Department of Chemistry
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Item Synthesis, Absorption, and Fluorescence Studies of Coumaryl-Labelled Amino Acids and Dipeptides Linked Via Triazole Ring(CSIRO, 2015-04-07) Sakhuja, Rajeev; Pant, Debi D.Fluorophores based on 4-triazolyl, 7-hydroxy-4-triazolylmethyl, 4-O-triazolylmethyl, and 7-O-triazolylmethyl coumaryl-tagged amino acids and dipeptides were synthesized by copper-catalyzed [3 + 2] cycloaddition reaction between azido- or alkynyl-functionalized coumarins with alkynyl- or azido-functionalized amino acid and dipeptides in good-to-excellent yields. Steady-state absorption and the fluorescence properties of the synthesized conjugates were studied. The chemical applicability of these amino acid and peptide-based fluorophores was successfully demonstrated by their linear elongation by further tagging them with appropriate C- or N-terminus amino acid.Item Estimation of ground and excited-state dipole moments of synthesized coumarin derivative, (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl 2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate from a solvatochromic shift and theoretical methods(Elsiever, 2015-09) Sakhuja, Rajeev; Pant, Debi D.The electronic absorption and fluorescence spectra of coumarin derivative, (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate have been studied in solvents of different polarities, and the data were used to study the solvatochromic properties. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. Synthesized compound (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate was characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecule were obtained from Bakshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. High value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of molecule. Also, fluorescence emission peak undergoes a bathochromic shift with increase in the polarity of the solvent, confirming π → π* transition. Numerical calculations are performed using B3LYP/6-31G(d) level of theory for the ground state using Gaussian 03. Studies in different solvents are also done using IEF-PCM method and UA0 radii. A comparative analysis between the values of dipole moment in gas phase and various solvents is also done for the ground state.Item Experimental and theoretical study: Determination of dipole moment of synthesized coumarin–triazole derivatives and application as turn off fluorescence sensor: High sensitivity for iron(III) ions(Elsiever, 2015-12) Sakhuja, Rajeev; Pant, Debi D.Electronic absorption and fluorescence spectra of two synthesized coumarin–triazole based probes (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl) methyl)-1H-1,2,3-triazol-4-yl)methyl 2-(tert-butoxycabonylamino)-3-phenylpropanoate and (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl) methyl 2-(benzyloxycabonylamino)-3-phenylpropanoate have been recorded at room temperature in wide range of solvents of different polarities. Synthesized compounds were characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecules were obtained from Bakshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. A DFT based studies in different solvents are also performed using IEF-PCM method and UA0 radii. A comparative analysis between the values of dipole moment in gas phase and various solvents is also performed for the ground state. The potential sensor behaviors of these compounds to metal ions have also been examined by fluorescence spectroscopy and these compounds exhibited as fluorescence sensor for the determination of Fe3+ ions in solution. Effect of various metal ions on fluorescent behavior was also studied. Both the synthesized compounds act as selective and sensitive sensor for micromolar detection of Fe3+ ions. Binding stoichiometry of Fe3+ ion detection was also investigated. Conventional binding energy calculations are performed to determine the relative stability of Fe(III) complexes.Item Highly sensitive fluorescent imidazolium-based sensors for nanomolar detection of explosive picric acid in aqueous medium(Elsiever, 2016-06-28) Sakhuja, Rajeev; Pant, Debi D.Two novel fluorescent coumaryl linked imidazolium salts have been synthesized, characterized and found to be highly selective for nanomolar detection of commonly used explosive picric acid, over other aromatic explosives in aqueous medium. The compounds are highly photostable and are practically applicable for sensing picric acid in real environmental samples, in presence of interfering aromatic/non-aromatic explosives and metal ions. In solution, the high sensitivity of the sensors toward picric acid can be predominantly attributed to the ground-state charge-transfer complex formation based on UV–vis studies, time resolved fluorescence results and DFT calculations.Item Solvatochromic shift and estimation of dipole moment of synthesized coumarin derivative: Application as sensor for fluorogenic recognition of Fe3 + and Cu2 + ions in aqueous solution(Elsiever, 2016-10) Sakhuja, Rajeev; Pant, Debi D.