NMR relaxation study of collective motions and viscoelastic properties in biomembranes

Althoff, Gerhard; Heaton, N.; Gröbner, Gerhard; Prosser, R. Scott; Kothe, G.

doi:10.1016/0927-7757(96)03612-6

Cited by 22 publications

(40 citation statements)

References 19 publications

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“…Extension of the variable frequency range, from MHz down to Hz values, has shown that collective fluctuations play an important role in membrane dynamics over the entire range investigated [8,141]. This contribution is suggested by relaxation rate-frequency dispersions recorded in T 2CPMG experiments, where frequencies below 50 kHz are employed in the multi-pulse NMR measurements [121,142].…”

Section: Analytical Theories Are Valuable Complements To Molecularmentioning

confidence: 99%

An NMR database for simulations of membrane dynamics

Leftin

Brown

2011

Biochimica et Biophysica Acta (BBA) - Biomembranes

102

119

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Computational methods are powerful in capturing the results of experimental studies in terms of force fields that both explain and predict biological structures. Validation of molecular simulations requires comparison with experimental data to test and confirm computational predictions. Here we report a comprehensive database of NMR results for membrane phospholipids with interpretations intended to be accessible by non-NMR specialists. Experimental 13C–1H and 2H NMR segmental order parameters (SCH or SCD) and spin-lattice (Zeeman) relaxation times (T1Z) are summarized in convenient tabular form for various saturated, unsaturated, and biological membrane phospholipids. Segmental order parameters give direct information about bilayer structural properties, including the area per lipid and volumetric hydrocarbon thickness. In addition, relaxation rates provide complementary information about molecular dynamics. Particular attention is paid to the magnetic field dependence (frequency dispersion) of the NMR relaxation rates in terms of various simplified power laws. Model-free reduction of the T1Z studies in terms of a power-law formalism shows that the relaxation rates for saturated phosphatidylcholines follow a single frequency-dispersive trend within the MHz regime. We show how analytical models can guide the continued development of atomistic and coarse-grained force fields. Our interpretation suggests that lipid diffusion and collective order fluctuations are implicitly governed by the viscoelastic nature of the liquid-crystalline ensemble. Collective bilayer excitations are emergent over mesoscopic length scales that fall between the molecular and bilayer dimensions, and are important for lipid organization and lipid-protein interactions. Future conceptual advances and theoretical reductions will foster understanding of biomembrane structural dynamics through a synergy of NMR measurements and molecular simulations.

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Section: Analytical Theories Are Valuable Complements To Molecularmentioning

confidence: 99%

An NMR database for simulations of membrane dynamics

Leftin

Brown

2011

Biochimica et Biophysica Acta (BBA) - Biomembranes

102

119

View full text Add to dashboard Cite

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“…What is more, transverse spin relaxation rates for pure DMPC and rhodopsin/DMPC MLVs are found to be virtually indistinguishable over a wide range of pulse frequencies. 49 In view of the notable difference in the size distributions for these two systems (see Figures 5 and 7), and the corresponding difference (i.e. a factor of approximately 4) in the respective mean rotational correlation times, this result is further evidence for the existence of some other mechanism dominating transverse spin relaxation.…”

Section: Discussionmentioning

confidence: 75%

Observation of Lateral Diffusion in Biomembranes by Excitation Transfer ³¹P NMR: Estimation of Vesicle Size Distributions

1996

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An excitation transfer 31 P NMR experiment is described which directly measures translationally induced rotation of lipid molecules in large membrane vesicles. The experiment involves selective excitation of a small subset of the lipid molecules whose axially symmetric chemical shift tensors are oriented at approximately 90°to the magnetic field. Line shapes due only to the selected molecules are then recorded as a function of the mixing time. The spectra directly reflect the time dependent orientational distribution of lipid molecules and may be analyzed in terms of the distribution of effective rotational diffusion constants, related analytically to the distribution of vesicle radii. Employing this 31 P NMR method, size distributions have been evaluated for multilamellar vesicles of dimyristoylphosphatidylcholine (DMPC) and DMPC/1.12% (mol/mol) bovine rhodopsin. In both cases the radius distributions are extremely broad, spanning more than 2 orders of magnitude in the case of the pure DMPC vesicles.

