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Hydrazine (HD) and mono‐methyl hydrazine (MMH), as the compositions of rocket fuels and corrosion inhibitor, have a significant impact on the atmospheric environment. The effects of them on the reaction between NO2 and H2O were investigated theoretically from mechanism and kinetics, and it is expected that they can promote the hydrolysis of NO2 due to their lower free energy barriers. For the subsequent reaction HNO3+HONO+HD/MMH, acid base complex and zwitterionic structure were produced through isomerization. When one or two water molecules were involved in the subsequent reaction, only zwitterionic structure can be found with the lower free energy barrier, and the products were more stable than those without water molecules. To study the atmospheric behavior of HD/MMH, the structures, thermodynamics, interaction forces and temperature dependence of the clusters, which were consisted with HNO3 and HONO with the base molecules including ammonia, amine and amide, were further calculated, and the results show that the hydrogen bond is the main interaction in the clusters. The global minima remained fixed when the temperature increases from 200 K to 325 K. The forming reactions of the clusters were spontaneous, suggesting that ammonia, amine and amide can promote the nucleation of HNO3 and HONO molecules. [ABSTRACT FROM AUTHOR]

Griseofulvin is an anti-fungal agent which has recently been determined to have potential anti-viral and anti-cancer applications. The role of specific enzymes involved in the biosynthesis of this natural product has previously been determined, but the mechanism by which a p450, GsfF, catalyzes the key oxidative cyclization of griseophenone B remains unknown. Using density functional theory (DFT), we have determined the mechanism of this oxidation that forms the oxa-spiro core of griseofulvin. Computations show GsfF preferentially performs two sequential phenolic O-H abstractions rather than epoxidation to form an arene oxide intermediate. This conclusion is supported by experimental kinetic isotope effects.

Dike foundation piping is one of the most important reasons for the dangerous situation and even the breach of dikes in Poyang Lake Area. It is of great significance to study and explain the disaster-causing mechanism of dike foundation piping in Poyang Lake Area from the mechanism so as to deal with the dangerous situation of piping and carry out emergency rescue scientifically.In this paper, an organic glass model tank is designed and manufactured, which integrates the functions of pore water pressure signal acquisition, seepage flow observation, erosion soil particle collection, graded constant head control, internal water circulation and so on. Based on the typical dike foundation structure of a dike in Poyang Lake Area, the physical model test of piping is carried out by using the prototype soil of dike foundation, and the whole process of piping occurrence, development and collapse of prototype multi-layer complex dike foundation is completely simulated. Combined with the experimental phenomena, the hydraulic conditions and soil particle erosion rate of the six stages (surface crack development stage, latent layer failure stage, overlying layer failure stage, piping channel upstream stage, embankment foundation failure stage, embankment foundation collapse stage ) in the process of piping occurrence and development are analyzed, and the special embankment foundation failure mechanism of the dike is explained by analyzing the effect of vertical seepage force.The results show that the piping failure in the dike foundation structure in Poyang Lake Area is concentrated in the underlying sand layer. Under the action of osmotic pressure, the overlying weak permeable layer is penetrated by seepage, and the piping channel is formed on the contact surface between the sand layer and the overlying layer, which accelerates the erosion of soil particles and eventually leads to the dike foundation collapse. The loam layer sandwiched in the clay layer in the embankment foundation of a typical dike in the Poyang Lake Area cannot play the role of the transition layer between the strong and weak permeable layers. The law of soil particle erosion is similar to that of the embankment foundation without the transition layer. The growth rate of the cumulative erosion of the soil particles forming the surface piping outlet and the embankment foundation cracking is less than 0.1 g/s; the average overall critical horizontal gradient of the dike foundation where piping occurs is about 0.1. [ABSTRACT FROM AUTHOR]

