An efficient and green preparation of 5-aminophosphonate substituted pyrimidine nucleosides under solvent-free conditions

<正>An environmentally benign and highly efficient one-pot preparation ofα-aminophosphonates under solvent-free conditions was developed.By employing this method,5-aminophosphonate substituted pyrimidine nucleosides were synthesized in good to excellent yields starting from 5-formyl-2'-deoxyuridine,aniline and dimethylphosphite.     

Organocatalytic Michael addition of aldehydes to a β-silylmethylene malonate to form intermediates for the enantioselective synthesis of hydroxylated valerolactones and piperidines

The direct Michael addition of enolizable aldehydes to dimethyl(phenyl)silylmethylene malonate was catalysed by an (S)-diphenylprolinol trimethylsilyl ether/acetic acid combination. The adducts were formed in good yield, high diastereoselectivity and excellent enantioselectivity. Chiral valerolactone and piperidine skeletons embedded with a silyl and other functionalities have been made out of the adducts. A total synthesis (+)-simplactone B has been achieved from one of the adducts.     

Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals

Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano‐emitters. Extended quantum‐confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi‐level blinking of entire individual organo–lead bromide perovskite microcrystals (volume=0.1–3 μm³) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long‐range (mesoscopic) electronic communication.     

B2O3-Bi2O3-ZnO-Al2O3玻璃助烧剂对BaTiO3陶瓷烧结条件、晶体结构和介电性能的影响

通过调节B₂O₃‐Bi₂O₃‐ZnO‐Al₂O₃(BBZA)玻璃的添加量研究其对钛酸钡(BaTiO₃)陶瓷烧结条件、晶体结构和介电性能的影响。结果表明：添加适量的BBZA玻璃能够有效地将BaTiO₃陶瓷烧结温度由1350℃降至950℃,并使其致密化。同时,添加BBZA玻璃后,BaTiO₃的晶体结构随着烧结温度的升高而发生转变(立方相→四方相)。另外,BBZA玻璃的引入使BaTiO₃陶瓷的居里峰得到了有效的抑制和拓宽。陶瓷微观形貌显示,玻璃相均匀分布在BaTiO₃晶粒表面。优化的BaTiO₃陶瓷制备条件如下：BBZA添加量(质量分数)为2.0%,烧结温度为950℃。在该条件下制备的BaTiO₃陶瓷介电常数达到1364,介电损耗低至1.2%。     

Kinetics and mechanism of the oxidation of some α‐hydroxy acids by tetrachloroaurate(III) in acetic acid‐sodium acetate buffer medium

The kinetics of oxidation of some neutralized α‐hydroxy compounds such as glycolic (GA), lactic (LA), α‐hydroxyisobutyric(IB), mandelic (MA), atrolactic (AL), and benzilic (BA) acids by tetrachloroaurate(III) have been studied. The substrates are oxidized to give formaldehyde, acetaldehyde, acetone, benzaldehyde, acetophenone, and benzophenone for the respective reactions. The rate of the reaction increases with increasing [substrate] and pH but decreases with increase in [Cl⁻¹]. Temperature influence is quite marked in all these reactions. A mechanism involving the formation of an unstable complex, which decomposes to give the respective reaction products, is proposed. The reactivity of the α‐hydroxy acids towards gold(III) are as follows: AL > MA > BA > IB > LA > GA. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 873–882, 1999     

电沉积法制备金属纳米线阵列膜的偏光特性

Metal nanowire array films were prepared by electrodepositing Cu, Ag, Ni, Co and Cu-Ag on porous anodic alumina film. Optical transmittance of both the porous anodic alumina film and metal nanowire array film was measured in the wavelength range of 400---2600 nm under an obliquely incident light. The experimental results show that metal nanowire array films exhibit a prominent polarization function. It was found that optical polarization properties can be improved by choosing suitable kinds of electrodepositing metal, controlling the shape and length of nanowire, and changing the incident angle.     

二(三甲硅亚甲基)锡二芳香羧酸酯的合成和结构表征

用二(三甲硅亚甲基)二氯化锡与芳香酸按1∶2的摩尔比进行反应, 合成了11个新的含硅有机锡化合物二(三甲硅亚甲基)锡二芳香羧酸酯. 通过IR, ¹H NMR, ¹³C NMR, MS以及元素分析对这些化合物的结构进行了表征. 部分化合物生物活性的初步测定结果表明, 该类化合物对肺癌细胞SPC-A-1具有较好的体外抗癌活性.     

三(三烃硅基亚甲基)锡吡啶甲酸酯的合成和结构表征

三(三烃硅基亚甲基)锡吡啶甲酸酯的合成和结构表征;含硅有机锡化合物;合成;结构表征;生物活性     

Synthesis of hydroxy and methoxy perylene quinones, their spectroscopic and computational characterization, and their antiviral activity

Hydroxy and methoxy perylene quinones are synthesized in an attempt to isolate the essential spectroscopic and biological features of light-induced antiviral agents such as hypericin and hypocrellin. Unlike their naturally occurring counterparts, these synthetic quinones bear the carbonyl, hydroxyl, and methoxy groups in the "bay region." The hydroxy and methoxy compounds have rich absorption spectra with broad features in the visible (approximately 450-800 nm) and relatively more intense and narrow features at wavelengths < or = 350 nm. High-level ab initio quantum mechanical calculations assign the features in the absorption spectra to electronic transitions from S0 to S2 and to higher-lying electronic states. The calculations indicate that in the ground state the trans dihydroxy isomer is 12.5 kcal/mol lower in energy than the cis dihydroxy isomer and is thus the only species present. The lowest-energy trans methoxy ground state isomer and the lowest-energy cis methoxy ground state isomer are found to be degenerate. An additional cis methoxy isomer 6.3 kcal/mol higher in energy than the global minimum is assumed to contribute to the spectrum and is also considered. Finally, the synthetic compounds exhibit similar light-induced antiviral activity to each other, but significantly less than that of hypericin.     

A Mild and Efficient Method for Chlorination of Baylis–Hillman Adducts Using PPh3/Cl3CCONH2

A new and convenient stereoselective synthesis of (Z)‐2‐(chloromethyl)alk‐2‐enoates has been achieved from Baylis–Hillman adducts by treatment with PPh₃/Cl₃CCONH₂ at room temperature. The synthesis can proceed under mild and acid‐free conditions to form the products in high yields.