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Born R, Feike M, Jäger C, Spiess HW. 2 D 31P Exchange NMR: A new Approach for a Direct Probing of the Connectivities of Qn Units in Glasses. ACTA ACUST UNITED AC 2014. [DOI: 10.1515/zna-1995-2-308] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Recently, 31P two-dimensional (2D) NMR has been proposed as a powerful tool for direct investigations of the connectivities between the Qn units in glasses, i.e. the medium-range order. In this paper, the principles of these experiments and applications to both polycrystalline Mg2P2O7 and a Na2O-P205 glass are demonstrated, including a theoretical description and modelling of the polarization transfer between the two inequivalent phosphorus sites in the magnesium pyrophosphate.
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Affiliation(s)
- R. Born
- Max-Planck-Institut für Polymerforschung, Postfach 31 48, D-55021 Mainz, Germany
| | - M. Feike
- Max-Planck-Institut für Polymerforschung, Postfach 31 48, D-55021 Mainz, Germany
| | - C. Jäger
- Max-Planck-Institut für Polymerforschung, Postfach 31 48, D-55021 Mainz, Germany
| | - H. W. Spiess
- Max-Planck-Institut für Polymerforschung, Postfach 31 48, D-55021 Mainz, Germany
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2
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Franzoni MB, Graafen D, Buljubasich L, Schreiber LM, Spiess HW, Münnemann K. Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation. Phys Chem Chem Phys 2014; 15:17233-9. [PMID: 24018735 DOI: 10.1039/c3cp52029c] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
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 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 (1)H singlet state lifetime of several minutes, the conversion of the NMR silent singlet state to observable magnetization is feasible due to the existence of singlet-triplet level anti-crossings. Here, we demonstrate that scaling the chemical shift Hamiltonian by rf irradiation is sufficient to transform the singlet into an observable triplet state. Moreover, because the application of one long rf pulse is only partially converting the singlet state, we developed a multiconversion sequence consisting of a train of long rf pulses resulting in successive singlet to triplet conversions. This sequence is used to measure the singlet state relaxation time in a simple way at two different magnetic fields. We show that this approach is valid for almost any magnetic field strength and can be performed even in the less homogeneous field of an MRI scanner, allowing for new applications of hyperpolarized NMR and MRI.
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Affiliation(s)
- M B Franzoni
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
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Ritter C, Müller-Warmuth W, Spiess HW, Schöllhorn R. Quasi-One-Dimensional Behaviour of Hydrogen in H0.35MoO3and H0.33WO3as Revealed by Proton NMR. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/bbpc.198200047] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Schmidt C, Blümich B, Wefing S, Kaufmann S, Spiess HW. Molecular motions from two-dimensional NMR of powders: Comparison of rotational jumps and diffusive reorientations. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/bbpc.19870911113] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Blüimich B, Böffel C, Harbison GS, Yang Y, Spiess HW. Two-dimensional MAS NMR: New prospects for the investigation of partially oriented polymers. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/bbpc.19870911105] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Graf R, Hansen MR, Hinderberger D, Muennemann K, Spiess HW. Advanced magnetic resonance strategies for the elucidation of nanostructured soft matter. Phys Chem Chem Phys 2014; 16:9700-12. [DOI: 10.1039/c3cp54614d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Buljubasich L, Prina I, Franzoni MB, Münnemann K, Spiess HW, Acosta RH. High resolution para-hydrogen induced polarization in inhomogeneous magnetic fields. J Magn Reson 2013; 230:155-159. [PMID: 23500529 DOI: 10.1016/j.jmr.2013.02.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2012] [Revised: 01/28/2013] [Accepted: 02/03/2013] [Indexed: 06/01/2023]
Abstract
The application of parahydrogen for the generation of hyperpolarization has increased continuously during the last years. When the chemical reaction is carried out at the same field as the NMR experiment (PASADENA protocol) an antiphase signal is obtained, with a separation of the resonance lines of a few Hz. This imposes a stringent limit to the homogeneity of the magnetic field in order to avoid signal cancellation. In this work we detect the signal arising from hyperpolarized Hexene by means of a CPMG pulse train. After Fourier transformation the obtained J-spectra not only presents an enhanced spectral resolution but also avoids partial peak cancellation.
