Sharif Digital Repository

At room temperature, alcohols and phenols are efficiently protected with hexamethyldisilazane (HMDS) in the presence of silica sulfuric acid in good to excellent yields. The catalyst can be recycled for subsequent reactions without any appreciable loss of efficiency. Copyright © Taylor and Francis Group, LLC  

A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO4 in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO2 system for silylation of alcohols in the presence of amine and phenolic hydroxy groups  

A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO4 in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO2 system for silylation of alcohols in the presence of amine and phenolic hydroxy groups. © 2005 Elsevier B.V. All rights reserved  

Titania was deposited on glass fibers with a partial epoxy layer coating from a solution containing TiO2 nanoparticles at T = 90°C, and the adsorption process was examined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, and photocatalytic activity measurements. XPS data demonstrated that about 25% of the surface was covered with TiO2 nanoparticles, with 10% on the epoxy layer and 15% on the glass body. It was found that TiO2 nanoparticles can be readily adsorbed on epoxy groups, whereas they have a low tendency to adsorb on carbon polymer chains. This difference can be... 

The pK a of an acyclic aliphatic heptaol ((HOCH 2CH 2CH(OH)CH 2) 3COH) was measured in DMSO, and its gas-phase acidity is reported as well. This tertiary alcohol was found to be 10 21 times more acidic than tert-butyl alcohol in DMSO and an order of magnitude more acidic than acetic acid (i.e., pK a = 11.4 vs 12.3). This can be attributed to a 21.9 kcal mol -1 stabilization of the charged oxygen center in the conjugate base by three hydrogen bonds and another 6.3 kcal mol -1 stabilization resulting from an additional three hydrogen bonds between the uncharged primary and secondary hydroxyl groups. Charge delocalization by both the first and second solvation shells may be used to facilitate... 

Natural and synthetic anion receptors are extensively employed, but the structures of their bound complexes are difficult to determine in the liquid phase. Infrared spectroscopy is used in this work to characterize the solution structures of bound anion receptors for the first time, and surprisingly only two of three hydroxyl groups of the neutral aliphatic triols are found to directly interact with Cl-. The binding constants of these triols with zero to three CF3 groups were measured in a polar environment, and KCD3CN(Cl-) = 1.1 × 106 M-1 for the tris(trifluoromethyl) derivative. This is a remarkably large value, and high selectivity with respect to interfering anions such as, Br-, NO3 -... 

Electro-oxidation of methanol on Ni in NaOH solutions with the alkali concentration in the range of 0.05-0.5 M and in the presence of 0.5 M Na 2SO4 supporting electrolyte is studied. All the mentioned species compete for adsorption on Ni and OH- is essential for the electro-oxidation process. The electro-oxidation seems to proceed through the electro-chemical reactions of adsorbed methanol and hydroxide species and the removal of the resulting intermediate by adsorbed hydroxyl groups. The mechanism is consistent with the cyclic voltammetry and impedance spectroscopy results and can semi-quantitatively account for the appearance of capacitive, inductive and negative resistance loops as well... 

The effect of oxygenate modifiers on the performance of PtSnγAl 2O3 catalyst in dehydrogenation of propane was studied. Dehydrogenation reaction was carried out in a fixed-bed quartz reactor in the temperature range of 575620 °C. Two types of oxygenate modifiers, namely water and methanol, were added to the feed. The optimum amounts of water for reaction temperatures of 575, 600 and 620 °C were 84, 120 and 140 ppm, respectively. The optimum amounts of methanol for the same reaction temperatures were 9.9, 25 and 50 ppm, respectively. Any further addition of water or methanol beyond these optimum levels resulted in a loss in activity. The addition of water or methanol led to the formation of... 

The synthesis of mono- and bi-supported Ziegler-Natta catalysts using magnesium etoxide Mg(OEt)2 and graphene oxide (GO) as catalyst support for production of Ultra High Molecular Weight Polyethylene (UHMWPE) is reported in this investigation. Nano-graphene oxide was prepared by the modified Hummer's method and its structure was analyzed by XRD and FTIR indicating the presence of hydroxyl groups on graphene oxide and the formation of an exfoliated structure. The activity of TiCl4/Mg(OEt)2, TiCl4/Mg(OEt)2-GO, and TiCl4/GO catalysts in terms of grams of PE produced per mmol of Ti per hour was experimentally obtained for catalysts with different ratios of co-catalyst (triisobutylaluminium) to... 

By modifying the mouth of a macrocyclic dicobalt Pacman complex, it is possible to both isolate new bridging-superoxo and hydroxyl complexes and to tune the reactivity of this system towards catalytic four-electron reduction of dioxygen to water  

The physical properties and chemical structure of a new biosurfactant (licheniformin) produced by Bacillus licheniformis MS3 were investigated. The purified biosurfactant was identified as a lipopeptide with amino acid sequence of Gly, Ala, Val, Asp, Ser, Gly, Tyr and a lactone linkage between the carboxyl group of Aspargine and hydroxyl group of Tyrosine residue. The fatty acid moiety was attached to N-terminal amino acid residue through an amide bond. The purified licheniformin could lower the surface tension of water from 72 to 38 mN/m at concentrations higher than 15 μg/mL and its relative emulsion volume (EV%) was equal to 36%. It also showed stable surface activity over a wide range of... 

