Translational diffusion coefficient of α-chymotrypsinogen A by laser-light-scattering spectroscopy

The translational diffusion coefficient of a pure sample of α-chymotrypsinogen A is measured by laser light scattering to give a value of D_20,w⁰ = (8.40 ± 0.15) × 10^?7 cm²/sec.     

The concentration dependence of the hemoglobin mutual diffusion coefficient

Laser correlation Spectroscopy was used to measure the mutual diffusion coefficient, D, of human cyanomethemoglobin (Fe⁺⁺⁺:CN) at varying protein concentrations. These measurements were male at 20°C in a 0.1 M phosphate buffer solution at pH 7.0. For low protein concentrations we find D = (6.43 ± 0.26) × 10^?7 cm²/S and that there is a near linear decrease from this value at higher concentrations. The linear relation between the diffusion coefficient and protein concentration allows us to deduce the value of the linear frictional volume fraction coefficient, K_f= 7.75. and to extrapolate to hemoglobin concentrations equivalent to that in the red blood cell where we estimate D = 4.25 × 10^?7 cm²/s Various theoretical predictions of the dependence of the mutual diffusion coefficient on concentration are tested; we find that the generalized Stokes-Einstein relation can be made to fit our high concentration data if we assume a hard-sphere model and if we include a term involving a hydrodynamic interaction integral.     

Glucose diffusion in crosslinked proteins containing streptomyces

Summary Diffusion measurements of glucose in a crosslinked water-swollen protein matrix containingStreptomyces thermovulgaris strain 127, are described. Solute diffusion coefficients in the gel phase were found to be considerably lower than for free diffusion. The range of diffusion coefficients was 0.83×10⁻¹⁰ to 2.68×10⁻¹⁰m²/s at corresponding ratios to free diffusion values 0.11 to 0.38. It is shown that polymer structure does not pose any significant effect on mass transfer for the small glucose molecule.     

Obtaining the concentration-dependent diffusion coefficient from ultrafiltration experiments: Application to hyaluronate

A method for determining the concentration-dependent mutual diffusion coefficient D(C) of a macromolecule-solvent combination over a wide macromolecular concentration range is presented. All necessary data are gathered from a single experiment, in which polymer concentration profiles are measured during one-dimensional dead-end ultrafiltration. Based on these profiles, the convection-diffusion equation is used to deduce the dependence of D on C. To demonstrate the utility of the approach, studies using sodium hyaluronate dissolved in either 10 mM NaCl or a phosphate buffer were carried out. For hyaluronate (HA) in 10 mM NaCl, the mutual diffusion coefficient varies approximately linearly with concentration according to D(C) = 4.1 × 10⁻⁶ C^0.96 cm²/s in the range 0 ≤ C ≤ 0.6 mass %, for C expressed in mass %. However, transition points (slope changes) in the D(C) curve are present at C ≅ 0.7 mass % and C ≅ 1.4 mass %. For HA in the phosphate buffer, the mutual diffusion coefficient is well described by D(C) = 1.9 × 10⁻⁶ C^0.825, for 0 ≤ C ≤ 1.8 mass %. These values agree well with previously published data. The technique is robust, and permits reasonably high polymer concentrations to be easily studied. © 1996 John Wiley & Sons, Inc.     

Effect of extraction temperature on the diffusion coefficient of polysaccharides from Spirulina and the optimal separation method

The extraction temperature had a significant impact on the concentration of polysaccharides derived from solid-liquid extraction of Spirulina. The polysaccharide concentration was significantly higher when the extraction was performed at 90°C than when it was performed at 80, 70, and 50°C. This result is related to the diffusion coefficients of the polysaccharides, which increased from 1.07 × 10^?12 at 50°C to 3.02 × 10^?12 m²/sec at 90°C. Using the Arrhenius equation, the pre-exponential factor (D ₀ ) and the activation energy (E _a ) for Spirulina polysaccharide extraction were calculated as 7.958 × 10^?9 m²/sec and 24.0 kJ/mol, respectively. Among the methods used for the separation of Spirulina polysaccharides, cetyltrimethylammonium bromide (CTAB, method I) and organic solvent (ethanol, in methods II and III) provided similar yields of polysaccharides. However, the separation of polysaccharides using an ultrafiltration (UF) process (method III) and ethanol precipitation was superior to separation via CTAB or vacuum rotary evaporation (method II). The use of a membrane with a molecular weight cut-off (MWCO) of 30 kDa and an area of 0.01 m² at a feed pressure of 103 kPa with a mean permeate flux of 39.3 L/m²/h and a retention rate of 95% was optimal for the UF process. The addition of two volumes (v/v) of ethanol, which gave a total polysaccharide content of approximately 4% dry weight, was found to be most suitable for polysaccharide precipitation. The results of a Sepharose 6B column separation showed that the molecular weights of the polysaccharides in fractions I and II were 212 and 12.6 kDa, respectively.     

