Thermophoresis of cyclodextrins and cyclodextrin-drug-complexes

The behaviour of biomolecules in a temperature gradient, known as thermodiffusion, changes when a ligand binds. In recent years, this effect has been used to gain detailed information on binding dynamics, although the physicochemical processes are still unclear [1]. We focused on the question how the hydration layer affects thermodiffusion when it changes due to complex formation. As model system we used cyclodextrin complexes with acetylsalicylic acid (Aspirin). Cyclodextrins are cyclic oligosaccharides that show a strong tendency towards complex formation. For that reason they are interesting as drug delivery systems [2,3.] The thermodiffusion of different cyclodextrins [4] and their aspirin complexes was investigated in a temperature range from 10 to 50°C by infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS). Additionally, NMR measurements were performed at 25 and 60°C to obtain information about stability and structure of the complexes. We found that all cyclodextrins show a stronger diffusion towards the cold side when Aspirin binds. This behaviour suggests a weaker interaction with the surrounding water that could be explained by hydrogen bond formation inside the complex.[1] M. Jerabek-Willemsen, T. André, W. Wanner, H. Roth, S. Duhr, P. Baaske, and D. Breitsprecher, J. Mol. Struct. (2014).[2] E. Del Valle, Process Biochemistry 39, 1033 (2004).[3] J. Szejtli, Drug Invest. 2, 11 (1990).[4] K. Eguchi, D. Niether, S. Wiegand, and R. Kita, Eur.Phys. J. E 39, 16086 (2016)