Satyen Saha

A new class of magnetic fluids: bmim[FeCl/sub 4/] and nbmim[FeCl/sub 4/] ionic liquids

The responses to a magnet of two room-temperature ionic liquids containing tetrachloroferrate(III) ions, 1-butyl-3-methylimidazolium tetrachloroferrate (bmim[FeCl/sub 4/]) and 1-butyronitrile-3-methylimidazolium tetrachloroferrate (nbmim[FeCl/sub 4/]) are compared. Although their magnetic susceptibilities are similar, the observed responses are distinct from each other, suggesting that the response is determined not only by the magnetic susceptibility but also by the other factors including density, viscosity, and surface tension. The two magnetic ionic liquids constitute a new class of magnetic fluids that hold many attractive physical properties for practical applications.

Fluorescence signalling of transition metal ions by multi-component systems comprising 4-chloro-1, 8-naphthalimide as fluorophore

Abstract Fluorescence of 1a and 1b is ‘switched on’ by the quenching transition metal ions and the extent of fluorescence enhancement is found to be considerably higher than that expected on the basis of photoinduced intramolecular electron transfer in the systems. The observation has been rationalised taking into account the hydrated nature of the transition metal salts and preferential solvation of the fluorophore by the water molecules.

Solvation dynamics of Nile Red in a room temperature ionic liquid using streak camera

Time-resolved fluorescence behavior of Nile Red (NR) has been studied using a streak camera in a room temperature ionic liquid, [bmim]PF6. Wavelength dependent fluorescence decay and time dependent fluorescence Stokes shift have been observed. The time-correlated spectral shift function, C(t), indicator for solvation dynamics of NR in [bmim]PF6, is found to be biexponential with two well-separated time constants: 0.13 and 1.25 ns. The short and the long component of the dynamics have been explained in terms of the translational motion of the anion and a collective motion of the cation and anion, respectively. The effect of two different conformers of the cation of this room temperature ionic liquid, as revealed in the recent studies, on the long time constant is also discussed.

Heteroleptic Dipyrrinato Complexes Containing 5-Ferrocenyldipyrromethene and Dithiocarbamates as Coligands: Selective Chromogenic and Redox Probes

Six heteroleptic dipyrrinato complexes [Ni(fcdpm)(dedtc)] (1), [Ni(fcdpm)(dipdtc)] (2), [Ni(fcdpm)(dbdtc)] (3), [Pd(fcdpm)(dedtc)] (4), [Pd(fcdpm)(dipdtc)] (5), and [Pd(fcdpm)(dbdtc)] (6) (fcdpm = 5-ferrocenyldipyrromethene; dedtc = diethyldithiocarbamate; dipdtc = diisopropyldithiocarbamate; dbdtc = dibutyldithiocarbamate) have been synthesized and characterized by elemental analyses and spectral (ESI-MS, IR, (1)H, (13)C NMR, UV-vis) and electrochemical studies. Crystal structures of 1, 2, 4, and 5 have been authenticated by X-ray single-crystal analyses. Nickel-based complexes 1-3 display selective chromogenic and redox sensing for Hg(2+) and Pb(2+) ions, while palladium complexes 4-6 display selective chromogenic and redox sensing only for Hg(2+). Electronic absorption, ESI-MS, and electrochemical studies indicated that sensing arises from interaction between 1-3 and Hg(2+)/Pb(2+) through sulfur of the coordinated dithiocarbamates, while it arises from the pyrrolic nitrogen of fcdpm and dithiocarbamate sulfur from 4-6 and Hg(2+). Different modes of binding between Ni and Pd complexes have further been supported by theoretical studies. The receptor-cation binding constants (K(a)) and stoichiometry between probes and Hg(2+)/Pb(2+) have been estimated by the Benesi-Hildebrand method and Jobs plot analysis. Detection limits for 1-3 toward Hg(2+)/Pb(2+) and 4-6 for Hg(2+) have been found to be reasonably high.

