High pH Region Research Articles

Novel saccharide-induced conformational changes in a boronic acid-appended poly(L-lysine) as detected by circular dichroism and fluorescence

Poly(L-lysine) has been modified with a 4-phenylboronic acid derivative which acts as a sugar-binding site and a dansyl group which acts as a fluorescence probing site. The helix content of this poly(L-lysine) derivative as estimated by CD spectroscopy became maximum at pH 10.3. The helix content was increased from 51 to 79% by complexation of D-fructose with the pendant boronic acid group and the maximum pH shifted from 10.3 to 7.9. Examination of the CD spectra revealed that the conformation changes in the order of β-sheet → α-helix → random coil with increasing medium pH. The D-glucose addition induced a similar increase in the helix content and a similar low pH shift of the helix content maximum but the mechanism was somewhat different: one D-glucose was bound to two boronic acid groups to form an intrapolymeric bridge and the resultant CD spectrum was similar to that of the β-turn structure. These saccharide-induced conformational changes were well reflected by plots of fluorescence intensity vs. pH. The decrease in the fluorescence intensity in the high pH region (random coil region) was confirmed by fluorescence polarization to be due to the increase in the molecular motion. This is a novel system to control the poly(amino acid) conformation by saccharides and to detect the conformational changes by convenient spectroscopic methods.

Acid–base and metal ion-binding properties of diaminopropyl D-glucopyranoside and diaminopropyl D-mannopyranoside compounds in aqueous solution

For three sugar-appended diamine compounds (1,3-diamino-2-propyl β-D-glucopyranoside (2-β-D-Glc-pn), (2S)-2,3-diaminopropyl β-D-glucopyranoside (1-β-D-Glc-pn) and 1,3-diamino-2-propyl α-D-mannopyranoside (2-α-D-Man-pn)), acidity constants and stability constants with Ni2+, Cu2+ and Zn2+ have been measured (I = 0.16 M NaCl, 25 °C). The two acidity constants of each of the three sugar-diamines differ by 101.65 to 103.09, indicating that removal of the proton from HL+ species is more difficult than deprotonation from the fully protonated dication H2L2+. Statistical and polar effects, as well as the formation of an intramolecular hydrogen bond, may cause this increased stability of the HL+ species. The strength of the hydrogen bond and the degree of its formation (percentage) were estimated. The sugar ring has only a small influence on the intramolecular hydrogen bond formation. For the different metal ion–ligand systems, the predominating species in solution are quite different. In the Cu2+–1-β-D-Glc-pn system, the dominant species are always CuL2+ and CuL22+ in the pH range 4 to 10, where the total ligand concentration is larger than total metal ion concentration. For Ni2+, NiL32+ is also important under these same conditions; however, for Zn2+, the hydrolysis species ZnL2(OH)+ and ZnL2(OH)2 predominate in the high pH region. All possible species in the system were included during the calculations, and the corresponding stability constants were determined. The hydrolysis of the metal ions themselves is important in some cases and all possible hydrolysis species were included in the fitting calculation. The stability constant plots log Kversus pK yielded straight reference lines for 1,3-diamine or 1,2-diamine ligands, reflecting the complete absence of sugar oxygen atoms in the metal ion coordination. The linkage between the metal ion and the diamine residue depends solely on the basicity of the ligand.

過酸化水素漂白におけるＰＨＡＳ（ポリ‐α‐ヒドロキシアクリル酸ソーダ）の特性

Hydrogen Peroxide will be remarked more and more as a clean bleaching agent because of global environmental issues. Although Hydrogen Peroxide is a stable substance thermally, it decomposes with traces of heavy metals. Therefore some stabilizer is required when bleaching, and Sodium Silicate has been used conventionally. It has, however, a problem in which hard scales are produced, and a non silicate stabilizer is desired. PHAS (Sodium poly-α-hydroxyacrylate) has unique characteristics. Introduced herewith are stabilizing characteristics of PHAS in alkaline Hydrogen Peroxide comparing with other general chelating agents. PHAS has excellent stabilizing abilities especially in higher pH region. Hydrogen Peroxide concentration and temperature condition.

