Pradeep Pratap Singh

Activity-guided isolation of antioxidant xanthones from Swertia chirayita (Roxb.) H. Karsten (Gentianaceae)

An activity-guided isolation and purification process was used to identify the DPPH (l,l-diphenyl-2-picrylhydrazyl) radical-scavenging components of Swertia chirayita. A dry, whole plant of S. chirayita was extracted with different solvents and tested for its DPPH radical-scavenging activity. The acetone : water (8 : 2) extract showed the highest total phenolic content (TPC) and DPPH radical-scavenging activity, which was column chromatographed to obtain decussatin, swertianin, bellidifolin, isobellidifolin, amarogentin, swertianolin and mangiferin as active components. Good correlation was observed between TPC and DPPH scavenging activity among the extracts. The unique structure of xanthones, including the catecholic moiety and the completely conjugated system, enables them to be promising antioxidants.

Chemoselective Esterification of Phenolic Acids in the Presence of Sodium Bicarbonate in Ionic Liquids

Abstract Chemoselective esterification of phenolic acids with dialkyl sulphates or alkyl halides in the presence of sodium bicarbonate in 1,3‐dialkylimidazolium ionic liquids is reported in excellent yields and less reaction time as compared to organic solvents.

Chemoselective epoxidation of electron rich and electron deficient olefins catalyzed by meso-tetraarylporphyrin iron(III) chlorides in imidazolium ionic liquids

The oxygenation of substrates containing both electron rich and electron deficient olefins (1a–b) catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides [TAPFe(III)Cl] with H2O2 gave epoxides at both electron rich and deficient olefin (2a–b, 3a–b), while with iodosyl benzene (PhIO) gave the epoxides only at electron rich olefin (3a–b) in imidazolium ionic liquids (ILs). Further reaction of 2a–b with sodium hydroxide in methanol gave 4a–b by base catalysed rearrangement of enedione epoxides. Similar reaction of 4a–b with H2O2 or PhIO gave the major epoxides of electron deficient olefins and electron rich olefins. The ferric peroxy anions (TAP-FeIII–OO−) are effective intermediates in the epoxidation of electron deficient olefins, whereas the high valent oxoferrylporphyrin π-cation radicals (TAP-FeIVO˙+) are involved in the epoxidation of electron rich olefins. The ILs provide the special microenvironments by the interactions of cations and anions, in which the generation of the active intermediates from TAPFe(III)Cl/[Bmim][PF6] and monooxygen donors could be accelerated significantly.

Activity-guided isolation of antioxidants from the leaves of Terminalia arjuna

An activity-guided isolation and purification process was used to identify the l,l-diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging components of the food plant (Terminalia arjuna) of Antheraea mylitta. Dry leaves of T. arjuna were extracted with different solvents and tested for their antioxidant activity against DPPH•. The acetone–water (8:2) extract expressed strong DPPH radical-scavenging activity, and was subjected to column chromatography over silica gel. Gallic acid, apigenin, luteolin, quercetin, epicatechin, ellagic acid and 1-O-β-galloyl glucose were isolated as active components and characterised by using different spectroscopic techniques.

Activity-guided isolation of antioxidants from the roots of Rheum emodi

An activity-guided isolation and purification process was used to identify the DPPH free radical scavenging components of Rheum emodi. The activity-guided isolation revealed that eugenol, gallic acid, quercetin, rutin, epicatechin, desoxyrhapontigenin, rhapontigenin and mesopsin are the major phenolic compounds responsible for the antioxidant activity of the roots of R. emodi.

Environmental remediation by nanoadsorbents-based polymer nanocomposite

Abstract Environmental pollution due to human activities has become a serious problem around us, which has affected various living organisms worldwide. Therefore, there is an urgent need for new materials to remediate the polluted environment. Nanostructured sorbents offer the high sorption capacity and may be designed to target specific contaminants. Recently, the development of hybrid sorbents such as polymer-nanocomposites has opened up new dimensions for applications in the removal of pollutants from the environment. Polymer-nanocomposites have been utilized for the removal of many organic and inorganic contaminants such as hydrocarbons, dyes, and heavy metals from wastewater. This article will focus on the emerging concept of environmental remediation using polymeric nanocomposites.