Heats of Mixing Using an Isothermal Titration Calorimeter: Associated Thermal Effects

The correct determination of the energy generated or absorbed in the sample cell of an Isothermal Titration Calorimeter (ITC) requires a thorough analysis of the calorimetric signal. This means the identification and quantification of any thermal effect inherent to the working method. In this work, it is carried out a review on several thermal effects, studied by us in previous work, and which appear when an ITC is used for measuring the heats of mixing of liquids in a continuous mode. These effects are due to: (i) the difference between the temperature of the injected liquid and the temperature of the mixture during the mixing process, (ii) the increase of the liquid volume located in the mixing cell and (iii) the stirring velocity. Besides, methods for the identification and quantification of the mentioned effects are suggested

A calorimetric study of β-sultams and β-lactams

The hydrolytic degradation of a series of β-sultams and β-lactams was investigated using isothermal microcalorimetry (IMC), to determine kinetic and enthalpic data. The importance of these studies was to model the process of hydrolysis as this was a simplification of the mechanism by which β-lactams and β-sultams function as serine protease inhibitors. Calorimetric studies were conducted using a Thermal Activity Monitor (TAM 2277). Three categories of experiments were conducted: in the solid state, varying relative humidity (R/H) and in aqueous solution. Hydrolytic rate constants and enthalpies were determined for the solid state studies and these were related to substituent effects. However, for the experiments relating to the R/H studies no conclusive results were obtained. As expected, for solution state studies the hydrolytic rate constant in all cases changed with temperature (298K, 310K and 323K). Theoretical predictions were then made for a novel β-sultam based on these results with an excellent correlation observed between theoretical calculations and experimental results. Finally, calorimetric experiments were conducted on a series of β-lactams. This was for two reasons firstly; to determine if calorimetry can monitor low reaction rates and secondly; to compare rates of hydrolysis with the β-sultams. For a series of β-lactams, solution state hydrolytic rate constants and enthalpies were determined. An overall comparison of β-lactams and β-sultams appeared to indicate that in all cases β-lactams reacted slower than β-sultams

Calorimetry of Immersion in the Energetic Characterization of Porous Solids

In order to study and understand the adsorption process in a liquid-solid interface, it is necessary to know both textural and chemical properties of the adsorbent. It is also important to know the behavior of the solid in a liquid medium, considering that the interaction can produce some changes in the texture and the electrochemical properties when the adsorbent is immersed in a solvent or a solution. The study of the influence of these properties in the adsorption process with techniques like immersion microcalorimetry can provide direct information on particular liquid–solid interactions. The parameter that is evaluated by immersion microcalorimetry is the immersion enthalpy, ΔHim. Immersion enthalpy is defined as the energy change at temperature and pressure constants when the surface of the solid is completely immersed in a wetting liquid in which the solid is insoluble and does not react. The immersion calorimetry can be a versatile, sensitive and precise technique that has many advantages for the characterization of porous solids. The versatility of immersion microcalorimetry is because changes in surface area, surface chemistry, or microporosity will result in a change in immersion energy. The interactions solid-liquid can be physical or chemical type, the physical present a lower amount of energy than that generated when exist chemical interactions

Effects of Ag or Si on precipitation in the alloy Al-2.5% Cu-1.5% Mg

International audienceCalorimetric measurements and electron microscopy observations were performed on Al-2.5 mass% Cu-1.5 mass% Mg alloys containing also 0.4, 1 or 2 % Ag or 0.5 % Si, in order to improve understanding of the relationships between precipitation processes and age hardening. The analogous behaviour of calorimetric and hardness data confirms that the first hardening stage is initiated in all alloys by GPB zone formation which occurs via a nucleation and growth controlled mechanism. The vacancy-trapping effect of Mg is increased by Ag and Si additions and leads to slower precipitation kinetics. Consequently refined GPB zones sizes are obtained leading to an increase in hardness with respect to the ternary alloy. During the second hardening stage, the formation of the more stable S' phase increases the total amount of strengthening precipitates in the ternary alloy. Phases typical for binary Al-Cu alloys form additionally in the Si-containing alloy. In the Ag-bearing alloys, precipitation of the hardening X' phase occurs the earlier the higher the Ag content is; it is followed by S' precipitation. During heating of the ternary alloy, the S'phase forms after substantial dissolution of GPB zones and of the S" phase identified by high resolution electron microscopy; this contradicts the concept of a continuous precipitation sequence

Micromachined Differential Scanning Calorimeter for Cellular Differentiation and Metabolism Monitoring

