Sharif Digital Repository

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... 

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... 

Understanding the nature of the interaction between metal nanoparticles and biomolecules has been important in the development and design of sensors. In this paper, structural, electronic, and bonding properties of the neutral and anionic forms of glutathione tripeptide (GSH) complexes with a Au 3 cluster were studied using the DFT-B3LYP with 6-31+G**-LANL2DZ mixed basis set. Binding of glutathione with the gold cluster is governed by two different kinds of interactions: Auâ€"X (X = N, O, and S) anchoring bond and Au··•·•H-X nonconventional hydrogen bonding. The influence of the intramolecular hydrogen bonding of glutathione on the interaction of this peptide with the gold cluster has been... 

In This paper, a simple single-dimension Space Vector Modulation (SVM) technique is introduced to implement on three-phase thirteen-level Modified Packed U-Cell (MPUC) inverter for photo-voltaic system in which many DC sources are avail-able. The three-phase thirteen-level converter con-sists of three single-phase seven-level MPUCs that each phase has six switches and two isolated DC sources. One major advantage of proposed method is to produce an output voltage with nearly constant amplitude in desired range in case of input DC voltage fluctuations, which is common in renewable sources like Photovoltaic Systems (PV). On the other hand, the conventional Pulse Width Modulation (PWM)... 

3g wireless communication is the next version of mobile networks. Load balancing in networks causes efficient using of network resources. In this paper, we propose an efficient algorithm for load balancing of Radio Network Controllers (RNCs) in Radio Access Networks (RANs). As the characteristics of connections between RNCs and BTSs in a RAN are similar to those of graphs, we make use of graphs to solve our problem. The algorithm is based on the finding a path by which the RNCs could exchange their overloads. By using these paths the algorithm load balances the RNCs in an efficient and fast way. By testing our algorithm on networks with different topology and comparing the results, the... 

A mild and efficient tandem process for the synthesis of new highly substituted 2-pyrones starting from commercially available 2-arylacetic acids has been developed. The synthesis is based on the Knoevenagel condensation of 1,3-cyclohexadiones with various β-formyl-esters, followed by lactonization in the presence of nano ZnO (20 mol %). Moderate to high yields and readily available cheap starting materials are the key features of the present method  

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... 

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.... 

The cation radicals of DNA constituents generated by the ionizing radiation initiate the alteration of the bases, which is one main type of cytotoxic DNA lesions. These cation radical spices are known for their role in producing nucleic acid strand break, and it is important to identify the cation radical formation at particular atomic site in these molecules so that the major pathway for the nucleic acid damage may be trapped. In the present study, we explored theoretically energetic, structural, and electronic properties of the possible radicals formed via proton atom abstraction at various sites of sugar part of deoxycytidine cation radical by employing density functional theory at... 

This study seeks to explore the ability of unsteady Reynolds-averaged Navier-Stokes (URANS) simulation approach for resolving two-dimensional (2D) gravity currents on fine computational meshes. A 2D URANS equations closed by a buoyancy-modified k-ε turbulence model are integrated in time with a second-order fractional step approach coupled with a direct implicit method and discretized in space on a staggered mesh using a second-order accurate finite volume approach incorporating a high resolution semi-Lagrangian technique for the convective terms. A series of 2D simulations are carried out for gravity currents from both discontinuous and continuous sources. Comparisons with experimental... 

Understanding the nature of interaction between metal nanoparticles and biomolecules such as amino acids is important in the development and design of biosensors. In this paper, binding of M3 clusters (M = Au, Ag and Cu) with neutral and anionic forms of histidine amino acid was studied using density functional theory (DFT-B3LYP). It was found that the interaction of histidine with M3 clusters is governed by two major bonding factors: (a) the anchoring N-M and O-M bonds and (b) the nonconventional N-H⋯M and O-H⋯M hydrogen bonds. The nature of these chemical bonds has been investigated based on quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. In the next... 

Copper(II) efficiently catalyzes the aerobic oxidation of aryl thioacetamides into the corresponding α-keto aryl thioamides in moderate to high yields in the presence of K2CO3 under O 2 atmosphere. This protocol is simple, clean, and generates water as the only byproduct. A mechanism is proposed for the reaction course. © Georg Thieme Verlag Stuttgart  

Efficient synthesis of protected and unprotected chlorohydrins has been achieved by ring opening of epoxides with acetyl/benzoyl chloride and TMSCl using a catalytic amount of ZnO as a reusable catalyst. The applicability of ZnO is further extended by performing the cleavage of the natural product 5,6-epoxysitosterol with acetyl chloride. © 2009 Wiley Periodicals, Inc  

An efficient one-pot, three-component synthesis of novel dispiro[oxindole-3,3′-pyrrolidines] by 1,3-dipolar cycloaddition of azomethine ylides, in situ generated by reaction of 1,2-diones with sarcosine and subsequent decarboxylation, with a series of (E)-3-benzylidene-2,3-dihydro- 1H-indol-2-ones is reported. Molecular complexity is generated in only one synthetic step. All reactions proceed with excellent regioselectivity and in good-to-excellent yields. The workup is easy, the reaction times are short, and no catalyst is required. © 2013 Verlag Helvetica Chimica Acta AG, Zürich