Measurement of the apparent diffusion coefficient of N‐butane in soil

Measurements of in‐soil diffusion coefficients and the application of an appropriate diffusional model can allow for a more accurate prediction of soil gas concentrations and movement to locate subterranean contamination of volatile materials. The present study was undertaken to measure and evaluate the “apparent in‐soil diffusion coefficient”; for n‐butane through soil columns under non‐steady‐state conditions. The term “apparent in‐soil diffusion coefficient”; refers to a numerical coefficient that primarily describes the movement of the material by diffusion but also contains effects due to other mechanisms (e.g., adsorption and solubility).

Six test columns were evaluated at three soil porosity levels ranging from 0.30 to 0.43 and at two column temperature conditions, nominally 18°C and 7°C. Soil columns measured 25.4 cm in diameter by 84 cm in height and contained a moist sand/silt/clay mixture. The numerical range for the apparent in‐soil diffusion coefficients for n‐butane was 0.447 × 10^‐3cm²/s to 0.561 × 10^‐3cm²/s. The lower coefficient values were associated with lower soil porosity levels and cooler column conditions.     

Hydrodynamics,size, and shape of bacteriophage T4D tails and baseplates

We have used translational diffusion coefficient measurements and subunit hydrodynamic theory to determine the dimensions and shape of bacterioophage T4D baseplates and tails. The diffusion coefficient of the baseplate, measured by quasielastic laser light scattering (QLS), was determined previously by Wagenknecht and Bloomfield to be D = 8.56 × 10^?8 cm²/s. For the tail, we found D = 5.88 × 10^?8 cm²/s by QLS, and D = 6.02 × 10^?8 cm²/s by combining sedimentation coefficient and molecular weight in the Svedberg equation. These values, which have an uncertainty of ±2.7%, when combined with subunit hydrodynamic theory, enabled us to refine estimates of dimensions obtained by electron microscopy. For the hexagonal baseplate, the vertex-to-vertex distance is about 480 Å, the thickness is 160 Å, and there are six extended short fibers 320-Å long and 40 Å in diameter. When a baseplate of these dimensions is attached to a tail tube-sheath-connector complex 1050-Å long and 240 Å in diameter, the calculated D is 5.93 × 10^?8 cm²/s, within 1% of experiment. This combined use of electron microscopy and hydrodynamics, using the former to ascertain shape, and the latter to obtain solution dimensions, is a powerful approach to the structure of biomolecular complexes.     

Effect of temperature on permeation of low‐density lipoprotein particles through human carotid artery tissues

Quantification of the diffusion of small molecules and large lipid transporting lipoproteins across arterial tissues could be useful in elucidating the mechanism(s) of atherosclerosis. Optical coherence tomography (OCT) was used to determine the effect of temperature on the rate of diffusion of glucose and low‐density lipoproteins (LDL) in human carotid endarterectomy tissue in vitro. The permeability rate for glucose was calculated to be (3.51 ± 0.27) × 10^–5 cm/s (n = 13) at 20 °C, and (3.70 ± 0.44) × 10^–5 cm/s (n = 5) at 37 °C; for LDL the rate was (2.42 ± 0.33) × 10^–5 cm/s (n = 5) at 20 °C and (4.77 ± 0.48) × 10^–5 cm/s (n = 7) at 37 °C, where n is the number of samples. These results demonstrate that temperature does not significantly influence the permeation of small molecules (e.g. glucose), however, raising the temperature does significantly increase the permeation of LDL. These results provide new information about the capacity of an atherogenic lipoprotein to traverse the intimal layer of the artery. These results also demonstrate the potential of OCT for elucidating the dynamics of lipoprotein perfusion across the arterial wall. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Physical properties of type i collagen in solution: Structure of α-Chains and β- and γ-components and two-component mixtures

