Determination of inorganic tin and organotin compounds by graphite-furnace atomic absorption spectrometry with a new matrix modifier

The determination of total tin in water samples by graphite-furnace atomic absorption spectrometry is described. A matrix modifier containing 0.4% (w/v) potassium dichromate and 0.2% ammonium dihydrogenphosphate in 2% nitric acid is proposed. Interferences from major ions in natural fresh waters decreased and the sensitivity is greatly improved. The procedure is compatible with all the commercial injection devices and requires no pretreatment of the graphite furnace or use of a stabilized temperature platform. The 3σ detection limit is 0.62 ng Sn ml^?1, and calibration is linear up to 30 ng ml^?1 tin.     

Preparation of ferrocene-containing phosphinamine ligands possessing central and planar chirality and their application in palladium-catalyzed asymmetric allylic alkylation

The preparation of [2-(S(p))-[(trans-(2R,5R)-2,5-dialkylpyrrolidinyl)methyl]]ferrocenyldiphenyl phosphines, new ferrocenylphosphinamine ligands possessing one site of planar and two stereogenic centers, is described. trans-(2R,5R)-2,5-Dialkyl-1-(ferrocenylmethyl)pyrrolidines were diastereoselectively lithiated and quenched with chlorodiphenylphosphine. For the dimethyl ligand, chemical yields of up to 65% and des of up to 90% were obtained whereas the diethyl ligand afforded lower chemical yields (10%) and des of 78%. Diastereomerically pure material was obtained in both cases after a single recrystallization from ethanol. (S)-Planar chirality was confirmed by X-ray crystallographic analysis of the dimethyl ligand. The palladium complexes of the new ligands were applied in the allylic alkylation of 1,3-diphenylprop-2-enyl acetate with reasonable chemical yields and moderate ees of up to 36% and 38% when dimethyl malonate and dimethyl methyl malonate were employed as nucleophiles, respectively. Importantly, it was found that the new ligands possessing the combination of planar and central chirality gave the opposite enantiomeric alkylation products compared to ligands which possess only the central chirality of the trans-2,5-dimethylpyrrolidinyl moiety. Solution NMR studies of the 1,3-diphenylallyl palladium complex of the dimethyl ligand revealed the presence of only the exo-configured allyl diastereomer.     

Synthesis, structural characterisation of new oligomeric alkyl aluminium (2,2′-methylene-p-chloro-bisphenoxides) and application as catalysts in polymerisation reactions involving cyclohexene oxide

The synthesis, spectroscopic characterisation and X-ray structure determination of the first aluminium para-chloro-bisphenoxides [Al₂(mbpcp)₂(C₂H₅)₂(THF)₂] and [Al₃(mbpcp)₂(C₂H₅)₅] (mbpcp = 2,2′-methylenebis(4-chlorophenol) are reported. 2,2′-Methylenebis(4-chlorophenol) was reacted with triethyl aluminium to yield under liberation of ethane, aluminium para-chloro-2,2′-methylene-bisphenoxides with different molecular complexities: a dinuclear and a trinuclear specie, both displaying two bridging bisphenoxide ligands. The nature of the solvent (coordinating or not) influences the aggregation degree of the final product. The use of a coordinating solvent like THF yields a dimeric structure with a bisphenol:metal ratio of 1 to 1 which displays a trigonal-bipyramidal coordination geometry around the aluminium atoms whereas using an apolar, weak-coordinating solvent like diethyl ether yields a trinuclear species with a bisphenol:metal ratio of 2 to 3, displaying aluminium atoms with both tetrahedral and trigonal-bipyramidal coordination geometries. These compounds were tested in preliminary screening tests as catalysts of the homopolymerisation of cyclohexene oxide (CHO) and copolymerisation of CHO with carbon dioxide. Both aluminium bisphenoxides are highly active in the ring opening polymerisation of CHO (RT, reaction time <5 min, M_n ranging from 31 000 to 40 700 g/mol, polydispersities from 1.2 to 1.4). Both compound are also active in the copolymerisation of CHO with CO₂ although the carbonate amount remains low (75 bar, 90 °C, reaction time 8 h, M_n ranging from 6800 to 15 200 g/mol, polydispersities from 1.9 to 2.5).     

