The determination of lead and nickel by atomic-absorption spectrometry with a flameless wire loop atomizer

In an extension of studies of flameless atomizers for atomic-absorption spectrometry, an electrically heated tungsten-rhenium alloy wire loop was examined. Reduction of metallic salts to ground-state metal atoms was accomplished with the high temperature produced by the loop. Lead and nickel were investigated. Experimental parameters such as wavelength, slit width, atomization temperature and sheathing gas flow rate were optimized. Absolute detection limits of 6.6·10^?10 and 1.2·10^?10, and absolute sensitivities of 7·10^?10 and 8·10^?11 g of lead, were established for unenclosed and enclosed cells, respectively. The interferences of twenty cations and sixteen anions were studied; foreign cations generally enhanced the lead absorption by retarding its vaporization, allowing the slow detection system to respond more efficiently. Nickel was investigated as a representative less volatile metal; an absolute detection limit of 1.6·10^?9 and an absolute sensitivity of 9·10^?10 g of nickel were established.     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Chemical algebra. IV: “Length” of transformation pathways between skeletal analogs

Even if the eq. of completely G-invariant distance extensions derived from a pairing product is not resolved, a distance is defined by means of a metric obtained by differential resolution. Under specified conditions, the linear element solution do² is homogeneous to square coordinate differentials. Integration of da along a curve of E affords a length relative to doe. Boundaries of the curve represent skeletal analogs u and v, whereas inner points represent intermediates in the transformation u v, where the ligand parameters are supposed to vary continuously: a stereogenic pairing equilibrium between infinitesimally close skeletal analogs is assumed. If the curve runs orthogonal to a unit representation space of G, the length is infinite and the curve might be regarded as a fractal transformation pathway. The thermodynamic gap D_p is always shorter than the kinetic distance of the metric do².     

Synthesis of Enantiomerically Pure Ferrocenes from Glycofuranosyl-cyclopentadienes,synthetic equivalents of (alkoxyalkyl)fulvenes

Cyclopentadienyl C-glycosides (= glycosyl-cyclopentadienes) have been prepared as latent fulvenes. Their reaction with nucleophiles leads to cyclopentadienes substituted with (protected) alditol moieties and, hence, to enantiomerically pure metallocenes. Treatment of 1 with cyclopentadienyl anion gave the epimeric glycosyl-cyclopentadienes 6 / 7 (Scheme 1). Each epimer consisted of a ca. 1:1 mixture of the 1, 3-and 1, 4-cyclopentadienes a and b , respectively, which were separated by prep. HPLC. Slow regioisomerisation occurred at room temperature. Diels-Alder addition of N-phenylmaleimide to 6a / b ca. 3:7 at room temperature yielded three ‘endo’-adducts, i.e., a disubstituted alkene ( 8 or 9 , 25%) and the trisubstituted alkenes 10 (45%) and 11 (13%). The structure of 10 was established by X-ray analysis. Reduction of 6 / 7 (after isolation or in situ) with LiAlH₄ gave the cyclopentadienylmannitols 12a / b (80%) which were converted to the silyl ethers 13a / b (Scheme 2). Lithiation of 13a / b and reaction with FeCl₂ or TiCl₄ led to the symmetric ferrocene 14 (76%) and the titanocene 15 (34%), respectively. The mixed ferrocene 16 (63%) was prepared from 13a / b and pentamethylcyclopentadiene. Treatment of 6 / 7 with PhLi at ?78° gave a 5:3 mixture of the 1-C-phenylated alcohols 17a / b and 18a / b (71%) which were silylated to 19a / b and 20a / b , respectively. Lithiation of 19 / 20 and reaction with FeCl₂ afforded the symmetric ferrocenes 21 and 22 and the mixed ferrocene 23 (54:15:31, 79%) which were partially separated by MPLC. The configuration at C(1) of 17–22 was assigned on the basis of a conformational analysis. The reaction of the ribofuranose 24 with cyclopentadienylsodium led to the epimeric C-glycosides 27a / b and 28a (57%, ca. 1:1, Scheme 3). The in-situ reduction of 27 / 28 with LiAlH₄ followed by isopropylidenation gave 25a / b (65%) which were transformed into the ferrocene 26 (79%) using the standard method. Phenylation of 27 / 28 , desilylation, and isopropylidenation gave a 20:1 mixture of 33a / b and 34a / b (86%) which was separated by prep. HPLC. The same mixture was obtained upon phenylation of the fulvene 32 which was obtained in 36% yield from the reaction of the aldehydo-ribose 30 with cyclopentadienylsodium at ?100°. Lithiation of 33 / 34 and reaction with FeCl₂ gave the symmetric ferrocene 35 (88%). Similarly, the aldehydo-arabinose 36 was transformed via the fulvene 37 (32%) into a 18:1 mixture of 38a / b and 39a / b (78%) and, hence, into the ferrocene 40 (83%). Conformational analysis allowed to assign the configuration of 33–35 , whereas an X-ray analysis of 40 established the (1S)-configuration of 38a / b and 40 . The opposite configuration at C(1) of 38a / b and 33a / b was established by chemical degradation (Scheme 4). Hydrogenation (→ 41 and 44 , resp.), deprotection (→ 42 and 45 , resp.), NaIO₄ oxidation, and NaBH₄ reduction yielded (+)-(S)- 43 and (?)-(R)- 43 , respectively.     

