Effect of sucrose on the properties of caffeine adsorption layers at the air/solution interface

Sweet and bitter tastes are known to be mediated by G-protein-coupled receptors. The relationship between the chemical structure of gustable molecules and their molecular organization in saliva (aqueous solution) near the surface of the tongue provides a useful tool for elucidating the mechanism of...

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Bibliographic Details
Published in:Journal of colloid and interface science 2004-08, Vol.276 (2), p.269-276
Main Authors: Aroulmoji, V., Aguié-Béghin, V., Mathlouthi, M., Douillard, R.
Format: Article
Language:English
Subjects:
Adsorption
Air
Caffeine
Caffeine - chemistry
Chemical Sciences
Chemistry
Ellipsometry
Exact sciences and technology
General and physical chemistry
Molecular Structure
Other
Solutions - chemistry
Sucrose
Sucrose - chemistry
Surface physical chemistry
Surface Properties
Surface Tension
Taste
Water - chemistry
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Summary:Sweet and bitter tastes are known to be mediated by G-protein-coupled receptors. The relationship between the chemical structure of gustable molecules and their molecular organization in saliva (aqueous solution) near the surface of the tongue provides a useful tool for elucidating the mechanism of chemoreception. The interactions between stimulus and membrane receptors occur in an anisotropic system. They might be influenced by the molecular packing of gustable molecules within an aqueous solvent (saliva) close to the receptor protein. To investigate the molecular organization of a sweet molecule (sucrose), a bitter molecule (caffeine), and their mixture in an aqueous phase near a “wall,” a hydrophobic phase, we modeled this using an air/liquid interface as an anisotropic system. The experimental (tensiometry and ellipsometry) data unambiguously show that caffeine molecules form an adsorption layer, whereas sucrose induces a desorption layer at the air/water interface. The adsorption of caffeine molecules at the air/water interface gradually increases with the volume concentration and is delayed when sucrose is added to the solution. Spectroscopic ellipsometry data show that caffeine in the adsorption layer has optical properties practically identical to those of the molecule in solution. The results are interpreted in terms of molecular association of caffeine with itself at the interface with and without sucrose in the subphase, using the theory of ideal gases.
ISSN:0021-9797
1095-7103
DOI:10.1016/j.jcis.2004.03.060