Thermokinetic Studies Research Articles

Thermokinetic Study on the Growth Metabolism of Ura-auxotrophic Mutant of

Thermokinetic Study on the Growth Metabolism of Ura-auxotrophic Mutant of

Thermo-kinetic and Spectral Studies of Cobalt(II), Nickel(II) and Copper(II) Complexes With Di(3-chloro-4-methylphenyl)carbazone

New complexes of Co(II), Ni(II) and Cu(II) with di(3-chloro-4-methylphenyl) carbazone having the general formula [M(DCMPC) 2 ] [where M=Co(II), Ni(II) or Cu(II); DCMPC=di(3-chloro-4-methylphenyl)carbazone] have been synthesized and characterized by elemental analyses, magnetic moment measurements, Uv-Vis., IR, EPR and thermal studies. The DCMPC behaves as a bidentate monoanionic ligand coordinating through the ketonic oxygen and azo nitrogen. The interpretation, mathematical analyses of the thermoanalytical data (TG and DTA) and evaluation of kinetic parameters are presented in this communication. The energy of activation for the two clear-cut steps of decomposition for all the complexes are compared by employing the Freeman-Carroll equation, the integration method using the Coats-Redfern equation and the approximation method using the Horowitz-Metzger equation. The Coats-Redfern equation was extended to evaluate other kinetic parameters such as pre-exponential factor and entropy of activation.

Thermo-kinetic and Spectral Studies of Lanthanide(III) Complexes with 2-Hydroxy-l -benzylidene-2-furoyl Hydrazine

Thermo-kinetic and Spectral Studies of Lanthanide(III) Complexes with 2-Hydroxy-l -benzylidene-2-furoyl Hydrazine

Thermokinetic Studies of the Process for Electrorefining Silver

In this work some calorimetric measurements were also carried out on the electrorefining silver by using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat ( $$Q$$ m) to the input electric energy ( $$Q$$ in) and the excess heat ( $$Q$$ ex), i.e., difference between $$Q$$ m and $$Q$$ in during the electrorefining process, were discussed in terms of general thermodynamics. It was found that the R and $$Q$$ ex for silver were related with the current density or cell voltage employed in the experiment. The results obtained here also indicate that the heat generation under different conditions, such as different currents or voltages may be caused partially by the irreversibility of the process or by some unknown processes.

Thermokinetic Studies of Porphyrin Complexation in Non-Aqueous Solutions by Heat Conduction Microcalorimetry

Abstract Porphyrins are known as unique ligands forming some of the most stable complexes with various metal ions. In this work the thermokinetic investigations of complex formation of tetraphenylporphyrins with copper(II) acetate were carried out in two anhydrous organic solvents: acetic acid and DMF at 25C. Measurements were performed in a heat conduction microcalorimeter [7] adapted for non-aqueous solvents. Total heat effects and thermokinetics were determined. The results were discussed together with spectrophotometric data. Taking into account the high stability of metalloporphyrin complexes, the heat of their formation is rather small (in the case of acetic acid ΔQ=32.71.2 kJ mol−1, for DMF ΔQ=26.21.3 kJ mol−1). Such result can suggest that: 1) the stability of complexes is influenced strongly by an entropy factor, 2) the complexation involves breaking of the NH-bond in the porphyrin coordination centre, accompanied by high consumption of energy.

Calorimetric Studies of Hydration of Cementitious Materials Varying in Basicity

This paper presents results of thermochemical and thermokinetic studies of the hydration of portland cement, alkaline cements with mineral additives and slag alkaline binder. The influence of the modulus of basicity of the binders on the thermochemical and thermokinetic characteristics of hydration was estimated.

Heats of chemisorption ofn-Aliphatic alcohols on α-Al2O3 at 25–200°C

A differential microcalorimeter (E. Calvet) was used to study the processes of adsorption of five aliphatic alcohols (C1-C5) on α-Al2O3 at 25, 50, 100, 150 and 200°C. In particular, the importance of the thermokinetic study of the chemisorption of such alcohols at different experimental temperatures was demonstrated, with regard to the variations in the thermokinetic parameters (tmax, t1/2 and t0) and the evolution of the alcohol vapor pressure on the adsorbent during the adsorption process. It was concluded that: a) all the heat emission peaks of alcohol adsorption have the same rounded shape at 25°C; b) on passing from methanol to 1-pentanol, the area of the adsorption peaks increases as the chain length or molecular weight increases; c) on passing from 25 to 200°C, the shape of the adsorption peaks becomes more pointed.

Thermo-kinetic research methods for simple order reactions: Analog curve and characteristic parameter methods

Abstract In order to simplify the thermo-kinetic research method and study faster reactions, two novel thermo-kinetic research methods, namely the thermo-analytical analog curve and characteristic parameter methods, have been proposed in this paper. The general formulae for calculating kinetic parameter K n and rate constant k n have been derived. The thermo-kinetics of five reactions with first, second, third, and fractional orders, respectively, have been studied with these methods, and their validity has been verified by the experimental results.

