Change In Free Energy Of Activation Research Articles

Thermal properties of graphene oxide prepared from different agricultural wastes

Graphene oxide (GO) extracted from different agricultural wastes such as sugarcane bagasse (SCB), rice straw (RS), lignin (L), mature beech pinewood sawdust (MW) in the presence and absence of ferrocene as a catalyst at 300℃ in a muffle have been prepared, characterized and evaluated by TGA and DTA. TGA decomposition curves of GO showed three decomposition stages for all studied samples except for GO prepared from SCB and MW in the absence of ferrocene, which revealed two decomposition stages. The residual weight of SCB was very low; this indicates its high purity and absence of inorganic residues. The high production of char residue from MW, and L pyrolysis can be ascribed to its lower content of methoxyl group (determined by FTIR). The activation energy (Ea) determined for thermal reduction of GO are found to be from 21.00 to 55.35 kJ/mol. From TGA, it was found that the rate of removal of oxygen-containing functional groups depends on the temperature, which agrees with the experimental findings and thermal degradation kinetics. The free energy change of activation (∆G) of this system is positive. Consequently, the thermodynamics of GO should be non spontaneous.

Ionic-interaction of aqueous and alcoholic poly(vinyl alcohol) in the presence of protons

The ionic-interactions of acetic acid in H2O-PVOH and H2O-Alcohol-PVOH solvent systems were studied at different temperatures by viscosity method. The viscosities of the poly(vinyl alcohol) were increased with the increase in the concentration of poly(vinyl alcohol) and decreased with the increase in the concentration of acetic acid. The viscosity data were used to evaluate the ion-ion interactions and ion-solvent interactions in terms of ?A? and ?B? coefficients of the Jones-Dole equation respectively. The negative values of B-coefficient increased with increase in temperature showed that acid behaves as structure breaker in poly(vinyl alcohol)-solvent mixtures and consequently the values of A-coefficient were decreased with the rise of temperature. Thermodynamic parameters such as energy of activation (Ea*), free energy change of activation (?G*) and entropy change of activation (?S*) were also calculated as a function of acid (CH3COOH) concentration, poly(vinyl alcohol) composition, alcohols, and temperature.

FTIR and thermodynamic study of Pakistani and international crude oils in 1,4-dioxane

ABSTRACTThis paper is the continuation of our previous paper, which concerned the viscosity of crude oils in 1,4-dioxane. In this paper, we present the Fourier Transform Infrared (FTIR) spectroscopy and thermodynamic study of Pakistani and International crude oils. Degree of branching, chain length, and degree of substitution in aromatic by FTIR data were calculated. Thermodynamic parameters viz., energy of activation (Eη), free energy change of activation (ΔG*), latent heat of vaporization (Lv), and entropy change of activation (ΔS*) have also been evaluated.

Conductometric, spectrophotometric and thermodynamic studies of nickel sulfate in aqueous polyvinyl alcohol + methanol systems at different temperatures

The electrical conductance of nickel sulfate (NiSO 4 .6H 2 O) solutions in aqueous, aqueous polyvinyl alcohol (PVOH; 0.1, 0.5 and 0.9 g/dL), aqueous methanol (CH 3 OH) system (30%, v : v ) and aqueous PVOH+CH 3 OH systems were measured in the concentration ranges 0.4×10 -2 to 10×10 -2 mol/L, at different temperatures (298, 303, 308, 313 and 318 K). Ionic interactions of nickel sulfate in aqueous and mixed solvent systems were measured by conductometric analysis. Different relations were used to evaluate conductometric data, for the calculation of molar conductance, molar conductance at infinite dilution (Ʌ° m ), degree of dissociation ( a ), dissociation constant ( K d ) and Walden product. The increased in Ʌ° m values with the increase in percent composition of aqueous PVOH, show that PVOH interaction with solvents (water and methanol) was higher as compare to PVOH interaction with NiSO 4 . Solvent effect was also studied by spectrophotometric analysis of NiSO 4 in aqueous, aqueous PVOH and aqueous PVOH + CH 3 OH system. Thermodynamic parameters for dissociation process such as energy of activation ( E a # ), free energy change of activation (Δ G d # ), enthalpy change of activation (Δ H d # ), and entropy change of activation (Δ S d # ) were also calculated as a function of temperature and solvent composition.

