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Electroreductive cross-electrophile coupling has emerged as a powerful and efficient method for constructing challenging C–C or C–X bonds, providing several advantages including highly efficient electron transfer, tunable reducing potential, direct electricity-activation of substrates and good scalability. In electroreductive cross-electrophile coupling, a high loading of a transition metal catalyst is required to facilitate the transfer of electrons from the cathode to organic halides, making it unsuitable for sensitive organic halides such as chloroformates. As a result, the electroreductive XEC of readily accessible chloroformates with alkyl halides for ester synthesis remains a largely unmet challenge. In this work, catalyst-free electrochemically driven cross-electrophile esterification of alkyl halides has been developed. A wide range of 2-phenylacetic esters which represent an important class of molecules in synthetic and medicinal chemistry are accessed from simple and cheap alkyl halides and alkyl chloroformates under mild reaction conditions. Various functional groups were well tolerated, affording up to 98% yields. This protocol would contribute a lot for the further development of electrochemically driven cross-electrophile coupling. [ABSTRACT FROM AUTHOR]

The electroreductive cross-electrophile coupling which has emerged as a powerful, green and efficient method for constructing challenging C–C bonds has attracted increasing attention from organic chemists. Most of the previous works focus on direct two-electrophile cross-coupling. In this work, the nickel-catalyzed three-electrophile electroreductive cross-electrophile coupling which offers direct convergent synthesis to target molecules from easily-available and cheap substrates has been developed. A wide range of alkyl aryl ketones are accessed from alkyl halides, aryl iodides and propyl chloroformate under mild conditions, avoiding the use of over-stoichiometric reductants, excess quantities of additives and activators, and superstoichiometric CO gas or metal carbonyl complexes which are toxic, environmentally unfriendly and can be inconvenient to handle. The scale-up experiment indicates the good scalability of electrosynthesis compared to traditional synthesis. High chemo-selectivity can be achieved through an increase in the current. Mechanistic investigation suggests that the electron transfer rate from the cathode to Ni catalysts plays a vital role in this protocol. Our approach demonstrates a novel electrochemical selectivity-controlled strategy in cross-electrophile coupling. [ABSTRACT FROM AUTHOR]

Tungsten tetraboride has been known so far as a non-stoichiometric compound with a variable composition (e.g. WB4−x, WB4+x). Its mechanical properties could exceed those of hard tungsten carbide, which is widely used nowadays in science and technology. The existence of stoichiometric WB4 has not been proven yet, and its structure and crystal chemistry remain debatable to date. Here we report the synthesis of single crystals of the stoichiometric WB4 phase under high-pressure high-temperature conditions. The crystal structure of WB4 was determined using synchrotron single-crystal X-ray diffraction. In situ high-pressure compressibility measurements show that the bulk modulus of WB4 is 238.6(2) GPa for B′ = 5.6(0). Measurements of mechanical properties of bulk polycrystalline sub-millimeter size samples under ambient conditions reveal a hardness of ∼36 GPa, confirming that the material falls in the category of superhard materials. [ABSTRACT FROM AUTHOR]

Bubble defects severely affect the optical properties of single-crystal fibers (SCFs), so it is necessary to avoid the incorporation of bubbles during crystal growth. The process of bubbles entering a crystal was observed during pulling of Lu3Al5O12 (LuAG) SCFs from ceramic pedestals by the laser-heated pedestal growth (LHPG) method. The effects of orientation and growth chamber pressure on the density and size of bubbles as well as on stress distribution were fully studied. <111>-oriented LuAG crystal fibers are likely to incorporate more and larger bubbles than <100>-oriented fibers. The low pressure in the growth chamber can limit the formation and transport of bubbles, and the bubble densities are decreased by nearly 50% with a chamber pressure of 0.3 atm. Notably, the <111>-oriented LuAG crystal fibers are more sensitive to pressure with an almost 40% decrease in the average bubble size and stress. [ABSTRACT FROM AUTHOR]

Lu2O3 crystals have attracted intense attention due to their great potential in the field of high power solid-state lasers. Lu2O3 single crystal fibers (SCFs) with a length-to-diameter ratio of >200 : 1 were successfully grown by the laser heated pedestal growth (LHPG) method for the first time. The relationships between the crystal diameter and thermal stress were investigated in detail. Crystal cracking was effectively solved by reducing the diameter of the crystal fiber. Besides, the influence of the growth atmosphere on the crystal growth was also demonstrated. The crystals grown in a mixture of 95% O2 and 5% Ar were colorless and transparent. The XRD pattern showed that the phase of Lu2O3 was pure, and the crystal quality along the axial and radial directions was measured by Laue back-reflection measurements. Meanwhile, the diameter fluctuations of the obtained Lu2O3 crystal fibers were further reduced by using optimized source rods. [ABSTRACT FROM AUTHOR]

