Synthesis and characterization of NaY zeolite-encapsulated Mn-hydrazone Schiff base: an efficient and reusable catalyst for oxidation of olefins

The Mn-hydrazone Schiff base has been prepared, characterized, and encapsulated into NaY to prepare a new heterogeneous catalyst. Elemental analysis, UV-Vis, infrared spectroscopic analysis, diffuse reflectance spectroscopy, thermal analysis, small angle X-ray diffraction, and N₂ sorption indicate the presence of Mn-hydrazone Schiff base within the nanocavity pores of zeolite-Y. The catalysts showed excellent catalytic efficiency in epoxidation with various olefinic compounds including cyclooctene, using tert-BuOOH as oxidant. Cyclooctene showed high conversion (97%) as well as epoxide selectivity (89%) with tert-BuOOH. Moreover, the encapsulated complex showed good recoverability without significant loss of activity and selectivity within successive runs.     

The Role of One‐Electron Reduction of Lipid Hydroperoxides in Causing DNA Damage

The in vivo metabolism of plasma lipids generates lipid hydroperoxides that, upon one‐electron reduction, give rise to a wide spectrum of genotoxic unsaturated aldehydes and epoxides. These metabolites react with cellular DNA to form a variety of pre‐mutagenic DNA lesions. The mechanisms of action of the radical precursors of these genotoxic electrophiles are poorly understood. In this work we investigated the nature of DNA products formed by a one‐electron reduction of (13S)‐hydroperoxy‐(9Z,11E)‐octadecadienoic acid (13S‐HPODE), a typical lipid molecule, and the reactions of the free radicals thus generated with neutral guanine radicals, G(?H)^.. A novel approach was devised to generate these intermediates in solution. The two‐photon‐induced ionization of 2‐aminopurine (2AP) within the 2′‐deoxyoligonucleotide 5′‐d(CC[2AP]TCGCTACC) by intense nanosecond 308 nm excimer laser pulses was employed to simultaneously generate hydrated electrons and radical cations 2AP^.+. The latter radicals either in cationic or neutral forms, rapidly oxidize the nearby G base to form G(?H)^.. In deoxygenated buffer solutions (pH 7.5), the hydrated electrons rapidly reduce 13S‐HPODE and the highly unstable alkoxyl radicals formed undergo a prompt β‐scission to pentyl radicals that readily combine with G(?H)^.. Two novel guanine products in these oligonucleotides, 8‐pentyl‐ and N²‐pentylguanine, were identified. It is shown that the DNA secondary structure significantly affects the ratio of 8‐pentyl‐ and N²‐pentylguanine lesions that changes from 0.9:1 in single‐stranded, to 1:0.2 in double‐stranded oligonucleotides. The alkylation of guanine by alkyl radicals derived from lipid hydroperoxides might contribute to the genotoxic modification of cellular DNA under hypoxic conditions. Thus, further research is warranted on the detection of pentylguanine lesions and other alkylguanines in vivo.     

Urea-induced Inactivation and Unfolding of Recombinant Phospholipid Hydroperoxide Glutathione Peroxidase from Oryza sativa

Phospholipid hydroperoxide glutathione peroxidase is an antioxidant enzyme that has the highest capability of reducing membrane-bound hydroperoxy lipids as compared to free organic and inorganic hydroperoxides amongst the glutathione peroxidases.In this study,urea-induced effects on the inactivation and unfolding of a recombinant phospholipid hydroperoxide glutathione peroxidase(PHGPx)from Oryza sativa were investigated by means of circular dichroism and fluorescence spectroscopy.With the increase of urea concentration,the residual activity of OsPHGPx decreases correspondingly.When the urea concentration is above 5.0 mol/L,there was no residual activity.In addition,the observed changes in intrinsic tryptophan fluorescence,the binding of the hydrophobic fluorescence probe ANS,and the far UV CD describe a common dependence on the concentration of urea suggesting that the conformational features of the native OsPHGPx are lost in a highly cooperative single transition.The unfolding process comprises of three zones:the native base-line zone between 0 and 2.5 mol/L urea,the transition zone between 2.5 and 5.5 mol/L urea,and the denatured base-line zone above 5.5 mol/L urea.The transition zone has a midpoint at about 4.0 mol/L urea.     

