ARTICLE pubs.acs.org/JPCC
Medium Dependent Dual Turn-On/Turn-Off Fluorescence System for Heavy Metal Ions Sensing Gemma Aragay,†,‡ Georgina Alarcon,†,§ Josefina Pons,‡ Merce Font-Bardía,|| and Arben Merkoc-i*,†,^ †
Nanobioelectronics & Biosensors Group, CIN2-ICN, Catalan Institute of Nanotechnology, Catalonia, Spain Department of Chemistry, Universitat Autonoma de Barcelona, 08193, Bellaterra, Catalonia, Spain § Basic Sciences Department, Autonomous Metropolitan University, Unit Azcapotzalco, 02200 Mexico City, Mexico Crystal 3 lografia, Mineralogia i Diposits Minerals & Unitat de difraccio de RX, Serveis científico-tecnics, Universitat de Barcelona, Martí i Franques s/n, 08028, Barcelona, Catalonia, Spain ^ ICREA, Barcelona, Catalonia, Spain
)
‡
bS Supporting Information ABSTRACT: A dual turn-on/turn-off fluorescence sensing system based on N-alkylaminopyrazole ligands for heavy metal ions, where the response can be tuned upon medium change, is developed. The synthesis and characterization of ZnII, CdII and HgII complexes with two N-alkylaminopyrazole ligands, used as metal receptors, are first presented. The acidity and complexation constants for a selected ligand (1-[2-(octylamino)ethyl]3,5-diphenylpyrazole ligand (L2)) with ZnII, CdII, and HgII are also determined. The fluorescent behavior of these complexes can be tuned by the different medium used (e.g., MeOH or HCl) giving rise to two different sensing mechanisms. The L2 ligand can be applied as a global heavy metal warning chemosensor (for PbII, ZnII, CdII, or HgII ions) for water samples achieving detection limits lower than the maximum concentration recommended by the environmental agencies (detection limit lower than 0.3 ng/mL for any of the mentioned metal ions). The utility of the developed sensing system for HgII detection in seawater without any previous sample pretreatment with interest for future in-field sensing kit like applications is also discussed.
1. INTRODUCTION The development of novel heavy metals sensing systems with interest for in situ environment control is of great interest for the safety and decision making in the case of pollution scenarios. Rapid and inexpensive techniques involving colorimetry,1 fluorimetry,2 and electrochemistry3 among others to allow miniaturization and in-field applications for heavy metal detection have already been reported. The development and efficiency of such systems, as an alternative to laboratory instrumentation, are strongly dependent on the receptors and the chemical (i.e., ligands) or biochemical molecules (i.e., DNA, antibodies) that are responsible for the selective detection of the heavy metal ions.4 Recently, detection systems using biological receptors have been reported as very interesting strategies for the detection of metal ions, mainly because of their high specificity.5 However, biological systems have poor chemical/physical stability that prevents their use in harsh environments (i.e., acids or bases, organic solvents, and high temperatures). In this context, more robust synthetic receptors for heavy metals are highly desired. Among various synthetic receptors the nitrogen containing ones have been reported. The study of the coordination properties of nitrogen containing ligands with heavy metals such as zinc, cadmium, and r 2011 American Chemical Society
mercury is of crucial interest for the design and development of efficient complexing agents that might be further used in fast, real time, and low cost monitoring systems in environmental, food, and clinical samples or even as metal ions extractants.6 8 One of the most attractive and sensitive methods for pointing out the host guest interaction between ligands and heavy metal ions is based on the use of fluorescent receptors due to their simplicity and high detection limits.1b,9 Fluorescent sensors for metal ions described in the literature are mainly based on photoinduced electron-transfer (PET),10 metal ligand charge transfer,11 chelation enhanced fluorescence (CHEF),12 and fluorescence resonance energy transfer (FRET).13 Pyrazole derived ligands have been described to be suitable ligands for the coordination of metal ions of group 12,14 17 and its connection to fluorescent units such as phenyl rings might be useful for the design of fluorescent chemosensors.18 In addition to their sensing interest, the coordination properties of such molecules as well as the study of the complexation strength (as expressed by pKf) are critical issues to be considered Received: November 7, 2011 Revised: December 15, 2011 Published: December 16, 2011 1987
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Figure 1. Scheme of the N-alkylaminopyrazole ligands L1 and L2 in different pH ranges.
