While this geometric argument appears to contradict our own work, this discrepancy could be a result of the different analysis techniques employed. For the shortest alkylthiols, a dip in the isothermal titration calorimetry plot is observed and attributed in the modeling process to the possible existence of two coordination sites on the nanocrystal surface. However, this feature looks highly reminiscent of the titration of indium chloride into indium phosphide quantum dots, which we previously determined to be caused by breaking stronger inter-ligand interactions. Additionally, the reaction stoichiometry model parameter n-which is the ratio between the actual exchanged ligands and the available surface sites from the fit-decreased as nanocrystal size increased. Our own composition dependent modeling of bent and straight chain ligand interligand interactions predict that the enthalpy of exchange parameter for the head groups should be independent of the extent of the reaction. Elimelech et al. used a "single set of independent binding sites" model for the analysis of isothermal titration calorimetry data; 57 however, this analysis does not account for composition dependent surfaces. While both isothermal titration calorimetry and 1 H NMR measurements were performed, only the isothermal titration calorimetry data was used to fit their model. However, using only isothermal titration calorimetry data or 1 H NMR data to model nanocrystal surface reactions does not account for the composition changes of the ligand shell, and thus changes in the adsorption energy due to the inter-ligand interactions. Fitting data to a single site isothermal titration calorimetry model or an adsorption isotherm may yield incorrect results, particularly when small changes in enthalpy are observed. This illustrates the power of using a composition dependent model such as the Ising model that combines enthalpic data from isothermal titration calorimetry with the coverage data from 1 H NMR to give a more complete picture of the reaction on the surface of colloidal quantum dots. 7, 9, 51