Rashid Ali

Selective Naked-Eye Detection of Hg2+ through an Efficient Turn-On Photoinduced Electron Transfer Fluorescent Probe and Its Real Applications

A simple molecular fluorescent probe 5 has been designed and synthesized by appending anthracene and benzhydryl moieties through a piperazine bridge. The probe upon interaction with different metal ions showed high selectivity and sensitivity (2 ppb) for Hg(2+) through fluorescence turn-on response in HEPES buffer. The significant fluorescence enhancement (~10-fold) is attributable to PET arrest due to complexation with nitrogen atoms of the piperazine unit and Hg(2+) in 1:2 stoichiometry, in which a naked-eye sensitive fluorescent blue color of solution changed to a blue-green (switched-on). As a proof of concept, promising prospects for application in environmental and biological sciences 5 have been utilized to detect Hg(2+) sensitively in real samples, on cellulose paper strips, in protein medium (like BSA), and intracellularly in HeLa cells. Moreover, the optical behavior of 5 upon providing different chemical inputs has been utilized to construct individual logic gates and a reusable combinational logic circuit. The combinational circuit (switch ON mode; OR logic gate) is easily resettable to the original position (switch OFF mode; INHIBIT logic gate) by applying reset chemical inputs (OH(-) and PO4(3-)) with great reproducibility.

Highly sensitive cell imaging "Off-On" fluorescent probe for mitochondria and ATP.

A smart Off-On molecular scaffold/fluorescent probe 1 has been designed and synthesized. The probe has shown considerable photostability, cell permeability, organelle specificity and selectivity for ATP. The multicolor live cell imaging experiments in HeLa cells showed high selectivity of probe 1 for mitochondria with fluorescence turn-on response. As a proof of concept and promising prospects for application in biological sciences probe 1 has been utilized to detect ATP sensitively in a partial aqueous medium and intracellularly in HeLa cells. The favorable interaction between triphosphate unit of ATP and piperazine N atoms of probe 1 is attributed to synergistic effects of H-bonding and electrostatic interactions that encouraged the CH-π and π→π stacking between anthracene and purine rings. Consequently, the observed enhanced turn-on emission and a naked-eye sensitive blue-green color in the medium is attributable to arrest in photoinduced electron transfer (PET) process.

An efficient multichannel probe to detect anions in different media and its real application in human blood plasma

A simple coumarin derived chromo and fluorogenic chemosensor has been synthesized and tested to detect anions in different medium. The designed chemosensor has shown a high colorimetric response for F− and AcO− ions in acetonitrile in which the color of solution changed from a yellow-green to red and orange respectively whereas, in aqueous medium the probe showed high fluorogenic response and selectively reacted with cyanide through a Michael type nucleophilic addition reaction in which a nonfluorescent (switched-off) color of the solution, “turn-on” to became fluorescent blue (switched-on). The multichannel mode of interaction between the probe and anions has been confirmed by absorption, emission, FT-IR, NMR, ESI-MS spectral data analysis. Moreover, the probe has shown high sensitivity to detect cyanide in a real sample, human blood plasma as well as on paper strips.

An azo based colorimetric probe for the detection of cysteine and lysine amino acids and its real application in human blood plasma

The present work describes the rational design and synthesis of a simple azo based colorimetric chemodosimeter to selectively detect Cys and Lys in the environment of competitive different class of amino acids in HEPES buffer under physiological conditions. The probes 3a and 3b containing aldehyde functionality upon interaction with Cys and Lys afforded stable thiazolidine and aldimine derivatives and displayed a sensitive ratiometric response in the absorption spectra due to a change in the intramolecular charge transfer (ICT) process. The whole recognition process for amino acids gives rise to a rapid significant colorimetric response with readily detectable naked-eye sensitive color changes in the real biological sample. The mechanism of interaction between the probes and amino acids has been confirmed by the optical behavior, FT-IR, NMR and ESI-MS data analysis.