for the sensitivity of the detection.19 For this reason, the combination of coordination chemistry and analytical chemistry is of great importance for further applications of the organic ligands in the sensing field and for a better understanding of the operational mechanisms of such ligands with heavy metal ions. In recent studies performed in our group, the synthesis and coordination chemistry of 1-[2-(ethylamino)ethyl]-3,5-diphenylpyrazole (L1) and 1-[2-(octylamino)ethyl]-3,5-diphenylpyrazole (L2; Figure 1) with PdII and PtII have been described.20 In addition, our group has recently reported the use of gold nanoparticles modified with N-alkylaminopyrazole ligands as optical heavy metal sensors being system selective to HgII at low concentration range using L2 ligand.21 Our aim now is to gain insight into the selectivity of N-alkylaminopyrazole ligands toward HgII ions through the study of complexation strengths of this ligand with metal ions of group 12 (ZnII, CdII, and HgII). Moreover, the coordination chemistry of such ligands with the aforementioned heavy metal ions including the application of the last one (L2) as a global heavy metal fluorescent chemosensor with interest in the fast control of the heavy metals presence in water samples such as seawater, tap water, or wastewater have been studied. Based on such new interesting clarifications, a dual turn-on/turn-off fluorescence detection mechanism sensitive enough for heavy metal ions sensing is proposed and applied for real samples analysis.
2. EXPERIMENTAL METHODS General Details. Elemental analyses (C, H, and N) were carried out by the staff of Chemical Analyses Service of the Universitat Autonoma de Barcelona on a Carlo Erba CHNS EA1108 instrument. Conductivity measurements were performed at room temperature in 1.0 3 10 3 M MeOH solutions, employing a CyberScan CON 500 (Euthech Instruments) conductimeter. Infrared spectra were run on a Perkin Elmer FT spectrophotometer, series 2000 cm 1, as KBr pellets or polyethylene films in the range 4000 100 cm 1 3 1H, 13C{1H} NMR, DEPT, COSY, HMQC, and NOESY spectra were recorded with a NMR-FT Bruker 250 MHz spectrometer in CDCl3 or DMSO solutions at room temperature. 1D 113Cd{1H} NMR spectra were recorded on a DPX-360 Bruker spectrometer equipped with a 5-nm broadband probe at 298 K in DMSO using a recycle time of 1 s. Spectra were processed with a line broadening of 1 Hz before Fourier transformation and externally referenced to aqueous solution of 0.1 M Cd(ClO4)2. All chemical-shift values (δ) are given in ppm. Electrospray (ESI+) mass spectra were obtained with an Esquire 3000 ion-trap mass spectrometer from Bruker Daltonics. Mass spectrometry assignments were supported by isotopic simulations. Fluorescence measurements were recorded
on a SpectraMax M2e spectrophotometer within the 200 600 nm wavelength (λ) range. All spectrophotometric determinations were carried out on a quarts cell at a constant room temperature. All chemicals used were of AR grade. L1 and L2 ligands were prepared as described in a previous work of our group.20 Synthesis of the Complexes. A solution of 0.23 mmol of the corresponding ligand (L1, 0.067 g; L2, 0.086 g) in 20 mL of absolute ethanol was added to a solution of 0.23 mmol of MCl2 (ZnCl2: 0.031 g for 1 and 2; CdCl2: 0.042 g for 3 and 4; 0.063 g for 5 and 6) and 4 mL of triethyl orthoformate (for drying purposes). The mixture was stirred at room temperature for 24 h. Then, most of the solvent was removed under vacuum (5 mL). Dry and cool diethyl ether (5 mL) was added to induce precipitation. The resulting white solid was filtered off and washed twice with 5 mL of diethyl ether. The complete characterization of the complexes can be found in the Supporting Information. Spectrophotometric Measurements. The absorption spectra were recorded by means of a SpectraMax M2e spectrophotometer within the 200 600 nm wavelength (λ) range. All spectrophotometric determinations were carried out on a quarts cell at a constant room temperature. The experimental A-λ data were fed to the data processing software SQUAD17 to calculate the complexation constants of the metal ligand, and to establish the pKa of the N-alkylaminopyrazole ligands. A Crison pH meter BASIC 20 was used