Design, Synthesis, and Photochemical Behavior of Poly(benzyl ester) Dendrimers with Azobenzene Groups throughout Their Architecture

A new class of dendrons and dendrimers containing azobenzene units (bearing up to 29 azobenzene groups for four generations) were designed and synthesized with the convergent method, which uses azobenzene derivatives as monomers and benzyl ester groups as linkages leading to photoresponsive dendrons and dendrimers with azobenzene units throughout their architecture. Photochemical isomerization experiments revealed that all of the dendrons and dendrimers undergo trans−cis isomerization by irradiation and cis−trans isomerization by either irradiation or heating

Design, Synthesis, and Photochemical Behavior of Poly(benzyl ester) Dendrimers with Azobenzene Groups throughout Their Architecture

A new class of dendrons and dendrimers containing azobenzene units (bearing up to 29 azobenzene groups for four generations) were designed and synthesized with the convergent method, which uses azobenzene derivatives as monomers and benzyl ester groups as linkages leading to photoresponsive dendrons and dendrimers with azobenzene units throughout their architecture. Photochemical isomerization experiments revealed that all of the dendrons and dendrimers undergo trans−cis isomerization by irradiation and cis−trans isomerization by either irradiation or heating

Design, Synthesis, and Photochemical Behavior of Poly(benzyl ester) Dendrimers with Azobenzene Groups throughout Their Architecture

A new class of dendrons and dendrimers containing azobenzene units (bearing up to 29 azobenzene groups for four generations) were designed and synthesized with the convergent method, which uses azobenzene derivatives as monomers and benzyl ester groups as linkages leading to photoresponsive dendrons and dendrimers with azobenzene units throughout their architecture. Photochemical isomerization experiments revealed that all of the dendrons and dendrimers undergo trans−cis isomerization by irradiation and cis−trans isomerization by either irradiation or heating

Design, Synthesis, and Photochemical Behavior of Poly(benzyl ester) Dendrimers with Azobenzene Groups throughout Their Architecture

A new class of dendrons and dendrimers containing azobenzene units (bearing up to 29 azobenzene groups for four generations) were designed and synthesized with the convergent method, which uses azobenzene derivatives as monomers and benzyl ester groups as linkages leading to photoresponsive dendrons and dendrimers with azobenzene units throughout their architecture. Photochemical isomerization experiments revealed that all of the dendrons and dendrimers undergo trans−cis isomerization by irradiation and cis−trans isomerization by either irradiation or heating

Study of Incorporating Cesium into Copper Hexacyanoferrate by Density Functional Theory Calculations

Copper hexacyanoferrate (Cu-HCF), a Prussian blue analogue, has the ability to incorporate Cs+ ions into its structure; it is thus a candidate to selectively extract radioactive Cs+ from water and to sequester it. We use density functional theory calculations to probe the incorporation of Cs+, K+, and Na+ ions into Cu-HCF. Specifically, we determine their incorporation energies, energies for the exchange of alkali ions, lattice stabilities, and the strengths of the bonds between the transition metal and CN ligand. We find that all of these are more favorable for Cs+ than for either Na+ or K+. In addition, we analyze the electronic structure to explain the favorability of Cs+ incorporation. Cu-HCF is found to switch from a ferromagnetic structure to an antiferromagnetic structure as the number of incorporated alkali ions increases

Electrochemical Oxidation of 2-Pyrimidinethiols and Theoretical Study of Their Dimers, Disulfides, Sulfenyl Radicals, and Tautomers

