Nuclear spin–lattice relaxation dispersion investigation of smectic order fluctuations in isotropic and nematic phases

Kumar, B. V. N. Phani; Satheesh, V.; Venu, K.; Sastry, V. S. S.; Dąbrowski, R.

doi:10.1016/j.cplett.2009.10.023

Cited by 11 publications

(11 citation statements)

References 16 publications

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“…Field-cycling Nuclear Magnetic Resonance (NMR) relaxometry is a widely used tool to study molecular mobility, which is applicable to a wide range of systems such as molecules in liquid solutions, polymers, molecular crystals, liquid crystals, and biomolecules. [1][2][3][4][5][6][7][8][9][10][11] In such experiments spin relaxation times are measured as a function of the external magnetic field; theoretical modeling of such field dependences, also termed Nuclear Magnetic Relaxation Dispersion (NMRD) curves, enables extracting motional parameters, i.e., motional correlation times, τ c . In general, the rate, R μν , of the relaxation transition for a pair of quantum spin states, |μ and |ν , can depend on the external magnetic field for three reasons.…”

Section: Introductionmentioning

confidence: 99%

High resolution NMR study of T1 magnetic relaxation dispersion. IV. Proton relaxation in amino acids and Met-enkephalin pentapeptide

Pravdivtsev

Yurkovskaya

Vieth

et al. 2014

The Journal of Chemical Physics

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Nuclear Magnetic Relaxation Dispersion (NMRD) of protons was studied in the pentapeptide Met-enkephalin and the amino acids, which constitute it. Experiments were run by using high-resolution Nuclear Magnetic Resonance (NMR) in combination with fast field-cycling, thus enabling measuring NMRD curves for all individual protons. As in earlier works, Papers I-III, pronounced effects of intramolecular scalar spin-spin interactions, J-couplings, on spin relaxation were found. Notably, at low fields J-couplings tend to equalize the apparent relaxation rates within networks of coupled protons. In Met-enkephalin, in contrast to the free amino acids, there is a sharp increase in the proton T1-relaxation times at high fields due to the changes in the regime of molecular motion. The experimental data are in good agreement with theory. From modelling the relaxation experiments we were able to determine motional correlation times of different residues in Met-enkephalin with atomic resolution. This allows us to draw conclusions about preferential conformation of the pentapeptide in solution, which is also in agreement with data from two-dimensional NMR experiments (rotating frame Overhauser effect spectroscopy). Altogether, our study demonstrates that high-resolution NMR studies of magnetic field-dependent relaxation allow one to probe molecular mobility in biomolecules with atomic resolution.

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Section: Introductionmentioning

confidence: 99%

High resolution NMR study of T1 magnetic relaxation dispersion. IV. Proton relaxation in amino acids and Met-enkephalin pentapeptide

Pravdivtsev

Yurkovskaya

Vieth

et al. 2014

The Journal of Chemical Physics

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“…A slight deviation from single-exponential magnetization recovery was observed in the lyophases of investigation (Figure S2). Such observations were noted earlier in the isotropic phases of thermotropic mesogens such as PAA, 6CHBT, and binary mixtures of 4DBT and 12CB interpreted as the consequence of slow spin-diffusion. However, R 1 reported here was considered as an averaged value over proton R 1 ’s of PEO and PPO and obtained by fitting the magnetization recovery data to a single-exponential (three-parameter fit).…”

Section: Methodsmentioning

confidence: 91%

“…The obtained FFC NMR profiles for isotropic and cubic phases reflect weak frequency dispersions of R 1 in the low-frequency regime (5–100 kHz), while relatively ordered phases such as hexagonal and lamellar phases encountered steeper dispersions in the same frequency range, as evident from Figure . Similar observations have been noted previously in the isotropic and mesophases of polymeric nematogen polydiethylsiloxane (PDES) and thermotropic mesogens …”

Section: Methodsmentioning

confidence: 99%

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry

2018

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Associative block copolymers of the type (EO) x (PO) y (EO) x (where EO and PO represent ethylene and propylene oxides, respectively) in aqueous solution have far reaching commercial applications such as solubilization, controlled-drug delivery, etc. The molecular dynamics of a self-associating triblock copolymer (EO) 20 (PO) 70 (EO) 20 (known as P123 with a molecular weight of ∼5800), in aqueous solution (D 2 O), consisting of various lyotropic liquid crystalline phases such as isotropic micellar, cubic, hexagonal, and lamellar phases, is investigated using the fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry technique in the Larmor frequency range from 5 kHz to 30 MHz. A nuclear spin-relaxation model consisting of chain modes (Rouse modes) and order fluctuation (OF) modes typical for polymers and liquid crystals, respectively, is considered to explain the observed proton magnetic relaxation dispersion (PMRD) data in the lyophases under investigation. The PMRD analysis in both isotropic micellar and cubic phases revealed a Rouse frequency dependence of spin−lattice relaxation rate (R 1 ), i.e., R 1 ∝ −τ s ln(ωτ s ), in the entire frequency range of study. Hexagonal and lamellar phase data show Rouse modes as well as OF modes, leaving the signature of the latter as R 1 ∝ ω −p , where p ∼ 0.5 is typical for nematic mesogens. The activation energies were also determined from segmental correlation times in the lyophases of study. To the best of our knowledge, the present FFC NMR relaxometry study is unique and quantitative in unraveling molecular dynamics of the associative copolymer P123 in aqueous solution.

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“…The properties of the mixture 12CB-4DBT were also explored by nuclear magnetic relaxation dispersion technique [177] for two 12CB concentrations: only for the first one in the central part of nematic gap, no layered smectic structure at low temperature region was seen; and for the second one, more rich in 12CB, the SmA d layer structure was retained at lowtemperature region. Persistence of a short-range nematic fluctuation up to 20°C above the clearing point and a cybotactic smectic cluster above the NSmA d transition were found as in 8OCB.…”

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confidence: 99%

From the discovery of the partially bilayer smectic A phase to blue phases in polar liquid crystals

Dąbrowski

2015

Liquid Crystals

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The significance of Gray's cyanobiphenyls in the discovery of the partially bilayer smectic A phase (SmA d ) and in the formulation of mixtures exhibiting the blue phase is described. The properties of the SmA d phase and its relationships to molecular structures are reviewed. Induced phenomena such as the transformation of nematics into smectics, SmA d or SmA 1 , as well as the opposite transformation of smectics into nematics are described and discussed.

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Nuclear spin–lattice relaxation dispersion investigation of smectic order fluctuations in isotropic and nematic phases

Cited by 11 publications

References 16 publications

High resolution NMR study of T1 magnetic relaxation dispersion. IV. Proton relaxation in amino acids and Met-enkephalin pentapeptide

High resolution NMR study of T1 magnetic relaxation dispersion. IV. Proton relaxation in amino acids and Met-enkephalin pentapeptide

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry

From the discovery of the partially bilayer smectic A phase to blue phases in polar liquid crystals

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