Humate Complexation of Neptunium(V) and its Modeling

1994 ◽  
Vol 353 ◽  
Author(s):  
Hirotake Moriyama ◽  
Yasuhiro Nakata ◽  
Kunio Higashi
Keyword(s):  
Functional Groups ◽  
Ph Dependence ◽  
Complexation Constants ◽  
Complexation Constant ◽  
Ph Dependent ◽  
Ph Range

AbstractThe complexation behavior of Np(V) with humate was investigated by spectrophotometry in the pH range from 5.7 to 10 in 0.01–0.5M NaClO4. The absorption peaks of NpO2+ and Np(V) humate were observed at 979.6nm and 989.9nm, respectively, and the apparent complexation constant of the Np(V) humate was found to be pH-dependent. A two-site complexation model was applied to the interpretation of the observed pH-dependence by considering the participation of the two functional groups of carboxylate and phenolate. The dissociation and complexation constants of both functional groups were determined.

Some Physicochemical Peculiarities of Poplar Plastocyanins a and b

2009 ◽  
Vol 64 (5-6) ◽  
pp. 399-404 ◽  
Author(s):  
Petya K. Christova ◽  
Anthony A. Donchev ◽  
Alexandra C. Shosheva ◽  
Vladimir I. Getov ◽  
Mitko I. Dimitrov
Keyword(s):  
Plant Species ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
The Other ◽  
Redox Potentials ◽  
Extinction Coefficients ◽  
Structural Differences ◽  
Ph Dependent ◽  
Ph Range ◽  
Reduced Forms

The redox potentials of poplar plastocyanins a and b (PCa, PCb) were determined by spectro photometric titrations of their reduced forms with [Fe(CN)6]3-. It was found that the two isoforms have the following millimolar extinction coefficients ε597, equilibrium constants Keq of one-electron exchange with [Fe(CN)6]4-/[Fe(CN)6]3-, and standard electron potentials E0′: PCa: ε597 = (4.72 ± 0.08) mM-1 cm-1, Keq = 0.133 ± 0.009, E0′ = (354 ± 11) mV; PCb: ε597 = (5.23 ± 0.16) mM-1 cm-1, Keq = 0.175 ± 0.010, E0′ = (363 ± 12) mV. The pH dependence of the redox potential of PCb was studied too. It was found, that the value of E0′ for PCb is constant in the pH range 6.5 - 9.5, but decreases in the range 4.8 - 6.5. On the whole, the dependence resembles that of PC from some well-known plant species, including poplar PCa. The changes of E0′ in the pH-dependent region for poplar PCb, however, are smaller and are 13 mV per pH unit, whereas in the other well-known plant species the changes are about 50 - 60 mV per pH unit. It has been assumed that the weaker pH dependence of E0′ of PCb accounts for some structural differences between PCa and PCb

An Infrared Spectroscopic Study of the Hydrogen-Deuterium Exchange of Bovine Submaxillary Mucin

1969 ◽  
Vol 23 (3) ◽  
pp. 245-248 ◽  
Author(s):  
Frank S. Parked ◽  
Martin H. Stryker
Keyword(s):  
Ph Dependence ◽  
Spectroscopic Method ◽  
Deuterium Exchange ◽  
Infrared Spectroscopic Study ◽  
Hydrogen Deuterium Exchange ◽  
Infrared Spectroscopic ◽  
Hydrogen Deuterium ◽  
Bovine Submaxillary Mucin ◽  
Ph Dependent ◽  
Ph Range

An infrared spectroscopic method was used to study the hydrogen-deuterium exchange of a glycoprotein, bovine submaxillary mucin (BSM), dissolved in D2O. The pH-dependence of the rate and extent of the H—D exchange of BSM was determined. The rate constant of the exchange decreased as pH increased from 3.7 to 5.3 and remained constant at a minimum value, (0.82 ± 0.09) X 10−2 min−1, from pH 5.3 to 7.2. The extent of the exchange decreased with increasing pH in the pH range 3.7 to 5.3 and levelled off from pH 5.3 to 7.2. It is suggested that these results are due to a pH-dependent conformational change.

scholarly journals Metal Ions and Hydrogen Peroxide. XXV

1972 ◽  
Vol 27 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Peter Waldmeier ◽  
Bernhard Prijs ◽  
Helmut Sigel
Keyword(s):  
Hydrogen Peroxide ◽  
Ionic Strength ◽  
Metal Ions ◽  
Experimental Evidence ◽  
Initial Rate ◽  
Reaction Order ◽  
Ph Dependence ◽  
Initial Concentration ◽  
Ph Dependent ◽  
Ph Range

