bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Alternate Mathematical Model for the TAP Technique for Numerical Integration
Authors: Wang Dezheng 
Published: May 2015

AbstractThe mathematical modeling of the reactor in the TAP technique describes it as composed of zones of different diffusivity, and it makes the model linear by imposing boundary conditions of the continuity of concentration and flux at zone boundaries so as to be able to use a Fourier transformation technique to solve the equations. An alternative description of the reactor that uses a spatially non‐constant diffusivity to obviate the need to impose auxiliary boundary conditions in the regions where diffusivities change is proposed. The reactor equation is the mass balance equation without the simplification to the case of constant diffusivity, that is, without the diffusivity taken out of the differential operator. Computations based on it are compared with those of the linear model. The computed response curves of both models are similar, which indicates that the alternate model is equally good as a description of the reaction system. The alternate model is useful for modeling reactor systems with a variable cross‐sectional area or with temperature non‐uniformity.
Density Functional Study of the Effect of SiH4/GeH4 and Si(001)/Ge(001) on Gas‐Surface Reactivity during Initial Dissociative Adsorption
Authors: Lin Jyh Shing , Lee Lien‐Feng , Chou Wen‐Chi 
Published: May 2015

AbstractUltrasoft pseudopotential total energy calculation based on density functional theory (DFT) with generalized gradient approximation (GGA) has been used to investigate 1) the energetic profile for the initial dissociative adsorption of XH4 (X = Si and Ge) onto Si(001) and Ge(001) surfaces to evaluate their gas‐surface reactivity in comparison with relevant measured gas‐surface reactivity using supersonic molecular beam techniques, and 2) the effect of different gaseous molecular precursors, i.e. XH4 (X = Si and Ge), and different surfaces, i.e. Si(001) and Ge(001), on their gas‐surface reactivity during initial dissociative adsorption. Our evaluated gas‐surface reactivity for GeH4 is approximately a factor of 18.45 better than that for SiH4 on Si(001)‐(2×2) surface. This calculated result is about three to four times higher than observed gas‐surface reactivity (as much as a factor of 5 depending on the incident kinetic energy) derived from measured gas‐surface reactivity using supersonic molecular beam techniques. We believe that the better evaluated gas‐surface reactivity for GeH4 than SiH4 is due to 1) the forming of a stronger bond of Si‐H between H within GeH4 and buckled‐down Si atom on the Si(001)‐(2×2) surface and 2) the smaller distortion of Ge‐H bond within GeH4 at the transition state. Additionally, our evaluated gas‐surface reactivity for SiH4 on Si(001)‐(2×2) surface is approximately a factor of 21.69 better than SiH4 on Ge(001)‐(2×2) surface. This calculated result is about two times higher than observed gas‐surface reactivity. We attributed this better evaluated gas‐surface reactivity for SiH4 on Si(001)‐(2×2) surface to 1) the smaller distortion of Si‐H bond within SiH4 and 2) the nature of weaker bond of Ge‐H between H within SiH4 and buckled‐down Ge atom on Ge(001)‐(2×2) surface in comparison with that of stronger bond of Si‐H between H within SiH4 and buckled‐down Si atom on Si(001)‐(2×2) surface even though there is the slightly shorter bond length of Ge‐H between H within SiH4 and buckled‐down Ge atom on Ge(001)‐(2×2) surface at the transition state.
New Basis Sets for Lanthanide and Actinide Energy‐consistent Small‐core Pseudopotentials
Authors: Cao Xiaoyan 
Published: May 2015

AbstractThe optimization of generalized contracted Gaussian (14s13p10d8f6g)/[6s6p5d4f3g] atomic natural orbital valence basis sets for relativistic energy‐consistent small‐core lanthanide and actinide pseudopotentials of the Stuttgart‐Bonn variety is described. Corresponding Gaussian valence basis sets using a segmented contraction scheme (14s13p10d8f6g)/[10s8p5d4f3g] for lanthanides and (14s13p10d8f6g)/[10s9p5d4f3g] for actinides are also discussed. The basis sets have been proven to be stable and reliable by atomic and molecular calibration studies. Application to the electronic ground states of some selected homonuclear lanthanide dimers shows that the derived molecular constants are the best theoretical estimates available at present and have a satisfactory agreement with experimental data. Remaining discrepancies in the vibrational constants of La2, Ce2 and Pr2 are shown to be probably related to quite large Ar‐matrix shifts.
The Valence Bond Calculations on Conjugated Hydrocarbons of Medium to Infinite Sizes
Authors: Ma Jing , Li Shuhua , Liu Chungen , Jiang Yuansheng 
Published: May 2015