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Affiliation(s)
- L Buljubasich
- FAMAF Universidad Nacional de Córdoba, IFEG CONICET, X5016LAE Córdoba, Argentina
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Graf R, Spiess HW, Floudas G, Butt HJ, Gkikas M, Iatrou H. Conformational Transitions of Poly(l-proline) in Copolypeptides with Poly(γ-benzyl-l-glutamate) Induced by Packing. Macromolecules 2012. [DOI: 10.1021/ma301906m] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- R. Graf
- Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany
| | - H. W. Spiess
- Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany
| | - G. Floudas
- Department
of Physics, University of Ioannina, P.O.
Box 1186, GR-45110 Ioannina,
Greece
- Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany
| | - H.-J. Butt
- Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany
| | - M. Gkikas
- Department of Chemistry, University of Athens, Panepistimiopolis, Zografou,
GR-15771 Athens, Greece
| | - H. Iatrou
- Department of Chemistry, University of Athens, Panepistimiopolis, Zografou,
GR-15771 Athens, Greece
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Buljubasich L, Franzoni MB, Spiess HW, Münnemann K. Level anti-crossings in ParaHydrogen Induced Polarization experiments with Cs-symmetric molecules. J Magn Reson 2012; 219:33-40. [PMID: 22595295 DOI: 10.1016/j.jmr.2012.03.020] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 03/15/2012] [Accepted: 03/22/2012] [Indexed: 05/22/2023]
Abstract
Hyperpolarization by means of ParaHydrogen Induced Polarization (PHIP) has found increasing applications since its discovery. However, in the last decade only a few experiments have been reported describing the hydrogenation of symmetric molecules. A general AA'BB' system is studied here. Calculations of the spin dynamics with the density matrix formalism support the experimental findings, providing profound understanding of the experiments in Cs-symmetric molecules. Level anti-crossings between states related to the triplet and the singlet state of one pair of the protons are identified as being responsible for hyperpolarization transfer in a PHIP experiment, when the former p-H(2) protons occupy the sites AA'. The hydrogenation of acetylene dicarboxylic acid dimethylester with parahydrogen is used to illustrate the case. The theoretical treatment applied to this particular reaction explains the signal enhancements in both groups of protons in the spectrum when the sample is placed in the proper magnetic field strength, including the phase inversion of the signal of the methyl group. The treatment described here can be extended to every molecule which can be approximated as an AA'BB' system.
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Affiliation(s)
- L Buljubasich
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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Hansen MR, Feng X, Macho V, Müllen K, Spiess HW, Floudas G. Fast and slow dynamics in a discotic liquid crystal with regions of columnar order and disorder. Phys Rev Lett 2011; 107:257801. [PMID: 22243114 DOI: 10.1103/physrevlett.107.257801] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 06/01/2011] [Indexed: 05/31/2023]
Abstract
Aromatic disk-shaped molecules tend to self-organize into a herringbone packing where the disks are inclined at angles ±θ with respect to the axis of the column. In discotic liquid crystals this can introduce defects between stacks of limited length. In a C(3)-symmetric hexa-peri-hexabenzocoronene, solid-state NMR, x-ray scattering, and rheology identifies such a packing with θ=43° and stacks of about seven disks. Disordered regions containing defects fill the space in between the ordered stacks. Biaxial intra- and intercolumnar dynamics differing by eight decades are identified.
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Affiliation(s)
- M R Hansen
- Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany.
