Ankur A. Awasthi

Bio: Ankur A. Awasthi is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Diffusion (business) & Solvation. The author has an hindex of 5, co-authored 11 publications receiving 98 citations. Previous affiliations of Ankur A. Awasthi include University of Mumbai & University of Victoria.

Stimulus-Responsive Supramolecular Aggregate Assembly of Auramine O Templated by Sulfated Cyclodextrin.

Abstract: Self-aggregation of organic molecules is rarely seen with macrocyclic hosts like β-cyclodextrin, as they preferentially involve the formation of inclusion complexes with the guest molecule In this contribution, we report the self-aggregation of a guest molecule induced by negatively charged sulfated β-cyclodextrin (SCD) to yield highly emissive aggregates of a recently projected amyloid marker dye, Auramine O (AuO) The SCD templated AuO aggregates display very different photophysics when compared to its reported behavior in a wide range of various chemical and biological environment but show a remarkable similarity with the recently reported photophysical behavior of AuO in human insulin fibrillar media, thus providing important insights into the molecular form of AuO responsible for its amyloid sensing ability The self-assembled AuO aggregates formed in the presence of SCD display a significantly long excited-state lifetime, suggesting the retardation of the torsional relaxation of dye in the aggregat

Thermally Activated Delayed Fluorescence (Green) in Undoped Film and Exciplex Emission (Blue) in Acridone–Carbazole Derivatives for OLEDs

Abstract: Donor–acceptor–donor materials (1,2) having acridone as acceptor unit and carbazole as donor were synthesized for optoelectronic applications. Carbazole was substituted on 2,7 positions of acridone in 1, while 3,6-trifluoromethylphenyl carbazole was substituted in 2. Steady-state and time-dependent emission properties of these compounds were studied in detail to get insight into their possible thermally activated delayed fluorescence (TADF) behavior. The singlet–triplet energy gap (ΔEST) was found to be as low as 0.17 eV (1) and 0.15 eV (2), favorable for TADF materials. Both these materials were found to be efficient green TADF emitters in organic light-emitting diode (OLED) devices. Interestingly, the TADF properties were observed for the first time in undoped 1,2-based devices, i.e., without host matrix, unlike the most commonly reported TADF emitters. Furthermore, an exciplex emission at 465 nm was observed in the blends of 1,2 with poly(vinylcarbazole) (PVK) in 1:7 (w/w) ratio. OLEDs with the blend o...

On the Molecular Form of Amyloid Marker, Auramine O, in Human Insulin Fibrils.

Abstract: Designing extrinsic fluorescence sensors for amyloid fibrils is a very active and important area of research. Recently, an ultrafast molecule rotor dye, Auramine O (AuO), has been projected as a fluorescent amyloid marker. It has been claimed that AuO scores better than the most extensively utilized gold-standard amyloid probe, Thioflavin-T (ThT). This advantage arises from the fact that AuO, in addition to its usual emission band (∼500 nm), also displays a large red-shifted emission band (∼560 nm), exclusively in the presence of human insulin fibril medium and not in the native protein or buffer media. On the contrary, for ThT, the emission maximum (∼490 nm) largely remains unchanged while going from protein to fibril. This otherwise unknown large red-shifted emission band of AuO, observed in the presence of human insulin fibrils, was tentatively attributed to a species formed upon fast proton dissociation from excited AuO. It was proposed that because of the long excited-state lifetime (∼1.8 ns) of AuO upon association with human insulin fibrils, this fast proton dissociation from excited AuO could be observed, which is otherwise not observed in buffer or native protein media, owing to its very short excited-state lifetime (∼1 ps). Herein, we show that despite the long excited-state lifetime of AuO in other fibrillar media (human serum albumin and lysozyme), the new red-shifted emission band at 560 nm is not observed, thus possibly suggesting a different origin of the red-shifted emission band of AuO in human insulin fibril medium. We convincingly show that this red-shifted band of AuO (∼560 nm) could be observed under conditions that promote dye aggregation, such as a premicellar concentration of surfactants and polyelectrolytes. These AuO aggregates display strong emission wavelength dependence of transient decay traces, similar to that for AuO in human insulin fibril medium. Detailed time-resolved emission spectral (TRES) measurements suggest that the AuO/premicellar surfactant and AuO/human insulin fibril system share similar features, such as a dynamic red-shift in TRES and an isoemissive point in the time-resolved area-normalized emission spectra, suggesting that the characteristic red-shifted emission band of AuO in human insulin fibril medium may arise from AuO aggregates.