Aggregation Behavior of Nonionic Clycolipid Vesicles in Acidic Region

Large unilamellar vesicles composed of a nonionic synthetic glycotipid, 1,3 - di- 0 - phylanyl -2-0-(β- maltotriosyl ) glycerol show pH-dependent aggregation - dissocialion process, that is, vesicle aggregation occurs in the lower pH region and vesicle dissociation occurs in the higher pH region. This process is almost reversible and the aggregation threshold pH is dependent on NaCl concentration. Fluorescence technique has been applied to study whether the vesicle fusion occurs or not during the aggregation-dissociation process. It is concluded pH can only induce the aggregation of this nonionic glycoltpid vesicle.

Coefficient d'activité de l'acide sulfurique déterminé par titrage infrarouge

The titration of sulphuric acid by infrared spectroscopy using the attenuated total reflection (ATR) technique was made in the 0 to 14 pH range for solutions ranging from 1.89 to 0.01 M. The subtraction of the water spectrum was made using acidic, neutral, and basic waters which exhibit different spectra. The results gave the spectra of mixtures of the HSO–4 and SO2–4 ionic species in solutions. For each concentration, factor analysis (FA) sorted the spectra of the pure ionic species and gave through the multiplying factors (MF) the distribution of the species as a function of pH. This distribution is the same as that obtained from the equilibrium equations. The IR measurements gave directly the ratios of the activity coefficients of HSO–4 and SO2–4 ions. This ratio varies with the total concentration of both ions but is independent of the relative concentration. The fitting of the experimental and theoretical volumetric titration curves in the high and low pH regions gave the mean activity coefficients of the other species present in the solutions. The values obtained are comparable to those obtained by electrochemical measurements. These results show that it is possible to use IR spectroscopy to study aqueous solutions of inorganic acids from low to high concentrations.Key words : IR spectroscopy, sulfuric acid, aqueous solutions, factor analysis, ATR, principal spectra, solvation, activity coefficients, IR titration.

Conformation of poly(methacrylic acid) in acidic aqueous solution studied by small angle X-ray scattering

The nature of the contracted form of poly(methacrylic acid) PMA chain in salt-free acidic aqueous solution was studied by analyzing scattering curves registered by small-angle X-ray scattering, comparing it with those of PMA in methanol at 26°C and of partially neutralized PMA in aqueous solution containing added salt (the concentration of added salt, Cs=0.1 M NaF). It is shown that the distribution of segments in the contracted form as well as that of PMA in methanol is that of a random-coil in a θ medium and that this distribution of segments is stable over a fair range of degrees of ionization α for Cs below 0.1 M. Moreover, the persistence length of PMA at Cs=0.1 M (4±0.5 Å) is substantially constant throughout the entire range of α, indicating that the contracted form of PMA changes to an expanded random-coil in a higher pH region without a significant change in the chain flexibility.

Electrokinetic remediation of heavy metal-contaminated soils under reducing environments

