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Analytical and Bioanalytical Chemistry (v.357, #5)
A significant improvement of the gradient selected SELINCOR technique by Ronald Wagner; S. Berger (pp. 470-472).
The gradient selected SELINCOR sandwich, a NMR pulse sequence for selecting the signal of a proton bound to a specific carbon atom, was modified and significantly improved by using a 180° selective pulse on carbon. The sequence provides artifact-free carbon selected proton spectra and can serve as a building block for various applications.
77Se shielding tensors of diphenyl diselenide, comparison of the results from CP/MAS NMR spectroscopy and IGLO calculations by Gert Balzer; H. Duddeck; U. Fleischer; Florian Röhr (pp. 473-476).
The cross-polarization/magic-angle-spinning (CP/MAS) 77SeNMR experiment of Ph-Se-Se-Ph affords two signal series with isotropic chemical shifts at δiso = 425 and 350. IGLO calculations allow to assign the 77Se signals and to predict the orientation of the shielding tensors. The different chemical shifts can be explained by different torsion angles Se-Se-Cipso-Cortho which produce different β effects of the phenyl rings upon the respective next but one selenium atom.
Assignment of E/Z isomers in Schiff bases of 3-acyltetramic acids with ethylenediamine by 1H and 13C NMR spectroscopy by Oliver Tietze; Birgit Schiefner; Burkhard Ziemer; A. Zschunke (pp. 477-481).
The reaction of ethylenediamine with an equivalent mixture of diversely substituted 3-acyltetramic acids leads to Z/Z, Z/E, E/Z and E/E isomers. The E/Z isomerisation is slow in the NMR time scale of the 1H and 13C chemical shifts; therefore at room temperature and in deuterochloroform all isomers of the new synthesized asymmetric compounds N,N′-ethylene-(1-ethyl-5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) a, N,N′-ethylene-(5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) b and, N,N′-ethylene-(1,5,5-trimethyl-1′,5′,5′-trimethyl-3-acetyl-3′-formyl-tetramic acid) c could be found in the corresponding spectra. To assign the 13C NMR signals we used two-dimensional 13C-1H one-bond (HMQC) and 13C-1H multibond (HMBC) correlated spectroscopy and the empirical rule that CO signals involved in hydrogen bonds are shifted to a lower field. The relative stability of isomers depending on substitution pattern could be estimated from the composition of the equilibria. b crystallizes as Z/Z isomer from ethanolic solution. The X-ray structural analysis of b has shown two CH-O hydrogen bonds.
Simultaneous comparison of δ31P and 1JPN for the assignment of E/Z-stereochemistry of the phosphorus-nitrogen double bond in iminophosphines R-P=N-R′ by D. Gudat; E. Niecke (pp. 482-484).
The analysis of 31P and 15N NMR data of a series of 40 iminophosphines R-P=N-R′ reveals that the E/Z-stereochemistry of the PN double bond can be predicted on the basis of a simultaneous comparison of the values of δ31P and 1JPN.
Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates by A.-R. Grimmer; D. Müller; G. Gözel; R. Kniep (pp. 485-488).
11B and 31P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO5 and BPO4 represent nearly pure samples, SrBPO5 contains β-Sr2P2O7 as well as BPO4 as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO4 and PO4 building units.
Di-tert-butyl(N-pyrrolyl)phosphane,-sulfide, and-selenide, studied by multinuclear magnetic resonance by B. Wrackmeyer; Gerald Kehr; Hong Zhou (pp. 489-493).