Corrosion inhibitors are broadly adopted for protecting metal from corrosion due to their advantages of low price and easy operation. However, the existing corrosion inhibitors suffer from the problems of complicated preparation and large dosages. To address these issues, this paper firstly employs organosilica nanodots (OSiNDs) synthesized by a facile one-step hydrothermal approach as an excellent corrosion inhibitor even at a small dosage. More importantly, the corrosion inhibition mechanism of OSiNDs is revealed according to the analyses of adsorption isotherm, corrosion morphology, and theoretical calculations. The results illustrate that OSiNDs possess abundant N- and O-containing functional groups, endowing them with wonderful long-term dispersion stability. And through the weight loss test and electrochemical measurement, the outstanding corrosion inhibition performance of OSiNDs is demonstrated. In detail, OSiNDs with only 100 mg/L provide a corrosion inhibition efficiency of 92.93 % for Q235 carbon steel in 1 mol/L HCl solution. The corrosion inhibition mechanism is attributed to the adsorption of OSiNDs on the surface of carbon steel. This study firstly develops OSiNDs as a unique high-performance corrosion inhibitor, not only broadening the application field of OSiNDs but also mitigating metal corrosion to reduce the associated environmental pollution and safety hazards. • OSiNDs with outstanding long-term dispersion stability are simply synthesized. • OSiNDs are firstly employed to improve inhibition performance for carbon steel. • 100 mg/L OSiNDs in 1 mol/L HCl inhibit corrosion by 92.93 % for carbon steel. • The corrosion inhibition mechanism of OSiNDs is revealed. [ABSTRACT FROM AUTHOR]

Vermiculite and vermiculite modified with hydrochloric acid were investigated to evaluate their flocculation efficiencies in freshwater containing harmful algae blooms (HABs) (Microcystis aeruginosa). Scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, converted fluorescence microscope, plasma-atomic emission spectrometry, and Zetasizer were used to study the flocculation mechanism of modified vermiculite. It was found that the vermiculite modified with hydrochloric acid could coagulate algae cells through charge neutralization, chemical bridging, and netting effect. The experimental results show that the efficiency of flocculation can be notably improved by modified vermiculite. Ninety-eight per cent of algae cells in algae solution could be removed within 10 min after the addition of modified vermiculite clay. The method that removal of HABs with modified vermiculite is economical with high efficiency, and more research is needed to assess their ecological impacts before using in practical application. [ABSTRACT FROM PUBLISHER]

Abstract: Natural attapulgite (N-AT) and modified attapulgite (M-AT) were used in this study to evaluate their flocculation efficiencies and mechanisms in freshwater containing harmful algal blooms through conventional jar test procedure. The experimental results showed that the efficiency of flocculation can be significantly improved by M-AT under appropriate conditions. It was found that the attapulgite modified by hydrochloric acid was similar to polyaluminum ferric silicate chloride (PAFSiC). The high efficiency for M-AT to flocculate Microcystis aeruginosa in freshwater was due to the mechanism of bridging and netting effect. Caenorhabditis elegans was used to detect the toxicity of N-AT and M-AT. The results showed that there was no significant toxicity on this organism. Attapulgite is a natural material, which can be readily available, abundant, and relatively inexpensive. Using modified attapulgite to remove the harmful algal blooms could have the advantages of high effectiveness, low cost, and low impact on the environment. [Copyright &y& Elsevier]

The mechanisms for the reaction of C2H5S with NO2 are investigated at the QCISD(T)/6-311++G(d, p)//B3LYP/6-311++G(d, p) level on both single and triple potential energy surfaces. The geometries, vibrational frequencies and zero-point energy (ZPE) corrections of all stationary points involved in the title reaction are calculated at the B3LYP/6-311++G(d, p) level. The results show that the reaction is more predominant on the single potential energy surface, while it is negligible on the triple potential energy surface. Without barrier height in the whole process, the major channel is R → C2H5SONO (IM1 and IM2) → P1 (C2H5SO+NO). With much heat released in the formation of C2H5SNO2 (IM3) and the transition state involved in the subsequent step more stable than reactants, P4 (CH3CHS + t-HONO) is subdominant product energetically. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

The mechanisms for the reaction of C2H5S with NO2 are investigated at the QCISD(T)/6-311++G(d, p)//B3LYP/6-311++G(d, p) level on both single and triple potential energy surfaces. The geometries, vibrational frequencies and zero-point energy (ZPE) corrections of all stationary points involved in the title reaction are calculated at the B3LYP/6-311++G(d, p) level. The results show that the reaction is more predominant on the single potential energy surface, while it is negligible on the triple potential energy surface. Without barrier height in the whole process, the major channel is R → C2H5SONO (IM1 and IM2) → P1 (C2H5SO+NO). With much heat released in the formation of C2H5SNO2 (IM3) and the transition state involved in the subsequent step more stable than reactants, P4 (CH3CHS + t-HONO) is subdominant product energetically. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero-point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6-311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6-311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero-point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6-311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6-311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

