Synthesis of Novel Tartaric Acid-derived Chiral Phosphite Ligands and Their Application in the Cu-catalyzed Conjugate Addition of Diethylzinc to Cyclic Enones

Five novel tropos (3R,4R)- and/or (3S,4S)-N-benzyltartarimide-derived biphenylphosphite ligands were synthesized and applied in the Cu-catalyzed asymmetric conjugate addition of diethylzinc to cyclic enones with up to 75% e.e. Compared with the reported ligand 1-N-benzylpyrrolidine-3,4-bis[(R)-1,1'-binaphthyl-2,2'-diyl]phosphite-L-tartaric acid, the issue that L-(+)-tartaric acid backbone and (R)-binaphthyl showed strong matched/mismatched character was solved with these tropos ligands. It was found that the enantioselectivity was mainly controlled by the absolute configuration of N-benzyltartarimide backbone, and both enantiomers of the addition products can be obtained by simply changing the configuration of N-benzyltartarimide substituent.     

Asymmetric synthesis of emericellamide B

Asymmetric total synthesis of emericellamide B(9.4%, 17 longest linear steps) is detailed in this report. In this synthetic route, the highly methylated(2R,3R,4S,6S)-3-hydroxy-2,4,6-trimethyldodecanoic acid(HTMD) unit was effectively prepared through the asymmetric methylation, Wittig and Horner–Wadsworth–Emmons reaction. Moreover, pentafluorophenyl diphenylphophinate(FDPP) proved to be an effective condensation reagent for the macrolactamization between C14 and C18.     

离子液体[BMIM]PF6中铬的电沉积行为简

以一氯丁烷、N-甲基咪唑和KPF6为原料,合成了1-丁基-3-甲基咪唑六氟磷酸盐离子液体([BMIM]PF6),用红外光谱(IR)对产物进行了结构分析. 用循环伏安法测试该离子液体在85 ℃下的电化学窗口为4.7 V. 考察了[BMIM]PF6-Cr(Ⅲ)电解液的电化学行为,结果表明,在85 ℃下Cr(Ⅲ)的还原过程是受扩散控制的一步还原不可逆过程,Cr(Ⅲ)的传递系数α=0.023,阴极扩散系数D0=1.142×10-6 cm2/s. 在85 ℃和-1.5 V条件下,用恒电势法在铜片上电沉积Cr(Ⅲ),并通过扫描电子显微镜(SEM)观察了铜片上镀层的表面结构,发现该镀层呈颗粒状,且颗粒的体积随沉积时间的延长而增大. X射线能量色散谱(EDS) 和X射线粉末衍射(XRD)测试结果表明,该镀层为无定形的金属铬.     

石墨烯修饰玻碳电极用于循环伏安法测定抗坏血酸

采用Hummers法制备了纳米石墨烯,并将该纳米材料分散在蒸馏水中得到悬浮液,取5μL的悬浮液滴涂在玻碳电极表面,制备石墨烯修饰电极。用循环伏安法研究了在pH 4.0磷酸盐电解质中,在-0.4～0.8V(vs.Ag/AgCl)电位范围内,抗坏血酸在修饰电极上的电化学行为。结果表明:抗坏血酸在修饰电极上在0.173V处可见明显的氧化峰,且氧化峰电流显著高于在裸玻碳电极上的氧化峰电流;并可有效排除肾上腺素、尿酸、多巴胺等物质的干扰。据此提出了用循环伏安法测定抗坏血酸的方法。抗坏血酸的线性范围为8.00×10-6～1.0×10-3 mol.L-1,检出限(3S/N)为1.0×10-7 mol.L-1。方法用于维生素C片的分析,回收率在96.3%～104.4%之间。     

Simultaneous Determination of Nitrophenol Isomers Based on β‐Cyclodextrin Functionalized Reduced Graphene Oxide

β‐CD modified reduced graphene oxide (RGO) sheets have been prepared and characterized by TEM, AFM, IR, EIS and CVs. In comparison with bare glass carbon electrode (GCE) and RGO modified GCE, CD‐RGO/GCE showed much higher peak currents to the reduction of nitrophenol isomers (NPs), attributed to the larger specific surface area of RGO and high quantities of host–guest recognition sites. Three pairs of redox peaks are observed on the CVs of CD‐RGO for p‐NP (0.3 V), o‐NP (?0.2 V) and m‐NP (0.05 V), separating well with each other. Under the optimized condition, the anodic peak currents were linear over ranges around 1–10 mg dm^?3 for p‐NP, 1–9 mg dm^?3 for o‐NP and 1–6 mg dm^?3 for m‐NP, with the detection limits of 0.05 mg dm^?3, 0.02 mg dm^?3 and 0.1 mg dm^?3, respectively. Thus, the CD‐RGO is expected to be a promising sensor material for detecting trace NPs in waste water.     

