Recognition Of Fluoride Ions Research Articles

Intramolecular hydrogen bonding steered optical recognition of fluoride ion and consequent opto-chemical logic responses: Spectroscopic and computational studies

This work demonstrates the synthesis and characterization of a thiosemicarbazide core containing Schiff base molecule (MNHC) and its use as a chemosensor for the selective, ratiometric, and colorimetric detection of fluoride ions. The study reveals that in the presence of F− ions, MNHC displays a ratiometric change of absorption maxima at two different wavelengths (432 and 330 nm). MNHC involves an intramolecular hydrogen bonding initiating the possibility of keto-enol tautomerism which is thoroughly investigated by DFT study. Interestingly, the intramolecular hydrogen bonding enhances the acidity of the –NH proton and consequently the –NH center becomes more labile for F− ions binding over the other –NH proton. This fact is confirmed by 1H NMR study. Remarkably, F− ion forms intermolecular hydrogen bonding with the –NH moiety disrupting the intramolecular hydrogen bonding. The changes in absorption spectra in the presence of F− ions occur due to the intermolecular hydrogen bonding-assisted abstraction of the –NH proton. On the other hand, when H2O is added to the MNHC-F− composite, the spectroscopic signature of free MNHC is completely regenerated due to the transfer of proton from H2O to the nitrogen center of MNHC. In addition, 1:1 binding stoichiometry and 53.7 μM detection limit for fluoride ion are also confirmed. Moreover, utilizing these spectroscopic responses, different kinds of important opto-chemical logic gates like YES, NOT, PASS 0, PASS 1, INHIBIT, TRANSFER, and IMPLICATION are developed. Moreover, the F− ion-assisted competitive nature between the intramolecular vs intermolecular hydrogen bonding is thoroughly explored by substantial DFT study.

In Situ Ni(II) Complexation Induced Deprotonation of Bis-Thiourea-Based Tweezers in DMSO-Water Medium: An Approach toward Recognition of Fluoride Ions in Water with Organic Probe Molecules.

Recognition of fluoride in water through the fluoride-induced Brönsted acid-base deprotonation reaction of an organic probe molecule is still a challenging task owing to the lower basicity of fluoride ions and the instability of the conjugate base of the probe molecules in aqueous medium. Herein, we report a complementary strategy in which the conjugate base of the studied bis-thiourea molecule in dimethyl sulfoxide (DMSO) medium is simultaneously stabilized through chelation of the Ni(II) ion, which eventually facilitates the recognition of the fluoride ion in water samples. The recognition methodology is validated colorimetrically and electrochemically, and finally, the applicability of the approach is explored with water samples collected from fluoride-affected areas. The limit of detection value for the fluoride ion in water medium was found to be 0.2 and 0.3 ppm with UV-visible spectroscopy and differential pulse voltammetry measurements, respectively. The methodology is also demonstrated on a paper strip for the detection of the fluoride ion with the naked eye and a smartphone-based RGB sensor. The scheme has been shown to be effective in enhancing the aqueous fluoride recognition ability of the organic probe molecules with acidic hydrogen prone to deprotonation by the fluoride ion.

Transition metal complexation assisted stabilization of the deprotonated organic moiety: A strategy for colorimetric and electrochemical recognition of fluoride ion in water medium with organic probe molecules