for all pH readings. The pH was altered in the 0.2 11 range by additions to the external titration cell of small amount of HCl as required using a micropipet. After each addition the system was allowed to mix prior recording the spectrum. The L2 ligand has low water solubility but can be studied spectrophotometrically at that concentration. Fluorescence Measurements and Sensing. Excitation emission matrix (EEM) fluorescence properties were determined on a Spectramax M2e fluorometer equipped with quartz cuvettes of 1 cm path length. The instrument was configured to collect the signal in ratio mode with dark off set using 5 nm band passes on both the excitation and emission monochromators. Replicate scans were generally within 5% agreement in terms of intensity and within band-pass reduction in terms of peak location. The fluorescent spectra of 20 μM L2 were recorded in two different media: MeOH and HCl 0.1 M. [Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-805614.]
3. RESULTS AND DISCUSSION Synthesis and Characterization of the Complexes. Complexes [MCl2(L)] (L = L1, M = ZnII (1); M = CdII (3); M = HgII (5); 1988
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Figure 2. ORTEP drawing of complex 1, showing all non-hydrogens atoms and the atom numbering scheme; 50% probability amplitude displacement ellipsoids are shown.
L = L2, M = ZnII (2); M = CdII (4); M = HgII (6)) were obtained by treatment of the corresponding ligand with MCl2 (M = ZnII, CdII, or HgII) in a 1:1 M/L ratio in absolute ethanol as solvent during 5 h. For a better understanding of the heavy metal sensing mechanism the synthesized complexes were previously characterized so as to clarify the role of their structures in complexation reactions and fluorescence changes discussed in the next sections. Several techniques were used for the characterization of all complexes: elemental analyses (consistent with the formula [MCl2(L)] for all complexes), mass spectrometry (giving peaks attributable to [MCl(L)]+), conductivity measurements (values in agreement with the presence of nonelectrolyte compounds),22 IR,23,24 1H and 13C{1H} NMR spectroscopies (recorded in CDCl3 for 1, 2, 5, and 6 and in DMSO for 3 and 4 due to the poor solubility of these complexes in CDCl3) and X-ray diffraction. 113Cd{1H} NMR spectra were also performed for the characterization of complexes 3 and 4 in DMSO which showed only a singlet for each complex around 400 ppm indicating the presence of a single tetracoordinated complex in solution (where CN = 4; two N and two Cl atoms).25 All the information about the complete characterization of compounds 1 6 is gathered in section 2 and Supporting Information sections. In addition, suitable crystals for X-ray analysis were obtained for compound 1 through crystallization from a dichloromethane/ diethyl ether (4:1) mixture. The L1 ligand acts as a bidentate chelate, forming a sixmembered metallocycle ring (N1N2C16C17N3Zn), with an
envelope conformation (Figure 2). The Namino H bonds are intermolecularly hydrogen bridged to a chlorine atom (Cl(2)) (see Table SI2 in the Supporting Information for contact parameters). Figure SI2 in the Supporting Information shows the disposition of the molecules in the crystalline network, revealing the alternation of the arrangement of the terminal ethyl chain along the single infinite one-dimensional chain along the (1,0,0) plane. Complexation Constants Determination. The study of acidity and complexation constants is highly important in order to evaluate the complexation properties of the synthesized ligands versus different metals in a certain media. In this context, L2 ligand was selected as a model ligand to study its acidity and complexation properties toward ZnII, CdII, and HgII ions. In a previous work we already show the affinity of such ligand toward mercury.21 The pKa values obtained from SQUAD26 software for L2 ligand are 7.30 ( 0.02 and 1.54 ( 0.02 with a σA = 0.005 (global standard deviation of refinement of absorbance data) for pKa1 and pKa2, respectively.27 Finally the log(Kf) values obtained for ML2H+ formation were 8.71 (for ZnII), 3.32 (for CdII), and 17.15 (for HgII) (see Table 1).28 The selectivity toward HgII ions observed in the recently reported mercury selective sensing system using gold nanoparticles modified with L2 ligand by our group,21 can now be justified by the obtained complexation constants in the present work. Moreover, we aim to show that the direct use of N-alkylaminopyrazole ligands for the heavy metal detection is another interesting alternative for metal 1989
