BITS Faculty Publications
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Item Mechanistic insights into the C-myc G-quadruplex and berberine binding inside an aqueous two-phase system mimicking biomolecular condensates(ACS, 2024-08) Patra, SatyajitWe investigated the binding between the c-MYC G-quadruplex (GQ) and berberine chloride (BCl) in an aqueous two-phase system (ATPS) with 12.3 wt % polyethylene glycol and 5.6 wt % dextran, mimicking the highly crowded intracellular biomolecular condensates formed via liquid–liquid phase separation. We found that in the ATPS, complex formation is significantly altered, leading to an increase in affinity and a change in the stoichiometry of the complex with respect to neat buffer conditions. Thermodynamic studies reveal that binding becomes more thermodynamically favorable in the ATPS due to entropic effects, as the strong excluded volume effect inside ATPS droplets reduces the entropic penalty associated with binding. Finally, the binding affinity of BCl for the c-MYC GQ is higher than those for other DNA structures, indicating potential specific interactions. Overall, these findings will be helpful in the design of potential drugs targeting the c-MYC GQ structures in cancer-related biocondensates.Item Acetylcholine structure-based small activatable fluorogenic probe for specific detection of acetylcholinesterase(ACS, 2023-05) Sidhu, Jagpreet SinghEarly detection of Alzheimer’s disease (AD) is important for taking proper measures against AD pathogenesis. Acetylcholinesterase (AChE) is widely reported to be associated with the pathogenicity of AD. Here, employing the “acetylcholine-mimic” approach, we designed and synthesized a new class of naphthalimide (Naph)-based fluorogenic probes for specific detection of AChE and avoiding interference of butyrylcholinesterase (BuChE), the pseudocholinesterase. We investigated the action of the probes on Electrophorus electricus AChE, and the native human brain AChE that we expressed in Escherichia coli and purified in the active form for the first time. The probe Naph-3 exhibited a substantial fluorescence enhancement with AChE and majorly avoided BuChE. Naph-3 successfully crossed the cell membrane of the Neuro-2a cells and fluoresced upon reaction with endogenous AChE. We further established that the probe could be effectively used for screening AChE inhibitors. Our study provides a new avenue for the specific detection of AChE, which can be extended to the diagnosis of AChE-related complications.Item Luminescent triazolo-fused pyrido[3,4-b]pyrazines as novel fluorophores(Elsevier, 2024-12) Khungar, Bharti; Sakhuja, RajeevA series of organic fluorophores based on novel [1,2,4]triazolo [4′,3':1,2]pyrido [3,4-b]pyrazine architecture were synthesized by a simple two-step protocol. Synthesized organic fluorophores exhibit blue-to-green fluorescence and their UV absorption and fluorescent emission properties were studied. The photophysical properties of synthesized derivatives were tuned by introducing functionalities of varying electronic nature on the core nucleus. The luminescence maxima of the synthesized compounds are found in the range from 427 nm to 503 nm, and the quantum yields ranging from 0.01 to 0.64 were calculated. Among various synthesized molecules, 3-(4-bromophenyl)-8,9-bis(4-methoxyphenyl)-[1,2,4]triazolo [4′,3':1,2]pyrido [3,4-b]pyrazine showed highest quantum yield (ΦF = 0.64), and was further explored for its solvatochromic, acidochromic, aggregation induced fluorescence studies along with theoretical HOMO-LUMO calculationsItem Nontoxic Aggregation-Induced Emissive Luminogen for the Detection of Amyloid Fibrils and Cellular Protein Aggregates(ACS, 2023-10) Chowdhury, Rajdeep; Addy, Partha SarathiProtein misfolding and aggregation resulting in amyloid formation is directly linked to various diseases. Hence, there is keen interest in developing probes for the selective detection of such misfolded aggregated proteins. In this paper, we have shown the use of a nontoxic aggregation-induced emissive luminogen (AIEgen), BIDCPV, for the selective detection of insulin amyloid fibrils and their various stages of formation. We further verified the selective response of BIDCPV toward amyloid fibrils by testing the probe against Aβ 42 peptides, which is well known to form the fibrils. Additionally, the low toxicity, efficient cellular internalization capability, and photostability make BIDCPV a unique candidate for sensing protein aggregates inside mammalian cells.Item Contrasting Solid-State Fluorescence of Diynes with Small and Large Aryl Substituents: Crystal Packing Dependence and Stimuli-Responsive Fluorescence Switching(ACS, 2015-09) Pati, Avik