Heteronuclear chemical shift correlation and J‐resolved MAS NMR spectroscopy of lipid membranes

Abstract

Direct observation of J-couplings remains a challenge in high-resolution solid-state NMR. In some cases, it is possible to use Lee-Goldburg (LG) homonuclear decoupling during rare spin observation in MAS NMR correlation spectroscopy of lipid membranes to obtain J-resolved spectra in the direct dimension. In one simple implementation, a wide line separation-type (13)C-(1)H HETCOR can provide high-resolution (1)H/(13)C spectra, which are J-resolved in both dimensions. Coupling constants, (1)J(HC), obtained from (1)H doublets, can be compared with scaled (1)J(θ)(CH)-values obtained from the (13)C multiplets to assess the LG efficiency and scaling factor. The use of homonuclear decoupling during proton evolution, LG-HETCOR-LG, can provide J-values, at least in the rare spin dimension, and allows measurements in less mobile membrane environments. The LG-decoupled spectroscopic approach is demonstrated on pure dioleoylphosphatidylcholine (DOPC) membranes and used to investigate lipid mixtures of DOPC/cholesterol and DOPC/cholesterol/sphingomyelin.

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“…7A and 8A show the 13 C CP/MAS-NMR of DOPC bilayers in D 2 O at 27 °C whereas the 13 C chemical shifts are shown in Table S1. The obtained values are in agreement with those reported by Zorin et al [10]. …”

“…In Tables S1 and S2 the chemical shifts of the two preparations are reported. As with 1 H NMR spectra the results were in agreement with those reported in the literature [10,40] and less than 2% deviations are observed. Additional information can be obtained by these spectra as almost all peaks attributed to cholesterol are clearly observed.…”

“…6A. The obtained spectra compare well with published spectra and thus the published assignment was used; see Table 2 [10]. …”

“…6B and Fig. S2 the 1 H NMR spectra of DOPC bilayers containing 30% and 15% molar ratio of cholesterol are shown respectively, and in Table 2 the 1 H chemical shifts of the corresponding spectra and the results by Zorin et al [10] are reported. The spectra were consistent with those reported in the literature (DOPC/CHOL 33%).…”

“…L2, L4 and L7 present the sites of deuteration of DPPC. For the terminology of the positions see [10]. …”