This thesis presents a micromachined differential scanning calorimeter (DSC) for cellular differentiation and metabolism monitoring. The misregulation of cell physiology due to disease increases the metabolic rate of the cell and therefore its heat output. Observing or monitoring the cell\u27s heat output will lead to a method to detect diseased cells and distinguish them from normal cells. The calorimetric chambers of the DSC were fabricated on a silicon nitride thin film, which allows for rapid thermal equilibrium and insulation. The temperature sensing element was a resistive temperature detector fabricated from nickel. The DSC incorporated integrated nickel resistive heaters to apply on chip heating and for calibration. The cell metabolism experiments carried out with the DSC were performed using JM-1 liver cancer cells and white blood cells (lymphocytes). Step voltage inputs were applied to the DSC while the response of the RTD to temperature was monitored. The results from initial testing showed a detectable increase in chamber temperature of 0.375ºC for the JM-1 liver cells. Further analysis was completed by obtaining the derivative of the DSC temperature curves. Two methods were explored: the direct derivative of the raw data curve and the derivative of the differential data curve. While both methods showed the ability to differentiate between the JM-1 liver cells and the lymphocytes, the derivative of the differential data curve was superior due to the elimination of common mode signals. The differential method also allowed the determination of the heat rates of the cells. JM-1 liver cells showed a positive heat rate which is consistent with its increased metabolism, while the lymphocytes showed a negative heat rate or absorption of thermal energy

Thermodynamics of interaction of macrocyclic ligands with multivalent ions and organic molecules of biological importance.

The first part of this work deals with the determination of the thermodynamic parameters for the complexation of lanthanide cations (La3+, Pr3+ and Nd3+) with Cryptand-221 and Cryptand-222 in acetonitrile and propylene carbonate at 298.15 K. The complexation process between these cations and these ligands in these solvents is enthalpy-controlled. The higher stability observed for these cations and these ligands in propylene carbonate with respect to acetonitrile is attributed to the increase in entropy observed for the complexation reaction in propylene carbonate. Enthalpies of solution of lanthanide and lanthanide cryptates are reported. These data are used to derive single-ion enthalpies of transfer of La3+, Pr3+ and Nd3+ from propylene carbonate to acetonitrile based on the Ph4AsPh4B convention. The results show that the cryptate conventions are not valid for the calculation of single-ion values for the transfer of tervalent lanthanide cations among dipolar aprotic media. Enthalpies of coordination of lanthanide(III) cryptates in the solid state are calculated. The second part of this study aims to investigate the properties of the synthetic macrocyclic ligands such as Cryptand-222 and 18-Crown-6 towards molecules of biological importance. Stability constants (hence free energies), enthalpies and entropies of complexation of a series of DL-amino acids with 18-Crown-6 and Cryptand-222 in methanol and ethanol, as obtained from titration calorimetry, are reported. No significant variations are found in the free energies of complexation of the different amino acids and these two ligands in these solvents as a result of an enthalpy-entropy compensation effect. This effect is for the first time shown in complexation reactions involving crown ethers and cryptands. The thermodynamic parameters of transfer of amino acids and their complexes with 18-Crown-6 and Cryptand-222 from methanol to ethanol have been calculated. Possible correlations between complexation and transfer data for the amino acids, the ligands and the amino acid-macrocyclic ligand complexes are investigated. The implications of these results to processes of biological importance are discussed. As a continuation of this study, the possibility of selectively extracting amino acids from methanol by polymeric resins containing crown ethers as anchor groups is investigated

The design and characterization of a microcalorimeter to aid drug discovery

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaves 61-62).This thesis describes the design and characterization of a microcalorimeter used to aid drug discovery. There are four key functional requirements for the device: (1.) 8.4 [mu]J energy resolution, (2.) 20 [mu]L reactant volume (combined total), (3.) 10% experimental variance, and (4.) 100 [mu]K baseline calorimeter drift over a two hour period. The calorimeter utilizes a novel heat sensor. This heat sensor combines thermal expansion and the dynamic response of an oscillating ribbon to transduce the signal from a heat event. A vacuum chamber improved the sensitivity of the sensor by approximately an order of magnitude by significantly reducing the losses due to air friction in the resonant sensor. Additional components such as a position sensor, temperature controlled vacuum chamber, software, and a syringe pump were constructed to complete the calorimeter system. The current calorimeter prototype nearly meets each functional requirement. In addition, the current sensitivity of the instrument is near that of a commercially available calorimeter but uses almost two orders of magnitude less solution. Finally, all of our calorimeter components are designed, built, integrated, and ready to begin more rigorous biological solution experimentation.by Scott Jacob McEuen.S.M