Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl series: Synthesis of (6,6′-dimethylbiphenyl-2,2′-diyl)bis(diphenylphosphine) (‘BIPHEMP’) and analogues,and their use in Rh(I)-catalyzed asymmetric isomerizations of N,N-diethylnerylamine

The axially dissymmetric diphosphines (?)-(R)- and (+)-(S)-(6-6′-dimethylbiphenyl-2,2′-diyl)bis(diphenyl-phosphine) ((?)-(R)- 10 and (+)-(S)- 10 ; ‘BIPHEMP’) have been synthesized, starting from (R)- and (S)-6,6′-dimethylbiphenyl-2,2′-diamine ((R)- and(S)- 16 ), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′- dimethyl- and 4,4′-bis(dimethylamino)-substituted analogues 11 and 12 respectively, and the 6,6′-bridged analogues 1,11-bis(diphenylphosphino)-5,7-dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)- and(S)-enantiomers via complexation with di-μ-chlorob is {(R)-2-[1-(dimethylamino)ethyl]pheny-C? N}dipalladium(II) ((R)- 18 ). The molecular structures of the diphosphines (S)- 10 and (R)- 13 and of two derived cationic Rh(I) complexes,[Rh((S)- 10 )(nbd)]BF₄ and [Rh((R)- 13 )(nbd)]BF 4 were determined by x-ray analyses. Absolute configurations were established for (+)-(S)- 10 by X-ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (?)-(R)- 13 by X-ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 11 12 were achieved by means of ¹H-NMR comparisons. The BIPHEMP ligand 10 and analogues 11 , 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry-inducing ligands in Rh(I)-catalyzed isomerizations of N,N-diethylnerylamine affording citronellat enamine of 98-99% ee.     

Hyperfine structure and isotope shift of some even parity levels in the YbI spectrum

Using laser induced fluorescence spectroscopy the hyperfine structure of the even parity levels 4f ¹⁴6s6d ³ D ₁, 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 as well as of the odd parity level 4f ¹⁴ 6s6p ³ P ₂ in neutral ytterbium has been investigated. The isotope shift of the transitions 4f ¹⁴6s6p ³ P ₀ → 4f ¹⁴ 6s6p ³ D ₁ and 4f ¹⁴ 6s6p ³ P ₂ → 4f ¹⁴ 6s8s ³ S ₁, 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 could be measured with high accuracy. The results for the 4f ¹⁴ 6s6p ³ D ₁ level show a considerable influence of second order effects of the hyperfine interaction. The isotope shifts of the 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1 levels indicate a possible configuration mixing for these levels.     

Automatic Bi trace analysis integrated in the manufacturing process of turbine blades

Summary In the manufacture of aero-engine components, auxiliary materials are used which impair mechanical properties if they are not completely removed afterwards. Taking the manufacture of turbine blades and vanes as an example, this investigation shows how the inclusion of an analysis stage in the fully-automatic production cycle makes it possible to monitor the thoroughness of the cleaning process. As indicator, the element Bi is used; the matrix consists of concentrated nitric acid with a high nickel content. Because of the imposition of a limiting value, it must be possible to determine differences in the Bi-content of 20 g/l. The main part of the paper concerns the selection of the most optimum process. The results using two types of AAS coupled with hydride generation are presented. The success of the complete system is illustrated by the summarized results.     

Polyacetylenes and Cumulenes,Potential Elements for Molecular Machines and Precursors of Carbon Clusters: A Theoretical Study

A recently described very simple procedure for estimating Hartree–Fock (H. F.) energy and accurate nonrelativistic energy has been used with simple hydrocarbons possessing C?C or C?C bonds and for the acetylene dimer. Experimental characteristics (heats of formation, ionization potentials, electron affinities), structural features, and reactivity have been discussed in terms of quantum‐chemistry characteristics at the H. F. level and also at a level including a part of electron correlation. Deviations from linearity with derivatives of long polyacetylenes and cumulenes are ascribed to the lowest‐energy deformation vibrations, which decrease rapidly when passing from short to long acetylenic and cumulenic chains. The role of derivatives and heteroanalogues of hydrocarbons under study in atmospheric and interstellar chemistry is briefly mentioned. Derivatives with enhanced stability represent potentially promising construction materials for molecular devices and also resources for the preparation of defined clusters of C‐atoms.     