Lateral diffusion and patch formation of H-2Kk antigens on mouse spleen lymphocytes

We have studied the diffusion and aggregation of H-2K^k antigens labeled with a fluorescent anti-H-2K^k monoclonal antibody (IgG) on mouse splenic lymphocytes, employing fluorescence photobleaching recovery and fluorescence microscopy. The H-2K^k antigens were initially distributed homogeneously on all lymphocytes. Upon antibody binding, sub-micron patches were formed on 50–60% of the cells. A lateral diffusion coefficient, D, of 7.1·10^?10 cm²/s and a mobile fraction of 0.73 were found for H-2K^k antigens on diffusely-labeled cells, while these antigens were immobile (D?5·10^?12 cm²/s) on patched cells. The patched and nonpatched sub-populations did not correspond to B- and T-lymphocytes. Subjection to low temperature or treatment with NaN₃ or cytoskeleton-disrupting drugs did not affect the diffusion or patching of H-2K^k, indicating no involvement of metabolic energy or drug-sensitive cytoskeletal components. These findings could be related to the interactions of H-2 antigens on the cell surface, and to the different susceptibilities of various cells to lysis by cytotoxic T-cells.     

Threonine diffusion and threonine transport in Corynebacterium glutamicum and their role in threonine production

Transmembrane threonine fluxes (i.e., uptake, diffusion, and carrier-mediated excretion) all contribut-ing to threonine production by a recombinant strain of Corynebacterium glutamicum, were analyzed and quantitated. A threonine-uptake carrier that transports threonine in symport with sodium ions was identified. Under production conditions (i.e., when internal threonine is high), this uptake system catalyzed predominantly threonine/threonine exchange. Threonine export via the uptake system was excluded. Threonine efflux from the cells was shown to comprise both carrier-mediated excretion and passive diffusion. The latter process was analyzed after inhibition of all carrier-mediated fluxes. Threonine diffusion was found to proceed with a first-order rate constant of 0.003 min^–1 or 0.004 μl min^–1 (mg dry wt.)^–1, which corresponds to a permeability of 8 × 10^–10 cm s^–1. According to this permeability, less than 10% of the efflux observed under optimal conditions takes place via diffusion, and more than 90% must result from the activity of the excretion carrier. In addition, the excretion carrier was identified by (1) inhibition of its activity by amino acid modifying reagents and (2) its dependence on metabolic energy in the form of the membrane potential. Activity of the excretion system depended on the membrane potential, but not on the presence of sodium ions. Threonine export in antiport against protons is proposed. Received: 25 August 1995 / Accepted: 18 October 1995     

Lateral diffusion of human histocompatibility antigens in isolated plasma membranes

We have prepared large (5–10 μm) plasma membrane fragments by lysis of VA-2, human, cells adherent to Sephadex beads. The membrane fragments may be removed from beads by sonication and stained with fluorescent antibodies to human histocompatibility antigens, HLA antigens. Lateral diffusion of labelled antigens is followed by the method of fluorescence photobleaching recovery (FPR). HLA antigens of isolated membranes diffuse at the same rate, approx. (2–4) · 10^?10 cm² · s^?1 as they do in intact cells. This rate may be modified by incubating membranes in a variety of media. Buffers of slightly acid pH (6.5 or less) enhance lateral diffusion, while the presence of divalent ions slightly reduces diffusion rates. Our major finding is that incubation of 37° in 0.10 M phosphate buffer increases lateral diffusion 3–5-fold.     

Limited rotational diffusion of DPH in human erythrocyte membranes

The rotational diffusion of diphenylhexatriene (DPH) determines its fluorescence depolarization. Time-resolved polarization measurements were used to calculate the coefficient of diffusion of this probe in human crythrocyte ghost membranes on the basis of a diffusion theory of limited rotation. The diffusion coefficient is 5.9 × 10⁷ sec^?1 at 37°C; this was compared with the diffusion coefficient of DPH in liquid paraffin for an estimation of the microviscosity of the membrane bilayer.     

