Crystal orbital studies of chemisorption: the adsorption of molecular hydrogen on beryllium

A semi-empirical tight-binding crystal orbital technique applicable to two dimensional systems is described and calculations on the adsorption of hydrogen on the (100) face of a beryllium crystal are reported. It is suggested that the method shows certain advantages over calculations on clusters of atoms in terms of avoiding “edge-effects” and including longer range adsorbent-metal interactions.     

Beryllepin,C6H6Be,and “Beryllium‐Inserted Benzenes,” C6H6Ben,n = 2–6: A Density Functional Computational Investigation

The seven‐membered beryllium‐containing heterocycle beryllepin, C₆H₆Be, has been examined computationally at the B3LYP/6‐311++G** density functional level of theory. Beryllepin is best described as a planar singlet heterocyclic conjugated triene with marginal aromatic character containing a C–Be–C moiety forced to be nonlinear (∠C‐Be‐C = 146.25°) by the cyclic constraints of the seven‐membered ring. The molecule can be considered to be derived from a benzene‐like system in which a neutral beryllium atom has been inserted between two adjacent carbon atoms. The 11 other possible “beryllium‐inserted benzenes,” C₆H₆Be_n, n = 2–6, have also been investigated. Only two of these heterocyclic systems, the eight‐membered 1,4‐diberyllocin and the nine‐membered 1,4,7‐triberyllonin, were found to be stable, singlet‐ground‐state systems, albeit with little aromatic character. Of the remaining nine beryllium‐inserted benzenes, with the exception of the 11‐membered ring containing five beryllium atoms and the 12‐membered ring containing six beryllium atoms, which were calculated to exist as a ground state pentet and septet, respectively, all were calculated to be ground state triplet systems.     

Beryllium Phosphine Complexes: Synthesis,Properties, and Reactivity of (PMe3)2BeCl2 and (Ph2PC3H6PPh2)BeCl2

The directed synthesis, spectroscopic properties, and reactivity of bis(trimethylphosphine) beryllium dichloride ( 1 ) and bis(diphenylphosphino)propane beryllium dichloride ( 2 ) are reported, including the crystal structure of (PMe₃)₂BeCl₂ ( 1 ). These four‐coordinate beryllium compounds can be alkylated with n‐butyllithium (ⁿBuLi) to give three‐coordinate (Ph₂PC₃H₆PPh₂)BeⁿBu₂ ( 3 ) and (PMe₃)BeⁿBu₂ ( 4 ). PMe₃ can be removed from (PMe₃)BeⁿBu₂ ( 4 ) in vacuo to yield [ⁿBu₂Be]₂ ( 5 ). For the first time, the presence of [ⁿBu₂Be]₂ as a dimer in solution, which has been postulated for decades, could be observed spectroscopically. This novel, ether‐free pathway provides access to beryllium dialkyl compounds that have never been in contact with oxygen‐atom‐containing reagents or solvents. This “freeness from oxygen” is crucial for semiconductor applications where oxygen is often unwanted and must be avoided at all costs.     

The possible discovery of neutron activation in 1910

One-hundred-two years ago, on 21 April 1910, the Austrian chemist Carl Auer von Welsbach published a short comment on a fundamental discovery he had made in the field of nuclear sciences. He reported that “jonium” (²³⁰Th) was able to induce radioactivity in other materials if stored in contact with the ionium sample. He was well aware that this observation was “not quite in agreement with current theories”, because, as a basic principle, a radioactive substance cannot activate an inactive substance. Since he could not remove any superficial contamination, he concluded that the previously inactive materials had become radioactive themselves. Auer von Welsbach predicted that this observation “might be of importance for the mysterious field of radioactivity research”. In fact, we believe that in this experiment he incidentally discovered neutron activation and the production of artificial radionuclides (24 years before I. Curie and F. Joliot) or even induced nuclear fission. The neutron source in his experiments is yet unknown and shall be identified in this project. The neutrons could have been produced from nuclear reactions with impurities of beryllium in the sample. Auer von Welsbach may even have observed nuclear fission 29 years before O. Hahn, F. Straßmann, L. Meitner and O. R. Frisch. In any case, he may have noticed the effects of neutron radiation—22 years before its discovery by J. Chadwick. The main aim of this interdisciplinary project (of which preliminary results are presented herein) is to repeat the 1910-experiment and to identify the source of the neutrons. It will be equally important to investigate the historical reasons and circumstances why Auer’s report remained mostly uncommented in the scientific community. The hypothetical consequences are worth discussion: Auer’s publication could have started the “nuclear age” much earlier than it finally began, with all the consequences for mankind.     

