Browsing by Author "Uzra Diwan"

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A Categorical Naked-Eye Detection of Cu2+ and Zn2+ through a Donor-Acceptor-Donor (D-A-D)-Type Salicylaldimine: An Experimental and Theoretical Approach
(Wiley-Blackwell, 2017) Virendra Kumar; Uzra Diwan; Isha Sanskriti; Rakesh K. Mishra; K.K. Upadhyay
A Schiff base viz., 2,3-bis-(3, 5-di-tert-butyl-2-hydroxybenzylidene) amino maleonitrile (TBCN), having donor–acceptor–donor (D–A–D) type constitution exhibited Cu2+ and Zn2+ guided specific modulations in its ICT (intramolecular charge transfer) characteristics. The corresponding naked eye changes for Cu2+ and Zn2+ involved the shifting of characteristic ICT band of TBCN at ∼472 nm (yellow) to ∼ 566 nm (pink) and ∼590 nm (indigo blue) respectively in a semi-aqueous medium (EtOH:H2O in a ratio of 8:2 v/v). The TBCN as well as its ensembles with Cu2+ and Zn2+ were fully characterized through their single crystal XRD studies along with spectroscopic and mass spectral studies. The DFT and the time-dependent DFT calculations provided a genuine rationale for separate naked eye colorimetric changes of TBCN for Cu2+ and Zn2+. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
A coumarin based fluorescent probe enabling nanomolar detection of Zn2+ and Cu2+
(Elsevier B.V., 2022) Virendra Kumar; Uzra Diwan; Nidhi Tyagi; Rakesh K. Mishra; Manish Kumar Singh; K.K. Upadhyay
A rationally designed fluorescent probe constructed on a coumarin platform (R-1) distinguished sequentially & distinctly two vital ions viz. Zn2+ and Cu2+ through different mechanistic approaches at their nanomolar concentrations. The native dark state (off-state) of R-1 was illuminated (on-state) upon its interaction with Zn2+ and further reverted back to its natural dark state in the presence of Cu2+ in aqueous medium. The structural details of R-1 and its ensemble with Zn2+ were unambiguously elucidated through their single-crystal XRD studies. The single crystals of R-1-Zn2+ with chloride and acetate counter anions displayed a fascinating 1-D co-ordination polymeric supramolecular structures. The strategic incorporation of pyridine –N in R-1 introduced a yet another binding site and consequently modulated its optical characteristics, while the analogous derivative R-3, inspite of having electron withdrawing –NO2 group, (instead of pyridine –N as in R-1 and R-2) was unable to produce any significant sensing response under similar conditions. The corresponding optical responses with Zn2+/Cu2+ were equated with INHIBIT logic- gate function. Moreover, the R-1 was deployed for imaging the above ionic analytes in rat glioblastoma cell lines (c6) through confocal laser scanning microscopy. © 2021 Elsevier B.V.
A pyrene-benzthiazolium conjugate portraying aggregation induced emission, a ratiometric detection and live cell visualization of HSO3-
(Elsevier B.V., 2016) Uzra Diwan; Virendra Kumar; Rakesh K. Mishra; Nishant Kumar Rana; Biplob Koch; Manish Kumar Singh; K.K. Upadhyay
The present study deals with the photophysical property of a pyrene-benzthiazolium conjugate R1, as a strong intramolecular charge transfer (ICT) probe exhibiting long wavelength emission in the red region. Unlike traditional planar polyaromatic hydrocarbons whose aggregation generally quenches the light emission, the pyrene based R1 was found to display aggregation-induced emission (AIE) property along with simultaneous increase in its quantum yield upon increasing the water content of the medium. The R1 exhibits high specificity towards HSO3-/SO32- by interrupting its own ICT producing there upon a large ratiometric blue shift of ~220 nm in its emission spectrum. The lowest detection limit for the above measurement was found to be 8.90 × 10-8 M. The fluorescent detection of HSO3- was also demonstrated excellently by test paper strip and silica coated TLC plate incorporating R1. The live cell imaging of HSO3 through R1 in HeLa cells was studied using fluorescence microscopic studies. The particle size and morphological features of R1 and R1-HSO3- aggregates in aqueous solution were characterized by DLS along with SEM analysis. © 2016 Elsevier B.V.
A radical approach for fluorescent turn 'on' detection, differentiation and bioimaging of methanol
(Royal Society of Chemistry, 2015) Virendra Kumar; Ajit Kumar; Uzra Diwan; Manish Kumar Singh; K.K. Upadhyay
A simple Schiff base (RC) has been explored as a smart example of fluorescent material for the selective detection, differentiation and bioimaging of methanol. The nucleophilic attack of methanol on the cyclic control unit of RC leads to its opening and formation of a highly fluorescent moiety, RO. The RC displays a good sensitivity for MeOH with a detection limit of 0.042 wt% in water. © The Royal Society of Chemistry 2015.