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Pannier M, Veit S, Godt A, Jeschke G, Spiess HW. Dead-time free measurement of dipole-dipole interactions between electron spins. 2000. J Magn Reson 2011; 213:316-325. [PMID: 22152351 DOI: 10.1016/j.jmr.2011.08.035] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
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Garro Linck Y, Chattah AK, Graf R, Romañuk CB, Olivera ME, Manzo RH, Monti GA, Spiess HW. Multinuclear solid state NMR investigation of two polymorphic forms of ciprofloxacin-saccharinate. Phys Chem Chem Phys 2011; 13:6590-6. [PMID: 21384011 DOI: 10.1039/c0cp02919j] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two polymorphic forms of a novel pharmaceutical compound, ciprofloxacin-saccharinate (CIP-SAC), are analyzed using one dimensional (1D) and two dimensional (2D) (1)H nuclear magnetic resonance (NMR) at fast magic angle spinning (MAS). Additionally (15)N spectroscopy and (1)H-(13)C correlation experiments were performed to complement our conclusions. The 1D (1)H NMR spectra of CIP and complexes reveal valuable information about the ionic bonding between ciprofloxacin and saccharine. Additionally, these spectra allow us to perform a clear characterization of each solid form, giving the number of molecules per unit cell in one of the polymorphs. From 2D (1)H-(1)H spectra obtained through double quantum correlations we can arrive at important conclusions about the hydrogen bonding, conformation, and intra and inter-molecular interactions present in these compounds. Comparing and contrasting the (1)H-(1)H correlation data obtained for both polymorphic forms and taking into account the single crystal structure data existing for the solid form CIP-SAC (II) was possible to extract some conclusions on the polymorph CIP-SAC (I) where no single crystal information is available. (1)H MAS NMR is shown to be an important tool in the field of polymorphism and for the characterization of multicomponent pharmaceutical compounds.
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Affiliation(s)
- Y Garro Linck
- Facultad de Matemática, Astronomía y Física, Universidad Nacional de Córdoba, Córdoba 5000, Argentina
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Landfester K, Boeffel C, Lambla M, Spiess HW. Synthesis and characterization of core-shell latexes with microscopic and solid-state NMR methods. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.19950920111] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Boese D, Eisenbach CD, Fischer EW, Hayen H, Nefzger H, Planer-Kühne G, Reynolds N, Spiess HW. Dynamics and deformation behaviour in non-hydrogen bonded model urethanes under heat and stress as studied by dielectric and infrared spectroscopy. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.19910500119] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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19
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Spiess HW. Deuteron NMR investigations of structure and dynamics in solid polymers, liquid crystalline polymers and polymer model membranes. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.19860040124] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Spiess HW. Structure, dynamics and phase separation in liquid crystalline polymers, block copolymers and blends as revealed by solid state NMR spectroscopy. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.19910500123] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Blümich B, Blümler P, Günther E, Schauss G, Spiess HW. Nondestructive evaluation of polymer materials by solid state NMR imaging. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.19910440106] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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22
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Jäger C, Hartmann P, Kunath-Fandrei G, Hirsch O, Rehak P, Vogel J, Feike M, Spiess HW, Herzog K, Thomas B. Novel opportunities of structural investigations of glasses by 2D NMR, multiple quantum NMR and 27Al MAS NMR lineshape analysis. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19961000942] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Spiess HW. Structure and Dynamics of Liquid-Crystalline Polymers with Different Molecular Architectures from Multidimensional NMR Plenary Lecture. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19930971018] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Leisen J, Ohlemacher A, Boeffel C, Spiess HW. Molecular Dynamics in Side-Group Polymers with and without Liquid Crystalline Phases from 2H NMR. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19930971019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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25
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Jurga S, Spiess HW. Phase Transitions and Molecular Motion in Dimethylammonium Perchlorate as Revealed by DSC, Proton and Deuteron NMR. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19850890709] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Jurga S, Harbison GS, Blümich B, Spiess HW, Fujara F, Olinger A. Static and MAS 35CI NMR and Molecular Motions of ClO −4 Ions in the Various Phases of Multimethylammonium Perchlorates. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19860901207] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Gitsas A, Floudas G, Mondeshki M, Lieberwirth I, Spiess HW, Iatrou H, Hadjichristidis N, Hirao A. Hierarchical Self-Assembly and Dynamics of a Miktoarm Star chimera Composed of Poly(γ-benzyl-l-glutamate), Polystyrene, and Polyisoprene. Macromolecules 2010. [DOI: 10.1021/ma902631e] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
| | | | | | | | | | | | | | - A. Hirao
- Polymeric and Organic Materials Department, Graduate School of Science and Engineering, Tokyo Institute of Technology, Tokyo, 152-8552, Japan
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Amor N, Zänker PP, Blümler P, Meise FM, Schreiber LM, Scholz A, Schmiedeskamp J, Spiess HW, Münnemann K. Magnetic resonance imaging of dissolved hyperpolarized 129Xe using a membrane-based continuous flow system. J Magn Reson 2009; 201:93-99. [PMID: 19729327 DOI: 10.1016/j.jmr.2009.08.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Revised: 08/11/2009] [Accepted: 08/11/2009] [Indexed: 05/28/2023]
Abstract
A technique for continuous production of solutions containing hyperpolarized (129)Xe 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 (129)Xe 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 (129)Xe contrast agents produced with our dissolution method for lung MRI by imaging hyperpolarized (129)Xe that has been both dissolved in and outgassed from a carrier liquid in a lung phantom, illustrating its potential for the measurement of lung perfusion and ventilation.
