How hexafluoroisopropanol solvent promotes Diels-Alder cycloadditions: ab initio metadynamics simulations.

The solvent effects in Diels-Alder cycloadditions were studied by using ab initio molecular dynamics simulations with explicit molecular treatments for both substrates and solvents. Energy decomposition analysis was used to investigate the role of H-bonding networks of hexafluoroisopropanol solvent in promoting both reactivity and regioselectivity.

Origins of Regioselectivity in CuH-Catalyzed Hydrofunctionalization of Alkenes.

Factors controlling the regioselectivity in alkene hydrocupration were computationally investigated using energy decomposition analysis. The results demonstrate that the Markovnikov-selective hydrocupration with electronically activated mono-substituted olefins is mostly affected by the destabilizing Pauli repulsion, which is due to the electron delocalization effect. The anti-Markovnikov-selective hydrocupration with 1,1-dialkyl-substituted terminal olefins is dominated by the repulsive electrostatic interactions, which is because of the unequal π electron distribution caused by the induction effect of alkyl substituents.

Ab Initio Metadynamics Simulations of Hexafluoroisopropanol Solvent Effects: Synergistic Role of Solvent H-Bonding Networks and Solvent-Solute C-H/π Interactions.

The solvent effects in Friedel-Crafts cycloalkylation of epoxides and Cope rearrangement of aldimines were investigated by using ab initio molecular dynamics simulations. Explicit molecular treatments were applied for both reactants and solvents. The reaction mechanisms were elucidated via free energy calculations based on metadynamics simulations. The results reveal that both reactions proceed in a concerted fashion. Key solvent-substrate interactions are identified from the structures of transition states with explicit solvent molecules. The remarkable promotion effect of hexafluoroisopropanol solvent is ascribed to the synergistic effect of H-bonding networks and C-H/π interactions with substrates.

Weak Electrostatic Interactions with Bisphosphine Ligands Facilitate Reductive Elimination of PhCF3 from Pd(II) Complexes.

The origins of ligand effects on PhCF3 reductive elimination from PdII complexes were computationally investigated by using energy decomposition analysis. The results indicate weak electrostatic interactions between ligands and Ph-Pd-CF3 lead to small barriers of PhCF3 reductive elimination. Two major factors affecting the electrostatic interactions are identified.

Origins of regioselectivity in Ni-catalyzed hydrofunctionalization of alkenes via ligand-to-ligand hydrogen transfer mechanism.

The origins of regioselectivity in Ni-catalyzed alkene hydrofunctionalizations were computationally investigated by using energy decomposition analysis. The results indicate the Markovnikov selectivity with aryl-substituted alkenes is favored due to the stabilizing charge transfer effect, and the anti-Markovnikov selectivity with alkyl-substituted alkenes is favored because of the destabilizing Pauli repulsion effect.

Computational insights into strain-increase allylborations for alkylidenecyclopropanes.

The origins of the reactivity of strain-increase allylborations were computationally investigated. The low reactivity of vinylcyclopropyl boronates is due to weak electronic interactions between benzaldehyde and allylboronates. By increasing the acidity of the boron center, the reactivity is significantly improved because the stronger stabilizing O→B interaction effectively compensates for destabilizing steric effects.

Origin of Ligand Effects on Stereoinversion in Pd-Catalyzed Synthesis of Tetrasubstituted Olefins.

The mechanism and origin of ligand effects on stereoinversion of Pd-catalyzed synthesis of tetrasubstituted olefins were investigated using DFT calculations and the approach of energy decomposition analysis (EDA). The results reveal that the stereoselectivity-determining steps are different when employing different phosphine ligands. This is mainly due to the steric properties of ligands. With the bulkier Xantphos ligand, the syn/anti-to-Pd 1,2-migrations determine the stereoselectivity. While using the less hindered P(o-tol)3 ligand, the 1,3-migration is the stereoselectivity-determining step. The EDA results demonstrate that Pauli repulsion and polarization are the dominant factors for controlling the stereochemistry in 1,2- and 1,3-migrations, respectively. The origins of differences of Pauli repulsion and polarization between the two stereoselective transition states are further identified.

Computational study of silver-catalyzed stereoselective hydroalkylation of alkynes: Pauli repulsion controlled Z/E selectivity.

The mechanism and origin of stereoselectivity of silver-catalyzed hydroalkylation of alkynes were computationally investigated at the B3LYP-D3BJ/6-311+G(d,p)-SDD//B3LYP/6-31G(d)-LANL2DZ level. The complex of alkynyl trialkylboronate with cationic silver is a key intermediate, which triggers the rate- and stereoselectivity-determining 1,2-migration step. Energy decomposition analysis indicates that the difference of Pauli repulsion dominates the stereoselectivity.

Study on Photocatalytic Degradation of 2,4-Dichlorophenol by ZnS Microsphere.