Comparison of the Effects of Biofouling on Voltammetric and Potentiometric Measurements

Biofouling of sensors is a common problem when measuring biological samples. The adherence of proteins and biomolecules, called hemostasis, is the first of four steps that lead to biofouling and eventually a foreign body response. This typically occurs within the first hours after the exposure of the biosensor to a biological sample. The purpose of this study was to assess the effect of this initial step of biofouling on cyclic voltammetry and potentiometric measurements. The results show that biofouling occurred rapidly within minutes and strongly affected cyclic voltammetry measurements, while potentiometric measurements were minimally affected even after 24 hours.     

Two New Cycloheptapeptides from Psammosilene tunicoides

Two new cycloheptapeptides, tunicyclins F and G, were isolated from the roots of Psammosilene tunicoides. Their chemical structures were elucidated by extensive analysis of 1D‐ and 2D‐NMR, as well as HR‐ESI‐MS data. Tunicyclin G contains an unusual α,β‐dehydrotryptophan (Δ^Z‐Trp) residue, which mainly occurs in the cyclic peptides from marine sponge and bacteria.     

Synthesis,Structure, and Characterization of [FeIIILCl3] (L = 1, 4, 8‐Triazacycloundecane, 1, 4, 7‐Triazacyclononane)

The structures of [Fe^III(tacud)Cl₃] ( 1 ) and [Fe^III(tacn)Cl₃] ( 2 ) (tacud = 1, 4, 8‐triazacycloundecane, tacn = 1, 4, 7‐triazacyclononane) are reported. Both compounds crystallize in the orthorhombic space group Pnma with a = 12.5570(9), b = 12.0028(9), c = 8.2577(6) Å, V = 1244.59(16) ų, and Z = 4 for 1 and a = 12.095(4), b = 11.125(4), c = 7.963(3) Å, V = 1071.5(6) ų, and Z = 4 for 2 . The structures of 1 and 2 feature iron(III) in distorted octahedral arrangement with three facially coordinated nitrogen ligands and three chlorides. Bidirectional intermolecular hydrogen bonding between N–H groups and coordinated chlorides is seen for 1 and 2 . Compound 1 is the first example of iron(III) bonded to tacud and compound 2 is only the second structure reported of a 1:1 complex between iron and tacn. The Fe^3+/2+ redox couple for 1 is observed at E_1/2 = 0.25 V (ΔE_p = 99 mV), and for 2 at E_1/2 = 0.09 V (ΔE_p = 108 mV) versus NHE in DMF at 298 K. Comparison of structural, magnetic, and electrochemical properties for 1 and 2 reveal subtle differences consistent with the stronger coordinating properties of tacn relative to tacud.     

Modified Glassy Carbon Electrode with Multiwall Carbon Nanotubes as a Voltammetric Sensor for Determination of Leucine in Biological and Pharmaceutical Samples

Abstract

A simple and highly sensitive method is described for voltammetric determination of leucine in blood and urine samples; namely, a glassy carbon electrode with an effective method is modified with multiwall carbon nanotubes (MWNTs). The cyclic voltammetric results indicated that MWNTs remarkably enhanced electrocatalytic activity toward the oxidation of leucine. Under the optimum condition the calibration curve was linear in the concentration range 9.0 × 10^?6 ? 1.5 × 10^?3 mol L^?1, with the detection limit of 3.0 × 10^?6 mol L^?1 and a relative standard deviation (RSD%) lower than 3.0% (n = 5). Also, some kinetic parameters were determined and a multistep mechanism for oxidation of leucine was proposed.     

Direct Electrochemistry of Hemoglobin at Silver Electrode Modified by Lipoic Acid Monolayer

Abstract

The direct electrochemistry of hemoglobin (Hb) was studied by cyclic voltammetry(CV) and flow injection analysis(FIA) on a silver electrode modified by a self-assembled monolayer of lipoic acid(LA). Lipoic acid molecules can strongly adsorb onto the Ag electrode surface through the cleavage of the S-H bond and the formation of the Ag-S bond. The observed adsorption coverage of LA demonstrates that the LA molecules spontaneously form a self-assembled monolayer. Experimental data show that LA can promote the redox process of Hb at the modified electrode surface. This chemically modified electrode (CME) exhibits good stability in the CV and FIA. Linear sweep voltammetric measurement of Hb at the CME reveals a linear relationship between the oxidative peak current and the concentration of Hb in the range of 5.0×10^?7-1.5×10^?5 mol/L. The relative standard derivation (RSD) for six replicate measurements of 5.0×10^?6 mol/L Hb in FIA is 2.8%. The detection limit is 2.0×10^?7 mol/L. The reaction mechanism involves the hydrogen bond/ salt bridge formation between the carboxylate of LA and the protonated lysine residues of Hb that can enhance the electron transfer reaction. It can be used to detect Hb in real examples.