N_2 Functionalization at Iron Metallaboratranes

The reactivity of the anionic dinitrogen complex [(TPB)Fe(N_2)]^− (TPB = tris[2-(diisopropylphosphino)phenyl]borane) toward silicon electrophiles has been examined. [(TPB)Fe(N_2)]^− reacts with trimethylsilyl chloride to yield the silyldiazenido complex (TPB)Fe(NNSiMe_3), which is reduced by Na/Hg in THF to yield the corresponding sodium-bound anion [(TPB)Fe(NNSiMe_3)]Na(THF). The use of 1,2-bis(chlorodimethylsilyl)ethane in the presence of excess Na/Hg results in the disilylation of the bound N_2 molecule to yield the disilylhydrazido(2−) complex (TPB)Fe≡NR (R = 2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentyl). One of the phosphine arms of TPB in (TPB)Fe≡NR can be substituted by CO or ^tBuNC to yield crystalline adducts (TPB)(L)Fe≡NR (L = CO, ^tBuNC). The N–N bond in (TPB)(^tBuNC)Fe≡NR is cleaved upon standing at room temperature to yield a phosphoraniminato/disilylamido iron(II) complex. The flexibility of the Fe–B linkage is thought to play a key role in these transformations of Fe-bound dinitrogen

Nanoparticles for fingermark detection: An insight into the reaction mechanism

© 2014 IOP Publishing Ltd. This publication presents one of the first uses of silicon oxide nanoparticles to detect fingermarks. The study is not confined to showing successful detection of fingermarks, but is focused on understanding the mechanisms involved in the fingermark detection process. To gain such an understanding, various chemical groups are grafted onto the nanoparticle surface, and parameters such as the pH of the solutions or zeta potential are varied to study their influence on the detection. An electrostatic interaction has been the generally accepted hypothesis of interaction between nanoparticles and fingermarks, but the results of this research challenge that hypothesis, showing that the interaction is chemically driven. Carboxyl groups grafted onto the nanoparticle surfaces react with amine groups of the fingermark secretion. This formation of amide linkage between carboxyl and amine groups has further been favoured by catalyzing the reaction with a compound of diimide type. The research strategy adopted here ought to be applicable to all detection techniques using nanoparticles. For most of them the nature of the interaction remains poorly understood

In Apple Blossom Time : Down On The Farm

https://digitalcommons.library.umaine.edu/mmb-vp/3613/thumbnail.jp

Migration of polypropylene oligomers into ready-to-eat vegetable soups

Polyolefin oligomeric hydrocarbons (POH) are non-intentionally added substances (NIAS) which mainly reside in the polymer (PE, PP) as a consequence of the polymerization process, and that under favorable conditions (high fat content, high temperature, and long contact time) may migrate at high amount from the packaging into the food. The food industry offers a wide range of ready-to-eat products, among these, vegetable soups designed to be stored at refrigeration temperature (for times around 6 weeks), and in most cases to be heated for a few minutes in a microwave oven (into the original container, mostly of PP) before consumption. The present work aimed to study for the first-time migration of POH during the shelf life of these products, including storage at refrigeration temperature and after microwave heating. On-line high-performance liquid chromatography (HPLC)-gas chromatography (GC), followed by flame ionization detection (FID), was applied for POH analysis in a number of ready-to-eat products purchased from the Italian market. Microwave heating determined a variable POH increase ranging from 0.1 to 6.2 mg/kg. Parameters possibly affecting migration such as fat content and heating time were also studied

A Polar Copper−Boron One-Electron σ‑Bond

Virtually all chemical bonds consist of one or several pairs of electrons shared by two atoms. Examples of σ-bonds made of a single electron delocalized over two neighboring atoms were until recently found only in gas-phase cations such as H_2^+ and Li_2^+ and in highly unstable species generated in solid matrices. Only in the past decade was bona fide one-electron bonding observed for molecules in fluid solution. Here we report the isolation and structural characterization of a thermally stable compound featuring a Cu–B one-electron bond, as well as its oxidized (nonbonded) and reduced (two-electrons-bonded) congeners. This triad provides an excellent opportunity to study the degree of σ-bonding in a metalloboratrane as a function of electron count

Microwave-based technique for fast and reliable extraction of organic contaminants from food, with a special focus on hydrocarbon contaminants

Due to food complexity and the low amount at which contaminants are usually present in food, their analytical determination can be particularly challenging. Conventional sample preparation methods making use of large solvent volumes and involving intensive sample manipulation can lead to sample contamination or losses of analytes. To overcome the disadvantages of conventional sample preparation, many researchers put their efforts toward the development of rapid and environmental-friendly methods, minimizing solvent consumption. In this context, microwave-assisted-extraction (MAE) has obtained, over the last years, increasing attention from analytical chemists and it has been successfully utilized for the extraction of various contaminants from different foods. In the first part of this review, an updated overview of the microwave-based extraction technique used for rapid and efficient extraction of organic contaminants from food is given. The principle of the technique, a description of available instrumentation, optimization of parameters affecting the extraction yield, as well as integrated techniques for further purification/enrichment prior to the analytical determination, are illustrated. In the second part of the review, the latest applications concerning the use of microwave energy for the determination of hydrocarbon contaminants-namely polycyclic aromatic hydrocarbons (PAHs) and mineral oil hydrocarbons (MOH)-are reported and critically overviewed and future trends are delineated

Conversion of Fe−NH_2 to Fe−N_2 with release of NH_3

Tris(phosphine)borane ligated Fe(I) centers featuring N_2H_4, NH_3, NH_2, and OH ligands are described. Conversion of Fe–NH_2 to Fe–NH_3^+ by the addition of acid, and subsequent reductive release of NH_3 to generate Fe–N_2, is demonstrated. This sequence models the final steps of proposed Fe–mediated nitrogen fixation pathways. The five-coordinate trigonal bipyramidal complexes described are unusual in that they adopt S = 3/2 ground states and are prepared from a four-coordinate, S = 3/2 trigonal pyramidal precursor