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Melinjo seed extract contains melinjo resveratrol compounds that has antioxidant activity. The radical-scavenging sites required for the antioxidant activity, however, is yet to be located. We report a computational study that aims to locate scavenging sites of the simplest resveratrol dimer, gnetin C. We consider the reaction of gnetin C and hydroperoxyl radical energetically with the basis of density-functional calculations, to be compared with the reaction of the resveratrol monomer, trans-resveratrol, and hydroperoxyl radical. The results show that OH group at the para position is the most reactive scavenging site for both molecules. Besides the OH group, gnetin C also provides two CH groups in the furan ring that are favorable as scavenging sites. Therefore, furan ring plays an important role in the scavenging activity, which is contrary to the experimental speculation that propose resorcinol ring. Our study shows the prospect of density-functional calculation for studying the radical-scavenging reaction.

A study on the molecular adsorption of a water (H2O) monomer on Pt alloy surfaces with binary Pt-Ru and Pt-Mo and ternary Pt-Ru-Mo surface models was conducted. Some calculations of the interaction between a H2O monomer and the Pt surface were also done for reference. This study is based on density functional theory (DFT) with periodic models and aims to understand the H2O adsorption mechanism. In Pt, Pt-Ru, and Pt-Mo surfaces, H2O preferably adsorbs via an oxygen atom in a flat configuration at the top sites of Pt, Ru, Mo, respectively. However, on the ternary Pt-Ru-Mo surface, the adsorption configuration has the most inclined H2O structure relative to the surface. The results showed that the binding energy of H2O/Pt-Ru-Mo > H2O/Pt-Mo > H2O/Pt-Ru > H2O/Pt. The adsorption mechanism was then clarified by charge transfer and natural bonding. The charge transfer from the surface to the adsorbate is observed in all models, with the greatest charge transfer occurring on the surface of Pt doped with two Mo atoms. This is probably due to the fact that oxygen can attract the most charge on Mo, because the difference in electronegativity is greatest. The calculation results also show that Ru is the most hydrophilic metal for oxygen. However, since the adsorption structure is parallel to the surface, hydrogen (H) is also more sensitive to receive the charge. Subsequently, the most acceptable reason for the most stable adsorption for H2O/Pt-Ru-Mo is that the inclined structure yields the most orbitals hybridization at the H2O's highest occupied molecular orbital (HOMO). This drives the interaction by forming bonding states at the lowest energy and anti-bonding states at the highest energy.

PdO is known to efficiently catalyze the oxidation of methane but suffers tremendously from sulfur poisoning that lowers its catalytic activity. In this paper, dispersion-corrected density functional theory based first principles calculations were performed to systematically screen the metal impurities M (where M is a transition metal) on a Pd1−xMxO catalyst that promote the desired adsorption energies for CH4 and SO2 to gain insights into the design of sulfation-resistant PdO-based methane oxidation catalysts. Specific Pd1−xMxO(101) catalyst was identified to thermodynamically avoid surface sulfation while maintaining the active sites for methane activation at typical experimental conditions. Results indicate a potential route of tuning the catalytic property of PdO by the introduction of a surface metal impurity.

Carbohydrazide (CH6N4O) is a potential substitute to hydrazine in fuel cell applications. This paper presents a theoretical study on the adsorption of carbohydrazide on Au(111) and Au3Ni(111) surfaces using first principles calculations based on density functional theory. Results show that without van der Waals correction in the calculations, carbohydrazide weakly physisorbs on Au(111), corroborating the experimentally observed high overpotential requirement for carbohydrazide oxidation on Au catalyst. An enhanced reactivity is observed by alloying Au with Ni due to the emergence of a localized d-band near the Fermi level that interacts strongly with the HOMO of carbohydrazide. On Au3Ni(111), a N–Ni bond between carbohydrazide and the surface is formed, characterized by the hybridization of N–pz and Ni–dzz states. These results pose insights into the use of 3d transition metals as alloying components in enhancing the reactivity of Au catalyst for carbohydrazide oxidation.

