SYNTHESIS OF SOME NOVEL CHEMICAL SENSOR FOR CYANIDE ION SENSING VIA DIFFERENT MECHANISM

Abstract

Structure of noble organic molecular scaffolds for recognition and sensing of environmentally and biologically important ions with high sensitivity and selectivity are constantly important for practical research in different fields of science. In current years there has been developed for constructing chemical sensors for on time, fast and costoperative monitoring of environmental samples. Associated with the traditional analysis instruments, chemical sensors are convenient, modest to use, in-situ and minuscule in size. These topographies are perfect for real-time on field measurements, hence the inaccuracies instigated by the sample transference and storage can be generally condensed. Over current years the progress of a plethora of potential chemosensors has concerned substantial consideration in supramolecular chemistry. The most appropriate properties for development of chromogenic and fluorogenic sensors is the capability to react to useful perturbation in a highly selective and sensitive method by dramatic variations in color and emission intensity due to simplicity, convenience, low-cost, sensitivity, immediate response, and naked-eye visualization. The present thesis entitled “SYNTHESIS OF SOME NOVEL CHEMICAL SENSOR FOR CYANIDE ION SENSING VIA DIFFERENT MECHANISM”, describes the design, synthesis and photophysical properties of some receptors based on salicylaldehyde, azo-dye, coumarin and napthylamine systems. The molecules were characterized by FT-IR, 1H, 13C NMR, and APCI-MS data. The photophysical behaviors of these receptors were observed through UV-vis and fluorescence spectroscopy. The receptors were developed for studying the interaction with cyanide ions. The thesis has been divided into five chapters, the first chapter deals with “General Introduction”, which defines numerous aspects comprising cyanide sources and lethal effects, brief discussion of electrochemical sensors (cyclic voltammetry) and optical sensor, principle of optical chemosensors, some common photophysical mechanisms like charge transfer (CT), photoinduced electron transfer (PET), intramolecular charge transfer (ICT), energy transfer (ET), excimer/exciplex, excited state intramolecular proton transfer (ESIPT), Aggregation-induced emission (AIE)/Aggregation-caused quenching (ACQ) and C=N isomerization, principles and general approach for CN¯ sensing and molecular logic gates. ii Second chapter presents; “Hydrogen Bonding Based Cyanide Sensor”, describes four Nobel azo linked [(3-methylpyridin-2-yl) iminomethyl-((4nitrophenyl) diazenyl) phenol (B1), (furan-2-yl methyl) iminomethyl-4-((4nitrophenyl) diazenyl) phenol (B2) and Enone based ((6-Fluoro-4-Oxo-4H-cromen-3-yl)methylene) isonicotinohydrazide (B3), and N-((4-oxo-4H-cromen-3yl)methylene)isonicotinohydrazide (B4)] anion receptors synthesis and characterized by FT-IR, 1H NMR, 13C NMR. Ligands B1-B4 displays large extent of selectivity toward CN¯ resulting instant color change expressions witnessed in 10% aq. medium. Job’s plot displays 1:1 stoichiometry along with all ligands. The limit of detection diagnosed for CN¯ ion is down to 0.48 (B1), 1.66 μM, (B2) 0.76 μM (B3) and 0.68 μM (B4) that is below the WHO level. The anion binding property of the receptors (via deprotonation mechanism) was monitored by FTIR, 1H NMR & hydroxyl titration and DFT calculation. The coated paper test strip was served as a mini colorimetric device for finding of CN¯ in aqueous solution. It can be practiced for quantitative assurance of CN¯ concentrations in water samples. The reversible behavior of B-CN complex with H+ also applied as a logic gate (in case of B3). Third chapter presents; “Metal Complexation Based Cyanide Sensor”, describes the synthesis of a novel effectual molecular receptor 2a [4hydroxy-6-methyl-3- (1-(-3methylpyridin-2-ylimine) ethyl)-2H-chromene-2-one] and characterized by spectroscopic techniques like, CHNS, FT-IR, 1H NMR, 13C NMR, and APCI-MS. Ligand 2a was the selective fluorescence turn-off sensor for the recognition of Co2+ via Photoinduced electron transfer quenching. Job's Plot analysis reveals the 2:1 stoichiometry iii between