1993

4-(4-Carboxyphenyl)-3,5-dioxo-1,2,4-triazolidin-1-yl moieties resulting from 4-(3,5-dioxo-1,2,4-triazolin-4-yl)benzoic acid (U4A) randomly attached to 1,4-polybutadiene form supramolecular aggregates which act as effective junction zones in new thermoplastic elastomers. Deuteron nuclear magnetic resonance (2H NMR) spectroscopy was used to investigate the molecular dynamics of the polymer backbone and the junction zones in selectively labelled samples. The spectra show motional heterogeneity along the polymer chain as well as in the supramolecular domains. Polybutadiene segments which are adjacent to these polar clusters are restricted in their mobility, even at temperatures 100 K above the …

Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation

2013

Hyperpolarization has found many applications in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, its usage is still limited to the observation of relatively fast processes because of its short lifetimes. This issue can be circumvented by storing the hyperpolarization in a slowly relaxing singlet state. Symmetrical molecules hyperpolarized by Parahydrogen Induced Hyperpolarization (PHIP) provide a straightforward access to hyperpolarized singlet states because the initial parahydrogen singlet state is preserved at almost any magnetic field strength. In these systems, which show a remarkably long 1H singlet state lifetime of several minutes, the conversion of t…

Struktur und Dynamik des Wirt-Gast-Komplexes einer molekularen Pinzette: Synthese, Festkörper-NMR-Spektroskopie und quantenchemische Rechnungen

2001

Hydrogen-Bonded Aggregates of Oligoaramide−Poly(ethylene glycol) Block Copolymers

2010

Rod−coil copolymers with an oligomeric rod aggregate on a nanometer length scale, which is important for many applications like e.g. organic photovoltaics. However, this aggregation behavior and the driving forces such as hydrogen bonding and π−π interactions, as well as the role of side groups, are not yet fully understood. Here, we investigated these noncovalent interactions in oligo(p-benzamide)−poly(ethylene glycol) (OPBA−PEG) copolymers using solid-state NMR supported by wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and polarization optical microscopy (POM). It was found that longer OPBAs form layered β-sheet-like aggregates and that these are stabilized …

Unravelling the fine structure of stacked bipyridine diamine-derived C-3-discotics as determined by X-ray diffraction, quantum-chemical calculations,…

2011

An in depth investigation of the fine structure adopted by the helical stacks of C3-discotics 1 incorporating three 3,3'-diamino-2,2'-bipyridine units is described. In the bulk the molecules display liquid crystalline behaviour in a temperature window of >300 K and an ordered rectangular columnar mesophase (Colro) with an inter-disc distance of 3.4 Å is assigned. X-Ray diffraction on aligned samples has also revealed a helical superstructure in the liquid crystalline state, and a rotation angle of 13–16° between consecutive discs. The proposed superstructure in the bulk phase has been further substantiated by a combination of quantum-chemical calculations and solid-state NMR spectroscopy…

Magnetic resonance imaging of dissolved hyperpolarized 129Xe using a membrane-based continuous flow system.

2009

Abstract A technique for continuous production of solutions containing hyperpolarized 129Xe is explored for MRI applications. The method is based on hollow fiber membranes which inhibit the formation of foams and bubbles. A systematic analysis of various carrier agents for hyperpolarized 129Xe has been carried out, which are applicable as contrast agents for in vivo MRI. The image quality of different hyperpolarized Xe solutions is compared and MRI results obtained in a clinical as well as in a nonclinical MRI setting are provided. Moreover, we demonstrate the application of 129Xe contrast agents produced with our dissolution method for lung MRI by imaging hyperpolarized 129Xe that has been…

Dynamical heterogeneities in glass-forming materials

1996

ABSTRACTCooperative dynamics around the glass transition leads to complex motional behavior of the individual molecules, resulting in non-exponential relaxation. The nature of this non-exponentiality is clarified theoretically as well as experimentally. The non-exponentiality may be due to heterogeneous relaxation (superposition of exponential processes with different rate constants) or homogeneous relaxation (identical intrinsically non-exponential processes). A precise definition of both limits is given. It is shown that the type of relaxation, i.e. to which degree heterogeneous and homogeneous contributions are present, reflects geometrical properties of the dynamics. The heterogeneous c…

