Activation Entropy Change Research Articles

Ionic studies of sodium alginate isolated from Sargassum terrarium (brown algea) karachi coast with 2,1-electrolyte

Physical and chemical analysis of the polysaccharide isolated from Sargassum Terarrium (brown algae) of Karachi coast showed characteristics of the sodium alginate. Optical rotations and sulphated ash content were found and FTIR spectra showed a sharp and strong absorption band at 1600cm−1 representing carboxylate ion which conforms high uronic acid content of the product. The viscosities of aqueous 0.1% sodium alginate solution were measured in the presence of copper II chloride (CuCl2). The viscosities were found to be increased with the increase in the concentration of electrolyte. Viscosities were also found affected with temperature. ‘A’ and ‘B’ coefficients of Jones–Dole equation were evaluated. The increase in positive values of ‘B’ coefficient with the rise of temperature led to conclusion that given electrolyte in 0.1% aqueous sodium alginate solution behaves as structure maker. Thermodynamic parameters regarding to activated state like energy of activation Eη, change in free energy of activation ΔGη and change of entropy of activation ΔSη were also evaluated. Straight-line plots of log η versus 1/T observed with positive slopes show the effect of temperature on the viscosities of solutions. Energy of activation (Eη) was found to be decreased with the rise of temperature. Change in free energy of activation (ΔGη) was also found to be increased with increase in concentrations of electrolyte and also with rise of temperature. The values of change in entropy of activation (ΔSη) were also calculated. Negative values of ΔSη were found to be increased with increase in concentration of electrolyte and also with rise of temperature.

Kinetics and mechanism of extraction of Cu(II) by CYANEX 302 from nitrate medium and oxidative stripping of Cu(I) using Lewis cell technique

The extraction of Cu(II) from nitrate medium using CYANEX 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) in kerosene under equilibrium conditions showed that copper is first extracted as Cu 2+ followed by reduction of CuA 2 (HA) 2 to Cu + while the CYANEX 302 extractant is correspondingly oxidized. The stripping of Cu(II) from loaded organic solutions by using different stripping agents showed that effective stripping is obtained upon using high concentration of nitric acid which oxidizes the extracted Cu(I) to Cu(II). In the present work, the forward extraction kinetics of Cu(II) from nitrate medium using CYANEX 302 in kerosene and kinetics of oxidative stripping of Cu(I)-CYANEX 302 chelate have been investigated using a Lewis cell. Extraction and stripping rates are governed by reactions at liquid–liquid interface rather than in the bulk phase. Extraction and stripping regimes are deduced to be chemical-controlled for Cu(II) and Cu(I). The different parameters affecting the extraction rate were separately studied and the extraction mechanism is discussed according to the dimeric model of CYANEX 302 in non-polar solvent. The stripping of Cu(I) from loaded organic solutions was achieved by using high concentration of nitric acid which oxidizes the extracted Cu(I) to Cu(II). Kinetic studies on the stripping of Cu(I) from loaded CYANEX 302 with nitric acid were also carried out using the same Lewis cell, and the mechanism of stripping process has been also proposed. From the temperature dependence of the rate measurement, the values of activation energy ( E), enthalpy change (Δ H) and entropy change (Δ S) are calculated for both systems.

Viscosities of ammonium salts in water and ethanol + water systems at different temperatures

Viscosities of different concentrations of ammonium chloride and ammonium bromide from 1 × 10 − 2 to 9 × 10 − 2 mol dm − 3 solutions in aqueous and aqueous alcoholic (10% v/v ethanol) mixtures were measured at temperatures ranging from 298 to 323 K respectively. It was observed that the viscosity of solution increased with the increase in the concentration of salts (ammonium chloride and ammonium bromide) in aqueous system and decreased in aqueous ethanol system. The viscosity data were used to evaluate ion–ion interactions and ion–solvent interactions in terms of ‘ A’ and ‘ B’ coefficients of Jones–Dole equation respectively. The positive values of B-coefficient for ammonium chloride and ammonium bromide in aqueous system indicate that ammonium chloride and ammonium bromide behave as structure maker in aqueous system while in aqueous ethanol system structure breaking behaviour was observed. With the help of viscosity data, the activation parameters such as energy of activation ( E η), free energy change of activation (Δ G⁎) and the entropy change of activation (Δ S⁎) were evaluated as a function of salt concentration, solvent composition and temperature.

