维生素E类化合物抗氧化活性的理论分析

用半径验方法AM1,对12种维生素E类化合物及2种单酚与羟基自由基反应的活化能、氧氢键离解能D进行了计算。发现Ea、D越低,其抗氧化活性愈高;Ea、D与化合物分子中芳环上烷基取代基的数目、种类及位置有关;14个化合物的反应活化能均小于56kJ·mol-1;从反应物到过渡态氧原子上的净电荷减少。

表征O-H解离能参数的AM1计算

对 17种酚类化合物用半经验量子化学方法AM1计算了表征OH解离能的参数△HOF值 ,即酚类化合物与其经抽氢反应产生的自由基的生成热之差。经过与实验测定的 17种酚类化合物的OH解离能比较 ,评价了AM1方法在计算△HOF值方面的有效性。发现AM1计算的△HOF值与OH解离能有很好的相关性 (r =0 .94 95 ) ,优于经验方法 ,比如加和规则对OH解离能的预测。虽然AM1方法在计算间位取代基对OH解离能的贡献方面是无效的 ,但将它用于计算解离能类的参数以预测抗氧化剂活性还是可行的。

Decomposition of a β-O-4 lignin model compound over solid Cs-substituted polyoxometalates in anhydrous ethanol: acidity or redox property dependence?

Production o f aromatics from lignin has attracted much attention. Because of the coexistence of C-O and C-C bonds and their complex combinations in the lignin macromolecular network, a plausible roadmap for developing a lignin catalytic decomposition process could be developed by exploring the transformation mechanisms of various model compounds. Herein, decomposition of a lignin model compound, 2-phenoxyacetophenone （2-PAP）, was investigated over several ce-sium-exchanged polyoxometalate （Cs-POM） catalysts. Decomposition of 2-PAP can follow two dif-ferent mechanisms： an active hydrogen transfer mechanism or an oxonium cation mechanism. The mechanism for most reactions depends on the competition between the acidity and redox proper-ties of the catalysts. The catalysts of POMs perform the following functions： promoting active hy-drogen liberated from ethanol and causing formation of and then temporarily stabilizing oxonium cations from 2-PAP. The use of Cs-PMo, which with strong redox ability, enhances hydrogen libera-tion and promotes liberated hydrogen transfer to the reaction intermediates. As a consequence, complete conversion of 2-PAP （〉99%） with excellent selectivities to the desired products （98.6% for phenol and 91.1% for acetophenone） can be achieved.

Direct oxidation of the C_(sp3)-H bonds of N-heterocyclic compounds to give the corresponding ketones using a reusable heterogeneous MnO_x-N@C catalyst

Novel reusable MnOx‐N@C catalyst has been developed for the direct oxidation of N‐heterocycles under solvent‐free conditions using TBHP as benign oxidant to give the corresponding N‐heterocyclic ketones. The catalytic system exhibited a broad substrate scope and excellent regi‐oselectivity, as well as being amenable to gram‐scale synthesis. This MnOx‐N@C catalyst also showed good reusability and was successfully recycled six times without any significant loss of activity.

Oxidative desulfurization of diesel fuel with caprolactam-based acidic deep eutectic solvents: Tailoring the reactivity of DESs by adjusting the composition

Despite the significance of hydrogen bonding in deep eutectic solvents（DESs） for desulfurization processes, little is understood about the relationship between the DES composition, hydrogen-bonding strength, and oxidative desulfurization activity. In this study, a new family of caprolactam-based acidic DESs was prepared with different molar ratios of caprolactam and oxalic acid. The prepared DESs were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, 1 H nuclear magnetic resonance, and thermogravimetric analyses. These DESs were employed for oxidative desulfurization reactions and the desulfurization efficiency was found to vary regularly with the DES composition. The factors influencing the removal of dibenzothiophene were systematically investigated and the desulfurization efficiency of the caprolactam-based acidic DESs reached as high as 98% under optimal conditions. The removal of different sulfur compounds followed the order： dibenzothiophene 4,6-dimethyldibenzothiophene benzothiophene. The combined experimental data and characterization results revealed that the oxidative desulfurization efficiency of the system was influenced by the hydrogen bonding interactions with the DES, which can be optimized by adjusting the DES composition. These findings regarding hydrogen bonding in DESs provide new insight for better understanding of the mechanism of diesel deep desulfurization processes.

Site-specific deposition creates electron-rich Pd atoms for unprecedented C-H activation in aerobic alcohol oxidation

Here,we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles.The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that the surface electronic structure of Pd can be continuously regulated by tailoring the Pd-to-Au molar ratio and the location of Pd atoms in Au Pd nanoparticles.It is revealed that electron-rich Pd atoms are considerably more active than the net Pd atoms in aerobic alcohol oxidation.Remarkably,the catalyst with the most electron-rich Pd sites(binding energy downshift:1.0 e V)exhibits an extremely high turnover frequency(~500000 h-1 vs 12000 h-1 for that with net Pd atoms)for solvent-free selective oxidation of benzyl alcohol,which is,to the best of our knowledge,the highest value ever reported.Kinetic studies reveal that electron-rich Pd atoms can accelerate the oxidation of benzyl alcohol by facilitating C-H cleavage,as indicated by the significant reduction in the activation energy as compared to net Pd atoms.

Theoretical perspective on mononuclear copper‐oxygen mediated C–H and O–H activations:A comparison between biological and synthetic systems

Dioxygen activations constitute one of core issues in copper-dependent metalloenzymes. Upon O_(2) activation, copper-dependent metalloenzymes such as particulate methane monooxygenases(pM MOs), lytic polysaccharide monooxygenases(LPMOs) and binuclear copper enzymes PHM and DβM, are able to perform various challenging C–H bond activations. Meanwhile, various copper-oxygen core containing complexes have been synthetized to mimic the active species of metalloenzymes. Dioxygen activation by mononuclear copper active site may generate various copper-oxygen intermediates, including Cu(Ⅱ)-superoxo, Cu(Ⅱ)-hydroperoxo, Cu(Ⅱ)-oxyl as well as the Cu(Ⅲ)-hydroxide species. Intriguingly, all these species have been invoked as the potential active intermediates for C–H/O–H activations in either biological or synthetic systems. Due to the poor understanding on reactivities of copper-oxygen complex, the nature of active species in both biological and synthetic systems are highly controversial. In this account, we will compare the reactivities of various mononuclear copper-oxygen species between biological systems and the synthetic systems. The present study is expected to provide the consistent understanding on reactivities of various copper-oxygen active species in both biological and synthetic systems.

Effects of indium on Ni/SiO_2 catalytic performance in hydrodeoxygenation of anisole as model bio-oil compound: Suppression of benzene ring hydrogenation and C–C bond hydrogenolysis

SiO2‐supported monometallic Ni and bimetallic Ni‐In catalysts were prepared and used for hydrodeoxygenation of anisole,which was used as a model bio‐oil compound,for BTX(benzene,toluene,and xylene)production.The effects of the Ni/In ratio and Ni content on the structures and performances of the catalysts were investigated.The results show that In atoms were incorporated into the Ni metal lattice.Although the Ni‐In bimetallic crystallites were similar in size to those of monometallic Ni at the same Ni content,H2uptake by the bimetallic Ni‐In catalyst was much lower than that by monometallic Ni because of dilution of Ni atoms by In atoms.Charge transfer from In to Ni was observed for the bimetallic Ni‐In catalysts.All the results indicate intimate contact between Ni and In atoms,and the In atoms geometrically and electronically modified the Ni atoms.In the hydrodeoxygenation of anisole,although the activities of the Ni‐In bimetallic catalysts in the conversion of anisole were lower than that of the monometallic Ni catalyst,they gave higher selectivities for BTX and cyclohexane as a result of suppression of benzene ring hydrogenation and C–C bond hydrogenolysis.They also showed lower methanation activity.These results will be useful for enhancing carbon yields and reducing H2consumption.In addition,the lower the Ni/In ratio was,the greater was the effect of In on the catalytic performance.The selectivity for BTX was primarily determined by the Ni/In ratio and was little affected by the Ni content.We suggest that the performance of the Ni‐In bimetallic catalyst can be ascribed to the geometric and electronic effects of In.

