One-pot synthesis of α-amino phosphonates from α-amino acids and β-amino alcohols

The one-pot radical fragmentation-phosphorylation reaction of α-amino acids and β-amino alcohols affords α-amino phosphonates in good yields. The reaction was applied to the synthesis of potentially bioactive phosphonates.     

Extended Longitudinal Scaling: Direct evidence of saturation

Multiparticle production of charged particles at high energies exhibit the phenomenon of Limiting Fragmentation. Furthermore, the region in rapidity over which the production of particles appears to be independent of energy, increases with energy. It is argued that this phenomenon, known as Extended Longitudinal Scaling, is a direct manifestation of some kind of saturation, akin to that in the Color Glass Condensate picture of particle production.     

Global classical solutions of coagulation-fragmentation equations with unbounded coagulation rates

We study discrete fragmentation coagulation equations in spaces X_p, p>1, consisting of distributions having the pth moments finite. We show that for sufficiently regular fragmentation laws the fragmentation semigroup is analytic in X_p, and fully characterize the domain of its generator. This allows for explicit characterization of the domains of the fractional powers of the generator through real interpolation. Finally, we use the linear results to show the existence of global classical solutions to fragmentation coagulation equations for a class of unbounded coagulation kernels.     

A fragmentation model with neighborhood interaction

Several models of fragmentation have been studied that suppose random fracture forces. In this article, we did a numerical study on a dynamic model for fragmentation in which the fracture forces are generated by neighboring fragments and are proportional to the size of the common boundary between two fragments. The following assumptions were also considered: the material defects are represented by a random distribution of point flaws; the total mass is conserved; and the iterative fracture of each fragment is randomly stopped by a condition that considers a constant probability and a minimal fragment size. The motivation for this model was to determine under what circumstances a continuous fragmentation model with fracture forces defined by the neighbors’ interaction produces results that are in agreement with the experimental evidence. The main result of this work establishes that the fragment size distribution follows a power-law for fragments of greater area than the minimal fragment size m_fs. The visualizations present complex fracture patterns that resemble real systems.     

G-SIMS and SMILES: Simulated fragmentation pathways for identification of complex molecules, amino acids and peptides

G-SIMS is a powerful method for the identification of organics and complex molecules at surfaces. We have previously shown that the molecular structure may be reassembled from fragment ions by studying the evolution of G-SIMS intensities as the surface plasma, with effective temperature T_p, is varied, using a method known as G-SIMS-FPM.Here, we develop a novel approach, based on SMILES (Simplified Molecular Input Line Entry Specification), to assist the reassembly process in an automated way through evaluation of the fragmentation pathways for given molecular structures. A computer program takes a parent structure and goes through every possible fragmentation to provide a tree structure of fragmentation products and simulated fragmentation pathways. For any fragment it is then possible to identify the molecular structure, its mass and a pathway to the parent. We find that there is a good correlation with peak evolution in G-SIMS-FPM data and simulated pathways for two amino acids and a simple peptide. This significantly enhances the application of G-SIMS-FPM to unknown materials.     

解吸附电晕束电离质谱法快速筛选保健食品中非法添加的5型磷酸二酯酶抑制剂

建立了解吸附电晕束离子源(DCBI)结合离子阱质谱快速检测保健食品中非法添加的3种磷酸二酯酶5(PDE5)抑制剂(伐地那非、西地那非、他达拉非)的方法。采用一级质谱筛选,二级质谱确证,对样品中非法添加物进行定性鉴别;通过二级特征碎片离子进行半定量分析,并与传统高效液相色谱-紫外(HPLC-UV)定量检测法对比。对12个市售保健品进行检测,DCBI-MS定性检测结果与HPLC-UV检测结果一致,有7个样品检出他达拉非,3个样品检出西地那非,1个样品检出伐地那非。通过研究3种PDE5抑制剂的二级质谱裂解规律,推测一个样品中含有羟基豪莫西地那非。本方法快速准确,适用于大批量复杂基质样品中PDE5抑制剂的筛查。     

Mass Spectra of 2- and 6-Substituted-3-Pyrones: Competition Between “RETRO-DIELS-ALDER” Fragmentation and Substituent Loss

The mass spectra of a series of 6-hydroxy-3-pyrones and their derivatives showed a marked dependence upon the nature of the substituent. The “retro-Diels-Alder” reaction is the primary decomposition observed for the parent compounds, while the α-cleavage (substituent loss) competes with the “retro-Diels-Alder” reaction for their derivatives. An interpretation of this difference based on the charge location and the thermochemical data is proposed.     

快原子轰击(FAB)离子化法测定头孢拉定的质谱及其裂解途径的解析

头孢拉定(Cefradine)是第一代合成头孢类抗生素药,也是目前最常用的抗生素之一。有胶囊、片剂也有注射针剂。具有广谱的抗菌性能,由于它对革兰氏阳性及阴性杆菌敏感,故对治疗呼吸道感染颇有效,用途广、用量大,属于高效的头孢菌素。国内不少药厂都有研制,为此,我们对其质谱行为进行了分析。头孢拉定,化学名(6R,7R-[(R)-2-氨基-2-(1,4-环己烯基)乙酰氨基]-3-甲基-8-氧代-5-硫杂-1-氮杂双环[4.2.0】辛-2-烯-2-羧酸,其产品为一水化物。分子式C16H19N3O4S·H2O,结构见图1。     

Implication of volume changes in uranium oxides: A density functional study

In severe nuclear accident scenarios (in air environments and high temperatures) UO₂ fuel pellets oxidise to produce uranium oxides with higher oxygen content, e.g., U₄O₉ or U₃O₈. As a first step in investigating the microstructural changes following UO₂ oxidation to hexagonal high temperature phase of U₃O₈, density functional quantum mechanical calculations of the structure, elastic properties and electronic structure of U₃O₈ have been performed. The calculated properties of hexagonal phase of U₃O₈ are compared to those of the orthorhombic pseudo-hexagonal phase which is stable at room temperature. The total energy technique based on the local density approximation plus Hubbard U as implemented in the CASTEP code is used to investigate changes in the lattice constants. The first-principles calculations predict a 35–42% increase in volume per uranium atom as a result of the transformation from UO₂ to U₃O₈, in agreement with experimental data. The implications of this prediction on the linear expansion and fragmentation of fuel are discussed.