Kinetics, equilibrium and thermodynamic study on removal of Cr (VI) from aqueous solutions using low-cost adsorbent Alligator weed

The removal of Cr (VI) from aqueous solutions using Alligator weed, a freshwater macrophyte, was investigated as a function of initial pH, contact time, reaction temperature and adsorbent concentration in batch studies. An initial solution pH of 1.0 was most favorable for Cr (VI) removal. The kinetic experimental data fitted the pseudo-second-order equation, Elovich equation and Langmuir–Hinshelwood equation very well. The adsorption of Cr (VI) onto Alligator weed conformed to the linear forms of the Langmuir, Freundlich and Temkin equations. The removal efficiencies increased with the increased adsorbent dose from 1 to 8 g/L and were 86.6, 97.6 and 99.7% at the adsorbent dose of 8 g/L, solution pH 1.0 and temperatures of 30, 40 and 50 °C, respectively. Thermodynamic parameters (activation enthalpy change, activation entropy change and activation free energy change) revealed that the adsorption of Cr (VI) onto Alligator weed is endothermic, non-spontaneous, with a decreased randomness in nature.

Ionic interaction of electrolyte with dilute solution of poly(vinyl alcohol) at different temperatures

The ionic interactions of ZnSO4 · 7H2O were studied, using dilute solution of polymer as a solvent. The ionic conductance of ZnSO4 · 7H2O in aqueous and mixed solvent systems of aqueous poly(vinyl alcohol) (0–0.9%) was measured in concentration range (2 × 10−3 to 10 × 10−2 m dm−3) at different temperatures (25–45°C), respectively. Conductance data were analyzed by Ostwald dilution law to get the limiting molar conductance (λm°). The limiting molar conductance () decreased with the increase in the composition of polymer showing decreased ion–solvent interaction. Walden product, degree of dissociation and dissociation constant were also calculated using conductance data. Thermodynamic parameters such as free energy change of activation (ΔG*), enthalpy change of activation (ΔH*) and entropy change of activation (ΔS*) were also calculated at various temperatures as function of concentration of electrolyte in aqueous and mixed solvent systems.

Isomers in the excited state of electron-transferring flavoprotein from Megasphaera elsdenii: Spectral resolution from the time-resolved fluorescence spectra

Electron-transferring flavoprotein (Holo-ETF) from Megasphaera elsdenii contains two FAD’s, one of which easily dissociates to form Iso-ETF (contains one FAD). Time-resolved fluorescence of FAD in Iso-ETF, and Holo-ETF were measured at 5 °C and 25 °C. Wavelength-dependent fluorescence decays of the both ETF at 5 °C and 25 °C were analyzed to resolve them into two independent spectra. It was found that Iso-ETF displayed two spectra with lifetime of 0.605 ns (emission peak, 508 nm) and with lifetime of 1.70 ns (emission peak, 540 nm) at 5 °C, and with lifetime of 0.693 ns (emission peak, 508 nm) and with lifetime of 2.75 ns (emission peak, 540 nm) at 25 °C. Holo-ETF displayed two spectra with lifetime of 0.739 ns (emission peak, 508 nm) and with lifetime of 2.06 ns (emission peak, 545 nm) at 5 °C, and with lifetime of 0.711 ns (emission peak, 527 nm) and with lifetime of 3.08 ns (emission peak, 540 nm) at 25 °C. Thus fluorescence lifetimes of every spectrum increased upon elevating temperature. Emission peaks Iso-ETF did not change much upon elevating temperature. Activation enthalpy changes, activation entropy changes and activation Gibbs energy changes of quenching rates all displayed negative. Two emission species in the both ETF may be hydrogen-bonding isomers, because isoalloxazine ring of FAD contains four hydrogen acceptors and one donor.

Effects of introducing negative charges into the molecular surface of thermolysin by site-directed mutagenesis on its activity and stability

Thermolysin is remarkably activated and stabilized by neutral salts, and surface charges are suggested important in its activity and stability. The effects of introducing negative charge into the molecular surface on its activity and stability are described. Seven serine residues were selected, and each of them was changed for aspartate by site-directed mutagenesis in a thermolysin mutant. In the hydrolysis of N-[3-(2-furyl)acryloyl]-glycyl- l-leucine amide, the k cat/ K m values of all mutants were almost similar to that of the wild-type enzyme (WT). However, those of six out of seven mutants were enhanced 17–19 times with 4 M NaCl, being slightly higher than WT. The remaining casein-hydrolyzing activities of the S53D and S65D mutants (Ser53 and Ser65 are replaced with Asp, respectively) after 30-min incubation with 10 mM CaCl 2 at 85 °C were 78 and 63%, being higher than those of WT (51%) and the other mutants (35–53%). S53D was stabilized with increase in the enthalpy change of activation for thermal inactivation while S65D was with decrease in the entropy change of activation. The stability of WT was enhanced by CaCl 2 and reached the level of S53D and S65D at 100 mM, suggesting that S53D and S65D might be stabilized by reinforcement of the Ca 2+-binding structures.

Comparison of the Thermal Stabilities of Reverse Transcriptases from Avian Myeloblastosis Virus and Moloney Murine Leukaemia Virus

Reverse transcriptases (RTs) from avian myeloblastosis virus (AMV) and Moloney murine leukaemia virus (MMLV) have been most extensively used as a tool for conversion of RNA to DNA. In this study, we compared the thermal stabilities of AMV RT and MMLV RT by observing their irreversible thermal inactivation. The temperatures reducing initial activity by 50% in 10-min incubation, T(50), of AMV RT were 47 degrees C without the template-primer (T/P), poly(rA)-p(dT)(12-18), and 52 degrees C with the T/P (28 microM). T(50) of MMLV RT were 44 degrees C without the T/P and 47 degrees C with the T/P (28 microM). Unexpectedly, AMV RT was considerably activated when incubated with the T/P at 45 and 48 degrees C. Such activation was not observed in MMLV RT. These results suggest that AMV RT and MMLV RT are different in the following: (i) The intrinsic thermal stability of AMV RT is higher than that of MMLV RT; (ii) AMV RT is activated by thermal treatment with the T/P at 45-48 degrees C; and (iii) AMV RT is stabilized by the T/P more potently than MMLV RT. Thermodynamic analysis indicates that thermal inactivation of AMV RT and MMLV RT is due to the large entropy change of activation for thermal inactivation.

Physicochemical characterization and ionic studies of sodium alginate from Sargassum terrarium (brown algae)

Physical and chemical analysis of the polysaccharides isolated from Sargassum terrarium (brown algae) of Karachi coast showed characteristics of sodium alginate. The optical rotation and sulphated ash content were found to be −113° and 30.6% respectively. FTIR spectra showed a sharp and strong absorption band at 1600 cm−1 representing carboxylate ion, which confirms high uronic acid content of the product. Viscosity measurements revealed a linear relationship with increases in concentration and decreased with the rise in temperature of aqueous solution of sodium alginate. Thermodynamic parameters were determined by the change in viscosity data as a function of temperature and concentration. The free energy change of activation (ΔGη) increased regularly as the concentration of sodium alginate increased, as well as rises in temperature. Higher values of free energy change of activation, showed the higher association of sodium alginate with water at a given temperature. The values of entropy change of activation (ΔSη) of viscous flow also increased with the increase in concentration and temperature of sodium alginate solution. The high negative values of entropy change of activation (ΔSη) showed that the solution of sodium alginate was more ordered in initial state than the activated one.