The continuous threat of increasing CO2 concentration in the atmosphere has altered the carbon balance of our planet causing global climate change. Biological fixation of atmospheric CO2 by unicellular microorganisms such as microalgae is a promising technology pursued extensively by researchers as a means for carbon capture. The study aimed to provide an atomic level of study that will demonstrate the effect of the salinity on the mechanism of CO2 absorption across microalgae lipid bilayer. Molecular dynamics simulations were utilized to calculate the free energies of CO2 molecule as it permeates inside the microalgae cell. In thermodynamics, the transport process of a molecule can be demonstrated through its free energy gradient. Thus, calculating the free energies of CO2 molecule across microalgae lipid bilayer can elucidate the mechanisms of permeation processes. Four microalgae lipid bilayer structures were constructed that contains 128-DPPC (dipalmitoylphosphatidylcholine) lipid bilayer with 3640 water molecules with different NaCl concentrations: 0, 3, 13, and 19 NaCl molecules which correspond to a salinity level of 0, 50, 200, and 300 mM, respectively. The cavity insertion Widom method was used to calculate the free energy of CO2 molecule along the lipid bilayer. The results demonstrated that the salinity does not affect the free energies significantly, thus, it does not hamper CO2 transport across microalgae lipid membrane.

The phase stability and surface effects on binary transition metal nano-alloy systems were investigated using density functional theory-based first principles calculations. In this study, we evaluated the cohesive and alloying energies of six binary metal alloy bulk systems that sample each type of alloys according to miscibility, i.e., Au-Ag and Pd-Ag for the solid solution-type alloys (SS), Pd-Ir and Pd-Rh for the high-temperature solid solution-type alloys (HTSS), and Au-Ir and Ag-Rh for the phase-separation (PS)-type alloys. Our results and analysis show consistency with experimental observations on the type of materials in the bulk phase. Varying the lattice parameter was also shown to have an effect on the stability of the bulk mixed alloy system. It was observed, particularly for the PS- and HTSS-type materials, that mixing gains energy from the increasing lattice constant. We furthermore evaluated the surface effects, which is an important factor to consider for nanoparticle-sized alloys, through analysis of the (001) and (111) surface facets. We found that the stability of the surface depends on the optimization of atomic positions and segregation of atoms near/at the surface, particularly for the HTSS and the PS types of metal alloys. Furthermore, the increase in energy for mixing atoms at the interface of the atomic boundaries of PS- and HTSS-type materials is low enough to overcome by the gain in energy through entropy. These, therefore, are the main proponents for the possibility of mixing alloys near the surface.

Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of the bottlenecks in the conversion of microalgae to biofuels is the drying process. A moisture content of at most 10 % is desired for algal biomass prior to oil extraction to maximise biofuel yield. Conventional means of drying results to longer drying time and uneven drying of algal biomass. This study investigated the drying characteristics of microwave for microalgae (Chlorella vulgaris). Three microwave intensity levels (300, 600, and 900 W) were considered to dry 10, 20, and 30 of algal mass. Page model gave a better fit on the moisture ratio with time of microwave drying than the exponential model. Furthermore, the specific energy requirement was computed, and a relationship was found between moisture ratio with power and mass. Fourier transform infrared spectroscopy results showed significant reduction of infrared signal intensities of the functional groups present in the algae after drying at higher microwave power level. It was concluded that the 20 W/g microwave drying setting gave a lower specific energy requirement with good quality of remaining high lipid content qualitatively. Furthermore, it was recommended to use gas chromatography mass spectroscopy to further quantify the algal lipids and other functional groups.

The resistance random access memory (RRAM™) device, with its electrically induced nanoscale resistive switching capacity, has attracted considerable attention as a future nonvolatile memory device. Here, we propose a mechanism of switching based on an oxygen vacancy migration-driven change in the electronic properties of the transition-metal oxide film stimulated by set pulse voltages. We used density functional theory-based calculations to account for the effect of oxygen vacancies and their migration on the electronic properties of HfO2 and Ta/HfO2 systems, thereby providing a complete explanation of the RRAM™ switching mechanism. Furthermore, computational results on the activation energy barrier for oxygen vacancy migration were found to be consistent with the set and reset pulse voltage obtained from experiments. Understanding this mechanism will be beneficial to effectively realizing the materials design in these devices.

We study the interaction between tin(II) porphyrin (SnPor) with platinum and non-precious Group 8B metals (iron, cobalt and nickel) by density functional theory and discuss the electronic properties of the resulting products. We also model the interaction of the resulting compounds with water where applicable. Our studies indicate that, SnPor-Ni possesses electronic properties similar to SnPor-Pt, suggesting that it may possess similar photocatalytic properties for reduction reactions, such as converting water to hydrogen gas.

