title: Substituent effects on the sensitivity of a quinoline photoremovable protecting group to one- and two-photon excitation.
abstract: Photoremovable protecting groups that can reveal biologically important functional groups through one- and two-photon excitation (1PE and 2PE, respectively) have promise in regulating physiological function in a temporally and spatially restricted manner. Only a few chromophores have sufficient sensitivity to 2PE suitable for use as "caging groups" in physiology experiments. It would be useful to develop structure-property relationships of chromophores, so that chromophores with high two-photon uncaging action cross-sections (delta(u)) can be designed. The 8-bromo-7-hydroxyquinolinyl chromophore (BHQ) releases a variety of functional groups through 1PE and 2PE. Swapping the bromine substituent for a nitro (NHQ), cyano (CyHQ), or chloro (CHQ) or exchanging the hydroxy for dimethylamino (DMAQ and DMAQ-Cl) or sulfhydryl (TQ) significantly alters the photochemical and photophysical properties of the quinoline chromophore. CyHQ-OAc demonstrated a 3-fold increase in sensitivity for acetate release, whereas NHQ-OAc was photochemically insensitive. The quantum efficiencies (Q(u)) of the amino and sulfhydryl derivatives were about an order of magnitude lower than that of BHQ-OAc. All of the chromophores showed diminished sensitivity to 2PE compared to BHQ-OAc, but the CyHQ, DMAQ, and DMAQ-Cl chromophores are sufficiently sensitive for physiological use. The high sensitivity of CyHQ to 1PE will be useful in biological applications requiring short exposure with low light intensity.
authors.affiliation: Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA.
authors.forename: M Jarrett
authors.initials: MJ
authors.lastname: Davis
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Kragor
authors.forename: Khalilah G
authors.initials: KG
authors.lastname: Reddie
authors.forename: Hunter C
authors.initials: HC
authors.lastname: Wilson
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhu
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Dore
mesh_terms: D007700:Kinetics; D010782:Photolysis; D017785:Photons; D011804:Quinolines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011804:Quinolines; C037219:quinoline