A highly efficient non-heme manganese complex in oxygenation reactions

A non-heme manganese(II) complex shows a high catalytic activity in the epoxidation of olefins by iodosyl benzene and in the oxidation of olefins, alcohols and alkanes by peracetic acid; a mechanism involving metal-based oxidants is proposed for the oxidation reactions.     

One step purification of flavanone glycosides from Poncirus trifoliata by centrifugal partition chromatography

Flavanone glycosides were successfully separated from the crude extract of Poncirus trifoliata by preparative centrifugal partition chromatography with a two-phase solvent system composed of ethyl acetate-acetonitrile-water (3:2:5, v/v/v). Naringin (50.0 mg), neoponcirin (16.8 mg), and poncirin (71.9 mg) were purified from the 524 mg crude extract in only one step. The purities of the isolated compounds were determined to be over 90% by HPLC analysis and their structures were elucidated by (1)H NMR, (13)C NMR, and ESI-MS.     

Separating classes of composition operators via subnormal condition

Several classes have been considered to study the weak subnormalities of Hilbert space operators. One of them is -hypnormality, which comes from the Bram-Halmos criterion for subnormal operators. In this note we consider -hyponormality, which is the parallel version corresponding to the Embry characterization for subnormal operators. We characterize -hyponormality of composition operators via -th Radon-Nikodym derivatives and present some examples to distinguish the classes.

     

Strict Feasibility of Variational Inequalities in Reflexive Banach Spaces

Strict feasibility is proved to be an equivalent characterization of （dual） variational inequalities having a nonempty bounded solution set, provided the mappings involved are stably properly quasimonotone. This generalizes an earlier result from finite-dimensional Euclidean spaces to infinitedimensional reflexive Banach spaces. Moreover, the monotonicity-type assumptions are also mildly relaxed.     

Measurement of carbonyls in exhaust gases of light-duty vehicles in China using pentafluorophenyl hydrazine derivatisation and GC/MS analysis

A method for determining carbonyl emissions from motor vehicles was developed in which exhaust gases from test vehicles running on a dynamometer are directly collected in 6-L Teflon bags and then introduced into pentafluorophenyl hydrazine -coated adsorbent tubes for derivatisation and subsequent analysis of generated derivatives by GC/MS. Twenty gasoline and LPG light-duty vehicles were sampled at a vehicle inspection station in Guangzhou, China, by running test vehicles over a transient testing cycle and analysed for carbonyls. Results show that the method can achieve a detection limit of 8–28 ng m^?3 for individual carbonyls with a relative standard deviation of 14.5%. Twenty-four carbonyls were identified in the gasoline vehicle exhaust gases and their total concentration was 19.2 mg m^?3. For the LPG vehicles, 20 carbonyls were found in the exhaust gases with a total concentration of 4.71 mg m^?3. Based on the results, carbonyl emission factors for the gasoline and LPG vehicles were estimated to be 25.0 and 7.36 mg km^?1, respectively.     

Mechanistic Understanding of the Divergent Cyclizations of o‐Alkynylbenzaldehyde Acetals and Thioacetals Catalyzed by Metal Halides

The mechanisms of regiodivergent cyclizations of o‐alkynylbenzaldehyde acetals and thioacetals catalyzed by Pd and Pt halides are studied. DFT calculations found that both reactions are initiated by electrophilic activation of the acetylenic moiety instead of the previously proposed metal‐triggered C?X (X=O, S) cleavage. Both the regioselective cyclization of the π‐alkyne complex and the chemoselective [1,2]‐migration in the carbenoid intermediate were determined as key steps to achieving the observed divergence. For acetal derivatives containing an internal alkyne, the 6‐endo‐dig cyclization is more favorable and leads to the carbenoid intermediate easily through further steps of C?X fragmentation and carbocation cyclization. Then, from the carbenoid intermediate, the [1,2]‐migration of sulfur is easier than that of H, Me, and Ph; whereas, a reversed aptitude was predicted for the oxygen analogue, which is consistent with the greater ability of sulfur atoms to stabilize β‐carbocations. However, for precursors containing a terminal alkyne, the 5‐exo‐dig pathway is preferred and only the 1,2‐disubstituted indene product is seen, irrespective of the nature of the acetal; thus, a different product from that reported in the literature is predicted for benzaldehyde acetal with a terminal alkyne at the ortho position. This prediction led us to reconsider some of the reported results and hidden realities were uncovered with solid new experimental evidence.     

Enantioselective Total Synthesis of (−)‐Hosieine A

The first total synthesis of (?)‐hosieine A was accomplished and features an unprecedented nitroso–ene cyclization to construct the 2‐azabicyclo[3.2.1]octane ring system. Phosphine‐enabled stereoselective bromohydrination provided interesting mechanistic insights into the anti‐Markovnikov process. Also noteworthy is the retention of stereochemistry at C9 in the facile radical debromination initiated by Et₃B/air.     

锚定基团对HKUST-1/TEMPO共催化体系催化性能的影响

用异烟酸(Iso-NTA)为桥接分子, 将有机小分子自由基4-氨基-2,2,6,6-四甲基哌啶-1-氧自由基(4-NH₂-TEMPO)与异烟酸缩合, 合成出含吡啶官能团的TEMPO自由基(Iso-NTA-TEMPO). 与TEMPO相比, Iso-NTA-TEMPO具有较高的氧化电位, 在无Cu(Ⅱ)辅助时, Iso-NTA-TEMPO对苯甲醇的氧化效率高于TEMPO. 在与HKUST-1组成的复合催化体系中, Iso-NTA-TEMPO可通过吡啶基团与HKUST-1孔道中的Cu(Ⅱ)相互作用, 从而在催化过程中(部分)锚定在HKUST-1孔道内部. 与TEMPO/HKUST-1体系相比, Iso-NTA-TEMPO/HKUST-1体系表现出对芳香醇更加高效的催化活性. 采用模板辅助溶剂诱导结晶法合成的HKUST-1晶体表面具有较多缺陷, 更有利于Iso-NTA-TEMPO自由基分子扩散进入HKUST-1孔道内部, 也有助于提高Iso-NTA-TEMPO/HKUST-1体系的催化效率. Iso-NTA-TEMPO/HKUST-1体系可将各种取代基(苄醇、 杂环醇以及二级脂肪醇)高效、 高选择性地氧化成相应的醛或酮.