On the potentially spurious contributions of cosolutes in protein 15N relaxation dispersion measurements

•A rigorous quantification of the thermodynamics, kinetic and structural changes can be approached by relaxation dispersion methods on proteins.•Cosolutes modulate the fitted parameters extracted from relaxation dispersion analyses.•Such modulation arises from direct or indirect effect of the cosolute and it may obscure the extraction of the pure thermodynamic parameters associated with the desired functional dynamics.•Solvent accessibility analysis is a good, but not definitive, approach to identify such spurious effect.•This observation aims to act as a word of caution for measurements of relaxation dispersion at a single-solvent condition that contains large amounts of cosolutes.