Observing High‐Pressure Chemistry in Graphene Bubbles

Using IR spectroscopy, high‐pressure reactions of molecules were observed in liquids entrapped by graphene nanobubbles formed at the graphene–diamond interface. Nanobubbles formed on graphene as a result of thermally induced bonding of its edges with diamond are highly impermeable, thus providing a good sealing of solvents within. Owing to the optical transparency of graphene and diamond, high‐pressure chemical reactions within the bubbles can be probed with vibrational spectroscopy. By monitoring the conformational changes of pressure‐sensitive molecules, the pressure within the nanobubble can be calibrated as a function of temperature and it is about 1 GPa at 600 K. The polymerization of buckministerfullerene (C₆₀), which is symmetrically forbidden under ambient conditions, is observed to proceed in well‐defined stages in the pressurized nanobubbles.     

Photochemically Engineering the Metal–Semiconductor Interface for Room‐Temperature Transfer Hydrogenation of Nitroarenes with Formic Acid

A mild photochemical approach was applied to construct highly coupled metal–semiconductor dyads, which were found to efficiently facilitate the hydrogenation of nitrobenzene. Aniline was produced in excellent yield (>99 %, TOF: 1183) using formic acid as hydrogen source and water as solvent at room temperature. This general and green catalytic process is applicable to a wide range of nitroarenes without the involvement of high‐pressure gases or sacrificial additives.     

An Unexpected Fluctuating Reactivity for Odd and Even Carbon Numbers in the TiO2‐Based Photocatalytic Decarboxylation of C2‐C6 Dicarboxylic Acids

The degradation behaviours of five straight‐chain dicarboxylic acids (from ethanedioic acid to hexanedioic acid) were compared in aqueous TiO₂‐based photocatalysis. When all other conditions were identical, the degradation rates were found to fluctuate regularly with the parity of the number of carbon atoms. Dicarboxylic acids with an even number of carbon atoms (e‐DAs) always degraded more slowly than those acids with an odd number of carbon atoms (o‐DAs). This unusual fluctuation in the reactivity for the degradation of dicarboxylic acids by TiO₂‐based photocatalysis is very closely related to the different pre‐coordination modes of the acids with the photocatalyst. Attenuated total reflection FTIR (ATR‐FTIR) of e‐DAs labelled with ¹³C showed that both carboxyl groups of the acid coordinate to TiO₂ through bidentate chelating forms. In contrast, only one carboxyl group of the o‐DAs coordinated to TiO₂ in a bidentate chelating manner, whereas the other formed a monodentate binding linkage. The bidentate chelating form with bilateral symmetric coordination did not favour degradation. Isotope‐labelling experiments were performed with ¹⁸O₂ to observe the different ways in which incorporated oxygen entered the initial decarboxylated products of e‐ and o‐DAs. For the degradation of butanedioic acid, (45.9±0.5) % of the oxygen in the formed propanedioic acid came from H₂O, whereas for pentanedioic acid, (97.4±0.2) % of the oxygen in the formed butanedioic acid came from H₂O. Our results demonstrate that in TiO₂‐based photocatalysis, the reactivity of active species, such as ^. OH/h_vb⁺, is far from non‐selective and that the attacks of these active species on organic substrates are significantly affected by the coordination patterns of the substrates on the TiO₂ surface.     

Visible‐Light‐Responsive Reversible Photoacid Based on a Metastable Carbanion

A new photoacid that reversibly changes from a weak to a strong acid under visible light was designed and synthesized. Irradiation generated a metastable state with high C?H acidity due to high stability of a trifluoromethyl‐phenyl‐tricyano‐furan (CF₃PhTCF) carbanion. This long‐lived metastable state allows a large proton concentration to be reversibly produced with moderate light intensity. Reversible pH change of about one unit was demonstrated by using a 0.1 mM solution of the photoacid in 95 % ethanol. The quantum yield was calculated to be as high as 0.24. Kinetics of the reverse process can be fitted well to a second‐order‐rate equation with k=9.78×10² M ^?1 s^?1. Response to visible light, high quantum yield, good reversibility, large photoinduced proton concentration under moderate light intensity, and good compatibility with organic media make this photoacid a promising material for macroscopic control of proton‐transfer processes in organic systems.     

Synthesis of Site‐Specifically Phosphate‐Caged siRNAs and Evaluation of Their RNAi Activity and Stability

A complete set of new photolabile nucleoside phosphoramidites were synthesized, then site‐specifically incorporated into sense or antisense strands of siRNA for phosphate caging. Single caging modification was made along siRNA strands and their photomodulation of gene silencing were examined by using the firefly luciferase reporter gene. Several key phosphate positions were then identified. Furthermore, multiple caging modifications at these key positions led to significantly enhanced photomodulation of gene silencing activity, suggesting a synergistic effect. The caging group on both the terminally phosphate‐caged siRNA and the single‐stranded caged RNA has comparatively high stability, whereas hydrolysis of the caged group from the internally caged siRNA was observed, irrespective of the presence of Mg²⁺. Molecular dynamic simulations demonstrated that enhanced hydrolysis of the caging group on internally phosphate‐caged siRNAs was due to easy fragmentation of the caging group upon formation of the pentavalent intermediate of the phosphotriester with attack by water. The caging group in the terminally phosphate‐caged siRNA or single‐stranded caged RNA prefers to form π–π stacks with nearby nucleobases. In addition to providing explanations for previous observations, this study sheds further light on the design of caged oligonucleotides and indicates the direction of future development of nucleic acid drugs with phosphate modifications.     

