Tamal Ghosh

Visual sensing of fluoride ions by dipyrrolyl derivatives bearing electron-withdrawing groups

Two new, easy-to-prepare dipyrrolyl derivatives endowed with electron-withdrawing quinone or dicyano functionalities in their architecture permit the detection of fluoride ions under visual (naked-eye) as well as optical (absorption and fluorescence) and electrochemical conditions in organic solvents

A colorimetric chemosensor for both fluoride and transition metal ions based on dipyrrolyl derivative

The synthesis, characterization and ion binding studies of 2,3-di(1H-2-pyrrolyl)pyrido[2,3-b]pyrazine (1) have been described. 1, which has been targeted with a view to sensing both F- and transition metal ions, exhibits binding-induced color changes from yellowish green to red/brown observable by the naked eye. The binding site for the metal ion in the system has been unambiguously established by single-crystal X-ray diffraction study of a Ni(II) complex of 1. While the estimated value of the binding constant of 1 with F- is 4.9 x 10(3) M(-1), the binding constants for the cations are found to be two orders higher in magnitude in acetonitrile. Even though 1 possesses two separate binding sites for F- and metal ions, it is shown that the presence of the cation influences the binding of the anion and vice versa. The binding constant values of an ion in the presence of oppositely charged species are measured to be significantly lower.

Highly selective colorimetric and fluorometric chemosensor for cyanide on silica gel and DMSO/H2O (7:3 v/v) mixed solvent and its imaging in living cells

The chemosensor 2,3-bis((E)-((2-hydroxynaphthalen-1-yl)methylene)amino)maleonitrile (1) has been synthesized using 2-hydroxy-1-napthaldehyde and 2,3-diaminomaleonitrile and characterized. Sensor 1 exhibits selective binding with CN(-) in dimethyl sulfoxide (DMSO)/H2O (7:3 v/v) and DMSO/aqueous Tris (Tris(hydroxymethyl)aminomethane) buffer (7:3 v/v, 10 mM, pH 7.2) media with significant changes in its UV-visible and fluorescence spectra. Titration of 1-Zn(II) complex with CN(-) ion in DMSO/aqueous Tris buffer (7:3 v/v, 10 mM, pH 7.2) regenerates the free sensor 1, as supported by UV-visible spectra. (1)H NMR titration of 1 with CN(‒) in (CD3)2SO confirms the hydrogen-bonding interaction between the two OH groups of the former and the latter in bidentate manner. Sensor 1 impregnated on silica gel thin layer chromatography (TLC) strip followed by dipping in anion solutions in DMSO/H2O (7:3 v/v) generates yellow to red spectacular colour change with CN(-) ion selectively which can be exploited as potential tool for ready-made detection of toxic CN(-) ion in environmental and analytical chemistry. Similar visual change in colour for 1 is observed selectively with CN(-) also when both of them are taken in DMSO/H2O (7:3 v/v) solution. Sensor 1 is used as an imaging reagent for detection of the cellular uptake of CN(-) ion in Baby Hamster Kidney (BHK-21) cells.

Chitosan containing azo-based Schiff bases: thermal, antibacterial and birefringence properties for bio-optical devices

The present investigation describes the preparation of chitosan/2-hydroxy-5-(4-nitrophenylazo)-benzaldehyde (CHNAB) and chitosan/2-hydroxy-5-(4-tolylazo)-benzaldehyde (CHMAB) derivatives (in 4 : 5 molar ratio) under mild conditions. These derivatives were synthesized by 79% and ≤90% deacetylated chitosan in an isopropyl alcohol/water mixture and dimethyl sulfoxide. The thermal properties of the derivatives were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). CHNAB shows an endothermic peak at 212 °C and exothermic peak at 231 °C due to phase change for cis–trans isomerisation, whereas, in CHMAB, only the endothermic peak at 222 °C is seen due to the absence of cis–trans isomerisation. Toxicity has been reduced in chitosan based azo derivatives, as compared to the corresponding azo compounds, as seen by the antibacterial results where S. aureus (Gram positive) shows ZOI 26 mm for CHNAB and 38 mm for CHMAB. The transmitted signal intensity induced by the birefringence as shown by CHNAB as πdΔn/λ is much less than 1. The transmitted signal is effectively proportional to (Δn)2 because of the nitro group behaving like an auxochrome. The study on the optical birefringence properties of the azo-based chitosan derivatives indicates that the prepared derivatives may be used as bio-optical devices for biomedical applications.