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Affiliation(s)
- N Amor
- Max Planck Institute for Polymer Research, 55128 Mainz, Germany
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Agulles-Pedrós L, Acosta RH, Blümler P, Spiess HW. Resolution enhancement in MRI of laser polarized 3He by control of diffusion. J Magn Reson 2009; 197:56-62. [PMID: 19128992 DOI: 10.1016/j.jmr.2008.12.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Revised: 12/03/2008] [Accepted: 12/03/2008] [Indexed: 05/27/2023]
Abstract
Diffusion of atoms or molecules in presence of magnetic field gradients not only attenuates the NMR signal but also leads to distortions close to restricting boundaries. This phenomenon is most evident in imaging with laser polarized (LP) noble gases. Diffusion of gases can be manipulated, however, by admixing inert gases of different molecular weight. In this work we analyze the effect of mixing LP-(3)He with SF(6) on the image quality of a phantom consisting of an arrangement of capillaries with different diameters. Admixing buffer gases of higher molecular weight changes the contrast and offers a means to record images with high spatial and time resolution. Additionally we demonstrate how distortions due to edge enhancement can be reduced even for long timed MRI-sequences.
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Affiliation(s)
- L Agulles-Pedrós
- Max Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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Gitsas A, Floudas G, Mondeshki M, Spiess HW, Aliferis T, Iatrou H, Hadjichristidis N. Control of Peptide Secondary Structure and Dynamics in Poly(γ-benzyl-l-glutamate)-b-polyalanine Peptides. Macromolecules 2008. [DOI: 10.1021/ma801770b] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A. Gitsas
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
| | - G. Floudas
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
| | - M. Mondeshki
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
| | - H. W. Spiess
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
| | - T. Aliferis
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
| | - H. Iatrou
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
| | - N. Hadjichristidis
- Department of Physics, University of Ioannina, and Foundation for Research and Technology-Hellas (FORTH), Biomedical Research Institute (BRI), P.O. Box 1186, GR-45110 Ioannina, Greece, Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany, and Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, GR-15771 Athens, Greece
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Jäger H, Koch A, Maus V, Spiess HW, Jeschke G. Relaxation-based distance measurements between a nitroxide and a lanthanide spin label. J Magn Reson 2008; 194:254-263. [PMID: 18674941 DOI: 10.1016/j.jmr.2008.07.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Revised: 07/15/2008] [Accepted: 07/15/2008] [Indexed: 05/26/2023]
Abstract
Distance measurements by electron paramagnetic resonance techniques between labels attached to biomacromolecules provide structural information on systems that cannot be crystallized or are too large to be characterized by NMR methods. However, existing techniques are limited in their distance range and sensitivity. It is anticipated by theoretical considerations that these limits could be extended by measuring the enhancement of longitudinal relaxation of a nitroxide label due to a lanthanide complex label at cryogenic temperatures. The relaxivity of the dysprosium complex with the macrocyclic ligand DOTA can be determined without direct measurements of longitudinal relaxation rates of the lanthanide and without recourse to model compounds with well defined distance by analyzing the dependence of relaxation enhancement on either temperature or concentration in homogeneous glassy frozen solutions. Relaxivities determined by the two calibration techniques are in satisfying agreement with each other. Error sources for both techniques are examined. A distance of about 2.7 nm is measured in a model compound of the type nitroxide-spacer-lanthanide complex and is found in good agreement with the distance in a modeled structure. Theoretical considerations suggest that an increase of the upper distance limit requires measurements at lower fields and temperatures.
