Potentiometric and conductometric analysis of the binding of Barium ions with alkali polyacrylate

 The interaction between Poly(acrylic acid) and barium ions is analyzed using potentiometric (barium specific electrode) and conductometric titrations. At full ionization of the polyelectrolyte, in the presence of M⁺ counterions (M⁺=Li⁺, Na⁺ and K⁺), the binding ratio [Ba²⁺]_bound/C _p on the chain is determined, showing no significant difference between the three alkali ions. When the added Ba²⁺ concentration does not exceed 0.2×C _p, all barium ions bind with the polymer, i.e. none can be detected in the solution with the barium selective electrode. Assuming that monovalent counterions divide the electrostatically condensed and “atmospheric” ions and using Eisenberg plots of the conductivity excess, the experimental data allows to calculate the distribution of the different acrylic species on the fully deprotonated chain (free carboxylate groups, bound groups with M⁺ and with Ba²⁺ ions). Assuming the formation of a bidentate Ba(COO)₂ species and taking into account that part of the remaining groups bind with M⁺ ions, the calculated complexation constant (log K _c=6.5) is satisfactorily independent of the complexation ratio. The displacement ratio of M⁺ ions by attaching Ba²⁺ ions is also calculated, showing interestingly a continuous decrease between 1.4 and 0.9 as r increases. The latter result is attributed to the change of the averaged electrostatic potential of the chain, in relation with the binding of barium ions. Received: 14 April 1998 Accepted: 23 April 1998     

A Thermodynamic Study on the Binding of Calcium Ion with Myelin Basic Protein

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent calcium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. The extended solvation model was used to reproduce the enthalpies of Ca²⁺-MBP interaction over the whole range of Ca²⁺ concentrations. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of two identical and non-interacting binding sites for Ca²⁺ ions. The association equilibrium constant is 0.021 μmol⋅dm⁻³. The molar enthalpy of binding is ΔH=−15.10 kJ⋅mol⁻¹.     

Ca<Superscript>+2</Superscript> Concentrations are Key Determinants of Ischemia–Reperfusion-Induced Apoptosis: Significance for the Molecular Mechanism of Bcl-2 Action

The mechanism of action of the anti-apoptotic oncogene Bcl-2 and Ca⁺² regulation in ischemia–reperfusion injury is still obscure. In this present study, we investigated mitochondrial Ca⁺² overloads and mechanism of action of Bcl-2. Eighteen Wistar rats were divided into sham-operated control group (I) (n = 6), ischemia and reperfusion group (II) (n = 6), and amlodipine-treated group (1 mg kg⁻¹ body weight/daily by oral route for 7 days before inducing ischemia–reperfusion maneuver) (III) (n = 6). Rats were subjected to 1 h of hepatic ischemia followed by 3-h reperfusion. Mitochondrial Ca²⁺ content was determined and damage was confirmed by transmission electron microscopy. Decrease of mitochondrial Ca⁺² level is related to reduction of apoptosis and cellular changes, viz. increased Bcl-2 expression followed by reduction in secondary endoplasmic reticulum, whereas ischemia/reperfusion group shows overloading Ca⁺² ions and decrease in Bcl-2 expression as compared to sham-operated rats. Thus, Bcl-2-dependent reduction of Ca⁺² is an important component of the anti-apoptotic program in ischemia–reperfusion injury.     

An optical chemical sensor for mercury ion based on 2-mercaptopyrimidine in PVC membrane

An optical chemical sensor based on 2-mercaptopyrimidine (2-MP) in plasticized poly(vinyl chloride) (PVC) membrane incorporating (N,N-diethyl-5-(octadecanoylimino)-5H benzo[a]phenoxazine-9-amine (ETH 5294) and sodium tetraphenyl borate (NaTPB) for batch and flow-through determination of mercury ion is described. The response of the sensor is based on selective complexation of Hg²⁺ with 2-MP in the membrane phase, resulting in an ion exchange process between H⁺ in the membrane and Hg²⁺ in the sample solution. The influences of several experimental parameters, such as membrane composition, pH, and type and concentration of the regenerating reagent, were investigated. The sensor has a response range of 2.0 × 10⁻⁹ to 2.0 × 10⁻⁵ mol L⁻¹ Hg²⁺ with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹ and a response time of ≤45 s at optimum pH of 6.5 with high measurement repeatability and sensor-to-sensor reproducibility. It shows high selectivity for Hg²⁺ over several transition metal ions, including Ag⁺, Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, and common alkali and alkaline earth ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, and Pb²⁺. The sensor membrane can be easily regenerated with dilute acid solutions. The sensor has been used for the determination of mercury ion concentration in water samples.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

