Pabitra Chattopadhyay

A new functionalized mesoporous matrix supported Pd(II)-Schiff base complex: an efficient catalyst for the Suzuki-Miyaura coupling reaction.

A new Pd(II) bounded 2D-hexagonally ordered functionalized MCM-41 type material (IV) has been synthesized. Functionalization was carried out by the anchoring of 3-aminopropyltriethoxysilane in the MCM-41 type mesoporous material, followed by grafting with 2,6-diacetylpyridine (DAP) to give a N3-type Schiff base chelating attachment for the Pd(II) species. Fourier transform infrared (FTIR), powder X-ray diffraction (PXRD) and high resolution transmission electron microscopy (HRTEM) studies have been used to characterize the material. Material IV behaves as a highly active catalyst towards Suzuki-Miyaura cross-coupling reaction for the synthesis of biaryl organics. In addition, IV acts as a true heterogeneous catalyst in coupling reaction. It was found that this catalyst is highly efficient and recyclable towards Suzuki-Miyaura reaction with high turn over frequencies. X-Ray photoelectron spectroscopic (XPS) analysis was employed to understand the oxidation state of the palladium atom in the catalyst (IV) and its loading in the material.

A New Half-Condensed Schiff Base Compound: Highly Selective and Sensitive pH-Responsive Fluorescent Sensor

A new probe, 3-[(3-benzyloxypyridin-2-ylimino)methyl]-2-hydroxy-5-methylbenzaldehyde (1-H) behaves as a highly selective fluorescent pH sensor in a Britton-Robinson buffer at 25 °C. The pH titrations show a 250-fold increase in fluorescence intensity within the pH range of 4.2 to 8.3 with a pK(a) value of 6.63 which is valuable for studying many of the biological organelles.

A highly selective fluorescent chemosensor for zinc ion and imaging application in living cells.

A new 2,6-bis(5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-4-methylphenol (1) serves as a highly selective and sensitive fluorescent probe for Zn(2+) in a HEPES buffer (50 mM, DMSO:water = 1:9 (v/v), pH = 7.2) at 25 °C. The increase in fluorescence in the presence of Zn(2+) is accounted for by the formation of dinuclear Zn(2+) complex [Zn(2)(C(35)H(25)N(6)O)(OH)(NO(3))(2)(H(2)O)] (2), characterized by X-ray crystallography. The fluorescence quantum yield of the chemosensor 1 is only 0.019, and it increases more than 12-fold (0.237) in the presence of 2 equiv of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to be either unchanged or weakened. By incubation of cultured living cells (A375 and HT-29) with the chemosensor 1, intracellular Zn(2+) concentrations could be monitored through selective fluorescence chemosensing.

A chelating resin containing bis(2-benzimidazolylmethyl)amine: synthesis and metal-ion uptake properties suitable for analytical application.

A new stable chelating resin was synthesized by incorporating the bis(2-benzimidazolyl methyl)amine into Merrifield polymer through CN covalent bond and characterized by elemental analysis, IR and thermal study. The sorption capacity of the newly formed resin for Ag(I), Cu(II), Fe(III), Hg(II) and Pb(II) as a function of pH have been studied. The resin exhibits no affinity for alkali or alkaline earth metals. In column operation it has been observed that Ag(I) in trace quantities can be separated from different complex matrices and Hg(II) can be removed from the river water spiked with Hg(II) at usual pH of natural waters.

Synthesis, spectral and electrochemical properties of 1-alkyl-2-(naphthyl-β-azo)imidazole complexes of platinum(II) and the reaction with pyridine bases. Single-crystal X-ray structure of dichloro-[1-ethyl-2-(naphthyl-β-azo)imidazole]platinum(II)

Abstract 1-Alkyl-2-(naphthyl-β-azo)imidazoles (β-NaiX, X=Me ( 3a ), Et ( 3b ), and CH 2 Ph ( 3c )) have been synthesized and reacted with K 2 PtCl 4 in boiling MeCN–water (1:1, v/v) and Pt(β-NaiX)Cl 2 ( 4 ) are isolated as orange–brown products. IR spectra support cis -PtCl 2 configuration and the structural configuration has been carried out by the X-ray diffraction study of Pt(β-NaiEt)Cl 2 ( 4b ). The treatment of aqueous silver nitrate solution, followed by the addition of pyridine bases (Rpy) and NaClO 4 to an acetonitrile solution of Pt(β-NaiX)Cl 2 under boiling conditions has yielded [Pt(β-NaiX)(Rpy) 2 ](ClO 4 ) 2 ( 5 – 7 ). The structure has been established by spectroscopic data (IR, UV–Vis, 1 H NMR). The redox properties of the complexes exhibit azo reductions.

