Visible Fluorescence Chemosensor for Saxitoxin

Abstract

Absorption spectra of a number of shellfish extracts have been obtained, and reveal prominent absorptions in all samples at 210 and 260 nm, and at 325 nm in some of them. These absorptions preclude the use of chromophores with similar absorptions in testing of shellfish samples for paralytic shellfish toxins. Two crown ether chemosensors featuring a boron azadipyrrin chromophore have been synthesized; both have absorption maxima at 650 nm, where all the shellfish extracts are transparent. The synthetic sensors feature either 18-or 27-membered crown-ether rings, and have been evaluated as visible sensors for the paralytic shellfish toxin saxitoxin. The binding constant for one of them is in the range of 3 -9 × 10 5 M -1 , and exhibits a fluoresence enhancement of over 100% at 680 nm, in the presence of 40 μM saxitoxin.Contamination of shellfish by paralytic shellfish toxins or poisons (PSTs, PSPs) continues to be a near-worldwide health risk. 1,2 Monitoring of shellfish beds for the presence of PSTs continues to use the mouse bioassay as the most common means of detection, 3,4 although recent advances in HPLC methods have been made and approved for use by monitoring agencies. 5 The mouse bioassay has obvious economic and ethical drawbacks, 6 and alternatives are being actively sought in a number of laboratories. 4,7-9Our work in this area has focussed on optical methods, and we have developed and explored a number of chemosensor systems that are based on the concept of photoinduced electron transfer, or PET. In PET-based chemosensors, a host for a given analyte is designed in which a chromophore is separated from the host by a spacer (see Figure 1). 10-12 In our case, the host component of the sensor is a crown ether that is separated from the fluorophore by a methylene spacer. In the absence of a guest such as saxitoxin, PET from the crown to the fluorophore quenches the excited state after photon absorption, and fluorescence is turned off (or more accurately, is minimized). When the host is complexed to the toxin, the relative energies of the molecular orbitals are perturbed so that PET is no longer favorable, and fluorescence is "turned on". 13,14 The sensitivity of a PET-based chemosensor is influenced by a number of factors, including the quantum yield of the fluorophore and the equilibrium, or binding constant, K b , between the chemosensor and the fluorescent complex.In past studies, we have evaluated anthracene, 13,14 coumarin, 15,16 and acridine 17 fluorophores in our chemosensors, all of which have absorption maxima in the ultraviolet. This class of chemosensors is selective for detection of saxitoxin over tetrodotoxin, 17 metal ions such as sodium and potassium, 15 and several other analytes. 13 They can also be incorporated into self-assembled monolayers for sensing on a surface. 16,18,19 Recently, we reported that incorporation of larger crown ether rings can significantly increase the binding constant. 14 We now report the synthesis and evaluation of boron azadipyrrins 1 and 2, having absorp...

Synthesis and optical characterization of novel azacrown ethers containing an acridinone or an N-methylacridinone unit as potential fluorescent chemosensors

“…The residue was purified by column chromatography on silica gel using 1:3 EtOAc/toluene as an eluent to give 19 (0. 44 …”

Visible‐Light Photoactive, Highly Efficient Triplet Sensitizers Based on Iodinated Aza‐BODIPYs: Synthesis, Photophysics and Redox Properties

“…Owing to their advantageous and tunable photophysical properties and ability to generate singlet oxygen ( 1 O 2 )c oupled with absorption of light from the socalled "therapeuticw indow"( 600 nm-1100 nm), aza-BODIPY dyes have been proposed as potential triplet photosensitizers for both anti-microbiala nd anti-cancer photodynamic therapy. [20,[30][31][32][33][34][35][36][37][38][39][40][41] Aza-BODIPYs continue to attracta ttention as chemosensors for the detection of ammonia, [42] cysteine, homocysteine and glutathione in living cells, [43] Hg 2 + , [44][45][46] F À , [47,48] in vivo detection of H 2 S, [49] carbon dioxide, [50] glucosei nw hole blood, [51] detection of saxitoxin [52] and pH-sensitive sensors. [52] Furthermore, aza-BODIPYs have been proposed as photoactive components in photovoltaic devices [54][55][56] and nonlinear optical materials.…”

Aza-27-crown-9 Amino Acid

“…The complete analytics for the intermediates 3 and 4 can be found in the supporting information. -3,5,6,8,9,11,12,13,14,15,17,18,20,21,23,24-hexadecahydro-2H-benzo[k] [1,4,7,10,13,16,19,22,25]octaoxaazacycloheptacosine-27,28-dicarboxylate (6) (a) To a mixture of 0.68 g dimethyl-4,5-dihydroxyphthalate (1) (3 mmol) and 1.38 g K 2 CO 3 (10 mmol) in DMF (5 mL), 3.5 g tetraethyleneglykole monotosylate (2) (10 mmol) in DMF (5 mL) were added and stirred under nitrogen at 60 °C overnight. After cooling to room temperature, the mixture was poured into 30 mL of ice-cold saturated NH 4 Cl solution.…”

“…The ability of benzo-27-crown-9 ethers to bind guanidinium ions is known [8,9], was applied in extraction experiments [10] and has been proven by crystal structures [11,12]. Examples of related chemosensors were employed for detecting naturally occurring toxins [13,14].…”