(49g) Continuous Injection Isothermal Titration Calorimetry to Determine Kinetic Parameters for Small Molecule Adsorption at Solvated Interfaces

Isothermal titration calorimetry (ITC) is used to elucidate binding interactions between two molecules, with one acting as a ligand and the other as a receptor. In biology, ITC has emerged as a pivotal technique for exploring association processes. Abiological systems, including solvated adsorbate-nanoparticle interactions have also been examined by ITC. Fundamental thermodynamic binding parameters – enthalpy (DH), entropy (DS) stoichiometry coefficient (n) and equilibrium constant (K) – are determined. ITC can be utilized for determining kinetic parameters (kinITC) through models with known kinetic data. In IIA-ITC experiments, the calculation of kinetic data, such as dissociation constants, k_off, is achieved by fitting the model predictions to the shape of each peak in the thermogram, which arises from the gradual injection of ligand into the calorimeter cell.

The continuous injection approach (CIA-ITC) is an alternative method to IIA-ITC. In this approach, a continuous flow of the ligand is delivered into the calorimetry cell. This continuous injection allows for an increased amount of data, resulting in high-density data around the inflection point of the thermogram. In the case of CIA-ITC, the application of kinITC is not feasible, as the continuous injection of the ligand does not result in the formation of peaks in the thermogram. Given the limitations encountered in computing kinetic parameters with kinITC, we developed novel methodology to obtain the desired kinetic data utilizing the thermogram derived from CIA-ITC. We determined k_on for the two independent binding site model. We utilized the binding of Ca²⁺ ions into a solution of ethylenediaminetetraacetic acid and 1,3-diaminopropane-N,N,N',N'-tetraacetic acid. We demonstrate this approach to extract k_on values for small molecule adsorption from solution to solvated nanoparticles. We determined the kinetics of adsorption of alkanethiolates to Au nanoparticles in water. Future applications of our newly formulated kinetic CIA-ITC approach will be applied to supported nanoparticle catalysts.