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Ashok Kumar Mishra
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Ashok Kumar Mishra
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Ashok Kumar Mishra
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Mishra, Ashok Kumar
Mishra, Ashok E.
Kumar Mishra, Ashok
Mishra, Ashok K.
Mishra, A. K.
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185 results
Now showing 1 - 10 of 185
- PublicationInteraction of Human Intestinal Bile Salt with Bioactive Diet Capsaicin and Indole-3-Carbinol(21-05-2021)
;Mishra, JhiliHuman 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. - PublicationDetermination of quenching inhibition factor and selective fluorescence quenching study of perylene, pyrene and fluoranthene in micelle by cetyl pyridinium chloride as a hydrophobic quencher molecule(01-01-2001)
;Patra, DigambaraThe fluorescence quenching study of perylene, pyrene and fluoranthene by cetyl pyridinium chloride (CPC) a hydrophobic quencher molecule has been carried out using synchronous fluorescence scan. A quenching inhibition factor (QIF) has been defined for added quencher in inert micellar medium. The other quenching parameters calculated are KQ and EQ. The obtained quenching parameter QIF well compares with these values. The quenching mechanism is found to be explainable by a quencher sphere of action model. In micellar medium the fluorescence quenching efficiency is in the order: pyrene > perylene > fluoranthene. A correlation between alternate and non-alternate PAHs and aromatic ring size with QIF has been reported for CPC in micelle. - PublicationInvestigation on thermally aged natural ester oil for real-time monitoring and analysis of transformer insulation(01-04-2020)
;Amalanathan, Arputhasamy Joseph; ;Prakash, Swayam; ;Gautam, RibhuThermal 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. - PublicationModifying the aggregation behavior of poly (N-isopropylacrylamide) thermoreversible gel by a bile salt(01-09-2007)
;Kumar, Anitha C. ;Boral, Shilpi ;Bohidar, H. B.One possible method of altering the critical solution temperature (CST) of poly (N-isopropylacrylamide) (PNIPAM) gel is the addition of surfactants. Because of the biological origin of bile salts, their inclusion in PNIPAM could lead to better biocompatibility when the materials are used for biomedical applications. The gelling behaviour of PNIPAM was studied at various concentrations: PNIPAM concentrations in the range of 1% to 12% (w/v) and sodium cholate (NaC) concentrations varied from 0 to 20 mM. From fluorescence, DLS, rheology and turbidity studies it was found that in the presence of NaC, the CST shifts to lower temperature. This effect of the bile salt is in contrast to the effect of conventional surfactants which are known to shift the CST to higher values, due to mutual solubilization. A study of fluorescence spectroscopic parameters like fluorescence anisotropy, spectral shift, intensity and DLS measurements suggest that a NaC-induced aggregation could be responsible for this unusual observation. © 2007 IOP Publishing Ltd. - PublicationSynthesis and aggregation properties of dansylated glycerol-based amphiphilic polyether dendrons(01-09-2010)
;Vuram, Prasanna K. ;Subuddhi, Usharani ;Krishnaji, Subrahmanian Tarakkad; Glycerol-based amphiphilic polyether mono azide third-generation dendrons were synthesized through a divergent strategy. A repetitive synthetic sequence of O-alkylation and isopropylidene deprotection reaction was adopted for the synthesis, pentamethylene was used as spacer. Dansyl chloride was attached to the focal point as a fluorophore. The photophysical property in aqueous solution of the protected dendrons showed self-association behaviour from second generation onwards even at a very low concentration (1×10-8 M). A hypsochromic shift of around 60 nm in the emission maximum, significant increase in fluorescence intensity, almost ten-fold increase in the fluorescence anisotropy and a fourfold increase in average fluorescence lifetime of dansyl moi-ety were observed on going from first generation dendron to higher generation dendrons in aqueous medium. The absence of such behavior in the corresponding unprotected, relatively hydrophilic dendritic units clearly indicated that the aggregation is due to the presence of hydrophobic isopropylidene end groups. Quenching studies of the dendrimers in aqueous solution using a hydrophilic quencher Ag+ revealed that the dansyl moiety in protected higher generations dendritic units is significantly shielded from the surroundings, which further rendered support to the fact that higher order dendrons undergo aggregation in aqueous medium. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. - PublicationDevelopment of an analytical method combining chemometrics synchronous fluorescence : Analysis of diesel-kerosene mixtures(01-04-2008)
