Somenath Lohar

A FRET-based ‘off–on’ molecular switch: an effective design strategy for the selective detection of nanomolar Al3+ ions in aqueous media

A new water-soluble rhodamine-based Al3+ ion-selective probe (L1) was synthesised and characterized by physico-chemico and spectroscopic tools. In the presence of a large excess of other competing ions, L1 specifically binds Al3+ ions with a concurrent visually observable change from colorless to pink in electronic spectral behavior, making it possible to detect the presence of Al3+ ions with the naked eye. The addition of Al3+ ions to a solution of L1 in HEPES buffer (1 mM, pH 7.4, 2% EtOH) at 25 °C, results in a decrease in the weak fluorescence intensity at λem = 470 nm, while a new peak (at λem = 588 nm) increases gradually through a fluorescence resonance energy transfer process. This ratiometric enhancement helps to detect Al3+ ions at a very low concentration of 33 nM. The detection limit of L1 for Al3+ ions was estimated to be 6.19 × 10−9 M using the 3σ method. This probe is also useful for imaging Al3+ ions in HeLa cells.

Development of a rhodamine–benzimidazol hybrid derivative as a novel FRET based chemosensor selective for trace level water

A newly designed rhodamine–benzimidazol hybrid molecule has been developed as a FRET-based chemosensor for the selective detection of trace level water in both polar protic and aprotic organic solvents.

Selective and Sensitive Turn-on Chemosensor for Arsenite Ion at the ppb Level in Aqueous Media Applicable in Cell Staining

A newly designed and structurally characterized cell permeable diformyl-p-cresol based receptor (HL) selectively senses the AsO3(3-) ion up to ca. 4.1 ppb in aqueous media over the other competitive ions at biological pH through an intermolecular H-bonding induced CHEF (chelation-enhanced fluorescence) process, established by detailed experimental and theoretical studies. This biofriendly probe is highly competent in recognizing the existence of AsO3(3-) ions in a living organism by developing an image under a fluorescence microscope and useful to estimate the amount of arsenite ions in various water samples.

Substituent effect on fluorescence signaling of the cell permeable HSO4- receptors through single point to ratiometric response in green solvent

Two new 2-(2-aminophenyl)benzimidazole-based HSO4− ion selective receptors, 6-(4-nitrophenyl)-5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazoline (L1H) and 6-(4-methoxyphenyl)-5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazoline (L2H), and their 1 : 1 molecular complexes with HSO4− were prepared in a facile synthetic method and characterized by physicochemical and spectroscopic techniques along with the detailed structural analysis of L1H by single crystal X-ray crystallography. Both receptors (L1H and L2H) behave as highly selective chemosensor for HSO4− ions at biological pH in ethanol–water HEPES buffer (1/5) (v/v) medium over other anions such as F−, CI−, Br−, I−, AcO−, H2PO4−, N3− and ClO4−. Theoretical and experimental studies showed that the emission efficiency of the receptors (L1H and L2H) was tuned successfully through single point to ratiometric detection by employing the substituent effects. Using 3σ method the LOD for HSO4− ions were found to be 18.08 nM and 14.11 nM for L1H and L2H, respectively, within a very short responsive time (15–20 s) in 100 mM HEPES buffer (ethanol–water: 1/5, v/v). Comparison of the utility of the probes (L1H and L2H) as biomarkers for the detection of intracellular HSO4− ions concentrations under a fluorescence microscope has also been included and both probes showed no cytotoxic effect.

