Boehmite Supported Pyrene Polyamine Systems as Probes for Iodide

Article pubs.acs.org/JPCC

Boehmite Supported Pyrene Polyamine Systems as Probes for Iodide Recognition Esther Carbonell,*,† Estefanía Delgado-Pinar,† Javier Pitarch-Jarque,† Javier Alarcón,‡ and Enrique García-España*,† †

Departament de Química Inorgànica, Universitat de València, Institut de Ciència Molecular (ICMOL), 46980 Paterna, València, Spain ‡ Departament de Química Inorgánica, Universitat de València, 46100 Burjassot, València, Spain S Supporting Information *

ABSTRACT: New organic−inorganic fluorescent probes made by attaching the tripodal polyamine (tris(2aminoethyl))amine (tren), propylamine, or diethylenetriamine functionalized with pyrene as a fluorophore to an γ-aluminum oxohydroxide matrix have been prepared and studied both in solution and supported on the surface of boehmite nanoparticles. Both kinds of systems have been revealed as sensitive and selective fluorescence turn-off chemosensors for iodide in aqueous solution with an estimated detection limit that reaches 36 ppb. The recognition characteristics and photophysical properties of these molecules are essentially preserved when they are grafted to the surface of the particles. Since the nanoparticles are stable over a wide pH window and they can be easily recovered by centrifugation and filtration, these systems present the advantage that can be repeatedly used for the detection of iodide.

■

nanoparticles as support in different fields.21−26 The use of boehmite nanoparticles presents advantages such as the possibility to make fluorescence emission studies in pure water with little scattering, and the recovering of the sensor system after their use by centrifugation because a change from a sol to a gel state occurs at basic pH. Moreover, boehmite, which is an aluminum oxyhydroxide (AlO(OH)), contains terminal groups that render high reactivity to the surface and provide a hydrophilic environment improving the homogeneity of the medium being for all these reasons a promising support. In this context, we have prepared three new organic− inorganic covalently linked materials which contain pyrene as the fluorophore, the polyamine as the coordination site (receptor), and boehmite as the support. To analyze the role played by the support, we have also prepared the analogous unsupported ligands. The materials will be named as BTpy/ Tpy, B3Npy/3Npy, and B1Npy, where B stands for boehmite, 3N and 1N stand for the number of nitrogen atoms in the lineal chain, T corresponds to the tris(2-aminoethyl)amine tripodal structure, and py stands for pyrene. We have examined the photophysical properties and the photochemical response of the supported and unsupported materials in a wide pH range. Finally, we have studied the interaction of both types of systems with fluoride, chloride, bromide, iodide, sulfate, and phosphate anions.

INTRODUCTION The design and synthesis of chemosensors capable of recognizing anions have attracted much attention in recent years due to fundamental roles played by the anions in a wide range of biological, chemical, and environmental processes.1−4 The anions have a variety of special features that must be addressed to prepare effective receptors. They generally have large size and variable shape, are strongly solvated, can only exist in specific media, and interact only through weak forces. The most effective way to bind anions consists of taking advantage of their negative charge. Accordingly, protonated polyamines have been the principal receptors of choice, since they ensure intense electrostatic attractions reinforced by hydrogen-bond contacts with the coordinated anions.5−9 In order to signal the binding of the analyte to the receptor, we need a unit with a property that changes largely following the binding event. In this respect, fluorescent signaling units are very efficient because of the high sensitivity, rapid response, and simple instrumentation required for the measurement.10 For this study, we have chosen pyrene as a fluorophore, since it presents high fluorescence quantum yield and long singlet lifetime. Therefore, pyrene has been widely used as a signaling unit for a variety of analytes including inorganic anions.11−14 On the other hand, aiming to obtain more efficient, selective, and sensitive chemosensors, an increasing number of papers have recently appeared in which the chemosensor is anchored to different supports such as microporous and mesoporous materials,15 silica nanoparticles,16,17 gold nanoparticles,18,19 quantum dots,20 and boehmite nanoparticles.21 In this regard, our group has been working in the use of boehmite © 2013 American Chemical Society