The relative energies and structures of 2-pyrimidinethiol (1), 4-methyl-2-pyrimidinethiol (3), 5-methyl-2-pyrimidinethiol (5), and 4,6-dimethylpyrimidinethiol (7), and their dimers, disulfides, sulfenyl radicals, and tautomers have been studied using restricted and unrestricted ab initio theory, density functional theory, complete basis set methods, coupled cluster theory, and quadratic configuration interaction calculations. The electrochemical oxidation of 2-pyrimidinethiol (1), 4-methyl-2-pyrimidinethiol (3), and 4,6-dimethylpyrimidinethiol (7) in ethanenitrile affords the respective disulfides in excellent yields. The less polar 2-pyrimidinethiol tautomers are predicted to be the dominant species in the gas phase. CBS-QB3, CBS-Q, CCD, CCSD(T), QCISD(T), and MP2 predict the energy difference (Erel) between (1) and its tautomer (2-pyrimidinethione, 2) to be in the narrow range from 7.23 to 7.87 kcal/mol. Similar trends are observed in the Erel values for the respective tautomers of 2-pyrimidinethiols (3), (5), and (7). The hybrid density functionals B3LYP, B3P86, B3PW91, and MPW1PW91 predict smaller values for Erel between the tautomers than any of the other models. Substitution of methyl groups at positions 4 and 6 of the pyrimidine ring lowers the energy difference between the respective tautomers while a methyl group at position 5 has little effect. The 2-pyrimidinethiol dimer (13) is predicted to be 5.52 and 4.12 kcal/mol, respectively, lower in energy than the isomeric 2-pyrimidinethione dimer (14) and heterodimer (15). The intramolecular four center transition states (TS1) for the tautomerization of 2-pyrimidinethiols (1, 3a, 3b, 5, and 7) in the gas phase have activation barriers of 34.84, 34.42, 34.02, 35.16, and 33.64 kcal/mol, respectively. Alternative lower energy pathways for tautomerism in the gas phase involve dimers and dimer transition states. Dimers and dimer transition states are also involved in the electrochemical oxidation of the 2-pyrimidinethiols. The APT, Mulliken (MPA), and NBO partial atomic charges are compared with the CHELPG and MKS charges that give the most consistent and similar results

Synthesis, Structure, and Catalytic Activity of Mononuclear Iron and (μ-Oxo)diiron Complexes with the Ligand 2,6-Bis(<i>N</i>-methylbenzimidazol-2-yl)pyridine

Iron complexes including polyimidazole and exchangeable ligands are studied with the aim of modeling the structural and functional features of the non-heme iron centers of dinuclear proteins, such as methane monooxygenase. In [Fe2OL2(MeOH)2(NO3)2](NO3)2 (1) (L = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine), each Fe(III) is in a distorted octahedral environment and has a donor set of N3O3 which includes three N atoms from L and three O atoms from a nitrate, μ-oxo, and methanol. In complex [FeLCl3] (2) (L = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine), Fe(III) is coordinated to three nitrogen atoms from L and three chloride ions. Complex 1 efficiently catalyzed the oxidation of cyclohexane with 51% conversion to cyclohexanol. It also catalyzed the epoxidation of styrene, cyclohexane, 2-methyl-2-butene, and cis- and trans-2-heptene with 51−84% conversions and high selectivity (71−99%) for epoxide products. Complex 2, however, has no specific reactivity toward these substrates. From the alcohol/ketone (A/K) ratio close to 1 in the oxidation of cyclohexane, the low KIE (kinetic isotope effect KH/KD ratio = 1.8) for cyclohexanol formation, and the nonstereospecificity of the oxidation of cis-dimethylcyclohexane, it can be concluded that long-lived alkyl radicals are involved in the oxidation catalyzed by complex 1. On the other hand, the stereospecific epoxidation of alkenes, the stereoselective oxidation of cumene, and the high degree of retention of configuration in the oxidation of cis- and trans-2-heptene suggest that a nonradical species, probably a metal-based intermediate, is involved in the oxidation of alkenes and cumene

Synthesis, Structure, and Catalytic Activity of Mononuclear Iron and (μ-Oxo)diiron Complexes with the Ligand 2,6-Bis(<i>N</i>-methylbenzimidazol-2-yl)pyridine

