A new chromogenic protocol for the selective detection of nerve agent mimics is reported.Costero Nieto, Ana Maria, Ana.Costero@uv.es ; Gil Grau, Salvador, Salvador.Gil@uv.es ; Parra Alvarez, Margarita, Margarita.Parra@uv.e

Ana M. Costero

Bencic-Nagale

Brown

Burnworth

Dale

Eubanks

Félix Sancenón

Giordano

Gooding

Gunnlaugsson

Hewage

Hill, Jr

Ilhan

Jenkins

Kady

Knapton

Létant

Margarita Parra

McBride

McKusick

Minin

Pavlov

Pedro M. E. Mancini

Ramón Martínez-Máñez

Royo

Salvador Gil

Santiago Royo

Shunmugam

Sohn

Southard

Terrier

Trettnak

Van Houten

Wallace

Wang

Zhang

Crossref

Chromogenic detection of nerve agent mimics

A new chromogenic protocol for the selective detection of nerve agent mimics is reported

Costero Nieto, Ana María

Gil Grau, Salvador

Parra Álvarez, Margarita

Mancini, Pedro M. E.

Martínez Máñez, Ramón

Sancenón Galarza, Felix

Royo, Santiago

Repositori d'Objectes Digitals per a l'Ensenyament la Recerca i la Cultura

Chromogenic detection of nerve agent mimicswAna M. Costero,*a Salvador Gil,a Margarita Parra,a Pedro M. E. Mancini,aRamo´n Martı´nez-Ma´n˜ez,*b Fe´lix Sanceno´na and Santiago RoyobReceived (in Cambridge, UK) 2nd July 2008, Accepted 2nd September 2008First published as an Advance Article on the web 14th October 2008DOI: 10.1039/b811247aA new chromogenic protocol for the selective detection of nerveagent mimics is reported.The current rise in international concern over criminal terroristattacks via chemical warfare (CW) agents has resulted in anincreasing interest in the detection of these lethal chemicals.Among CW species, nerve agents are extremely dangerous andtheir high toxicity and ease of production underscore the need todetect these deadly chemicals via quick and reliable procedures. Anumber of detection systems have been developed, most of thembased on enzymatic and physical methodologies.1 However, theseusually show limitations such as low selectivity, lack of portabilityand a certain complexity in their use. An alternative to theseclassical methods that has been gaining interest in recent years isthe development of ﬂuorogenic or chromogenic chemosensors orreagents.2 Reported paradigms involve PET-based ﬂuorescentprobes,3 colorimetric probes with oximate-containing deriva-tives,4 molecular imprinting polymers,5 nanoparticles,6 carbonnanotubes,7 porous silicon8 or displacement-like assays.9 Mostof these reported protocols rely on ﬂuorescence changes and asfar as we know chromogenic systems for nerve agent detection inaqueous solution or as vapour are rare. Some reported colori-metric examples employ enzymatic methods and are based on theinhibition of the activity of the enzyme acetylcholine esterase.10Despite these interesting examples, colorimetric detection is par-ticularly appealing as it requires low-cost and widely used in-strumentation and oﬀers the possibility to detect ‘‘with the nakedeye’’ target analytes in rapid semi-quantitative assays. Followingour interest in using supramolecular-inspired concepts for thedevelopment of chromogenic protocols, we report herein thedesign of colorimetric probes for nerve agents.Traditionally the development of colorimetric probes usuallyrelies on the advanced design of two components: (i) a tailor-madebinding or reactive site and (ii) a colorimetric event. For theformer we selected the suitable properties of 2-(2-(dimethylamino)-phenyl)ethanol derivatives (see Scheme 1). This group contains anucleophile, the hydroxyl moiety, which is known to undergoacylation reactions with phosphonate substrates to form inter-mediate II that suﬀers a rapid intramolecularN-alkylation to yieldIII, a quaternary ammonium salt.3Remaining with the versatility of the last approach and at thesame time being interested in the design of colorimetric probes weenvisioned that the coupling of the dimethylaminophenyl donorgroup with an acceptor moiety (A) could be a suitable approachfor the design of tailor-made colorimetric probes for nerve agents’detection. We expected that the conversion of the tertiary amine Ito the quaternary ammonium III upon reaction with certainorganophosphorus (OP) substrates would dramatically changethe electronic donor properties of the nitrogen atom thus resultingin a decrease of the push–pull character of the dye and in a colourmodulation.As a proof-of-the-concept and using 2-(2-(dimethylamino)-phenyl)ethanol (DAPE) as a building block we prepared thechromoreactand 1 (see Scheme 2).z The starting compoundDAPE was synthesized from 2-nitrotoluene that was in aﬁrst step converted into 2-(2-nitrophenyl)ethanol following apreviously described method.11 Then, a reductive aminationin the presence of formaldehyde gives rise to 2-(2-(dimethyl-amino)phenyl)ethanol.12 The new probe 1 was prepared fromthe reaction of DAPE with the diazonium salt of 4-nitroanilineusing known procedures for the preparation of azo dyes.13As a ﬁrst step, the reactivity of 1 was tested with diethylchlorophosphate (DCP), diisopropyl ﬂuorophosphate (DFP)and diethyl cyanophosphate (DCNP) in acetonitrile. Theseorganophosphates have been widely used as simulants as theydisplay a reactivity similar to that of nerve agents such asTabun, Sarin and Soman, yet they lack their toxicity. Aceto-nitrile solutions of chromoreactand 1 display an absorptionspectrum typical of azo dyes with an intense absorption band(log e 44) at 410 nm. This yellow band has a charge-transfercharacter due to the presence of an electron donor aniliniumgroup and a nitrophenyl moiety acting as electron acceptor.Upon addition of 100 equiv. of DCP to acetonitrile solutionsof chromoreactand 1 a hypsochromic shift of 85 nm (Fig. 1)was observed that resulted in a modulation from yellow tocolourless. This shift to shorter wavelengths is consistent withthe intramolecular cyclization process; i.e. the N,N-dimethyl-anilino moiety drastically reduces its donor characterScheme 1 Colorimetric sensing protocol. A 2-(2-(dimethylamino)-phenyl)ethanol (DAPE) group acts as donor in charge-transfer dyessuch as I containing an acceptor group (A). In III there is a drasticreduction of the donor ability of the amine group resulting in aremarkable weakening of the charge-transfer (CT) band.aDepartamento de Quı´mica Orga´nica, Facultad de Ciencias Quı´micas,Universitat de Valencia, 46100 Burjassot Valencia, Spain.E-mail: ana.costero@uv.esb Instituto de Quı´mica Molecular Aplicada, Departamento de Quı´mica,Universidad Polite´cnica de Valencia, Camino de Vera s/n, 