DESIGN AND SYNTHESIS OF CHELATING IONOPHORES AS CHEMOSENSORS BASED ON ANALYTICAL STUDIES

Abstract

Generally, chemical sensor comprises of a selective detection of molecule which is sensitive to stimuli by the analyte and a transduction material that develop an analytically advantageous signal whose significance is functionally contributing to the concentration of the analyte or substance. Based on working principal of chemosensors it can be categorized such as electrochemical, thermal sensor, mass sensors, magnetic sensor and optical sensors. The inexpensive optical sensors have vast applications in various area like medicine, environmental pollution and many others. It attracts the scientific community such as researcher, scientist and biologist due to highly sensitive and selective nature towards the various transition metal ions, other toxic metal ions and anions. Optical sensors depend on the optical changes observed upon the detection of targeted analyte with chemosensor. These are simple to use, portable, in-situ and miniature in size, these features are necessary for real-time on field measurements. The thesis is managed with some chemosensors and their analytical studies. For the convenience and clarity, the work in the thesis divided into six chapters and arranged as follows: Chapter 1 deals with “Introduction” of chemical sensor as well as classification of optical sensors. Chemosensors are generally based on chelating ligands such as Schiff bases, coumarin, bipyridine, indole, quinoline, calixrene, BODIPY, crown ether, porphyrin, rhodamine and nanoparticles. The theory behind the mechanism to sense the analyte has been described. The details of analytical (photoluminescence) processes is discussed in the different subsections. The optical chemosensors has been classified according to performance of the signal transmitted by the active unit and diverse possible mechanisms like PET, ICT, ET, CHEF/CHQF for signal transduction upon analyte binding to chemosensors and the term used in the fluorescence sensing have also been discussed in this chapter. Chapter 2, entitled “Thiosemicarbazide based chemosensor for Arsenite and cyanide ion” described the synthesis and characterization of 2-((2-Hydroxynaphthalen-1- yl)methylene)hydrazinecarbothioamide (L1) and successfully applied for the detection of toxic anions arsenite and cyanide ion among other anions. L1 is utilized as a turn-on v sensor for arsenite and cyanide ions via deprotonation and hydrogen bonding mechanism upon interaction with both analytes in DMF: H2O (HEPES buffer, pH = 7.2, 9:1 v/v solution) medium. This L1 was characterized by different techniques including UV-vis, FT-IR, NMR and mass spectroscopy. This ligand shows 1:1 and 1:2 stoichiometry with arsenite and cyanide ions respectively via Job’s plot. The binding constant of AsO2 - and CN- with L1 was calculated by using B-H (Benesi-Hilderbrand) plot and found as 3.1 ×105 and 1.9 × 106 for AsO2 - and CN- respectively and limit of detection of AsO2 - and CN- was 66 nM and 77 nM with ligand L1 respectively. Further the binding affinity of probe L1 with both anions was manifested using NMR, theoretical optimization, mass spectroscopy, optical studies and electrochemical studies and used in real time water analysis for the detection of both anions. L1 Chapter 3 entitled “Pyridine dicarbohydrazide based chemosensor for the detection Copper and cyanide ions” described the synthesis and characterization of bis- (4-hydroxy-3,5-dimethoxybenzylidene)pyridine-2,6-dicarbohydrazide (L2), bis(-(1Hpyrrol- 2-yl)methylene)pyridine-2,6-dicarbohydrazide (L3), bis(-(2-hydroxynaphthalen-1- yl)methylene)pyridine-2,6-dicarbohydrazide (L4), bis(-anthracen-9- ylmethylene)pyridine-2,6-dicarbohydrazide (L5) by NMR, FT-IR, UV-vis spectroscopy, elemental analysis and mass spectroscopy, SC-XRD and emission spectra. These ligands were recognized copper ion among other metal ions and cyanide ion detection by copper complex via in-situ experiment with turn on-off-on behavior in MeOH: H2O (9:1, v/v solution) medium. The red shift was observed in absorption spectra and quenching behavior observed in emission spectra of these ligands with copper ions through PET mechanism and further copper complex was applied for CN- ion detection. The ligands vi (L2-L5) were showed 1:2, 1:3, 1:2 and 1:2 stoichiometric ratios respectively, with copper ion via