Hydroxypropyl-Substituted β-Cyclodextrins: Influence of Degree of Substitution on the Thermodynamics of Complexation with Tauroconjugated and Glycoconjugated Bile Salts

The effect of the degree of substitution (DS) on the ability of hydroxypropylated β-cyclodextrin (HPβCD) to form inclusion complexes with six different bile salts, found within the intestinal tracts of rats, dogs, and humans, was studied by isothermal titration calorimetry. The composition and molec...

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Bibliographic Details
Published in:Langmuir 2010-12, Vol.26 (23), p.17949-17957
Main Authors: Schönbeck, Christian, Westh, Peter, Madsen, Jens Christian, Larsen, Kim Lambertsen, Städe, Lars Wagner, Holm, René
Format: Article
Language:English
Subjects:
Animals
Anions
beta-Cyclodextrins - chemistry
Bile Acids and Salts - chemistry
Calorimetry - methods
Chemistry
Chemistry - methods
Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams
Dogs
Exact sciences and technology
General and physical chemistry
Humans
Magnetic Resonance Spectroscopy - methods
Molecular Structure
Pyrans - chemistry
Rats
Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
Thermodynamics
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Summary:The effect of the degree of substitution (DS) on the ability of hydroxypropylated β-cyclodextrin (HPβCD) to form inclusion complexes with six different bile salts, found within the intestinal tracts of rats, dogs, and humans, was studied by isothermal titration calorimetry. The composition and molecular structure of the cyclodextrin samples were characterized by MALDI-TOF mass spectrometry together with 1D and 2D-NMR, and some of the complexes were studied by 2D ROESY NMR. The stability and structure of the complexes were mainly determined by the position of hydroxyl groups on the bile salts and depended relatively little on the number of hydroxypropyl side chains on the CDs. The enthalpy and entropy of complexation exhibited a strong linear increase as the DS increased from 0 to 1, and a pronounced enthalpy−entropy compensation was observed. These observations are interpreted as an increased release of ordered water from the hydration shells of the bile salts, caused by the hydroxypropyl substituents on the rim of the CD. It is estimated that each CD hydroxypropyl substituent dehydrates a hydrophobic surface area of approximately 10 Å2.
ISSN:0743-7463
1520-5827
DOI:10.1021/la103124n