Dynamic light scattering from collagen solutions. I. Translational diffusion coefficient and aggregation effects

Solutions of native collagen extracted from rat tail tendons in neutral salt solution have been studied by dynamic light scattering. The spectra obtained are consistent with the presence in solution of both single rod-shaped collagen molecules and aggregates of molecules. No contribution to the spectrum has been detected at any scattering angle from rotational diffusion of single molecules, although a measurable broadening effect is expected at high angles. The translational diffusion coefficient D of single molecules, calculated from the broader spectral component, shows an anomalous dependence on collagen concentration with a maximum value of D_20,w = 8.6 ± 0.2 × 10^?12 m²/sec near the concentration 0.04% by weight. Above 0.05% D falls linearly with increasing concentration and takes the value D _20,w = 8.1 ± 0.2 × 10^?12 m²/sec at 0.064% collagen.     

Variation in protein lateral diffusion coefficients is related to variation in protein concentration found in mitochondrial inner membranes

The electrophoretic freeze-fracture electron microscopy method (Sowers, A.E. and Hackenbrock, C.R. (1984) Proc. Natl. Acad. Sci. USA 78, 6246–6250) for measuring the lateral diffusion coefficient of integral proteins was applied to a large population of spherical-shaped mitochondrial inner membranes. Membrane integral protein concentration was estimated by determining the intramembrane particle concentration. Analysis of the data reveals that: (a) the radii of the spherical inner membranes in the selected population ranged from 0.22 to 1.2 μm, (b) the intramembrane particle concentrations ranged from 2300 to 6400 per μm², and (c) the calculated lateral diffusion coefficients of the intramembrane particles ranged from 1.3·10⁻¹⁰ to 3.35·10⁻⁹ cm²/s. The data clearly show a naturally occurring large range in protein concentration in the mitochondrial inner membrane and an inverse correlation of lateral diffusion coefficient with the membrane protein concentration. This study is the first to show that the lateral diffusion coefficient of integral proteins in a native membrane varies as the membrane protein concentration.     

A robust ex vivo method to evaluate the diffusion properties of agents in biological tissues

A robust method is presented for evaluating the diffusion properties of chemicals in ex vivo biological tissues. Using this method that relies only on thickness and collimated transmittance measurements, the diffusion properties of glycerol, fructose, polypropylene glycol and water in muscle tissues were evaluated. Amongst other results, the diffusion coefficient of glycerol in colorectal muscle was estimated with a value of 3.3 × 10^?7 cm²/s. Due to the robustness and simplicity of the method, it can be used in other fields of biomedical engineering, namely in organ cryoprotection and food industry.      

New dextrin-vinylacrylate hydrogel: Studies on protein diffusion and release

New dextrin hydrogels with degrees of substitution (DS) from ca. 10% (DS 10) to 70% (DS 70) were prepared by radical polymerization of aqueous solutions of vinylacrylate (VA)-derivatized dextrin. A preliminary analysis on the potential of these hydrogels for the controlled release of bioactive molecules was carried out. The protein (bovine serum albumin) diffusion coefficients on the hydrogels were calculated using the lag-time analysis. Values in range 10^?7 cm²/s were obtained for DS 20 and DS 40 and a smaller value of 10^?8 cm²/s arised upon DS increasing to 70%, revealing the dependence of the diffusivity on the crosslinking density. The release of BSA from dextrin-VA hydrogels, in the presence of amyloglucosidase was shown to be mainly dependent on the diffusion and, to a smaller extent, on the degradation kinetics. The protein release can be tailored from days to months by varying the DS.     

Low‐frequency conductivity tensor of rat brain tissues inferred from diffusion MRI

Conductivity tensor maps of the rat brain were obtained using diffusion magnetic resonance imaging (MRI). Signal attenuations in the cortex and the corpus callosum were measured using the stimulated echo acquisition mode (STEAM) sequence with b factors up to 6000 s/mm². Our previously published method was improved to infer 3 × 3 conductivity tensor at the low‐frequency limit. The conductivity tensor of the tissue was inferred from the fast component of the diffusion tensor and a fraction of the fast component. The mean conductivity (MC) of the cortex and the corpus callosum was 0.52 and 0.62 S/m, respectively. Diffusion‐weighted images were obtained with b factors up to 4500 s/mm². Conductivity tensor images were calculated from the fast diffusion tensor images. Tissues with highly anisotropic cellular structures, such as the corpus callosum, the internal capsule, and the trigeminal nerve, exhibited high anisotropy in conductivity. The resulting values corresponded to conductivities at the low‐frequency limit because our method assumed electric currents flowing only through extracellular fluid. Bioelectromagnetics 30:489–499, 2009. © 2009 Wiley‐Liss, Inc.     