Polyols were used as model ligands for Mg2+, Ca2+, and Zn2+ complexes to study the role of the hydrogen bond network on the metal binding affinity and modulation of successive pKa values using density functional theory. The results confirm that the acidity of polyols dramatically increases upon metal complexation in the order Zn2+ > Mg2+ > Ca2+. For example, the three H-site positions in the hydroxyl groups of the heptaol, bound to Zn2+, are 11.2, 29.9, and 30.9 pKa units (in methanol) more acidic than those of pure heptaol. This acidity enhancement leads to making polyols as good ligands toward complexation. For instance, the formation constants of the heptaol in the presence of Zn2+, Mg2+,... 

Comparison of the traditional linear heating method of TPD with an original stepwise heating scheme was reported for the first time. Stepwise heating TPD was carried out by keeping the temperature constant as soon as ammonia desorption signal rises until the signal returns to the baseline. More ammonia desorption peaks on a SAPO-34 catalyst were identified using TPD with stepwise heating. The effect of temperature ramp on desorption peak broadening in TPD curve was also addressed. The more distinct ammonia desorption peaks in stepwise TPD indicates that ammonia adsorbs in about five or six different ways on SAPO-34, and attribution of different adsorptions may be explained considering some... 

Effect of alumina nanoparticle (ANP) on the properties of rubber compounds based on nitrile-butadiene-rub- ber (NBR) and NBR/phenolic-resin (PH) blend is examined. To investigate the surface characteristics of the nanoparticles on the performance of nanoalumina- filled compounds, trimethoxyvinylsilane (MVS) is attached chemically on the surface of ANP through an appropriate functionalization process. Various NBR and NBR/Ph compounds filled with ANP and functionalized ANP (f-ANP) are prepared via melt mixing using traditional open two-roll mill. Microscopic analysis carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveals good dispersion of... 

The derivatives of glucose such as glucosamine (β-D-GlcN) and N-acetyl-D-β-glucosamine (GlcNAc) are significant in several biological systems. D-GlcN has been used widely to treat osteoarthritis in humans and animal models as well as GlcNAc has been proposed as a treatment for autoimmune diseases. The DFT/B3LYP/6–311++G (d,p) method as well as QTAIM and NBO analyses were used to the acidity values of D-GlcN and GlcNAc sugars and their complexes with alkali ions in the gas phase. The Li+, Na+ and K+ prefer bi-dentate chelate in these complexes. The computed results indicate that metal ion affinity (MIA) in GlcNAc is higher than that in D-GlcN. There are direct correlations between the MIA... 

In this work, a novel carrier based-on modified graphene oxide was designed for co-delivery of hydrophobic and hydrophilic anticancer drugs (curcumin (Cur) and doxorubicin (DOX) as the model of drugs). The hydroxyl groups at the edges of graphene oxide (GO) sheets were used as the initiation sites for growing poly(epichlorohydrin) (PCH) chains. Then, hyperbranched polyglycerol (HPG) was grafted on the hydroxyl end groups of PCH (PCH-g-HPG). Pendant chlorines in the main chain of GO-PCH-g-HPG were replaced with hydrazine. The modification of GO sheets with oxygen-rich polymers increased water solubility of graphene oxide. Doxorubicin was loaded onto the nanocarrier by covalent bonding with... 

Artificial neural networks were used to predict the oxidation peaks potentials of 7 monosaccharides under linear sweep voltammetry regime. Two sets of descriptors, one based on molecular properties calculated through DFT and another based on simple geometric distributions of hydroxyl groups and asymmetric carbon atoms along molecular chains, were employed to introduce the molecules to networks. Relatively, simple networks of (3,3,1) and (3,3,3,1) structures with the number of epochs not exceeding 15 through training process were capable of correctly predicting the peaks positions with R values in the range of 0.97-0.99. © 2008 Elsevier Ltd. All rights reserved  

The rheological properties of fuel suspensions with various solid loadings up to close their maximum packing fraction and suspending media having different viscosities are investigated using the rotational viscometer at relatively low shear rates in which suspensions behave as Newtonian fluids. Aluminum (Al) and ammonium perchlorate (AP) particles are major solid components of any solid fuel system which should be distributed uniformly inside a polymeric binder based on hydroxyl terminated polybutadiene (HTPB). The experimental data generated in this investigation indicates that the relative viscosity of the suspensions is independent of viscosity of polymer binder, but in addition to solid... 

In this research, ultrahigh-molecular-weight polyethylene (UHMWPE)/multiwalled carbon nanotube (MWCNT) nanocomposites with different nanotube concentrations (0.5, 1.5, 2.5, and 3.5 wt %) were prepared via in situ polymerization with a novel, bisupported Ziegler-Natta catalytic system. Magnesium ethoxide [Mg(OEt) 2] and surface-functionalized MWCNTs were used as the support of the catalyst. Titanium tetrachloride (TiCl 4) accompanied by triethylaluminum constituted the Ziegler-Natta catalytic system. Preparation of the catalyst and the polymerization were carried out in the slurry phase under an argon atmosphere. Support of the catalyst on the MWCNTs was investigated with Fourier transform... 

Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler-Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl4 and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nano- structure of composites was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay...