Microcalorimetric Experiments Research Articles

Chiral discrimination of the enantiomers of δ‐phenyl‐δ‐valerolactone by cellulose triacetate: A chromatographic and microcalorimetric study of the thermodynamics

AbstractThe resolution of racemic δ‐phenyl‐δ‐valerolactone by chromatography on cellulose triacetate CTA I results in one of the best separations of optical antipodes observed so far on this chiral stationary phase. The thermodynamics of the stereoselective interaction of the enantiomers of δ‐phenly‐δ‐valerolactone have been studied by chromatography at different temperatures and by direct microcalorimetric investigations of the complexation with CTA I. This analysis suggests that the separation process is mainly controlled thermodynamically and that kinetic effects, if any, play a minor role. Microcalorimetric titration experiments indicate that specific (optimum) complexation sites on CTA I for the stronger retained enantiomer of δ‐phenly‐δ‐valerolactone are rapidly saturated, whereas the first eluted enantiomer seems to interact much less selectively with defined interaction sites on the chiral polymer matrix. © 1993 Wiley‐Liss, Inc.

Microcalorimetric Study of Self‐Discharge of Nickel Hydroxide Electrode

Microcalorimetric, open‐circuit potential, and capacity measurements were made to investigate the effects of hydrogen pressure and concentration on the self‐discharge characteristics of nickel hydroxide electrodes at 25°C. By carrying out microcalorimetric experiments with powders of the constituents of the nickel hydroxide electrode, i.e., the active material and substrate, separately and combined, it was shown that hydrogen oxidation occurs predominantly on the active material with simultaneous reduction of the oxide. The results also show that the rate of heat generation by powders, immersed in , increases with the increase of hydrogen pressure; this result explains the shift of the open‐circuit potential of the nickel hydroxide electrode in a negative direction, this shift occurring much more rapidly in a hydrogen environment than in an inert atmosphere. From the microcalorimetric data, it was deduced that the rate of heat generation corresponds to a capacity loss of about 3.1% per day when the hydrogen pressure is about 50 atm. Nickel hydroxide electrodes, at high pressures of hydrogen (e.g., 700 psi), lose capacity more rapidly in a concentration of 23% than in 26% or 31%. However, no significant effects of concentration on self‐discharge rates of the nickel hydroxide electrode were observed at a lower pressure of hydrogen (150 psi).

Solid-state stability studies of 13-cis-retinoic acid and all-trans-retinoic acid using microcalorimetry and HPLC analysis.

The solid-state stabilities of 13-cis-retinoic acid and all-trans-retinoic acid in the presence and absence of oxygen were investigated. The samples were first evaluated using microcalorimetry. The rate laws of different samples under different conditions were deduced from the shapes of the heat flow curves, and the activation energies of the reactions were determined from Arrhenius plots. Under an air atmosphere, the decomposition of 13-cis-retinoic acid is an autocatalytic reaction, while all-trans-retinoic acid undergoes a zero-order process. The degradation of the two compounds at a selected elevated temperature was also determined utilizing HPLC analysis. This technique confirmed the decomposition kinetics. Hence, their half-lives and shelf lives at room temperature could be calculated. Under a nitrogen atmosphere, the microcalorimetric experiment showed a first-order phenomenon for both samples, but HPLC analysis showed no degradation, suggesting that the two samples, in the absence of oxygen, undergo only a physical change.

Microcalorimetric investigations of microbial activities: Decomposition of needle litter under laboratory conditions

Microcalorimetric experiments on litter degradation included in a forestal amelioration program are reported. Abolition of water limitation in needle litter induced a strong initial peak in heat evolution. This transitory activation is due to easily degradable substrates utilized equally well by fungi and bacteria as shown by the addition of selective inhibitors. Degradation proceeded in three phases of changing activity depending on individual additives (lime, ammonium chloride, cellulose). Addition of cellulose alone stimulated degradation while nitrogen supply had no significant effect. Addition of lime always reduced the degradation rate. Particularly in combination with nitrogen addition, lime strongly inhibited the microbial activity by a release of ammonia, total weight loss after seven months being also reduced. No physical reactions were found interfering with true metabolic heat production, thus proving the validity of the method.

