Investigation of structural and electronic properties by pnictogen substitution in the layered oxypnictides (LaO)ZnPn (Pn = P,As, Sb)

We study the structural and electronic properties of p-type layered oxypnictides (LaO)ZnPn (Pn = P, As, Sb), calculated by first principles. Pn substitution from P to Sb increases D_2d-type local symmetry distortions at ZnPn₄ and OLa₄ tetrahedra. (LaO)ZnP and (LaO)ZnAs exhibit direct band gaps (Γ → Γ) of 0.621 eV and 0.528 eV, respectively, while (LaO)ZnSb exhibits an indirect band gap (Γ → 0.2Λ) of 0.029 eV. The band gaps come from valence Pn p _x/p _y and conduction Zn 4s states. Moreover, the substitution increases split-off energy at Z and Γ points. We find localized valence degeneracy-lifted Zn 3d states because of the possible second-order Jahn-Teller effect, which induces the local symmetry distortions. The localized Zn 3d states are followed by minor bonding s-p hybridization of Zn and Pn. Above them, we show major bonding s-p hybridization; O 2p states in electron-blocking [LaO]⁺ layers, which are essential for thermoelectricity; and nonbonding Pn p states near Fermi level. In the conduction band, antibonding s-p hybridization is found. Our result shows new insights and findings of structural and electronic properties, which explain previous experimental results, as the focus of this study is related to inorganic chemistry. This study is important for future functional device applications.     

Application of the Peak Fitting Programme “Galactic” For FTIR-Analysis of OH-Ions in Natural and Synthetic Apatites

Abstract

Most of the studies on heavy metals binding ability of apatites have been carried out on hydroxyapatites (HA_P) [Ca_l0(PO₄)₆(OH)₂]. As the chemical characteristics of apatite depend substantially on the substitutions in its structure, the apatites with F substitution for OH and CO₃ ²for PO₄ ³ were studied.     

Charge-transport in tin-iodide perovskite CH3NH3SnI3: origin of high conductivity

The structural and electrical properties of a metal-halide cubic perovskite, CH(3)NH(3)SnI(3), have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity.     

A neutral polysaccharide from <Emphasis Type="Italic">Glycyrrhiza inflata</Emphasis>

A neutral polysaccharide Gi-A1 was isolated from the roots of Glycyrrhiza inflata Bat. It had a molecular mass of over 2000 kDa and showed [α]_D²⁰ + 81.4° (c 1.05, H₂O). Acid hydrolysis and methylation analysis indicated that Gi-A1 was mainly composed of α-D-glucose, α-L-arabinose, and α-D-galactose with a molar ratio of 8.0:1.8:1.0. It can significantly stimulate spleen cell proliferation in vitro (P < 0.01). Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 13–14, January–February, 2009.     

HILIC LC‐MS for the determination of 2′‐C‐methyl‐cytidine‐triphosphate in rat liver

A very accurate and selective LC‐MS/MS method was developed and validated for the quantification of 2′‐C‐modified nucleoside triphosphate in liver tissue samples. An efficient pretreatment procedure of liver tissue samples was developed, using a fully automated SPE procedure with 96‐well SPE plate (weak anion exchange sorbent, 30 mg). Nucleotide hydrophilic interaction chromatography has been performed on an aminopropyl column (100 mm×2.0 mm, 3 μm) using a gradient mixture of ACN and ACN/water (5:95 v/v) with 20 mM ammonium acetate at pH 9.45 as mobile phase at 300 μL/min flow rate. The 2′‐C‐modified nucleoside triphosphate was detected in the negative ESI mode in multiple reaction monitoring (MRM) mode. Calibration curve was linear over the 0.05–50 μM concentration range. Satisfying results, confirming the high reliability of the established LC‐MS/MS method, were obtained for intraday precision (CV = 2.5–9.1%) and accuracy (92.6–94.8%) and interday precision (CV = 9.6–11.5%) and accuracy (94.4–102.4%) as well as for recovery (82.0–112.6%) and selectivity. The method has been successfully applied for pharmacokinetic studies of 2′‐C‐methyl‐cytidine‐triphosphate in liver tissue samples.     

Third-harmonic generation in regular domain structures

The process of frequency conversion in regular domain structures is studied using the constant-intensity approximation. The investigations are carried out at values of complex amplitudes of the fundamental radiation and third harmonic at the output of each domain equal to the values of the corresponding complex amplitudes at the input of the subsequent domain. We show that the optimum length of each domain depends on the input pump intensity in the given domain. Thus, it is possible by choosing the optimum lengths of domains, phase mismatch, and pump intensity even at a low number of periods of nonlinear susceptibility modulation of the lattice to reach considerable values of conversion efficiency at the structure output in comparison with the traditional case of homogeneous nonlinear media.     

Alpha-N-acetylmannosamine (ManNAc) synthesis via rhodium(II)-catalyzed oxidative cyclization of glucal 3-carbamates

[reaction: see text] Glucal 3-carbamates 1 and 7 underwent oxidative cyclization with iodobenzene diacetate or iodosobenzene in the presence of Rh2(OAc)4, providing mannosamine 2-N,3-O-oxazolidinones. With iodosobenzene, incorporation of 4-penten-1-ol provided a readily separable anomeric mixture of n-pentenyl glycosides, with the anomers exhibiting pronounced differences in reactivity as glycosyl donors. N-acylation of the sugar oxazolidinones led to alpha-selective glycosyl donors for the elaboration of various 2-mannosamine frameworks. Alternatively, the anomeric n-pentenyl glycosides of N-Cbz 2-mannosamine oxazolidinones were converted separately to oxazolidinone-opened derivatives 28alpha and 28beta. These served as stereoconvergent glycosyl donors, and the alpha-linked products were readily advanced to a variety of N-acetylmannosamine (ManNAc) frameworks, using an intramolecular O-->N acetyl transfer as the final step.     

Liquid crystalline semirigid polyesters based on phenylstilbene analogues of 1,3,4-thiadiazole

Semirigid polyesters composed of phenylstilbene analogues of 1,3,4-thiadiazole, 2-(2-phenylethenyl)-5-phenyl-1,3,4-thiadiazole (PEPT), linking an octamethylene chain at different disubstituted (3,3'-, 3,4'-, 4,3'- and 4,4'-) positions, were prepared from four diphenols of the PEPT and sebacoyl chloride by interfacial polycondensation. The effect of polymer structure on thermotropic liquid crystalline (LC) and optical properties is discussed. Differential scanning calorimetry (DSC) measurements, optical texture observations and powder X-ray diffraction patterns showed that the polymer linking the octamethylene chain at the 4,4'-position (4,4'-PEPT) has a linear structure and forms an enantiotropic nematic LC phase. Polymers linking the octamethylene chains at the 4,3'- (4,3'-PEPT), the 3,4'- (3,4'-PEPT) and the 3,3'-positions (3,3'-PEPT) positions have a less linear structure and display monotropic smectic phase or no LC phase. Solution and solid-state UV-visible and emission spectra indicated that the polyesters exhibit absorption maxima due to the PEPT moieties and fluoresce blue light, but low or no quantum efficiencies were recognized. The polyesters emitted weak polarized fluorescent light at room temperature.