46022Valencia, Spain. E-mail: rmaez@qim.upv.esw Electronic supplementary information (ESI) available: 1H-NMRand 13C-NMR spectra of receptor 1 and 1H-NMR spectrum ofreceptor 2. See DOI: 10.1039/b811247a6002 | Chem. Commun., 2008, 6002–6004 This journal is c The Royal Society of Chemistry 2008COMMUNICATION www.rsc.org/chemcomm | ChemComm(vide ante). A similar behaviour was observed in the presenceof DFP and DCNP. For instance, a detection limit of1.0  104 mol dm3 for DCNP and DCP was found.Additionally, in order to assess the mechanism involved inthe observed chromogenic response, compound 2 was alsoprepared following a diﬀerent synthetic route involving thereaction of chromoreactand 1 with p-toluenesulfonyl chloridein the presence of sodium carbonate in acetonitrile. This givesthe corresponding tosylated derivative that suﬀered a sponta-neous cyclization to give 2. The formation of 2 is easilydetected in the 1H-NMR spectra of the ﬁnal productthat shows one triplet centered at 4.36 ppm indicative of amethylene subunit located near the quaternary ammonium.Also, a signiﬁcant long-range 1H–13C coupling between thissignal and those 13C signals corresponding to the methyls(54 ppm) and to the aromatic carbon (149 ppm) attached tothe N,N-dimethylanilinium fragment points toward theunambiguous formation of the cyclized product. It wasunambiguously conﬁrmed that the product obtained by tosyla-tion was the same as that obtained from the reaction of 1 withthe DCP simulant (see Fig. 1 for the UV spectrum), indicatingthat the reaction in Scheme 1 is responsible for the colourmodulation.In a further step, the reactivity of 1 with the organophos-phorus (OP) compounds shown in Fig. 2 was studied in mixedwater–acetonitrile 75 : 25 v/v mixtures buﬀered at pH 7 (MES5.0  102 mol dm3). As stated above, a selective bleachingwas found in the presence of DCP, DFP and DCNP, whereassolutions stay orange–yellow for the remaining OP species (noreaction was observed even after a long time). In order toachieve a better understanding of the reaction, the reactivitybetween 1 and DCP, DCNP or DFP in acetonitrile underpseudo ﬁrst-order kinetic conditions with an excess of thecorresponding simulant was studied. As has been suggested forsimilar systems, the reaction of the alcohol with the phosphatederivatives to form the phosphate ester intermediate is slowrelative to the intramolecular cyclization.3 Monitoring theabsorbance intensity at 410 nm and plotting ln [(A0  A)/A]versus time (where A0 is the ﬁnal absorbance and A is theabsorbance at a given time) allowed the determination of therate constants (k) with values of 0.13 s1, 0.061 s1 and0.20 s1 for DCP, DCNP and DFP, respectively. Thereforethe half-life was calculated (t1/2 = ln 2/k) to be approximately5.3 s, 11.4 s and 3.5 s for DCP, DCNP and DFP, respectively.Fig. 3 shows the absorbance decrease of the visible band of dye1 on reaction with DCP.Motivated by these favourable features we took a step forwardtowards the potential use of 1 for in situ sensing and rapidscreening applications. For this purpose the molecularprobe 1 was adsorbed on silica gel. First, a solution of 1(1  105 mol dm3) and MES (5  102 mol dm3) inacetonitrile–water (1 : 3) was prepared. Then, 2 mL of thissolution were adsorbed