Alkaline Salt Research Articles

Effects of alkaline salt stress on growth, physiological properties and medicinal components of clonal Glechoma longituba (Nakai) Kupr.

BackgroundGlechoma longituba, recognized as a medicinal plant, provides valuable pharmaceutical raw materials for treating various diseases. Saline-alkali stress may effectively enhance the medicinal quality of G. longituba by promoting the synthesis of secondary metabolites. To investigate the changes in the primary medicinal components of G. longituba under saline-alkali stress and improve the quality of medicinal materials, Na2CO3 was applied to induce short-term stress under different conditions and the biomass, physiologically active substances and primary medicinal components of G. longituba were measured in this study.ResultsUnder alkaline salt stress, the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) were elevated in G. longituba, accompanied by increased accumulation of proline (Pro) and malondialdehyde (MDA). Furthermore, analysis of the medicinal constituents revealed that G. longituba produced the highest levels of soluble sugars, flavonoids, ursolic acid, and oleanolic acid under 0.6% Na2CO3 stress for 48 h, 0.2% Na2CO3 stress for 72 h, 0.4% Na2CO3 stress for 12 h, and 0.4% Na2CO3 stress for 8 h, respectively.ConclusionsShort-term Na2CO3 stress enhances the synthesis of medicinal components in G. longituba. By manipulating stress conditions, the production of various medicinal substances could be optimized. This approach may serve as a basis for the targeted cultivation of G. longituba, offering potential applications in the treatment of diverse diseases.

Ionome composition influence wheat yield on saline and calcareous soils: the case of Triticum aestivum L. var. ‘Sirvan’

Soil pH and salinity significantly affect plant biogeochemical safety, ionome, and nutritional balance. Under such conditions, we established local compositional nutrient diagnosis standards using the centered log ratio (CNDclr*) means and standard deviations of the ionome from high-yield and nutritionally balanced ‘Sirvan’ wheat specimens (Triticum aestivum L. var. ‘Sirvan’). Critical nutrient indices (I2 X) and the critical yield of the wheat fields were determined based on the Cate-Nelson method. The Cate-Nelson model indicates that for yields above 6974.9 kg/ha, the CNDr2 index value must be below 17.645. According to clr indices the most critical leaf nutritional indices influencing the performance of low-yield ‘Sirvan’ wheat fields on calcareous and saline soils were identified. Among the leaf nutrient indices in low-yield populations of ‘Sirvan’ wheat fields, increasing leaf Ca, P, Mn, Cu, N, and Zn, while decreasing Mg, B, and K, and bringing them closer to zero within the range of nutritional balance, can have significant effects on yield under saline and calcareous soil conditions, countering the negative impact of high pH due to alkaline salt stress.

Enhancing Plant Stress Tolerance: The Role of LcWRKY40 Gene in Drought and Alkaline Salt Resistance in Tobacco and Yeast.

Leymus chinensis, a halophytic perennial grass belonging to the Poaceae family, thrives in saline-alkali grasslands and harbors a rich repository of resistance-related genetic resources. This study focused on deciphering the stress-responsive mechanisms of L. chinensis by conducting transcriptomic sequencing under NaHCO3 stress, which resulted in the annotation of a segment corresponding to the 51WRKY gene. The alkali-induced gene LcWRKY40 (QIG37591) was identified by phylogenetic analysis. Real-time quantitative PCR analysis was performed on L. chinensis plants subjected to PEG6000 and alkaline salt (NaHCO3) stress, and the results indicated that the LcWRKY40 gene was upregulated in both the leaves and roots. The localization of the LcWRKY40 protein was confirmed by the use of green fluorescent protein (GFP) fusion technology in transformed rice protoplast cells. The GAL4-driven transformation of the LcWRKY40 gene in INVScI yeast cells, which exhibited enhanced tolerance upon overexpression of the LcWRKY40 gene under mannitol and alkaline salt (NaHCO3) stress conditions. Under drought stress using mannitol, the fresh weight of Nicotiana tabacum overexpressing the LcWRKY40 gene was significantly higher than that of wild-type(WT) tobacco. Through drought and salt alkali stress, we found that overexpressed tobacco at different stages always outperformed the wild type in terms of fresh weight, SOD, MDA, and Fv/Fm. This study provides preliminary insights into the involvement of the LcWRKY40 gene in responding to drought and alkaline salt stresses, highlighting its role in enhancing plant resistance to drought and saline-alkaline conditions. These findings lay the foundation for future molecular breeding strategies aimed at improving grass resistance from different aspects.

