Copper(I) Nitro Complex with an Anionic [HB(3,5-Me(2)Pz)(3)](-) Ligand: A Synthetic Model for the Copper Nitrite Reductase Active Site

The new copper(I) nitro complex [(Ph(3)P)(2)N][Cu(HB(3,5-Me(2)Pz)(3))(NO(2))] (2), containing the anionic hydrotris(3,5-dimethylpyrazolyl)borate ligand, was synthesized, and its structural features were probed using X-ray crystallography. Complex 2 was found to cocrystallize with a water molecule, and X-ray crystallographic analysis showed that the resulting molecule had the structure [(Ph(3)P)(2)N][Cu(HB(3,5-Me(2)Pz)(3))(NO(2))]·H(2)O (3), containing a water hydrogen bonded to an oxygen of the nitrite moiety. This complex represents the first example in the solid state of an analogue of the nitrous acid intermediate (CuNO(2)H). A comparison of the nitrite reduction reactivity of the electron-rich ligand containing the CuNO(2) complex 2 with that of the known neutral ligand containing the CuNO(2) complex [Cu(HC(3,5-Me(2)Pz)(3))(NO(2))] (1) shows that reactivity is significantly influenced by the electron density around the copper and nitrite centers. The detailed mechanisms of nitrite reduction reactions of 1 and 2 with acetic acid were explored by using density functional theory calculations. Overall, the results of this effort show that synthetic models, based on neutral HC(3,5-Me(2)Pz)(3) and anionic [HB(3,5-Me(2)Pz)(3)](-) ligands, mimic the electronic influence of (His)(3) ligands in the environment of the type II copper center of copper nitrite reductases (Cu-NIRs).     

Preparation, characterization of Mo, Ag-loaded BiVO4 and comparison of their degradation of methylene blue

Two types of metal-loaded visible-light-driven photocatalysts,Mo-BiVO4and Ag-BiVO4,were synthesized by wet impregnation method.Material poperties were characterized by UV-vis diffuse reflectance spectroscopy,X-ray diffraction,field emission scanning electron microscopy,X-ray photoelectron spectroscopy and low temperature nitrogen adsorption-desorption.Photocatalytic activity of the obtained materials was investigated through degrading methylene blue(MB) solution under visible-light irradiation.The results reveal that both metal loaded-BiVO4catalysts have monoclinic scheelite structure.Mo and Ag exist as oxides on the surface of the particles.The changes of absorption in visible-light region,band gap(E g) and specific surface area(A BET) caused by loading Ag are more obvious than those caused by loading Mo.But the isoelectric point of Ag-BiVO4decreases less than that of Mo-BiVO4does.Both catalysts show higher photocatalytic activity than pure BiVO4,resulting in the significantly improved efficiency of degradation of MB.And the degradation efficiency of these two metal-loaded BiVO4photocatalysts is similar to each other.However,mechanisms of such enhancement are different.The decrease of isoelectric point helps Mo-BiVO4improve the degradation efficiency.As for Ag-BiVO4,the augmentation of absorption in visible-light region as well as the abatement of E g plays more important roles.     

Graphene–Au composite sensor for electrochemical detection of para-nitrophenol

A novel electrochemical sensor for para-nitrophenol (p-NP) was constructed with graphene–Au composite containing 10 % Au (G–Au 10 %). In the composite, Au nanoparticles with the size of ca. 11 nm were regularly scattered on graphene sheet without aggregation, which offers dramatically higher electrocatalytic activity on the redox of K₃[Fe(CN)₆]/K₄[Fe(CN)₆] couple than sole Au nanoparticles. Compared to sole Au nanoparticles, the G–Au 10 % also exhibited dramatically improved electrocatalytic activity on the reduction of p-NP. Amperometric detection of p-NP at G–Au 10 % modified electrode displayed a wide linear range of 0.47–10.75 mM with detection limit of 0.47 μM and a high sensitivity of 52.85 μA/mM. Considering the thrifty in utilization of noble Au, the G–Au 10 % can be successfully applied as a low-cost and powerful sensing material for trace detection of p-NP.     

基于纳米金与纳米银簇间表面等离子增强能量转移效应特异性检测microRNA

microRNAs(miRNAs)的灵敏检测对临床诊断具有十分重要的意义.本研究采用偶联DNA聚合酶和核酸内切酶介导的恒温扩增反应实现靶标循环再生的策略,利用纳米金(AuNPs)与纳米银簇(AgNCs)间表面等离子增强能量转移效应,开发了一种miRNA定量检测方法.在AuNPs表面组装两种探针(Probe a和Probe b)制备响应元件Probe b-Probe a-AuNP,其中Probe a通过3′端巯基共价偶联到AuNPs表面,此外具有靶标miRNA互补序列、核酸内切酶酶切序列和Probe b互补序列,Probe b为荧光AgNCs合成模板.靶标miRNA存在时,启动酶级联恒温扩增反应,导致Probe b脱离AuNPs表面,抑制了Probe b为模板合成的AgNCs与AuNPs间表面等离子增强能量转移效应,使得反应体系荧光信号增强.本方法的检出限为2.5×10-11 mol/L,与miRNAs商业化检测试剂盒相比,避免了逆转录反应,而且操作简单,检测成本低,可应用于生物样本中miRNAs分析.     

