Sharif Digital Repository

The free radical scavenging activity of a series of hydroxybenzohydroxamic acid derivatives have been studied in gas phase, water and benzene environments, using the density functional theory. Different mechanisms of reactions have been considered: single electron transfer (SET), hydrogen atom transfer (HAT). Rate constants were determined to know if the radical scavenging activity of these compounds proceeds via an H-atom or an electron-transfer mechanism. Calculations showed that the presence of the adjacent hydroxyl groups on phenyl ring increases the radical stability through intramolecular hydrogen bonds. The calculated bond dissociation enthalpy (BDE) values for hydroxyl groups on... 

Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired... 

Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au3 cluster on RO• vs its impacts on RO-H bond dissociation enthalpy, at B3LYP/ LACVP+* level (RH, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). In the presence of Au3 cluster, bond dissociation enthalpy of O-H bond and the spin density at the RO• oxygen are reduced dramatically. These are clear evidences for both the Au3 facilitation of the RO-H bond breakage and its scavenging of RO• radical. Since O-Au anchoring... 

Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au3 cluster on RO• vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). In the presence of Au3 cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO• oxygen are reduced dramatically. These are clear evidences for both the Au3 facilitation of the RO–H bond breakage and its scavenging of RO• radical. Since O–Au... 

Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of upmost importance in the living cell. Thymol derivatives exhibit various antioxidant activities and potential health benefits. Exploration of structure-radical scavenging activity (SAR) was approached with a wide range of thymol derivatives. To accomplish this task, the DPPH experimental assay along with quantum-chemical calculations were also employed for these compounds. By comparing the structural properties of the derivatives of interest, their antioxidant activity was explained by the formation of an intramolecular hydrogen bond and the presence of unsaturated double bond (–CHdouble bond; length... 

Rice bran is one of the most important co-products in the rice milling. In this research, antioxidant activity of two Iranian rice bran varieties, Fajr and Tarem, extracted by three different solvents (methanol, ethanol and ethyl acetate) was evaluated. The order of antioxidant activity was evaluated by measurement of total phenolic content, antioxidant activity in linoleic acid system, reducing power and scavenging capacity by DPPH radical. The methanolic extract of Fajr rice bran showed a total phenolic content of 3.31 mg Gallic acid/gr rice bran and a DPPH free radical-scavenging activity of 93.91%, achieved at 50 mg/ml concentration, and a percent inhibition of linoleic acid peroxidation... 

The free radical activity of lespedezacoumestan was investigated toward hydroxyl (˙OH) radical in polar and nonpolar media using density functional theory. Four reaction mechanisms including radical adduct formation, hydrogen atom transfer, sequential single electron-proton transfer (SET-PT), and sequential proton loss electron transfer were considered. The rate constants and branching ratio for all possible sites of reaction were calculated and reported for the first time. According to the obtained results, lespedezacoumestan reacts faster with ˙OH radical in aqueous solution than in nonpolar media. Also, lespedezacoumestan is an excellent ˙OH radical scavenger regardless of the environment... 

Organ ischemia with inadequate oxygen supply followed by reperfusion (which initiates a complex of inflammatory responses and oxidative stress) occurs in different clinical conditions and surgical procedures including stroke, myocardial infarction, limb ischemia, renal failure, organ transplantation, free-tissue-transfer, cardiopulmonary bypass, and vascular surgery. Even though pharmacological treatments protect against experimental ischemia reperfusion (I/R) injury, there has not been enough success in their application for patient benefits. The main hurdles in the treatment of I/R injury are the lack of diagnosis tools for understanding the complicated chains of I/R-induced signaling... 

Titanium nanotubes (TNTs) were prepared using TiO2 and decorated with CuO and Cu2O to have photocatalytic efficiency under visible light. TNTs decorated with copper oxides (TNT-CuO and TNT-Cu2O) were confirmed by the elemental mapping and XPS results. Unlike TNT and TiO2, TNT-CuO and TNT-Cu2O showed higher photocatalytic activity, such as antimicrobial and ethylene scavenging activities under visible light. Between the two types of copper oxide-decorated TNTs, TNT-Cu2O showed photocatalytic activity higher than that of TNT-CuO. The ethylene scavenging activity of TNT-Cu2O was about 40% higher than that of TNTs and TNT-CuO. The photocatalytic activity of titanium-based nanoparticles was... 