AbstractIn the past decade, we devoted time to the valence bond (VB) study of huge conjugated hydrocarbons by employing the Heisenberg model. Due to the dimension of the covalent space exponentially increasing with the size of molecule, the exact solution of the VB model for large molecules encounters a fundamental difficulty. Before 1990, Alexander and Schmalz published ground‐state energy results on a set of benzenoids of up to 24 π‐electrons using the graphical unitary group approach. Around 1995, we employed Lanczos technique to diagonalize the VB Hamiltonian and presented the low‐lying state energies and wave functions of benzenoids with up to 22 π‐centers. In terms of wave functions, the physical and chemical behaviors of these conjugated species have been discussed in detail. In succession, we generalized the VB calculation to larger systems by proposing an algorithm in coding all Slater determinants of the covalent space with conserved spin quantum number. The exact solutions of the VB model have been obtained for conjugated species with up to 30 π‐electrons. Recently, we broke through this limitation by extending the density‐matrix renormalization group (DMRG) method of White to the quasi‐one‐dimensional system. The VB energies of the ground states for two series of polycyclic aromatic hydrocarbons, polyacene and polyphenanthrene, of arbitrary lengths defined by the number of constituent hexagons have been obtained. The effective conjugated length for these infinite long‐chain polymers could be estimated.
Solid Phase Synthesis of 3‐Toluenesulfonylglutarimides
Authors: Chang Meng‐Yang , Lin Kuo‐Ging , Chen Shui‐Tein , Chang Nein‐Chen 
Published: May 2015

AbstractA novel route for the synthesis of 3‐toluenesulfonylglutarimides on a solid support is described. The cyclization step involves stepwise [3+3] strategy of Rink Amide resin bound onto an α‐toluenesulfonyl group with various α,β‐unsaturated esters.
A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism
Authors: Shih Shawn 
Published: May 2015

AbstractA large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called “hyperconjugation”) are estimated to be small in compared with the total energy of the molecule.We used theories of both isotropic and anisotropic proton hyperfine interactions in the π‐electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non‐planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn‐Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non‐planar structures of the open‐chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line‐width effect of the four methyl groups observed in the 2,3‐dimethyl‐2‐butene cation radicals also confirmed the positive sign of the electron‐proton hyperfine constant of hyper‐conjugation mechanism.A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the π electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in the design of dye molecules.
Oxidative Coupling of Thiols to Disulfides with Ti(IV) in the Presence of NaI under Air Atmosphere
Authors: Zeynizadeh Behzad , Iranpoor Nasser 
Published: May 2015

AbstractTi(IV) as TiCl3(O3SCF3) and TiO(O2CCF3)2 are used as efficient catalysts for oxidative coupling of aliphatic, aromatic and heteroaromatic thiols to their disulfides in the presence of NaI under air atmosphere.
Separation of Mercury with an Ammonium Sulfate‐Ammonium Thiocyanate‐Ethyl Violet Flotation System
Authors: Chen Bingyi , Bai Haixin , Li Quanmin , Liu Guoguang 
Published: May 2015

AbstractThe separation behavior of mercury by a flotation system consisting of ammonium sulfate, ammonium thiocyanate and ethyl violet, and the conditions for the separation of Hg(II) with other common metal ions have been studied. The studies show that in aqueous solutions, Hg(II) combines with NH4SCN and ethyl violet(EV) into dissoluble ternary ion‐association complex [Hg(SCN)42−]•(EV)2. In the presence of ammonium sulfate, the precipitate is floats well on the surface of the water phase and separates from water thoroughly. It shows that Hg(II) can be separated completely from Cd(II), Fe(II), Co(II), Ni(II), Mn(II) and Al(III) by flotation at pH1.0. The flotation mechanism of Hg(II) is described in this paper.
An Improved Method for the Addition Reactions of 1,3‐Dichloroacetone with Combined Organolithium‐Cerium Trichloride Reagents
Authors: Chen Same‐Ting , Fang Jim‐Min 
Published: May 2015