Separation of oil from rapeseed protein rich extracts by microfiltration using hydrophilic ceramic membranes

Rapeseed, containing up to 40 % protein along with a well-balanced profile of essential amino acids, stands out as a promising novel plant-based protein source. Yet, protein extraction faces challenges, due to adverse effects of oil extraction on protein properties and down-stream processing. In this work was explored the potential of using hydrophilic silicon carbide ceramic (SiC) membranes to separate oil from a protein rich extract and produce permeates rich in protein and retentates containing oleosomes. Various solvents including water, sodium chloride, alkaline (pH 8.5) and a complex alkaline salt solvent were used to obtain a variety of protein and oil extracts from the whole rapeseeds. The type of solvent significantly affected the composition and colloidal structure of the feed which has minor effect on the oil separation but significant effect on filtration performance and composition of the permeates and retentates obtained. The membrane filtration process achieved significant oil separation, with permeates exhibiting minimal oil content ranging from 0.1 to 1.3 % (w/w), for water and alkaline solvents respectively. Assessment of the filtration performance showed fluxes from 23 to 50 L·h−1·m−2 and final volume concentration ratios of 1.3, 1.4, 1.6 and 1.9 for salt, alkaline-salt, alkaline and water solvents. The retentate, composed of 11.8–19.8 % protein and 23.6–28.7 % w/w dry matter, is a relevant and innovative ingredient for plant food formulations. These findings show the potential of membrane filtration with SiC in enabling removal of oil and producing streams with potential for diverse applications in the food industry.

High Stability Titanium Adsorbents for Lithium Recovery from Alkaline Salt Lake Brine: A Long-Term Pilot Study

High Stability Titanium Adsorbents for Lithium Recovery from Alkaline Salt Lake Brine: A Long-Term Pilot Study

Development of Enteric Diclofenac Sodium Microparticles Through a Spray-Drying Process Facilitated by Different Aqueous Dispersion Systems

The objective of this study was to prepare enteric diclofenac sodium microparticles using an aqueous dispersion system via spray-drying. Two aqueous-based solvent systems, phosphate buffer at pH 7.0 and ammonium hydrogen carbonate solution, were employed as the feed dispersion media in the spray-drying process based on the solubility characteristics of Eudragit® L100. At a drug-to-polymer ratio of 1:1, the optimal solids concentration in the feed dispersion was determined to be 2% w/v, as it enabled an approximately 5-30 µm smooth-surfaced spherical microparticle with a high production yield. Diclofenac sodium was efficiently encapsulated within the microparticles, existing as solid dispersion in a partially amorphous form. Notably, the spray-drying conditions utilized in this study obviated the need for further heating for microparticles prepared using ammonium hydrogen carbonate solution, as the residual ammonium could be completely eliminated during the spray-drying process. The two-stage biorelevant drug release profile of enteric microparticles demonstrated their ability to inhibit drug dissolution under acidic conditions while facilitating drug release under basic conditions. The phosphate buffer-based microparticles exhibited greater protection efficiency under acidic conditions compared to ammonium hydrogen carbonate-based systems, despite residual alkaline salt being present in the microparticles. These results validate the potential of the developed microparticles for use as an enteric drug delivery system.

Multi-omics integrative analysis provided new insights into alkaline stress in alfalfa

Saline-alkali stress is one of the main abiotic stresses that limits plant growth. Salt stress has been widely studied, but alkaline salt degradation caused by NaHCO3 has rarely been investigated. In the present study, the alfalfa cultivar ‘Zhongmu No. 1′ was treated with 50 mM NaHCO3 (0, 4, 8, 12 and 24 h) to study the resulting enzyme activity and changes in mRNA, miRNA and metabolites in the roots. The results showed that the enzyme activity changed significantly after alkali stress treatment. The genomic analysis revealed 14,970 differentially expressed mRNAs (DEMs), 53 differentially expressed miRNAs (DEMis), and 463 differentially accumulated metabolites (DAMs). Combined analysis of DEMs and DEMis revealed that 21 DEMis negatively regulated 42 DEMs. In addition, when combined with Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of DEMs and DAMs, we found that phenylpropanoid biosynthesis, flavonoid biosynthesis, starch and sucrose metabolism and plant hormone signal transduction played important roles in the alkali stress response. The results of this study further elucidated the regulatory mechanism underlying the plant response to alkali stress and provided valuable information for the breeding of new saline-alkaline tolerance plant varieties.

Carboniferous–Permian interglacial warming and volcanism temporally linked to the world's oldest alkaline lake deposit of the Fengcheng Formation, NW China

In addition to being an important lacustrine hydrocarbon source rock, the Fengcheng Formation possesses well-preserved sodium‑carbonate evaporite units and tuff beds. Known ancient alkaline salt-lake deposits bearing sodium‑carbonate evaporite minerals like the Late Paleozoic Fengcheng Formation are limited beyond the modern day. However, hitherto the absolute age of the alkaline lacustrine Fengcheng Formation of the Junggar Basin (China) is debated (Late Carboniferous and/or Early Permian), and therefore its temporal link to a specific stage of the Late Paleozoic Ice Age (LPIA) remains unclear. Here, new ReOs geochronology demonstrates that the Fengcheng Formation is predominately of Late Carboniferous-age (304.4 to 297.3 Ma), and therefore its deposition coincides with the interglacial climate warming interval between glaciation C4 and P1 of the LPIA and not the younger interglacial stages as previously proposed. The ReOs isotope systematics indicate that the lake water column during the deposition of the Fengcheng Formation had a relatively unradiogenic Os (187Os/188Os, Osi) isotope composition (0.32 to 0.36), which is in contrast to the typical radiogenic Osi recorded for lacustrine deposits throughout geological time. The unradiogenic Osi for the Fengcheng Formation ties the source of the Os in the lake to the weathering of adjacent mafic volcanic rocks and/or hydrothermal input (∼0.13). As a result, the penecontemporaneous relationship to the Late Paleozoic interglacial climate warming (causing enhanced evaporation) coupled with weathering of volcanic rocks and/or hydrothermal fluid input into the lake is considered to have been mechanistic in the formation of an alkaline salt lake dominated by sodium and carbonate.

Biocompatible Synthesis of Macrocyclic Thiazol(in)e Peptides.

Macrocyclic peptides containing a thiazole or thiazoline in the backbone are considered privileged structures in both natural compounds and drug discovery, owing to their enhanced bioactivity, stability, and permeability. Here, we present the biocompatible synthesis of macrocyclic peptides from N-terminal cysteine and C-terminal nitrile. While the N-terminal cysteine is incorporated during solid-phase peptide synthesis, the C-terminal nitrile is introduced during cleavage with aminoacetonitrile, utilizing a cleavable benzotriazole linker. This method directly yields the fully functionalized linear peptide precursor. The biocompatible cyclization reaction occurs in buffer at physiological pH and room temperature. The resulting thiazoline heterocycle remains stable in buffer but hydrolyzes under acidic conditions. While such hydrolysis enables access to macrocyclic peptides with a complete amide backbone, mild oxidation of the thiazoline leads to the stable thiazole macrocyclic peptide. While conventional oxidation strategies involve metals, we developed a protocol simply relying on alkaline salt and air. Therefore, we offer a rapid and metal-free pathway to macrocyclic thiazole peptides, featuring a biocompatible key cyclization step.

