pH Dependence Data Research Articles

Ferrate(VI) in wastewater treatment contaminated with metal(II)-iminodiacetic acid complexed species

The aim of this investigation is to assess the suitability and applicability of ferrate(VI) in the treatment of wastewaters contaminated with the Cu(II)-IDA and Zn(II)-IDA (IDA: iminodiacetic acid) complexed species in an attempt to provide safe and environmentally benign treatment process. The study was conducted for the degradation of metal(II)-IDA, followed by the oxidation of IDA and simultaneous removal of metal(II) species by the coagulation/flocculation process obtained by the reduced Fe(VI) into Fe(III). The high purity of ferrate(VI) was synthesized by the wet oxidation process in the laboratory and a regulated dose was imparted to the water contained with metal(II)-IDA species in solution. The batch reactor operations were performed for various parametric studies viz., effect of solution pH and metal(II)-IDA concentration for a fixed dose of ferrate(VI). The pH dependence data obtained from varying pH from 8.0 to 12.0 showed that higher efficiency of degradation of Fe(VI) was occurred at lower pH value i.e., at pH 8.0. Similarly, the total organic carbon (TOC) values showed in accordance to the UV–Vis data that the lower pH values (i.e., pH at 8.0) favored an enhanced degradation/mineralization of IDA since low TOC values were obtained at low pH values. The simultaneous removal of Cu(II) and Zn(II) was obtained through the process showed that insignificant percent of metal (Cu(II) or Zn(II)) was removed by the process which was significantly enhanced at pH 12.0. The UV–Vis data recorded at different time intervals for the reduction of Fe(VI) at varied metal(II)-IDA concentrations was utilized to demonstrate the kinetics of degradation. Further, this was employed in obtaining the overall rate constant of the degradation. These kinetic data revealed that an efficient degradation of IDA was achieved using the Fe(VI) treatment.

Novel hybrid materials in the remediation of ground waters contaminated with As(III) and As(V)

Natural mica type of clay mineral sericite was modified to obtain the materials viz., Al-HDTMA-sericite (AH) and Al-AMBA-sericite (AA) which was characterized by the FT-IR and XRD data and morphologically analyzed by the SEM images. Further, the simulated batch reactor data indicated that increase in sorptive concentration enhanced the uptake of these pollutants and the 1000 times increase in ionic strength i.e., background electrolyte concentration (NaNO3) caused an insignificant decrease in As(V) removal, which inferred that As(V) was adsorbed specifically onto the solid surface. However, it was affected greatly with As(III) pointed that As(III) was sorbed mainly through electrostatic or even with van der Waals attraction. pH dependence data showed that arsenic removal was greatly affected with change in solution pH. Simultaneous presence of phenol in the removal of As(III) or As(V) showed insignificant change in arsenic removal by these materials pointed that different sorption sites available for these two different contaminants. Results obtained under dynamic conditions inferred that materials were reasonably useful in the speciation/attenuation of these two metal ions from water bodies. The breakthrough data was fitted well to the Thomas equation and hence, the maximum amount of the As(III) or As(V) to be loaded was found to be 0.338 and 0.433mg/g respectively for AA and AH for As(III) and 0.541 and 0.852mg/g respectively for AA and AH for As(V) under the specified column reactor conditions. Comparing these two materials AH possessed with higher removal capacity than AA, at least, for these two contaminants.

Removal of Mn(II) from Aqueous Solutions Using Manganese-Coated Sand Samples

Two different manganese-coated samples, that is, manganese-coated sand (MCS1) (laboratory preparation) and a Birm sample (Birm, a commercial product; MCS2), were employed to assess their removal efficiencies for Mn(II) from aqueous solutions over a wide pH range (i.e., pH 5.0 to 10.5). The study was performed in both the absence and presence of sodium hypochlorite. The pH dependence data obtained through batch tests showed that the removal of Mn(II) by these solids significantly increased with increasing solution pH from 5.0 to 10.0. Moreover, the removal efficiency was more favored in the presence of sodium hypochlorite (4.0 mg·L−1). This suggested that the presence of NaClO caused the oxidation of Mn(II) to Mn(IV); hence, the formation of MnO2 at the surface of the manganese-coated samples further enhanced the removal efficiency of the solids. Moreover, the removal of Mn(II) was also performed under dynamic conditions in column experiments. The data from the column experiments also showed that the presence of NaClO significantly enhanced the removal capacity of MCS1, that is, from (10.93 to 20.21) mg·g−1, but only slightly increased that for MCS2, that is, from (59.34 to 65.44) mg·g−1 in the absence and presence of sodium hypochlorite, respectively.