Flow microcalorimetric study of the 1:1 stoichiometric reaction

A new mathematical treatment is presented for determination of the enthalpy change and equilibrium constant for the 1:1 stoichiometric reaction using flow microcalorimetric data. A reaction for which the thermodynamic parameters are known has been carried out in order to demonstrate the applicability of the method. The advantage of the proposed method is that the thermodynamic values are calculated directly by solving a biquadratic equation involving only measured experimental quantities, with no initial estimates being required. A dilution cell has been incorporated in the experimental set-up so that the concentration of one of the reactants could be varied continuously. It is also shown that the volume of the dilution cell may be directly determined with a flow microcalorimetric experiment.

Metabolic oscillations of [formula omitted] recorded by microcalorimetry

Microcalorimetric experiments on the periodic heat production of a culture of Escherichi coli are described. The behaviour is detected in a hermetically closed environment long after nutrients and oxygen are exhausted in the medium. The calorimetric technique is reported for a plausible cooperative behaviour of cells induced in the case by the final mixed-acid fermentation metabolism.

Solubilization of pentanol in sodium dodecylsulphate micelles. Interpretation of calorimetric results using a theoretical model

Microcalorimetric titration experiments have been performed to study the solubilization of pentanol in sodium dodecylsulphate, SDS, micelles. A concentrated SDS solution was titrated into water solutions containing 0.059, 0.118 or 0.176 mol dm–3 of pentanol. The enthalpic titration curves were determined at each pentanol concentration in the range 0–0.035 mol dm–3 of SDS at 25 and 35 °C. The observed differential enthalpies of dilution vary in a complex manner with SDS and alcohol concentration and temperature.A thermodynamic model for the association of ionic amphiphiles proposed by Jonsson and Wennerstrom and extended to deal with alcohol as a third component has been used to analyse the calorimetric results. The concentrations of SDS and pentanol in monomer and micellar states were calculated and the composition of the mixed micelles was derived using the chosen model. The enthalpy change for the formation of SDS–pentanol micelles is regarded as the sum of the following contributions: the enthalpy of formation of pure SDS micelles, ΔHrefmic, the electrostatic and surface enthalpy contributions Hel and Hs, respectively, in mixed micelles and an enthalpy of formation of a hypothetical alcohol micelle ΔHreftr. Values of Hel and Hs were calculated from the model for micelles of varying composition and ΔHrefmic was determined from dilution experiments in pure water. This leaves ΔHreftr as the only adjustable parameter in the calculation of theoretical titration curves. A satisfactory agreement is seen between the experimental and calculated titration curves, which means that the model can describe the essential features of the solubilization of pentanol in SDS micelles.

Oscillatory heat production in cell free extract from yeast: Batch and infusion experiments

Microcalorimetric experiments on the periodic heat production in metabolizing cell free cytoplasmic extract from baker's yeast are described. The sugar substrates for glycolysis are supplied by two different techniques: (a) one-time addition of trehalose; (b) continuous infusion of glucose. For the first time the combination of calorimetry and substrate infusion technique is reported for oscillating biochemical reactions.

Thermodynamic parameters of cytochrome c3-ferredoxin complex formation.

The complex formation between cytochrome c3 and ferredoxin I from Desulfovibrio desulfuricans Norway was studied by microcalorimetric and pH-stat titration measurements. The stoichiometry of the complex was found to be one molecule of cytochrome c3 per monomer of ferredoxin I. The association constant determined at T = 283 K in tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer, 10(-2) M and pH 7.7, was KA = 1.3 X 10(6) M-1. Though the enthalpy (delta H = 19 +/- 1 kJ.mol-1) and the entropy (delta S = 183 J.K-1.mol-1) were positive and consistent with a hydrophobic process involved in the interaction, the analysis of ionic strength dependence exhibited an important electrostatic effect on the association. The use of both Tris-HCl and phosphate buffers during microcalorimetric experiments showed proton release at pH 6.6. The pH-stat study of proton release indicated that one of the charged groups involved in the interacting site underwent a pK shift from 7.35 to 6.05.

Thermoset Matrices for Structural Adhesives: Imidazole-Catalysed Curing of Epoxy Resins

Abstract The thermoset epoxy systems of diglycidyl ether of bisphenol-A (DGEBA) and different imidazoles (unsubstituted imidazole, N-methyl-im., 2-methyl-im., 4(5)-methyl-im., 2-ethyl,4-methyl-im., 2-ethyl-im., 2-phenyl-im.) as catalytical curing agents were characterized. From microcalorimetric experiments it was deduced that each molecule of imidazole induces more than 20 epoxy groups to undergo polyaddition. Therefore, optimum glass transition temperature-ranges can be obtained with 0.025 to 0.05 mol of catalyst/equivalent of epoxy. The different alkyl-and aryl-substituted imidazoles show rather similar catalytic effects, with the kinetics differing by a factor of 3 at most. Mechanical properties (flexural modulus and strength, ultimate strain and fracture toughness) at ambient temperature do not correlate with the crosslinking density of the polymer network.

