Günter Hempel - Academia.edu (original) (raw)
Papers by Günter Hempel
CCDC 105864: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Porous interpenetrated zirconium-organic frameworks (PIZOFs) are a class of Zr-based metal-organi... more Porous interpenetrated zirconium-organic frameworks (PIZOFs) are a class of Zr-based metal-organic frameworks (MOFs) which are composed of long, rod-like dicarboxylate linkers and Zr 6 O 4 (OH) 4 (O 2 C) 12 nodes. Long oligoethylene glycol or aliphatic side chains are covalently attached to the linker molecules in the cases of PIZOF-10 and PIZOF-11, respectively. These side chains are supposedly highly mobile, thus mimicking a solvent environment. It is anticipated that such MOFs could be used as a solid catalyst-the MOF-with pore systems showing properties similar to a liquid reaction medium. To quantify the side-chain mobility, here we have applied different 1D and 2D NMR solid-state spectroscopic techniques like cross-polarization (CP) and dipolar-coupling chemical-shift correlation (DIPSHIFT) studies. The rather high 1 H-13 C CP efficiency observed for the CH 2 groups of the side chains indicates that the long side chains are unexpectedly immobile or at least that their motions are strongly anisotropic. More detailed information about the mobility of the side chains was then obtained from DIPSHIFT experiments. Analytical expressions for elaborate data analysis are derived. These expressions are used to correlate order parameters and to slow motional rates with signals in indirect spectral dimensions, thus enabling the quantification of order parameters for the CH 2 groups. The ends of the chains are rather mobile, whereas the carbon atoms close to the linker are more spatially restricted in mobility.
Müller, August Eberhard
Oxford University Press eBooks, 2001
Solid-state 13C-NMR spectroscopic determination of sidechain mobilities in zirconium-based metal-organic frameworks
. Porous Interpenetrated Zirconium-Organic Frameworks (PIZOFs) are a class of Zr-based metal-orga... more . Porous Interpenetrated Zirconium-Organic Frameworks (PIZOFs) are a class of Zr-based metal-organic frameworks (MOFs) which are composed of long, rodlike dicarboxylate linkers and Zr6O4(OH)4(O2C)12 nodes. Long oligoethylene glycol or aliphatic side chains are covalently attached to the linker molecules in the case of PIZOF-10 and PIZOF-11, respectively. These side chains are supposedly highly mobile thus mimicking a solvent environment. It is anticipated that such MOFs could be used as solid catalyst – the MOF – with pore systems showing properties similar like a liquid reaction medium. To quantify the side chain mobility, we have here applied different 1D and 2D NMR solid-state spectroscopic techniques like cross polarization (CP) and dipolar-coupling chemical-shift correlation (DIPSHIFT) studies. The rather high 1H-13C CP efficiency observed for the methylene groups of the side chains indicates that the long side chains are unexpectedly immobile or at least that their motions are strongly anisotropic. More detailed information about the mobility of the side chains was then obtained from DIPSHIFT experiments. Analytical expressions for elaborate data analysis are derived. These expressions are used to correlate order parameters and slow motional rates with signals in indirect spectral dimension thus enabling the quantification of order parameters for the methylene groups. The ends of the chains are rather mobile whereas the carbon atoms close to the linker are stronger spatiallly restricted in mobility.
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
RSC Advances, 2019
NMR spectroscopy at two magnetic field strengths was employed to investigate the dynamics of dime... more NMR spectroscopy at two magnetic field strengths was employed to investigate the dynamics of dimethylimidazolium dimethylphosphate ([C 1 C 1 IM][(CH 3) 2 PO 4 ]). [C 1 C 1 IM][(CH 3) 2 PO 4 ] is a low-melting, halogen-free ionic liquid comprising of only methyl groups. 13 C spin-lattice relaxation rates as well as self-diffusion coefficients were measured for [C 1 C 1 IM][(CH 3) 2 PO 4 ] as a function of temperature. The rotational correlation times, s c , for the cation and the anion were obtained from the 13 C spin-lattice relaxation rates. Although from a theoretical point of view cations and anions are similar in size, they show different reorientation mobilities and diffusivities. The self-diffusion coefficients and the rotational correlation times were related to the radii of the diffusing spheres. The analysis reveals that the radii of the cation and the anion, respectively, are different from each other but constant at temperatures ranging from 293 to 353 K. The experimental results are rationalised by a discrete and individual cation and anion diffusion. The [(CH 3) 2 PO 4 ] À anion reorients faster compared to the cation but diffuses significantly slower indicating the formation of anionic aggregates. Relaxation data were acquired with standard liquid and magic-angle-spinning NMR probes to estimate residual dipolar interactions, chemical shift anisotropy or differences in magnetic susceptibility within the sample.
