Chanchal Chakraborty

Fluorene-based chemodosimeter for “turn-on” sensing of cyanide by hampering ESIPT and live cell imaging

A new salicylaldehyde appended fluorene-based chemodosimeter (FSal) has been designed by taking consideration of the special nucleophilicity of cyanide ion. FSal shows selective affinity towards CN- over other anions (namely F-, Br-, NO3 -, ClO4 -, N3 -, H2PO4 -, AcO-, I-, Cl-, and NO2 -) through turn-on fluorescence with a minimum detection limit of 0.06 ppm. The turn-on fluorescence of the FSal-CN complex resulting from hampering ESIPT is also supported by DFT and TDDFT calculations. Biological compatibility and live cell imaging of this unique probe have also been explored.

Complexation of amyloid fibrils with charged conjugated polymers.

It has been suggested that conjugated charged polymers are amyloid imaging agents and promising therapeutic candidates for neurological disorders. However, very less is known about their efficacy in modulating the amyloid aggregation pathway. Here, we studied the modulation of Parkinsons disease associated α-synuclein (AS) amyloid assembly kinetics using conjugated polyfluorene polymers (PF, cationic; PFS, anionic). We also explored the complexation of these charged polymers with the various AS aggregated species including amyloid fibrils and oligomers using multidisciplinary biophysical techniques. Our data suggests that both polymers irrespective of their different charges in the side chains increase the fibrilization kinetics of AS and also remarkably change the morphology of the resultant amyloid fibrils. Both polymers were incorporated/aligned onto the AS amyloid fibrils as evident from electron microscopy (EM) and atomic force microscopy (AFM), and the resultant complexes were structurally distinct from their pristine form of both polymers and AS supported by FTIR study. Additionally, we observed that the mechanism of interactions between the polymers with different species of AS aggregates were markedly different.

Immobilization of poly(fluorene) within clay nanocomposite: an easy way to control keto defect.

Blue light emitting cationic polyfluorene polymer(PF)/montmorillonite (MMT) nanocomposites were prepared by solution intercalation and exfoliation method to evaluate the effect of MMT on the nanocomposite structures, properties and morphologies. The properties of PF-MMT composites, containing 1-50 mass% MMT, were characterized unambiguously with the help of multiple analytical techniques, with focus on the keto defect and photostability of PF in the nanocomposites. XRD and HRTEM studies reveal both exfoliation of MMT galleries at lower content of MMT in composites and intercalation of PF chains into the MMT galleries at higher MMT content. The nanocomposites show higher thermal stability than pristine PF as anchorage of nanoclay in PF matrix occur through the electrostatic interaction between nanoclay and polymer. The decrease in Si-O-Si stretching frequency during exfoliation is much higher than in intercalation, as Si-O-Si experience lesser hindrance to vibrate in exfoliated MMT galleries. The gradual redshift of π-π(*) transition peak of PF with increasing MMT content in composites confirms the uncoiling of PF in clay galleries. The photoluminescence characteristics reveal interruption of interchain interaction in this intercalated and exfoliated organic/inorganic hybrid system, which reduces the low-energy emission that results from keto defect. Due to very high aspect ratio of MMT, it can act as an efficient exciton blocking layer and a barrier to oxygen diffusion, which may lead to a device with high color purity and enhanced photostability. Again current-voltage characteristics of nanocomposite films confirm the retention of LED properties after nanocomposite formation.

Platinum(II)-Based Metallo-Supramolecular Polymer with Controlled Unidirectional Dipoles for Tunable Rectification.