Ordered domain characterization in α-Cu-Al alloys from dissolution kinetics studies

Through microcalorimetric experiments, disperse order (DO) dissolution kinetics in preannealedα-Cu-Al alloys containing 19, 13 and 6.5 at % aluminium were adequately described by the integrated kinetic model function arising from the steady-state part of the diffusion field:f(y)=1 − (1−y) 2/3. Domain sizes after the annealing treatment, and also critical radii, were determined from differential scanning calorimetry data analysis at different heating rates. The existence of critical radii indicates that the disperse-order dissolution process is a first-order transition. Nevertheless, it was inferred that for very dilute alloys, only short-range order is present. After pre-annealing the alloys at different temperatures, volume fractions and domain concentrations were computed by employing the above kinetic model under high heating-rate conditions. On the basis of appropriate time constant and diffusion time calculations, the range of such temperatures compatible with equilibrium attainment was established. Prolonged pre-anneals alter the particle distribution, but do not influence either volume fractions or domain sizes. A semi-quantitative particle radius-particle concentration-temperature diagram was proposed forα-Cu-Al alloys.

Thermodynamics of the Ca2+ binding to bovine alpha-lactalbumin.

Bovine alpha-lactalbumin contains one strong Ca2+-binding site. The free energy (delta G0), enthalpy (delta H0), and entropy (delta S0) of binding of Ca2+ to this site have been calculated from microcalorimetric experiments. The enthalpy of binding was dependent on the metal-free bovine alpha-lactalbumin concentration. At 0.8 mg ml-1, metal-free bovine alpha-lactalbumin delta H0 was -110 +/- 6 kJ mol-1. At this concentration the binding constant was estimated from a mathematical analysis of the titration curves to be greater than 10(7) M-1. This means that delta G0 is smaller than -40 kJ mol-1 and delta S0 is less negative than -235 J.K-1 mol-1. The binding of Ca2+ is therefore enthalpy-driven. From binding experiments as a function of temperature, a delta Cp value of -4.1 kJ.K-1 mol-1 was calculated. This value is dependent on the protein concentration. A tentative explanation for this large value is given.

Time evolution of the excess energy in supersaturated solid solutions: microcalorimetric experiments, computer simulations and theory

The authors describe, compare and analyse a series of microcalorimetric experiments and computer simulations focusing on the temporal behaviour of the excess energy in supersaturated solid solutions, e.g. quenched Al-Zn alloys with different compositions. Both systems, real samples and computer models, show a qualitatively very similar behaviour. The main common features are the scaling of the data corresponding to different compositions, temperature and even systems, and its consistency with a combination of simple power laws. These facts confirm and extend some previous conclusions about the microscopic mechanisms present during the temporal evolution of the system. They also estimated equilibrium energy values in the case of the binary alloy or Ising model.

Heating rate dependence of disordering in αCu-AI alloys

Microcalorimetric experiments in pre-annealed and furnace cooled αCu-Al alloys containing 19,13, and 6.5 at. pct aluminum were performed at different heating rates. The features displayed by the differential scanning calorimetric traces were studied with reference to the rate of equilibration of the processes associated to a disperse order model (volume fraction and particle number adjustment, and domain dissolution). Such a comparison indicates that the observed features harmonize quite well with this model. The disordering reactions were found to be first order transitions. Volume fractions and radii of the ordered particles as well as latent and molar heats of dissolution were calculated. The decrease of the critical temperatureT c with increasing Al content is explained through a combination of the lattice parameter and the quasichemical effects. The molar entropy of dissolution increases as the alloy becomes more concentrated, indicating that internal order within domains also increases correspondingly.

Interaction of calcium ions with α‐elastin: An equilibrium dialysis, circular dichroism, and microcalorimetric study

AbstractThe interaction of calcium ions with α‐elastin has been investigated by equilibrium dialysis, CD, and microcalorimetric techniques. Consistent with literature data, it was found that the interaction in water is very poor. In trifluoroethanol (TFE), equilibrium dialysis experiments showed that calcium ions bind to ∼‐elastin with an association constant of ∼250 L × mol−1. Such a figure is not consistent with highly specific, highly selective binding. It was also found that the CD response is not directly proportional to the amount of bound calcium but depends on the protein concentration. From microcalorimetric experiments it was found that the heat effect relative to the binding process is of the order of 1.9 kcal/g ion. From this figure and from the binding constant, a positive ΔS value of about 17 e.u. was evaluated, leading to the conclusion that the binding process is entropy driven. From microcalorimetric measurements a ΔH of 1.5 kcal/residue was found for the calcium‐induced conformational transition of the protein.