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
Investigation of the Polymer Structure Using the High-Resolution 13C-NMR in Solids
Springer eBooks, 1979
From highly resolved 13C spectra of solid polymers we obtained distribution functions for the shi... more From highly resolved 13C spectra of solid polymers we obtained distribution functions for the shielding tensor elements. These functions contain information about the structure of the amorphous regions. Furthermore, in oriented polymers it is possible to get a function which describes the distribution of the monomer unit orientations
Chemical Physics Letters, May 1, 2012
An NMR experiment is presented for measuring spin-diffusion coefficients and observing homonuclea... more An NMR experiment is presented for measuring spin-diffusion coefficients and observing homonuclear spin-flip processes. The magnetization is erased or even inverted in a multitude of spatially confined regions containing only one or a few spins ('hole burning'). During the following time evolution of these holes, the following three time regimes can be observed: (i) local spin dynamics, (ii) spin diffusion towards a uniform average magnetization, and (iii) longitudinal nuclear magnetic relaxation. The oscillating characteristic of magnetization exchange between neighboring protons is demonstrated on a liquid crystal.
Physical Chemistry Chemical Physics
Pulse sequence of the proton-decoupled 15N R1ρ experiment.
Trajectory-Based Approach for the Analysis of CODEX Solid-State Exchange Experiments in the Slow and Intermediate Motion Regime: Comparison of Experiment, Simulation, and Analytical Treatment
The Journal of Physical Chemistry C, 2021
We present an efficient approach to analyze CODEX-MAS exchange NMR data by comparing the experime... more We present an efficient approach to analyze CODEX-MAS exchange NMR data by comparing the experimental results with simulated data that are calculated from separately simulated motional trajectories...
Solid State Nuclear Magnetic Resonance, 2002
Solid-state spin-lattice relaxation in the rotating frame permits the investigation of dynamic pr... more Solid-state spin-lattice relaxation in the rotating frame permits the investigation of dynamic processes with correlation times in the range of microseconds. The relaxation process in organic solids is driven by the fluctuation of the local magnetic field due to the dipole-dipole interaction of the probe nuclei (13 C; 15 N) with 1 H in close proximity. However, its effect is often hidden by a competing relaxation process due to the contact between the rotating frame 13 C= 15 N Zeeman and 1 H dipolar reservoirs. In most cases the latter process becomes superior for the commonly applied low and moderate spin-lock fields and practically does not provide information about the molecular dynamics. To suppress this undesired process and to expand the dynamic range of T 1r experiments, we present two approaches. The first one uses a resonance offset of the frequency of the spin-lock irradiation, which leads to a significant enhancement of the effective spin-lock frequency without the application of destructive high transmitter powers. We derive the theory and demonstrate the applicability of the method on various model compounds. The second approach utilizes heteronuclear 1 H decoupling during the 13 C= 15 N spin-lock irradiation which disrupts the contact between the 13 C= 15 N Zeeman and 1 H dipolar reservoirs. We demonstrate the method and discuss the results qualitatively.
Characteristic Length of Dynamic Glass Transition near Tg for a Wide Assortment of Glass-Forming Substances
The Journal of Physical Chemistry B, 2000
... within nanoporous glass or confined within mobile amorphous layers between crystal lamellas, ... more ... within nanoporous glass or confined within mobile amorphous layers between crystal lamellas, 10 confined thin film liquids under shear, 11 ... to reach such slow dynamics that is expected to have a dynamic heterogeneity, ie, below the crossover region of ... (i) The dimension of eq ...