K.There has been a significant current interest in solid state luminescence of organic molecules and their stimuli responsive fluorescence switching behavior. Although small organic derivatives with olefinic, acetylenic, phenylenevinylenic, phenyleneethynylenic spacers are widely documented as solid state emitters in the literature, the solid state photophysics of organic derivatives with “butadiyne” spacer still remains unexplored. We provide detailed investigation on the solid state fluorescence properties of a series of butadiynyl fluorophores. Replacement of a phenyl ring, which is at periphery of the butadiyne bridge, with a large moiety such as pyrenyl group furnishes contrasting emissions in the solid state. While the butadiyne bridged phenyl derivatives show a blue shift of emission maxima in the solid powder with respect to monomer spectra in solution state, the butadiyne bridged pyrenyl derivatives exhibit a red shift in the solid state. The blue shift of the emission maxima of the butadiyne bridged phenyl derivatives in the solid powder is attributed to allowed excitonic transition in aggregates with nearly parallel transition dipoles. On the other hand, formation of pyrenyl excimer accounts for the red shift of the butadiyne bridged pyrenyl derivatives in the solid powder. In addition to that, the solid state fluorescence of the pyrenyl analogues is reversibly switched between two aggregate forms through external heating and rubbing stimuli.Item Photophysics of Diphenylbutadiynes in Water, Acetonitrile–Water, and Acetonitrile Solvent Systems: Application to Single Component White Light Emission(ACS, 2016-07) Pati, Avik K.Diacetylenes have been the subject of current research because of their interesting optoelectronic properties. Herein, we report that substituted diphenylbutadiynes exhibit locally excited (LE) and excimer emissions in water and multiple emissions from the LE, excimer, and intramolecular charge transfer (ICT) states in acetonitrile–water solvent systems. The LE, excimer, and ICT emissions are clearly distinguishable for a diphenylbutadiynyl derivative with push (−NMe2)–pull (−CN) substituents and those are closely overlapped for non-push–pull analogues. In neat acetonitrile, the excimer emission disappears and the LE and ICT emissions predominate. In the case of the push (−NMe2)–pull (−CN) diphenylbutadiyne, the intensity of the ICT emission increases with increasing the fluorophore concentration. This suggests that the ICT emission accompanies with intermolecular CT emission which is of exciplex type. As the LE and exciplex emissions of the push–pull diphenylbutadiyne together cover the visible region (400–700 nm) in acetonitrile, a control of the fluorophore concentration makes the relative intensities of the LE and exciplex emissions such that pure white light emission is achieved. The white light emission is not observed in those diphenylbutadiynyl analogues in which the peripheral substituents of the phenyl rings do not possess strong push–pull character.Item White Light Emission in Butadiyne Bridged Pyrene–Phenyl Hybrid Fluorophore: Understanding the Photophysical Importance of Diyne Spacer and Utilizing the Excited-State Photophysics for Vapor Detection(ACS, 2016-07) Pati, Avik K.Generation of white light emission (WLE) from a single organic fluorophore is challenging because of the need to get fluorescence covering the visible region (400–700 nm) upon excitation of the dye at near-ultraviolet wavelength. Herein, we report WLE from a butadiyne bridged pyrene–phenyl hybrid fluorophore in mixed-aqueous solvents as well as in polymer film matrices. The ability of the butadiynyl dye to emit from multiple excited states such as locally excited (LE; 400–500 nm), aggregate (excimer type; 475–600 nm), and charge transfer (CT; 500–750 nm) states spanning the emission almost throughout the visible range has made the generation of the white light to be possible. In highly polar solvent such as acetonitrile, the butadiynyl dye emits from the LE and CT states, and the WLE is achieved through a control of the dye concentration such that intermolecular CT (exciplex type) contributes along with the intramolecular CT and LE emissions. In mixed-aqueous systems such as water–acetonitrile and water–N,N-dimethylformamide, the CT emission is red-shifted (because of the high dielctric constant of water), and the contribution of the aggregate emission (originated because of the poor solvent water) is important in maintaining the relative distribution of the fluorescence intensities (LE, excimer, and CT) in the entire visible region. The significance of the diyne spacer in achieving the WLE is delineated through a control study