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detection in addition to their use while being immobilized onto nanoparticles.21 This sensing platform might be with interest for other in-field detection technologies such as simple colorimetric kits or even lateral flow devices. The procedure followed to obtain such acidity and complexation constats for L2 ligand is detailed in the Supporting Information. Fluorescence Studies and Heavy Metal Sensing. In order to evaluate the capability of the ligands to act as heavy metal sensors we have chosen fluorescence techniques due to their higher sensitivity in comparison to UV Vis absorbance techniques.9f Along with the well-known fluorophores, such as naphthalene, anthracene derivatives,29 coumarine30 and several organic dyes, heterocycles like 1-(2-pyridyl)pyrazole derived ligands have already found their place as fluorescent units.31 In this way, our group has previously reported the fluorescence properties of some alcohol derived pyrazole ligands with methyl moieties in 3 and 5 positions of the pyrazole ring.15 These ligands, although the low sensitivity, showed an increase of fluorescence intensity upon the addition of metal ions being this effect greater mercury ions. The change of the 3 and 5 pyrazole methyl moieties for Table 1. Values for the Acidity (K1 and K2) and Complexation (Kf) Constants Obtained for Ligand L2 complexation reaction
log K
ref
H + OH T H2O
14.00
27d
L2+ + H+ T L2H+
7.03
this work
L2H+ + H+ T L2H2+
1.54
this work
L2H+ + ZnII T ZnL2H+
8.71
this work
L2H+ + CdII T CdL2H+T
3.32
this work
L2H+ + HgII T HgL2H+
17.15
this work
+
phenyl moieties proposed in this work is expected to improve the fluorescence properties. The combination of a fluorophoric unit and a site for guest binding purposes is interesting for building up fluorescent signaling systems for biological, environmental or clinical research. The fluorescence properties of L1 and L2 ligands in both methanol (for comparison purposes due to its earlier reporting)15 and water (due to further analytical applications) have been evaluated in detail. Figure 3 shows the emission spectra of L1 (dashed line) and L2 (solid line) ligands in aqueous (HCl 0.1 M) (Figure 3a) and MeOH (Figure 3b) solutions. L2 ligand shows greater fluorescence intensity in both media compared to L1 ligand. This effect may be due to the different length of the terminal alkyl chain which may affect the fluorescence intensity of the compounds probably due to the different interactions between the molecules that yield a different arrangement of the phenyl rings. Different fluorescent intensities could be ascribed to the possible presence of π π interactions between phenyl rings in L2 ligand as it is known that the fluorescent properties are strongly dependent on the molecular stacking feature.32 Fluorescence studies of metal complexes 2, 4, and 6 have also been performed in aqueous (HCl 0.1 M) (Figure 3c) and in MeOH (Figure 3d) solutions. Interestingly, the fluorescence response of these complexes was found to be strongly dependent upon the medium used due to the different sensing mechanisms in each media coming from the different ligand species present at different pHs (see Figure 1). While for aqueous solutions the fluorescence is quenched after the complex formation, for MeOH solutions a high increase of the fluorescence intensity can be observed. A proposal of the possible sensing mechanism is depicted in Figure 4. The polarity and pH dependence of the fluorescence emission intensity is consistent with the inhibition of photoinduced
Figure 3. Fluorescence spectra for L1 (dashed line) and L2 (solid line) ligands (20 μM) in HCl 0.1 M (a) and MeOH (b) and the corresponding metal complexes 2, 4, and 6 (20 μM) in HCl 0.1 M (c) and MeOH (d). 1990
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Figure 5. Schematic of the possible twisting of the phenyl moieties.
Figure 4. (a) Schematic representation of L2 ligand. (b) and (c) Proposed mechanism of fluorescence emission change upon the addition of metal ions in the different media MeOH (b) and HCl (0.1 M) (c), respectively.
electron transfer via amine protonation to the π-system in the free ligands in aqueous solutions (HCl 0.1 M). This may also be responsible for the different fluorescence trends observed after the complexes formation in the different media. In MeOH solution the azine nitrogen of the pyrazole moiety might not be protonated (pKa ≈ 1.5) leading to a high photoinduced electron transfer (PET) effect quenching the fluorescence of the free ligand by the nitrogen lone pair. Involvement of these lone pair in the coordination of the metals lessens the PET quenching effect, leading to a chelationenhanced fluorescence (CHEF) effect, where the metals can be sensed by the increased fluorescence intensity.10,33 The proposed mechanism of the metals fluorescence sensing in MeOH solution is depicted in Figure 4b. It shows that the involvement of the lone pair of the azine nitrogen in the metal bonding decreases the PET quenching effect giving rise to a turn-on fluorescence mechanism. On the other hand, in acidic aqueous solution (HCl 0.1 M), the azine nitrogen (pKa ≈ 1.5) may be protonated. In this case, the lone pair of the azine nitrogen is involved in the nitrogen hydrogen bound not being available for the fluorescent quenching by the PET mechanism and giving raise to certain fluorescence intensity (higher than in MeOH solution). After the metal addition, the azine nitrogen proton could be exchanged by the metal ion and the quenching of the fluorescence (turn-off mechanism) might probably have occurred due to two different reasons. By one side, the strength of the nitrogen metal bond is weaker than the nitrogen-proton bond. In this case, the CHEF effect is decreased when the metal is exchanged by the proton, giving rise to a quenching of the fluorescence. On the other side, the fluorescence quenching occurring as a result of intermolecular hydrogen bonds is a well-known phenomenon.34 If this phenomenon occurs, intermolecular hydrogen bonds between a chlorine atom and the hydrogen of the amino group as shown in Figure 4c might also have affected the fluorescence intensity due to the aggregates formation and the self-quenching phenomenon. This possible interaction mechanism may be suggested considering also the formation of a zwitterionic structure of the same type as the one for PdII, earlier reported by our group, using a similar pyrazole ligand.35 The crystal structure of the compound shown in our previous
work confirms the possibility of intermolecular hydrogen bound interactions on this kind of structure. In addition to the mentioned mechanism, which seems to follow the experimental results obtained, another mechanistic possibility that involves the twisted internal charge transfer (TICT) excitated states can also be considered.36 In this case probably changes on the system such as the different polarities of the solvent or interaction with the metal might have provoked a twisting on the conjugated π-system (TICT) with a further dcrease or enhancement of the system’s fluorescence. In this case, we can expect that lowering the solvent polarity (from aqueous HCl to MeOH) a twisting of the phenyl ring (see Figure 5) may be induced causing a destabilization and a lowering in this way of the fluorescence emission. Although both mechanisms can be possible we cannot discard other strategies that may consider for example the effect of aryl moieties.37 Considering the selectivity of the system, L2 ligand seems