%0 Journal Article %J Journal of Physical Chemistry A %D 2000 %T Exploring single-file diffusion in one-dimensional nanochannels by laser-polarized Xe-129 NMR spectroscopy (Cover Article) %A Meersmann, T. %A Logan, J. W. %A Simonutti, R. %A Caldarelli, S. %A Comotti, A. %A Sozzani, P. %A Kaiser, L. G. %A Pines, A. %K model %X

Single-file diffusion behavior is expected for atoms and molecules in one-dimensional gas phases of nanochannels with transverse dimensions that do not allow for the particles to bypass each other. Although single-file diffusion may play an important role in a wide range of industrial catalytic, geologic, and biological processes, experimental evidence is scarce despite the fact that the dynamics differ substantially from ordinary diffusion. We demonstrate the application of continuous-flow laser-polarized Xe-129 NMR spectroscopy for the study of gas transport into the effectively one-dimensional channels of a microporous material. The novel methodology makes it possible to monitor diffusion over a time scale of tens of seconds, often inaccessible by conventional NMR experiments. The technique can also be applied to systems with very small mobility factors or diffusion constants that are difficult to determine by currently available methods for diffusion measurement. Experiments using xenon in nanochannel systems can distinguish between unidirectional diffusion and single-file diffusion. The experimental observations indicate that single-file behavior for xenon in an organic nanochannel is persistent even at long diffusion times of over tens of seconds. Finally;using continuous flow laser-polarized Xe-129 NMR spectroscopy, we describe an intriguing correlation between the observed NMR line shape of xenon within the nanochannels and the gas transport into these channels.

%B Journal of Physical Chemistry A %V 104 %P 11665-11670 %8 Dec 21 %@ 1089-5639 %G English %U ://WOS:000165869600001 %N 50 %M WOS:000165869600001 %! Exploring single-file diffusion in one-dimensional nanochannels by laser-polarized Xe-129 NMR spectroscopy %R Doi 10.1021/Jp002322v %0 Journal Article %J Journal of Physical Chemistry %D 1996 %T Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy %A Hong, M. %A Pines, A. %A Caldarelli, S. %K shape %X

We describe multidimensional NMR techniques to measure and assign C-13-H-1 dipolar couplings in nematic liquid crystals with high resolution. In particular, dipolar couplings between aromatic and aliphatic sites are extracted, providing valuable information on the structural correlations between these two components of thermotropic liquid crystal molecules. The NMR techniques are demonstrated on 4-pentyl-4'-biphenylcarbonitrile (5CB), a well-characterized room-temperature nematic liquid crystal. Proton-detected local-field NMR spectroscopy is employed to obtain highly resolved C-H dipolar couplings that are separated according to the chemical shifts of the carbon sites. Each C-13 cross section in the 2D spectra exhibits several doublet splittings, with the largest one resulting from the directly bonded C-H coupling, The smaller splittings originate from the long-range C-H dipolar couplings and can be assigned qualitatively by a chemical shift heteronuclear correlation (HETCOR) experiment. The HETCOR experiment incorporates a mixing period for proton spin diffusion to occur, so that maximal polarization transfer can be achieved between the unbonded C-13 and H-1 nuclei. To assign the long-range C-H couplings quantitatively, we combined these two techniques into a novel reduced-3D experiment, in which the H-1 chemical shift-displaced C-H dipolar couplings are correlated with the C-13 chemical shifts. The time domain of this experiment involves separate but synchronous incrementation of the evolution periods for the C-H dipolar couplings and the H-1 chemical shifts, with a variable ratio of the respective dwell times to optimize the resolution and facilitate resonance assignment in the spectrum.

%B Journal of Physical Chemistry %V 100 %P 14815-14822 %8 Aug 29 %@ 0022-3654 %G English %U ://WOS:A1996VE37300036 %N 35 %M WOS:A1996VE37300036 %! Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy %R Doi 10.1021/Jp960972m %0 Journal Article %J Journal of Physical Chemistry %D 1996 %T Measurement of carbon-proton dipolar couplings in liquid crystals by local dipolar field NMR spectroscopy %A Caldarelli, S. %A Hong, M. %A Emsley, L. %A Pines, A. %K solids %X

The performance of several different two-dimensional NMR methods for the measurement of carbon-proton dipolar couplings in liquid crystalline phases is analyzed. Proton-detected local field spectroscopy allows the measurements of short range C-H couplings, which correspond to directly bond pairs, by direct inspection of the spectra. Off magic angle (OMAS) spinning techniques can be applied to anisotropic phases that can be oriented mechanically at an angle to the magnetic field, such as nematic phases. The consequent scaling of the chemical shift anisotropy and dipolar couplings can be used to resolve otherwise overlapping resonances, Moreover, an estimate of the accuracy of the technique can be achieved by performing a series of OMAS experiments with different sample orientations.

%B Journal of Physical Chemistry %V 100 %P 18696-18701 %8 Nov 28 %@ 0022-3654 %G English %U ://WOS:A1996VV35400008 %N 48 %M WOS:A1996VV35400008 %! Measurement of carbon-proton dipolar couplings in liquid crystals by local dipolar field NMR spectroscopy %R Doi 10.1021/Jp962023z