Biomedical subjects

Tulsi Mukherjee

Publications and source records attributed to Tulsi Mukherjee.

25 records · Page 2Linked to original sources

PubMed2004

Radioprotection of DNA by glycyrrhizic acid through scavenging free radicals.

Gamma-radiation induced strand breaks in plasmid pBR322 DNA. Glycyrrhizic acid (GZA) protected plasmid DNA from radiation-induced strand breaks, as the disappearance of super-coiled (ccc) form was prevented by the compound with a dose-reduction factor of 2.04 at 2.5 mM concentration. Studies of comet assay on human peripheral blood leukocytes exposed to gamma radiation in the presence and absence of glycyrrhizic acid ex vivo revealed that this compound protected the cellular DNA from radiation-induced strand breaks in a concentration-dependent manner. An intraperitoneal administration of the GZA to mice one hour before exposure to gamma radiation protected cellular DNA from radiation-induced strand breaks in peripheral blood leucocytes and bone marrow cells, as revealed by comet assay. Pulse radiolysis studies indicated that glycyrrhizic acid offered radioprotection by scavenging free radicals. The rate constants for the reaction of glycyrrhizic acid with OH* and e(aq)- are 1.2 x 10(10 ) M(-1) s(-1) and 3.9 x 10(9 ) M(-1) s(-1), respectively.

Adult↗

PubMed2003

Synthesis and stabilization of cadmium and thallium metal nanoparticles in a polymer matrix.

In situ synthesis of fine thallium and cadmium particles has been carried out by gamma-irradiation at room temperature in a preorganized polyacrylamide gel. It appears that Cd and Tl ions are chelated by the polymer matrix through physical entrapment as well as by weak chemical complexation. The metallic nanoparticles of Cd or Tl are well dispersed in the polymer matrix. The nanoparticles are stable in air and transfer electrons to methyl viologen (paraquat; 1,1'-dimethyl-4,4'-dipyridinium dichloride; MV(2+)(Cl(-))(2)). The radical, MV(+.), formed upon electron transfer, also gets trapped in the polymer matrix and shows high stability even in the presence of air.

Journal Article↗

PubMed2003

Growth and reactivity of silver clusters in amino polycarboxylic acid solutions.

Reduction and subsequent aggregation of silver ions in the presence of various chelating agents such as trans-1,2-diaminocyclohexanetetraacetic acid (DCTA) 1,2-propylenediaminetetraacetic acid (PDTA), diethylenetriaminepentaacetic acid (DTPA), and triethylenetetraaminehexaacetic acid (TTHA) have been studied by pulse radiolysis. Rate constants of formation and transient absorption spectra for the ligand-complexed Ag(0) and Ag(2)(+) have been determined. The redox potential of Ag(+)(L)/Ag(0)(L) becomes more negative than that of Ag(+)/Ag(0). Growth and reactivity of silver clusters were also studied in the presence of methyl viologen (MV(2+)). The kinetics of formation of the MV(+*) radical, produced by the same pulse as in the case of silver atoms, confirms the catalytic electron transfer toward super critical silver clusters in the presence of ligands. The results suggest that catalytic electron transfer activity of silver clusters depends on the ligand.

Journal Article↗

PubMed2002

Charge transfer between tryptophan and tyrosine in casein: a pulse radiolysis study.

Charge transfer from tyrosine to tryptophan radicals in bovine milk casein, as observed using pulse radiolysis technique, is reported. The reactions of casein with hydroxyl, azide, Br(2)(*-) and CCl(3)O(2)(*) radicals have also been studied. Radical transformation was found to take place at a rate of 1.5 x10(4) s(-1). The effect of pH, oxidising radical and the proximity of tyrosine and tryptophan on this radical transformation, as well as repair of the casein radical by ascorbate, have also been studied.

Caseins↗

PubMed2002

Protective activities of some phenolic 1,3-diketones against lipid peroxidation: possible involvement of the 1,3-diketone moiety.

