Solution pH Conditions Research Articles

EFFECT OF SOLUTION pH CONDITIONS ON FLUORESCENCE OF SPRAY DEPOSITION TRACERS

Stable analysis of fluorescence is essential to ensure accurate evaluation of pesticide spray application efficiencywhen fluorescent tracers are used to quantify deposition and drift. The fluorescent intensity of five fluorescent tracerscommonly used for the quantitative assessment of spray deposition and off-target loss was investigated with wash solutionsover pH conditions from 6.86 to 10.4. The tracers selected in the tests were Acid Yellow 7, Eosin, Fluorescein, Pyranine, andTinopal. The fluorescence of Pyranine was the most sensitive to the solution pH conditions, followed by Fluorescein andTinopal. Acid Yellow 7 and Eosin had a nearly constant fluorescent intensity over the pH range from 6.86 to 10.40. Thefluorescent strength of Fluorescein increased 1.3 times, Tinopal 1.25 times, and Pyranine 3.0 times as the pH value increasedfrom 6.86 to 8.43, but it became nearly constant when pH value was greater than 8.43. However, Pyranine, Fluorescein, andTinopal showed much stronger fluorescence than Acid Yellow 7 and Eosin with the same concentrations. A solution containingFluorescein at pH 8.43 and higher demonstrated 124 times greater fluorescent intensity than the solution containing the sameamount of Acid Yellow 7. The fluorescent strength should be examined not only with purified distilled water but also undervarious wash solution pH conditions during the selection of tracers for pesticide spray deposition and drift trials.

The Solvent Extraction of Boron with Synthesized Aliphatic 1,3‐Diols: Stripping and Extraction Behavior of Boron by 2,2,5‐Trimethyl‐1,3‐hexanediol

A variety of aliphatic 1,3‐diols (4a–c, 5a–c, 6a–c) was synthesized from β‐hydroxy carbonyl compounds (1–3) for potential use in the solvent extraction of boron. Primary‐secondary and primary‐tertiary alcohol structures of 1,3‐diols substituted with isopropyl, isobutyl, and isopentyl groups have been demonstrated to be very efficient for the solvent extraction of boric acid from aqueous solutions. The extraction ability of 2,2,5‐trimethyl‐1,3‐hexanediol (5b) was investigated as a function of 5b concentration, solution pH, solvent properties, and stripping conditions. Extraction efficiency increased with increasing concentration of 5b, and the best extraction of boron (96.8%) was found to be at an equilibrium pH of 2 with 0.5 M of 5b. Chloroform, toluene, chlorobenzene, 2‐octanol, and n‐amyl alcohol were found to be suitable solvents for the solvent extraction of boron. The boron complex can be recovered from the organic phase by treatment with an aqueous solution of sodium hydroxide. The highest ratio (96.7%) of boron was recovered by 0.1 M of sodium hydroxide solution.

Effects of pH and phosphate on the adsorptive fractionation of purified Aldrich humic acid on kaolinite and hematite.

The molecular weight (MW) fractionation of purified Aldrich humic acid (PAHA) resulting from adsorption on kaolinite and hematite was investigated for different solution pH and phosphate conditions. Adsorption was highly pH-dependent, with higher uptake at lower pH values. For all pH conditions, the weight-average MW (MWw) of residual PAHA remaining in solution after adsorption deviated from the original MWw, indicating that preferential adsorption of certain MW components occurred. The extent of preferential adsorption depended on the percent carbon adsorption at a given pH condition. For similar percent carbon adsorption ranges, a greater extent of preferential adsorption of the higher MW PAHA components was observed with higher pH values as demonstrated by the lowest residual MWw value occurring at pH 9. Detailed analyses of selected residual PAHA samples clearly showed that adsorption selectivity for particular MW components was strongly influenced by solution pH. The extent of preferential adsorption of lower MW PAHA components decreased in the presence of a small amount of phosphate. This effect was more evident for hematite than kaolinite, and became greater with lower solution pH irrespective of the mineral type. The different fractionation patterns observed for PAHA were reasonably well explained by the physicochemical trends occurring in its MWw fractions and the underlying sorption processes.