Novel Copper(II) Complexes with Dipinodiazafluorene Ligands: Synthesis,Structure, Magnetic and Catalytic Properties

The reactions of CuX₂ (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX₂L₁]₂ (X = Cl (1), Br (2), L₁ = (1R,3R,8R,10R)-2,2,9,9-Tetramethyl-3,4,7,8,9,10-hexahydro-1H-1,3:8,10-dimethanocyclopenta [1,2-b:5,4-b’]diquinolin-12(2H)-one) and [(CuX₂)₂L₂]n (X = Cl (3), Br (4), L₂ = (1R,3R,8R,10R,1’R,3’R,8’R,10’R)-2,2,2’,2’,9,9,9’,9’-Octamethyl-1,1’,2,2’,3,3’,4,4’,7,7’,8,8’,9,9’,10,10’-hexadecahydro-1,3:1’,3’:8,10:8’,10’-tetramethano-12,12’-bi(cyclopenta [1,2-b:5,4-b’]diquinolinylidene). The complexes were characterized by IR and EPR spectroscopy, HR-ESI-MS and elemental analysis. The crystal structures of compounds 1, 2 and 4 were determined by X-ray diffraction (XRD) analysis. Complexes 1–2 have a monomeric structure, while complex 4 has a polymeric structure due to additional coordinating N,N sites in L₂. All complexes contain a binuclear fragment {Cu₂(μ-X)_2×2} (X = Cl, Br) in their structures. Each copper atom has a distorted square-pyramidal coordination environment formed by two nitrogen atoms and three halogen atoms. The Cu-N_ax distance is elongated compared to Cu-N_eq. The EPR spectra of compounds 1–4 in CH₃CN confirm their paramagnetic nature due to the d⁹ electronic configuration of the copper(II) ion. The magnetic properties of all compounds were studied by the method of static magnetic susceptibility. For complexes 1 and 2, the effective magnetic moments are µ_eff ≈ 1.87 and 1.83 µ_B (per each Cu²⁺ ion), respectively, in the temperature range 50–300 K, which are close to the theoretical spin value (1.73 µ_B). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu₂(μ-X)₂X₂} (X = Cl, Br) dimers (J/k_B ≈ 25 and 31 K for 1 and 2, respectively) or between dimers (θ′ ≈ 0.30 and 0.47 K for 1 and 2, respectively) were found at low temperatures. For compounds 3 and 4, the magnetic susceptibility is well described by the Curie–Weiss law in the temperature range 1.77–300 K with µ_eff ≈ 1.72 and 1.70 µ_B for 3 and 4, respectively, and weak antiferromagnetic interactions (θ ≈ −0.4 K for 3 and −0.65 K for 4). Complexes 1–4 exhibit high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The maximum yield of cyclohexane oxidation products reached 50% (complex 3). Based on the data on the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play a decisive role in the oxidation reaction. The initial products in reactions with alkanes are alkyl hydroperoxides.     

氯原子引发的甲基过氧化氢大气光化学反应

有机过氧化物在大气化学过程中起着重要作用 ,并对城市大气质量有着重要影响 ,然而 ,目前对它们大气化学行为的了解还非常不够 ,尤其缺少定量的研究。文章利用长光路傅里叶变换红外光谱 (长光路FTIR)仪原位跟踪反应进程 ,进行实验室模拟研究大气中非常重要的一种有机过氧化物 ,即甲基过氧化氢(CH3OOH ,MHP)的大气光化学反应。反应在内配有红外光多次反射镜 (White镜 )的 2 8 5L静态石英反应池中进行 ,采用氯原子 (Cl)引发反应 ,温度为 (2 92± 2 )K ,压力为 9 3× 10 4 Pa(2 0 %O2 80 %N2 )。FTIR光谱表明反应产物中主要包括甲醛 (HCHO)、甲酸 (HCOOH)、一氧化碳 (CO)和二氧化碳 (CO2 ) ,此外还有少量的甲醇 (CH3OH)生成。测定了前三种主要产物在反应 6 0min内的产率 :HCOOH和CO产率分别为 2 4 %和 6 % ;而HCHO浓度先增后减 ,浓度达到峰值时产率为 5 0 %。根据实验结果探讨了可能的反应机理 ,指出MHP是大气中HOx 自由基的储库分子 ,对整个大气光化学反应的进程有重要作用     