Thermokinetic Study of the Limited Growth of Bacteria

Thermokinetic Study of the Limited Growth of Bacteria

Thermokinetic studies of the product inhibition of single-substrate, enzyme-catalyzed reactions

A thermokinetic reduced extent method for the product inhibition of single-substrate, enzyme-catalyzed reactions is proposed in this paper. By analyzing the calorimetric curves of these reactions, this method can be conveniently used to calculate both kinetic parameters ( K m, K i and V m) and molar reaction enthalpy ( Δ r H m), and to establish the type of product inhibition simultaneously without adding product. The arginase-catalyzed hydrolysis of L-arginine has been studied by microcalorimetry and the product, L-ornithine, has been established as a competitive reversible inhibitor. The kinetic parameters calculated with this method are in agreement with those given in the literature.

Thermokinetic studies of the irreversible inhibition of single-substrate, enzyme-catalyzed reactions

A thermokinetic ratio method for the irreversible inhibition of single-substrate enzymecatalyzed reactions is proposed in this paper. By analyzing a measured curve this method can be used to calculate the apparent rate constant of the inhibited reaction without letting the reaction go to completion. Using the LKB-2107 batch microcalorimeter, the arginase-catalyzed hydrolysis of L-arginine in the presence of p-chloromercuribenzoate (PCMB) has been studied and PCMB established as an irreversible mixed inhibitor. The second-order rate constants for inhibition of arginase by PCMB in the absence and presence of L-arginine have been determined by this ratio method to be k EI = 94.4 M − s −1 and k ESI = 35.2 M −1 s −1, respectively, at 298.15 K. Chemical modification with PCMB indicates that arginase contains three reactive cysteinyl residues at most but these residues are not present at the active site of arginase.

Thermokinetic features of the early stages of hydration of slag alkaline binders

This paper presents results of thermokinetic studies on the early stages of hydration of some slag minerals, slag alkaline binders of traditional and new-generation compounds. A possibility of adjustment and control of hardening processes through thermokinetic indices of hydration (intensity and completeness of heat evolution) for various compounds, types and quantities of the alkaline components and temperatures is proved.

Application of a reduced-extent method to thermokinetic studies of enzyme-catalyzed reactions

The relationship between the rate of enthalpy change of a chemical reaction and the formation rates of its constituents is derived, and then transformation equations for the thermokinetics of single-substrate enzyme-catalyzed reactions are deduced, and the validity and prerequisite of application of the chemical amplification of enthalpy changes to thermokinetic investigations are proved. A reduced-extent method is applied to thermokinetic studies of enzyme-catalyzed reactions, and then a reduced-extent equation for the kinetics and a mathematical model for the thermokinetics of the single-substrate enzyme-catalyzed reaction are suggested. According to this model, the kinetic parameters and molar enthalpy can be calculated simultaneously with the data from a single thermogram. Three enzymatic reaction systems have been investigated with a heat conduction calorimeter, and the thermokinetic research method in this paper is discussed in detail.

Application of thermogram reconstruction to thermokinetic studies with conduction calorimeters

The application of thermogram reconstruction and the reduced extent method to thermokinetic studies of chemical reactions is proposed in this paper. The reliability of this has been verified by experimental results.

A thermokinetic study of bacterial metabolism

Thermograms of growth metabolism, endogenous metabolism and non-growth metabolism of resting cells of E. coli were obtained using an LKB-2277 Bioactivity Monitor. From these thermograms it can be established that the thermokinetic equation for the growth metabolism of E. coli is d p/d t = k 1 p, with order of metabolism n = 1, k 1 = 0.03993 min −1 ( k 1, multiplication rate constant; p, power output; t time). The corresponding thermokinetic equation for the non-growth metabolism of resting cells is d p/d t = 0, k o = 0. The equation for endogenous metabolism is dependent on the previous equation, but it can be divided into two parts: at an early phase, d p/d t = 0, k 0 = 0; at a later phase, d p/d t = k −1 p, n = 1, k −1 = −0.01769 min −1. Thus, thermokinetic equations for the various different kinds of metabolism in cells (in this case, bacteria) can be obtained by microcalorimetric methods.

Thermokinetic studies in adsorption and heterogeneous catalysis

Thermokinetic studies in adsorption and heterogeneous catalysis

A thermokinetic study of the clathration of isomeric xylenes by the Ni(NCS)2 (4-methylpyridine)4 host

A detailed analysis of the thermokinetic course of the reaction α-Ni(NCS)2(4-methylpyridine)4+xylen-e»β-Ni(NCS)2 (4-methylpyridine)4·(xylene) (at 25 °C), for 21 samples of purep-xylene andm-xylene, as well as two-and three-component mixtures of theo-,m-andp-isomers was performed by using the dynamic optimization method. The mechanism of the reaction is discussed. Firstly, a relatively rapid α»β-phase transformation and uptake of 60–80% of the total guest takes place. Then follows the slower diffusion-controlled absorption of xylene up to the maximum filling corresponding to 1:1 guest/host stoichiometry.