Proton Transfer Reaction Dynamics of Pyranine in DMSO/Water Mixtures.

Abstract: Photoinduced intermolecular excited-state proton transfer (ESPT) reactions are ubiquitous in chemistry and biology. ESPT reactions are extremely sensitive to the nature of water molecules in its microenvironment and thus serve as a sensitive reporter for the water structure and dynamics in a system. Herein, the photoinduced intermolecular ESPT reaction of 8-hydroxypyrene-1,3,5-trisulfonic acid (HPTS, also known as pyranine) has been investigated in various DMSO/water mixtures by using steady-state and time-resolved emission spectroscopy. The DMSO/water binary mixture yields an interesting and anomalous behavior for the proton transfer reaction dynamics of HPTS at a mole fraction of DMSO (XDMSO ) of 0.41-0.51, which has also been previously investigated and projected as an anomalous region by molecular dynamics simulation and other experimental techniques. The extreme slowdown of the proton transfer reaction observed at XDMSO =0.41-0.51 has been attributed to the slow solvation dynamics, as well as the non-availability of free water molecules at this composition, which are required to solvate the newly generated proton. These observations have been also corroborated by time-resolved area-normalized emission spectra. The dimensionality of the proton diffusion process has been investigated by analyzing the geminate recombination process, and is found to be significantly different in DMSO/water mixtures (XDMSO =0.41-0.51) compared with three-dimensional proton diffusion in neat water.

Excited-State Proton Transfer on the Surface of a Therapeutic Protein, Protamine

Abstract: Proton transfer reactions on biosurfaces play an important role in a myriad of biological processes. Herein, the excited-state proton transfer reaction of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) has been investigated in the presence of an important therapeutic protein, Protamine (PrS), using ground-state absorption, steady-state, and detailed time-resolved emission measurements. HPTS forms a 1:1 complex with Protamine with a high association constant of 2.6 × 104 M–1. The binding of HPTS with Protamine leads to a significant modulation in the ground-state prototropic equilibrium causing a downward shift of 1.1 unit in the acidity constant (pKa). In contrast to a large number of reports of slow proton transfer of HPTS on biosurfaces, interestingly, HPTS registers a faster proton transfer event in the presence of Protamine as compared to that of even the bulk aqueous buffer medium. Furthermore, the dimensionality of the proton diffusion process is also significantly reduced on the surface of Protamine tha...

Principles Of Fluorescence Spectroscopy

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Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

A pH-responsive and magnetic Fe3O4@silica@MIL-100(Fe)/β-CD nanocomposite as a drug nanocarrier: loading and release study of cephalexin

Abstract: In the present work, a novel magnetic and pH-responsive porous nanocomposite was prepared by the surface grafting of β-cyclodextrin onto Fe3O4@silica@MIL-100(Fe). The effect of pH and temperature on the adsorption of cephalexin and release behavior of the developed nanocomposite was studied. It was found that the maximum adsorption occurs at room temperature while fast release occurs at higher temperature. Among different two-parameter isotherm models, the results showed that the adsorption of the drug was well described by the Langmuir isotherm model. Different kinetic models including film-transfer, intra-particle diffusion, and pseudo-second order kinetic models were used to investigate the mechanism of adsorption. Thermodynamic studies indicated that the adsorption of cephalexin onto the nanocomposite was exothermic and spontaneous. In addition, the nanocomposite showed sensitive pH-dependent behavior. Finally, mathematical kinetic models such as zero-order, first-order, Korsmeyer-Peppas and Higuchi were studied to investigate the drug release profile where the kinetics of release were well described by the Higuchi model.

Stimulus-Responsive Supramolecular Aggregate Assembly of Auramine O Templated by Sulfated Cyclodextrin.

Abstract: Self-aggregation of organic molecules is rarely seen with macrocyclic hosts like β-cyclodextrin, as they preferentially involve the formation of inclusion complexes with the guest molecule In this contribution, we report the self-aggregation of a guest molecule induced by negatively charged sulfated β-cyclodextrin (SCD) to yield highly emissive aggregates of a recently projected amyloid marker dye, Auramine O (AuO) The SCD templated AuO aggregates display very different photophysics when compared to its reported behavior in a wide range of various chemical and biological environment but show a remarkable similarity with the recently reported photophysical behavior of AuO in human insulin fibrillar media, thus providing important insights into the molecular form of AuO responsible for its amyloid sensing ability The self-assembled AuO aggregates formed in the presence of SCD display a significantly long excited-state lifetime, suggesting the retardation of the torsional relaxation of dye in the aggregat