Do the solvent properties affect the propensity for self-association of α-cyclodextrin? Insights from NMR self-diffusion

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T1 - Do the solvent properties affect the propensity for self-association of α-cyclodextrin? Insights from NMR self-diffusion

AU - Valente, Artur J.M.

AU - Söderman, Olle

PY - 2019

Y1 - 2019

N2 - Whether cyclodextrins (CDs) self-aggregate or not in solution is an interesting and timely scientific question. Yet, we are far from a scientific consensus as regards the nature of the phenomenon. Those who are in favor of the formation of CD aggregates justify the phenomenon by the presence of H-bonds, occurring between the hydroxyl groups located at both rims of cyclodextrins. To gain further insight with regard to the importance of these intermolecular CD-CD interactions, a systematic study of 1H NMR self-diffusion of α-cyclodextrin in binary mixtures of deuterated DMSO and water, at different mole fractions, has been carried out. The choice of these solvents was made based on their different degree of polarity and the fact that they are miscible at any molar ratio. The experimental α-CD diffusion coefficients scale with the solution viscosity. Moreover, hydrodynamic radii of α-CD are independent of the solvent composition. No evidence of α-cyclodextrin aggregation at any DMSO mole fraction is found. Finally, experimental diffusion data are compared with those obtained from atomic level hydrodynamic calculations. In addition, diffusion coefficients of heavy water and DMSO in binary mixed solvents are also measured and analyzed. The obtained diffusion coefficients for DMSOd6 and D2O show a minimum at the eutectic composition and depend on the solution viscosity. The experimental results are compared with published molecular dynamic simulations.

AB - Whether cyclodextrins (CDs) self-aggregate or not in solution is an interesting and timely scientific question. Yet, we are far from a scientific consensus as regards the nature of the phenomenon. Those who are in favor of the formation of CD aggregates justify the phenomenon by the presence of H-bonds, occurring between the hydroxyl groups located at both rims of cyclodextrins. To gain further insight with regard to the importance of these intermolecular CD-CD interactions, a systematic study of 1H NMR self-diffusion of α-cyclodextrin in binary mixtures of deuterated DMSO and water, at different mole fractions, has been carried out. The choice of these solvents was made based on their different degree of polarity and the fact that they are miscible at any molar ratio. The experimental α-CD diffusion coefficients scale with the solution viscosity. Moreover, hydrodynamic radii of α-CD are independent of the solvent composition. No evidence of α-cyclodextrin aggregation at any DMSO mole fraction is found. Finally, experimental diffusion data are compared with those obtained from atomic level hydrodynamic calculations. In addition, diffusion coefficients of heavy water and DMSO in binary mixed solvents are also measured and analyzed. The obtained diffusion coefficients for DMSOd6 and D2O show a minimum at the eutectic composition and depend on the solution viscosity. The experimental results are compared with published molecular dynamic simulations.

KW - DMSO

KW - PFG NMR

KW - Self-diffusion coefficients

KW - Water

KW - α-Cyclodextrin

U2 - 10.1016/j.molliq.2019.111869

DO - 10.1016/j.molliq.2019.111869

M3 - Article

AN - SCOPUS:85072898477

VL - 295

JO - Journal of Molecular Liquids

JF - Journal of Molecular Liquids

SN - 0167-7322

M1 - 111869

ER -