High-Resolution 2D NMR Spectroscopy of Bicelles To Measure the Membrane Interaction of Ligands

Abstract

Magnetically aligned bicelles are increasingly being used as model membranes in solutionand solidstate NMR studies of the structure, dynamics, topology, and interaction of membraneassociated peptides and proteins. These studies commonly utilize the PISEMA pulse sequence to measure dipolar coupling and chemical shift, the two key parameters used in subsequent structural analysis. In the present study, we demonstrate that the PISEMA and other rotating-frame pulse sequences are not suitable for the measurement of long-range heteronuclear dipolar couplings, and that they provide inaccurate values when multiple protons are coupled to a 13 C nucleus. Furthermore, we demonstrate that a laboratory-frame separated-local-field experiment is capable of overcoming these difficulties in magnetically aligned bicelles. An extension of this approach to accurately measure 13 C-31 P and 1 H-31 P couplings from phospholipids, which are useful to understand the interaction of molecules with the membrane, is also described. In these 2D experiments, natural abundance 13 C was observed from bicelles containing DMPC and DHPC lipid molecules. As a first application, these solid-state NMR approaches were utilized to probe the membrane interaction of an antidepressant molecule, desipramine, and its location in the membrane.

Confocal Raman microscopy for simultaneous monitoring of partitioning and disordering of tricyclic antidepressants in phospholipid vesicle membranes

“…Indeed, an NMR study has shown that the TCAs are probably located with their cyclic rings near the acyl chains and their polar carbon tail 'snorkeling' up near the lipid headgroup; in other words, TCAs are mostly in the lipid interfacial/headgroup region, disrupting lipid packing and providing the acyl chains with more room to move. [59] In general, the literature suggests that TCAs are located with the rings near the lipid acyl chains and the charged tail near the lipid headgroup, [60] although one report concludes that the drug conformation in DPPC is quite mobile but preferentially assumes a state where the charged tail is folded back on the rings. [49,51,61] Indeed, ring flexibility in TCA differs depending on specific drug structure.…”

RETRACTED ARTICLE: Microstructure of poly(vinyl acetate)-block-poly(methyl acrylate-co-methyl methacrylate) block terpolymers. 2D NMR and thermal study

“…[1][2][3][4][5][6][7][8] Among the several block copolymers and terpolymers with controlled structures which were synthesized via ATRP, [9][10][11][12][13][14][15][16][17][18][19][20] good agreement between the molecular structures and morphological, thermal, electrical, mechanical, and transport properties have been observed.…”

High-Resolution Characterization of Liquid-Crystalline [60]Fullerenes Using Solid-State Nuclear Magnetic Resonance Spectroscopy

“…26, 30 Our recent studies reported that some of the rotating frame SLF pulse sequences like PISEMA (polarization inversion spin exchange at the magic angle), 26 BB-PISEMA (broadband-PISEMA), and HIMSELF (heteronuclear isotropic mixing spin exchange via local field) provide very high-resolution heteronuclear dipolar coupling spectral lines, whereas laboratory frame SLF pulse sequences like PDLF 27,31 in general are not efficient in suppressing homonuclear 1 H-1 H dipolar couplings; therefore, the resultant SLF spectra are not that high in spectral resolution for rigid solids. 32 In addition, our studies showed that the laboratory frame SLF sequence, PDLF (proton-encoded SLF), is useful for the accurate measurement of heteronuclear dipolar couplings from dynamical semisolids like liquid crystals. 32 Therefore, in this C dipolar coupling spectral slices extracted from 2D PDLF spectra of compounds 1 (left column) and 2 (right column) in oriented mesophase at 160 and 140°C, respectively.…”

“…32 In addition, our studies showed that the laboratory frame SLF sequence, PDLF (proton-encoded SLF), is useful for the accurate measurement of heteronuclear dipolar couplings from dynamical semisolids like liquid crystals. 32 Therefore, in this C dipolar coupling spectral slices extracted from 2D PDLF spectra of compounds 1 (left column) and 2 (right column) in oriented mesophase at 160 and 140°C, respectively. Slices were taken from the corresponding 2D spectra at the chemical shift positions (from top to bottom) 14, 30, 63, 65, 164, and 221 ppm as indicated in Figure 9 for compound 1. study, we apply the PDLF pulse sequence to characterize the liquid-crystalline compounds at a higher resolution using the experimentally measured C-H dipolar couplings.…”