the ligand-Co2+ complex. The resultant matallo-supramolecular complex of 2a- Co2+ exhibits the change in optical properties with CN¯ (0.12 μM LOD) over complexation method in 1:2 stoichiometry. The possible binding mode was confirmed by FTIR, NMR and mass spectroscopic studies. Further, CN¯ binding sturdily perturbs the redox properties of 2a-Co2+ complex. The ‘On-Off-On’ emission variation outlines the working principle of IMPLICATION logic gate. Besides, ligand 2a and 2a-Co2+ complex also exhibit antimicrobial activity against Gram negative bacteria P. diminuta and Gram positive bacteria: S. aureus, B. brevis using disc diffusion method. Fourth chapter presents; “Nucleophilic Addition Based Cyanide Sensor”, describes synthesis of doubly activated Michael type receptors 2-((2-methoxynaphthalene-1-yl) methylene) -2H-indene-1-3dione (L1), 2-cyano-3-(2-methoxynaphthalene-1-yl) acrylic acid (L2) and indolium based spiropyran type receptors 1,3,3-trimethylspiro[indoline- 2,2’-pyrano[3,2-c]chromen]-6-ium (L3), 9’fluoro-1,3,3-trimethylspiro[indoline-2,2’- pyrano[3,2-c]chromen]-6-ium (L4). In case of L1-L2 the donor-acceptor molecular arrangement was interrupted by Michael addition of CN¯ on electron-deficient alkene bridge, which blocks intramolecular charge transfer and showed colorimetric blue shift and fluorescence enhancement. On the other hand, in case of receptors L3-L4 emerging red shift in absorption and emission enhancement is a consequence ring opening with conversion of enolate chromophore as merocyanine forms with CN¯. The 1 : 1 stoichiometry of L-CN- complex was proved by Job’s plot and pseudo first-order rate constant were calculated found to be 0.025 s-1 (L1), 0.029 s-1 (L2) and 0.022 S-1 (L4). The detection limit analysed for CN¯ is 1.2 nm (L1), 1.15 nm and 57.9 nM (L4) that is very below the WHO level. The FTIR, NMR, mass spectroscopy and DFT (Density functional theory) further supported the suggested mechanism of interaction between receptors and CN¯. Cyclic iv Voltammetry studies were also confirmed the recognition of CN¯ with all lignds L1-L4. Thus, ligands for the spectroscopic identification of CN¯ can principal to the practical application as in paper strips and biological activities (antifungal, antibacterial). Fifth chapter presents; “Metal Displacement Based Cyanide Sensor (Indirect Approach)”, describes synthesis of excited state intramolecular proton transfer (ESIPT) based four Nobel receptors S1- (2-ethoxy-3-((p-nitrophenyl-1- ylimino)methyl) -2H-chromen-4-ol) S2- (2-methoxy-3-((p-nitrophenyl-1- ylimino)methyl) -2H-chromen-4-ol), S3- (2-methoxy-3-((naphthalen-1-ylimino) methyl) -2H-chromen-4-ol) and S4- 2-ethoxy-3-((naphthalen-1-ylimino) methyl) - 2H-chromen-4-ol), which are shown the remarkable aggregation-induced emission enhancement (AIEE) in aqueous medium. ON basis of this phenomenon further developed fluorescent organic nanoparticles of S3. All receptors express good water solubility and subsequent in-situ sensing of Cu2+ and CN‾ in aqueous and biological settings. Cu2+ displayed a blue shift in absorption wavelength and efficiently quenches the emission intensity. Under the optimised conditions, the fluorescence intensity change established the feasibility for quantifiable analysis of ultra-trace concentrations of Cu2+ as inferred from an absolutely low detection limit 1.69 μM, 12.3 nM with S1 and S3-FONs respectively. Standardized exercise revealed the in-situ formed S-Cu2+ assembly acted as a secondary sensor for CN‾ via regeneration of fluorescence intensity with a limit of detection 0.168 μM, 21.4 nM with S1-Cu2+ and S3-FONs-Cu2+ respectively. Additionally the receptors were v mimic as the function of a sequential logic circuit at molecular level based on “On– Off–On” sensing behavior by the inputs of Cu2+ and CN¯. The recovery analysis executed by spiking the known concentrations of Cu2+ and CN‾ in deionised water, tap water and river water samples. Further, S1 and S1-Cu2+ complex shows the antimicrobial activities against fungi: Bipolaris oryzae and Rhizoctonia solani using the agar well diffusion method. Similarly S3-FONs express promising applications in intracellular recognition of Cu2+ and CN‾ via cellular imaging in HeLa cells.