Thermodynamic study of monovalent and divalent cations in mixed solvent system by conductance method

The ionic conductivities of potassium chloride (KCl) and calcium chloride (CaCl2) solutions in aqueous ethanol (0 to 50% mixtures) were measured at various concentrations (0.50 × 10−3 to 50 × 10−3 M) and at different temperatures (25 to 45°C) respectively. The viscosities of v/v aqueous ethanol compositions (0 to 50%) at different temperatures (25 to 45°C) were also measured. The conductivity data have been analyzed by various equations to evaluate molar conductivity at infinite dilution (), degree of dissociation (α), dissociation constant (K d), Walden constant, and energy of activation (E a). The values of ion--ion interactions (A) and ion--solvent interactions (B) have been calculated by the Debye--Huckel relation. The increase in value of B with rising temperature led to conclusion that potassium chloride (KCl) and calcium chloride (CaCl2) behave as structure breaker in aqueous ethanol mixtures. The thermodynamic parameters such as free energy change of activation (ΔG #), enthalpy change of activation (ΔH #) and entropy change of activation (ΔS #) have also been calculated.

Synthesis, characterization, cytotoxicity, antibacterial and antifungal evaluation of some new platinum (IV) and palladium (II) complexes of thiodiamines

Some new platinum (IV) and palladium (II) thiodiamine complexes of type [Pt(L) 2Cl 2] and [Pd(L)Cl 2], [where, L = (cyclohexyl- N-thio)-1,2-ethylenediamine (L 1) and (cyclohexyl- N-thio)-1,3-propanediamine (L 2)] have been synthesized. The thiodiamines coordinate as a bidentate N–S ligand. The synthesized platinum (IV) and palladium (II) complexes of the thiodiamines were characterized by elemental analysis, IR, mass, electronic and 1H NMR spectroscopic studies. These complexes were also screened for cytotoxicity, in vitro antifungal and in vitro antibacterial activities. Thermodynamic parameters such as activation energy ( E a), apparent activation entropy ( S #) and enthalpy change (Δ H) for the dehydration and decomposition reactions of one complex has also been evaluated.

Kinetics of Solvent Extraction of Iron(III) from Sulfate Medium by Purified Cyanex 272 using a Lewis Cell

The kinetics of the forward and backward extraction of the title process have been investigated using a Lewis cell operated at 3 Hz and flux or (F) – method of data treatment. The dependences of (F) in the forward extraction on [Fe3+], [H2A2](o), pH, and [HSO4 −] are 1, 0.5, 1, and −1, respectively. The value of the forward extraction rate constant (k f ) has been estimated to be 10−7.37 kmol3/2 m−7/2 s−1. The analysis of the experimentally found flux equation gives the following simple equation: F f =100.13 [FeHSO4 2+] [A−], on considering the monomeric model of BTMPPA and the stability constants of Fe(III)‐HSO4 − complexes. This indicates the following elementary reaction occurring in the aqueous film of the interface as rate determining: [FeHSO4]2++A−→[FeHSO4.A]+. The very high activation energy of 91 kJ mol−1 supports this chemical reaction step as rate-determining. The negative value of the entropy change of activation (−94 J mol−1 K−1) indicates that the slow chemical reaction step occurs via the SN2 mechanism. The backward extraction rate can be expressed by the equation: F b =10−5.13 [[FeHSO4A2]](o) [H+] [H2A2](o) −0.5. An analysis of this equation leads to the following chemical reaction step as rate-determining: [FeHSO4A2](int)→[FeHSO4A]+A(i) −. However, the activation energy of 24 kJ mol−1 suggests that the backward extraction process is intermediate controlled with greater contribution of the diffusion of one or the other species as a slow process. The equilibrium constant obtained from the rate study matches well with that obtained from the equilibrium study.

Enthalpy/entropy driven activation of the first interquinone electron transfer in bacterial photosynthetic reaction centers embedded in vesicles of physiologically important phospholipids

The thermodynamics and kinetics of light-induced electron transfer in bacterial photosynthetic RCs are sensitive to physiologically important lipids (phosphatidylcholine, cardiolipin and phosphatidylglycerol) in the environment. The analysis of the temperature-dependence of the rate of the P +Q A −Q B→P +Q AQ B − interquinone electron transfer revealed high enthalpy change of activation in zwitterionic or neutral micelles and vesicles and low enthalpy change of activation in vesicles constituted of negatively charged phospholipids. The entropy change of activation was compensated by the changes of enthalpy, thus the free energy change of activation (≈ 500 meV) did not show large variation in vesicles of different lipids.