Hydrogen auto-transfer under aerobic oxidative conditions: Efficient synthesis of saturated ketones by aerobic C-C cross-coupling of primary and secondary alcohols catalyzed by a Au_6Pd/resin catalyst

Au and Au-containing bimetallic nanoparticles are promising catalysts for the green synthesis of fine chemicals. Here, we used a Au6Pd/resin catalyst for the aerobic C-C cross-coupling of primary and secondary alcohols to produce higher ketones under mild conditions. This is of importance to the construction of a C-C bond. Various substrates were used in the reaction system, and moderate to good yields were obtained. The catalysts can be reused at least five times without decrease of yield. The control experiment and XAFS characterization results showed that hydrogen au- to-transfer occurred on metallic Pd sites even under oxidative conditions. On alloying with Au, the Pd sites became resistant to oxidation and readily abstracted the β-H of the alcohols and transferred the hydride to the C=C bond in the reaction intermediate to give the saturated product.

过氧化氢原位生成驱动过氧合酶催化反应研究进展

C—H键的选择性催化氧官能团化反应是有机化学中非常具有挑战的一类反应.与贵金属络合物催化剂相比,生物酶在选择性和活性等方面表现出一定优势.其中,过氧合酶(peroxygenase)作为近年来研究热点,能够直接利用过氧化氢(H_(2)O_(2))作为共底物催化C—H键的氧官能团化反应.过氧合酶结合了P450单加氧酶的催化多功能性且无须依赖辅酶及其再生体系,因此在有机合成中引起越来越多的重视.但是,过氧合酶在实际应用中存在一个瓶颈:即过氧合酶对其催化所必须的H_(2)O_(2)浓度敏感,当反应体系中H_(2)O_(2)浓度过高时,会引起过氧合酶中的亚铁血红素氧化分解,从而导致酶失活.为突破该瓶颈,调控反应体系中H_(2)O_(2)的浓度对于高效应用过氧合酶来说格外重要.概括了近年来多种原位生成H_(2)O_(2)驱动过氧合酶催化的方法.从酶催化、光催化、电催化原位生成H_(2)O_(2)角度出发,全面分析了近年来开发的高原子经济性H_(2)O_(2)原位生成技术驱动过氧合酶催化体系的优缺点,为促进该酶在有机合成中的应用提供参考.

Halogen Bonding or Hydrogen Bonding between 2,2,6,6-Tetramethyl- piperidine-noxyl Radical and Trihalomethanes CHX3 （X=CI, Br, I）

The halogen and hydrogen bonding complexes and trihalomethanes （CHX3, X=C1, Br, I） are between 2,2,6,6-tetramethylpiperidine-noxyl simulated by computational quantum chem- istry. The molecular electrostatic potentials, geometrical parameters and interaction energy of halogen and hydrogen bonding complexes combined with natural bond orbital analysis are obtained. The results indicate that both halogen and hydrogen bonding interactions obey the order CI〈Br〈I, and hydrogen bonding is stronger than the corresponding halogen bond- ing. So, hydrogen bonding complexes should be dominant in trihalomethanes. However, it is possible that halogen bonding complex is competitive, even preponderant, in triiodomethane due to the similar interaction energy. This work might provide useful information on specific solvent effects as well as for understanding the mechanism of nitroxide radicals as a bioprobe to interact with the halogenated compounds in biological and biochemical fields.

