Research works p roposed that RADICAL SCAVENGING ACTIVITY of flavonoids is due to ring B, and the remaining part of the molecule can be disregarded. Thus the objective of this work is to observe whether hydroxytoluenes account the RADICAL SCAVENGING ACTIVITY of flavonoid and to establish structural requirements for their ACTIVITY (as they showed appreciable ACTIVITY) and elucidate a comprehensive mechanism that can explain their ACTIVITY and termination. Thus, the RADICAL-SCAVENGING ACTIVITY of nine hydroxytoluene derivatives against 2, 2-diphenyl-1- picrylhydrazyl, DPPH was determined. The relative change in energy (DHf) associated with the formation of phenolic RADICALs and the spin distributions in these RADICALs were determined using computational programs (Density function theory and Hartree Fock). By correlating experimental data with DHf, the most active compounds and structural features that are responsible for their activities were identified. Reaction product of 4-methyl catechol with 2, 2-diphenyl-1-picrylhydrazyl, DPPH was isolated and characterized in order to unravel the mechanism of termination of most active hydroxytoluenes.Termination enthalpy (DH2) of methyl-catechols and methyl-hydroquinone, once the termination mechanism explained, was calculated to understand its role in the RADICAL SCAVENGING ACTIVITY.

In the present study, extracts of Echinops echinatus Roxb, roots were evaluated for RADICAL SCAVENGING activities using different in vitro models like SCAVENGING of 2,2 diphenyl-1-picrylhydrazyl (DPPH) RADICAL, nitric oxide RADICAL and superoxide anion RADICAL. The ethanolic extract of Echinops echinatus Roxb,root showed potent free RADICAL ACTIVITY when compared to standard Ascorbic acid. The observed ACTIVITY may be due to the presence of flavonoid and higher phenolic content in the extract.

The present study was carried out to determine the free RADICAL SCAVENGING properties of some plants found in Malaysia such as, Muntingia calabura; Bauhinia purpurea; Dicranopteris linearis; Melastoma malabathricum; Corchorus capsularis. The air-dried leaves of each plant (20 g) were soaked in distilled water (1:20; w/v) for 72 h at room temperature. The collected supernatants were tested for the free RADICAL SCAVENGING ACTIVITY against the DPPH and superoxide anion RADICAL SCAVENGING assays. All extracts were found to show remarkable antioxidant ACTIVITY in both assays with the percentage of inhibition (%) yielded 94–99% and 83–100%, respectively. Phytochemicals screening of all plants demonstrated the presence of flavonoids, saponins, triterpenes and steroids, but not alkaloids. Tannins was detected only in the leaves of M. calabura, D. linearis, M. malabathricum. The ability to scavenge free RADICALs indicates these plants could be used as a new source of antioxidant agents, and the ACTIVITY seen could be attributed to the synergistic effect of various bioactive compounds present in these extracts, particularly of the flavonoids type. Further study has been designed in our laboratory to isolate and to identify the bioactive compounds responsible for the observed antioxidant ACTIVITY.

Bay leaves (BL) (Laurus nobilis, Family: Lauraceae) are traditionally used orally to treat the symptoms of gastrointestinal problems, such as epigastric bloating, impaired digestion, eructation, and flatulence. In this study, lyophilized extracts (both water and ethanol) of BL were studied for their antioxidant properties. The antioxidant ACTIVITY, reducing power, free RADICAL SCAVENGING, superoxide anion RADICAL SCAVENGING, hydrogen peroxide SCAVENGING and metal chelating activities were evaluated to determine the total antioxidant capacity of both BL extracts. Both extracts exhibited strong total antioxidant ACTIVITY in linoleic acid emulsion. Concentrations of 20, 40, and 60 μg ml-1 showed 84.9, 95.7, 96.8, and 94.2, 97.7, and 98.6% inhibition of lipid peroxidation of linoleic acid emulsion, for water and ethanol extracts, respectively. On the other hand, 60 μg ml-1 of the standard antioxidants butylated hydroxyianisole (BHA), butylated hydroxytoluene (BHT), and α-tocopherol exhibited 96.6, 99.1, and 76.9% inhibition of lipid peroxidation in linoleic acid emulsion, respectively. In addition, the both BL extracts had effective reducing power, DPPH· free RADICAL SCAVENGING, superoxide anion RADICAL SCAVENGING, hydrogen peroxide SCAVENGING and metal chelating activities at 20, 40, and 60 μg ml-1. The total amount of phenolic compounds in each BL extract was determined as gallic acid equivalents.