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Berlin Brandenburg

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  • American Chemical Society (CrossRef)  (34)
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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
    Language: English
    In: The journal of physical chemistry. B, 30 April 2009, Vol.113(17), pp.5752-9
    Description: Trajectories obtained from molecular dynamics (MD) simulations of some large-ring cyclodextrins (LR-CDs) were analyzed by a statistical method, principal component analysis (PCA), thus enabling the monitoring of the dominant PCA modes for concerted motions of the macroring atoms in a lower-dimensions subspace. Earlier analyses of macrorings' conformational deformations based on examination of snapshots extracted from the MD simulation trajectories were further supported on more quantitative grounds. The first 10 lowest-indexed modes describe more than 90% of the total atomic motion in all cases, with more than 50% of the contribution coming from the two highest-eigenvalue principal components. Representative average geometries of the cyclodextrin macroring were also obtained.
    Keywords: Computer Simulation ; Models, Chemical ; Principal Component Analysis ; Cyclodextrins -- Chemistry
    ISSN: 1520-6106
    E-ISSN: 15205207
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  • 3
    Language: English
    In: The Journal of organic chemistry, 03 March 2006, Vol.71(5), pp.2056-63
    Description: The complexation of an adamantyl-phosphate derivative with one beta-cyclodextrin, with two beta-cyclodextrins, and with two beta-cyclodextrins dimerized with a disulfide bridge was studied by computational methods (MD, MM/PBSA, and MM/GBSA) to analyze and rationalize the chelate effect. Although this effect is usually explained by invoking favorable entropy contribution due to the preorganization of the ligand, it has been determined experimentally that in this case it is enthalpy-driven. The computational results are in accord with this finding, although the entropy contribution due to the solvent structural organization around the complex is crucial for the final estimates of the free energy of complexation.
    Keywords: Computer Simulation ; Chelating Agents -- Chemistry ; Beta-Cyclodextrins -- Chemistry
    ISSN: 0022-3263
    E-ISSN: 15206904
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  • 4
    In: Journal of Physical Chemistry A, Oct 18, 2001, Vol.105(41), p.9415(7)
    Keywords: Physical Chemistry -- Research ; Surface Chemistry -- Research ; Carbon Compounds -- Research ; Monomolecular Films -- Research
    ISSN: 1089-5639
    E-ISSN: 15205215
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  • 5
    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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  • 6
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 13 January 2015, Vol.31(1), pp.529-34
    Description: Noble metal nanoparticles with ligand shells are of interest for applications in catalysis, thermo-plasmonics, and others, involving heating processes. To gain insight into the structure-formation processes in such systems, self-assembly of carbohydrate-functionalized gold nanoparticles during precipitation from solution and during further heating to ca. 340 °C was explored by in situ combination of nanobeam SAXS/WAXS and nanocalorimetry. Upon precipitation from solution, X-ray scattering reveals the appearance of small 2D domains of close-packed nanoparticles. During heating, increasing interpenetration of the nanoparticle soft shells in the domains is observed up to ca. 81 °C, followed by cluster formation at ca. 125 °C, which transform into crystalline gold nuclei at around 160 °C. Above ca. 200 °C, one observes the onset of coalescence and grain growth resulting in gold crystallites of average size of about 100 nm. The observed microstructural changes are in agreement with the in situ heat capacity measurements with nanocalorimetry.
    ISSN: 07437463
    E-ISSN: 1520-5827
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  • 7
    Language: English
    In: Macromolecules, 09/25/2012, Vol.45(18), pp.7454-7460
    Keywords: Chemistry;
    ISSN: 0024-9297
    E-ISSN: 1520-5835
    Source: American Chemical Society (via CrossRef)
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  • 8
    Language: English
    In: Macromolecules, 06/15/2017
    Description: We report on the structure of a system of wedge-shaped molecules with a sulfonic end group incorporated into the both the homopolymer P2VP and the block copolymer P2VP-b-PEO, at degrees of complexing of 25%, 50%, and 100%. From X-ray scattering in the bulk all three homopolymer complexes reveal a lamellar phase, which is, however, for 100% mixed with a hexagonal phase. In agreement with earlier work on thin films, the corresponding block copolymers show all a structure of PEO cylinders perpendicular to lamellae of the ligands. Between 25% and 50% neutralization the packing changes from relatively loose layers consisting of several backbone chains with ligands for 25% to a situation of single backbones with highly stretched ligands for higher degrees of neutralization. In the latter cases crystallization of the confined PEO blocks is strongly reduced.
    Keywords: Ligand ; Homopolymer ; Blockcopolymer ; X-Strahl ; Lamelle ; Sulfonierte Endgruppe ; Dünnfilm ; Hexagonale Kristallstruktur ; Chemistry;
    ISSN: 0024-9297
    E-ISSN: 1520-5835
    Source: American Chemical Society (via CrossRef)
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  • 9
    Language: English
    In: Macromolecules, 12/09/2014, Vol.47(23), pp.8295-8304
    ISSN: 0024-9297
    E-ISSN: 1520-5835
    Source: American Chemical Society (via CrossRef)
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  • 10
    Language: English
    In: Journal of Physical Chemistry B, Nov 23, 2016, Vol.120(46), pp.11978-11986
    Description: We describe an NMR method to generate singlet order in spin pairs from longitudinal spin magnetization and suppress residual background signals. This method can also be used for generating and observing long-lived spin states. A singlet order selection (SOS) filter is proposed, which allows us to find signals of the spin pair of interest buried in a crowded NMR spectrum. Likewise, SOS filtering enables proton NMR measurements in H2O without pulse sequences for solvent suppression. We demonstrate that the method works perfectly for both weakly and strongly coupled spin pairs. Furthermore, it can be combined with standard NMR pulse sequences: in this way, T1- and T2-relaxation times for spin pairs of interest can be measured. The power of the SOS-filter is demonstrated by relaxation studies in biomolecules.
    Keywords: Nuclear Magnetic Resonance – Research ; Magnetization – Analysis ; Spin Coupling – Research
    ISSN: 1520-6106
    E-ISSN: 15205207
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