Titration calorimetric

Table II shows the "heats of formation" of the conjugate phases, that is, the excess enthalpies for mixing the appropriate amounts of water and amphiphile (at the same initial temperature and pressure as the final system) to make a unit amount of the conjugate phase. Values labeled "calorimeter" and "phase volume," respectively, are based on the same set of calorimetric titrations. In the former case the phase composition was taken from the calorimetric measurements, and in the latter case the composition was taken from our phase-volume compositions. Literature values for the heats of formation are based on data from references 13-16.

In some instances, a calorimetric titration procedure may be used to obtain both log K and AH values simultaneously. Thus, the titration curve (heat change versus volume of reactant added) gives a measure of the degree of complex formation at each titration point and, provided... 

The surface proton adsorption which occurs after Step 2, however, complicates the determination of the heat content change resulting from anion adsorption. In order to make this correction, the heat associated with proton adsorption must be determined from the previous potentiometric-calorimetric titrations. Proton adsorption on goethite is exothermic, and Figure 1 provides an average value of -29.6 kj/mol near pH 4. This value, when multiplied by the moles of protons required to return to pH 4 after anion adsorption, allows correction for the heat associated with proton adsorption. This correction, however, is based on the assumption that the proposed two-step anion adsorption mechanism described above represents the only surface reactions which occur during anion adsorption. As such, the results obtained by this procedure are model dependent and are best used for comparative purposes. 

Figure 13.10 Calorimetric titration response showing the exothermic raw (downward-projecting peaks, upper panel) heats of the binding reaction over a series of injections titrating 0.061 mM RNase A (sample) with 2.13 mM 2CMP at 30°C. Bottom panel shows the binding isotherm obtained by plotting the areas under the peaks in the upper panel against the molar ratio of titrant added. The thermodynamic parameters were estimated (shown in the inlay of the upper panel) from a fit of the binding isotherm.

Adsorption and desorption reactions of protons on iron oxides have been measured by the pressure jump relaxation method using conductimetric titration and found to be fast (Tab. 10.3). The desorption rate constant appears to be related to the acidity of the surface hydroxyl groups (Astumian et al., 1981). Proton adsorption on iron oxides is exothermic potentiometric calorimetric titration measurements indicated that the enthalpy of proton adsorption is -25 to -38 kj mol (Tab. 10.3). For hematite, the enthalpy of proton adsorption is -36.6 kJ mol and the free energy of adsorption, -48.8 kJ mol (Lyklema, 1987). 

Heats of formation of MI3 and MI4- in a variety of non-aqueous solvents have been obtained by calorimetric titration of MI2 with Nal (M = Zn, Cd or Hg).1008 Interaction of MBr2 (M = Zn, Cd or Hg) with AlBr3 in DMF gives (AlBr2)2MBr4.1009... 

Alumina, silica-alumina, clays Calorimetric titration with n-butylamine and trichloroacetic acid 71... 

Method C The calorimetric back titration method, the sample of engine oil was dissolved in a mixture of toluene-isopropanol-water (50 49.5 0.5,v/v) and 0.25 M HC104 in isopropanol-toluene (1 1) was used as the titrant the excess acid was titrated by 1 M (CH3)4NOH in isopropanol. Method D The determination of the TAN and AH was performed by direct calorimetric titration. (CH3)4NOH in isopropanol was used as the titrant and a toluene-isopropanol-water (50 49.5 0.5,v/v) was used as the solvent... 

An estimation of the amounts of weak acid was made from direct titration on the samples (method D). Most oil samples have TAN of 1 to 2 units (mg KOH g 1 oil) however, samples 8 and 9 have an acidity index of around 4.5 units. Heat of neutralization of acidic products ranges from -3.7 to -20.4 kJ mol"1 and indicates the presence of weak acids in engine oil samples. The precision of calorimetric titration is comparable with conductometric and potentiometric methods. The advantages of calorimetric and conductometric techniques are rapidity, good reproducibility and avoidance of poisoning of detectors by organic substances. 

As a consequence monomeric complexes are obtained much more easily. Also, the tendency to bridge lanthanide centers is less distinct and, for example, a small cluster chemistry as it exists for alkoxides, e.g. OiPr [13] and OtBu derivatives [14], is not yet known. However, the Ln-N(amide) bond is less strong than the Ln-O(alkoxide) bond, and even comparable to Ln-C(alkyl) bonds, which has an effect in synthetic chemistry. This has been confirmed by the determination of absolute bond disruption enthalpies D by means of calorimetric titrations for the representative systems Cp Sm X (X = OrBu, D = 82.4 kcalmol-1 NMe2, 48.2 CH(SiMe3)2, 47.0) [15]. 

A clearly pronounced acceptor ability of the tetravalent organogermanes RnGeCl4 (n = 1, 3, R = Ph n = 2, R = Me) toward N-, P- and O-donor molecules was deduced from calorimetric titration. Me2GeCl2 forms 1 2 complexes with Bu3N54, but, as well as... 

Dimethyl tellurium dibromide and boron tribromide formed a thermally unstable 2 1 adduct4. Calorimetric titrations indicated that 1 1 complexes are formed between diphenyl tellurium dihalides and aluminum tribromide or gallium trichloride5 6. 

Fig. 2. UV-visible spectra of gold nanorods (a) before and after calorimetric titration with cysteine and (b) taken at different stages of the calorimetric titration with MPA as indicated in Fig. 4b.

The following data were obtained in dimethyl acetamide for La and Nd by calorimetric titration technique. 

Support for a concerted model for the yeast enzyme has come from X-ray small angle scattering experiments (162) as well as from hydro-dynamic and optical rotation studies (163, 164). A. volume contraction of about 5% occurs on binding of NAD to the apoenzyme, presumably related to tightening of the tetramer and expulsion of water mojecules. The relation between NAD bound (R) and change of volume (Y) was hyperbolic, in accord with the concerted model. It was lator shown (166) from buoyant density and preferential hydration studies that water is indeed excluded from the yeast enzyme on binding to NAD, such that a volume contraction of about 6% occurs. Furthermore, fluorimetric and calorimetric titrations over the range 6°-40° showed independence of... 

Vasil ev and Kozlovskii (37) have also obtained enthalpy data for these reactions by calorimetric titration. The average AH =... 

Figure 7-27. An illustrative isothermal calorimetric titration of the binding of a ligand to a protein.

Finally, it should be noted that calorimetric measurements can also be used to monitor adsorption phenomena at the solid-liquid interface (in a solvent). This method has been used to measure the adsorption heats evolved upon injection of dilute solutions of pyridine in alkanes ( -hexane, cyclohexane) onto an acidic solid itself in a slurry with -hexane. The amount of free base in solution is measured separately with a UV-Vis spectrometer, leading to an adsorption isotherm that is measured over the range of base addition used in the calorimetric titrations. The combined data from the calorimetric titration and adsorption measurements are analyzed simultaneously to determine equihbrium constants, quantities of sites per gram and acid site strengths for different acid sites on the solid. 

Calorimetric Titrations. The calorimeter was of about 50 ml. capacity and jacketed so it could be insulated by vacuum. The top, fitted to the calorimeter by a ground glass joint, had tubes which housed thermistor, heater and buret inlets. The solutions were stirred magnetically. The buret was attached to a 30 ml. reservoir which, together with the calorimeter, was immersed in a constant temperature water bath at 25.00 0.02 °C. More details are to be found in previous publications (6, 23). 

Calorimetric Titrations. The procedure and calculations have been described previously (6). 

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