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Berlin Brandenburg

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  • 1
    Language: English
    In: The journal of physical chemistry. B, 20 March 2014, Vol.118(11), pp.3207-17
    Description: Supramolecular assembly allows for enhanced control of bulk material properties through the fine modulation of intermolecular interactions. We present a comprehensive study of a cross-linkable amphiphilic wedge molecule based on a sulfonated trialkoxybenzene with a sodium counterion that forms liquid crystalline (LC) phases with ionic nanochannel structures. This compound exhibits drastic structural changes as a function of relative humidity (RH). Our combined structural, dynamical, and transport studies reveal deep and novel information on the coupling of water and wedge molecule transport to structural motifs, including the significant influence of domain boundaries within the material. Over a range of RH values, we employ (23)Na solid-state NMR on the counterions to complement detailed structural studies by grazing-incidence small-angle X-ray scattering. RH-dependent pulsed-field-gradient (PFG) NMR diffusion studies on both water and the wedge amphiphiles show multiple components, corresponding to species diffusing within LC domains as well as in the domain boundaries that compose 10% of the material. The rich transport and dynamical behaviors described here represent an important window into the world of supramolecular soft materials, carrying implications for optimization of these materials in many venues. Cubic phases present at high RH show fast transport of water (2 × 10(-10) m(2)/s), competitive with that observed in benchmark polymeric ion conductors. Understanding the self-assembly of these supramolecular building blocks shows promise for generating cross-linked membranes with fast ion conduction for applications such as next-generation batteries.
    Keywords: Strukturumwandlung ; Röntgenstrahl ; Diffusion ; Natrium ; Ionenkanal ; Relative Feuchtigkeit ; Dynamisches Verhalten ; Ionenleitung ; Baugruppe ; Selbstassemblierung ; Membran ; Chemistry;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 2
    In: Physical Chemistry Chemical Physics, 2014, Vol.16(16), pp.7584-7594
    Description: Magnetic field dependence of long-lived spin states (LLSs) of the -CH 2 protons of aromatic amino acids was studied. LLSs are spin states, which are immune to dipolar relaxation, thus having lifetimes far exceeding the longitudinal relaxation times; the simplest example of an LLS is given by the singlet state of two coupled spins. LLSs were created by means of the photo-chemically induced dynamic nuclear polarization technique. The systems studied were amino acids, histidine and tyrosine, with different isotopomers. For labeled amino acids with the -CH and aromatic protons substituted by deuterium at low fields the LLS lifetime, T LLS , for the -CH 2 protons was more than 40 times longer than the T 1 -relaxation time. Upon increasing the number of protons the ratio T LLS / T 1 was reduced; however, even in the fully protonated amino acids it was about 10; that is, the long-lived mode was still preserved in the system. In addition, the effect of paramagnetic impurities on spin relaxation was studied; field dependencies of T 1 and T LLS were measured. LLSs were also formed in tyrosine-containing dyads; a T LLS / T 1 ratio of 7 was found, usable for extending the spin polarization lifetime in such systems.
    Keywords: Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 3
    In: Physical Chemistry Chemical Physics, 2013, Vol.15(35), pp.14660-14669
    Description: Spin hyperpolarization can be coherently transferred to other nuclei in field-cycling NMR experiments. At low magnetic fields spin polarization is redistributed in a strongly coupled network of spins. Polarization transfer is most efficient at fields where level anti-crossings (LACs) occur for the nuclear spin-states. A further condition is that field switching to the LAC positions is non-adiabatic in order to convert the starting population differences into spin coherences that cause time-dependent mixing of states. The power of this method has been demonstrated by studying transfer of photo-Chemically Induced Dynamic Nuclear Polarization (photo-CIDNP) in N -acetyl-tryptophan. We have investigated the magnetic field dependence and time dependence of coherent CIDNP transfer and directly assessed nuclear spin LACs by studying polarization transfer at specific field positions. The proposed approach based on LACs is not limited to CIDNP but is advantageous for enhancing NMR signals by spin order transfer from any type of hyper-polarized nuclei.
    Keywords: Magnetic Fields ; Coherence ; Dynamic Tests ; Polarization ; Nuclei ; Nuclear Magnetic Resonance ; Nuclear Spin ; Time Dependence ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 4
    Language: English
    In: Tetrahedron: Asymmetry, 2005, Vol.16(18), pp.2993-2997
    Description: The enantiorecognition of 1-aminoindane and -1-amino-2-indanol by ( , )-α,α′-bis(trifluoromethyl)-9,10-anthracenedimethanol is reported. The examination of the bidentate associations between and revealed that the conformation of is responsible for the separation of the NMR signals. Two types of bimodal associations resulted from a conformation when - isomer was tested. Molecular mechanics modelling studies gave the possible structures of the associate species.