to be slightly more selective to ZnII ions rather than to CdII ions and much more sensitive to HgII ions as the calculated complexation constants revealed. Nevertheless, using fluorescence techniques, L2 ligand cannot be considered as a mercury selective sensor due to the fact that the changes produced in the fluorescence spectra after the metal additions are similar for the different studied heavy metals (PbII, ZnII, CdII, or HgII). However, such a fluorescence change induced by heavy metals would be with interest as a global warning heavy metals sensing signal. In addition, this described global affinity would be interesting for future uses of this ligand as a capturing agent to remove heavy metals in waters. For this reason, we have extended the fluorescence sensing studies to different ions to see the effect on the fluorescence of L2 ligand in aqueous media. Figure 6 shows the effect on the L2 fluorescence intensity of the different ions such as PbII, ZnII, CdII, HgII, CuII, FeIII, CaII, MgII, and NaI. As observed in Figure 6 only the addition of 100 ng/mL of PbII, ZnII, CdII, or HgII ions affect L2 fluorescence intensity (with a decrease of around 15%). The addition of 100 ng/mL of FeIII, 1 ppm of CuII, or 50 000 ppm of CaII, MgII, and NaI does not substantially affect L2 fluorescence intensity (the highest decrease is of around 0.4%). The selected metals concentrations for the interference study were chosen based on their usual values in the studied samples shown below. Tap and seawater matrices have been also checked. The sensing system can work in acidified tap water and seawater obtaining similar results that the ones obtained in HCl 0.1 M. As shown in Figure 6, seawater and tap water does not affect the fluorescence of the system. These results confirm the possibility of the application of this system as a heavy metal chemosensor for environmental application without previous tedious sample pretreatments. The L2 ligand compared to the one described before in the research group (1-(2-hydroxyethyl)-3,5-dimethylpyrazole)15 present a stronger fluorescence (250 times higher fluorescence intensity) 1991
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Figure 6. Fluorescence intensities of L2 ligand upon the addition of different metal ions.
Figure 7. (a) Calibration curve for HgII detection using L2 ligand in the range from 0 to 100 ng/mL. (b) (b.1) Amplification of the calibration curve for HgII detection in the range from 0 to 2 ng/mL HgII. Inset: Fluorescent spectra of L2 ligand upon the addition of increasing amounts of HgII (0 to 2 ng/mL). (b.2) Amplification of the calibration curve for HgII detection in the range from 5 to 100 ng/mL HgII. Inset: Fluorescent spectra of L2 ligand upon the addition of increasing amounts of HgII (5 to 100 ng/mL).
which allows its applicability in the sensing field at a low concentration range. Figure 7 shows the fluorescence variation of L2 ligand upon increasing amounts of metals when used as a fast global heavy metals sensor in a range of concentrations from 0.3 to 100 ng/mL of MII (MII = PbII, ZnII, CdII, or HgII) with interest for tap water and seawater analysis. The system presents two different ranges of response, one from 0.3 to 2 ng/mL (Figure 7b) and the other one from 5 to 100 ng/mL (Figure 7c). The presence of the different ranges could be due to “saturation” like phenomena of this detection
