Preferential solvation of carbohydrates in water-trifluoroethanol mixtures: a solvent detected heteronuclear NMR approach.

The present study aims to establish a simple approach involving multi-field multinuclear longitudinal relaxation (R1) analysis of the solvents to decipher solute-solvent interactions during the solvation of model carbohydrates in aqueous trifluoroethanol (TFE) co-solvent systems (TFE:D2O). The behavior of D2O and TFE is monitored around β-CD (β-cyclodextrin) and glucose through R1D (2H) and R1F (19F), respectively. Correlation times (τc) are estimated for D2O and TFE for various % (v/v) compositions of TFE:D2O mixtures.

Magnetic resonance imaging of enhanced mobility of light non aqueous phase liquid (LNAPL) during drying of water wet porous media.

Visualization of NAPLs in multiphase systems in porous media is important for determining contaminant transport in the environment. In this study, magnetic resonance imaging (MRI) was used to confirm the recent observations of mobilisation of a light non aqueous phase liquid (LNAPL) trapped in wet sand under natural drying conditions of the wet porous medium. Visualization of LNAPL (motor oil) and water mobility during the drying of wet glass beads (0.

Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature C ODNP at Moderately Low Fields and Natural Abundance.

Overhauser dynamic nuclear polarization (ODNP) is investigated at a moderately low field (1.2 T) for natural abundance C NMR of small molecules in solution state at room temperature. It is shown that ODNP transferred from H to C by NMR coherence transfer is in general significantly more efficient than direct ODNP of C.

Slow Molecular Motions in Ionic Liquids Probed by Cross-Relaxation of Nuclear Spins During Overhauser Dynamic Nuclear Polarization.

Solution-state Overhauser dynamic nuclear polarization (ODNP) at moderate fields, performed by saturating the electron spin resonance (ESR) of a free radical added to the sample of interest, is well known to lead to significant NMR signal enhancements in the steady state, owing to electron-nuclear cross-relaxation. Here it is shown that under conditions which limit radical access to the molecules of interest, the time course of establishment of ODNP can provide a unique window into internuclear cross-relaxation, and reflects relatively slow molecular motions. This behavior, modeled mathematically by a three-spin version of the Solomon equations (one unpaired electron and two nuclear spins), is demonstrated experimentally on the F/ H system in ionic liquids.

Quantification in Hyperpolarized NMR.

Quantitative aspects of hyperpolarized NMR are analyzed in the present work, and it is shown theoretically and experimentally that measured "apparent" signal enhancements could deviate significantly from real enhancements of polarization. Expressions are given as a function of spin count to deduce real enhancements from measured "apparent" enhancements, and vice versa. While the findings are of particular relevance to high-field work employing high-Q probes, and to analytical applications of hyperpolarized NMR whose objective is the measurement of spin count, our experiments demonstrate their significance even for low- and moderate-field work with probes of moderate Q-factor.

Two-dimensional nuclear magnetic resonance: exploiting spin echoes to maximize information content by suppression of diagonal peaks in homonuclear experiments.

Two-dimensional nuclear magnetic resonance (2D NMR) correlation spectra help visualize inter- or intra-molecular spin connectivity through space or through bonds. This is accomplished by magnetization transfer between interacting ("connected") spins located at different sites in molecules. In homonuclear 2D experiments, cross peaks which demonstrate spin connectivity and result from magnetization transfer between sites are unfortunately invariably accompanied by other peaks that result from magnetization that has not undergone any transfer, viz.

Chemical-shift-resolved ¹⁹F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy.

Overhauser-DNP-enhanced homonuclear 2D (19)F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000 MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra.

(119/117/115)Sn low-abundance single-transition correlation spectroscopy (LASSY): sensitivity-enhanced homonuclear correlation experiments for Sn NMR.

We report the implementation of our novel rare-spin homonuclear correlation experiment, namely, Low-Abundance Single-transition correlation SpectroscopY (LASSY), for (119/117/115)Sn NMR at natural abundance. Our pulse sequence results in diagonal suppressed COSY-style display and outperforms the optimal homonuclear correlation experiment for rare spins, which involves double quantum evolution (INADEQUATE CR). The new experiment maximizes efficiency both in respect of pulse transformations as well as relaxation effects, and gives rise to a simplified two-dimensional (2D) spectrum with considerably reduced crowding, exhibiting only one transition in each cross peak, instead of four.

Postharvest ripening study of sweet lime (Citrus limettioides) in situ by volume-localized NMR spectroscopy.

Spatially resolved NMR--especially volume-localized spectroscopy (VLS)is useful in various fields including clinical diagnosis, process monitoring, etc. VLS carries high significance because of its ability to identify molecular species and hence track molecular events. This paper reports the application of VLS at 200 MHz to study the postharvest ripening of sweet lime ( Citrus limettioides ) in situ, including a comparative study of normal and acetylene-mediated ripening.

1H detected (13)C echo planar imaging.

Cyclic J cross polarisation (CYCLCROP) is a sensitive method for the noninvasive monitoring of (13)C distributions and fluxes. The PRAWN rotating frame Hartmann-Hahn mixing sequence ameliorates problems associated with sensitivity to Hartmann-Hahn mismatch and reduces RF power deposition. The combination of CYCLCROP with echo planar imaging (EPI) for spatial encoding of the proton detected carbon signal allows efficient use of the available signal to be made, permitting a significant improvement in the temporal resolution of any study.