二乙基锌的同步辐射真空紫外光电离光解离

利用同步辐射光源和反射式飞行时间质谱, 在超声冷却条件下对二乙基锌(ZnC4H10)进行真空紫外(VUV, 能量范围为8-22 eV)光电离光解离研究. 实验获得ZnC4H10的光电离质谱图; 通过测量各碎片离子的光电离效率(PIE)曲线, 获得ZnC4H10的电离势(IP=8.20±0.05 eV)及其碎片离子(ZnC2H5+、ZnH+、Zn+、C2H5+、C2H3+等)的出现势. 根据实验结果, 并结合相关文献所给的热力学数据, 推导出这些主要碎片离子的生成焓, 并分析它们可能的解离通道和主要离子的分支比. 结果表明, 其主要解离通道是母体离子发生Zn—C 键的断裂形成ZnC2H5+和C2H5+离子, ZnC2H5+离子再进一步解离形成Zn+离子, 并且含锌碎片离子的丰度占75%以上.     

Synthesis of optically active amphiphilic tetrathiafulvalene derivatives

The synthesis and characterization of novel chiral tetrathiafulvalenes bearing two long alkyl chains at one end of the π-electron rich unit and different functional groups—ester, acid or thiolate—at the other extreme is described. The synthetic method requires the preparation of 1,3-dithiol derivatives with two stereogenic centers. Different routes and reaction conditions were explored to form these compounds, whose optimized synthesis involved the nucleophilic substitution of a chiral bromo methylene derivative with tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolate)zincate. The tetrathiafulvalenes were prepared by coupling the 1,3-dithiol derivative with 4,5-bis(methoxycarbonyl)-1,3-dithiol-2-one or 4,5-bis(2-cyanotehylthio)-1,3-dithiol-2-thione. The products were fully characterized, including by circular dichroism spectroscopy, which confirmed their optical activity. They are promising candidates to be used as building blocks in supramolecular materials for molecular electronics, to produce systems with unique electrical, magnetic or optical properties that stem from their chirality.     

A Valence Photoelectron Imaging Investigation of Chiral Asymmetry in the Photoionization of Fenchone and Camphor

Photoelectron circular dichroism (PECD) is investigated in the valence ionization of selected fenchone enantiomers using a photoelectron imaging technique and circularly polarized synchrotron radiation. Theoretical modelling of the results using electron scattering calculations demonstrates that the observed chiral asymmetry in the photoelectron angular distributions depends strongly upon the final state scattering, and upon the quality of the molecular potential used for these calculations. However, very pronounced dependence on the orbital from which ionization occurs is also observed. Comparison with analogous results previously obtained for camphor reveals striking differences in the PECD, even when the ionizing orbitals are themselves left substantially unaffected by the changes in methyl groups’ substitution site. PECD measurements readily differentiate these molecules despite their very similar photoelectron spectra, demonstrating PECD to be a structurally sensitive probe.     

VUV photoionization of acetamide studied by electron/ion coincidence spectroscopy in the 8-24 eV photon energy range

A VUV photoionization study of acetamide was carried out over the 8-24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E. (1²A′) = (9.71 ± 0.02) eV, in agreement with an earlier reported photoionization mass spectrometry (PIMS) value. The adiabatic energy of the first excited state of the ion, 1²A″, was determined to be ≈10.1 eV. Assignments of the fragment ions and the pathways of their formation by dissociative photoionization were made. The neutral species lost in the principal dissociative photoionization processes are CH₃, NH₂, NH₃, CO, HCCO and NH₂CO. Heats of formation are derived for all ions detected and are compared with literature values. Some astrophysical implications of these results are discussed.     

Determination of the absolute configuration and identity of chiral carboxylic acids using a Cu(II) complex of pyridine–benzimidazole-based ligand

We report a new achiral Cu host [Cu(bmb–bpy)(H₂O)(OTf)₂] (bmb–bpy = 6,6′-bis[((1-methylbenzimidazol-2-yl)thio)methyl]-2,2′-bipyridine) for the enantioselective and chemoselective recognition of chiral carboxylic acids. The binding of chiral carboxylic acids to [Cu(bmb–bpy)(H₂O)(OTf)₂] produced an exciton-coupled circular dichroism signal; the linear discriminant analysis allowed the assignment of the absolute configuration, enantiomeric excess, and identity of chiral carboxylic acids.     

Ca掺杂的CeO2模型催化剂的形貌和电子结构及其与CO2分子的相互作用

利用扫描隧道显微镜、X射线光电子能谱和同步辐射光电子能谱研究了CeO₂(111),部分还原的CeO_2-x(111) (0＜x＜0.5)以及Ca掺杂的CeO₂模型催化剂的形貌、电子结构以及它们与CO₂分子间的相互作用。CeO₂(111)和部分还原的CeO_2-x(111)薄膜外延生长于Cu(111)单晶表面。不同Ca掺杂的CeO₂薄膜是通过在CeO₂(111)薄膜表面室温物理沉积金属Ca及随后真空退火到不同温度而得到的。不同的制备过程导致样品具有不同的表面组成,化学态和结构。CO₂吸附到CeO₂和部分还原的CeO_2-x表面后导致表面羧酸盐的形成。此外,相比于CeO₂表面,羧酸盐物种更易在部分还原的CeO_2-x表面生成,而且更加稳定。而在Ca掺杂的氧化铈薄膜表面,Ca²⁺离子的存在有利于CO₂的吸附,且探测到碳酸盐物种的形成。     

Structure investigations on assembled astaxanthin molecules

The carotenoid r,r-astaxanthin (3R,3′R-dihydroxy-4,4′-diketo-β-carotene) forms different types of aggregates in acetone–water mixtures. H-type aggregates were found in mixtures with a high part of water (e.g. 1:9 acetone–water mixture) whereas two different types of J-aggregates were identified in mixtures with a lower part of water (3:7 acetone–water mixture). These aggregates were characterized by recording UV/vis-absorption spectra, CD-spectra and fluorescence emissions. The sizes of the molecular assemblies were determined by dynamic light scattering experiments. The hydrodynamic diameter of the assemblies amounts 40 nm in 1:9 acetone–water mixtures and exceeds up to 1 μm in 3:7 acetone–water mixtures. Scanning tunneling microscopy monitored astaxanthin aggregates on graphite surfaces. The structure of the H-aggregate was obtained by molecular modeling calculations. The structure was confirmed by calculating the electronic absorption spectrum and the CD-spectrum where the molecular modeling structure was used as input.