An Optochemical Oxygen Scavenger Enabling Spatiotemporal Control of Hypoxia

We present an optochemical O₂ scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O₂ by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560–590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O₂ consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca²⁺) influx into HEK293T cells expressing the hypoxia-responsive Ca²⁺ channel TRPA1.     

Reaction of diphenylphosphine oxide with a 10-methylacridinium salt. Reversible formation of a P?C covalent bond

Diphenylphosphine oxide ( 1 ′) reacts reversibly with a 10-methylacridinium salt ( 2 ) in acetonitrile at 20°C to equilibrate with a new salt 3 formed by the addition of 1 ′ to the cation of 2 . The forward reaction in this equilibrium proceeds via nucleophilic attack by the phosphorus atom of diphenylphosphinous acid ( 1 ), the trivalent tautomer of 1 ′, upon the 9-carbon atom of the cation of 2 , forming a phosphorus–carbon covalent bond. The equilibrium constant has been determined by UV-vis and ¹H NMR spectroscopy as well as by HPLC analysis. The reaction has been analyzed kinetically, and the results have been compared with those obtained in the similar reaction of an alkyl ester of 1 , the diphenylphosphinite ( 5 ), with 2 that gives the phosphonium salt 6 . It is suggested that 6 is much more stable than 3 . The equilibrium constant for the tautomerism between 1 ′ and 1 has also been estimated. © 1995 John Wiley & Sons, Inc.