A colorimetric sensor 1,N,N'-di-(2-hydroxy-5-(phenldiazenyl)benzaldehyde)-1,3-diiminothiourea for acetate in DMSO and 9/1 DMSO/H(2)O (v/v) mixtures was designed and synthesized. The binding ability evaluated by UV-vis experiment reveals that sensor 1 can selectively recognize acetate. In addition, the color changes induced by anions can provide a way of detection by 'naked-eye'. The further insights to the nature of interactions between the sensor 1 and AcO(-) were investigated by (1)H NMR titration experiments in 9/1 DMSO-d(6)/H(2)O (v/v). (c) 2010 Elsevier B.V. All rights reserved

Huang WW

Li JW

Lin H

Lin HK

Su HY

Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy

English

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AWabaARRAKCAA1a[tFictwbma[tWedeiCpti1dSpectrochimica Acta Part A 77 (2010) 146–149Contents lists available at ScienceDirectSpectrochimica Acta Part A: Molecular andBiomolecular Spectroscopyjourna l homepage: www.e lsev ier .com/ locate /saan acetate sensor based on azo in aqueous mediaeiwei Huanga, Hongyan Sua, Jianwei Lia, Hai Linb, Huakuan Lina,∗Department of Chemistry, Nankai University, Tianjin 300071, PR ChinaKey Laboratory of Functional Polymer Materials of Ministry of Education, Nankai University, Tianjin 300071, PR Chinar t i c l e i n f orticle history:a b s t r a c tA colorimetric sensor 1,N,N′-di-(2-hydroxy-5-(phenldiazenyl)benzaldehyde)-1,3-diiminothiourea foreceived 2 November 2009eceived in revised form 3 March 2010ccepted 30 April 2010eywords:olorimetriccetate sensoracetate in DMSO and 9/1 DMSO/H2O (v/v) mixtures was designed and synthesized. The binding abil-ity evaluated by UV–vis experiment reveals that sensor 1 can selectively recognize acetate. In addition,the color changes induced by anions can provide a way of detection by ‘naked-eye’. The further insightsto the nature of interactions between the sensor 1 and AcO− were investigated by 1H NMR titrationexperiments in 9/1 DMSO-d6/H2O (v/v).© 2010 Elsevier B.V. All rights reserved.queous solution. IntroductionOver the past few years, the recognition of inorganic and bioticnions has been a key research area of supramolecular chemistry1,2] owing to the fundamental role of anions in the environmen-al and biological systems, and in the clinic practices and so on.or example, the carboxylate anions [3] exhibit specific biochem-cal functions in the enzymes and antibodies and are also criticalomponents of numerous metabolic processes. Acetate is one ofhe carboxylate anions with the unique trigonal chemical structure,hich can form strong hydrogen-bond interaction with hydrogen-ond donors.Very recently, the selective recognition of acetate has attractedore and more attention. For example, an effective sensor forcetate ion in dry DMSO was reported by Cheng and co-workers4]. Ito et al. reported a novel Fipronil-based receptor can selec-ively recognize actetate among a group of anions in DMSO [5].e found that the phenylhydrazone-based indole receptor was anffective sensor for acetate ion in dry DMSO [6].Despite these remarkable achievements, there are still manyisadvantages recognized in many examples of literatures. Forxample, the recognition and/or sensing of anions could only occurn biochemically noncompetitive organic solvents [7,8] (e.g. CH3CN,H2Cl2, etc.) but unable to sense anions in biochemically com-etitive protic solvents such as H2O, CH3CH2OH. Consequently,here is a need to develop receptors capable of binding anionn competitive media, which is also hopeful to be simultane-∗ Corresponding author. Tel.: +86 2223502624; fax: +86 22 23502458.E-mail address: hklin@nankai.edu.cn (H. Lin).386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2010.04.042ously accompanied with ‘naked-eyed’ detectable color changes[9–11].By exploiting the optical properties of an azo group, we haverecently reported a chromo- and fluorogenic