;Divya, O.Synchronous fluorescence spectroscopy (SFS) is a widely accepted technique for the analysis of multifluorophoric samples. Petroleum products are multifluorophoric: since they contain a mixture of variety polycyclic aromatic compounds (PACs). In this work, chemometric multivariate methods have been combined with SFS data to develop a reliable calibration for the estimation of kerosene fraction present in diesel. Efficient and robust models are created using multivariate techniques such as principal component analysis (PCA), principal component regression (PCR) and partial least square regression (PLSR). The models developed by these methods are able to perceive very low level of kerosene contamination with low prediction error. - PublicationDisaggregation of amphotericin B by sodium deoxycholate micellar aggregates(13-11-2008)
;Selvam, SusithraAmphotericin B (AmB) is present as aggregates in aqueous media. Sodium deoxycholate (NaDC) is known to cause disaggregation of AmB and to form monomers, as is observed by the increase of absorbance at 414 nm. By following the fluorescence intensity at 472 nm (λex 335 nm), it was found that with increasing NaDC concentration there is a progressive disaggregation of AmB leading to increase in both monomeric and dimeric forms. Although the presence of dimeric AmB form in NaDC micellar media is known, observation of the growth of the dimeric species is novel. Studies in fluorescence lifetime and steady state fluorescence anisotropy also support this conclusion. As NaDC (at ca. 10 mM) is the preferred choice of medium for AmB delivery and AmB aggregation has been implicated for its toxicity, the observation of dimeric AmB at these NaDC concentrations assumes significance. © 2008 Elsevier B.V. All rights reserved. - PublicationDisaggregation induced solvatochromic switch: A study of dansylated polyglycerol dendrons in binary solvent mixture(15-07-2014)
;Subuddhi, Usharani ;Vuram, Prasanna K.; A reversal in solvatochromic behaviour was observed in second and third generation glycerol based dansylated polyether dendrons in water on addition of a second solvent like methanol or acetonitrile. Below a certain percentage of the nonaqueous solvent there is a negative-solvatochromism observed and above that there is a switch to positive-solvatochromism. The negative-solvatochromism is attributed to the progressive disaggregation of the dendron aggregates by the nonaqueous solvent component. Once the disaggregation process is complete, positive-solvatochromism is exhibited by the dendron monomers. Higher the hydrophobicity of the dendron more is the amount of the second solvent required for disaggregation. © 2014 Elsevier B.V. All rights reserved. - PublicationInvestigation on simultaneous analysis of multicomponent polycyclic aromatic hydrocarbon mixtures in water samples: A simple synchronous fluorimetric method(03-08-2001)
;Patra, DigambaraSimultaneous analysis of multicomponent polycyclic aromatic hydrocarbons in mixture of micellar solution (CTAB) has been investigated. A simple synchronous fluorimetric method has been used, which does not require pretreatment of data, solving of large amount of data and large amount of solution preparation for internal calibration, thus making the analysis simple and fast. The method is fairly successful for analysis of 6, 7 and 10 components in a mixture solution. Attempt for 18-component analysis, however, shows a poor recovery for PAHs with low fluorescence. The detection limits are generally between 0.055 and 12.97 ng ml-1 except for benzo[b]anthracene with detection limit of 32.21 ng ml-1. © 2001 Elsevier Science B.V. - PublicationRecent developments in multi-component synchronous fluorescence scan analysis(01-12-2002)
;Patra, DigambaraThe ability to analyse complex multi-component mixtures without resorting to tedious separation procedures is extremely useful for routine analysis. Single-wavelength fluorescence measurement is limited in its ability to analyse complicated multi-component samples when they have severely overlapping emission and/or excitation spectra. This can be overcome by using synchronous fluorescence scan (SFS), where overlapping of spectra can be minimized. The selectivity of SFS can still be increased by taking derivative spectrum, applying different multivariate methods, selective fluorescence quenching, three-dimensional synchronous measurement or using some of these procedures in combination. Recent developments in various synchronous fluorescence methods for analysis of multi-component systems are discussed in this review. © 2002 Published by Elsevier Science B.V. All rights reserved.