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Affiliation(s)
- H Jäger
- Max Planck Institute for Polymer Research, Mainz, Germany
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Gitsas A, Floudas G, Mondeshki M, Butt HJ, Spiess HW, Iatrou H, Hadjichristidis N. Effect of Chain Topology on the Self-Organization and Dynamics of Block Copolypeptides: From Diblock Copolymers to Stars. Biomacromolecules 2008; 9:1959-66. [DOI: 10.1021/bm800221n] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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35
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Elmahdy MM, Floudas G, Mondeshki M, Spiess HW, Dou X, Müllen K. Origin of the complex molecular dynamics in functionalized discotic liquid crystals. Phys Rev Lett 2008; 100:107801. [PMID: 18352232 DOI: 10.1103/physrevlett.100.107801] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Indexed: 05/26/2023]
Abstract
The molecular dynamics of three dipole functionalized hexa-peri-hexabenzocoronenes have been studied using site-specific NMR techniques and dielectric spectroscopy as a function of temperature and pressure. These probes (i) suggest that the thermodynamic state completely controls the dynamic response, (ii) clarify the origin of two dynamic processes associated with the presence of two glass temperatures, and (iii) provide the first phase diagram for substances of this kind.
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Affiliation(s)
- M M Elmahdy
- Department of Physics, University of Ioannina, 451 10 Ioannina, Greece and Foundation for Research and Technology-Hellas, Biomedical Research Institute, Ioannina, Greece
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36
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Yao YF, Graf R, Spiess HW, Rastogi S. Restricted Segmental Mobility Can Facilitate Medium-Range Chain Diffusion: A NMR Study of Morphological Influence on Chain Dynamics of Polyethylene. Macromolecules 2008. [DOI: 10.1021/ma702815k] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Y.-F. Yao
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany, and Department of Chemical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands
| | - R. Graf
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany, and Department of Chemical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands
| | - H. W. Spiess
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany, and Department of Chemical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands
| | - S. Rastogi
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany, and Department of Chemical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands
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37
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Münnemann K, Bauer C, Schmiedeskamp J, Spiess HW, Schreiber WG, Hinderberger D. Transportabler DNP Polarisator zur klinischen Anwendung. ROFO-FORTSCHR RONTG 2008. [DOI: 10.1055/s-2008-1073735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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38
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Yao YF, Graf R, Spiess HW, Lippits DR, Rastogi S. Morphological differences in semicrystalline polymers: Implications for local dynamics and chain diffusion. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:060801. [PMID: 18233807 DOI: 10.1103/physreve.76.060801] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2007] [Indexed: 05/25/2023]
Abstract
Morphological differences in semicrystalline polymers due to different crystallization conditions have implications for the chain motion. The local dynamics in the noncrystalline regions of solution-crystallized linear polyethylene is lower than in a melt-crystallized sample, but the opposite is observed for chain diffusion between noncrystalline and crystalline regions. The activation enthalpy for chain diffusion, however, is the same, indicating that entropic differences in the noncrystalline regions strongly influence the chain diffusion of the same polymer in different morphologies.
