Asymmetry in molecular ordering in the nematic phase: DMR study
摘要:
Deuterium nuclear magnetic resonance (2H-NMR) was performed on the rigid perdeuterated fluorene segment of the compound 2-fluorenyl-4′-tetradecyloxy benzoate (FLOC 14-d9) to unambiguously measure the order parameter U which reflects the degree of asymmetric ordering of the molecule in the nematic liquid crystalline phase. Measurements of U showed this parameter to be finite at all temperatures in the nematic phase indicative of the uniaxial phase U2 described in the Allender–Lee generalized Landau theory. Mixtures of FLOC 14-d9 with compounds consisting of molecules more cylindrical in shape were also studied to examine their effect on the parameter U. Other parameters such as the degree of order S and the orientation of the principal axes of the Maier–Saupe order matrix were measured and are discussed.
多环芳烃(PAHs)是普遍存在的环境污染物,其中许多具有致癌性。测量暴露于尿液中的一种方法是确定尿液中代谢物的浓度。numerous代谢物1-羟基py已被用作许多研究中暴露的生物标志物。但是,确定相对几种PAH的暴露量可能是有利的,因为相对量可能会根据暴露源而变化。我们开发了一种液相色谱-串联质谱法,用于测定人尿中萘,芴,菲和pyr的酚类代谢物。在酶促切割葡糖醛酸苷和硫酸盐结合物之后,从尿液中提取酚类代谢物,并将其转化为五氟苄基醚。这些衍生物极大地提高了在负离子模式下通过大气压化学电离进行检测的灵敏度。定量下限为0.01至0.5 ng / mL。稳定同位素标记的内标已合成或可商购获得。给出了吸烟者和非吸烟者尿液中几种PAH代谢产物的尿排泄数据。