Corrosion behavior of YSZ and YSZ/NiCo coatings on inconel 625 exposed alkali chlorides

Alkali chloride attack on boiler pipe walls is considered the main problem of corrosion in the waste-to-energy (WTE) industry, even though uses superalloy. Electrophoretic deposited (EPD) yttria-stabilized zirconia (YSZ) coating is carried out to protect the Inconel 625 substrate. YSZ is deposited directly both on the Inconel 625 substrate and NiCo-Inconel 625. Corrosion resistance was conducted using the 3.5% NaCl electrochemical test and the hot salt corrosion test at 600°C in alkaline salt media such as NaCl, KCl, and CaCl2. The potentiodynamic polarization curve shows that the YSZ coating deposited on the substrate (single-layer) has a corrosion rate of 0.065 mm∙y‒1, lower than that deposited on NiCo coating (double-layer). The double-layer, NiO2 is formed in the NiCo layer due to the NaCl solution being trapped. Meanwhile, in hot salt corrosion at 600°C, CaCrO4 is formed as a protective oxide layer. Furthermore, in the double-layer, an imperfect oxide layer is formed causing spallation and coating failure. The corrosion rate for single-layer hot salt corrosion for 40 h is 0.310 mm∙y‒1. As a result, the corrosion resistance of the single-layer is increased by the presence of the Cr2O3 oxide layer formed during sintering.

Freeze-thaw procedure as an alternative method to reduce the cooking time of Jack bean (Canavalia ensiformis (L.) DC) while retaining its nutritional quality

This study explored the effect of freeze-thaw procedures on the Jack bean's cell wall, cooking times, and nutritional quality.Confocal laser microscopy was used to examine bean's microstructure. Optimal cooking times, hemagglutination activity, and mineral content were evaluated on beans subjected to freeze-thaw procedures and those cooked with sodium bicarbonate (AC) and demineralized water (DC). The freeze-thaw procedure that yield the largest reduction in cooking times, AC, and DC samples were used for in vitro protein and starch digestion.Freeze-thaw procedure at −20 °C for 24 h resulted in the biggest enlargement of intercellular spaces and the largest reduction in cooking time although it was less effective compared to alkaline salt cooking. No hemagglutination activity was observed in any cooked beans and mineral loss was correlated with duration of cooking times. Protein digestibility increased in freeze-thaw treated beans compared to control beans cooked in demineralized water, with no effect on starch digestibility. The findings suggest that enlargement of intercellular space due to freeze-thawing treatment can reduce cooking times and that the shorter duration of cooking may increase protein digestibility. The absence of hemagglutination activity and the observed mineral loss emphasize the importance of efficient cooking methods in preserving nutritional properties.

Response of photosynthetic characteristics and antioxidant system in the leaves of safflower to NaCl and NaHCO3.

Compared with NaCl, NaHCO3 caused more serious oxidative damage and photosynthesis inhibition in safflower by down-regulating the expression of related genes. Salt-alkali stress is one of the important factors that limit plant growth. NaCl and sodium bicarbonate (NaHCO3) are neutral and alkaline salts, respectively. This study investigated the physiological characteristics and molecular responses of safflower (Carthamus tinctorius L.) leaves treated with 200mmolL-1 of NaCl or NaHCO3. The plants treated with NaCl treatment were less effective at inhibiting the growth of safflower, but increased the content of malondialdehyde (MDA) in leaves. Meanwhile, safflower alleviated stress damage by increasing proline (Pro), soluble protein (SP), and soluble sugar (SS). Both fresh weight and dry weight of safflower was severely decreased when it was subjected to NaHCO3 stress, and there was a significant increase in the permeability of cell membranes and the contents of osmotic regulatory substances. An enrichment analysis of the differentially expressed genes (DEGs) using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes identified significant enrichment of photosynthesis and pathways related to oxidative stress. Furthermore, a weighted gene co-expression network analysis (WGCNA) showed that the darkgreen module had the highest correlation with photosynthesis and oxidative stress traits. Large numbers of transcription factors, primarily from the MYB, GRAS, WRKY, and C2H2 families, were predicted from the genes within the darkgreen module. An analysis of physiological indicators and DEGs, it was found that under saline-alkali stress, genes related to chlorophyll synthesis enzymes were downregulated, while those related to degradation were upregulated, resulting in inhibited chlorophyll biosynthesis and decreased chlorophyll content. Additionally, NaCl and NaHCO3 stress downregulated the expression of genes related to the Calvin cycle, photosynthetic antenna proteins, and the activity of photosynthetic reaction centers to varying degrees, hindering the photosynthetic electron transfer process, suppressing photosynthesis, with NaHCO3 stress causing more pronounced adverse effects. In terms of oxidative stress, the level of reactive oxygen species (ROS) did not change significantly under the NaCl treatment, but the contents of hydrogen peroxide and the rate of production of superoxide anions increased significantly under NaHCO3 stress. In addition, treatment with NaCl upregulated the levels of expression of the key genes for superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the ascorbate-glutathione cycle, and the thioredoxin-peroxiredoxin pathway, and increased the activity of these enzymes, thus, reducing oxidative damage. Similarly, NaHCO3 stress increased the activities of SOD, CAT, and POD and the content of ascorbic acid and initiated the glutathione-S-transferase pathway to remove excess ROS but suppressed the regeneration of glutathione and the activity of peroxiredoxin. Overall, both neutral and alkaline salts inhibited the photosynthetic process of safflower, although alkaline salt caused a higher level of stress than neutral salt. Safflower alleviated the oxidative damage induced by stress by regulating its antioxidant system.

