William S. Price

195Pt NMR--theory and application.

This critical review highlights the progress in (195)Pt NMR over the last 25 years. In particular, some of the recent applications of (195)Pt NMR in catalytic and mechanistic studies, intermetallics and drug binding studies are discussed. (195)Pt NMR chemical shifts obtained from both theoretical studies and experiments are presented for Pt(0), Pt(II), Pt(III) and Pt(IV) complexes. (195)Pt coupling with various nuclei (viz. coupling constants) have also been collected in addition to data on (195)Pt relaxation. The latest developments in the theoretical knowledge and experimental advances have made (195)Pt NMR into a rich source of information in many fields. (164 references.).

NMR studies of translational motion

1. Diffusion and its measurement 2. Theory of NMR diffusion measurements 3. PGSE measurements in simple porous systems 4. PGSE measurements in complex and exchanging systems 5. PGSE hardware 6. Setup and analysis of PGSE experiments 7. PGSE hardware and sample problems 8. Specialised PGSE and related techniques 9. NMR imaging studies of translational motion 10. B1 gradient methods 11. Applications Appendices References.

Water Signal Suppression in NMR Spectroscopy

The area of solvent suppression has a long history and is an indispensable part of almost every NMR experiment conducted in a solvent containing nuclei of the type to be detected. This chapter provides a general coverage of solvent suppression methodr in NMR with special attention to the enormous developments in the past decade that have occurred due to the widespread usage of magnetic field gradients and shaped RF pulses. The general considerations and instrumental complications associated with the presence of a large signal are first discussed. The complications resulting from the radiation damping and demagnetizing fiela3 are considered in some detail since their effects are becoming more manifest with the increasingly higher field strengths available. The methods of solvent suppression are then covered including their application to multidimensional experiments. Brief coverage is also given to suppression in imaging experiments, experiments involving high-molecular-weight compounds and also 17 O NMR.

Ion Transport Properties of Six Lithium Salts Dissolved in γ-Butyrolactone Studied by Self-Diffusion and Ionic Conductivity Measurements

The self-diffusion coefficients of the lithium ion, anion, and solvent in electrolytes prepared by dissolving six lithium salts (LiBF 4 , LiPF 6 , LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , and lithium bis(oxalateborate)) in γ-butyrolactone (GBL) were measured using pulsed gradient spin-echo nuclear magnetic resonance. The ionic conductivity calculated from the ion self-diffusion coefficients was compared with the electrochemically measured ionic conductivity. In each sample, GBL diffused the fastest, followed by the anion and then the lithium ion. The diffusion of the solvent and cation were insensitive to the anions. On average each lithium ion was solvated by about two GBL molecules. The hydrodynamic size of the anions normalized by their respective van der Waals radius was determined and almost independent of the salt concentration for PF - 6, N(SO 2 CF 3 ) - 2, N(SO 2 C 2 F 5 ) - 2, and B(C 4 O 8 ) - , but increased with salt concentration for BF - 4 and CF 3 SO - 3 due to ion association.

Correlating the NMR self-diffusion and relaxation measurements with ionic conductivity in polymer electrolytes composed of cross-linked poly(ethylene oxide-propylene oxide) doped with LiN(SO2CF3)2

A solvent-free solid-polymer electrolyte based on a cross-linked poly(ethylene oxide-propylene oxide) random copolymer doped with LiN(SO2CF3)2, was studied using multinuclear NMR and ionic conductivity. The NMR spin-lattice relaxation times, T1, of the bulk polymer (1H), the lithium ion (7Li) and the anion (19F) were analyzed using single exponential analysis above the glass transition temperatures. Since the temperature dependent 1H and 7Li NMR T1 values had minima, the reorientational correlation times were obtained for the segmental motion of the CH2CH2O/CH2CH(CH3)O moiety of the bulk polymer and the hopping motion of the lithium ions correlated with the segmental motion. The spin–spin relaxation of the anion signals appeared single exponential with respect to time, whereas that of the polymer and the lithium echo signals were at least bi-exponential. Since both the spin-lattice and spin–spin relaxation of the anion indicated a single component, the self-diffusion coefficients, D, were measured using 1...

Ionic conduction and self-diffusion near infinitesimal concentration in lithium salt-organic solvent electrolytes

The Debye–Huckel–Onsager and Nernst–Einstein equations, which are based on two different conceptual approaches, constitute the most widely used equations for relating ionic conduction to ionic mobility. However, both of these classical (simple) equations are predictive of ionic conductivity only at very low salt concentrations. In the present work the ionic conductivity of four organic solvent-lithium salt-based electrolytes were measured. These experimental conductivity values were then contrasted with theoretical values calculated using the translational diffusion (also known as self-diffusion or intradiffusion) coefficients of all of the species present obtained using pulsed-gradient spin–echo (1H, 19F and 7Li) nuclear magnetic resonance self-diffusion measurements. The experimental results verified the applicability of both theoretical approaches at very low salt concentrations for these particular systems as well as helping to clarify the reasons for the divergence between theory and experiment. In p...