Translational diffusion in the plasma membrane of sea urchin eggs

Translational diffusion in the plasma membrane of individual egg cells from the sea urchin species Paracentrotus lividus has been studied by fluorescence microphotolysis (FM). In order to probe the lipid phase of the membrane, procedures have been worked out by which the fluorescent analog 3,3′-dioctadecyl-oxatricarbocyanine (C₁₈diO) can be incorporated into the membrane. In the unfertilized egg a fraction R = 0.9 of C₁₈diO was mobile having an apparent diffusion coefficient of D = 6.0 × 10^?9 cm² sec^?1. Fifteen to twenty-five minutes after fertilization R and D were reduced to 0.8 and 2.7 × 10^?9 cm² sec^?1, respectively. In order to study diffusion of membrane proteins, procedures have been worked out by which the cell surface can be labeled with fluorescein-isothiocyanate (FITC). FITC binds to both the plasma membrane and the vitelline layer. Together with the vitelline layer two-thirds of the FITC-fluorescence could be removed from the egg surface. Gel electropherograms of isolated egg cortices showed various protein bands; however, only two of the protein bands were labeled with FITC. In the unfertilized egg a fraction R = 0.9 of the FITC-labeled membrane proteins was mobile having an apparent diffusion coefficient of D = 35 × 10^?11 cm² sem^?1. Fiteen to twenty-five minutes after fertilization R and D were reduced to 0.8 and 7.0 × 10^?11 cm² sec^?1, respectively. FITC-labeled proteins of the fertilization envelope were immobile. Our studies have shown (i) that the egg surface can be fluorescently labeled without blocking fertilization and early development, (ii) that the plasma membrane of unfertilized eggs is a fluid environment permitting a rapid movement of lipids and proteins, and (iii) that after fertilization a substantial degree of lipid and protein mobility is maintained.     

Hyaluronate diffusion in semidilute solutions

Analysis of the mutual diffusion coefficient of hyaluronate reveals that it rapidly increases with increasing concentration or decreasing ionic strength. The mutual diffusion coefficients analyzed by boundary relaxation in the analytical ultracentrifuge by either Raleigh interference optics or absorption optics (through the use of fluorescein-labeled hyaluronate) yielded similar values. The theoretical treatment of the mutual diffusion coefficient has been analyzed in terms of experimentally measured intradiffusion coefficients and thermodynamic virial coefficients. Only approximate agreement between theory and experiment was found. The concept of formation of transient statistical network structures in semidilute solutions of hyaluronate was applied to evaluate a critical concentration at which network formation occurs. This has been discussed in relation to the marked decrease in the intradiffusion coefficient of hyaluronate with concentration. The formation of network structures in hyaluronate was found not to preclude the hyaluronate undergoing extremely rapid rates of mutual diffusion (with diffusion coefficients ～30 × 10^?11 m² s¹) under conditions of relatively large initial chemical potential gradients. Measurements of the unidirectional flux of hyaluronate for nonzero gradients demonstrated their marked sensitivity to the magnitude of the concentration difference across the boundary. An experimental feature of the unidrectional diffusion coefficients of hyaluronate is that they may be analyzed purely in terms of mutual and intradiffusion processes. The backflux diffusion coefficient (describing the flux against the imposed concentration gradient) appeared identical with the intradiffusion coefficient. The analysis of the various sources of errors made in this study suggests that the magnitude of the diffusion coefficients measured may be regarded only as approximate.     