1995

Supramolecular structures based on 4-(3,5-dioxo-1,2,4-triazolidin-4-yl) benzoic acid (U4A) units act as effective junction zones in functionalized polybutadienes, resulting in the formation of thermoplastic elastomers. The dynamics on a molecular scale of the phenyl rings have been probed by 2H-NMR. In the polymeric system, there are three spatially separated environments, which are reflected in the mobility of the polar units. Phenyl rings which are incorporated in the structures are either rigid or undergo 180° phenyl flips. The small fraction of free functional groups move isotropically and their mobility is coupled to the dynamics of the polybutadiene matrix. In two model compounds, whe…

2H NMR studies of phase behaviour and molecular motions of doped discotic liquid-crystalline systems

1990

Abstract A discotic triphenylene monomer as well as a dimer and a main chain polymer, all substituted with heptyloxy side groups, were doped with an electron acceptor (2,4,7-trinitrofluorenone (TNF)) to give charge transfer complexes. These doped systems were aligned in a magnetic field, thus proving their liquid crystallinity. 2H NMR measurements show that the electron acceptor molecules are incorporated into the columns built of triphenylene cores. In the charge transfer complex with the triphenylene monomer almost all the electron acceptor molecules stack in the columns even close to the clearing temperature T 1, while for the dimer and especially for the polymer a significant fraction o…

1986

Etude de deux systemes differents avec de l'hydroxy-4 benzoate de phenyle comme unite mesogene. Les separateurs sont formes de 6 unites methylene et le squelette est de l'acide poly(meth)acrylique

Molecular dynamics of discotic charge-transfer complexes, dielectric spectroscopy and2H NMR studie

1994

Abstract Using a combination of solid state 2H NMR spectroscopy on selectively deuteriated samples and dielectric spectroscopy, the molecular dynamics of discotic charge-transfer (CT) complexes were investigated. These complexes show particular thermodynamic and flow properties. Considered were mixtures of low molar mass donors and acceptors, low molar mass donors with main chain acceptor polymers and covalently linked donor-acceptor twins with different lengths of the spacer. A main result is that correlated rotational motions of discotic molecules or groups about the columnar axis are observed in all systems except for the twin with the short spacer. This type of motion seems to be a gene…

Rotation of Molecules and Nuclear Spin Relaxation

1978

Nuclear spin relaxation has been developed as a standard method for studying molecular motions in liquids, solids, polymers, and—to a lesser extent—gases, staring with the pioneering work of Bloembergen, Purcell, and Pound [1]. Of the great variety of molecular motions possible (e.g., translations, rotations, vibrations) rotations are particularly important for nuclear spin relaxation. Conversely, nuclear spin relaxation can be especially successful if information about rotational motions is desired. In this case nuclear spin relaxation can yield quantitative information over an extraordinary wide range of characteristic frequencies, from about 1 Hz to 1014Hz. It shoud be noted that, typica…

1984

Molecular dynamics near the glass transition

1993

Solid state 13C NMR spectroscopy has been applied to investigate the time scale and the geometry of rotational motions near the glass transition of the low-molar-mass van der Waals glass former 1,3,5-tri-α-naphthylbenzene (T g = 342 K). Two-dimensional 13C exchange spectra were taken between 347 and 372 K. With the principal values of the 13C chemical shift tensors determined from 13C CP/MAS spectra and static one-dimensional 13C spectra, the two-dimensional spectra are interpreted according to the isotropic rotational diffusional model to yield mean correlation times τ0 in the range 10 ms ˇ- τ0 ˇ- 50 s, and a log-Gaussian distribution of correlation times with a width of 1·5 decades. The m…

Solid-state NMR and computational studies of tetratolyl urea calix[4]arene inclusion compounds.

