BITS Faculty Publications

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    Screening the Band Shape of Molecules by Optimal Tuning of Range-Separated Hybrid Functional with TD-DFT: A Molecular Designing Approach
    (ACS, 2022-08) Roy, Ram Kinkar
    In the present article we have demonstrated the effectiveness of optimally tuned range-separated hybrid (RSH) functional to determine the electronic transitions from two fluorophore moieties (blue and yellow/orange) within a single white light emitter (WLE). First, the optimally tuned range separation parameter (ω) is calculated for two white emitting fluorophores (W1 and W2) already reported in the literature. The success of the optimally tuned RSH functional ω*B97XD, used in the TDDFT study, encouraged the authors to design eight new single organic white light emitters with frustrated energy transfer between the two individual fluorophore moieties (blue and yellow/orange). The simulated spectra (the band shapes, to be more specific) generated by TDDFT study and outcomes through natural transition orbital (NTO) and natural bond orbital (NBO) studies clearly demonstrate that all the designed eight organic molecules are potential white light emitters and can be synthesized in future.
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    Enantioselective Discrimination of Histidine by Means of an Achiral Cubane-Bridged Bis-Porphyrin
    (ACS, 2021-11) Grover, Nitika
    A Langmuir film of cubane-bridged bisporphyrin (H2por-cubane-H2por) at the air/water interface was developed and characterized. The floating film was successfully employed for the chiral discrimination between l- and d-histidine. The enantioselective behavior persisted after the deposition of the film on a solid support using the Langmuir–Schaefer method. Distinct absorption and reflection spectra were observed in the presence of l- or d-histidine, revealing that conformational switching was governed by the interaction between H2por-cubane-H2por and the histidine enantiomer. The mechanism of chiral selection was investigated using an ad hoc modified nulling ellipsometer, indicating the anti-conformation was dominant in the presence of l-histidine, whereas the presence of d-histidine promoted the formation of tweezer conformation.
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    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 Sarathi
    Donor–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 technologies
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    Long-Range Single-Molecule Förster Resonance Energy Transfer between Alexa Dyes in Zero-Mode Waveguides
    (ACS, 2020-03) Patra, Satyajit
    Zero-mode waveguide (ZMW) nano-apertures milled in metal films were proposed to improve the Förster resonance energy transfer (FRET) efficiency and enable single-molecule FRET detection beyond the 10 nm barrier, overcoming the restrictions of diffraction-limited detection in a homogeneous medium. However, the earlier ZMW demonstrations were limited to the Atto 550–Atto 647N fluorophore pair, asking the question whether the FRET enhancement observation was an artifact related to this specific set of fluorescent dyes. Here, we use Alexa Fluor 546 and Alexa Fluor 647 to investigate single-molecule FRET at large donor–acceptor separations exceeding 10 nm inside ZMWs. These Alexa fluorescent dyes feature a markedly different chemical structure, surface charge, and hydrophobicity as compared to their Atto counterparts. Our single molecule data on Alexa 546–Alexa 647 demonstrate enhanced FRET efficiencies at large separations exceeding 10 nm, extending the spatial range available for FRET and confirming the earlier conclusions. By showing that the FRET enhancement inside a ZMW does not depend on the set of fluorescent dyes, this report is an important step to establish the relevance of ZMWs to extend the sensitivity and detection range of FRET, while preserving its ability to work on regular fluorescent dye pairs.
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    Deep Ultraviolet Plasmonic Enhancement of Single Protein Autofluorescence in Zero-Mode Waveguides
    (ACS, 2019-09) Patra, Satyajit
    Single molecule detection provides detailed information about molecular structures and functions but it generally requires the presence of a fluorescent marker which can interfere with the activity of the target molecule or complicate the sample production. Detecting a single protein with its natural UV autofluorescence is an attractive approach to avoid all the issues related to fluorescence labeling. However, the UV autofluorescence signal from a single protein is generally extremely weak. Here, we use aluminum plasmonics to enhance the tryptophan autofluorescence emission of single proteins in the UV range. Zero-mode waveguide nanoapertures enable the observation of the UV fluorescence of single label-free β-galactosidase proteins with increased brightness, microsecond transit times, and operation at micromolar concentrations. We demonstrate quantitative measurements of the local concentration, diffusion coefficient, and hydrodynamic radius of the label-free protein over a broad range of zero-mode waveguide diameters. Although the plasmonic fluorescence enhancement has generated a tremendous interest in the visible and near-infrared parts of the spectrum, this work pushes further the limits of plasmonic-enhanced single molecule detection into the UV range and constitutes a major step forward in our ability to interrogate single proteins in their native state at physiological concentrations.
