1385Tryptanthrin (T, Fig. 1a) is a weak basic alkaloid formed in a number of plant species.1 This compound possesses antibacterial activity against a variety of pathogenic bacteria.2 However, the optical absorption and fluorescence properties of T and its derivatives have never been reported. Recently, we investigated the optical absorption and fluorescence properties of T and its derivatives. As results of measurements of their UV-vis absorption and fluorescence spectra, we found that 2-aminotryptanthrin (T2NH2, Fig. 1b) had excellent photophysical properties, such as wide-wavelength absorption and emission, and a high fluorescence quantum yield (Φf = 0.5 in acetonitrile).3 T2NH2 will become a good energy acceptor for FRET (fluorescence resonance energy transfer), 4,5 compatible with an energy donor having a wide excitation wavelength range of over 300 nm.FRET is defined as an excited-state energy interaction between two fluorophores in which excited donor energy is transferred to an acceptor part without any photon-emission. 4,5 FRET thus requires a certain degree of spectral overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor. In pursuit of FRET-based metal cation sensors, we report here a new receptor, 1-(2-tryptanthrinylaminoacetoxy)-14-(1-pyrenecarboxy)-3,6,9,12-tetraoxatetradecane (T2NH-P5P, Fig. 1c), in which a pyrene group as an energy donor and a 2-aminotryptanthrin unit as energy acceptor are anchored with pentaethyleneglycol, displaying change in the FRET behavior upon Al 3+ addition. T2NH-P5P was obtained in four steps. The electron-spray ionization mass spectra of T2NH-P5P showed corresponding molecular ion peaks, and the NMR spectra were appropriate for the compound.6 A stock solution of T2NH-P5P was prepared by dissolving a weighed amount of T2NH-P5P in acetonitrile.The titration of T2NH-P5P ([T2NH-P5P] = 1 μM, M = mol dm -3 ) against metal-ion solutions was performed in a spectro photometric cell of 1-cm path length. The UV-vis spectra (between 200 and 600 nm) of the resulting solutions were recorded at room temperature with a JASCO V-670 spectrophotometer after the addition of each metal salt: Ca(ClO4)2, Ba(ClO4)2, Zn(ClO4)2, and Al(ClO4)3. The fluorescence spectra were measured between 350 and 700 nm with a Hitachi F-4500 fluorometer using an excitation wavelength of 325 nm. Titrations were performed with metal ions (10 -1000 μM) as a titrant and T2NH-P5P (1 μM) as a titrate. The metal-ion sources were identical to those used to 2009 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. E-mail: jun@cc.hirosaki-u.ac.jp
2-aminotryptanthrin Derivative with Pyrene as a FrET-based Fluorescent chemosensor for al
3+Jun kawakami,* † kenta kikucHi,* kazunori cHiba,* Noriyuki maTsusHima,* asako yamaya,* shunji iTo,* masahiko Nagaki,* and Haruo kiTaHara** * Graduate School of Science and Technology, Hirosaki University, Hirosaki, Japan ** Department of Natural Science, Faculty of Education, Hirosaki University, Hirosaki,, Ja...