Spectrophotometric Study on Kinetics of Solvatochromism of Methyl Violet in Aqueous Methanol

AbstractThe kinetics of the reaction of methyl violet with iodide in aqueous methanol system was studied by spectrophotometric method. The rate of reaction of methyl violet in different alcoholic composition in presence of potassium iodide was observed at pH 4 and 6 at various temperatures (298–318 K). Solvatochromic effect was studied in different percentages of methanol (0–50%). Bathochromic shift was observed with the decrease in polarity of solvent. The color change was attributed to molecule's structure, the delocalization of unit electrical charge causes deepening of color and decrease of delocalization causes fading of color due to reduction of dye. Increase in the rate of reaction was observed with increase in alcoholic content and also affected by potassium iodide salt and increased with increase in concentration of potassium iodide. Energy of activation (Ea) and transition energy (ET) were calculated with the help of kinetic data. Thermodynamic parameters such as enthalpy change of activation (ΔH*), Gibbs free energy change of activation (ΔG*) and entropy change of activation (ΔS*) were evaluated as a function of concentration of solvent and salt.

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.

Spectroscopic characterizations and biological studies on newly synthesized Cu 2+ and Zn 2+ complexes of first and second generation dendrimers

The novel Cu(II) and Zn(II) complexes of first and second generation poly(propylene amine) dendrimers (PPA), comprising 1,8-naphthalimde units on periphery have been synthesized. These new complexes were characterized by elemental analysis, molar conductivity, spectral methods (IR, 1H NMR and UV–vis spectra) and thermal analysis (TG and DTG) techniques. From elemental analysis as well as thermal studies it has found that the first generation dendrimer behaves as bidentate ligand and forming chelates with 1:2 (ligand:metal) and 1:4 (ligand:metal) stoichiometry for second generation dendrimer. Different kinetic parameters namely activation energy (Δ E*), enthalpy of activation (Δ H*), entropy of activation (Δ S*) and free energy change of activation (Δ G*) are calculated using Coats–Redfern equation. The antibacterial activity of dendrimers and their complexes was evaluated against some Gram positive and negative bacteria.

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.

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.

Spectroscopic, and thermal studies of some new binuclear transition metal(II) complexes with hydrazone ligands containing acetoacetanilide and isoxazole

A new chelating ligand, 2-(2-(5- tert-butylisoxazol-3-yl)hydrazono)- N-(2,4-dimethylphenyl)-3-oxobutanamide (HL), and its four binuclear transition metal complexes, M 2(L) 2 (μ-OCH 3) 2 [M = Ni(II), Co(II), Cu(II), Zn(II)], were synthesized using the procedure of diazotization, coupling and metallization. Their structures were postulated based on elemental analysis, 1H NMR, MALDI-MS, FT-IR spectra and UV–vis electronic absorption spectra. Smooth films of these complexes on K9 glass substrates were prepared using the spin-coating method and their absorption properties were evaluated. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Different thermodynamic and kinetic parameters namely activation energy ( E *), enthalpy of activation (Δ H *), entropy of activation (Δ S *) and free energy change of activation (Δ G *) are calculated using Coats–Redfern (CR) equation.

