Physical Chemistry Research
Volume:4 Issue: 2, Spring 2016

In this work, for the first time, the rheological properties of nanofluids of lanthania nanoparticles (NPs) in ethylene glycol (EG) as functions of shear rate, volume fraction, and temperature were measured. The results showed that both EG and the nanofluids behave as non-Newtonian fluids at lower shear rates and transform to Newtonian fluids at higher shear rates. The values of viscosity for both EG and the nanofluids decrease with raising temperature. The viscosity of nanofluids increases with increasing the volume fraction of lanthania NPs. A maximum of 66.4% increase in viscosity of EG at 25 °C and shear rate of 60 s-1 was observed when 5% v/v of lanthania NPs was added. The nearly pure hexagonal lanthania NPs were successfully synthesized using hydrothermal method. The NPs were characterized using seven techniques including X-ray powder diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, far infrared spectroscopy, and ultraviolet-visible absorption spectroscopy.

Cobalt oxide (Co3O4) nanorods were prepared by a simple co-precipitation method using ethanol solution of cobalt nitrate as precursor and cetyl trimethylammonium bromide (CTAB) as surfactant. Morphological properties of the nanoparticles were characterized. XRD measurement exhibited the structure of Co3O4 nanocrystals for annealed samples. The SEM images revealed that the particles changed from spherical shape to rod-like shaped by increasing annealing temperature. The TEM results exhibited that the size of cobalt oxide nanoparicles decreased from 25 nm for as-made particles to 50 nm for annealed samples with increasing temperature. The FTIR analysis confirmed the functional group presents in the cobalt oxide nanoparticles. The sharp peaks in FTIRspectrum determined the purity of Co3O4 nanoparticles and existence of Co-O group. Absorbance peak of UV-Vis spectrum showed the band gap energy of 3.69 eV corresponding to wavelength about 335 nm for as-prepared samples and the band gap energy of 3.49 eV corresponding to wavelength about 355 nm for annealed Co3O4 nanoparticles. The results of magnetic measurements indicated a good coercive field and saturation magnetism around 447.81 G and 17.295 emu g-1, respectively.

Interactions of cationic tetrakis (N,N´,N´´,N´´´-tetramethyltetra-3,4-pyridinoporphyrazinatocobalt(II) (Co(tmtppa)) with synthetic polynucleotides, poly(A-T), poly(G-C) and calf thymus DNA have been characterized in 5 mM phosphate buffer, pH 7.2, by optical absorption and fluorescence spectroscopy. The appearance of hypochromicity effect and the red shift in UV-Vis spectrum of porphyrazine was due to the interaction of both poly(A-T) and poly(G-C) which is similar to interaction of porphyrazine with DNA. The binding constants (K) were determined from the changes in the optical absorption spectra at various poly(G-C), poly(A-T) and DNA concentrations. According to the results, the values of K were 2.50 × 106 M-1, 2.25 × 106 M-1 and 2.25 × 105 M-1 for poly(A-T), poly(G-C) and DNA, respectively, at 25 ºC. The thermodynamic parameters were calculated by the van’t Hoff equation. The positive values of the entropy and enthalpy suggest that coulombic interactions may play an important role in stabilization of the complex formed. The influence of the ionic strength was also investigated. It was concluded that the apparent binding constants decrease with increasing salt concentration. The fluorescence quenching of the DNA-ethidium bromide complex by the porphyrazine was also investigated. The values of the quenching constant (KSV) was determined by the Stern-Volmer equation. The results revealed groove binding mode of porphyrazine for both A-T and G-C rich region of polynucleotides of DNA.

ONIOM calculation is carried out to estimate the acidity of five aliphatic alcohols before and after adsorbing on the tip of (8,0) single-walled carbon nanotube. The ONIOM method is performed using a combination of density functional theory and AM1 semiemperical method for alcohols and their corresponding conjugated bases. Deprotonation Gibbs free energies of alcohols are calculated and compared before and after adsorbing on the nanotube. Solute-solvent interactions are taken into account by employing the conductor polarized continuum model (CPCM). The results show that the acidity of alcohols change after adsorbing on the nanotubes and these alcohols have a little effect on (8,0) SWCNT.