Effects of pH and phosphate on the adsorptive fractionation of purified Aldrich humic acid on kaolinite and hematite

The molecular weight (MW) fractionation of purified Aldrich humic acid (PAHA) resulting from adsorption on kaolinite and hematite was investigated for different solution pH and phosphate conditions. Adsorption was highly pH-dependent, with higher uptake at lower pH values. For all pH conditions, the weight-average MW (MW w ) of residual PAHA remaining in solution after adsorption deviated from the original MW w , indicating that preferential adsorption of certain MW components occurred. The extent of preferential adsorption depended on the percent carbon adsorption at a given pH condition. For similar percent carbon adsorption ranges, a greater extent of preferential adsorption of the higher MW PAHA components was observed with higher pH values as demonstrated by the lowest residual MW w value occurring at pH 9. Detailed analyses of selected residual PAHA samples clearly showed that adsorption selectivity for particular MW components was strongly influenced by solution pH. The extent of preferential adsorption of lower MW PAHA components decreased in the presence of a small amount of phosphate. This effect was more evident for hematite than kaolinite, and became greater with lower solution pH irrespective of the mineral type. The different fractionation patterns observed for PAHA were reasonably well explained by the physicochemical trends occurring in its MW w fractions and the underlying sorption processes.

Modeling tetracycline antibiotic sorption to clays.

Sorption interactions of three high-use tetracycline antibiotics (oxytetracycline, chlortetracycline, tetracycline) with montmorillonite and kaolinite clays were investigated undervaried pH and ionic strength conditions. Sorption edges were best described with a model that included cation exchange plus surface complexation of zwitterion forms of these compounds. Zwitterion sorption was accompanied by proton uptake, was more favorable on acidic clay, and was relatively insensitive to ionic strength effects. Calcium salts promoted oxytetracycline sorption at alkaline pHs likely by a surface-bridging mechanism. Substituent effects among the compounds in the tetracycline class had only minor effects on sorption edges and isotherms under the same solution pH and ionic strength conditions. At low ionic strength, greater sorption to montmorillonite than kaolinite was observed at all pHs tested, even after normalizing for cation exchange capacity. These results indicate that soil and sediment sorption models for tetracyclines, and other pharmaceuticals with similar chemistry, must account for solution speciation and the presence of other competitor ions in soil or sediment pore waters.

EF Loop Conformational Change Triggers Ligand Binding in β-Lactoglobulins

Beta-lactoglobulins, belonging to the lipocalin family, are a widely studied group of proteins, characterized by the ability to solubilize and transport hydrophobic ligands, especially fatty acids. Despite many reports, the mechanism of ligand binding and the functional role of these proteins is still unclear, and many contradicting concepts are often encountered in the literature. In the present paper the comparative analysis of the binding properties of beta-lactoglobulins has been performed using sequence-derived information, structure-based electrostatic calculations, docking simulations, and NMR experiments. Our results reveal for the first time the mechanism of beta-lactoglobulin ligand binding, which is completely determined by the opening-closing of EF loop, triggered by Glu89 protonation. The alkaline shift observed for Glu89 pKa in porcine beta-lactoglobulin (pKa 9.7) with respect to the bovine species (pKa 5.5) depends upon the interplay of electrostatic effects of few nearby key residues. Porcine protein is therefore able to bind fatty acids provided that the appropriate pH solution conditions are met (pH > 8.6), where the EF loop conformational change can take place. The unusually high pH of binding detected for porcine beta-lactoglobulin seems to be functional to lipases activity. Theoretical pKa calculations extended to representative beta-lactoglobulins allowed the identification of key residues involved in structurally and functionally important electrostatic interactions. The results presented here provide a strong indication that the described conformational change is a common feature of all beta-lactoglobulins.

A study on the cadmium removal from aqueous solutions by zinc cementation

The cementation of cadmium ions from aqueous solutions on zinc powder was studied as a function of solution pH and temperature, amount of zinc, concentration of cadmium ion, contact time, and the addition of several organic compounds, including surfactant and chelating agent. Cementation of cadmium was shown to be a feasible treatment process to achieve a high degree of cadmium removal within a fairly reasonable contact time. The deposition of cadmium and zinc consumption are highly dependent on solution pH conditions and is most practically operated at weak acidic conditions of pH 4–5. The reaction rate is approximately first order with respect to both the amount of zinc and the concentration of cadmium ion. Among the surfactants used in this study, only the presence of sodium dodecyl sulfonate, an anionic surfactant, noticeably enhanced the cementation rate of cadmium by zinc powder. The presence of ethylene-diaminetetraacetic acid (EDTA) in aqueous solutions inhibited the removal of cadmium by zinc due to the possible formation of Cd–EDTA chelates, which possess higher redox potential than that of free cadmium ions.