dual respondingH2PO4− sensor in dry DMSO [12]. Considering the limited appli-cation of this sensor, in this paper, we designed and synthesized anew and simple azo-based receptor (Scheme 1), which is an organiccolorimetric chemosensor. The sensing of the biologically impor-tant AcO− is achieved in DMSO solution even in aqueous solution9/1 DMSO/H2O (v/v).2. Experimental2.1. Apparatus1H NMR spectra were obtained on a Varian UNITY Plus-400 MHZSpectrometer. ESI-MS performed with a MARINER apparatus. C, H,N elemental analyses were made on an elementar vario EL. UV–visspectra were recorded on a Shimadzu UV-2450 Spectrophotometer(Shimadzu 2.1 Apparatus Corp., Kyoto, Japan) with a quartz cuvette(path length = 1 cm) at 298.2 ± 0.1 K.2.2. ReagentsAll reagents for synthesis obtained commercially were usedwithout further purification. In the titration experiments, all theanions were added in the form of tetrabutylammonium (TBA) salts,which were purchased from Sigma–Aldrich Chemical, stored in avacuum desiccator containing self-indicating silica and dried fullybefore using. DMSO was dried with CaH2 and then distilled inreduced pressure.W. Huang et al. / Spectrochimica Acta Part A 77 (2010) 146–149 147tic routes to the target sensor 1.2ouKpfoaudata2d(s(tfıNEN533tsHssp4astFtfrom azophenyl. And the color of the sensor 1 solution changedfrom light yellow to heavy yellow at the same time (Fig. 3). Obvi-ously, there was only one well-defined isosbestic points at 380 nm,which indicated that there existed sole type of 1–AcO− complex.Similarly, the additions of F− and H2PO4− also led spectral changes.Scheme 1. General synthe.3. General methodAll experiments were carried out at 298.2 ± 0.1 K, unlesstherwise mentioned. UV–vis spectra were measured using anltraviolet–visible spectrophotometer, UV-2450 (Shimadzu Corp.,yoto, Japan). A 2.0 × 10−4 M solution of the sensor 1 in DMSO wasrepared and stored in the dry atmosphere. This solution was usedor all spectroscopic studies after appropriate dilution. Solutionsf 1.0 × 10−2 M tetrabutyl ammonium (TBA) salts of the respectivenions were prepared in dried and distilled DMSO and were storednder a dry atmosphere.1H NMR titration experiments were carried out in 9/1 DMSO-6/H2O (v/v) solution (TMS as the internal standard). Certainmount of the sensor 1 solution was prepared with a concentra-ion of 0.01 M. 1H NMR of the host–guest system was recorded bydding increasing amount of acetate into the sensor 1 solution..4. Syntheses and characterizationN,N′-di-(2-hydroxy-5-(phenldiazenyl)benzaldehyde)-1,3-iiminothiourea (1)A solution of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde0.904 g, 4 mmol) in ethanol (20 ml) was added dropwise to a hotolution of 1,3-diaminothiourea (0.212 g, 2 mmol) in ethanol/water20 ml, v/v = 1/1) with stirring at reflux. After being stirred for 2 h,he solvent was removed by evaporation after recrystallizationrom ethanol. This procedure yielded yellow crystals 0.970 g (87%).H (400 MHz, DMSO-d6, Me4Si): 12.26 (s, 2H, O–H), 12.23 (s, 2H,–H), 7.87 (dd, 3H, Ar–H), 7.61 (s, 1H, N C–H), 7.52 (dd, 3H, Ar–H).lemental analysis: Calc. for C27H22N8O2S: C, 62.04%; H, 4.24%;, 21.44%; Found: C, 62.13%; H, 4.02%; N, 21.37%. ESI-mass: m/z23.58 (M+H)+.. Results and discussion.1. UV–vis spectroscopyFirstly, to evaluate the affinity ability to anions, the UV–vis titra-ion experiments of the sensor 1 were carried out in dry DMSOolution using standard tetrabutylammonium salts of AcO−, F−,2PO4−, Cl−, Br− and I− at 298.2 ± 0.1 K. UV–vis spectrum of theolution of 1 (1.0 × 10−5 M) recorded upon the addition of AcO− ishown in Fig. 1. Upon the addition of AcO−, the broad absorptioneaks at 338 nm was decreasing, whereas an absorption peak at23 nm formed. The resulting titration revealed an isosbestic pointt 390 nm.Secondly, to explore more about the applicability of the sen-or 1 for acetate in minor-water-containing solution, the UV–visitrations were performed in the 9/1 DMSO/H2O (v/v) mixtures.ig. 2 shows the UV–vis spectral changes of 1 during the titra-ion with acetate. The original absorbance peaks appeared at theFig. 