Job’s plot based on UV-vis spectra. The S-V plot demonstrate the linear quenching of the ligands with copper ions. The formation constant of L2 to L5 was as 8.866, 17.645, 11.145 and 6.45 respectively. The limit of detection for copper ion with ligands (L2-L5) were calculated as 0.12, 0.10, 0.097, 0.098 μM respectively, using emission spectra. The binding affinity of copper ion with ligands was supported by FTIR, mass spectroscopy, redox studies and optical studies. furthermore, cyanide detection was found by the copper complexes of ligands via in-situ experiment with displacement approach. Further, these ligands were applied for practical applications such as real water analysis and in logic gate behavior. Chapter 4 entitled “Pyrimidine based fluorescent sensor for aluminum ion detection” illustrated the synthesis and characterization of 6-amino-5(((2- hydroxynaphthalen-1-yl)methylene)amino)-2-mercaptopyrimidin-4-ol (L6) and 6-amino- 5((4-bromobenzylidene)amino)-2-mercaptopyrimidin-4-ol (L7) by different techniques (UV-vis, FT-IR, Mass spectroscopy and NMR and fluorescence spectroscopy) and found that L6 recognize the aluminum ion among other metal ion whereas L7 didn’t show any vii change in UV-vis and emission spectra with any metal ions. So further all studies have been performed only with L6 ligand. L6 was more selective towards aluminum ion with “OFF-ON type” behavior. The fluorescent sensor recommended 1:1 stoichiometry with aluminum ion by Job’s plot in CH3CN medium. The high sensitivity of ligand L6 towards aluminum ion supports the high detection limit viz. 99 nM with 3.5 × 104 association constant (Ka). There was no interference was found by another metal ions. The binding was supported by NMR titration, Theoretical studies and cyclic voltammetry studies. Further, it was used in different practical applications such as bacterial cell imaging with E. coli DHα bacteria and logic gate applications that manifested the red and green fluorescent images in green and red channel with Al3+ ion as well as in logic gate application it showed INHIBIT logic gate in switching behavior. Chapter 5 entitled “Oxalohdrazonamide based turn-off chemosensor for Hg2+ and Cu2+ and turn-on for Cd2+ ion” described the synthesis and characterization of Bis((indol-3-yl)methylene)oxalohydrazonamide (L8) via different spectroscopic techniques. It was found that ligand L8 was shown colorimetric and turn-off behavior with Hg2+ and Cu2+ ion among other metal ions through CHQF and PET mechanism whereas in fluorometric studies it shows turn-on demeanor for Cd2+ ion with CHEF mechanism in aqueous medium. The binding constant of Cu2+, Hg2+ and Cd2+ with ligands L8 viz. 7.35 × 106, 2.33 × 106 and 11.612 (log β) respectively. It has high sensitivity towards Cu2+, Hg2+ and Cd2+ ions and LOD was ca. 0.16 μM, 0.33 μM and 0.11 μM respectively. The binding of these metal ions was supported by NMR titration, mass spectrometry, electrochemical studies and FT-IR spectra. Further, in situ viii experiment for the detection of cyanide ion with ligand appended copper ion. The practical application such as logic gate and real water analysis was successfully applied. L8 Chapter 6 entitled “Carbohydrazide based chemosensors for magnesium, manganese and copper ion” was determined the synthesis and characterization of ((6- nitro-4-oxo-4H-chromen-3-yl)methylene)furan-2-carbohydrazide (L9) and ((6-bromo-4- oxo-4H-chromen-3-yl)methylene)furan-2-carbohydrazide (L10) through various techniques such as NMR, FT-IR, UV-vis spectroscopy and fluorescence spectroscopy. Ligand L9 shown the detection of manganese and magnesium ion by UV-vis and emission spectra among other metal ions. However, L10 detected the Cu2+ ion by UV-vis studies and Mg2+ ion by emission studies. These ligands show good affinity towards these metal ions. The formation constant of Mn2+ and Mg2+ ion with L9, is 1.68 × 105 and 1.2 × 105, respectively. Similarly, the association constant of L10 with Cu2+ and Mg2+ ion as 1.99 ×105 and 5.25 × 104 respectively. The limit of detection of magnesium and manganese ion with L9 was as 2.56 × 10-6 and 1.63 × 10-7 respectively and LOD for Cu2+ and Mg2+ with L10 was 3.71 × 10-7 and 1.28 × 10-6 respectively. Binding of these metal ions is confirmed by NMR and cyclic voltammetry. Further these ligands and ligands with magnesium ion was used in different applications such as bioimaging.