Iron complexes including polyimidazole and exchangeable ligands are studied with the aim of modeling the structural and functional features of the non-heme iron centers of dinuclear proteins, such as methane monooxygenase. In [Fe2OL2(MeOH)2(NO3)2](NO3)2 (1) (L = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine), each Fe(III) is in a distorted octahedral environment and has a donor set of N3O3 which includes three N atoms from L and three O atoms from a nitrate, μ-oxo, and methanol. In complex [FeLCl3] (2) (L = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine), Fe(III) is coordinated to three nitrogen atoms from L and three chloride ions. Complex 1 efficiently catalyzed the oxidation of cyclohexane with 51% conversion to cyclohexanol. It also catalyzed the epoxidation of styrene, cyclohexane, 2-methyl-2-butene, and cis- and trans-2-heptene with 51−84% conversions and high selectivity (71−99%) for epoxide products. Complex 2, however, has no specific reactivity toward these substrates. From the alcohol/ketone (A/K) ratio close to 1 in the oxidation of cyclohexane, the low KIE (kinetic isotope effect KH/KD ratio = 1.8) for cyclohexanol formation, and the nonstereospecificity of the oxidation of cis-dimethylcyclohexane, it can be concluded that long-lived alkyl radicals are involved in the oxidation catalyzed by complex 1. On the other hand, the stereospecific epoxidation of alkenes, the stereoselective oxidation of cumene, and the high degree of retention of configuration in the oxidation of cis- and trans-2-heptene suggest that a nonradical species, probably a metal-based intermediate, is involved in the oxidation of alkenes and cumene

Investigation of Supercritical Methane Adsorption of Overmature Shale in Wufeng-Longmaxi Formation, Southern Sichuan Basin, China

Accurately determining the gas sorption capacity of a specific shale reservoir is critical for further assessment of shale gas reserves. A series of high-pressure methane adsorption measurements were conducted at 60 °C with a pressure of up to 30 MPa for Wufeng-Longmaxi shales from the southern Sichuan Basin, which is considered as the most promising shale-gas target in China, to evaluate the fitting quality of different excess adsorption models and to determine the effect of organic matter content, maturity, mineralogy, and pore structure on the gas adsorption capacity. Both the Langmuir- and supercritical Dubinin–Radushkevich (SDR)-based adsorption models are closely fitted with the measured excess adsorption amount. However, the freely fitted SDR model is considered to be the most reasonable model, in which the adsorbed-phase density is always lower than the liquid methane density at the boiling point (0.424 g/cm3) and the average relative error (ARE) is relatively small. Adsorbed-phase density is a key parameter for calculating absolute adsorption isotherms. For a specific shale, a lower constant adsorbed-phase density applied in the adsorption model would result in higher absolute adsorption capacity. For the Langmuir-based model, the actual absolute adsorption capacity would be underestimated when adsorption experiments were only conducted at the low-pressure range (0–15 MPa). The methane adsorption capacities show a great positive correlation with the total organic carbon (TOC) content. The TOC-normalized adsorption capacities have a negative relationship with maturity at an overmature stage. The clay content shows a positive correlation with the TOC-normalized adsorption capacities, indicating that clays also make some contribution to methane sorption on these organic-rich shales. Furthermore, methane adsorption in overmature shales is mainly controlled by the structure of the pore <20 nm in size, revealing that the adsorbed methane is occupied not only in micropores but also in fine mesopores

DataSheet1_A spatial network analysis of vegetable prices based on a partial granger causality approach.xlsx

The spatial difference in agricultural product prices is a crucial factor affecting the benefits of related stakeholders. This study aims to analyze the mechanisms of spatial price transmission. In this paper, taking garlic as an example, we present a vector autoregression model analyzing relations of the price transmission between producing and selling cities. The partial Granger causality test is used to determine the direction and path of price transmission between the main producing areas and the main consuming areas. We find that the prices in different areas have a complex transmission network and fluctuate in correlation with each other. The results reveal the characteristics of agricultural product price transmission in China and provide reasons and evidence for market regulation.</p