Excess consumption of fluoride through drinking water causes detrimental effects to human health which has been a serious global concern. This situation demands routine monitoring of fluoride in drinking water in fluoride affected regions around the world. A plethora of organic molecules has been demonstrated as chemosensors based on the fluoride induced deprotonation reaction of the probe molecules. However, most of the probe molecules fail to react with fluoride in aqueous medium which limits their application. Herein, we have demonstrated a metal ion, Ni(II) mediated strategy to retain the reactivity and the sensitivity of the probe molecule towards fluoride ion in aqueous medium with the help of two benzothiazole based probe molecules (R and P). Both the probe molecules showed retention of the affinity towards fluoride ion in aqueous medium in presence of Cu2+ ion but the colorimetric response is not upto the mark. On the other hand, the probe molecule P showed excellent affinity and colorimetric response towards aqueous fluoride ion in presence of Ni2+ ion. The methodology is validated with UV–Vis spectroscopy and Differential pulse voltammetry (DPV) technique. Probe molecule P in presence of Ni2+ ion showed limit of detection values 0.60 ppm and 0.57 ppm w.r.t. UV–Visible spectroscopy and DPV technique respectively. Furthermore, the efficiency of the methodology w.r.t. P was tested with real samples collected from the fluoride affected areas of Assam, India and found that the data corroborates well with the results of ion selective electrode. This methodology can provide a new dimension in the development of a low cost method for routine sensing of fluoride ion with organic probe molecules in drinking water for low resource world.

Iminoboronate-based chiral dynamic covalent polymer for selective and sensitive fluoride recognition

The construction of chiral polymers using dynamic covalent chemistry is a convenient and straightforward strategy for obtaining functional materials. In this paper, we report the dynamic covalent polymers DCP1, DCP2, and DCP3 with dual dynamic covalent bonds of imine and boronic ester, and their recognition of fluoride ions. The three polymers are prepared from L-DOPA hexyl ester and 2-, 3-, and 4-formylphenylboronic acids, respectively. Iminoboronate, formed within repeated DCP1 units, results in the formation of a spirochiral structure centered at sp3-B and, consequently, the chiral twist or helix conformation of the polymer backbone. DCP1 exhibits distinctive chiroptical features that distinguish it from DCP2 and DCP3. Due to the strong competitive bonding of fluoride with boron, DCP1 has a low LOD (Limit of detection) for fluoride (0.018 mg/L). DCP1 also has good selectivity for fluoride via the responsive destruction of the spirochiral structure and the chiral conformation of the backbone. The construction of these chiral dynamic polymers provides a rapid and effective approach to designing functional polymers.

New type of tin(IV) complex based turn-on fluorescent chemosensor for fluoride ion recognition: elucidating the effect of molecular structure on sensing property.

A novel type of chemosensor based on tin(IV) complexes incorporating hydroxyquinoline derivatives has been designed and investigated for selectively detecting fluoride ions. Sn(meq)2Cl2 (meq = 2-methyl-8-quinolinol) (complex 1) exhibits a significant enhancement in luminescence upon the introduction of fluoride ions. This enhancement greatly surpasses that observed with Snq2Cl2 and Sn(dmqo)2Cl2 (q = 8-hydroxyquinnoline; dmqo = 5,7-dimethyl-8-quinolinol). Furthermore, complex 1 displays excellent sensitivity and selectivity for fluoride detection in comparison to halides and other anions. As a result, complex 1 serves as an outstanding turn-on fluorescent chemosensor, effectively sensing fluoride ions. The Benesi-Hilderbrand method and Job's plot confirmed that complex 1 associates with F- in a 1 : 2 binding stoichiometry. Also, complex 1 exhibited a large binding constant (pKb = 10.4 M-2) and a low detection limit (100 nM). To gain a deeper insight into the photophysical properties and the underlying mechanism governing the formation of the tin(IV) fluoride complex via halide exchange, we successfully synthesized partially fluorinated Sn(meq)2F0.67Cl1.33 (2) and fully fluorinated Sn(meq)2F2 (3), all of which were characterized through computational studies, thereby elucidating their photophysical properties. DFT studies reveal that converting Sn(meq)2Cl2 to Sn(meq)2F2, an endergonic process, leads to greater stability due to reducing steric hindrance about the metal center. Furthermore, the fluorinated complex significantly increases dipole moment, resulting in high affinity toward the F- ion.