Di-tert-butyl(N-pyrrolyl)phosphane (1),-sulfide (2) and-selenide (3) were studied by 1H, 13C, 15N, 31P and 77Se NMR spectroscopy in solution. Restricted rotation about the P–N bond was observed for 1 (ΔG≠ C≈58.5 kJ/mol) and 2, 3 (ΔG≠ C≈45 kJ/mol) by 1H and 13C NMR at variable temperature. The fairly high pyrrolyl rotation barrier in 1 is ascribed to the expected steric effects exerted by the tert-butyl groups and to repulsion between the lone pairs of electrons at the phosphorus and nitrogen atoms. These repulsive forces are reduced in 2 or 3, or in di-tert-butyl(phenyl) phosphane (ΔG≠ C≈44 kJ/mol). Signs of coupling constants nJ(31P, 13C) and n+1J(31P, 1H) (n=2, 3) were determined by two-dimensional (2D) 13C/1H heteronuclear shift correlations. The preferred orientation of the pyrrolyl group in 1 is evident from the coupling constants 2J(31P, 13C(2))=+35.4 Hz and 2J(31P, 13C(5))=−9.3 Hz, typical of C(2) in syn and C(5) in anti position with respect to the assumed axis of the phosphorus lone pair. Hahn-echo extended (HEED) polarization transfer pulse sequences served for measuring 1J(31P, 15N) and isotope induced chemical shifts 1Δ15/14N(31P) from 31P NMR spectra.
Discrimination by NMR spectroscopy of isomeric ar,ar′-disubstituted [2.2] paracyclophanes carrying identical substituents by Ludger Ernst (pp. 494-497).
Four diastereomers are formed when precursors of the type 2-R-1,4-(CH2X)2C6H3 are coupled in the synthesis of symmetrical [2.2]paracyclophanes with one substituent R per aromatic ring. The stereochemistry of the diastereomers is derived from the symmetry of their 1H NMR spectra and from NOE difference and 2D C,H-COSY and -COLOC spectra for the case of R=CO2CH3. This substituent causes only small 1H chemical shift effects in the distant aromatic ring; so the results of chemical shift increment calculations should be regarded with caution. For the present compounds, the use of 13C shift increments is safer, but the disadvantage of increment calculations is the need for the mono-substituted derivative and the analysis of its spectra.
Structure elucidation of β-carotene isomers by HPLC-NMR coupling using a C30 bonded phase by Sabine Strohschein; Matthias Pursch; Heidrun Händel; K. Albert (pp. 498-502).
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.
29Si NMR investigations on oligosilane dendrimers by U. Herzog; C. Notheis; E. Brendler; G. Roewer; B. Thomas (pp. 503-504).
Starting with the high functionalized trisilane SiClMe(SiCl2Me)2 and tetrasilane SiMe(SiCl2Me)3 several octa- and decasilane dendrimers containing directly neighboured branchings were prepared. In these compounds the 29Si NMR chemical shifts of the different silyl groups are shifted towards lower field compared with those of analogous groups in tetra- or hexasilanes. This observation is a helpful tool for the characterization of further dendritic oligomers by 29Si NMR.
Solid state 13C MAS NMR as a tool for the study of reactions between compounds adsorbed on porous materials by Michael Ebener; Volkhard Francke; H. Günther (pp. 505-507).
It is shown that magic angle spinning (MAS) solid state 13C NMR spectroscopy is a valuable tool for the study of reactions between compounds adsorbed on porous materials because it allows the direct characterization of surface species. The mobility of the adsorbed species yields high-resolution 13C spectra at moderate spinning speeds (4 kHz) from which the reactions can be traced. Catalysis of KMnO4 oxidation of alcohols and proton transfer by the solid support is demonstrated.
Determination of the pore widths of highly porous materials with NMR microscopy by J. Pauli; G. Scheying; C. Mügge; A. Zschunke; P. Lorenz (pp. 508-513).
The quantitative characterization of macro-porous materials with regard to pore width and pore width distribution was accomplished for the first time by using 1H-NMR microscopy in combination with suitable methods of digital image analysis. Here we present the newly developed algorithm and discuss the first experimental results. Large-pored glass filter systems filled with silicon oil as intrusion fluid were used as references. Silicates of unknown pore width were analyzed both with the new method and with Hg intrusion. NMR image data were recorded using a 3D spin echo sequence, which gave 128 slice images with a spatial resolution of 14.5 μm × 14.5 μm within each slice, with a slice-thickness of 37 μm or 48 μm. A quantitative evaluation of the 3D NMR data, with regard to pore width and pore width distribution, was done using the appropriate image processing function of the HORUS program. Individual slice evaluation was performed first, followed by an analysis of the binding elements between the slices. Pore widths of the glass filters determined using this analytical algorithm were in accordance with the manufacturer’s values, and silicate pore widths were in good agreement with the values determined by Hg intrusion.
The use of 29Si NMR to characterize the sol-gel synthesis of cordierite by H. Jancke; B. Unger; R. Müller (pp. 514-516).
Cordierite powder was synthesized via different sol-gel procedures. The use of 29Si NMR spectra of all stages beginning from tetraethoxysilane (TEOS) up to final ceramic powder material is discussed. In the early stages of the sol-gel process all oligomeric structure units can be identified. Spectra of the higher condensed sols only allow the quantification of Qn-groups. MAS spectra of gels heated up to 750 °C show no fine structure to be evaluated. Spectra of samples heated to 1250 °C indicate a sluggish disorder-order transformation from hexagonal α-cordierite to orthorhombic cordierite.
Dynamic NMR study of the flexibility of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts by Matthias Heydenreich; Andreas Koch; E. Kleinpeter; Thomas Zimmermann (pp. 517-521).
Dynamic NMR investigations of a number of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts were carried out. The barrier to rotation of the partial C, N double bond was determined and proved to be in the range of 62 to 63 kJ/mol. Quantum chemical calculations of bond orders and electron densities of the different atoms in the molecules show the distinct double bond character of the exocyclic C, N bond. This is in agreement with the relatively high barrier to rotation. By quantum chemical ab initio 3-21G calculations, the dynamic behaviour of this kind of compounds was simulated; two pairs (image and mirror image) of ground state conformations, in coincidence with the experiment, were obtained.
Three-way Principal Components Analysis for fluorescence spectroscopic classification of algae species by R. Henrion; G. Henrion; M. Böhme; H. Behrendt (pp. 522-526).
Excitation-emission matrices (EEM) from fluorescence spectroscopy may contain characteristic information about different algae species. As a result of measurements, one gets a whole stack of EEMs each of them corresponding to one species. Such a stack of matrices has to be understood as a cubic data array spanned by the dimensions ‘excitation’, ‘emission’ and ‘species’. The interpretation of higher dimensional data arrays requires efficient tools from multivariate data analysis. In this paper, it is illustrated how Three-way Principal Components Analysis as the appropriate generalization of conventional Principal Components Analysis may serve as a powerful method for classification of algae species.
Representation of extended infrared spectrum-structure-correlations based on fuzzy theory by F. Ehrentreich (pp. 527-533).
The theory of fuzzy sets was applied to specific infrared spectrum-structure-correlations. The scheme was translated into a rule base named CorTab (from Correlation Tables). The data are split into three main data files consisting of the structural information, the spectral properties and the cross references. The first two files contain the fragments and the ranges of the spectroscopic features, i.e. position, intensity and band width, and also the empirical knowledge about the plausibility or constraints of the correlations. The cross references assign the spectral to the structural properties and contain the connections between the fragments in the network of the fragments. The flexibility of the design allows the ongoing accumulation of spectrum-structure-correlations from different literature sources or the storage of computer derived rules. The rule base CorTab is a prerequisite for the structure elucidation performed by an ensemble of interpretation systems relying on fuzzy logic. A survey of the arrangement and contents of the rule base and the procedures that transform the verbally given knowledge into linguistic – fuzzified – variables are reported herein.
Activated platinum electrodes as transducer for a glucose sensor using glucose oxidase in a photopolymer membrane by D. Wilke; H. Müller; N. Kolytsheva (pp. 534-538).
A planar platinum electrode was covered by a photopolymer membrane containing glucose oxidase (GOD) to construct an amperometric glucose sensor. The application of a photopolymer system in membrane formation gives the opportunity to manufacture cheap biosensors with good reproducibility by means of automated techniques and to miniaturise sensors using photolithography. The electrodes were pretreated mechanically and chemically resulting in a half-wave potential (E1/2) of the H2O2 oxidation shifted towards more negative potentials. This shift allows the determination of glucose at a low working potential (300 mV vs. SCE) without addition of mediators. The important advantage of such applied potential decreasing lies in minimising the interference of oxidisable substances such as uric acid, bilirubin and paracetamol. The selectivity to ascorbic acid could also be proved without the application of additional protection layers. The glucose sensor developed has a high life-time, selectivity and sensitivity and a linear working concentration range from 0.05 up to 10 mmol/l of glucose. The sensor was used for the glucose determination in human serum samples with a very good correlation to a common photometric reference method.