Accurate electron density and one-electron properties for the beryllium atom

An accurate analytical electron density for the beryllium atom is obtained by using a fast and systematic method recently developed and tested for the neon atom. Asymptotic conditions both at the nucleus and at large distances are obeyed. A point-by-point comparison between our density and the one obtained from an almost “exact” configuration interaction wave function shows that differences are less than 0.5% for r between 0 and 5 bohrs and less than 1 % up to 9 bohrs. The accuracy of the density is also assessed by comparing results of density moments and x-ray scattering factors.     

煤燃烧过程中铍的迁移转化特性研究

通过热力学平衡模拟计算煤燃烧过程中铍的形态转化,采用高温真空管式炉进行含铍化合物与矿物的固固反应实验,以及富铍煤中加入添加剂的燃烧实验,通过X射线衍射仪(XRD)、X射线荧光探针(XRF)以及电感耦合等离子质谱仪(ICP-MS)揭示煤燃烧过程中铍的迁移转化规律。结果表明,模拟计算发现铍只与含铝化合物反应生成BeAl_2O_4和Be Al6O10,同时固固反应实验也印证了这一结论,但反应温度在1 000℃左右,明显高于模拟计算温度650℃。添加Al_2O_3的富铍煤在燃烧时,由于铍与Al_2O_3发生反应,铍的释放率明显降低,最高降低33%以上;添加了伊利石的富铍煤,由于伊利石与铍的反应温度高于Al_2O_3,其抑制作用弱于Al_2O_3;而高岭石由于与铍的反应温度过高,在高岭石与铍发生反应产生抑制效果之前,部分铍已经在燃烧过程中释放出去,因此,抑制效果最差。     

Determination of lithium in biological samples by inductively coupled plasma mass spectrometry

Lithium was determined in human serum by inductively coupled plasma mass spectrometry. Sample preparation was kept to the minimum: serum samples were diluted and beryllium was added as internal standard. Special attention was given to the choice of the internal standard and to the occurrence of memory effects. To test the accuracy of the method several biological reference materials were analysed, namely a “Second-Generation” Biological Reference Material (Freeze-Dried Human Serum) (University of Ghent), Human Serum SRM 909, Whole Egg Powder SRM 1845 and Mixed Human Diet SRM 1548 (National Institute of Standards and Technology). The results were compared with those obtained by other techniques. For the “second-generation” reference freeze-dried human serum a mean lithium concentration of 15.10 ng g^?1 with a standard deviation of 0.54 ng g^?1 dry weight was found. Analyses on serum samples from healthy individuals yielded lithium concentrations ranging from 0.22 to 0.97 μg l^?1.     

Simultaneous determination of aluminium and beryllium by first-derivative synchronous solid-phase spectrofluorimetry

A method for the simultaneous determination of aluminium and beryllium in mixtures by first-deravative synchronous solid-phase spectrofluorimetry has been developed. Aluminium and beryllium reacted with morin to give fluorescent complexes, which were fixed on a dextran-type resin. The fluoresnce of the resin, packed in a 1-mm silica cell, was measured directly with a solid-surface attachment. The constant wavelength difference chosen to optimize the determination was Deltalambda = lambda(em) = 75 nm. Aluminium was measured at lambda(em)lambda = 445/520 nm and beryllium at lambda(em)lambda(em) = 430/505 nm. The range of application is between 0.5 and 5.0 ng/ml for both aluminium and beryllium. The accuracy and precision of the method are reported. The method has been successfully applied to the determination of aluminium and beryllium in synthetic mixtures and natural waters.     

Local-scaling transformation version of density functional theory

The local-scaling transformation version of density functional theory (LS-DFT ) is reviewed. It is shown that in the context of LS-DFT it is possible to construct N-representable energy density functionals and that the theory provides systematic ways for calculating strict upper bounds to the exact energies. The importance of the concept of “orbit” in LS-DFT is indicated and several approaches leading to intraorbit and interorbit optimization are discussed. Results of the application of these optimization procedures to the determination of upper bounds for the ground-state energy of the beryllium atom are given. Also, numerical results are reported on the use of local scaling transformations for the direct solution of the Kohn-Sham equations via the density-constrained minimization of the kinetic energy of a noninteracting system. © 1995 John Wiley & Sons, Inc.     