Synthesis, spectral and electrochemical studies of arylazopyridine complexes of palladium(ii) with dioxolenes

Abstract Mixed-ligand complexes of the formula Pd(aap) ( o o ⌢ ) (5-8), where aap = 2 (arylazo)-pyridines and o o ⌢ = dioxolenes, viz. catechol (CATH 2 ), 4-tert-butyl catechol (TBCATH 2 ), 3,5-di-tert-butylcatechol (DTBCATH 2 ), and 2,3-dihydroxynaphthalene (DHN), were prepared and characterized by elemental analyses, IR, UV-vis and 1 H NMR data. Cyclic voltammograms suggest four successive one-electron responses and are highly sensitive to the nature of substituents. These complexes were found to show a ligand-toligand charge transfer (LLCT) band. The position of the LLCT band is largely dependent on the substituent type on the catechol frame and is qualitatively assigned as the 3b 1 (cat) → π*(aap) transition. Copyright

A water soluble FRET-based ratiometric chemosensor for Hg(II) and S2− applicable in living cell staining

A new highly sensitive and selective Hg(II) probe, 2-(rhodamine-b-hydrazido)-N-(quinolin-8-yl)acetamide (L1) was developed and characterized. L1 specifically binds to Hg(II) in the presence of a large excess of other competing ions with visually observable changes in both electronic and fluorescence spectral behaviour to make possible the naked eye detection of Hg(II) at a very low level (up to 4.5 × 10−7 M) through a fluorescence resonance energy transfer (FRET) process in HEPES buffer (1 mM, pH 7.4; 2% EtOH) at 25 °C. The theoretical and experimental kinetic study also support the binding of Hg(II) ion to induce the opening of the spirolactam ring in L1 for enabling the FRET process. Further studies reveal that the selective dissociation of the L–Hg complex in the presence of sulphide anions to restore the native structure of L1 is also useful in the detection of sulfide anions with a detection limit of a submicromolar range in the same medium of HEPES buffer (1 mM, pH 7.4; 2% EtOH) at 25 °C. L1 could be employed as a FRET based time dependent reversible chemosensor for imaging Hg(II) in living cells and whole bodies, and also could be used as an imaging probe for the detection of sulfide anions in HeLa cells.

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.

A cell permeable Cr3+ selective chemosensor and its application in living cell imaging

An efficient fluorescent Cr3+ receptor, 2-(5,6-dihydro-benzo-[4,5]imidazo[1,2-c]quinazolin-6-yl)-quinolin-8-ol (H2L1) was synthesized and characterized by physico–chemico and spectroscopic tools along with single crystal X-ray crystallography. This probe (H2L1) behaves as a highly selective fluorescent sensor for Cr3+ ions at biological pH in ethanol–water (1 : 5, v/v) HEPES buffer (0.1 M, pH 7.4) at 27 °C. Metal ions, viz. alkali (Na+, K+), alkaline earth (Mg2+, Ca2+), and transition-metal ions ((Mn2+, Fe3+, Co3+, Ni2+, Cu2+, Zn2+) and Pb2+, Ag+ did not interfere. The lowest detection limit for Cr3+ was calculated to be 3.6 × 10−7 mol L−1 within a very short responsive time (15–20 s) in ethanol–water (1 : 5, v/v) HEPES buffer (0.1 M, pH 7.4) at 27 °C. The sensor is efficient for detection of Cr3+ in vitro, developing a good image of the biological organelles.

Synthesis, characterization, crystal structure, and DNA-binding of ruthenium(II) complexes of heterocyclic nitrogen ligands resulting from a benzimidazole-based quinazoline derivative

The reaction of cis-[RuCl2(dmso)4] with [6-(2-pyridinyl)-5,6-dihydrobenzimidazo[1,2-c]quinazoline] (L) afforded in pure form a blue ruthenium(II) complex, [Ru(L1)2] (1), where the original L changed to [2-(1H-benzoimidazol-2-yl)-phenyl]-pyridin-2-ylmethylene-amine (HL1 ). Treatment of RuCl3 · 3H2O with L in dry tetrahydrofuran in inert atmosphere led to a green ruthenium(II) complex, trans-[RuCl2(L2)2] (2), where L was oxidized in situ to the neutral species 6-pyridin-yl-benzo[4,5]imidazo[1,2-c]quinazoline (L2 ). Complex 2 was also obtained from the reaction of RuCl3 · 3H2O with L2 in dry ethanol. Complexes 1 and 2 have been characterized by physico-chemical and spectroscopic tools, and 1 has been structurally characterized by single-crystal X-ray crystallography. The electrochemical behavior of the complexes shows the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of these complexes with calf thymus DNA by using absorption and emission spectral studies allowed determination of the binding constant K b and the linear Stern–Volmer quenching constant K SV.