scholarly journals On the pH-dependent strontium adsorption by Al-PILCs, impregnated with carboxylate groups of various acid strengths

2019 ◽  
Vol 11 ◽  
Author(s):  
C. A. Papachristodoulou ◽  
P. A. Assimakopoulos ◽  
N-H. J. Gangas
Keyword(s):  
Acid Strength ◽  
Adsorption Properties ◽  
Solution Ph ◽  
Cation Uptake ◽  
Carboxylate Groups ◽  
Constant Ph ◽  
Strontium Ions ◽  
Ph Dependent ◽  
Ph Range

The impregnation of a PILC with carboxylate groups is proposed as a means to improve the adsorption properties of the material for strontium ions. The role of solution pH and carboxylate acid strength in the functionalization of the organic groups is probed by base titrations. In comparing the pristine-PILC with PILCs carrying either oxalate or acetate impregnates, enhanced strontium uptake is evidenced by the modified solids, initiated at pH 6 and 8 in the presence of oxalate and acetate, respectively. The effect on uptake is higher in the former case, amounting to an increase in strontium adsorption by a factor between two and three, depending on the pH range. To further elucidate the significance of the carboxylate acid strength in cation uptake phenomena, strontium adsorption isotherms are presented for PILCs carrying acetate, oxalate, malonate and citrate groups. The results demonstrate that, at constant pH, adsorption increases with increasing acid strength

Ionic exchanges of turtle shell in vitro and their relevance to shell function in the anoxic turtle

1999 ◽  
Vol 202 (5) ◽  
pp. 513-520 ◽  
Author(s):  
D.C. Jackson ◽  
Z. Goldberger ◽  
S. Visuri ◽  
R.N. Armstrong
Keyword(s):  
Extracellular Fluid ◽  
Storage Site ◽  
Solution Ph ◽  
Turtle Shell ◽  
Constant Ph ◽  
Acid Titration ◽  
Solution Acidity

To understand more fully the role of the in vivo turtle shell in buffering lactic acid produced during prolonged anoxia, powdered turtle shell was incubated in vitro at constant pH (6.0, 6.5, 7.0, 7. 5 or 8.0) in electrolyte solutions simulating extracellular fluid. Exchanges of ions and CO2 between the shell and solution were evaluated by measuring pre- and post-incubation solution concentrations of calcium, magnesium, sodium, potassium, chloride, phosphate and lactate. The production of CO2 from the shell and lactate within the shell were also measured. We observed that calcium and magnesium, but not phosphate, were released from the shell in association with CO2 and that the magnitude of release of each increased with solution acidity. The amount of acid titration required to maintain constant pH also increased as solution pH fell. The CO2 loss, in mmol, was approximately half the acid titration (in mmol), indicating that the evolved CO2 derives from carbonate. When the incubating solution contained lactate (50 mmol l-1), lactate entered the shell and again the amount entering the shell increased with solution acidity. Shell samples containing high initial lactate levels lost lactate to the solution and at high pH (7.5) acidified the solution and required NaOH titration for pH-stat control. These results are consistent with observations on anoxic turtles in vivo and confirm the important role of the shell as a source of buffer and as a storage site for lactate.

scholarly journals pH-Dependent Cooperativity and Existence of a Dry Molten Globule in the Folding of a Miniprotein BBL

2017 ◽  
Author(s):  
Jana Shen ◽  
Zhi Yue
Keyword(s):  
Molecular Dynamics ◽  
Protein Dynamics ◽  
Molten Globule ◽  
Hydrophobic Core ◽  
Solution Ph ◽  
Downhill Folding ◽  
Constant Ph ◽  
Ph Dependent ◽  
Constant Ph Molecular Dynamics ◽  
Dynamics Stability

<p>Solution pH plays an important role in protein dynamics, stability, and folding; however, detailed mechanisms remain poorly understood. Here we use continuous constant pH molecular dynamics in explicit solvent with pH replica exchange to explore the pH-dependent stability and folding mechanism of a miniprotein BBL, which has drawn intense debate in the past. Consistent with the two-state model, simulations showed native and denatured states with pH-dependent populations. However, at pH 7, the folding barrier is marginal and it vanishes as pH is decreased to 5, in agreement with the downhill folding hypothesis. As pH continues to decrease, the unfolding barrier lowers and denaturation is triggered by the protonation of Asp162, consistent with experimental evidence. Interestingly, unfolding proceeded via a sparsely populated intermediate, with intact secondary structure and a compact, unlocked hydrophobic core shielded from solvent, lending support to the recent hypothesis of a universal dry molten globule in protein folding. Our work demonstrates that constant pH molecular dynamics is a unique tool for testing this and other hypotheses to advance the knowledge in protein dynamics, stability, and folding.</p>

