New Technology for Turn-On Fluorescence Detection of Cyanide in Water

New Technology for Turn-On Fluorescence Detection of Cyanide in Water

A molecular probe was prepared that selectively responds to cyanide in aqueous solutions by fluorescence enhancement. Using the peptide ?-turn as a structural template, we designed a series of diphenylacetylene derivatives in which the ?-conjugated backbone was functionalized with an aldehyde group to render the molecule nonfluorescent. The N-H···O hydrogen bond across the 2,2?-functionalized diphenylacetylene turn motif activates the carbonyl group toward nucleophilic attack, and chemical transformation of this internal quencher site by reaction with CN- elicits a rapid (k = 72 M-1 s-1) enhancement in the emission at ?max = 375 nm. Tethering of an ammonium group to the hydrogen bond donor fragment significantly increased both the response kinetics and the intensity of the fluorescence signal. In addition to providing electrostatic attraction toward the CN- ion, this positively charged R-NH3+ fragment can engage in a secondary hydrogen bond to facilitate the formation of the cyanohydrin adduct responsible for the signaling event. The structurally optimized molecular probe 3 responds exclusively to ?M-level cyanide in neutral aqueous solutions, with no interference from other common anions including F- and AcO-.

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54645kcn New Technology for Turn On Fluorescence Detection of Cyanide in WaterScientists from Indiana University Bloomington are reporting in J. Am. Chem. Soc. the development of a fluorescent molecular probe that can detect minuscule concentrations of cyanide in water at normal pH levels. This research can conceivably be extended into a commercialization stage to develop a simple and cheap cyanide detector:

“This is the first system that works in water at normal pH levels and can be modified at will to enhance its reactivity,” said IU Bloomington chemist Dongwhan Lee, who led the research. “We are now looking at how to make the detector more sensitive.”

Graduate student Junyong Jo is the report’s first author.

One of the reasons the detector is not ready for market, Lee says, is that its optical properties need to be improved to emit light at longer wavelengths with less interference from background signals, especially those of biological origin. Since pond or river water is likely to contain living organisms and other organic matter, Lee says the detector system must be perfected.

Another unique aspect of the detector molecule is its modular structure.

“This is an essentially three-component chemical device with an activator, a receptor, and a reporter module,” Lee said. “These three components we can change at will in the future, either to make the detector more sensitive, or have it detect an entirely different toxin by sending out signals as different colors of light. Because of the structure’s modularity, a change in one of the three components doesn’t really affect the others.”

Lee and Jo were inspired by life itself — the natural properties of proteins — when they began designing their sensor molecule. The design of this novel system takes advantage of the structure-organizing “beta turn” motif commonly found in protein structures. The detector is essentially inert, except in the presence of cyanide, with which it preferentially reacts. The addition of cyanide induces a subtle but important structural change in the detector that turns it into a pigment that absorbs ultraviolet light (currently 270 nm) and convert it to light emission at around 375 nm, a purplish color at the very edge of human beings’ normal vision range.

Cyanide is a negatively charged ion composed of one carbon and one nitrogen atom. Among its many chemical targets inside cells is the oxidative phosphorylation system, which is a crucial producer of energy. Cyanide disrupts the system, making it impossible for cells to maintain even the most basic processes, which is one reason cyanide is considered a poison.

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