Alizarin Complexone on Nanocrystalline TiO<sub>2</sub>: A Heterogeneous Approach to Anion Sensing

Palomares, Emilio; Vilar, Ramón; Green, A.; Durrant, James R.

doi:10.1002/adfm.200304444

Cited by 100 publications

(52 citation statements)

References 25 publications

(21 reference statements)

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“…[11][12][13][14][15][16] Surfactants have been extensively used in these template-directed syntheses, due to their ability to organize in typical structures such as micelles, rods, vesicles, and lamellae. The technological potential of employing surfactants as structure-directing agents has been implemented in many applications such as in adsorptions and separations, [17][18][19] catalysis, [20][21][22][23] sensing, [24,25] and for ion-exchange. [26] To conclude this background we mention that chiral surfactants are of course widely used in chemistry, [27][28][29][30][31] and some of the many examples include chiral catalysis, [32] enantioseparation by micellar electrokinetic chromatography, [33,34] and synthesis of helical materials.…”

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confidence: 99%

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

2007

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The formation of chiral porous materials is an on-going quest because of the numerous applications of such materials in separation science, chiral catalysis, and in pharmaceutics and so forth. Here, we describe two new methods for preparing bulk chiral silica materials, based on the use of a chiral surfactant. By one method the surfactant is used for the imprinting of chiral porosity, and by the second method we use the entrapped surfactant molecules as chiral centers within the silica. The chiral entity in the two types of matrices is different and therefore the enantioselective preferences before and after surfactant removal are not necessarily the same; indeed it was found that chiral discrimination changes before and after surfactant removal. Notably, these adsorbents are capable of recognizing chirality in molecules that have no structural similarity to the imprinting molecule. An additional attractive feature of these materials is their ability to enantioselect in both aqueous media and organic solvents. Specifically, phenylated silica sol-gel (PSG) matrices were doped with the chiral cationic surfactant, (-)-N-dodecyl-N-methylephedrinium bromide (DMB, 1, Scheme 1), and then the DMB was extracted with methanol. The powdered silica matrix was thus rendered chiral both before and after surfactant removal: before, by virtue of the entrapped chiral surfactant within the matrix; and after surfactant removal by forming chiral cavities. Both types of matrices showed general enantioselectivity by preferential adsorption of one enantiomer over several other molecules which are different from the surfactant. The pairs of enantiomers included (R)-and (S)-propranolol (2), (R)-and (S)-binaphthyl-2,2-diyl hydrogenphosphate (BINAP) (3), and (R)-and (S)-naproxen (4). In all cases good enantioselectivities were observed, both for the chirally imprinted powdered monoliths and for the chirally doped ones, with discrimination ratios in the range of 1.22-1.34. The chiral entity in the two types of matrices is different and therefore the enantioselective preferences before and after surfactant removal are not necessarily the same, as indeed was found to be the case. The fact that the discrimination changes before and after surfactant removal attests to the authenticity of the observed enantioselectivity in the two types of chiral materials.It is in order to cite some relevant background references now: Enantioselectivity towards the enantiomers of the imprinting molecule is more common [1] than enantioselectivity towards molecules different than the imprinting one, but which are still related to it. Thus, enantioselectivity towards morphine derivatives different than the imprinting derivative was demonstrated by Becket et al. [2] and by Bartels et al. [3] for silica prepared from sodium silicate. Enantioselective recognition of structurally related enantiomers is also known for organic polymers. We reiterate here that the enantioselectivity shown in this report is towards unrelated molecules. In another type of study Izutsu et a...

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confidence: 99%

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

2007

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“…The advantages of doing this is that dip-in sensing is then possible (which is much more practical), and as we and others have previously demonstrated, [26,27] receptors that are not soluble in water (as is the case with 1) once supported onto films, can be exposed to aqueous solutions of the analytes to be measured.…”

Section: Sensitivity and Detection Limit In Solutionmentioning

confidence: 96%

“…[10][11][12][13][14][15][16][17][18] Methods based on anion-induced changes of the optical properties (either absorption or emission) of a receptor are especially attractive. Recent examples that use this approach have been reported by the groups of Geddes, [19][20][21] Martinez-MaÇez, [22][23][24][25] Palomares [26,27] and Raymo [9,28] amongst others. [29][30][31][32][33] In spite of these developments there are still relatively few examples of selective probes for cyanide owing to high interference from other anions, in particular, fluoride.…”

Section: Introductionmentioning

confidence: 95%

Cyanide Sensing with Organic Dyes: Studies in Solution and on Nanostructured Al₂O₃ Surfaces

Gimeno

Durrant

et al. 2008

Chemistry A European J

179

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The synthesis of two new azo phenyl thiourea compounds and their optical response to different anions is reported herein. Solution studies in methanol indicate that cyanide induces a colour change in these dyes (whereas no changes are observed in the presence of other anions, such as F(-), Cl(-), Br(-), CH(3)COO(-), H(2)PO(4) (-), HSO(4) (-)). Interestingly, in DMSO these dyes are responsive not only to cyanide, but also to fluoride, acetate and dihydrogen phosphate. Each of these anions induces a different colour change. In the second part of the paper, we report the attachment of one of these dyes onto nanostructured TiO(2) and Al(2)O(3) films. The stability of these sensitised films to pH was studied and we concluded that the sensitised Al(2)O(3) films are more robust, and hence, better than the TiO(2) for anion sensing. The dye-sensitised Al(2)O(3) films were immersed in solutions of different anions and their response studied. The films can detect cyanide down to 3 ppm in aqueous solution with relatively good selectivity over other anions.

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“…The results show that the present chemosensor exhibits excellent sensitivity and stability of the color for the detection of fluoride from 1.5 × 10 -5 M to 1.5 × 10 -4 M, which are very high compared to the reported methods. 1,26 Kinetic studies indicate that the reaction occurs impulsively at room temperature, whereas the method reported by Wada et al 27 needs heating the sample at 60˚C; also the color of the reaction was stable for more than two weeks.…”

Section: Naked-eye Detection Of Fluoride and Advantagesmentioning

confidence: 98%

Naked-Eye Detection of Fluoride Using Zr(IV)-EDTA Complex and Pyrocatechol Violet

Balaji

Matsunaga

2005

ANAL. SCI.

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The use of fluoride has been increasing because of its great potential for industrial and biological applications. 1,2 However, the World Health Organization (WHO) upper limit of fluoride in drinking water is 7.9 × 10 -5 mol dm -3 , and the high levels of fluoride have caused toxicity in animals and mottled teeth in humans. Several methods, such as ion-selective electrodes (ISE), 3 colorimetry, [4][5][6][7] fluorescence [8][9][10] and capillary electrophoresis, 11 have been reported for the determination of fluoride.Among these, the chemical systems that respond to the presence of ions by color change detectable by vision are rare. 12 These chemosensors do not have any need to use a potentiostat or a spectrometer to detect redox or optical perturbations, and as a result, have substantial advantages over other molecular chemosensors. 13 Lanthanum(III), Zr(IV) and Ce(III) complexes with dye compounds have been used for the colorimetric detection of fluoride.14 These systems have a lack of chemical stability, and take a long time for color development. Supramolecular compounds, such as trianthryl borane derivatives and calix(4)pyrrole derivatives have been examined as fluoride chemosensors via strong hydrogen-bond formation. 5,15 The observed color changes in these systems take place only in organic media, but are reversed upon the addition of water. As a result, procedures for the naked-eye detection of anions in aqueous media are needed to overcome the above shortcomings.A fluoride, because of its high electro negativity, forms stable binary or ternary complexes with many trivalent and tetravalent metal ions, and even with their complexes. It has been reported that Zr-EDTA can bind fluoride as well as oxo anions of arsenic and selenium by a ligand-exchange mechanism with coordinated water. [16][17][18] Hence, the combined use of Zr(H2O)2EDTA as an anion receptor and an appropriate chromophore was expected to give a good chemosensor for the nacked-eye detection of fluoride.In the present study, we observed that PV forms a ternary complex with Zr-EDTA by replacing water molecules, and produces an intense blue color. The blue color of this system readily shifts to orange red by the addition of fluoride, along with the release of free PV.These observations have successfully allowed us to construct a chemosensor for the visual detection of fluoride in aqueous solution. Experimental ReagentsAll reagents and solvents used were of analytical reagent grade. A stock solution of fluoride (0.0526 mol dm -3 ) was prepared by dissolving 99.9% NaF (Wako, Japan) in distilled water and standardized using the Alfusone method. 19 Zr(H2O)2EDTA·2H2O was prepared as a white crystal according to the procedure 20 and a 1 × 10 -2 M (M = mol dm -3 ) stock solution was prepared using distilled water. Pyrocatechol Violet was purchased from Dojindo Laboratories, Japan and a 1 × 10 -3 M stock solution was prepared by dissolving an appropriate amount in distilled water. Working solutions, as required, of the above reagents were prepared by app...

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Alizarin Complexone on Nanocrystalline TiO₂: A Heterogeneous Approach to Anion Sensing

Cited by 100 publications

References 25 publications

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

Cyanide Sensing with Organic Dyes: Studies in Solution and on Nanostructured Al₂O₃ Surfaces

Naked-Eye Detection of Fluoride Using Zr(IV)-EDTA Complex and Pyrocatechol Violet

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Alizarin Complexone on Nanocrystalline TiO2: A Heterogeneous Approach to Anion Sensing

Cited by 100 publications

References 25 publications

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

Cyanide Sensing with Organic Dyes: Studies in Solution and on Nanostructured Al2O3 Surfaces

Naked-Eye Detection of Fluoride Using Zr(IV)-EDTA Complex and Pyrocatechol Violet

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Alizarin Complexone on Nanocrystalline TiO₂: A Heterogeneous Approach to Anion Sensing

Cyanide Sensing with Organic Dyes: Studies in Solution and on Nanostructured Al₂O₃ Surfaces