The cubic mesophase formed by monoacylglycerols and water is an important medium for the crystallogenesis of membrane proteins. To investigate molecular level lipid and additive interactions within the cubic phase, a method was developed for improving the resolution of H-1 NMR spectra when using a conventional solution state NMR probe. Using this approach we obtained well-resolved J-coupling multiplets in the one-dimensional NMR spectrum of the cubic-Ia3d phase prepared with hydrated monoolein.
The Carr-Purcell-Meiboom-Gill (CPMG) experiment has gained popularity in solid-state NMR as a method for enhancing sensitivity for anisotropically broadened spectra of both spin 1/2 and half integer quadrupolar nuclei. Larger sensitivity enhancements are observed as the delay between the 180 degree pulses is shortened. However, as the duration between the 180 degree pulses is shortened, the echoes become truncated and information about the nuclear spin interactions is lost. We explored the relationship between enhanced sensitivity and loss of information as a function of the product span and inter pulse delay and additionally TOP data processing approach is presented.
The anisotropic components of chemical shift contain information on the local structure around a particular nuclei of interest that is typically averaged away during magic angle spinning (MAS). While information of the full tensor can be obtained through acquisition of a static powder pattern or analysis of characteristic spinning sideband patterns during MAS, each of these one dimensional spectra are complex when multiple chemical sites are present. To better determine the relative contributions from multiple chemical sites it is, therefore, advantageous to utilize 2D techniques such as Magic Angle Flipping (MAF), Magic Angle Hopping (MAH), Magic Angle Turning (MAT), or 2D Phase Adjusted Spinning Sideband. However, each of these techniques suffers from low sensitivity making applications to samples with low natural abundance, such as Si-29 (4.6%), limited. Here, we couple 2D PASS with CPMG acquisition for added sensitivity enhancement.It is shown that echoes following odd 180 degree pulses satisfy the conditions described by Dixon (1982) while echoes following the even 180 degree pulses do not and in this manner a significant sensitivity gain is observed.
The analysis of compounds with paramagnetic atoms incorporated in the structure is a growing field in solid state nuclear magnetic resonance. In typical H-2 NMR studies of diamagnetic materials, analysis of the observed first order quadrupolar powder patter or Pake patter is able to provide insight into molecular structure and dynamics. However, for paramagnetic materials the magnitude of the paramagnetic/chemical shift anisotropy becomes significant. In this study, we present a shifted Hahn echo sequence to separate components of the chemical shift and quadrupolar interactions, for nuclei where I = 1. A two times sensitivity is observed in shifted Hahn echo sequence compared to shifted solid echo sequence presented by Antonijevic et al. A formalism is also discussed to visualize how echoes will be refocused during a NMR experiment.