Browsing by Author "Mrigendra Dubey"

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A dual-responsive "turn-on" bifunctional receptor: A chemosensor for Fe3+ and chemodosimeter for Hg2+
(Royal Society of Chemistry, 2015) Sujay Mukhopadhyay; Rakesh Kumar Gupta; Arnab Biswas; Amit Kumar; Mrigendra Dubey; Maninder Singh Hundal; Daya Shankar Pandey
Synthesis of L1-L3, their thorough characterization by spectral as well as structural studies and use in selective photochemical detection of Fe3+ and Hg2+ at ppb level have been described. Notably, these exhibit bifunctional behaviour toward Fe3+ (CHEF) and Hg2+ (chemodosimetric) which has been unequivocally established by various studies. © The Royal Society of Chemistry 2015.
A saponification-triggered gelation of ester-based Zn(II) complex through conformational transformations
(2014) Ashish Kumar; Mrigendra Dubey; Amit Kumar; Daya Shankar Pandey
Novel saponification-triggered gelation in an ester-based bis-salen Zn(II) complex (1) is described. Strategic structural modifications induced by NaOH in 1 tune the dipolar-/π-interactions leading to J-aggregation and the creation of an inorganic gel material (IGM>), which has been established by photophysical, DFT and rheological studies. © 2014 Partner Organisations.
A schiff base and its copper(II) complex as a highly selective chemodosimeter for mercury(II) involving preferential hydrolysis of aldimine over an ester group
(American Chemical Society, 2014) Ashish Kumar; Mrigendra Dubey; Rampal Pandey; Rakesh Kumar Gupta; Amit Kumar; Alok Ch. Kalita; Daya Shankar Pandey
The syntheses of a new Schiff base, diethyl-5-(2-hydroxybenzylidene) aminoisophthalate (HL), and a copper complex, [Cu(L2)] (1), imparting L-, have been described. Both the ligand HL and complex 1 have been thoroughly characterized by elemental analyses, electrospray ionization mass spectrometry, FT-IR, NMR (1H and 13C), electronic absorption, and emission spectral studies and their structures determined by X-ray single-crystal analyses. Distinctive chemodosimetric behavior of HL and 1 toward Hg2+ has been established by UV/vis, emission, and mass spectral studies. Comparative studies further revealed that the chemodosimetric response solely originates from selective hydrolysis of the aldimine moiety over the ester group and 1 exhibited greater selectivity toward Hg2+ relative to HL while the sensitivity order is reversed. Further, these followed different hydrolytic pathways but ended up with the same product analyzed for diethyl-5-aminoisophthalate (DEA). Hg2+-induced displacement of Cu2+ and subsequent hydrolysis of the -HC=N- moiety in 1 affirmed the identity of the actual species undergoing hydrolysis as HL. The occurrence of Cu2+ displacement and Hg2+ detection via hydrolytic transformation has been supported by various physicochemical studies. © 2014 American Chemical Society.
Anion triggered metallogels: Demetalation and crystal growth inside the gel matrix and improvement in viscoelastic properties using Au-NPs
(Royal Society of Chemistry, 2016) Arnab Biswas; Mrigendra Dubey; Sujay Mukhopadhyay; Ashish Kumar; Daya Shankar Pandey
Progelator complex Zn-TRPA-2 undergoes Cl- triggered gelation to afford ZTP2G, while Zn-TRPA-2 capped Au-NPs under similar conditions gave another gel GNZTP2G which also represents a rare nano-composite metallogel. When Zn-TRPA-2 was triggered by Cl- and NO3- simultaneously, crystals of demetalated species NA-TRPA-2 grew inside the ZTP2G matrix. Interestingly, GNZTP2G exhibits superior viscoelastic properties over ZTP2G. © The Royal Society of Chemistry 2016.