Singlet excited state dipole moments of dual fluorescent N-phenylpyrroles and 4-(dimethylamino)benzonitrile from solvatochromic and thermochromic spectral shifts

The excited state dipole moments mue(ICT) and mue(LE) of the dual fluorescent molecules N-phenylpyrrole (PP), N-(4-cyanophenyl)pyrrole (PP4C) and N-(3-cyanophenyl)pyrrole (PP3C) are determined from solvatochromic and thermochromic measurements. It is shown that the best results are obtained when the solvatochromic as well as the thermochromic analysis of the spectral shifts is made relative to 4-(dimethylamino)benzonitrile (DMABN) as the model compound. Direct thermochromic experiments with PP4C, PP3C and DMABN in diethyl ether lead to reasonable results, but unrealistically large dipole moments mue(ICT) are found for PP, PP4C, PP3C and DMABN in acetonitrile, ethyl cyanide and n-propyl cyanide. The mue(ICT) values obtained for the N-phenylpyrroles from the thermochromic analysis in these solvents relative to DMABN (17 D) do not depend on solvent polarity: 13 D for PP, 15 D for PP4C and PP3C. The spectral shifts for the LE emission of the N-phenylpyrroles and aminobenzonitriles are much smaller than those for the ICT fluorescence, resulting in relatively small values for mue(LE). With PP and N-(4-methylphenyl)pyrrole (PP4M) the problem arises that one of the two values calculated by solving the quadratic equation for mue(LE) in the solvatochromic and thermochromic analysis cannot be discarded on photophysical or molecular grounds, as is the case for the other molecules. The experimental data for mue(ICT) of PP and PP4C are compared with theoretical values calculated for coplanar (PICT) and perpendicular (TICT) conformations of the pyrrole and phenyl or cyanophenyl groups. The experimental ICT dipole moment of PP4C has a value in between the theoretical results for mue(PICT) and mue(TICT), whereas the data for PP tend to favour the TICT configuration. It appears that in the LE state of PP and PP4M a negative charge remains on the pyrrole moiety, whereas a charge reversal takes place for the LE state of PP3C and the ICT state of PP, PP4C and PP3C.

Synthesis and Characterization of Stereocontrolled Poly(N-isopropylacrylamide) Hydrogel Prepared in the Presence of Y(OTf)3 Lewis Acid

Macroporous poly(N-isopropylacrylamide) (PNIPAM) hydrogels have been prepared in methanol-water (1:1, v/v) mixture in the presence of 0, 0.05, 0.1, 0.15, and 0.2 M Y(OTf)(3) Lewis acid concentrations. Synthesis of the corresponding linear PNIPAM homopolymers in the absence of a cross-linker keeping all other conditions the same shows that the isotacticity (meso dyad, %) and the cloud point temperature of the resulted in polymers increases and decreases, respectively, with the increase in the concentration of the Lewis acid. SEM micrographs reveal that the resulted hydrogels are highly porous. Swelling ratios of all the hydrogels in water decrease with the increase in the temperature. Moreover, swelling ratios of all the hydrogels in different methanol-water mixtures pass through a minimum in the co-nonsolvency zone, and the co-nonsolvency zone shifts toward the lower methanol-content solvent mixture with gradual increase in the Lewis acid concentration. Deswelling rate of the hydrogel prepared in methanol-water (1:1, v/v) mixture is much faster than that of the conventional hydrogel prepared in water. Moreover, the deswelling rate slightly increases with the hydrogels prepared with the increasing concentrations of Lewis acid. But, the reswelling rate of the hydrogels follows almost the reverse order. All these results have been explained on the basis of the formation of highly porous hydrogels with higher isotactic PNIPAM chain segment owing to the faster polymerization rate in the methanol-water mixture in the presence of Lewis acid and the co-nonsolvency behavior of the methanol-water (1:1, v/v) mixture toward PNIPAM chain segment in the PNIPAM hydrogel.

Recyclable, magnetic ionic liquid bmim[FeCl4]-catalyzed, multicomponent, solvent-free, green synthesis of quinazolines

An atom-efficient, eco-friendly, solvent-free, high yielding, multicomponent green strategy to synthesize highly functionalized quinazoline derivatives by the one-pot reaction of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate is presented. Magnetic IL, butylmethylimidazolium tetrachloroferrate (bmim[FeCl4]) has been used successfully as a catalyst in a multicomponent synthetic strategy for the first time. The catalytic cycle and a tentative reaction mechanism were discussed and experimentally verified. Structural and optical properties of the synthesized quinazolines are also described.

Synthesis and study of the properties of stereocontrolled poly(N-isopropylacrylamide) gel and its linear homopolymer prepared in the presence of a Y(OTf)3 Lewis acid: effect of the composition of methanol-water mixtures as synthesis media.