Received: April 2, 2013 Revised: June 12, 2013 Published: June 17, 2013 14325

dx.doi.org/10.1021/jp4032546 | J. Phys. Chem. C 2013, 117, 14325−14331

The Journal of Physical Chemistry C

■

Article

Laser flash photolysis (LFP) experiments were carried out by using the third harmonic (355 nm) of a Q-switched Nd:YAG laser. Quantum yield was determined in deaerated medium using the quantum yield measurement system from Hamamatsu model C9920-0 by direct method.33 The system is made up of an excitation light source, consisting of a xenon lamp linked to a monochromator, an integration sphere, and a multichannel spectrometer. Also, the fluorescence quantum yield has been measured by the comparative method using pyrene in EtOH solution as a reference,34 obtaining similar results in both cases. The detection limit (DL) depends on the instrumentation (i.e., the signal-to-noise ratio gives you a quantitative indication of the sensitivity, in this case around 700) and on the sensitivity of the ligand defined as the d(luminescence)/d[cation]. Using these two parameters, the detection limit can then be calculated as 3·SNR/sensitivity. Synthesis and Characterization. Boehmite nanoparticles were prepared by the sol−gel procedure consisting in the hydrolysis of aluminum secbutoxide at 80 °C under vigorous stirring. The gel immediately formed was kept under stirring for 1 h until it evolved to give a white opaque suspension. After that, a peptization was reached by adding concentrated nitric acid and maintaining under stirring at 90 °C for 1 week. Then, the final transparent colloidal solution was vacuum evaporated to dryness. The solid was dried in an oven at 120 °C for 48 h.22 For preparing the working solutions, the dried solid was grounded in a mortar and the corresponding amounts were taken by weight. Scheme S1 in the Supporting Information shows the general procedure employed for the synthesis of the organic molecules and for the preparation materials. Tpy was synthesized by the reaction of 1-pyrenecarboxaldehyde (8.7 × 10−3 mol) with a 4fold excess of tris(2-aminoethyl)amine (tren) (3.5 × 10−2 mol) in dry EtOH. The resulting mixture was stirred for 2 h at room temperature under argon, and then, a 4-fold excess of sodium borohydride (3.5 × 10−2 mol) was added portionwise. After 2 h, the solvent was evaporated to dryness. The residue was treated with water and repeatedly extracted with CH2Cl2 (3 × 40 mL). The organic phase was dried with anhydrous MgSO4 and the solvent evaporated to dryness to give an oil. The oil was then taken in a minimum amount of EtOH and precipitated with HCl in dioxane to obtain its hydrochloride salt. The salt was purified washing with CH2Cl2 (2.88 g, 71%). C23H31Cl3N4: 468.16. Anal. Calcd for C23H31Cl3N4: C, 58.79; H, 6.64; N, 11.92. Found: C, 58.6; H, 6.8; N, 11.5. ESI-MS: m/ z calcd for C23H28N4, 360.23; found, 361.23 [L + H]+. 1 H NMR (300 MHz, D2O) and 13C NMR (300 MHz, D2O) (see Figures S1 and S2, Supporting Information). 3Npy was prepared by reaction of 1-pyrenecarboxaldehyde (5 × 10−3 mol) and diethylenetriamine (5 × 10−3 mol) in dry EtOH. The resulting mixture was stirred for 2 h at room temperature, and then, a 4-fold excess of sodium borohydride was added. The reaction was kept for a further hour under stirring. The compound was isolated and characterized as its HCl salts. C21H22Cl3N3: 422.5. Anal. Calcd for C21H22Cl3N3: C, 59.64; H, 5.21; N, 9.94. Found: C, 59.0; H, 5.0; N, 9.4. 1H NMR (300 MHz, D2O) and 13C NMR (300 MHz, D2O) (see Figures S3 and S4, Supporting Information). BTpy was synthesized by reaction of Tpy (5 × 10−3 mol) solved in dry EtOH (125 mL) with (3-iodopropyl)trimethoxysilane (5 × 10−3 mol) in an inert atmosphere for 24 h under stirring. Following, 1 g of boehmite nanoparticles

