Isothermal titration calorimeter

Instrumentation. H and NMR spectra were recorded on a Bruker AV 400 spectrometer (400.2 MHz for proton and 100.6 MHz for carbon) at 310 K. Chemical shifts (< are expressed in ppm coupling constants (J) in Hz. Deuterated DMSO and/or water were used as solvent chemical shift values are reported relative to residual signals (DMSO 5 = 2.50 for H and 5 = 39.5 for C). ESl-MS data were obtained on a VG Trio-2000 Fisons Instruments Mass Spectrometer with VG MassLynx software. Vers. 2.00 in CH3CN/H2O at 60°C. Isothermal titration calorimetry (ITC) experiments were conducted on a VP isothermal titration calorimeter from Microcal at 30°C. 

The principles of titration calorimetry will now be introduced using isoperibol continuous titration calorimetry as an example. These principles, with slight modifications, can be adapted to the incremental method and to techniques based on other types of calorimeters, such as heat flow isothermal titration calorimetry. This method, which has gained increasing importance, is covered in section 11.2. 

The enthalpy change associated with formation of a thermodynamically ideal solution is equal to zero. Therefore any heat change measured in a mixing calorimetry experiment is a direct indicator of the interactions in the system (Prigogine and Defay, 1954). For a simple biopolymer solution, calorimetric measurements can be conveniently made using titra-tion/flow calorimeter equipment. For example, from isothermal titration calorimetry of solutions of bovine P-casein, Portnaya et al. (2006) have determined the association behaviour, the critical micelle concentration (CMC), and the enthalpy of (de)micellization. 

Figure 7.22 Schematic diagram of Isothermal titration calorimeter (ITC) device showing how a solution of receptor R is maintained in an ITC cell within an adiabatic shield and ligand L is injected in with stirring from above.

High-predsion versions of isothermal titration calorimeters (ITCs) are commercially available ... 

Isothermal titration calorimeter. The instrument used for these studies was purchased from Microcal, Inc., Northhampton, MA. 

Rinse the cell of the isothermal titration calorimeter once with this receptor solution, then fill the ceU with a second aliquot of the same solution. 

Any good-quality heat-flux calorimeter or isothermal titration calorimeter, such as those marketed by TA Instruments (USA) and the associated company Thermometric (Sweden), CSC (USA), Microcal (USA) or Setaram (France). 

A 5 ml volume of the 0.5 mol 1 solution of BF3 etherate in nitrobenzene is placed in the calorimetric cell under dry nitrogen or argon. The syringe pusher is filled with a sufficient volume of 2.5 mol 1 pyridine solution. Using these values, 0.100-0.200 ml injection steps allow for 5-10 additions. For an isothermal titration calorimeter, the time interval between each injection should be sufficient for the signal to return to the baseline (for a Dewar calorimeter, allowance is made for temperature stabilization after each injection). When the temperature of the system is equilibrated, the data acquisition and the injection programme are started. A preliminary experiment should be carried out to measure the blank value, corresponding to the heat of dilution of pyridine solution in the pure solvent. 

As it has been already mentioned, isothermal microcalorimeters are those calorimeters designed to work in the microwatt range under essentially isothermal conditions. Isothermal titration microcalorimetry (IT xC) is designed to connect extremely sensitive thermal measurement equipment (approx. 20-100 nanowatts) with an automatic syringe able to add reactants in successive injections to the solution with a precision of few nanoliters [32, 33]. Each injection produces specific heat effect, as shown in Fig. 10.5. The determination of heats evolved as a result of interaction between molecules is a main application of this variation of calorimetry. Consequently, isothermal titration calorimetry is a suitable method for studying degradations and biodegradations of versatile pollutants. 

As mentioned above, titration methods have also been adapted to calorimeters whose working principle relies on the detection of a heat flow to or from the calorimetric vessel, as a result of the phenomenon under study [195-196,206], Heat flow calorimetry was discussed in chapter 9, where two general modes of operation were presented. In some instruments, the heat flow rate between the calorimetric vessel and a heat sink is measured by use of thermopiles. Others, such as the calorimeter in figure 11.1, are based on a power compensation mechanism that enables operation under isothermal conditions. 

Figure 11.5 Typical curve for a continuous titration calorimetry study of an exothermic reaction, using the calorimeter of Figure 11.1 in the heat flow isothermal mode of measurement./ is the frequency of the constant energy pulses supplied to the heater C in Figure 11.1 b. Adapted from [196,197],...

Calorimetry is the measurement of the heat changes which occur during a process. The calorimetric experiment is conducted under particular, controlled conditions, for example, either at constant volume in a bomb calorimeter or at constant temperature in an isothermal calorimeter. Calorimetry encompasses a very large variety of techniques, including titration, flow, reaction and sorption, and is used to study reactions of all sorts of materials from pyrotechnics to pharmaceuticals. 

This technique has also been used for the determination of carbon surface polarity [100]. It was assumed that the water molecules interact only with oxygen surface complexes located on the polar sites at graphene edges. Starting from active carbons with different surface chemistry, the authors determined the enthalpies of immersion into water (298 K) with an isothermal calorimeter of the Tian-Calvet type, in conjunction with FTIR, XPS, and Boehm titration. The enthalpy increased linearly with the sum of acidic and basic sites. 

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