In this study, the densities, excess molar volumes and partial molar volumes of four binary systems containing N,N-dimethyl acetamide (DMAc) with 1-alkanols (1-butanol up to 1-heptanol) are measured at 298.15 K. The results showed both constructive and expansive excess volumetric behavior for studying binary mixtures. Deviation values of heavy alcohol have more positive and less negative excess properties. The excess molar volumes of binary systems consisting of DMAc and 1-alkanols are fitted by the fifth degree of Redlich-Kister equation, and resulting coefficients have been calculated.

The reaction of CH₃NH₂ with O₂ on the singlet potential energy surfaces (PES) was carried out using the B3LYP, CCSD(T) and G3B3 theoretical approaches along with 6-311(3df,3pd) basis set. The suggested mechanism for the title reaction consists of one pre-reactive complex. From the pre-reactive complex, nine types of products, CH2NHὣ, CH3NH㣡, NH2CHOὣ, CH2NHOὣ, NH3ᰣ, CH2NHὯ, HCHO㑽, CH2NH2᳣ and CH2NHὣ are obtained. Six adducts are found to be thermodynamically stable with the negative value in Gibbs free energy and three products are not stable with positive value in Gibbs free energy at standard condition. NH2CHOὣ and NH3ᰣ with more free energy values are the thermodynamic products. CH2NH and H2O2 are the major products for the title reaction. The rate constant for the major pathway is calculated in the temperature range of 300-1000 K at atmospheric pressure at the B3LYP//6-311(3df,3pd) level of computation.

In this article, the crystallization of polyethylene is investigated by the modified weighted density approximation. Also, a direct correlation function of polyethylene based on the RISM theory is used. The free energy of a polyethylene is calculated using the density functional theory. The crystallization and also the solid and liquid densities of polyethylene are calculated and compared with the PRISM simulations and experimental results. It is shown that the results obtained by modified weighted density approximation (MWDA) are in a better agreement with the experimental results rather than the PRISM simulations.

The kinetics of the reactions between triphenylphosphine 1 and dialkyl acetylenedicarboxylates 2, in the presence of a NH-acid such as 5-nitroindazole 3,were studied. Corresponding kinetic parameters to all reactions were evaluated, with the second order rate constant (k) values calculated. Effects of solvent, temperature, and reactants (dialkyl acetylenedicarboxylates) structure and concentration were evaluated on the reaction rates. Theoretical studies were performed to evaluate potential energy surfaces for all structures participating in the reaction mechanism. For all reactions, the first step was recognized as the rate-determining step, on the basis of experimental and theoretical data. Quantum mechanical calculations were utilized to clarify how the ylides exist in solution as a mixture of two geometrical isomers (Z- and E-) -the issue of majority isomer.

Graphyne and graphdiyne families of flat carbon (sp2/sp) networks with high degrees of π-conjunction are attracting much attention due to their promising electronic, optical, and mechanical properties. In the present investigation we have studied the structural, mechanical, electrical and optical properties of halogenated graphdiyne and graphyne. The optical spectra of pure and halogenated structures are calculated. The optical absorption is dominated by excitonic effects with a high electron-hole binding energy within the Bethe-Salpeter equation. Band structures of graphdiyne and halogenated graphdiyne show that these nanostructures are semiconductors with a direct band gap of ~0.5 eV at the center of Brillouin zone. Halogenation of graphdiyne can effectively modulate the band gap. The second-order elastic constants and other related quantities such as the Young’s modulus and Poisson’s ratio have also been calculated in the present work.

Dosulepin and doxepin are tricyclic antidepressants. The molecular geometries, harmonic vibrational frequencies, quantum chemical parameters and thermodynamic properties of dosulepin and doxepin were calculated by Generalized Gradient Approximation methods developed by Perdew and Wang (GGA-PW91) and Becke-Lee-Yang-Parr (GGA-BLYP) in the gas phase and solution media. The local reactivity of these drugs was studied by the Fukui indices in order to predict both the reactive centers and the possible sites of nucleophilic and electrophilic attacks. Computational and chemical simulations were carried out for these drugs. Quantum chemical parameters of dosulepin and doxepin were calculated and compared. The simulation results show that dosulepin is quite a reactive drug. The fundamental modes of the vibrational frequencies were determined for dosulepin and doxepin. The BLYP/PW91 analyses of the wavenumbers show that the frequencies assigned to doxepin are higher than those assigned to dosulepin in the gas phase and solution media.