Colorimetric and ON–OFF–ON fluorescent chemosensor for the sequential detection of Cu(II) and cysteine and its application in imaging of living cells

An easy-to-prepare colorimetric and ON–OFF–ON fluorescent naphthol derivative 1 has been synthesized and characterized for sequential detection of Cu2+ and cysteine. Chemosensor 1 detects Cu2+ selectively in DMSO/H2O (3 : 7 v/v) by changing its UV-visible spectrum and color (colorless to yellow), leading to the formation of 1-Cu(II) complex. The resultant 1-Cu(II) complex recognizes cysteine (Cys) and the solution turns colorless with regeneration of the absorption band of 1. The detection limit of 1 for Cu2+ ion is found to be 0.27 μM, which is much lower than that recommended by WHO for drinking water (30 μM). Cu2+ ion exhibits quenching of the fluorescence intensity of 1, which is restored upon the addition of cysteine. Chemosensor 1 is used as an imaging reagent for detection of the cellular uptake of Cu2+ ion in A549 cell line (human lung carcinoma cell).

Studies on thermo-optic property of chitosan–alizarin yellow GG complex: a direction for devices for biomedical applications

The optical parameters including the refractive index (n) and thermo-optic coefficient, TOC (dn/dT), the dielectric constant (ε) and its variation with temperature, and the thermal volume expansion coefficient (β) and its variation with temperature of chitosan–alizarin yellow GG (CS–AY GG) complex were examined. The dn/dT and ε-values for the polymer derivative were in the range −2.5 × 10−4 to 1.2 × 10−4°C−1 and 2.2 to 2.3, respectively. The dn/dT values were larger than that of inorganic glasses such as zinc silicate glass (5.5 × 10−6°C−1) and borosilicate glass (4.1 × 10−6°C−1) and were larger than that of organic polymers such as polystyrene (−1.23 × 10−4°C−1) and PMMA (−1.20 × 10−4°C−1). The ε-values are lower than optically estimated ε-values of conventional polymer (3.00), aliphatic polyimide (2.5) and semi-aromatic polyamide (2.83). The obtained results of chitosan derivative are expected to be useful for optical switching and optical waveguide areas for devices of biomedical applications.

Selective colorimetric sensing of CN− by dihydropyrazol-3-ol derivative in CH3CN/H2O medium

The synthesis, characterisation and anion binding studies of 2-(2,4-dinitrophenyl)-3-ethoxy-5-methyl-3,4-dihydro-2H-pyrazol-3-ol (1) have been described. 1, bearing electron withdrawing 2,4-dinitophenyl group in its structure, recognises CN− selectively in CH3CN/H2O (4:1, v/v) medium with a binding constant of 440 M− 1 and visible colour change from yellow to red, whereas no colour change is observed in the presence of other anions such as F− , Cl− , Br− , I− , , AcO− , PhCOO− . Interestingly, in CH3CN, 1 is responsive not only to CN− but also to F− , , AcO− and PhCOO− with a binding-induced visible colour change from yellow to reddish-brown. The strongest binding ability of 1 is observed with CN− in CH3CN, the binding constant being 1.34 × 105 M− 1, whereas the binding constants of F− and oxyanions ( , AcO− , PhCOO− ) are found to be lower by one order or more in magnitude. 1H NMR titrations of 1 are carried out with CN− and F− , which not only provide the evidence for the hydrogen-bonding interaction between the alcohol –OH of 1 and anions, but also offer some invaluable information about the structure of the sensor–anion complexes.