and binding is not fully understood. We explore the molecular pathways of association of Aβ40 monomers to fibril tips by combining time-resolved in situ scanning probe microscopy with molecular modeling. The comparison between experimental and simulation results shows that a complex supported by nonnative contacts is present in the equilibrium structure of the fibril tip and impedes fibril growth in a supersaturated solution. The unraveling of this frustrated state determines the rate of fibril growth. The kinetics of growth of freshly cut fibrils, in which the bulk fibril structure persists at the tip, complemented by molecular simulations, indicate that this frustrated complex comprises three or four monomers in nonnative conformations and likely is contained on the top of a single stack of peptide chains in the fibril structure. This pathway of fibril growth strongly deviates from the common view that the conformational transformation of each captured peptide chain is templated by the previously arrived peptide. The insights into the ensemble structure of the frustrated complex may guide the search for suppressors of Aβ fibrillization. The uncovered dynamics of coupled structuring and assembly during fibril growth are more complex than during the folding of most globular proteins, as they involve the collective motions of several peptide chains that are not guided by a funneled energy landscape.

The pH Dependence of Niclosamide Solubility, Dissolution and Morphology Motivates a Potentially More Bioavailable Mucin-Penetrating Nasal and Throat Spray for COVID19, it's Contagious Variants, and Other Respiratory Viral Infections

Motivation: With the coronavirus pandemic still raging, prophylactic nasal and early treatment throat sprays that "puts the virus in lockdown", could help prevent infection and reduce viral load. Niclosamide has the potential to treat a broad range of viral infections if local bioavailability is optimized as mucin-penetrating solutions instead of microparticles that cannot penetrate the mucin. Experimental: pH-dependence of supernatant concentrations and dissolution rates of niclosamide were measured in buffered solutions by Nanodrop-UV/Vis-spectroscopy for niclosamide from different suppliers, as precipitated material and as cosolvates. Data was compared to predictions from Henderson Hasselbalch and precipitation pH models. Optimal microscopy was used to observe the morphologies of precipitated and converted niclosamide. Results: Supernatant-concentrations of niclosamide increased with increasing pH: from 1.77uM at pH 3.66 to 30uM at pH 8; more rapidly from 90uM at pH8.5 to 300uM at pH9.1, reaching 641uM at pH 9.5. Logarithmic rates for dissolution increased by ~3x for pHs 8.62 to 9.44. However, when precipitated from supersaturated solution, niclosamide equilibrated to much lower final supernatant concentrations, reflective of more stable polymorphs at each pH that were also apparent for niclosamide from other suppliers and cosolvates. Conclusions: Niclosamide is not niclosamide is not niclosamide. A low dose (20uM) prophylactic solution of niclosamide at a nasally safe pH of 7.9 and a (up to 300uM) throat spray at pH 9.1 would be one of the simplest and potentially most effective formulations from both an efficacy standpoint as well as manufacturing and distribution, with no cold chain. It now needs testing.

A complete analytical solution to the integro-differential model describing the nucleation and evolution of ellipsoidal particles

In this paper, a complete analytical solution to the integro-differential model describing the nucleation and growth of ellipsoidal crystals in a supersaturated solution is obtained. The asymptotic solution of the model equations is constructed using the saddle-point method to evaluate the Laplace-type integral. Numerical simulations carried out for physical parameters of real solutions show that the first four terms of the asymptotic series give a convergent solution. The developed theory was compared with the experimental data on desupersaturation kinetics in proteins. It is shown that the theory and experiments are in good agreement.

The Ambiguous Functions of the Precursors That Enable Nonclassical Modes of Olanzapine Nucleation and Growth

One of the most consequential assumptions of the classical theories of crystal nucleation and growth is the Szilard postulate, which states that molecules from a supersaturated phase join a nucleus or a growing crystal individually. In the last 20 years, observations in complex biological, geological, and engineered environments have brought to light violations of the Szilard rule, whereby molecules assemble into ordered or disordered precursors that then host and promote nucleation or contribute to fast crystal growth. Nonclassical crystallization has risen to a default mode presumed to operate in the majority of the inspected crystallizing systems. In some cases, the existence of precursors in the growth media is admitted as proof for their role in nucleation and growth. With the example of olanzapine, a marketed drug for schizophrenia and bipolar disorder, we demonstrate that molecular assemblies in the solution selectively participate in crystal nucleation and growth. In aqueous and organic solutions, olanzapine assembles into both mesoscopic solute-rich clusters and dimers. The clusters facilitate nucleation of crystals and crystal form transformations. During growth, however, the clusters land on the crystal surface and transform into defects, but do not support step growth. The dimers are present at low concentrations in the supersaturated solution, yet the crystals grow by the association of dimers, and not of the majority monomers. The observations with olanzapine emphasize that detailed studies of the crystal and solution structures and the dynamics of molecular association may empower classical and nonclassical models that advance the understanding of natural crystallization, and support the design and manufacture of promising functional materials.