Simultaneous determination of beryllium and aluminium in mixtures using derivative spectrophotometry

The spectrophotometric determination of beryllium and aluminium with 5,8-dihydroxy-1,4-naphthoquinone in the presence of a non-ionic surfactant is reported. Absorption maxima, molar absorptivity and Sandell's Sensitivity of 1:2 (M:L) beryllium and aluminium complexes are, 585 nm and 598 nm, 1.63 x 10(4) l.mole(-1).cm(-1) and 2.04 x 10(4) l.mole(-1).cm(-1), and 0.55 ng/cm(2) and 1.32 ng/cm(2) respectively. Beer's law is obeyed between 7.20-3.96 x 10(2) ng/ml beryllium and 1.08 x 10(1)-1.08 x 10(3) ng/ml aluminium. A method for simultaneous determination of beryllium and aluminium in their mixture using derivative spectra is described. The range 3.6 x 10(1)-3.6 x 10(2) ng/ml beryllium could be determined in the presence of 1.08 x 10(2)-1.08 x 10(3) ng/ml aluminium, and vice versa.     

Applications of the ring oven method in enzymatic analysis

The use of the ring oven technique in enzymatic analysis is described. The “segment technique” for catalyzed reactions is applied for the determination of enzymes, inhibitors and substrates. Three different methods have been worked out for this purpose, none of them needs a stable standard scale. These methods are illustrated by various examples: determinations of the enzymes acid and alkaline phosphatase, hyaluronidase, acetylcholinesterase, lipase and alcohol dehydrogenase; indirect determinations of the inhibitors copper, beryllium, molybdenum, the insecticides carbaryl and paraoxon, the herbicides 2, 4-D, mecoprop and bentazcn, and the fungicide phenylmercury acetate; and determinations of the substrates ethanol and glucose.     

“Surface water” and “strong-bonded water” in cyclodextrins: a Karl Fischer titration approach

Cyclodextrins are some of the most used carriers for bioactive compounds (as host–guest complex) and many factors influence the association–dissociation of this complex, some of them being related to hydrophobicity. In the solid state, cyclodextrins contain two types of water molecules: “surface” water molecules (especially close to the crystal surface) and “strong-bonded” water molecules (especially from the cyclodextrin cavity), but the classification is hard to do, and the concentration of these water molecules are relatively difficult to estimate by simple methods. In the present study we used the volumetric Karl Fischer titration to estimate these types of water molecules in cyclodextrins by means of the rate of water reaction (related to diffusion from cyclodextrin crystals). “Surface” water molecules are titrated with rates between 1.8–2.8 mM/s for α-cyclodextrin, while for β-cyclodextrin these rates are little bit higher (2.9–3.4 mM/s). The rates corresponding to “strong-bonded” water molecules are approximately tens fold lower (0.05–0.3 mM/s for α-cyclodextrin and 0.15–0.33 mM/s for β-cyclodextrin). The approximate ratio between “surface” and “strong-bonded” water molecules could also be estimated by this simple and rapid method.     

Determination of Small Dialkyl Organophosphonates at Microgram/L Concentrations in Contaminated Groundwaters Using Multiple Extraction Membrane Disks

Abstract

Di-isopropyl methylphosphonate (DIMP) and dimethyl methylphosphonate (DMMP), which are manufacturing by-products of. and surrogate compounds for, the nerve agents Sarin (GB) and VX, respectively, are readily quantitated at microgram per liter concentrations in contaminated groundwaters. Aqueous samples (typically 1 L) are first fortified with triethylphosphate (TEP) as a surrogate, then passed through a “sandwiched” set of three preconditioned extraction disks consisting of the following (in filtration order): (a) glass fiber filter, to remove unwanted particulate matter; (b) C₁₈-based extraction disk, to collect DIMP; and (c) carbon-based extraction disk, to collect DMMP. The glass fiber filter is discarded; the two extraction disks are dried and extracted with a small volume of methanol. After the extract is fortified with diethyl ethylphosphonate (DEEP) internal standard, it is analyzed using a gas chromatograph equipped with a nitrogen-phosphorus detector (NPD). Quantitation of DMMP, DIMP, and TEP is performed using the method of internal standards.

The procedure was used to obtain statistically-unbiased reporting limits for a “regulatory” criterion of 0.39 μg/L and a “pump and treat” criterion of 2 μg/L for both analytes. Two standardized protocols were used to validate a detection limit of 0.20 μg/L for DMMP and 0.48 μg/L for DIMP when the regulatory criterion was used as the “target concentration.” When the “pump and treat” criterion was used as the “target concentration,” the detection limits for both DMMP and DIMP were both 2 μg/L using the same protocols as for the “regulatory” criterion. The method recovery is approximately 40–50%, based on synthetic groundwaters containing between 0.2–50 μg/L of each analyte. DIMP and DMMP are cleanly resolved from each other, the internal standard, the surrogate, and the potential interference trimethylphosphate (TMP).     

Coprecipitation with metal hydroxides for the determination of beryllium in seawater by graphite furnace atomic absorption spectrometry

Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater.     

