Tomi Nath Das

Monomer and dimer radical cations of benzene, toluene, and naphthalene.

Pulse radiolytic generation of monomeric and dimeric cations of benzene, toluene, and naphthalene in aqueous acid media at room temperature and their spectrophotometric characterization is discussed. Results presented include measurements of each aromatics solubility in H(2)O-H(2)SO(4) and H(2)O-HClO(4) media over the acidity range pH 1 to H(0) -7.0, facile oxidative generation, and real-time identification of appropriate cationic transients with respective lambda(max) (nm) and epsilon (M(-1) cm(-1)) values measured as follows: C(6)H(6)(*+) (443, 1145 +/- 75), C(6)H(5)CH(3)(*+) (428, 1230 +/- 90), C(10)H(8)(*+) (381, 3650 +/- 225, and 687, 2210 +/- 160), (C(6)H(6))(2)(*+) (860, 2835 +/- 235), (C(6)H(5)CH(3))(2)(*+) (950, 1685 +/- 155), and (C(10)H(8))(2)(*+) (1040, 4170 +/- 320). Kinetic measurements reveal the respective formation rates of monomeric cations to be near-diffusion controlled, while the forward rate values for the dimeric species generation are marginally slower. The proton activity corrected pK(a) values are found to remain between -2.6 and -1.3 for the ArH(*+) species (C(6)H(6)(*+) most acidic, C(10)H(8)(*+) least acidic), while the pK(a) values of (ArH)(2)(*+) species vary from -5.0 to -3.0 ((C(6)H(6))(2)(*+) most acidic, (C(10)H(8))(2)(*+) least acidic). In H(0) -5 in aqueous H(2)SO(4), the respective stabilization energy of (C(6)H(6))(2)(*+), (C(6)H(5)CH(3))(2)(*+), and (C(10)H(8))(2)(*+) is estimated to be 16.6, 15.0, and 13.7 kcal mol(-1). Thus, the aqueous acid solution emerges as an alternative medium for typical radical-cationic studies, while offering compatibility for the deprotonated radical characterization near neutral pH.

Methane from benzene in argon dielectric barrier discharge

A first-time account of direct, on-line, instantaneous and efficient chemical conversion of gas phase benzene to methane in argon Dielectric Barrier Discharge (DBD) is presented. In the absence of another overt hydrogen-donating source, potency of analogous parents toward methane generation is found to follow the order: benzene>toluene>p-xylene. Simultaneous production of trace amounts of phenolic surface deposits suggest (a) prompt decomposition of the parent molecules, including a large fraction yielding atomic transients (H-atom), (b) continuous and appropriate recombination of such parts, and (c) trace moisture in parent contributing OH radicals and additional H-atoms, which suitably react with the unreacted fraction of the parent, and also other intermediates. Results highlight Ar DBD to be a simple and exploitable technology for transforming undesirable hazardous aromatics to usable/useful low molecular weight open-chain products following the principles of green chemistry and engineering.

Ozone Generation from Argon-Oxygen Mixtures in Presence of Different Packing Materials within Dielectric Barrier Discharge Gap

Assessments of ozone yield and concentration in Dielectric Barrier Discharge of argon-oxygen mixtures in presence of various packing materials are discussed. These include zeolite molecular sieve 13X pellets, Pyrex beads, Pyrex wool, and porous TiO2-beads, which presented differential reactive surfaces, nano cavities, photo-catalysis, and dissimilar ionic environments. Their utility was evaluated in conjunction with varied gas composition, flow rate, and electrical inputs. In a mixture of 3–21% O2 in argon, the ozone concentration ranged between 16–980 ppm, simultaneous measurements of in situ energy dissipation revealed its yield, G(O3) to change independently from 0.002 to 2.020 μmol J−1. TiO2 packing emerged as the most versatile material to produce O3 in high concentration and yield.

Septum Bleed during GC–MS Analysis: Utility of Septa of Various Makes

The significant presence of septum-related ghost peaks, causing interference in routine gas chromatography-mass spectrometry analyses at sample injection port temperatures above 100°C, is demonstrated. A comparative study with commonly employed septa of various types and makes under varying analytical conditions, e.g., injection port temperature, carrier flow rate, capillary column type and oven heating rate reveal that long-chain hydrocarbons, substituted phthalate derivatives and silanes (silicon compounds) are responsible for such interferences, which is confirmed from their respective peak fragmentation patterns after comparison with standard mass spectrometry library data. Consequently, prior blank studies at actual analysis conditions may become mandatory for quantification and reduction of such interferences, ignoring septa quality and performance claims.

Cold atmospheric plasma-modulated phorbol 12-myristate 13-acetate-induced differentiation of U937 cells to macrophage-like cells

Abstract Monocytes are recruited to injured tissue sites and differentiate into tissue macrophages or dendritic cells to protect against pathogens and repair the damaged tissues. Phorbol-12-myristate-13-acetate (PMA) is a well-known stimulus commonly used for differentiation of monocytes into macrophage-like cells (MϕLC). Here, we report the effect of Cold Atmospheric Plasma (CAP) on PMA-induced U937 differentiation into MϕLC. Treatment of U937 cells with PMA for 3 days and resting for 4 days increased the size of cytoplasm as compared with nucleus, and exposure to CAP before addition of PMA led to further increase in cytoplasm indicating the ability of CAP to modulate the differentiation of monocytes. Exposure of U937 cells to CAP or PMA increased cellular reactive oxygen species (ROS) level and the combination led to further augmentation of ROS. Treatment of U937 cells with PMA displayed a biphasic activation of proinflammatory transcription factor NF-κB, which plays an important role in differentiation and pretreatment with CAP further increased PMA induced NF-κB-DNA-binding activity. CAP also increased lipopolysaccharide induced secretion of TNF-α and IL-6 in MϕLC. Further investigation revealed that MϕLC or CAP-treated MϕLC were more resistant to anticancer drugs such as doxorubicin and 5-fluorouracil (5-FU) than U937 cells. Our present studies suggest an alternate protocol to modulate the differentiation of U937 cells into MϕLC by combining CAP and PMA.