Acta Polymerica, 1991
Das thermische Verhalten der Poly(bis‐alkylthio‐acetylen)e wurde im Temperaturbereich von 30°C bi... more Das thermische Verhalten der Poly(bis‐alkylthio‐acetylen)e wurde im Temperaturbereich von 30°C bis 600°C untersucht. Aus den Ergebnissen der thermischen Analyse, aus 13C‐Festkörper‐NMR‐ und ESR‐Messungen an den festen Thermolyserückständen und der Untersuchung der flüchtigen Pyrolyseprodukte werden mögliche Abbaureaktionen abgeleitet. Für einen weiten Zeit‐ und Temperaturbereich wird für Poly(bis‐methylthio‐acetylen) ein einfaches kinetisches Modell formuliert.
Soft Matter, 2010
The purity of all compounds and products was checked by thin layer chromatography (TLC plates; Me... more The purity of all compounds and products was checked by thin layer chromatography (TLC plates; Merck, Darmstadt, Germany). The purification of the bolaamphiphiles was carried out by middle pressure liquid chromatography (MPLC; Cartriger C-670, Fraction Collector C-660, Pump Module C-601, Pump Manager C-615, Büchi, Essen, Germany) using silica gel 60 (0.040-0.063 mm, Merck, Darmstadt, Germany) and chloroform/methanol/water as eluent (gradient technique). Melting points are uncorrected and were determined with a Boetius apparatus. NMR spectra were obtained using a Varian Inova 500 or Varian Gemini 2000 NMR spectrometer with CDCl 3 and CD 3 OD as internal standards. Mass spectrometric data were obtained with a Finnigan mass spectrometer model MAT SSQ 710 C (ESI-MS; Thermo Separation Products, San José, CA, USA and Thermoquest, Engelsbach, Germany) or were recorded on an AMD 402 spectrometer (EI-MS; 70 eV, AMD Intecta GmbH, Harpstedt, Germany). Elemental analyses were performed with a Leco CHNS-932 (Leco-Corporation, St. Joseph, MI, USA). All solvents were purified and dried before use. Commercially available reagents were supplied by Aldrich Co (Steinheim, Germany) and were used without further purification. The perdeuterated 1,12-dibromododecane (2c) was supplied by CDN-Isotopes (Dr. Ehrenstorfer GmbH, Augsburg, Germany). Sodium acetate and acetic acid (100%) were purchased from Merck (Darmstadt, Germany) and Riedel-de Haën (Seelze, Germany), respectively. 2 Hand 31 P-NMR measurements were performed in deuterium depleted water. For the SANS measurements D 2 O from Isotec Inc. (Miamisburg, OH, USA) was used. The bolalipids PC-Cn-PC (n = 34, 36), Me 2 PE-Cn-Me 2 PE (n = 34, 36), dPC-C34-PC and dMe 2 PE-C34-Me 2 PE were synthesized according to the procedure described below. Deuterated bolalipids were synthesized to get additional information about the conformation and mobility of the alkyl chain within the aggregates by FT-IR, SANS and 2 H-NMR measurements.
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
Pure and Applied Chemistry, 1982
Cross-polarization 13C NNR spectroscopy was applied to get information about the structure in iso... more Cross-polarization 13C NNR spectroscopy was applied to get information about the structure in isotropic and oriented solid polymers. From the variation of the line shape caused by the stretching of the sample have been calculated mean orientations in highly oriented fibres (polyimide) and orientation distributions of chain segments in a weakly oriented polymer (polycarbonate). Shielding tensor component distributions obtained numerically from the spectra were compared with the degree of crystallinity and were used to distinguish regions of different order (polycarbonate) and to study the abundance of various conformations (polyethylene).