Worldwide energy and environmental issues are forcing researchers to develop a green approach to produce a clean energy. However, traditional methods in reforming of fossil fuels to produce hydrogen (H2) are causing CO2 emission. Hydrogen is therefore an indirect greenhouse gas with a global warming potential. Hydrogen with high specific energy density can be considered as an efficient energy carrier as compared to fossil fuels. But hydrogen production from water splitting reaction has low efficiency, which limits its generation by green approach. For addressing this issue, different chemical hole scavengers have been applied, which is causing further environmental and economic problems. By... 

Manganese doped on cubic phase nanoparticles of ZrO2 was synthesized by an impregnation method. These novel particles were carefully analyzed by various chemico-physical methods. The catalytic degradation of an organic dye, methylene blue, in the presence of Mn-doped ZrO2 nanoparticles, as well as ZrO2 nanoparticles as catalyst with aqueous hydrogen peroxide, H2O2, as an oxidizing agent has been studied in aqueous solution at room temperature. Effects of solution pH, catalyst composition and radical scavenging agents on the degree of degradation of methylene blue were also studied. Finally, the recoverability and reusability of the... 

Two types of nanosized photocatalyst, TiO 2 P-25 and ap/Ag/AgBr/TiO 2, were used for decolorization of Acid Blue 92 (AB92) in dark, visible light (V-L), and UV media. Under UV and V-L, the effect of three possible photodegradation processes of AB92 including photocatalytic degradation, self-photosensitization, and direct photolysis were studied. Results showed that in UV/photocatalysts, photocatalytic degradation is the major process for photodecolorization. However, in the presence of TiO 2, self-photosensitization has the major role under V-L. Because of the presence of AgBr as photoactive center in ap/Ag/AgBr/TiO 2, the main process is the photocatalytic degradation in V-L. By using... 

Herein, an electrochemical technique as a cost-effective and one-step approach was utilized to fabricate graphene quantum dots (GQDs). Different amounts of GQDs (0, 0.2, 0.4, 0.8, and 1.2 wt %) were decorated uniformly on the surface of anodized ZnO nanowires (NWs) forming GQD/ZnO NWs. Transmission electron microscopy and atomic force microscopy confirmed formation of GQDs on the ZnO NWs, 12-22 nm in width and 1-3 graphene layers thick. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were employed to verify the functional groups on the surface of GQDs, and the results indicated that GQDs readily anchored on the surface of ZnO NWs. The GQD/ZnO NWs exhibited a... 

Vanadium supported on spinel cobalt ferrite nanoparticles was synthesized and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray analysis and transmission electron microscopy. For the first time, the prepared material was used for the catalytic degradation of methylene blue as an organic dye in the presence of hydrogen peroxide as a green oxidant and NaHCO3 as a co-reagent at room temperature. The dependency of removal percentage on various parameters such as amount of catalyst, pH, reaction time and temperature and the effect of radical scavenging agents were studied. Finally, recoverability and reusability of the vanadium supported on... 

TiO2 nanotubes (TNTs) were synthesized hydrothermally and modified by Cu2O using a sol-gel method to provide photocatalytic activity in visible light. Cellulose nanofiber (CNF)-based films were prepared by adding TiO2, TNTs, and Cu2O-modified TNT (TNT-Cu2O). The TiO2-based nanoparticles (TiO2, TNTs, and TNT-Cu2O) were uniformly distributed in the base polymer to make compatible and flexible films. The incorporation of nanoparticles significantly enhanced the UV-shielding properties of the film while slightly decreasing the transparency. Incorporating nanofillers improved the film's mechanical and water resistance properties depending on the nanoparticle type. The TNT-Cu2O-added CNF film... 

The mechanism of surfactants in surfactant-in situ chemical oxidation (S-ISCO) coupled process for trichloroethene (TCE) degradation was firstly reported. The performance of TCE solubilization and inhibition of TCE degradation in three nonionic surfactants (TW-80, Brij-35, TX-100) in PS/Fe(II)/citric acid (CA) system was compared and TW-80 was evaluated to be the optimal surfactant in S-ISCO coupled process due to the best TCE solubilizing ability and minimal inhibition for TCE degradation (only 31.8% TCE inhibition in the presence of 1 g L−1 TW-80 surfactant). The inhibition mechanism in TCE degradation was also demonstrated by comparing the strength of ROSs and PS utilization. In the...