Chemical analyses of martian soil and rocks obtained by the Pathfinder Alpha Proton X-ray spectrometer

The US Mars Pathfinder spacecraft, which landed on the red planet on the 4th of July 1997, carried an Alpha Proton X-ray Spectrometer (APXS) that obtained the chemical composition of martian soil and rocks. The principles of the APXS operation are based on three interactions of alpha particles with matter: Rutherford alpha backscattering; (, p) nuclear reactions; and X-ray generation by charged particles and X-ray excitation. The APXS, as was implemented on the Pathfinder mission, uses for all three modes of operation a monoenergetic beam of alpha particles from about 40 mCi of ²⁴⁴Cm radioisotope. It employs Si charged particle detectors for alpha and proton modes and a specially designed silicon PIN detector for its X-ray mode that does not require cooling for its operation. The APXS can detect all of the elements (except H and He) present above a few tenths of a percent for all major elements and several hundred ppm for many minor and trace elements.

The APXS on Pathfinder was transported to various locations on the martian surface by the Sojourner rover which enabled it to analyze multiple soil and rock samples selected by the science team from the lander camera images. The APXS performed excellently under the adverse martian environment conditions and provided important information about the chemical composition of the martian soil and rocks. All of the analyzed rocks at the Pathfinder site were found to have high concentrations of silica, sulfur and iron, and low in magnesium, similar to those of the terrestrial basaltic andesites and definitely different from the SNC meteorites that are believed to have originated from Mars. All of the soil samples analyzed by the APXS have similar composition and are very close to the soil analyses obtained by the two Viking missions. The information derived from the Pathfinder APXS has significant implications about the origin and evolution of planet Mars.     

New supports for enzyme immobilization based on copolymers of vinylene carbonate and acrylamide

In this study, a series of beadlike and hydrophilic supports containing reactive cyclic carbonate groups for enzyme immobilization were prepared via reverse-phase suspension copolymerization of the aqueous solutions of vinylene carbonate (VCA), acrylamide (AA), and N,N′-methylene bisacrylamide in paraffin oil. The supports were used as a matrix for immobilization of trypsin and showed a considerable capacity to couple with trypsin and reasonable retention of activity for the immobilized trypsin, depending on the immobilization conditions, such as the content of VCA structural units, reaction time, and pH of the medium.     

Attempt to Synthesize Hindered 2,4,6‐Tri‐Aryloxy‐s‐Triazines: Bis(2,4‐di‐tert‐Butylphenyl) Carbonate – Crystal Structure

Some less hindered 2,4,6‐tri‐aryloxy‐s‐triazines were synthesized through the reaction of the corresponding phenols as a starting materials with cyanogen bromide (BrCN) to obtain the corresponding arylcyanates and then trimerized. Unexpectedly, 2,4‐di‐tert‐butyl‐1‐cyanatobenzene derived from 2,4‐di‐tert‐butylphenol did not trimerize but, indeed, yielded bis(2,4‐di‐tert‐butylphenyl) carbonate. The structures of 2,4,6‐tri‐aryloxy‐s‐triazines and bis(2,4‐di‐tert‐butylphenyl) carbonate were characterized by means of IR, ¹H, and ¹³C NMR spectroscopies. Also the structure of the latter compound was studied by X‐ray crystallography.     

Composite poly(ethylene carbonate) electrolytes with electrospun silica nanofibers

We prepared a ternary composite polymer electrolyte from poly(ethylene carbonate) (PEC), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and non‐calcined silica nanofibers (SNFs) having 3 average diameters (300, 700, and 1000 nm). The SNF composite electrolytes were obtained as homogeneous, self‐standing membranes. The ionic conductivity of PEC/LiTFSI 100 mol% was increased by the addition of SNFs, and the thinner SNFs with average diameter 300 nm were most effective in improving the conductivity. The conductivity was of the order of 10⁻⁴ S/cm at 60°C. The lithium transference number of the SNF₃₀₀ composite was greater than 0.7. Stress‐strain curves of the composites indicated significant increases in Young's modulus and maximum stress for the PEC electrolytes. The 5% weight‐loss temperature of the composites also improved with the addition of SNF.     