Self-diffusion coefficients of lithium, anion, polymer, and solvent in polymer gel electrolytes measured using 7Li, 19F, and 1H pulsed-gradient spin-echo NMR

Abstract Four series of solution and corresponding polymer gel electrolyte systems were studied. The systems were composed of a solvent (γ-butyrolactone (GBL) or propylene carbonate (PC)), (three different concentrations of) a lithium salt (LiBF 4 or lithium bis(trifluromethanesulfonyl)-imide (LiTFSI, LiN(SO 2 CF 3 ) 2 )), and poly(ethylene glycol diacrylate) of molecular weight 4000 (PEO), which was cross-linked to form the polymer gels. The self-diffusion coefficients of the lithium, the anions, the solvents and the polymer were obtained independently using 7 Li, 19 F and 1 H pulsed-gradient spin-echo NMR measurements. From the individual diffusion coefficients of each component of the GBL–LiBF 4 , GBL–LiTFSI, PC–LiBF 4 , and PC–LiTFSI solutions and the corresponding polymer gel electrolytes, the solvation and the solvent-dependent behaviour of the lithium and the anions are clearly shown. Especially in the gels, the lithium binding with the PEO matrix were found to be quite different depending on whether the solvent was PC or GBL.

Visualization of Freezing Behaviors in Leaf and Flower Buds of Full-Moon Maple by Nuclear Magnetic Resonance Microscopy

1H-Nuclear magnetic resonance (NMR) microscopy was used to study the freezing behavior of wintering buds of full-moon maple (Acer japonicum Thunb.). The images obtained predominantly reflected the density of mobile (i.e. non-ice) protons from unfrozen water. A comparison of NMR images taken at different subfreezing temperatures revealed which tissues produced high- and low-temperature exotherms in differential thermal analyses. In leaf and lower buds of A. japonicum, the scales and stem bark tissues were already frozen by -7[deg]C, but the primordial inflorescence and terminal primordial shoots remained supercooled at -14[deg]C, and the lateral primordial shoots were unfrozen even at -21[deg]C. The freezing of these supercooled tissues was associated with their loss of viability. The size of the supercooled primordial shoots and inflorescences was gradually reduced with decreasing temperature, indicating extraorgan freezing in these tissues. During this process the formation of dark regions beneath the primordia and subsequent gradual darkening in the basal part of supercooled primordia were visible. As the lateral shoot primordia were cooled, the unfrozen area was considerably reduced. Since the lateral primordia remained viable down to -40[deg]C, with no detectable low-temperature exotherms, they probably underwent type I extraorgan freezing. Deep supercooling in the xylem was clearly imaged. NMR microscopy is a powerful tool for noninvasively visualizing harmonized freezing behaviors in complex plant organs.

J‐compensated PGSE: an improved NMR diffusion experiment with fewer phase distortions

Peak distortion caused by homonuclear 1H J‐coupling is a major problem in many spin‐echo‐based experiments such as pulsed gradient spin‐echo (PGSE) experiments. Although peak phase distortions can be lessened by the incorporation of anti‐phase purging sequences, the sensitivity is substantially decreased. Techniques for lessening the effect of homonuclear J‐coupling evolution in spin‐echo‐based experiments have been investigated. Two potentially useful candidates include a J‐compensated inversion sequence that is efficient over a wide range of J‐coupling values and a pulse sequence that refocuses homonuclear J‐evolution during the spin‐echo. The latter was found to work superbly on samples containing two spin (AX or AB) systems and still provided significant advantage over the standard method on samples containing more complicated spin systems. Implementation of this J‐refocusing technique into a PGSE‐type experiment (J‐PGSE) leads to dramatic improvement of spectra and easier data analysis. The J‐PGSE sequence should find applications in many diffusion studies where the PGSE‐type method is required and should be a viable alternative to PGSTE especially in dilute samples due to its enhanced sensitivity. Copyright

Determination of pore space shape and size in porous systems using NMR diffusometry. Beyond the short gradient pulse approximation.

The influence of finite length gradient pulses on NMR diffusion experiments on liquids confined to diffuse between two parallel planes is investigated. It is experimentally verified that the pore size decreases when determined using finite gradient pulses if the results are analyzed within the short gradient pulse approximation. The results are analyzed using the matrix formulation. The observed minima in the echo decay profiles are considerably less sharp than theoretical analysis would indicate and we suggest that this is due to the presence of a distribution of pore sizes in the sample. In addition, effects due to the presence of background gradients are discussed. It is argued that effects due to the finite length gradient pulses are relatively minor and in realistic applications the effects due to inhomogeneities in pore sizes and effects due to background gradients will constitute more serious problems in pore size determinations by means of NMR diffusometry.