Total synthesis of (+)-cymbodiacetal: a re-evaluation of the biomimetic route

A total synthesis of (+)-cymbodiacetal (1) has been completed from (R)-(+)-limonene oxide using a hetero-Diels-Alder cycloaddition as a key step. The key Diels-Alder cycloaddition proceeds with endo-selectivity (2:1, endo/exo) in quantitative yield, and the two diastereomeric spirochroman products are isolable, stable products. Furthermore, the exo- and the endo-hetero-Diels-Alder cycloaddition products (2 and 7) can be oxidized with m-CPBA to produce (+)-cymbodiacetal (1) and the C(2)-symmetric bis-hemiacetal structure 8, respectively. The isomeric hemiacetal 9 is produced in both oxidation reactions. The structures of (+)-cymbodiacetal (1), its C(2)-symmetric diastereoisomer 8, and the isomeric hemiacetal 9 were confirmed using X-ray crystallography.     

品红甲亚胺染料影像光稳定性的研究 Ⅱ.抗氧化剂猝灭单重态氧的反应速率常数测定

本文利用高效液相色谱法测定了色满类,双螺色满类,对一甲氧基苯酚类和双螺茚类抗氧化剂与单重态氧反应的物理猝灭速率常数和化学猝灭速率常数。实验结果表明,抗氧化剂猝灭单重态氧的过程以物理猝灭为主,物理猝灭速率常数和总猝灭速率常数愈大,品红甲亚胺染料的防褪色效果愈好,但存在一极限褪色率。     

Reaction of the fischer base with nitro- and bromo-substituted o-hydroxycinnamaldehydes

The Fischer base reacts with -ethyl-5-nitro-, 5-bromo-, and 3,5-dibromo-2-hydroxy-cinnamaldehydes to give bisindoline spirochromans, with 3-bromo-5-nitro-2-hydroxy-cinnamaldehyde to give a mixture of a spirochroman and a monoindoline merocyanine, and with 3,5-dinitro-2-hydroxycinnamaldehyde to give only a merocyanine. The monoindoline merocyanines obtained do not display a tendency to undergo intramolecular cyclization to give spiro-2H-oxocines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 775–778, June, 1984.     

品红甲亚胺染料影像光稳定性的研究——抗氧化剂和单重态氧的反应能力及其对染料影像光褪色的影响

本文研究了苯酚类(A),双酚类(B),对苯二酚类(C),色满类(D)和双螺色满类(E)抗氧化剂的性能。通过循环伏安法测定了它们的氧化电位;用类似Stern-Volmer关系图求得各抗氧化剂和单重态氧的反应速率常数。抗氧化剂的氧化电位越小,和单重态氧的反应速率常数越大,对品红甲亚胺染料影像的防褪色效果越好,进一步证实了染料褪色的光氧化反应机理。在这些抗氧化剂中,它们的防褪色效果依次为D>E>C>B>A。     

Electrospun core–sheath fibers for integrating the biocompatibility of silk fibroin and the mechanical properties of PLCL

In the process of preparing core–sheath fibers via coaxial electrospinning, the relative evaporation rates of core and sheath solvents play a key role in the formation of the core–sheath structure of the fiber. Both silk fibroin (SF) and poly(lactide‐co‐ε‐caprolactone) (PLCL) have good biocompatibility and biodegradability. SF has better cell affinity than PLCL, whereas PLCL has higher breaking strength and elongation than SF. In this work, hexafluoroisopropanol (HFIP)‐formic acid (volume ratio 8:2), HFIP and HFIP–dichloromethane (volume ratio 8:2) were used to dissolve PLCL as the core solutions, and HFIP was used to dissolve SF as the sheath solution. Then, core–sheath structured SF/PLCL (C‐SF/PLCL) fibers were prepared by coaxial electrospinning with the core and sheath solutions. Transmission electron microscopy images indicated the existence of the core–shell structure of the fibers, and energy dispersive X‐ray analysis results revealed that the fiber mat with the greatest content of core–shell structure fibers was obtained when the core solvent was HFIP–dichloromethane (volume ratio 8:2). Tensile tests showed that the C‐SF/PLCL fiber mat displayed improved tensile properties, with strength and elongation that were significantly higher than those of the pure SF mat. The C‐SF/PLCL fiber mat was further investigated as a scaffold for culturing EA.hy926 cells, and the results showed that the fiber mat permitted cellular adhesion, proliferation and spreading in a manner similar to that of the pure SF fiber mat. These results indicated that the coaxial electrospun SF/PLCL fiber mat could be considered a promising candidate for tissue engineering scaffolds for blood vessels. Copyright © 2014 John Wiley & Sons, Ltd.     

A rapid and convergent synthesis of the integrastatin core

The tetracyclic core of the integrastatin natural products has been prepared in a convergent and rapid manner. Our strategy relies upon a palladium(II)-catalyzed oxidative cyclization to form the central [3.3.1]-dioxabicycle of the natural product core. Overall, the core has been completed in only 4 linear steps from known compounds.     