1. UV–vis spectrum changes of sensor 1 (2.0 × 10−5 M) upon addition of acetateion (0–4.2 equiv.) in DMSO at 298.2 ± 0.1 K. Inset: Job’s plot for complexation ofsensor 1 with AcO− in DMSO [host] + [guest] = 2.0 × 10−5 M.max of 340 nm, i.e. the –* transition bands of the chromophore(azophenyl). With the addition of more and more doses of acetateions, the peak at 338 nm decreased but a new peak appeared at435 nm, which was ascribed to the charge transfer (CT) between theanion-bound –NH and –OH units and the electron-deficient effectFig. 2. UV–vis spectrum changes of sensor 1 (2.0 × 10−5 M) upon additionof acetate ion (0–23 equiv.) in 9/1 DMSO/H2O (v/v) at 298.2 ± 0.1 K. Inset:Job’s plot for complexation of sensor 1 with AcO− in 9/1 DMSO/H2O (v/v)[host] + [guest] = 2.0 × 10−5 M.148 W. Huang et al. / Spectrochimica Acta Part A 77 (2010) 146–149Fig. 3. Color changes of the sensor 1 in 9/1 DMSO/H2O (v/v) in absence and presence of anions (from the left to right: 1 only, 1 + AcO− , 1 + F− , 1 + H2PO4− , 1 + Cl− , 1 + Br− and1 + I−).Table 1Association constants for various anions toward receptor 1 in DMSO and 9/1 DMSO/H2O (v/v) at 298.2 ± 0.1 K, respectively.Anionsa AcO− H2PO4− F− Cl− Br− I−Kass (M−1)b 3.14(±0.12) × 105 7.14(±0.53) × 104 7.57(±0.62) × 104 NDc ND NDKass (M−1)d 7.37(±0.54) × 103 1.62(±0.19) × 102 2.73(±0.24) × 102 ND ND NDion sHnip(Twobi[Xss(veFea The anions were added as their tetrabutylammonium salts.b Kass was determined in dry DMSO.c ND indicated that the spectra showed little or no change with the addition of and Kass was determined in 9/1DMSO/H2O (v/v)solution.owever, as adding Cl−, Br− and I− to 1, the spectra responses areot obvious.Continuous variation method was used to determine the sto-chiometric ratio of the receptor to the fluoride anion guest. Job’slot [13,14] of sensor 1 and AcO− in DMSO and 9/1 DMSO/H2O (v/v)Figs. 1 and 2) shows the maxima are all at a molar fraction of 0.5.his result indicates that the sensor 1 binds acetate anion guestith a 1:1 ratio. Moreover, similar results can also be obtained forther anions (F− and H2PO4−).For a complex of 1:1 stoichiometry, the relation in Eq. (1) coulde derived easily, where X is the absorption intensity, and CH or CGs the concentration of the host or the anion guest correspondingly15].= X0 + (X lim − X0){CH + CG + 1/Kass − [(CH + CG + 1/Kass)2 − 4CHCG]1/2}/2CH(1)The affinity constants of receptors 1 for the studied anionicpecies are calculated and listed in Table 1 below.As a validation to the above qualitative and quantitative analy-is, UV–vis changes (Fig. 4) of sensor 1 operated in 9/1 DMSO/H2Ov/v) (2.0 × 10−5 M) after the additions of 17 equiv. of anions pro-ided a more convincing evidence that sensor 1 was indeed anxcellent sensor for AcO−.ig. 4. UV–vis spectra spectra of 1 (1 × 10−5 M) in 9/1 DMSO/H2O (v/v) in the pres-nce of 17 equiv. of F− , or AcO− , H2PO4− , Cl− , Br− and I− .o that the association constants cannot be determined using the spectra.As clearly shown in Table 1, the order of bindingaffinity of 1 with anions (in DMSO or DMSO/water) isAcO− » F− > H2PO4− ∼ Cl− ∼ Br− ∼ I−. The recognition functionof sensor 1 for AcO− is the most remarkable property. The mainreason for preferring AcO− is its triangular shape which deter-mines the angle of O–C–O is about 120◦ while the angle of O–P–Oin H2PO4− is about 108◦. The distance of two oxygen atoms ofAcO− might be more fit to the hydrogen atoms of the recognitionsites than those spherical and tetrahedral anions. That is, theconfiguration of AcO− is more matching with 1 than F− andH2PO4−.Compared with the previous research in our laboratory [12], thesensor 1 has higher selectivity for acetate than receptor 1, becausethe structure of sensor 1 is symmetrical while receptor 1 is unsym-metrical in the lecture [12]. The advantage of configuration madesensor 1 has better selectivity than receptor 1. So the associationconstant of sensor 1 with AcO− is much bigger than receptor 1 inthe lecture.3.2. 