Synthesis and characterization of poly(methyl methacrylate)/casein nanoparticles with a well‐defined core‐shell structure

Well‐defined, core‐shell poly(methyl methacrylate) (PMMA)/casein nanoparticles, ranging from 80 to 130 nm in diameter, were prepared via a direct graft copolymerization of methyl methacrylate (MMA) from casein. The polymerization was induced by a small amount of alkyl hydroperoxide (ROOH) in water at 80 °C. Free radicals on the amino groups of casein and alkoxy radicals were generated concurrently, which initiated the graft copolymerization and homopolymerization of MMA, respectively. The presence of casein micelles promoted the emulsion polymerization of the monomer and provided particle stability. The conversion and grafting efficiency of the monomer strongly depended on the type of radical initiator, ROOH concentration, casein to MMA ratio, and reaction temperature. The graft copolymers and homopolymer of PMMA were isolated and characterized with Fourier transform infrared spectroscopy and differential scanning calorimetry. The molecular weight determination of both the grafted and homopolymer of PMMA suggested that the graft copolymerization and homopolymerization of MMA proceeded at a similar rate. The transmission electron microscopic image of the nanoparticles clearly showed a well‐defined core‐shell morphology, where PMMA cores were coated with casein shells. The casein shells were further confirmed with a zeta‐potential measurement. Finally, this synthetic method allowed us to prepare PMMA/casein nanoparticles with a solid content of up to 31%. Thus, our new process is commercially viable. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3346–3353, 2003     

纳米氧化铜用于温和条件下的异丙苯氧化研究

采用水热合成方法制备了具有片状结构的纳米CuO催化剂.该催化剂在温和的条件下对以分子氧为氧化剂的异丙苯氧化反应表现出高效的催化活性.在85℃、常压、催化剂用量为0.02g/mL异丙苯的条件下,反应9h,异丙苯的转化率、选择性和收率分别为55.1%、94.1%和51.8%.研究发现,该纳米CuO催化剂可以循环使用.同时对该纳米CuO催化剂催化其它含有α-H的芳烃化合物甲苯和乙苯的氧化反应进行了研究.实验结果表明,该催化剂的活性顺序为异丙苯>乙苯>>甲苯.     

在溶胶-凝胶法制备的MoO3/SiO2催化丙烯的环氧化反应

 以sol－gel法制备了MoO3／SiO2催化剂，并用BET比表面积测定，XRD和FT－IR等手段对催化剂进行了表征；研究了以过氧化氢异丙苯为氧化剂的丙烯一步环氧化反应，考察了催化剂的制备条件和反应条件对丙烯环氧化反应的影响．结果表明，在制备过程中，酸性水解剂对MoO3／SiO2催化剂的分散度、比表面积和催化性能有较大的影响．用HCl溶液作为水解剂制备的催化剂，其性能明显优于用HNO3或HAc作水解剂制备的催化剂．在110℃和0．6MPa的条件下反应2h，过氧化氢异丙苯转化率为89％，环氧丙烷选择性为80％．     

片状纳米CuO用于苯乙烯氧化反应的研究

苯甲醛又称安息香醛,是医药、染料、香料工业的一种重要的中间体,主要用于制造品绿、月桂醛、月桂酸等;也有时用作有机溶剂,测定臭氧及位于羰基旁边的亚甲基及检定酚和生物碱的试剂.传统的工业生产方法是以石油化工中的甲苯为原料,经氯化生成二氯化苄,再经酸性或碱性水解、真空     

Solvent-free oxidation of alcohols by t-butyl hydroperoxide catalyzed by water-soluble copper complex

The catalytic system composed of CuCl₂ and 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC), was found to be highly efficient for the selective oxidation of secondary benzylic, allylic and propargylic alcohols to the corresponding ketones, with aqueous t-butyl hydroperoxide under phase-transfer catalysis conditions. The catalytic system is stable and can be recycled and reused several times without loss of activity.