Synthesis of Imides by Palladium‐Catalyzed C?H Functionalization of Aldehydes with Secondary Amides

An efficient palladium‐catalyzed C? H functionalization of aldehydes with various N‐substituted N‐heteroarene‐2‐carboxamides has been developed for the synthesis of secondary imides. The reaction tolerates various functionalities, such as methoxy, fluoro, chloro, and bromo groups. A tentative radical mechanism for a Pd^II/Pd^IV catalytic cycle is proposed.     

Activation of Hydrogen Peroxide by Ionic Liquids: Mechanistic Studies and Application in the Epoxidation of Olefins

Imidazolium‐based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H₂O₂ as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long‐known molecular transition‐metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H₂O₂, urea hydrogen peroxide, and tert‐butyl hydrogen peroxide) on the efficiency of the epoxidation of cis‐cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.     

Unusual Inherent Electrochemistry of Graphene Oxides Prepared Using Permanganate Oxidants

Graphene and graphene oxides are materials of significant interest in electrochemical devices such as supercapacitors, batteries, fuel cells, and sensors. Graphene oxides and reduced graphenes are typically prepared by oxidizing graphite in strong mineral acid mixtures with chlorate (Staudenmaier, Hofmann) or permanganate (Hummers, Tour) oxidants. Herein, we reveal that graphene oxides pose inherent electrochemistry, that is, they can be oxidized or reduced at relatively mild potentials (within the range ±1 V) that are lower than typical battery potentials. This inherent electrochemistry of graphene differs dramatically from that of the used oxidants. Graphene oxides prepared using chlorate exhibit chemically irreversible reductions, whereas graphene oxides prepared through permanganate‐based methods exhibit very unusual inherent chemically reversible electrochemistry of oxygen‐containing groups. Insight into the electrochemical behaviour was obtained through cyclic voltammetry, chronoamperometry, and X‐ray photoelectron spectroscopy experiments. Our findings are of extreme importance for the electrochemistry community as they reveal that electrode materials undergo cyclic changes in charge/discharge cycles, which has strong implications for energy‐storage and sensing devices.     

Collective Total Synthesis of Englerin A and B,Orientalol E and F,and Oxyphyllol: Application of the Organocatalytic [4+3] Cycloaddition Reaction

The concise collective total synthesis of englerin A and B, orientalol E and F, and oxyphyllol has been accomplished in 10–15 steps, with the total synthesis of orientalol E and oxyphyllol being achieved for the first time. The success obtained was enabled by the realization of the [4+3] cycloaddition reaction of 9 and 10 . Other features of the synthesis include 1) the intramolecular Heck reaction to access the azulene core, 2) the epoxidation–S_N2′ reduction sequence to access the allylic alcohol, 3) the efficient regioselective and stereoselective formal hydration of the bridging C?C bond in the synthesis of englerins, and 4) the late‐stage chemo‐ and stereoselective C? H oxidation in the synthesis of orientalol E. The total synthesis of these natural products has enabled the structural revision of oxyphyllol and established the absolute stereochemical features of the organocatalytic [4+3] cycloaddition reaction. The identification of 5 as the natural product oxyphyllol, the success in converting 5 to orientalol E, along with the fact that englerins and oxyphyllol were isolated from plants of the same genus Phyllanthus gives support to our proposed biosynthetic pathways. This work may enable detailed biological evaluations of these natural products and their analogues and derivatives, especially of their potential in the fight against renal cell carcinoma (RCC).     

Cellulose polymorphism study with sum-frequency-generation (SFG) vibration spectroscopy: identification of exocyclic CH2OH conformation and chain orientation

Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H₂ and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (I_β, II, III_I and III_II) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H₂ asymmetric stretching peaks at 2,944 cm^?1 for cellulose I_β and 2,960 cm^?1 for cellulose II, III_I and III_II corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O–H group implies that the chain arrangement in cellulose crystal is parallel in I_β and III_I, and antiparallel in II and III_II.     

