Isothermal calorimetry is a technique that researchers use to determine how small molecules can bind to larger molecules by defining the substances’ thermodynamic parameters. Most often, researchers use this technique in food science and pharmaceutical development. However, alternatives to isothermal calorimetry may be more effective in certain applications. Here’s what you need to know about isothermal calorimetry and its effectiveness.
How Does Isothermal Calorimetry Work?
Isothermal calorimetry measures heat that a chemical reaction either releases or absorbs. This allows researchers to characterize certain chemical processes occurring during the reaction, helping them determine compatibility, stability, and material interaction. Most often, scientists use isothermal calorimetry to study the binding of small molecules to larger macromolecules.
Scientists use an isothermal titration calorimeter to conduct this process. Two identical cells made of a chemically inert material that can conduct thermal energy are inside an adiabatic jacket, and this instrument forms the calorimeter. One cell is a sample cell that the calorimetry actually takes place in, while the other cell acts as a reference. Researchers will fill the reference cell with buffer or water and the sample cell with the macromolecule, such as proteins or DNA.
Next, researchers apply a constant power to the reference cell to direct a feedback circuit to a heater on the sample cell. They will then titrate the other molecule in the experiment, known as a ligand, into the sample cell. The sample cell will either absorb heat or evolve heat – in an exothermic reaction, the sample cell will increase in temperature and the reference cell’s feedback power will decrease to maintain a consistent temperature. In an endothermic reaction, the sample cell temperature lowers, and the feedback circuit will increase in power.
What Applications Is Isothermal Calorimetry Useful For?
Isothermal calorimetry is useful in a number of processes. It is particularly useful in pharmaceutical studies, allowing scientists to understand how different materials will interact in drugs. For example, compatibility screenings, the stability of liquid and solid products, and polymer relaxation all involve isothermal calorimetry. In addition, food sciences also depend on isothermal calorimetry. Scientists use isothermal calorimetry to study wine fermentation, vegetable respiration, and blanching, as well as spoilage prevention techniques.
Alternatives to Isothermal Calorimetry
While isothermal calorimetry may be useful in food and drug development applications, it has many weaknesses. It requires large quantities of sample and ligand, works on limited buffers and has low throughput due to the long time it takes for each titration. For pharmaceutical researchers who want to test the effectiveness and safety of new drugs, there are some alternatives to isothermal calorimetry.
TRIC technology, which stands for temperature related intensity change, is another technology that scientists can use to measure the strength of the interactions between two molecules and calculate a dissociation constant or Kd.
TRIC is based on the fact that a fluorophore’s chemical environment (ie, molecular conformation and fluorophore proximity) is affected when the two binding partners interact as a result of an induced temperature change. This in turn affects the fluorescence intensity of the fluorophore.
To perform a TRIC assay, scientists mix a fluorescently labeled target biomolecule with a series of dilutions of a ligand molecule while they apply heat.
TRIC’s main benefits are that it can measure the affinity between any biomolecules (proteins, viruses, liposomes, vesicles, nanoparticles, and nanodiscs) in solution in close to native conditions in virtually any buffer with very little sample. And high throughput is never an issue as measurements take just a few minutes.
If you are looking for an updated way to measure interactions between molecules in your pharmaceutical laboratory, think twice about using isothermal calorimetry. While the method is traditional, you may find a second perspective through TRIC technology.
Gupta, Amit J.; Duhr, Stefan; Baaske, P. (2018). Microscale Thermophoresis (MST). Encycl. Biophys. Living Edi.