Improving the accuracy of 1H–19F internuclear distance measurement using 2D 1H–19F HOESY

With the rise in fluorinated pharmaceuticals, it is becoming increasingly important to develop new ¹⁹F NMR-based methods to assist in their analysis. Crucially, obtaining information regarding the conformational dynamics of a molecule in solution can aid the design of strongly binding therapeutics. Herein, we report the development of a 2D ¹H–¹⁹F Heteronuclear Overhauser Spectroscopy (HOESY) experiment to measure ¹H–¹⁹F internuclear distances, with accuracies of ~5% when compared with ¹H–¹⁹F internuclear distances calculated by quantum chemical methods. We demonstrate that correcting for cross-relaxation of ¹H, using the diagonal peaks from the 2D ¹H–¹H Nuclear Overhauser Enhancement Spectroscopy (NOESY), is critical in obtaining accurate values for ¹H–¹⁹F internuclear distances. Finally, we show that by using the proposed method to measure ¹H–¹⁹F internuclear distances, we are able to determine the relative stereochemistry of two fluorinated pharmaceuticals.     

Deuteriated Analogs as Internal Standards for the Quantitation of Environmental Alkanes by Gas Chromatography

Abstract

Quantitation by gas chromatography requires the use of suitable internal standards. Deuteriated analogs are superior, but usually require a mass spectrometer as the gas chromatographic detector to distinguish them from the compounds being measured. Completely deuteriated alkanes are, however, completely separated from the corresponding unlabelled alkanes and serve as suitable internal standards for the quantitation of environmental alkanes by gas chromatography alone.     

In situ powder diffraction study of belite sulfoaluminate clinkering

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO₂ into the atmosphere when compared with ordinary Portland cement fabrication. However, their formation mechanism has not been studied in detail so far. Here, an in situ high‐temperature high‐resolution synchrotron X‐ray powder diffraction study is reported. Two types of BSA clinkers have been characterized, both containing 50–60 wt% C₂S and 20–30 wt% C₄A₃ as main phases. One type is iron‐rich and a second type (with different phase assemblage) is aluminium‐rich. Furthermore, the C₂S phase reacts slowly with water, thus activation of this compound is desirable in order to enhance the mechanical strength development of the resulting cements. To do so, iron‐rich BSA clinkers have been doped with minor amounts of B₂O₃ and Na₂O to promote stabilization of α‐forms of C₂S, which are more reactive with water. The decarbonated raw materials were loaded into Pt tubes and heated to between 973 K and 1673 K, and patterns were collected using a high‐energy synchrotron beam of wavelength λ = 0.30 Å. The thermal stability of Klein's salt in these clinkers has been clarified. Several reactions have been followed: formation and decomposition of Klein's salt, melting of aluminates and ferrite, and polymorphic transformations of dicalcium silicate: ‐C₂S →α‐C₂S. Changes in mineralogical phase assemblages at a given temperature owing to the addition of minor amounts of selected elements have also been determined.     

评价污水处理系统的Fuzzy模式识别方法

综合考虑了所有对污水处理系统的相关因素,应用Fuzzy模式识别的数学方法,对评价污水处理系统建立了数学模型.由于此模型对污水处理系统给出了等级划分和对各相关因素等级指数之间的中介状态进行了恰当处理,所以它应用于评价污水处理系统将更科学.     

Recent progress in quantitative analysis of DNA adducts of nephrotoxin aristolochic acid

Aristolochic acid (AA), a mixture of structure-related nitrophenanthrene carboxylic acid derivatives derived from Aristolochia spp, is associated with nephrotoxin and carcinogen. AA-DNA adducts induced by reductive metabolic activation of AA were detected in tissues of animals and in patients exposed to AA. The DNA adducts were generally used as biomarkers in toxicological study of AA. In this short review, quantitative analysis of AA-DNA adducts in various in vitro and in vivo systems by using 32P-postlabe...     

行业投入产出技术系数与行业获利性波动识别

企业经营环境外部系统因素的不确定性是影响企业所有者与经营者之间委托代理问题解决的主要因素,目前还没有文献系统建立企业经营环境信息的识别方法。本文利用技术效率评价中的理论来研究企业经营环境信息的识别问题。基于(k,y)空间的生产可能集与技术效率发展了描述不同行业投入产出差别的技术系数,给出行业获利性波动的时序识别方法。这些方法对弱化企业所有者与经营者之间信息非对称程度,解决二者之间的委托代理问题提供了一个有效途径。     

社会投入与社会发展关系实证分析:1995-2005

社会活动的投入是社会发展的动力,社会发展目标的实现,需要大规模的要素投入来支撑.在这篇文章中,我们采集了大量的社会经济统计数据,对1995-2005期间我国社会发展过程的要素投入与社会发展成果之间的关系进行了分析.全文主要内容有:社会投入体系的整体评估,社会发展成果的综合评价,社会投入与社会发展成果关系的数量分析,及在此基础上形成的相关结论.     

浙江交通运输与经济发展的相关性分析

本文运用灰色系统建模理论和数量经济的方法对浙江省交通运输与经济发展之间的关系进行相关性分析,研究交通运输业内各重要指标对经济发展的内在联系.这对充分发挥交通运输对经济活动中的重要作用,研究交通运输与经济的协调发展都将提供必要的参考依据.     

脂肪族饱和一元醇沸点的拓扑研究

基于邻接矩阵与边价 (fi)定义边价连接性指数 ( mF) ,其中的0 F、醇距离参数L及醇类型参数与 119种脂肪族饱和一元醇的沸点 (Tb)关联、得到良好的数学模型 :ln( 72 4-Tb) =6 0 70 10 -0 0 5 7180 F -0 0 0 3 71L -0 0 75 49δ-1 (n =119) ,R =0 9974.相关性优于文献值 .可以预示 ,该模型能更精确的预测饱和醇的沸点 .