This paper describes the migration of hexavalent chromium, Cr(VI), nickel, Ni(II), and cadmium, Cd(II), in clayey soils that contain different reducing agents under an induced electric potential. Bench-scale electrokinetic experiments were conducted using two different clays, kaolin and glacial till, both with and without a reducing agent. The reducing agent used was either humic acid, ferrous iron, or sulfide, in a concentration of 1000 mg/kg. These soils were then spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1000, 500 and 250 mg/kg, respectively, and tested under an induced electric potential of 1 VDC/cm for a duration of over 200 h. The reduction of chromium from Cr(VI) to Cr(III) occurred prior to electrokinetic treatment. The extent of this Cr(VI) reduction was found to be dependent on the type and amount of reducing agents present in the soil. The maximum reduction occurred in the presence of sulfides, while the minimum reduction occurred in the presence of humic acid. The concentration profiles in both soils following electrokinetic treatment showed that Cr(VI) migration was retarded significantly in the presence of sulfides due both to the reduction of Cr(VI) to Cr(III) as well as an increase in soil pH. This low migration of chromium is attributed to: (1) migration of Cr(VI) and the reduced Cr(III) fraction in opposite directions, (2) low Cr(III) migration due to adsorption and precipitation in high pH regions near the cathode in kaolin and throughout the glacial till, and (3) low Cr(VI) migration due to adsorption in low pH regions near the anode in both soils. Ni(II) and Cd(II) migrated towards the cathode in kaolin; however, the migration was significantly retarded in the presence of sulfides due to increased pH through most of the soil. Initial high pH conditions within the glacial till resulted in Ni(II) and Cd(II) precipitation, so the effects of reducing agenets were inconsequential. Overall, this study demonstrated that the reducing agents, particularly sulfides, in soils may affect redox chemistry and soil pH, ultimately affecting the electrokinetic remediation process.

Potential‐pH Diagram of the Cd ‐ Te ‐ NH 3 ‐ H 2 O System and Electrodeposition Behavior of CdTe from Ammoniacal Alkaline Baths

A potential‐pH diagram of the system was constructed based on diagrams of the and systems and discussed in connection with the redox behavior of an ammonia‐alkaline CdTe electrolytic bath with pH 10.7. CdTe has a wide domain of stability throughout the acidic and alkaline regions, and the redox behavior was well explained with the diagram. The diagram indicated that the cathodic electrodeposition of CdTe occurs across a domain of stability of tellurium metal, i.e., at lower potentials than the deposition potential of bulk Te and higher than that of bulk Cd, with respect to the bath with pH < ca. 11.5, while in the higher pH region, CdTe is expected to deposit directly from Te(IV) and Cd(II) ions. The deposition mechanism is considered as follows: (i) deposition of tellurium layer followed by (ii) an immediate underpotential deposition of Cd on it, which prevents the bulk deposition of tellurium. It can be considered that the stoichiometric CdTe is more easily electrodeposited from alkaline baths, since the domain for tellurium metal is narrower in the alkaline region compared to the conventionally employed acidic region with pH 0–2. Therefore, the bulk deposition of elemental tellurium is less apt to occur from an alkaline bath. © 1999 The Electrochemical Society. All rights reserved.

Coagulation of Quartz Particles in Aqueous Solutions of Copper(II)

The colloidal stability of quartz suspension was determined over a wide range of pH in aqueous copper nitrate where the state of Cu(II) is changed from mainly aqua ions and monohydroxyl complexes in the acid and neutral pH to polynuclear hydroxo complexes and colloidal precipitated copper hydroxide at higher pH. Two regions of instability were observed and in both cases the particles were shown to have low electrophoretic mobility. In the neutral pH region, the uptake of Cu(II) was sufficient to reduce the mobility of the particles to zero, while in the high-pH region evidence suggested coagulation between precipitated Cu(OH)2and the quartz particles. It was shown that in all cases the coagulation was reversible and that the uptake of Cu(II) was dependent on the uncharged surface hydroxyl density. Studies of the coagulation kinetics showed that extended time scales were involved (several minutes in the neutral pH region to tens of minutes at high pH).

In-situ remediation of nitrate-contaminated ground water by electrokinetics/iron wall processes

