2-Aminotryptanthrin Derivative with Pyrene as a FRET-based Fluorescent Chemosensor for Al3+

Abstract

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...

Tryptanthrin from indigo: Synthesis, excited state deactivation routes and efficient singlet oxygen sensitization

“…Due to the scarcity of the natural existence of TRYP, together with its unique bioactive properties, the synthesis of this compound has generated great interest with the development of several synthetic strategies reported [14,17,[24][25][26][27][28], such as the oxidation of indigo or the cyclization of isatin and isatoic anhydride [16,29]. Despite these studies, significant synthetic challenges still remain, since many of these methods are burdensome and are not environmentally friendly [13,16,26,27,29,30]. Therefore the development of a new efficient, low cost, one-pot protocol to access TRYP is both attractive and valuable.…”

“…Successful fluorescent imaging in cells and tissues requires the application of dyes which absorb and emit in the "optical window" (concerning the near-infrared (NIR) region of the electromagnetic spectrum -650-900 nm). This selectivity is required to avoid the interference of endogenous substances during the fluorescent imaging process, as well as to improve tissue penetration levels [30][31][32][33][34][35].…”

2-Aminotryptanthrin Derivative with Pyrene as a FRET-based Fluorescent Chemosensor for Metal Ions

“…7 When Fe, Ni, Cu, Cd, and Hg salts were added to the acetonitrile solution of T2NH-P5P, the same behavior was observed. The absorption and fluorescence spectra of T2NH-P5P with and without Hg 2+ at several concentrations are shown in Fig.…”

“…The association constants were determined from the emissionintensity changes at the 600 nm emission maxima for T2NH-P5P using Eq. (7). The values of log K of T2NH-P5P with the metal ions are reported in Cu 2+ and Hg 2+ usually behave as fluorescence quenchers via an electron transfer from the excited-state fluorophore to the empty d-orbital [14][15][16] ; therefore, many of the reported molecular systems show a fluorescence-quenching response upon the addition of Cu 2+ and Hg 2+ .…”

Tryptanthrin derivatives as efficient singlet oxygen sensitizers

“…Moreover, encapsulation of TRYP in various nanoparticles [31] improves its delivery and its sustained release. These unique properties have led to obtain tryptanthrin derivatives that absorb and emit even at longer wavelength (wavelengths that are desirable for applications in biological systems) as well as fluorescent chemosensors for metal ions [32][33][34][35][36][37][38].…”