on silica gel (500 mg) and air-dried, ﬁnallyresulting in a light orange solid. In a ﬁrst test, the colouredsupport containing 1 was placed in a 1000 mL ﬂask thatcontained ca. 5 ppm of DCP vapour (obtained by evaporationof a solution of the simulant into the ﬂask volume). A clearchange from orange–yellow to colourless was observed for thesensor-loaded silica gel.In a second test, the orange–yellow coloured silica wasplaced on a column and a water–acetonitrile 75 : 25 v/v solutioncontaining DCP buﬀered at pH 7 (CDCP= 1.0 103 mol dm3,MES 5.0  102 mol dm3) was passed through. As the silicacomes into contact with the sample solution it becomes colourless(see Fig. 4). In both tests the response time was a few seconds. Thebleaching of the coloured silica support containing 1 in thepresence of vapours or mixed aqueous solutions of DCP isconsistent with the reaction shown in Scheme 2.Scheme 2 Transformation of the azo dye 1 to the correspondingammonium derivative via acylation with a phosphate substrate andfurther intramolecular cyclization.Fig. 1 Normalized absorption spectra of: (a) chromoreactand 1(acetonitrile, 1.0  105 mol dm3), (b) 1 with 100 equiv. of DCPand (c) the cyclization product obtained on reaction of 1 withp-toluenesulfonyl chloride (see text). The inset photographs show thecolour of probe 1 and the bleaching observed upon addition of DCP.Fig. 2 Chemical structures of the warfare agent simulants.Fig. 3 Absorption changes at 410 nm upon reaction of 1 with DCP.Inset: ﬁrst-order kinetic plot.This journal is c The Royal Society of Chemistry 2008 Chem. Commun., 2008, 6002–6004 | 6003In summary, a new chromoreactand for the colorimetricsensing of nerve agent simulants has been prepared. Thischromoreactand displays an intramolecular cyclization reac-tion coupled with a colour change upon interaction withcertain nerve agent simulants. The facts that the probe retainsits signalling abilities upon adsorption on silica and displayscolour modulations to nerve agent simulants as both vapoursor in mixed aqueous solution make this method a suitablealternative to other systems used in the detection of toxic nerveagents. It is noteworthy that the chemosensor 1 reacts onlywith DCP, DFP and DCNP that show close chemical struc-tures to Sarin, Soman and Tabun, whereas 1 remains silent inthe presence of other organophosphorus derivatives such asOP-2–5. Additionally, the approach is highly modular inconcept bearing in mind that a number of acceptor groupscan be anchored to the 2-(2-(dimethylamino)phenyl)ethanoldonor moiety (see Scheme 1) pointing towards the potentialpreparation of a range of colorimetric probes for the detectionof nerve agents based on push–pull chromophores.Notes and referencesz Synthesis of 2-(2-N,N-dimethylaminophenyl)ethanol: 2-nitrotoluene(9.2 g, 67.2 mmol), sodium phenoxide (0.06 g, 0.56 mmol) andparaformaldehyde (95%) (0.9 g, 25 mmol) in DMSO (20 mL) wereheated under stirring at 60–70 1C for 1 h. The cold reaction mixturewas poured into water (20 mL) and extracted with ethyl ether. Thecombined organic phases were washed (aq. NaCl), dried (MgSO4),evaporated and the residue was distilled (Kugelrohr, 160 1C,0.2 mmHg) to yield 2-(2-nitrophenyl)ethanol (4.3 g, 37%). Spectraldata were in