Biosorption of Strontium Ions by Low-Cost Sunflower Stem and Leaf

2014 ◽  
Vol 804 ◽  
pp. 59-62
Author(s):  
Lian Ai ◽  
Xue Gang Luo ◽  
Xiao Yan Lin
Keyword(s):  
Low Cost ◽  
Solution Ph ◽  
Maximum Sorption Capacity ◽  
Adsorption Data ◽  
Maximum Sorption ◽  
Initial Ph ◽  
Isotherm Adsorption ◽  
Strontium Ions ◽  
Ph Range ◽  
By Products

Low cost agricultural by-products are potential materials for water pollution treatment such as removal of radionuclide. This paper deals with removal of strontium ions from aqueous solution using sunflower stem (SFS) and leaf (SFL). Batch sorption experiments were performed as a function of initial solution pH, adsorbent dosage and initial strontium (II) concentration. The removal efficiency of strontium (II) increased with initial pH and achieved maximum values at a pH range of 4.0-7.0 both for SFS and SFL. The isotherm adsorption data was modeled best by the nonlinear Langmuir-Freundlich equation. The maximum sorption capacity of SFS and SFL were observed to be 17.87 and 22.31 mg/g under optimal conditions, respectively.

scholarly journals pH-Dependent Cooperativity and Existence of a Dry Molten Globule in the Folding of a Miniprotein BBL

2017 ◽  
Author(s):  
Jana Shen ◽  
Zhi Yue
Keyword(s):  
Molecular Dynamics ◽  
Protein Dynamics ◽  
Molten Globule ◽  
Hydrophobic Core ◽  
Solution Ph ◽  
Downhill Folding ◽  
Constant Ph ◽  
Ph Dependent ◽  
Constant Ph Molecular Dynamics ◽  
Dynamics Stability

<p>Solution pH plays an important role in protein dynamics, stability, and folding; however, detailed mechanisms remain poorly understood. Here we use continuous constant pH molecular dynamics in explicit solvent with pH replica exchange to explore the pH-dependent stability and folding mechanism of a miniprotein BBL, which has drawn intense debate in the past. Consistent with the two-state model, simulations showed native and denatured states with pH-dependent populations. However, at pH 7, the folding barrier is marginal and it vanishes as pH is decreased to 5, in agreement with the downhill folding hypothesis. As pH continues to decrease, the unfolding barrier lowers and denaturation is triggered by the protonation of Asp162, consistent with experimental evidence. Interestingly, unfolding proceeded via a sparsely populated intermediate, with intact secondary structure and a compact, unlocked hydrophobic core shielded from solvent, lending support to the recent hypothesis of a universal dry molten globule in protein folding. Our work demonstrates that constant pH molecular dynamics is a unique tool for testing this and other hypotheses to advance the knowledge in protein dynamics, stability, and folding.</p>

Preparation and Structure of Zinc Complexes of Cysteine Derivatives

1984 ◽  
Vol 39 (12) ◽  
pp. 1732-1737 ◽  
Author(s):  
P. Bell ◽  
W. S. Sheldrick
Keyword(s):  
Structural Analysis ◽  
Acid Solutions ◽  
Carboxylate Group ◽  
Alkaline Ph ◽  
Solution Ph ◽  
Binding Properties ◽  
X Ray ◽  
Zwitterionic Form ◽  
Carboxylate Groups

Sodium bis(L-cysteinato)zincate(II) hexahydrate (1) and bis(O-ethvl-L -cysteinato)zinc(II) (2) have been prepared from respectively alkaline (pH > 11) and neutral aqueous solutions and their structures determined by X-ray structural analysis. N ,S-coordination of the Zn atoms with the formation of two five-membered chelate rings is observed for both complexes. The deprotonated carboxylate groups in 1 do not coordinate the Zn atom. Dibromo-bis(DL-penicillamine)zinc(II) (3) and dibromo-bis(D-penicillamine)zinc(II) have been isolated from acid solutions with a pH of 2. The penicillamine moieties which are present in the zwitterionic form HS-C(CH3)2-CH(NH3+) - COO- behave as m onodentate ligands with the deprotonated carboxylate group as binding site. The role of solution pH in determining the binding properties of cysteine and penicillamine with zinc(II) is discussed.

