Sharif Digital Repository

A mixture of cobalt(II) and manganese(II) salts of 4-aminobenzoic acid supported on silica gel catalyses the oxidation of thiols to disulfides in the presence of oxygen or air  

Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5-17 wt pct graphite were isothermally oxidized at 1000-1350°C. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range... 

A novel silica-functionalized dual Brønsted acidic ionic liquid (ionic liquid with two Brønsted acidic species) has been reported as a highly efficient catalyst for thioacetalization of carbonyl compounds. The reaction was efficiently performed in water as an environmentally benign solvent with good to high yields. Thermal gravimetric analysis showed that the catalyst is stable at least up to 350 C. Furthermore, the catalyst can be recycled and reused for six runs of reaction without appreciable loss of activity. The structure of the catalyst is modelized to gain more realistic structural insight about the functionalized ionic liquid  

The efficient oxidative coupling of thiols to disulfides with N-chlorosuccinimide (NCS) at room temperature is described. Simple workup, economical method, high yields of products are some advantages of this method. © 2006 Taylor & Francis  

Montmorillonite K10-supported manganese(II) chloride was found to be an efficient and convenient catalyst for the oxidative cleavage of oximes, phenylhydrazones and semicarbazones to the corresponding carbonyl compounds with molecular oxygen. © 2006 Bentham Science Publishers Ltd  

Various alkyl, aryl, and heterocyclic Hantzsch 1,4-dihydropyridines were converted to the corresponding pyridines in excellent yields and short times using sodium nitrite in the presence of a catalytic amount of acidic silica gel at room temperature. © Springer-Verlag 2006  

Sodium hypochlorite adsorbed on montmorillonite K10 is a useful oxidant for the oxidation of thiols to disulfides under the room temperature. © 2005 Bentham Science Publishers Ltd  

4-Aminoperoxybenzoic acid supported on silica gel in presence of oxygen or air was found to be a convenient and selective oxidant for the oxidation of benzylic methylene compounds to the corresponding ketones  

Kieselguhr supported copper chloride catalyses the oxidation of thiols to disulfides in the presence of oxygen or air  

The effects of resin type and content as well as graphite content on physical and mechanical properties of MgO-C refractories, such as density, porosity and strength were studied. The samples were formulated with various amounts of graphite and resin, and their oxidation behavior was isothermally investigated using a thermo gravimeter (TG), in air and at a temperature ranges from 900 to 1300 °C. The results indicated that, low-viscosity resins improved compressibility, but it degraded the strength. Higher resin content also improved the compressibility, but it caused higher porosity after preheating at 600 °C. The results also showed that the porosity and density of tempered samples were... 

The effects of graphite content on the density and oxidation behavior of MgO-C refractory samples were studied. The samples were formulated with various amounts of graphite and their oxidation behavior was investigated (in an isothermal condition); using a Thermo Gravimetric system (TG), in air and at temperatures ranging from 900"C to 1450"C. The preliminary results showed that the porosity and density of tempered samples were decreased when the graphite content was increased. However, after heating the samples at higher temperatures, the decreasing rate of porosity was lowered. At the beginning of the oxidation process, the rate of weight loss was high, but was gradually decreased when the... 

A solid state method for the oxidation of phenols to quinones is described using ammonium persulfate/wet silica gel as oxidant  

Benzoins are rapidly oxidised to benzils in high yields by iodic acid supported on alumina under solvent-free conditions and microwave irradiation  

Neurological diseases have different etiological causes. Contemporary, developing an ef-fective treatment for these diseases is an ongoing challenge. Cell therapy is recognized as one of the promising solutions for the treatment of these diseases. Amongst various types of stem cells, bone marrow-derived mesenchymal stem cells (BM-MSC) are known to be the most widely used stem cells. These cells are endowed with appealing properties such as the ability to differentiate into other cell types, including the muscle, liver, glial, and nerve cells. In this review study, we have systematically evaluated the ability of a variety of chemical compounds used in the last ten years to differentiate... 

Kinetics of oxidation of MgO-C refractory bricks containing 14.3% graphite, 80.9% magnesia, and 4.8% phenolic resin is investigated comprehensively. Effect of temperature and grain size distribution on the rate of oxidation of graphite is evaluated by application of a mathematical model developed on the basis of shrinking core/progressive conversion regime to the gas-solid processes involved. Incorporation of the experimental data into the mathematical model indicates that a mixed controlling mechanism governs the oxidation rate. Three activation energies were recognized: (a) 68 kJ/mol for chemical adsorption of gas on the surface of the graphite flakes, (b) 22 kJ/mol for pore diffusion of... 

Iodic acid supported on wet silica gel and K10 clay are used for the efficient oxidation of benzylic alcohols under microwave irradiation and solvent free condition  

The reaction pathway (including the transition state) of ethylene addition to permanganate (MnO4-) in the presence of ethylene glycol (EG) has been qualitatively and quantitatively studied by means of B3LYP/6-311++G* theoretical analysis. Interestingly, by cluster formation of the EG with permanganate, oxidation reaction becomes thermodynamically and kinetically more favorable. The influences of electron-withdrawing as well as electron-donating substituents were also explored. Results of the quantum theory of atoms in molecules and natural bond orbital analyses revealed that [3 + 2] addition reaction of alkenes in the presence of EG as hydrogen bonding donor to MnO4- becomes more exothermic.... 

Abstraction of hydrogen atom from DNA and RNA subunits leads to formation of a neutral radical. The formation of these radicals can lead to harmful structural alternations and formation of multiple lesions in helixes of DNA and RNA. In the present work, we explore theoretically energetic and structural properties of the possible radicals formed via hydrogen atom abstraction at various sites of sugar part of cytosine nucleosides by employing B3LYP exchange-correlation functional with 6-311++G (d,p) orbital basis sets. Two types of free radicals may be found by hydrogen abstraction of sugar part of cytosine nucleosides: carbon centered radicals and the oxygen centered radicals. The computation... 

The radical cations of DNA constituents generated by the ionizing radiation initiate an alteration of the bases, which is one of the main types of cytotoxic DNA lesions. These cation radical spices are known for their role in producing nucleic acid strand break. In this study, the gas-phase intrinsic chemical properties of the gaseous radical cations of cytosine and its base pair with guanine were examined by employing density functional theory (B3LYP) with the 6-311++G(d,p) basis set. Structures, geometries, adiabatic ionization energies, adiabatic electron affinities, charge distributions, molecular orbital analysis and proton-transfer process of these molecules were investigated. The... 

In this paper, we explore theoretically energetic and structural properties of the possible cations formed via hydride ion abstraction at various sites of sugar part of cytosine nucleosides by employing B3LYP exchange-correlation functional with 6-311++G (d,p) orbital basis sets. In general, the hydride ion abstracted sugar cations of cytosine nucleosides have the following stability sequence: caH2′ > caH1′ > caH3′ > caH4′ > caH5′ for cytidine and caH1′ > caH4′ > caH3′ > caH5′ > caH2′ for deoxycytidine. Furthermore, the effect of solvent environment on the stability order of cations integral equation formalism of the polarized model (IEF-PCM) was employed to model aqueous solution. The...