Isothermal Titration Calorimetry

Almost every student at Mines takes a thermodynamics course in their academic career. Whether the topic is enjoyable or not, Muneera Beach, PhD in Biochemistry and Biophysics, explains the importance of thermodynamics in technology today. Beach works with a microcalorimetry. Microcalorimetry is essentially the study of thermodynamics at a microscopic level. This helps scientists understand the complex binding phenomena through heat interactions. The two capital methods of microcalorimetry are Differential Scanning Calorimetry (DSC) and Isothermal Titration Calorimetry (ITC).

A UCSD graduate, Beach originally thought she would go to medical school. Realizing that she disliked anatomy, Beach changed her course and went for calorimetry, “I decided to get a Ph.D. and haven’t looked back since. ” Being an application scientist, Beach uses simulations to help run experiments and return reports for specific projects for GE Healthcare. She has been with the company since 2008.

More specifically, Beach uses ITC to measure the entropy, enthalpies, and stoichiometry of mixing molecules. ITC utilizes two cells, the sample cell and the reference cell. The given molecule is placed in the sample cell while the reference cell typically contains water. A syringe then injects the other molecule being measuring into the sample cell. The sides of the cells have sensors and the capability to raise and lower temperature. The reference cell matches the temperature change in the sample cell to equate the differential temperature for the entire mechanism to zero.

During her seminar last week, Beach covered three major examples of how ITC is used in the modern world: biomimetic interactions of proteins with functionalized nanoparticles, polymer surfactant complexes, and pharmaceutical applications.

These readings can be used to calculate the enthalpy, entropy, or stoichiometry of the mixture caused by hydrogen bonds and Van der Waals attraction.
Measuring amino acid functionalized particles bonding with different proteins can be used to modulate enzyme activity. These experiments can also show scientists how many of the amino acids are bonding with the proteins and how many of them are bonding the same way. Amino acids are placed in the sample cell while the proteins are titrated into the cell using the syringe. Beach points out that these reactions can rely on both electrostatics and hydrophobic characteristics of the molecules. The temperature at which the experiments occur is also crucial to the results. Mixing the same amino acid to the same protein can result in vastly different numbers for the enthalpy and entropy.

Polymer Surfactant Complexes can also be analyzed using ITC. Detergents, cosmetics, environmental health and safety, pharmaceutical aspects and energy, are a few of the areas polymer surfactant interactions affect. Beach discusses the concentration of sodium dodecyl sulfate (SDS) when mixed with polymers in water. She also discusses the major difference one ethyl group can make in a peptide when being mixed with SDS. For example, Beach compares polyethylene glycol to polypropylene glycol. The two polymers produce opposite concentrations of SDS when using ITC. Beach explains that polyethylene glycol produces hydrophobic effects while polypropylene glycol causes enthalpic effects.

ITC also vastly affects the pharmaceutical industry. Beach explains a recent experiment done to stabilize a certain protein using polysorbate-80. Trials revealed that pharmacists were overusing polysorbate-80. After the correctly calculated ratio was used, the proteins were then able to disassociate in the body during consumption which allowed for the drugs to be more effective. ITC can also be used to measure the quality of proteins. Companies wanting to measure the activity in a protein could use ITC to see reactions caused when mixing proteins. Beach says that the activity in quinidine antibodies were recently measured using a similar process.

ITC can be used for a magnitude of applications as Beach closes with, “size does not matter in ITC, as long as you have a binding event.” She points out that ITC is used for a vast and diverse amount of applications. Nanoparticle, proteins, and polymers are just a few examples of science utilizing thermodynamics to improve products and medicine in the modern world.