Bis(Acylhydrazone)-Based Bolaamphiphiles: Effect of Spacer Length on Metalloorganogel Formation, Fluorescence, and Conductance Properties
(John Wiley and Sons Inc, 2022) Manish Kumar Dixit; Yeeshu Kumar; Jay Shukla; Chinthakuntla Mahendar; Mrigendra Dubey
Gelation of chain-length-selective bolaamphiphiles (1 % w/v) from succinic (n=2, H2SL) and adipic acid (n=4, H2AL) derived ligands from six different bis(acylhydrazone)-based saturated homologous dicarboxlylates has been demonstrated. Deprotonation of H2SL (SL2−) with LiOH led to the formation of a fluorescent metalloorganogel upon addition of Cd(OAc)2. The coordination complexes responsible for metalloorganogel or solution formation have been studied with UV/Vis, Job's plot, ESI-MS and fluorescence studies. Transmission electron microscopy (TEM) of the diluted metalloorganogel revealed unusual nanospherical aggregates (∼50 nm diameter) aligned together to create fibrous morphology, which was further supported by scanning electron microscopy (SEM) imaging. Nyquist impedance plot indicated that the metalloorganogel has a much lower resistance (R1=3.6 kΩ) than its non-gelling counterpart (R2=5.6 kΩ) suggesting the formation of well-organized fibres. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Can enantiomer ligands produce structurally distinct homochiral MOFs?
(Royal Society of Chemistry, 2015) Mrigendra Dubey; Ashish Kumar; Vishal M. Dhavale; Sreekumar Kurungot; Daya Shankar Pandey
Here, we report a self-assembled homochiral metal-organic framework [Cu1.5(H2Ll-leu)(Ac)H2O]n·3H2O (1) obtained from an l-leucine-derived ligand (H4Ll-leu) and Cu(Ac)2·H2O in a 1 : 1 ratio. Coordination-induced conformational change in the ligand has been monitored by circular dichroism which has been further attested by synthesizing a d-leucine-containing enantiomer H4Ld-leu and its Cu(ii) complex [Cu1.5(H2Ld-leu)H2O]n·10H2O (2). Structure determination revealed entirely different structures for the homochiral MOFs (1 and 2) obtained from the l/d-leucine-derived enantiomer ligands under analogous reaction conditions. Further, structural dissimilarity in these MOFs has been judicially supported by proton conductance studies. MOF 1 shows higher proton (10-5 S cm-1) conductance in comparison to 2 (10-6 S cm-1) due to dissimilar alignment of the hydrogen-bonded water molecules in the hydrophilic pocket as well as crystal packing. © The Royal Society of Chemistry.
Cd2+-induced Fluorescent Metallogel: A Case of CHEF and ACQ Phenomena
(John Wiley and Sons Ltd, 2022) Manish Kumar Dixit; Chinthakuntla Mahendar; Mrigendra Dubey
A fluorescent metallogel (1 %w/v) has been synthesized from deprotonation of a non-fluorescent adipic acid-derived ligand H2AL with LiOH followed by coordination with Cd2+ in DMF. Cd2+ not only induces the coordination complex formation but also leads to aggregation, formation of nanofibers of about ≈12 nm average diameter and gelation. The metallogel was also found to be reversibly stimuli-responsive towards heating and mechanical shaking whereas it was resistant to ultrasound. The involvement of chelation-enhanced fluorescence (CHEF), aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) during the course of gelation has been well established by fluorescence experiments. Further, the coordination complex involved in metallogel formation has been well characterized by ESI-MS and Job's plot. The synthesized metallogel has a true gel phase as shown by detailed rheological studies. The mechanism of gelation is well established by using FTIR, UV-vis, fluorescence, lifetime measurement, Job's plot, ESI-MS, PXRD and TEM techniques. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Detection of copper(II) and aluminium(III) by a new bis-benzimidazole Schiff base in aqueous media via distinct routes
(Royal Society of Chemistry, 2015) Ashish Kumar; Amit Kumar; Mrigendra Dubey; Arnab Biswas; Daya Shankar Pandey
The synthesis is described of a new bis-benzimidazole appended Schiff base ligand [2-(3,5-bis(1H-benz-imidazol-2-yl)-phenyliminomethyl)phenol] (H3L) followed by its thorough characterization by elemental analyses, spectroscopic studies (FT-IR, 1H, 13C NMR, ESI-MS, UV/vis, fluorescence) and X-ray single crystal analyses. The excellent selectivity of H3L towards Cu2+ and Al3+via distinct responses in mixed aqueous conditions was established by spectroscopic studies. The selective detection of Cu2+ due to the creation of complex 1 in which Cu2+ occupied only the salen-type N2O2 coordination site and the strong binding with Al3+ through both benzimidazole and salen moieties to yield complex 2 was confirmed by various studies. The disparate detection of these cations by H3L was substantiated by comparative studies, performed under analogous conditions, of the precursor compound 3,5-bis(1H-benzimidazol-2-yl)-aniline (BBA). The distinct interaction of H3L with Cu2+ and Al3+ and the sensing mechanisms were investigated in detail by spectroscopic studies and were supported by theoretical studies (Density Functional Theory). It has been clearly shown that the use of appropriate substituents may facilitate the design and development of probes suitable for the real time detection of more than one analyte. © The Royal Society of Chemistry 2015.