Site-specific amide hydrogen/deuterium exchange in E. coli thioredoxins measured by electrospray ionization mass spectrometry

Mass spectrometry as an analytical tool to study protein folding and structure by hydrogen/deuterium exchange is a relatively new approach. In this study, site-specific amide deuterium content was measured in oxidized and reduced E. coli thioredoxins by using the b(n) ions in electrospray ionization CID MS/MS experiments after 20-s incubation in D(2)O phosphate-buffered solution (pH 5.7). The deuterium levels correlated well with reported NMR-determined H/D exchange rate constants. The deuterium measured by y(n) ions, however, showed much less reliable correlation with rate exchange data. In general, residues in alpha helices and beta sheets, when measured by b(n) ions, showed low incorporation of deuterium while loops and turns had high deuterium levels. Most amide sites in the two protein forms showed similar deuterium levels consistent with the expected similarity of their structures, but there were some differences. The turn consisting of residues 18-22 in particular showed more variability in deuterium content consistent with reported structural differences in the two forms. The deuterium uptake by thioredoxins alkylated at Cys-32 by S-(2-chloroethyl)glutathione and S-(2-chloroethyl)cysteine, in peptides 1-24 and 45-58, was similar to that observed for oxidized and reduced thioredoxins, but several residues, particularly Leu-53 and Thr-54, showed slightly elevated deuterium levels, suggesting that structural changes had occurred from alkylation of the protein at Cys-32. It is concluded that b(n) ions are reliable for determining the extent of site-specific amide hydrogen isotope exchange and that mass spectrometry is useful as a complementary technique to NMR and other analytical methods for probing regional structural characteristics of proteins.     

Synthesis of a Sialyl Lewis x Mimic with Fixed Carboxylic Acid Group: Chemical Approach toward the Elucidation of the Bioactive Conformation of Sialyl Lewis x

The relation of the solution and bioactive conformation of sialyl Lewis x (sLe(x)) has been addressed by chemical means. To mimic the preferred solution conformation of sLe(x) 1, the more rigid analog 2 has been designed and synthesized. The sialic acid residue of 1 was replaced by a carboxylic acid function which is fixed in the equatorial position of a six membered ring acetal fused to galactose. Due to entropic considerations, an increased biological activity could be expected if the preferred solution conformation and bound form of sLe(x) were similar. Since mimic 2 was found to be inactive in an E-selectin binding assay, the bound form of sLe(x) most probably differs from the prevailing solution conformation.     

S(N)1-like reactions of bicyclic alpha-amino ethers with sulfur,nitrogen, and carbon nucleophiles. Synthesis of 1-azabicyclo[3.2.2]nonanes functionalized at carbon C2 and C6 with complete stereocontrol

[reaction: see text] In the presence of nucleophiles, Lewis acid mediated cleavage of alpha-amino ethers derived from quincorine and quincoridine affords a variety of C2-substituted and C6-vinylated 1-azabicyclo[3.2.2]nonanes. These are enantiopure and are formed in S(N)1-like reactions with complete stereocontrol. There is no leakage into 2-Nu en route to product 1-Nu or vice versa. Me(3)SiCN provides new Strecker-type alpha-amino nitriles. In the presence of TTMPP-BF(3).OEt(2), the ketene acetal Me(2)C=C(OMe)OSiMe(3) delivers enantiopure bicyclic beta-amino acid esters.     

Electrophoretic clean-up of organic acids from coffee for the GC/MS analysis

The clean-up presented here includes a free flow field step electrophoresis followed by ultrafiltration. Thus, organic acids can be separated from non-acidic and high-molecular compounds in roasted and instant coffee. The acids are identified by gas chromatography/mass spectrometry after freeze-drying and trimethylsilylation. With the method presented, 31 acids could be identified in commercial roasted coffee blends and in instant coffee, among them for the first time in coffee: 3-hydroxypropionic, 2-oxobutyric, glyceric, 2,4-dihydroxybutyric, 5-hydroxymethylfuran-2-carboxylic and 2-hydroxyglutaric acid.     

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces

Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface.