Calorimetric measurements of microtubule assembly in vitro

The assembly of microtubules in extracts of mammalian brain tissue has been characterized by electron microscopy and the course of the temperature-induced polymerization of the heterodimers of α-tubulin and β-tubulin has been followed by the help of an adiabatic scanning calorimeter. Tubulin was purified by the reversible, temperature-dependent assembly procedure and was analyzed by gel electrophoresis. In a typical calorimetric experiment 1 ml of a protein solution (7.5 mg ml^?1) was placed into the sample cell while the same amount of this solution containing 5 mM Ca²⁺ to prevent tubulin aggregation, was placed into the reference cell. After cooling the cells to 0°C, the solutions were heated at a rate of 1 deg min^?1 and the excess energy to keep the temperature difference of both cells close to zero was recorded as a function of temperature. The peak due to compensation of the heat of polymerization starts to rise at 20°C and declines to the base line at 32°C. The area of the peak can be calibrated in energy units by the help of an electric calibration signal. The heat of polymerization per mole of the heterodimers calculated from the experiments is 8.3 kcal. The entropy change due to this process is 27.8 e.u. The van't Hoff enthalpy calculated from the calorimetric curve is 212 kcal mole^?1 tubulin. The heat of denaturation of tubulin was determined to be 180 kcal mole^?1. The polymerization reaction was shown to be reversible whereas the denaturation is an irreversible process.     

Calorimetric determination of equilibrium phase diagrams of inorganic systems

Calorimetric isobaric determination of the heat involved during mixing processes gives the concentration dependence of the enthalpy of mixing ΔH_M = F(x) and also, under particular conditions, some liquids concentrations of the phase diagram.For some simple typical diagrams (with a eutectic point or miscibility gaps, or a definite compound etc.) direct calorimetric experiments at many temperatures give the liquidus (e.g. NaBrNaNO₃, KBrKNO₃, NaBKNO₃, KBrNaNO₃, GaHg, GaSb).For more complicated or multicomponent systems, the setting up of the equilibrium phase diagram needs both experimental measurement and thermodynamic calculations (e.g. GaInSb).     

Thermodynamic properties of trilaurylammonium bisulphate in benzene

We have studied the thermodynamic properties of trilaurylammonium bisulphate (TLAH₂SO₄) in benzene at several temperatures by vapour pressure osmometry (VPO). Values of the activity coefficients, γ_i, are given, which allows calculation of the excess thermodynamic functions, G^E, S^E and H^E.     

Liquid-liquid equilibria of (cyclohexane + acetonitrile + methylcyclohexane + toluene) and of {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene} at 298.15 K

Tie-line results at 298.15 K and atmospheric pressure are reported for (cyclohexane + acetonitrile + methylcyclohexane + toluene) and for {(acetonitrile + methylcyclohexane) + benzene or + toluene or + cyclohexane or + chlorobenzene). The extended UNIQUAC and UNIQUAC equations are used to correlate binary vapour-liquid equilibria and mutual solubilities for 10 mixtures constituting the ternary mixtures and to predict the ternary and quaternary liquid-liquid equilibria by use of only binary parameters.     

Electrochemical bromination of benzene,toluene and xylene in acetonitrile

A method for the preparation of bromo derivative compounds of aromatics is proposed and the electrodic process involved in the bromination on the third wave of the system Br^?/aromatic substrate in acetonitrile is discussed.     

Calorimetric and thermoanalytical assessment of mechanically activated PbCO3

Excess enthalpy values, ΔH*, were obtained through the change in the heats of dissolution into Na—EDTA (ΔH*_L) as well as of decomposition to PbO (ΔH*_D). They tallied fairly well with each other, although a slight systematic discrepancy depending on the conditions of vibro-milling was recognized. A good correlation between ΔH* and the relative non-crystallinity was observed when the material was activated under the same conditions with a varying grinding time. Changes in the grinding conditions, such as in amplitude or atmosphere, brought about a considerable shift of the correlation between ΔH* and the non-crystallinity. Thus, under the same degree of non-crystallinity, materials ground in cyclohexane stored a larger amount of energy than those ground in air. These differences in the correlation were discussed by referring the degree of dispersion, the distribution of active sites, and the effect of temperature.     

