Transport of vanadium (V) in saturated porous media: effects of pH,ionic-strength and clay mineral

Vanadium, a hazardous pollutant, has been frequently detected in soil and groundwater, however, its transport behavior in porous media were not clearly understood. In this study, the effects of solution pH, ionic strength (IS) and the effect of clay mineral on the transport of vanadium in saturated porous media were investigated. Laboratory experiments using a series of columns packed with quartz sand were carried out to explore the retention and transport of vanadium with a range of ionic-strength (0.001–0.1 M) and pH (4–8) and two different types of clay minerals montmorillonite and kaolinite. Results of the breakthrough experiments showed that vanadium was highly mobile in the saturated porous media. The increase in pH rendered a higher transport of vanadium in saturated porous media. The study also indicated an easier transfer of vanadium with an increase in IS. Montmorillonite enhanced the mobility of vanadium in the column when compared to kaolinite. A mathematical model based on advection-dispersion equation coupled with equilibrium and kinetic reactions was used to describe the retention and transport of vanadium in the columns very well.     

The effects of pH and ionic strength on the partitioning of four proteins in reverse micelle systems

Four proteins with different physicochemical properties have been partitioned in reversed micelle systems: thaumatin, ribonuclease A, soybean trypsin inhibitor, and alpha-lactalbumin. The organic phase was formed by sodium salt (AOT) in isooctane, and the aqueous phase contained KCl, KBr, MgCl(2), or NaCl. Aqueous phase pH was varied between 2 and 13 and ionic strength from 0.1 to 1.0 M. Small changes in pH [around the isoelecric point (pl)] were found to influence the solubilization of ribonuclease A and trypsin inhibitor, but for thaumatin the pH change necessary to affect partition was much greater as a consequence of the difference in net charge (titration curves) of these protein molecules as pH changes. The type of ions present in the system was also a determining factor for partition; the larger ions (K(+)) produced more electrostatic screening and hence less protein solubilization than the smaller ions (Na(+)). With changes in ionic strength surface hydrophobicity was a dominant factor affecting solubilization of thaumatin in NaCl-containing systems at high pH. Charge distribution and hydrophobicity are thought to be important parameters when partitioning the protein alpha-lactalbumin. (c) 1994 John Wiley & Sons, Inc.     

Transport of ammonium and nitrate in saturated porous media incorporating physiobiotransformations and bioclogging

The vertical transport of nitrates from fertilizer application and wastewater irrigation through the subsurface and saturated zone is of major concern to assess the vulnerability of groundwater contamination. The present study addresses the transport of nitrogenous fertilizers such as ammonium and nitrate in the presence of organic carbon (acetate) in a one-dimensional soil column under saturated conditions, considering the effect of adsorption and biotransformation. The soil had a neutral pH range and was classified as loamy sand, with a 0.89% organic carbon content. Batch studies revealed that sorption occurred in the order of ammonium > acetate > nitrate following a Freundlich isotherm model. Mixed heterotrophic native soil bacteria for aerobic nitrification and anoxic denitrification were developed, and the growth kinetic parameters were simulated using a Haldane inhibition model for nitrification and a Monod inhibition model for denitrification. Results from biotransformation studies suggested that denitrification was the predominant process, with significant bacterial growth and clogging of pores occurring monotonously reaching a stationary phase by 12 days. Pore-clogging phenomenon not only reduces the permeability of the soil by 5 orders of magnitude but also increases the contact time of the contaminant with the soil microbe and thereby delays the transport process and decreases the effluent ammonium and nitrate concentrations. A tailing breakthrough in a leaching study illustrates that water flux variation (0.153 and 0.509 cm/min) did not influence the transport of solutes, rather irreversible chemical bonding retains more ammonium than nitrate in the soil matrix.     