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Affiliation(s)
- Y-F Yao
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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39
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Gitsas A, Floudas G, Dietz M, Mondeshki M, Spiess HW, Wegner G. Self-Assembly and Molecular Dynamics of Copolymers of γ-Methyl-l-glutamate and Stearyl-l-glutamate. Macromolecules 2007. [DOI: 10.1021/ma070792i] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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40
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Koynov K, Mihov G, Mondeshki M, Moon C, Spiess HW, Müllen K, Butt HJ, Floudas G. Diffusion and Conformation of Peptide-Functionalized Polyphenylene Dendrimers Studied by Fluorescence Correlation and 13C NMR Spectroscopy. Biomacromolecules 2007; 8:1745-50. [PMID: 17441768 DOI: 10.1021/bm0702760] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report on the combined use of fluorescence correlation spectroscopy (FCS) and 1H and 13C NMR spectroscopy to detect the size and type of peptide secondary structures in a series of poly-Z-L-lysine functionalized polyphenylene dendrimers bearing the fluorescent perylenediimide core in solution. In dilute solution, the size of the molecule as detected from FCS and 1H NMR diffusion measurements matches nicely. We show that FCS is a sensitive probe of the core size as well as of the change in the peptide secondary structure. However, FCS is less sensitive to functionality. A change in the peptide secondary conformation from beta-sheets to alpha-helices detected by 13C NMR spectroscopy gives rise to a steep increase in the hydrodynamic radii for number of residues n > or = 16. Nevertheless, helices are objects of low persistence.
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Affiliation(s)
- K Koynov
- Max-Planck-Institut für Polymerforschung, D-55021 Mainz, Germany
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41
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Steininger H, Schuster M, Kreuer KD, Kaltbeitzel A, Bingöl B, Meyer WH, Schauff S, Brunklaus G, Maier J, Spiess HW. Intermediate temperature proton conductors for PEM fuel cells based on phosphonic acid as protogenic group: A progress report. Phys Chem Chem Phys 2007; 9:1764-73. [PMID: 17415487 DOI: 10.1039/b618686f] [Citation(s) in RCA: 180] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The melting behaviour and transport properties of straight chain alkanes mono- and difunctionalized with phosphonic acid groups have been investigated as a function of their length. The increase of melting temperature and decrease of proton conductivity with increasing chain length is suggested to be the consequence of an increasing ordering of the alkane segments which constrains the free aggregation of the phosphonic acid groups. However, the proton mobility is reduced to a greater extent than the proton diffusion coefficient indicating an increasing cooperativity of proton transport with increasing length of the alkane segment. The results clearly indicate that the "spacer concept", which had been proven successful in the optimization of the proton conductivity of heterocycle based systems, fails in the case of phosphonic acid functionalized polymers. Instead, a very high concentration of phosphonic acid functional groups forming "bulky" hydrogen bonded aggregates is suggested to be essential for obtaining very high proton conductivity. Aggregation is also suggested to reduce condensation reactions generally observed in phosphonic acid containing systems. On the basis of this understanding, the proton conductivities of poly(vinyl phosphonic acid) and poly(meta-phenylene phosphonic acid) are discussed. Though both polymers exhibit a substantial concentration of phosphonic acid groups, aggregation seems to be constrained to such an extent that intrinsic proton conductivity is limited to values below sigma = 10(-3) S cm(-1) at T = 150 degrees C. The results suggest that different immobilization concepts have to be developed in order to minimize the conductivity reduction compared to the very high intrinsic proton conductivity of neat phosphonic acid under quasi dry conditions. In the presence of high water activities, however, (as usually present in PEM fuel cells) the very high ion exchange capacities (IEC) possible for phosphonic acid functionalized ionomers (IEC >10 meq g(-1)) may allow for high proton conductivities in the intermediate temperature range (T approximately 120 -160 degrees C).