Influence of gangliosides GM 1 and GD 1a on structural and thermotropic properties of sonicated small 1,2-dipalmitoyl- l-α-phosphatidylcholine vesicles

The effect of the gangliosides GM 1 and GD 1a on the structure- and temperature-induced transition behavior of sonicated, small 1,2-dipalmitoylphosphatidylcholine (DPPC) vesicles has been studied by 1H- and 13C-NMR, laser light scattering and differential scanning microcalorimetry. It became apparent from comparison of the results obtained by the various methods that great care must be taken when the occurrence of phase transitions is postulated on the basis of methods other than high-sensitivity microcalorimetry. Detection of a temperature-dependent decrease in the half-width of methylene signals, which was reminiscent of a phase transition, was not paralleled by characteristic changes in heat capacity in the microcalorimetric experiments. Probing of the local mobility of the choline head groups in vesicles of mixed composition by 1H-NMR and 13C-NMR spin-lattice relaxation time ( T 1 ) measurements suggested a decrease of mobility of the hydrophilic DPPC head groups in the presence of either ganglioside. The decreases in T 1 were identical for both gangliosides irrespective of the differences in the structure of the sugar moieties of GM 1 and GD 1a, whereas the heat capacity vs. temperature curves were rather different. Since also the average dimensions of pure DPPC vesicles and vesicles containing GM 1 or GD 1a were the same, the differences in temperature dependence of heat capacity in the presence of the gangliosides were attributed to differences in interaction of the hydrophobic parts of the molecules. The higher content of C 20 sphingosines in GD 1a as compared to GM 1 was envisaged as a possible source for these differences. The presence of a physiological CaCl 2 concentration (2 mM) did not affect the transition behavior of GD 1a-containing vesicles to any detectable level, as monitored by calorimetry.

Binding of galactose and lactose to ricin. Equilibrium studies

The interaction of ricin, one of the two lectins of Ricinus sanguineus, with its specific ligands galactose and lactose ( 4-O-β- d- galactopyranosyl- d- glucopyranose ) has been studied by means of equilibrium dialysis, analytical ultracentrifugation and fluorescence polarization. In the studied concentration range, only one molecule of galactose is bound per molecule of ricin with an association constant, K a = 6900 m −1 at 4°C. Scatchard plots of equilibrium dialysis data show that two molecules of lactose bind to one molecule of ricin, without modification of molecular weight of the lectin. Together with results of microcalorimetric experiments and agglutination of erythrocytes by ricin, equilibrium dialysis data indicate that the lectin contains two distinct saccharide binding sites. Regardless of the existence of extended sites, it is not possible to select between the two models: (a) two independent sites ( K a1 = 35 000 M −1, K a2 = 2800 M −1 at 4°C) or (b) two identical sites with negative cooperativity.

Microcalorimetric investigation of the metabolism of yeasts. V. Influence of ploidy on growth and metabolism.

Microcalorimetric experiments on growth and maintenance metabolism of Saccharomyces strains ranging from haploid to hexaploid are described. During growth, the mean dry weight, the mean volume and the maximum heat flux of the cells are nearly linear functions of ploidy. These parameters are correlated with the cell concentration in such a manner that the weight-specific heat production and the grown biomass are independent of ploidy. For the metabolism of maintenance, two levels of the specific heat flux are found, the lower of which is occupied by the haploids, diploids and triploids. The higher polyploids exhibit the higher level.

Catalytic properties of thorium oxide in the oxidation of carbon monoxide: I. Calorimetric confirmations of adsorption and catalysis processes

Adsorptive and catalytic properties of thoria have been reexamined in the light of some new microcalorimetric experiments. It has been shown that oxygen can be weakly adsorbed under a neutral form, that chemisorption heat of carbon monoxide on n-type thoria linearly decreases with the logarithm of the adsorbed volume, and that carbon dioxide is chemisorbed under two forms, one of which is an intermediary in carbon monoxide oxidation, the other one being an inhibitor of this catalysis.