Use of ETAAS,FAAS and ICP-OES for production and post-certification monitoring of a multielemental certified reference material according to national regulation limits for elements in drinking water

Accreditation and Quality Assurance - This paper describes the development of a certified reference material (CRM), produced in the National Institute of Quality from Peru (INACAL) in order to...     

Aerobic Epoxidation of Alkenes Catalysed by Cobalt(II) 1,1,1,5,5,5-Hexafluoroacetylacetonate or Cobalt(II) Benzoylacetonate

The aerobic epoxidation of terminal or electron deficient alkenes with an aldehyde does not proceed with cobalt(II) acetylacetonate but goes to completion with the cobalt(II) benzoylacetonate and cobalt(II) 1,1,1,5,5,5-hexafluoroacetylacetonate complexes.     

Comment on “A numerical investigation of the acoustic mode waves in a deviated borehole penetrating a transversely isotropic formation”

正In the paper"A numerical investigation of the acoustic mode waves in a deviated borehole penetrating a transversely isotropic formation"by Liu et al.[1]numerical experiments are reported for a dipole sonic logging scenario with a deviated borehole penetrating a VTI anisotropic medium.In such a situation it is important to clearly define the meaning of group and phase velocities as this has led to much confusion in the literature as discussed by Miller,Horne and Walsh[2].     

Non-fused polyaromatic hydrocarbons: interactions of aromatic and antiaromatic rings through a CC bond

The interaction of the moieties of benzene, cyclobutadiene, cyclopentadinyl anion, and the cyclopentadianide cation upon each other and upon a CC bond connecting pairs of these rings is investigated computationally. The resulting non-fused bicycles include biphenyl, phenylcyclobutadiene, phenylcyclopentadienylium, phenylcyclopentadienide, pentafulvalene, cyclobutadienyl–cyclopentadienylium, cyclobutadienyl–cyclopentadienide, and bicyclobutadiene. The relative stability and aromaticity are assessed from hydrogenation energies, aromatic stabilization energies, ring separation energies, nucleus-independent chemical-shift, harmonic oscillator model of aromaticity, and natural bond orbital analysis. Calculations are performed with density functional theory (B3LYP) and Møller–Plesset perturbation theory of second order (MP2). Enthalpy quantities are also determined by G3. When both rings are aromatic in character, the bridging bond is mostly σ in character. When one or both of the rings is antiaromatic, the bridging bond has significant π character. Systems with contrasting aromaticities have CC bridging bonds of lengths between CC single bond lengths and CC double bond lengths and where the systems were charged, the charge is evenly distributed between the rings.     

Optical studies of dynamic director configurations in ferroelectric liquid crystal devices

An investigation into the transmission spectrum of a ferroelectric liquid crystal device is undertaken. This is done both for an initial static state and during a switching process. Comparisons are made between experimental data and theoretical predictions. The dynamic internal director configurations in the device is shown to be consistent with a simple model during both monopolar and bipolar addressing pulses.     

A Hybrid Ring‐Opening Metathesis Polymerization Catalyst Based on an Engineered Variant of the β‐Barrel Protein FhuA

A β‐barrel protein hybrid catalyst was prepared by covalently anchoring a Grubbs–Hoveyda type olefin metathesis catalyst at a single accessible cysteine amino acid in the barrel interior of a variant of β‐barrel transmembrane protein ferric hydroxamate uptake protein component A (FhuA). Activity of this hybrid catalyst type was demonstrated by ring‐opening metathesis polymerization of a 7‐oxanorbornene derivative in aqueous solution.     

Noncovalent Bonds through Sigma and Pi-Hole Located on the Same Molecule. Guiding Principles and Comparisons

Over the last years, scientific interest in noncovalent interactions based on the presence of electron-depleted regions called σ-holes or π-holes has markedly accelerated. Their high directionality and strength, comparable to hydrogen bonds, has been documented in many fields of modern chemistry. The current review gathers and digests recent results concerning these bonds, with a focus on those systems where both σ and π-holes are present on the same molecule. The underlying principles guiding the bonding in both sorts of interactions are discussed, and the trends that emerge from recent work offer a guide as to how one might design systems that allow multiple noncovalent bonds to occur simultaneously, or that prefer one bond type over another.     

Chromatographic separation simulation of metal‐chelating peptides from surface plasmon resonance binding parameters

Some metal‐chelating peptides have antioxidant properties, with potential nutrition, health, and cosmetics applications. This study aimed to simulate their separation on immobilized metal ion affinity chromatography from their affinity constant for immobilized metal ion determined in surface plasmon resonance, both technics are based on peptide‐metal ion interactions. In our approach, first, the affinity constant of synthetic peptides was determined by surface plasmon resonance and used as input data to numerically simulate the chromatographic separation with a transport‐dispersive model based on Langmuir adsorption isotherm. Then, chromatographic separation was applied on the same peptides to determine their retention time and compare this experimental t_R with the simulated t_R obtained from simulation from surface plasmon resonance data. For the investigated peptides, the relative values of t_R were comparable. Hence, our study demonstrated the pertinence of such numerical simulation correlating immobilized metal ion affinity chromatography and surface plasmon resonance.     

Preparation and structural determination of siloxane-modified sulfone-containing epoxy resins

Siloxane-modified sulfone-containing epoxy resins (ESBS) were prepared by polycondensation of PMPS and/or PDMS siloxane oligomers with EBS, the sulfone-containing epoxy resin. Structures were analyzed by IR, ¹H-, and ¹³C-NMR. The siloxane content in the copolymers was determined by ¹H-NMR with an integration technique. Epoxy equivalent weight (EEW) determination indicated that the oxirane ring of EBS was intact with this hot-melt procedure. The GPC measurement of these ESBS copolymers showed that molecular weight (MW) increased with increasing siloxane content in PMPS-modified copolymers. Evidence of siloxane incorporation in the copolymer was discussed. © 1996 John Wiley & Sons, Inc.