Spectroscopic analysis of asymmetric top free radicals——Application to pure rotational spectra of NO_2 in the ground vibronic state

Several key problems involved in the analyses of spectra of asymmetric top molecules, i.e., the effective Hamiltonian, the representation and basis vector, identification of energy levels, the selection rules, the relative intensity, and Zeeman tuning rate, were elucidated systematically. Introducing the high-order centrifugal distortion terms into the effective Hamiltonian, the precision for calculation has been improved substantially, which allows us to analyze the high-lying rotational transitions. A global analysis of all available spectra of 14N16O2 in the ground vibronic state has been made to obtain a set of molecular constants of 14N16O2 in the ground vibronic state which is the most precise and extensive so far. Using the improved parameters, some FIR LMR lines left unassigned hitherto have been identified successfully.     

Two New Meroterpenes from the Mangrove Endophytic Fungus Aspergillus sp. 085241B

Two new meroterpenes, ‘acetoxydehydroaustin B’ ( 1 ) and ‘1,2‐dihydro‐acetoxydehydroaustin B’ ( 2 ) were isolated in the form of a mixed crystal from the mangrove endophytic fungus Aspergillus sp. 085241B. Their structures and absolute configurations were determined by extensive analysis of their spectra and X‐ray diffraction data. In a preliminary bioassay, the mixed crystal did not exhibit activities against cancer cell lines of MDA‐MB‐435, SKBR3, HepG2, HEP3B, PC‐3, and A549, as well as against α‐glucosidase and tyrosinase.     

A novel C3-symmetric prolinol-squaramide catalyst for the asymmetric reduction of ketones by borane

A novel C₃-symmetric prolinol-squaramide has been developed for the asymmetric reduction of ketones by borane. By using only 5 mol % catalyst 1a for the reaction, high yields and excellent enantioselectivities (up to 95% yield, 93% ee) were obtained. Moreover, 1a can be easily recovered by simple precipitation and re-used for four cycles without losing the selectivity.     

表面活性剂及水溶性功能高分子的NMR研究

核磁共振（NMR）技术是研究表面活性剂在溶液中聚集状态的一种非常有用的工具,本文运用多种NMR技术研究了几种不同类型表面活性剂及水溶性功能高分子在水溶液中的聚集行为： 1. 季铵盐型双子表面活性剂16-4-16的聚集行为季铵盐型双子表面活性剂N,N′-双(十六烷基二甲基)-α,ω-丁烷溴化铵(16-4-16)分子中联接基团及靠近离子头的质子位于胶束的壳层, 运动受到一定限制. 而距离离子头较远的烷烃链位于胶束的内部,运动相对自由. 与对应的单链表面活性剂十六烷基三甲基溴化铵(CTAB)相比,16-4-16形成的胶束堆积更为紧密. 通过NOESY谱中交叉峰强度的定量计算,认为16-4-16在胶束中分子以上下交错排列的方式形成球形聚集体.  2. 脱氧胆酸钠与十六烷基三甲基溴化铵的相互作用在脱氧胆酸钠(NaDC)溶液中,NaDC质子H3与其他质子不同,其横向弛豫时间(T₂)表现为双指数衰减,表明此质子可能存在两种不同的状态. 实验证明,其它胆酸盐的H3的横向弛豫也呈现双指数衰减. 因此推测在胆酸盐的稀溶液中,3-OH质子和羰基氧之间有可能存在氢键作用,形成了头尾相连的分子对结构.  在NaDC和CTAB的混合溶液中,两者形成1∶1的混合胶束. 用NOESY和ROESY研究混合胶束的结构,显示CTAB的离子头位于NaDC的羧酸基团附近. 这可能是正负离子之间的静电性相互作用的结果.  3. 丙烯酰胺/丙烯酸模板共聚物的微结构研究了不同pH值条件下,丙烯酰胺和丙烯酸共聚物分子在水溶液中的聚集形态. 在酸性溶液中,分子内的氢键致使聚集体形成较为紧密的堆积,侧链的苯氧基团运动受阻;随着溶液pH值的增大,丙烯酸电离产生的阴离子使得分子间的静电斥力增大,分子链变得伸展,分子间的氢键作用导致了聚集体体积变大. 当溶液呈强碱性,丙烯酸完全电离,氢键作用力被破坏,分子呈现自由伸展的状态,侧链的苯氧基团运动相对自由.     