Genome-wide identification of chalcone synthase (CHS) family members and their expression patterns at the sprouting stage of common bean (Phaseolus vulgaris) under abiotic stress

Secondary metabolites such as flavonoids, produced by plants, could help plants cope with external stress. Flavonoid synthesis is catalyzed by chalcone synthase (CHS). CHS plays a broad role in the growth, development, and physiological activities of plants. However, studies of the CHS gene family in Phaseolus vulgaris are limited. In this study, the HMMER search tool was used to identify 29 CHS members in the reference genome of P. vulgaris. These PvCHS members were divided into 5 subgroups. Notably, subfamilies with close genetic relationships exhibited similarities in motifs and gene structures of PvCHSs. Additionally, analysis of the cis-element indicated the involvement of PvCHSs in response to abiotic stress. Furthermore, quantitative real-time PCR (qRT-PCR) analysis under various abiotic stress conditions revealed that the majority of PvCHSs were associated with the response to salt stress (NaCl), alkaline salt stress (NaHCO3), and heavy metal stress (CdCl2). Particularly, PvCHS01, PvCHS05, PvCHS14, and PvCHS25 were significantly up-regulated under alkaline salt stress. PvCHSs were also correlated with CHS activity and flavonoid content. In addition, exogenous flavonoids were observed to significantly decrease accumulation of ROS in P. vulgaris under alkaline salt stress. This study provides a basis for further analysis of the mechanisms underlying the response of PvCHSs to abiotic stress.

Metabolomic characterization of alkali stress responses in rice

Soil alkalinity due to the accumulation of alkaline salts greatly impairs crop production. Despite advancements in crop stress response studies through metabolomic analyses, limited progress has been made in understanding cultivar differences in alkali tolerance due to the scarcity of suitable genetic material. This study aimed to characterize the metabolic responses to alkali stress in two rice cultivars, Kasalath (alkali-sensitive) and Gharib (alkali-tolerant), which were screened in an alkali soil field. A metabolomic analysis of the responses of hydroponically grown seedlings of both cultivars to alkaline and neutral salt stress was performed. Under alkali stress, the tolerant cultivar Gharib showed a significant accumulation of metabolites from the TCA organic acid and arginine synthesis pathways. This accumulation is consistent with observations in alkaliphilic wild grasses and may account for the superior alkali tolerance of Gharib. Although amino acids and nitrogen-containing metabolites, such as asparagine and allantoin, also accumulated under alkali stress, their accumulation was not specific to alkali stress, as previously reported. They accumulated similarly in both Kasalath and Gharib, suggesting that while these metabolites may alleviate alkali stress, they are unlikely to be responsible for cultivar differences in rice alkali tolerance.