Diffusion in surfactant solutions

The diffusion coefficients in water of Triton X-100 and sodium dodecyl sulfate were measured as a function of concentration using the Taylor dispersion technique. For Triton X-100, a nonionic surfactant, the diffusion coefficient drops from 7.4 × 10^-7 cm²/sec at 0.45 g/liter to 6.45 x 10^-7 cm²/sec at 5 g/liter. The diffusion coefficient of methyl yellow solubilized in Triton X-100 is close to that of the surfactant. This behavior is quantitatively consistent with a chemical equilibrium between monomer and micelle. For sodium dodecyl sulfate, an anionic surfactant, the diffusion coefficient increases from 1.76 x 10^-6 cm²/sec at 0.01 M to 4.53 x 10^-6 cm²/sec at 0.125 M. The increase is less when 0.1 M NaCl is added. The diffusion coefficient of the methyl yellow solubilized by the SDS is significantly less than that of the surfactant, particularly at low ionic strength. This behavior can be quantitatively explained by including electrostatic coupling between monomer, micelle, and counterion.     

Quenching of the lowest benzene triplet state in the vapor phase by nitric oxide

the rate constant for quenching of the triplet state (³B_1u) of benzene vapor by nitric oxide has been determined from a study of the flash photosensitization of biacetyl phosphorescence. The rate constant has been found to be (1.08 ± 0.2) × 10^?11 cm³ molecule^?1 sec^?1. Although this value is much larger than expected, it is in agreement with rate constants reported for quenching of some liquid phase aromatics.     

Calorimetric determination of the thermodynamic properties involved in the complex formation of silver(I) with some sulphur-containing pyridines

The enthalpy changes involved in the complex formation of Ag⁺ with several sulphur-containing pyridines of general formula

where R = Ch₃, C₂H₅ and CH₂CH₂OH and x=1,2 have been determined by direct calorimetric measurements at 25°C in 0.5 M KNO₃ solution.From the ΔH values obtained and from the free energy changes reported in an earlier publication, the corresponding entropy changes ΔS have been calculated. Changes in ΔH and ΔS are discussed in terms of inductive and steric effects. It is shown that enthalpy values are linearly correlated with the Taft σ^* parameters of the substituents on the ligand.     

Excess enthalpies of some aromatic aldehydes in n-hexane, n-heptane and benzene

Calorimetric measurements of molar excess enthalpies, H^E, at 298.15 K, of mixtures containing aromatic aldehydes of general formula C₆H₅(CH₂)_mCHO (with m = 0, 1 and 2) + n-hexane, n-heptane or benzene are reported, together with the values of H^E at equimolar composition compared with the corresponding values of H^E for the aromatic ketones in the same solvents. The experimental results clearly indicate that the intermolecular interactions between the carbonyl groups (CHO) are influenced by the intramolecular interactions between the carbonyl and phenyl groups, particularly for the mixtures containing benzaldehyde.     

Excess enthalpies and complex formation of acetonitrile with acetone,chloroform, and benzene

Excess enthalpies of binary systems of acetonitrile—acetone, chloroform—acetone and chloroform—benzene, and ternary systems of acetonitrile—chloroform—acetone and acetonitrile—chloroform—benzene are reported at 25°C. The results are analyzed with thermodynamic association theory for complex ternary liquid mixtures. The theory involves two types of self-association of acetonitrile, formation and binary complexes for component pairs of a ternary system, and a nonspecific interaction term expressed by the NRTL equation between various chemical species.     

Calorimetric studies of binary systems of 1,3,5-trinitrobenzene with naphthalene, anthracene and carbazole. II. Phase diagrams

The phase diagrams of the binary systems of 1,3,5-trinitrobenzene (TNB) with naphthalene, anthracene and carbazole have been determined by differential scanning calorimetry and optical microscopy over the temperature range 180 K to just above the melting point. All systems show the same features: (i) systems form nearly ideal double simple-eutectic type phase diagrams with 1 : 1 complex, (ii) each one of three known modifications of TNB may exist as a component of the complex—TNB eutectic mixtures. (iii) measured liquidus lines of complexes agree within experimental error with those calculated by the Vieland equation for a completely dissociated complex in the liquid phase, whereas the experimental liquidus lines for the parent components deviate slightly from those predicted by the Schröder—van Laar equation, indicating some degree of complexing in the liquid phase.