Ion-specific swelling behavior of poly(vinyl alcohol) gel prepared by γ-ray irradiation

Poly(vinyl alcohol) gel was prepared by γ-ray irradiation of an aqueous solution of the polymer and its swelling behavior in solutions of the alkali-metal and alkaline-earth-metal salts was investigated. The gel deswelled in solutions containing strongly hydrated anions and swelled in solutions containing strongly hydrated cations. The degree of swelling of the gel was in the following order: SO₄ ²⁻<Cl⁻<Br⁻ ≅ NO₃ ⁻<I⁻ for the anions and K⁺<Na⁺<Li⁺ and Sr²⁺<Ca²⁺<Mg²⁺ for the cations. These results were interpreted in terms of interactions between the polymer and the ions through the hydration layers. Received: 6 November 2000 Accepted: 24 May 2001     

Synthetic Crystalline Calcium Silicate Hydrate (I): Cation Exchange and Caesium Selectivity

Summary.  Solid crystalline calcium silicate hydrate (I) synthesized from equimolar amounts of Ca and Si under hydrothermal conditions at 120°C shows cation exchange properties towards divalent metal cations such as Ni, Cu, Cd, or Hg. It also exhibits caesium selectivity in the presence of Na⁺. The exchange capacity and selectivity of the solid can be increased by 10 and 28%, respectively, upon substitution of 0.01 mol of the Ca²⁺ in its structure by Na⁺. The ability of metal cation uptake by the solid was found to obey the order Ni²⁺ > Hg²⁺ > Cu²⁺ > Cd²⁺. The different affinities of calcium silicate hydrate (I) towards these ions can be used for their separation from solutions and also in nuclear waste treatment. The mechanism of the exchange reaction is discussed. Received June 11, 2001. Accepted September 10, 2001     

Selectivity study of strongly acidic cation exchange resin Amberlite IR-120

The thermodynamic measurements was carried out to study the selectivity of cation exchange resin Amberlite IR-120 in protonated form with respect to Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ ions in solution. The equilibrium constant K was calculated using the activity coefficients of ions in solution as well as in the resin. The K values calculated for the reacting systems increase with temperature that suggests the endothermic exchange reactions with estimated enthalpy values of 38.8, 20.6, 8.45, and 7.24 kJ mol⁻¹, respectively. On the basis of calculated parameters, the selectivity of ion exchange resin with respect to various bivalent ions in the solution was predicted. The method used in our experimental work provides a basis for characterization of ion exchange resins, which can be promising materials for efficient separation of ions from industrial waste effluents.     

Kinetics for the Oxygen Evolution Reaction and Application of the Ti/SnO<Subscript>2</Subscript> + RuO<Subscript>2</Subscript> + MnO<Subscript>2</Subscript> Electrode

A Ti/SnO₂ + RuO₂ + MnO₂ electrode was prepared by thermal decomposition of their salts. Results from SEM and XPS analyses, respectively, indicate that the coating layer exhibits a compact structure and the oxidation state of Mn in the coating layer is +IV. The experimental activation energy for the oxygen evolution reaction, which increased linearly with increasing overpotential, is about 8 kJ⋅mol⁻¹ at the equilibrium potential (η=0). The electrocatalytic characteristics of the anode are discussed in terms of ligand substitution reaction mechanisms (Sn1 and Sn2). It was found that the transition state for oxygen evolution at the anode in acidic solution follows a dissociative mechanism (Sn1 reaction). The Ti/SnO₂ + RuO₂ + MnO₂ anode in conjunction with UV illumination was used to degrade phenol solutions, where the concentration of phenol remaining was determined by high-performance liquid chromatography (HPLC). The results indicate that the degradation efficiency of phenol on the anode can reach 96.3% after photoelectrocatalytic oxidation for 3 h.     

Solvent extraction of some divalent metal cations into nitrobenzene by using a synergistic mixture of strontium dicarbollylcobaltate and nonactin

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq) + 1 · Sr²⁺(nb) ⇔ 1 · M²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Mn²⁺, Ni²⁺; 1 = nonactin; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1 · M²⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following order: Mg²⁺, Mn²⁺ < Ba²⁺, Cu²⁺, Zn²⁺, Ni²⁺ < Sr²⁺ < Ca²⁺ < Pb²⁺.     

Thermodynamic Study of the Binding of Mercury Ion to Human Growth Hormone at Different Temperatures

The interaction of human growth hormone (hGH) with the divalent mercury ion was studied by isothermal titration calorimetry at two temperatures of 27 °C and 37 °C in aqueous solutions. We found that there is a set of two identical and non-interacting binding sites for Hg²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 4.2 mmol⋅L⁻¹ and −14.8 kJ⋅mol⁻¹ at 27 °C and 5.1 mmol⋅L⁻¹ and −14.2 kJ⋅mol⁻¹ at 37 °C, respectively. The results obtained indicate that the stability of the protein increases due to the binding of mercury ions using the extended solvation theory.     