The structure of thermally denatured Type I collagen has been studied using laser light scattering. The results indicate that the diffusion coefficients of α-chains and β- and γ-components are 1.550 ± 0.08 × 10^?7, 1.000 ± 0.05 × 10^?7, and 0.835 ± 0.04 × 10^?7 cm²/sec, respectively, at temperatures between 20 and 40°C. It is concluded from diffusion data that these species have hydrodynamic radii of about 13.8 nm (α-chain), 21.5 nm (β-component), and 25.7 nm (γ-component), consistent with previous studies of thermal denaturation by light scattering. It is also concluded, based on volume calculations, that a large volume increase occurs when the triple helix unfolds. Homodyne correlation functions for two component mixtures of α-chains and β-and γ-components appeared to decay exponentially. In all but one case discussed the correlation function could be fitted with a single component having a translational diffusion coefficient which was an intensity weighted average of the diffusion coefficient of each component present.     

Hydrodynamic properties of mucins secreted by primary cultures of Guinea-pig tracheal epithelial cells: determination of diffusion coefficients by analytical ultracentrifugation and kinetic analysis of mucus gel hydration and dissolution

We have used two different approaches to determine hydrodynamic parameters for mucins secreted by guinea-pig tracheal epithelial cells in primary culture. Cells were cultured under conditions that promote mucous cell differentiation. Secreted mucins were isolated as the excluded fraction from a Sepharose CL-4B gel filtration column run under strongly dissociating conditions. Biochemical analysis confirmed the identity of the high molecular weight material as mucins. Analytical ultracentrifugation was used to study the physical properties of the purified mucins. The weight average molecular mass (M _w ) for three different preparations ranged from 3.3×10⁶ to 4.7×10⁶ g/mol (corresponding to an average structure of 1 – 2 subunits), and the sedimentation coefficient from 25.5 to 35 S. Diffusion coefficients ranging from 4.5×10^–8 to 6.4×10^–8 cm²/s were calculated using the Svedberg equation. A polydispersity index (M _z /M _w ) of ∼1.4 was obtained. Diffusivity values were also determined by image analysis of mucin granule exocytosis captured by videomicroscopy. The time course of hydration and dissolution of mucin was measured and a relationship is presented which models both phases, each with first order kinetics, in terms of a maximum radius and rate constants for hydration and dissolution. A median diffusivity value of 8.05×10^–8 cm²/s (inter-quartile range = 1.11×10^–7 to 6.08×10^–8 cm²/sec) was determined for the hydration phase. For the dissolution phase, a median diffusivity value of 6.98×10^–9 cm²/s (inter-quartile range = 1.47×10^–8 to 3.25×10^–9 cm²/sec) was determined. These values were compared with the macromolecular diffusion coefficients (D _20,w ) obtained by analytical ultracentrifugation. When differences in temperature and viscosity were taken into account, the resulting D _37,g was within the range of diffusivity values for dissolution. Our findings show that the physicochemical properties of mucins secreted by cultured guinea-pig tracheal epithelial cells are similar to those of mucins of the single or double subunit type purified from respiratory mucus or sputum. These data also suggest that measurement of the diffusivity of dissolution may be a useful means to estimate the diffusion coefficient of mucins in mucus gel at the time of exocytosis from a secretory cell. Received: 10 March 1998 / Accepted: 27 March 1998     

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.     

Extraction of total phenolic content from Azadirachta indica or (neem) leaves: Kinetics study

The objective of this work is to put forth the optimization and kinetics of total phenolic compounds extraction from Azadirachta indica leaves in a stirred batch extraction. Various experiential extraction parameters have been studied for maximum extraction of the total phenolic compounds. The maximum yield of total phenolic compounds was found to be 10.80?mg?g^?1 of dried neem powder under the optimized conditions. The extraction kinetics behavior followed first-order kinetics with diffusion coefficient ranged from 1.8?×?10^?12 to 3.2?×?10^?12?m² s^?1 for all sets. Activation energy (E_a) value for the extraction of the total phenolic compounds was found to be 22.87?kJ?mol^?1. The kinetic expression model developed by Spiro and Siddique showed a good agreement with the experimental outcomes. The obtained results can be used to scale up the operations for industrial purposes.     