Unraveling the Crystal Structure of Lanthanide–Murexide Complexes: Use of an Ancient Complexometry Indicator as a Near‐Infrared‐Emitting Single‐Ion Magnet

Herein, we provide some structural evidence of the complexation color‐change of murexide solutions in presence of lanthanide, which has been used for decades in complexometric studies. For Ln=Sm to Lu and Y, the compounds crystallize as monomeric [Ln(Murex)₃] ? 11 H₂O with an N3O6 tricapped square‐antiprism environment, which are stable up to 250 °C. Single‐ion magnet (SIM) behavior is then observed on the Yb^III derivative in an original nine‐coordinated environment. In‐field slow relaxation (Δ=(15.6±1) K; τ₀=2.73×10^?6 s) is observed with a very narrow distribution of the relaxation time (α_max=0.09). Magnetic and photophysical properties can be correlated. On one hand the analysis of NIR emission spectrum permits to have access to crystal field parameters and to compare them with those extracted from dc measurements. On the other hand, magnetic measurements permit to identify the nature of the M _J states involved in the ²F_5/2→²F_7/2 luminescence spectrum. The gap between the low‐lying states is in agreement with the energy barrier obtained from magnetic slow‐relaxation measurement.     

乙酰丙酮氧钼催化的苯乙烯双羟化反应

以钼酸铵与乙酰丙酮反应生成催化剂乙酰丙酮氧钼MoO2(acac)2,考察了反应溶剂、氧化剂存在形式、不同助催化剂、反应温度、底物配比和催化剂量对苯乙烯双羟化反应的影响。在优化的反应条件下,以过氧叔丁醇为氧化剂得到苯乙烯双羟化反应的转化率、化学选择性和分离产率分别为85.2%、70.7%和53.3%。并探讨了可能的催化机理以及改进方向。     

甲基绿褪色光度法测定琥乙红霉素

在pH 7.8的磷酸盐缓冲溶液中,琥乙红霉素和甲基绿在50℃下可以反应形成稳定的离子缔合物。冷却至室温后以水做参比测定体系的吸收光谱,发现琥乙红霉素溶液在550~670 nm几乎无吸收,甲基绿在此区域有强烈的吸收,甲基绿与琥乙红霉素生成的离子缔合物的吸光度与甲基绿相比有明显降低,最大褪色波长在634 nm附近,且吸光度变化ΔA与琥乙红霉素的浓度成正比。琥乙红霉素的质量浓度在0.0009~0.1530 mg/mL范围内服从Beer定律,线性回归方程为:A=-3.037ρ+0.0355,r=0.9995;对10.00 mL 5.0×10-3mg/mL琥乙红霉素测定6次,RSD=0.6%,在634 nm测得ε=6.19×104L·mol-1·cm-1。研究了琥乙红霉素-甲基绿反应体系的光谱特性、反应的影响因素、共存物质的影响,做了反应的条件优化实验,对所建立的方法进行了一些初步的分析应用。在实验基础上,建立了测定琥乙红霉素的褪色分光光度法,检出限为0.21μg/mL,可用于琥乙红霉素片中琥乙红霉素含量的测定。     

稀土对管线钢中碳化物溶解与析出行为的影响

以X80管线钢为研究对象,研究了稀土对含铌钢奥氏体化与析出行为的影响。利用热力学固溶度积公式,计算了铌碳化物的溶解温度;借助显微组织观察与硬度测试,对比分析了稀土对高温下奥氏体晶粒粗化及不同温度淬火回火后硬度的影响;通过热模拟实验并利用透射电镜,研究了稀土对实验钢在热变形过程中铌碳氮化物析出行为的作用机制。结果表明:稀土元素的加入降低了碳氮化物的固溶温度,促进了Nb(C,N)等第二相粒子的固溶,稀土能够促进热变形过程中Nb(C,N)的析出,从而提高铌元素的析出强化效果。     

Redox Chemistry of a Hydroxyphenyl‐Substituted Borane

Chemical reduction of a hydroxyphenyl‐substituted borane triggers a sequential electron‐ and intramolecular hydrogen‐atom‐transfer process to afford a hydridoborate phenoxide dianion. On the other hand, hydrogen‐atom abstraction of the borane leads to the isolation of a neutral borylated phenoxyl radical, which can be transformed to the corresponding benzoquinone borataalkene derivative by reduction with cobaltocene.