AbstractAlkyl‐, phenyl‐ and alkynyllithium reagents in combination with anhydrous cerium(III) chloride underwent addition reactions with 1,3‐dichloroacetone in a very efficient manner. The addition products are versatile precursors for 2‐substituted epichlorohydrins and glycidols. Fluconazole, a potent antifungal agent, was thus synthesized in 67% yield by addition of 1,3‐dichloroacetone to 2,4‐difluorophenyllithium in the presence of cerium(III) chloride, followed by substitution of the chlorine atoms with 1,2,4‐triazole.
A Semiempirical Study of Carbon Nanotubes with Finite Tubular Length and Various Tubular Diameters
Authors: Wang Bo‐Cheng , Wang Houng‐Wei , Lin I‐Chun , Lin Yun‐Shan , Chou Yu‐Ma , Chiu Houn‐Lin 
Published: May 2015

AbstractA semiempirical PM3 quantum computational method has been used to generate the electronic and optimized geometrical structure of SWNT of zigzag and armchair types. We shed light on the electronic structures of SWNT with various diameters and lengths of the tube. Particularly, the calculated HOMO, LUMO and band‐gap of SWNT are not monotonic but exhibit a well‐defined oscillation, which depends on the tubular diameter and the tubular length. Calculated HOMO, LUMO and band‐gap of the zigzag SWNTs have oscillated with tubular diameter as they contain an odd or even number of benzenoids in the circular plane of the carbon nanotube. The zigzag SWNTs with an odd number of benzenoids have a higher band‐gap than those of SWNTs with an even number of benzenoids in the circular plane of the carbon nanotube. Calculated results also reveal that the tubular length in the zigzag SWNTs influences the band‐gaps very little. For the armchair SWNT, calculated HOMO, LUMO and band‐gap contained the oscillate depending on the number of carbon sections in the tubular length axis. Their repeat sections are 3n‐1, 3n and 3n+1. The armchair SWNT with 3n+1 sections has a high band‐gap while the SWNTs with 3n‐1 sections have a low band‐gap. The tubular diameters of armchair SWNT influence the HOMO, LUMO and band gap very little.
Volumetric Properties and Volumetric Interaction Parameters of the CsCl‐saccharides (D‐glucose, D‐fructose)‐water Solutions at 298.15 K
Authors: Jiang Yucheng , Gao Shiyang , Xia Shuping , Wang Jianji , Zhuo Kelei , Hu Mancheng 
Published: May 2015

AbstractDensities have been measured for the CsCl‐saccharide (D‐glucose, D‐fructose)‐water systems at 298.15 K. These data were used to calculate the apparent molar volume of CsCl (Vφ,E) and the saccharides (Vφ,S), and the infinite dilution apparent molar volume Vφ,E0 and Vφ,S0 in the studied solutions. In addition, the standard transfer volume ΔtVφ,E0 of CsCl from water to aqueous saccharides solutions, and ΔtVφ,S0 of saccharides from water to CsCl solutions have been evaluated and discussed using the structural interaction model. The volumetric interaction parameters for CsCl with saccharide in water were obtained and analyzed by the group additivity principle and the stereochemistry of the saccharide molecules.
Thin Layer Chromatography of Purines on Silica Gel G Impregnated with Transition Metal Ions; Assay of Caffeine and Theophylline in Pharmaceutical Formulations
Authors: Singh D. K. , Srivastava Bhavana , Sahu Archana 
Published: May 2015

AbstractThis study was undertaken to develop thin layers of silica gel G impregnated with transition metal ions for separation, identification and estimation of purines. The influence of transition metal ions and eluting solvents on chromatographic behaviour (hRf) has been studied. The method was applied for qualitative analysis of purines in the mixtures and quantitative analysis of purine bases in the mixture as well as in pharmaceutical formulations. The results were compared statistically with those obtained by official methods. The method is simple, reproducible, and accurate within 1.3 ± 0.6%.
Metal Binding and Selectivity in Zinc Proteins
Authors: Dudev Todor , Lim Carmay 
Published: May 2015

AbstractZinc is one of the most abundant metals in living organisms and is an essential co‐factor of many metabolic enzymes and transcription factors. In this review, based on a recent body of theoretical and experimental results, the physical bases are delineated for the following aspects of zinc binding and selectivity in proteins: (1) What is the most thermodynamically preferable coordination geometry of a bidentate ligand (such as carboxylate) or Zn in Zn‐binding sites? (2) What is the protonation state of the Cys side chain in Cys4 zinc‐finger cores? (3) How does a protein select Zn from the mixture of ions in the surrounding fluids? (4) What is the role of the second shell in metal binding and selectivity? The key results are summarized and the physical basis and/or implications of the findings are discussed.
Mixed Ground‐State in the Trinuclear Complex: [Mn3O(O2CCCl3)6(H2O)3]
Authors: Tsai Hui‐Lien , Jwo Tyn‐Yih , Yang Chen‐I , Wur Ching‐Shuei , Lee Gene‐Hsiang , Wang Yu 
Published: May 2015