A polynuclear hetero atom containing molecular organic scaffold to detect Al3+ ion through a fluorescence turn-on response

A simple polynuclear hetero atom (N and O) containing molecular organic scaffold/probe, 3 has been designed and synthesized and explored as a potential chemosensor to detect Al3+ (22 nM; ∼0.6 ppb) ion in a HEPES buffer. Upon interaction with different metal ions and anions the weak emission intensity (switched Off) of 3 (at 528 nm; λex = 376 nm) was enhanced significantly (switched On; ∼6.0 fold; Φ3+Al3+ = 0.07) only in the presence of Al3+ wherein, the color of the solution changed from a naked-eye sensitive fluorescent dark green to bright yellow-green. The observed chelation enhanced fluorescence (CHEF) is attributable to restricted ESIPT and CN isomerization processes due to complexation between the potential coordination sites (N and O atoms; hard base) of 3 and Al3+ (hard acid) in a 1u2006:u20061 stoichiometry, consequently. The mechanism of the interaction has been confirmed by the change in optical behaviors, 1H/13C NMR, FTIR, and ESI-MS spectroscopy data analysis. Moreover, chemosensor 3 has also been utilized to detect Al3+ in real water samples and on test paper strips.

Hybrid macrocycle formation and spiro annulation on cis-syn-cis-tricyclo[6.3.0.02,6]undeca-3,11-dione and its congeners via ring-closing metathesis

Summary We have developed a simple methodology to transform cis-syn-cis-triquinane derivative 2 into the diindole based macrocycle 6 involving Fischer indolization and ring-closing metathesis (RCM). Various spiro-polyquinane derivatives have been assembled via RCM as a key step.

Smart excimer fluorescence probe for visual detection, cell imaging and extraction of Hg2+

Smart pyrene-based simple fluorescent probes 2 and 4 were designed, synthesized and characterized by different spectroscopic methods. The photophysical properties of the probes and their affinity towards different metal ions in phosphate buffer were investigated. Upon selective interaction with Hg2+, the molecular probes showed enhanced static excimer emission at 506 nm along with a naked-eye detectable chromo- and fluoro-genic response. Probe 2 sensitively showed a high limit of detection (3.4 pM) for Hg2+ in the solution. The pyrene silicate derivative, 4, was utilized to detect and extract Hg2+ in solution as well as in the solid state. The data obtained from NMR and ESI-MS spectroscopy supported the postulate that the mode of interaction of the probe with Hg2+ involves the N and O atoms of the –CN and –OH functional groups to complex Hg2+ in 2:1 stoichiometry. Moreover, probe 2 exhibited excellent selectivity for Hg2+ in protein medium (BSA/HSA) and was used to detect Hg2+ in live HeLa cells, on test paper strips and in real contaminated water samples.

Spiro annulation of cage polycycles via Grignard reaction and ring-closing metathesis as key steps

Summary A simple synthetic strategy to C 2-symmetric bis-spiro-pyrano cage compound 7 involving ring-closing metathesis is reported. The hexacyclic dione 10 was prepared from simple and readily available starting materials such as 1,4-naphthoquinone and cyclopentadiene. The synthesis of an unprecedented octacyclic cage compound through intramolecular Diels–Alder (DA) reaction as a key step is described. The structures of three new cage compounds 7, 12 and 18 were confirmed by single crystal X-ray diffraction studies.

Off–On–Off fluorescence behavior of an intramolecular charge transfer probe toward anions and CO2

The photophysical behavior of a newly developed fluorescent probe, tricyanoethylphenyl phenanthroimidazole (TCPPI) has been studied. Upon interaction of different class of anions TCPPI displayed naked-eye sensitive fluorescence turn-on response to detect selectively F(-) (0.98μM, 18.62ppb) and CN(-) (1.12μM, 29.12ppb) anions in acetonitrile (MeCN). Jobs plot analysis revealed a 1:1 binding stoichiometry between probe and anions. The spectral data analysis and 1H NMR titration studies suggested about the affinity of F(-) and CN(-) anions with moderately acidic -NH fragment of imidazolyl unit of probe through deprotonation and H-bonding interaction. Moreover, the anion activated probe upon interaction with CO2 revived photophysical properties of probe, On-Off-On type fluorescence and enabled anion-induced CO2 sensing in the medium.

Synthesis and application of a new class of D–π–A type charge transfer probe containing imidazole – naphthalene units for detection of F− and CO2

A new class of D–π–A type charge transfer probe, 3 and 4, containing imidazole – naphthalene moieties as donor and acceptor, respectively, has been synthesized via a Suzuki coupling reaction. Probe 3, upon interaction with different classes of anions, showed high selectivity toward fluoride with a detection sensitivity of 4 ppb (0.22 μM). The in situ generated imidazolyl ion (3 + F−) enables the detection of CO2 with the restoration of the original absorption and emission properties of 3. The mode of interaction has been confirmed by 1H NMR and DFT studies which suggested the deprotonation of the –NH fragment of the imidazolyl unit in the presence of F−.