Catalytic Properties of Active Site Mutants of Glyoxasomal Malate Dehydrogenase

The active site of Malate Dehydrogenase contains a Histidine-Aspartate pair where the aspartate is presumed to enhance the basicity of the catalytic histidine. In an attempt to more fully define the role of the various amino acid side chains in the active site cavity of Malate dehydrogenase, we have used site directed mutagenesis in conjunction with initial rate and stopped flow kinetics and structural determination. After the crystal structure was first determined by Banaszak and Bradshaw in the late 1970s, the focus of thought about the catalytic mechanism was on the His-Asp pair in the active site cavity. The results presented here suggest a more complex role of many residues in the active site cavity in overall catalysis. The expressed proteins have been purified using NTA Chromatography and the purified proteins characterized using initial rate kinetics studies to give Km and Vmax values. Activation energies for the various mutants have been determined using temperature dependence of Vmax. The native enzyme exhibits significant substrate inhibition at high oxaloacetate concentrations. Stopped flow initial rate kinetics data demonstrates that catalysis is, in fact, the rate limiting step. The pH dependence of the various kinetic parameters suggests that the role of the histidine residue is more complex than simple base catalysis. The pH dependence data indicate that H182 might not be dominating the proton abstraction as the contemporary mechanism suggests; however, the greatly decreased turnover of the H182Q mutant does confirm H182 plays an integral role in catalysis. The crystal structure of the D157N mutant shows that in at least this mutant there is no significant change in structure This work is supported by NSF Grant MCB 0448905 to EB.

Why Is Trehalose an Exceptional Protein Stabilizer?: AN ANALYSIS OF THE THERMAL STABILITY OF PROTEINS IN THE PRESENCE OF THE COMPATIBLE OSMOLYTE TREHALOSE

Trehalose, a naturally occurring osmolyte, is known to be an exceptional stabilizer of proteins and helps retain the activity of enzymes in solution as well as in the freeze-dried state. To understand the mechanism of action of trehalose in detail, we have conducted a thorough investigation of its effect on the thermal stability in aqueous solutions of five well characterized proteins differing in their various physico-chemical properties. Among them, RNase A has been used as a model enzyme to investigate the effect of trehalose on the retention of enzymatic activity upon incubation at high temperatures. 2 m trehalose was observed to raise the transition temperature, Tm of RNase A by as much as 18 degrees C and Gibbs free energy by 4.8 kcal mol-1 at pH 2.5. There is a decrease in the heat capacity of protein denaturation (DeltaCp) in trehalose solutions for all the studied proteins. An increase in the DeltaG and a decrease in the DeltaCp values for all the proteins points toward a general mechanism of stabilization due to the elevation and broadening of the stability curve (DeltaG versus T). A direct correlation of the surface tension of trehalose solutions and the thermal stability of various proteins has been observed. Wyman linkage analysis indicates that at 1.5 m concentration 4-7 molecules of trehalose are excluded from the vicinity of protein molecules upon denaturation. We further show that an increase in the stability of proteins in the presence of trehalose depends upon the length of the polypeptide chain. The pH dependence data suggest that even though the charge status of a protein contributes significantly, trehalose can be expected to work as a universal stabilizer of protein conformation due to its exceptional effect on the structure and properties of solvent water compared with other sugars and polyols.

Inner-sphere complexation of cobalt(II) 2,9-dimethyl-1,10-phenanthroline ([Co(neo)]2+) with commercial and sol-gel derived silica gel surfaces.

