Raihan Uddin

A BODIPY/pyrene-based chemodosimetric fluorescent chemosensor for selective sensing of hydrazine in the gas and aqueous solution state and its imaging in living cells

A BODIPY-based pyrenebutyrate-linked (BPB) chromogenic and fluorogenic probe was synthesized and characterized for the specific detection of hydrazine. In the presence of hydrazine, BODIPY-based pyrenebutyrate was selectively deprotected, producing switch off meso-phenoxyBODIPY along with a color change from yellow to brown, allowing colorimetric detection of hydrazine by the naked eye. Selectivity experiments proved BPB has excellent selectivity to hydrazine over other environmentally abundant ions and common amine-containing species. Probe BPB was also successfully applied in vapor hydrazine detection into a solid state over other interfering volatile analytes. Furthermore, the probe BPB coated with silica gel TLC plates could act as a visual and fluorimetric probe for hydrazine vapor detection. The probe (BPB) has been shown to detect hydrazine up to 1.87 μM at pH 7.4. DFT and TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of the probe and hydrazinolysis product. BPB can also be used for the detection of hydrazine in Vero cells without appreciable interference from other biologically abundant analytes.

A highly sensitive fluorescent probe for detection of hydrazine in gas and solution phases based on the Gabriel mechanism and its bioimaging

A new probe 2-benzo[1,2,5]thiadiazol-4-yl-isoindole-1,3-dione (BTI) based on the Gabriel reaction mechanism was synthesized and characterized for the specific detection of hydrazine with high selectivity against other amines in an organo-aqueous solution. Upon hydrazinolysis of BTI in the presence of hydrazine in a H2O–DMSO (4 : 6, v/v) solution (10 mM HEPES buffer, pH 7.4) at room temperature, the chemosensor produces fluorescent aminobenzthiadiazole with a maximum emission at 498 nm along with a color change from colorless to green, allowing selective colorimetric and fluorometric detection of hydrazine by the naked eye. Probe BTI was also successfully applied in vapor phase hydrazine detection into a solid state over other interfering volatile analytes. Furthermore, the probe BTI coated with silica gel TLC plates could act as a visual and fluorimetric probe for hydrazine vapor detection. The experimental detection limit of hydrazine is 2.9 ppb, which is well below the accepted limit (10 ppb) for hydrazine set by the U.S. Environmental Protection Agency (EPA). DFT and TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of probe and hydrazinolysis products. Additionally, probe BTI could also be applied for the imaging of hydrazine in living cells.

Pyrene appended thymine derivative for selective turn-on fluorescence sensing of uric acid in live cells

A new ‘turn-ON’ fluorescent probe, pyrene appended thymine acetamide (PTA), with high sensitivity and selectivity for the detection of uric acid (UA) was developed and first time imaging of uric acid in living cells in water was achieved. 1H NMR and density functional studies on the system have been carried out to determine the nature of the interaction between probe PTA and UA.

Phenanthroline-fluorescein molecular hybrid as a ratiometric and selective fluorescent chemosensor for Cu2+ via FRET strategy: synthesis, computational studies and in vitro applications

Abstract A FRET-based chemosensor L containing donor phenanthroline and acceptor fluorescein moiety was designed, synthesised and characterised for the ratiometric fluorescent detection of Cu2+ in organo-aqueous solution. Probe L showed high selectivity and excellent sensitivity towards Cu2+ ions by exhibiting both colorimetric and fluorometric changes due to opening of the spirolactum ring of fluorescein upon complexation with Cu2+. In presence of Cu2+ ions, probe L formed L-Cu2+ complex in 1:1 stoichiometric fashion which is established on the basis of Job’s plot and mass spectroscopy. We also performed DFT computational studies to know the binding nature and coordination feature of the complex. Furthermore, fluorescence imaging studies revealed that probe L was cell permeable and could be used to detect intracellular Cu2+ in living cells.

Segregation of nod-containing and nod-deficient bradyrhizobia as endosymbionts of Arachis hypogaea and as endophytes of Oryza sativa in intercropped fields of Bengal Basin, India.

Bradyrhizobial invasion in dalbergoid legumes like Arachis hypogaea and endophytic bacterial invasions in non-legumes like Oryza sativa occur through epidermal cracks. Here, we show that there is no overlap between the bradyrhizobial consortia that endosymbiotically and endophytically colonise these plants. To minimise contrast due to phylogeographic isolation, strains were collected from Arachis/Oryza intercropped fields and a total of 17 bradyrhizobia from Arachis (WBAH) and 13 from Oryza (WBOS) were investigated. 16SrRNA and concatenated dnaK-glnII-recA phylogeny clustered the nodABC-positive WBAH and nodABC-deficient WBOS strains in two distinct clades. The in-field segregation is reproducible under controlled conditions which limits the factors that influence their competitive exclusion. While WBAH renodulated Arachis successfully, WBOS nodulated in an inefficient manner. Thus, Arachis, like other Aeschynomene legumes support nod-independent symbiosis that was ineffectual in natural fields. In Oryza, WBOS recolonised endophytically and promoted its growth. WBAH however caused severe chlorosis that was completely overcome when coinfected with WBOS. This explains the exclusive recovery of WBOS in Oryza in natural fields and suggests Nod-factors to have a role in counterselection of WBAH. Finally, canonical soxY1 and thiosulphate oxidation could only be detected in WBOS indicating loss of metabolic traits in WBAH with adaptation of symbiotic lifestyle.

“Turn-on” fluorescence sensing of cytosine: development of a chemosensor for quantification of cytosine in human cancer cells

A simple new chemosensor, pyrene-appended 5-hydroxyisophthalic acid derivative (PIA), was developed and characterized for selective detection and quantification of cytosine in different human cancer cells. PIA shows “turn-on” fluorescence in presence of cytosine through intermolecular hydrogen bonding with a detection limit of 32 nM at neutral pH.

Installation of efficient quenching groups of a fluorescent probe for the specific detection of cysteine and homocysteine over glutathione in solution and imaging of living cells

Abstract Herein, we report the synthesis and characterisation of a new fluorescent probe 4-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-benzaldehyde (NBOB) installed with quenching groups for highly selective and sensitive sensing of biothiols. The probe itself is non-fluorescent due to the presence of quenching groups and photoinduced electron transfer (PET) process. Thus, sensitivity of the probe towards thiols was significantly improved by quenching effects. NBOB has been shown to exhibit selective reactivity towards cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) under stoichiometric conditions. The response mechanism was proved by 1H NMR, LCMS and theoretical calculation. The probe NBOB has been shown to react with Cys present in Vero cells by fluorescence microscopy.