| 1. |
- Dvinskikh, Sergey V., et al.
(författare)
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Heating caused by radiofrequency irradiation and sample rotation in C-13 magic angle spinning NMR studies of lipid membranes
- 2004
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 42:10, s. 875-881
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Tidskriftsartikel (refereegranskat)abstract
- Application of rapid sample rotation and radiofrequency irradiation in magic angle spinning (MAS) NMR of lipid bilayers can significantly increase the sample temperature. In this work, we studied the extent of heating during the acquisition of H-1-decoupled C-13 MAS spectra of hydrated dimyristoylphosphatidyl-choline (DMPC) in the L. phase. First, we describe a simple procedure for determining the increase in temperature by observing the shift of the H-1 water signal. The method is then used to identify and assess the various factors that contribute to the sample heating. The important factors discussed in this paper include: (i) the spinning speed, (ii) the variable-temperature gas pressure, (iii) the rotor geometry, (iv) the power, duration and frequency of the radiofrequency irradiation and (v) the hydration level. A comparison of different heteronuclear decoupling schemes in terms of their ability to produce highly resolved C-13 spectra of DMPC is also reported.
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| 2. |
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| 3. |
- Dvinskikh, Sergey V., et al.
(författare)
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C-13-detected H-1-H-2 separated local field NMR spectroscopy
- 2003
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 382:04-mar, s. 410-417
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Tidskriftsartikel (refereegranskat)abstract
- We present a new NMR method for measuring H-1-H-2 dipolar couplings in macroscopically oriented media. To overcome the lack of dipolar resolution in 1D H-1 and H-2 spectra of deuterated molecules, we use a 2D heteronuclear correlation experiment where H-1 chemical shifts and H-1-H-2 dipolar interactions in the first dimension are. correlated with C-13 chemical shifts and H-2-C-13 dipolar interactions in the second dimension. The technique is demonstrated on a columnar liquid-crystalline phase.
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| 4. |
- Dvinskikh, Sergey V., et al.
(författare)
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Deuterium stimulated-echo-type PGSE NMR experiments for measuring diffusion : Application to a liquid crystal
- 2001
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 153:1, s. 83-91
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Tidskriftsartikel (refereegranskat)abstract
- The accessibility of molecular self-diffusion coefficients in anisotropic materials, such as liquid crystals or solids, by stimulated-echo-type H-2 PGSE NMR is examined. The amplitude and phase modulation of the signal in the stimulated-echo-type sequence by the static quadrupole coupling during the encoding/decoding delays is suppressed by adjusting the pulse flip angles and the phase cycle. For nuclei that experience both nonnegligible quadrupole and dipole couplings, the application of magic echoes during the evolution periods of stimulated echo is demonstrated as a helpful technique in the case of slow diffusion. These findings are demonstrated by experimental results in the thermotropic liquid crystal of partially deuterated 8CB. The obtained diffusion coefficients are also compared to data obtained by a H-1 homonuclear-decoupling-type PGSE NMR method in the same material.
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| 5. |
- Dvinskikh, Sergey V., et al.
(författare)
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Heteronuclear dipolar recoupling in liquid crystals and solids by PISEMA-type pulse sequences
- 2003
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 164:1, s. 165-170
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Tidskriftsartikel (refereegranskat)abstract
- A pulse sequence is described for the recoupling of heteronuclear dipolar interactions under MAS. The method is similar to the PISEMA experiment, but employs a well-defined amplitude modulation of one of the two radio-frequency fields. The technique is used for measurements of H-1-C-13 dipolar couplings in unoriented solid and liquid-crystalline samples.
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| 6. |
- Dvinskikh, Sergey V., et al.
(författare)
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Measurements of motionally averaged heteronuclear dipolar couplings in MAS NMR using R-type recoupling
- 2004
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 168:2, s. 194-201
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Tidskriftsartikel (refereegranskat)abstract
- A novel MAS NMR approach is presented for the determination of heteronuclear dipolar couplings in unoriented materials. The technique is based on the proton-detected local field (PDLF) protocol, and achieves dipolar recoupling by R-type radio-frequency irradiation. The experiment, which is called R-PDLF spectroscopy, is demonstrated on solid and liquid-crystalline systems. For mobile systems, it is shown that the R-PDLF scheme provides better dipolar resolution as compared to techniques combining conventional separated local field (SLF) spectroscopy with R-type recoupling.
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| 7. |
- Dvinskikh, Sergey V., et al.
(författare)
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Molecular characterization of hexaoctyloxy-rufigallol in the solid and columnar phases : A local field NMR study
- 2003
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 107:9, s. 1969-1976
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Tidskriftsartikel (refereegranskat)abstract
- Separated local field NMR spectroscopy was used to obtain H-1-C-13 dipolar interactions in the solid and columnar phases of the discotic compound 1,2,3,5,6,7-hexaoctyloxy-rufigallol (RufH8O). The couplings were measured and assigned by a variety of advanced NMR techniques performed under both static and magic-angle spinning conditions. The analysis of the dipolar couplings shows that the three nonequivalent aliphatic chains in RufH8O exhibit vastly different structural and dynamical characteristics. It was also found that one of the alpha methylene signals exhibits two H-1-C-13 dipolar splittings at low temperatures in the columnar phase. Similar pairs of doublets have previously been observed in a H-2 NMR study of RufH8O-H-2(alpha) and were there interpreted in terms of dynamic packing fluctuations along the columns. We will present an alternative explanation and show that these two doublets most likely originate from nonequivalent protons (or deuterons) in the alpha methylene group and not from density modulations.
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| 8. |
- Dvinskikh, Sergey V., et al.
(författare)
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Molecular structure and order of hexaoctyloxy-rufigallol in the solid and columnar phases : Analysis of H-2-C-13 dipolar and C-13 chemical-shift interactions
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:1, s. 413-422
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Tidskriftsartikel (refereegranskat)abstract
- We report a C-13 NMR investigation of 1,2,3,5,6,7-hexaoctyloxy-rufigallol in the solid and columnar phases using various H-2- and C-13-labeled isotopomers. The measurements were performed under both static and magic-angle spinning conditions. The conformations of the aliphatic side chains were derived from an analysis of H-2-C-13 dipolar and C-13 chemical-shift interactions. The nonequivalent chains exhibit significantly different structural behavior in both solid and columnar phase. It emerged that one of the side chains adopts an in-plane structure, while the other two chains prefer antiparallel out-of-plane conformations. Quantum-chemical calculations of the C-13 chemical-shift tensors were also carried out. These calculations support the experimental findings.
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| 9. |
- Dvinskikh, Sergey V., et al.
(författare)
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Separated local field spectroscopy of columnar and nematic liquid crystals
- 2003
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 163:1, s. 46-55
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Tidskriftsartikel (refereegranskat)abstract
- We are in this work comparing the efficiencies of various H-1-C-13 separated local field (SLF) experiments when applied to columnar and nematic liquid crystals. In particular, the performances of the conventional SLF, proton-detected local field (PDLF), and polarization inversion spin exchange at the magic angle (PISEMA) methods in terms of spectral resolution, robustness, and ability to measure long-range couplings are investigated. The PDLF sequence provides in most cases the best dipolar resolution. This is especially obvious for weakly coupled H-1-C-13 spin pairs.
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| 10. |
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