2009

Solid-state guest dynamics of tetratolyl tetraurea calix[4]arene tetrapentylether dimeric capsules filled with different types of aromatic guests such as benzene-d6, fluorobenzene-d5 and 1,4-difluorobenzene were studied. Upon inclusion, all guest moieties revealed complexation-induced shifts varying from 2.8 ppm to 5.1 ppm. All guest molecules were shown to undergo distinct motions, ranging from mere C6-rotations of benzene-d6 to (ill-defined) 180 degrees phenyl flips of fluorobenzene-d5. In all cases, dynamic heterogeneities were identified based on 2H lineshape deconvolution. In addition, by combination of both a computed nucleus independent chemical shift (NICS) map and explicit 19F and …

1979

2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component…

Imaging of a mixture of hyperpolarized 3He and 129Xe.

2004

Abstract With the use of hyperpolarized gases, a great number of experiments have been carried out in order to improve the diagnostics of the lung, both from a structural and a functional point of view. 3 He is best suited for structural studies, whereas 129 Xe gives more detailed information about the functionality of the lung because it enters the bloodstream. In this work, we propose the use of a gas mixture to perform consecutive analysis of lung structure and functionality upon the delivery of a single bolus of gas. We show images of a helium–xenon gas mixture in the presence of a small amount of liquid toluene in order to demonstrate how both nuclei can be detected independently, extr…

ChemInform Abstract: The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework.

2010

Orientation of polybutadiene chains in a thermoplastic elastomer

1996

The orientation of polybutadiene chains in thermoplastic elastomers based on hydrogen bonding complexes is investigated under uniaxial deformation by two-dimensional small-angle neutron scattering (SANS), deuteron magnetic resonance spectroscopy (2H-NMR), optical birefringence and infrared dichroism spectroscopy (FTIR-D). While SANS probes orientation on the length scale of the radius of gyration,2H-NMR, birefringence and FTIR-D monitor orientation on a segmental scale. The deformation of the elastomer chains appears to be affine on the different length scales.

Lack of mutagenic and co-mutagenic effects of magnetic fields during magnetic resonance imaging

2001

Mutagenic and co-mutagenic effects of static, pulsed bipolar gradient, and high-frequency magnetic fields, as well as combinations of them, were examined using the Ames test. The Ames test using Salmonella typhimurium bacteria, wild-type strain RTA, preincubation assay, without metabolic activation, was performed. All combinations of magnetic fields were tested with and without co-exposure to N-methyl-N′-nitro-N-nitrosoguanidine and benzo[a]pyrene-4,5-oxide, ethylene oxide, carboplatin, or cisplatin. As expected, chemical mutagens caused a clear-cut increase of the revertants in the Ames test. However, neither the static fields nor a combination of a static magnetic field with the time-vary…

No influence of magnetic fields on cell cycle progression using conditions relevant for patients during MRI.

2003

The purpose of this study was to examine whether exposure to magnetic fields (MFs) relevant for magnetic resonance imaging (MRI) in clinical routine influences cell cycle progression in two tumor cell lines in vitro. HL60 and EA2 cells were exposed to four types of MFs: (i) static MF of 1.5 and 7.05 T, (ii) extremely low frequency magnetic gradient fields (ELFMGFs) with ± 10 mT/m and 100 Hz, as well as ± 100 mT/m and 100 Hz, (iii) pulsed high frequency MF in the radiofrequency (RF) range (63.6 MHz, 5.8 μT), and (iv) a combination of (i–iii). Exposure periods ranged from 1 to 24 h. Cell cycle distribution (G0/G1, S, and G2/M phases) was analyzed by flow cytometry. Cell cycle analysis did not…

Determining the Geometry of Hydrogen Bonds in Solids with Picometer Accuracy by Quantum-Chemical Calculations and NMR Spectroscopy

