Ultrafast IR spectroscopy of polymeric cytosine nucleic acids reveal the long-lived species is due to a localised state

The decay pathways of UV-excited cytosine polymers are investigated using picosecond time-resolved infrared spectroscopy. Similar yields of a non-emissive (1)nπ* state are found in the single-stranded dC(30) polymer as in the dCMP monomer, but with a longer lifetime in the polymer (80 ps vs. 39 ps). A longer lifetime is also found in the d(CpC) dinucleotide. No evidence of excimer states is observed, suggesting that localised (1)nπ* excited states are the most significant intermediates present on the picosecond timescale.     

Topological ferroelectric bistability in a polarization-modulated orthogonal smectic liquid crystal

We report a bent-core liquid crystal (LC) compound exhibiting two fluid smectic phases in which two-dimensional, polar, orthorhombic layers order into three-dimensional ferroelectric states. The lower-temperature phase has a uniform polarization field which responds in an analog fashion to applied electric field. The higher-temperature phase is a new smectic state with periodic undulation of the polarization, structurally modulated layers, and a bistable response to applied electric field which originates in the periodically splay-modulated bulk of the LC rather than by surface stabilization at the cell boundaries.     

分光光度法测定血清铁含量

为了达到简化操作流程、缩短测定时间的目的,本实验从样品的前处理、二氮杂菲添加量、反应时间等方面对国标测定水中铁含量的方法(二氮杂菲分光光度法,GB 8538-2008-4.15)作出改进。实验结果表明,采用干湿结合法对血清进行前处理可缩短处理时间,减少由于硝酸挥发给人体带来的伤害;二氮杂菲添加量为3mL,反应时间达14min后检测效果好,定量下限可达5mg/L。改进后测定血清铁的方法操作相对简单、检测时间短,易于推广应用。     

Tricationic analogues of boroxines and polyborate anions

Addition of E(2)O (E = Me(3)Si or H) to [(pyridyl)BX(2)][AlX(4)] (X = Cl or Br) and subsequent heating produced the unprecedented trications [(2,6-lutidine)(4)B(5)O(6)](3+) and [(pyridine)(4)B(3)O(3)](3+).     

Lions and tigers and bears, oh my! Three barriers to progress in computer-aided molecular design

The computational chemistry and cheminformatics community faces many challenges to advancing the state of the art. We discuss three of those challenges here: accurately estimating the contribution of entropy to ligand binding; reliably estimating the uncertainties in model predictions for new molecules; and being able to effectively curate the ever-expanding literature and commercial databases needed to build new models.     

Studies of the H-D exchange mechanism of malonganenone B

Malonganenone B (1) exhibits an unusual H-D exchange of a formyl proton when in deuteric-NMR solvents. Synthetic and kinetic investigations were made to probe the mechanism of this exchange, which appears to occur via an uncommon and transient amine-amide NHC intermediate.     

Atom-Transfer Cyclization with CuSO(4)/KBH(4): A Formal "Activators Generated by Electron Transfer" Process Also Applicable to Atom-Transfer Polymerization

The 4-exo and 5-exo-trig atom-transfer cyclizations of 1, 8a-e, 9, 12, and 13 can be mediated with as little as 0.05 mol % of Cu(TPMA)SO(4)·5H(2)O in the presence of 2.5 mol % of borohydride salts in 10 min at room temperature in air. This formal "activators generated by electron transfer" (AGET) procedure utilizes a cheap and oxidatively stable copper source (CuSO(4)·5H(2)O) and can be carried out in environmentally benign solvents (EtOH). It is possible to alter the product distribution in the 5-endo radical-polar crossover reactions of 10a,b and 11 by tailoring the amount of borohydride. Cyclization onto alkynes 14 and 15 is also possible in only 20 min. Controlled radical polymerization of styrene, with increased rates over conventional atom-transfer radical polymerization (ATRP), can be carried out in a controlled fashion (Mn, PDI) using either CuBr or CuSO(4)·5H(2)O and Bu(4)NBH(4).     

一类欠驱动旋转摆的非线性控制

欠驱动系统是一类构成系统的广义坐标维数多于控制输入维数的非线性系统.旋转摆属于典型的欠驱动系统,通过驱动杆的水平转动可使欠驱动杆由垂直下摆位置转到竖直向上位置.利用基于能量的控制方法设计了摇起控制器,使欠驱动杆由稳定平衡位置到达非稳定平衡区域,再由LQR方法设计平衡控制器,使其控制在非稳定平衡位置.两种控制器通过切换实现摇起和平衡控制转换.最后通过仿真实验验证了文中设计的两种控制器的有效性.