A detailed theoretical survey of the potential energy surface (PES) for the CH2CO + O(3P) reaction is carried out at the QCISD(T)/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level. The geometries, vibrational frequencies, and energies of all stationary points involved in the reaction are calculated at the B3LYP/6-311+G(d,p) level. More accurate energy information is provided by single-point calculations at the QCISD(T)/6-311+G(3df,2p) level. Relationships of the reactants, transition states, intermediates, and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. The results suggest that P1(CH2+CO2) is the most important product. This study presents highlights of the mechanism of the title reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

• First theoretical study on earthworm bioluminescence. • Calculations involve all reactions in bioluminescence of earthworm F. heliota. • Helpful for understanding F. heliota bioluminescence as well as oligochaete bioluminescence. Fridericia heliota (F. heliota) is a kind of bioluminescent earthworm discovered in Siberia. As a novel ATP-dependent bioluminescent system, its luciferin and oxyluciferin structures have been elucidated by Yampolsky group recently. Based on reliable experimental evidences, this group outlined the bioluminescent mechanism of F. heliota , which represents a momentous breakthrough in the research of earthworm bioluminescence (BL). Understandably, the experimentally proposed mechanism does not embody the details of the related chemical reactions and light emission. For the first time, the theoretical investigation in the present paper concretely described the entire process of F. heliota BL from luciferin to light emission at the molecular and electronic-state level. The calculated results indicated that the F. heliota BL initiates from the oxygenation of luciferin induced by a single electron transfer (SET) and produces the light emitter through the thermolysis of a dioxtanone intermediate via a mechanism of gradually reversible charge-transfer initiated luminescence (GRCTIL). This study not only supports and improves experimentally proposed BL mechanism, but also enriches the details of the BL process. It will be helpful for understanding F. heliota BL as well as oligochaete BL in nature. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the influence of alkalinity, A =[Na2O/H2O]b (b=batch), of the reaction mixture on structural, particulate, morphological and chemical properties of the crystalline end products obtained by hydrothermal treatment (heating at 483K for 2h) of the TPA-free reaction mixture: 1.0Al2O3/100SiO2/xNa2O/4000H2O seeded by silicalite-1 nanocrystals (260nm, 4wt.% of silica in gel mixture), was investigated by different characterization methods such as powder X-ray diffraction (XRD), scanning-electron microscopy (SEM), particle size distribution (PSD) measuring by laser light scattering (LLS) and X-ray fluorescence (XRF). The obtained results showed that, when silicalite-1 having the size of 260nm was used as seed, fully crystalline product (silicalite-1/ZSM-5) having the size in the range of 400–600nm and Si/Al ratio of 10–18 can be obtained for 0.006⩽ A ⩽0.01, in less than 2h. However, the product obtained at low (A ⩽0.005) or high (A ⩾0.011) alkalinities possess amorphous and/or phillipsite impurities, respectively. The influence of alkalinity, A, on the mentioned properties of the crystalline end product was discussed in relation to the influence of alkalinity on the relevant critical process of zeolite ZSM-crystallization in the absence of organic templates. [ABSTRACT FROM AUTHOR]

Abstract: A method based on seed surface crystallization (SSC) mechanism has been proposed for facile, rapid, controllable and low-cost synthesis of ZSM-5 zeolite with submicron-size and interesting core–shell structure. The crystallization process of the ZSM-5 zeolite with all sizes can be accomplished within 2.5h. The morphology and size of zeolite ZSM-5 products can both be facilely adjustable in the domain of 270–1100nm depending upon the characters of silicalite-1 seeds, while the thickness of aluminum-containing zeolite ZSM-5 shells can be well tuned by changing the amount of silicalite-1 seed. More interestingly, the siliceous silicalite-1 seeds within the obtained zeolite crystals could be selectively removed by alkaline treatment. By systematically tracking the crystallization process combined with mathematical analysis, the crystallization of ZSM-5 zeolites in the reaction system is revealed as SSC mechanism with a size-independent, linear growth process. Their crystal growth rate is calculated as c.a. 0.15μmh−1 regardless of the seed size and amount. [Copyright &y& Elsevier]