    Keywords: Chemistry
    ISSN: 0957-4166
    E-ISSN: 1362-511X
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  • 5
    In: Physical Chemistry Chemical Physics, 2010, Vol.12(7), pp.1444-1452
    Description: A wedge-shaped amphiphilic molecule, 3,4,5-tridodecyloxycinnamic acid, was used as a model system to explore the role of different constitutive elements of the chemical structure in the formation of 2D and 3D self-assemblies. The polar heads forming cyclic hydrogen-bonded dimers determine the two largest unit cell parameters, which depend only slightly on the dimensionality of the system ( i.e. 2D versus 3D) and on the sample thermal history. By contrast, the structure of the alkyl side chains is very sensitive to the phase transformations, and is likely to be responsible for the rich polymorphic behaviour of the studied compound. Thus, in the monotropic SmC phase, the alkyl chains form a liquid-crystalline sub-lattice with hexagonal symmetry that can further crystallize either in a triclinic sub-cell (metastable crystalline phase) or in an orthorhombic sub-cell (stable crystalline phase). In 2D, at the interface with the graphite surface the molecular orientation is guided by the epitaxy. Although the largest lattice parameters are close to those in the bulk, the alkyl chains adopt a particular alternating orientation. In one molecule of the dimer, two alkyl chains have their molecular planes parallel to the substrate while the third chain is perpendicular to it, and the other way around for the other molecule of the dimer. To our knowledge, such alternating orientation of the alkyl chains in the monolayer is reported for the first time.
    Keywords: Kunststoff ; Selbstorganisation ; Werkstoffgefüge ; Modellierung ; Chemische Struktur ; Zweidimensionale Darstellung ; Dreidimensionale Abbildung ; Morphologie ; Dimer ; Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 6
    Language: English
    In: Journal of Molecular Structure, 2007, Vol.828(1), pp.59-67
    Description: Results are reported from molecular mechanics (MM), molecular dynamics (MD) and a combined mode – MD with a subsequent MM minimization, of the complexes of the chiral solvating agent (CSA) α,α′-bis(trifluoromethyl)-9,10-anthracenedimethanol ( ) in two of its diastereoisomeric forms (( , )- and -) with the substrates (1 ,2 )- and (1 ,2 )- -1-amino-2-indanol ( ). Our computational work was stimulated by preceding NMR study of the enantio differentiation capacity of the CSA manifested in the formation of bidentate complexes with the substrates. The molecular modeling and simulation studies gave possible structures and relative stabilities of the associated species. MM minimizations were sufficient in order to find the lowest energy minima of - /(1 ,2 )- and ( , )- /(1 ,2 )- , while the lowest energy structure of ( , )- /(1 ,2 )- was detected after the MD and MDMM studies. The complexes with the ( , )- isomer have higher total energies than those with - , in accord with an NMR estimate for longer lifetimes of the complexes with - .
    Keywords: Chiral Solvating Agents ; Bidentate Complexes ; Molecular Mechanics ; Molecular Dynamics ; Chemistry ; Physics
    ISSN: 0022-2860
    E-ISSN: 1872-8014
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  • 7
    Language: English
    In: The journal of physical chemistry. B, 29 October 2015, Vol.119(43), pp.13619-29
    Description: A new technique is developed that allows one to carry out the signal amplification by reversible exchange (SABRE) experiments at high magnetic field. SABRE is a hyperpolarization method, which utilizes transfer of spin order from para-hydrogen to the spins of a substrate in transient iridium complexes. Previously, it has been thought that such a transfer of spin order is only efficient at low magnetic fields, notably, at level anti-crossing (LAC) regions. Here it is demonstrated that LAC conditions can also be fulfilled at high fields under the action of a RF field. The high-field RF-SABRE experiment can be implemented using commercially available nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) machines and does not require technically demanding field-cycling. The achievable NMR enhancements are around 100 for several substrates as compared to their NMR signals at thermal equilibrium conditions at 4.7 T. The frequency dependence of RF-SABRE is comprised of well pronounced peaks and dips, whose position and amplitude are conditioned solely by the magnetic resonance parameters such as chemical shifts and scalar coupling of the spin system involved in the polarization transfer and by the amplitude of the RF field. Thus, the proposed method can serve as a new sensitive tool for probing transient complexes. Simulations of the dependence of magnetization transfer (i.e., NMR signal amplifications) on the frequency and amplitude of the RF field are in good agreement with the developed theoretical approach. Furthermore, the method enables continuous re-hyperpolarization of the SABRE substrate over a long period of time, giving a straightforward way to repetitive NMR experiments.