The feasibility of using electrokinetics coupled with a zero valent iron (Fe0) treatment wall to abiotically remediate nitrate-contaminated soils was investigated. Upon completion of each test run, the contaminated soil specimen was sliced into five parts and analyzed for nitrate-nitrogen, ammonia-nitrogen and nitrite-nitrogen. Nitrogen mass balance was used to determine the major transformation products. In control experiments where only electrokinetics was used at various constant voltages, 25 to 37% of the nitrate-nitrogen was transformed. The amount of nitrate-nitrogen transformed improved when a Fe0 wall (20 g or about 8-10% by weight) was placed near the anode. For test runs at various constant voltages, the amount of nitrate-nitrogen transformed ranged from 54 to 87%. By switching to constant currents, the amount of nitrate-nitrogen - transformed was about 84 to 88%. The major transformation products were ammonia-nitrogen and nitrogen gases. Nitrite-nitrogen was less than 1% in all experimental runs. Two localized pH conditions exist in the system, a low pH region near the anode and a high pH region near the cathode. Placing of an iron wall near the anode increases the pH in that area as time increases. Movement of the acid front did not flush across the cathode. This research has demonstrated that the electrokinetics/iron wall process can be used to remediate nitrate-contaminated groundwater.

Signal-responsive gating by a polyelectrolyte pelage on a nanoporous membrane

Poly(L-glutamic acid) (PLGA) carrying a terminal disulfide group at one end of the chain was self-assembled on a porous membrane. The rate of water permeation through the surface-modified porous membrane depended on pH. In the region of low pH, the PLGA chain is protonated and folded to form an -helix; in the region of high pH, it is de-protonated to have extended random coil structure. The ionic strength also regulated the rate of water permeation. Increasing ionic strength reduced the pH dependence of permeation due to a shielding effect. The permeation through the porous membrane, the surface of which was covered with the self-assembled polypeptide pelage, was sensitively regulated by changing the pH because of direct contact of pelage chains with the environment.

Catalytic wet air oxidation of ammonia over alumina supported metals

Wet air oxidation (WAO) of ammonia to dinitrogen has been investigated using various heterogeneous catalysts. Among them RuO 2/Al 2O 3 exhibited remarkable activities that at least 99% of ammonia (1500 ppm) was decomposed at 503 K under 1.5 MPa in a NaOH added water (pH of 12). The product was dinitrogen exclusively, and the quantities of NO − 3 formed were very small. The reaction proceeded rapidly in the high pH region indicating that ammonia was more reactive than ammonium ion. The activity and selectivity were found to have a relation with the oxygen affinity of the metal element. It was discussed that elements (Ru, Pd) with medium weakness of M–O bond showed the high activity and selectivity and the reason was proposed.

Adsorption of Organic Acids on Polyaminated Highly Porous Chitosan: Equilibria

The adsorption of organic acids on a new weakly basic ion exchanger, highly porous polyaminated chitosan (Chitopearl CCS), which has the primary amino group of chitosan and the primary, secondary, and tertiary amino groups of poly(ethylene imine), appeared feasible technically. Three different organic acids, acetic acid (R‘-COOH), malic acid (R‘‘-(COOH)2) and citric acid (R‘‘‘-(COOH)3) were used in this experimental study. These organic acids were adsorbed on the resin by an acid/base neutralization reaction. The adsorption isotherms were independent of the initial concentrations of organic acids. The theoretical equations for the adsorption isotherms were derived by considering the dissociation of organic acids in the solution and the adsorption on each functional group and by applying the mass action law. They correlated the experimental adsorption isotherms and titration curves well. Chitopearl CCS was observed to be a feasible medium for the adsorption of organic acids. Especially in high pH region (low concentration region), Chitopearl CCS could adsorb more organic acids than a commercial ion exchanger, DIAION WA30.

In-situ remediation of nitrate-contaminated ground water by electrokinetics/iron wall processes

