Diastereo-divergent synthesis of chiral hindered ethers via a synergistic calcium(II)/gold(I) catalyzed cascade hydration/1,4-addition reaction.

Hindered ethers are ubiquitous in natural products and bioactive molecules. However, developing an efficient method for the stereocontrolled synthesis of all stereoisomers of chiral hindered ethers is highly desirable but challenging. Here we show a strategy that utilizes in situ-generated water as a nucleophile in an asymmetric cascade reaction involving two highly reactive intermediates, 3-furyl methyl cations and ortho-quinone methides (o-QMs), to synthesize chiral hindered ethers. The Ca(II)/Au(I) synergistic catalytic system enables the control of diastereoselectivity and enantioselectivity by selecting suitable chiral phosphine ligands in this cascade hydration/1,4-addition reaction, affording all four stereoisomers of a diverse range of chiral tetra-aryl substituted ethers with high diastereoselectivities (up to >20/1) and enantioselectivities (up to 95% ee). This work provides an example of chiral Ca(II)/Au(I) bimetallic catalytic system controlling two stereogenic centers via a cascade reaction in a single operation.

A Reactive Force Field for Molecular Dynamics Simulations of Glucose in Aqueous Solution.

To expand the capabilities of reactive force field (ReaxFF) in simulations of biological processes involving glucose, in this work, using Metropolis Monte Carlo algorithm, new ReaxFF parameters for glucose have been developed to better describe the properties of glucose in water during molecular dynamics (MD) simulations. With the newly trained ReaxFF, the mutarotation of glucose in water can be better described, as suggested by our metadynamics simulations. In addition, the newly trained ReaxFF can better describe the distributions of the three stable conformers along the key dihedral angle of α-anomer and ß-anomer. With better descriptions of hydration around glucose, the Raman and Raman optical activity spectra can be more accurately calculated. In addition, the infrared spectra obtained from simulations with the new glucose ReaxFF are more accurate than those obtained with the original ReaxFF. We note that although our trained ReaxFF performs better than the original ReaxFF, it is not generally applicable to all carbohydrates, which require further parametrization. We also find that the absence of explicit water molecules in the training sets may lead to inaccurate descriptions of water-water interactions around the glucose, implicating that it is necessary to optimize the water ReaxFF parameters together with the target molecule. The improved ReaxFF makes it possible to explore interesting biological processes involving glucose more accurately and efficiently.

Improving upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+ by polyvalent Sb co-doping.

BiTa7O19:Er3+/Yb3+/Sb phosphors were successfully synthesized by high temperature solid sintering. X-ray diffraction (XRD), fluorescence spectrometry and X-ray photoelectron spectroscopy (XPS), were used to analyze the phase structure, upconversion luminescence (UCL) features and Sb valence state, respectively. The results suggest that polyvalent Sb with Sb3+ and Sb5+ can replace the Ta5+ sites in a BiTa7O19 host to form a pure phase. Compared with BiTa7O19:0.1Er3+/0.4Yb3+, polyvalent Sb doping further improves UCL intensity by 1.2 times under 980 nm laser stimulation with a powder density of 44.59 W cm-2. This is due to the adjustment of the local lattice structure of BiTa7O19 by the polyvalent Sb. The maximum absolute sensitivity (SA) and relative sensitivity (SR) can be estimated from the UCL variable-temperature spectra as 0.0098 K-1 at 356 K and 0.0078 K-1 at 303 K using the luminescence intensity ratio (LIR) approach. The outcomes show that host local lattice adjustment using polyvalent elements is an effective way to improve luminescence intensity, and it is possible to use BiTa7O19:Er3+/Yb3+/Sb as a temperature sensor.

Thermal enhancing effect of upconversion luminescence in Er3+/Yb3+ co-doped Cs3BiSr(P2O7)2 phosphors.

A series of Er3+/Yb3+ co-doped Cs3BiSr(P2O7)2 (CBSPO) phosphors with significant thermal enhancement were successfully prepared using the solid-state method and the thermal-enhancing effect was studied in detail. When the temperature increased from 303 to 723 K, the upconversion luminescence (UCL) emission intensities of 2H11/2 → 4I15/2 and 2H11/2 + 4S3/2 → 4I15/2 of Er3+ in CBSPO:0.1Er3+/0.2Yb3+ were enhanced 22.81 and 10.06 times under 980 nm laser excitation, respectively. Meanwhile, the UCL color of the sample obviously changed from orange to green with the increase in temperature. Furthermore, the UCL thermal enhancement mechanism was demonstrated, which originates from phonon-assisted transitions. In addition, the maximum absolute temperature sensitivity for CBSPO:0.1Er3+/0.2Yb3+ was calculated to be 0.01026 K-1 at 563 K via luminescence intensity ratio (LIR) technology. All the results show that the CBSPO:Er3+/Yb3+ phosphors can be used for safety warning and temperature measurement at high temperatures.

Polarizable force field parameterization and theoretical simulations of ThCl4 -LiCl molten salts.

Recycle of thorium is an essential process in the thorium-uranium closed fuel cycle of molten salt reactor (MSR). Pyrochemical treatment of spent nuclear fuel using chloride molten salts as medium has been considered as a promising method. In this article, we performed molecular dynamics simulations on the ThCl4 LiCl molten salts using a polarizable force field parameterized by us from first-principles calculations. The microscopic structures and macroscopic properties at different compositions were investigated using the developed force field to understand the structure/property relationship in the mixture. The differences between ThCl4 LiCl and ThF4 LiF MSs are compared to understand the behaviors of Th4+ in the fluoride-chloride mixed media. In the molten fluorides, the coordination number of Th4+ is larger, and the resulting more shared anions lead to lower ThF dissociation barrier and shorter lifetime of the Th4+ first solvation shell. Our results also indicate the Pauling's structural rules for crystals can be used to rationalize the local structures in molten salts. © 2018 Wiley Periodicals, Inc.

The influence of NHCs on C-Si and C-C reductive elimination: a computational study of the selectivity of Ni-catalyzed C-H activation of arenes with vinylsilanes.

Density functional theory calculations were performed to investigate the mechanism and origins of the NHC-controlled selectivity of Ni-catalyzed C-H activation of arenes with vinylsilanes. The key to the selectivity is the different impacts of NHCs on the C-Si/C-C reductive elimination of the square-planar/T-shaped intermediate.