Microcalorimetric titration

Usually the acid-base properties of poly electrolyte are studied by potentiometric titrations. However it is well known, that understanding of polyelectrolyte properties in solution is based on the knowledge of the thermodynamic properties. Up to now, there is only a small number of microcalorimetry titrations of polyelectrolyte solutions published. Therefore we carried out potentiometric and microcalorimetric titrations of hydrochloric form of the linear and branched polyamines at 25°C and 65°C, to study the influence of the stmcture on the acid-base properties. 

Spectroscopic techniques may provide the least ambiguous methods for verification of actual sorption mechanisms. Zeltner et al. (Chapter 8) have applied FTIR (Fourier Transform Infrared) spectroscopy and microcalorimetric titrations in a study of the adsorption of salicylic acid by goethite these techniques provide new information on the structure of organic acid complexes formed at the goethite-water interface. Ambe et al. (Chapter 19) present the results of an emission Mossbauer spectroscopic study of sorbed Co(II) and Sb(V). Although Mossbauer spectroscopy can only be used for a few chemical elements, the technique provides detailed information about the molecular bonding of sorbed species and may be used to differentiate between adsorption and surface precipitation. 

Figure 9. Calorimetric record from a microcalorimetric titration experiment. Four pi of 2 CMP were injected stepwise into the calorimetric vessel (volume 1.4 ml) which was charged with 0.65 mM RNase solution. Adapted from Wieseman et al. (1989).

A noteworthy finding emerging from these detailed studies was that the monotopic cyclopeptide 44 actually proved to be a more efficient receptor for sulfate anions than the ditopic system 45 (for 44, AH = 19.3kJ/mol and logKT = 6.48 in 50% D20/CH30H, where /< , = K n-K.l2 M 2 ). Furthermore, in contrast with the design expectations, microcalorimetric titrations (e.g., ITC analyses) revealed that sulfate is bound to receptor 45 with a 2 1 binding stoichiometry. 

The apparent shape of the titration curve obtained in microcalorimetric titration experiments varies significantly, depending on the host and guest concentrations and the magnitude of the equilibrium constant. If the equilibrium constant is small and the initial reactant concentrations are low, only a small portion of the added guest can interact with the host in the cell to give a typical titration curve illustrated in Fig. 8.1. 

In the case of 1 1 complexation, a typical microcalorimetric titration run consists of 15-25 successive injections of constant volume (5-10 pL per injection) of guest... 

Fig. 8.1. Typical results obtained in a microcalorimetric titration experiment (a) heat effect observed upon each injection of titrant solution and (b) non-linear curve fitting of the experimental results using a simple 1 1 model.

Fig. 8.3. Typical results of microcalorimetric titration experiment for 1 2 host-guest complexation (a) plots of heat effects observed upon (i) dilution of a Cbz-Gly solution added to the buffer solution and (ii)...

As was the case with Cbz-Gly, the stepwise 1 2 complexation model was used as the simplest, most reasonable, choice for the treatment of the microcalorimetric titration data obtained for the complexation of Ph-C4, Ph-Cs, and Ph-C with y-CyD to afford a satisfactory match between the experimental data and the theoretical curve. 

Except for microcalorimetric titrations, readers are referred to the literature [14]. Microcalorimetric experiments at 298.15 K were carried out using the titration vessel of the 2277 Thermal Activity Monitor. The vessel was filled with 2.8 mL of a solution of p-te/t-butylcalix[4]eirene in benzonitrile (5 x 10 mol dm ) or in nitrobenzene (5 x 10" or 9 x 10 mol dm ). Triethylamine solutions in the appropriate solvent (concentration range 0.07-0.95 mol dm ) were injected (16 injections 0.015-0.025 mL for each run) from a 0.5 mL gas-tight Hamilton syringe, attached to a computer-operated syringe drive at 5 minute intervals, p-tert-Butylphenol solutions were 0.04 mol dm in both solvents. A dynamic correction... 

Figure 37. This shows the principle arrangement of a microcalorimetric titration vessel equipped for light absorption. An electrode is also positioned in the vessel, (a) lamp and the other optical equipment, b) light guide, (c) titration syringe, (d) microcalorimetric vessel, (e) electrode, (/) light path in the medium, (g) spectrometer (Reproduced from Reference [129] with permission).

Johansson, R, and I. Wadso (1999). An isothermal microcalorimetric titration/ perfusion vessel equipped with electrodes and spectrophotometer . Thermochimica Acta 342(1-2) 19-29. 

N. M. Gorman, J. Laynez, A. Schon, J. Suurkuusk, I. Wadso. Design and Testing of a New Microcalorimetric Vessel for Use with Living Cellular Systems and in Titration Experiments. J. Biochem. Biophys. Methods 1984,10, 187-202. 

Figure 11. Electrodes in microcalorimetric vessels. A Schematic diagram of a section through a titration-perfusion microcalorimetric vessel equipped with a polarographic oxygen electrode and a pH electrode, a, sample compartment, volume 3 ml b, hollow stirrer shaft c, steel tube d, turbine stirrer e, O-rings f, combination pH electrode protected by a steel tube g, polarographic oxygen sensor (Clark electrode). B Record from a growth experiment with T-lymphoma cells. The vessel was completely filled with medium. Once the baseline had been established, the experiment was started (as indicated by the arrow) by the injection of 100 pi concentrated cell suspension.

Interactions between water vapor and amorphous pharmaceutical solids were evaluated using isothermal microcalorimetry. " The desorption of water from theophylline monohydrate has been investigated using microcalorimetric approaches.The properties of surfactants and surface-active drugs in solution were studied by Attwood et al. " using calorimetry, while titration microcalorimetry has been utilized to elucidate the nature of specific interactions in several pharmaceutical polymer-surfactants systems. " Drug decomposition was evaluated as a function of different... 

Clays have both Brpnsted and Lewis acid sites, the amount and strength of which can be substantially modified by acid treatments and/or ion exchange [31-34], The strength of the Brpnsted sites can be determined in different ways Hammett indicators, butylamine titration, IR spectroscopy using probe molecules, microcalorimetric or temperature programmed desorption methods [7,9,34-39], There is a direct correlation between acid strength and composition (Table 2),... 

Despite the great diversity in the design of microcalorimeters and the experimental procedures described in the literature [1-10], only two microcalorimetric methods have found widespread application in cydodextrin (CyD) studies and drug-design research. These two methods are differential scanning calorimetry (DSC) and isothermal titration microcalorimetry (ITC). DSC and ITC can be con-... 

Binding or association constants in principle can be obtained by any spectroscopic method, which permits the analysis of solutions, i.e., H NMR (Chapter 9), UV-Vis and fluorescence spectra (Section 10.3), and CD, and also by microcalorimetric methods (Chapter 8), potentiometric titrations (Section 10.5), etc. [5,10]. Information about the supramolecular structure in solution, on the other hand, only can be gained by NMR (NOESY or ROESY) or CD spectroscopy - preferably in combination with computational methods [11-17] (see, however, Chapter 11, which details the limitations of CyD modeling). 

This topic has recently been reviewed, and in order that we may be brief we would like to refer the reader to the article of Karge [23] for more information on methods other than IR spectroscopy for detecting and characterizing the various kinds of sites such as titration, MAS-NMR, ESR, TDS, microcalorimetric measurements and application of test reactions. 

Fig. 3. Microcalorimetric recorded graph for the titration of p-tc/t-butylcalix[4]arene and triethylamine in nitrobenzene at 298.13 K.

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