An efficient chiral phosphorus derivatizing agent for the determination of the enantiomeric excess of chiral alcohols and amines by 31P NMR spectroscopy

The chiral phosphorus derivatizing agent (CDA) 1 was prepared from optically pure (S)‐1,1‐bis‐2‐naphthol. It was first used in the determination of the enantiomeric excess of chiral alcohols and amines by means of ³¹P NMR spectroscopy. It showed that, for the chiral aromatic alcohols, no apparent kinetic resolution was noted and good base‐line separation was observed. Furthermore, the chemical shift difference (Δδ) of ³¹P NMR spectroscopy was much larger than those determined by the use of other chiral phosphorus derivatizing agents reported previously. However, for aliphatic alcohols, it showed not only obvious kinetic resolutions but incomplete base‐line separation. Moreover, we also found that the use of CDA 1 was suitable for the determination of enantiomeric excess of chiral primary amines. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:93–95, 2002; DOI 10.1002/hc.10018     

Palladium tetrazole–supported complex as an efficient catalyst for the Heck reaction

Abstract  

A tetrazole-supported polymeric ligand has been synthesized. The palladium complex derived from the polymeric material has been evaluated as a catalyst for the Heck reaction of aryl iodides and bromides with styrene to provide the corresponding products in high yields. The reaction proceeded smoothly in the presence of 1 mol% with respect to Pd of catalyst in DMF at 125 or 140 °C within 1–3 h. Recycling studies showed that the catalyst can be readily recovered and reused for several times without significant loss of catalytic activity.     

Silica Sulfuric Acid‐Catalyzed Five‐component Efficient Synthesis of Five‐Substituted Tetrahydropyridines

A highly atom‐economic one‐pot synthesis of five‐substituted tetrahydropyridines via a five‐component condensation of two equivalents of aromatic aldehyde, two equivalents of aromatic aniline, and one equivalent of β‐keto ester catalyzed by silica sulfuric acid is reported. In this reaction, up to five new bonds and one new ring were formed in one pot with water as the only one by‐product.     

Screening of bioactive compounds in Rhizoma Polygoni Cuspidati with hepatocyte membranes by HPLC and LC–MS

A new method employing HPLC, LC–MS, and hepatocyte membranes for the screening of bioactive compounds in traditional Chinese medicines (TCMs) has been proposed. We hypothesized that exposure of the TCM extracts to hepatocyte membranes should decrease the concentration of membrane‐permeable compounds in the solution. Using this approach, the permeability of the compounds in Rhizoma Polygoni Cuspidati was investigated. By comparing chromatograms of samples prepared both before and after interaction with hepatocyte membranes, seven permeable compounds of Rhizoma Polygoni Cuspidati were identified. Additionally, it was found that piceid, resveratrol, emodin‐8‐β‐d‐glucoside, physcion‐8‐β‐d‐glucoside, aloe‐emodin, emodin, and physcion combined specifically with hepatocyte membranes, which might indicate a useful approach for revealing the antiatherosclerotic effects of Rhizoma Polygoni Cuspidati. Therefore, the proposed method could be a good approach to predict the potential bioactivities of multiple compounds in TCMs simultaneously. Based on the significance of these results, this method could be a novel approach for identifying potentially bioactive components in other TCMs.     

Investigation on Photophysical Properties of D–π–A–π–D‐Type Fluorenone‐Based Linear Conjugated Oligomers by Using Femtosecond Transient Absorption Spectroscopy

The effects of π‐spacer and electron donor groups on the photophysical behaviors of fluorenone‐based linear conjugated oligomers have been systemically investigated. Solvent‐dependent steady‐state measurements exhibit that the fluorene vinylene (FV) spacer and the electron‐donating ability of donor group are able to modulate the spectral features of oligomers and the fluorescence quantum yield could decrease with the increasing of the solvent polarity. Meanwhile, quantum chemical calculation simulates their absorption spectra, and analyzes their electron transition components simultaneously. The transient absorption measurements focus on the photoexcitation dynamics of these oligomers in the toluene solution, which show that an intramolecular charge transfer state exists in the relaxation process of excited states, and its generation process could accelerate with the introduction of FV spacer and the enhancement of donor strength.     