Synthesis,spectroscopic, thermal and biological aspect of mixed ligand copper(II) complexes

Derivative of 8-hydroxyquinoline i.e. Clioquinol is well known for its antibiotic properties, drug design and coordinating ability towards metal ion such as Copper(II). The structure of mixed ligand complexes has been investigated using spectral, elemental and thermal analysis. In vitro anti microbial activity against four bacterial species were performed i.e. Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus substilis and found that synthesized complexes (15–37 mm) were found to be significant potent compared to standard drugs (clioquinol i.e. 10–26 mm), parental ligands and metal salts employed for complexation. The kinetic parameters such as order of reaction (n = 0.96–1.49), and the energy of activation (E _a = 3.065–142.9 kJ mol⁻¹), have been calculated using Freeman–Carroll method. The range found for the pre-exponential factor (A), the activation entropy (S* = −91.03 to−102.6 JK⁻¹ mol⁻¹), the activation enthalpy (H* = 0.380–135.15 kJ mol⁻¹), and the free energy (G* = 33.52–222.4 kJ mol⁻¹) of activation reveals that the complexes are more stable. Order of stability of complexes were found to be [Cu(A⁴)(CQ)OH] · 4H₂O > [Cu(A³)(CQ)OH] · 5H₂O > [Cu(A¹)(CQ)OH] · H₂O > [Cu(A²)(CQ)OH] · 3H₂O     

The saddle point of the nucleophilic substitution reaction Cl− + CH3Cl: results of large-scale coupled cluster calculations

On the basis of large-scale coupled cluster calculations including connectedz triple substitutions in a perturbative way, the geometrical parameters of the D _{3 h} saddle point of the Walden inversion reaction Cl⁻ + CH₃Cl′→ ClCH₃ + Cl′⁻ are predicted to be R _s (C—Cl) = 2.301 ? and r _s (C—H) = 1.069 ?. The barrier height with respect to the reactants is recommended to be 11.5 ± 1.0 kJ mol⁻¹. Connected triple substitutions lower the barrier height by almost a factor of 2, but have very little influence on the geometric structure of the saddle point. Received: 26 June 1998 / Accepted: 15 July 1998 / Published online: 28 September 1998     

Theoretical study on decomposition of γ-halo allylalkoxide and β-halo acrylate ions

β, γ-Substituted γ-halo allylalkoxide ions decompose to form a halogen ion, formaldehyde, and an alkyne under mild conditions, for example at room temperature. The E isomer does not differ from the Z isomer in terms of activation energy. We attempted to shed light on the mechanism of the reaction by using ab initio molecular orbital calculations. The observed propensity was confirmed by the present calculation on model molecules, γ-chloro allylalkoxide ions. We conducted further calculations and compared the alkoxide results with a similar reaction of β-haloacrylate ions that release carbon dioxide instead of formaldehyde. This similar reaction needs heating as high as 150°C. The activation energy of the acrylate ions (36–39 kcal mol⁻¹) was calculated to be about 10 kcal mol⁻¹ higher than that of the alkoxide ions. The activation energy of the E acrylate ion is smaller by 0.8 kcal mol⁻¹ than that of the Z isomer at the MP2/6-31+G**//RHF/6-31+G* level of theory. This is consistent with experimental results. While the ready deprotonation from the carboxylic group does not activate the acrylate ion very much, the alkoxide ion is destabilized to a great degree in the process of anion formation. The difficulty in deprotonation that proceeds from the neutral molecule is seen in the difference in the activation energies for the decomposition of the corresponding anions. Therefore, the pK _a of a hydroxy or a carboxylic group plays the leading role in determining the magnitude of activation energies of allyl halides with a negatively charged fragment. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

A thermodynamic study on the interaction of nickel ion with myelin basic protein by isothermal titration calorimetry

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent nickel ion was studied by isothermal titration calorimetry at 37 and 47 °C in Tris buffer solution at pH = 7. The new solvation model was used to reproduce the heats of MBP + Ni²⁺ interaction over the whole Ni²⁺ concentrations. It was found that MBP has three identical and independent binding sites for Ni²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 89.953 μM, −14.403 kJ mol⁻¹ and 106.978 μM, −14.026 kJ mol⁻¹ at 37 and 47 °C, respectively. The binding parameters recovered from the new solvation model were correlated to the structural changes of MBP due to its interaction with nickel ion interaction. It was found that in the low and high concentrations of the nickel ions, the MBP structure was destabilized.     

