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Relaxation (NMR)

About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.


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Journal ArticleDOI
TL;DR: Structure and dynamics of the partially folded A state of ubiquitin in a 60%/40% methanol/water mixture at pH 2 was studied by two- and three-dimensional nuclear magnetic resonance spectroscopy (NMR) using fully 13C,15N, and 1HN-labeled ubiquitins.
Abstract: Structure and dynamics of the partially folded A state of ubiquitin in a 60%/40% methanol/water mixture at pH 2 was studied by two- and three-dimensional nuclear magnetic resonance spectroscopy (NMR) using fully 13C,15N-labeled ubiquitin. Complete backbone 13CO, 13Cα, 15N, and 1HN assignment was achieved. 13CO and 13Cα chemical shifts and 1H−1H nuclear Overhauser enhancement (NOE) connectivities indicate different behavior for the N-terminal and the C-terminal halves of the protein. In the N-terminal half of the A state, comprising the antiparallel β-sheet and the central α-helix, the native secondary structural elements are largely conserved. The C-terminal half, which is in the native form rich in β-strand character, undergoes a methanol-induced transition to a dynamic state with a uniformly high propensity for helical structure. This behavior is also reflected in backbone 15N relaxation data, indicating the presence of three loosely coupled secondary structural segments with enhanced internal mobility ...

176 citations

Journal ArticleDOI
TL;DR: In this article, the dipole-dipole interactions between protons in a glucopyranose derivative have been studied by means of the nuclear Overhauser effect and by spin-lattice relaxation experiments.
Abstract: Dipole‐dipole interactions between protons in a glucopyranose derivative have been studied by means of the nuclear Overhauser effect and by spin‐lattice relaxation experiments. The Overhauser enhancement measurements utilize a new pulse technique which permits the saturating field to have any specified spectral density function so that finite frequency bands in the NMR spectrum can be irradiated. By this method, the dipolar interactions between the various pairs of protons are evaluated. In contrast, the dipolar relaxation of a chosen proton by all other protons in the sample has been determined by comparing the inversion‐recovery rates after selective and nonselective 180° pulses. The relaxation measurements indicate that the relaxation in this molecule is purely dipolar in origin. The Overhauser enhancement measurements of one proton are used to determine the contribution to its relaxation from two neighboring protons and, from these results, information about the geometry of the pyranose ring is evaluated.

176 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the relaxation dynamics of photoexcitations in cast films of polydiacetylenes, poly[4,6-decadiyne-1,10-diol bis([(n-butoxycarbonyl)methyl]urethane)] (PDA-3BCMU) and poly[5,7-dodecadiyn- 1,12-diox bis([n- butoxycarbonyl)methyl)urethANE)] (pDA-4BCMU), and in electrochemically prepared
Abstract: The relaxation dynamics of photoexcitations in cast films of the polydiacetylenes, poly[4,6-decadiyne-1,10-diol bis([(n-butoxycarbonyl)methyl]urethane)] (PDA-3BCMU) and poly[5,7-dodecadiyne-1,12-diol bis([n-butoxycarbonyl)methyl]urethane)] (PDA-4BCMU), and in electrochemically prepared films of poly(3-methylthiophene) (P3MT) were investigated by femtosecond absorption and picosecond luminescence spectroscopies. 1Bu free excitons, generated by 100-fsec pump pulses, relaxed to the self-trapped (ST) state with time constants of 150 ± 50 fsec in PDA-3BCMU and 70 ± 50 fsec in P3MT. The difference was explained in terms of the relative sizes of the side chains. PDA-3BCMU has bulky side chains that are linked by hydrogen bonds, while P3MT has a repeating unit that contains a ring structure with a small methyl group. The lifetimes of the ST excitons at 10 K (290 K) were 2.0 ± 0.1 (1.5 ± 0.1) psec in PDA-3BCMU, 3.0 ± 0.3 (2.1 ± 0.2) psec in PDA-4BCMU, and 800 ± 100 (800 ± 100) fsec in P3MT. The decay kinetics of the ST exciton were explained by potential crossing and tunneling between two potential curves of the ST exciton and the ground state. The weak temperature dependence indicates that the activation process over the potential barrier between the ST exciton and the ground state is not dominant in the radiationless relaxation of the ST exciton. The relaxation dynamics of fluorescence from the PDA-4BCMU film cannot be represented by a single exponential decay; however, it can be described in terms of a random walk in the fractal dimension. By applying the fractal-dimension model, the spectral dimension was determined to be between 0.50 and 0.85. The spectral changes that are due to several nonlinear-optical processes, i.e., hole burning, Raman gain, and the dynamic Stark effect, were also observed in femtosecond-resolved spectra. The third-order susceptibility was determined for these nonlinear processes, such as absorption saturation at the exciton transition, Raman gain, and the resonant Kerr effect from the observed spectral change. The third-order susceptibility that corresponds to absorption saturation in PDA-3BCMU and in P3MT was obtained as Im[χ1111(3)(−ω;ω,ω,−ω)] equal to −2.6 × 10−9 and −3.5 × 10−10 esu, respectively, for ħω = 1.97 eV. The third-order susceptibility that corresponds to the Raman gain in PDA-3BCMU and in P3MT was determined to be Im[χ1111(3)(−ω2;ω2,ω1,−ω1)] equal to 5.8 × 10−10 and −1.5 × 10−10 esu, respectively, for ħω1 = 1.97 eV and ħω2 = 1.79 eV. From the resonant Kerr experiment in the P3MT film, |Δχ(3)|≡|χ1111(3)(−ω2;ω2,ω1,−ω1)−χ1122(3)(−ω2;ω2,ω1,−ω1)|=3.9×10−11 esu was determined for ħω1 = 1.97 eV and ħω2 = 1.88 eV.