The feasibility of using electrokinetics coupled with a zero valent iron (Fe0) treatment wall to abiotically remediate nitrate-contaminated soils was investigated. Upon completion of each test run, the contaminated soil specimen was sliced into five parts and analyzed for nitrate-nitrogen, ammonia-nitrogen and nitrite-nitrogen. Nitrogen mass balance was used to determine the major transformation products. In control experiments where only electrokinetics was used at various constant voltages, 25 to 37% of the nitrate-nitrogen was transformed. The amount of nitrate-nitrogen transformed improved when a Fe0 wall (20 g or about 8–10% by weight) was placed near the anode. For test runs at various constant voltages, the amount of nitrate-nitrogen transformed ranged from 54 to 87%. By switching to constant currents, the amount of nitrate-nitrogen — transformed was about 84 to 88%. The major transformation products were ammonia-nitrogen and nitrogen gases. Nitrite-nitrogen was less than 1% in all experimental runs. Two localized pH conditions exist in the system, a low pH region near the anode and a high pH region near the cathode. Placing of an iron wall near the anode increases the pH in that area as time increases. Movement of the acid front did not flush across the cathode. This research has demonstrated that the electrokinetics/iron wall process can be used to remediate nitrate-contaminated groundwater.

Practical study of liquid-liquid extraction process for separation of rare earth elements with bis(2-ethylhexyl) phosphinic acid.

A separation process for rare earth elements (Pr/Nd and Y/Er) by liquid-liquid extraction with bis(2-ethylhexyl) phosphinic acid is investigated. Extraction equilibrium formulations for these elements are established and extraction constants are determined employing kerosene and toluene as diluents, in which MR3(RH)3 is formed at low loading, and then the larger aggregated species, (MR3)2(RH)4, appears with increasing loading ratio. The proposed formulations and constants successfully express the extraction behaviors over the whole range of loading ratio up to 0.4 in single element systems. These are valid for binary element systems of Pr/Nd and Y/Er and also for the distribution behaviors in scrubbing treatment. The separation is enhanced at high pH region, that is, at high loadings. Scrubbing is also effective for separation. Simulation of Pr/Nd separation by continuous counter-current mixer-settler cascades shows that separation is enhanced by employing appropriate pH control and scrubbing treatment.

Application of Tumbling Melt Granulation (TMG) Method for Controlled Enteric-Release Beads by Coating Mixture of Hydrogenated Castor Oil and Higher Fatty Acid.

Controlled-release beads which can release drugs faster in the higher pH regions (pH 5-7.5) than in the acidic region (pH 1-5) were prepared using the newly developed tumbling melt granulation (TMG) method, in which process a powdered meltable material was coated onto the core beads without use of any organic solvent. This function could be obtained by using a mixture of hydrogenated castor oil (HCO) and higher fatty acids as coating materials. Controlled-release beads containing various kinds of drugs were prepared. Use of stearic acid as a fatty acid resulted in excellent coating producibilities when the mixing ratio of stearic acid (XFA) was less than 30%. The dissolution rates determined in purified water, 1st fluid, and 2nd fluid tended to increase with the increase of XFA. This tendency was especially remarkable in the 2nd fluid. The effect of the carbon number (12-22) of the fatty acid was then determined. The permeability coefficient, P, calculated from the dissolution rate, decreased with the increase of carbon number. This seemed to be due to the difference of the release rate of fatty acid from the coating layer composed of HCO and fatty acid. Determination of the dependency of P value on the pH of the dissolution medium showed that the P values changed little in the acidic region (pH 1.2 to 5.0), but increased exponentially with an increase of pH over pH 5.5. Logarithm of relative P values (PpH/Pw : Pw means the P values in purified water) plotted against pH were distributed on the same line irrespective of fatty acid. An empirical equation which predicts the dissolution rates in the enteric medium was proposed using this relationship.

PH and Temperature Dependence of Tyrosine Z Decay Kinetics in Tris-Treated PSII Particles Studied by Time-Resolved EPR

The decay kinetics of tyrosine Z¨ (Y¨z) in Tris-treated Photosystem II particles were measured by time-resolved EPR at different pH values (pH 5.5 to 7.5) between 230 and 297 K. Y¨z induced by laser flashes decayed in a biphasic wav; t½ values were about 100 ms in the fast phase and about 1 s in the slow one, respectively, at room temperature. The fast phase was attributed to a recombination of charges on Y¨z and Q−A. The activation energies for the reaction of Y¨z with Q−A between 245 and 297 K have been estimated to be more than 38 kJ mol−1 at pH (>6.5) and less than 32 kJ mol−1 at pH (<6.0), respectively. The activation energy gap between high pH (>6.5) and low pH (<6.0) ranges was found to be ΔE=4.4 kJ mol−1. Judging from the fact that pH 6.2 appears to be the border between the high and low pH regions, we suggest that the kinetics of Y¨z is strongly influenced by the dissociation of the nearby histidine residue.