Magnetic Resonance
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
CCDC 105864: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Porous interpenetrated zirconium-organic frameworks (PIZOFs) are a class of Zr-based metal-organi... more Porous interpenetrated zirconium-organic frameworks (PIZOFs) are a class of Zr-based metal-organic frameworks (MOFs) which are composed of long, rod-like dicarboxylate linkers and Zr 6 O 4 (OH) 4 (O 2 C) 12 nodes. Long oligoethylene glycol or aliphatic side chains are covalently attached to the linker molecules in the cases of PIZOF-10 and PIZOF-11, respectively. These side chains are supposedly highly mobile, thus mimicking a solvent environment. It is anticipated that such MOFs could be used as a solid catalyst-the MOF-with pore systems showing properties similar to a liquid reaction medium. To quantify the side-chain mobility, here we have applied different 1D and 2D NMR solid-state spectroscopic techniques like cross-polarization (CP) and dipolar-coupling chemical-shift correlation (DIPSHIFT) studies. The rather high 1 H-13 C CP efficiency observed for the CH 2 groups of the side chains indicates that the long side chains are unexpectedly immobile or at least that their motions are strongly anisotropic. More detailed information about the mobility of the side chains was then obtained from DIPSHIFT experiments. Analytical expressions for elaborate data analysis are derived. These expressions are used to correlate order parameters and to slow motional rates with signals in indirect spectral dimensions, thus enabling the quantification of order parameters for the CH 2 groups. The ends of the chains are rather mobile, whereas the carbon atoms close to the linker are more spatially restricted in mobility.
Müller, August Eberhard
Oxford University Press eBooks, 2001
Solid-state 13C-NMR spectroscopic determination of sidechain mobilities in zirconium-based metal-organic frameworks
. Porous Interpenetrated Zirconium-Organic Frameworks (PIZOFs) are a class of Zr-based metal-orga... more . Porous Interpenetrated Zirconium-Organic Frameworks (PIZOFs) are a class of Zr-based metal-organic frameworks (MOFs) which are composed of long, rodlike dicarboxylate linkers and Zr6O4(OH)4(O2C)12 nodes. Long oligoethylene glycol or aliphatic side chains are covalently attached to the linker molecules in the case of PIZOF-10 and PIZOF-11, respectively. These side chains are supposedly highly mobile thus mimicking a solvent environment. It is anticipated that such MOFs could be used as solid catalyst – the MOF – with pore systems showing properties similar like a liquid reaction medium. To quantify the side chain mobility, we have here applied different 1D and 2D NMR solid-state spectroscopic techniques like cross polarization (CP) and dipolar-coupling chemical-shift correlation (DIPSHIFT) studies. The rather high 1H-13C CP efficiency observed for the methylene groups of the side chains indicates that the long side chains are unexpectedly immobile or at least that their motions are strongly anisotropic. More detailed information about the mobility of the side chains was then obtained from DIPSHIFT experiments. Analytical expressions for elaborate data analysis are derived. These expressions are used to correlate order parameters and slow motional rates with signals in indirect spectral dimension thus enabling the quantification of order parameters for the methylene groups. The ends of the chains are rather mobile whereas the carbon atoms close to the linker are stronger spatiallly restricted in mobility.
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
RSC Advances, 2019
NMR spectroscopy at two magnetic field strengths was employed to investigate the dynamics of dime... more NMR spectroscopy at two magnetic field strengths was employed to investigate the dynamics of dimethylimidazolium dimethylphosphate ([C 1 C 1 IM][(CH 3) 2 PO 4 ]). [C 1 C 1 IM][(CH 3) 2 PO 4 ] is a low-melting, halogen-free ionic liquid comprising of only methyl groups. 13 C spin-lattice relaxation rates as well as self-diffusion coefficients were measured for [C 1 C 1 IM][(CH 3) 2 PO 4 ] as a function of temperature. The rotational correlation times, s c , for the cation and the anion were obtained from the 13 C spin-lattice relaxation rates. Although from a theoretical point of view cations and anions are similar in size, they show different reorientation mobilities and diffusivities. The self-diffusion coefficients and the rotational correlation times were related to the radii of the diffusing spheres. The analysis reveals that the radii of the cation and the anion, respectively, are different from each other but constant at temperatures ranging from 293 to 353 K. The experimental results are rationalised by a discrete and individual cation and anion diffusion. The [(CH 3) 2 PO 4 ] À anion reorients faster compared to the cation but diffuses significantly slower indicating the formation of anionic aggregates. Relaxation data were acquired with standard liquid and magic-angle-spinning NMR probes to estimate residual dipolar interactions, chemical shift anisotropy or differences in magnetic susceptibility within the sample.