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels and the corresponding linear homopolymers were synthesized in different methanol-water mixtures (x(m) = 0, 0.13, 0.21, 0.31, 0.43, 0.57, and 0.76, where x(m) is the mole fraction of methanol) in the presence of 0.1 M Y(OTf)(3) Lewis acid. The isotacticity (meso dyad (m), %) and cloud-point temperature of these homopolymers were gradually increased and decreased, respectively, with the increase in the x(m) values of the synthesis solvent mixtures. Moreover, the corresponding linear PNIPAM homopolymers prepared in the absence of Y(OTf)(3) showed an almost constant isotacticity of m = 45% and a cloud-point temperature of 33.0 °C. A SEM study revealed that the resulting hydrogels were highly porous except for the gels prepared at x(m) = 0 and 0.76. The swelling ratios of these hydrogels in water at different temperatures and in different methanol-water mixtures at 20 °C and the deswelling rate and the reswelling rate of these hydrogels were studied. All of these swelling results were compared with that of the corresponding gels prepared in the absence of a Lewis acid (Biswas, C. S.; Patel, V. K.; Vishwakarma, N. K.; Mishra, A. K.; Bhimireddi, R.; Rai, R.; Ray, B. J. Appl. Polym. Sci.2012, DOI: 10.1002/app.36318) and explained on the basis of the porosity of the gel, the state of aggregation and isotacticity of the PNIPAM chain segment, and the cononsolvency of the methanol-water mixture toward the PNIPAM chain segment.

Anti-cancer therapeutic potential of quinazoline based small molecules via global upregulation of miRNAs

Three quinazoline based small molecules showed global upregulation of miRNA expression with a selective enrichment of tumor suppressor miRNAs. The target genes of the upregulated miRNAs were predicted to be enriched for apoptotic pathways. Apoptotic induction following treatment with quinazoline compounds was confirmed by in cellulo studies. Thus, these small molecules having the core structural moiety (2,4-diphenyl-quinazoline) can be used as scaffolds to design activators of miRNA expression paving the way for novel anti-cancer drugs.

Chain of dimers to assembly of trimers: temperature and ligand influenced formation of novel supramolecular assemblies of Cu(II) with isomeric (aminomethyl) pyridines and azide

Five new complexes, viz., [Ni(2-aminomethylpyridine)2(N3)2] (1), [Cu(2-aminomethylpyridine)(N3)2]n (2), [Cu(2-aminomethylpyridine)2(N3)2] (3), [Cu3(3-aminomethylpyridine)2(N3)6]n (4) and [Zn(2-aminomethylpyridine)2(N3)2] (5), were synthesized and structurally characterized to probe the role of temperature as well as ligand geometry in the formation of novel supramolecular assemblies. The influential and preferential role of temperature as well as ligand geometry is observed in the supramolecular structure formation of Cu(II) complexes alone, with isomeric (aminomethyl)pyridines and azide. With 2-amp as the ligand, temperature greatly influences the product formation, resulting in thermodynamically stable 2 at RT and kinetically stable 3 at LTs. However, such a temperature influence is not evident with the analogous 3-amp derivative. Interestingly, the change in ligand geometry from 2-amp to 3-amp has resulted in drastic changes in the final supramolecular structure formation. The change in ligand geometry from chelating in 2-amp, to bridging in 3-amp leads to a 1-D polymeric chain of dimers bridged by asymmetric end-on azides in 2 to a 1-D assembly of trimers bridged by symmetric end-on azides in 4. The change in the ligand geometry appears to be responsible for the changes in the metal ions geometrical preferences from square pyramidal in 2 to simultaneous octahedral and square planar in 4, assisted by a change in azides bridging modes. Magnetic studies on both 2 and 4 revealed antiferromagnetic Cu–Cu interactions with J = −2.26 cm−1 (H = −JS1S2) and −7.5 cm−1 (H = −J(S1S2 + S2S3)) respectively. While the observed AFM interactions in 4 are in accordance with the theoretical predictions based on the crossover in the magnetic property from FM to AFM at α > 104°, in asymmetric end-on azide bridged dimers of transition metal complexes, the magnetic interactions in 2 are contrary to the predictions. The results once again emphasize that the predictions are valid only for the basal–basal mode of azide bridging, but not for basal–apical mode of bridging in square pyramidal complexes.