Detritiation of the Organic Material in the MSO Process

Tritium is a radioactive isotope of hydrogen, and due to its limited supply and related high price, it is necessary to recover it from tritiated materials via detritiation technologies. The number of tritiated materials arises during fusion. Tritium from fusion reactors is deposited in the outer layer of plasma-facing materials, which must be dealt with during maintenance or decommissioning processes. A second source of waste is laboratory equipment that could be contaminated with tritium. High-temperature treatment in an oxidation environment can achieve the release of tritium from metals or organic materials. The tritiated vapor is then captured in a series of water bubblers and reprocessed into pure T2. One of the high-temperature methods is molten salt oxidation (MSO), which uses high temperatures, alkaline salt, and an oxidative environment for flameless oxidation of different types of waste. This work aimed to simulate the detritiation processes of tritiated organic materials in MSO technology. First, a series of experiments with D2O absorbed in ion resins was conducted. The organic waste was decomposed within the molten salt, and the flue gas was measured to determine the oxidation efficiency. The D2O was captured in a series of water bubblers, and the water was then analyzed with attenuated total reflectance (ATR)–Fourier transform infrared spectroscopy (FTIR). The results showed that all deuterium in the form of D2O was caught in the first water bubbler. The capture efficiency ranged from 22.32% to 61.13%. The lower efficiency capture can be explained as D2O in water can form a HDO molecule and its correct determination is problematic. The second type of experiment was carried out with T2O with an activity of 851 Bq and with tritiated oil with an activity of 2495 Bq. The T2O was added to the set amount of ion resins and dosed into MSO. A peristaltic pump dosed the tritiated oil. The flue gas was measured to determine oxidation efficiency, and the T2O was captured within the water bubblers. The water was analyzed with liquid scintillation spectroscopy. The capture efficiency ranged between 76.42% to 97.87%. The results showed that this technology is suitable for the detritiation of tritiated organic materials.

Integrated Metabolomics and Transcriptomics Analyses Highlight the Flavonoid Compounds Response to Alkaline Salt Stress in Glycyrrhiza uralensis Leaves.

Glycyrrhiza uralensis is a saline-alkali-tolerant plant whose aerial parts are rich in flavonoids; however, the role of these flavonoids in saline-alkali tolerance remains unclear. Herein, we performed physiological, metabolomics, and transcriptomics analyses in G. uralensis leaves under alkaline salt stress for different durations. Alkaline salt stress stimulated excessive accumulation of reactive oxygen species and consequently destroyed the cell membrane, causing cell death, and G. uralensis initiated osmotic regulation and the antioxidant system to respond to stress. In total, 803 metabolites, including 244 flavonoids, were detected via metabolomics analysis. Differentially altered metabolites and differentially expressed genes were coenriched in flavonoid-related pathways. Genes such as novel.4890, Glyur001511s00039602, and Glyur000775s00025737 were highly expressed, and flavonoid metabolites such as 2'-hydroxygenistein, apigenin, and 3-O-methylquercetin were upregulated. Thus, flavonoids as nonenzymatic antioxidants play an important role in stress tolerance. These findings provide novel insights into the response of G. uralensis to alkaline salt stress.

Influence of process conditions of alkalization on quality of cocoa powder

In this study, the effects of independent variables such as alkaline (NaOH) salt concentration (3.0–6.0 g/100 mL), alkalization temperature (60–90 °C), and time (20–40 min) on cocoa powder (low-fat) properties were investigated by using Central Composite Design. The physicochemical and color properties of samples, powder characteristics, volatile component profile, total polyphenol content (TPC), as well as antioxidant activity potentials using different methods (DPPH and ABTS) were determined. Significant models were identified for the effects on major alkalization indicators (L*, a*/b*, pH), as well as TPC and antioxidant activity potential (DPPH), which are the main motivators for the preference and consumption of cocoa products (p < 0.05). The established model was validated, and their predicted values were found to be very close to real results. It was determined that the alkali concentration had a more significant effect on dependent variables, especially on alkalization indicators, compared to the other independent variables. Furthermore, strong correlations were determined between TPC and antioxidant activity potential and color properties (L*, a*, b*, and a*/b*). Optimum concentration, temperature and time were found to be 5.3 %, 84 °C and 35.7 min for maximizing a*/b* value. The establishment of such models lead to optimizing process conditions of alkalization with minimum effort and labor force for obtaining cocoa powder with desired quality depending on the usage purpose.