EXPERIMENTAL SECTION

Materials. 1-Pyrenecarboxaldehyde, tris(2-aminoethyl))amine, (3-iodopropyl)trimethoxysilane, diethylenetriamine, N1-(3-trimethoxysilylpropyl)diethylenetriamine, (3-aminopropyl) triethoxysilane, and sodium borohydride were commercially available reactants and were used without further purification. The ethanol used in the preparation was previously dried over 4 Å molecular sieves. Characterization Techniques. X-ray diffraction analysis was performed on a Siemens D-5000 diffractometer using graphite monochromatic Cu Kα radiation (λ = 1.5418 Å). Powdered samples were sprayed on glass sample holders and data collected in Bragg−Brentano geometry from 5 to 65° 2θ and a counting time of 5 s per step. 29 Si NMR studies were carried out on a Varian UNITY 300 spectrometer at a resonance frequency of 59.59 MHz. The solvents used for the spectrofluorimetric measurements were of spectroscopic or equivalent grade. Water was twice distilled and passed through a Millipore apparatus. All solutions were prepared in pure water. The pH values were measured with a Mettler-Toledo MP-120 pH-meter, and adjustment of the hydrogen ion concentration of the solution was made with diluted HCl or NaOH solutions. Electromotive Force Measurements. The potentiometric titrations were carried out at 298.1 ± 0.1 K using 0.15 M NaCl as supporting electrolyte. The experimental procedure (buret, potentiometer, cell, stirrer, microcomputer, etc.) has been fully described elsewhere.27 The acquisition of the emf data was performed with the computer program PASAT.28 The reference electrode was a Ag/AgCl electrode in saturated KCl solution. The glass electrode was calibrated as a hydrogen-ion concentration probe by titration of previously standardized amounts of HCl with CO 2-free NaOH solutions and determining the equivalent point by Gran’s method,29,30 which gives the standard potential, E°′, and the ionic product of water (pKw = 13.73(1)). The computer program HYPERQUAD31 was used to calculate the protonation and stability constants. The pH range investigated was 2.5−11.0. The different titration curves for each system were treated as separated curves without significant variations in the values of the stability constants. Finally, the sets of data were merged together and treated simultaneously to give the final stability constants. The distribution diagrams were plotted with the HYSS program.32 UV−vis spectra of the samples were recorded using quartz cuvettes in a UV−visible spectrophotometer (Agilent 8453E). Steady-state fluorescence spectra were measured on a spectrofluorometer (PTI), equipped with a lamp power supply LPS-220B, MD-5020, and 814 Photomultiplier Detection System, and working at room temperature. All the samples were measured under the same conditions at λex = 340 nm OD340 nm = 0.3 in aqueous solution using 1 cm × 1 cm path length quartz cuvettes. Time-resolved measurements were made with a Time Master fluorescence lifetime spectrometer TM-2/2003 from PTI. Sample excitation was afforded by PTI’s own GL-3300 nitrogen laser. The kinetic traces were fitted by monoexponential decay functions and reconvolution of the instrument response. The accuracy of the fits was evaluated by the reduced χ2 values as close to 1 as possible. 14326



Article

Scheme 1. Chemical Structure of the Compounds and Materials Prepared

of pyrene−polyamine attached per gram of boehmite, being 3.5 × 10−4, 1.2 × 10−4, and 1.93 × 10−4 mol/g for BTpy, B3Npy, and B1Npy, respectively. These values are similar to those we have previously reported for the functionalization of boehmite nanoparticles with other organic substrates.21,22 In the case of Bpy, the moles of pyrene−polyamine attached per gram of boehmite was 5.34 × 10−5 mol/g. X-ray powder diffractograms of BTpy, B3Npy, and B1Npy present peaks at 13.7, 28.3, 38.4, 49.2, and 64.8° 2θ, which are characteristic of the boehmite structure. The presence of these peaks after the funcionalization confirms that the matrix has not been disrupted throughout the synthetic procedure. Transmission electron microscopy of the samples reveals that the boehmite particles are dispersed and the particle size is in the 10−15 nm range. 29Si NMR spectra of the BTpy, B3Npy, and B1Npy present signals in the −50 to −61 ppm range, which support the covalent attachment of the fluorophore polyamine silane group to the boehmite surface through Si−O−Al bonds.22

was added to a solution of the functionalized pyrene-amine compound, keeping the stirring for 3 h. The functionalized nanoparticles were collected by centrifugation, and the product was successively washed with toluene/EtOH, EtOH, EtOH/ H2O mixture, and EtOH. In each washing step, the solid was collected by centrifugation. Anal.: C, 10.8%; H, 2.9%; N, 2.8%. B3Npy was prepared by reaction of 1-pyrenecarboxaldehyde (3 × 10 −3 mol) and N′-[3-(trimethoxysilyl)-propyl]diethylentriamine (3 × 10−3 mol) in methanol (150 mL). After 2 h of stirring at room temperature, a 4-fold excess of sodium borohydride was added. Finally, the hybrid inorganic− organic systems were prepared by adding 1 g of boehmite nanoparticles to a solution of the functionalized pyrene-amine compound, keeping the stirred samples for 3 h. The functionalized nanoparticles were collected by centrifugation, and the product was successively washed with CH2Cl2, MeOH, and a MeOH/H2O mixture. Anal.: C, 3.3%; H, 2.8%; N, 0.5%. B1Npy was prepared by reaction of (3-aminopropyl)triethoxysilane and 1-pyrenecarboxaldehyde dissolved in ethanol; this was added dropwise. The resulting mixture was stirred for 2 h, and then, a 4-fold excess of sodium borohydride was added. The reaction was kept for a further hour under stirring, and then, 1 g of boehmite was added. After 1 day, the solid was separated by centrifugation. Then, the solid was repeatedly washed with ethanol, dichloromethane, and ether. In each washing step, the solid was collected by centrifugation. Anal.: C, 1.5%; H, 1.9%; N, 0.3%. Bpy was prepared by reduction of 1-pyrenecarboxaldehyde (4.5 × 10−3 mol) with a 4-fold excess of sodium borohydride at room temperature. After that, the product was extracted with water and the resulting alcohol was reacting with the boehmite nanoparticles by condensation. Finally, the solid was repeatedly washed with ethanol, dichloromethane, and ether. In each washing step, it was collected by centrifugation. Anal.: C, 1.0%; H, 2.7%. The final supported materials were characterized by elemental analysis, XRD, TEM, and NMR. The results of the elemental analysis permit one to deduce the number of moles

