The NH as well as the protonated nitrogen of the benzimidazole moiety donate hydrogen bonding interactions to the dihydrogen phosphate anion. Another interesting behavior is shown by the nitro groups in the three-dimensional decoration of the conformers.
Visual detection of fluoride ion in solid state 78
O3 from the bound sulfate is coordinated to one benzimidazole arm with its single −NH⋯O interaction. The O4-binding interactions consist of one unit of benzimidazole −NH and one unit of amide –NH. The branched O5 contains hydrogen bonds of two benzimidazole NHs, while the exclusively monofurcated O6 is hydrogen bonded to one aromatic –CH of the benzimidazole group.
Among these hydrogen bonding interactions, the stronger hydrogen bonds are given by the benzimidazole-NH interactions (N10HꞏꞏꞏO4=1.82Å, ∠N−HꞏꞏꞏO=171.0°; N7HꞏꞏꞏꞏꞏꞏꞏO5=1. bonding interactions mainly of five −NH⋯O (average N−O = 2,748 Å) and one −CH⋯O interactions (C−O = 3.274 Å).NH and one amide –NH.
One single hydrogen bond is available to the O10 atom of bound S2 from one −CH from the benzimidazole group of the protonated receptor. Similarly, as in the case of the S1 environment, benzimidazole –NHs dominate, which are stronger hydrogen bond donors against the bound oxygen atoms with the S2 center. All S1- and S2-centered sulfate oxygens are consistent with the electronic structure calculations of Hay et al.
These studies strengthen the potential candidacy of the L2 probe towards more rapid and convenient detection of fluoride ions.
Conclusion 79
With the deprotonation of the probe playing a key role in the detection of fluoride ions in the solution phase, the protonation of the probe led to the detection of sulfate anions in the solid state study. In the case of two bound sulfates, two different binding environments were present, where the strongest hydrogen bonds are offered by the benzimidazole –NH moiety. Rissanen, Highlights of modern recognition and detection of fluoride anion in solution and solid state, Chem.
Gabbaï, 1-Pyrenyl- and 3-Perylenyl-Antimony(V) Derivatives for the Fluorescence Switch-on Sensing of Fluoride Ions in Water at Sub-ppm Concentrations, Organometallic. Zhang, A highly selective colorimetric and ratiometric fluorescent chemodosimeter for imaging fluoride ions in living cells, Chem. Tamao, A colorimetric and ratiometric fluorescent chemosensor with three emission changes: fluoride ion sensing by a triarylborane-porphyrin conjugate, Angew.
Mandal, A Colorimetric and Ratiometric Fluorescent Chemosensor for Fluoride Ions Based on Phenanthroimidazole (PI): Spectroscopic, NMR and Density Studies, RSC Adv. Sun, Highly sensitive ratiometric fluorescent paper sensors for fluoride ion detection, ACS omega. Quiocho, 2 Å resolution structure of a sulfate-binding protein involved in active transport in Salmonella typhimurium., J.
Soto, Rational Design of a Chromo- and Fluorogenic Hybrid Chemosensor Material for the Detection of Long-chain Carboxylates, J. Wang, Design and application of tri-benzimidazolyl star-shaped molecules as fluorescent chemosensors for the fast-response detection of fluoride ion, Sens. Wang, Colorimetric and ratiometric fluorescent sensor for F− based on benzimidazole-naphthalene conjugate: Reversible and reusable study &.
Sun, highly sensitive ratio fluorescent paper sensors for the detection of fluoride ions, ACS Omega.
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Schiff base probes were synthesized from one-step condensation reactions and were fully characterized by 1H, 13C and mass analysis. The L3 probe previously reported by our group 5.35 was based on a naphthyl chromophore, while L4 was decorated with a coumarin chromophore to improve the chromogenic properties. The chloro (Cl) group present in the coumarin moiety of L4 is expected to increase the acidity of the −NH proton and assist in charge transfer interactions, leading to a likely improvement in photophysical properties.
Previously reported L5 was used as a modification of probe L3 by introducing another similar imine-linked benzothiazole arm to form a dimeric cage-like structure5.36. All these probes were used chronologically to visualize its sensing ability and selectivity studies towards the targeted anions in the solution phase.
- Absorption studies 91
- Fluorescence studies 95
- Reversibility study and interpretation of related logic gate 101
The intensity of the peak at 550 nm was increasing until it reached saturation value with the addition of 3 equiv. Inset: Changes in absorption maxima at 384 nm and 456 nm with the stepwise addition of TBAF. Inset: changes in absorption maxima at 332 nm and 445 nm with stepwise addition of TBAF.
To obtain a quantitative estimate of the interaction, an analogous titration experiment was performed with increasing addition of acetate ions in acetonitrile (Figure A5.7a). The addition of TBAF beyond 1.0 equivalent may have induced deprotonation of the L3 probe, which was reflected in the more pronounced upshift of the aromatic -CH proton signals, ie. The signals gradually decreased in the middle until it was revived by the addition of excess TBAOAc solution (up to 3.0 equiv).