Occurrence and Formation Mechanisms of High-Fluoride Groundwater in Xiong’an New Area, Northern China

While extant research has predominantly focused on elucidating the mechanisms of fluorine (F−) enrichment in groundwater within the North China Plain, the occurrence and formation mechanisms of high-F− groundwater in Xiong’an New Area remain unexplored. Consequently, 365 groundwater samples (172 from shallow groundwater, 193 from deep groundwater) were collected from Xiong’an New Area. Hydrochemical analysis, geochemical modeling, and statistical analysis were used to explore the occurrence and formation mechanisms of high-F− groundwater. The results reveal that the highest F− concentrations in shallow and deep groundwater were up to 3.22 mg/L and 1.79 mg/L, respectively. High-F− groundwater was primarily located at the eastern part of the study area. The distribution area of high-F− shallow groundwater was much greater than that of deep groundwater. F-bearing minerals dissolution and ion exchange were the principal formation mechanisms of high-F− groundwater in both shallow and deep aquifers. Moreover, competitive adsorption, evaporation, and the impacts of Ca2+ and Mg2+ dissolution equilibrium on F-bearing dissolution were crucial to the formation of high-F− groundwater in shallow aquifers. Desorption in an alkaline environment, evaporites dissolution and salt effects were vital to the formation of high-F− groundwater in deep aquifers. These findings can contribute to the support of local groundwater security and management.

Use of solid thermolytic salts to facilitate microwave-induced in situ amorphization

Moisture was frequently used as dielectric heating source in classical microwave-able systems to facilitate microwave-induced in situ amorphization, however such systems may face the potential of drug hydrolysis. In this study, solid thermolytic salts were proposed to function as moisture substitutes and their feasibility and impacts on microwave-induced in situ amorphization were investigated. It was found that NH4HCO3 was a promising solid alkaline salt to facilitate both microwave-induced in situ amorphization and in situ salt formation of acidic indomethacin (IND). Moreover, it could improve the chemical stability of the drug and the dissolution performance of compacts relative to classical moisture-based compacts upon microwaving. Further mechanistic study suggested that the in situ amorphization occurred prior to the in situ salt formation, especially in formulations with low drug loadings and high solid salt mass ratios. For compacts with low polymer ratios, in situ salt formation took place subsequently, where the previously amorphized IND within compacts could interact with the NH3 gas produced in situ by the decomposition of NH4HCO3 and form the ammonium IND salt. Microwaving time showed great impacts on the decomposition of NH4HCO3 and the in situ generation of water and NH3, which indirectly affected the amorphization and salt formation of IND. In comparison to the moisture-based systems, the NH4HCO3-based system showed a number of advantages, including the reduced potential of IND hydrolysis due to the absence of absorbed moisture, a wider category of applicable polymeric carriers other than hygroscopic polymers, and an increase in drug loading up to 50% (w/w).

Photocatalytic CO2 reduction by Ni-substituted polyoxometalates: Structure-activity relationships and mechanistic insights

The photocatalytic activity for CO2 reduction of a series of Ni-substituted polyoxometalates (POMs) differing in nuclearity, shape and size, has been investigated under visible light irradiation, with [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) as photosensitizer and triethanolamine as sacrificial donor. The tetrabutylammonium salt of the Ni4 tetranuclear species was found to exhibit the highest CO production and its stability under photocatalytic conditions was demonstrated. The catalytic performance was significantly lower for the alkaline salt due to the separation of the POM from its counter-ions occurring only for the tetrabutylammonium salt. Photophysical experiments evidenced a bimolecular electron transfer from the reduced photosensitizer [Ru(bpy)3]+ to the Ni4 POM, the former arising from the reductive quenching of the [Ru(bpy)3]2+ excited state by triethanolamine. This was further supported by DFT calculations, which also showed that the Ni4 POM accumulates at least two electrons and four protons to carry out the CO2 reduction catalytic process.