DDB liver drug as a novel ionophore for potentiometric barium (II) membrane sensor

Dimethyl-4,4-dimethoxy-5,6,5′,6′-dimethylene dioxy biphenyl-2,2-dicarboxylate (DDB) liver drug is used as a novel ionophore in plasticized poly (vinyl chloride) (PVC) matrix membrane sensors for barium ions. Optimum performance characteristics are displayed by membrane sensor incorporating DDB ionophore, potassium tetrakis(4-chlorophenyl)borate as lipophilic salt, and o-nitrophenyloctyl ether as plasticizer. The sensor exhibits a linear response over the concentration range 10⁻¹-10⁻⁵ mol l⁻¹ BaCl₂ with a Nernstian slope of 30 mV per decade and high selectivity towards Ba²⁺ with respect to Li⁺, Na⁺, K⁺, Rb⁺, NH₄⁺, Mg²⁺, Ca²⁺, Sr²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cd²⁺, Al³⁺, La³⁺, and Ce³⁺ ions. The sensor response is stable over a wide pH range (4-9) and the lifetime is about 2 months. The proposed sensor is successfully applied to the determination of Ba²⁺contents of some rocks.     

Selective Kinetic Determination of Cu2+ with Tetraazamacrocyclic Bis(Methylphosphonate) Ligand (Dipon)

A new macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid) (refered to as dipon) exhibits high thermodynamic and kinetic selectivity for Cu²⁺ compared to other transition metal ions. The initial-rate method (=310nm, pH=3.75, c_L4.6×10^–3molL^–1) was chosen as an optimal experimental approach in order to achieve maximum sensitivity of determination. The dynamic range of the method is (5–200)×10^–6molL^–1, and the detection limit is 2.5×10^–6molL^–1. A standard addition procedure was applied to the kinetic determination of Cu²⁺ to eliminate the effect of interfering ions (e.g. Zn²⁺, Ca²⁺, Mg²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Co²⁺, Ni²⁺, HCO^–₃, Cl^–, SO₄^2–, etc.). The method was tested on artificial and real samples (alloys, pure and spiked mineral water) and gave satisfactory results which are in agreement with the values for some certified materials. The advantage of the proposed method is rapidity, simplicity and robustness in the presence of other metal ions.     

Donnan equilibrium and the effective charge of sodium polyacrylate

Osmometry using an external stressor is a very useful method to measure the equilibrium osmotic pressure for dilute solutions of polyelectrolyte. By taking into account the contribution of the ideal gas law, the excluded volume, the solvency effect, and the Donnan equilibrium effect on the measured pressure it is possible to estimate the effective charge of sodium polyacrylate 35 kgmol⁻¹ as a function of the polymer concentration, the pH, the ionic strength, and the presence of Ca²⁺ ion. The numerical resolution of state equations has shown that the effective charge increases with the ionic strength or with the decreasing polymer concentration, in agreement with recent theoretical models. On the other hand, the effective charge is pH-independent. This statement remains valid as long as the degree of neutralization of the polyacrylate is over 0.5. Above this degree of neutralization, any further neutralization promoted by NaOH addition leads to the condensation of the Na⁺ counterion, in agreement with the general concept of ionic condensation. The effective charge represents only 10–20% of the total number of monomer units for pH within 6 and 9 and ionic strength below 0.1 M. The polymer can tolerate the presence of Ca²⁺ at least up to a molar ratio Ca²⁺/–COOH = 0.222 without any influence on the effective charge. Received: 11 July 2000/Accepted: 23 October 2000     

Direct Synthesis of Nanocrystalline Hydroxyapatite by Hydrothermal Hydrolysis of Alkylphosphates

Summary.  The influence of reaction conditions (temperature, type of catalyst, time) on the base-catalyzed reaction of mono-, di-, and trialkylphosphates (alkyl = methyl, ethyl, i-propyl, n-butyl) with Ca²⁺ ions and on the structure and composition of the reaction products was studied. The composition of the calcium phosphates depends mainly on the reaction temperature. At temperatures below 100°C, a nanocrystalline solid product transforming into dicalcium phosphate by heating (calcination) was found. Pure nanocrystalline hydroxyapatite was prepared by hydrothermal synthesis at 160°C from mono- and dialkylphosphates. The size of hydroxyapatite crystallites was about 1 nm, the particle size about 150 nm. Agglomerated particles of hydroxyapatite larger than 2 μm were prepared at 200°C. Hydrothermal reaction of trialkylphosphates with Ca²⁺ ions at 200°C produced CaHPO₄. The experimental results were used to propose a reaction mechanism for base-catalyzed hydrothermal reactions of alkylphosphates with Ca²⁺ ions. Received October 4, 2001. Accepted (revised) November 19, 2001