A water compatible turn 'on' optical probe for Cu2+ based on a fluorescein-sugar conjugate
(2014) Uzra Diwan; Ajit Kumar; Virendra Kumar; K.K. Upadhyay; P.K. Roychowdhury
A fluorescein-sugar conjugated chromo-fluorogenic turn 'on' probe (FG) has been synthesized for detection of Cu2+. The FG comprises of fluorescein as an efficient fluorophore and a sugar moiety, viz., galactose as the binding unit. The inclusion of galactose into FG led towards its good water compatibility. When Cu2+ was added in 70% aqueous HEPES buffered solution (pH 7.4) of FG, the absorbance and the fluorescence spectral pattern of the same were modulated dramatically with observation of absorption and emission bands at 632 and 515 nm, respectively. The detection limit from fluorescence titration was calculated as 6.32 nM which further establishes high sensitivity of FG towards Cu2+. The spectral studies for the interaction of FG with Cu2+ indicated towards metal ion triggered spirolactam ring opening of FG as the mechanistic pathway of the sensing phenomenon. © 2014 Elsevier B.V. All rights reserved.
A Zn2+-responsive highly sensitive fluorescent probe and 1D coordination polymer based on a coumarin platform
(2013) Virendra Kumar; Ajit Kumar; Uzra Diwan; K.K. Upadhyay
A coumarin-based Schiff base (receptor 1) exhibited fluorescence enhancement selectively with Zn2+ at a nanomolar level in near-aqueous medium (EtOH–H2O; 1 : 1, v/v). The response was instantaneous with a detection limit of 3.26 × 10−9 M. The sensing event is supposed to incorporate a combinational effect of intramolecular charge transfer (ICT), chelation-enhanced fluorescence (CHEF) and C═N isomerization mechanisms. Various spectroscopic methods, viz. IR, UV-visible, fluorescence and NMR in association with single crystal XRD studies, were used for thorough investigation of the structure of receptor 1 as well as of the sensing event. The Zn2+ complex of receptor 1 exhibited a very nice 1D chain coordination polymeric framework in its single crystal XRD. © 2013 The Royal Society of Chemistry.
Designing of a fluoride selective receptor through molecular orbital engineering
(2012) Rakesh K. Mishra; Virendra Kumar; Uzra Diwan; K.K. Upadhyay; P.K. Roy Chowdhury
The stepwise substitution of appropriate groups over the 3-[(2,4-dinitro-phenyl)-hydrazono]-butyric acid ethyl ester (R3) lead receptor R1 which showed selectivity towards fluoride in DMSO. The UV-vis and 1H NMR titration studies revealed the details of the binding between receptor R1 and fluoride. The receptor R1 also recognized fluoride in a toothpaste solution to as low as 50 ppm. The theoretical simulations of recognition event at Density Functional Theory (DFT) level using B3LYP/6-31G basis set and polarizable continuum model (PCM) approach lead a semi-quantitative match with the experimental results. © 2012 Elsevier B.V. All rights reserved.
Harvesting red fluorescence through design specific tuning of ICT and ESIPT: An efficient optical detection of cysteine and live cell imaging
(Royal Society of Chemistry, 2016) Uzra Diwan; Virendra Kumar; Rakesh K. Mishra; Nishant Kumar Rana; Biplob Koch; K.K. Upadhyay
In this report, we constructed 2-(2-hydroxyphenyl)benzothiazole (HBT) based ratiometric fluorescent probe R1, highly selective for cysteine (Cys) in the red channel with a nanomolar detection limit. The rational combination of benzothiazole and benzothiazolium unit within the same molecular frame work act as "two-heads" that allowed the simultaneous harvesting of intramolecular charge transfer (ICT) as well as excited state intramolecular proton transfer (ESIPT). This coupling of dual mechanism in R1 provides selective colorimetric and ratiometric fluorescence response towards Cys from the mixture of various anions and amino acids including foremost interfering thiols viz. HS-, Hcy and GSH. R1 shows a weak ESIPT at 497 nm (green fluorescence, N∗) which undergoes shifting to 625 nm (red channel K∗) upon addition of Cys selectively. Henceforth, R1 was also utilized for marking Cys in live cell imaging in HeLa cells. The sensing phenomenon of R1 for Cys was studied through a number of spectroscopic techniques viz., NMR, IR along with HRMS studies. The density functional theory calculations further strengthened the experimental findings. © 2016 The Royal Society of Chemistry.
