Synthesis,Crystal Structure and Luminescent Property of Mg(II) Complex with N-Benzenesulphonyl-L-Leucine and 1,10-Phenanthroline

A new complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ [L= N-benzenesulphonyl-L-leucine] was synthesized by the reaction of magnesium chloride hexahydrate with N-benzenesulphonyl-L-leucine and 1,10-phenanthroline in the CH₃CH₂OH/H₂O (v:v = 5:1). It was characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The crystal of the title complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ belongs to triclinic, space group P-1 with a = 0.72772(15) nm, b = 1.4279(3) nm, c = 1.4418(3) nm, α = 63.53(3)°, β = 79.75(3)°, γ = 81.83(3)°, V = 1.3163(5) nm³, Z =1, D_c= 1.258 μg·m⁻³, μ = 0.177 mm⁻¹, F(000) = 526, and final R₁ = 0.0506, ωR₂ = 0.1328. The complex comprises a six-coordinated magnesium(II) center, with a N₂O₄ distorted octahedron coordination environment. The molecules are connected by hydrogen bonds and π-π stacking to form one dimensional chain structure. The luminescent property of the Mg(II) complex has been investigated in solid.     

Crystal and molecular structure of n,n'-diethyl-n,n'-diphenylurea

N,N′-diphenyl-N,N′-diethylurea (C₁₇H₂₀N₂O) crystallizes in the space group P2₁/c. The unit cell constants are: a = 10.42 ± 0.01 Å, b = 16.86 ± 0.02 Å, c = 10.66 ± 0.001 Å, β = 125°16′ ± 5′; Z = 4, D_x = 1.16 g·cm^-3, D_meas = 1.16 ± 0.01 g·cm^-3. Data for 1392 reflections were collected at room temperature on a Picker automated diffractometer. The crystal structure was solved by direct methods and refined by bloc-diagonalized matrix least-squares calculations. The molecule is characterized by a pseudo C₂ symmetry; both phenyl groups are trans with respect to the oxygen atom. The hybridization of the two nitrogen atoms is intermediate between trigonal and tetrahedral; the nonplanar distortion of the amide groups is about 30°. The amide C-N bond lengths are 1.37 Å.     

Structure of an Iron(II) Dioxygen Complex; A Model for Oxygen Carrying Hemeproteins

The preliminary structural characterization of a reversible ferrous dioxygen complex is reported. Mono(N-methyl imidazole) (dioxygen) meso-tetra (α,α,α,α-o-pivalamidephenyl) porphinatorino(II), [Fe(O₂)-(N-Me imid) (α,α,α,α-TpivPP)], 1, isolated from toluene solution, crystallizes in the monoclinic system with four molecules in a unit cell of dimensions a = 18.690 (3), b = 19.514 (3), c = 18.638 (3) Å, and β = 91.00 (1)°. R = 0.15 for 841 reflections having F² > 3σ (F²).The complex 1 has four pivalamido groups on one side of the porphyrin forming a hydrophobic pocket of 5.4-Å depth which encloses coordinated dioxygen. The dioxygen is coordinated “end-on,” with a bent Fe-O-O bond. The Fe-O-O plane bisects an N-Fe-N right angle of the equatorial iron porphyrin plane and is four way statistically disordered. In addition there is a crystallographic 2-fold axis through iron, coordinated oxygen, and nitrogen of the axially bound N-methyl imidazole. Thus there are two types of coordinated dioxygen with the Fe-O-O plane either parallel or perpendicular to the trans axial imidazole plane. Corresponding values for the Fe-O-O bond angles are 135-(4)° and 137(4)° and for the O-O bond lengths are 1.23 (0.08) and 1.26 (0.08) Å, with a dihedral angle of 90° between alternative orientations of the Fe-O-O plane. The Fe-O distance is 1.75 (0.02) Å and Fe-N (imidazole) is 2.07 (0.02) Å, suggesting multiple bond character in the Fe-O moiety. The similarity of the Mössbauer spectrum of the model complex, 1, with oxyhemoglobin indicates that 1 may be a good model for oxygen binding in the oxygen transport hemeproteins.     

Uptake of bacterial lipopolysaccharide and expression of tumor necrosis factor-α-mRNA in isolated rat intrahepatic bile duct epithelial cells

AIM: To study the uptake of bacterial lipopolysaccharides (LPS) and expression of tumor necrosis factor α-mRNA (TNF-α-mRNA) with cultured rat intrahepatic bile duct epithelial cells.METHODS: By using fluorescent, immunohistochemical and in situ hybridization techniques, the uptake of Escherichia coli LPS and expression of TNF-α-mRNA with isolated rat intrahepatic bile duct epithelial cells were observed with confocal laser scanning microscopy.RESULTS: Positive reactions to LPS were found in the cytoplasm of isolated intrahepatic bile duct epithelial cells after incubation with LPS for 15 min and the FITC fluorescent intensity against LPS was significantly higher than that of the controls (121.45 μFI/μm² ± 15.62 μFI/μm² vs 32.12 μFI/μm² ± 9.64 μFI/μm², P < 0.01). After incubation with LPS for 3 h, fluorescein isocyanate (FITC) fluorescent intensities of the expression of TNF-α-mRNA with fluorescent in situ hybridization in the cytoplasm and nuclei of the cultured bile duct epithelial cells were significantly higher than those of the controls (189.15 μFI/μm² ± 21.33 μFI/μm² vs 10.00 μFI/μm² ± 8.99 μFI/μm², 64.85 μFI/μm² ± 14.99 μFI/μm² vs 21.20 μFI/μm² ± 2.04 μFI/μm², respectively (P < 0.01)). The increase of FITC fluorescent intensity of TNF-α-mRNA expression in the cytoplasm peaked at 6 h after incubation (221.38 μFI/μm² ± 22.99 μFI/μm²). At various time points after incubation with LPS, the increase of fluorescent intensities of TNF-α-mRNA in the cytoplasm were much higher than those in the nuclei (P < 0.01).CONCLUSION: LPS can act on and enter into isolated intrahepatic bile duct epithelial cells and stimulate the expression of TNF-α-mRNA.     