Prediction of the in-core power and the average core temperature using dose-rate measurements in the Syrian Miniature Neutron Source Reactor

Summary The measurement of the dose-rate on the top-surface of the Miniature Neutron Source Reactor (MNSR) has been used to monitor the in-core reactor power and estimate the average core temperature. An experimental correlation for the prediction of both reactor power level and average core-coolant temperature as functions of dose-rate measurement have been obtained. An alternative method for both neutron flux monitoring and average core temperature using dose-rate measurement has been suggested. Comparing the results with the calibrated reactor power, reasonable agreement between predicted and real data measurement has been found. Despite of this agreement, the measurement of dose-rate on top of the MNSR surface as an additional mean for the prediction of in-core power or average core temperature should be considered carefully.     

Fibrous projections from the core of a bacteriophage T7 procapsid

A cylindrical core previously demonstrated in a bacteriophage T7 procapsid (capsid I) has been further examined by electron microscopy. Fibrous extensions of the core have been observed; these fibers appear to connect the core to the capsid I envelope. After infection of a nonpermissive host with bacteriophage T7 amber mutant in any gene coding for a core protein, the resulting lysates contained more noncapsid assemblies of capsid envelope protein than did wild-type lysates; these assemblies had a mass two to at least 500 times greater than the mass of capsid I. This suggests that the internal core and fibers assist the assembly of subunits in the envelope of capsid I.     

X射线荧光光谱扫描法在实物地质资料中应用的可行性探讨

实物地质资料的定量无损检测对于地质学研究具有十分重要的意义,在国外x射线荧光光谱（XRF）扫描分析方法在岩芯分析测试方面的应用研究,已取得了十分显著的成果。XRF岩芯扫描分析方法具有分析速度快、无损检测、连续定量测试多元素和样品制备简单等特点,在获取高分辨测试方面更具独特的优势。因此,这一分析方法在实物地质资料分析方面具有极好的应用前景,它能提高分析的准确性和精确度,降低分析测试成本,保护实物地质资料的完整性,加强实物资料的整体性研究,为实物地质数据采集与信息共享提供更加准确的数据。从介绍XRF岩芯扫描分析方法的原理、特点、影响因素、分析结果的校正人手,进而探讨该测试方法在实物地质资料中应用的可行性。     

Laser-induced mutual transposition of the core and the shell of a Au@Pt nanosphere

The mutual transposition of the core and the shell of a Au@Pt core-shell nanosphere has been obtained by employing picosecond laser pulses to excite the surface-plasmon resonances of platinum. The thermalized energy of the plasmon resonances makes the core metal of the gold melt earlier than the shell metal of platinum because of melting temperature differences and causes the gold to soak out of the core to the surface of the nanosphere. A new reversed core/shell Pt@Au core-shell nanosphere is formed with further irradiation.     

Total synthesis of haouamine A: the indeno-tetrahydropyridine core

A full account of synthetic efforts toward the indeno-tetrahydropyridine core of haouamine A is presented. Initial failed strategies led to the unexpected discovery of a mild abnormal Chichibabin pyridine synthesis and provided knowledge and inspiration for the development of a cascade annulation that has enabled rapid and scalable access to the core in either racemic or enantiopure form.     

Orbital relaxation in the Rydberg series of the He atom

The orbital behavior of both the singlet and triplet Rydberg series for 1sns configurations of the He atom has been investigated using one- and two-configuration Hartree–Fock wave functions. The core orbital within the triplet series changes negligibly; however, a contract trend is noticeable as the Rydberg orbital penetrates more into the core region, which is in contrast to that found in the 1s²ns ²S Rydberg series of Li atom. Although some properties of the whole atom can be calculated, the core relaxation of the singlet series can not be drawn without ambiguity because a two-configuration correlated wave function has to be used, and thus the orbital picture is lost.     

Characterization of the core oligosaccharide and the O-antigen biological repeating unit from Halomonas stevensii lipopolysaccharide: the first case of O-antigen linked to the inner core

A novel core structure among bacterial lipopolysaccharides (LPS) that belong to the genus Halomonas has been characterized. H. stevensii is a moderately halophilic microorganism, as are the majority of the Halomonadaceae. It brought to light the pathogenic potential of this genus. On account of their role in immune system elicitation, elucidation of LPS structure is the mandatory starting point for a deeper understanding of the interaction mechanisms between host and pathogen. In this paper we report the structure of the complete saccharidic portion of the LPS from H. stevensii. In contrast to the finding that the O-antigen is usually covalently linked to the outer core oligosaccharide, we could demonstrate that the O-polysaccharide of H. stevensii is linked to the inner core of an LPS. By means of high-performance anion-exchange chromatography with pulsed amperometric detection we were able to isolate the core decasaccharide as well as a tridecasaccharide constituted by the core region plus one O-repeating unit after alkaline degradation of the LPS. The structure was elucidated by one- and two-dimensional NMR spectroscopy, ESI Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, and chemical analysis.     