The decomposition of H2O2, catalyzed by the Co2® complex of 4,4′,4″,4″′-tetrasulfophthalocyanine (CoIIPTS), was investigated in the pH range 3.8 through 10 by measuring the initial rate, v0=d(O2)/dt, of the increasing formation of O2 (25°; I=0.1). In this pH range v0 is proportional to the initial concentration of H2O2 (determined at pH 5.0 and 9.2). Due to the dimerization (log KD=5.47 ±0.09 at natural ionic strength and about 7.63 ±0.16 in 0.1 M NaClO4; 25°) and polymerization of CoIIPTS the catalyst and its reaction order are difficult to establish: Based on the experimental evidence it is suggested that v0 is proportional to the concentration of monomer CoIIPTS. Additionally, there is evidence that the experimentally determined v0 contains the contributions of a pH-independent and a pH-dependent reaction course. These results are analog to those obtained earlier with FeIIIPTS as catalyst. A mechanism for the catalyzed disproportionation of H2O2 by CoIIPTS is proposed. The catalase-like activity of CoIIIPTS (OH) is smaller than that of CoIIPTS and the pH-dependence is different.

scholarly journals Local pH-dependent conformational changes leading to proteolytic susceptibility of cystatin C

1994 ◽  
Vol 302 (2) ◽  
pp. 411-416 ◽  
Author(s):  
P J Berti ◽  
A C Storer
Keyword(s):  
Ionic Strength ◽  
Conformational Change ◽  
Cystatin C ◽  
Conformational Changes ◽  
Ph Dependence ◽  
Significant Proportion ◽  
Cysteine Protease Inhibitor ◽  
Ionic Strength Dependence ◽  
Ph Dependent ◽  
Ph Range

Cystatin C, a cysteine protease inhibitor, was subject to hydrolysis at two sites when complexed with papain and in the presence of excess papain. A pH-dependent cleavage at His-86 increases Asp-87 was observed, as well as a pH-independent one at Gly-4 increases Lys-5. His-86 increases Asp-87 hydrolysis increased with decreasing pH and was characterized kinetically. It could be described by a single ionization with pKa = 3.4 +/- 0.2 and (kcat./Km)max. = 1.4 (+/- 0.4) x 10(4) M-1.s-1 at I = 0.3 M. C.d. spectroscopy, also at I = 0.3 M, demonstrated a conformational change with pKa = 3.2 +/- 0.2, indicating that the pH-dependence of hydrolysis was due to a conformational change in cystatin C. At I = 0.15 M, the pKa of the conformational change observed by c.d. shifted to 4.1 +/- 0.1. This indicates that at physiological ionic strength of 0.15 M, a significant proportion of cystatin C complexed with protease would be in a proteolytically labile conformation over the pH range 4.5 to 5, which is encountered in lysosomes. This may constitute a mechanism for clearing inappropriately localized cystatins. A pH-dependent conformational variability in this region of the inhibitor could explain the differences in the X-ray crystallographic and n.m.r. structures of the homologous chicken cystatin. The ionic-strength dependence of ionization indicates a hydrophobic stabilization of the ionizable group. The lack of pH-dependence of hydrolysis at Gly-4 increases Lys-5, with kcat./Km = 220 +/- 41 M-1.s-1 in the pH range 3.89 to 7.96 was unexpected in light of the normal, bell-shaped pH-dependence of papain-catalysed hydrolyses. This may reflect a different rate-limiting step of cystatin C hydrolysis.

scholarly journals pH dependent octanol–water partitioning coefficients of microcystin congeners

2018 ◽  
Vol 16 (3) ◽  
pp. 340-345 ◽  
Author(s):  
James McCord ◽  
Johnsie R. Lang ◽  
Donna Hill ◽  
Mark Strynar ◽  
Neil Chernoff
Keyword(s):  
Algal Blooms ◽  
Environmental Fate ◽  
Ph Dependence ◽  
Significant Heterogeneity ◽  
Algal Toxins ◽  
Amino Acid Region ◽  
Log Kow ◽  
Partitioning Coefficients ◽  
Ph Dependent ◽  
Ph Range

Abstract Hazardous algal blooms can generate toxic compounds with significant health impacts for exposed communities. The ubiquitous class of algal toxins known as microcystins exhibits significant heterogeneity in its peptide structure, which has been minimally studied, given the significant impact this has on hydrophobicity, acid/base character and related environmental fate and health effects. Octanol–water partition coefficients for the microcystin congeners MCLR, MCRR, MCLY, MCLF, and MCLA were calculated over an environmentally and physiologically relevant pH range. Microcystin-LR log(Kow) partition coefficient values were found to be consistent with previously established literature values, 1.67 to −1.41 between pH 1 and 8. Microcystin RR was found to be pH insensitive with a log(Kow) of −0.7. The remaining congeners exhibit similar pH dependence as MCLR, with systematic increases in hydrophobicity driven by the introduction of more hydrophobic residues to their variable amino acid region. The variation in pH dependent hydrophobicity suggests increased propensity for bioaccumulation and alternate environmental fates for differing microcystin forms, requiring further investigation.