Synthesis of metalla-dual-azulenes with fluoride ion recognition properties

Azulene-based conjugated systems are of great interests due to their unusual structures and photophysical properties. Incorporation of a transition metal into azulene skeleton presents an intriguing opportunity to combine the dπ-pπ and pπ-pπ conjugated properties. No such metallaazulene skeleton however has been reported to date. Here, we describe our development of an efficient [5 + 2] annulation reaction to rapid construction of a unique metal-containing [5-5-7] scaffold, termed metalla-dual-azulene (MDA), which includes a metallaazulene and a metal-free organic azulene intertwined by sharing the tropylium motif. The two azulene motifs in MDA exhibit distinct reactivities. The azulene motif readily undergoes nucleophilic addition, leading to N-, O- and S-substituted cycloheptanetrienyl species. Demetalation of the metallaazulene moiety occurs when it reacts with nBu4NF, which enables highly selective recognition of fluoride anion and a noticeable color change. The practical [5 + 2] annulation methodology, facile functional-group modification, high and selective fluoride detection make this new π-conjugated polycyclic system very suitable for potential applications in photoelectric and sensing materials.

A neutral rhenium–biimidazole complex for the selective recognition of fluoride ions

The neutral rhenium(I)-biimidazole complex [Re(CO)3(biimH)(1,4-NVP)] (1) was designed and synthesized by a one-pot reaction of Re2(CO)10, 2,2′-biimidazole (biimH2) and 4-(1-naphthylvinyl)pyridine (1,4-NVP). The structure of 1 was characterized by various spectroscopic techniques including IR, 1H NMR, FAB-MS, and elemental analysis and further confirmed by a single-crystal X-ray diffraction analysis. The mononuclear complex 1, a relatively simple structure with an octahedral geometry, is comprised of facial-arranged carbonyl groups, one chelated biimH monoanion, and one 1,4-NVP. Complex 1 shows the lowest energy absorption band at around 357 nm and an emission band at 408 nm in THF. The luminescent characteristics of 1 combined with the hydrogen bonding ability of the partially coordinated monoionic biimidazole ligand permits the complex to selectively recognize fluoride ions (F–) in the presence of other halides through a dramatic luminescence enhancement. The recognition mechanism of 1 can be convincingly explained in terms of H-bond formation and proton abstraction upon the addition of F– ions by 1H and 19F NMR titration experiments. The electronic properties of 1 were further supported by time dependent density functional theory (TDDFT) computational studies.

Colorimetric sensing of fluoride ion by a Chlorophosphonazo III-based Al3+ complex in aqueous media via indicator displacement approach

We have developed a colorimetric chemosensor for fluoride ion in pure aqueous solution using an Al3+ complex of Chlorophosphonazo III (CPA) via indicator displacement approach. CPA can form a complex with Al3+ in a 1:1 M ratio (CPA-Al3+), resulting in the change of the solution color from red to purple. The CPA-Al3+ complex showed a selective response to fluoride ion with a hypsochromic shift in absorption spectra with the clear color change from purple to red through the regeneration of CPA by the binding of fluoride ion to Al3+ in a 3:1 M ratio. Moreover, the recognition of fluoride ion was not hampered by the presence of other anions. Hence, CPA-Al3+ is efficient in the highly selective and sensitive colorimetric detection of fluoride ion in 100 % aqueous media.

A novel turn-on type fluorescent probe with a large red-shift based on TPE for detection of F−

A tetraphenylethylene derivative with AIE properties was successfully synthesized, displayed a large Stokes shift (Δλ = 123 nm) in THF. TBIP could also be used as a turn-on fluorescent probe for fluoride ion recognition, with a large red-shift (101 nm), rapid response, and excellent selectivity. The limit of detection (LOD) was calculated and derived as 0.006 μM in solvent, which was far lower than the maximum pollutant level of fluorine ion in drinking water, and fluorescence color changing from blue-purple to yellow. The application research indicated that the sensor could detect F− in natural water sensitively, and could prepare qualitative test strips for fluorine ion detection.

