Physical Chemistry Research
Volume:2 Issue: 2, Autumn 2014

The hydrogen abstraction reaction by OH radical from CH2BrCH2Br (R1) and CH₃CHBr2 (R2) is investigated theoretically by semi-classical transition state theory. The stationary points for both reactions are located by using ωB97X-D and KMLYP density functional methods along with cc-pVTZ basis. Single-point energy calculations are performed at the QCISD(T) and CCSD(T) levels of theory with different basis sets. The results show that the activation energies are very sensitive to effects of electron correlation and basis set. In order to correct basis set effects on the calculated energetic, a correction factor (CF) is determined from the energy difference between the MP2/cc-pVTZ and MP2/aug-cc-pVTZ levels. xij vibrational anharmonicity coefficients, needed for semi-classical transition state theory, are calculated at the KMLYP/cc-pVTZ level of theory. Thermal rate coefficients are computed over the temperature range from 200 to 3000 K and they are shown to be in accordance with available experimental data. The computed rate constants for the reactions R1 and R2 are fitted to the equation k(T)=A T^n exp[-E(T_0 )/(T^2 T_0^2 ) ].

To improve drug selectivity toward target cells, one interesting approach for drug delivery is to use polymer nanoparticles. A two-layered ONIOM Becke3- LYP: UFF calculation was carried out to study the structural and thermodynamic properties of the interaction between acetamide derivatives and the PCA-PEG-PCA copolymers. The Interaction enthalpies and the Gibbs free energies between acetamide derivatives as anti-HIV and polymeric nanoparticles in the gas and solution phases were calculated. The structure as well as the thermodynamics of optimized complexes was discussed from the biological point of view. In the gas phase, substitutes of phenyl, flurophenyl, 4-acetyl-2-bromophenyl, and 3-Methyl-acetate-thiophen-2-yl had the highest energies, and in the water phase, the enthalpies and Gibbs free energies of the interaction for most compounds were almost identical. In the both phases the interaction is relatively weak and copolymers can be used for drug delivery.

In this article, the effect of the nonextensivity parameter on the energy fluctuations of nonextensive systems is studied in two different versions of the Tsallis statistical mechanics. Once a general expression has been reported for the energy fluctuations in the second version (Tsallis work in 1988), the energy fluctuations of an ideal gas and a harmonic oscillator are studied in the second and fourth(OLM choice for the mean energy constrain) versions of the Tsallis statistical mechanics. The results for the fourth version indicate that relative energy fluctuations are strongly affected by the nonextensivity parameter via the number of accessible states. In fact, in the case of subextensive systems, the nonextensivity parameter leads to fewer accessible states as compared to extensive systems and, therefore, smaller relative energy fluctuations are expected. For super-extensive systems, however, relative energy fluctuations are found to be larger than those in extensive systems because of the greater accessible states available. Our studies show that very large relative energy fluctuations are caused as a result of the un-normalized nature of the second version which, in some cases, limits its application.

We study the coherent spin-polarized transport through a zigzag-edge graphene flake (ZGF), using Hubbard model in the nearest neighbor approximation within the framework of the Green function’s technique and Landauer formalism. The system considered consists of electrode/ (ZGF)/electrode, in which the electrodes are chosen to be armchair nanoribbons. The study was performed for two types of electrodes i.e., armchair-edge graphene nanoribbons (AGNRs) and armchair-edge boron-nitride nanoribbons (ABNNRs). Our calculations of the electronic and transport properties of these systems show that both systems posses spin filtering properties, while the spin filtering is higher in the full graphene system than the second system with boron nitride nanoribbon electrodes. The spin filtering in these systems is due to the interaction of the spin of the carriers with the local zigzag-edge magnetism in ZGF. However, the reduction of the spin filtering property in the case of the system with boron-nitride nanoribbon electrodes could be due to the decrease in the effective spin interaction of boron atoms in the contact sites and magnetization of the zigzag-edge of the ZGF.