A platinum(II)-based, luminescent, metallo-supramolecular polymer (PolyPtL1) having an inherent dipole moment was synthesized via complexation of Pt(II) ions with an asymmetric ligand L1, containing terpyridyl and pyridyl moieties. The synthesized ligand and polymer were well characterized by various NMR techniques, optical spectroscopy, and cyclic voltammetry studies. The morphological study by atomic force microscopy revealed the individual and assembled polymer chains of 1-4 nm height. The polymer was specifically attached on Au-electrodes to produce two types of film (films 1 and 2) in which the polymer chains were aligned with their dipoles in opposite directions. The Au-surface bounded films were characterized by UV-vis, Raman spectroscopy, cyclic voltammetry, and atomic force microscopy study. The quantum mechanical calculation determined the average dipole moment for each monomer unit in PolyPtL1 to be about 5.8 D. The precise surface derivatization permitted effective tuning of the direction dipole moment, as well as the direction of rectification of the resulting polymer-attached molecular diodes. Film 1 was more conductive in positive bias region with an average rectification ratio (RR = I(+4 V)/I(-4 V)) ≈ 20, whereas film 2 was more conducting in negative bias with an average rectification ratio (RR = I(-4 V)/I(+4 V)) ≈ 18.

Selective detection of cyanide by a polyfluorene-based organoboron fluorescent chemodosimeter

Organoboron-based polymeric fluorescent probes have been designed and synthesized for the sensitive and selective detection of toxic cyanide ions by a fluorescence “turn off” mechanism. Bis-(bromohexyl)-polyfluorenes have been synthesized by Pd catalyzed Suzuki cross-coupling polymerization. Its treatment with (Mes)2BF achieved organoboron-appended polyfluorene (PFBP). PFBP that is soluble in common organic solvents shows bright blue luminescence under UV-irradiation. The substantial quenching of the luminescence of a PFBP solution in the presence of toxic cyanide ions (CN−) has been observed. This is due to the formation of strong covalent bonds between the cyanide ions and trivalent boron centres of the side chains of the PFBP, which is further supported by NMR studies. The polyfluorene backbone of the PFBP acts as the fluorophore, and the boron centre as the cyanide acceptor. This novel type of polymeric material will find a potential application in sensor technology, as the detection limit is very low at ∼0.5 μM.

Layered double hydroxide induced advancement in joint prosthesis using bone cement: the effect of metal substitution

Poly(methyl methacrylate) based bone cement and its nanocomposites with layered double hydroxide (LDH) have been developed with greater mechanical strength and biocompatibility as a grouting material for total joint arthroplasty. Bivalent magnesium has been replaced with trivalent aluminium with various mole ratios, keeping the layered pattern of the LDH intact, to cater for the effect of varying substitution on the property enhancement of the nanocomposites. The intercalation of polymer inside the LDH layers makes them disordered and mechanically stiffer and tougher by more than 100%. The thermal stability of bone cement has increased by more than 30 °C in the presence of 1 wt% of nanoLDH, homogenously distributed in the bone cement matrix by creating an inorganic thermal barrier out of the LDH dispersion. The improvement in the properties of the nanocomposites has been explained in terms of the strong interaction between nanoLDH and polymer. The superior bioactivity and biocompatibility of the nanocomposites, as compared to pure bone cement, has been established through hemolysis assay, cell adhesion, MTT assay and cell proliferation using fluorescence imaging. The developed nanocomposites have been used as a grouting material and significant improvements have been achieved in fatigue behaviour with gradual increment of Al substitution in the Mg : Al mole ratio in nanoLDH, demonstrating the real use of the material in the biomedical area. In vivo experiments on rabbits clearly revealed the superior efficacy of bone cement nanocomposites, over pure bone cement and a blank.

How the stereochemistry decides the selectivity: an approach towards metal ion detection

