THE NATURE OF THE HOMONUCLEAR BOND IN ORGANIC AND INORGANIC DICHALCOGENIDES

Abstract

The electronic structures of a number of disulfide R₂S₂, and peroxide, R₂O₂, compounds are theoretically investigated or reinvestigated, and the results are compared and contrasted with each other as well as with experimental data. The results show that the enormous bond length variations in these compounds cannot be explained on the basis of the simple electronegativity difference model, but rather one must take into consideration terminal group atomic orbital contributions to the predominately homonuclear bonding molecular orbitals. The qualitative aspects of the bonding parameters of a large number of disulfide and peroxide compounds are explained.     

Multivariate calibration combined differential pulse voltammetry for simultaneous electroanalytical determination of phenolic compounds using a Fe3O4-modified carbon paste electrode

Journal of Solid State Electrochemistry - In present study, a simple carbon paste electrode modified with iron oxide nanoparticles was used as an electrochemical sensor to analyze phenolic...     

Influences of Seven Taiwan‐Produced Adulterants on Gas Chromatographic‐Mass Spectrometric (GC‐MS) Urinalysis of Amphetamines

This study was conducted to better understand the influences exerted by seven Taiwan‐produced adulterants on the forensic gas chromatographic‐mass spectrometric (GC‐MS) confirmatory urinalysis of amphetamines. The results verified that, when added at 5‐15% (w/w), chlorine bleach would lower the GC‐MS outcomes of the spiked and case specimens by 36‐63%, and was most likely to cause false negatives. Liquid soap, potassium dichromate, soda water for drinking, and tap water would decrease the GC‐MS outcomes by 9‐29%, 8‐20%, 8‐20%, and 5‐16%, respectively, and also had the risk of negating near‐cutoff initial positives into false confirmatory negatives. The negative‐directing effects were mostly due to degradation of analytes and/or deactivation of the derivatizing agent by oxidizing adulterants and/or dilution of analytes by the added liquid. Alum and table salt added as powder had little impact on the test. Responsible institutions and relevant laboratories should face the facts seriously and include the specimen validity testing (SVT) battery in the routine drug testing procedures.     

Highly Amino Acid Selective Hydrolysis of Myoglobin at Aspartate Residues as Promoted by Zirconium(IV)‐Substituted Polyoxometalates

SDS‐PAGE/Edman degradation and HPLC MS/MS showed that zirconium(IV)‐substituted Lindqvist‐, Keggin‐, and Wells–Dawson‐type polyoxometalates (POMs) selectively hydrolyze the protein myoglobin at Asp? X peptide bonds under mildly acidic and neutral conditions. This transformation is the first example of highly sequence selective protein hydrolysis by POMs, a novel class of protein‐hydrolyzing agents. The selectivity is directed by Asp residues located on the surface of the protein and is further assisted by electrostatic interactions between the negatively charged POMs and positively charged surface patches in the vicinity of the cleavage site.     

Application of the taraxerane–oleanane rearrangement to the synthesis of seco-oleanane triterpenoids from taraxerone

Synthetic oleananes and seco-oleananes form a group of promising anti-inflammatory and cancer chemopreventive agents with an excellent safety profile. These compounds are usually prepared by semi-synthesis from natural oleanane triterpenoids. Since a taraxer-14-ene was reported to be rearranged into an olean-12-ene under mild reaction conditions, a rapid synthesis of seco-oleananes from taraxerone, which is a readily available starting material, was explored by us. Treatment of taraxerone with m-chloroperoxybenzoic acid gave 14,15-epoxy lactones, which underwent the taraxerane–oleanane rearrangement leading to new seco-oleanane triterpenoids.     

New insights into the adsorption of 3-(trimethoxysilyl)propylmethacrylate on hydroxylated ZnO nanopowders

Functionalization of zinc oxide (ZnO) nano-objects by silane grafting is an attractive method to provide nanostructured materials with a variety of surface properties. Active hydroxyl groups on the oxide surface are one of the causes governing the interfacial bond strength in nanohybrid particles. Here, "as-prepared" and commercially available zinc oxide nanopowders with a wide range of surface hydroxyl density were functionalized by a well-known polymerizable silane coupling agent, i.e., 3-(trimethoxysilyl)propylmethacrylate (MPS). Fourier transform infrared (FTIR) and solid-state (13)C and (29)Si nuclear magnetic resonance (NMR) spectroscopic investigations demonstrated that the silane coupling agent was fully hydrolyzed and linked to the hydroxyl groups already present on the particle surface through covalent and hydrogen bonds. Due to a basic catalyzed condensation of MPS with water, a siloxane layer was shown to be anchored to the nanoparticles through mono- and tridentate structures. Quantitative investigations were performed by thermogravimetric (TGA) and elemental analyses. The amount of silane linked to ZnO particles was shown to be affected by the amount of isolated hydroxyl groups available to react on the particle surface. For as-prepared ZnO nanoparticles, the number of isolated and available hydroxyl groups per square nanometer was up to 3 times higher than the one found on commercially available ZnO nanoparticles, leading to higher amounts of polymerizable silane agent linked to the surface. The MPS molecules were shown to be mainly oriented perpendicular to the oxide surface for all the as-prepared ZnO nanoparticles, whereas a parallel orientation was found for the preheated commercially ZnO nanopowders. In addition, ZnO nanoparticles were shown to be hydrophobized by the MPS treatment with water contact angles higher than 60°.     

Effects of elicitors on the enhancement of asiaticoside biosynthesis in cell cultures of centella (Centella asiatica L. Urban)

In this work, the effects of elicitor concentration and elicitation day on the growth and asiaticoside production of centella cells were investigated. The results showed that 2-hydroxybenzoic acid from 50?C200 ??M and yeast extract from 2?C5 g L^?1 had different eliciting influences. The addition of 2-hydroxybenzoic acid and yeast extract to the cultures strongly enhanced asiaticoside production in centella cells. The increase in asiaticoside content induced by the addition of 100 ??M of 2-hydroxybenzoic acid and 4 g L^?1 of yeast extract at day 10 of inoculation was about 5- and 3.5-fold, respectively, as compared with that of the reference cells. In general, 2-hydroxybenzoic acid (abiotic elicitor) was more effective in enhancing asiaticoside biosynthesis than yeast extract (biotic elicitor).