For the probe L4, as shown in Figure 5.6a, the addition of TBAF solution from 0 to 1.5 equivalents resulted in the downward shift (=0.34 ppm) and broadening of the hydrazone –NH, Ha- proton signal at 12.75 ppm. As shown in Figure 5.6b, the addition of initial amounts of acetate anions (up to 1.0 equiv.) to probe L4 stimulated both the broadening and downward shift (=0.26 ppm) of the hydrazone –NH, Ha ( 12.75 ppm). ) proton signals. Addition of 0.2 equivalents of TBAF solution resulted in the broadening of the –OH proton signal, which eventually disappeared upon further addition of TBAF solution.
At the same time, the Ha signal experienced a significant downward shift from =1.12 ppm to the addition of 3.0 equiv. Upon addition of acetate ions at a low concentration (up to 0.2 equiv.), the acidic –OH proton Ho experienced a broadening and disappeared immediately, as shown in Figure 5.7b. The occurrence of the original peak at 403 nm with the addition of H+ was taken as Output 1 (Out 1), while incremental additions of F gave us a response at 550 nm as Output 2 (Out 2).
With the addition of F¯, Output 1 was turned off and at the same time Output 2 (Out2) at 550 nm was turned ON or '1'.
Conclusion 103
This “Off-On-Off” switching behavior led us to fabricate an INHIBIT logic gate where the output “turn on” fluorescence at 520 nm was assigned as “1” and the “off” behavior was designated as “0”. . Brief, The application of the fluoride reactivation process to the detection of sarin and soman nerve agent exposure in biological samples, Drug Chem Toxicol. Qi, a dual-function smartphone-based sensor for colorimetric and chemiluminescent detection: a case study for fluoride concentration mapping, Sens.
Arai, Intermolecular Excited-State Proton Transfer Dependent on the Substitution Pattern of Anthracene-Diure Compounds Involved in the ON1-OFF-ON2 Fluorescence Response Upon Addition of Acetate Ions, Org. Ren, An "off-on" naphthalimide-based fluorescent sensor for anions: its application to visual discrimination of F- and AcO- in a self-assembled gel state, New J. Kim, A single chemosensor for multiple analytes: fluorogenic detection of Zn2+ and OAc− ions in aqueous solution, and an application to biological imaging, New J.
Sahoo, Vitamin B6 cofactor-derived chemosensor for the selective colorimetric detection of acetate anions, Tetrahedron Lett. Zhang, TICT–ICT State Change Mechanism-Based Acetate Fluorescent Sensor Acts as an “Off-On-Off” Switch and Logic Gate, Sens. Churchill, New reversible Zn2+-supported biological phosphate “turn on” probe through stable aryl-hydrazone salicylaldimine conjugation that attenuates ligand hydrolysis, Inorg.
Das, a benzothiazole containing CHEF-based fluorescent turn-on sensor for Zn2+ and Cd2+ and subsequent detection of H2PO4− and P4O74− in physiological pH, Sens. Lee, Fluorescence activation of coumarin derivatives by metal cations: a novel signaling mechanism based on C=N isomerization, Org. Wang, Benzo-selenadiazole fluorescent probes - near-IR optical and ratiometric fluorescent sensor for fluoride ion, Org.
Wei, An easily prepared two-channel chemosensor for the selective and immediate detection of fluoride based on double Schiff base, Spectrochim.
107
In summary, this thesis reports the efforts and results in designing and improvising certain benzimidazole- and benzothiazole-functionalized receptors and their propensity to bind to biologically and environmentally relevant anions in both the solution phase and the solid state. As discussed in Chapter 3, the introduction of an amide-linked nitrophenyl group as the third arm of the symmetric benzimidazole arms has made L1 suitable for selective recognition of octahedral SiF62 and tetrahedral SO42/HSO4ˉ anions in the solid state. By tuning the functionalities of the third arm, our design of nonsymmetric tripod receptors successfully recognized anions in both the solution phase and the solid state, which is otherwise a stimulating task to undertake.
Paper strips from the chemosensor L1 and L2 can also be used for the rapid detection of fluoride ions. Since selective anion binding in both solid and solution phases has been demonstrated using the nonsymmetric tripod connections, we accentuated our push to achieve better selectivity and sensitivity in the solution phase. The benzothiazole-based Schiff base receptors L3, L4, and L5 can selectively detect fluoride and acetate ions in acetonitrile solution via absorption spectroscopy.
Boolean logic gates have also been fabricated at the molecular level based on the reversible behavior of the probes. Concisely, this thesis portrays a succession of systematic developments in the field of chemosensing as well as solid state studies. Starting with the synthesis of a new non-symmetric tripod study and its anion binding both in the solid state and in solution (Chapter 3), we have continued our study with another non-symmetric tripod analogue in solution study based on emission spectroscopy assisted by its solid-state anion recognition (Chapter 4) to conclude with a series of three simple Schiff bases as selective and sensitive anion sensors only in the solution phase (Chapter 5) .
For these applications to achieve their potential, the fundamental work lies in tuning and modifying the receptor molecules. Combined solid-state and solution-phase studies of biologically and environmentally relevant anions in a non-symmetrical tripodal framework. Das, Competitive anion binding ability of benzimidazole and amide functionality of a nonsymmetric receptor in solid state and solution phase, Supramol.
Das, An asymmetric benzimidazole-based ternary receptor for ratiometric fluorescence detection of fluoride ions and solid-state recognition of sulfate ions, New J.