The solubility parameter theory has been used to clarify this discrepancy. Applying this theory to the liquidus lines of complexes, we have found that these TNB complexes are still stable upon fusion, and an approximate degree of dissociation amounted to 90% at the melting point in all three cases.

The enthalpy of complex formation, ΔH⁰, both in the liquid and solid state has been determined. The values of ΔH⁰ show that in the solid state the carbazole—TNB complex is the most stable, and the naphthalene—TNB complex is the least stable.     

Interaction of cyclopentane with benzene,carbon tetrachloride and cyclohexane

Heats of mixing cyclopentane + benzene, + carbon tetrachloride, + cyclohexane at 308.15 K and for cyclohexane + carbon tetrachloride at 298.15 K have been determined in an adiabatic calorimeter. The data have been examined for current theories (McGlashan, Flory and Barker) of solutions and show that McGlashan's theory predicts values for H^E and G^E that are in good agreement with their corresponding experimental values. Interaction energy between the components of these mixtures has also been determined.     

Thermodynamics of solutions of methanol and solvating components

A model is proposed to correlate the excess Gibbs free energies and excess enthalpies of binary solutions of methanol and a solvating component. Solution nonideality from ideal solutions is given by the sum of the chemical contribution term, which is due to self-association of methanol and solvation between methanol and a nonassociating component, and the physical contribution term with allowance for the NRTL equation. The model uses the following data for methanol: two enthalpies for formation of the hydrogen bonds for the dimer and all larger polymeric species, three equilibrium constants of stepwise association for the dimer, trimer and other polymeric species, and an equilibrium constant for cyclic species of more than tetramer. The association model further includes an additional solvation equilibrium to allow for the interaction between the terminal hydroxyl group of methanol polymeric species and a solvating component. The model is extended to predict vapor—liquid equilibria, liquid—liquid equilibria and excess enthalpies for ternary solutions containing methanol and two nonassociating components from only binary information. Calculated results are in good agreement with experimental data as shown by selected illustrative examples.     

Excess enthalpies of 2-propanol + cyclohexane and 2-propanol + benzene + cyclohexane at 298.15 K

With an isothermal dilution calorimeter excess enthalpies have been determined at 298.15 K for 2-propanol + cyclohexane and 2-propanol + benzene + cyclohexane mixtures. The results are fitted with an associated-solution model. Predicted excess enthalpies for the ternary mixture agree well with the experimental results.     

Study of the (210) face of gold in aqueous solutions

Among all the gold faces studied to date, the (210) face has the most negative pzc and therefore should be less affected by preoxidation than the other faces. But the (210) gold face-sodium fluoride solution interface is ideally polarizable only in a short range of potential. Nevertheless, differential capacity-potential curves have been tentatively exploited. There seems to be adsorption of the fluoride ions on the (210) face of gold. The inner-layer capacity-charge curves are discussed.     

Solvent extraction studies of cobalt in aqueous thiocyanate solutions using Aliquat-336

Cobalt ions in aqueous thiocyanate solution react with Aliquat-336-xylene solution to form anion-association complex which is easily extracted into the organic phase. A typical extraction procedure involves extracting a solution which is 10 ppm in cobalt and 0.06 M,

5. Stripping of Cobalt from 2% Aliquat-336-Xylene Solutions

     

Strippant	Cobalt stripped (%)
Na2S (M) 1.0	18.3
2.0	10.7
Na2SO3 (M) 0.1	10.7
0.5	49.6
1.0	52.9
EDA (%) 2.5	76.6
NaOH (M) 0.1	4.1
0.5	74.1
1.0	90.8
2.0	76.8
NH4OH (M) 0.1	24.1
0.5	91.8
1.0	97.5
2.0	99.9
EDTA (M) 0.02	>99.9
0.05	>99.9
0.1	>99.9
EDTA (%) 0.1	>99.9
0.5	>99.9
1.0	>99.9