A Method for the Determination of Diffusion Constants and the Calculation of the Radius and Weight of the Hemoglobin Molecule

Northrop, John H.; Anson, M. L.

doi:10.1085/jgp.12.4.543

Cited by 237 publications

(54 citation statements)

References 2 publications

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“…It should be noted that to is not necessarily zero time but rather that time at which the initial sample, required for each measurement of Pd is withdrawn. Equation (2) is a suitable modification of the equation of Northrop & Anson (1929) and has been derived on the assumption that both vI and v2 remain constant. In any single experiment the maximum reduction in vI or v2, caused by withdrawing samples, was less than 4 % and, therefore, we have not attempted to compensate for these changes in our calculations of Pd.…”

Section: Methodsmentioning

confidence: 99%

An examination of the evidence for membrane pores in frog skin

Dainty¹,

House²

1966

The Journal of Physiology

107

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SUMMARY1. Measurements of the diffusional permeability, Pd, of tritiated water in isolated frog skin bathed in sulphate Ringer have been made under different stirring conditions.2. The mean + S.E. values for Pd were found to be (6.5 + 0.3), (7.9 + 0-5), (9.7 + 0.7) and (11.1 + 0.8) x 10-5 cm sec-' at 120, 300, 500 and 1000 rev/min. It is considered that these results indicate the existence of 'unstirred layers' associated with frog skin.3. The hydraulic conductivity, LP, of the skin in sulphate Ringer was found to be (2.36 + 0.07) x 10-7 cm sec-1 atm-1 (± S.E. of estimate), and no marked increase in this value for Lp was found when the stirring rate was increased from 0 to 500 rev/min. 4. It is considered that these results show that previous comparisons of the relative magnitudes of LPRT/IV,, (where VF, is the partial molar volume of water) and Pd for frog skin have been in error because of the presence of 'unstirred layers'. 5. The bearing of our results and other evidence on the question of pores in cell membranes has been discussed.

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Section: Methodsmentioning

confidence: 99%

An examination of the evidence for membrane pores in frog skin

Dainty¹,

House²

1966

The Journal of Physiology

107

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“…3,5 Therefore, the goal of this research is to provide atomic-level insights into the contribution of microscopic surface effects to the diffusion process of uranyl species in porous media with nano-to microsized pores using atomistic simulation techniques. The experimental determination of self-diffusion coefficients with techniques such as the nuclear magnetic resonance spin echoes in the presence of pulsed magnetic field gradients 5,18 or the diaphragm cell technique 19 is particularly challenging for uranyl species because of the coexistence of various U(VI) aqueous species under most experimental conditions. 20 Therefore, atomistic simulation is a powerful tool that can be used to determine the diffusion coefficients of individual uranyl species and that can isolate and quantify the microscopic surface effects.…”

Section: ■ Introductionmentioning

confidence: 99%

Diffusion and Adsorption of Uranyl Carbonate Species in Nanosized Mineral Fractures

Kerisit

Liu

2012

Environ. Sci. Technol.

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Atomistic simulations were performed to study the diffusion and adsorption of Ca 2 UO 2 (CO 3 ) 3 and of some of its constituent species, i.e., UO 2 2+ , CO 3 2− , and UO 2 CO 3 , in feldspar nanosized fractures. Feldspar is important to uranium remediation efforts at the U.S. Department of Energy Hanford site as it has been found in recent studies to host contaminants within its intragrain fractures. In addition, uranyl carbonate species are known to dominate U(VI) speciation in conditions relevant to the Hanford site. Molecular dynamics (MD) simulations showed that the presence of the feldspar surface diminishes the diffusion coefficients of all of the species considered in this work and that the diffusion coefficients do not reach their bulk aqueous solution values in the center of a 2.5 nm fracture. Moreover, the MD simulations showed that the rate of decrease in the diffusion coefficients with decreasing distance from the surface is greater for larger adsorbing species. Free energy profiles of the same species adsorbing on the feldspar surface revealed a large favorable free energy of adsorption for UO 2 2+ and UO 2 CO 3 , which are able to adsorb to the surface with their uranium atom directly bonded to a surface hydroxyl oxygen, whereas adsorption of CO 3 2− and Ca 2 UO 2 (CO 3 ) 3 , which attach to the surface via hydrogen bonding from a surface hydroxyl group to a carbonate oxygen, was calculated to be either only slightly favorable or unfavorable. ■ INTRODUCTIONUranium is a major radionuclide contaminant in groundwater systems at sites where nuclear materials were processed and stored. 1 Consequently, one of the main challenges for uranium remediation at nuclear facilities is to develop a comprehensive understanding of the reactivity and stability of uranium in order to predict its fate in subsurface environments. Uranium has been found predominantly in microscopic intragrain domains in contaminated sediments such as from the US Department of Energy (DOE) Hanford Site. 2,3 In addition, ion diffusion has been shown to be a major process contributing to the preferential uranium concentration in these sediments and is predicted to control the future release of uranium from the sediments. 2,4,5 One important limitation in studies of uranium diffusion is the lack of self-diffusion coefficients for uranyl species in groundwater, 6 which has led to the development of diffusion models, referred to here as apparent diffusion models, whereby the total dissolved U(VI) concentration is considered as a single chemical species. Recently, the self-diffusion coefficients of alkaline-earth uranyl carbonate species were determined using molecular dynamics (MD) simulations. 7 This allowed for the development of a species-based diffusion model 6 that explicitly treats the variations in mass, charge, and diffusion coefficient of aqueous uranyl species, which proportions can be determined from speciation reactions. In test cases, the species-based diffusion model was shown to give a good description of the uranyl release fro...

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“…Although experimental techniques have been developed for determining water and ion self-diffusion coefficients such as the nuclear magnetic resonance spin echoes in the presence of pulsed magnetic field gradients (Stejskal and Tanner, 1965) (PGSE-NMR) or the diaphragm cell technique (Northrop and Anson, 1929), the determination of self-diffusion coefficients for uranyl species is often challenging because of the co-existence of various U(VI) aqueous species under most experimental conditions (Guillaumont et al, 2003). In this regard, the use of molecular simulation techniques provides an attractive alternative method to determine the self-diffusion coefficients of uranyl species.…”

Section: Introductionmentioning

confidence: 99%