Synthesis and Characterization of Partially Substituted at Lower Rim Phosphorus Containing Calix(4)arenes

The synthesis and characterization of several new phosphorus-containing partially lower rim substituted derivatives of 5,11,17,23-tetra(t-butyl) calix(4)arene (I) and 5,11,17,23-tetra(t-octyl)calix(4)arene (II), namely 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(diphenylphosphinoyl-oxy) calix(4)arene (IV); 5,11,17,23-tetra(t-butyl)-25-hydroxy-26,27,28-tris(tetramethyldiamido-phosphinoyl-oxy) calix(4)arene (Vb); 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VI); 5,11,17,23-tetra (t-octyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VII) are reported. The structure of the synthesized calix(4)arene derivatives are identified and confirmed by elemental analysis, IR, ¹H, ¹³C, ³¹P{¹H} NMR spectroscopy and mass spectrometry as and X-ray crystallographic analysis of 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene VI. According to the NMR spectra, all calix(4)arenes are in cone conformation.     

Uncommon suffix tries

Common assumptions on the source producing the words inserted in a suffix trie with n leaves lead to a height and saturation level. We provide an example of a suffix trie whose height increases faster than a power of n and another one whose saturation level is negligible with respect to . Both are built from VLMC (Variable Length Markov Chain) probabilistic sources and are easily extended to families of tries having the same properties. The first example corresponds to a “logarithmic infinite comb” and enjoys a non uniform polynomial mixing. The second one corresponds to a “factorial infinite comb” for which mixing is uniform and exponential. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 46, 117–141, 2015     

Inelastic scattering of 108.5 MeV 3He particles at very small momentum transfer to the giant monopole resonance of 90Zr and 208Pb

Inelastic scattering spectra from the (³He, ³He′) reaction at 108.5 MeV have been measured down to 1.85° scattering angle on ⁹⁰Zr and ²⁰⁸Pb, allowing a giant monopole resonance study in these nuclei. DWBA analysis is reported.     

Transient dark photovoltaic spatial solitons and induced guiding in slab LiNbO(3) waveguides

Dark photorefractive photovoltaic spatial solitons are demonstrated at 532 nm in nominally undoped and slightly Fe-doped LiNbO(3) planar optical waveguides. The spatial solitons are observed in a transient regime before transverse modulation instability occurs. Their widths are intensity independent as predicted by theory. Meanwhile, excited mode distribution and Fe-doping concentration are shown to influence soliton width. The guiding properties of soliton-induced waveguides are also presented.