Transport of Cr(VI) in Soils Contaminated with Chromite Ore Processing Residue (COPR)

Chromium leaching experiments were conducted using soils rich in chromite ore processing residue (COPR). Experiments were performed with acrylic columns under a constant hydraulic head and a free board. Air was purged continuously through the influent solution (simulated rainwater) in order to create an oxidative condition in soils. It was found that the mass of Cr(VI) leached was strongly dependent on temperature. The leaching process accelerated above 8°C. Under the conditions of an influent solution pH of 4.3, air atmosphere, and temperatures ranging from 3 to 38°C, the total mass of Cr(VI) leached was in the range of 0.206 to 0.260 mg/g, which accounted for about 1% of the total Cr (25.5 mg/g) in the soil sample. A one-dimensional transport model was used to simulate the leaching of Cr(VI) from soils. Model simulation results revealed that the leaching process was governed by adsorption/desorption and was attenuated by redox reactions.

Comparison of Adsorption Capacity of p-Cresol & p-Nitrophenol by Activated Carbon in Single and Double Solute

Adsorption of p-Cresol and p-Nitrophenol by untreated activated carbon in single and multisolute solutions was carried out at 301 K and at controlled pH conditions. In acidic conditions, well below the pKa of both solutes, it was observed that the adsorbate solubility and the electron density of aromatic rings influenced the extent of adsorption by affecting the extent of London dispersion forces. The fitted parameters obtained from single-solute Langmuir equation show that Qmax and the adsorption affinity of carbon for the compound with low pKa decrease more significantly. In higher solution pH conditions, on the other hand, it was found that electrostatic forces played a significant role on the extent of adsorption. The presence of another compound decreases Qmax and the adsorption affinity of carbon for the principal compound. The effect of pH, on the carbon surface and on the solute molecules, must be considered. Adsorption of the solute at higher pH values was found to be dependent on the concentration of anionic form of the solute. The isotherm data were fitted to the Langmuir isotherm equation for both single and double solute solutions.

Surface Forces between Adsorbed Quaternarized Poly(2-vinylpyridine) Layers: Molecular Rearrangements and Bridging Interactions

The surface forces between quaternarized poly(2-vinylpyridine) (QP2VP) layers adsorbed onto mica have been measured over a range of solution pH conditions. It was found that QP2VP overcompensates the mica's negative charge, resulting in a positively charged interface. The surface potential at the mica/polyelectrolyte interface is a balance of the charge on the adsorbed polyelectrolyte and the charge on the underlying mica surface. It was also found that, below and near the pKa of the polyelectrolyte, segment−segment repulsion results in the polyelectrolyte adopting a conformation with significant extension into solution. Interpenetration of the extended chains leads to a bridging attraction. At high pH a decrease in the polyelectrolyte charge density decreases segment−segment repulsion, resulting in a compact adsorbed conformation where no bridging attractive jump is observed. An adhesion is measured between adjacent layers under all pH conditions, regardless of the presence of an attractive jump in. Here the important distinction is made between an attractive force caused by the overlap of anchored polyelectrolyte chains extending into solution and chain entanglement that occurs due to molecular rearrangements when polyelectrolyte layers are under compression.

Molecular dynamics simulations of human alpha-lactalbumin: changes to the structural and dynamical properties of the protein at low pH.

