Water in barnacle muscle. IV. Factors contributing to reduced self-diffusion

The imposition of magnetic field gradients on a nuclear magnetic resonance experiment imparts a spatial tag to the molecules via the Larmor frequencies of the nuclei (commonly protons) within. A sensitive measure of changes in the frequency distribution is afforded by detecting the loss of phase coherence in a spin-echo experiment performed in the presence of gradient pulses. Here the molecular displacements may be measured over the duration given by the pulse separation. Pulsed field gradient nuclear magnetic resonance (PFGNMR) employs timesca1es of tens of milliseconds and has a displacement sensitivity of the order 100 nm.For molecules undergoing Brownian motion, PFGNMR can determine molecular self-diffusion coefficients in liquid and mesomorphic phases down to a lower limit of 10-14 m 2 S-1. These coefficients directly probe dynamical processes. For example, in polymer systems such measurements are sensitive to molecular conformation and chain relaxation processes such as reptation. 10 disperse phases PFGNMR can be used to probe diffusive barriers and reveal molecular organization. The timescale dependence of displacement is especially useful in this regard. Examples of studies on poly-and mono-domain lyotropic liquid crystals are presented.Recent use of nuclei with spin >t offers interesting prospects for PFGNMR. The deuterium quadrupole interaction can be used as a signature for order in anisotropic molecular environments. The preparation in the NMR experi~ent of tensor polarization, such as states of two quantum coherence, increases precessional dephasing and may yield a considerable increase in displacement sensitivity.

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“…. Shape factors have similarly been obtained for ovalbumin andbovine-serumalbumin (Clark et al 1982). Fig.…”

Section: (B) Macromoleculesmentioning

confidence: 75%

Pulsed Field Gradient Nuclear Magnetic Resonance as a Probe of Liquid State Molecular Organization

Callaghan¹

1984

Aust. J. Phys.

234

131

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“…With an MPG perpendicular to the cylindrical axis, ADC is given by DE(1-2VC)/(1-VC) ¥DE(1-VC) for VC91, where VC is the volume fraction of the cylinders and DE is the extracellular water self-diŠusion coe‹cient. 26,[48][49][50][51] For a medium with spherical obstacles, ADC is given by DEs 1-(3/2)VSt /(1-VS)¥DEs 1-(1/2)VSt for VS91, where VS is the volume fraction of the spheres. 48,[51][52][53] From these relationships, we assume that an addition of a small volume of obstacles to a medium of an ADC ＝D would change the ADC by the amount DD determined by these formulae: DD＝-DDVC for adding cylinders and DD＝-(1/2)DDVS for adding spheres.…”

Section: Appendix Amentioning

confidence: 99%

How Does Water Diffusion in Human White Matter Change Following Ischemic Stroke?