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
Investigation of the Polymer Structure Using the High-Resolution 13C-NMR in Solids
Springer eBooks, 1979
From highly resolved 13C spectra of solid polymers we obtained distribution functions for the shi... more From highly resolved 13C spectra of solid polymers we obtained distribution functions for the shielding tensor elements. These functions contain information about the structure of the amorphous regions. Furthermore, in oriented polymers it is possible to get a function which describes the distribution of the monomer unit orientations
Chemical Physics Letters, May 1, 2012
An NMR experiment is presented for measuring spin-diffusion coefficients and observing homonuclea... more An NMR experiment is presented for measuring spin-diffusion coefficients and observing homonuclear spin-flip processes. The magnetization is erased or even inverted in a multitude of spatially confined regions containing only one or a few spins ('hole burning'). During the following time evolution of these holes, the following three time regimes can be observed: (i) local spin dynamics, (ii) spin diffusion towards a uniform average magnetization, and (iii) longitudinal nuclear magnetic relaxation. The oscillating characteristic of magnetization exchange between neighboring protons is demonstrated on a liquid crystal.
Physical Chemistry Chemical Physics
Pulse sequence of the proton-decoupled 15N R1ρ experiment.
Trajectory-Based Approach for the Analysis of CODEX Solid-State Exchange Experiments in the Slow and Intermediate Motion Regime: Comparison of Experiment, Simulation, and Analytical Treatment
The Journal of Physical Chemistry C, 2021
We present an efficient approach to analyze CODEX-MAS exchange NMR data by comparing the experime... more We present an efficient approach to analyze CODEX-MAS exchange NMR data by comparing the experimental results with simulated data that are calculated from separately simulated motional trajectories...
Solid State Nuclear Magnetic Resonance, 2002
Solid-state spin-lattice relaxation in the rotating frame permits the investigation of dynamic pr... more Solid-state spin-lattice relaxation in the rotating frame permits the investigation of dynamic processes with correlation times in the range of microseconds. The relaxation process in organic solids is driven by the fluctuation of the local magnetic field due to the dipole-dipole interaction of the probe nuclei (13 C; 15 N) with 1 H in close proximity. However, its effect is often hidden by a competing relaxation process due to the contact between the rotating frame 13 C= 15 N Zeeman and 1 H dipolar reservoirs. In most cases the latter process becomes superior for the commonly applied low and moderate spin-lock fields and practically does not provide information about the molecular dynamics. To suppress this undesired process and to expand the dynamic range of T 1r experiments, we present two approaches. The first one uses a resonance offset of the frequency of the spin-lock irradiation, which leads to a significant enhancement of the effective spin-lock frequency without the application of destructive high transmitter powers. We derive the theory and demonstrate the applicability of the method on various model compounds. The second approach utilizes heteronuclear 1 H decoupling during the 13 C= 15 N spin-lock irradiation which disrupts the contact between the 13 C= 15 N Zeeman and 1 H dipolar reservoirs. We demonstrate the method and discuss the results qualitatively.
Characteristic Length of Dynamic Glass Transition near Tg for a Wide Assortment of Glass-Forming Substances
The Journal of Physical Chemistry B, 2000
... within nanoporous glass or confined within mobile amorphous layers between crystal lamellas, ... more ... within nanoporous glass or confined within mobile amorphous layers between crystal lamellas, 10 confined thin film liquids under shear, 11 ... to reach such slow dynamics that is expected to have a dynamic heterogeneity, ie, below the crossover region of ... (i) The dimension of eq ...
