Magnetic Properties of Fullerene–Thermally Exfoliated Graphite Composites Doped with Sodium

Physics of the Solid State - The magnetic properties (field range H = 0–50 kOe, temperature range T = 3–300 K), and structural features of a sodium-doped carbon composite material based...     

Pressure effects on structural,electronic, absorption,and thermodynamic properties of crystalline 2,4,6‐triamino‐3,5‐dinitropyridine‐1‐oxide: A DFT study

Density functional theory calculations have been performed to study the structural, electronic, absorption, and thermodynamic properties of crystalline 2,4,6‐triamino‐3,5‐dinitropyridine‐1‐oxide (TANPyo) in the pressure range of 0–50 GPa. The variation trends of the lattice constants, bond lengths, bond angles, intramolecular H‐bonds, and dihedral angles under compression show that there are two structural transformations at 17 and 38 GPa, respectively. The remarkable changes in the bond lengths indicate that there are two possible initiation decomposition mechanisms of TANPyo under compression. As the pressure increases, the intramolecular H‐bond strengthens. The obvious changes of the dihedral angles show that the planar structure of the TANPyo molecule is damaged under compression. Its absorption spectra show that as the pressure increases, the absorption coefficient of the N–H stretching decreases, while that of the O–H stretching increases. TANPyo has relatively high optical activity at high pressure. An analysis of thermodynamic properties indicates that both two structural transformations are endothermic and not spontaneous at room temperature. Copyright © 2013 John Wiley & Sons, Ltd.     

Ultrasonic-assisted modifications of macroporous resin to improve anthocyanin purification from a Pyrus communis var. Starkrimson extract

The present study presents an attempt to modify the surface properties of macroporous resins (MRs) in order to improve anthocyanin adsorption and desorption from Pyrus communis var Starkrimson fruit peel extract. A number of MRs were tested to optimise the ultrasonic-assisted adsorption (UAA) conditions; including ultrasonic power (100–400 W), resin-to-extract ratio (1–3 g/50 mL) and temperature (20–40 °C). Similarly, varying ultrasonic-assisted desorption (UAD) conditions were optimised; including ultrasonic power (200–600 W), resin-to-solvent ratio (1–4 g/50 mL), ethanol concentration (60–90% v/v) and temperature (20–40 °C). The Amberlyst 15 (H) cationic resin was found to be superior to the other tested resins. The maximum adsorption capacity (659 µg/g) of cyanidin 3-galactoside (Cy 3-gal) was achieved under the optimised UAA conditions (400 W, 20 °C and 1 g/50 mL), while 616 µg/g of Cy 3-gal was recovered under the optimised UAD conditions (582 W, 1 g/50 mL, 60% and 20 °C). Moreover, titratable-acid and total-sugar contents were found to be significantly lower under UAA than under conventional-assisted adsorption (CAA). ANOVA revealed that process factors had significant effects on the Cy 3-gal purification, as depicted by their linear, quadratic and interactive effects. While anthocyanin adsorption was found to be significantly improved at lower ultrasonic power, higher power promoted the desorption process. Adsorption under optimized UAA conditions followed pseudo second-order kinetics and multilayer adsorption (Freundlich isotherm) onto the Amberlyst 15 (H) resin surface was observed. The particle-size distribution curve and scanning electron microscopic images also revealed higher resin-surface roughness, peeling and the appearance of pores on the surface under ultrasonication. This is the first study to use ultrasonication to modify a cationic exchange resin for the improvement of Cy 3-gal purification from a fruit extract. This study can recommend the use of ultrasonication as a low-cost green technique that can improve macroporous resin characteristics for better purification of compounds from an extract.     

Calculation of Nuclear Stopping in the Semiclassical Approximation

Technical Physics - The results of calculating nuclear stopping in the semiclassical approximation for the H–Be, H–C, H–W, O–C, O–Be, and O–Al systems are...     

Transition from low-spin to high-spin states in clusters of polimerized acetylacetonate of Fe3+

A study is made of Fe³⁺ iron cation groups in the temperature range 4.2–200 K and in the fields from 0 to 70 k0e. The transition temperature T_k=22 K and the critical field of transition from a low-spin state to a high-spin one H = 50 k0e have been revealed.     

