DOI: 10.1002/asia.201300049 Turn-On Fluorogenic Probes for the Selective and Quantitative Detection of the Cyanide Anion from Natural Sources Teresa Gómez, Daniel Moreno, Borja Díaz de GreÇu, A. Cristina Fernµndez, Teresa Rodríguez, Josefa Rojo, JosØV. Cuevas, and Tomµs Torroba* [a] This paper is dedicated to the memory of Dr. Stefano Marcaccini, who passed away on October 1, 2012 Introduction The cyanide anion, a largely known poison (it is an inhibitor of aerobic respiration), still poses a threat to human health because of its increasing use in heap leaching of gold from ore, and also in electroplating. Consequently, cyanide is a commonly encountered contaminant in water and soil from exposed geographical regions. [1] Because of the high degree of toxicity of cyanide, acceptable levels of cyanide compounds are generally very low. The maximum contami- nant level for free cyanide in drinking water in the U.S. is 0.2 mg L 1 , whereas the U.S. ambient water quality criteria for acute exposures in freshwater systems is 22 mgL 1 , as some aquatic organisms are significantly more sensitive to cyanide than are humans. [2a] Over 2650 species of plants (130 families) produce cyanogenic glycosides as part of their natural defense mechanisms. Upon stress or injury, cyano- genic glycosides are hydrolyzed by a coexisting plant enzyme and release HCN. [2b] Many cyanide-producing plant species have social and economic importance in our daily life in areas such as food, forage, and horticulture. With ever-increasing demands for food and increased cultivation of cyanide-producing plants, there could be environmental implications in the processing of food plants like cassava. Human ingestion of improperly processed bitter cassava has severe consequences and can result in epidemic spastic para- paresis, more commonly referred to as Konzo disease. Bitter almonds could contain up to 2500 mg kg 1 HCN from amyg- dalin, a cyanogenic glycoside also found in other Rosaceae, such as apricot seeds (almond, apple, apricot, cherry, peach, pear, plum, and quince). The most common cyanide mea- surement performed is total cyanide analysis through manual distillation followed by colorimetric, titrimetric, or electrochemical finish techniques. [2c] Because of the inherent complexity of these methods, several colorimetric and fluori- metric probes have been developed for fast detection of the cyanide anion. [3] Because of their increased selectivity, off– on fluorimetric probes are of high interest; [4] however, very few are suitable for bioimaging [5] or quantitative detection in biological samples. [6] Therefore, the development of new fluorogenic probes for practical evaluation of the cyanide anion in natural samples is of high interest. A good ap- proach is the reversible addition of cyanide anions to Mi- chael acceptors, [7] in which the addition of cyanide usually triggers a color change and, eventually, the appearance of a fluorescent species. [8] In the search for new selective fluo- rogenic probes, we have prepared new fluorescent materials that are effectively converted into nonfluorescent deriva- tives by chemical introduction of an internal charge-transfer mechanism. Such compounds are therefore good candidates for fluorescent chemodosimeters by triggering a fluorescent emission in the presence of selective analytes. Herein, we report a new selective turn-on fluorogenic probe based on the reversible addition of cyanide to the indene core of one of the indene dyes. Results and Discussion First, we synthesized the new fluorescent compounds 1–4 by the Knoevenagel addition of malononitrile to 5-(6-methoxy- naphthalen-2-yl)indanone, [9] 5-(4-N,N-dimethylaminophe- Abstract: We report new indene deriv- atives that are good fluorogenic probes for the cyanide anion, one of which is a highly selective and sensitive fluoro- genic probe for the fluorescent detec- tion—as well as reliable quantifica- tion—of the cyanide anion in water or buffer, with a 10 3 -fold increase of fluo- rescence and low detection limit. It is therefore useful for the quantification of natural cyanide from aqueous ex- tracts of green almond seeds, thus proving that the system is suitable for fast detection and quantification of cy- anide from natural sources. Keywords: cyanides · fluorescence · indenes · Michael addition · sensors [a] Dr. T. Gómez, Dr. D. Moreno, B. Díaz deGreÇu, A. C. Fernµndez, Dr. T. Rodríguez, Dr. J. Rojo, Dr. J.V. Cuevas, Prof.Dr. T. Torroba Department of Chemistry, University of Burgos Faculty of Science, 09001 Burgos (Spain) Fax: (+ 34) 947258831 E-mail : ttorroba@ubu.es Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201300049. Chem. Asian J. 2013, 8, 1271 – 1278  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1271 FULL PAPER