Characteristics of nonconventional hydrogen bonds and stability of dimers of chalcogenoaldehyde derivatives: a noticeable role of oxygen compared to other chalcogens

In this work, twenty-four stable dimers of RCHZ with R = H, F, Cl, Br, CH3 or NH2 and Z = O, S, Se or Te were determined. It was found that the stability of most dimers is primarily contributed by the electrostatic force, except for the dominant role of the induction term in those involving a Te atom, which has been rarely observed. Both electron-donating and -withdrawing groups in substituted formaldehyde cause an increase in the strength of nonconventional Csp2-H⋯Z hydrogen bonds, as well as the dimers, in which the electron donating effect plays a more crucial role. The strength of nonconventional hydrogen bonds decreases in the following order: Csp2-H⋯O ≫ Csp2-H⋯S > Csp2-H⋯Se > Csp2-H⋯Te. Remarkably, a highly significant role of the O atom compared to S, Se and Te in increasing the Csp2-H stretching frequency and strength of the nonconventional hydrogen bonds and dimers is found. A Csp2-H stretching frequency red-shift is observed in Csp2-H⋯S/Se/Te, while a blue-shift is obtained in Csp2-H⋯O. When Z changes from O to S to Se and to Te, the Csp2-H blue-shift tends to decrease and eventually turns to a red-shift, in agreement with the increasing order of the proton affinity at Z in the isolated monomer. The magnitude of the Csp2-H stretching frequency red-shift is larger for Csp2-H⋯Te than Csp2-H⋯S/Se, consistent with the rising trend of proton affinity at the Z site and the polarity of the Csp2-H bond in the substituted chalcogenoaldehydes. The Csp2-H blue-shifting of the Csp2-H⋯O hydrogen bonds is observed in all dimers regardless of the electron effect of the substituents. Following complexation, the electron-donating derivatives exhibit a stronger Csp2-H blue-shift compared to the electron-withdrawing ones. Notably, the stronger Csp2-H blue-shift turns out to involve a less polarized Csp2-H bond and a decrease in the occupation at the σ*(Csp2-H) antibonding orbital in the isolated monomer.

Revealing the high efficiency of fluorescence quenching of rhodamine B by triangular silver nanodisks due to the inner filter effect mechanism

Performing effective fluorescence quenching based on a metal nanomaterial is essential to construct fluorescence sensors. Silver nanomaterials are well known as an excellent candidate for an absorber in fluorescence sensing systems. Herein, we investigated the fluorescence quenching of rhodamine B (RhB) in the presence of triangular silver nanodisks in which perfect overlap between the absorption of the absorber and the fluorescence of the fluorophore was observed. The fluorescence quenching mechanism of RhB was investigated under various excitation wavelengths, together with measurement of the fluorescence lifetime. The quenching efficiency of RhB was proportional to the wavelength excitation. Remarkably, the highest efficiency of fluorescence quenching of RhB was achieved (∼60%). The quenching mechanism was investigated and revealed to be mostly due to the inner filter effect (IFE) mechanism, without the contribution of energy transfer. This result shows a completely different story from most previous studies based on silver nanoparticles, where energy transfer was reported to play a significant role.

New insights on the luminescence properties and Judd-Ofelt analysis of Er-doped ZnO semiconductor quantum dots

In this study, Er3+ doped ZnO semiconductor quantum dots (QDs) were synthesized using a wet chemical method. The successful doping of Er3+ ions into the ZnO host lattice and the elemental composition was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The ZnO and Er3+ doped ZnO QDs with a hexagonal structure, spherical shape, and particle size of approximately 5 nm were revealed by XRD and transmission electron microscopy (TEM). The absorption, luminescence properties, and fluorescence lifetimes of the samples were studied as the concentration of Er3+ ions varied. The intensity parameters, emission transition probabilities, branching ratios, and emission lifetimes of the excited levels of Er3+ ions in the ZnO host were determined using the Judd-Ofelt theory, which provided insight into the covalent relationship between the ions and ligands as well as the nature of the ZnO host lattice. Moreover, the energy transfer process from the ZnO host to Er3+ ions and the yield of this process are explained in detail along with specific calculations. The Er3+ doped ZnO QDs displayed a significantly longer lifetime than undoped ZnO, which opens up many potential applications in fields such as photocatalysis, optoelectronics, photovoltaics, and biosensing.