单链和gemini表面活性剂的NMR研究

应用核磁共振技术,对几种典型的表面活性剂在水溶液中的聚集行为、结构特征、动力学特性和相互作用等进行了研究. 
利用1D ¹H NMR方法测得4-癸基萘磺酸钠（SDNS）在313 K温度时的临界胶束浓度（CMC）在0.82~0.92 mmol/L之间,与报道的298 K时的CMC范围相同. 弛豫时间和2D NOESY实验结果表明,与298 K时的SDNS胶束相比,313 K温度时,SDNS胶束中烷烃链排列得更紧密,其中与萘环相连的第一和第二个亚甲基参与了胶束紧密层的形成,更紧密地堆积在萘环之间. SDNS质子T₂值随温度的变化表明,在单体和胶束两种状态下,质子运动对温度的敏感性明显不同. 由自扩散系数分析得到,SDNS胶束的水合半径约为其单体水合半径的5.3倍. 而在十二烷基磺酸钠（SDSN）胶束中,由于静电排斥力的作用,在同样温度下SDSN的胶束紧密层排列比SDNS更疏松. 
NMR实验表明,在SDNS/Triton X-100 (TX-100)和SDNS/SDSN体系中形成了混合胶束. 在SDNS/TX-100混合胶束中,TX-100的苯环靠近SDNS的烷烃链,而它的聚烷氧链除与苯环相连的第一个乙氧基基团以外都被限制在SDNS的萘环附近. 在SDNS/SDSN混合胶束中,SDSN的磺酸基比SDNS分子更靠近胶束内部. 而SDNS的萘环将SDSN的磺酸基分隔开,在降低带负电荷的磺酸基极性头之间的静电排斥力中起到了积极的作用,有助于混合胶束的形成.
从自扩散系数、横向弛豫和质子距离等NMR测定参数推测,在浓度为0.26 mmol/L（318 K）的N,N′-双(十六烷基二甲基)-α,ω-丙烷溴化铵(16-3-16)溶液中形成了近似球形的胶束,胶束表面的带正电荷的铵基极性头呈锯齿状排列以减弱分子间静电排斥力的影响. 弛豫时间测定表明,与N,N′-双(十六烷基二甲基)-α,ω-丁烷溴化铵(16-4-16)相比,16-3-16在胶束表面的spacer链段更僵硬, 在胶束核区的烷烃侧链排列的更紧密. NMR共振峰的线形分析表明,16-3-16和16-4-16侧链末端的甲基在胶束中位于两个不同的位置.      

Ultrafast Excited State Dynamics of t~rans-4-Aminoazobenzene Studied by Femtosecond Transient Absorption Spectroscopy

The ultrafast excited state dynamics of trans-4-aminoazobenzene （trans-4-AAB） in ethanol was investigated by femtosecond transient absorption spectroscopy. After being excited to the S2 state by 400 nm, trans-4-AAB decays from the S2 state to the hot S1 state by internal conversion with time constant of -70 fs. The photoisomerization through inversion mechanism on the S1 potential energy surface and the internal conversion from the S1 state to the hot So state are observed, respectively. The average timescale of these two decay pathways is -0.7 ps. And the vibrational cooling of the hot So state of cis- and trans-4- AAB occur with time constants of -4 and N13 ps, respectively. Furthermore, the ultrafast intersystem crossing process are also observed. The timescale of intersystem crossing from the S2 state to the T4 state is about 480 ps while from the S1 state to the T2 state is -180 ps.     

Highly sensitive detection of mercury (II) in aqueous media by tetraphenylporphyrin with a metal ion receptor

We provide a highly sensitive and selective assay to detect Hg²⁺ in aqueous solutions using a novel β-functionalised porphyrin-based chemosensor 5 at room temperature. The binding properties of the chemosensor 5 for cations were examined by UV–vis spectroscopy and ¹H NMR. The results indicate that a 1:1 stoichiometric complex is formed between chemosensor 5 and mercury (II) ion. The recognition mechanism between chemosensor 5 and metal ion was discussed based on their absorbance changes and the chemical shift changes when they interact with each other. Control experiments revealed that chemosensor 5 has a selective response to mercury (II) ion compared with other metal ions.     

Sn-Al-β分子筛酸性在葡萄糖转化反应中作用的固体NMR研究

制备了一系列具有不同酸性质的β分子筛催化剂, 通过固体核磁共振(NMR)探针分子技术对其酸性质进行了表征, 并考察了其催化葡萄糖转化为乙酰丙酸甲酯的性能. 吸附三甲基磷的³¹P NMR实验结果表明, 含有骨架Sn以及Al原子的Sn-Al-β催化剂同时具有Br?nsted与Lewis酸性. 通过2-¹³C-丙酮探针分子区分出 3种酸强度的Br?nsted酸位, 其中一种酸强度接近“超强酸”, 可能是由于空间邻近的Br?nsted酸位和Lewis酸位发生协同作用产生的. 葡萄糖转化为乙酰丙酸甲酯的催化反应结果表明, 相比于分别只含有Lewis酸位和Br?nsted酸位的Sn-β和Al-β样品以及两者的物理混合样品, Sn-Al-β分子筛催化剂具有高催化活性与产物选择性, 这主要是由于Br?nsted酸位和Lewis酸位的协同作用产生了强Br?nsted酸位, 这种强Br?nsted酸位进一步导致了更高的催化活性.