Ferron逐时比色法中显色剂Ferron浓度对Al-Ferron体系反应动力学的影响

Ferron逐时比色法中Al-Ferron体系反应动力学常被视为准一级反应,由此可推得相应的拟合方程并测得相应的反应速率常数kb,显色剂Ferron作为反应物之一其用量必然直接影响测量的结果。以不同OH/Al比的聚合氯化铝溶液为研究对象,抓住Ferron浓度这一核心要素,对Al-Ferron体系反应动力学过程进行了系统研究。结果表明,[Ferron]≥2.0×10^(-3)mol/L是确保动力学速率常数kb准确测量的基本保证。     

碱金属掺杂叔丁基杯[4]芳烃体系的结构及非线性光学性质

采用密度泛函理论B3LYP方法得到了M@t-Bu-calix[4]arene和(M@t-Bu-calix[4]arene)Li′(M=Li,Na,K)体系的几何结构.其中(M@t-Bu-calix[4]arene)Li′(M=Li,Na,K)三个体系各有5个稳定异构体,在前三个异构体中,碱金属与t-Bu-calix[4]arene分子间具有很强的相互作用能,说明了体系的稳定性.在部分(M@t-Bucalix[4]arene)Li异构体中Li′原子以阴离子形式存在,整个体系表现出碱金属化物的特性.此外,使用CAMB3LYP方法计算了t-Bu-calix[4]arene及碱金属掺杂后体系的非线性光学性质.结果表明,t-Bu-calix[4]arene内部掺杂一个碱金属原子M后,体系的一阶超极化率(β0)有较大提高,而在配体外部又掺杂一个Li原子后,体系具有更大的β0值.其中(M@t-Bu-calix[4]arene)Li′体系的MLi′-4异构体表现出最高的β0值(41827-114354 a.u.),并且随着M原子序数的增加而逐渐增大.可见,碱金属掺杂是提高t-Bu-calix[4]arene非线性光学响应的一种有效策略.     

Boron‐Double‐Ring Sheet,Fullerene, and Nanotubes: Potential Hydrogen Storage Materials

Similar to carbon‐based graphene, fullerenes and carbon nanotubes, boron atoms can form sheets, fullerenes, and nanotubes. Here we investigate several of these novel boron structures all based on the boron double ring within the framework of density functional theory. The boron sheet is found to be metallic and flat in its ground state. The spherical boron cage containing 180 atoms is also stable and has I symmetry. Stable nanotubes are obtained by rolling up the boron sheet, and all are metallic. The hydrogen storage capacity of boron nanostructures is also explored, and it is found that Li‐decorated boron sheets and nanotubes are potential candidates for hydrogen storage. For Li‐decorated boron sheets, each Li atom can adsorb a maximum of 4 H₂ molecules with g_d=7.892 wt %. The hydrogen gravimetric density increases to g_d=12.309 wt % for the Li‐decorated (0,6) boron nanotube.     

Substituent Effects on the Hydrogen Bonding Between Phenolate and HF, H2O and NH3

IntroductionSubstituent effects have been well known forthe covalently bonded systems for many years,they have found tremendous applications in medicalchemistry,biochemistry,organic chemistry,andmaterial chemistry[1] . In fact,the studies ofsubstituent effects have greatly contributed to ourunderstanding of chemical mechanisms,and theestablishments of many chemical theories haveheavily relied on the observed substituent effects.However,it turns out that little have beenknown so far the substit…     

烟草中多酚热裂解产物研究

多酚类化合物对烟草品质、色泽和烟气生理强度等方面有着重要影响,因此是衡量烟草质量的一个重要因素[7],对卷烟的香气品质有很重要的作用.绿原酸、芸香苷和莨菪亭是烟草中最主要的酚类物质[7],有证据表明酚类物质的存在能显著提高多环芳烃的致癌活性[1,6].卷烟主流烟气中酚类物质的含量的多少直接影响到卷烟的安全性.另外某些酚类物质可能是影响卷烟的口感,引起涩味、辣味、余味不干净的一种因素.研究它们的裂解产物对探索降低卷烟烟气有害成分,提高卷烟的吸食品质十分必要[2,5].