176 citations

Journal ArticleDOI
TL;DR: The quadrupolar spin-lattice (T1) relaxation of deuterium labeled phospholipid bilayers has been investigated at a resonance frequency of 54.4 MHz as mentioned in this paper.
Abstract: The quadrupolar spin–lattice (T1) relaxation of deuterium labeled phospholipid bilayers has been investigated at a resonance frequency of 54.4 MHz. T1 measurements are reported for multilamellar dispersions, single bilayer vesicles, and chloroform/methanol solutions of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC), selectively deuterated at ten different positions in each of the fatty acyl chains and at the sn‐3 carbon of the glycerol backbone. At all segment positions investigated, the T1 relaxation times of the multilamellar and vesicle samples of DPPC were found to be similar. The profiles of the spin–lattice relaxation rate (1/T1) as a function of the deuterated chain segment position resemble the previously determined order profiles [A. Seelig and J. Seelig, Biochem. 13, 4839 (1974)]. In particular, the relaxation rates are approximately constant over the first part of the fatty acyl chains (carbon segments C3–C9), then decreasing in the central region of the bilayer. In chloroform/methanol solution, by contrast, the relaxation rates decrease continuously from the glycerol backbone region to the chain terminal methyl groups. The contributions from molecular order and motion to the T1 relaxation rates have been evaluated and correlation time profiles derived as a function of chain position. The results suggest that the motions of the various methylene segments are correlated in the first part of the fatty acyl chains (C3–C9), occurring at frequencies up to 1/τc?1010 Hz. Beyond C9, the rate and amplitude of the chain segmental motions increase, approaching that of simple paraffinic liquids in the central region of the bilayer (1/τc?1011 Hz). The T1 relaxation rates of multilamellar dispersions of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) deuterated at the 9, 10 double bond of the sn‐2 chain were also determined and found to be significantly faster than those of the CD2 chain segments of DPPC bilayers. This is most likely due to the larger size and correspondingly slower motion of the chain segment containing the double bond. At segments close to the lipid–water interface the rate of motion is considerably less than in the hydrocarbon region of the bilayer.

175 citations

Journal ArticleDOI
TL;DR: In this paper, a 1H nuclear magnetic resonance (NMR) relaxation analysis of water in progressively dried white cement paste is used to estimate the width and relative specific area of intra-C-S-H sheet pores and inter-C−S−H particle gel pores.

175 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202227
2021652
2020582
2019614
2018638
2017645