ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2014, том 69, № 2, с. 171-175
ОРИГИНАЛЬНЫЕ СТАТЬИ
УДК 543
A SELECTIVE FLUORESCENT AND COLORIMETRY COMPETITION ASSAY FOR FLUORIDE IONS IN DMSO MEDIA BASED ON 4-CHLORO-2,6-
tfTS(HYDROXYMETHYL) PHENOL © 2014 H. Tavallali", G. Deilamy-Rad", A. Parhami", A. Khalafi-Nezhad4
aDepartment of Chemistry, Payame Noor University 19395-4697 Tehran, I. R. of Iran bDepartment of Chemistry, College of Sciences, Shiraz University Shiraz 71454, Iran Received 10.04.2011; in final form 05.07.2012
We report here a selective, efficient and very simple receptor which can easily detect F- in the presence of a wide range of other anions [Cl-, Br-, I-, HSO-, NO-, Acetate (AcO-) and Benzoate (BzO-)] by use of col-orimetric or fluorometric detection. 4-Chloro-2,6-bis(hydroxymethyl) phenol (CBHMP) is a simple and available phenolic receptor having no special chromophoric function. In this colorimetric method, naked-eye detection of F- with CBHMP is described. Interestingly, fluorometric detection of F- is also possible by highly selective fluorescent quenching response CBHMP in dimethyl sulfoxide (DMSO) media.
Keywords: 4-chloro-2,6-bis(hydroxymethyl) phenol, colorimetry, fluorometry, fluoride, chromophore.
DOI: 10.7868/S0044450214020133
It is well known that anions play an important role in a wide range of chemical and biological processes; therefore the search for chemosensors for recognizing and sensing anions has attracted growing attention. Most chemosensors developed so far are chromogenic and/or fluorescent sensors, which efficiently change their photophysical properties (^max shift of the UV-vis spectrum, change in the quantum yield or emission wavelength, etc.) in the presence of anions [1—6]. Color changes, which can be detected by the naked eye, are widely used to signal events since they are inexpensive and do not require any spectroscopic instrumentation. The nature of the interaction between anions and neutral organic receptors has been described in different ways [7]. One of them intraction types hydro-genbonding. In this sense, the receptors must provide one or more hydrogen-bonding donor groups, X—H, where X is typically a nitrogen or oxygen atom. The recognition studies are preferably carried out in apro-tic media (e.g., DMSO, acetonitrile, CHCl3, etc.), to avoid competition of the protic solvent as a hydrogen-bonding donor [2]. Fluorescent anion chemosensors are of great importance, owing it to their high sensitivity and low detection limit [8].
Among the biologically important ions, fluoride is a common ingredient in hypnotics, anesthetics, psychiatric drugs and cockroach poison and is a contaminant in drinking water. Excess fluoride ion exposure
causes fluorosis, thyroid activity depression, bone disorders and immune system disruption [9]. In the previous works, amide groups containing macrocycles
[10] such as 2,3-dipyrrol-2'-ylquinoxalines derivatives
[11], quinoxaline-bridged porphyrinoid compound
[12], the incorporations of nitrobenzene [13] and an-thraquinone [14] into the calix[4]pyrroles and disul-fonamide porphyrin anion [15], have been used as selective colorimetric sensors for F-. Cavitand-based dipyrrolylquinoxaline, featuring four anion detecting walls [16], and two ^-nitrophenylthioure a groups in a 4,5-dimethyl-1,2-diaminobenzene, have been proven to be colorimetric chemosensors for F- and AcO- [17].
On the other hand many chromogenic chemosensors for fluoride have been recently developed, anions these an effective sensor for fluoride ion in dry DMSO [18], a selective center for acetate based on the fluorinated derivative of the dipyrrolyl-diketone BF2 complex in DMSO [19], and a series of indolocarbazole-quinoxalines for fluoride and acetate anion sensing in DMSO [20]. All these are complicated compounds, and their preparation is difficult. All this prompted us to develop a novel and sensitive colorimetric and fluorometric receptor, the 4-chloro-2,6-te(hydroxylme-thyl) phenol (CBHMP) (Fig. 1), which is a very simple compound that can easily optically detect F- in the presence of a wide range of other anions (Cl-, Br-, I-, AcO-, HSO-, NO- and BzO ). CBHMP is one of the
OH
Cl
Fig. 1. Molecular structure of CBHMP (H3L).
significant precursors for preparation of an important series of compounds such as calixarens [21-25], and this receptor does not contain any particular chro-mophores. The interaction between the hydrogen atom of phenolic unit and the substrate enhances n de-localization and shifts the n ^ n* transition from UV to the visible region and results in the generation of yellow color. CBHMP is the selective complexing agent of F- in DMSO media and signaling is present via marked color changes using the receptor as an optical-signaling chromophoric unit. Since the color is changed with an addition of 1.38 x 10-3 M of F- to 5.0 x 10-5 M solution of CBHMP, F- can be detected with the naked eye even at a low concentration of CBHMP (5.0 x10-5 M). Interestingly, a fluorometric detection of anion binding is also possible because the fluorescence of CBHMP is quenched. CBHMP is a very simple fluorophore, which gives highly selective fluorescent quenching response toward F- in DMSO media. This work compared with the previous by published ones for similar organic compound (4-bromo-2,6-Ws(hydroxymethyl) phenol) [26] is wider on the linear range and has a lower detection limit.
EXPERIMENTAL PART
All reagents for synthesis were obtained commercially and used without further purification. In the titration experiments, all anions were added in the form of TBA salts, which were purchased from Fluka, stored in vacuum desiccators containing self-indicating silica which was fully dried before use. DMSO (Merck) was dried with CaH2 and then distilled in reduced pressure.
CBHMP was synthesized according to the literature [25]. This compound was purified by short-column chromatography, and its purity was identified by means of Hydrogen Nuclear Magnetic Resonance Spectroscopy (1H NMR) in DMSO-d6 (250 MHz) and Fourier transform infrared spectroscopy (FT-IR, Shimadzu, 8300).
The Nuclear Magnetic Resonance Spectroscopy (NMR) indicates the characteristics of this compound (CBHMP): 1H NMR (DMSO-d6, 250MHZ) 8 8.73 (s, 1H, 1 phenolic OH exchangeable with D2O), 7.17
(s, 2H, aromatic ring), 5.09 (s, 2H, 2 benzylic OH are exchangeable with D2O), 4.52 (s, 4H, 2CH2)].
The FT-IR characteristics of this receptor are as follows: vmax 3600-3100 (br, OH), 3100 (m, C-H, aromatic), 2890 (m, CH2-H, aliphatic), 1600 (s, C-C, aromatic), 1250-1150 (m, C-O, aromatic, aliphatic), 750 (s, C-Cl) cm-1.
Apparatus. The absorption spectra were recorded on a Perkin-Elmer UV-Vis spectrometer Lambda 2, containing a thermoelectrically temperature-controlled cell holder in the wavelength range of 200-700 nm, with a quartz cells (path length = 1 cm). A Perkin-Elmer LS50 luminescence spectrophotometer with excitation and emission slits of 10.0 nm was used for fluorescence measurements. A 50-^L Hamilton Syringe was used for the addition of a standard anion to the solution. 1H NMR spectra were measured with Varian unity plus 400 MHZ spectrometer using tet-ramethylsilane (TMS) as an internal standard.
Procedure for determination of fluoride. All experiments were carried out at 298.2 ± 0.1 K, unless otherwise mentioned. UV-vis spectra were measured using an ultraviolet-visible spectrophotometer, and fluorescence intensity was measured by luminescence spectrophotometer (Perkin Elmer). A 5.0 x10-5 M solution of CBHMP in DMSO was prepared and stored in dry atmosphere. This solution was used for all spectro-scopic studies. Solutions of 1.0 x 10-2 M TBA salts of the respective anions were prepared in dried and distilled DMSO and stored in dry atmosphere. Then, the mixtures of solutions were prepared in the cell by addition of appropriate volumes of anion solutions to receptor solutions (2.5 mL), and their absorbance or fluorescence intensities were measured immediately.
RESULTS AND DISCUSSION
UV-vis studies of CBHMP in the presence of anions in DMSO. The interaction of CBHMP with a variety of anions was investigated through spectrophotomet-ric titrations in DMSO by addition of a standard solution of the tetrabutylammonium (TBA) salts to a solution of CBHMP. The solution of CBHMP (5.0 x x 10~5 M) is colorless with maximum absorption wavelength (^max) at 284 nm (Figs. 2a, a and 2b). The same UV-vis spectrum was observed upon the addition of 1.38 x 10-3 M of F- (TBA salt) to the solution of CBHMP inducing a large red shift at maximum wavelength of 316 to 413 nm. This shift toward low energy values instantaneously changed the color from colorless to yellow. A red shift to the rkm2DC = 316 nm was observed in the presence of AcO- (Figs. 2a, f and 2b) and NO- (Figs. 2a, h and 2b), however the intensity of ab-sorbance was much lower than F-. In the DMSO media, the linear range of quantitative detection for F-was determined to be 1.10 x 10-5-1.06 x 10-4 M with a detection limit of 1.7 x 10-6 M (3a).
A SELECTIVE FLUORESCENT AND COLORIMETRY COMPETITION ASSAY
173
(a)
Absorbance
(b)
A316, nm
260 310 360 410 460
Wavelength, nm
Fig. 2. (a) Photographs of the solution of CBHMP (5.0 x x10-5 M in DMSO: (a) no additives; (b) F-; (c) Cl-;
(d) Br-; (e) I-; (f AcO-; (g) HSO-; (h) NO-; (i) BzO-(all the anions were added in the form of TBA salts in DMSO and the quantity of salts was 0.01 equivalents). (b) UV-vis absorption spectra corresponding the different assays in photograph (a) (concentration of TBA salts is 1.38 x 10-3 M).The inset displays a molar ratio plot for the interaction of CBHMP with fluoride ions at 316 nm, which clearly indicates a 1 : 1 stoichiometry.
(a)
OH
HO^^OH
Cl
/
J
J_L.
OH
HO^pOH
6 (b)
+ BU4NV
Cl
i
9
8
7
6
J
J_I_I_I_L
5
4
3
Fig. 3. 1H NMR spectra: a) CBHMP in DMSO-d6 (0.01 M) b) CBHMP in DMSO-d6 (0.01 M) in the presence of 0.01 equivalents of F-.
9
8
7
5
4
3
*H NMR titra
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.