Structural characterization of pseudo-binary semiconducting alloys using molecular simulations

Monte Carlo simulations with the Keating model have been performed to predict the lattice constant and bond length variations with composition for pseudo-binary semiconducting alloys. In general, it is observed that the deviations of the lattice constants from Vegard's law predictions are larger as the lattice mismatch between the constituent binaries increases. Further, it is noted that these alloys have partial virtual crystal model characteristics and tend to be more towards the flexible (floppy) crystal limit as compared to the rigid crystal limit. The topological rigidity parameters are bond-type dependent. The angular deviations from perfect tetrahedral structure are also measured.     

Identification of functionally key residues in maltose transporter with an elastic network model-based thermodynamic method

Periplasmic binding protein-dependent maltose transport system (MBP-MalFGK₂) of Escherichia coli, an important member of the Adenosine triphosphate-binding cassette transporter superfamily, is in charge of the transportation of maltoses across cellular membrane. Studies have shown that this transport processes are activated by the binding of maltose and are accompanied by large-scale cooperative movements between different domains which are mediated by a network of important residues related to signal transduction and allosteric regulation. In this paper, the functionally crucial residues and long-range allosteric pathway of the regulation of the system by substrate were identified by utilising a coarse-grained thermodynamic method proposed by our group. The residues whose perturbations markedly change the binding free energy between maltoses and MBP-MalFGK₂ were considered to be key residues. In result, the key residues in 62 clusters distributed in different subdomains were identified successfully, and the results from our calculation are highly consistent with experimental and theoretical observations. Furthermore, we explored the long-range cooperation within the transporter. These studies will help us better understand the physical mechanism of the effects of the maltose on MBP-MalFGK₂ by long-range allosteric modulation.     

Stoichiometry,Association Constant,and Solvation Model of Chiral Hydroxyfuranones in the Presence of Pirkle's Alcohols

ABSTRACT

(S)-(+)-Dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone, (R)-(-)-dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone, (S)-(-)-dihydro-4-hydroxy-2(3H)-furanone, and (S)-(-)-5-hydroxymethyl-2(5H)-furanone in the presence of pure enantiomers of 2,2,2-trifluoro-1-(9-anthryl)ethanol were studied by ¹H NMR in deuterated chloroform solutions. Experimental Job's plots suggest that the resulting solvates are formed with one molecule of solute and one of the chiral solvating agent. From the magnitude of the association constant determined for (S)-(+)-dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone in the presence of (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol (1.26 ± 0.09 M^?1), it is inferred that the solvate is weak and cannot be isolated at 298 K. The correlation between the magnitude of induced chemical shifts, NOESY maps, and the known configuration of solutes and chiral solvating agents suggests that intermolecular hydroxyl-hydroxyl interaction is the primary interaction. Accordingly, the secondary interaction might occur between benzylic-hydrogen of the chiral solvating agent and the carbonyl- or furan ring-oxygen atoms of the solute.     

Hydrophobic Bimetallic Catalysts for H/D Exchange Reaction between Hydrogen and Water

Hydrophobic bimetallic catalysts of Pt-M on styrenedivinylbenzene were prepared, where M represents successively: Ir, Rh, Pd, Cu and Ag. The total metal loading was 0.5 wt% and the weight fractions of the metal M were: 0.0,0.05,0.1,0.25,0.5,0.75 and 1.0. For each sample, the catalytic activity for H/D exchange between hydrogen and water vapor was measured. In case of monometallic catalysts, no activity was detected for M = Cu and M = Ag, and the order of the activity values for the other metals was: Pt < Ir < Rh < Pd. For each bimetallic catalyst, the activity measurements indicated a clear interaction between the platinum and the second metal, thus the activity was significantly increased for M = Ir, increased for M = Rh, decreased for M = Pd, drastically decreased for M = Cu and M = Ag.     

Radiation Effects on Optical Properties of Ethylene Vinyl Acetate Copolymer Films

The optical properties of ethylene vinyl acetate (EVA) film have been studied. The effects of gamma irradiations on the optical spectrum of EVA films have been investigated using spectrophotometric measurements of reflectance and transmittance in the wavelength range 200–1100 nm. The absorption spectra were recorded in the UV–vis region for the unirradiated and irradiated films (from 0 to 50 kGy). Optical constants such as refractive index (n), extinction coefficient (K), and complex dielectric constant have been determined, as well as the optical dispersion parameters and high frequency dielectric constants. A large dependence of the fundamental optical constants on the irradiation dose was noticed. On irradiation, a higher refractive index was obtained as compared with that for unirradiated film. The dispersion parameters, such as E ₀ (single‐oscillator energy), E _d (dispersive energy), and M _?1 and M _?3 (moments), are discussed in terms of the single‐oscillator Wemple–DiDomenico model.     

A Convenient Synthesis and a Nuclear Magnetic Resonance Spectroscopic Study of a β-D Linked Trisaccharide

The building block derivatives of the monosaccharide, O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl) trichloroacetimidate (1), and the disaccharide α, α-trehalose, 2′,3′6′-tri-O-benzoyl-α-D-glucopyranosyl-2,3,4,6-tetra-O-benzoyl-α-D- glucopyranoside (2) were coupled to produce trisaccharide 3. A detailed n.m.r. analysis [ ¹H, ¹³C, ¹³C-¹H correlation, and 2D ¹H-¹H correlation experiment (COSY)] was used for the structural elucidation of the building blocks 1, 2 and the trisaccharide product 3.     

Electron-spin-dependent 4He+ ion scattering on Bi surfaces

We studied low-energy (～ 1.55 keV) electron-spin-polarized ⁴He⁺ ion scattering on a Bi(111) ultrathin film epitaxially grown on a Si(111) substrate. We observed that the scattered ion intensity differed between the incident He⁺ ions with up and down spins even though Bi is a non-magnetic element. To analyze the origin of this spin-dependent ion scattering (the spin asymmetry), we investigated the detailed relationship between the spin asymmetry and the incident angle, the azimuthal angle, the scattering angle, and the incident energy. All the data indicate that the spin asymmetry originates from the scattering cross section owing to the non-central force in the He⁺–Bi atom binary collision. The non-central force is most likely attributed to the spin–orbit coupling that acts transiently on the He⁺ 1s electron spin in the binary collision.     

Theoretical explanation of optical absorption spectra and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal

The optical absorption spectra (d-d transition bands) and covalent effect of Ni²⁺ ions in octahedral sites of Ca₃Sc₂Ge₃O₁₂ crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is R_i?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni²⁺ center in Ca₃Sc₂Ge₃O₁₂ crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni²⁺ ion in the octahedral site of Ga₃Sc₂Ge₃O₁₂ is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d⁸ ions in octahedral lattices.     

Mossbauer study of ferrite systems Co x Mn1−x Fe2O4 and Ni x Mn1−x Fe2O4

Mössbauer spectra of Co _x Mn_1?x Fe₂O₄ and Ni _x Mn_1?x Fe₂O₄ ferrites withx values ranging from 0·1 to 0·8 in steps of 0·1 have been recorded at room temperature. All spectra exhibit well-defined Zeeman hyperfine patterns. It has been observed that hyperfine field at Fe³⁺ nucleus increases more rapidly by nickel substitution than by cobalt substitution. This has been explained in terms of exchange interactions and cation distribution in the spinels. Hyperfine fields, isomer shifts and quadrupole splittings have been determined.