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    Microheterogeneity of Some Imidazolium Ionic Liquids As Revealed by Fluorescence Correlation Spectroscopy and Lifetime Studies
    (ACS, 2012-10) Patra, Satyajit
    The microscopic structure and dynamics of the room temperature ionic liquids (RTILs) that are responsible for some of the peculiar properties of this class of solvents continue to intrigue the researchers and stimulate new investigations. Herein, we use the fluorescence correlation spectroscopy (FCS) technique to study the diffusion of some probe molecules in RTILs, the results of which, when combined with those obtained from fluorescence lifetime studies, provide insights into the microscopic structural details of this class of novel solvents. Experiments performed with three charged and neutral probe molecules in five carefully selected 1-alkyl-3-methylimidazolium ionic liquids reveal that unlike in conventional solvents these probes exhibit a bimodal diffusion behavior in RTILs thus indicating the presence of two distinct environments. It is found that the contribution of the slow component of the diffusion increases with increasing alkyl chain length of the cation. Not only are these results supported by the biexponential decay behavior of the fluorescence intensity of the systems, but the individual values of the lifetime components and their weight allow determination of the nature of the two major environments. In essence, the results point to the potential of the two combined techniques in unraveling some of the complex features of the ionic liquids.
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    Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br– (s = 5, 6, 8)/n-Propanol/Cyclohexane
    (ACS, 2020-03) Gangopadhyay, Subhashis
    The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12-s-12 (s = 5, 6, 8).2Br–/n-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content (Wo) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given Wo are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.
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    Polar Solvation Dynamics of H2O and D2O at the Surface of Zirconia Nanoparticles
    (ACS, 1999-08) Pant, Debi D.
    Time-resolved fluorescence-upconversion spectroscopy has been used to study the polar solvation dynamics of H2O and D2O at the surface of zirconia (ZrO2) nanoparticles. While an isotope effect is observed for the solvation dynamics of bulk D2O, there is no isotope effect on the interfacial solvation dynamics. The interfacial solvation dynamics are the same for H2O and D2O and are faster than the bulk solutions. The bulk isotope effect is due to stronger hydrogen bonding in D2O compared to H2O, slowing the reorientation of the excited-state dipoles in the bulk D2O. The lack of isotope effect for the interfacial dynamics is explained in terms of the solvent interacting with the ZrO2 surface.
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    Polar Solvation Dynamics of H2O and D2O at the Surface of Zirconia Nanoparticles
    (ACS, 1999) Pant, Debi D.
    Time-resolved fluorescence-upconversion spectroscopy has been used to study the polar solvation dynamics of H2O and D2O at the surface of zirconia (ZrO2) nanoparticles. While an isotope effect is observed for the solvation dynamics of bulk D2O, there is no isotope effect on the interfacial solvation dynamics. The interfacial solvation dynamics are the same for H2O and D2O and are faster than the bulk solutions. The bulk isotope effect is due to stronger hydrogen bonding in D2O compared to H2O, slowing the reorientation of the excited-state dipoles in the bulk D2O. The lack of isotope effect for the interfacial dynamics is explained in terms of the solvent interacting with the ZrO2 surface.
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    Basic Nitrogen (BaN) Is a Key Property of Antimalarial Chemical Space
    (ACS, 2023-06) Sundriyal, Sandeep
    Most antimalarials are based on basic N-heterocycles and possess amine functionalities. Despite this, the role of basic nitrogen (BaN) in antimalarial drug design has not been studied systematically. Our cheminformatics analysis indicates that BaN is an important feature of antimalarial space. We show that potent research antiplasmodials (RAP) and advanced-stage antimalarials (ASAMs) consistently show a higher BaN count (#BaN) compared to oral drugs. Similarly, BaN is often a vital feature of the hits obtained from phenotypic screenings despite the use of varied assay conditions. The literature review demonstrates that in several unrelated scaffolds, the addition of BaN results in enhanced antiplasmodial activity. In addition, potent antiplasmodials and HTS hits are bulky, lipophilic, and less polar and have a high aromatic ring count (#AR). This characterization of antimalarial space may be used to collate a focused compound collection to achieve higher hit rates in HTS, as shown retrospectively in this perspective.