膦手性丙炔胺脯氨酸磷酸酯螺旋聚合物的合成与表征

通过添加对映体拆分剂,合成了4种含膦手性的丙炔胺磷酸酯单体[HC帒CC H2NH(PO)R1R2].单体1,R1=OPh,R2=NC4H7COOCH3;单体2,R1=OPh,R2=NC4H7COOCH2CH3;单体3,R1=OPh,R2=NC4H7-COOC(CH3)3;单体4,R1=Ph,R2=NC4H7COOC(CH3)3].1H-NMR和31P-NMR表征可知对映体(单体1)不能被拆分剂拆分,而单体2、单体3、单体4通过拆分剂可以制得单一手性的磷化合物.以(nbd)Rh+[η6-C6H5B--(C6H5)3]为催化剂,以三氯甲烷为溶剂成功得到聚合物分子量范围在0.4×10-4～0.7×10-4,分子量分布在1.26～1.98范围的3种含手性膦侧基的丙炔胺类聚合物.比旋光度([α]D)、圆二色谱(CD)对聚合物的不同侧基及温度对光学活性的影响表明,聚合物具有良好的光学活性且能够形成单一方向的螺旋构象,说明膦手性在构建螺旋聚合物具有重要作用.     

基于自交联杂萘联苯聚芳醚阴离子交换膜制备及其物理化学性质

以氯甲基杂环聚醚酮(CMPPEK)为原料,加入三乙胺进行铵化,并分别加入二乙烯三胺(DETA)和二乙胺(DEA),生成的仲胺基(或叔胺基)与邻近分子链氯甲基团进行自交联.经过制膜和离子交换反应,制备了DETA自交联杂萘联苯聚芳醚阴离子交换膜(DETA-QPPEK-OH)和DEA自交联杂萘联苯聚芳醚阴离子交换膜(DEA-QPPEK-OH).采用傅里叶变换红外(FTIR)光谱对制备自交联膜的化学结构进行表征.研究了DETA-QPPEK-OH和DEA-QPPEK-OH膜的理化性质,结果表明前者具有较低吸水率和更低溶胀度.通过研究DETAQPPEK-OH和DEA-QPPEK-OH膜的离子传导率随温度的变化规律,结果表明在80°C时其离子传导率分别达到0.060和0.028 S cm-1,表明本文制备的自交联膜具有较高离子传导率.此外还通过热重分析(TGA)对两类自交联膜的热稳定性进行了研究.     

N3/Al2O3/N749交替组装结构拓宽准固态染料敏化太阳能电池光响应范围和界面修饰效果

研究了染料敏化太阳能电池(DSCs)中N3/Al₂O₃/N749交替组装结构的作用. 该结构使用Al₂O₃作为介质层吸附第二层染料, 可以有效拓宽DSCs的光响应范围, 提高电池的光电转化效率. UV-Vis 吸收光谱和单色光转换效率(IPCE)谱测试结果表明, 相对于单一染料, 使用交替组装结构的电池光响应范围变宽. 电流-电压(I-V)曲线结果表明, 该结构有效增加了DSCs 电池的光电转化效率, 从单一N3 和N749 染料的4.22%和3.09%增加到了5.75%, 分别增加了36%和86%. 为了研究该结构的作用机理, 本文对其界面修饰作用及界面电子过程进行了讨论. 暗电流测试结果表明交替组装结构可以有效阻止电荷复合过程; 电化学阻抗谱(EIS)结果表明在黑暗条件下, N3/Al₂O₃/N749结构可以提高界面电阻, 从而抑制电荷复合过程; 本文建立了等效电路模型, 并使用该模型讨论了交替组装结构的界面电子过程; 调制强度光电流谱(IMPS)和调制强度光电压谱(IMVS)的结果表明该结构可以提高电子寿命和改善电子扩散.     

内部激励源二自由度结构扬声器振动特性分析

有别于多数基于简单振子结构的扬声器,针对一类内部激励源二自由度(IE2DOF)结构的扬声器,用类比线路图法建立集总参数模型,计算分析了这种结构的频率响应,同时计算了其固有共振频率和固有反共振频率。使用叠加法分析内部激励源对频响的影响。最后实际测量和理论计算吻合,进一步支持了理论模型,揭示了IE2DOF结构扬声器的振动特性。     

挖掘机器人视觉目标定位

为实现挖掘机器人的自动挖掘,在挖掘机实验模型基础上进行了电路改造,构建了以单片机为核心的控制电路,通过无线蓝牙与上位机进行通讯,实现对挖掘机操作装置的控制。通过视觉传感器采集挖掘机铲斗、目标物的实时图像,经图像处理后,对目标物中心及铲斗标记中心进行提取、定位,计算出二者之间的实时距离,进而控制挖掘机铲斗对目标物进行挖掘。