Activation Parameters of the Eu3+/Eu2+ Electrode Reaction in Mixed Solvents

Summary The rate constants for the electrochemical reduction of Eu3+ in water–acetone and water–dimethylformamide solvent mixtures with different parts of the organic component were measured in the temperature range 15°C–40°C. The activation parameters for this reaction were evaluated. While the activation enthalpy does not depend on the composition of the solvent, the activation entropy changes follows the changes of reaction rates. The entropy contribution (responsible for the form of dependence of rate constants on the composition of the solvent) is obviously related to structure changes of the resolvatated particle.

Kinetic and thermodynamic studies of the isothermal curing reaction of the diglycidyl ether of bisphenol A/Ni(II) chelate system

AbstractThe curing reaction of a system consisting of a diglycidyl ether of bisphenol A (DGEBA) based epoxy and a new inorganic complex curing agent based on Ni(II) chelate with ethylendiamine (en) as a ligand was studied with an isothermal Fourier transform infrared (FTIR) technique. The hardener was prepared and characterized by means of FTIR spectroscopy, elemental analysis, and ICP–plasma techniques. The results of kinetic studies with two kinetic models, Horie et al. and Kamal, showed that the Kamal method gave the best fit to the experimental data. The overall values of the rate constants and activation energy for the DGEBA/Ni(en)3Br2 system were calculated. The activation energy of the curing process was also determined by an isoconversional method, which showed that with the progress of curing time, the activation energy increased. Further, the results obtained from thermodynamic studies give the entropy change of activation, which was more negative for the nth‐order path, whereas the activation heat of the reaction was more negative for the autocatalytic path. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1540–1547, 2005

Thermal Stability of α-Amylase from Malted Jowar (Sorghum bicolor)

Malted cereals are rich sources of alpha-amylase, which catalyzes the random hydrolysis of internal alpha-(1-4)-glycosidic bonds of starch, leading to liquefaction. Amylases play a role in the predigestion of starch, leading to a reduction in the water absorption capacity of the cereal. Among the three cereal amylases (barley, ragi, and jowar), jowar amylase is found to be the most thermostable. The major amylase from malted jowar, a 47 kDa alpha-amylase, purified to homogeneity, is rich in beta structure ( approximately 60%) like other cereal amylases. T(m), the midpoint of thermal inactivation, is found to be 69.6 +/- 0.3 degrees C. Thermal inactivation is found to follow first-order kinetics at pH 4.8, the pH optimum of the enzyme. Activation energy, E(a), is found to be 45.3 +/- 0.2 kcal mol(-)(1). The activation enthalpy (DeltaH), entropy (DeltaS*), and free energy change (DeltaG) are calculated to be 44.6 +/- 0.2 kcal mol(-)(1), 57.1 +/- 0.3 cal mol(-)(1) K(-)(1), and 25.2 +/- 0.2 kcal mol(-)(1), respectively. The thermal stability of the enzyme in the presence of the commonly used food additives NaCl and sucrose has been studied. T(m) is found to decrease to 66.3 +/- 0.3, 58.1 +/- 0.2, and 48.1 +/- 0.5 degrees C, corresponding to the presence of 0.1, 0.5, and 1 M NaCl, respectively. Sucrose acts as a stabilizer; the T(m) value is found to be 77.3 +/- 0.3 degrees C compared to 69.6 +/- 0.3 degrees C in the control.

Activation energy, free energy, enthalpy, and entropy changes associated with viscometric changes of extremely to moderately dilute aqueous solutions of polyvinylpyrrolidone at 288.15–313.15 K

AbstractViscometric behavior of polyvinylpyrrolidone (PVP) was investigated for extremely dilute (0.002–0.010 g dL−1), dilute (0.02–0.10 g dL−1), and moderately dilute (0.20–1.00 g dL−1) solutions at 288.15, 290.15, 293.15, 295.15, 298.15, 300.15, 303.15, 305.15, 308.15, 311.15, and 313.15 K. The experimental data were plotted according to Jones–Dole, Fuoss, and Fedors equations. Intrinsic viscosity ([η]) variation with temperature indicated the existence of different hydrodynamic states of PVP in solution at different temperatures. The PVP was found to show polyelectrolyte behavior in extremely dilute solutions, probably attributable to the presence of partially polarizable >CO groups in the chain. Activation energy (ΔE), differential enthalpy (∂ΔH), entropy (∂ΔS), and free energy (∂ΔG) changes of viscous flow were derived from flow velocity and taken into account for interpretation of the results to better understand the hydrodynamic and conformational behavior of PVP. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 47–55, 2004