(S)-4-((4-((3-amino-2-oxo-4-phenylbutoxy)methyl)-1H-1,2,3-triazol-1-yl)methyl)-7 hydroxy-2H-chromen-2-one hydrochloride was synthesized and characterized by detailed spectroscopic studies such as 1H, 13C NMR and HRMS. Excited state dipole moment of synthesized compound was obtained using different solvatochromic shift methods. High value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of molecule. Also, fluorescence emission peak undergoes a bathochromic shift with increase in the polarity of the solvent, confirming π → π* transition. The potential sensor behavior of the compound to metal ions has also been examined. Chemosensor shows the sensitivity for Fe3 + and Cu2 + over other metal cations in aqueous solution. The detection limits of Fe3 + and Cu2 + were calculated to be 143 nM and 71.31 μM, respectively. The LC–mass analysis indicated that 1:1 complex was formed between Fe3 + (or) Cu2 + and compound. Binding energy values for the complexation of the compound with metal ions are theoretically computed at M06/6–31 + G(d,p) level. The DFT based binding energy values show good correlation with the experimental observations.Item Design and synthesis of amino acid appended azo dye hybrid: Characterization, solvatochromic and quantum-chemical calculations using experimental and theoretical approach(Elsiever, 2016-09) Sakhuja, Rajeev; Pant, Debi D.Amino acid appended azobenzene hybrid was synthesized and characterized using Spectroscopic techniques like 1H NMR, 13C NMR, FT-IR and Mass spectrometry analysis and its optical properties were investigated using UV–vis absorption and fluorescence spectroscopy in solvents of different polarity. Based on solvent refractive index and relative permittivity, by using the theory of solvatochromism, the excited-state (μe) and ground-state (μg) dipole moments was determined for (E)-4-((4-(heptyloxy)phenyl)diazenyl)benzyl((benzyloxy)carbonyl)glycinate (Gly-Azo-O7) based on the variation of Stokes shift as an effect of various solvent's. A bathochromic shift observed in absorption and emission spectra with increasing solvent polarity, which implied that the transition involved is π → π*. The ground state and excited state dipole moments were also calculated and compared using experimental and DFT calculations.Item Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces(ACS, 2016) Sakhuja, Rajeev; Pant, Debi D.The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (Kb) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.Item Highly Selective Sensing of Li+ in H2O/CH3CN via Fluorescence ‘Turn-on’ Response of a Coumarin-Indole Linked Dyad: an Experimental and Theoretical Study(Springer, 2016-08-27) Sakhuja, Rajeev; Pant, Debi D.A coumarin-indole dyad, N-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-indole-2-carboxamide has been synthesized and characterized by 1H-NMR and 13C-NMR. Effect of various metal ions on fluorescent behavior was also studied. The synthesized compound showed remarkable specificity towards Li+ in organo-aqueous medium over other metal ions. Coordination of the compound with Li+ induces a turn-on fluorescence response. The sensor exhibited good binding constant and low detection limit towards Li+. Experimental results have been verified with Density Functional Theory and Time Dependent Density Functional Theory calculations.Item Solvent effects on the absorption and emission spectra of novel (E)-4-((4-(heptyloxy)phenyl)diazenyl)benzyl (((9H-fluoren-9-yl)methoxy)carbonyl)-d-alaninate (Fmoc-al-az): Determination of dipole moment by experimental and theoretical study(Elsiever, 2017-02-05) Sakhuja, Rajeev; Pant, Debi D.Amino acid appended azobenzene hybrid has been synthesized (Fmoc-al-az) and its electronic absorbance and fluorescence spectra were recorded at room temperature in a series of polar and non-polar solvents. The ground state and excited state dipole moments were calculated using solvatochromic shift method. A DFT based study was also performed using- Gaussian09 program package. We have observed that the absorption spectra don't show sensitive behavior to the change in the polarity of the solvent, whereas a bathochromic shift was observed in the fluorescence spectra as we moved from non-polar to polar solvents indicating a π→π* transition. It was observed that the dipole moment in the excited state is much higher than the ground state, due to the amino acid containing hydrogen bond acceptor (Osingle bondCdouble bondO) and hydrogen bond donor (single bondNH) in Fmoc-al-az increasing the reorientation tendency of the solvent molecule around the dye therefore enhancing the stabilization of the excited state which is attributed to the high polarity of the excited states. DFT level electronic structure calculations are also performed for a better molecular level understanding of the experimental observations. We obtained a good correlation between the theoretical studies and experimental results.Item Detection of Hg2+ ions in aqueous medium using an indole-based fluorescent probe: Experimental and theoretical investigations(Elsiever, 2017-12) Sakhuja, Rajeev; Pant, Debi D.Mercury pollution is a widespread danger to human health and environment. Due to limitations associated with the existing Hg2+ chemosensors, development of new, efficient and selective chemosensors capable of sensing mercury ions in aqueous medium remains a demanding area of research. In this regard, an indole-based fluorescent probe has been synthesized and characterized by detailed spectroscopic analysis. The probe showed a high selectivity and sensitivity towards Hg2+ by giving significant fluorescence quenching over other tested cations in H2O/DMF (7:3, v/v) medium. The association constant (Ka) was 6.4 × 103 M− 1 between sensor and Hg2+. The detection limit of sensor to Hg2+ was found to be 0.143 μM (143 nM). The experimental results have been verified with Density Functional Theory.