Acta Polymerica, 1991
Das thermische Verhalten der Poly(bis‐alkylthio‐acetylen)e wurde im Temperaturbereich von 30°C bi... more Das thermische Verhalten der Poly(bis‐alkylthio‐acetylen)e wurde im Temperaturbereich von 30°C bis 600°C untersucht. Aus den Ergebnissen der thermischen Analyse, aus 13C‐Festkörper‐NMR‐ und ESR‐Messungen an den festen Thermolyserückständen und der Untersuchung der flüchtigen Pyrolyseprodukte werden mögliche Abbaureaktionen abgeleitet. Für einen weiten Zeit‐ und Temperaturbereich wird für Poly(bis‐methylthio‐acetylen) ein einfaches kinetisches Modell formuliert.
Soft Matter, 2010
The purity of all compounds and products was checked by thin layer chromatography (TLC plates; Me... more The purity of all compounds and products was checked by thin layer chromatography (TLC plates; Merck, Darmstadt, Germany). The purification of the bolaamphiphiles was carried out by middle pressure liquid chromatography (MPLC; Cartriger C-670, Fraction Collector C-660, Pump Module C-601, Pump Manager C-615, Büchi, Essen, Germany) using silica gel 60 (0.040-0.063 mm, Merck, Darmstadt, Germany) and chloroform/methanol/water as eluent (gradient technique). Melting points are uncorrected and were determined with a Boetius apparatus. NMR spectra were obtained using a Varian Inova 500 or Varian Gemini 2000 NMR spectrometer with CDCl 3 and CD 3 OD as internal standards. Mass spectrometric data were obtained with a Finnigan mass spectrometer model MAT SSQ 710 C (ESI-MS; Thermo Separation Products, San José, CA, USA and Thermoquest, Engelsbach, Germany) or were recorded on an AMD 402 spectrometer (EI-MS; 70 eV, AMD Intecta GmbH, Harpstedt, Germany). Elemental analyses were performed with a Leco CHNS-932 (Leco-Corporation, St. Joseph, MI, USA). All solvents were purified and dried before use. Commercially available reagents were supplied by Aldrich Co (Steinheim, Germany) and were used without further purification. The perdeuterated 1,12-dibromododecane (2c) was supplied by CDN-Isotopes (Dr. Ehrenstorfer GmbH, Augsburg, Germany). Sodium acetate and acetic acid (100%) were purchased from Merck (Darmstadt, Germany) and Riedel-de Haën (Seelze, Germany), respectively. 2 Hand 31 P-NMR measurements were performed in deuterium depleted water. For the SANS measurements D 2 O from Isotec Inc. (Miamisburg, OH, USA) was used. The bolalipids PC-Cn-PC (n = 34, 36), Me 2 PE-Cn-Me 2 PE (n = 34, 36), dPC-C34-PC and dMe 2 PE-C34-Me 2 PE were synthesized according to the procedure described below. Deuterated bolalipids were synthesized to get additional information about the conformation and mobility of the alkyl chain within the aggregates by FT-IR, SANS and 2 H-NMR measurements.
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.
Pure and Applied Chemistry, 1982
Cross-polarization 13C NNR spectroscopy was applied to get information about the structure in iso... more Cross-polarization 13C NNR spectroscopy was applied to get information about the structure in isotropic and oriented solid polymers. From the variation of the line shape caused by the stretching of the sample have been calculated mean orientations in highly oriented fibres (polyimide) and orientation distributions of chain segments in a weakly oriented polymer (polycarbonate). Shielding tensor component distributions obtained numerically from the spectra were compared with the degree of crystallinity and were used to distinguish regions of different order (polycarbonate) and to study the abundance of various conformations (polyethylene).
Magnetic Resonance
Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chem... more Chemical shift tensors in 13 C solid-state NMR provide valuable localized information on the chemical bonding environment in organic matter, and deviations from isotropic static-limit powder line shapes sensitively encode dynamic-averaging or orientation effects. Studies in 13 C natural abundance require magic-angle spinning (MAS), where the analysis must thus focus on spinning sidebands. We propose an alternative fitting procedure for spinning sidebands based upon a polynomial expansion that is more efficient than the common numerical solution of the powder average. The approach plays out its advantages in the determination of CST (chemical-shift tensor) principal values from spinning-sideband intensities and order parameters in non-isotropic samples, which is here illustrated with the example of stretched glassy polycarbonate.