Entropy‐Driven Asymmetric Synthesis with Chiral Tethers

AbstractThe 2,4‐pentanediol (PD)‐tethered reaction is a stereocontrolled reaction having versatile applicability. When reactant and reagent elements are connected through a PD tether prior to their reaction, stereochemical purity of the product is very high for nine different types of reactions so far studied. Selectivity of one of the reactions shows temperature independency over a wide range from −78 to 150 °C, which indicates that the stereocontrol is driven by the entropy term. The strict stereocontrol of this reaction at high temperatures can be extended to vapor phase reactions performed above 250 °C. To understand how the two methyl groups on the PD tether stereocontrol the reaction, a new parameter, a chiral perturbation factor, is introduced. By this analysis, it is disclosed that the methyl groups promote an activation entropy change for both the diastereomeric processes, and the strict stereocontrol is achieved when the changes have opposite signs. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Multiple forms of soluble invertases in sugarcane juice: Kinetic and thermodynamic analysis

Soluble invertases were partially purified from storage tissue of an early maturing and high sucrose accumulating genotype Co89003 using ammonium sulphate fractionation and DEAE-cellulose column chromatography. The three different acid invertase isoforms named as A-I, A-II and A-III were identified at late grand growth stage of cane development, whereas only one neutral invertase isoform was detected at maturity stage of cane growth. The final purification achieved for A-I, A-II, A-III and neutral invertase isoform was 37, 45, 7 and 17-fold, respectively. The optimum pH values for A-I, A-II, A-III and neutral isoform were observed to be 5.0, 4.5, 4.5 and 7.0, respectively. Apparent Michaelis constant i.e. Km of different acidic isoforms at its optimum pH and temperature varied from 50.0 to 83.3 mM. For neutral invertase isoform, Km value was 44.0mM at its optimum pH and temperature. The highest Vmax/Km value of A-I isoform indicates the maximum kinetic perfection of this isoform and it may be the major vacuolar enzyme involved in sucrose hydrolysis. From the study of effect of temperature on Km and Vmax values of neutral invertase isoform, the enthalpy change, entropy change and energy of activation were observed to be -21.1 kJ mol-1,-40.5 JK-1 mol-1, and 42.5 kJmol-1, respectively. Among the different metal ions tested, manganese chloride strongly inhibited the activity of all soluble acid invertase isoforms and thus, may be utilized to induce early maturity and controlling sucrose inversion in sugarcane thereby increasing sugar recovery.

A role of methionine 100 in facilitating PYP(M)-decay process in the photocycle of photoactive yellow protein.

PYP (photoactive yellow protein) is a photoreceptor protein, which is activated upon photo-isomerization of the p-coumaric acid chromophore and is inactivated as the chromophore is thermally back-isomerized within a second (in PYP(M)-to-PYP(dark) conversion). Here we have examined the mechanism of the rapid thermal isomerization by analyzing mutant PYPs of Met100, which was previously shown to play a major role in facilitating the reaction [Devanathan, S. et al. (1998) Biochemistry 37, 11563-11568]. The mutation to Lys, Leu, Ala, or Glu decelerated the dark state recovery by one to three orders of magnitude. By evaluating temperature-dependence of the kinetics, it was found that the retardation resulted unequivocally from elevations of activation enthalpy (DeltaH( double dagger )) but not the other parameters such as activation entropy or heat capacity changes. Another effect exerted by the mutations was an up-shift of the apparent pK(a) of the chromophore [the pK(a) of a titratable group (X) that controls the pK(a) of the chromophore] in the PYP(M)-decay process. The pK(a) up-shift and the DeltaH( double dagger ) elevation show an approximately linear correlation. We, therefore, postulate that the role of Met100 is to reduce the energy barrier of the PYP(M)-decay process by an indirect interaction through X and that the process is thereby facilitated.