Homochiral coordination polymeric gel: Zn2+-induced conformational changes leading to J-aggregated helical fibres formation
(2014) Mrigendra Dubey; Ashish Kumar; Daya Shankar Pandey
A novel chiral coordination polymeric gel based on an amino acid derived symmetrical ligand, specific base, and Zn2+has been described. Zn2+induced conformational reorganization in the ligand leads to gelation via J-aggregated helical fibres. The vital role played by σ–σ stacking in gelation has been monitored by fluorescence and NMR spectroscopy. © 2014 The Royal Society of Chemistry.
Li+-induced selective gelation of discrete homochiral structural isomers derived from l-tartaric acid
(Royal Society of Chemistry, 2014) Mrigendra Dubey; Ashish Kumar; Rakesh Kumar Gupta; Daya Shankar Pandey
Two chiral structural isomers have been synthesized by molecular engineering of l-tartaric acid. In the presence of LiOH isomer 1 forms a thermally stable, fluorescent gel which exhibits interesting nano-cluster morphology, anomalous optical and rheological properties whilst 2 forms a non-fluorescent solution under similar conditions. The current-voltage (I-V) curve followed a non-linear trend, rationally in close proximity to the diode characteristic curve. This journal is © the Partner Organisations 2014.
Li+-induced selective gelation of discrete homochiral structural isomers derived from l-tartaric acid
(2014) Mrigendra Dubey; Ashish Kumar; Rakesh Kumar Gupta; Daya Shankar Pandey
Two chiral structural isomers have been synthesized by molecular engineering of l-tartaric acid. In the presence of LiOH isomer 1 forms a thermally stable, fluorescent gel which exhibits interesting nano-cluster morphology, anomalous optical and rheological properties whilst 2 forms a non-fluorescent solution under similar conditions. The current–voltage (I–V) curve followed a non-linear trend, rationally in close proximity to the diode characteristic curve. © The Partner Organisations 2014.
Morphological tuning via structural modulations in AIE luminogens with the minimum number of possible variables and their use in live cell imaging
(Royal Society of Chemistry, 2015) Roop Shikha Singh; Rakesh Kumar Gupta; Rajendra Prasad Paitandi; Mrigendra Dubey; Gunjan Sharma; Biplob Koch; Daya Shankar Pandey
With intent to fine tune the morphological and photophysical properties, three novel AIE luminogens (BQ1-BQ3) based on quinoline-BODIPY have been synthesized. A judicious choice of substituents (-H, -CH3, -OCH3) in these systems led to nanoballs in BQ1 and BQ2, while in BQ3 it led to reticulated nanofibers with diverse photophysical behaviours. This journal is © The Royal Society of Chemistry 2015.
Novel tetranuclear copper 2 + 4 cubanes resulting from unprecedented C-O bond formation cum dearomatization
(Royal Society of Chemistry, 2014) Amit Kumar; Rampal Pandey; Rakesh Kumar Gupta; Mrigendra Dubey; Daya Shankar Pandey
Novel tetranuclear copper 2 + 4 cubanes 1 and 2 have been synthesized from the reaction of hydrated copper salts/precursors with N,O chelating β-ketoaminato ligands. Creation of 1 and 2 occurs by in situ generation of the tridentate chelating species HL1O2-via copper mediated C-O bond formation and dearomatization of H3L1, while anhydrous salts afforded mononuclear complex 3. © 2014 The Royal Society of Chemistry.
Potential apoptosis inducing agents based on a new benzimidazole schiff base ligand and its dicopper(ii) complex
(Royal Society of Chemistry, 2014) Anup Paul; Rakesh Kumar Gupta; Mrigendra Dubey; Gunjan Sharma; Biplob Koch; Geeta Hundal; Maninderjeet Singh Hundal; Daya Shankar Pandey
Synthesis, characterization and antiproliferative activity of a new benzimidazole based Schiff base 2-(1-methyl-1-H-benzimidazol-2-yl)phenyl)imino)methyl)phenol (HL) and dicopper(ii) complex [{Cu(L)NO3}2] (CuL) containing L-has been described. Both HL and CuL have been meticulously characterized by satisfactory elemental analyses, FT-IR, NMR, ESI-MS, electronic absorption and emission spectroscopy, and their structures unambiguously determined by X-ray single crystal analyses. Titration studies (absorption and emission) revealed interaction of the ligand and its dicopper(ii) complex with DNA/BSA and stronger affinity of the CuL relative to HL. Binding of the HL and CuL with DNA/BSA have been validated by in silico studies and their cytotoxic effect on human breast cancer cell lines (MCF-7) by MTT assay. IC50values (458 μM and 22 μM for HL, CuL) clearly suggested substantial cytotoxicity of the complex CuL toward MCF-7 compared to the ligand HL. Greater antiproliferative efficacy of the CuL in contrast to HL has been evidenced by fluorescence activated cell sorting (FACS) and AO/EB fluorescence staining. The possible mode of the apoptotic pathway for CuL has further been affirmed by reactive oxygen species (ROS) generation studies. This journal is © the Partner Organisations 2014.
Pyrene-fluorescein-based colour-tunable AIE-active hybrid fluorophore material for potential live cell imaging applications
(Royal Society of Chemistry, 2017) Vikas Kumar Singh; Ritika Prasad; Biplob Koch; Syed Hadi Hasan; Mrigendra Dubey
A novel hybrid fluorophore (FHPY) has been synthesized based on a condensation reaction of two standard fluorescent hydrophobic-hydrophilic molecules, viz. pyrene and fluorescein, with an objective to tune the aggregation-induced emission (AIE) along with the morphology. Owing to the distinct photophysical properties of pyrene and fluorescein, the hybrid FHPY dramatically exhibits a fluorescence change from colourless to yellow-green via a blue colour upon varying the volume fraction of water (poor solvent) in methanol (good solvent). FHPY has exhibited not only AIE, but also an outstanding quantum yield (ΦF) of 97% at a 70% water fraction in methanol (70-:-30, v/v). We attribute the reason behind the tuning of the AIE and quantum yield to the opening of the lactam ring of fluorescein as well as to the amassing of hydrophobic pyrene at a certain water fraction. The mechanism involved in the AIE has been well supported by detailed UV-vis, fluorescence, lifetime, SEM, AFM, DFT, PXRD and 1H NMR experiments. In addition, FHPY serves as a good candidate for the live cell imaging of HeLa cells. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2017.
Retention of Cs-Cl bond induces coordination polymer formation over trinuclear chiral assembly of copper(II) complexes of L-leucine derived ligand
(2013) Mrigendra Dubey; Manabendra Ray
The use of caesium is a less trodden path in terms of the synthesis of coordination polymers. The chemical similarity and mild toxic nature of caesium salts does not provide much impetus to work with these compounds compared to their potassium analogues. However, are the potassium and caesium salts really close in terms of coordination polymer formation? The result presented in this manuscript shows that while neither potassium halides or potassium nitrate inhibit the formation of a trinuclear chiral assembly of a copper(ii) complex from a mononuclear Cu(ii) complex, caesium chloride preferentially forms a coordination polymer while keeping the Cs-Cl bond intact. Under the same conditions, caesium nitrate does not inhibit the assembly formation. Structural characterization of {[CsCl{Cu(HLl-leu)2}(H 2O)]}n (2) showed it to be a two-dimensional coordination polymer in the ab plane, where penta-coordinated Cu(HLl-leu) 2 complex units (HLl-leu = reduced Schiff base of l-leucine and the salicylaldehyde condensation product) were interconnected through the formation of Cu-Cl-Cs bonds. Multitudes of intermolecular H-bonds were observed as well. The use of KCl, KBr, KI or CsNO3 in lieu of CsCl to the [Cu(HLl-leu)2(CH3CN)] (1) facilitated the formation of the trinuclear assembly, [M{Cu(HL l-leu)2}3]X, where M = K+ or Cs + and X = Cl, Br, I or NO3 depending on the salt used. The Cu(HLl-leu)2 units in these assemblies are hexacoordinated Cu(ii) complexes. © 2013 The Royal Society of Chemistry.