Fluorescence chemosensor for fluoride ion using quinoline-derived probe: Molecular logic gate application

• Cadmium existing fluorescent probe used for the detection of fluoride ions. • The binding stoichiometric ratio of P-F − complex is 1:1 by 1 H NMR titration, Jobs plot, MS, and DFT. • The detection limit of probe for fluoride ions is 0.128 μM. • The probe was fruitfully applied to molecular logic gates and reala samples analysis. Here, we tested the existing cadmium probe ( P ) that could be used for the fluorescent detection of fluoride ions selectively over other anions. The strong emission was scrutinized at 500 nm for fluoride ions by P and concluded that it was caused by the hydrogen bonding interaction proceeded by deprotonation. As per Job’s graph, the binding stoichiometric ratio between P and fluoride ion is 1:1 which has been confirmed by 1 H NMR titration, MS, and density functional theory studies (DFT). The detection limit for fluoride ion is 0.128 μM based on the concentration-reliant fluorescence titration. According to the findings, the probe is a strong contender for fluoride ion recognition. Further, P was also beneficial in the molecular logic gate and real water samples.

Benzimidazole-isoquinolinone functioned thiourea for selective and reversible recognition of fluoride ion

Two novel fluoride ion probes 11-(2-iminothiourea-2-phenyl)benzimidazole-isoquinolinone (3) and 10-(2-iminothiourea-2-phenyl)benzimidazole-isoquinolinone (3′) have been designed, synthesized and confirmed structurally by 1H NMR、13C NMR and HRMS-ESI. Obvious color changes could be seen by naked-eye after the addition of F− to the DMSO solution of above probes. Both probes showed dual-channel properties: UV–vis absorption red-shift and fluorescence turn-off upon reacting with F−. More importantly, the F− induced visual and spectroscopic changes were fully reversible upon addingHSO4-.And the new probes could realize the distinguish recognition of F− and OH− by adding over 40 equivalents OH−. The detection limits of new probes were 0.6 nM. The recognition mechanism deduced from the 1H NMR titration experiment and theoretical calculation was a combined process including hydrogen bonding and deprotonation between the probes and fluoride ion.

Efficient Optical and UV-Vis Chemosensor Based on Chromo Probes-Polymeric Nanocomposite Hybrid for Selective Recognition of Fluoride Ions.

A novel colorimetric sensor based on the TiO2/poly(acrylamide-co-methylene bis acrylamide-co-2-(3-(4-nitro-phenyl)thioureido)ethyl methacrylate) nanocomposite was synthesized via a surface modification strategy; methacryloxypropyltrimethoxysilane was used to provide reactive vinyl groups on the surface of TiO2 nanoparticles for the successful surface polymerization of Am (acrylamide), MBA (methylenbisacrylamide), and NPhM (2-(3-(4-nitrophenyl)thioureido)ethyl methacrylate) components. The successful preparation of nanocomposites was confirmed using Fourier transform infrared, 1H NMR, 13C NMR, scanning electron microscopy, transmission electron microscopy, thermogravimetry analysis, and X-ray diffraction methods, and the sensing ability of the probe toward fluoride ions was investigated using naked-eye detection and UV–vis measurement. The interaction of the prepared polymeric nanocomposite with fluoride ions elicited a significant visible change in color from pale yellow to orange and was further affirmed by a clean interconversion of the two absorption bands at 330 and 485 nm. The selective binding ability of the polymeric nanocomposite towards fluoride over other anions, such as I–, Cl–, Br–, AcO–, H2PO4–, and H2SO4– was further explored; the prepared chemosensor could detect fluoride ions in acetonitrile with a detection limit of 3 μM.

Naked-Eye Heterogeneous Sensing of Fluoride Ions by Co-Polymeric Nanosponge Systems Comprising Aromatic-Imide-Functionalized Nanocellulose and Branched Polyethyleneimine.

