Bifunctional pyridyl alcohols with the bicyclo[3.3.0]octane scaffold in the asymmetric addition of diethylzinc to aldehydes

Some new pyridyl alcohols with the cis-bicyclo[3.3.0]octane scaffold were synthesized and used as chiral ligands for the enantioselective addition of diethylzinc to aldehydes. Ligands 4 were found to be far superior to the C₂-symmetric ligands 2 in terms of enantioselectivities. Quantitative yields and enantiomeric excesses of up to 92% were obtained when the ligand 4 was used. The carbonyl function in 4 proved to be beneficial for the high enantioselectivities in the addition of diethylzinc to aldehydes. Conversion of the carbonyl group into oxime or oxime ether group led to a sort of more active ligands, which catalyzed the same reaction with rate acceleration.     

Combinatorial enantiomeric separation of diverse compounds using capillary array electrophoresis

Combinatorial chiral separations were performed on a 96-capillary array electrophoresis system. A comprehensive enantioseparation protocol employing neutral and sulfated cyclodextrins as chiral selectors for common basic, neutral and acidic compounds was developed. By using only four judiciously chosen separation buffers, successful enantioseparations were achieved for 49 out of 54 test compounds spanning a large variety of pK and structures. Therefore, unknown compounds can be screened in this manner to identify the optimal enantioselective conditions in just one run.     

A general method for the preparation of 4- and 6-azaindoles

Nitropyridines reacted with an excess of vinyl Grignard reagent to produce 4- or 6-azaindoles. Improved yields were obtained when a halogen atom was present at the position alpha to the nitrogen atom in the pyridine ring.     

THE STRUCTURAL BASIS OF THE POOR FIBRIN SPECIFICITY OF UROKINASE(Ⅰ)——KNOWLEDGE-BASED PREDICTION OF KRINGLE STRUCTURES OF UROKINASE AND ITS RELATED PROTEINS

The Kringle-1 structure of plasminogen (PGK-1), the Kringle-2 structure of tissue plasminogen activator (PAK-2) and the Kringle structure of prourokinase (UKK) has been modeled on the basis of the three-dimensional structure of Kringle-1 of prothrombin (PTK-1) at 2.8 resolution. The predicted three-dimensional structure of these Kringles shows that the binding site of PGK-1 is characterized by an apparent dipolar site, the polar parts of which are separated by a hydrophobic region. PAK-2 possesses the anionic center but has not a cationic binding center which might be provided by a guanidinium group from Arg-69 located adjacent to the Arg-71 position. UKK possesses neither the anionic binding center nor the cationic center which are probably the main reason for the poor fibrin specificity of urokinase.     

过氧化氢与N—甲基苯胺盐酸盐引发体系的研究

在水介质中,研究了新型的过氧化氢/N-甲基苯胺盐酸盐引发体系对 AM 与 PVA 的接枝共聚。产物经紫外光谱、红外光谱和 ~1H-核磁共振进行表征,并提出了引发机理。     

Theoretical formalism and experimental verification of line shapes of NMR intermolecular multiple-quantum coherence spectra

Although the theories and potential applications of intermolecular multiple-quantum coherences (iMQCs) have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems.     

Rapid chiral analysis based on liquid-phase cyclic chemiluminescence

Rapid chiral analysis has become one of the important aspects of academic and industrial research. Here we describe a new strategy based on liquid-phase cyclic chemiluminescence (CCL) for rapid resolution of enantiomers and determination of enantiomeric excess (ee). A single CCL measurement can acquire multistage signals that provide a unique way to examine the intermolecular interactions between chiral hosts and chiral guests, because the lifetime (τ) of the multistage signals is a concentration-independent and distinguishable constant for a given chiral host–guest system. According to the τ values, CCL allows discrimination between a wide range of enantiomeric pairs including chiral alcohols, amines and acids by using only one chiral host. Even the chiral systems hardly distinguished by nuclear magnetic resonance and fluorescence methods can be distinguished easily by CCL. Additionally, the τ value of a mixture of two enantiomers is equal to the weighted average of each enantiomer, which can be used for the direct determination of ee without the need to separate the chiral mixture and create calibration curves. This is extremely crucial for the cases without readily available enantiomerically pure samples. This strategy was successfully applied to monitoring of the Walden inversion reaction and analysis of chiral drugs. The results were in good agreement with those obtained by high-performance liquid chromatography, indicating the utility of CCL for routine quick ee analysis. Mechanism study revealed that the τ value is possibly related to the activity of the chiral substance to catalyze a luminol–H₂O₂ reaction. Our research provides an unprecedented and general protocol for chirality differentiation and ee determination, which is anticipated to be a useful technology that will find wide application in chirality-related fields, particularly in asymmetric synthesis and the pharmaceutical industry.

Rapid chiral analysis has become one of the important aspects of academic and industrial research.     

Adiabatic cooling of ions in the penning trap

An ion cloud in a Penning trap can be cooled by adiabatic expansion by reducing the trap's magnetic and electric fields. We treat the ion cloud as a classical gas and obtain the relations between the temperature and the trapping fields. This cooling method may be useful in trapping and cooling of antiprotons with the aim of measuring the gravitational accleration of anti-protons and other experiments on heavy ions.     

Characterization of polyethylene glycol-modified proteins by semi-aqueous capillary electrophoresis

A new program to characterize polyethylene glycol-modified (PEGylated) proteins is outlined using capillary zone electrophoresis (CZE). PEGylated ribonuclease A and lysozyme were selected as examples. Five separation procedures were compared to select out the mixed buffer of acetonitrile-water (1:1, v/v) at pH 2.5 as the best to characterize the PEGylated proteins without sample pretreatment. Polyethylene oxide (PEO) with a high molecular mass of 8 x 10(6) was applied to rinse the capillary to form a dynamic coating which would decrease the undesirable proteins adsorbed to the inner wall of the silica. The electroosmotic flow (EOF) mobility of the five procedures was determined, respectively. It is found that acetonitrile is mainly responsible for the good resolution of PEGylated proteins with the help of PEO coating in the semi-aqueous system. The low EOF mobility and current in the semi-aqueous system might also have some responsibility for the high resolution. The semi-aqueous procedure described in this paper also demonstrates higher resolution of natural proteins than aqueous ones.     

平面药包的最佳间距

在矿山剥离、场地平整以及建(构)筑物基坑开挖等露天爆破中,为了充分利用炸药能量将岩石松动或抛掷到一定区域,并确保底板满足一定平整度要求,按照爆破技术设计和工程质量要求,需要设计平面布药结构.本文通过在施工现场进行的大量小型模拟实验,对平面药包间、排距与爆破漏斗的开口面积、可见深度、爆岩的抛掷距离和堆积形态等关系进行了系统分析与研究.实验结果表明,当平面药包间、排距满足一定范围时,爆破漏斗的可见深度较小,而开口面积和抛掷距离最大,爆堆形态较好.平面布药结构存在一个有利于抛掷堆积的最佳间、排距.