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Paramita Das

Publications and source records attributed to Paramita Das.

7 recordsLinked to original sources
PubMed2006

Effect of nanocavity confinement on the rotational relaxation dynamics: 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine in micelles.

In continuation of our recent study on the steady state photophysics of a biologically active beta-carboline derivative, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in the present article we have investigated the effect of nanocavity confinement on the excited state dynamics and rotational relaxation of the probe using picosecond time resolved fluorescence and fluorescence anisotropy techniques. The polarity dependent intramolecular charge transfer process is responsible for the remarkable sensitivity of this biological fluorophore in micellar environments. The fluorescence anisotropy decay of AODIQ incorporated inside the micelle is biexponential. The rotational motion of the probe was interpreted on the basis of a two step model consisting of a fast restricted rotation of the probe and a slow lateral diffusion of the probe in the micelle; both coupled to the overall rotation of the micelle. Experimental results reveal that micellar environment causes significant retardation of both the wobbling as well as the translational motion of the probe.

Journal Article↗
PubMed2006

Fluorometric and isothermal titration calorimetric studies on binding interaction of a telechelic polymer with sodium alkyl sulfates of varying chain length.

Steady-state fluorescence measurements and isothermal titration calorimetric experiments have been performed to study the interaction between a telechelic polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), and sodium alkyl sulfate surfactants having decyl, dodecyl, and tetradecyl hydrocarbon tails. Fluorometric results suggest polymer-surfactant interaction in the very low range of polymer concentrations. The relative variation in the excimer to monomer pyrene emission intensities with varying surfactant concentration reveals that initial addition of surfactant favors intramolecular preassociation until the surfactant molecules start binding with the ethylene oxide (EO) chain. With the growing number of surfactant aggregates along the EO chain, the association becomes hindered due to the polyelectrolyte effect. The results from microcalorimetric titrations in the low concentration range of PYPY solution (approximately 10(-6) M) with alkyl sulfates suggest two kinds of surfactant-polymer interactions, one with the polymer hydrophobic end groups and the other with the ethylene oxide backbone. The overall polymer-surfactant interaction starts at a much lower surfactant concentration for the hydrophobically modified polymers compared to that in the case of unsubstituted poly(ethylene oxide) homopolymer. From the experiments critical aggregation concentration values and the second critical concentration where free micelles start forming have been determined. An endeavor has been made to unveil the mechanism underlying the corresponding associations of the surfactants with the polymer.

Journal Article↗
PubMed2006

Surfactant-induced modulation of fluorosensor activity: a simple way to maximize the sensor efficiency.

Tuning of the sensory capability of a potentially bioactive indoloquinolizine system, namely, 3-acetyl-4-oxo-6,7-dihydro-12H-indolo-[2,3-a]-quinolizine (AODIQ), is described in a biomimicking micellar nanocage. It has been shown that surfactant concentration dictates the sensing behavior of the fluorophore toward physiologically essential trace metals, such as Cu2+. This is a simple, efficient, and general technique that allows one to utilize the sensor to its maximum efficiency.

Biosensing Techniques↗
PubMed2006

Screening of antihelminthic effects of Indian plant extracts: a preliminary report.

INTRODUCTION: The purpose of the present study was to evaluate the antihelminthic effect of plants from the Ayurvedic system of medicine traditionally used in India. MATERIALS AND METHODS: Six plant extracts were assayed for their activity against free-living nematodes. Inhibitory effects on free-living nematodes were evaluated in vitro using aqueous or ethanolic extracts. CONCLUSIONS: Of six plants assayed, Momordica charantia yielded the best results, its crude extract producing 96% mortality.

Animals↗
PubMed2004

Single drop microextraction or solid phase microextraction-gas chromatography-mass spectrometry for the determination of iodine in pharmaceuticals, iodized salt, milk powder and vegetables involving conversion into 4-iodo-N,N-dimethylaniline.

A rapid sequence of oxidation and iodination using 2-iodosobenzoate as an oxidizing agent and N,N-dimethylaniline as an iodine scavenger at pH 6.4, when 4-iodo-N,N-dimethylaniline is formed, has been used for the determination of iodide by GC-MS. Solid phase microextraction (SPME) and single drop microextraction (SDME) have been used for the extraction of the iodo-derivative and their relative efficiencies compared. Pharmaceutical samples were subjected to solid phase extraction (SPE) for cleanup and the eluate analyzed for iodide. Iodate in salt samples was reduced to iodide with ascorbic acid. Milk powder and dried vegetables were wet combusted with peroxydisulfate to liberate covalently bound iodine as iodate which was reduced before derivatization. A rectilinear calibration graph was obtained for 0.1 microg-10 mg l(-1) iodide by both extraction methods, the correlation coefficient and limit of detection (LOD) were 0.9995 and 25 ng l(-1) iodide by SPME method, and 0.9998 and 10 ng l(-1) iodide by SDME method, respectively. SDME appeared to be more efficient technique than SPME for the present system. From the pooled data, the average recovery of spiked iodide to real samples was 100.7% (range 96.5-107.0%) with an average R.S.D. of 3.1% (range 2.6-4.5%).

Aniline Compounds↗
PubMed2003

Apoptosis is associated with an inhibition of aminophospholipid translocase (APTL) in CNS-derived HN2-5 and HOG cells and phosphatidylserine is a recognition molecule in microglial uptake of the apoptotic HN2-5 cells.

A balance of the activities of multiple enzymes maintains the typical asymmetry of plasma membrane lipids in healthy cells. Such enzyme activities are (a) the aminophopholipid translocase (APTL) (a lipid-selective P-type ATPase that catalyzes inward movement of aminophospholipids), (b) the scramblase (a calcium-dependent and ATP-independent enzyme that catalyzes both inward and outward movement of lipids), (c) the floppase (an ATP-dependent enzyme that catalyzes only outward movement of lipids). Activation or inhibition of any one of these enzymes would lead to a loss in this asymmetry. Apoptosis-associated externalization of phophatidylserine has been reported for many different cell-types, but the exact mechanism involved in this loss of membrane asymmetry has not been identified yet. In this report we demonstrate concurrence of APTL inhibition, caspase-3 activation and apoptosis in CNS-derived HN2-5 and HOG cells. Additionally, we provide data to demonstrate that the phagocytosis of apoptotic, CNS-derived HN2-5 cells by the microglial cells requires recognition through phosphatidylserine (PS). Thus the enzyme aminopholipid translocase is inhibited during apoptosis of CNS-derived cells and this alone could account for the loss of plasma membrane lipid-asymmetry observed in these cells.

Animals↗