1H NMR titrationTo further look into the nature of host–guest interactions,1H NMR titration experiments were conducted in 9/1 DMSO-d6/H2O (v/v) mixtures. 1H NMR acetate titration spectra of thesensor 1 is shown in Fig. 5. Upon addition of 0.5 equiv. ofacetate ions, the peaks at 12.23 ppm and 12.26 ppm, which wereFig. 5. 1H NMR titration of a 1 × 10−2 M solution of 1 in 9/1 DMSO-d6/H2O (v/v) with[Bu4N]AcO.W. Huang et al. / Spectrochimica Acta Part A 77 (2010) 146–149 149–AcO−adphtsttbtfiaispS4caTta[[Scheme 2. The proposed 1ssigned to aniline–NH and phenole–OH, respectively, were shiftedownfield to 12.43 ppm and 12.57 ppm and the signals on thehenyl rings changed slightly. This indicated the formation of aydrogen-bonding complex was at this stage. With further addi-ion of acetate ions, upon the addition of 2 equiv. AcO−, theignals of –NH and –OH were disappeared and the phenyl pro-ons moved upfield significantly, which indicated the increase ofhe electron density on the phenyl ring owing to the through-ond electronic effects. All the results observed indicate thathere are two stages during the 1H NMR titration: (1) in therst stage, the acetate ion exhibits a hydrogen-bonding inter-ction with 1, and (2) in the second stage, the excess acetateon results the deprotonation of the sensor to take place. Con-equently, according to the results of 1H NMR titration, theroposed binding mode of 1 and AcO− was given below incheme 2.. ConclusionIn summary, we have succeeded in presenting a new kind ofolorimetric chemosensor, which showed strong binding affinitys well as a good selectivity for acetate ion in aqueous solution.his outstanding property was bolstered by UV–vis and 1H NMRitration experiments. It is expected to be applied for detection ofcetate in real life for its easy synthesis and highly selectivity.[[[[binding mode in solution.AcknowledgementThis project was supported by the National Natural ScienceFoundation of China (20371028, 20671052).References[1] T. Gunnlaugsson, M. Glynn, G.M. Tocci, P.E. Kruger, F.M. Pfeffer, Coord. Chem.Rev. 250 (2006) 3094–3177.[2] E.A. Katayev, Y.A. Ustynyuk, J.L. Sessler, Coord. Chem. Rev. 250 (2006)3004–3037.[3] T. Gunnlaugsson, A.P. Davis, J.E. O’Brien, M. Glynn, Org. Lett. 4 (2002)2449–2452.[4] Y.H. Zhang, Zh.M. Yin, J.Q. He, J.P. Cheng, Tetrahedron Lett. 48 (2007)6039–6043.[5] H. Maeda, Y. Ito, Inorg. Chem. 45 (2006) 8205–8210.[6] J. Shao, Y.H. Wang, H. Lin, J.W. Li, H.K. Lin, Sensors Actuator B 134 (2008)849–853.[7] M. Yu, H. Lin, G.H. Zhao, H.K. Lin, J. Mol. Recognition 20 (2007) 69–73.[8] T. Gunnlaugsson, P.E. Kruger, P. Jensen, J. Tierney, H.D.P. Ali, G.M. Hussey, J. Org.Chem. 70 (2005) 10875–10878.[9] X.F. Shang, H. Lin, Z.S. Cai, H.K. Lin, Talanta 73 (2007) 296–303.10] C. Caltagirone, J.R. Hiscock, M.B. Hursthouse, M.E. Light, P.A. Gale, Chem. Eur. J.14 (2008) 10236–10243.11] H.J. Kim, S. Bhuniya, R.K. Mahajan, R. Puri, H.G. Liu, K.C. Ko, J.Y. Lee, J.S. Kim,Chem. Commun. (2009) 7128–7130.12] J. Shao, H. Lin, H.K. Lin, Dyes and Pigments 80 (2009) 259–263.13] T.D. Thangadural, N.J. Singh, I.C. Hwang, J.W. Lee, R.P. Chandran, K.S. Kim, J. Org.Chem. 72 (2007) 5461–5464.14] M.M. Linn, D.C. Poncio, V.G. Machado, Tetrahedron Lett. 48 (2007) 4547–4551.15] J. Bourson, J. Pouget, B. Valeur, J. Phys. 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An acetate sensor based on azo in aqueous media

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An acetate sensor based on azo in aqueous media

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