system and could be useful to be applied according to the expected concentration ranges of the samples to be analyzed. Real Samples Application. The utility of the developed sensing system for the analysis of HgII in real seawater samples is also studied. Two different spiked seawater samples (10 and 40 ppb of HgII) were evaluated. The calibration curve obtained in seawater matrix is shown in Figure SI5 in the Supporting Information showing the decrease on the fluorescence of the solution upon the increase of the HgII concentration in seawater. 1992
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The Journal of Physical Chemistry C HgII concentrations of 8 and 55 ppb (RSD = 26 and 14%, respectively) for seawater samples spiked with 10 and 40 ppb HgII, respectively were obtained. These preliminary results point out the possible application of the described system for real environmental samples in a simple way and without the need of tedious pretreatments. However, further studies must be performed in order to improve the detection limit and the sensitivity for real samples and extend its application to other kinds of samples. The obtained recoveries of spiked seawater samples may be related to a matrix effect as well as reproducibility of the system. This aspect should be carefully considered prior real samples application. Compared to traditional methods (i.e., ICP-MS and AAS) which are still being applied for metals detection,38 the presented system can be considered nonexpensive, rapid, friendly to use, and suitable for in situ analysis of global heavy metals residues. It has the main advantage of direct metals detection in water solution compared to other reports working with fluorescence techniques which involve the use organic solvents (i.e., acetonitrile).39 In this context, this strategy does not require a pretreatment of the sample which is usually a nontrivial, tedious, and time-consuming task. In addition, the developed system has extremely low detection limits in comparison to other works dealing with the detection of metal ions through fluorescence techniques in solution.39
4. CONCLUSIONS In summary, we have presented a simple fluorescent system to be applied for fast and direct global heavy metals (PbII, ZnII, CdII, or HgII ions) warning in samples such as seawater. The response of the developed systems is clarified through several structural characterizations. Acidity constants (pKa1 and pKa2) and complexation constants for L2 ligand with ZnII, CdII, and HgII have been evaluated confirming the following affinity order of the ligand toward metals: HgII . ZnII> CdII. On the other hand, the fluorescence of the ligands has been evaluated in two different media (MeOH and HCl) in the presence or absence of the metals. The obtained results give rise to two different sensing mechanisms depending on the used media. This dual turn-on/turn-off fluorescence detection mechanism seems to be sensitive enough for heavy metal ions sensing in real samples. Detection limits in water samples lower than 0.3 ng/mL of MII (MII = PbII, ZnII, CdII, or HgII) which are under the maximum level allowed for waters by different environmental agencies (i.e., WHO and EPA) have been achieved with the higher fluorescence ligand.40 ’ ASSOCIATED CONTENT
bS
Supporting Information. Characterization of the complexes; complexation constants studies; crystallographic data for [ZnCl2(L1)]; contact parameters for hydrogen bonds for compound 1; experimental and the corresponding theoretical isotopic distribution ESI-MS spectra of [MClL1]+ fragment of complexes 1, 3, and 5; view of bonding interactions in the crystal structure network of 1; experimental and simulated UV vis spectra of different forms of L2 ligand at different pH; relationship of pH and molar fractions of the various forms of L2 ligand; experimental UV Vis spectra titrations for the complexation of L2 ligand with different metals (ZnII, CdII, and HgII); calibration curve in real seawater matrix. This material is available free of charge via the Internet at http://pubs.acs.org.
