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91.
A recently characterized oviposition-deterring pheromone (ODP, structure 1) of the European cherry fruit fly was used as a test case for probing the potential of tandem mass spectrometry (MS/MS) in structure elucidation as a stand-alone technique. The glycolipid-taurinate 1 was subjected to MS/MS analyses under a variety of conditions with and without preceding chemical degradation. Acidic methanolysis of 1 and subsequent in-batch derivatization (trideuterioacetylation) yielded methyl 2,3,4,6-tetrakis-O-trideuterioacetyl-glucopyranoside (2), methyl 8,15-bis-trideuterioacetoxy-palmitate (3), and taurine (4) as suitable target compounds for direct mixture analysis.Low energy collision induced dissociation (CID) on selected precursor ions (MS/MS on [M + H – CH3OH]+ and [M + H]+ produced by fast atom bombardment (FAB)) allowed direct identification of 2 and 4, respectively, by comparison with appropriate reference ions. In the case of 3, low energy CID (desorption chemical ionization (DCI) instead of FAB, MS/MS on [M + H]+) permitted deduction of gross molecular structure, but failed to provide positional detail. In sharp contrast,high energy CID of trideuterioacetylated intact 1 (FAB-MS/MS on [M – H]– ions of la) clearly revealed a linear 8,15-hydroxylated palmitic acid backbone. Less certain was assignment of 15-O-glucosylation by this approach. 相似文献
92.
93.
Konrad Seppelt 《Angewandte Chemie (International ed. in English)》1991,30(4):361-374
Alkylidene and alkylidyne sulfur fluorides contain sulfur–carbon multiple bonds. In contrast to the sulfur ylides, alkylidene sulfur fluorides fulfill all the criteria for double bonds, i.e. they have short bond lengths, strong anisotropic distribution of electron density, and rotation about the C? S bond is restricted. Alkylidyne sulfur fluorides have especially short bond distances and, due to a high amplitude bending motion, appear to be more or less linear, depending on the physical state. The advantage of the C? S multiple bond systems in contrast with numerous others, e.g. those of phosphorus and silicon, is that they exist without steric stabilization. Moreover, the limits of the triple-bond principle are outlined: the prognosis for triple bonds between two elements of higher periods is poor, because carbene-like or fully bridged structures win in terms of stability. 相似文献
94.
Corinne De Dobbeleer 《Tetrahedron letters》2005,46(22):3889-3893
Functionalised medium-ring systems of various sizes can be efficiently prepared by a novel approach that embodies a radical-induced fragmentation of bicyclic β-hydroxy ketones, followed by a second radical-coupling reaction. The unexpected reactivity of α-keto radicals is also discussed. 相似文献
95.
Americo Inglese Fabio Mavelli Rosario De Lisi Stefania Milioto 《Journal of solution chemistry》1997,26(3):319-336
Densities of binary mixtures of polar organic solvents with alcohols were measured at 25‡C. The solvents studied were N,N-dimethylformamide,
dimethylsulfoxide, and formamide while alcohols were butanol, pentanol, hexanol, and 1,4-butanediol. Density measurements
of hydrocarbons (from pentane to dodecane and some heptane isomers) + N,N-dimethylformamide were also performed. From these
data the apparent molar volumes of alcohols and hydrocarbons as functions of concentration were calculated. The standard partial
molar volumes were obtained by extrapolation to infinite dilution and are discussed in terms of group contributions. 相似文献
96.
Frank J. Millero 《Journal of solution chemistry》1973,2(1):1-22
The apparent equivalent volume V, expansibility E, and compressibility K of an artificial seawater solution containing10 ionic components (Na+, Mg2+, Ca2+, K+, Sr2+, Cl–, SO
4
2–
, HCO
3
–
, Br–, and F–) and one nonionic component (H3BO3) has been determined from0 to40°C (in5° intervals) and from0.1 to0.8 m ionic strength at1 atm. The concentration dependence (Iv=volume ionic strength) of the V's, E's, and K's have been examined by using a Masson-type equation, = ° +S'I
V
1/2, and a Redlich-type equation, = ° +SI
V
1/2 +BI
V, where ° is the infinite-dilution value, S is the empirical Masson slope, S is the theoretical Debye-Hückel slope, and B is an empirical deviation constant. By using Young's rule, = Ei(i), the apparent equivalent volumes, expansibilities, and compressibilities for sea salt have been estimated from the ionic and nonionic components making up the mixture. The estimated apparent molal quantities agree very well with the directly measured values providing the concentration terms, S
i
and Bi, are weighted according to the methods of Wood and Reilly.Contribution Number 1599 from the University of Miami. 相似文献
97.
98.
以计量置换吸附理论(SDT A)为基础,从理论上推导出计量吸附模型中表征溶质对固定相亲合势大小的参数βa值与流动相中强置换剂浓度的对数呈线性关系。计量置换模型中的参数n和q(n和q分别代表1摩尔溶剂化溶质被吸附时,从吸附剂表面和从溶质分子表面所释放出的溶剂的物质的量)是计量置换参数Z值的分量,是两个非常有用的参数,可以从这个定量关系中直接获得。推导出的方程用苯的衍生物进行了实验验证,获得了较满意的结果。将这种方法计算得到的分量值与SDT A与计量置换保留模型(SDT R)相结合的方法得到的分量值进行了比较。 相似文献
99.
Three-dimensional quantum mechanical calculations for vibrational predissociation of HeI2(B) van der Waals molecules are presented using the time-dependent wave packet technique within the golden rule approxima tion.The total and partial decay widths,lifetimes,rates and their dependence on initial vibrational states were obtained for HeI2 at low initial vibrational excited levels.Our calculations show that the calculated tota decay widths,lifetimes and rates agree well with those extrapolated from experimental data available The predicted total decay widths as a function of initial vibrational states exhibit highly nonlinear behavior.The very short propagation time (less.than 1 ps) required in the golden rule wave packet calculation is determined by the duration time of the final state inter-action between the fragments on the vibrationally deexcited adiabatic potential surface.The final state interaction between the fragments is shown to play an important role in determining the final rotational distri 相似文献
100.
食品中化学性有害物是导致食品安全问题的重要原因,质谱是对食品中化学性有害物进行定性定量分析的有效方法。该文按照化合物结构类别,综述了食品中重要化学性有害物的质谱软电离裂解机理,包括农药、兽药、真菌毒素,以及其他化学污染物。对于每类化合物,重点综述化合物质谱裂解产生的特征碎片、中性丢失等,以及这些质谱软电离裂解机理在食品中化学性有害物筛查及发现中的应用。研究化合物的质谱裂解机理可以帮助研究者对化合物进行结构解析和结构确证,为食品中同类结构新型化学性有害物的发掘提供理论依据。 相似文献