    Keywords: Amplitude ; Magnetic-Field ; Exchange ; Chemical-Shift ; Thermal-Equilibrium ; Iridium-Complex ; Spinning-System ; Hydrogen ; Magnetisation-Transfer ; Amplitude ; Magnetisches Feld ; Austausch ; Chemische Verschiebung ; Thermisches Gleichgewicht ; Iridiumkomplex ; Spinnsystem ; Wasserstoff ; Magnetisierungstransfer ; Chemistry;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 8
    Language: English
    In: The Journal of Chemical Physics, 28 December 2013, Vol.139(24)
    Description: Coherent polarization transfer effects in a coupled spin network have been studied over a wide field range. The transfer mechanism is based on exciting zero-quantum coherences between the nuclear spin states by means of non-adiabatic field jump from high to low magnetic field. Subsequent evolution of these coherences enables conversion of spin order in the system, which is monitored after field jump back to high field. Such processes are most efficient when the spin system passes through an avoided level crossing during the field variation. The polarization transfer effects have been demonstrated for N-acetyl histidine, which has five scalar coupled protons; the initial spin order has been prepared by applying RF-pulses at high magnetic field. The observed oscillatory transfer kinetics is taken as a clear indication of a coherent mechanism; level crossing effects have also been demonstrated. The experimental data are in very good agreement with the theoretical model of coherent polarization transfer. The method suggested is also valid for other types of initial polarization in the spin system, most notably, for spin hyperpolarization.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 9
    Language: English
    In: The Journal of Chemical Physics, 21 October 2014, Vol.141(15)
    Description: Nuclear Magnetic Relaxation Dispersion (NMRD) of protons was studied in the pentapeptide Met-enkephalin and the amino acids, which constitute it. Experiments were run by using high-resolution Nuclear Magnetic Resonance (NMR) in combination with fast field-cycling, thus enabling measuring NMRD curves for all individual protons. As in earlier works, Papers I–III, pronounced effects of intramolecular scalar spin-spin interactions, J-couplings, on spin relaxation were found. Notably, at low fields J-couplings tend to equalize the apparent relaxation rates within networks of coupled protons. In Met-enkephalin, in contrast to the free amino acids, there is a sharp increase in the proton T 1 -relaxation times at high fields due to the changes in the regime of molecular motion. The experimental data are in good agreement with theory. From modelling the relaxation experiments we were able to determine motional correlation times of different residues in Met-enkephalin with atomic resolution. This allows us to draw conclusions about preferential conformation of the pentapeptide in solution, which is also in agreement with data from two-dimensional NMR experiments (rotating frame Overhauser effect spectroscopy). Altogether, our study demonstrates that high-resolution NMR studies of magnetic field-dependent relaxation allow one to probe molecular mobility in biomolecules with atomic resolution.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 10
    Language: English
    In: Chemistry - A European Journal, 03/25/2013, Vol.19(13), pp.4300-4307
    Description: Keywords: alkynes; photochemistry; polymerization; topochemistry; X-ray diffraction Abstract A novel wedge-shaped compound containing two diacetylene tails, namely, methyl 3,5-bis(trideca-2,4-diyn-1yloxyl)benzoate (DDABM), was synthesized. As shown by UV/Vis spectroscopy this compound can be polymerized under UV irradiation. The crystalline structure of DDABM was investigated by grazing-incidence wide-angle X-ray diffraction on oriented crystalline films deposited on PTFE-rubbed silicon wafer substrates. Furthermore, the spherulites formed in thicker films were analyzed by wide-angle X-ray diffraction. A molecular packing model of DDABM based on the X-ray diffraction data is proposed. The diacetylene units are oriented along a defined lattice direction with a reticular distance of 4.85aA, which fulfills the requirements for topochemical polymerization. It was observed that UV polymerization does not affect the phase behavior of the compound, but mainly alters its optical properties. Author Affiliation: Interactive Materials Research - DWI an der RWTH Aachen e.V. and Institute for Technical and Macromolecular Chemistry of RWTH Aachen University, Forckenbeckstrasse 50, 52056 Aachen (Germany), Fax: (+49)241-80-233-01 Institut de Sciences des Materiaux de Mulhouse (IS2M-CNRS), 15 rue Jean Starcky, 68057 Mulhouse (France), Fax: (+33)389-60-87-99 Moscow State University, Faculty of Fundamental Physical and Chemical Engineering, GSP-1, 1-51 Leninskie Gory, Moscow, 119991 (Russian Federation) Interactive Materials Research - DWI an der RWTH Aachen e.V. and Institute for Technical and Macromolecular Chemistry of RWTH Aachen University, Forckenbeckstrasse 50, 52056 Aachen (Germany), Fax: (+49)241-80-233-01 Institut de Sciences des Materiaux de Mulhouse (IS2M-CNRS), 15 rue Jean Starcky, 68057 Mulhouse (France), Fax: (+33)389-60-87-99 Article Note: These authors contributed equally.
    Keywords: Crystal Structure -- Optical Properties ; Crystal Structure -- Analysis ; Polymerization -- Optical Properties ; Polymerization -- Analysis ; Polytetrafluoroethylene -- Optical Properties ; Polytetrafluoroethylene -- Analysis ; Alkynes -- Optical Properties ; Alkynes -- Analysis;
    ISSN: Chemistry - A European Journal
    E-ISSN: 09476539
    E-ISSN: 15213765
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