Rationalizing the pH-Activity Response for Escherichia Coli’s Glycinamide Ribonucleotidetransformylase Through Computational Methods

2019 ◽  
Author(s):  
Adrian Roitberg ◽  
Pancham Lal Gupta
Keyword(s):  
Transfer Reaction ◽  
Catalytic Mechanism ◽  
Ph Dependence ◽  
Ph Effects ◽  
Dependent Manner ◽  
E Coli ◽  
Gar Tfase ◽  
Activity Curve ◽  
Ph Dependent ◽  
Formyl Transfer

<div>Human Glycinamide ribonucleotide transformylase (GAR Tfase), a regulatory enzyme in the de novo purine biosynthesis pathway, has been established as an anti-cancer target. GAR Tfase catalyzes the formyl transfer reaction from the folate cofactor to the GAR ligand. In the present work, we study E. coli GAR Tfase, which has high sequence similarity with the human GAR Tfase with most functional residues conserved. E. coli GAR Tfase exhibits structural changes and the binding of ligands that varies with pH which leads to change the rate of the formyl transfer reaction in a pH-dependent manner. Thus, the inclusion of pH becomes essential for the study of its catalytic mechanism. Experimentally, the pH-dependence of the kinetic parameter kcat is measured to evaluate the pH-range of enzymatic activity. However, insufficient information about residues governing the pH-effects on the catalytic activity leads to ambiguous assignments of the general acid and base catalysts and consequently its catalytic mechanism. In the present work, we use pH-replica exchange molecular dynamics (pH-REMD) simulations to study the effects of pH on E. coli GAR Tfase enzyme. We identify the titratable residues governing the pH-dependent conformational changes in the system. Furthermore, we filter out the protonation states which are essential in maintaining the structural integrity, keeping the ligands bound and assisting the catalysis. We reproduce the experimental pH-activity curve by computing the population of key protonation states. Moreover, we provide a detailed description of residues governing the acidic and basic limbs of the pH-activity curve.</div>

pH-Dependent Thermal Stability of Vibrio cholerae L-asparaginase

2019 ◽  
Vol 26 (10) ◽  
pp. 743-750 ◽  
Author(s):  
Remya Radha ◽  
Sathyanarayana N. Gummadi
Keyword(s):  
Vibrio Cholerae ◽  
Conformational Changes ◽  
Kinetic Studies ◽  
Structural Features ◽  
Structure Stability ◽  
Kcal Mole ◽  
Scanning Calorimetry ◽  
Wide Range ◽  
Ph Dependent ◽  
Ph Range

Background:pH is one of the decisive macromolecular properties of proteins that significantly affects enzyme structure, stability and reaction rate. Change in pH may protonate or deprotonate the side group of aminoacid residues in the protein, thereby resulting in changes in chemical and structural features. Hence studies on the kinetics of enzyme deactivation by pH are important for assessing the bio-functionality of industrial enzymes. L-asparaginase is one such important enzyme that has potent applications in cancer therapy and food industry.Objective:The objective of the study is to understand and analyze the influence of pH on deactivation and stability of Vibrio cholerae L-asparaginase.Methods:Kinetic studies were conducted to analyze the effect of pH on stability and deactivation of Vibrio cholerae L-asparaginase. Circular Dichroism (CD) and Differential Scanning Calorimetry (DSC) studies have been carried out to understand the pH-dependent conformational changes in the secondary structure of V. cholerae L-asparaginase.Results:The enzyme was found to be least stable at extreme acidic conditions (pH< 4.5) and exhibited a gradual increase in melting temperature from 40 to 81 °C within pH range of 4.0 to 7.0. Thermodynamic properties of protein were estimated and at pH 7.0 the protein exhibited ΔG37of 26.31 kcal mole-1, ΔH of 204.27 kcal mole-1 and ΔS of 574.06 cal mole-1 K-1.Conclusion:The stability and thermodynamic analysis revealed that V. cholerae L-asparaginase was highly stable over a wide range of pH, with the highest stability in the pH range of 5.0–7.0.