A quinazoline derivative as quick-response red-shifted reporter for nanomolar Al3+ and applicable to living cell staining

A newly synthesized and structurally characterized quinazoline derivative (L) has been shown to act as a quick-response chemosensor for Al3+ with a high selectivity over other metal ions in water-DMSO. In the presence of Al3+, L shows a red-shifted ratiometric enhancement in fluorescence as a result of internal charge transfer and chelation-enhanced fluorescence through the inhibition of a photo-induced electron transfer mechanism. This probe detects Al3+ at concentrations as low as 1.48 nM in 100 mM HEPES buffer (DMSO-water, 1 : 9 v/v) at biological pH with a very short response time (15-20 s). L was applied to biological imaging to validate its utility as a fluorescent probe for monitoring Al3+ ions in living cells, illustrating its value in practical environmental and biological systems.

A new turn-on benzimidazole-based greenish-yellow fluorescent sensor for Zn2+ ions at biological pH applicable in cell imaging

A newly designed and structurally characterized benzimidazole containing compound, 2,4-di-tert-butyl-6-(5,6-dihydro benzo[4,5] imidazo [1,2-c] quinazolin-6-yl)-phenol) (HL), behaves as a ‘turn-on’ fluorescent sensor selective for Zn2+ ions at as low as 39.91 nM within a very short responsive time (15–20 s) in 5 mM HEPES buffer (DMSO/water: 1/5, v/v) at biological pH. Thorough experimental and theoretical (DFT) studies indicate the occurrence of greenish yellow fluorescence through a chelation enhanced fluorescence (CHEF) process. Using this organic moiety (HL) as a probe, almost no interference of other competitive ions in the detection of Zn2+ ions was observed. The reaction of HL with Zn2+ led to the in situ formation of a tridentate monobasic ligand (HL1) to produce the complex as [Zn(L1)2] through a [1,5] sigmatropic-type shift of HL prior to metal coordination. HL is also capable of detecting the intercellular distribution of Zn2+ ions in Candida sp. cells under a fluorescence microscope by developing the image.

A turn-on green channel Zn2+ sensor and the resulting zinc(II) complex as a red channel HPO42− ion sensor: a new approach

A newly synthesized and spectroscopically characterized non-fluorescent organic moiety (L′H) selectively sensed Zn2+ ions based on a chelation-enhanced fluorescence (CHEF) process at the λem of 520 nm through the formation of a new dinuclear zinc(II) complex (1). Upon the addition of Zn2+ ions to the solution of L′H in dimethyl sulphoxide at 25 °C, a systematic enhancement of fluorescence was observed, which was not affected by the presence of competitive ions. The reaction of L′H with Zn2+ ions led to the formation of a dinuclear zinc(II) complex, featuring a new in situ formed macrocyclic ligand (L), which was isolated in pure form and then characterized. The formulation of 1 was established by spectroscopic tools along with a detailed structural analysis carried out using single crystal X-ray crystallography. In addition, the complex 1 also behaved as a red-shifted, HPO42− ion-selective chemosensor at the λem of 595 nm based on a displacement approach in dimethyl sulphoxide. Interestingly, 1 showed remarkable sensitivity towards HPO42− ions via fluorescence modulation of the dinuclear zinc(II) complex (1) compared with the other anions examined herein.

A bio-attuned ratiometric hydrogen sulfate ion selective receptor in aqueous solvent: structural proof of the H-bonded adduct

A new cell permeable quinazoline based receptor (1) selectively senses HSO4− ions of nanomolar region in 0.1 M HEPES buffer (ethanol–water: 1/5, v/v) at biological pH over other competitive ions through the proton transfer followed by hydrogen bond formation and subsequent anion coordination to yield the [LHSO4]−LH+·3H2O (2) ensemble, which has been crystallographically characterised to ensure the structure property relationship. This non-cytotoxic HSO4− ion selective biomarker has great potential to recognize the intercellular distribution of HSO4− ions in HeLa cells under fluorescence microscope.

A new rhodamine based ‘turn-on’ \(\hbox {Cu}^{2+}\) ion selective chemosensor in aqueous system applicable in bioimaging

A new rhodamine-based Schiff base (L) has been synthesized and characterized by physicochemical and spectroscopic tools. This organic molecule selectively reacts with Cu2+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}