High-temperature synthesis, single-crystal X-ray structure determination and solid-state NMR investigations of Ba7[SiO4][BO3]3CN and Sr7[SiO4][BO3]3CN

The novel alkaline earth silicate borate cyanides Ba₇[SiO₄][BO₃]₃CN and Sr₇[SiO₄][BO₃]₃CN have been obtained by the reaction of the respective alkaline earth metals M=Sr, Ba, the carbonates M^IICO₃, BN, and SiO₂ using a radiofrequency furnace at a maximum reaction temperature of 1350°C and 1450°C, respectively. The crystal structures of the isotypic compounds M^II₇[SiO₄][BO₃]₃CN have been determined by single-crystal X-ray crystallography (P6₃mc (no. 186), Z=2, a=1129.9(1) pm, c=733.4(2) pm, R₁=0.0336, wR₂=0.0743 for M^II=Ba and a=1081.3(1) pm, c=695.2(1) pm, R₁=0.0457, wR₂=0.0838 for M^II=Sr). Both ionic compounds represent a new structure type, and they are the first examples of silicate borate cyanides. The cyanide ions are disordered and they are surrounded by Ba²⁺/Sr²⁺ octahedra, respectively. These octahedra share common faces building chains along [001]. The [BO₃]³⁻ ions are arranged around these chains. The [SiO₄]⁴⁻ units are surrounded by Ba²⁺/Sr²⁺ tetrahedra, respectively. The title compounds additionally have been investigated by ¹¹B, ¹³C, ²⁹Si, and ¹H MAS-NMR as well as IR and Raman spectroscopy confirming the presence of [SiO₄]⁴⁻, [BO₃]³⁻, and CN⁻ ions.     

Structure elucidation of β-carotene isomers by HPLC-NMR coupling using a C30 bonded phase

The separation of cis/trans isomers of β-carotene has been performed with a C₃₀ stationary phase employing ¹H NMR spectroscopy as an on-line detection technique. 1D as well as 2D NMR spectra have been recorded in the stopped-flow mode for the predominant chromatographic peaks. Structural assignment of the five identified isomers was performed via comparison of simulated 1D ¹H NMR spectra on the basis of the structures of β-carotene cis/trans isomers with the experimental data, and also by the analysis of the proton-proton connectivities in the 2D NMR spectra of three isomers with the highest concentration. The chromatographic retention behaviour of the isomers agreed well with previously reported data. The advantage of the applied hyphenated coupling technique compared to conventional off-line techniques lies in the fact that chromatographic separation and NMR detection are performed in a closed system, so that reisomerization of the separated compounds is inhibited. Received: 29 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996     

Detection of Amadori compounds by capillary electrophoresis coupled to tandem mass spectrometry

Capillary electrophoresis coupled to mass spectrometry (CE-MS) is reported for the first time as an alternative and powerful analytical method for the characterization and monitoring of N-substituted 1-amino-1-deoxyketoses (Amadori compounds). It allows rapid separation and identification of Amadori compounds, while benefiting from the well-known advantages of MS, such as specificity and sensitivity. Amadori compounds of several amino acids, such as glycine, valine, isoleucine, methionine, proline, and phenylalanine, as well as a cysteine-derived compound, were separated and/or discriminated using CE-MS/MS under standard conditions. The technique may also be useful to study the stability and degradation kinetics of other labile charged Maillard intermediates that play an important role in food and medical science.     

Resolution enhancement in multidimensional solid-state NMR spectroscopy of proteins using spin-state selection

We show that the resolution of homonuclear multidimensional solid-state NMR correlation experiments can be significantly improved using transition selection and spin-state-selective polarization transfer techniques. The selection and transfer of single states allow the removal of the J-coupling contribution from the line width in both the direct and indirect spectral dimensions. This is demonstrated with a new spin-state-selective CO-Calpha correlation experiment, applied to a microcrystalline 85-residue protein. With this new sequence, all four components of the CO-Calpha cross-peaks are separated into different spectra, obtained by linear combination of four recorded data sets. Line narrowing of up to 44% was obtained on the protein sample for the spin-state-selective CO-Calpha spectrum compared to a standard spin-diffusion experiment. The new technique also allows an easy distinction between "direct" and "relayed" transfer cross-peaks.     