Self-assembled copper(II) metallacycles derived from asymmetric Schiff base ligands: Efficient hosts for ADP/ATP in phosphate buffer
(Royal Society of Chemistry, 2015) Amit Kumar; Rampal Pandey; Ashish Kumar; Rakesh Kumar Gupta; Mrigendra Dubey; Akbar Mohammed; Shaikh M. Mobin; Daya Shankar Pandey
Novel asymmetric Schiff base ligands 2-{[3-(3-hydroxy-1-methyl-but-2-enylideneamino)-2,4,6-trimethylphenylimino]-methyl}-phenol (H2L1) and 1-{[3-(3-hydroxy-1-methyl-but-2-enylideneamino)-2,4,6-trimethylphenylimino]-methyl}-naphthalen-2-ol (H2L2) possessing dissimilar N,O-chelating sites and copper(ii) metallacycles (CuL1)4 (1) and (CuL2)4 (2) based on these ligands have been described. The ligands and complexes have been thoroughly characterized by satisfactory elemental analyses, and spectral (IR, 1H, 13C NMR, ESI-MS, UV/vis) and electrochemical studies. Structures of H2L2 and 1 have been unambiguously determined by X-ray single crystal analyses. The crystal structure of H2L2 revealed the presence of two distinct N,O-chelating sites on dissimilar cores (naphthalene and β-ketoaminato groups) offering a diverse coordination environment. Metallacycles 1 and 2 having a cavity created by four Cu(ii) centres coordinated in a homo- and heteroleptic fashion with respective ligands act as efficient hosts for adenosine-5′-diphosphate (ADP) and adenosine-5′-triphosphate (ATP) respectively, over other nucleoside polyphosphates (NPPs). The disparate sensitivity of these metallacycles toward ADP and ATP has been attributed to the size of the ligands assuming diverse dimensions and spatial orientations. These are attuned for π-π stacking and electrostatic interactions suitable for different guest molecules under analogous conditions, metallacycle 1 offers better orientation for ADP, while 2 for ATP. The mechanism of the host-guest interaction has been investigated by spectral and electrochemical studies and supported by molecular docking studies. © The Royal Society of Chemistry 2015.
Size-controlled synthesis of Ag nanoparticles functionalized by heteroleptic dipyrrinato complexes having meso- pyridyl substituents and their catalytic applications
(American Chemical Society, 2015) Rakesh Kumar Gupta; Mrigendra Dubey; Pei Zhou Li; Qiang Xu; Daya Shankar Pandey
The syntheses of heteroleptic dipyrrinato nickel(II) complexes [Ni(4-pydpm)(dedtc)] (1) and [Ni(4-pydpm)(dipdtc)] (2) [4-pydpm = 5-(4-pyridyl)dipyrromethene; dedtc = diethyldithiocarabamate; and dipdtc = diisopropyldithiocarbamate] and the thorough characterization of these complexes by satisfactory elemental analyses, electrospray ionization mass spectrometry, Fourier-transform infrared, NMR (1H, 13C), and UV-vis spectroscopies, and electrochemical studies was achieved. Structure of 1 was authenticated by X-ray single-crystal analysis. Both the complexes 1 and 2 were successfully utilized as a capping agent in the preparation of silver nanoparticles. Availability of free pyridyl nitrogen on the dipyrrin core of these complexes was meticulously exploited in functionalization and stabilization of the silver nanoparticles (AgNPs). Morphological and structural investigations on colloidal nanoparticles were followed by UV-vis spectroscopy and transmission electron microscopy (TEM). Overall results revealed that average size of the silver nanoparticles (∼10, 15, 20 nm, and aggregation) is strongly influenced by ratio of Ag/[1/2] (03, 06, 10, 20). Correlation between particle size and capping agents was realized by UV-vis and TEM studies. Catalytic activity of the AgNPs obtained through this route was successfully employed in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It was established that reduction process follows a pseudo-first-order kinetics. © 2015 American Chemical Society.