AbstractThe reaction of [Mn12O12(OAc)16(H2O)4]·4H2O·2HOAc with Cl3CCO2H in dichloromethane leads to formation of mixed‐valence trinuclear oxo‐centered [Mn3O(O2CCCl3)6(H2O)3]·2H2O (1). Complex 1 crystallizes in two forms; the monoclinic and hexagonal systems. [Mn3O(O2CCCl3)6(H2O)3]·3H2O (1a) crystallizes in hexagonal, space group P63/m (295 K) with a = 10.0741(1) Å, c = 22.8668(4) Å, and z = 2. [Mn3O(O2CCCl3)6(H2O)3]·0.5C6H14 (1b) crystallizes in monoclinic, space group P21/n (150 K) with a = 11.8258(2) Å, b = 41.9370(5) Å, c = 25.9619(4) Å, β = 95.297(1)°, and z = 12. Complex 1 possesses an oxo‐centered Mn3O unit with peripheral ligands provided by bridging trichloroacetate and terminal H2O groups. Each manganese ion is distorted octahedral, and consideration of overall charge of the trinuclear unit necessitates a mixed‐valence MnIIMnIII2 description. Magnetization measurement at 2.0 K up to 70 kG indicates the mixed ground state S = 3/2 and S = 1/2 for complex 1. X‐band EPR spectra measured at 4.0–100.0 K on polycrystalline sample of complex 1. There is a transition centered at g ≈︁ 4, which decreases in intensity with increasing temperature. Also, there is a transition centered at g ≈︁ 2, which does not disappear with increasing temperature.
The Ionic Conductivity of Ultrafine Solid Electrolytes for Li4.4Al0.4Si0.6O4‐xY2O3 Systems
Authors: Chen Rufen , Liu Huating , Song Xiuqin 
Published: May 2015

AbstractThe Li4.4Al0.4Si0.6O4‐xY2O3 (x = 0 to 0.5) ion conductors were prepared by the Sol‐Gel method and examined in detail. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The experimental results show that the conductivity and sinterability increased with the amount of excess Y2O3 in the silicate. The particle size of the powder samples is about 0.12 μm. The maximum conductivity at 16 °C is 2.925 × 10−5s·cm−1 for Li4.4Al0.4Si0.6O4‐0.3 Y2O3.
The HPLC Enantioresolution of Phenyl Isothiocyanated Amino Acids on Vancomycin Bonded Phase Using the Acetonitrile‐Based Mobile Phase: A Comparison to the Teicoplanin Phase
Authors: Chen Shushi 
Published: May 2015

AbstractThe phenyl isothiocyanate, an electrophilic reagent for peptide chain sequencing, is used to pre‐column derivatize a variety of α‐amino acids in alkaline medium before their enantioresolution on a vancomycin bonded chiral phase using the acetonitrile‐based mobile phase. The observed resolution is believed to be due to the re‐location of the hydrogen receptor site from sulfur to nitrogen on the isothiocyanyl fragment of derivatizing reagent, which in turn changes the enantioselectivity. Under the same chromatographic conditions, the resolution for N‐benzoylated, 3,5‐dinitrobenzoylated and N‐carbobenzyloxylated amino acids is either not found or unsatisfactory. Also, no resolution is obtained in the reversed‐ or normal phase mode for all phenyl isothiocyanated amino acids examined in this study.
The Effects of Various Alcohols on the Stability of Melittin: A Molecular Dynamics Study
Authors: Liu Hsuan‐Liang , Hsu Chia‐Ming 
Published: May 2015

AbstractIn this study, 200 ps molecular dynamics simulations were conducted to investigate the effects of various alcohols on the structural stability of melittin. The averaged helicity of melittin remained 80% in pure butanol, whereas it was below 60% both in pure water and in pure methanol. The α‐helix propensity of melittin increased with the aliphatic chain length of the alcohol. Charge‐charge interaction between Lys21 and Arg24 and polar‐nonpolar interaction between Trp19 and Arg22 are probably responsible for the higher structural integrity of the C‐terminal α‐helix over the N‐terminal one. The weaker dielectric constant of longer aliphatic chain length of alcohol possibly reduces the hydrogen bonding between amide protons and surrounding solvent molecules and simultaneously promotes the intramolecular hydrogen bonding in melittin and therefore stabilizes the secondary structure of melittin. The effect of various alcohols on stabilizing melittin is most likely due to their ability to form clusters on the surface of melittin effectively, favoring the formation of intramolecular hydrogen bonds instead of intermolecular hydrogen bonds and promoting the formation of stable α‐helices.
Photooxidation of Methane over TiO2
Authors: Lien Chen‐Fu , Chen Meng‐Tso , Lin Yu‐Feng , Lin Jong‐Liang 
Published: May 2015