Optoelectronic and conductivity of ᴫ‐conjugated polymers based on phenylenevinylene, 1,3,4‐thiadiazole and thiophene: Suitable candidates for n‐type organic semiconductors

New poly‐phenylenevinylenes PPVs containing 1,3,4‐thiadiazole as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) and time‐dependent DFT levels. This study has been conducted in order to investigate the geometrical and electronic properties as well as the conductivity of a series of PPV–thiophene–1,3,4–thiadiazole–thiophene (H–PhTAT–H) containing –CHO, –CH₂–P(=O)(OCH₃)₂, and phenyl–CHO (PhCHO) terminal groups. The impact of terminal groups on the optical bandgaps, electron affinity, LUMO energy, and intramolecular reorganization energy was studied for different oligomers and for a limit polymer. The incorporation of terminal groups did not affect the chain length evolution and the vertical transition energy E_vert value for a polymer limit compared with the unsubstituted oligomer (H–PhTAT–H). All studied properties showed that CHO–PhTAT–PhCHO and H–PhTAT–H oligomers can be considered as n‐type semiconductors.     

Thermal,surface, nanomechanical and electrical properties of epoxidized natural rubber (ENR-50)/ polyaniline composite films

A new composite material from epoxidized natural rubber (ENR-50) and polyaniline have been successfully prepared. Aniline which was polymerized in the presence of dodecylbenzene sulfonic acid (DBSA), then added to ENR-50 for the preparations of ENR-50/Pani.DBSA composite films. The hydrogen bonding which contribute to the formation of ENR-50/Pani.DBSA composites was observed in FT–IR, UV–Visible and DSC. It showed hydrogen bonding interactions between the epoxy groups in ENR-50 and the amine groups in Pani.DBSA. The morphologies of the prepared materials were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and conductivity measurements revealed that the percolation threshold is at 2.5 w% of Pani.DBSA content. Atomic force microscopy (AFM) micrographs showed that ENR-50 with 5 wt% Pani.DBSA addition has the lowest surface roughness. In addition thermogravimetric analysis indicates improved thermal stability at low Pani.DBSA content. DSC measurements revealed that T_g value increases with increasing Pani.DBSA, indicating that the formation of homogenous composite material. Nanoindentation results show that the hardness (H) and Young's modulus (E_s) increased with higher addition of Pani.DBSA polymer.     

Co2?+? interaction with Azospirillum brasilense Sp7 cells: a 57Co emission M?ssbauer spectroscopic study

The Thylacine Hole–001 meteorite was recovered from the Nullarbor Desert (Australia) in 1977 and is an Ordinary Chondrite, Group H4/5br, which has undergone moderate to severe (B/C) weathering. We have characterised the Fe-bearing phases in Thylacine Hole–001 by ⁵⁷Fe M?ssbauer Spectroscopy at 300?K, 100?K, 50?K and 4?K. The spectrum at 300?K is dominated by the paramagnetic doublets of Olivine, Pyroxene and a Ferric component which is most likely nanoparticulate Goethite. Magnetically split sextets due to Maghemite or Magnetite are also present, consistent with the relatively advanced terrrestrial age of 28,500 yrs The nanoparticulate Goethite component shows a blocked, magnetically split sextet at low temperatures. We also observe the effects of magnetic ordering of the Olivine and Pyroxene below 50?K.     

Hydrogen-bonding studies of amino acid side-chains with DNA base pairs

The interactions of the amino acid side-chains arginine (ARG), aspartic acid (ASP), asparagine (ASN), lysine (LYS) and serine (SER) with nucleic acid base pairs have been investigated using theoretical methods. The interaction energy of the short intermolecular N–H?···?N, N–H?···?O, O–H?···?O, O–H?···?N, C–H?···?O and C–H?···?N hydrogen bonds present in both isolated base pairs and complexes and its role in providing stability to the complexes have been explored. The homonuclear interactions are found to be stronger than the heteronuclear interactions. An improper hydrogen bond has been observed for some of the N–H?···?O and N–H?···?N hydrogen-bond interactions with the contraction of the N–H bond varying from 0.001 to 0.0260?Å and the corresponding blue shift of the stretching frequency by 4–291?cm^?1. Localized molecular orbital energy decomposition analysis (LMOEDA) reveals that the major contributions to the energetics are from the long-range polarization (PL) interaction, and the short-range attractive (ES, EX) and repulsive (REP) interactions. The Bader's atoms in molecules (AIM) theory shows good correlation for the electron density and its Laplacian at the bond critical points (BCP) with the N–H?···?N and N–H?···?O hydrogen-bond lengths in the complexes, and gives a proper explanation for the stability of the structure. The charge-transfer from the proton acceptor to the antibonding orbital of the X–H bond in the complexes was studied using natural bond orbital (NBO) analysis.     