We investigate and discuss the adsorption of a few amino acids on (3,3) carbon nanotubes and on graphite sheets through calculations within density functional theory. Results show weak binding of the biomolecules on both substrates, but through generally favourable adsorption pathways. Zwitterion adsorption through the charged amine and carboxylate groups are bound stronger to the nanotube surface in comparison to their nonionic counterparts, as well as on histidine, phenylalanine, and cysteine side chain groups fixed in specific orientations. Binding strengths on graphite suggest dissimilar trends for amino acid interactions with increasing nanotube diameter.

It has been reported that acetylcholine hyperpolarizes the maximum diastolic potential of canine Purkinje fibers through a pathway involving a G protein and induces a decrease in their automaticity. It is unclear, however, whether the negative chronotropic action of acetylcholine in the presence of beta-adrenergic stimulation is due to the hyperpolarization of the maximum diastolic potential or a decrease in the slope of phase 4 depolarization. We used standard microelectrode techniques to study the negative chronotropic mechanism of acetylcholine in the presence of isoproterenol in adult canine Purkinje fibers. Fibers were incubated for 24 hours in Tyrode's solution alone (n = 10) or plus pertussis toxin (n = 10), and then superfused with acetylcholine (10(-9) to 10(-4) M) in the presence of isoproterenol (10(-7) M). Acetylcholine in the presence of isoproterenol significantly decreased automaticity without hyperpolarization of the maximum diastolic potential, and decreased the slope of phase 4 depolarization. The effects of acetylcholine on automaticity and the slope of phase 4 depolarization were attenuated by pertussis toxin. The present findings indicate that the negative chronotropic action of acetylcholine in the presence of isoproterenol is due to the decrease in the slope of phase 4 depolarization through a pathway involving a pertussis toxin-sensitive G protein and that it is not the result of hyperpolarization of the maximum diastolic potential.

We investigate the molecular orientation dependence of the (o)rtho-(p)ara H2 conversion on Fe(OH)3 cluster. Taking Fermi's contact interaction as perturbation, we find that the o-p H2 conversion yield for the molecular orientation angle θ= 10○ with respect to the surface normal is larger than that for θ= 70○.

The structure, electric properties and emission rate of linear-trans-quinacridone are investigated within the density functional theory (DFT) calculations. We find the structure of the molecule to be planar with an energy gap of 3.06 eV. The emission lifetime from the lowest unoccupied molecular orbital (LUMO) to the highest occupied molecular orbital (HOMO) of this material is found to be 24 ns, which is in good agreement with experimental results.

We investigate the side-on interaction of O2 with manganese-porphyrin (MnP) and iron-porphyrin (FeP) using ab initio density functional calculations. The MnP–O2 adduct takes a side-on configuration in the sextet state while the FeP–O2 adduct takes it in the singlet state. The O–O bond of the side-on FeP–O2 is weaker than that of the side-on MnP–O2 because of more reactive singlet O2 for the adsorption on the substrate. Moreover, the O2 dissociation barrier on FeP is lower than that on MnP via the side-on O2 adduct. It is energetically comparable to that of the well-known platinum catalyst.

A quantum mechanical coupled channels approach to associative or recombinative desorption and scattering of diatomic molecules is described. The formulation is based on the concept of a reaction path and allows prediction of the vibrational excitation of desorbing molecules. We first consider very light molecules such as H2 and D2 desorbing via a Langmuir-Hinshelwood reaction. In a simple model neglecting rotations and substrate vibrations, the dependence of molecular vibrational excitation on incident energy, the curvature of the reaction path and the position and height of the saddle point are discussed. Various experimental results can be described with reasonable parameters. Vibrational excitation in Eley-Rideal reactions and rotational excitations in general are discussed only in a semiquantitative way. For heavier molecules the coupling to substrate vibrations in principle will become more important. Arguments will be presented that for the problem of vibrational excitation in desorption and scattering this coupling may still be neglected approximately. Results for vibrational excitations of CuF desorbing from Cu are in support of this simple point of view.

