纳升电喷雾串联质谱(Q-TOF)测序中Na+加合肽的分析

电喷雾串联质谱测序法是蛋白质组研究中蛋白质鉴定的最有力的手段之一。肽段离子在ESI-Q-TOF中往往以多电荷形式出现(2～4个电荷),其中m／z在500～1000之间带双电荷的离子最适合测序。但这样的肽段很容易和Na+加合,有时加合峰的相对强度比原肽段高很多,有时甚至只有加合峰。Na+加合肽的序列分析比较困难,因数据库查寻不支持Na+加合,且Na+加合是非氨基酸特异的,序列分析中不能按修饰编辑,一旦有一个氨基酸的序列发生偏差,整个肽段序列就不正确。因此,Na+加合肽的序列分析很重要。在Na+加合肽序列分析中,寻找m／z相差22Da的离子,以其为起点分别按m／z从高到低和从低到高进行分析,可得到完整序列,用序列进行数据库检索可鉴定蛋白质,本文用此方法分析了5个Na+加合肽的序列,鉴定5个蛋白质。Na+加合位点分别为丝氨酸S、脯氨酸P和酪氨酸Y。     

Effect of Supermolecular Structure Changes on the Glass Transition of Polymer

The idea of two miscellaneous amorphous fractions in one polymeric system is under consideration. A new factor influencing the glass transition and a relaxation observed in polymers exhibiting different supermolecular structures is discussed. In order to clarify the specific arrangement of backbone chains two types of polymers were taken under investigation: semicrystalline poly(4-methyl-1-pentene) and a liquid-crystalline poly(norbornene) derivative. In both cases,it was possible to find two well separated glass transitions. Differential scanning calorimetry and dynamic mechanical thermal analysis were used to study the effect of thermal history on the assignment of the glass transition event associated with two miscellaneous amorphous phases. The problem of molecular arrangement in the amorphous phases is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

顺,反式环丙烷衍生物异构体的区分

在化学电离条件下，研究了４种顺、反式环丙烷衍生物与丙酮和醋酸乙烯酸乙烯酯的分子离子反应。异构体１，２的丙酮ＣＩ谱及其加合离子「Ｍ＋Ｈ＋Ａ」的ＣＩＤ谱都 可以区分该对异构体。化合物２，３和４可以和质子化丙酮及质子化二聚体发生加合反应，但化合物１仅能与质子化丙酮发生加合反应。在醋酸乙烯酯的ＣＩ谱中，观察到４个化合物的质子化二聚体，其中异构体１，２的质子化二聚体的ＣＩＤ谱也能反映它们立体结构的差异。     

Metallic samarium and iodine promoted facile and efficient syntheses of trisubstituted alkenes from the acetates of Baylis-Hillman adducts

Promoted by samarium metal in the presence of a catalytic amount of iodine, the Baylis-Hillman adducts underwent reductive elimination to form (E)-methylcinnamic ester derivatives. When the iodine was used in 1:1 ratio with metallic samarium, stereospecific syntheses of allylic iodide derivatives, (2Z)-2-(iodomethyl)alk-2-enoates, were achieved. Thus, this gives a new approach to the selective construction of stereo-defined trisubstituted alkenes with the simple Sm/I₂ system.     

N-PHOSPHORYL AMINO ACIDS AND PEPTIDES: PART I. THE CRYSTAL AND MOLECULAR STRUCTURE OF N-(O,O-DIISOPROPYL PHOSPHORYL)-TRANS-4-HYDROXY-D,L-PROLINE

Abstract

The crystal and molecular structure of N-(O,O-diisopropyl phosphoryl)-trans-4-hydroxy-D,L-proline has been determined by X-ray diffraction analysis and is compared with proline or hydroxyproline residue in a peptide chain described in the literature. The compound crystallized in orthorhombic system with space group P2₁2₁2₁, a=6.934(2), b=8.694(3), c=26.727(7) Å, V=1611.3(8) ų, Z=4, Dx=1.22 g/cm³. The structure was solved by direct method and refined by anisotropic least squares to a discrepancy index R=0.072. In the compound, the nitrogen atom is trigonal and its remaining 2p orbital is conjugated with the P?Oπ system; the conformation of the phosphorimidate function is favoured by the trans orientation of the P=O bond with respect to the N-C4 bond. In the pyrrolidine ring moeity, the C2-C1-N-C4 atoms are nearly copolnar and the C3 atom is out of the plane by about 0.47 Å.     

Oxidative oxo Diels–Alder Reactions of Baylis–Hillman Adducts with Electron-Rich Alkenes in the Presence of IBX

Baylis–Hillman adducts were oxidized by iodoxybenzoic acid (IBX) to 2-methylene-1,3-dicarbonyl compounds, which can act as oxodiene to react with electron-rich alkenes to generate a variety of oxo Diels–Alder adducts in good yields.     

Vibrational Studies of Palladium(II) Acetate Compounds Ii. Infrared Spectra of the Diethylamine Adduct of Palladium(II) Acetate

Recorded and discussed are the infrared spectra of the diethylamine adduct of palladium(II) acetate. An empirical assignment of the spectra is proposed. The palladium-oxygen bonds in the adduct are not much different in strength from those in hexa-μ-acetato-triangulo-tripalladium(II)-water (2/1). The diethylanine molecules are present as such, as evidenced by the appearance of a rather strong band attributed to the N-H stretching vibrations.     

Replacing the hydrogen in the intermolecular hydrogen bond of the cyanuric acid-bipyridyl adduct by Ag(I)

A complex between cyanuric acid (CA), 4,4′-bipyridyl (BP) and Ag(I), with the composition, [Ag₂(C₃H₂N₃O₃-κN)₂ (C₁₀H₈N₂-κN)] has been prepared. Crystal structure analysis shows that it has a chain structure in which the CA molecules are linked to the BP units through silver atoms by the formation of N-Ag-N bonds, wherein one of the hydrogens of CA is replaced by Ag(I), showing thereby the chains connected to one another by N-H...O hydrogen bonds formed between the CA molecules. This intermolecular chain structure resembles the chain structure of the CA.BP adduct where CA-BP-CA chains formed by N-H...N hydrogen bonds are linked to one another by N-H...O hydrogen bonds between the CA molecules.     

EPR/Spin‐trapping study of free radical intermediates in the photolysis of trifluoromethyl ketones with initiators

Photolysis of trifluoromethyl ketones (TFMKs) 1a–1e versus the non‐fluorinated ketones 2a–2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2‐methyl‐2‐nitrosopropane (MNP) and 2,4,6‐tri‐tert‐butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t‐butylperoxide, short‐chain TFMKs, such as 1,1,1‐trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long‐chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one α‐methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a γ‐hydrogen to the carbonyl group. Copyright © 2010 John Wiley & Sons, Ltd.