Heterogeneous colorimetric sensors for fluoride ions were obtained by cross-linking TEMPO-oxidized cellulose nanofibers (TOCNF) with chemically modified branched polyethyleneimine 25 kDa (bPEI). Functionalization of bPEI primary amino groups with aromatic anhydrides led to the formation of the corresponding mono- and bis-imides on the grafted polymers (f-bPEI). A microwave-assisted procedure allowed the optimization of the synthetic protocol by reducing reaction time from 17 h to 30 minutes. Hydrogels obtained by mixing different ratios of TOCNF, bPEI and f-bPEI were lyophilized and thermally treated at about 100 °C to promote the formation of amide bonds between the amino groups of poly-cationic polymers and the carboxylic groups of cellulose nanofibers. This approach generated a series of cellulose nanosponges S1-S3 which were characterized by FT-IR and by solid state 13 C CPMAS NMR. These sponge materials can act as colorimetric sensors for the selective naked-eye recognition of fluoride ions over chloride, phosphate and acetate ions at concentrations of up to 0.05 M in DMSO. Moreover, when the sponges were functionalized with perylene tetracarboxylic diimide, successful naked-eye detection was achieved with only 0.02 % w/w of chromophore units per gram of material.

Multi-point interaction-based recognition of fluoride ions by tert-butyldihomooxacalix[4]arenes bearing phenolic hydroxyls and thiourea

A series of p-tert-butyldihomooxacalix[4]arenes bearing phenolic hydroxyls and thiourea moieties were prepared to investigate their anion binding behavior.

Trifluoromethyl group containing C3 symmetric coumarin-triazole based fluorometric tripodal receptors for selective fluoride ion recognition: A theoretical and experimental approach

A series of unique C3 symmetric tripodal receptors, A–E containing hexasubstituted aryl core decorated with an alternate array of coumarin-triazole moieties and methyl groups have been synthesized, characterized and investigated for fluoride ion recognition (tetrabutylammonium salt) in dimethyl sulphoxide (DMSO). A pleothora of spectroscopic studies (fluorescence, UV–vis, 1H NMR and 19F NMR titrations) exhibits that out of the five derivatives synthesized, only one, receptor D displays selective five fold fluorescence enhancement with fluoride ion (TBA salt) at 480 nm wavelength over other anions at a detection limit of 2.6 × 10−5 M. Selectivity may be ascribed to strategical incorporation of trifluoromethyl group in the scaffold of receptor D which modulated the binding ability of the receptor, so that it is able to bind fluoride ion exclusively and selectively in preorganized C3 symmetric cavity formed by its three arms. 1H NMR and 19F NMR titration validate CH⋯F- hydrogen binding interactions via downfield shift of CH peak at δ 8.47 ppm by δ 0.5 ppm and upfield shift of peak at δ −102 ppm due to free fluoride ion 2.98 ppm, respectively. Further, HRMS study of receptor-fluoride complex gave evidence for the formation of 1:1 stoichiometric ratio between receptor and fluoride ion. Computations using density functional theory have shown that in 1:1 complex of receptor and fluoride ion, the three arms are directed in same orientation forming a cavity where it fits fluoride ion by CH⋯F- hydrogen binding interactions.

Novel Isophthalohydrazide-cDB24C8 cryptand derivative for the selective recognition of fluoride ion: An experimental and DFT study

A highly selective and sensitive novel Isophthalohydrazide-cDB24C8 cryptand derivative was developed for fluoride recognition at a very low concentration of 2.31 × 10−10 M. The binding was established by UV–Vis, fluorescence and 1H NMR titration. The receptor formed very strong H-bonded complex with fluoride, furnished a sharp new UV–Vis absorption peak at 280 nm which was also supported by the DFT-study. The fluorescence emission spectra showed large quenching up to 79.13% upon addition of fluoride.