■

RESULTS AND DISCUSSION Photophysical Studies. For all the samples prepared (Scheme 1), the structured absorption bands of pyrene remain unperturbed, indicating the absence of any direct ground-state interaction. On the other hand, although the absorption spectra do not change significantly with pH, the fluorescence emission intensities dramatically depend on the protonation state (see Figure 1 for BTpy; the corresponding figures for B3Npy and B1Npy are presented in Figures S5 and S6 of the Supporting Information, respectively). Figure S7 (Supporting Information) compares the variation with pH of the fluorescence intensity of the three supported materials. As described for related compounds, the fully protonated forms exhibit the most intense fluorescence emission. Unprotonated amines are efficient electron transfer quenchers of the aromatic excited state and, depending on the distance to the fluorophore, can produce a partial or a complete quenching.35 This trend is illustrated in Figure 2, where the fluorescence emission intensity monitored at 375 nm is plotted 14327



Article

Figure 3. Steady-state fluorescence emission for Tpy (line) and BTpy (dot) at λex = 340 nm and OD = 0.3 in aqueous solution at pH 3 and s = 1 nm.

Figure 1. Variation with pH of the emission spectra of the BTpy (λex = 340 nm, OD = 0.3).

Table 1. Photophysical Properties of the Samples: Tpy, BTpy, B3Npy, and B1Npy in Deoxygenated Aqueous Solution at pH 3 PLQY (%) Tpy BTpy 3Npy B3Npy B1Npy

51 36 55 35 22

τ (ns) 138 127 162 136 159

± ± ± ± ±

1 2 5 1 3

kr (×106) (s−1)

knr (×106) (s−1)

3.69 2.83 3.39 2.57 1.38

3.55 5.04 2.78 4.78 4.91

Φ(B3Npy) = 0.35. In the same way, the fluorescence quantum yields in the supported materials are lower when the length of the polyamine chain is reduced, B3Npy vs B1Npy. However, the quantum yields of B3Npy and BTpy are similar regardless of their different topology, which can be attributed to the larger size of these two polyamines. Protonation of the polyamine chains at the working pH of 3 keeps the molecule in an extended conformation that prevents the pyrene groups from adsorbing into the surface. According to the bibliography, the fluorescence quantum yields of several arenes adsorbed on oxide surfaces are found to be lower than those in solution.36 These studies show that such lower quantum yields are due to the adsorption of some pyrene molecules at reactive sites that produce charge transfer states. Thus, in our case, the lower decreasing fluorescence quantum yield suggests the existence of an interaction between the aromatic π-system of the pyrene and the surface of the boehmite nanoparticles. We can observe that the influence is greater when the fluorophore is closer to the nanoparticle, showing the B1Npy has the lowest fluorescence quantum yield. To corroborate this point, we have prepared pyrene anchored directly to the boehmite nanoparticle (Bpy), with the fluorescence quantum yield being less than 10%. Likewise, for pyrene in solution, the calculated radiative and nonradiative rate constants are in the order of 106 for all the samples prepared.37 However, a consequence of supporting the ligands is an increase in the nonradiative decay rate being the major difference for B1Npy (knr ≫ kr, see Table 1); the net result is a lower fluorescence quantum yield as we have previously commented. On the other hand, the fluorescence decays are first-order in all the samples prepared. Laser excitation at 355 nm of the samples Tpy and BTpy shows in both cases two different transients that were assigned to 3py* (λmax = 420 nm) and py + (λmax = 460 nm). This assignment is supported by results of Ar and O2 purging as well as previous

Figure 2. Fluorescence titration curves of Tpy (black squared points) and BTpy (red circle points) recorded in water. The data points are normalized to the fluorescence of the fully protonated form (I/Io). Molar fractions of the species are also plotted and were calculated from potentiometric constants.

together with the mole fraction distribution of the different protonated species calculated from the protonation constants determined potentiometrically for Tpy (see Table S1, Supporting Information). In such a graphic, it can be seen as a strong quenching of the emission is produced following the first deprotonation of the ligand. On the other hand, it should be noted that the basicity is not significantly modified when the ligand is supported with the fluorescent titration curves of Tpy and BTpy being similar. The samples prepared (Tpy, 3Npy, BTpy, B3Npy, and B1Npy) containing pyrene as the fluorophore exhibit strong monomer fluorescence emission in all cases upon excitation at 340 nm with OD340 nm = 0.3 in aqueous acidic medium, as shown in Figure 3 for Tpy and BTpy; in none of these cases did we observe a significant broad emission band between 450 and 550 nm characteristic of excimer formation. These results indicate that the molecules of pyrene should be separated enough on the nanoparticle surface to avoid any interaction between them. Selected photophysical data are reported in Table 1. Fluorescent decays were first-order. The radiative (kr) and nonradiative (knr) rate constants were calculated using the equations ΦF = kr/(kr + knr) and ΦF = kr·τ, and the fluorescent quantum yields were measured by the comparative and absolute methods obtaining similar values. Table 1 shows that fluorescence quantum yields of pyrene are lower in the supported materials than in the free molecules, Φ(Tpy) = 0.51 vs Φ(BTpy) = 0.36 and Φ(3Npy) = 0.55 vs 14328