Drying of Pomegranate Arils and Selection of a Suitable Drying Model

The drying characteristics of pomegranate arils were investigated in temperature range of 50–70 °C. The increase in drying air temperature resulted in a decrease in drying time. The drying rate was found to increase with temperature, thereby reducing the total drying time. Thirteen drying models were evaluated in the kinetics research. The goodness of fit of the proposed models was evaluated by using the determination of coefficient (R ² ), mean relative percent error (P), reduced chi-square (χ ²), and root means square error (RMSE). The Midilli et al. model showed a better fit to experimental drying data as compared to other models. Effective moisture diffusivity (D _eff) ranged from 9.447 × 10⁻¹¹ to 3.481 × 10⁻¹⁰ m²/s as calculated by the Fick’s second law of diffusion. The temperature dependence of the value of effective moisture diffusivity followed an Arrhenius-type relationship. The activation energy for the moisture diffusion was determined to be 60.34 kJ/mol.     

Oxygen Diffusion from the Roots of Rice Grown under Non-waterlogged Conditions

Three rice varieties, cv. Norin 36, cv. Norin 37 and cv. Yubae, were grown in a loam with a 20 cm water-table which gave aerobic conditions to a depth of not less than 15 to 17 cm. Under these conditions Norin 36 grew more vigorously and tillered more frequently than the other two varieties. The rates of oxygen diffusion at 23°C from roots up to 11 cm in length were however appreciably lower for Norin 36 (4.3 × 10^?8g · cm^?2 of root surface · min^?1) than for Norin 37 or Yubae (c. 7.8 × 10^?8g). A considerable increase (up to 200 %) in the oxygen diffusion rate (ODR) from the roots occurred if they were cooled to 3°C, and at this temperature differences in ODR between the varieties were not significant. For a purely physical system, because of the decrease in the diffusion coefficient of oxygen in water, and, the increase in oxygen solubility, a drop of c. 20 % in ODR should accompany the above 20°C drop in temperature. A 16 % drop was recorded for artificial ‘roots’ under these conditions. It was concluded that respiratory activity at the higher temperature must have been responsible for the low readings and intervarietal differences observed at 23°C. By increasing the 3°C values by 25 % a mean value of 14.2 × 10^?8g · cm^?2 of root surface · min^?1 was recorded for the three varieties, being the probable ODR at 23°C in the absence of a respiratory factor. Calculations show that respiratory activity removed enough oxygen to reduce the ODR for Norin 36 by more than 9 × 10^?8g, and for Norin 37 and Yubae by c. 6.7 × 10^?8g · cm^?2 of root surface · min^?1. Anatomical investigations showed that cortical breakdown was always extensive at 4 to 4.5 cm from the apex of the roots. In some cases however breakdown had not occurred in the basal segment of the root. No opinion could be formed as to whether differences in the amount of cortical breakdown between the varieties might have occasioned the respiratory differences observed. An interesting feature of the root anatomy was the failure of breakdown in those regions of the roots through which lateral roots emerged.     

Multifunctional 0D–2D Ni2P Nanocrystals–Black Phosphorus Heterostructure

0D transition metal phosphides (TMPs) nanocrystals (NCs)–2D ultrathin black phosphorus (BP) heterostructure (Ni₂P@BP) have been synthesized via a facile sonication‐assisted exfoliation followed by a solvothermal process. Compared with the bare BP, the specially designed Ni₂P@BP architecture can enhance the electrical conductivity (from 2.12 × 10² to 6.25 × 10⁴ S m^–1), tune the charge carrier concentration (from 1.25 × 10¹⁷ to 1.37 × 10²⁰ cm^–3), and reduce the thermal conductivity (from 44.5 to 7.69 W m^–1 K^–1) at 300 K, which can be considered for multiple applications. As a result, the Ni₂P@BP exhibits excellent Li storage properties and high hydrogen evolution reaction electrocatalytic activities. The Ni₂P@BP shows improved Li diffusion kinetics (e.g., the Li ions diffusion coefficient increases from 1.14 × 10^–14 cm² s^–1 for pure BP nanosheets to 8.02 × 10^–13 cm² s^–1 for Ni₂P@BP). In addition, the Ni₂P@BP electrode sustains hydrogen production with almost unchanged activity over 3000 cycles, which indicates its good chemical stability when operating under strong reducing environment.     