Tamura¹,

Kurihara

Machida³

et al. 2009

magn reson med sci

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Purpose: Temporal evolution of the water apparent diŠusion coe‹cients (ADC) parallel (ADC¿) and perpendicular (ADC¥) to the human white matter tract following ischemia has not been investigated systematically. We attempted to quantify the evolution of ADC¿ and ADC¥ and examine whether it can be interpreted by a model of ischemic edema.Methods: We retrospectively selected 53 patients with ischemic lesions involving the posterior limb of the internal capsule (PLIC) and placed regions of interest in the right and left PLIC on ADC maps. We performed regression analysis of lesion-to-contralateral ratios of ADC¿ and ADC¥against the time (t＝1-1600 h) from onset. We thenˆtted the estimated time courses of ADC¿ and ADC¥obtained from the analysis to a model of nerve tissue composed of cylinders (axons) and spheres corresponding to isotropic structures, particularly focal cytoplasmic swellings of glial cells and axons seen in ischemic white matter.Results: The evolution of ADC¥ and ADC¿ diŠered. The estimated time course of ADC¿ in mm 2 ･ms -1 was 0.64＋0.88 exp (-0.24t) for 1ºtº54 h and 0.00059t＋0.61 for tAE54 h (contralateral normal value, 1.52). That of ADC¥ was 0.19-0.063 exp (-0.24t) for 1ºtº54 h and 0.00040t＋0.17 for tAE54 h (normal value 0.22). The modelˆtted to these values showed that the volume of the cylinders decreased, that of the spheres increased, and extracellular volume changed little from one hour to approximately one day after stroke onset.Conclusion: In the human PLIC, ADC¿ continued to decrease from one hour to a few days after stroke onset, and ADC¥tended to increase. The temporal evolution could be interpreted by progression of the focal cytoplasmic swelling of glial cells and axons previously observed in animal studies.Keywords: cytotoxic edema, glia, intracellular space, vasogenic edema Introduction DiŠusion-weighted (DW) magnetic resonance (MR) imaging enables noninvasive measurement of the diŠusivity of water molecules in the human brain. Prompt reduction of the apparent diŠusion coe‹cient (ADC) in ischemic tissue causes hyperintensity on DW images, which aids detection of early changes in the brain after onset of ischemic stroke. [1][2][3] ADC measurement may also be useful in characterizing ischemic damage and selecting therapeutic procedure. 4 Many studies have demonstrated temporal evolution of the mean diŠusivity (, trace/3 of the diŠusion tensor) in patients with stroke. 5-13Follow-122 122 H. Tamura et al. Magnetic Resonance in Medical Sciencesing acute reduction of after the onset of cerebral ischemia, decreases slightly over 24 hours in many cases, [5][6][7][8][9] reaches a minimum, gradually increases to a normal value (pseudonormalization) between several days and one month, and continues to increase. Although the decrease is generally attributed to cellular edema and the increase to vasogenic edema and degradation of membrane structure, 1,[10][11][12] the exact mechanisms of these changes in remain unclear.Human and animal studies show a decline in diŠusion anisot...

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“…7). Instead, we treat extracellular macromolecules (and the water molecules that they bind) as random obstacles that impose an additional path increase (28). We postulate that small diffusing molecules flow in the medium with a constant rate whereas the viscous drag phenomena in the vicinity of the macromolecules are simply reflected by the effective size (volume) of these obstacles.…”

Section: ϫ23mentioning

confidence: 99%

Geometric and viscous components of the tortuosity of the extracellular space in the brain

Rusakov¹,

Kullmann²

1998

Proc. Natl. Acad. Sci. U.S.A.

167

142

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To understand the function of neuro-active molecules, it is necessary to know how far they can diffuse in the brain. Experimental measurements show that substances confined to the extracellular space diffuse more slowly than in free solution. The diffusion coefficients in the two situations are commonly related by a tortuosity factor, which represents the increase in path length in a porous medium approximating the brain tissue. Thus far, it has not been clear what component of tortuosity is due to cellular obstacles and what component represents interactions with the extracellular medium (''geometric'' and ''viscous'' tortuosity, respectively). We show that the geometric tortuosity of any random assembly of space-filling obstacles has a unique value (Ϸ1.40 for radial f lux and Ϸ1.57 for linear f lux) irrespective of their size and shape, as long as their surfaces have no preferred orientation. We also argue that the Stokes-Einstein law is likely to be violated in the extracellular medium. For molecules whose size is comparable with the extracellular cleft, the predominant effect is the viscous drag of the cell walls. For small diffusing particles, in contrast, macromolecular obstacles in the extracellular space retard diffusion. The main parameters relating the diffusion coefficient within the extracellular medium to that in free solution are the intercellular gap width and the volume fraction occupied by macromolecules. The upper limit of tortuosity for small molecules predicted by this theory is Ϸ2.2 (implying a diffusion coefficient approximately five times lower than that in a free medium). The results provide a quantitative framework to estimate the diffusion of molecules ranging in size from Ca 2؉ ions to neurotrophins.

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Water in barnacle muscle. IV. Factors contributing to reduced self-diffusion

Cited by 59 publications

References 24 publications

Pulsed Field Gradient Nuclear Magnetic Resonance as a Probe of Liquid State Molecular Organization

Pulsed Field Gradient Nuclear Magnetic Resonance as a Probe of Liquid State Molecular Organization

How Does Water Diffusion in Human White Matter Change Following Ischemic Stroke?

Geometric and viscous components of the tortuosity of the extracellular space in the brain

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