Electrochemically synthesized polymer of the plant substance embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone)

Among the possible new materials for microelectronics, quinones have a number of significant advantages. Similarly, polymers with quinone functionality possess biodegradability. Because natural polymers are promising candidates for functional materials for the future, we have initiated studies on the polymers of natural products. In the present study, a natural quinone (a plant substance) extracted from Embelier libes distributed in the Kerala state of India was electrochemically polymerized and its properties were investigated. The redox activity, electrical conductivity, and biodegradability are discussed.     

Determination of perfluorooctanoate and perfluorooctanesulfonate in water matrices by inline matrix elimination liquid chromatography with reversed phase separation and suppressed conductivity detection

This work describes a new method for the determination of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in water matrices by suppressed conductivity detection. Separation was achieved by isocratic elution on a reversed-phase column thermostated at 45°C using an aqueous mobile phase containing boric acid and acetonitrile. The PFOA and PFOS content in the water matrix were quantified by a pre-concentration technique. For the concentration range of 1 to 15 ng/mL and 2 to 30 ng/mL, the linear calibration curve for PFOA and PFOS yielded coefficients of determination (R(2)) of 0.9995 and 0.9985, respectively. The relative standard deviations were smaller than 1.5% for PFOA and PFOS. The retention-time precision of four consecutive 12 h injections was smaller than 0.641% and 0.818%, respectively. The presence of common divalent cations, such as calcium, magnesium, and iron in water matrices impairs PFOS recovery. This drawback was overcome by applying inline matrix elimination method. The optimized method was successfully applied for drinking water, ground water, and seawater samples.     

Sterically encumbered regioselective cycloaddition of a calixarene derived bis(spirodienone) with 1,2-benzoquinones

A calix[4]arene derived bis(spirodienone) acts as the 2π component in a cycloaddition reaction with two molecules of 3,5-di-tert-butyl-1,2-benzoquinone in the [2+4] manner leading to macrocycles with a benzodioxin moiety. A theoretical rationalization of the results suggested a sterically encumbered regioselective pathway, which gives sterically crowded products.     

一种香豆素衍生物分子的红外光谱及核磁共振谱的理论研究

用密度泛函理论(Density Functional Theory,DFT)方法,在B3LYP/6-31G(d,p)水平上对一种香豆素衍生物分子进行几何结构优化,得到其最稳定构型、分子能量及HOMO、LUMO轨道能量。在优化结构的基础上用同样的方法,在B3LYP/6-31G基组水平上计算了该分子的红外振动光谱和核磁共振1HNMR谱,并对其红外光谱峰位及1HNMR化学位移进行了归属。     

Palladium‐Mediated Cleavage of Proteins with Thiazolidine‐Modified Backbone in Live Cells

Chemical protein synthesis and biorthogonal modification chemistries allow production of unique proteins for a range of biological studies. Bond‐forming reactions for site‐selective protein labeling are commonly used in these endeavors. Selective bond‐cleavage reactions, however, are much less explored and still pose a great challenge. In addition, most of studies with modified proteins prepared by either total synthesis or semisynthesis have been applied mainly for in vitro experiments with very limited extension to live cells. Reported here is an approach for studying uniquely modified proteins containing a traceless cell delivery unit and palladium‐based cleavable element for chemical activation, and monitoring the effect of these proteins in live cells. This approach is demonstrated for the synthesis of a caged ubiquitin‐aldehyde, which was decaged for the inhibition of deubiquitinases in live cells.     

Electron delocalization in the metallabenzenes: a computational analysis of ring currents

Many metallabenzene complexes appear to exhibit an enhanced thermodynamic stability which has been attributed to the concept of aromaticity. Analysis of the ring currents induced by a magnetic field, either by direct visualization or by considering nuclear or nucleus-independent chemical shielding values (NMR or NICS), have become useful theoretical tools to characterize the aromaticity of many molecules involving the main group elements. We have analyzed 21 metallabenzenes using variations of these techniques, which take account of the large core and metal orbital contributions which often lead to transition-metal-containing systems exhibiting anomalous shielding values. Analysis of individual orbital contributions to both the ring currents and chemical shielding values based upon the ipsocentric and CSGT (continuous set of gauge transformations) methods has shown that complexes such as the 18 electron Ir or Rh(C 5H 5)(PH 3) 2Cl 2 molecules should be classed as aromatic, whereas the 16 electron complexes such as Os or Ru(C 5H 5)(PH 3) 2Cl 2 should not, despite having the same occupancy of pi-MOs. The differences can be directly attributed to the HOMO/LUMO b 2 in-plane (d xy ) molecular orbital, which, when unoccupied, is available to disrupt the delocalized currents typical of aromatic systems. A range of Pd and Pt metallabenzenes with cyclopentadienyl and phosphine ligands is also discussed as having aromatic and nonaromatic character, respectively.     

Determination of arsenic species in Solanum Lyratum Thunb using capillary electrophoresis with inductively coupled plasma mass spectrometry

A simple and highly efficient interface to couple capillary electrophoresis with inductively coupled plasma mass spectrometry by a microflow polyfluoroalkoxy nebulizer and a quadruple ion deflector was developed in this study. By using this interface, six arsenic species, including arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, and arsenocholine, were baseline‐separated and determined in a single run within 11 min under the optimized separation conditions. The instrumental detection limit was in the range of 0.02–0.06 ng/mL for the six arsenic compounds. Repeatability expressed as the relative standard deviation (n = 5) of both migration time and peak area were better than 2.5 and 4.3% for six arsenic compounds. The proposed method, combined with a closed‐vessel microwave‐assisted extraction procedure, was successfully applied for the determination of arsenic species in the Solanum Lyratum Thunb samples from Anhui province in China with the relative standard deviations (n = 5) ≤4%, method detection limits of 0.2–0.6 ng As/g and a recovery of 98–104%. The experimental results showed that arsenobetaine was the main speciation of arsenic in the Solanum Lyratum Thunb samples from different provinces in China, with a concentration of 0.42–1.30 μg/g.     

The binding of nitric oxide at the Cu(i) site of copper nitrite reductase and of inorganic models: DFT calculations of the energetics and EPR parameters of side-on and end-on structures

Density functional theory calculations have been used to probe the end-on and side-on bonding motifs of nitric oxide at the Cu(i) centre in the enzyme copper nitrite reductase and in three inorganic model systems. We find that irrespective of a range of functionals used, the end-on structure is preferred by up to 40 kJ mol(-1), although this preference is smaller for the enzyme than for the inorganic model systems. We have calculated the g-tensor and atomic hyperfine coupling constants for these structures. When compared to available experimental data, for one model compound the calculated EPR parameters definitely favour an end-on structure, although this preference is somewhat less for the enzyme. Our prediction of NO end-on binding in the enzyme is at variance with structural data.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.