Characterization of ionic strength for X-MuLV inactivation by low pH treatment for monoclonal antibody purification

In the production of monoclonal antibodies (mAbs) intended for use in humans, it is a global regulatory requirement that the manufacturing process includes unit operations that are proven to inactivate or remove adventitious agents to ensure viral safety. Viral inactivation by low pH hold (LPH) is typically used to ensure this viral safety in the purification process of mAbs and other biotherapeutics derived from mammalian cell lines. To ascertain the effectiveness of the LPH step, viral clearance studies have evaluated LPH under worst-case conditions of pH above the manufacturing set point and hold duration at or below the manufacturing minimum. Highly acidic conditions (i.e., pH < 3.60) provide robust and effective enveloped virus inactivation but may lead to reduced product quality of the therapeutic protein. However, when viral inactivation is operated above pH 3.60 to ensure product stability, effective (>4 log₁₀ reduction factor) viral inactivation may not be observed under these worst-case pH conditions in viral clearance studies. A multivariate design of experiments was conducted to further characterize the operating space for low pH viral inactivation of a model retrovirus, xenotropic murine leukemia virus (X-MuLV). The statistically designed experiment evaluated the effect of mAb isotype, pH, temperature, acid titrant, sodium chloride (NaCl) concentration, virus spike timing, and post-spike filtration on X-MuLV inactivation. Data from the characterization study were used to generate predictive models to identify conditions that reliably achieve effective viral inactivation at pH ≥ 3.60. Results of the study demonstrated that NaCl concentration has the greatest effect on virus inactivation in the range studied, and pH has a large effect when the load material has no additional NaCl. Overall, robust and effective inactivation of X-MuLV at pH 3.65–3.80 can be achieved by manipulating either the pH or the NaCl concentration of the load material. This study contributes to the understanding of ionic strength as an influential parameter in low pH viral inactivation studies.     

Computation of pH evolution versus ionic products concentration in a fermentation broth

An algorithm developed for pH computation has been tested to calculate the theoretical pH changes in a culture medium during the course of a fermentation. A divergence between the computed pH value and the value measured with the electrode allows us to highlight the presence of undetected ionic products. The calculation with the algorithm by means of a computer requires only the knowledge of the ionic properties of the substrates and detected products and existing thermodynamic constants. (c) 1993 Wiley & Sons, Inc.     

Transport of bacteria in porous media: II. A model for convective Transport and growth

A model is presented for the coupled processes of bacterial growth and convective transport of bacteria has been modeled using a fractional flow approach. The various mechanisms of bacteria retention can be incorporated into the model through selection of an appropriate shape of the fractional flow curve. Permeability reduction due to pore plugging by bacteria was simulated using the effective medium theory. In porous media, the rates of transport and growth of bacteria, the generation of metabolic products, and the consumption of nutrients are strongly coupled processes. Consequently, the set of governing conservation equations form a set of coupled, nonlinear partial differential equations that were solved numerically. Reasonably good agreement between the model and experimental data has been obtained indicating that the physical processes incorporated in the model are adequate. The model has been used to predict the in situ transport and growth of bacteria, nutrient consumption, and metabolite production. It can be particularly useful in simulating laboratory experiments and in scaling microbial-enhanced oil recovery or bioremediation processes to the field. (c) 1994 John Wiley & Sons, Inc.     

Influence of ionic strength and pH on the interaction between high-affinity heparin and antithrombin

Binding constants for the binding of high-affinity heparin to antithrombin at different ionic strengths were determined by fluorescence titrations and were also estimated from dissociation curves of the heparin-antithrombin complex. These curves were monitored by near-ultraviolet circular dichroism or fluorescence. The dependence of the binding constant on the activity of NaCl suggested that maximally 5–6 charged groups are directly involved in the interaction between the two macromolecules. Major pH-dependent changes of the interaction, as evident by changes of the spectroscopic properties of the complex between the molecules, were found to occur below pH 5.5 and above pH 8.5. The acid change, which was irreversible, was most likely caused by an irreversible conformational change of antithrombin. At alkaline pH, however, the gross conformation of antithrombin was stable up to pH 12, while the affinity of high-affinity heparin for antithrombin began to decrease markedly at pH 8.5. The dissociation curve, which was reversible, had a midpoint around pH 9.5. This is compatible with the loss of affinity being caused by either a local conformational change, by ionization of tyrosine or by titration of one or more amino groups.     

Transport of bacteria in porous media: I. An experimental investigation

The convective transport of concentrated suspension of bacteria in porous media is of interest for several processes such as microbial enhanced oil recovery and in situ bioremediation. The parameters which affect the transport of the bacterium Bacillus licheniformis JF-2, a candidate microorganism for microbial enhanced oil recovery, were investigated experimentally in sandpacks. Bacteria retention and permeability reduction occurred primarily in the first few centimeters upon entering the porous medium. In downstream sections of the sandpack, the permeability reduction was low, even in cases in which high cell concentrations (10(8) cfu/mL) were detected in the effluent. The effect of (i) addition of a dispersant, (ii) linear velocity of injection, (iii) cell concentration, (iv) salinity (v) temperature, and (vi) the presence of a residual oleic phase were determined experimentally. A lower reduction in permeability and a higher effluent bacterial concentration were obtained in the presence of dispersant, high injection velocities, low salinities, and at a higher temperature. Macroscopic measurements at different linear velocities and in the presence or absence of dispersants suggest that the formation of reversible microaggregates and multiparticle hydrodynamic exclusion may be the primary mechanisms for bacterial retention and permeability reduction. (c) 1994 John Wiley & Sons, Inc.     

Models for relating pH measurements in water and calcium chloride for a wide range of pH,soil types and depths

Soil pH is commonly measured in water (pHw) or 0.01 M CaCl₂ (pH_Ca). The need to convert between these methods has led to the publication of linear, quadratic and cubic polynomial relationships for limited suites of soils. Concerns over the applicability of such relationships when mapping a wide range of soils and pH led to the establishment of a database of pH_W and pH_Ca values on each of 7894 samples from soil survey and field experimental sites in Queensland. The relationship between pH_W and pH_Ca across all soils was investigated and preliminary results examining the effect of soil depth and soil type on the relationship are presented.For all soils and depths, a linear regression accounted for 93.2% of the variation but did not predict pH_Ca well at very high or low pH_W values. The inclusion of second and third powers of pH_W accounted for significantly more of the variation (R²=0.94) in pH_Ca and the resultant curve matched the data better at high and low pH.Analysis of surface, sub-surface and subsoil groupings did not reveal any appreciable differences in the relationship between pH_W and pH_Ca attributable to depth. In contrast, differences in the relationship were evident between soil types. Generally, the mildly leached soils had linear relationships, while the weathered soils were distinctly curvilinear at low pH.     

The response of DNA length and twist to changes in ionic strength

We examine twist‐stretch coupling of unconstrained DNA using polyelectrolyte theory as applied to a line‐charge model along with published data on the ionic‐strength dependence of the twist angle. We conclude that twist‐stretch coupling is negative: environmental changes that stretch free DNA, unconstrained by externally applied pulling or twisting forces, are accompanied by unwinding of the double helix. We also analyze a helical model and conclude that the observed unwinding of the DNA helix when ionic strength is decreased is driven by radial swelling of the helix. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 223–226, 2015.     

Interaction of Artepillin C with model membranes: Effects of pH and ionic strength

Artepillin C is the major constituent of green propolis, one of the most consumed products in popular medicine owing to its therapeutic effects, including antitumor activity. Artepillin C differs from other cinnamic acid derivatives due to the presence of two prenylated groups in its structure, believed to enhance access to the cell membrane and resulting in pharmacological activity. The membrane outer leaflet of tumor cells is exposed to an acidic extracellular environment, which could modulate the protonation state of antitumor drugs and hence their interaction with the cell membrane. Herein, we investigated the interaction of Artepillin C with Langmuir monolayers and giant unilamellar vesicles (GUVs) of 1,2?dipalmitoyl?sn?glycerol?3?phosphocholine (DPPC) used as model membranes, in physiological and acidic environments. We observed that protonation of the carboxyl group of Artepillin C is essential for the interaction, with larger shifts induced in the surface pressure isotherms of DPPC monolayers in comparison with deprotonated Artepillin C. Also observed was a decrease in lipid packing inferred from the compressibility modulus and Brewster angle microscopy (BAM) images for monolayers on acidic subphases. Results with microscopy techniques on GUVs confirmed that.Artepillin C causes a curvature stress of the lipid bilayer only in its neutral state, causing the GUVs to burst. The stronger effects of neutral Artepillin C on both monolayers and GUVs were maintained when the ionic strength was increased. Taken together, the results indicate that Artepillin C may have preferential attachment to a more acidic environment which might be an important feature for its antitumor activity.     

黏土矿物对全氟辛酸在饱和多孔介质中运移行为的影响

本研究以蒙脱石(M)和高岭土(K)为代表性黏土矿物,探究了饱和条件下黏土矿物对全氟辛酸(PFOA)运移行为的影响。结果表明: 较低量的M或K添加增强了石英砂中PFOA的运移阻滞,较高量添加则减弱其阻滞。随黏土矿物添加量的增加(0～50%,重量比),添加M的PFOA阻滞系数由1.03±0.00增至1.31±0.03后降至0.72±0.06;添加K的PFOA阻滞系数增至1.30±0.02后降至0.49±0.11。示踪试验结果显示,较低量的M或K添加未形成优先流,而较高量的M或K添加产生了明显的优先流,该条件下PFOA阻滞减弱。此外,受M或K改性石英砂电负性强及柱试验固液比等限制,试验条件下M或K改性石英砂对PFOA吸附量较低,几乎未影响PFOA滞留,但黏土矿物对PFOA的吸附和脱附作用仍可能是较低量的M或K添加增强PFOA运移阻滞的原因。本研究结果对准确评估土壤-地下水系统中PFOA的迁移过程和生态环境风险具有重要意义。     

Cooperativity and effects of ionic strength on the binding of sodium n-dodecyl sulphate to lysozyme

The binding of sodium n-dodecyl sulphate to lysozyme has been measured by equilibrium dialysis at 25°C and pH 3.2 over a range of ionic strengts from 0.0119 to 0.2119. Binding isotherms in the region corresponding to ionic binding between the surfactant anions and cationic amino acid residues on the protein have been interpreted in terms of the Hill equation and exhibit positive cooperativity with Hill coefficients in the region of 7–11. The Gibbs energies of binding have been calculated from the Hill binding constants and from the Wyman binding potentials. The stability of the surfactant-protein complexes is discussed in relation to the stability of surfactant micelles. Ionic binding of the surfactant is weakened and hydrophobic binding strengthened by increasing ionic strength.     

Effect of annual variation in soil pH on available soil nutrients in pear orchards

Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH₄⁺) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH₄⁺ and NO₃^-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH₄⁺), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.     

Mechanoformation of neutral giant phospholipid vesicles in high ionic strength solution

We present new and simple method for formation of giant unilamellar vesicles (GUVs) in high ionic strength solutions, such as phosphate buffered saline (PBS). Mechanoformation method is an alternative method to electroformation method. The advantage of the mechanoformation procedure is that there are no limitations with respect to the ionic strength of the aqueous solutions, because there is no applied electric potential thus no current flow through the formation cell and no electrolysis is induced.     

Effect of annual variation in soil pH on available soil nutrients in pear orchards

Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH₄⁺) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH₄⁺ and NO₃^-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH₄⁺), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.     

The effect of pH and ionic strength on the pre-steady-state reaction of cytochrome c and cytochrome aa3

(1) In the pH range between 5.0 and 8.0, the rate constants for the reaction of ferrocytochrome c with both the high- and low-affinity sites on cytochrome aa₃ increase by a factor of approx. 2 per pH unit. (2) The pre-steady-state reaction between ferrocytochrome c and cytochrome aa₃ did not cause a change in the pH of an unbuffered medium. Furthermore, it was found that this reaction and the steady-state reaction are equally fast in H₂O and ²H₂O. From these results it was concluded that no protons are directly involved in a rate-determining reaction step. (3) Arrhenius plots show that the reaction between ferrocytochrome c and cytochrome aa₃ requires a higher enthalpy of activation at temperatures below 20°C (15–16 kcal/mol) as compared to that at higher temperature (9 kcal/mol). We found no effect of ionic strength on the activation enthalpy of the pre-steady-state reaction, nor on that of the steady-state reaction. This suggests that ionic strength does not change the character of these reactions, but merely affects the electrostatic interaction between both cytochromes.     

Influence of root-induced pH on the solubility of soil aluminium in the rhizosphere

Increase in solubility of soil aluminium (Al) as a result of root-induced decrease of soil pH was studied. Soil samples of known distances from the roots of NH₄-N fertilized Ryegrass were analyzed for pH and aluminium extractable with 0.01 M CaCl₂. Results showed that though no Al was found in bulk soil (pH 6.8), its concentration in the vicinity of roots increased to 0.023 mM with a concomitant decrease of soil pH from 6.8 to 4.4.