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“…The molecular mobility at the interface seems to be fast enough to be affected by changes in the oil droplet surface area that are in the µm 2 range. This interface shows characteristics of a two-dimensional liquid resembling biological membranes, where a fast diffusion in the plane of the phospholipid bilayers and a slow displacement perpendicular to this are detected (22). A more quantitative treatment of the results, especially of the relaxation measurements, is complicated owing to the rather polydisperse character of the emulsions examined here.…”

Section: Resultsmentioning

confidence: 94%

³¹P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil‐in‐water emulsions

Plass

Emeis

Blümich

2001

J Surfact & Detergents

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Cosmetic oil-in-water emulsions with a stearyl phosphate emulsifier are examined by means of static and dynamic 31 P nuclear magnetic resonance (NMR) techniques to characterize the molecular properties of the emulsifier in situ. The interfacially bound emulsifier can be detected by highresolution NMR spectroscopy, whereas the excess emulsifier exists as a solid lipid phase not detectable by this technique. The emulsions and the emulsifier raw material, consisting of monostearyl phosphate as well as distearyl phosphate, are examined by solid state cross polarization magic angle spinning NMR spectroscopy to prove the existence of solid emulsifier phases in the emulsions. By applying dynamic 31 P NMR methods to the interfacially bound emulsifier, information about the molecular dynamics at the interface is obtained. The results of the T 1 and T 2 relaxation time measurements indicate a restricted motion of the molecules that is dependent on the oil droplet size in the emulsions. This is verified by 31 P NMR pulsed gradient spin echo self-diffusion measurements on emulsions with different droplet sizes. Only about 5 wt% of the total emulsifier used is bound at the interface; the excess forms solid lipid phases. The coverage of the interface seems to be independent of the emulsifier concentration. Only the monoester of the emulsifier raw material shows interfacial activity. Its mobility indicates the two-dimensional environment of the molecules on the surface of the oil droplets.Emulsifiers are amphiphilic molecules that, owing to their hydrophilic and lipophilic molecular segments, can be solvated at the interface of immiscible liquids, thus reducing the interfacial tension. The development of emulsion-based cosmetic products requires efficient emulsifier systems that ensure the stability of the dispersion even after three years of storage. Although the composition of the formulation ingredients is determined mainly from a cosmetic viewpoint, the emulsifier must also stabilize the emulsion independently over a wide range of solution variables such as the pH, characteristics of the oil phase, and the salt concentration (1).In the case of oil-in-water emulsions (o/w emulsions) anionic emulsifiers of the form R-(CH 2 ) n -CH 3 (n = 12-20, R = carboxylate, sulfate, phosphate) are frequently used. Furthermore, the ability of many ionic emulsifiers to form aggregates in the water phase (also denoted as an emulsifier network) is an important stabilization factor for o/w emulsions because of a steric hindrance of droplet coalescence. For the development of new products and formulations, a better comprehension of the molecular properties of the emulsifier and the emulsifier's interfacial interactions is essential.Nuclear magnetic resonance (NMR) spectroscopic methods are frequently applied to complex surfactant systems such as colloids, microemulsions, and emulsions because noninvasive measurements make in situ examinations possible (2-5). NMR spectra of the molecules reflect the chemical environment of the nuclei, which enab...

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NMR relaxation study of collective motions and viscoelastic properties in biomembranes

Cited by 22 publications

References 19 publications

An NMR database for simulations of membrane dynamics

An NMR database for simulations of membrane dynamics

Observation of Lateral Diffusion in Biomembranes by Excitation Transfer ³¹P NMR: Estimation of Vesicle Size Distributions

³¹P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil‐in‐water emulsions

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NMR relaxation study of collective motions and viscoelastic properties in biomembranes

Cited by 22 publications

References 19 publications

An NMR database for simulations of membrane dynamics

An NMR database for simulations of membrane dynamics

Observation of Lateral Diffusion in Biomembranes by Excitation Transfer 31P NMR: Estimation of Vesicle Size Distributions

31P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil‐in‐water emulsions

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Product

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Observation of Lateral Diffusion in Biomembranes by Excitation Transfer ³¹P NMR: Estimation of Vesicle Size Distributions

³¹P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil‐in‐water emulsions