agreement with those described in the literature.8 Then,2-(2-nitrophenyl)ethanol (3.30 g, 19.7 mmol), formaldehyde (37%)(4.83 mL, 32.3 mmol), abs. ethanol (200 ml) and Pd/C (10%) (480 mg)were placed under an H2 atmosphere until the uptake of hydrogenceased. After ﬁltration through Celite the solvent was evaporated andthe residue was dissolved in chloroform and extracted with aq. HCl(1 M, 2  50 mL). The aqueous phase was basiﬁed with sat. Na2CO3and extracted with chloroform. After drying (MgSO4) the solvent wasevaporated to give 2-(2-N,N-dimethylaminophenyl)ethanol (2.85 g,84%) as a light yellow oil.1H NMR (CDCl3, 400 MHz) d 7.3–7.0 (m, 4H), 5.3 (br. s, 1H), 3.85(t, J = 11.6 Hz, 2H), 3.01 (t, J = 11.6 Hz, 2H), 2.70 (s, 6H) ppm;13C{1H} NMR (CDCl3, 100 MHz): d 152.1, 136.0, 131.1, 127.6, 124.9,120.0, 64.2, 44.9, 36.0 ppm; IR (neat) 3367, 3059, 3020, 2937, 2360,2826, 2785, 1597, 1492, 1451, 1046, 945, 768 and 749 cm1. HRMS-EIm/z 165.1153 [M+; calcd for C10H15NO: 165.1154].Synthesis of 1: 4-Nitroaniline (0.836 g, 6.05 mmol), conc. sulfuric acid(1.25 mL, 23 mmol) and water (8 mL) were stirred and slightly heateduntil the 4-nitroaniline was completely dissolved and then the mixturewas placed in an ice-bath (0–5 1C) for 10 min before a NaNO2 (0.418 g,6.05 mmol) solution in water (4 mL) was added dropwise. Afterstirring for an additional 10 min at 0–5 1C, a solution of the aminesynthesised above (1.0 g, 6.05 mmol), conc. HCl (1.3 mL, 15.1 mmol)and water (4 mL) was added dropwise during 15 min. The resultingorange solution was stirred for 15 min in an ice-bath and 15 min atroom temperature, then it was neutralized with Na2CO3 and extractedwith CH2Cl2. The dried (MgSO4) organic phases were evaporated togive a dark oil that was dissolved in ethyl acetate. Upon addition ofhexane, a dark red precipitate appeared, identiﬁed as 1 (1.2 g, 63%),mp 98–100 1C. 1H NMR (CDCl3, 400 MHz) d 8.36 (d, J = 9.0 Hz,2H), 7.98 (d, J = 9.0 Hz, 2H), 7.85 (d, J = 8.1 Hz, 1H), 7.81 (s, 1H),7.26 (d, J= 8.1 Hz, 1H), 3.95 (t, J= 5.8 Hz, 2H), 3.10 (t, J= 5.8 Hz,2H), 2.83 (s, 6H) ppm; 13C{1H} NMR (CDCl3, 100 MHz): d 156.7,155.9, 148.8, 148.4, 135.4, 125.4, 124.7, 123.9, 123.2, 119.9, 63.8, 44.6,35.8 ppm; IR (neat) 2948, 2873, 1591, 1517, 1345, 1099, 1039, 858 and827 cm1. HRMS-EI m/z 314.1371 [M+; calcd. for C16H18N4O3:314.1379].Synthesis of 2: To a stirred mixture of 1 (63 mg, 0.2 mmol) and K2CO3(56 mg, 0.4 mmol) in acetonitrile (1 mL), tosyl chloride (36 mg,0.2 mmol) in acetonitrile (0.5 mL) was slowly added. After stirringat room temperature for 6 h, toluene (5 mL) was added. The formedprecipitate was ﬁltered to give 2 (as its tosylate salt) (46 mg, 0.1 mmol)as a white solid, mp 4350 1C. 1H NMR (CD3OD, 400 MHz) d 8.46(d, J = 8.8 Hz, 2H), 8.15 (m, 4H), 8.02 (d, J = 8.7 Hz, 1H), 7.72 (d,J = 7.8 Hz, 2H), 7.25 (d, J = 7.8 Hz, 2H), 4.36 (t, J = 7.2 Hz, 2H),3.65 (s, 6H), 3.59 (t, J = 7.2 Hz, 2H) ppm; 13C{1H} NMR (CDCl3,100 MHz): d 155.2, 153.8, 149.0, 142.1, 140.4, 128.4, 125.6, 124.9,124.6, 123.6, 120.3, 118.2, 68.5, 54.0, 26.6, 19.9 ppm; IR (neat) 3082,2961, 1628, 1398, 1381, 1127, 1007, 831, 701, and 664 cm1. HRMS-EIm/z 297.1355 [M+; calcd. for C16H17N4O2: 297.1352].1 L. M. Eubanks, T. J. Dickerson and K. D. Janda, Chem. Soc. Rev.,2007, 36, 