Thermokinetic studies for reactions of lanthanum(III) and nickel(III) oxides with barium perchlorate trihydrate

TG, DTG and DTA have been used in non-isothermal investigations of binary systems of Ni 2O 3 and La 2O 3 with barium perchlorate trihydrate, BP·3 H 2O, in various molar ratios, carried out under an air (static) atmosphere from ambient to 1000°C. Ni 2O 3 catalysed the dehydration process of BP·3 H 2O and lowered its T f by 20°C. The discontinuity on the TG curve due to an incomplete perchlorate—chlorate reaction vanished in the presence of either of the oxides: a mechanism is proposed. La 2O 3 lowered T f by 50°C; T i for the decomposition of BP was lowered by 150 and 100°C in the presence of La 2O 3 and Ni 2O 3, respectively. X-Ray diffractometry did not reveal any reaction between BP and the two oxides. Kinetic parameters for the decomposition steps in the presence of either of the oxides have been determined.

Energetics of the adsorption of Cu(II) on activated sludge

Dried activated sludge (DS) and thermally modified samples (MDS) [1] were used as adsorbents of Cu(II) from water at zero and 0.1 ionic strength. Three mechanisms are essentially implied at the solid-liquid interface: 1. ion exchange of free metals and hydroxo-complexes with surface protons 2. adsorption and hydrolysis at the surface 3. hydrolysis followed by an adsorption reaction The use of activated sludge as adsorbent is also justified by its bacterial nature [2]. Experimental Two kinds of adsorbent were prepared: the samples obtained from a pilot plant were thickened and dried at 100 °C in air, powdered and sieved in the 42–200 mesh range (DS), and heated at 110 °C in air for 24 h (MDS). The BET surface evaluation resulted in 2±0.1 m 2/g for DS and 0.5±0.1 m 2/g for MDS; this may be interpreted assuming that grain agglomeration takes place. The calometric experiments were carried out using a SETARAM rotating C.R.M.T. calorimeter [3], with a cell we constructed because of the impossibility of any handling from outside after introduction of the sample. The method has already been described in detail [4]. Results and Discussion In Fig. 1 we have reported the enthalpies of displacement, -H12 (J/g), as a function of the specific quantities of Cu(II) adsorbed, n 2s (mg/g). ▪ Heat changes measured are actually heats of displacement, the water being gradually replaced by the solute [3]. The trend of the enthalpies of displacement in Fig. 1 considering influence of the thermal treatment shows that the MDS exhibit at every surface coverage a higher enthalpy of displacement; this fact is interpreted by supposing that the thermal treatment favours the exhibition at the surface of chemical and polar groups capable of strong interaction with the Cu(II) ions. This fact could be interpreted as due to an increase in the electrical potential of the Stern Gouy diffuse layer [5] with a consequent more difficult diffusion of Cu(II) ions toward the polar surface: analogous results have been obtained on an oxide surface [6]. From the analysis of calometric peaks, relative to DS and MDS samples, we can deduce that the thermokinetic trend is somewhat different, the MDS showing an apparently smaller reaction rate. Starting from the hypothesis that the rate determining step is the diffusion of the solute, we have tried to apply a semiempirical treatment assuming a time dependence of the diffusion equation [8]. In Fig.2 we have reported the function: F(t) = log P + 3 2 log t where P ≅KW is the instantaneous deviation of the calorimeter vs. the reciprocal of time. The linearity of the curves in Fig. 2 is satisfactory enough both for DS and MDS samples. ▪ The MDS samples show a greater slope, that means a smaller diffusion coefficient; that would correspond to a more dense Gouy layer; in other words, the MDS sample that exhibits a greater number of polar and ionic groups would have a higher repulsive potential field in the diffuse layer. We may conclude that kinetic [1] and thermokinetic studies are in agreement and show that the initial uptake rate is smaller on MDS than DS; but the limiting adsorption quantities are higher for the former. This situation could be interpreted by assuming that the determining step is the diffusion of the ions through the double layer which should be characterized by a higher electrical potential in the case of MDS.

Comportement des calorimetres a conduction dans le domaine des basses frequences

The behaviour of conduction calorimeters has been studied in the field of low frequencies. Limitations of the procedure are described in the case of thermokinetic studies. The method discussed here is based upon the study of the transfer function of the calorimeters. Experimental data show that it is necessary to correct signals given by instruments (by physical or numerical techniques).