Crystal Structure of Binuclear Oxomolybdenum(V), [Fe(H_2O)_6][Mo_2O_4(EDTA)]·5H_2O

The reduction of an aqueous solution of sodium molybdate by iron powder at low pH value (～0.83), in the presence of ethylenediaminetetraacetate (EDTA) ligand, gives the title compound [Fe(H 2O) 6][Mo 2O 4(EDTA)]·5H 2O 1, which was characterized by elemental analysis, IR and X ray single crystal diffraction techniques. Compound 1 crystallizes in monoclinic system, space group P2 1/c, C 10 H 34 N 2FeMo 2O 23 , M r=798.12, a=8.781(1), b=14.081(1), c=21.353(1) , β= 92\^688(1)°, V = 2637.2(3) 3, Z = 4, D c = 2.010 g·cm -3 , μ = 1.579 mm -1 , F (000)=1608, the final R =0.0530 and wR =0.1271 for 3312 observed reflections. The binuclear oxomolybdenum(V) anion and the six coordinated Fe(II) cation are linked to infinite three dimensional network through several hydrogen bonds towards different directions between crystal waters, Fe(II) cation and Mo(V) anion.

A Three-dimensional Organic-inorganic Hybrid Material Supported by Decavanadate Clusters and Na-O Chains: Synthesis and Crystal Structure of [Na_6(H_2O)_(16)(dod)_4V_(10)O_(28)]

A new organic-inorganic hybrid material [Na6(H2O)16(dod)2V10O28] (dod = 1,4- diazoniabicyclo[2,2,2]octane-1,4-diacetate) has been synthesized and X-ray single-crystal structural analysis reveals it crystallizes in triclinic, space group P with a = 11.533(7), b = 12.031(7), c = 12.187(4) ? a = 72.47(1), b = 73.16(1), g = 68.21(1)o, C20H64N4Na6O52V10, V = 1467(1) ?, Z = 1, Mr = 1840.1, Dc = 2.083 g/cm3, MoKa, l = 0.71073 ? m = 1.686, F(000) = 924, S = 1.027, the final R = 0.0538 and wR = 0.1272 for 4398 observed reflections. The compound has a three-dimensional frame- work constructed from decavanadate clusters, NaO chains and dod ligands. A variety of OH…O and CH…O hydrogen bonds play an important role in stabilizing the framework.

Hydrothermal Synthesis and Crystal Structure of [H_4As_8V_(14)O_(42)(H_2O)]·6H_2O

The title compound [H4As8V14O42(H2O)]6H2O 1 has been synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction analysis. It crystallizes in trigonal, space group R3c with a = b = 36.447(6), c = 21.485(5) ? V = 24717(8) 3, Z = 18, Mr = 2114.66, Dc = 2.557g/cm3, F(000) = 17928, m = 7.149 mm-1, R = 0.0792 and wR = 0.1265. The [H4As8V14O42- (H2O)] cluster consists of fourteen VO5 square pyramids linked by four As2O5 handle-like units.

Activity and selectivity of propane oxidative dehydrogenation over VO_3/CeO_2(111) catalysts: A density functional theory study

The oxidative dehydrogenation（ODH） of propane on monomeric VO3 supported by CeO2（111）（VO3/CeO 2（111）） is studied by periodic density functional theory calculations. Detailed energetic, structural, and electronic properties of these reactions are determined. The calculated activation energies of the breaking of the first and second C–H bonds of propane on the VO3/CeO2（111） catalyst are compared, and it is found that both the unique structural and electronic effects of the VO3/CeO2（111） catalyst contribute to the relatively easy rupture of the first C–H bond of the propane molecule during the ODH reaction. In particular, the so-called new empty localized states that are mainly constituted of O2 porbitals of the ceria-supported VO3 species are determined to be crucial for assisting the cleavage of the first C–H bond of the propane molecule. Following this they become occupied and the remaining C–H bonds become increasingly difficult to break owing to the increasing repulsion between the localized 4 felectrons at the Cecations, resulting in the adsorption of more H and other moieties. This work illustrates that CeO2-supported monomeric vanadium oxides can exhibit unique activity and selectivity for the catalytic ODH of alkanes to alkenes.

