Probing the Behavior of Confined Water by Proton-Transfer Reactions

• Published in: The journal of physical chemistry. B Vol. 110; no. 47; pp. 24231 - 24237
• Main Authors: Angulo, G, Organero, J. A, Carranza, M. A, Douhal, A
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 30.11.2006
• Subjects: Deuterium Oxide - chemistry; Fluorescence; Hydrogen Bonding; Hydroxyquinolines - chemistry; Kinetics; Micelles; Protons; Solvents - chemistry; Spectrometry, Fluorescence; Surface-Active Agents - chemistry; Thermodynamics; Water - chemistry
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp064257g

The picosecond dynamics of a bifunctional and H-bonding molecule, 7-hydroxyquinoline (7HQ), has been studied in a reverse micelle with increasing water content. The fluorescence kinetics has a complex behavior as the water content is changed. All reactions are irreversible, and a two-step mechanism is invoked to explain the observations. H2O/D2O exchange and excitation energy effects show that the second step has a higher barrier and that the corresponding reaction occurs through tunneling. The results clearly indicate two regimes of water nanopool behavior switching at W 0 ≈ 5 (W 0 = [water]/[surfactant]). Water collective dynamics explains these observations. The lower fluidity of confined water within the reverse micelle with respect to normal bulk water alters the related H-bond network dynamics and therefore is responsible for the slower proton-transfer processes.