The synthesis of a natural product family: from debromoisolaurinterol to the aplysins

Total syntheses of (±)-aplysin 1, (±)-debromoaplysin 2, (±)-isoaplysin 3, (±)-aplysinol 4, (±)-debromoaplysinol 5, (±)-aplysinal 6, (±)-isolaurinterol 7 and (±)-debromoisolaurinterol 8 are described. Key features are a diastereoselective, sulfur mediated radical cyclisation of diene 12 to give 35; a new radical to polar crossover sequence mediated by Bu₃Sn that transforms diene 12 into (±)-debromoisolaurinterol 8; and a series of biomimetic cyclisation and oxidation reactions.     

Photophysical Properties and Electropolymerization of Regioregular Head-to-Tail Oligothiophenes-Functionalized 9,9′-spirobifluorene Derivatives

The photophysical properties of oligothiophenes-functionalized 9,9′-spirobifluorene derivatives in solution and in solid state were investigated in detail. The enhanced red-shift was observed from the absorption and the photoluminescence (PL) spectra of these derivatives in dilute THF solution with the increase of thiophene unit at one branch of 9,9′-spirobifluorene identical with the increased p-electron delocalization and the more effective conjugation length of the whole molecular system. The investigation on the photophysical properties of these compounds further demonstrated that the sp3-hybrid carbon at the spiro-center completely obstructed the correlation between two branches of the 9,9′-spirobifluorene system and made every branch become an independent chromophore. The electrochemical polymerization of 6b as a representative was also investigated.     

Fused multifunctionalized bridge aromatic hydrocarbons from in situ-generated arynes and anthracene derivatives

This study presents a facile strategy for the formation of highly substituted butterfly 1,4-adducts/9,10-adducts via the Diels–Alder reaction of benzyne intermediates. The method achieves very good to excellent yields of the respective anthracene derivatives under mild conditions. This practical protocol is compatible with a variety of sensitive functional groups and provides access to difunctionalized bridge 1,4-adducts/9,10-adducts.     

Using 211At as internal alpha radiolysis source allowing for simple detection of radiolysis products

The determination of radiolysis products is an important field both for the basic understanding of the radiolysis process and for process development. The latter case mainly dealing with processes for handling radioactive wastes. There are several kinds of radiolysis processes that originate from the different kinds of radiation. Gamma rays and high-energy beta has a high ability to penetrate barriers while alpha irradiation in principle has to be performed with the radiation emitting nuclide inside the actual sample. This can be a problem since most laboratories able to identify radiolysis products cannot handle alpha contaminated samples. In this paper we suggest the use of ²¹¹At as internal alpha emitting radionuclide. Due to its short half-life and decay to more or less stable daughters the radiolysis products may be examined using normal equipment without causing contamination.     

Studies on the valveless scheme to produce high-frequency detonations with different purge methods

Producing high-frequency detonations is an important topic for pulse detonations which has received considerable attentions. The valveless scheme has been verified to be able to obtain high-frequency detonations more than 100 Hz. This work has been conducted to investigate the possibility to achieve a higher detonation frequency and clarify the limits of stable operations preliminarily for the valveless scheme with different purge methods. Oxygen, ethylene, and nitrogen or liquid water are utilized as oxidizer, fuel, and purge medium in the experiments while two injection configurations are employed. The maximum detonation frequencies of 180 Hz and 330 Hz have been achieved in stable operations for two different injection configurations when nitrogen is used as the purge gas. The ceiling frequency for stable detonations is 300 Hz if nitrogen is replaced by liquid water, which indicates that water vapor is capable to create an efficient buffer zone to ensure stable operations. The results imply that the injection configuration also has a great impact on the ceiling stable detonation frequency. Three operating modes have been observed in this study, i.e., a stable detonation mode, an unstable detonation mode, and a deflagration mode. In the unstable mode, failure of detonation initiation occurs frequently and one interesting phenomenon is that the detonation frequency is reduced by half exactly when insufficient filling happens. The supply pressure ratios of oxidizer to fuel and purge to fuel are obtained for different operating modes when the purge method is changed. Furthermore, the equivalence ratios have been also studied for different operating modes which reveals that the range will change when different purge methods and injection configurations are employed. According to the equivalence ratio and the mass flow rates, an equivalent volume fraction of oxygen is defined and its range for the stable detonation mode is clarified.     

Infrared remote sensing of planetary atmospheres

Infrared remote sensing is a powerful tool for studying the chemical composition and the thermal structure of planetary atmospheres. Infrared spectra, in particular, are used to derive molecular abundances and to infer elemental and isotopic ratios, which allow to constrain theoretical models of the formation and early evolution of the solar system, as well as the history of planetary atmospheres. Infrared imaging and spectroscopy have been performed from the ground but also from space planetary missions (Mariner 9 on Mars, Voyager on the giant planets, Galileo on Jupiter), and from the ISO Earth-orbiting infrared satellite. In the forthcoming decade, the Cassini mission will explore the Saturn system. Planetary exploration from Earth orbit will be performed by the FIRST and NGST space observatories.     

Highly efficient synthesis of (R)- and (S)-piperazic acids using proline-catalyzed asymmetric α-hydrazination

The highly efficient synthesis of (R)- and (S)-piperazic acids, components of naturally occurring antibiotic cyclodepsipeptides, was achieved in 80% overall yield by the use of a proline-catalyzed asymmetric α-hydrazination as the key step.     

Thermodynamic analysis of the cation binding to a phosphatidylcholine monolayer at a polarised interface between two immiscible electrolyte solutions

Thermodynamic analysis of the polarised interface between two immiscible electrolyte solutions (ITIES) was outlined, which accounts for the adsorption of phosphatidylcholine (PC) both as a zwitterion and a cation formed by the aqueous cation association with the zwitterionic PC form, as well as for the aqueous cation transfer facilitated by PC leading to its depletion from the interface. Electrocapillary equation was derived clarifying the physical significance of the surface charge density; the differential capacity and the PC surface excess concentration. The potential dependence of the interfacial tension calculated using the Damaskin’s adsorption model of a compound adsorbed in two different forms was found to agree well with that measured for the polarised water|1,2-dichloroethane interface in the presence of dl-α-dipalmitoylphosphatidylcholine. Experimentally observed effect of the nature of the aqueous cation on the interfacial tension was ascribed to the difference in the PC association constant.     

Block transitivity and degree matrices: (Extended abstract)

We say that a square matrix M is a degree matrix of a given graph G if there is a so called equitable partition of its vertices into r blocks such that whenever two vertices belong to the same block, they have the same number of neighbors inside any block.We ask now whether for a given degree matrix M, there exists a graph G such that M is a degree matrix of G, and in addition, for any two edges e, f spanning between the same pair of blocks there exists an automorphism of G that sends e to f. In this work, we fully characterize the matrices for which such a graph exists and show a way to construct one.     

Palladium-catalyzed meta-CH bond iodination of arenes with I2

Palladium-catalyzed highly meta-selective CH iodination of phenylacetic acid, benzylphosphonate and benzylsulfonate scaffolds with molecular I₂ is developed using a pyridine-type template. The practical ester linkages enable the directing template easily installed and readily removed. The substrate scope is broad, and alkyl, methoxyl, trifluomethyl, and halo substituents are compatible with this reaction. Further transformations of ibuprofen iodide intermediates by Pd-catalyzed CC and C–heteroatom bond formation illustrate the broad utility of this method.