Metal-free and selective cleavage of unstrained carbon–carbon single bonds: Synthesis of β-ketosulfones from β-chlorohydrins and sodium sulfinates

A metal-free protocol for the selective cleavage of unstrained C–C single bonds was developed. Under the catalysis of KI and in the presence of NaHCO₃, the readily available α-chloro-β-hydroxy ketones underwent bond breaking and sulfonylation smoothly to afford β-ketosulfones with high efficiency and broad substrate scope. Mechanism investigations, both experimental and theoretical, showed that a retro-aldol cleavage/nucleophilic substitution sequence might be involved.     

Biosynthetic approach to modeling and understanding metalloproteins using unnatural amino acids

Metalloproteins have inspired chemists for many years to synthesize artificial catalysts that mimic native enzymes.As a complementary approach to studying native enzymes or making synthetic models,biosynthetic approach using small and stable proteins to model native enzymes has offered advantages of incorporating non-covalent secondary sphere interactions under physiological conditions.However,most biosynthetic models are restricted to natural amino acids.To overcome this limitation,incorporating unnatural amino acids into the biosynthetic models has shown promises.In this review,we summarize first synthetic,semisynthetic and biological methods of incorporates unnatural amino acids(UAAs)into proteins,followed by progress made in incorporating UAAs into both native metalloproteins and their biosynthetic models to fine-tune functional properties beyond native enzymes or their variants containing natural amino acids,such as reduction potentials of azurin,O_2 reduction rates and percentages of product formation of HCO models in Mb,the rate of radical transport in ribonucleotide reductase(RNR)and the proton and electron transfer pathways in photosystemⅡ(PSⅡ).We also discuss how this endeavour has allowed systematic investigations of precise roles of conserved residues in metalloproteins,such as Metl21 in azurin,Tyr244 that is cross-linked to one of the three His ligands to CuB in HCO,Tyr122,356,730 and 731 in RNR and TyrZ in PSⅡ.These examples have demonstrated that incorporating UAAs has provided a new dimension in our efforts to mimic native enzymes and in providing deeper insights into structural features responsible high enzymatic activity and reaction mechanisms,making it possible to design highly efficient artificial catalysts with similar or even higher activity than native enzymes.     

Comparative resin kinetics using in situ fluorescence measurements

The aminolysis of a novel activated ester resin was utilized for kinetic study via continuous in situ fluorescence measurements. A variety of resin compositions (polystyrene, JandaJel, ArgoPore, TentaGel, NovaGel, and PEGA) and solvents (dimethylformamide, acetonitrile, tetrahydrofuran, 1,2-dichlorethane, and toluene) were tested to compare their effects on the reaction rate. A linear relationship between the reaction rate and (solvent polarity x swelling of resin) was elucidated for the aminolysis reaction.     

Activation of gold on titania: adsorption and reaction of SO(2) on Au/TiO(2)(110)

Synchrotron-based high-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of gold with titania and the chemistry of SO(2) on Au/TiO(2)(110) surfaces. The deposition of Au nanoparticles on TiO(2)(110) produces a system with an extraordinary ability to adsorb and dissociate SO(2). In this respect, Au/TiO(2) is much more chemically active than metallic gold or stoichiometric titania. On Au(111) and rough polycrystalline surfaces of gold, SO(2) bonds weakly and desorbs intact at temperatures below 200 K. For the adsorption of SO(2) on TiO(2)(110) at 300 K, SO(4) is the only product (SO(2) + O(oxide) --> SO(4,ads)). In contrast, Au/TiO(2)(110) surfaces (theta;(Au) < or = 0.5 ML) fully dissociate the SO(2) molecule under identical reaction conditions. Interactions with titania electronically perturb gold, making it more chemically active. Furthermore, our experimental and theoretical results show quite clearly that not only gold is perturbed when gold and titania interact. The adsorbed gold, on its part, enhances the reactivity of titania by facilitating the migration of O vacancies from the bulk to the surface of the oxide. In general, the complex coupling of these phenomena must be taken into consideration when trying to explain the unusual chemical and catalytic activity of Au/TiO(2). In many situations, the oxide support can be much more than a simple spectator.     

Theoretical studies on N-loss predissociation mechanisms of N2O+ (A?2Σ+) in Cs symmetry

The N-loss predissociation mechanisms of the A ²Σ⁺ (2 ² A′) state of N₂O⁺ to the first and second dissociation limits were studied in the C _s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C _s states of N₂O⁺ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A ²Σ⁺ (2 ² A′) to the first and second limits. The first two steps in the two processes are the same: A ²Σ⁺ passes through the 2 ² A′/1 ⁴ A″ MECP and then reaches the 1 ⁴ A″ (1 ⁴Σ⁻) PEC. The 2 ² A′/1 ⁴ A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 ⁴ A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 ⁴Π).