Article

reports in the literature15 (see Figure S8, Supporting Information). Anion Sensing. The fluorescent behavior of Tpy, 3Npy, BTpy, B3Npy, and B1Npy in aqueous solution at pH 3 was studied in the presence of the anions fluoride, chloride, bromide, iodide, sulfate, and phosphate. A decrease in intensity of the pyrene fluorescence emission as a function of the quencher concentration was observed only in the case of the iodide anion. The obtained results are given as a classic Stern− Volmer plot in Figure 4. The corresponding results for B3Npy and B1Npy are collected in Figures S9 and S10 (Supporting Information).

Tpy shows some interaction with iodide in aqueous solutions, we have seen less interaction for the linear amines. Moreover, this might be the reason why we do not observe any difference for B3Npy and B1Npy (vide inf ra). Therefore, the topology of the polyamine chain seems to play a role in the quenching. To describe the quenching mechanism of the pyrene, the bimolecular quenching rate constant kq was determined and the pyrene lifetimes were determined from time-resolved fluorescence measurements (see Table 2). The values of kq for Table 2. Stern−Volmer Constants Fluorescence Lifetimes ([KI] = 0.005 M) and Bimolecular Quenching Rate Constant for Pyrene-Ligands in the Presence of Iodide Anions Ksv (M−1)a Tpy BTpy B3Npy B1Npy

1340 1310 670 714

τ (ns)

Kq × 109 (M−1 s−1)

± ± ± ±

9.7 10.3 4.9 4.5

14 9 12 21

3 1 2 1

a

The Ksv for pyrene in acetonitrile adding a KI solution was 89.6 [M−1].39

BTpy and Tpy are around 1 × 1010 M−1 s−1 corresponding to typical values for diffusion-controlled quenching. In the case of B3Npy and B1Npy, the quenching rate constants are lower, approximately 5 × 109 M−1 s−1 in both cases due to a lower accessibility of pyrene in the case of the lineal polyamine chain. For the polyamine tren, the collision is more effective. The fluorescence decay is shortened in all the materials by the presence of I−, changing from 138 ns for Tpy to 14 ns for Tpy in the presence of 5 mM KI at pH 3 (see Figure 6). For

Figure 4. Fluorescent emission changes of BTpy (OD340 = 0.3) upon the addition of KI (100 μL, 0.1 M) in aqueous solution at pH 3 (λex = 340, s = 1 nm). Inset: I0/I versus [I−] relationship used to determine the association constant.

In order to know the range of applicability of these chemosensors in aqueous solution, we have calculated the Stern−Volmer constants for the interaction of iodide with Tpy, BTpy, B3Npy, and B1Npy at various pH values (see Figure 5).

Figure 6. Emission decay (λex = 337 nm) measured at 375 nm of B3Npy in the absence (red line) and presence (black line) of KI (5 mM) aqueous solution.

BTpy, B3Npy, and B1Npy, the fluorescent lifetime is 9, 12, and 21 ns, respectively, under the same conditions. It is important to notice that not only the fluorescence intensity but also the emission temporal profile responds to the iodide concentration in all cases. Thus, we suggest a dynamic quenching with a static contribution due to the interaction of the iodide with the positively charged amine linkers. While a combination of static and dynamic quenching typically results in a curvature of the Stern−Volmer plot, there are examples in which such a curvature is not appreciable.38 In such cases, the equation Φ0/ Φ = τ0/τ, where the subscript “0” indicates data in the absence of quencher, does not apply. This clearly indicates that the

Figure 5. Variations of the Stern−Volmer constant with the pH for Tpy (square), BTpy (circle), B3Npy (up triangle), and B1Npy (down triangle).