AbstractFourier‐transform infrared spectroscopy has been employed to investigate the adsorption and photo‐oxidation of CH4 over powdered TiO2. The interaction between the CH4 and TiO2 surface is weak. It is found that no CH4 molecules are adsorbed on the surface at 35 °C in a vacuum. Under UV irradiation, CH4 decomposes to form CO(a), CO2(g), H20(a), and HCOO(a) in the presence of O2. The photoreaction rate is retarded and only small amounts of CO(a) and HCOO(a) are formed in the absence of O2. It is observed that the oxygen atoms of O2 are incorporated into these photoproducts as 18O2 is used. The major 18O‐containing products are C18O(a), C18O2(g), H2 18O(a), HC16O18O(a), and HC18O18O(a) after 180 min UV irradiation. However, the extent of 18O incorporating into the adsorbed formate is dependent on UV irradiation time. In the early stage of UV irradiation HC16O16O(a) is the major formate form indicating the involvement of TiO2 lattice oxygens for its formation, but HC18O18O(a) becomes the major one after 180 min indicating the involvement of 18O2. Formate on TiO2 further photodecomposes to CO2(g), but not to CO(a). CO(a) formation is directly from CH4 photodecomposition with the participation of TiO2 lattice oxygens and O2.
Neolignans from the Parasitic Plants. Part 2. Cassytha Filiformis
Authors: Ho Jiau‐Ching , Chen Chiu‐Ming , Row Lie‐Ching 
Published: May 2015

AbstractFrom the whole plant of Cassytha filiformis Linn. (Lauraceae), two new neolignans, named 4‐O‐methylbalanophonin and cassyformin together with three known compounds have been isolated. Their structures were established by spectroscopic and chemical methods.
Synthesis and Second‐Order Nonlinearities of Chiral Prolinol‐Substituted Chromophores
Authors: Chou Shang‐Shing P. , Yu Chiung‐Yi , Lin Hong‐Cheu , Yang Pao‐Keng 
Published: May 2015

AbstractA new series of thiophene‐ and furan‐containing chromophores with a chiral prolinol donor and a sulfone acceptor has been synthesized. The UV‐vis absorptions, second‐order nonlinear optical properties, and X‐ray crystal structures are described.
Sulfur‐Assisted Intermolecular Triphenylphosphine Dissociation of Thiocarbamoyl Ligand in Platinum(II). X‐ray Structure of Complex [Pt(PPh3)2(η1‐SCNMe2)(Cl)]
Authors: Yih Kuang‐Hway , Lee Gene‐Hsiang , Huang Shou‐Ling , Wang Yu 
Published: May 2015

AbstractTreatment of Pt(PPh3)4 with N,N‐dimethylthiocarbamoyl chloride, Me2NC(=S)Cl, in dichloromethane at −20 °C processes the oxidative addition reaction to produce platinum complex [Pt(PPh3)2(η1‐SCNMe2)(Cl)], 2 with releasing two triphenylphosphine molecules. The 31P{1H} NMR spectra of complex 2 shows the dissociation of the triphenylphosphine ligand to form diplatinum complex [Pt(PPh3)Cl]2(μ,η2‐SCNMe2)2, 3 in which the two SCNMe2 ligands coordinated through carbon to one metal center and bridging the other metal through sulfur. Complex 2 is characterized by X‐ray diffraction analysis.
Determination of Sulfide in Spring and Wastewater by a New Kinetic Spectrophotometric Method
Authors: Emami Marjan , Mousavi Mir Fazlollah , Barzegar Mohsen 
Published: May 2015

AbstractA simple, rapid, and sensitive method has been developed for the determination of trace amounts of sulfide based on its reaction with thionine. The reaction is monitored spectrophotometrically by measuring the decreasing absorbance of the dyestuff at 600 nm by the fixed time method. After optimization of the measuring conditions the calibration curves were found linear up to 38.0 ppm (four regions), and the theoretical limit of detection was 0.076 ppm and the relative standard deviation for determination of 1.0 ppm sulfide (n = 10) was found to be 2.7%. The proposed method was applied successfully to the determination of sulfide in spring water and wastewater samples.