The protective activities of four ginger-derived phenolic 1,3-diketones (1-4) and curcumin (5) against lipid peroxidation was studied by using different biologically relevant model systems and pulse radiolysis. The extraordinary activity of 5 vis-à-vis 1-4 against Fe(2+)-mediated peroxidation may be attributed to the additional phenolic hydroxy group in the former, which lends it better iron-chelating and radical-scavenging properties. In iron-independent peroxidation, however, the ginger constituent [6]-dehydrogingerdione (1) showed activity comparable to that of 5; this indicates its higher affinity for the lipid peroxide radical (LOO(.)), due to its higher hydrophobicity. A very high rate constant for the reaction between 1 and Cl(3)COO(.), measured by pulse radiolysis, not only confirmed this, but also established the superior antioxidant efficacy of 1 in comparison to vitamins E and C. This was also evident from the results obtained from a liposomal peroxidation study with 1 and vitamin C. This study also established a synergistic effect of the latter on the antioxidant activity of 1. HPLC analysis of the products of the reaction between 1 and Cl(3)COO(.) revealed the formation of higher concentrations of ferulic acid (7), along with vanillin (6). The presence of ascorbate affected the generation of 7 more than it did that of 6. On this basis, a mechanism for the antioxidant action of 1 has been proposed, which suggests the contribution of the phenolic group as well as the active methylene group of the 1,3-diketones.

Animals↗

PubMed2002

Redox reactions of tocopherol monoglucoside in aqueous solutions: a pulse radiolysis study.

The reactions between tocopherol monoglucoside (TMG), a water-soluble vitamin-E derivative, with Br2.-, N3., (SCN)2.-, NO2., OH. and various halogenated peroxyl radicals were examined using a pulse radiolysis technique. The results demonstrate that TMG forms a stable phenoxyl radical at pH > 6.8. The thus-formed phenoxyl radical shows pH-dependent decay kinetics and is disproportionated by 2nd order kinetics at pH 2.3. It was observed that the TMG reactivity towards a halogenated peroxyl radical increases with the number of halogen atoms at the carbon atom having a peroxyl group. The reaction between the TMG phenoxyl radical and ascorbic acid was also examined using a pulse radiolysis technique. The results indicate that the TMG phenoxyl radical is repaired by ascorbate. Kinetic studies indicate that TMG may act as an antioxidant to repair free-radical damage to some biologically important compounds. The one-electron reduction potential for TMG was found to be 0.522 V +/- 0.06 vs. NHE.

Ascorbic Acid↗

PubMedDate not supplied

Temperature effect on the fluorescence anisotropy decay dynamics of Coumarin-153 dye in Triton-X-100 and Brij-35 micellar solutions.

The fluorescence anisotropy decay dynamics of the fluorescent probe Coumarin-153 (C153) have been investigated in two neutral micelles, Triton-X-100 (TX-100) and Brij-35 (BJ-35), at different temperatures and analyzed on the basis of the well-known two-step model. Because steady-state fluorescence spectra of the above probe do not show any noticeable changes with respect to temperature, for either of the studied micelles, suggests a similar polarity in the microenvironment around the probe at all the temperatures studied. The anisotropy results indicated that, for both the micelles, the fluidity inside the Palisade layer increases with temperature. However, the temperature effect on the anisotropy decay is relatively more pronounced in TX-100 than in BJ-35. It is inferred that the temperature effect on the anisotropy decay in the BJ-35 micelle is mainly due to the thermal effect on the microviscosity in the micellar phase. In the case of TX-100, the results indicate that, along with the above thermal effect, an additional effect is observed due to the increased size and hydration of the micelle with temperature, with the result being that the fluorescence anisotropy decay in TX-100 is more sensitive to temperature than in BJ-35. In the TX-100 micelle, our studies show that with an increase in temperature, even though the micellar size increases substantially, the distance of the probe from the micellar core does not increase that significantly. Thus, with increasing temperature, the probe undergoes a relative migration toward the micellar core to avoid the increased hydration in the micellar Palisade layer.

Anisotropy↗