高超声速飞行流场中的最大氧离解度分析简

针对大气层内高超声速飞行时的化学非平衡现象,建立了沿驻点线流动的空气中氧离解度的计算模型. 模型假设氮气在氧气未充分离解时不发生离解,并且不涉及边界层内的复合反应. 理论计算发现,空气中氧的离解度随飞行高度的增加呈先增后减的非单调变化规律,其原因是由于化学反应平衡移动与非平衡效应相互作用的结果. 这一结论得到了数值模拟结果的验证,同时也解释了文献中当飞行高度较高时真实气体效应减弱的现象. 基于驻点线的近似理论模型,计算得到了轴对称钝头体绕流流场中的最大氧离解度及边界层外缘温度随飞行速度和高度变化的等值线图谱,相关结果可以为工程设计所用.     

Characterization of pigments and ligands in a wall painting fragment from Liternum archaeological park (Italy)

Spectroscopic and MS techniques were used to characterize the pigments and the composition of polar and nonpolar binders of a stray wall painting fragment from Liternum (Italy) archaeological excavation. X‐ray fluorescence and diffraction analysis of the decorations indicated mainly the presence of calcite, quartz, hematite, cinnabar, and cuprorivaite. Infrared spectroscopy, GC coupled to flame‐ionization detector, and MS analysis of the polar and nonpolar components extracted from paint layers from three different color regions revealed the presence of free amino acids, sugars, and fatty acids. Interestingly, LC‐MS shotgun analysis of the red painting region showed the presence of αS1‐casein of buffalo origin. Compared to our previous results from Pompeii's wall paintings, even though the Liternum painting mixture contained also binders of animal origin, the data strongly suggest that in both cases a tempera painting technique was utilized.     

自建电喷雾解吸电离源（DESI）在大分子分析中的应用及离子化机理探索

自建了简易的电喷雾解吸电离源(DESI),优化了DESI源喷口的位置和角度,并将其用于常见多肽和蛋白质的分析。多肽和小质量蛋白质(<20 kDa)可以容易地从表面解吸电离,生成清晰的质谱。而牛血清白蛋白(66.4 kDa)不能产生清晰的多电荷分布的质谱,说明当前DESI源的设计可能存在一个电离的分子量上限。通过比较不同的实验条件并对比ESI-MS,发现溶剂分子的挥发过程对电荷分布以及峰宽均有显著影响,可能是由于ESI更软引起。载样表面的性质对DESI-MS的信号强度有较大影响。金表面的自组装单分子膜(SAM)相对于纯金表面有较好的绝缘性,并有助于产生较强信号,说明来自表面的电子转移(电中和)是电喷雾解吸电离过程中的一个重要因素。该文的研究有助于对DESI-MS的实验条件和载样表面的选择,同时增进了对电喷雾解吸电离机理的了解。     

Methane hydrate stability in the presence of water-soluble hydroxyalkyl cellulose

The effect of low-dosage water-soluble hydroxyethyl cellulose (approximate MW～90,000 and 250,000) as a member of hydroxyalkyl cellulosic polymer group on methane hydrate stability was investigated by monitoring hydrate dissociation at pressures greater than atmospheric pressure in a closed vessel. In particular, the influence of molecular weight and mass concentration of hydroxyethyl cellulose (HEC) was studied with respect to hydrate formation and dissociation. Methane hydrate formation was performed at 2℃ and at a pressure greater than 100 bar. Afterwards, hydrate dissociation was initiated by step heating from -10℃ at a mild pressure of 13 bar to 3℃, 0℃ and 2℃. With respect to the results obtained for methane hydrate formation/dissociation and the amount of gas uptake, we concluded that HEC 90,000 at 5000 ppm is suitable for long-term gas storage and transportation under a mild pressure of 13 bar and at temperatures below the freezing point.     

Structure and charge-state dependence of the gas-phase ionization energy of proteins

Photoionization of protein ions: The ionization energy of polyprotonated protein cations in the gas phase measured using VUV synchrotron radiation appears to be correlated with the charge state z of the protein and its tertiary structure. A simple electrostatic model accounts for the results and also shows predictive capabilities to derive a mean radius R(m) of the protein ion from the ionization energy, and vice versa.     

Defying entropy: forming large head-to-tail macrocycles in the gas phase

Spectral fingerprints: Collision-induced dissociation (CID) of protonated peptides in the gas phase results in linear fragment ions with a five-membered oxazolone ring on their C-terminal side. Infrared spectroscopy confirms that smaller fragments adopt oxazolone structures. Conversely, in mid-sized and larger fragments an isomerization to "head-to-tail" macrocycles is observed (see picture).     

Laser Mass Spectrometry with Circularly Polarized Light: Circular Dichroism of Molecular Ions

In recent experiments of resonance‐enhanced laser ionization, large differences between circular dichroism measured for molecular and fragment ions were found by several research groups for different molecular systems. In the case of 3‐methylcyclopentanone (3‐MCP) we attributed this effect to a large circular dichroism of the molecular ion. In the work presented here, this effect in 3‐MCP is studied by ion spectroscopy, by varying the neutral intermediate excited state involved in resonance‐enhanced multiphoton ionization (REMPI) and by performing REMPI‐induced measurements of circular dichroism at different laser pulse energies. It turns out that the dynamics of structural changes in the ionic ground state strongly influences the observed ionic circular dichroism.     

Viscosalines B1,2 and E1,2: Challenging New 3‐Alkyl Pyridinium Alkaloids from the Marine Sponge Haliclona viscosa

Four new 3‐alkyl pyridinium alkaloids, the viscosalines B₁ ( 1 a ), B₂ ( 1 b ), E₁ ( 2 a ), and E₂ ( 2 b ), were isolated from the Arctic sponge Haliclona viscosa. The structure elucidation of these isomeric compounds was challenging due to ambiguous fragments that derive during “standard” mass spectrometric fragmentation experiments. The final structure elucidation relied on the use of a combination of synthesis, liquid chromatography, and mass spectrometry. Three different mass spectrometers were used to differentiate between the synthetic structural isomers: a time‐of‐flight (TOF) mass spectrometer and two ion‐trap mass spectrometers with different ion‐transfer technologies (i.e., skimmer versus funnel optics). Although at first none of the spectrometers returned spectra that permitted structure elucidation, all three mass spectrometers provided analysis that successfully differentiated between the isomers after thorough method optimization. The use of in‐source collision‐induced dissociation (CID) with the ion trap and TOF instrument returned the most interesting results. The mode of fragmentation of the viscosalines under different experimental conditions is described herein. After successful optimization of the mass spectrometric method applied, the chromatographic method was improved to distinguish the previously inseparable isomers. Finally, both the liquid chromatography and mass spectrometric methods were applied to the natural products and the results compared to those from the synthetic compounds.