The values of the Stern−Volmer constants for B3Npy and B1Npy at pH 3 are close between them but markedly lower than the value obtained for the tren derivatives: BTpy ≈ Tpy > B3Npy ≈ B1Npy

At acidic pH, the electrostatic attraction between halide ions and the fully protonated polyamine chain also favors the process of collisions being more favorable for the case of the tripodal polyamine. This is corroborated by the fact that, while 14329



Article

successfully developed by employing a fluorescence quenching and recovery strategy when the pyrene with a polyamine chain is supported on boehmite nanoparticles, with BTpy being a particularly efficient system. Moreover, the sensor device can be recovered by increasing the pH until a gel is formed. Centrifugation and extensive washing with water leads to the removal of iodide and to the recovery of the functionalized boehmite nanoparticles for further use.

mechanism is not a simple dynamic quenching and provides support for ground-state complexation as it happens for BTpy where Φ0/Φ = 7 and τ0/τ = 14. At pH 5, we observe a similar photochemical behavior than at pH 3 for all the materials but with a slight decrease in the KSV. At basic pH, the polyamine chain is deprotonated and the quenching mechanism is also by PET of the amine groups. Moreover, at this more basic pH, there is less interaction of the iodide with the polyamine. It is interesting to remark that the decrease in the Stern−Volmer constant occurs at higher pH for B1NPy than for B3NPy, in correspondence with the higher pH at which B1Npy deprotonates (see Figure 5). Bianchi et al. studied the interaction of tris(2-aminoethyl)amine (tren) with anions such as NO3−, SO42−, and HPO42− corroborating the intrinsic ability of the ligand tren to bind anions even in water.9 In our systems, pH-metric titrations of Tpy in the presence of an excess of sulfate, phosphate, or iodide show the formation of the [HpL·A](p−n)+ anion:receptor adducts whose constants are included in Table S2 and the distribution diagram in Figure S11 of the Supporting Information. However, considering that only in the presence of iodide we observe a decrease in the fluorescence intensity of pyrene, the anion:polyamine receptor adducts with SO42− and HPO42− formed in the ground state do not seem to modify the pyrene emission at pH 3. In the case of the iodide adduct, the anion interaction with the protonated polyamine chain would be favoring the proximity or accessibility of the iodide quencher to the fluorophores. Furthermore, the emission responses of the ligands for 5 mM aqueous solution of iodide are the same in the presence or absence of the other anions, with these chemosensors being selective for iodide determination. The fluorescence intensity at 375 nm decreases linearly with the iodide concentration for all the samples, allowing estimated detection limits (DL) of 45 ppb for Tpy, 36 ppb for BTpy, 58 ppb for B3Npy, and 202 ppb for B1Npy. According to the World Health Organization, the maximum recommended iodide concentration in drinking water is 18 ppm. Our materials present a lower detection limit, especially for Tpy and BTpy; therefore, they can be considered as very promising chemosensors that can be used for iodide detection. In particular, the supported chemosensors might be used in the detection of iodide anion in water with the advantage that permits an easy recovery of the supported chemosensor by centrifugation.

■

ASSOCIATED CONTENT

S Supporting Information *

Scheme of the synthetic procedure and 1H and 13C NMR spectra of Tpy and 3Npy. The following are also included: fluorescence quenching experiments, differential absorption spectrum, basicity, and association constants of the Tpy and 3Npy in water. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Phone: +34 96 354 4403 (E.C.); +34 96 354 4879 (E.G.-E.). E-mail: [email protected] (E.C.); [email protected] (E.G.-E.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support from the Spanish Ministry of Science and Innovation (CTQ2009-14288-CO4-01 and CONSOLIDER INGENIO 2010 CSD2010-00065 Projects), FEDER funds, and Generalitat Valenciana PROMETEO 2011/008 is gratefully acknowledged. J.P.J. thanks MINECO of Spain for a Ph.D. grant. E.C. thanks MINECO for a Juan de la Cierva grant.

■

REFERENCES

(1) Sessler, J. L.; Gale, P.; Cho, W.-S. Anion Receptor Chemistry; Royal Society of Chemistry: Cambridge, U.K., 2006; p 414. (2) Bianchi, A.; Bowman-James, K.; García-España, E. Supramolecular Chemistry of Anions; Wiley-VCH: Weinheim, Germany, 1997; p 461. (3) Amendola, V.; Fabbrizzi, L.; Licchelli, M.; Taglietti, A. Anion Sensing by Fluorescence Quenching or Revival. In Anion Coordination Chemistry; Bowman-James, K., Bianchi, A., García-España, E., Eds.; Angewandte Chemie International Edition/Wiley-VCH: Weinheim, Germany, 2012; pp 521−552. (4) Kubik, S. Receptors for Biologically Relevant Anions. In Anion Coordination Chemistry; Bowman-James, K., Bianchi, A., GarcíaEspaña, E., Eds.; Angewandte Chemie International Edition/WileyVCH: Weinheim, Germany, 2012; pp 363−464. (5) Bencini, A.; Bernardo, M. A.; Bianchi, A.; García-España, E.; Giorgi, C.; Luis, S.; Pina, F.; Valtancoli, B. Sensing Cations and Anions by Luminescent Polyamine Receptors in Solution. Adv. Supramol. Chem. 2002, 8, 79−130. (6) García-España, E.; Díaz, P.; Llinares, J. M.; Bianchi, A. Anion Coordination Chemistry in Aqueous Solution of Polyammonium Receptors. Coord. Chem. Rev. 2006, 250, 2952−2986. (7) Huston, M. E.; Akkaya, E. U.; Czarnik, A. W. Chelation Enhanced Fluorescence Detection of Non-Metal Ions. J. Am. Chem. Soc. 1989, 111, 8735−8737. (8) Pina, F.; Bernardo, M. A.; García-España, E. Fluorescent Chemosensors Containing Polyamine Receptors. Eur. J. Inorg. Chem. 2000, 2143−2157. (9) Bazzicalupi, C.; Bencini, A.; Bianchi, A.; Danesi, A.; Giorgi, C.; Valtancoli, B. Anion Binding by Protonated Forms of the Tripodal Ligand Tren. Inorg. Chem. 2009, 48, 2391−2398.

