The focus of this review is the presentation of the most important aspects of chemical bonding in molecules of the main group atoms according to the current state of knowledge. Special attention is ...given to the difference between the physical mechanism of covalent bond formation and its description with chemical bonding models, which are often confused. This is partly due to historical reasons, since until the development of quantum theory there was no physical basis for understanding the chemical bond. In the absence of such a basis, chemists developed heuristic models that proved extremely valuable for understanding and predicting experimental studies. The great success of these simple models and the associated rules led to the fact that the model conceptions were regarded as real images of physical reality. The complicated world of quantum theory, which eludes human imagination, made it difficult to link heuristic models of chemical bonding with quantum chemical knowledge. In the early days of quantum chemistry, some suggestions were made which have since proved untenable. In recent decades, there has been a stormy development of quantum chemical methods, which are not limited to the quantitative accuracy of the calculated properties. Also, methods have been developed where the experimentally developed models can be quantitatively expressed and visually represented using mathematically well-defined terms that are derived from quantum chemical calculations. The calculated numbers may however not be measurable values. Nevertheless, as orientation data for the interpretation and classification of experimental findings as well as a guideline for new experiments, they form a coordinate system that defines the multidimensional world of chemistry, which corresponds to the Hilbert space formalism of physics. The nonmeasurability of model values is not a weakness of chemistry but a characteristic by which the infinite complexity of the material world becomes scientifically accessible and very useful for chemical research. This review examines the basis of the commonly used quantum chemical methods for calculating molecules and for analyzing their electronic structure. The bonding situation in selected representative molecules of main-group atoms is discussed. The results are compared with textbook knowledge of common chemistry.
Energy decomposition analysis Zhao, Lili; von Hopffgarten, Moritz; Andrada, Diego M. ...
Wiley interdisciplinary reviews. Computational molecular science,
May/June 2018, Letnik:
8, Številka:
3
Journal Article
Recenzirano
The energy decomposition analysis (EDA) is a powerful method for a quantitative interpretation of chemical bonds in terms of three major components. The instantaneous interaction energy ΔEint between ...two fragments A and B in a molecule A–B is partitioned in three terms, namely (1) the quasiclassical electrostatic interaction ΔEelstat between the fragments; (2) the repulsive exchange (Pauli) interaction ΔEPauli between electrons of the two fragments having the same spin, and (3) the orbital (covalent) interaction ΔEorb which comes from the orbital relaxation and the orbital mixing between the fragments. The latter term can be decomposed into contributions of orbitals with different symmetry which makes it possible to distinguish between σ, π, and δ bonding. After a short introduction into the theoretical background of the EDA we present illustrative examples of main group and transition metal chemistry. The results show that the EDA terms can be interpreted in chemically meaningful way thus providing a bridge between quantum chemical calculations and heuristic bonding models of traditional chemistry. The extension to the EDA–Natural Orbitals for Chemical Valence (NOCV) method makes it possible to breakdown the orbital term ΔEorb into pairwise orbital contributions of the interacting fragments. The method provides a bridge between MO correlations diagrams and pairwise orbital interactions, which have been shown in the past to correlate with the structures and reactivities of molecules. There is a link between frontier orbital theory and orbital symmetry rules and the quantitative charge‐ and energy partitioning scheme that is provided by the EDA–NOCV terms. The strength of the pairwise orbital interactions can quantitatively be estimated and the associated change in the electronic structure can be visualized by plotting the deformation densities.
This article is categorized under:
Structure and Mechanism > Molecular Structures
Electronic Structure Theory > Density Functional Theory
Computer and Information Science > Visualization
First column: Plot of the deformation densities Δρ1–4 with associated stabilization energies ΔE1–4 of the four most important orbital interactions in B2(NHCMe)2. The color code for the charge flow is red→light blue. Third and fourth column: Plot of the interacting donor and acceptor orbitals and calculated eigenvalues ε of (NHCMe)2 and (1Σg+) B2. Second column: Resulting MOs of the complex B2(NHCMe)2.
The purpose of this paper is to analyze the diffusion and interaction of air pollutants in different cities, and point out a method to evaluate the efficient correlation between air pollutants in the ...data of cities and nearby areas, so as to establish the air pollution information of surrounding towns. In addition, this paper analyzes the weather forecast according to the mobile migration and the impact of rural green tourism. Tourism is increasingly becoming a tool for achieving sustainable development, especially from the perspective of poverty reduction. The number of overseas travel receipts increases and can be recognized as the easiest way to reduce poverty. Strategic research aims to use tourism to alleviate poverty a significant amount, but there is little understanding of macro levels of poverty alleviation, especially at different levels of poverty. Mature tourist objections require a consistently expanding assortment of items and markets. To be effective, this system requires a point by point comprehension of the degree of likely sightseers and utilization designs. Experimental examinations on the travel industry burning through the will, in general, utilize standard least-squares relapse for this reason. Most important of this technology, however, is that it is higher, has significant limitations, and is unable to distinguish below average tourists. Intra-digit regression also considers exploration of the overall conditional distribution of a given predictor response variable, thus producing a more comprehensive map of significant predictors.