Composites of poly(L‐lactide‐trimethylene carbonate‐glycolide) and surface modified SBA‐15 as bone repair material

This work aims to develop novel composites from a poly(L ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer and mesoporous silica (SBA‐15) nanofillers surface modified by post‐synthetic functionalization. SBA‐15 first reacts with a silane coupling agent, γ‐aminopropyl‐trimethoxysilane to introduce ammonium group. PLLA chains were then grafted on the surface of SBA‐15 through ammonium initiated ring‐opening polymerization of L ‐lactide. Composites were prepared via solution mixing of PLTG terpolymer and surface modified SBA‐15. The structures and properties of pure SBA‐15, γ‐aminopropyl‐trimethoxysilane modified SBA‐15 (H₂N‐SBA‐15), PLLA modified SBA‐15 (PLLA‐NH‐SBA‐15), and PLTG/PLLA‐NH‐SBA‐15 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, N₂ adsorption‐desorption, differential scanning calorimetry, contact angle measurement, and mechanical testing. The results demonstrated that PLLA chains were successfully grafted onto the surface of SBA‐15 with grafting amounts up to 16 wt.%. The PLTG/PLLA‐NH‐SBA‐15 composites exhibit good mechanical properties. The tensile strength, Young's modulus, and elongation at break of the composite containing 5 wt.% of PLLA‐NH‐SBA‐15 were 39.9 MPa, 1.3 GPa, and 273.6%, respectively, which were all higher than those of neat PLTG or of the composite containing 5 wt.% of pure SBA‐15. Cytocompatibility tests showed that the composites present very low cytotoxicity.     

碳酸乙烯酯选择加氢合成甲醇与乙二醇高效稳定Cu/SiO2催化剂研究

CO2作为重要的碳氧资源, 具有来源丰富、价格低廉、安全等突出优点. 近年来, 由于蕴含的巨大利用潜力,CO2间接利用制备基础化学品、能源燃料对于可持续制备大宗化工品中具有重要研究意义, 日益受到研究者和工业界的广泛重视.甲醇与乙二醇是化学工业中的两种重要大宗原料. 甲醇不仅是重要的有机化工原料、清洁环保的液体燃料, 同时也是氢气和能量储存的良好载体. 乙二醇作为一种重要的有机化工原料, 在聚酯等领域具有广泛应用.CO2经碳酸乙烯酯氢解制备甲醇/乙二醇是典型的原子经济反应, 对资源、能源和环境的可持续发展具有重要意义. 需要指出的是,CO2与环氧乙烷环加成制备碳酸乙烯酯已具备成熟的工业化技术. 因此, 该路线研究重点在于发展碳酸乙烯酯选择加氢联产甲醇和乙二醇高效稳定的催化体系. 近年来, 铜基多相催化剂催化碳酸乙烯酯加氢联产甲醇乙二醇得到了广泛重视. 由于铜基催化剂存在活性较低、高温易失活等问题, 开发高效且具有良好稳定性的铜基催化剂是目前碳酸乙烯酯加氢研究重点.本文针对碳酸乙烯酯选择氢解合成甲醇乙二醇新型铜基催化体系构建和构效关系研究, 采用硅溶胶蒸氨法制备高分散 Cu/SiO2过程中引入多羟基β-环糊精修饰催化剂前驱体的合成策略, 并通过惰性气体中煅烧后的积碳有效抑制活性铜物种的团聚, 获得了β-环糊精改性的 Cu/SiO2催化剂. 通过 N2吸脱附、XRD、N2O 滴定、H2-TPR、TEM 和 XPS 等系统表征,发现β-环糊精可有效调控催化剂结构和表面不同价态活性铜物种分布. 碳酸乙烯酯加氢性能评价结果表明引入适量β-环糊精的 5β-25%Cu/SiO2具有较优催化活性, 乙二醇选择性 98.8% 和甲醇选择性 71.6%, 且相应的催化活性可达 1178 mgEC gcat-1h-1. 高活性的原因很可能归因于不同价态 Cu0与 Cu+物种协同催化作用及适宜的 Cu+/(Cu0+Cu+) 比例. 结合密度泛函理论模拟计算, 我们提出了 Cu0促进氢气解离、Cu+吸附活化碳酸乙烯酯分子中酯羰基的反应机理. 催化剂重复使用和表征结果表明, 5β-25%Cu/SiO2具有良好的稳定性, 使用前后铜粒子大小和铜物种分布几乎未发生明显变化. 本文为解决铜基催化剂高温易烧结等难题提供了简单有效的活性铜物种稳定化方法, 并为CO2经碳酸乙烯酯绿色合成甲醇、乙二醇高效稳定铜基催化新体系的构筑提供了有益借鉴.     

采用金属有机骨架材料M(HBTC)(4,4'-bipy)·3DMF(M=Ni,Co,Zn)催化CO2与环氧丙烷的环加成反应

采用溶剂热法合成了三种M(HBTC)(4,4’-bipy)·3DMF (M = Ni, Co, Zn, HBTC = 1,3,5-均苯三甲酸, 4,4’-bipy = 4,4′-联吡啶)结构的支柱层金属有机骨架材料(MOFs). 首次采用溶剂热和微波法合成了Zn(HBTC)(4,4’-bipy)·3DMF, 并采用多种物理化学方法对其进行了表征. M(HBTC)(4,4’-bipy)·3DMF中包含有M2+离子的蜂窝网格层和BTC单元, BTC单元与4,4’-联吡啶柱进一步交联形成三维多孔骨架材料. 在采用烷基铵卤化物作为助催化剂和无溶剂的条件下, 所有MOFs材料均对催化固定CO2与环氧化合物环加成制备环状碳酸酯反应表现出非常好的协同催化性能, 其催化活性高低顺序为: Zn ＞ Co ＞Ni, 这可通过酸-碱双功能特性进行解释. 采用微波法合成的Zn(HBTC)(4,4’-bipy)·3DMF材料表现出与常规催化剂相似的物理化学性质和催化性能. 考察了不同制备参数的影响和材料的重复使用性能, 并提出了该反应的可能机理.     

Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen

Solid alkali metal carbonates are universal passivation layer components of intercalation battery materials and common side products in metal‐O₂ batteries, and are believed to form and decompose reversibly in metal‐O₂/CO₂ cells. In these cathodes, Li₂CO₃ decomposes to CO₂ when exposed to potentials above 3.8 V vs. Li/Li⁺. However, O₂ evolution, as would be expected according to the decomposition reaction 2 Li₂CO₃→4 Li⁺+4 e^?+2 CO₂+O₂, is not detected. O atoms are thus unaccounted for, which was previously ascribed to unidentified parasitic reactions. Here, we show that highly reactive singlet oxygen (¹O₂) forms upon oxidizing Li₂CO₃ in an aprotic electrolyte and therefore does not evolve as O₂. These results have substantial implications for the long‐term cyclability of batteries: they underpin the importance of avoiding ¹O₂ in metal‐O₂ batteries, question the possibility of a reversible metal‐O₂/CO₂ battery based on a carbonate discharge product, and help explain the interfacial reactivity of transition‐metal cathodes with residual Li₂CO₃.     

Expeditious synthesis of 9-allenylpurines via cesium carbonate catalyzed isomerization of 9-alkynylpurines

An expeditious and convenient method to synthesize 9-allenylpurines via cesium carbonate catalyzed isomerization of 9-alkynylpurines has been successfully developed. The reactions proceeded rapidly under the base conditions and formed the desired products in good to excellent yields. The method was suitable with a broad substrate scope and proceeded well even on a multgram-scale. The obtained 9-allenylpurines were successfully applied to prepare various potential bioactive 9-acyclic nucleosides with high regioselectivity promoted by AgNO₃.     

Biodegradation of copolymers composed of optically active L‐lactide and (R)‐ or (S)‐1‐methyltrimethylene carbonate

Random copolymerizations of L ‐lactide with (R)‐, (S)‐, or rac‐1‐methyltrimethylene carbonate with bis(pentamethylcyclopentadienyl) samarium‐methyl tetrahydrofuranate [(C₅Me₅)₂SmMe(THF)] as a novel initiator provided high molecular weight polymers with low polydispersities. Biodegradation of the resulting polymers with tricine and {N‐[tris(hydroxymethyl)methyl]‐2‐aminoethane sulfonic acid (TES) buffers as well as activated sludge showed only a small weight loss, whereas the polymer with proteinase K revealed high biodegradability independent of the optical activity of 1‐methyltrimethylene carbonate. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3916–3927, 2001