In this work, we combine ultrasonic temperature sensing technology with single crystal fibers (SCFs) and demonstrate the performance of a high-sensitivity ultrasonic temperature sensor using YAG and LuAG crystal fibers. The high sensitivity of the sensor facilitates precision temperature sensing. We systematically explored the effects of the ultrasonic mode, doping concentration, and crystal orientation on the sensitivity of the sensor. The results illustrate that transverse waves (S-waves) are better suited to achieving high unit sensitivity compared to longitudinal waves (P-waves), by a factor of approximately 1.5. It was also determined that the unit sensitivity of the sensor, anisotropic, and increases with the increase of doping concentration within a specific range. We found that the [111]-oriented garnet crystal fiber sensors have a lower ultrasonic velocity at high temperature, and therefore possess higher unit sensitivity. The mean unit sensitivity of the [111]-oriented 10 at% Yb:LuAG SCF ultrasonic sensor in the range of 20–1100 °C was optimized to 25.21–34.83 ns °C−1 m−1, which is more than 50% higher than that of the pure YAG SCF sensor. Meanwhile, the obtained crystal fiber sensors demonstrate excellent stability at high temperature with the standard deviation of the mean unit sensitivity being less than ±5%. This work represents a feasible approach for enabling high-precision temperature measurement via the ultrasonic technique and crystal design. [ABSTRACT FROM AUTHOR]

High quality Er,Yb:CaGdAlO4 (Er,Yb:CALGO) single crystals with a diameter around 1 mm were successfully grown and investigated for the first time by the laser heated pedestal growth (LHPG) method. The cracking mechanism of (001) planes was studied via density functional theory (DFT). The doping concentration of Er3+ and Yb3+ was calculated by X-ray fluorescence analysis (XRF). The XRD pattern confirms that the phase of Er,Yb:CALGO is consistent with pure CALGO and the crystal quality was measured through Laue back-reflection measurements. The optical properties including absorption spectra, mid-infrared fluorescence spectra and fluorescence lifetime of the Er3+, Yb3+ co-doped CALGO crystal were measured at room temperature to assess its potential for improving absorption efficiency. Further research found that the disordered structure of the CALGO crystal could achieve wider absorption and emission bands accompanied with efficient energy transfer from the excited Yb3+ to Er3+. Our results indicated that the Er,Yb:CALGO crystal is a promising material for achieving tunable mid-infrared lasers. [ABSTRACT FROM AUTHOR]

A facile approach for the synthesis of enzyme–inorganic hybrid nanoflowers and their application as an immobilized α-chymotrypsin (ChT) reactor (IMER) for highly efficient protein digestion was described. The hybrid nanoflowers were room-temperature synthesized in aqueous solution using calcium phosphate (Ca3(PO4)2) as the inorganic component and ChT as the organic component. The effects of reaction parameters on the formation of the enzyme-embedded hybrid nanoflowers and their growth mechanism were investigated systematically. By monitoring the reaction of N-benzoyl-l-tyrosine ethyl ester (BTEE), the enzymatic activity of the immobilized ChT was calculated and the results showed 266% enhancement in enzymatic activity. The performance of such a nanoreactor was further demonstrated by digesting bovine serum albumin (BSA) and human serum albumin (HSA), with a stringent threshold for unambiguous identification of these digests, the yielding sequence coverages for nanoflower-based digestion were 48% and 34%, higher than those obtained with the free enzyme. The digestion time of BSA and HSA in the former case was less than 2 min, about 1/360 of that performed in the latter case (12 h). Furthermore, the residual activity of the nanoflowers decreased slightly even after eight repeated use, demonstrating promising stability. In addition, the hybrid nanoflower-based IMER was applicable to the digestion of a complex human sample, showing great promise for proteome analysis. [ABSTRACT FROM AUTHOR]

Enzymatic glucose sensors usually exhibit excellent sensitivity and selectivity but suffer from poor stability due to the negative influence of temperature and humidity on enzyme molecules. As compared to enzymatic glucose sensors, non-enzymatic counterparts are generally more stable but are facing challenges in concurrently improving both sensitivity and selectivity of a trace amount of glucose molecules in physiological samples such as saliva and sweat. Here, a novel non-enzymatic glucose sensor based on nanostructured Cu 3 Al alloy films has been fabricated by a facile magnetron-sputtering followed by controllable electrochemical etching approach. Since the metal Al is more reductive than Cu, by selectively etching aluminum in the Cu 3 Al alloys, nanostructured alloy films were obtained with increased surface contact area and electrocatalytic active sites which resulted in enhanced glucose-sensing performance. Thus, non-enzymatic glucose sensors based on nanostructured Cu 3 Al alloy films not only exhibited a high sensitivity of 1680 μA mM -1 cm -2 but also achieved a reliable selectivity to glucose without interference by other species in physiological samples. Consequently, this study sparked the potential for the development of non-enzymatic biosensors for the continuous monitoring of blood glucose levels with high sensitivity and impressive selectivity for glucose molecules., Competing Interests: The authors declare that they have no competing financial interests or personal relationships that could have influenced the work reported in this paper., (This journal is © The Royal Society of Chemistry.)