THE STUDY OF DEHYDRATION OF COLEMANITE IN NON-ISOTHERMAL CONDITIONS

The regularities of colemanite dehydration under non-isothermal conditions are investigated. It is established that colemanite, supplied to the Russian Federation from Turkey, has calcite in its composition. The chemical composition of colemanite is determined using the X-ray fluorescence analysis method. It is shown that the processes of dehydration of colemanite under non-isothermal conditions at a heating rate of 10 °С / min are accompanied by two endothermic effects at 660,7 K and 675,7 K with a total mass loss of 17,3 %. The rate of mass loss of colemanite from the temperature at heating up to 773 K, at which colemanite dehydrates and passes into the amorphous phase, is also studied. The regularities of changes in the rate of dehydration of colemanite are established. It is shown that the maximum values of the dehydration rate of colemanite are observed in the temperature range of 653–678 K. The activation energy of colemanite dehydration is determined to be 86,000 J/mol. Based on the experimentally obtained data, the rate constant of the colemanite dehydration process is calculated. The process of dehydration of colemanite is adequately described by the formal equation of kinetics. Most of the kinetic curve is adequately described by the resulting kinetic equation. It is proposed to describe the mechanism of dehydration of colemanite by a two-stage process, accompanied at the first stage by the removal of crystallization water, and at the second stage-by the removal of hydroxyl groups

Transcriptome and Expression Profiling Analysis of Recalcitrant Tea (Camellia sinensis L.) Seeds Sensitive to Dehydration

The tea plant (Camellia sinensis (L.) O. Kuntze) is an economically important woody perennial nonalcoholic health beverage crop. Tea seeds are categorized as recalcitrant and are sensitive to dehydration treatment. However, the molecular basis of this phenomenon has not been investigated. Thus, we analyzed the genome-wide expression profiles of three dehydration stages using RNA-Seq and digital gene expression (DGE) technologies. We performed de novo assembly and obtained a total of 91,925 nonredundant unigenes, of which 58,472 were extensively annotated. By a hierarchical clustering of differentially expressed genes (DEGs), we found that 8929 DEGs were downregulated and 5875 DEGs were upregulated during dehydration treatment. A series of genes related to ABA biosynthesis and signal transduction, transcription factor, antioxidant enzyme, LEA protein, and proline metabolism that have been reported to function in dehydration process were found to be downregulated. Additionally, the expression profiles of 12 selected genes related to tea seed dehydration treatment were confirmed by qRT-PCR analysis. To our knowledge, this is the first genome-wide study elucidating the possible molecular mechanisms of sensitivity of recalcitrant tea seeds to dehydration. The results obtained in this study contribute to the preservation of tea seeds as genetic resources and can also be used to explore the mechanism of dehydration sensitivity of other recalcitrant seeds.

Mechanism of dehydration in a non-porous variable hydrate

Paroxetine hydrochloride form II (PHCl-II) is a variable hydrate with a peculiar behaviour [1]. It changes its water content in response to changes in relative humidity with remarkable speed and in a completely reversible fashion. This is commonly observed for channel hydrates, but no continuous channels exist in the PHCl-II structure [2]. Powder diffraction results showed that loss of water produces an isostructural anhydrate, suggesting a simple, non-destructive mechanism of dehydration. The aim of the present contribution is to explain this unusual behaviour at a molecular level by using molecular dynamics simulations. Models of both the hydrated and anhydrous state could be created from the experimental hydrate structure by simple energy minimisation, which is in accordance with the experimentally observed smooth transition. A partially dehydrated supercell model was used to study the mechanism which allows water molecules to cross the steric barrier between adjacent solvent cavities. Since such transitions are rare on the simulation timescale (µs to ms), a steered molecular dynamics approach was applied. The results show that the passage of water molecules is facilitated by conformational changes, in which a ring system acts as a gate between cavities. When passing through the 'gate', water molecules are relayed between two chloride ions: as one Cl...HOH hydrogen bond is broken, another HOH...Cl one is formed. The progress of water molecules along the gated channel is not continuous, they spend a significant amount of time in each cavity between consecutive passages.