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Wide-line 1 H NMR measurements were extended and all results were reinterpreted in a new thermodynamics-based approach to study aqueous solutions of thymosin-β 4 (Tβ 4 ), stabilin C-terminal domain (CTD) and their 1:1 complex. The energy distributions of the potential barriers, which control motion of protein-bound water molecules, were determined. Heterogeneous and homogeneous regions were found at the protein-water interface. The measure of heterogeneity gives a quantitative value for the portion of disordered parts in the protein. Ordered structural elements were found extending up to 20 % of the whole proteins. About 40 % of the binding sites of free Tβ 4 become involved in bonds holding the complex together. The complex has the most heterogeneous solvent accessible surface (SAS) in terms of protein-water interactions. The complex is more disordered than Tβ 4 or stabilin CTD. The greater SAS area of the complex is interpreted as a clear sign of its open structure., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)