Structural and electronic properties of a single Si chain doped zigzag AlN nanoribbon

The first-principles projector-augmented wave (PAW) potentials within the density function theory (DFT) framework have been used to determine the geometry structures and electronic properties of the zigzag edge AlN nanoribbons (ZAlNNRs) doped with a single Si chain under generalized gradient approximation (GGA). The average Al–Si, Si–Si, Al–N, Si–N, Al–H and N–H bond lengths are 2.39, 2.16, 1.83, 1.74, 1.59 and 1.03 Å, respectively. Pure 7-ZAlNNR is an indirect semiconductor with a large band gap of 2.235 eV, while a semiconductor to metal transformation is taken place after a single Si chain substituting for a single Al–N chain at various positions. In pure 7-ZAlNNR, the HVB and LCB are mainly attributed to the edge N and Al atoms, respectively, while in a single Si chain substituting doped 7-ZAlNNR, the HVB and LCB are mainly attributed to the Si atoms. The Al–N, Al–H and Al–Si bonds are ionic bond, the Si–Si and Si–H bonds are covalent bond, the N–H and N–Si bonds are covalent bond modified ionic bond.     

Simulation of the Electronic Structure of Graphene–Polyvinylidene Fluoride Composite Material

Physics of the Solid State - Theoretical models of shockproof composite materials based on two-layer graphenes and multilayer polyvinylidene fluoride C124H40 + n(H–(C2H2F2)5–H) (n =...     

Mathematical modeling of the temperature effect on the character of linking between monomeric proteins in aqueous solutions

Technical Physics - This work is devoted to the mathematical modeling of the temperature effect on the stability of H2A–H2B and Н3–H4 histone dimers by studying their behavior in...     

A theory of vibrational frequency shifts revisited: application to dimers of LiH with the inert gases He,Ne, Ar and Kr

The objective of this paper is to contribute towards an understanding of the anomalous blue vibrational shifts that have been observed on forming some hydrogen bonds. It is shown that linear complexes of the LiH molecule with an inert gas atom Rg exhibit red or blue shifts of the LiH vibrational frequency depending upon whether Rg is attached to the Li or the H atom.

The shifts in the frequency of the Li–H vibration on forming the weakly bound linear complexes Li–H…Rg and H–Li…Rg (Rg?=?He, Ne, Ar, Kr) were determined by ab initio computations at the MP2/6-311++G(2d,?2p) level of theory. These frequency shifts were found to be in good agreement with predictions from a model based on perturbation theory and involving first and second derivatives U′ and U′′ of the interaction energy with respect to displacement of the Li–H bond length from its equilibrium value in the isolated molecule. Concentration of the Li–H vibrational motion in the light H atom causes U′ and U′′ to be dominated by repulsion in Li–H…Rg and by attraction in H–Li…Rg, producing blue and red shifts, respectively. The bond length changes on complexation are well predicted by U′.     

Computational study on structures,thermochemical properties,and bond energies of disulfide oxygen (S–S–O)‐bridged CH3SSOH and CH3SS(=O)H and radicals

Cleavage of disulfide bonds is a common method used in linking peptides to proteins in biochemical reactions. The structures, internal rotor potentials, bond energies, and thermochemical properties (Δ_fH°, S°, and Cp(T)) of the S–S bridge molecules CH₃SSOH and CH₃SS(=O)H and the radicals CH₃SS?=O and C?H₂SSOH that correspond to H‐atom loss are determined by computational chemistry. Structure and thermochemical parameters (S° and Cp(T)) are determined using density functional Becke, three‐parameter, Lee–Yang–Parr (B3LYP)/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p). The enthalpies of formation for stable species are calculated using the total energies at B3LYP/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p), and the higher level composite CBS–QB3 levels with work reactions that are close to isodesmic in most cases. The enthalpies of formation for CH₃SSOH, CH₃SS(=O)H are ?38.3 and ?16.6 kcal mol^?1, respectively, where the difference is in enthalpy RSO–H versus RS(=O)–H bonding. The C–H bond energy of CH₃SSOH is 99.2 kcal mol^?1, and the O–H bond energy is weaker at 76.9 kcal mol^?1. Cleavage of the weak O–H bond in CH₃SSOH results in an electron rearrangement upon loss of the CH₃SSO–H hydrogen atom; the radical rearranges to form the more stable CH₃SS· = O radical structure. Cleavage of the C–H bond in CH₃SS(=O)H results in an unstable [CH₂SS(=O)H]* intermediate, which decomposes exothermically to lower energy CH₂ = S + HSO. The CH₃SS(=O)–H bond energy is quite weak at 54.8 kcal mol^?1 with the H–C bond estimated at between 91 and 98 kcal mol^?1. Disulfide bond energies for CH₃S–SOH and CH3S–S(=O)H are low: 67.1 and 39.2 kcal mol^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

A study on structural and electrical properties of low dielectric constant SiOC(–H) thin films deposited via PECVD