Synthesis and Crystal Structure of a New Chain Coordination Polymer [Cu(inio)_2(H_2O)]_∞(Inio = Isonicotinic Acid N-Oxide)

A new Cu(Ⅱ) coordination polymer [Cu(inio)2(H2O)] (inio = isonicotinic acid N-oxide) with chemical formula C12H10CuN2O7 was prepared and its crystal structure has been determined by X-ray analysis. The complex crystallizes in the monoclinic system, space group C2/c with a = 12.455(3), b = 6.202(1), c = 16.555(3) ? b = 106.776(3), V = 1224.3(4) 3, Z = 4, Mr = 357.76, Dc =1.941 g/cm3, m(MoKa) = 1.827 mm-1, F(000) = 724, R = 0.0601 and wR = 0.1417 for 908 observed reflections (I > 2s(I)). The Cu(Ⅱ) atom is coordinated by an elongated square pyramid geometry. The deprotonated isonicotinic acid N-oxides form a double-bridge between each pair of Cu(Ⅱ) ions in trans form through two oxygen atoms from the carboxyl groups and two other oxygen atoms from the -NO groups, respectively, which leads to an infinite one dimensional chain. The two adjacent elongated Cu(Ⅱ) square pyramidal geometries are arranged in trans form in the same chain. The OH…O hydrogen bonds extend the chain structure into two-dimensional layers.

酯加氢制乙二醇/乙醇高效铜基催化剂的构筑

酯加氢反应是由合成气制高附加值大宗含氧化学品的关键步骤之一,也是天然油脂、生物质衍生物等转化利用的关键环节.铜基催化剂因其良好的C=O/C–O键选择性加氢性能被广泛应用于酯加氢反应中,受到了越来越多的关注.本文重点综述了近几年铜基催化剂在酯加氢催化作用机制与构效关系解析方面的最新进展,探讨了催化剂构筑策略及其反应-吸附-扩散耦合作用规律,介绍了催化剂的工业实践及发展方向.

The adsorption and dissociation of multilayer CH_3OH on TiO_2(110)

The adsorption and dissociation of CH3OH on TiO2 （110） were studied using density functional theory methods. Our results suggest that CH3OH molecules can adsorb up to 3/4 ML （1 ML=5.2× 10^14 molecules/cm2） coverage at five-coordinated titanium （Tisc） sites to form the first layer. In the second layer, the CH3OH is adsorbed at bridge-bonded oxygen, and from the third layer, the CH3OH molecules form a hydrogen-bonded network with each other. The theoretical results show that dissociation of multilayer adsorbed methanol to aldehyde occurs through a stepwise pathway, with easy O-H bond dissociation and rate-determining C-H bond dissociation. The dissociation barriers for 8 or 12 CH3OH molecules on TiO2 are higher than that for low coverage by 0.15-0.21 eV; this suggests that the dissociation of multilayer adsorbed CH3OH is harder.

Heterogeneous self-healing assembly of MXene and graphene oxide enables producing free-standing and self-reparable soft electronics and robots

Self-healing materials(SHMs)with unique mechanical and electronic properties are promising for self-reparable electronics and robots.However,the self-healing ability of emerging two-dimensional(2D)materials,for instance,MXenes,has not been systematically investigated,which limits their applications in self-healing electronics.Herein,we report the homogeneous self-healing assembly(homoSHA)of MXene and the heterogeneous self-healing assembly(hetero-SHA)of MXene and graphene oxide(GO)under moisture treatments.The self-healing mechanism has been attributed to the hydration induced interlayer swelling of MXene and GO and the recombination of hydrogen bond networks after water desorption.The multiform hetero-SHA of MXene and GO not only enables facile fabrication of free-standing soft electronics and robots,but also endows the resultant devices with damage-healing properties.As proof-of-concept demonstrations,free-standing soft electronic devices including a generator,a humidity sensor,a pressure sensor,and several robotic devices have been fabricated.The hetero-SHA of MXene and GO is simple yet effective,and it may pioneer a new avenue to develop miniature soft electronics and robots based on 2D materials.