PHYTOCHROME EVOLUTION: A PHYLOGENETIC TREE WITH THE FIRST COMPLETE SEQUENCE OF PHYTOCHROME FROM A CRYPTOGAMIC PLANT: (Selaginella martensii SPRING)

We have sequenced cDNA and genomic clones coding for phytochrome of the fern Selaginella. On the amino acid level, this phytochrome shares sequence homologies with phytochromes of higher plants which range between 62 (phytochrome B of Arabidopsis) and 55 (56)% [phytochrome C of Arabidopsis (Avena)]. Introns in the Selaginella gene are short and occupy positions known from phytochrome sequences of higher plants. A rooted phylogenetic tree based on mutation distances puts Selaginella phytochrome closest to the hypothetical ancestor. A similar tree arises if the tree is constructed with partial sequences (about 200 amino acids) around the chromophore attachment site. An extension of this tree by sequences of other cryptogamic plants (Mougeotia, Ceratodon, Psilotum) shows all these sequences including those of the phytochromes B and C of Arabidopsis on a branch, well separated from the branch formed by phytochromes known to accumulate in etiolated plants. The rooted phytochrome phylogenetic tree, however, is difficult to reconcile with the fossil record.     

Influence of the coordination number of nitrogen on the structure of 6aλ4-thia-1,3,4,6-tetraazapentalenic systems. Crystal structure analyses of 3-(2-pyridylimino)-3H-[1,2,4]thiadiazolo[4,3-a]pyridine and its 1-methylated salt

Structural data were obtained by X-ray crystallography for the title compounds which show that they are essentially planar and exhibit an approximately linear N2-S1-N8 arrangement. In compound 3 the separation between the sulfur atom and the pyridine nitrogen atom (2.61 Å) is larger than the Huggins constant energy distance (2.58 Å), suggesting that there is little or no bonding between them. The methylated salt 4 , on the contrary, has a closer S…N(pyridine) distance (2.19 Å) with an estimated bond dissociation energy of 6 kcal/mole.     

Laccase-catalyzed carbon-carbon bond formation: oxidative dimerization of salicylic esters by air in aqueous solution

The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated.     

Carbohydrate chain of ganglioside GM1 as a ligand: identification of the binding strategies of three 15 mer peptides and their divergence from the binding modes of growth-regulatory galectin-1 and cholera toxin

The branched pentasaccharide chain of ganglioside GM1 is a prominent cell surface ligand, for example, for cholera toxin or tumor growth-regulatory homodimeric galectins. This activity profile via protein recognition prompted us to examine the binding properties of peptides with this specificity. Our study provides insights into the mechanism of molecular interaction of this thus far unexplored size limit of the protein part. We used three pentadecapeptides in a combined approach of mass spectrometry, NMR spectroscopy and molecular modelling to analyze the ligand binding in solution. Availability of charged and hydrophobic functionalities affected the intramolecular flexibility of the peptides differently. Backfolding led to restrictions in two cases; the flexibility was not reduced significantly by association of the ligand in its energetically privileged conformations. Major contributions to the interaction energy arise from the sialic acid moiety contacting Arg/Lys residues and the N-terminal charge. Considerable involvement of stacking between the monovalent ligand and aromatic rings could not be detected. This carbohydrate binding strategy is similar to how an adenoviral fiber knob targets sialylated glycans. Rational manipulation for an affinity enhancement can now be directed to reduce the flexibility, exploit the potential for stacking and acquire the cross-linking capacity of the natural lectins by peptide attachment to a suitable scaffold.     

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La _x Sr _y MnO₃ cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.Dedicated to Professor Dr. rer. nat. Hubertus Nickel on the occasion of his 65th birthday     

Reactivity sequences of dipolarophiles towards diazocarbonyl compounds - MO perturbation treatment

Whereas diazomethane cycloadditions are only accelerated by electron-attracting substituents in the olefinic or acetylenic dipolarophile, the cycloadditions of diazoacetic, diazomalonic and diazo(phenylsulfonyl)acetic ester show in accordance with the PMO treatment U-shaped activity functions when log k₂ is plotted versus the lowest IP of the dipolarophiles.