A novel naphthalimide-based probe for highly sensitive and selective recognition of fluoride ion

Considering the excessive ingestion of fluoride ion (F−) may result in many diseases, herein, by introducing 2-hydroxy-1-naphthaldehyde azine framework to 1,8-naphthalimide derivatives, we have developed a unique colorimetric/fluorometric probe (NYL) for detection of fluoride. The response of NYL toward F− is an integration of ESIPT and PET processes with a large stokes’ shift (173 nm). The striking color change from yellow to light-purple and fluorescent quenching of probe NYL can be observed only in the presence of fluoride ions. Furthermore, 1H NMR titration indicates the probe undergoes the deprotonation of hydroxyl through the Hydrogen-bond interaction between phenolic OH and F− ions.

Colorimetric chemosensors based on diketopyrrolopyrrole for selective and reversible recognition of fluoride ions

A series of colorimetric and reversible receptors for fluoride anions based on diketopyrrolopyrrole (DPP) were designed and synthesized successfully. The position of nitro substituent on the phenylhydrazide affected the alteration of photophysical properties to varying degrees. While the photoluminescence intensity of receptor 1 was weaker than that of receptor 2 and receptor 3 on account of the formation of intramolecular hydrogen bond deriving from oxygen atom of nitro substituent and hydrogen atom of hydrazide. The receptor 2 was a preferable chemosensor for responding fluoride anions. The fluorescence was quenched in the presence of fluoride anion resulted from the photo-induced electron transfer (PET) effect from the amide. The formation of deprotonation species, which produced by hydrazide NH moiety and F− was answerable for the spectral changes. Especially, the spectral and color responses of receptors could be switched back and forth successively by adding F− and HSO4− anions in DMSO solution. These receptors could response fluoride anion sensitively, visually and selectively in a manner of reversible with a low determination.

Metal-free synthesis of calixsalen-type cavitands for the recognition of fluoride ion

ABSTRACTNovel calixsalen-type cavitands have been synthesized using metal-free synthesis from simple and inexpensive materials, such as ethylenediamine and 5,5′-methylene-bis-salicylaldehyde derivatives. The cavitand 1 containing salen functionality recognizes fluoride ion. Fluoride ions switch on fluorescence on binding with the cavitand 1. Substitution on bis-salicylaldehyde part of calixsalen-type cavitand shows change in recognition behavior. On the attachment of electron withdrawing substituent, such as nitro group, the cavitand lost its fluorescence properties but proved to be a better colorimetric probe showing marked color change from pale yellow to red on addition of tetrabutyl ammonium salt of fluoride ion to the solution of cavitand. The nitro substituted cavitand is highly sensitive and selective for fluoride anion and hence is a promising candidate for development of colorimetric chemosensor. The binding of the cavitands with fluoride ion is investigated using 1H NMR-titration experiments.

Naphthalenyl appended semicarbazone as “turn on” fluorescent chemosensor for selective recognition of fluoride ion

The reaction of 1-isocyanatonaphthalene with hydrazine hydrate in presence of acetone resulted in the formation of napthyl based semicarbazone (1). The compound has been characterized using UV–Visible, FT-IR, NMR, mass spectroscopic and single crystal X-ray diffraction (XRD) tools. The interaction between 1 and fluoride ion has been investigated by means of UV–Visible and fluorescence spectra. The fluoride ion sensing mechanism of 1 has been studied by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) methods. The added fluoride ion formed intermolecular hydrogen bonds with the protons of N1H1 and N2H2 groups of 1 in the ground state. The N1H1 proton which is closer to naphthalene moiety prefers to bind fluoride anion in the excited state after deprotonation, which lead to excited state proton transfer (ESPT). The fluoride ion sensing process shows a moderate (31.99 kcal/mol) Gibbs free energy. To understand the dynamic features, the transition state (TS) calculation is performed and the change in entropy is found to be −0.6259 kJ/mol, which shows that the sensing process is thermodynamically allowed.