Decorating step-by-step and independently the surface and the core of dendrons

Dendrons possessing one activated vinyl group at the core and several chlorine atoms at the end of the branches are used as starting materials to study the possibility to react independently the surface functions and the core function. In particular, the most powerful sequence of reactions for decorating them by organometallic complexes as end groups and amine or alcohol at the core has been determined. In the first step, phenol phosphines are grafted as end groups of the dendrons, and they can be used for the complexation of metals. However, these phosphines must be kept free when amines are used to react with the vinyl core in the next step. Depending on the type of phosphine end groups and on the type of function of the core (amine or alcohol), the complexation of ruthenium ([RuCl₂(p-cymene)]₂) and rhodium ([RhCl(COD)]₂) derivatives by the phosphine end groups can occur without side reaction at the core.     

Poly(vinylpyridine) core/poly(N-isopropylacrylamide) shell microgel particles: their characterization and the uptake and release of an anionic surfactant

The use of microgel particles for controlled uptake and release of active species has great potential. The compatibility of microgel particles with their environment and the functionality of the particles can be achieved by modification of the core microgel through the addition of a shell. In this work, core-shell microgel particles, with a pH-responsive core (polyvinylpyridine) and a temperature-responsive shell (poly-N-isopropylacrylamide), have been prepared and characterized. The uptake and release of an anionic surfactant from the microgels has been investigated as a function of solution pH and temperature. The results indicate that electrostatic attraction between the anionic surfactant and the cationically charged core of the microgel particles is the dominant mechanism for absorption of the surfactant into the core-shell microgel particles.     

Expanded electronic states of the fluorine molecule

Potential curves of electronically excited states of F₂ with an expanded outer orbital have been calculated using a modified frozen core technique: The ionic core has been described with a two-determinant wave function and for the excited states a mixing of configurations with different cores has been employed. An investigation of the valence shell states of F₂ is presented and potential curves for a singly excited as well as a doubly excited V-state of ¹Σ_u⁺ symmetry have been calculated. Further a low lying two-configuration state resulting from simultaneous excitation to a valence and a Rydberg orbital is predicted.     

A convergent synthesis of the 11-oxa prostaglandin analogue AL-12182

[reaction: see text] The 11-oxa prostaglandin analogue AL-12182 1 has potent topical ocular hypotensive activity. A convergent and concise general synthesis of this class of prostanoid was developed employing a stereoselective coupling reaction between a tetrahydrofuran core electrophile and a nucleophilic omega side chain component, providing a route that should be suitable for commercial scale production. The tetrahydrofuran core was assembled from dimethyl d-malate using a stereoselective beta-hydroxy ester dianion alkylation reaction.     

Structural characterization of the epitaxially grown core–shell ZnTe/ZnMgTe nanowires

We report the method of the epitaxial growth of the core–shell ZnTe/ZnMgTe nanowires. The morphology and the crystal structure of several samples grown in different processes have been studied by scanning electron microscopy, high resolution transmission electron microscopy and X-ray diffraction methods. It was shown that the ZnMgTe shell growth was clearly epitaxial with a good crystal quality. The average lattice spacing of the ZnTe cores and ZnMgTe shells have been calculated and Mg content in the shells has been estimated. It was documented that growing the shell lattice mismatched to the core induces the strain in the core. The model of the strain creation mechanism has been proposed. The presence of a shell with a larger energy gap than that of the core results in a strong emission in the spectral region near the band edge.     

Ionic-charge dependence of the intermolecular coulombic decay time scale for aqueous ions probed by the core-hole clock

Auger electron spectroscopy combined with theoretical calculations has been applied to investigate the decay of the Ca 2p core hole of aqueous Ca(2+). Beyond the localized two-hole final states on the calcium ion, originating from a normal Auger process, we have further identified the final states delocalized between the calcium ion and its water surroundings and produced by core level intermolecular Coulombic decay (ICD) processes. By applying the core-hole clock method, the time scale of the core level ICD was determined to be 33 ± 1 fs for the 2p core hole of the aqueous Ca(2+). The comparison of this time constant to those associated with the aqueous K(+), Na(+), Mg(2+), and Al(3+) ions reveals differences of 1 and up to 2 orders of magnitude. Such large variations in the characteristic time scales of the core level ICD processes is qualitatively explained by different internal decay mechanisms in different ions as well as by different ion-solvent distances and interactions.     

Core Functionality and Scaling Behavior of Lysine Dendrimers

Summary: A scaling exponent to describe the dependence of the hydrodynamic radius as a characteristic length of the molecule on the molecular weight, has been determined for low generation dendrimers with a thiacalixarene core and lysine dendrons. The hydrodynamic radius has been calculated from the diffusion coefficient measured by pulsed‐field‐gradient NMR spectroscopy. Scaling exponents of 2.0 for the lysine monodendron, 2.3 for a dendrimer with a bifunctional core, and 3.9 for a dendrimer with a tetrafunctional core have been determined. For a given structure of the dendrons, the scaling exponent reflects the functionality of the core of the dendrimers.

Hydrodynamic radius of lysine dendrons as a function of molar mass.