Highly sensitive and selective naked-eye detection of Cu2+ in aqueous medium by a ninhydrin-quinoxaline derivative
(Elsevier B.V., 2013) Ajit Kumar; Virendra Kumar; Uzra Diwan; K.K. Upadhyay
A simple ninhydrin-quinoxaline based colorimetric receptor 1 was designed, synthesized and characterized. The same exhibited high sensitivity and selectivity towards Cu2+ in aqueous medium (ethanol:H2O, 1:9, v/v) over a wide variation of cations such as Na+, Mg2+, Al3+, Co2+, Fe3+, Ni2+, Zn2+, Cd 2+, Hg2+ and Pb2+. The addition of Cu 2+ to the receptor 1 solution gave clear colour change from olive green to pink. The detection limit of receptor 1 was found to be 3.43 × 10-7M which is probably the lowest one for the Cu2+ in an aqueous solution by any naked-eye receptor till date. The sensitivity and specificity of receptor 1 towards Cu2+ along with control compound receptor 2 were investigated in detail. This is only the second report where ninhydrin is used for the construction of any colorimetric sensor. © 2012 Elsevier B.V. All rights reserved.
Salicylideneimines as efficient dual channel emissive probes for Al3+: Harnessing ESIPT and ICT processes
(Elsevier B.V., 2015) Virendra Kumar; Ajit Kumar; Uzra Diwan; Shweta; Ramesh; S.K. Srivastava; K.K. Upadhyay
Two simple fluorescent chemosensors (CS1 & CS2) based upon salicylideneimine derivatives were evaluated for their selective fluorescent sensing of Al3+. An attractive glowing green/blue colour was observed in the presence of Al3+ with dual channel emissions for CS1 (λem 499 & 535 nm) and CS2 (λem 485 & 515 nm) both. The inhibition of PET and CN isomerization after Al3+ binding was responsible for the turn 'on' fluorescence response while the dual emissions were well justified in terms of ESIPT and ICT. The binding stochiometries between CS1/CS2 and Al3+ were found to be 1:1 and 2:1 respectively while the limit of detection (LOD) of Al3+ by CS1 was found to be ∼10 times lower than that of CS2. © 2014 Elsevier B.V. All rights reserved.
Solvent viscosity tuned highly selective NIR and ratiometric fluorescent sensing of Fe3+ by a symmetric chalcone analogue
(2013) Uzra Diwan; Ajit Kumar; Virendra Kumar; K.K. Upadhyay
The present communication outlined for the first time a novel combination of chromogenic near-infrared (NIR) and ratiometric fluorescence responses for Fe3+ by a symmetric chalcone analogue (receptor 1). The key step behind NIR chromogenic response was attributed to chelation of Fe3+ with receptor 1 upon its unfolding in aprotic, low viscosity solvents. The receptor 1 also exhibited Fe3+ selective ratiometric changes at 538 nm and 463 nm. The chromogenic detection limit of the receptor 1 for Fe 3+ is the lowest ever (5.8 × 10-8 M). The mechanistic details of NIR/fluorescence sensing of receptor 1 along with its solvent dependency have been discussed in detail. © 2013 The Royal Society of Chemistry.
Turn "off-on" fluorescent recognition of Cu2+ and Cys in aqueous medium: Implementation of molecular logic gate and cell imaging studies
(Chemical Society of Japan, 2016) Virendra Kumar; Ajit Kumar; Uzra Diwan; Manish Kumar Singh; K.K. Upadhyay
The present communication incorporates utilization of a simple Schiff base (RO) fruitfully for the turn "off-on" successive fluorescent recognition of Cu2+ and Cys in aqueous media. The single crystal of RO-Cu2+ ensemble revealed a binding pattern which ultimately leads to quenching of the green fluorescence of RO. Interestingly the quenched fluorescence of the RO-Cus2+ ensemble was revived selectively in the presence of Cys via Cu2+ displacement approach. The selective "off-on" behavior of RO towards Cu2+ and Cys was consequently used as inputs to build up an implication (IMP) logic gate. Moreover, the RO exhibited successful bio-imaging of Cu2+ and Cys also in E. coli cells. © 2016 The Chemical Society of Japan.
Uncovering the true mechanism of optical detection of HSO4- in water by Schiff-base receptors – hydrolysis vs. hydrogen bonding
(2012) Virendra Kumar; Ajit Kumar; Uzra Diwan; K.K. Upadhyay
The mechanism of optical detection of HSO4- in aqueous medium by Schiff-base receptors has previously been proposed to depend on selective hydrogen-bond interactions. Here, we clearly demonstrate for the first time that the acidic nature of this anion gives rise to hydrolysis of the Schiff base, which leads to the optical changes observed in this family of receptors. © 2012 The Royal Society of Chemistry.