磁共振弥散加权成像及ADC值对鼻咽癌颅底放疗疗效的评价价值

目的:探讨磁共振弥散加权成像(DWI)及表观扩散系数(ADC)值在鼻咽癌颅底放疗中的临床价值。方法:收集我院于2013年6月~2014年6月复查的40例鼻咽癌患者,分别于放疗前及放疗结束12个月以后对所有患者行常规核磁共振成像(MRI)及DWI检查,测量放疗前、后ADC值,根据影像学检查以及临床诊断结果分为复发组(n=5)及未复发组(n=35)。结果:复发组放疗前ADC值为(0.797±0.031)×10~(-3)mm~2/s,与未复发组放疗前ADC值(0.805±0.028)×10~(-3)mm~2/s比较,差异无统计学意义(P0.05)。复发组放疗结束12个月以后ADC值为(1.097±0.091)×10~(-3)mm~2/s,与未复发组放疗结束12个月以后ADC值(1.705±0.128)×10~(-3)mm~2/s比较,差异有统计学意义(P0.05)。结论:DWI作为一种新兴的磁共振成像技术,对于鼻咽癌颅底放疗疗效的评价具有重要价值,通过DWI对ADC值的测量,可有效的预测患者预后是否良好。     

Dynamic light scattering as a probe of superhelical DNA-intercalating agent interaction

Polarized dynamic light-scattering measurements on superhelical pBR322-plasmid DNA solutions in 0.2M NaCl, 2 mM NaPi, pH 7.0, 2 mM EDTA result in a translational diffusion coefficient D = (3.77 ± 0.10) × 10^?8 cm²/s for the native molecule. Modeling the DNA, in the simplest approximation, as a 10 × 440-nm effective hydrodynamic rigid rod yields a good fit to the apparent diffusion coefficient angular-dependence data up to 70°; the model fails at higher angles, probably due to the effects of flexibility or branching of the rod. Diffusion coefficient titration experiments with a platinum complex intercalating agent (PtTS) result in a titratable superhelix density of σ = ?0.079 ± 0.008 under our experimental conditions, corresponding to about 34 superhelical turns in the native DNA. The DNA contour length predicted by our two independent results, the rod dimensions and the number of superhelical turns, is in excellent agreement with the contour length calculated from the number of base pairs, supporting the hydrodynamic approximation of an effective rodlike structure for this small DNA molecule in solution.     

Hydrodynamic properties of mushroom tyrosinase

The hydrodynamic properties of mushroom tyrosinase were determined at pH 6.5 using a Sephadex G-200 column. From the comparison of its gel-filtration behaviour with those of standard proteins, the following parameters were calculated: MW (122 500 ± 1%), Stokes' radius (42.75 × 10^?8 cm²/sec), diffusion coefficient (5.048 × 10^?7 cm²/sec) and frictional ratio (1.26). These values suggest a globular conformation of this enzyme.     

Ar + H<Subscript>2</Subscript> Plasma Interacting with Lithium-Filled Capillary Porous Structure

Ar + H₂ plasma interacting with liquid lithium was carried out on a one-cathode linear plasma device (SCU-PSI). The lithium sample was covered with capillary porous structure (CPS). It is found that the electron temperature of applied plasma ranged from ~0–1 eV and electron density ranged from 0.1 × 10²⁰ to 1 × 10²⁰ m^?3. The experimental results indicate that a reduction in the electron temperature and the lithium evaporation is found as the percentage of H₂ increases When the ratio of argon and hydrogen keeps constant, the electron temperature and lithium evaporation increase with applied input power, respectively. The retention of hydrogen atoms in lithium surface results in reducing the lithium evaporation. The XRD analysis result shows that during plasma radiation no LiH is formed.     

Shear‐induced diffusion of red blood cells measured with dynamic light scattering‐optical coherence tomography

Quantitative measurements of intravascular microscopic dynamics, such as absolute blood flow velocity, shear stress and the diffusion coefficient of red blood cells (RBCs), are fundamental in understanding the blood flow behavior within the microcirculation, and for understanding why diffuse correlation spectroscopy (DCS) measurements of blood flow are dominantly sensitive to the diffusive motion of RBCs. Dynamic light scattering‐optical coherence tomography (DLS‐OCT) takes the advantages of using DLS to measure particle flow and diffusion within an OCT resolution‐constrained three‐dimensional volume, enabling the simultaneous measurements of absolute RBC velocity and diffusion coefficient with high spatial resolution. In this work, we applied DLS‐OCT to measure both RBC velocity and the shear‐induced diffusion coefficient within penetrating venules of the somatosensory cortex of anesthetized mice. Blood flow laminar profile measurements indicate a blunted laminar flow profile and the degree of blunting decreases with increasing vessel diameter. The measured shear‐induced diffusion coefficient was proportional to the flow shear rate with a magnitude of ~0.1 to 0.5 × 10^?6 mm². These results provide important experimental support for the recent theoretical explanation for why DCS is dominantly sensitive to RBC diffusive motion.      

Rates of Shrinkage and Growth of Air Bubbles Entrained in Wheat Flour Dough

The rates of shrinkage at constant temperature, and growth under a temperature rise below 100°C, of bubbles entrained in wheat flour dough were analyzed and compared with those of a bubble in water. The rate of shrinkage of bubbles in flour dough was controlled by the diffusion of dissolved air from the surface of bubbles to the bulk of flour dough. The apparent diffusion coefficient of the dissolved air in wheat flour dough with the water fraction of 0.49 calculated from the shrinkage of bubbles, was (3.2 ± 1.5) × 10^1?1 m²/sec (19°C), and (6.4 ± 2.0) × 10^?11 m²/sec (42°C). However, the growth behavior of bubbles in flour dough under a temperature rise was very different from that predicted from the diffusion theory. The critical radius of bubbles to grow was larger than that estimated from the diffusion theory. The mechanism of growth of bubbles in wheat flour dough, which was different from that of a bubble in water, is a subject that needs to be clarified.     

A critical evaluation of models for complex molecular dynamics: application of NMR studies of double- and single-stranded DNA

The nature of internal and overall motions in native (double-stranded) and denatured (single-stranded) DNA fragments 120–160 base pairs (bp) long is examined by molecular-dynamics modeling using ¹³C-nmr spin-relaxation data obtained over the frequency range of 37–125 MHz. The broad range of ¹³C frequencies is required to differentiate among various models. Relatively narrow linewidths, large nuclear Overhauser enhancements (NOEs), and short T₁ values all vary significantly with frequency and indicate the presence of rapid, restricted internal motions on the nanosecond time scale. For double-stranded DNA monomer fragments (147 bp, 24 Å diam at 32°C), the overall motion is that of an axially symmetric cylinder (τ_x = ～10^?6 s;τ_Z = ～1.8 × 10^?8s), which is in good agreement with values calculated from hydrodynamic theory (τ_x = ～1.8 × 10^?6 s; τ_Z = ～2.7 × 10^?8 s). The DNA internal motion can be modeled as restricted amplitude internal diffusion of individual C? H vectors of deoxyribose methine carbons C1′, C3′, and C4′, either with conic boundary conditions (τ_w = ～4 × 10^?9 s, θ_cone = ～21°) or as a bistable jump (τ_A = τ_B = ～2 × 10^?9 s, θ = ～15°). We discuss the critical role in molecular-dynamics modeling played by the angle (β) that individual C? H vectors make with the long axis of the DNA helix. Heat denaturation brings about increases in both the rate and amplitude of the internal motion (described by the wobble model with τ_W = ～0.2 × 10^?9 s, θ_cone = ～50°), and overall motion is affected by becoming essentially isotropic (τ_x = τ_Z = ～5 × 10^?8 s) for the single-stranded molecules. Since ¹³C-nmr data obtained at various DNA concentrations for C2′ of the deoxyribose ring is not described well by the above models, a new model incorporating an additional internal motion is proposed to take into account the rapid, extensive, and weakly coupled motion of C2′.     