■

CONCLUSION The synthesis and photophysical properties of a series of new chemosensors containing pyrene as a fluorophore and tripodal or lineal polyamines as a receptor unit have been described in solution and supported on boehmite nanoparticles. We have studied the photophysical properties of the materials prepared when the ligand is supported in the boehmite surface, also depending of the distance of the pyrene to the boehmite surface. In addition, neither solutions of the free molecules nor solutions of the supported materials show excimer emission being the signal mechanism the monomer emission. We have observed just a slight decrease variation in the response factor of the chemosensor from the homogeneous to the heterogeneous state, with the detection limit being just slightly lower in the supported material. On the other hand, the topology of the polyamine chain plays a role in the iodide recognition. Therefore, it can be concluded that a selective fluorescence sensing system for iodide in a wide pH range has been 14330



Article

(28) Fontanelli, M.; Micheloni, M. In Procedings of the Spanish-Italian Congress on Thermodynamics of Metal Complexes; Castellón, D. d., Ed.; Castellón, Spain, 1990. (29) Gran, G. Determination of the Equivalence Point in PotentiometricTitrations II. Analyst 1952, 77, 661−671. (30) Rossotti, F. J. C.; Rossotti, H. Potentiometric Titrations Using Gran Plots. J. Chem. Educ. 1965, 42, 375−378. (31) Gans, P.; Sabatini, A.; Vacca, A. Investigation of Equilibria in Solution. Determination of Equilibrium Constants with HYPERQUAD Suite of Programs. Talanta 1996, 43, 1739−1753. (32) Alderighi, L.; Gans, P.; Ienco, A.; Peters, D.; Sabatini, A.; Vacca, A. Hyperquad Simulation and Speciation (HySS): a Utility Program for the Investigation of Equilibria Involving Soluble and Partially Soluble Species. Coord. Chem. Rev. 1999, 184, 311−318. (33) Porres, L.; Holland, A.; Palsson, L.-O.; Monkman, A. P.; Kemp, C.; Beeby, A. Absolute Measurements of Photoluminescence Quantum Yields of Solutions Using an Integrating Sphere. J. Fluoresc. 2006, 16, 267−273. (34) Berlman, I. B. Handbook of Fluorescence Spectra of Aromatic Molecules, 2nd ed.; Academic Press: New York and London, 1971; p 473. (35) Pina, F.; Lima, J. C.; Lodeiro, C.; Seixas de Melo, J.; Díaz, P.; Albelda, M. T.; García-España, E. Long Range Electron Transfer Quenching in Polyamine Chains Bearing a Terminal Naphthalene Unit. J. Phys. Chem. A 2002, 106, 8207−8212. (36) Ruetten, S. A.; Thomas, J. K. Fluorescence and Triplet Quantum Yields of Arenes on Surfaces. J. Phys. Chem. B 1998, 102, 598−606. (37) Taratula, O.; Rochford, J.; Piotrowiak, P.; Galoppini, E.; Carlisle, R. A.; Meyer, G. J. Pyrene-Terminated Phenylenethynylene Rigid Linkers Anchored to Metal Oxide Nanoparticles. J. Phys. Chem. B 2006, 110, 15734−15741. (38) Perry, M.; Carra, C.; Chrétien, M. N.; Scaiano, J. C. Effect of Hexafluorobenzene on the Photophysics of Pyrene. J. Phys. Chem. A 2007, 111, 6. (39) Li, L.; Zhang, Z.; Long, W.; Tong, A. Study of Properties on Non-Protected Room Temperature Phosphorescence and Delayed Excimer Fluorescence of Pyrene Solution. Spectrochim. Acta, Part A 2001, 57, 385−393.

