Polarized fluorescence spectra of poly(ethylene terephthalate) films

The polarized excitation and fluorescence spectra of lowcrystalline, isotropic poly(ethylene terephthalate) (PET) film samples were measured in the glassy state at room temperature. Whereas the emission anisotropy r₀ of the excitation spectrum, recorded at the fluorescence maximum, changes sharply from 0.35 to 0 with decreasing wavelength in the region around 317 nm, the polarization of the fluorescence spectrum of PET is independent of wavelength. The fluorescence polarization of PET remains constant, if the temperature is increased up to 22 °C above T_g until the light scattering due to the crystallization causes complete depolarization. The photophysical behaviour supports the existence of a dilute solution of groundstate - stable sandwich dimers in the non-crystalline regions of PET.     

pH-induced protonation of lysine in aqueous solution causes chemical shifts in X-ray photoelectron spectroscopy

We demonstrate the applicability of X-ray photoelectron spectroscopy to obtain charge- and site-specific electronic structural information of biomolecules in aqueous solution. Changing the pH of an aqueous solution of lysine from basic to acidic results in nitrogen 1s and carbon 1s chemical shifts to higher binding energies. These shifts are associated with the sequential protonation of the two amino groups, which affects both charge state and hydrogen bonding to the surrounding water molecules. The N1s chemical shift is 2.2 eV, and for carbon atoms directly neighboring a nitrogen the shift for C1s is approximately 0.4 eV. The experimental binding energies agree reasonably with our calculated energies of lysine(aq) for different pH values.     

Die konstitution der fungistatischen ansamycin-antibiotica ansatrienin A und B

The structure of ansatrienin A ($\text{1}$) and B ($\text{6}$) is assigned by spin decoupling experiments and chemical reactions. The ansatrienins are unique members among the ansamycin-antibiotics because of their substituent pattern in the ansa bridge.     

Unexpected phenyl group rearrangement during an intramolecular Scholl reaction leading to an alkoxy-substituted hexa-peri-hexabenzocoronene

A simple dimethoxy-substituted hexa-peri-hexabenzocoronene (m-dimethoxy HBC) was unexpectedly obtained along with a bis-spirocyclic dienone during an intramolecular Scholl reaction of its para isomer.     

Unambiguous detection of astaxanthin and astaxanthin fatty acid esters in krill (Euphausia superba Dana)

HPLC atmospheric pressure chemical ionization (APCI)/MS, GC MS, HPLC diode array detection (DAD), and NMR were used for the identification of astaxanthin and astaxanthin fatty acid esters in krill (Euphausia superba Dana). Matrix solid phase dispersion was applied for the extraction of the carotenoids. This gentle and expeditious extraction technique for solid and viscous samples leads to distinct higher enrichment rates than the conventional liquid-liquid extraction. The chromatographic separation was achieved employing a C30 RP column that allows the separation of shape-constrained geometrical isomers. A methanol/tert-butylmethyl ether/water gradient was applied. (all-E) Astaxanthin and the geometrical isomers were identified by HPLC APCI/MS, by coelution with isomerized authentical standard, by UV spectroscopy (DAD), and three isomers were unambiguously assigned by microcoil NMR spectroscopy. In this method, microcoils are transversally aligned to the magnetic field and have an increased sensitivity compared to the conventional double-saddle Helmholtz coils, thus enabling the measurement on small samples. The carotenol fatty acid esters were saponified enzymatically with Lipase type VII from Candida rugosa. The fatty acids were detected by GC MS after transesterification, but also without previous derivatization by HPLC APCI/MS. C14:0, C16:0, C16:1, C18:1, C20:0, C20:5, and C22:6 were found in astaxanthin monoesters and in astaxanthin diesters. (all-E) Astaxanthin was identified as the main isomer in six fatty acid ester fractions by NMR. Quantitation was carried out by the method of internal standard. (13-cis) Astaxanthin (70 microg/g), 542 microg/g (all-E) astaxanthin, 36 microg/g unidentified astaxanthin isomer, 62 microg/g (9-cis) astaxanthin, and 7842 microg/g astaxanthin fatty acid esters were found.     

Cu-ZSM-5/堇青石整体式催化剂上NO的吸附态及分解反应机理

 用傅里叶变换漫反射红外光谱法研究了原位合成的不同硅铝比的Cu－ZSM－5／堇青石整体式催化剂上一氧化氮的吸附态,以及温度和一氧化氮浓度对吸附态的影响．结果表明,铜在整体式催化剂中主要以二价铜离子的形式存在,未发现一氧化氮在一价铜离子上的特征吸收峰;由二价铜的一氧化氮吸附物种衍生的Cu2＋（O）（NO）是与活性密切相关的物种．探讨了NO分解可能的反应机理．     

基于HPLC-DAD-SPE-CryoNMR-MS技术的代谢物快速定性和结构确定

快速定性并有效地确定代谢物结构是代谢组学、植物化学和天然药物发现等研究的重要内容. 本文以迷迭香的两种溶剂提取物（氯仿/甲醇=3/1和50%含水甲醇）作为模型样品,通过分析其中的一些化学成分,展现了HPLC-DAD-SPE-CryoNMR-MS无缝联仪技术在确定代谢物结构方面的应用潜力. 基于高效液相色谱、紫外吸收、核磁共振波谱及质谱数据,具有代表性的6个迷迭香代谢物的结构得到了确定,它们分别为1个酚类二萜（鼠尾草酚）、2个酚酸（迷迭香酸和咖啡酸）、2个黄酮（6-甲氧基木樨草素-7-葡萄糖苷和高车前甙）和1个香豆酸 (顺-4-香豆酸葡萄糖苷). 该技术使分析型HPLC柱所分离的组分可以获得高质量同核及异核二维核磁共振波谱,从而能够更加便捷地确定微量成分的结构. 这些研究结果不仅提供了上述6种代谢物详细的谱学数据,而且证实HPLC-DAD-SPE-CryoNMR-MS技术是天然产物以及其他复杂体系结构分析的重要工具,即使同一色谱峰中含有浓度相差一个数量级的多个代谢物时,该方法依然有效.