Low-dielectric constant SiOC(–H) films were deposited on p-type Si(100) substrates using plasma enhanced chemical vapor deposition (PECVD) at different radio frequency (rf) powers. The structural characteristics of the SiOC(–H) films were characterized using Fourier transform infrared spectroscopy (FTIR) in the absorbance mode. The bonding configurations of the SiOC(–H) films remained unchanged upon annealing, showing their good thermal stability. Electrical characteristics of the SiOC(–H) thin films with Al/SiOC(–H)/p-Si(100)/Al metal-insulator-semiconductor (MIS) structures were analyzed using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) at different frequencies. The conductance and the capacitance measurements were used to extract the interface state density in the MIS structures. From the experimental data and the subsequent quasi-static C–V analysis, the energy distribution of interface state density was obtained. The interface state density of the as-deposited and 400 °C annealed MIS structures increased with increasing rf powers, whereas the fixed charge density decreased with increasing rf powers. The interface state densities and their electrical properties of the SiOC(–H) films strongly affected by the radio frequency power.     

Doublon–holon-binding mechanism of Mott transition in 2D Hubbard model

The mechanism of nonmagnetic Mott transitions in the Hubbard model on the square lattice is studied, using a variational Monte Carlo method. A simple doublon (D)–holon (H) binding mechanism a previous study proposed [J. Phys. Soc. Jpn. 75 (2006) 114706] has to be modified, because even a wave function with completely bound D–H pairs brings about a Mott transition at a finite correlation strength. By introducing two characteristic lengths, D–H pair binding length, ξ_DH, and minimum inter-doublon distance, ξ_DD, we can properly describe the physics of Mott transitions, and determine the critical point by ξ_DD ～ ξ_DH. This concept seems universal, because it is valid not only for newly introduced wave functions with long-range D–H and D–D (H–H) correlation factors discussed here, but for a wide range of wave functions with D–H binding factors.     

Structure and phase composition of thin a-C:H films modified by Ag and Ti

The structure and phase composition of thin a-C:H and a-C:H〈M〉 films (M = Ag, Ti, or Ag + Ti) have been studied by Raman and X-ray photoelectron spectroscopy. The a-C:H〈M〉 films were prepared by ion-plasma magnetron sputtering of a combined target of graphite and metal in an Ar–CH₄ gas mixture. The Raman spectra of these films indicate that their structure is amorphous. The a-C:H〈Ag + Ti〉 films have a more graphitized structure in comparison with pure a-C:H films and films containing only one metal. It is established that carbon in the a-C:H〈Ag + Ti〉 films is in the sp ², sp ³, and C=O states, which are characteristic of the a-C:H, a-C:H〈Ag〉, and a-C:H〈Ti〉 films. In addition, there are also ether (–C–O–C–) or epoxy (?C?O–) carbon groups in the a-C:H〈Ag + Ti〉 films. It has been revealed that silver atoms in the a-C:H〈Ag〉 and a-C:H〈Ag + Ti〉 films form no chemical bonds with carbon, oxygen, and titanium. Titanium in the a-C:H〈Ti〉 and a-C:H〈Ag + Ti〉 films exists in the form of titanium IV oxide (TiO₂).     

Noncovalent Hydrogen Isotope Effects in Paramagnetic Molecules

Zero-point energies (ZPE) of intermolecular, non-bonded vibrations and isotope effects, induced by noncovalent interactions, are computed for paramagnetic molecules. They appear to be not significant for complexation of HO₂ and oxygen with C–H bonds and results to isotope effect, which deviates from unit by 5–10%. However, ZPE and isotope effects in complexes of HO₂ and nitroxyl radicals with water are larger and reach 50–70%. The largest effect, about 12, is found for complexation of hydrogen atom with water. Complexation of nitroxyl and peroxy radicals by hydrogen bonds is accompanied by transfer of spin density of unpaired electron from radical to the ligand molecules and induces high field paramagnetic shifts of the ligand NMR lines. It evidences that the spin transfer via intermolecular bonds occurs by mechanism of spin polarization.     

Blue and red shifts in Rg···HCN and Rg···HNC complexes (Rg=He,Ne, Ar,Kr)

The shift in the harmonic vibrational frequency of the H–C stretch of HCN on formation of the linear Rg···HCN complexes, and of the H–N stretch of HNC on the formation of Rg···HNC complexes (Rg?=?He, Ne, Ar, Kr), has been determined by ab initio computations. These shifts are in agreement with predictions from a model based on perturbation theory and involving the first and second derivatives of the interaction energy with respect to displacement of the H–C (H–N) bond length from its equilibrium value in the monomer. Small blue shifts were obtained for He···HCN, Ne···HCN and He···HNC, while red shifts were obtained for the other weakly bound complexes. These vibrational characteristics are rationalized by considering the balance between the interaction energy derivatives obtained from the perturbative model. For all complexes, the IR intensity of the H–C or H–N stretch was increased from the isolated monomer values on complexation.