Nickel(II) and copper(II) complexes containing 2-(2-(5-substitued isoxazol-3-yl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione ligands: Synthesis, spectral and thermal characterizations

Two new hydrazone chelating ligands, 2-(2-(5-methylisoxazol-3-yl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione (HL 1) and 2-(2-(5- tert-butylisoxazol-3-yl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione (HL 2), and their nickel(II) and copper(II) complexes were synthesized using the procedure of diazotization, coupling and metallization. Their structures were postulated based on elemental analysis, 1H NMR, ESI-MS, FT-IR spectra and UV–vis electronic absorption spectra. Smooth films of these complexes on K9 glass substrates were prepared using spin-coating and their absorption properties were evaluated. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential thermogravimetry (DTG). Different thermodynamic and kinetic parameters namely activation energy ( E ∗), enthalpy of activation (Δ H ∗), entropy of activation (Δ S ∗) and the free energy change of activation (Δ G ∗) were calculated using the Coats–Redfern (CR) equation.

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.

Thermodynamics of Light‐induced and Thermal Degradation of Bacteriochlorins in Reaction Center Protein of Photosynthetic Bacteria

The rate constants of thermal (irreversible) damage of bacteriochlorin pigments (bacteriochlorophyll monomer [B], bacteriochlorophyll dimer [P] and bacteriopheophytine [H]) in reaction center [RC] protein from the photosynthetic bacterium Rhodobacter sphaeroides were studied in the dark and during intense (400 mW x cm(-2)) laser light excitation (wavelengths 488 and 515 nm) under deoxygenated conditions. While the kinetics of degradation of P and B were monoexponential, the decay kinetics of H were overlapped by an initial lag phase at elevated (>40 degrees C) temperature. This is explained by removal of the central metal ion from the bacteriochlorophylls as part of their degradation processes. At all temperatures, the rates of damage were very similar for all bacteriochlorin pigments and were larger in the light than in the dark. The logarithm of the rate constant of pigment degradation and loss of photochemistry as a function of reciprocal (absolute) temperature (Arrhenius/Eyring plot) showed single phase in the light and double phases in the dark. Below 20 degrees C, the rate of pigment degradation in the RC decreased so dramatically in the dark that it became limited by the natural degradation process of bacteriochlorophyll measured in solution. The function of loss of photochemistry in the dark was also biphasic and had a break point at 40 degrees C. The damage in the dark required high enthalpy change (DeltaH(++) = 64 kcal/mol for P and DeltaH(++) = 60 kcal/mol for B) and entropy increase (T x DeltaS(++) = 38 kcal/mol for P and T x DeltaS(++) = 34 kcal/mol for B at T = 300 K), whereas significantly smaller enthalpy change (DeltaH(++) = 21 kcal/mol for P and B and DeltaH(++) = 13 kcal/mol for H) and practically no (T x DeltaS(++) = -1 kcal/mol for P and B at T = 300 K) or small (T x DeltaS(++) = -9 kcal/mol for H at T = 300 K) entropy change was needed in the light. The thermodynamic parameters of activation reveal major steps common in the degradation of all bacteriochlorin pigments: ring opening reactions at C5 or C20 meso-bridges (or both) and breaking/removal of the phytyl chain. Their contribution in the degradation is probably reflected in the observed enthalpy/entropy compensation at an almost constant (DeltaG(++) = 22-26 kcal/mol at T = 300 K) free energy change of activation.

Metal complexes of antibiotic drugs. Studies on dicluxacillin complexes of Fe II, Fe III, Co II, Ni II and Cu II

The synthesis and characterization of dicluxacillin (DC) complexes with di- and tri-valent metal ions are described. The nature of bonding of the chelated DC and its metal complexes structures have been elucidated on the basis of their spectroscopic (infrared, solid reflectance, magnetic spectra, mass and thermal analysis) properties. In all the complexes studied, the DC acts as a chelate monoanionic ligand with coordination involving the carboxylate O atom and the endocyclic N of the thiazole ring. The DC ligand forms mono-ligand complexes of the general formula [M(DC)(H 2O) x (A)]. yH 2O where DC is the uninegatively charged bidentate ligand and A=OAc in case of Cu II and Cl in case of Fe III, Fe II, Co II and Ni II ions. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordinating capacity of the ligand. From the thermal decomposition curves, the water molecules of crystallization are removed in a single stage while the decomposition of the ligand and coordinated water molecules occur in the second and subsequent stages. Different thermodynamic kinetic parameters namely activation energy ( E*), enthalpy of activation (Δ H*), entropy of activation (Δ S*) and free energy change of activation (Δ G*) are calculated using Coats and Redfern equation.