Dependence of apparent diffusion coefficient measurement on diffusion gradient direction and spatial position – A quality assurance intercomparison study of forty-four scanners for quantitative diffusion-weighted imaging

PurposeTo propose an MRI quality assurance procedure that can be used for routine controls and multi-centre comparison of different MR-scanners for quantitative diffusion-weighted imaging (DWI).Materials and methods44 MR-scanners with different field strengths (1 T, 1.5 T and 3 T) were included in the study. DWI acquisitions (b-value range 0–1000 s/mm²), with three different orthogonal diffusion gradient directions, were performed for each MR-scanner. All DWI acquisitions were performed by using a standard spherical plastic doped water phantom. Phantom solution ADC value and its dependence with temperature was measured using a DOSY sequence on a 600 MHz NMR spectrometer. Apparent diffusion coefficient (ADC) along each diffusion gradient direction and mean ADC were estimated, both at magnet isocentre and in six different position 50 mm away from isocentre, along positive and negative AP, RL and HF directions.ResultsA good agreement was found between the nominal and measured mean ADC at isocentre: more than 90% of mean ADC measurements were within 5% from the nominal value, and the highest deviation was 11.3%. Away from isocentre, the effect of the diffusion gradient direction on ADC estimation was larger than 5% in 47% of included scanners and a spatial non uniformity larger than 5% was reported in 13% of centres.ConclusionADC accuracy and spatial uniformity can vary appreciably depending on MR scanner model, sequence implementation (i.e. gradient diffusion direction) and hardware characteristics. The DWI quality assurance protocol proposed in this study can be employed in order to assess the accuracy and spatial uniformity of estimated ADC values, in single- as well as multi-centre studies.     

How to predict diffusion of medium-sized molecules in polymer matrices. From atomistic to coarse grain simulations

The normal diffusion regime of many small and medium-sized molecules occurs on a time scale that is too long to be studied by atomistic simulations. Coarse-grained (CG) molecular simulations allow to investigate length and time scales that are orders of magnitude larger compared to classical molecular dynamics simulations, hence providing a valuable approach to span time and length scales where normal diffusion occurs. Here we develop a novel multi-scale method for the prediction of diffusivity in polymer matrices which combines classical and CG molecular simulations. We applied an atomistic-based method in order to parameterize the CG MARTINI force field, providing an extension for the study of diffusion behavior of penetrant molecules in polymer matrices. As a case study, we found the parameters for benzene (as medium sized penetrant molecule whose diffusivity cannot be determined through atomistic models) and Poly (vinyl alcohol) (PVA) as polymer matrix. We validated our extended MARTINI force field determining the self diffusion coefficient of benzene (2.27·10⁻⁹ m² s⁻¹) and the diffusion coefficient of benzene in PVA (0.263·10⁻¹² m² s⁻¹). The obtained diffusion coefficients are in remarkable agreement with experimental data (2.20·10⁻⁹ m² s⁻¹ and 0.25·10⁻¹² m² s⁻¹, respectively). We believe that this method can extend the application range of computational modeling, providing modeling tools to study the diffusion of larger molecules and complex polymeric materials.     

A versatile shear cell for diffusion measurements on small sample volumes allowing analytical recording of multicomponent transport: II. Applications

A diffusion cell described in the preceding paper has been used to determine mutual and intradiffusion coefficients for various compounds in the range 2–2000 × 10^?12 m² s^?1. The results are in good agreement with previously reported values. The standard deviation in a series of 13 runs on serum albumin performed in four different instruments was 6%.     

Metabolic threshold and sulfide-buffering in diffusion controlled marine sediments impacted by continuous organic enrichment

The effects of organic enrichment on sediment biogeochemistry was studied in diffusion controlled sediment mesocosms, where labile organic matter (OM) (fish feed) pulses were added once a week to the sediment surface. Two types of sediments, differing mainly in content of reactive Fe, were used. The aim of this experiment was two-fold, (1) to evaluate the importance of Fe-driven sulfide buffering for sulfide accumulation in surface enriched sediments, and (2) to estimate the diagenetic capacity for degradation of labile OM near the sediment surface. The simulated OM loading rate of 375 mmol C m^?2 day^?1 led to a 5–6 times increase in CO₂-production and a 4–5 times increase in O₂-uptake. Sulfate reduction estimated by radiotracer experiments and CO₂-release was 105–131 mmol m^?2 day^?1, but accumulation of porewater sulfide was low in both sediment types. Instead 99% of sulfide was oxidized with O₂ at the sediment water interface in the low Fe treatment, whereas 46% of produced sulfide precipitated as Fe-S compound in the high Fe treatment resulting in significantly lower O₂-uptake. Furthermore, the accumulation of up to 30% of added OM by the end of the experiment indicated a saturation of the heterotrophic microbial communities in the upper enriched surface layer. These results suggest a maximum diagenetic capacity for OM degradation in the range of ~25 μmol C cm^?3 day^?1 or 260 mmol m^?2 day^?1 for the present sediment types.