Synthesis, X-ray Crystal Structure Determination, and NMR Spectroscopic Investigation of Two Homoleptic Four-Coordinate Lanthanide Complexes: Trivalent ((t)Bu(2)P)(2)La[(&mgr;-P(t)Bu(2))(2)Li(thf)] and Divalent Yb[(&mgr;-P(t)Bu(2))(2)Li(thf)](2)(,)(1)

La(OSO(2)CF(3))(3) reacts with 4 equiv of LiP(t)Bu(2) in tetrahydrofuran to give dark red ((t)Bu(2)P)(2)La[(&mgr;-P(t)Bu(2))(2)Li(thf)] (1). Yb(OSO(2)CF(3))(3) reacts with LiP(t)Bu(2) in tetrahydrofuran in a 1:5 ratio to produce Yb[(&mgr;-P(t)Bu(2))(2)Li(thf)](2) (2) and 1/2 an equiv of (t)Bu(2)P-P(t)Bu(2). Both 1 and 2 crystallize in the monoclinic space group P2(1)/c. Crystal data for 1 at 214 K: a = 11.562 (1) ?, b = 15.914 (1) ?, c = 25.373 (3) ?, beta = 92.40 (1) degrees; V = 4664.5 ?(3); Z = 4; D(calcd) = 1.137 g cm(-)(3); R(F)() = 2.61%. Crystal data for 2 at 217 K: a = 21.641 (2) ?, b = 12.189 (1) ?, c = 20.485 (2) ?, beta = 109.01 (1) degrees; V = 5108.9 ?(3); Z = 4; D(calcd) = 1.185 g cm(-)(3); R(F)() = 2.80%. The molecular structures of 1 and 2 show the four-coordinate lanthanide atoms in distorted tetrahedral environments. These complexes are the first representatives of the lanthanide elements surrounded by four only-phosphorus-containing substituents. The main features of the crystal structure of 1 are the shortest La-P distances (2.857(1) and 2.861(1) ?) reported so far and a three-coordinate lithium cation. The molecular structure of 2 represents a divalent bis "ate" complex with two three-coordinate lithium cations. Complex 2 shows photoluminescent properties. VT NMR spectra ((7)Li and (31)P) are reported for 1and 2.     

Bimanes 28: Extraction of sulfur from fluorescent models for biological thiols

Sulfur extraction from the tripeptide thiol, glutathione (α-glu-cys-gly) ( 1 ) via reaction with syn-(1-bromo-ethyl, methyl)bimane ( 2 ) yields glutathione slfide and the thiabridged bimane, μ(S)-syn-(methylmethylene, methyl)bimane ( 3 ) [1]. The reaction with 2 has been extended to dithiols as models for important biological thiols such as reduced trypanothione. The fluorescent dithiols were derived through reductive cleavage with triphenylphosphine (tetrahydrofuan, Hcl−Kbr solution, pH 1.5) of the dithiatriclic bimane esters, μ(O₂C(CH₂)SS(CH₂)_nCO₂)-syn-(CH₂,CH₃)B, n = 1, 2, 3, prepared from syn-(bromomethyl, methyl)bimane ( 4 ) and the corresponding dithiadicarboxylic acids. Sulfur extraction led to 3 and the cyclic sulfide derived from the dithiol in moderate yields. The dithiols, dithiothreitol and dithioerythritol, also yielded moderate amounts of 3 . Sterically hindered thiols (e.g., those in hemoglobin) gave 3 in lower yields. Treatment of human red blood cells and red cells membranes (hemoglobin-free ghosts) with 2 gave rise to some 3 . A side product in some reactions was the oxabridged bimane, μ(O)-syn-(methylmethylene, methyl)bimane.     

Identification of Finite-Motion Parameters of Serial Chains via Measurement of 6 × 6 Stiffness Matrices

This paper describes a procedure for identifying geometric and stiffness parameters of a mechanical serial chain of know structure by measuring spatial 6×6 stiffness matrices at different positions. The method uses standard optimization routines to determine model parameters such that the model stiffness matrix features in the Frobenius norm the closest distance possible to the measured matrix. From this local identification, a rough model of parameters of finite-motion is created, from which new measuring positions are guessed. By applying this step repeatedly, a model for finite-displacement parameters can be obtained by a sequence of small force-displacement tests. The method is tested with a dummy device consisting of a revolute joint connecting two rigid links dressed with soft material to mimic for example muscle masses of a surrogate mechanism for the elbow joint of a human arm. Two robots grasping the upper and lower arm generate the motion while the force measurement is carried out by a six-axis force sensor. This makes the method potentially suitable for detecting anatomical parameters by in-vivo measurements. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and Structure of Magnesium Bis(hydrogen β‐glutamate) Hexahydrate

The dissociation equilibria of aqueous solutions of β‐glutamic acid were studied by potentiometric titration and the three pK values determined under standard conditions. The hydrogen β‐glutamate anion β‐GluH⁻ was found to be the dominating species in the physiologically relevant pH range 4.0–9.4. Neutralization of β‐glutamic acid by magnesium oxide affords magnesium bis(hydrogen β‐glutamate) Mg (β‐GluH)₂, which crystallizes as the hexahydrate from dilute aqueous solution. A single‐crystal X‐ray study showed that the β‐GluH⁻ anions are not part of the coordination sphere of the magnesium ion. Instead hexahydrated dications [Mg(H₂O)₆]²⁺ are intimately associated with free β‐GluH⁻ anions through a three‐dimensional network of H‐bonds. This study provides the first structural and conformational reference data for the β‐GluH⁻ anion.