Ashok Kumar Mishra

Human intestinal bile salts are well-known for their solubilization and emulsification action in cosmetics, medicines, and chemicals. Here, an effort has been made to understand the solubilization mechanism of bioactive diet capsaicin (Cap) and indole-3-carbinol (I3C) in sodium taurocholate (NaTC) bile salt aggregates using both intrinsic and extrinsic fluorescent probes. Fluorescence study concludes that the NaTC micelle solubilizes both Cap and I3C. An increase in nonpolarity of the NaTC micellar environment is responsible for the solubilization of both Cap and I3C which is further confirmed by using an extrinsic probe Nile red (NR). Both Cap and I3C bind to the NaTC micelle as confirmed from the binding constant value. The location of both the bioactive molecules in the NaTC micelle has been confirmed from fluorescence quenching study using potassium iodide as a quencher. The effect of both I3C and Cap on the size of the NaTC micelle has been analyzed using dynamic light scattering.

Thermal aging of natural ester oil shows drastic reduction in partial discharge inception voltage (PDIV) and a significant variation is observed only above a certain aging time, under AC, DC, high frequency AC voltages and with harmonic voltages with different total harmonic distortion. Weibull distribution studies on PDIV measurements indicate a reduction in scale parameter (α) with increase in thermal aging temperature. A characteristic reduction in breakdown voltage was observed with the thermally aged ester oil, under AC, DC and standard lightning impulse voltage. The breakdown voltage variation with aged ester oil follows normal distribution. Ultraviolet (UV) analysis of ester oil thermally aged at 160°C has revealed a regular shift of the derived absorbance parameter to longer wavelengths. The interfacial tension and turbidity exhibits an inverse relationship with the thermally aged ester oil. Gas chromatography/mass spectrometric analysis of the thermally aged ester oil predicted the formation of more carboxylic acids and ketones with aging duration. The steady-state fluorescence on thermally aged ester oil exhibits a shift in its emission profile, which is in tandem with the UV absorption spectroscopic analysis. Fluorescence analysis can be adopted as a real-time monitoring tool in transformers, to understand the condition of liquid insulation. The viscosity dependence on the wavelength of derivative absorption maxima follows a direct relationship with the thermally aged natural ester oil.

A detailed photophysical study of two faecal pigments (FPs), Urobilin (UB) and Stercobilin (SB), and their zinc complexes [FP-Zn(II)] was carried out. The enhancement of UB and SB fluorescence resulting from the formation of their Zn(II) complexes was attributed to the complexation-induced rigidity of the chromophoric units, and the corresponding decrease of nonradiative decay rate constants of the excited singlet states (knr). The effect of various physicochemical environments was also studied in detail in order to understand the fluorescence behaviour of the Zn(II) complexes. FP-Zn(II) complexes have a lower solubility in water that results in the formation of molecular aggregates. The aggregation-induced loss of fluorescence of FP-Zn(II) complexes could be overcome by using the appropriate mixture of ethanol and water (70:30). Molecular orbital calculations on the FP-Zn(II) complexes provided a good idea of the geometry of the complexes and helped rationalise the enhancement of fluorescence after complexation. This study could pave the way towards developing a convenient non-extraction aqueous phase analytical procedure for detection of FPs using Zn(II) complexation method.

We designed and synthesized phenanthro[9,10-d]imidazoles (PIs) in a D-A fashion to achieve a balance of charge carriers. Solution processable bottom gate-top contact organic field-effect transistors (OFET) were fabricated using a binary solvent system. The devices exhibited excellent p-channel characteristics with a high mobility of 0.70 cm2 V-1 s-1 and an on/off ratio of 107. Frontier molecular orbital levels and packing modes obtained from computational analysis supported the observed high mobility of the synthesized PI. Solvatochromism study of the compounds marked them insensitive toward solvent polarity. Photophysical behavior of the compounds in tetrahydrofuran/H2O inferred efficient aggregate behavior. Scanning electron microscopy images of the aggregates in high water content show the formation of nanoaggregates. Dynamic light scattering experiments suggested a unimodal distribution of the nanoaggregates. This research work reports functionalized PIs with excellent OFET performance.

3-Pentadecylphenol (PDP) is a phenolic lipid easily available from natural sources. This compound has different pharmacological, biological and industrial applications. A molecular level understanding on the membrane modification properties of PDP on the dipalmitoylphosphatidylcholine (DPPC) bilayer has been carried out using fisetin as a sensitive interfacial head group region membrane probe. Membrane-inserted fisetin shows sensitive variation in its fluorescence properties (fluorescence intensity, lifetime, and anisotropy) with variation in the PDP concentration at the interfacial region of the lipid bilayer membrane. The formation of a mixed lipid system (i.e., DPPC + PDP) at a higher mol% of PDP (above 20 mol%) is responsible for the physico-chemical changes of the lipid bilayer membrane. The intrinsic fluorescence anisotropy data of PDP are also sensitive towards the membrane organizational changes of the DPPC lipid bilayer. The sensitivity of fisetin at the head group region of lipid membranes demonstrates that the alteration of bilayer properties is primarily caused by the abundance of the large phenolic headgroup.