[Co(2,9-dimethyl-1,10-phenanthroline)(solvent)4]2+ ([Co(neo)]2+) undergoes a significant decrease in symmetry to form an inner-sphere surface complex when grafted directly on performed silica or introduced during the sol-gel process. The visible and X-ray absorption spectra of the surface adducts are interpreted in terms of a binding mode in which the Co(II) center has a highly distorted pseudo-C2v symmetry. The interaction of [Co(neo)]2+ with the silica surface was analyzed using an acid-base equilibrium relationship. Half-maximal surface binding was observed at pH ca. 6. Linear fits to the pH dependence data are consistent with inner-sphere binding of a single silanol group to the cobalt center. The formation of the surface species in tetramethoxyorthosilicate (TMOS) sol-gels required approximately 2 equiv of hydroxide anion per cobalt center, suggesting a two-proton-dependent binding event to form a species such as [Co(neo)(SiO)2]. Both sol-gel and silica samples showed essentially identical visible and X-ray absorption spectra, indicating formation of very similar surface adducts when the different synthesis procedures were employed. The maximal binding of [Co(neo)]2+ on three silica samples with different pore diameters and surface areas was compared. Increased binding was found to be inversely proportional to surface area and proportional to pore diameter, indicating a preference for less sterically demanding surface sites.

Stability Of A Commercial Lipase From Mucor Jav Anicus: Kinetic Modelling Of Ph And Temperature Dependencies

The present communication reports experimental and modelling work pertaining to the independent roles of pH and temperature on deactivation of a crude lipase from Mucor juvanicus. Experimental data of lipolytic activities were generated by a classic pH-stat assay on a triolein emulsion following incubation at several pH values for a fixed time, or at several temperatures for various times; postulated models were then fitted by nonlinear fitting to such data. The pH-dependence data were best fit by assumption of three forms of enzyme with increasing states of protonation, with pKa values of 6.2 and 11.3, respectively, where only the intermediate form is stable within the time frame considered. The thermal-dependence data were best fit by assumption of parallel steps of deactivation and rearrangement, with activation energies of 228.8 and 221.7 kJ mol-1, respectively.

Characterization of the role of side-chain interactions in the binding of ligands to apo trp repressor: pH dependence studies

The pH dependence of the association of apo trp repressor with the series of ligands, tryptophan, tryptamine, indole propionic acid (IPA), and trans-β-indole acrylic acid (IAA), has been studied using fluorescence titrations and isothermal titration microcalorimetry (ITC). The purpose of such a comparison of ligands and the pH dependency studies is to reveal the role played by the side-chain functional groups in the energetics of the binding of the ligands to the protein. We find that, whereas the binding of tryptamine and IPA have essentially no pH dependence between pH 6 and 10, the binding of tryptophan and IAA depends on pH. For IAA, the affinity drops between pH 6 and 10, consistent with a shift in p K a of some group on the protein from a value of p K a 7.4 to 7.9 upon binding of this ligand. The affinity of IAA also drops below pH 5, but shows saturable binding at pH 2–3, where the protein has previously been found to exist as a partially folded monomeric state. For tryptophan, the pH dependence data indicate that the equilibrium is complicated. We present a model to describe the data in which the α-ammonium group of tryptophan has its p K a shifted upward upon binding (i.e. preferential binding of the protonated form of this functional group) and in which the p K a of an unknown group on the protein also has its p K a increased.

PH dependence of the reaction rate of His 48 with p-bromophenacyl bromide and of the binding constant to Ca2+ of the monomeric forms of intact and alpha-NH2 modified phospholipases A2 from Trimeresurus flavoviridis.

The phospholipase A2 of Trimeresurus flavoviridis was found to show monomer-dimer equilibria. Under conditions where the enzyme exists predominantly in the monomeric form, the chemical reaction rate of p-bromophenacyl bromide (BPB) with the catalytic group, His 48, was studied at 25 degrees C and ionic strength 0.2 by measuring the residual enzymic activity using a fluorescent substrate, 1,2-bis[4-(1-pyreno)butanoyl]-sn-glycero-3-phosphorylcholine (diPBPC). The pH-dependence curve of the reaction rate for the intact enzyme was practically the same as that for the modified enzyme, in which the N-terminal alpha-NH2 group had been selectively converted into an alpha-keto group. The pH-dependence curves were monophasic (sigmoidal) with a midpoint at pH 7.53, which corresponds to the pKa value of His 48. The pH dependences of the binding constants of Ca2+ to the intact and the alpha-NH2 modified enzymes were also studied at 25 degrees C and ionic strength 0.2 by measuring the changes in the tryptophyl fluorescence and/or aromatic CD spectra. The pH-dependence data for the modified enzyme were interpreted in terms of participation of Asp 49 (pKa 5.40) and His 48 (pKa 7.53), assuming that the protonation of Asp 49 competes with the Ca2+ binding. The pH-dependence data for the intact enzyme were similarly interpreted in terms of participation of the alpha-NH2 group (pKa 9.40) in addition to that of Asp 49 (pKa 5.40) and His 48 (pKa 7.53).(ABSTRACT TRUNCATED AT 250 WORDS)