2005

The structure of multiply hydrogen-bonded systems is determined with picometer accuracy by a combined solid-state NMR and quantum-chemical approach. On the experimental side, advanced 1H-15N dipolar recoupling NMR techniques are capable of providing proton-nitrogen distances of up to about 250 pm with an accuracy level of +/-1 pm for short distances (i.e., around 100 pm) and +/-5 pm for longer ones (i.e., 180 to 250 pm). The experiments were performed under fast magic-angle spinning, which ensures sufficient dipolar decoupling and spectral resolution of the 1H resonance lines. On the quantum-chemical side, the structures of the hydrogen-bonded systems were computationally optimised, yieldin…

1984

Static and MAS 35CI NMR and Molecular Motions of ClO −4 Ions in the Various Phases of Multimethylammonium Perchlorates

1986

Static and MAS*) 35CI NMR data of CIO−4 ions in the low-, intermediate- and high-temperature phases of trimethylammonium, dimethylammonium and monomethylammonium perchlorates are reported. The observed solid-solid phase transitions are interrelated with the motional state of the perchlorate ions. In the low-temperature phase III of trimethylammonium perchlorate there is an anisotropic motion of the ClO−4 ions with a constant quadrupole frequency of 185 kHz and an increasing value of the asymmetry parameter when approaching phase transition III-II. The activation energy for this motion is found to be 44.3 kj/mol. At the transition III-II the ClO−4 ions gain orientational degrees of freedom m…

Junction Dynamics in Telechelic Hydrogen Bonded Polyisobutylene Networks

1996

4-Urazoylbenzoic acid groups are attached to the chain ends of polyisobutylene. The cooperative assembling process of these polar groups is studied by DSC and dielectric and dynamic mechanical spectroscopy. The melting of the ordered clusters occurs in the temperature range 380-390 K. Distortions within the U4A clusters (Σ process) are monitored below the melting temperature T m with dielectric spectroscopy. On a larger length scale, these distortions also lead to stress relaxation which can be probed by dynamic mechanical measurements. Near T m , the relaxation ofU4A multiplets (α* relaxation) is detected with dielectric spectroscopy. In this temperature range, dynamic mechanical measureme…

The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework

1999

Saccharide modified silica particles by enzymatic grafting

1997

The surface of silica particles has been chemically modified with oligo- or poly-(α,1→4)-D-glucopyranose (amylose) chains of various length by covalently attaching maltoheptaose derivatives to the solid support and enzymatic polymerization of glucose-1-phosphate with a potato phosphorylase as catalyst. The characterization of the products by solid-state NMR spectroscopy showed an interesting dependence of the linewidth with the grafting density of the glucan chains. The modified silica particles showed chiral discrimination in liquid chromatography.

1986

The molecular order and mobility of two liquid-crystalline polyacrylates with phenyl benzoate moieties as mesogenic side groups and (CH2)m spacers (m = 2 and m = 6) were investigated by pulsed 2H NMR. The mesogenic side groups were isotopically labelled at the terminal phenylene ring. In the glassy state the orientational distribution function was characterized from the angular dependence of the 2H NMR line shape of samples macroscopically ordered in their nematic phase by the 8,4 T magnetic field of an NMR spectrometer. It was found to be Gaussian with widths of ± 18,5° and ± 10,5° for the m = 2 frozen nematic and m = 6 frozen smectic system, respectively. The phenylene rings undergo 180° …

Structure Formation of Polymeric Building Blocks: Complex Polymer Architectures

2013

This chapter describes macromolecules with a complex structure, their defined aggregation in solution, their adsorption to surfaces, and their possible aggregation on surfaces. The term “complex structure” implies that the macromolecules show different, distinct structural elements or building blocks on a supra-atomic length scale. Key to understanding the complex structure of macromolecules, their aggregation, and adsorption to surfaces are intra- and intermolecular interactions such as van der Waals, electrostatic, π–π interactions, and hydrogen bonds.

Phase behavior of discotic liquid crystalline polymers and related model compounds

1990

Proton magnetic resonance imaging with para-hydrogen induced polarization.

