A CIDEP study of photolysis of duroquinone/hydrogen-donor homogeneous and triton micelle solutions

The CIDEP spectra of transient radicals during photolysis of the duroquinone (DQ)/ethylene glycol (EG) system in acid, basic, and micellar environments were measured with a home-made highly time-resolved ESR spectrometer. In the DQ/EG homogeneous solution, the enhanced emissive CIDEP signal of the neutral durosemiquinone radical DQH^• was observed. When the DQ/EG solution at pH 9 or the DQ/EG/TX-100/H₂O micelle system was photolyzed, the CIDEP signal of the duroquinone anion radical (DQ^•−) was obtained. When the DQ/EG solution at pH 2.5 was irradiated, the CIDEP signal of DQH^• appeared. These experimental results indicate that the neutral radical DQH^• was formed by proton transfer from EG to ³DQ*, and that DQ^•− was formed by dissociation of DQH^• accompanying polarization transfer.     

新型手性N,P配体的合成及其在烯丙基化中的应用

以手性5,6,7,8-四氢-8-喹啉醇为原料合成了新型手性N,P配体, 并将该配体应用于钯催化的1,3-二苯基-2-烯丙基乙酸酯的不对称烯丙基化反应, 得到100%的取代产物, 对映体过量达到73% ee.     

手性二茂铁基膦氧配体-铜络合物催化的二乙基锌对β-芳基硝基烯的不对称共轭加成反应

研究了手性二茂铁基膦氧配体.铜络合物催化的二乙基锌对β-芳基硝基烯的不对称加成反应,在优化的反应条件(8(mol)%配体和6(mol)%的Cu(OTf)2,以甲苯为溶剂,在-30℃下反应12h)下,取得了最高77%的产率和58%的ee值.     

Flavonol glycosides from Epimedium pubescens

Five new flavonol glycosides (1, 3, 5-7) were isolated from the aerial parts of Epimedium pubescens Maxim., along with two known compounds, sagittasine C (2) and 4',5-dihydroxyl-8-(3,3-dimethylallyl)-flavonol 3-O-[β-D-xylopyranosyl(1→3)-4-O-acetyl-α-L-rhamnopyranoside]-7-O-β-D-glucopyranoside (4). The structures were elucidated on the basis of their 1D-, 2D-NMR, MS, UV and IR spectra data.     

Quenching dynamics study on photoinduced excited triplet duroquinone by TEMPO in 1,2-propandiol

Chemically induced dynamic electron polarization (CIDEP) spectrum and transient absorptive spectrum are recorded in photolysis of duroquinone (DQ) in 1,2-propanodiol (PG). Durosemiquinone neutral radical DQH^• and PG ketyl radical \textCH₃[(\textC)\dot]\textOHCH₂\textOH{\text{CH}}_{3}{{{\dot{\text{C}}}\text{OHCH}}}_{2}{\text{OH}} are produced through hydrogen transfer reaction from PG to ³DQ*. When stable radical TEMPO is added to DQ/PG solution, photolysis results in CIDEP on TEMPO, which can be interpreted as a quartet precursor radical-triplet pair mechanism (QP-RTPM). There is competition between PG and TEMPO to quench ³DQ*. The CIDEP intensity of DQH^• decreases with the increase of TEMPO concentration. The quenching dynamics in photolysis of DQ/TEMPO/PG system is analyzed in detail. Based on the dynamics analysis and the measurement of the lifetime of ³DQ* by its transient absorbance decay, the quenching rate constant of ³DQ* by TEMPO in PG is obtained as 1.34 × 10⁷ L mol⁻¹ s⁻¹. This quenching rate constant is closely diffusion-controlled.     

Synthesis of Racemic Δ3‐2‐Hydroxybakuchiol and Its Analogues

The first synthetic approach to (±)‐Δ³‐2‐hydroxybakuchiol (=4‐[(1E,5E)‐3‐ethenyl‐7‐hydroxy‐3,7‐dimethylocta‐1,5‐dien‐1‐yl]phenol; 14 ) and its analogues 13a – 13f was developed by 12 steps (Schemes 2 and 3). The key features of the approach are the construction of the quaternary C‐center bearing the ethenyl group by a Johnson–Claisen rearrangement (→ 6 ); and of an (E)‐alkenyl iodide via a Takai–Utimoto reaction (→ 11 ); and an arylation via a Negishi cross‐coupling reaction (→ 12e – 12f ).     

Free-standing nanofibrous platinum sheets and their conductivity

Nanofibrous platinum sheets with a thickness of one to a few tens of nanometres were prepared over the submicron pores of polymer substrates by using long and rigid cadmium hydroxide nanostrands as templates, and these free-standing sheets gave metallic conductivity that varied greatly with the thickness.     

First stereospecific synthesis of (E)- or (Z)-alpha-fluoroenones via a kinetically controlled Negishi coupling reaction

A highly stereospecific synthesis of (E)- or (Z)-alpha-fluoro-alpha,beta-unsaturated ketones 4, via a kinetically controlled Negishi palladium-catalyzed coupling reaction, was developed, providing an easy and general access to valuable fluorinated intermediates (pharmaceutical, peptide mimic, and so on). The synthesis involved a reaction between E/Z gem-bromofluoroolefins 2 and alkoxyvinylzinc species 6 under controlled reaction temperature. At 10 degrees C, (Z)-4 (70 to 99% yields) was obtained along with unreacted (Z)-2 (66 to 99% yields). At THF reflux, the recovered olefin was transformed into (E)-4 (up to 98% yield).     

The analysis of expected fitness and success ratio of two heuristic optimizations on two bimodal MaxSAT problems

Heuristic algorithms, especially hill-climbing algorithms, are prone to being trapped by local optimization. Many researchers have focused on analyzing convergence and runtime of some heuristic algorithms on SAT-solving problems. However, there is rare work on analyzing success ratio (the ratio of the number of runs that find the global maxima of optimization versus the total runs) and expected fitness at each generation. Expected fitness at each generation could lead us to better understand the expected fitness of a heuristic algorithm could find on the problem to be solve at a certain generation. Success ratio help us understand with what a probability a heuristic algorithm could find the global optimization of the problem to be solved. So, this paper analyzed expected fitness and success ratio of two hill-climbing algorithms on two bimodal MaxSAT problems by using Markov chain. The theoretical and experimental results showed that though hill-climbing algorithms (both hill-climbing RandomWalk and Local (1+1)EA) converged faster, they could not always find global maxima of bimodal SAT-solving problems. The success ratios of hill-climbing algorithms usually have their own limits. The limit of success ratio is dependent on the SAT-solving problem itself and the expected distribution of initial bit string, and independent on whether hill-climbing RandomWalk or Local (1+1)EA is used.     

Subset selection for vector autoregressive processes via adaptive Lasso

Subset selection is a critical component of vector autoregressive (VAR) modeling. This paper proposes simple and hybrid subset selection procedures for VAR models via the adaptive Lasso. By a proper choice of tuning parameters, one can identify the correct subset and obtain the asymptotic normality of the nonzero parameters with probability tending to one. Simulation results show that for small samples, a particular hybrid procedure has the best performance in terms of prediction mean squared errors, estimation errors and subset selection accuracy under various settings. The proposed method is also applied to modeling the IS-LM data for illustration.