Highlights
Bifunctional electrode and electrolytic cell configuration for electrochemical water splitting are reviewed.
The different green energy systems powered water splitting are summarized and ...discussed.
An outlook of future research prospects for the development of green energy system powered water splitting in practical application process is proposed.
Hydrogen (H
2
) production is a latent feasibility of renewable clean energy. The industrial H
2
production is obtained from reforming of natural gas, which consumes a large amount of nonrenewable energy and simultaneously produces greenhouse gas carbon dioxide. Electrochemical water splitting is a promising approach for the H
2
production, which is sustainable and pollution-free. Therefore, developing efficient and economic technologies for electrochemical water splitting has been an important goal for researchers around the world. The utilization of green energy systems to reduce overall energy consumption is more important for H
2
production. Harvesting and converting energy from the environment by different green energy systems for water splitting can efficiently decrease the external power consumption. A variety of green energy systems for efficient producing H
2
, such as two-electrode electrolysis of water, water splitting driven by photoelectrode devices, solar cells, thermoelectric devices, triboelectric nanogenerator, pyroelectric device or electrochemical water–gas shift device, have been developed recently. In this review, some notable progress made in the different green energy cells for water splitting is discussed in detail. We hoped this review can guide people to pay more attention to the development of green energy system to generate pollution-free H
2
energy, which will realize the whole process of H
2
production with low cost, pollution-free and energy sustainability conversion.
This work reports the design and fabrication of a proton conductive 2D metal–organic framework (MOF), Cu(p‐IPhHIDC)n (1) (p‐IPhH3IDC=2‐(p‐N‐imidazol‐1‐yl)‐phenyl‐1 H‐imidazole‐4,5‐dicarboxylic acid) ...as an advanced ammonia impedance sensor at room temperature and 68–98 % relative humidity (RH). MOF 1 shows the optimized proton conductivity value of 1.51×10−3 S cm−1 at 100 °C and 98 % RH. Its temperature‐dependent and humidity‐dependent proton conduction properties have been explored. The large amount of uncoordinated carboxylate groups between the layers plays a vital role in the resultant conductivity. Distinctly, the fabricated MOF‐based sensor displays the required stability toward NH3, enhanced sensitivity, and notable selectivity for NH3 gas. At room temperature and 68 % RH, it gives a remarkable gas response of 8620 % to 130 ppm NH3 gas and lower detection limit of 2 ppm towards NH3 gas. It is also found that the gas response of the ammonia sensor increases linearly with the increase of NH3 gas concentration under 68–98 % RH and room temperature. Moreover, the sensor indicates excellent reversibility and selectivity toward NH3 versus N2, H2, O2, CO, CO2, benzene, and MeOH. Based on structural analyses, activation energy calculations, water and NH3 vapor absorptions, and PXRD determinations, proton conduction and NH3 sensing mechanisms are suggested.
Ammonia detection: Proton conductivity and ammonia sensing properties of a 2D Cu‐based metal–organic framework (MOF) were explored. The experimental results reveal that the proton conductivity of MOF 1 reaches a maximum of 1.51×10−3 S cm−1 at 100 °C and 98 % relative humidity (RH). At room temperature and 68 % RH, the MOF‐based sensor indicates a remarkable gas response of 8620 % to 130 ppm NH3 gas and lower detection limit of 2 ppm towards NH3 gas.
Carcinogens in food are an important issue that threat people's health right now. Lactic acid bacteria (LAB) strains as well-known probiotics have shown numerous perspectives in being used as a good ...food additive to confront cancerogenic compounds in recent years. Some LAB strains can remove cancerogenic compounds from medium environment via direct physical binding and avoid re-pollution of poisonous secondary metabolites which are generated from degradation of cancerogenic compounds. This article presents a whole overview of the physical-binding of LAB strains to such common cancerogenic compounds existed in food and feed environments as mycotoxins, polycyclic aromatic hydrocarbons (PAHs), heterocyclic amines (HAs) and pthalic acid esters (PAEs).In most cases, summaries of these published researches show that the binding of LAB strains to cancerogenic compounds is a physical process. Binding sites generally take place in cell wall, and peptidoglycan from LAB cells is the chief binding site. The adsorption of lactic acid bacteria to cancerogenic compounds is strain-specific. Specially, the strains from the two genera Lactobacillus and Bifidobacterium show a better potential in binding cancerogenic compounds. Moreover, we firstly used molecular dynamic computer model as a highly potential tool to simulate the binding behavior of peptidoglycan from Lactobacillus acidophilus to DBP, one of pthalic acid esters with genetic toxicity. It was seen that the theoretical data were quite consistent with the experimental results in terms of the ability of this bacterium to bind DBP. Also, the toxicity reduction of cancerogenic compounds by LAB strains could be achieved either in gastrointestinal model or animal tests and clinical researches as well. In conclusion, carefully selected LAB strains should be a good solution as one of safety strategies to reduce potential risk of cancerogenic compounds from food-based products.