458; H. H. Hill, Jr and S. J. Martin, Pure Appl. Chem.,2002, 74, 2281; J. J. Gooding, Anal. Chim. Acta, 2006, 559, 137; K.Brown, Science, 2004, 305, 1228; M. T. McBride, S. Gammon, M.Pitesky, T. W. O’Brien, T. Smith, J. Aldrich, R. G. Langlois, B.Colston and K. S. Venkateswaran, Anal. Chem., 2003, 75, 1924.2 S. Royo, R. Martı´nez-Ma´n˜ez, F. Sanceno´n, A. M. Costero, M.Parra and S. Gil, Chem. Commun., 2007, 4839; B. C. Giordano andG. E. Collins, Curr. Org. Chem., 2007, 11, 255; M. Burnworth, S. J.Rowan and C. Werder, Chem.–Eur. J., 2007, 13, 7828.3 K. A. Van Houten, D. C. Heath and R. S. Pilato, J. Am. Chem.Soc., 1998, 120, 12359; S.-W. Zhang and T. M. Swager, J. Am.Chem. Soc., 2003, 125, 3420; T. J. Dale and J. Rebek, Jr, J. Am.Chem. Soc., 2006, 128, 4500; F. Ilhan, D. S. Tyson and M. A.Meador, Chem. Mater., 2004, 16, 2978; S. Bencic-Nagale, T.Sternfeld and D. R. Walt, J. Am. Chem. Soc., 2006, 128, 5041.4 K. J. Wallace, J. Morey, V. M. Lynch and E. V. Anslyn, New J.Chem., 2005, 29, 1469; K. J. Wallace, R. I. Fagbemi, F. J. Folmer-Andersen, J. Morey, V. M. Lynch and E. V. Anslyn, Chem.Commun., 2006, 3886; F. Terrier, P. Rodrı´guez-Dafonte, E. LeGue´vel and G. Moutiers, Org. Biomol. Chem., 2006, 4, 4352; H. S.Hewage, K. J. Wallace and E. V. Anslyn, Chem. Commun., 2007,3909.5 A. L. Jenkins, O. M. Uy and G. M. Murray, Anal. Commun., 1997,34, 221; A. L. Jenkins, O. M. Uy and G. M. Murray, Anal. Chem.,1999, 71, 373; A. L. Jenkins and S. Y. Bae, Anal. Chim. Acta, 2005,542, 32; G. E. Southard, K. A. Van Houten, E. W. Ott, Jr and G.M. Murray, Anal. Chim. Acta, 2007, 581, 202; R. Shunmugam andG. N. Tew, Chem.–Eur. J., 2008, 14, 5409.6 V. Pavlov, Y. Xiao and I. Willner, Nano Lett., 2005, 5, 649; L.Wang, K. D. Cole, A. K. Gaigalas and Y.-Z. Zhang, BioconjugateChem., 2005, 16, 194.7 F. Wang, H. Gu and T. M. Swager, J. Am. Chem. Soc., 2008, 130,5392.8 H. Sohn, S. Le´tant, M. J. Sailor and W. C. Troger, J. Am. Chem.Soc., 2000, 122, 5399; S. Le´tant, B. R. Hart, S. R. Kane, M. Z.Hadi, S. J. Shields, T.-C. Cheng, V. K. Rastogi, J. Del Eckels andJ. G. Reynolds, Mater. Res. Soc. Symp. Proc., 2005, 828, A1.8.1.9 D. Knapton, M. Burnworth, S. J. Rowan and C. Weder, Angew.Chem., Int. Ed., 2006, 45, 5825.10 See for example: W. Trettnak, F. Reininger, E. Zinterl and O. S.Wolfbeis, Sens. Actuators, B, 1993, 11, 87.11 P. L. Minin and J. C. Walton, J. Org. Chem., 2003, 68, 2960.12 I. O. Kady and B. Tan, Tetrahedron Lett., 1995, 36, 4031.13 T. Gunnlaugsson, J. P. Leonard and N. S. Murray, Org. Lett.,2004, 6, 1557; B. C. McKusick, R. E. Heckert, T. L. Cairns, D. D.Coﬀman and H. F. Mower, J. Am. Chem. Soc., 1958, 80, 2806.Fig. 4 Left: a glass tube containing silica gel with dispersed 1.Right: silica gel containing 1 after the addition of water–acetonitrile75 : 25 v/v mixtures containing DCP buﬀered at pH 7 (CDCP = 1.0 103 mol dm3, MES 5.0  102 mol dm3).6004 | Chem. Commun., 2008, 6002–6004 This journal is c The Royal Society of Chemistry 2008

http://roderic.uv.es/bitstream/10550/16736/1/8.COSTERO_CHEMICAL%20COMMUNICATIONS_45_6002_2008.pdf

Chromogenic detection of nerve agent mimics

Abstract

Similar works

Full text

Available Versions

Crossref

Crossref

Repositori d'Objectes Digitals per a l'Ensenyament la Recerca i la Cultura