Novel two-dimensional Janus β-Ge2XY (X/Y = S, Se, Te) structures: first-principles examinations

Two-dimensional (2D) structures can stably exist in different allotropes. In this manuscript, we propose a new series of Janus structures based on the β-phase of germanium monochalcogenides, namely, β-Ge2XY (X/Y = S, Se, and Te) monolayers. Our calculations indicate that Janus β-Ge2XY monolayers have a stable crystal structure and possess anisotropic mechanical properties. At the ground state, β-Ge2XY monolayers are semiconductors with a large bandgap and their electronic properties depend strongly on a biaxial strain. Strains not only change the bandgap but can also lead to a change in the bandgap characteristic, namely transitions from indirect to direct bandgap. Our findings not only introduce a new structure of germanium chalcogenide compounds but also show that they have superior physical properties suitable for applications in nanoelectronics.

In situ magnesiothermic reduction synthesis of a Ge@C composite for high-performance lithium-ion batterie anodes

Metallothermic, especially magnesiothermic, solid-state reactions have been widely applied to synthesize various materials. However, further investigations regarding the use of this method for composite syntheses are needed because of the high reactivity of magnesium. Herein, we report an in situ magnesiothermic reduction to synthesize a composite of Ge@C as an anode material for lithium-ion batteries. The obtained electrode delivered a specific capacity of 454.2 mAh·g-1 after 200 cycles at a specific current of 1000 mA·g-1. The stable electrochemical performance and good rate performance of the electrode (432.3 mAh·g-1 at a specific current of 5000 mA·g-1) are attributed to the enhancement in distribution and chemical contact between Ge nanoparticles and the biomass-based carbon matrix. A comparison with other synthesis routes has been conducted to demonstrate the effectiveness of contact formation during in situ synthesis.

First-principles examination of two-dimensional Janus quintuple-layer atomic structures XCrSiN2 (X = S, Se, and Te)

In this work, we propose novel two-dimensional Janus XCrSiN₂ (X = S, Se, and Te) single-layers and comprehensively investigate their crystal structure, electronic properties, and carrier mobility by using a first-principles method. These configurations are the combination of the CrSi₂N₄ material and a transition metal dichalcogenide. The X-Cr-SiN₂ single-layers are constructed by replacing the N-Si-N atomic layer on one side with chalcogen atoms (S, Se, or Te). The structural characteristics, mechanical or thermal stabilities, and electronic properties are investigated adequately. All three examined configurations are energetically stable and are all small-bandgap semiconductors (<1 eV). Since the mirror symmetry is broken in the Janus material, there exists a remarkable built-in electric field and intrinsic dipole moment. Therefore, the spin-orbit interaction is considered intensively. However, it is observed that the spin-orbit coupling has insignificant effects on the electronic properties of XCrSiN₂ (X = S, Se, and Te). Moreover, an external electric field and strain are applied to evaluate the adjustment of the electronic features of the three structures. The transport properties of the proposed configurations are calculated and analyzed systematically, indicating the highly directional isotropy. Our results suggest that the proposed Janus XCrSiN₂ could be potential candidates for various applications, especially in nanoscale electronic devices.

Multifunctional optical thermometry using dual-mode green emission of CaZrO3:Er/Yb/Mo perovskite phosphors

The weak emission intensity of rare-earth element-doped dual-mode materials leads to low-sensor sensitivity, which is a challenge in optical sensor applications. The present work achieved high-sensor sensitivity and high green color purity based on the intense green dual-mode emission of Er/Yb/Mo-doped CaZrO₃ perovskite phosphors. Their structure, morphology, luminescent properties, and optical temperature sensing properties have been investigated in detail. Phosphor shows a uniform cubic morphology with an average size of approximately 1 μm. Rietveld refinement confirms the formation of single-phase orthorhombic CaZrO₃. Under the excitation of 975 and 379 nm, the phosphor emits pure green up and down-conversion (UC and DC) emission at 525/546 nm corresponding to ²H_11/2/⁴S_3/2-⁴I_15/2 transitions of Er³⁺ ions, respectively. Intense green UC emissions were achieved because of energy transfer (ET) from the high-energy excited state of Yb³⁺-MoO₄^2- dimer to the ⁴F_7/2 level of Er³⁺ ion. Furthermore, the decay kinetics of all obtained phosphors confirmed ET efficiency from Yb³⁺-MoO₄^2- dimer to Er³⁺ ions, leading to strong green DC emission. Moreover, the DC of the obtained phosphor shows that a sensor sensitivity value of 0.697% K^-1 at 303 K is higher than the UC (0.667% K^-1 at 313 K) because the thermal effect generated by the DC excitation source light is ignored compared with UC luminescence. CaZrO₃:Er-Yb-Mo phosphor shows intense green dual-mode emission with high green color purity, 96.50% of DC and 98% of UC emissions, and high sensitivity, making it suitable for optoelectronic devices and thermal sensor applications.