with a single acetylenic analogue. The LE, aggregate, and CT emissions are involved in generating bluish-white light in a poly(vinyl alcohol) film matrix of the butadiynyl dye. Blue emission is noted in a poly(methyl methacrylate) (PMMA) film matrix of the dye with a major contribution from the LE and a minor contribution from the aggregate state. Exposure of the PMMA film of the dye to polar aprotic vapors assists in gaining the CT state emission such that the LE, aggregate, CT emissions cover the entire visible region to produce the WLE. This opens a new strategy for selective vapor sensing.Item One-Pot Synthesis of Vinylogous Cyano Aminoaryls (VinCAs) as Benzenic Fluorophores: Tailoring Diverse Emission Colors for White Light Emitting Materials and Cell Imaging(ACS, 2024-05) Ghosh, Sarbani; Chowdhury, Rajdeep; Addy, Partha SarathiDonor–acceptor-based organic small molecules with an electronic push–pull effect can demonstrate intramolecular charge transfer to show interesting photoluminescence properties. This is an essential criterion for designing fluorogenic probes for cell imaging studies and the development of organic light-emitting diodes. Now, to design such optical materials sometimes it is necessary to tune the band gap by controlling the energies of the highest occupied molecular orbital and lowest unoccupied molecular orbital. Typically, the band gaps could be modulated by installing unsaturated handles between electron-rich donors and electron-deficient acceptors. However, these methods are often synthetically and economically challenging due to the involvement of expensive catalysts and difficult reaction setups. In our present study, we show a straightforward, cost-effective method for obtaining a series of donor–acceptor-type Vinylogous Cyano Aminoaryls (VinCAs) with diverse emission colors. Further studies reveal that these VinCAs can serve as effective cell imaging agents, showcasing potential use in chemical biology. Additionally, these molecules could be further used to generate white light emission (WLE), showing their potential utility in advanced lighting technologiesItem Acetylcholine Structure-Based Small Activatable Fluorogenic Probe for Specific Detection of Acetylcholinesterase(ACS, 2023-05) Sidhu, Jagpreet SinghEarly detection of Alzheimer’s disease (AD) is important for taking proper measures against AD pathogenesis. Acetylcholinesterase (AChE) is widely reported to be associated with the pathogenicity of AD. Here, employing the “acetylcholine-mimic” approach, we designed and synthesized a new class of naphthalimide (Naph)-based fluorogenic probes for specific detection of AChE and avoiding interference of butyrylcholinesterase (BuChE), the pseudocholinesterase. We investigated the action of the probes on Electrophorus electricus AChE, and the native human brain AChE that we expressed in Escherichia coli and purified in the active form for the first time. The probe Naph-3 exhibited a substantial fluorescence enhancement with AChE and majorly avoided BuChE. Naph-3 successfully crossed the cell membrane of the Neuro-2a cells and fluoresced upon reaction with endogenous AChE. We further established that the probe could be effectively used for screening AChE inhibitors. Our study provides a new avenue for the specific detection of AChE, which can be extended to the diagnosis of AChE-related complications.Item Gold conjugated carbon dots nano assembly: FRET paired fluorescence probe for cysteine recognition(Elsevier, 2019-03) Sidhu, Jagpreet SinghThe detection and discrimination of Cys amino acid from numerous other related biomolecules has great importance in clinical field for diagnosis of various diseases. Herein, to detect the Cys, we embedded the carbon dots (CDs), gold, and naphthalimide (L1) into a single ratiometric fluorescence sensor assembly. Sensor assembly works on the principle of FRET mechanism between CDs and naphthalimide when CDs and L1 adhered on gold nanoparticles surface. Gold metal was turned into solid support by in situ reduction of HAuCl4 in the presence of CDs and L1. When the assembly was excited at 360 nm, emission maxima at 568 nm corresponded to naphthalimide emission was emerged that signifies the existence of a FRET between the CDs and naphthalimide fluorophores. With the addition of Cys, the FRET mechanism eliminated and the change in the fluorescence emission at two different wavelengths (450 nm and 568 nm) was recorded. The endogenous images of Cys was recorded by collecting the fluorescence images of HeLa cells under fluorescence microscope and also applied for the assay of Cys in blood serum. Cytotoxicity studies of CDs and sensor assembly were evaluated by performing the MTT assay.