Anion Binding to Liver Alcohol Dehydrogenase

1. Complex formation at the general anion-binding site of the liver alcohol dehydrogenase subunit has been characterized by transient-state kinetic methods, using NADH as a reporter ligand. Equilibrium dissociation constants for anion binding at the site are reported. They conform basically to the lyotropic series of affinity order, with exceptionally tight binding of sulphate. The particular specificity for sulphate might be a general characteristic of anion-binding enzymic arginyl sites. 2. Anionic species of phosphate and pyrophosphate buffer solutions do not interact significantly with the general anion-binding site over the pH range 8-10. At lower pH, phosphate binding becomes significant due to complex formation with the monovalent H2PO4 species. The latter interaction corresponds to a dissociation constant of about 60 mM, indicating that phosphate binding is comparatively weak also at low pH. 3. It is concluded that previously reported pH dependence data for coenzyme binding to liver alcohol dehydrogenase cannot be much affected by coenzyme-competitive effects of buffer anion binding. Kinetic parameter estimates now determined for NADH binding in weakly buffered solutions agree within experimental precision with those obtained previously from measurements made in buffer solutions of 0.1 M ionic strength.

AN EQUILIBRIUM AND RATE STUDY OF THE INTERACTION OF AQUEOUS CHROMIUM(III) ION WITH ADENINE

Abstract Potentiometric titration data obtained at 50° for aqueous solutions containing aquochromium(III) ions and adenine were analyzed to yield values for the acid dissociation constants of adenine and the formation constants of 1:1 and 1:2 mononuclear complexes. There is also evidence for a 2:2 dimer for which elemental analysis data suggest a structure of the form (HL=neutral adenine): [(H2 O)2 (HL)Cr-μ(OH)3 -Cr(HL)(H2 O)2]3+. The kinetic studies indicate that the 1:1 complex is formed in excess adenine with a half-time of about two hours at pH=4.4 and 60°. The proposed mechanism involves an outer-sphere associative intermediate of appreciable stability (KA ∼ 200) followed by rate-determining substitution of adenine for ligand water to produce the 1:1 complex. A much slower subsequent reaction yields the dimer as the final stable product. The formation of the 1:1 complex is an equilibration and both forward and reverse rate constants were determined. The pH dependence data indicate that the reactive s...

Studies of binding of parathyroid hormone to a detergent-dispersed preparation from bovine kidney cortex plasma membranes.

Bovine kidney plasma membranes containing parathyroid hormone-sensitive adenylate cyclase activity were dispersed with 1% Triton X-100 and centrifuged at 150,000 X g for 2 h. Approximately 40% of the total membrane protein was extracted by this procedure. The extraction greatly reduces the fluoride-stimulated and the parathyroid hormone-sensitive adenylate cyclase activity of the membranes and yields a supernatnat which binds biologically active, tritiated parathyroid hormone. Hormone binding is stable for up to 15 h and has a linear dependence on protein concentration in the extract. Binding of the labeled hormone at concentrations of 5 to 10 nM is inhibited by preincubation with unlabeled min, and displays a dependence on temperature, time, and pH. Binding specificity is maximal at physiological pH, being inhibited by only the native hormone or its synthetic 1-34 NH2-terminal, biologically active fragment. Binding increases dramatically at pH 6.0, but is nonspecific in character. Half-maximal inhibition of the binding was achieved at 3.2 X 10(-7) M concentrations of the native hormone and 5.0 X 10(-7) M concentrations of the synthetic 1-34 NH2-terminal fragment. Calcium does not inhibit either total or specific binding. Inhibition, kinetic, and pH dependence data suggest that the extracted component(s) represent the parathyroid hormone binding protein(s) formerly identified in particulate membrane preparations.