This paper is mainly focusing on the determination of mean molal activity coefficient of HCl in aqueous acidic medium. The present investigations have been carried out to determine the activity coefficients of hydrochloric acid in 2-propanol water mixture solutions under various conditions to study the ion solvent interactions in different temperatures. The standard molar potential Em0 of the cell; Pt; H2(g) /HCl(m) x% 2-propanol; Hg2Cl2(S)/Hg have been determined in 10%; 20% and 30% (w/w) of 2-Propanol-water mixture solution at three different temperatures 308K, 313K and 318K and molality ranging from 0.005 to 0.1 mol Kg-1. Eo of the cell can be computed by modified Davies equation as below, where K= 2.3026(RT/F), A΄ = appropriate Debye-Hückel constant and Mean molal activity coefficient, The mean molal activity coefficients of hydrochloric acid in aqua organic media and temperature are also computed. The primary ion-solvent effects and the secondary ion-solvent effects are also reported.

Systematic studies on the vapor-liquid equilibria (VLE) and conductometric properties of aqueous solutions of model surface-active ionic liquid 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) are performed in the absence and presence of a large series of electrolytes in order to achieve a deeper understanding about the molecular mechanism behind the specific salt effect on the aggregation behavior of [C12mim]Br in aqueous solution. For this purpose, 6 chloride electrolytes (NaCl, KCl, NH4Cl, (CH3)4NCl, MgCl2 and FeCl3) and 5 sodium electrolytes (NaCl, NaNO3, Na2CO3, Na2SO4, and Na3Cit.) were used in order to individualize the effect of the anion and the cation. The values of the critical aggregation concentration (CAC) were obtained and it was found that all the investigated electrolytes have salting-out effect on the aggregation of [C12mim]Br in aqueous solutions, leading to significant downward shifts of the CAC. The magnitude of the shifts depends on the water-structuring nature of the electrolyte and follows the Hofmeister series. Furthermore the effect of electrolyte on the degree of anionic binding and thermodynamic parameters of aggregation for [C12mim]Br in aqueous solutions were determined.

MP2 calculations with cc-pVTZ basis set were used to analyze intermolecular interactions in F3CX···YLi···NCCN and F3CX···NCCN···LiY triads (X = Cl, Br; Y = CN, NC) which are connected via halogen and lithium bonds. Those complexes with the role of LiY as halogen acceptor and lithium donor show cooperativity with energy values ranging between -1.97 and -2.92 kJ mol-1. Those complexes with simultaneous role of NCCN as halogen and lithium acceptor are diminutive with energetic effects between 1.24 and 1.86 kJ mol-1. Results of energy decomposition analysis revealed that the electrostatic interactions are the major source of the attraction in the title complexes. The nuclear quadrupole coupling constant values at the sites of halogen atoms can be regarded as good descriptors to quantify the degree of cooperative/diminutive effects in the title systems.
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Fischer-Tropsch synthesis is a promising route for production of light olefins via CO hydrogenation over transition metals. Co is one of the most active metals for Fischer-Tropsch synthesis. Some different variables such as preparation parameters and operational factors can strongly affect the selectivity of Fischer-Tropsch synthesis toward the special products. In the case of preparation variables, several parameters such as catalyst preparation method, effect of different supports, and influence of promoters have been studied. Also, some operational factors including pretreatment conditions and experimental parameters such as temperature, pressure, and H2/CO ratio have been investigated. In addition, the stability of the Co-based catalyst is one of the most important characteristics. Therefore, catalyst deactivation is the main phenomenon and should be considered and controlled during the CO hydrogenation over the Co-based catalysts. Several factors such as poisoning, sintering, etc., lead to catalyst deactivation. According to the above-mentioned parameters and variables, we present here a review of Fischer-Tropsch synthesis for production of light olefins over the Co-based catalyst in a micro- fixed-bed reactor.

A time-of-flight mass spectrometer (TOF-MS) developed in our laboratory at Isfahan University of Technology is described here. The TOF-MS instrument uses laser as the ionization source which provides an opportunity to investigate the ions formed in laser ablation or desorption. The TOF-MS has an ionization chamber containing an accelerator and an ion lens to focus the ions into a one meter linear flight tube mass analyzer. Laser beam enters the ionization chamber through quartz window and can be focused either on the accelerator plates or in between. Solid sample may be deposited on the accelerator plate. Gas samples can also be admitted into the ionization chamber perpendicular to the accelerator axis through a leak valve. Mass spectra were obtained for gas samples as well as test solid samples. For the gas phase ionization, the laser was focused in the space between the accelerator plates while for the solid samples the laser beam was focused on the sample deposited on the repeller plate of the accelerator. Operational condition of the instrument were examined and mass calibration was achieved by measuring the flight time of the known alkali ions; Li, Na, K, Cs and Rb. Ions of type Alk(Alk.Halide)n were observed for all alkali salts. In addition, spectra of alkali earth salts were obtained and assigned. An average mass accuracy of 0.016% was obtained and a mass resolution of 540 (m/Dm) was achieved for benzaldehyde (m/z = 106) as a test sample. The instrument is capable of being used for MALDI analysis.