Electroanalytical chemistry of vanadium complexes: Electrochemical oxidation of [V(IV)O(nta)(H2O)]-

1989 ◽  
Vol 54 (1) ◽  
pp. 64-69 ◽  
Author(s):  
Roland Meier ◽  
Gerhard Werner ◽  
Matthias Otto
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Oxidation ◽  
Ph Dependence ◽  
Differential Pulse ◽  
Nitrilotriacetic Acid ◽  
Reduced Form ◽  
Vanadium Complexes ◽  
Differential Pulse Polarography ◽  
Electroanalytical Chemistry ◽  
Ph Range

Electrochemical oxidation of [V(IV)O(nta)(H2O)]- (H3nta nitrilotriacetic acid) was studied in aqueous solution by means of cyclic voltammetry, differential pulse polarography, and current sampled DC polarography on mercury as electrode material. In the pH-range under study (5.5-9.0) the corresponding V(V) complex is produced by one-electron oxidation of the parent V(IV) species. The oxidation product is stable within the time scale of cyclic voltammetry. The evaluation of the pH-dependence of the half-wave potentials leads to a pKa value for [V(IV)O(nta)(H2O)]- which is in a good agreement with previous determinations. The measured value for E1/2 is very close to the formal potential E0 calculated via the Nernst equation on the basis of known literature values for log Kox and log Kred, the complex stability constants for the oxidized and reduced form, respectively.

Measurements of Metal Adsorption in Oxide-Clay Mixtures: “Competitive-Additivity” Among Mixture Components

1992 ◽  
Vol 294 ◽  
Author(s):  
V. S. Tripathi ◽  
M.D. Siegel ◽  
Z. S. Kooner
Keyword(s):  
Surface Complexation ◽  
Particle Interactions ◽  
Complexation Constants ◽  
Lead Adsorption ◽  
Adsorption Sites ◽  
Adsorption Behaviors ◽  
Limited Success ◽  
Ph Dependent ◽  
Waste Repositories ◽  
Zinc Adsorption

ABSTRACTAn important question concerning the transport of radionuclides from nuclear waste repositories is whether the adsorption of metals by rocks and soils can be predicted from the properties of the constituent minerals. Attempts by previous researchers to use sorption models based on linear adsorption or weighted "sorptive additivity" have met with limited success. In this study, a “competitive-additivity” model based on surface complexation theory was used to model the pH-dependent adsorption of lead by goethite/Ca-montmorillonite mixtures using complexation constants obtained from single sorbent systems. Measurements of lead adsorption by goethite, Ca-montmorillonite, and goethite-Ca-montmorillonite mixtures (and similar studies of copper and zinc adsorption) demonstrate that the two adsorbents compete for adsorption of metals over wide ranges of pH and concentrations of adsorbents and metals. The adsorption behaviors of the mixtures are determined by the relative concentrations of the adsorbents and their respective affinities for the adsorbate metal. Particle-particle interactions such as heterocoagulation of the oxide and clay do not appear to be significant for the majority of the adsorption sites in this system.

Enhanced Analytic Approach for Describing pH Triggered Fast Drug Release Systems

2021 ◽  
Vol 18 ◽  
Author(s):  
Aykut Elmas ◽  
Guliz Akyuz ◽  
Ayhan Bergal ◽  
Muberra Andac ◽  
Omer Andac
Keyword(s):  
Drug Release ◽  
Ph Dependence ◽  
Slope Angle ◽  
Ph Sensitive ◽  
Analytic Model ◽  
Two Dimensional ◽  
Analytic Equation ◽  
One Dimensional ◽  
Ph Dependent ◽  
Fast Release

Background: pH sensitive dendrimers attached to nanocarriers, as one of the drug release systems, has become quite popular due to their ease of manufacture in experimental conditions and ability to generate fast drug release in the targeted area. This kind of fast release behavior cannot be represented properly most of the existing kinetic mathematical models. Besides, these models have either no pH dependence or pH dependence added separately. So, they have remained one dimensional. Objective: The aim of this study was to establish the proper analytic equation to describe the fast release of drugs from pH sensitive nanocarrier systems. Then, to combine it with the pH dependent equation for establishing a two-dimensional model for whole system. Methods: We used four common kinetic models for comparison and we fitted them to the release data. Finding that, only Higuchi and Korsmeyer-Peppas models show acceptable fit results. None of these models have pH dependence. To get a better description for pH triggered fast release, we observed the behavior of the slope angle of the release curve. Then we puroposed a new analytic equation by using relation between the slope angle and time. Result: To add a pH dependent equation, we assumed the drug release is “on” or “off” above/below specific pH value and we modified a step function to get a desired behavior. Conclusion: Our new analytic model shows good fitting, not only one-dimensional time dependent release, but also two-dimensional pH dependent release, that provides a useful analytic model to represent release profiles of pH sensitive fast drug release systems.

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