Kinetic Analysis of Catalytic Reductive Dechlorination of Chlorobenzene in Aqueous Solutions

2013 ◽  
Vol 777 ◽  
pp. 65-70 ◽  
Author(s):  
Hong Yi Zhou ◽  
Si Liang ◽  
Si Si Zeng ◽  
Shuang Jian Lei
Keyword(s):  
Rate Constant ◽  
Organic Contaminants ◽  
Room Temperature ◽  
Solution Ph ◽  
First Order ◽  
Effective Removal ◽  
Chlorinated Organic ◽  
Ph Range ◽  
Increasing Temperature

Deposition of Pd on the surface of zero-valent iron (Pd/Fe) further enhances the ability of the metal to reductively dechlorinate organic contaminants. This work determined the dechlorination of chlorobenzene in water by Pd/Fe and evaluated the effects of Pd loading in Fe, Pd/Fe dosage, solution pH and temperature on the reaction. Pseudo-first-order rate constants were obtained to analyze the reaction kinetics. Chlorobenzene was nearly completely dechlorinated within 60 min by Pd/Fe at room temperature. Benzene was the end product of the reaction, along with the release of chloride into water. The rate constant of chlorobenzene dechlorination increased with increasing Pd loading in Fe and Pd/Fe dosage within the tested ranges of 0.005 - 0.020% and 2.0 - 6.0 g/75 mL, respectively. The rate constant increased with decreasing solution pH over the tested pH range of 4.5 - 6.5, indicating the role of protons in dechlorination. The reaction was considered to occur primarily on the surface of Pd where protons were reduced to hydrogen species and chlorobenzene was subsequently dechlorinated by the hydrogen species. The rate of chlorobenzene dechlorination increased with increasing temperature. The estimated activation energy of the reaction was 47.94 kJ/mol within the temperature range of 15 - 40°C, indicating that the dechlorination of chlorobenzene by Pd/Fe readily occurs at room temperature. Pd/Fe may be a potential reductant for effective removal of chlorinated organic contaminants from water.

Kinetic of oxidation of methyl orange by vanadium(V) under conditions VO2+ and decavanadates coexist: Catalysis by Triton X-100 micellar medium

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Methyl Orange ◽  
Solution Ph ◽  
Vanadium Concentration ◽  
Limiting Behavior ◽  
First Order ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetic Pattern ◽  
Triton X ◽  
Kinetics Of

The kinetics of oxidation of methyl orange by vanadium(V) {V(V)} has been investigated in the pH range 2.3-3.79. In this pH range V(V) exists both in the form of decavanadates and VO2+. The kinetic results are distinctly different from the results obtained for the same reaction in highly acidic solution (pH &lt; 1) where V(V) exists only in the form of VO2+. The reaction obeys first order kinetics with respect to methyl orange but the rate has very little dependence on total vanadium concentration. The reaction is accelerated by H+ ion but the dependence of rate on [H+] is less than that corresponding to first order dependence. The equilibrium between decavanadates and VO2+ explains the different kinetic pattern observed in this pH range. The reaction is markedly accelerated by Triton X-100 micelles. The rate-[surfactant] profile shows a limiting behavior indicative of a unimolecular pathway in the micellar pseudophase.

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.

scholarly journals The Role of the Disulfide Bridge in the Copper (II) Binding by the Cyclic His4-Peptide

2021 ◽  
Vol 22 (12) ◽  
pp. 6458
Author(s):  
Aleksandra Pieniężna ◽  
Weronika Witak ◽  
Aneta Szymańska ◽  
Justyna Brasuń
Keyword(s):  
Metal Ions ◽  
Coordination Mode ◽  
Transition Metal Ions ◽  
Disulfide Bridge ◽  
Chain Flexibility ◽  
Vis Spectroscopy ◽  
Ph Range ◽  
Cd Studies ◽  
Metal Ratios

In this paper, we present studies on the influence of the disulfide bridge on the copper (II) ions’ binding abilities by the cyclic His4-peptide. The studied ligand HKHPHRHC-S-S-C consists of nine amino acids. The cyclic structure was obtained through a disulfide bridge between two cysteinyl groups. Moreover, this peptide is characterized by the presence of four His residues in the sequence, which makes it an interesting ligand for transition metal ions. The potentiometric and spectroscopic (UV-Vis spectroscopy and circular dichroism spectroscopy (CD)) studies were carried out in various molar ligand to metal ratios: 2:1, 1:1, and 1:2, in the pH range of 2.5–11 at 25 °C. The results showed that the cyclic His4-peptide promotes dinuclear complexes in each of these systems and forms the final dinuclear species with the {NIm, 3N-amide}{NIm, 3N-amide} coordination mode. The obtained data shows that cyclization by the formation of the disulfide bond has an impact on the peptide chain flexibility and appearance of additional potential donors for metal ions and influences the copper (II) ions’ coordination.

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