Ion cyclotron resonance excitatio/de-excitation: A basis for Stochastic fourier transform ion cyclotron mass spectrometry

Previous mass spectrometers based on the ion cyclotron resonance principle have employed continuous excitation (single-pulse or frequency-sweep), With detection during (frequency-sweep) or after (single-pulse or frequency sweep) the excitation. The present paper introduces an experiment in which an ion is first excited to a Larger orbit by continuous excitation, and then “de-excited” back to its starting point. The effect is demonstrated for the C₉F₂₀N⁺ peak (m/z = 502) in the Fourier transform ion cyclotron mass spectrum of perfluorotributylamine. By choosing which ion m/z ratios are “de-excited”, it should be possible to generate mass “windows” within which ions experience no net excitation. Potential applications of the method include the generation of an excitation with sharply defined “windows” or “steps”, with major advantages for MS/MS or multiple-ion-monitoring experiments.     

Modulation of Kinetic Pathways of Enzyme–Substrate Interaction in a Microfluidic Channel: Nanoscopic Water Dynamics as a Switch

Enzyme-mediated catalysis is attributed to enzyme–substrate interactions, with models such as “induced fit” and “conformational selection” emphasizing the role of protein conformational transitions. The dynamic nature of the protein structure, thus, plays a crucial role in molecular recognition and substrate binding. As large-scale protein motions are coupled to water motions, hydration dynamics play a key role in protein dynamics, and hence, in enzyme catalysis. Here, microfluidic techniques and time-dependent fluorescence Stokes shift (TDFSS) measurements are employed to elucidate the role of nanoscopic water dynamics in the interaction of an enzyme, α-Chymotrypsin (CHT), with a substrate, Ala-Ala-Phe-7-amido-4-methylcoumarin (AMC) in the cationic reverse micelles of benzylhexadecyldimethylammonium chloride (BHDC/benzene) and anionic reverse micelles of sodium bis(2-ethylhexyl)sulfosuccinate (AOT/benzene). The kinetic pathways unraveled from the microfluidic setup are consistent with the “conformational selection” fit for the interaction of CHT with AMC in the cationic reverse micelles, whereas an “induced fit” mechanism is indicated for the anionic reverse micelles. In the cationic reverse micelles of BHDC, faster hydration dynamics (≈550 ps) aid the pathway of “conformational selection”, whereas in the anionic reverse micelles of AOT, the significantly slower dynamics of hydration (≈1600 ps) facilitate an “induced fit” mechanism for the formation of the final enzyme–substrate complex. The role of water dynamics in dictating the mechanism of enzyme–substrate interaction becomes further manifest in the neutral reverse micelles of Brij-30 and Triton X-100. In the former, the faster water dynamics aid the “conformational selection” pathway, whereas the significantly slower dynamics of water molecules in the latter are conducive to the “induced fit” mechanism in the enzyme–substrate interaction. Thus, nanoscopic water dynamics act as a switch in modulating the pathway of recognition of an enzyme (CHT) by the substrate (AMC) in reverse micelles.     

Géométrie de micelles à deux compartiments hydrophobes

We discuss a “comb block copolymer” with a hydrophilic backbone (N polar heads), Nf/2 side chains of type A, and Nf/2 side chains of type B. Imposing an area per head and a volume per side chain, we predict various conformations based on two spherical portions. In certain cases, two distinct conformations are permitted by this criterion: the best one should minimise the A/B interfacial energy. We also discuss “multiplets” (p polymers per double micelle) and “necklaces” (k double micelles for one polymer chain).     

Simulated moving bed technology: old and new

The Simulated Moving Bed (SMB) concept has been applied to the separation of different mixtures as a continuous counter current separation process, avoiding several problems related with solid motion. The aim of this work is to present some relevant examples of SMB separations corresponding to the two major ages in the use of the SMB concept, here named “old” and “new” applications. The “old” applications of SMB technology in the petrochemical industry are still important, with large and highly productive units; and the “new” applications of the second “age” of SMB concept are from the fine chemical, pharmaceutical and biochemistry areas, associated with the demand of high purity products during the last 10 years. Different examples are presented for different ages: a UOP Parex ^® process for the “old”, modelled with the equivalent True Moving Bed (TMB) approach; and a chiral resolution for the “new”, modelled by the real SMB model. Some of the latest developments are also mentioned: the non conventional techniques as the Varicol ^® process, PowerFeed, Modicon, M3C or Enriched Extract-SMB (EE-SMB), MultiFeed (MF), Outlet Streams Swing (OSS) or Pseudo-SMB, involving considerable changes in the SMB concept itself. The use of the last optimization/modelling packages for the development of design techniques, either at the conception stage as well as for performance improvements of existing units is emphasized.