(10) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Signaling Recognition Events with Fluorescent Sensors and Switches. Chem. Rev. 1997, 97, 1515−1566. (11) Manandhar, E.; Wallace, K. J. Host-Guest Chemistry of PyreneBased Molecular Receptors. Inorg. Chim. Acta 2012, 381, 15−43. (12) Kim, S. K.; Bok, J. H.; Bartsch, R. A.; Lee, J. Y.; Kim, J. S. A Fluoride-Selective PCT Chemosensor Based on Formation of a Static Pyrene Excimer. Org. Lett. 2005, 7, 4839−4842. (13) Lee, H. N.; Singh, N. J.; Kim, S. K.; Kwon, J. Y.; Kim, Y. Y.; Kim, K. S.; Yoon, J. New Imidazolium Systems Bearing Two Pyrene Groups as Fluorescent Chemosensors for Anions and Anion Induced Logic Gates. Tetrahedron Lett. 2007, 48, 169−172. (14) Shiraishi, Y.; Tokitoh, Y.; Hirai, T. pH- and H2O-Driven TripleMode Pyrene Fluorescence. Org. Lett. 2006, 8, 3841−3844. (15) Corma, A.; Galletero, M. S.; García, H.; Palomares, E.; Rey, F. Pyrene Covalently Anchored on a Large External Surface Area Zeolite as a Selective Heterogeneous Sensor for Iodide. Chem. Commun. 2002, 1100−1101. (16) Montalti, M.; Rampazzo, E.; Zaccheroni, N.; Prodi, L. Luminescent Chemosensors Based on Silica Nanoparticles for the Detection of Ionic Species. New J. Chem. 2013, 37, 28−34. (17) Candel, I.; Calero, P.; Martínez-Mañez, R.; Sancenón, F.; Dolores Marcos, M.; Pardo, T.; Soto, J. Sensing Properties of Silica Nanoparticles Functionalized with Anion Binding Sites and Sulforhodamine B as Fluorogenic Signalling Unit. Inorg. Chim. Acta 2012, 381, 188−194. (18) Jiang, Y.; Zhao, H.; Zhu, N.; Lin, Y.; Yu, P.; Mao, L. A Simple Assay for Direct Colorimetric Visualization of Trinitrotoluene at Picomolar Levels Using Gold Nanoparticles. Angew. Chem. 2008, 47, 8601−8604. (19) Lu, F.; Doane, T. L.; Zhu, J.-J.; Burda, C. Gold Nanoparticles for Diagnostic Sensing and Therapy. Inorg. Chim. Acta 2012, 393, 142− 153. (20) Agudelo-Morales, C. E.; Galián, R. E.; Pérez-Prieto, J. PyreneFunctionalized Nanoparticles: Two Independent Sensors, the Excimer and the Monomer. Anal. Chem. 2012, 84, 8083−8087. (21) Delgado-Pinar, E.; Montoya, N.; Galiana, M.; Albelda, M. T.; Frías, J. C.; Jiménez, H. R.; García-España, E.; Alarcón, J. Preparation of Hg2+ Selective Fluorescent Chemosensors Based on Surface Modified Core-Shell Aluminosilicate Nanoparticles. New J. Chem. 2010, 34, 567−570. (22) Aucejo, R.; Alarcón, J.; Soriano, C.; Carmen Guillem, M.; García-España, E.; Torres, F. New Sensing Devices Part 1: IndoleContaining Polyamines Supported in Nanosized Boehmite Particles. J. Mater. Chem. 2005, 15, 2920−2927. (23) Aucejo, R.; Díaz, P.; García-España, E.; Alarcón, J.; DelgadoPinar, E.; Torres, F.; Soriano, C.; Guillem, M. C. NaphthaleneContaining Polyamines Supported in Nanosized Boehmite Particles. New J. Chem. 2007, 31, 44−51. (24) Delgado-Pinar, E.; Albelda, M. T.; Frías, J. C.; Barreiro, O.; Tejera, E.; Kubicek, V.; Jimenez-Borreguero, L. J.; Sánchez-Madrid, F.; Toth, E.; Alarcón, J.; García-España, E. Lanthanide Complexes as Imaging Agents Anchored on Nano-Sized Particles of Boehmite. Dalton Trans. 2011, 40, 6451−6457. (25) Delgado-Pinar, E.; Frías Juan, C.; Jiménez-Borreguero Luis, J.; Albelda, M. T.; Alarcón, J.; García-España, E. One-Pot Preparation of Surface Modified Boehmite Nanoparticles with Rare-Earth Cyclen Complexes. Chem. Commun. 2007, 3392−3394. (26) Delgado-Pinar, E.; Rotger, C.; Costa, A.; Pina, M. N.; Jiménez Hermas, R.; Alarcón, J.; García-España, E. Grafted Squaramide Monoamine Nanoparticles as Simple Systems for Sulfate Recognition in Pure Water. Chem Commun 2012, 48, 2609−2611. (27) García-España, E.; Ballester, M. J.; Lloret, F.; Moratal, J. M.; Faus, J.; Bianchi, A. Low-Spin Six-Coordinate Cobalt(II) Complexes. A Solution Study of Tris(violurato)cobaltate(II) Ions. J. Chem. Soc., Dalton Trans. 1988, 101−104. 14331


Boehmite Supported Pyrene Polyamine Systems as Probes for Iodide

Recommend Documents