Dynamic and magnetic susceptibility effects on the MAS NMR linewidth of a tetrapeptide bound to different resins

Abstract

Under magic angle spinning, the NMR spectrum of the tetrapeptide Ala-Ile-Gly-Met bound to a Wang resin, and swollen in DMF, exhibits proton and carbon linewidths that are sharp enough to allow the complete characterization of the peptide using classical liquid-state NMR methods. The proton linewidths of the bound peptide remain, however, about three times larger than those of the free peptide in solution. The residual NMR linewidth originates essentially from incompletely averaged magnetic susceptibility effects due to the Wang resin. Replacing the aromatic Wang resin with a PEGA or POEPOP resin removes this effect. To investigate the contribution to line broadening of the peptide dynamics, relaxation studies were performed on the peptide bound to Wang and POEPOP resins.

Alignment and structural analysis of membrane polypeptides by 15N and 31P solid‐state NMR spectroscopy

“…This technique results in averaging of the anisotropy of dipolar, quadrupolar, and chemical shift interactions (11, 45, 47, 74 -76). MAS solid-state NMR spectroscopy has been used, for example, during the investigation of peptides that are coupled to the resins used during solid-phase peptide synthesis (77)(78)(79). MAS results in well-resolved NMR spectra in which the heterogeneity of the sample determines to a large extent the half-width of the NMR resonances.…”

Chromatographic NMR: a tool for the analysis of mixtures of small molecules

“…17,18 The presence of anisotropic susceptibility has been clearly shown in cases in which aromatic moieties are abundant in the medium, as in some resins used for solid-phase organing synthesis (SPOS). 4,19 The magnitude of the susceptibility broadening naturally increases linearly with the magnetic field size, a point that should not be forgotten when designing HRMAS experiments at high field, and variable field experiment actually demonstrated that this mechanism may be the dominant one behind residual line broadening in HRMAS. 19 Further enhancement of the resolution can be achieved though partial compensation for line distortions, which in MAS can be achieved by magnetic field compensation coils (shims), as in regular nonspinning or parallel spinning NMR.…”

“…4,19 The magnitude of the susceptibility broadening naturally increases linearly with the magnetic field size, a point that should not be forgotten when designing HRMAS experiments at high field, and variable field experiment actually demonstrated that this mechanism may be the dominant one behind residual line broadening in HRMAS. 19 Further enhancement of the resolution can be achieved though partial compensation for line distortions, which in MAS can be achieved by magnetic field compensation coils (shims), as in regular nonspinning or parallel spinning NMR. However, the field corrections should be now performed considering the spinning axis as the principal (quantization) direction.…”

“…In favorable cases, even linewidths comparable to liquid-state can be achieved, but otherwise the spectral resolution achieved HRMAS is extremely variable, depending essentially on the local mobility of the observed species and on the physical constitution of the medium. 19 Interestingly, variations in mobility can be expected to induce a plethora of effects, from different relaxation times, possibly residual homonuclear dipolar broadening, to interference with the averaging MAS process. Limitations of the sample holder volume as well as a careful design of its geometry may counter, to some extent, the contribution to the resolution loss due to variable magnetic susceptibility.…”

Proton Dipolar Recoupling in Resin-Bound Peptides under High-Resolution Magic Angle Spinning

“…High resolution magic angle spinning (HRMAS) (1, 2) is a powerful tool for the characterization of molecules bound to swollen resins (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), swollen polymers (15), or other soft materials such as lipid membranes (16,17 ), biological tissues (18,19), or fluids contained in solid media (20). The linewidth observed in the static 1 H NMR spectra of such samples originates mainly from large variations in the bulk magnetic susceptibility of the sample (14,21).…”