In this paper, covalent immobilization of beta amylase enzyme on the surface of modified magnetic nano particles (ZnFe2O4@SiO2-NH2) is reported. For doing so, at first, the magnetic nanoparticles of ZnFe2O4 were synthesized by chemical co-precipitation method and then tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxy silane (APTES) were used for modification of ZnFe2O4 nanoparticles with silica and amine groups (ZnFe2O4@SiO2-NH2). Then, the aminated surface of ZnFe2O4 nanoparticles was exposed to beta amylase immobilization using trichlorotriazine (TCT) as covalent agent. The immobilized beta-amylase enzyme was characterized by techniques such as Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX). The kinetics studies corroborate the Michaelis-Menten model and show much progress in the efficiency of immobilized enzyme compared to the free enzyme. Also, the thermal stability of the beta-amylase enzyme is increased after immobilization. By applying a magnetic active support, simple and facile separation of beta-amylase from the reaction mixture and higher catalytic activity is possible. The highest activity for immobilized beta-amylase enzyme is observed at pH and temperature of 7.0 and 40 °C, respectively.

Development of an eco-friendly, low cost and high energy density LiMnPO4 cathode material has attracted much attention due to its high operating voltage vs. Li falling within the electrochemical stability window of conventional electrolyte solutions and offers more safety features due to the presence of a strong P-O covalent bond.Synthesis of battery materials integrates the battery technology specially in development of cathode materials. Solvothermal method is used for the synthesis of In LiMnPO4 nanomaterials. The dried LiMnPO4 nanoparticles were mixed with 10 wt% conductive carbon such as acetylene black and 10 wt% polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) binder for LiMnPO4/C sample. The structure of the as-prepared LiMnPO4 nanomaterial were studied by X-ray diffraction tool, morphology by scannining electron micrograph tool. The galvanostatic charge-discharge measurements of LiMnPO4/C nanostructures is undertaken.

In this work, magnetically separable ZnO-ZnFe2O4-PPy nanocomposite as an efficient adsorbent was synthesized by two steps. At first, zinc oxide (ZnO) and ZnFe2O4 nanoparticles were synthesized using simple and facile precipitation method. Then, ZnO-ZnFe2O4 mixed oxide was modified by polypyrrole (PPy). The adsorbent was characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV-Vis and scanning electron microscopy (SEM). The synthesized nanocomposite were used as adsorbent to remove Congo red dye from aqueous solution and were compared with pure ZnO and ZnO-PPy adsorbents. The ZnO-ZnFe2O4-PPy nanocomposite adsorbent showed a superior Congo red removal efficiency than ZnO and ZnO-PPy adsorbents. This efficiency is attributed to the charge of surface obtained in nanocomposite adsorbent. Furthermore, the adsorption kinetics of Congo red onto the nanocomposite followed by the pseudo-second-order kinetic model.

In this research, we report the results of DFT calculations using xc-hybrid functional, B3LYP and employ NBO interpretation to investigate the stereoelectronic effects. Electrostatic and steric impacts on the conformational properties of 1,2-difluorodiazene (1), 1,2-dichlorodiazene (2) and 1,2-dibromodiazene (3) are also studied. Factors determining the thermodynamically stable molecular structure of 1,2-dihalodiazenes and their analogues containing P and As atom are discussed, and the energetic effects of intra-molecular hyperconjugations and steric repulsion in each molecular system are theoretically estimated using NBO theory. The Energy components calculated help us to justify the conformational behaviour of our target compounds. One of the interesting features extracted from NBO analysis is that dissociation energies are controlled by the stabilization energies associated with electron delocalizations in these compounds. The main parameter considered in this study is the Gibbs free energy estimated for cis and trans configurations of compounds and for the cis-to-trans conversion through rotation and inversion mechanisms.