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Affiliation(s)
- H Steininger
- Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany
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42
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Mondeshki M, Mihov G, Graf R, Spiess HW, Müllen K, Papadopoulos P, Gitsas A, Floudas G. Self-Assembly and Molecular Dynamics of Peptide-Functionalized Polyphenylene Dendrimers. Macromolecules 2006. [DOI: 10.1021/ma0621270] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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43
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Schmidt J, Hoffmann A, Spiess HW, Sebastiani D. Bulk Chemical Shifts in Hydrogen-Bonded Systems from First-Principles Calculations and Solid-State-NMR. J Phys Chem B 2006; 110:23204-10. [PMID: 17107166 DOI: 10.1021/jp0640732] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present an analysis of bulk (1)H NMR chemical shifts for a series of biochemically relevant molecular crystals in analogy to the well-known solvent NMR chemical shifts. The term bulk shifts denotes the change in NMR frequency of a gas-phase molecule when it undergoes crystallization. We compute NMR parameters from first-principles electronic structure calculations under full periodic boundary conditions and for isolated molecules and compare them to the corresponding experimental fast magic-angle spinning solid-state NMR spectra. The agreement between computed and experimental lines is generally very good. The main phenomena responsible for bulk shifts are packing effects (hydrogen bonding and pi-stacking) in the condensed phase. By using these NMR bulk shifts in well-ordered crystalline model systems composed of biologically relevant molecules, we can understand the individual spectroscopic signatures of packing effects. These local structural driving forces, hydrogen bonding, pi-stacking, and related phenomena, stand as a model for the forces that govern the assembly of much more complex supramolecular aggregates. We show to which accuracy condensed-phase ab initio calculations can predict structure and structure-property relationships for noncovalent interactions in complex supramolecular systems.
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Affiliation(s)
- J Schmidt
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
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44
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Somma E, Chi C, Loppinet B, Grinshtein J, Graf R, Fytas G, Spiess HW, Wegner G. Orientation dynamics in isotropic phases of model oligofluorenes: Glass or liquid crystal. J Chem Phys 2006; 124:204910. [PMID: 16774387 DOI: 10.1063/1.2191059] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Orientation molecular dynamics were investigated in a series of "defect-free" oligofluorenes by depolarized dynamic light scattering and dynamic NMR spectroscopy. Typical liquid crystalline pretransitional dynamics were observed upon cooling the isotropic phase to the liquid crystalline phase with strong increase of the scattered intensity and slowing down of the characteristic time of the probed collective relaxation. This is well accounted for by the Landau-de Gennes theory, however, with a strong temperature dependence of the viscosity coefficient, reflecting the proximity of the glass transition. For the trimer the two transitions almost overlap and the molecular orientation coincide with the alpha-relaxation associated with the glass transition. The NMR measurements confirm that the time scale of the dynamics is completely governed by the glass process, yet the geometry of the motion is anisotropic, yielding order parameters ranging from 0.15 to 0.25 for the long axis in the liquid crystalline phase. The glass transition is therefore geometrically restricted with poorly ordered mesophase which is consistent with the weak transverse phonons in the light scattering experiment down to Tg+20 K.
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Affiliation(s)
- E Somma
- FORTH-IESL and Department of Materials Science, University of Crete, P.O. Box 1527, 71110 Heraklion, Greece
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45
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Panek G, Schleidt S, Mao Q, Wolkenhauer M, Spiess HW, Jeschke G. Heterogeneity of the Surfactant Layer in Organically Modified Silicates and Polymer/Layered Silicate Composites. Macromolecules 2006. [DOI: 10.1021/ma0527449] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- G. Panek
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
| | - S. Schleidt
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
| | - Q. Mao
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
| | - M. Wolkenhauer
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
| | - H. W. Spiess
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
| | - G. Jeschke
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
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46
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Schleidt S, Spiess HW, Jeschke G. A site-directed spin-labeling study of surfactants in polymer-clay nanocomposites. Colloid Polym Sci 2006; 284:1211-1219. [PMID: 24058231 PMCID: PMC3776279 DOI: 10.1007/s00396-006-1499-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2006] [Accepted: 04/11/2006] [Indexed: 10/25/2022]
Abstract
Polymer-clay nanocomposites exhibit much improved mechanical, physical, and chemical properties compared to the pure polymer. The interaction of polymer and organically modified silicates is mainly influenced by the surfactant layer in the system. To investigate the structure and dynamics of this surfactant layer, various electron paramagnetic spectroscopy (EPR) techniques were applied. Continuous wave EPR experiments showed a temperature-dependent heterogeneous mobility of the surfactant layer in organoclay as well as a difference in dynamics along the alkyl chain. Intercalation of polystyrene causes a significant slowdown in surfactant dynamics. Electron spin echo envelope modulation indicates a closer contact of the polymer with the mid of the surfactant tail than with the end of the tail. From the obtained data the picture of flatly lying surfactants on clay platelets with a mobility gradient along their alkyl chains can be drawn.
