Activation energy is “the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport.” Simply put, it is the energy needed for a chemical reaction to occur.
Extracting activation energy from temperature dependent viscosity data is one characterization tool to quantify protein-protein interactions of concentrated protein formulations. The activation energy of these solutions reflects the dynamics of protein clusters and aggregates. It can be used to rank different buffer formulations based on their risk for large protein cluster or aggregate formation.
The viscosity of protein formulations is sensitive to changes in temperature. This sensitivity to temperature changes can be exploited to characterize protein behavior in solution. Combining temperature and scattering experiments has enabled detailed characterization of formulation microstructure and protein cluster dynamics in the past (Dharmaraj et. al., 2016). In that study, activation energy (Ea) was determined using the Arrhenius equation to determine the extent to which proteins clustered and aggregated in solution.
The Arrhenius equation is “a formula for the temperature dependence of reaction rates.” The Arrhenius equation provides the dependence of the rate constant of a chemical reaction on the absolute temperature. This equation can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, along with many other thermally-induced processes/reactions.
Performing temperature sweeps to determine activation energy of protein formulations can help characterize protein-protein interactions of concentrated protein solutions. The activation energy derived from the Arrhenius model can be a useful tool to rank a formulations’ performance. Activation energy quantifies protein-protein interactions (PPI). An increase in activation energy implies that motion between proteins sliding past each other is hindered and that there is a reduction in exchange of proteins between protein clusters.
In our application note, “Calculating Activation Energy with Arrhenius”, we walk you through how to determine activation energy using the Arrhenius equation on data collected on the VROC® initium one plus. The fully automated VROC initium one plus with the retrieval feature activated makes measurement at multiple temperatures possible with a single loaded volume. The closed system design also eliminates any artifacts due to evaporation.
Written by: Eden Reid, RheoSense Senior Marketing and Sales Operations