2012

A major challenge in imaging is the detection of small amounts of molecules of interest. In the case of magnetic resonance imaging (MRI) their signals are typically concealed by the large background signal of e.g. the body. This problem can be tackled by hyperpolarization which increases the NMR signals up to several orders of magnitude. However, this strategy is limited for (1)H, the most widely used nucleus in NMR and MRI, because the enormous number of protons in the body screens the small amount of hyperpolarized ones. Here, we describe a method giving rise to high (1)H MRI contrast for hyperpolarized molecules against a large background signal. The contrast is based on the J-coupling i…

Nature of the non-exponential primary relaxation in structural glass-formers probed by dynamically selective experiments

1998

Several experimental methods feature the potential to distinguish between slow and fast contributions to the non-exponential, ensemble averaged primary response in glass-forming materials. Some of these techniques are based on the selection of subensembles using multi-dimensional nuclear magnetic resonance, optical bleaching, and non-resonant spectral hole burning. Others, such as the time-dependent solvation spectroscopy, measure microscopic responses induced by local perturbations. Using several of these methods it could be demonstrated for various glass-forming materials that the non-exponential relaxation results from a superposition of dynamically distinguishable entities. The experime…

Deuteron n.m.r. in relation to the glass transition in polymers

1985

Abstract 2H n.m.r. is introduced as a tool for investigating slow molecular motion in the glass transition region of amorphous polymers. In particular, we compare 2H spin alignment echo spectra of chain deuterated polystyrene with models for restricted rotational Brownian motion. Molecular motion in the polystyrene-toluene system has been investigated by analysing 2H n.m.r. of partially deuterated polystyrene and toluene, respectively. The diluent mobility in the mixed glass has been decomposed into ‘solid’ and ‘liquid’ components where the respective average correlation times differ by more than 5 decades.

Spin‐Labeled Heparins as Polarizing Agents for Dynamic Nuclear Polarization

2010

A potentially biocompatible class of spin-labeled macromolecules, spin-labeled (SL) heparins, and their use as nuclear magnetic resonance (NMR) signal enhancers are introduced. The signal enhancement is achieved through Overhauser-type dynamic nuclear polarization (DNP). All presented SL-heparins show high 1 H DNP enhancement factors up to E=-110, which validates that effectively more than one hyperfine line can be saturated even for spin-labeled polarizing agents. The parameters for the Overhauser-type DNP are determined and discussed. A striking result is that for spin-labeled heparins, the off-resonant electron paramagnetic resonance (EPR) hyperfine lines contribute a non-negligible part…

Magnetic resonance imaging of (1)H long lived states derived from parahydrogen induced polarization in a clinical system.

2015

Hyperpolarization is a powerful tool to overcome the low sensitivity of nuclear magnetic resonance (NMR). However, applications are limited due to the short lifetime of this non equilibrium spin state caused by relaxation processes. This issue can be addressed by storing hyperpolarization in slowly decaying singlet spin states which was so far mostly demonstrated for non-proton spin pairs, e.g. 13C-13C. Protons hyperpolarized by parahydrogen induced polarization (PHIP) in symmetrical molecules, are very well suited for this strategy because they naturally exhibit a long-lived singlet state. The conversion of the NMR silent singlet spin state to observable magnetization can be achieved by ma…

Structure and Dynamics of the Host-Guest Complex of a Molecular Tweezer: Coupling Synthesis, Solid-State NMR, and Quantum-Chemical Calculations

2001

A novel approach to polymer-template mesoporous molecular sieves

2000

A novel synthesis route was developed to produce spherical silica particles. The synthesis is based on a modified Stoeber method and the room-temperature synthesis of MCM 41S-materials applying tetraethoxysilane, alcohol, water, ammonia and homopolymers as template. The specific surface area, the specific pore volume and the average pore diameter were varied in the following ranges: 5 – 1,000 m2/g; 0.1 – 1.0 cm3/g and 2-50 nm. With respect to catalytic applications hetero-atoms e.g. Al were incorporated into the silica framework.

Papers accepted for publication in The Analyst

1973