Totally stereoselective synthesis of 1,3-disaccharides through Diels-Alder reactions

A nonclassical, totally stereoselective synthesis of orthogonally protected 1,3-disaccharides is reported. Enantiomerically pure beta-keto-delta-lactones, efficiently obtained from glucal and galactal, are transformed into electron-poor heterodienes and chemo-, regio-, and stereoselectively cycloadded to glycals as electron-rich dienophiles, to directly afford 2-thiodisaccharides. The reductive desulfurization of the latter smoothly gave the corresponding 2,2'-dideoxydisaccharides.     

Criteria sensitivity analysis: a new approach to parameter sensitivity

The problem of parameter sensitivity is not well defined. This paper aims to make it well defined. This is done by requiring the modeller to provide a performance indicator l(X,t,β) which is a measure of how the behaviour of the system is to be judged. This forces the modeller to be precise about what he/she regards as acceptable behaviour. Mathematically we define behaviour to be acceptable at β if l >0 for that β, and we define the system as sensitive if the set of acceptable β's is small. The analysis which is required is termed criteria sensitivity analysis. This method is applicable to many different kinds of models. The basic ideas of criteria sensitivity analysis are presented here. A static model is used to demonstrate major points. The power of this new approach is illustrated by an application to a dynamic model.     

Schrödinger equations with unique positive isolated singularities

We investigate the class of nonnegative potentialsV(x) for which the Schrödinger equation ?Δu+V u=0 admits a unique type of singular solution such thatu(x)→∞ asx→0. This class includes the potentials with inverse-square growth at 0, i.e. 0≤V(x)≤C|x|^?2. If for instance we fix boundary datau=g at |x|=1 then the singular solution is unique up to a multiplicative factor.     

真空Einstein方程所容许的群及方程的局部不变解

该文提出李变换群延拓群的概念,并运用纤维丛方法解决了延拓群算子中的系数问题.在此基础上,作者着重求出了真空Einstein方程所容许的群,同时还提出求方程局部不变解的一种可能方案.     

Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend—Effects of specific substrate interaction

We report on the effect of the substrate on the vertical phase separation in spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] (APFO-3) blended with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). Compositional depth profiles of the films are measured by dynamic secondary ion mass spectrometry (SIMS). We found that changing the substrate from silicon to gold affects the composition profile near the substrate interface. This is caused by a specific interaction between the polymer (APFO-3) and the gold surface, as confirmed by X-ray photoelectron spectroscopy (XPS). The composition profile in the area away from the substrate interface, as well as the enrichment of the free surface with APFO-3, remain however unaffected by the choice of substrate. The vertical composition was also analysed for APFO-3:PCBM films spin-coated on indium tin oxide (ITO) coated with a thin layer of (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).     

Synthesis of 1,2-dimethoxy-1,2-di(pyridin-2-yl)-1,2-ethanediol: Crystal and molecular structure determination

The compound, 2-hydroxy-[1,2-di(pyridin-2-yl)]ethane-1-one, 1, was isolated from the reaction of 2-pyridinecarboxaldehyde and 2-pyridinemethanol at 140°C without catalyst or solvent and characterized by¹H-NMR and IR spectral data. The compound 1 was treated with ethyl acetate to produce the 1,2-di(pyridin-2-yl)ethane-1,2-dione, 2. When 2 was dissolved in an excess of CH₃OH, crystals of 1,2-dimethoxy-1,2-di(pyridin-2-yl)-1,2-ethanediol, 3, were obtained. The molecular and crystal structure of 3 was determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic system belonging to the P2₁/n space group with a = 6.867(2) ?, b=9.546(4) ?, c=10.522(5) ?, α=90°, β=98.48(4)°, γ=90°. The asymmetric unit comprises two molecules of 3. Although the di-hemiketal was obtained in crystal form, it was found to be unstable, because its IR spectrum changed after a short time, indicating that it had been converted back to the original diketone, 2. The IR showed signals at 1713, and 1690 due to νC =O assigned to di-ketone group.     

