Tuesday, January 05, 2010

Solid State Nuclear Magnetic Resonance

Multiple quadrupolar spin echoes in the La-filled skutterudite LaOs4As12

Publication year: 2009
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 23 December 2009
B., Nowak , O., Żogał , Z., Henkie , M.B., Maple

We report experimental results of 139La pulse NMR studies in LaOs4As12. Measurements have been performed on a powder sample obtained from high quality single crystals. For the first time the pattern of quadrupole echoes for 139La nuclei (I=7/2) was obtained. All the allowed quadrupolar echoes expected for spin I=7/2 were observed at times t = (4/3)tau, (3/2) tau, (5/3) tau, 2 tau, (5/2) tau, 3 tau, 4 tau. The presence of quadrupolar echoes is the fingerprint of the deviation from perfect cubic symmetry of the structure and can be used as a simple and fast test of the sample quality.

Saving transverse magnetization

Publication year: 2009
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 21 December 2009
Takeshi, Kobayashi , Joseph A., DiVerdi , Rebecca A., Faulkner , Gary E., Maciel

A magnetization storage sequence, ALT-1 (alternating longitudinal and transverse components), is reported. The ALT-1 sequence is a hybrid of two types of storage sequences, the Carr–Purcell type and store-and-restore sequences. During incremental storage periods within the ALT-1 sequence, essentially half of the initially transverse magnetization is stored along the z-axis and the other half is prolonged by an echo-generating pulse. The portions of initial magnetization that are stored as longitudinal components or transverse components are alternated by a π/2 pulse during the cycle. Both transverse components of the initial magnetization are treated the same in the ALT-1 sequence and orientational (phase) information of the initial magnetization is kept during the storage period. The ALT-1 sequence can preserve magnetization more effectively than a published class of modified Carr–Purcell type sequences, because essentially half of the magnetization during incremental storage periods is not subjected to relaxation from T2 effects.

Magnetic resonance tensors in uracil: Calculation of 13C, 15N, 17O NMR chemical shifts, 17O and 14N electric field gradients and measurement of 13C and 15N chemical shifts

Publication year: 2009
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 16 December 2009
Saeed K., Amini , Hoora, Shaghaghi , Alex D., Bain , Ammar, Chabok , Mohsen, Tafazzoli

The experimental 13C NMR chemical shift components of uracil in the solid state are reported for the first time (to our knowledge), as well as newer data for the 15N nuclei. These experimental values are supported by extensive calculated data of the 13C, 15N and 17O chemical shielding and 17O and 14N electric field gradient (EFG) tensors. In the crystal, uracil forms a number of strong and weak hydrogen bonds, and the effect of these on the 13C and 15N chemical shift tensors is studied. This powerful combination of the structural methods and theoretical calculations gives a very detailed view of the strong and weak hydrogen bond formation by this molecule. Good calculated results for the optimized cluster in most cases (except for the EFG values of the 14N3 and 17O4 nuclei) certify the accuracy of our optimized coordinates for the hydrogen nuclei. Our reported RMSD values for the calculated chemical shielding and EFG tensors are smaller than those reported previously. In the optimized cluster the 6-311+G** basis set is the optimal one in the chemical shielding and EFG calculations, except for the EFG calculations of the oxygen nuclei, in which the 6-31+G** basis set is the optimal one. The optimal method for the chemical shielding and EFG calculations of the oxygen and nitrogen nuclei is the PW91PW91 method, while for the chemical shielding calculations of the 13C nuclei the B3LYP method gives the best results.

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