This study demonstrates that significant perturbation of tween20:cholesterol(1:1) niosome membrane takes place even at premicellar concentration of bile salts. Here, 1-naphthol (1-NpOH), a known and sensitive excited state proton transfer (ESPT) probe, was used to understand the nature of perturbation of the membrane in an unbuffered medium. The significant decrease in 1-NpOH fluorescence intensity in niosome-bile salt mixed system at both lower (10 °C) and higher (50 °C) temperatures indicates the bile salts [sodium cholate (NaC) and sodium deoxycholate (NaDC)] induce perturbation of niosome membranes. Variations in the fluorescence lifetime values of both the prototropic emissions (neutral and anionic species) along with the proton transfer rate of 1-NpOH confirm the bile salts perturb up to the hydrophobic core domain of the niosomal membranes. Bile salts induce size change of the niosomal membrane is confirmed through dynamic light scattering study.

Flavonols have been studied extensively because of their interesting biological activities and excited-state intramolecular proton transfer (ESIPT) behavior. Galangin, kaempferol, quercetin, and myricetin are structurally related flavonols that differ only in the number of B-ring hydroxyl substituents. In this work, we have carried out a detailed study on the photophysical behavior of these structurally related flavonols in various solvents and a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) small unilamellar vesicles (SUVs) model membrane. We observed that these flavonols exist in different forms in the ground and excited states depending on the nature of the solvent. The weak intrinsic fluorescence of these flavonols gets enhanced in hydrogen-bond-accepting and alcoholic solvents. The phototautomer fluorescence intensity of these flavonols increases significantly in the DMPC membrane compared to water, suggesting ESIPT activation via binding interaction between flavonols and the membrane. According to our findings, both the number of B-ring hydroxy groups and membrane fluidity affect the flavonol binding with the membrane. The steady-state fluorescence intensity, steady-state anisotropy, fluorescence lifetime, and fluorescence anisotropy decay of flavonols were sensitive towards the temperature-induced DMPC membrane phase change. A quenching study has been performed to investigate the location and distribution of flavonols in the DMPC SUVs. Moreover, the antioxidant potential of flavonols in DMPC SUVs has been examined using the DPPH scavenging method. Our results reveal that the B-ring hydroxy groups significantly affect the photophysics, binding affinity, location, distribution, and DPPH scavenging activity of polyhydroxy-flavonols in the DMPC SUVs.

The nature of heterogeneity in maline deep eutectic system (DES) is characterised by inspecting the properties of the mixture at DES composition (1:1 choline chloride/malonic acid) and various mole fractions of the components at the vicinity of DES. Steady-state and time-resolved emission, and fluorescence anisotropy of suitable fluorescent probes in different choline chloride-malonic acid mixtures are used to describe the heterogeneity in various mixtures. Herein, we establish that nanodomains consisting of different molecule-ion clusters render DES' heterogeneous nature. The intermolecular interaction and the formation of molecule-ion structures are studied by spectroscopic technique including 1H NMR, 1H-1H-nuclear Overhauser effect, NMR diffusometry and mass spectrometry. It is demonstrated that the DES mixture comprises of a particular relative population of two different domains: a less polar domain (LP, 34%) and a more polar domain (MP, 66%). The physical properties of these domains strongly depend on the molar ratio of choline chloride and malonic acid. The experimental findings are further supported with theoretical predictions.

FDAPT (2-formyl-5-(4′-N,N-dimethylaminophenyl)thiophene) is an efficient environment-sensitive fluorescent probe, which senses the alteration of its microenvironment with six different fluorescent parameters, namely, emission intensity, wavelength, fluorescence anisotropy, and corresponding three time-dependent parameters fluorescence lifetime, time-resolved emission spectrum, and anisotropy decay. In the present work, the nature of saccharide-induced dehydration of a F127 polymeric micelle is investigated in detail with FDAPT emission. Using a multiparametric fluorescence approach, it is observed that the saccharide molecules not only decrease the critical micellization temperature of the F127 solution but also strongly alter the physical properties inside the micellar structures. The local polarity and fluidity significantly decrease in the saccharide-induced micelle as compared to the normal F127 micelle. The probe solvation dynamics study reveals that the water content in the core as well as corona domain diminishes significantly in the saccharide-induced micelle as compared to the normal micelle. More precisely, dehydration occurs more in the core region than in the corona region. Also, the saccharide-induced dehydration alters the relative size of the core and corona regions. The extent of dehydration varies with different saccharide molecules. It is also found that the dehydration efficiency order is trisaccharide (raffinose) > disaccharide (sucrose) > monosaccharide (glucose and fructose).

Fecal matter is considered to be one of the primary sources of water pollution. Understanding the aggregation behavior of the fecal pigments (FPs) could play a critical role in their detection and analysis. This work shows that in aqueous media, the fluorescence of FPs indicates the presence of multiple emitting species, which have been assigned to monomers, lower-order H-aggregates (dimers), and higher-order H-aggregates. Steady-state absorbance, fluorescence and time-resolved fluorescence decay studies conclude that the emission of FPs in aqueous medium indicates H-type of aggregation, even up to nanomolar and sub-nanomolar concentrations. Four sets of independent experiments involving the variation of (i) concentration of FPs, (ii) temperature, (III) pH, and (iv) ethanol/water composition as solvent media suggest the presence of monomer (540 nm), dimer (516 nm), and higher-order aggregates (500 nm) of FPs in aqueous solutions. The dimeric FP species appear to be present in the entire concentration range of 1 pM to 1 μM. Fluorescence lifetimes of H-aggregates are relatively longer as compared to the corresponding monomers. Hydrogen bonding appears to play an important role in forming H-aggregates in the aqueous phase of FPs as observed in the IR spectra of the FPs in dichloromethane. Density functional theory (DFT) calculations using the B3LYP functional and the LANL2DZ basis set show the contributions of Ï-πstacking and hydrogen-bonding interactions toward the formation of H-aggregated dimer of FPs in aqueous media.