The interaction of conduction and valence bands in narrow gap semiconductors such as InSb and HgCdTe influences the position and width of subband energy levels in space-charge layers. While a nonzero width can only occur if electrons from the conduction band can tunnel into approximately degenerate states of the valence band the level shifts due to band mixing are always present. We present a Green's function treatment which allows in a simple way to discuss the dependence of band mixing effects on the parameters of thek·p-Hamiltonian in particular the band gap. The essential qualitative feature of the level shifts is adecrease of subband energy separation withdecreasing effective mass. This agrees with recent experimental results for Hg1-x Cd x Te.

The problem of atom scattering from surfaces covered with adsorbates is considered within the Einstein model for the adsorbate phonons. In this case the problem can be solved exactly by the use of a numerical method developed earlier by the present authors. In particular we investigate the temperature dependence of the elastic scattering. It turns out that the deviations from conventional Debye-Waller-factor theory occurring in neutron scattering and Mosbauer effect for single oscillators also show up in atom surface scattering: At higher momentum transfers the elastic scattering probability does not decrease monotonously with temperature but exhibits a maximum at non-zero temperature.

Dimers were preferably obtained in the oligomerization of styrene derivatives by diphenyl hydrogen phosphate. The reaction was assumed to proceed through the formation of esters from the monomers and diphenyl hydrogen phosphate as intermediate. This assumption was confirmed by the fact that treatment of the esters with alternative styrene derivatives gave linear codimers.

New bicyclic ethers, 2,3- and 2,5-dimethyl-7-oxabicyclo[2.2.1]heptanes were synthesized from 2,3- and 2,5-dimethylphenols as starting materials. Each of them was separated by fractional distillation and preparative gas chromatography into the corresponding exo,exo-,endo,exo-, and endo,endo-isomers. Ring-opening polymerizations of these isomeric monomers were carried out in CH2Cl2 using cationic initiators such as BF3—tetrahydrofuran (THF) complex—epichlorohydrin (ECH), SnCl4—ECH, SbCl5—ECH, and FeCl3—SOCl2 systems. The SbCl5—ECH catalyst system brought about high monomer conversions, but it induced a chain-transfer reaction during the polymerization. The exo,exo- and endo,exo- 2,3-dimethyl monomers (1a and 1b) yielded white powdery polymers in yields of 58 and 63 %, respectively, using the SbCl5—ECH system. NMR spectroscopic analysis of poly(1b) showed that it contained a chair-formed trans,trans,trans-1,2,3,4-tetrasubstituted cyclohexane ring in its monomeric unit. Both exo,exo- and endo,endo-2,5-dimgthyl monomers (2a and 2c) yielded grease-like polymers in 16 and 17-% yields, and its endo,exo-isomer (2b) yielded a highly crystalline polymer, which was insoluble in the usual organic solvents, in 26-% yield using BF3–ECH. A monomeric unit in poly(2b) was assumed to be trans,cis,trans-1,2,4,5-tetrasubstituted cyclohexane. In the polymerization of the monomers 1b and 2b, it has been shown that the monomer attacks the propagating end at the bridgehead carbon in position 4 (C-4), but not in position 1 (C-1). Nucleophilicities of the monomers 2a and 2b were compared based on their copolymerizations with the exo-monomethyl analogue (3a). The exo-methyl group relative to the endo-methyl group tends to lower the monomer nucleophilicity. The polymer yield is controlled by three factors; the steric crowding around the bridgehead carbon due to the methyl group, the nucleophilicity, and the ring strain of the monomer.

Quantum mechanical calculations of final rotational state distributions are carried out for a simple model of the scattering of NO from surfaces. The dependence of the results on parameters of the potential such as sign and size of the anisotropy and asymmetry, the well depth etc. is discussed. Certain difficulties in explaining experimental results for NO scattered from Ag (111) are pointed out. The dependence of the results on an initial rotational temperature is discussed also. Its main effect — which is well known from the literature — is to average out the quantum oscillations of the cross sections around the rainbow structures. The oscillations may become visible at rotational temperatures slightly lower than used up to now.

Two co-dimers of styrene and p-chlorostyrene having regulated monomer sequences were obtained by the reactions of 1-(4-chlorophenyl) ethyl diphenyl phosphate with styrene and of 1-phenylethyl diphenyl phosphate with p-chlorostyrene. The structures of the co-dimers were confirmed by GC-MS and analyses of the oxidative cleavage products.