title: Excited-state proton transfer from pyranine to acetate in gamma-cyclodextrin and hydroxypropyl gamma-cyclodextrin.
abstract: Excited-state proton transfer (ESPT) from pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) to acetate has been studied by picosecond and femtosecond emission spectroscopy in gamma-cyclodextrin (gamma-CD) and 2-hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) cavities. In both the CDs, ESPT from HPTS to acetate is found to be very much slower (90 and 200 ps) than that in bulk water (0.15 and 6 ps). From molecular modeling, it is shown that in the cyclodextrin cavity the acetate is separated from the OH group of HPTS by water bridges. As a result, proton transfer in the cavity requires rearrangement of the hydrogen-bond network involving the cyclodextrin. This is responsible for the marked slowdown of ESPT. ESPT of HPTS in substituted gamma-CD is found to be slower than that in the unsubstituted one. This is attributed to the hydroxypropyl groups, which prevent close approach of acetate to HPTS.
authors.affiliation: Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
authors.forename: Sudip Kumar
authors.initials: SK
authors.lastname: Mondal
authors.forename: Kalyanasis
authors.initials: K
authors.lastname: Sahu
authors.forename: Subhadip
authors.initials: S
authors.lastname: Ghosh
authors.forename: Pratik
authors.initials: P
authors.lastname: Sen
authors.forename: Kankan
authors.initials: K
authors.lastname: Bhattacharyya
mesh_terms: D000085:Acetates / Q000737:chemistry*; D001190:Arylsulfonates / Q000737:chemistry*; D006860:Hydrogen Bonding; D015394:Molecular Structure; D011522:Protons; D013052:Spectrometry, X-Ray Emission; D047408:gamma-Cyclodextrins / Q000737:chemistry*
chemical_list: D000085:Acetates; D001190:Arylsulfonates; D011522:Protons; D047408:gamma-Cyclodextrins; C479659:hydroxypropyl-gamma-cyclodextrin; C005047:pyranine