The self-supported ZnS microsphere composed of interwoven nanosheets was synthesized by hydrothermal method. The as-prepared ZnS powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activity of the fabricated ZnS powders was evaluated by the degradation of 2,4-dichlorophenol (DCP) under UV light. Effects of DCP initial concentration, ZnS dosage, solution pH, light source, and dissolved oxygen on DCP photocatalytic degradation efficiency were investigated and optimized systematically. Results demonstrated that 53% of DCP could be effectively degraded under the optimal experimental conditions. Finally, high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) were used to analyze the degradation products. Based on the experimental results obtained, a prob- able degradation pathway was proposed.

The relationship between photoluminescence (PL) decay and crystal growth kinetics in thioglycolic acid (TGA) capped CdTe quantum dots (QDs).

The PL lifetime optimization of CdTe QDs capped with TGA has yet to be understood from a perspective of growth kinetics. In this work, the growth kinetics and PL properties of CdTe QDs growing in aqueous solutions of two TGA concentrations, 0 mM and 57 mM, were systematically investigated using UV, TEM, and PL methods. CdTe QDs in 0 mM TGA solution were found to follow the mixed OA (Oriented Attachment)-OR (Ostwald Ripening) growth kinetics. The PL peaks experienced a red-shift with almost unchanged intensity and the PL lifetimes increased gradually. In 57 mM TGA solution, the QDs followed the OA dominated growth mechanism. The PL peak broadened greatly with a red-shift and its intensity decreased significantly. The PL lifetime increased much higher than that in 0 mM TGA solution. Based on the different growth kinetic models of the two systems, we suggest that in the low (0 mM) TGA solution, the increased surface defects induced by TGA desorption and the existence of partial internal defects caused by OA growth were the main reasons for the gradual increase of PL lifetime, while in high (57 mM) TGA solution, the increase of PL lifetime was ascribed to the abundant internal defects produced by OA collision. Finally, kinetic data showed the effect of the TGA concentration on crystal growth and PL lifetime of CdTe QDs. The results might provide guidance for understanding the mechanism behind the phenomena of ligand-related PL properties.

Use of high-pressure CO2 for concentrating CrVI from electroplating wastewater by Mg-Al layered double hydroxide.

The desorption of Cr(VI) from Cr(VI)-adsorbed layered double hydroxide (Cr(VI)-LDH) and the recycling of LDH adsorbent are the bottlenecks that limit the practical application of LDH in treating Cr(VI)-containing industrial wastewater. Given the strong affinity of LDH for CO2, we studied desorption and enrichment of Cr(VI) from Cr(VI)-LDH as well as recycling of LDH in the presence of high-pressure CO2. Results showed that Cr(VI) solution with concentration of 500 mg/L could be enriched more than 20 times in each adsorption-desorption cycle. The regenerated LDH maintained the layer structure and the sheets as revealed by XRD and TEM patterns. FT-IR data showed CO2 formed HCO3(-) at high pressure. The transformation from CO2 to HCO3(-) followed by the anion-exchange with CrO4(2-) was the critical factor for Cr(VI) desorption and LDH regeneration. A pilot-scale experiment was carried out with 20 L Cr(VI)-containing electroplating wastewater. The concentration of the desorbed Cr(VI) solution could reach up to 10000 mg/L, which could be used in electroplating after appropriate adjustment. The main advantages of this method are high concentration of Cr(VI), direct reuse of enriched Cr(VI), and efficient regeneration of LDH adsorbent. This method showed promises in recycling Cr(VI) and regenerating LDH in treating industrial wastewater.

Photochromic metal complexes of N-methyl-4,4'-bipyridinium: mechanism and influence of halogen atoms.

Photochromism of N-methyl-4,4'-bipyridinium (MQ(+)) salts and their metal complexes has never been reported. A series of MQ(+) coordinated halozinc complexes [(MQ)ZnX(3)] (X = Cl (1), Br (2), I (3)) and [(MQ)ZnCl(1.53)I(1.47)](2)(MQ)ZnCl(1.68)I(1.32) (4), with better physicochemical stability than halide salts of the MQ(+) cation, have been found to exhibit different photochromic behaviors. Compounds 1-3 are isostructural, but only 1 and 2 show photochromism. Introduction of partial Cl atoms to nonphotochromic compound 3 yields compound 4, which also displays photochromism. The photochromic response of 1, 2, and 4 indicates the presence of their long-lived charge separation states, which originate from X → MQ(+) electron transfer according to ESR and XPS measurements. Studies on the influence of different coordinated halogen atoms demonstrate that the Cl atom may be a more suitable electron donor than Br and I atoms to design redox photochromic metal complexes.

A room-temperature X-ray-induced photochromic material for X-ray detection.

A color change: X-ray-induced photochromic species are rare and can be used for detection of X-rays. A highly robust X-ray-sensitive material with the discrete structure of a metal-organic complex has been found to show both soft and hard X-ray-induced photochromism at room temperature. A new ligand-to-ligand electron-transfer mechanism was proposed to elucidate this photochromic phenomenon.