Enhanced Fluorescence Cyanide Detection at Physiologically Lethal Levels:  Reduced ICT-Based Signal Transduction

Abstract

Three water-soluble fluorescent probes have been specifically designed to determine free cyanide concentrations up to physiologically lethal levels, >20 microM. The probes have been designed in such a way as to afford many notable sensing features, which render them unique with regard to signal transduction, photophysical characteristics, and their application to physiological cyanide determination and safeguard. The probes are readily able to reversibly bind free aqueous cyanide with dissociation constants around 4 microM3. Subsequent cyanide binding modulates the intramolecular charge transfer within the probes, a change in the electronic properties within the probes, resulting in enhanced fluorescence optical signals as a function of increased solution cyanide concentration. The ground-state chelation with cyanide produces wavelength shifts, which also enable the probes to sense cyanide in both an excitation and emission ratiometric manner, in addition to enhanced fluorescence signaling. This has enabled a generic cyanide sensing platform to be realized that is not dependent on fluorescent probe concentration, probe photodegradation, or fluctuations in the intensity of any employed excitation sources, ideal for remote cyanide sensing applications. Further, the >600 nm fluorescence emission of the probes potentially allows for enhanced fluorescence ratiometric cyanide sensing in the optical window of tissues and blood, facilitating their use for the transdermal monitoring of cyanide for mammalian safeguard or postmortem in fire victims, both areas of active research.

Recent Advances in the Colorimetric Detection of Cyanide

“…This has led to the development of a variety of different chelating receptors and sensors based on threecoordinated boron species. [20] Boronic acid derivatives have been successfully applied in the fluorometric sensing of micromolar aqueous cyanide, [12] whereas fluorescent triarylborane polymers probe micromolar cyanide in organic solvents. [37] Recently, Gabbai et al applied two isomeric cationic ammonium boron derivatives for the selective recognition of either cyanide or fluoride ions in water (Scheme 3E).…”

“…[1] Therefore it is necessary to safely monitor and remove this dangerous anion either in industrial wastewater, after accidental release or during food production. Since the first report on the argentometric determination of cyanide by von Liebig in 1851, [8] many different detection methods including electrometric, [9][10][11] fluorometric [12,13] and chromatographic techniques [14] have been established. Drawbacks are either the laborious multistep sample pretreatment, the use of special reaction conditions as well as the low tolerance towards the presence of other anions.…”

“…[15][16][17][18][19][20] Ideally, these systems show a colour change in the presence of the target molecule which is easily detectable with the 'nakedeye'. [21][22][23][24] For cyanide sensing, their mode of action is based on hydrogen bonding, [25,26] bond-forming reactions between either the nucleophilic cyanide and an electrophilic carbon [27][28][29][30][31][32][33][34][35][36] or boron centre [12,[37][38][39] or metal coordination [40][41][42][43] (Scheme 1). Progress is observed for all of these different systems, but a sensor that meets all of following three criteria has not yet been synthesized: i) optical detection below the maximum permissible level of cyanide in drinking water (1.7 μM); ii) demonstrating a fast and unambiguous response in pure water (<5 sec) without the need for special reaction conditions or sample pre-treatment; iii) displaying high selectivity in the presence of other anions.…”

“…[64] We assume that a mixture of different isomers was applied in these experiments, since we observed in our studies the hydrolysis of the methylester functionalities of 7 under the reported conditions. [66] We communicated recently the optical detection of millimolar cyanide in water at pH 7.5 with commercial available vitamin B 12 . [40] The mode of operation is controlled by the natural benzimidazole trigger of being able to switch between different conformations (Scheme 6).…”

Naphthalimide–coumarin conjugate: ratiometric fluorescent receptor for self-calibrating quantification of cyanide anions in cells

“…3 Absorption of a very small amount of CN À , as little as 0.5-3.5 mg per kilogram of body weight, is enough to cause human death. 4 Cyanides are, however, versatile reagents for synthesis 5 and metallurgy.…”