Thermodynamic and Kinetic Stabilities of Hen-Egg Lysozyme and Its Chemically Modified Derivatives: Analysis of the Transition State of the Protein Unfolding

For the stabilization of a protein against irreversible denaturation caused by rapid reaction of the unfolded form of the protein (kinetic stabilization), the free energy change of activation for unfolding should be increased. First, we demonstrated that this strategy was effective to stabilize a protein against protease digestion. For kinetic stabilization, it is important to stabilize a protein at a site where the local structures are largely unfolded in the transition state for unfolding. We developed a method to find such sites by comparison of the thermodynamic stabilities and the unfolding rate constants between unmodified and modified proteins. Application of this method to analyze the transition state of hen-egg lysozyme using some chemically modified derivatives is also described. Moreover, it was confirmed that the protease digestion method is superior to the relaxation method for estimation of the unfolding rate constant. Namely, the protease digestion method may be useful in analyzing the transition state of protein unfolding.

β-Cyclopiazonate oxidocyclase from Penicillium cyclopium. II. Studies on electron acceptors, inhibitors, enzyme kinetics, amino acid composition, flavin prosthetic group and other properties

1. 1. 2,6-Dichlorophenolindophenol, phenazine methosulphate and cytochrome c were effective electron acceptors in the dehydrogenation reaction catalysed by the β-cyclopiazonate oxidocyclases. Oxygen was an effective terminal electron acceptor, but only in the presence of phenazine methosulphate as an intermediate electron carrier. Other electron acceptors and carriers were studied as was the effect of various metal ions and possible inhibitors. Most bivalent metal ions were found to inhibit the enzymes. Inhibition of the dehydrogenation and cyclization reactions by 2,4-dinitro-1-fluorobenzene and l-1-tosylamide-2-phenylethylchloromethyl ketone indicates the possible roles of amino groups and the histidine imidazole group in these reactions. Similar conclusions were made from studies of the effect of pH on the reactions. Mechanisms involving the abovementioned groups are proposed for the dehydrogenation as well as the cyclization reaction. 2. 2. The thermodynamic properties of the isoenzymes were found to be similar. With respect to the dehydrogenation reaction, the following values were found: activation energy ( E a approx. 7.2 kcal· mole −1); enthalpy change of activation ( ΔH ∗ approx. 6.6 kcal·mole −1); entropy change of activation ( ΔS ∗ approx. −42 cal·mole −1. degree −1); and free energy change of activation ( ΔG ∗ approx. 19.3 kcal·mole −1). The five isoenzymes were also similar with respect to their response towards inhibitors and electron acceptors; K m values for 2,6-dichlorophenolindophenol ( K m approx. 1.6 μM, isoenzyme II somewhat higher) and catalytic constants ( k 2 approx. 0.048 sec −1, isoenzyme II somewhat lower). 3. 3. The isoenzymes of β-cyclopiazonate oxidocyclase differed in the order of the dehydrogenation reaction with respect to β-cyclopiazonic acid, the half periods of the dehydrogenation reaction, the Michaelis constants for β-cyclopiazonic acid (2.1–14 μM), amino acid composition as far as the ratio of basic to acidic amino acids are concerned, and ammonia and carbohydrate content. 4. 4. All the isoenzymes contained one covalently linked molecule of flavin per molecule of enzyme. Absorption spectra of the isoenzymes showed characteristic peaks at 276, 366 and 450 nm and a shoulder at 290 nm. Their fluorescence emission spectra showed a peak at about 527 nm and the flavin residue (most probably FAD), released by proteolytic digestion with pronase showed a fluorescence peak at 518 nm similar to that of FMN and FAD.