Selective Adsorption of Metal Ions on Novel Chitosan-Supported Sulfonic Acid Resin.

A novel chitosan-supported sulfonic acid resin modified by propane sultone was prepared and the adsorption characteristics of metal ions are examined by using a crosslinked chitosan-supported sulfonic acid resin (PSC) and a crosslinked chitosan resin (CLC).In the low acidity region, the metal selectivity of PSC is similar to that of CLC. This suggested that the selectivity of PSC was attributed not to the sulfonate group but to the chitosan matrix. The role of the sulfonate is believed to be enriching the metal concentration in the neighborhood of the chitosan matrix. At the same time, since the hydrogen ion is also enriched in a thin layer near the surface of the main, the characteristic adsorption curves of PSC shift to the high pH region compared with those of CLC. The adsorption equilibrium constants of metal ion on PSC and CLC are evaluated. The maximum adsorption capacity for PSC in the case of adsorption of copper is 1.6 times that of CLC. On the other hand, in the high acidity region, the maximum adsorption capacity for PSC in the case of adsorption of palladium is lower than that for CLC because of steric hindrance.

Mechanisms of Nickel Sorption on Pyrophyllite: Macroscopic and Microscopic Approaches

AbstractRetention of heavy metal ions on soil mineral surfaces is a crucial process for maintaining environmental quality. A thorough understanding of the sorption mechanisms of heavy metals on soil mineral surfaces is therefore of fundamental importance. This study examined Ni(II) sorption mechanisms on pyrophyllite. The removal of Ni from solution was studied as a function of pH (pH = 5–8.5), initial Ni concentration (1 × 10−4 to 1 × 10−2 M), and ionic strength (0.01–1 M). The data suggest that Ni sorption behavior can be divided into two distinct pH regions. In the lower pH region (i.e., pH &lt;7), relative Ni sorption increased with decreasing ionic strength and initial Ni concentration. The adsorption maximum at pH = 6 was significantly higher than the cation‐exchange capacity (CEC) at the same pH. Based on these findings, we propose that both specific and nonspecific adsorption are involved. In the higher pH region (pH &gt;7), nickel sorption becomes slow and does not seem to be affected by the ionic strength and the initial Ni concentration. We employed high‐resolution transmission electron microscopy (HRTEM) to ascertain whether any alteration in the surface structure of pyrophyllite could be detected after reaction with Ni at pH &gt;7. Surface deposits, not present on untreated samples, were found. At low Ni sorption densities, surface precipitation seems to occur preferentially along the edges of the particles. Based on the HRTEM findings, and on results from a previous x‐ray absorption fine structure spectroscopy (XAFS) study, we hypothesize that the formation of a mixed Ni‐Al hydroxide phase on the pyrophyllite surface is responsible for the sorption behavior above pH 7.

キレート化フェライトメッキ法によるＭｎＺｎフェライト膜の作製

Polycrystalline films of MnxZnyFe3-x-yO4 with a spine1 structure were synthesized from a highly alkaline (pH=13) aqueous solution containing FeC13, MnC12, ZnC12, and KNaC4H4O6(R ochelle salt). The metal ions, Fe3+,M n2+,and Zn2+, were chelated with Rochelle salt, which prevented them from being precipitated in the high pH region. The solubility limit, x, of the Mn ions was much higher (reaching up to 1.5) than that (x≤∼0.12) obtained in conventional ferrite plating by using a neutral (pH∼7) aqueous solution.On the other hand, the solubility of the Zn ions was lower than that obtained by using a neutral aqueous solution.