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’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT The financial support by the Spanish Ministry of Science and Innovation through MAT2011-25870 and PIB2010JP-00278 projects. G.A. thanks Generalitat de Catalunya for the predoctoral fellowship (FI 2009). ’ REFERENCES (1) (a) Knecht, M. R.; Sethi, M. Anal. Bioanal. Chem. 2009, 394, 33–46. (b) Wallace, K. J. Supramolec. Chem. 2009, 21, 89–102. (2) Liu, J.; Lu, Y. Angew. Chem., Int. Ed. 2007, 46, 7587–1790. (3) (a) Zhu, Z.; Su, Y.; Li, J.; Li, D.; Zhang, J.; Song, S.; Zhao, Y.; Li, G.; Fan, C. Anal. Chem. 2009, 81, 7660–7666. (b) Miao, P.; Liu, L.; Li, Y.; Li, G. Electrochem. Commun. 2009, 11, 1904–1907. (4) Aragay, G.; Pons, J.; Merkoc-i, A. Chem. Rev. 2011, 111, 3433– 3458. (5) Liu, C.; Huang, C.; Chang, H. Anal. Chem. 2009, 81, 2383–2387. (6) Hass, A.; Fine, P. Crit. Rev. Environ. Sci. Technol. 2010, 40, 365–399. (7) Barbaras, D.; Brozio, J.; Johannsen, I.; Allmendinger, T. Org. Proc. Res. Develop. 2009, 13, 1068–1079. (8) Suchy, M.; Hudson, R. H. E. Eur. J. Org. Chem. 2008, 29, 4847–4865. (9) (a) Leray, I.; Valeur, B. Eur. J. Inorg. Chem. 2009, 24, 3525–3535. (b) Ray, D.; Bharadwaj, P. K. Inorg. Chem. 2008, 47, 2252–2254. (c) Aoki, S.; Kaido, S.; Fujioka, H.; Kimura, E. Inorg. Chem. 2003, 42, 1023–1030. (d) Mizukami, S.; Okada, S.; Kimura, S.; Kikuchi, K. Inorg. Chem. 2009, 48, 7630–7638. (e) Valeur, B.; Leray, I. Coord. Chem. Rev. 2000, 205, 3–40. (f) Zhu, L.; Zhang, L.; Younes, A. H. Supramol. Chem. 2009, 21, 268–283. (10) Williams, N. J.; Gan, W.; Reibenspies, J. H.; Hancock, R. D. Inorg. Chem. 2009, 48, 1407–1415. (11) Kim, M. J.; Konduri, R.; Ye, H.; MacDonnell, F. M.; Puntoriero, F.; Serroni, S.; Campagna, S.; Holder, T.; Kinsel, G.; Rajeshwar, K. Inorg. Chem. 2002, 41, 2471. (12) Lim, N. C.; Schuster, J. V.; Porto, M. C.; Tanudra, M. A.; Yao, L.; Freake, H. C.; Bruckner, C. Inorg. Chem. 2005, 44, 2018. (13) Othman, A. B.; Lee, J. W.; Wu, J.; Kim, J. S.; Abidi, R.; Thuery, P.; Strub, J. M.; Van Dorsselaer, A.; Vicens, J. J. Org. Chem. 2007, 72, 7634–7640. (14) Mukherjee, R. Coord. Chem. Rev. 2000, 203, 151–218. (15) Guerrero, M.; Pons, J.; Font-Bardia, M.; Calvet, T.; Ros, J. Aust. J. Chem. 2010, 63, 958–964. (16) Castellano, M.; Pons, J.; García-Anton, J.; Solans, X.; Font-Bardía, M.; Ros, J. Inorg. Chim. Acta 2008, 361, 2923–2928. (17) Pons, J.; García-Anton, J.; Font-Bardía, M.; Calvet, T.; Ros, J. Inorg. Chim. Acta 2009, 362, 2698–2703. (18) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Springer Science Business Media: New York, 2006. (19) Ha-Thi, M.; Penhoat, M.; Drouin, D.; Blanchard-Desce, M.; Michelet, V.; Leray, I. Chem.—Eur. J. 2008, 14, 5941–5950. (20) Aragay, G.; Pons, J.; García-Anton, J.; Branchadell, V.; Calvet, T.; Font-Bardía, M.; Ros, J. Aust. J. Chem. 2010, 63, 257–269. (21) Aragay, G.; Pons, J.; Ros, J.; Merkoc-i, A Langmuir 2010, 26, 10165–10170. (22) (a) Geary, W. J. Coord. Chem. Rev. 1971, 7, 81–122. (b) Thompson, L. K.; Lee, F. L.; Gabe, E. J. Inorg. Chem. 1988, 27, 39–46. (23) (a) Pretch, E.; Clerc, T.; Seibl, J.; Simon, W. Tables of Determination of Organic Compounds. 13C-NMR, 1H-NMR, IR, MS, UV/VIS, Chemical Laboratory Practice; Springer: Berlin, Germany, 1989. (b) Williams, D. H.; Fleming, I. Spectroscopic Methods in Organic Chemistry; McGraw-Hill: London, 1995. 1993
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dx.doi.org/10.1021/jp210687v |J. Phys. Chem. C 2012, 116, 1987–1994