The dependence of some thermodynamic properties of spin-polarized liquid 3He such as the velocity of sound, adiabatic index, isentropic compressibility and temperature on the spin polarization has been investigated along different isentropic paths. The Lennard- Jones potential has been used in our calculations. It has been found that for higher values of entropy, the spin polarization has greater effect on velocity of sound and adiabatic index with respect to those of lower entropies. Also for a certain value of entropy and density, the isentropic compressibility is almost insensitive to the variations in polarization.

In the present study, the interactions of three different lithium species Li, Li3 and CH3Li with several different sites of the most stable tautomers of DNA nucleo-bases are presented. This investigation is based on the results of thermochemical properties, Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analysis, obtained at B3LYP/6-311(d,p) level of theory. The calculated results showed that guanine and cytosine have more tendencies for interaction with lithium in all above three lithium species. Also, it was shown that for each tautomer of the same nucleobase, coordination mode of lithium highly affects the value of Metal Ion Affinity (MIA). Bidentate base has more lithium affinity and the carbonyl oxygen is generally preferred over amino nitrogen. Furthermore, the analysis revealed the electrostatic nature of interactions. Li+DNA-Base has the most MIA value and CH3Li-DNA-Base has the least one.

The research in new organic π-conjugated molecules with specific properties has become one of the most interesting topics in fields of materials chemistry. These materials are promising for optoelectronic device technology such as solar cells. On the other hand, the use of low band gap materials is a viable method for better harvesting of the solar spectrum and increasing its efficiency. The Control of this parameter is essential to predict and study the electronic parameters for possible applications in optoelectronics. In this work, quantum chemical investigations have been performed to explore the optical and electronic properties of two compounds based on carbazole. Firstly, we have determined the effect of grafting the Fluorine atoms on their opto-electronic and physico-chemical properties. In addition to the solubility in the polar solvents and the modification in geometric parameters, the substitution of Fluorine destabilize the HOMO and LUMO levels, decreases the band gap energy and raises conjugation length. Electronic, optical and photovoltaic properties have been reported in order to predict the BHJ solar cell device efficiency for studied compounds.

We have used a variational approach to calculate some thermodynamic properties of the quasi-one dimensional liquid 3He such as the energy, entropy, free energy, equation of state and heat capacity at finite temperature. We have employed the Lennard-Jones potential as the inter-atomic interaction. We have seen that the total energy increases by increasing both temperature and density. As expected, it is seen that the entropy decreases by increasing density and decreasing temperature. There is no minimum point in the free energy curve, showing that there is not any bond state for the quasi-one dimensional liquid 3He. The results of our calculations indicate that the equation of state of this system becomes stiffer as the temperature increases. Our results for the specific heat show that there is not any lambda transition for this system.

The antibacterial activity of a series of ionic liquids containing short-chained 1-alkyl-3-methylimidazolium cations ([Cnmim]; n = 2, 4, 6 and 8) and bis (trifluoromethylsulfonyl) imide anion ([Tf2N]) against E. coli and B. subtilis was measured, for the first time. All ILs used in this work were synthesized and analyzed by Fourier transform infrared (FT-IR) spectroscopy, NMR, and Karl-Fischer titration. Antimicrobial activity was determined by the tube dilution method. The ILs investigated showed antibacterial activity against E. coli and B. subtilis. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were in the ranges of 0.041-6.39 mM and 0.67-12.78 mM, respectively. The antibacterial activity for ionic liquids with longer alkyl chain (n ≥ 4) increased with increasing alkyl chain length. The highest inhibition against E. coli was found for [C8mim][Tf2N] (MIC = 0.041 mM and MBC = 0.67 mM). The mechanism of action of these ionic liquids was bacteriostatic.