Statistical Analysis for Understanding PM2.5 Air Quality and the Impacts of COVID-19 Social Distancing in Several Provinces and Cities in Vietnam

Air pollution, especially in urban regions, is receiving increasing attention in Vietnam. Consequently, this work aimed to study and analyze the air quality in several provinces and cities in the country focusing on PM_2.5. Moreover, the impacts of COVID-19 social distancing on the PM_2.5 level were investigated. For this purpose, descriptive statistic, Box and Whisker plot, correlation matrix, temporal variation, and trend analysis were conducted. R-based program and the R package "openair" were employed for the calculations. Hourly PM_2.5 data were obtained from 8 national air quality monitoring sites. The study results indicated that provinces and cities in the North experienced more PM_2.5 pollution compared to the Central and South. PM_2.5 concentrations at each monitoring site varied significantly. Among monitoring sites, the northern sites showed high PM_2.5 correlations with each other than the other sites. Seasonal variation was observed with high PM_2.5 concentration in the dry season and low PM_2.5 concentration in the wet season. PM_2.5 concentration variation during the week was not so different. Diurnal variation showed that PM_2.5 concentration rose at peak traffic hours and dropped in the afternoon. There was mainly a decreasing trend in PM_2.5 concentration over the studied period. The COVID-19 pandemic has contributed to PM_2.5 reduction. In the months implemented social distancing for preventing the epidemic, PM_2.5 concentration declined but it would mostly increase in the following months. This study provided updated and valuable assessments of recent PM_2.5 air quality in Vietnam.

Green synthesis of zinc oxide nanoparticles toward highly efficient photocatalysis and antibacterial application

Zinc oxide nanoparticles (ZnO NPs) were successfully synthesized by a green method using rosin and zinc chloride as salt precursors. The phase structure, morphology, and particle size of ZnO were determined by X-ray powder diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The fabricated ZnO NP samples are crystalline with a grain size of 30-100 nm. The ZnO NPs were used as catalysts for the photodegradation of methylene blue (MB) and methyl orange (MO) under visible and UV light. The results indicate that the prepared ZnO material excellently removed MB and MO (c _initial = 10 mg/L) with efficiencies of 100% and 82.78%, respectively, after 210 min under UV radiation with a ZnO NP dose of 2 g/L. The photocatalyst activity of the synthesized material was also tested under visible light radiation with the same conditions; however, it achieved lower efficiencies. In addition, ZnO NPs were also tested regarding their antibacterial activity, and the results showed that the prepared ZnO samples had the highest (i.e., 100%) antibacterial efficiency against E. coli.

Combination of long-term 13CO2 labeling and isotopolog profiling allows turnover analysis of photosynthetic pigments in Arabidopsis leaves

BACKGROUND

Living cells maintain and adjust structural and functional integrity by continual synthesis and degradation of metabolites and macromolecules. The maintenance and adjustment of thylakoid membrane involve turnover of photosynthetic pigments along with subunits of protein complexes. Quantifying their turnover is essential to understand the mechanisms of homeostasis and long-term acclimation of photosynthetic apparatus. Here we report methods combining whole-plant long-term ¹³CO₂ labeling and liquid chromatography - mass spectrometry (LC-MS) analysis to determine the size of non-labeled population (NLP) of carotenoids and chlorophylls (Chl) in leaf pigment extracts of partially ¹³C-labeled plants.

RESULTS

The labeling chamber enabled parallel ¹³CO₂ labeling of up to 15 plants of Arabidopsis thaliana with real-time environmental monitoring ([CO₂], light intensity, temperature, relative air humidity and pressure) and recording. No significant difference in growth or photosynthetic pigment composition was found in leaves after 7-d exposure to normal CO₂ (~ 400 ppm) or ¹³CO₂ in the labeling chamber, or in ambient air outside the labeling chamber (control). Following chromatographic separation of the pigments and mass peak assignment by high-resolution Fourier-transform ion cyclotron resonance MS, mass spectra of photosynthetic pigments were analyzed by triple quadrupole MS to calculate NLP. The size of NLP remaining after the 7-d ¹³CO₂ labeling was ~ 10.3% and ~ 11.5% for all-trans- and 9-cis-β-carotene, ~ 21.9% for lutein, ~ 18.8% for Chl a and 33.6% for Chl b, highlighting non-uniform turnover of these pigments in thylakoids. Comparable results were obtained in all replicate plants of the ¹³CO₂ labeling experiment except for three that were showing anthocyanin accumulation and growth impairment due to insufficient water supply (leading to stomatal closure and less ¹³C incorporation).

CONCLUSIONS

Our methods allow ¹³CO₂ labeling and estimation of NLP for photosynthetic pigments with high reproducibility despite potential variations in [¹³CO₂] between the experiments. The results indicate distinct turnover rates of carotenoids and Chls in thylakoid membrane, which can be investigated in the future by time course experiments. Since ¹³C enrichment can be measured in a range of compounds, long-term ¹³CO₂ labeling chamber, in combination with appropriate MS methods, facilitates turnover analysis of various metabolites and macromolecules in plants on a time scale of hours to days.

A comprehensive procedure to develop water quality index: A case study to the Huong river in Thua Thien Hue province, Central Vietnam

This work proposed a novel procedure of Water Quality Index (WQI) development that could be used for practical applications on a local or regional scale, based on available monitoring data. Principal component analysis (PCA) was applied to the monthly data of 11 water quality parameters (pH, conductivity (EC), total suspended solid (TSS), dissolved oxygen (DO), five -day biological oxygen demand (BOD), chemical oxygen demand (COD), ammonia (N-NH₄), nitrate (N-NO₃), phosphate (P-PO₄), total coliform, and total dissolved iron monitored at 11 sites at Huong river in the years 2014–2016. From the PCA, the three extracted principal components explained 67% of the total variance of original variables. From the set of communality values, the weight (w_i) for each parameter was determined. Linear sub-index functions were established based on the permissible limits from the National Technical Regulations on Surface Water Quality set up by the Vietnam Environment Agency (VEA) to derive the sub-index (q_i) for each parameter. The multiplicative formula that is the product of the sub-indices (q_i) raised to the respective weights (w_i), was used for calculation of the final WQI values. The proposed index (WQI) was then applied to the river with quarterly data of the 11 parameters monitored at ten sites in the years 2017–2020. The WQI representatively reflected the actual status of the river overall water quality, of which 97.8% of the WQI values belonged to grades of EXCELLENT and GOOD, and 2.2% of grade MODERATE. Comparison between the river water quality evaluations resulting from the developed WQI with the WQI adopted by National Sanitation Foundation (NSF-WQI) and the index issued by Vietnam Environment Agency (VN-WQI) indicated that the proposed WQI was more suitable for river quality assessment.

Antioxidant activity and α-glucosidase inhibitability of Distichochlamys citrea M.F. Newman rhizome fractionated extracts: in vitro and in silico screenings

Distichochlamys citrea M.F. Newman (commonly known as “Black Ginger”) is an endemic plant to Vietnam and has been extensively exploited by folk medication for treatments of infection-related diseases and diabetes. In this work, its rhizomes were subjected to fractionated extraction, phytochemical examination, evaluation of antioxidant effect by DDPH free radical neutralization, and inhibitory activity toward α-glucosidase. The compositional components were subjected to in silico screening, including density functional theory calculation, molecular docking simulation, physicochemical analysis, and pharmacokinetic regression. In the trials, EtOAc fraction is found as the bioactive part of most effectiveness, regarding both antioxidant effect (IC₅₀ = 90.27 µg mL⁻¹) and α-glucosidase inhibitory activity (IC₅₀ = 115.75 μg mL⁻¹). Chemical determination reveals there are 13 components of its composition. DFT-based calculations find no abnormal constraints in their structures. Docking-based simulation provides order of inhibitory effectiveness: 3-P53341 > 12-P53341 > 7-P53341 > 4-P53341 > 11-P53341 > 10-P53341. QSARIS-based investigations implicate their biocompatibility. ADMET-based regressions indicate that all candidates are generally safe for medicinal applications. The findings would contribute to the basis for further studies on the chemical compositions of Distichochlamys citrea and their biological activities.

Facile Synthesis of Carboxymethyl Cellulose Coated Core/Shell SiO2@Cu Nanoparticles and Their Antifungal Activity against Phytophthora capsici

Cu nanoparticles are a potential material for creating novel alternative antimicrobial products due to their unique antibacterial/antifungal properties, stability, dispersion, low cost and abundance as well as being economical and ecofriendly. In this work, carboxymethyl cellulose coated core/shell SiO2@Cu nanoparticles (NPs) were synthesized by a simple and effective chemical reduction process. The initial SiO2 NPs, which were prepared from rice husk ash, were coated by a copper ultrathin film using hydrazine and carboxymethyl cellulose (CMC) as reducing agent and stable agent, respectively. The core/shell SiO2@Cu nanoparticles with an average size of ~19 nm were surrounded by CMC. The results indicated that the SiO2@Cu@CMC suspension was a homogenous morphology with a spherical shape, regular dispersion and good stability. Furthermore, the multicomponent SiO2@Cu@CMC NPs showed good antifungal activity against Phytophthora capsici (P. capsici). The novel Cu NPs-based multicomponent suspension is a key compound in the development of new fungicides for the control of the Phytophthora disease.