Separation of ADAM derivatives of carnitine and acyl-carnitines by capillary electrophoresis by S. Kiessig; C. Vogt; G. Werner (pp. 539-542).
The separation of carnitine, acetylcarnitine and palmitoylcarnitine as ADAM (9-anthryldiazo-methane) derivatives was performed using capillary electrophoresis. A buffer system with 90% methanol and various amounts of phosphoric acid and micelle forming SDS was optimized with respect to the best resolution of the carnitine derivatives. A detection limit of 10 μmol/l or 32 ng carnitine was determined by laser induced fluorescence detection. Under optimized conditions low carnitine contents in acylcarnitine standards have been determined.
Rock porosity determination by combination of X-ray computerized tomography with mercury porosimetry by P. Klobes; H. Riesemeier; K. Meyer; J. Goebbels; K.-H. Hellmuth (pp. 543-547).
First results are described of coupling of mercury porosimetry with X-ray computerized tomography (CT) as a new combination technique for rock porosity studies. This technique is suitable for rock samples with a pronounced mercury intrusion-extrusion hysteresis and includes CT measurements before and after mercury intrusion. The entrapped portion of mercury, when the pressure after the intrusion into the rock sample is reduced to 0.1 MPa, serves as a contrast agent in the porous network to localize spatial distribution of rock porosity by CT. The results obtained show that the mercury intrusion and therefore the porosity were quite different for the separate mineral phases. Therefore the combination of mercury porosimetry and computer tomography can give 3-D data on mineral-specific porosity distributions with additional pore size information. In contrast to mercury porosimetry as a single method, results of the combination technique with CT represent a direct visualization of porosity variation and do not depend on any special pore network model.
HPLC fractionation and structural dynamics of humic acids by G. Woelki; S. Friedrich; G. Hanschmann; R. Salzer (pp. 548-552).
Different soil extracted humic acids as well as a commercial humic acid sodium salt were fractionated by HPLC. An almost complete recovery could be achieved for the dissolved material. All humic samples show a typical chromatogram of at least five fractions. The separation of humic substances is influenced by an altered hydrophobicity due to changes in the tertiary structure. Three fractions were further investigated by Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy and by HPLC/HPLC separation. DRIFT spectroscopy provided data on the primary structure, whereas HPLC/HPLC results gave insight into the secondary and tertiary structure and their changes.
Direct analysis of mineral components in wine by inductively coupled plasma optical emission spectrometry (ICP-OES) by G. Thiel; K. Danzer (pp. 553-557).
A direct measuring method for the determination of 15 inorganic components in wine by ICP-OES was developed. It was applied to 17 white wines from 6 German wine-growing regions. In these investigations 15 elements (B, V, Mn, Zn, Fe, Al, Cu, Sr, Ba, Rb, Na, P, Ca, Mg and K) were involved. By using alcoholic calibration solutions the results of the direct measuring method are comparable with those of the control methods. Typical patterns of elements obtained by the multicomponent analyses can be evaluated by multivariate data analysis to recognize the origin of the wines.
Water pollution screening by large-volume injection of aqueous samples and application to GC/MS analysis of a river Elbe sample by S. Müller; J. Efer; W. Engewald (pp. 558-560).
The large-volume sampling of aqueous samples in a programmed temperature vaporizer (PTV) injector was used successfully for the target and non-target analysis of real samples. In this still rarely applied method, e.g., 1 mL of the water sample to be analyzed is slowly injected direct into the PTV. The vaporized water is eliminated through the split vent. The analytes are concentrated onto an adsorbent inside the insert and subsequently thermally desorbed. The capability of the method is demonstrated using a sample from the river Elbe. By means of coupling this method with a mass selective detector in SIM mode (target analysis) the method allows the determination of pollutants in the concentration range up to 0.01 μg/L. Furthermore, PTV enrichment is an effective and time-saving method for non-target analysis in SCAN mode. In a sample from the river Elbe over 20 compounds were identified.