Two 700-ps molecular dynamics simulations of human alpha-lactalbumin have been compared. Both were initiated from an X-ray structure determined at pH 6.5. One simulation was designed to represent native conditions and the other the protein in solution at pH 2.0 without a bound calcium ion. The low pH conditions were modelled by protonating the aspartate, glutamate, and histidine side chains and the protein C-terminus. Significant changes were observed for the C-terminal region of the sequence in the simulation at low pH. Most notably an alpha-helix, helix D, and the C-terminal 3(10) helix were substantially disrupted relative to the simulation at high pH. These perturbations to the native fold are similar to those observed in an X-ray structure of alpha-lactalbumin at pH 4.2. In addition, larger fluctuations about side chain torsion angles were observed in the low pH simulation than in that corresponding to the higher pH. These structural and dynamical changes might be representative of the early stages of the transition to the molten-globule state of the protein known to be formed under low pH conditions in solution.

Experimental study on surface reactions of heavy metal ions with Quartz-Aqueous Ion concentration dependence

Adsorption of divalent metal ions, including Cu2+, Pb2+, Zn2+, Cd2+ and Ni2+, on quartz surface was measured as a function of metal ion concentration at 30°C under conditions of solution pH= 6. 5 and ion strength I = 0. 1mol/L. Results of the experimental measurements can be described very well by adsorption isotherm equations of Freudlich. The correlation coefficients (r) of adsorption isotherm lines are > 0. 96. Moreover, the experimental data were interpreted on the basis of surface complexation model. The experimental results showed that the monodentate-coordinated metal ion surface complex species (SOM+) are predominant over the bidentate-coordinated metal ion surface complex species [(SO)2M] formed only by the ions Cu2+, Zn2+ and Ni2+. And the relevant apparent surface complexation constants are lgKM = 2.2–3.3 in order of KCd≥KPb > KZn > KNi≥KCu, and lgβM = 5.9-6.8 in order of βNi > βZn > βCu. Therefore, the reactive ability of the ions onto mineral surface of quartz follows the order of Cd > Pb > Zn > Ni> Cu under the above-mentioned solution conditions. The apparent surface complexation constants, influenced by the surface potential, surface species and hydrolysis of metal ions, depend mainly on the Born solvation coefficient of the metal ions.

Theoretical Modeling and Experimental Verification of Electrochemical Equilibria in the Ba−Ti−C−H2O System

The thermodynamic principles controlling the electrochemical synthesis of barium titanate (BaTiO3) films are discussed and explored. a variety of Eh−pH diagrams were generated for the Ba−Ti−C−H2O system as a function of temperature and whether CO2 was in the system. Barium titanate is predicted to form at 25 °C and higher temperatures under alkaline conditions. It is demosnstrated that the phase field for BaTiO3 enlarges as a function of pH with increasing temperature in the absence of CO2. The role of CO2, although still important in controlling the phase stability of BaTiO3 via the formation of BaCO3, becomes less important under solution pH conditions greater than pH ∼13 and temperatures greater than 100 °C. The theoretical Eh−pH predictions compare favorably with experimentally determined regimes, where BaTiO3 and films in the Ba−Ti−C−H2O system form through electrochemical reactions.

Electrochemical study on copper cementation from cyanide liquors using zinc

A rotating-disc electrode system was used to study the half-cell reactions involved in the cementation of copper from cyanide liquors onto zinc. Using scanning voltammetry, the reduction of copper cyanide onto glassy carbon and copper discs and the oxidation of zinc from a zinc disc were evaluated at different conditions of solution pH, temperature and free cyanide concentration. Evans diagrams were constructed yielding mechanistic information and rate of the cementation process. Thermodynamic modelling of the copper cyanide system also predicts the electrochemical active species responsible for the reduction of copper cyanide as Cu(CN) 2 −. The study allows optimised conditions to be chosen for the selective recovery of gold from copper–gold cyanide mixture using zinc powder cementation.

Molar Masses and Radii of Humic Substances Measured by Light Scattering

A bulk aquatic natural organic material (NOM) was characterized by high-performance size exclusion chromatography (HPSEC) coupled with multi-angle laser light scattering (MALLS), UV-Vis, and refractive index detection. This technique was used to measure the molar mass and radius of the natural organic matter in solution. Results indicate that the NOM aggregates to a large extent at the concentrations used in this study (5...15 mg mL -1 ). The solution conditions of pH and ionic strength were also shown to affect the measured size of NOM. The number and type of HPSEC columns also influenced these measurements. The importance of using multiple detectors was illustrated by peaks that were not detected by all the detectors. While these data are preliminary and have large errors associated with them, it is nevertheless an indication that HPSEC-MALLS can be used to investigate the effects of solution conditions and aggregation on the size of humic substances in solution.

