Unraveling the mechanism of the photodeprotection reaction of 8-bromo- and 8-chloro-7-hydroxyquinoline caged acetates

Jiani Ma, Adam C. Rea, Huiying An, Chensheng Ma, Xiangguo Guan, Ming De Li, Tao Su, Chi Shun Yeung, Kyle T. Harris, Yue Zhu, Jameil L. Nganga, Olesya D. Fedoryak, Timothy M. Dore, David Lee Phillips

Research output: Contribution to journalArticlepeer-review

Abstract

Photoremovable protecting groups (PPGs) when conjugated to biological effectors forming "caged compounds" are a powerful means to regulate the action of physiologically active messengers in vivo through 1-photon excitation (1PE) and 2-photon excitation (2PE). Understanding the photodeprotection mechanism is important for their physiological use. We compared the quantum efficiencies and product outcomes in different solvent and pH conditions for the photolysis reactions of (8-chloro-7-hydroxyquinolin-2-yl) methyl acetate (CHQ-OAc) and (8-bromo-7-hydroxyquinolin-2-yl)methyl acetate (BHQ-OAc), representatives of the quinoline class of phototriggers for biological use, and conducted nanosecond time-resolved spectroscopic studies using transient emission (ns-EM), transient absorption (ns-TA), transient resonance Raman (ns-TR 2), and time-resolved resonance Raman (ns-TR 3) spectroscopies. The results indicate differences in the photochemical mechanisms and product outcomes, and reveal that the triplet excited state is most likely on the pathway to the product and that dehalogenation competes with release of acetate from BHQ-OAc, but not CHQ-OAc. A high fluorescence quantum yield and a more efficient excited-state proton transfer (ESPT) in CHQ-OAc compared to BHQ-OAc explain the lower quantum efficiency of CHQ-OAc relative to BHQ-OAc.

Original languageEnglish (US)
Pages (from-to)6854-6865
Number of pages12
JournalChemistry - A European Journal
Volume18
Issue number22
DOIs
StatePublished - May 29 2012

Keywords

  • cage compounds
  • photodeprotection
  • proton transfer
  • quinoline
  • time-resolved spectroscopy

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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