The stereochemistry of the coordination sites of a ligand plays a specific role in its binding with metals in a specific geometry. Herein, we designed and successfully prepared three different fluorene-based (A–B)n-type salen polymers (achiral FSP1, FSP2, and chiral FSP3), wherein the A-part is fluorophore and the B-part is the receptor. In the receptor, the coordination sites have four atoms (ONNO) that can bind any metal ion, but the orientation of ONNO differs in the three polymers. This orientation of the coordination site (i.e., the stereochemistry) into the receptor part of the polymer makes them more selective for a particular metal ion. In this study, it is shown that the orientation of the coordination sites of the receptor in the main chain polymer significantly determines the selective detection behavior for metal ions. Among the three polymers, FSP1 and FSP2 are sensitive towards different metal ions but are not selective towards any particular metal ion. However, in contrast, FSP3 is highly sensitive and selective to Zn2+ ions over other metal ions with a turn-on visible bright blue fluorescent color. This turn-on detection of the polymer is possibly due to the suppression of photo-induced electron transfer (PET) upon binding with Zn2+ ions. Theoretical calculations were also performed to show the orientation of the coordination sites. In FSP3, the coordination sites orient in a distorted tetrahedral fashion, which is very much prone to bind Zn2+ in a nearly tetrahedral geometry and that makes it more selective for Zn2+ ions only. The coordination geometry was also supported by 2D NMR studies. This report provides a template for the suitable design of a Zn2+ sensor, depending on the nature of the receptor incorporated into the main chain polymer.

One-Dimensional Anhydrous Proton Conducting Channel Formation at High Temperature in a Pt(II)-Based Metallo-Supramolecular Polymer and Imidazole System

One dimensional (1D) Pt(II)-based metallo-supramolecular polymer with carboxylic acids (polyPtC) was synthesized using a new asymmetrical ditopic ligand with a pyridine moiety bearing two carboxylic acids. The carboxylic acids in the polymer successfully served as apohosts for imidazole loaded in the polymer interlayer scaffold to generate highly ordered 1D imidazole channels through the metallo-supramolecular polymer chains. The 1D structure of imidazole loaded polymer (polyPtC-Im) was analyzed in detail by thermogravimetric analysis, powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet-visible and photoluminescence spectroscopic measurements. PolyPtC-Im exhibited proton conductivity of 1.5 × 10-5 S cm-1 at 120 °C under completely anhydrous conditions, which is 6 orders of magnitude higher than that of the pristine metallo-supramolecular polymer.

Geometrically isomeric Pt( ii )/Fe( ii )-based heterometallo-supramolecular polymers with organometallic ligands for electrochromism and the electrochemical switching of Raman scattering

Heterometallo-supramolecular polymers with Pt(II) and Fe(II) ions introduced alternately (cis-polyPtFe and trans-polyPtFe) in a precise way were prepared successfully by the 1:1 complexation of Fe(II) ions with cis- or trans-conformational organo-Pt(II) ligands. The conformational difference between cis- and trans-greatly changed the morphology, crystallinity, ionic conductivity, electrochromic properties, and redox-triggered fluorescence of the polymers. The cis-polyPtFe exhibited better crystallinity and low ionic conductivity, whereas trans-polyPtFe showed an amorphous nature with high ionic conductivity. Both the polymers exhibited reversible electrochromism between purple and yellow colors due to the redox of Fe(II)/(III) upon applying a potential of 0 V or +3 V. The trans-polyPtFe showed better electrochromic stability and response times compared to cis-polyPtFe. In addition, the trans-polyPtFe also showed an improved response in redox-triggered Raman scattering switching compared to cis-polyPtFe over a long time range.

A polyfluorene based zwitterionic fluorescent probe for response towards biological species in aqueous media

Water soluble zwitterionic fluorescent conjugated boronic acid-bearing polyfluorene (PFBA) has been prepared from poly(9,9′-(6′′-bromohexyl)fluorene-co-alt-1,4-phenylene) (polymer 3) through a post-polymerized quaternization with 3-pyridineboronic acid. Titration of diol containing monosaccharides (D-glucose and D-fructose), L-ascorbic acid and L-DOPA with PFBA polymer in 0.1 M phosphate buffer (pH 7.4) solution results in significant concentration dependent quenching of the blue fluorescence of the polymer due to static quenching as the bio-analytes form a ground state boronate ester complex with PFBA. Upon addition of D-glucose, the emission colour of PFBA changes to greenish-yellow owing to the effective induced aggregated polymer structure. PFBA also exhibits maximum response to the biological analytes at pH 7.4 which provides a scope for PFBA to be used in biological systems.