Quantum chemical topology at the spin–orbit configuration interaction level: Application to astatine compounds

We report a methodology that allows the investigation of the consequences of the spin–orbit coupling by means of the QTAIM and ELF topological analyses performed on top of relativistic and multiconfigurational wave functions. In practice, it relies on the “state-specific” natural orbitals (NOs; expressed in a Cartesian Gaussian-type orbital basis) and their occupation numbers (ONs) for the quantum state of interest, arising from a spin–orbit configuration interaction calculation. The ground states of astatine diatomic molecules (AtX with X = At F) and trihalide anions (IAtI⁻ , BrAtBr⁻ , and IAtBr⁻ ) are studied, at exact two-component relativistic coupled cluster geometries, revealing unusual topological properties as well as a significant role of the spin–orbit coupling on these. In essence, the presented methodology can also be applied to the ground and/or excited states of any compound, with controlled validity up to including elements with active 5d, 6p, and/or 5f shells, and potential limitations starting with active 6d, 7p, and/or 6f shells bearing strong spin–orbit couplings.     

Thermal Decomposition of Ternary Sodium Graphite Intercalation Compounds

Graphite intercalation compounds (GICs) are often used to produce exfoliated or functionalised graphene related materials (GRMs) in a specific solvent. This study explores the formation of the Na-tetrahydrofuran (THF)-GIC and a new ternary system based on dimethylacetamide (DMAc). Detailed comparisons of in situ temperature dependent XRD with TGA-MS and Raman measurements reveal a series of dynamic transformations during heating. Surprisingly, the bulk of the intercalation compound is stable under ambient conditions, trapped between the graphene sheets. The heating process drives a reorganisation of the solvent and Na molecules, then an evaporation of the solvent; however, the solvent loss is arrested by restacking of the graphene layers, leading to trapped solvent bubbles. Eventually, the bubbles rupture, releasing the remaining solvent and creating expanded graphite. These trapped dopants may provide useful property enhancements, but also potentially confound measurements of grafting efficiency in liquid-phase covalent functionalization experiments on 2D materials.     

Purification of clenbuterol-like beta2-agonist drugs of new generation from bovine urine and hair by alpha1-acid glycoprotein affinity chromatography and determination by gas chromatography-mass spectrometry

The control of illegal use of clenbuterol and other β₂-agonist drugs as growth promoters in the European Union countries has led to outlaw practices for synthesizing new concept molecules, showing similar biological activity but not detectable by test methods usually employed to perform the official monitoring programmes. The synthesis schemes of some β₂-agonist compounds, formally derived from clenbuterol, were found out by Italian detective authorities. These compounds were synthesised ex novo in our laboratories: then, both their molecular structures and biological activities were characterised. In this paper, we describe different strategies for purifying some β₂-agonist drugs of new concept, more hydrophobic than clenbuterol. A two-step clean up procedure, prior to gas chromatography-mass spectrometry analysis, was developed for the multi-residue determination of these β₂-agonists from bovine hair and urine. The purification strategy we chose was based on adsorption solid phase extraction and, subsequently, on specific molecular recognition by affinity chromatography. The affinity columns were homemade by coupling bovine α₁-acid glycoprotein, a plasmatic acceptor for basic drugs, to a chromatographic support; their effectiveness for purifying new β₂-agonists was discussed. The data about method recoveries and repeatability were also reported.     

Identification of a probable new adrenergic agonist by nuclear magnetic resonance and mass spectrometry

In animal production, it is consolidated the synthesis and the illegal use of growth promoters of new generation, able to skip routine screening and confirmatory analysis. In this work it is reported the nuclear magnetic resonance (NMR) and the mass spectrometry identification of a probable new adrenergic drug found in a feed premix. The substance was selectively purified on alpha 1 acid glycoprotein affinity columns; then its structure was first achieved by recording the 13C NMR spectrum that gave the total number of carbons of the molecule, successively sorted by DEPT experiments into quaternary, CH, CH2, and CH3 groups. However, the complete assignments of all resonances were derived from the bi-dimensional analysis and the crucial indications from the 1H-13C reverse experiments. Further characterisation was performed by atmospheric pressure chemical ionisation both in positive and negative ion mode, matching the molecular ion and the fragmentation pattern with those of most recently described new adrenergic agonists. After the loss of a ter-butylic group, the structure shows an internal symmetry along with the presence of Chlorine clusters. The proposed formula of the compound, the 8,8'-diamino-9,9'-dichloro-1-terbutyl-1,1',4,4-tetrahydro-5H,5'H-2,2'-bi-1-benzazepine-5,5'-dione, partially resembles that of Zilpaterol for the presence of a heterocyclic ring; Further work is in progress to characterise the structure-activity relationship.