Molecular dynamics investigation of nitric oxide (II) interaction with a model biological membrane

Nitric oxide (II) diffusion through a model two-component (phosphatidylcholine and phosphatidylethanolamine molecules) biological membrane is investigated using the molecular dynamics method. It is shown that NO molecules are rotating in the process of diffusion into the phospholipid bilayer. The calculated diffusion coefficient D[NO] = 0.35 (±0.23) × 10^?5 (cm²/s) is in a good agreement with literature data. This testifies that free diffusion of NO molecules may be a plausible mechanism of the NO permeation through the membranes.     

The effect of SDS on protein zone dispersion in polyacrylamide gel electrophoresis

The zone dispersions of the reduced subunit of β-lactoglobulin B and its derivative with sodium dodecyl sulfate (SDS) were measured during polyacrylamide gel electrophoresis (PAGE) using the apparatus for continuous optical scanning at 280 nm. The ratio of apparent diffusion coefficients (D′) of the reduced subunit of β-lactoglobulin B (1.71 × 10^?6 cm²/s) and of its SDS-derivative (7.1 × 10^?7 cm²/s) was found to be 2.4 under the conditions of PAGE (pH 10.4, 0.015 ionic strength, 1°C, 4 mA/cm² current density, 50 μg protein load, 10% T gel) used. This is nearly twice the value of 1.3 predicted, under the assumption of sphericity for these protein molecules, on the basis of the binding of 1.4 g of SDS per gram of protein. It is postulated that the increment in zone sharpness (decrease in apparent diffusion coefficient) over that predicted by SDS binding alone is a general property of SDS-proteins providing gel electrophoresis in SDS-containing buffers with a resolving power larger than that obtained in the absence of the detergent.     

Diffusion of antibiotics in intervertebral disc

Delivering charged antibiotics to the intervertebral disc is challenging because of the avascular, negatively charged extracellular matrix (ECM) of the tissue. The purpose of this study was to measure the apparent diffusion coefficient of two clinically relevant, charged antibiotics, vancomycin (positively charged) and oxacillin (negatively charged) in IVD. A one-dimensional steady state diffusion experiment was employed to measure the apparent diffusion coefficient of the two antibiotics in bovine coccygeal annulus fibrosus (AF) tissue. The averaged apparent diffusion coefficient for vancomycin under 20% compressive strain was 7.94 ± 2.00 × 10⁻¹² m²/s (n = 10), while that of oxacillin was 2.26 ± 0.68 × 10⁻¹⁰ m²/s (n = 10). A student’s t-test showed that the diffusivity of vancomycin was significantly lower than that of oxacillin. This finding may be attributed to two factors: solute size and possible binding effects. Vancomycin is approximately 3 times larger in molecular weight than oxacillin, meaning that steric hindrance likely plays a role in the slower transport. Reversible binding between positive vancomycin and the negative ECM could also slow down the rate of diffusion. Therefore, more investigation is necessary to determine the specific relationship between net charge on antibiotic and diffusion coefficients in IVD. This study provides essential quantitative information regarding the transport rates of antibiotics in the IVD, which is critical in using computational modeling to design effective strategies to treat disc infection.