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470 results on '"Chaudhuri, Tapas"'

28. Comparative phytochemical profiling and effects of Nerium oleander extracts on the activities of murine peritoneal macrophages

Author

Dey Priyankar and Chaudhuri Tapas Kumar

Subjects
GC-MS, immunomodulatory, macrophage, Nerium oleander, nitric oxide, phagocytosis, Biology (General), QH301-705.5
Abstract

Nerium oleander is a medicinal plant. Apart from its ethnopharmacological uses, pharmacognostic studies have revealed several of its bioactivities. Previously we demonstrated that the phenolic and flavonoid rich extracts of oleander leaf, stem and root possess potent antioxidant and free radical scavenging activities. Moreover, the leaf extract actively modulates the Th1/Th2 cytokine balance and exerts anti-inflammatory activities on murine splenic lymphocytes. Therefore, the present study was designed to evaluate the effect of oleander leaf, stem and root extracts on phagocytosis and the free radical-related activities of murine peritoneal macrophages. In addition, phytochemical profiling was performed using gas chromatography-mass spectrometry (GC-MS). The results demonstrated that the increase in phagocytosis and decrease in myeloperoxidase (MPO) were in the order of leaf>root>stem. The inhibition of cell adhesion, nitric oxide (NO) and elevation of respiratory burst activity was in the order of leaf>stem>root. However, the bioactivities of the leaf extract were much high than those of the stem and root extracts. Phytochemical analysis also revealed the presence of several bioactive constituents in oleander extracts. Therefore, the present study demonstrated that oleander possesses the capacity to modulate macrophage activities and the bioactivities are attributed to the numerous phytochemicals identified in oleander extracts.

Published
2016
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35. Electrical and photo-electrical properties of spin-coated nanocrystalline PbS thin films evaluated using thermoelectric effect.

Author

Vankhade, Dhaval and Chaudhuri, Tapas K.

Subjects
*THIN films, *SEEBECK coefficient, *ELECTRON traps, *THERMOELECTRIC power, *THERMOELECTRIC effects, *CONDUCTION bands, *ELECTRIC conductivity
Abstract

Nanocrystalline (NC) PbS films have the potential to be used as tunable photodetectors and solar cells, but their electrical properties are not yet understood. The electrical and photo-electrical properties of NC PbS thin films deposited by spin-coating have been investigated. The films are p-type and photoconducting. Electrical conductivity (σ), thermoelectric power (αth), hole concentration (p), and mobility (μ) of the films in dark and under illumination were measured in the temperature range of 77–300 K. These parameters behaved differently in the low temperature region (LTR) of 77–150 K and the high temperature region (HTR) of 250–300 K. In LTR, dark p was constant (∼1014 cm−3) while thermally activated in HTR. In LTR, dark μ varied as T1.5 due to impurity scattering, while in HTR, μ varied as T−(4.2–9.2) due to lattice scattering. Under light, p was ∼1018 cm−3 in LTR while thermal quenching occurred in HTR suggesting the existence of electron traps below the conduction band, which act as sensitization centers. The quenching energy was 130–90 meV, which varied with film thickness. The μ of illuminated PbS films decreased with temperature as T−n due to lattice scattering. The NC PbS films showed high photoconductivity in LTR with a light to dark conductivity ratio of 103. Photoconductivity is explained on the basis of trapping of minority carriers by sensitization centers. [ABSTRACT FROM AUTHOR]

Published
2020
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