Although the ecological function of dark septate endophytes (DSEs) is well studied, little is known about the responses of the host plant to DSEs obtained from other plants, especially under ...conditions of heavy metal stress. This study aimed to investigate how DSEs from a heavy-metal habitat affect non-host plants in cadmium (Cd) stress soils, which then provides a basis for the application of DSEs in the cultivation of different plant and soil remediation strategies for polluted ecosystems. We isolated and identified two species of DSE (
and
) inhabiting the roots of
(host plant) which are grown in metal-polluted habitats. Then, the Cd stress tolerance of the DSEs was tested using a pure culture of which the Cd concentration has been adjusted. Subsequently, we examined the performance of non-host plants (
and
) which were inoculated with DSEs under Cd stress in a growth chamber. The results indicated that the two DSEs could grow under Cd stress
, even when not exhibiting high levels of tolerance to Cd. The superoxide dismutase (SOD), malondialdehyde (MDA), glutathione (GSH), soluble protein, and melanin of the DSE fungi reached maximal levels at concentrations of 30-60 mg Cd/L, indicating the important preventive strategies adopted by the DSE fungi in environments contaminated by Cd. Despite a decreased biomass of DSE hyphae with enhanced Cd concentrations, the accumulation of Cd in the DSE hyphae tended to show an increasing trend. Both DSEs were effective colonizers of the non-host plants.
and
inoculation significantly promoted the biomass and the root architecture of the two non-host plants under Cd stress.
inoculation increased the total nitrogen (TN) of
, whereas inoculation with
significantly increased the organic carbon (OC) of
. In particular, the DSE inoculation significantly improved the accumulation of Cd in plant tissues under Cd stress, demonstrating a potential application in the bio-remediation of heavy-metal-pollution areas. Our findings suggest that the DSE inoculation improved the root growth and nutrient absorption of non-host plants, altered the soil Cd concentration, and facilitated plant growth and survival under Cd stress. These results contribute to a better understanding of DSE-plant interactions in habitats contaminated by heavy metals.
In view of environmental protection and the need for early prediction of major diseases, it is necessary to accurately monitor the change of trace ammonia concentration in air or in exhaled breath. ...However, the adoption of proton-conductive metal–organic frameworks (MOFs) as smart sensors in this field is limited by a lack of ultrasensitive gas-detecting performance at high relative humidity (RH). Here, the pellet fabrication of a water-stable proton-conductive MOF, Ba(o-CbPhH2IDC)(H2O)4 n (1) (o-CbPhH4IDC = 2-(2-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid) is reported. The MOF 1 displays enhanced sensitivity and selectivity to NH3 gas at high RHs (>85%) and 30 °C, and the sensing mechanism is suggested. The electrochemical impedance gas sensor fabricated by MOF 1 is a promising sensor for ammonia at mild temperature and high RHs.
Myeloid-derived suppressor cells (MDSCs) inhibit anti-tumor immunity. Aerobic glycolysis is a hallmark of cancer. However, the link between MDSCs and glycolysis is unknown in patients with ...triple-negative breast cancer (TNBC). Here, we detect abundant glycolytic activities in human TNBC. In two TNBC mouse models, 4T1 and Py8119, glycolysis restriction inhibits tumor granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF) expression and reduces MDSCs. These are accompanied with enhanced T cell immunity, reduced tumor growth and metastasis, and prolonged mouse survival. Mechanistically, glycolysis restriction represses the expression of a specific CCAAT/enhancer-binding protein beta (CEBPB) isoform, liver-enriched activator protein (LAP), via the AMP-activated protein kinase (AMPK)-ULK1 and autophagy pathways, whereas LAP controls G-CSF and GM-CSF expression to support MDSC development. Glycolytic signatures that include lactate dehydrogenase A correlate with high MDSCs and low T cells, and are associated with poor human TNBC outcome. Collectively, tumor glycolysis orchestrates a molecular network of the AMPK-ULK1, autophagy, and CEBPB pathways to affect MDSCs and maintain tumor immunosuppression.
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•Aerobic glycolysis affects G-CSF and GM-CSF expression in TNBC•Aerobic glycolysis regulates CEBPB isoform, LAP, via AMPK-ULK1-autophagy pathway•LAP controls G-CSF and GM-CSF expression and MDSC development•Aerobic glycolysis impacts tumor immunity and patient outcome through MDSCs
Tumor-derived myeloid-derived suppressor cells (MDSCs) are critical tumor immunosuppression components. Li et al. show that the high glycolytic rate in triple-negative breast cancer cells is associated with MDSC promotion through an AMPK-ULK1 and autophagy pathway. Glycolysis restriction inhibits tumor G-CSF and GM-CSF and consequently MDSC development.
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