Structural mechanism of Co (super 2+) oxidation by the phyllomanganate buserite

Structural mechanism of Co (super 2+) oxidation by the phyllomanganate buserite

Matrix performance in matrix-assisted laser desorption/ionization for molecular weight determination in sialyl and non-sialyl oligosaccharide proteins.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry relies on the formation of intact molecular ions to determine molecular weight. In biochemical research, conventional methods of protein analysis at picomol to fentomol sensitivity, such as sodium dodecyl sulphate polyacrylamide gel electrophoresis, have been replaced by this new ionization method. Unfortunately, problems caused by the mass accuracy and low resolution restrict the use of this ionization technique, particularly when a high mass accuracy in a high mass range is required. In this paper it is shown that the appropriate choice of parameters which determine the desorption/ionization of glycoproteins can improve the quality of MALDI mass spectra as well as mass reproducibility and resolution. The study of sample-matrix solution composition, pH and instrumental conditions allow the molecular weight determination of highly glycosylated proteins with a high percentage of sialic acid, e.g. erythropoietin. The glycosylation of this molecule which interferes with the production of multiply charged ions in electrospray ionization does not affect the desorption/ionization in MALDI analysis. We report the best operating conditions used to establish the degree of heterogeneity of erythropoietin.

Reactions of boron with soils

Boron is an essential micronutrient for plants, but the range between deficient and toxic B concentration is smaller than for any other nutrient element. Plants respond directly to the activity of B in soil solution and only indirectly to B adsorbed on soil constituents. Soil factors affecting availability of B to plants are: pH, texture, moisture, temperature, organic matter and clay mineralogy. Boron adsorbing surfaces in soils are: aluminium and iron oxides, magnesium hydroxide, clay minerals, calcium carbonate, and organic matter. Boron adsorption reactions can be described empirically using the Langmuir adsorption isotherm equation, the Freundlich adsorption isotherm equation, and the phenomenological Keren model. Chemical models such as the constant capacitance model, the triple layer model, and the Stern VSC-VSP model can describe B adsorption over changing conditions of solution pH and B concentration. Boron desorption reactions often exhibit hysteresis. The rate of B desorption can be described using the first order rate equation, the Elovich reaction rate equation, and the power function equation.

An experimental and theoretical study of the adsorption of aromatics possessing electron-withdrawing and electron-donating functional groups by chemically modified activated carbons

The adsorption of model aromatic compounds (aniline and nitrobenzene) on chemically tailored activated carbons has been systematically investigated. Adsorption experiments at controlled solution pH conditions confirmed that both electrostatic and dispersive adsorbate/adsorbent interactions can have a significant influence on the equilibrium uptakes of ionic and nonionic adsorbate species. For aniline (a weak electrolyte), maximum uptakes were found on oxidized carbon surfaces at solution pH near the adsorbate's point of zero charge (pH PZC ). In contrast, nondissociating nitrobenzene uptakes were enhanced on heat-treated surfaces with graphene layers unperturbed by electron-withdrawing functional groups, particularly at solution pH ~ pH PZC . A theoretical model that can successfully account for the observed trends is hereby proposed as a much needed predictor of the experimental conditions and adsorbent surface chemical properties that will maximize the uptake of aromatic compounds by activated carbons.

Biological availability of aluminum in commercial ATP

Aluminum is a contaminant of commercial ATP. We have used the fluorescent chelation agent morin to define the conditions of solution pH and incubation period under which this contaminating aluminum was biologically available. The biological significance of our model ligand morin was tested in media in which the morin was replaced with the AβP(25–35) peptide. Aluminum-contaminated ATP was shown to promote the formation of Thioflavin T-reactive amyloid aggregates relative to equimolar concentrations of either aluminum added in the absence of ATP or aluminum-free ATP. Our demonstration of the biological availability of aluminum in commercial ATP should serve as a cautionary note to its use in biochemistry, and might also be interpreted to invoke ATP as an intracellular (intraneuronal) pool of biologically available aluminum in vivo.