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Affiliation(s)
- S Schleidt
- Max Planck Institute for Polymer Research, Postfach 3148, 55021 Mainz, Germany
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47
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Acosta RH, Agulles-Pedrós L, Komin S, Sebastiani D, Spiess HW, Blümler P. Diffusion in binary gas mixtures studied by NMR of hyperpolarized gases and molecular dynamics simulations. Phys Chem Chem Phys 2006; 8:4182-8. [PMID: 16971986 DOI: 10.1039/b609316g] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dependence of the individual mean square displacement of rare gases in binary mixtures is studied by a combined experimental and theoretical approach. We show that the diffusion constant can be varied in a considerable range by changing the molar fractions of the mixtures. On the experimental side, NMR diffusion measurements are done on hyperpolarized 3He and 129Xe, mixed with several inert buffer gases, in the presence of a magnetic field gradient. The results are compared to diffusion coefficients obtained from atomistic molecular dynamics simulations based on Lennard-Jones type potentials of the corresponding gas mixtures, and to appropriate analytical expressions, yielding very good mutual agreement. This study is the first quantitative validation of the effects of the mutual interactions between gas particles on the individual diffusion properties. It is shown that the dependency of gas phase diffusion properties on the local chemical environment may not be neglected, e.g. in diffusion-controlled chemical reactions.
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Affiliation(s)
- R H Acosta
- Max-Planck Institute for Polymer Research, Mainz, Germany
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48
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Wind M, Graf R, Renker S, Spiess HW, Steffen W. Structure of amorphous poly-(ethylmethacrylate): A wide-angle x-ray scattering study. J Chem Phys 2005; 122:14906. [PMID: 15638699 DOI: 10.1063/1.1826031] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The local, temperature dependent structure of poly-(ethylmethacrylate) was studied with wide-angle x-ray scattering. The results were set into context to recent wide-angle neutron scattering results as well as to the results from a multitude of studies of the dynamics of this polymer. The temperature dependence of the wide angle x-ray results point to the development of local order which is backed by the neutron scattering results and which is connected to characteristic temperatures of the relaxation dynamic T(g) and T(c). The poly-(ethylmethacrylate) was studied in its predominantly syndiotactic as well as predominantly isotactic state displaying vastly different local structures as manifested in the x-ray results.
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Affiliation(s)
- M Wind
- Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
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49
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Acosta RH, Blümler P, Han S, Appelt S, Häsing FW, Schmiedeskamp J, Heil W, Spiess HW. Imaging of a mixture of hyperpolarized 3He and 129Xe. Magn Reson Imaging 2004; 22:1077-83. [PMID: 15527994 DOI: 10.1016/j.mri.2004.08.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2004] [Accepted: 08/01/2004] [Indexed: 10/26/2022]
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. 3He is best suited for structural studies, whereas 129Xe 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, extracting the spectroscopic information provided by the 129Xe spectra and obtaining an image with high sensitivity for 3He. A second experiment performed on a dissected mouse lung was used to demonstrate how the mixture of gases can enhance sensitivity in the larger airways of the lung.
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Affiliation(s)
- R H Acosta
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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50
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Pollard M, Klimke K, Graf R, Spiess HW, Wilhelm M, Sperber O, Piel C, Kaminsky W. Observation of Chain Branching in Polyethylene in the Solid State and Melt via 13C NMR Spectroscopy and Melt NMR Relaxation Time Measurements. Macromolecules 2004. [DOI: 10.1021/ma0349130] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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