Alkylation of Benzene with Propylene in a Flow-Through Membrane Reactor and Fixed-Bed Reactor: Preliminary Results

Benzene alkylation with propylene was studied in the gas phase using a catalytic membrane reactor and a fixed-bed reactor in the temperature range of 200–300 °C and with a weight hourly space velocity (WHSV) of 51 h⁻¹. β-zeolite was prepared by hydrothermal synthesis using silica, aluminum metal and TEAOH as precursors. The membrane’s XRD patterns showed good crystallinity for the β-zeolite film, while scanning electron microscopy SEM results indicated that its random polycrystalline film was approximately 1 μm thick. The powders’ specific area was determined to be 400 m²·g⁻¹ by N₂ adsorption/desorption, and the TPD results indicated an overall acidity of 3.4 mmol NH₃·g⁻¹. Relative to the powdered catalyst, the catalytic membrane showed good activity and product selectivity for cumene.     

Potential effect of chronic Helicobacter pylori infection on glucose metabolism of Mongolian gerbils

AIM: To assess the effect of Helicobacter pylori(H. pylori) infection on metabolic parameters in Mongolian gerbils.METHODS: A total of 40 male, 5- to 8-wk-old, specific-pathogen-free Mongolian gerbils(30-50 g) were randomly allocated into two groups: a control group(n = 20) and an H. pylori group(n = 20). After a two-week acclimation period, the control group was administered Brucella broth and the H. pylori group was challenged intra-gastrically five times every other day with approximately 109/CFU H. pylori ATCC43504(Cag A+, Vac A+). Each group was then divided into two subgroups, which were sacrificed at either 6 or 12 mo. The control and H. pylori subgroups each contained 10 Mongolian gerbils. Body weight, abdominal circumference, and body length were measured, and body mass index(BMI) and Lee's index were calculated. Biochemical assays were used to detect serum indexes, including glucose, glycated hemoglobin(GHb), glycated hemoglobin A1c(Hb A1c), triacylglycerol, and total cholesterol, using an automatic biochemistry analyzer. Inflammatory cytokines, including interleukin(IL)-1β, IL-2, IL-4,IL-10, IL-12, tumor necrosis factor-α(TNF-α) and interferon(IFN)-g, were assayed using ELISA. The expression of insulin and insulin-like growth factor 1(IGF-1) was detected by immunohistochemistry, and islet apoptosis was measured using the terminal deoxynucleotidyl transferase-mediated d UTP nick end labeling(TUNEL) assay.RESULTS: At each time point, body weight, abdominal circumference, BMI, and Lee's index were increased after H. pylori infection. However, these differences were not significant. H. pylori infection significantly increased the GHb(5.45 ± 0.53 vs 4.98 ± 0.22, P 0.05) and Hb A1c(4.91 ± 0.61 vs 4.61 ± 0.15, P 0.05) levels at 12 mo. We observed no significant differences in serum biochemical indexes, including fasting blood glucose, triacylglycerol and total cholesterol, at 6 or 12 mo after infection. H. pylori infection significantly increased the expression of IGF-1(P 0.05). Insulin levels from the pancreas and the apoptotic rate of islet β-cells remained unchanged. Also, we observed no significant differences among cytokines levels, including IL-1β, IL-2, IL-4, IL-10, IL-12, TNF-α and IFN-g. IL-4 was the only exception, which increased at 6(44.36 ± 25.17 vs 17.38 ± 3.47, P 0.05) and 12 mo(33.41 ± 10.00 vs 18.91 ± 5.31, P 0.05) after H. pylori infection.CONCLUSION: Long-term H. pylori infection is significantly associated with high levels of Hb A1 c in Mongolian gerbils, indicating a potential role of H. pylori infection in glucose dysregulation.     

Conformation of cyclo(Gly-L-Pro-L-Pro-Gly-L-Pro-L-Pro)(2)Mg complex crystallized from CH(3)CN solution

The cyclic hexapeptides (Gly-L-Pro-L-Pro-Gly-L-Pro-L-Pro) in the (peptide—Mg—peptide)²⁺ complex have nearly identical asymmetric conformations. Each has two cis Pro-Pro linkages and lacks any intraring hydrogen bonds. The Mg²⁺ ion forms six ligands in a regular octahedral array with the carbonyl oxygen atoms of the two Gly residues and one Pro residue of each peptide. The “sandwich” complex has an approximate 2-fold rotation axis through the Mg²⁺ relating the two peptide moieties. Cyclo(Gly-Pro-Pro-Gly-Pro-Pro)₂Mg(ClO₄)₂· 4C²H₃CN crystallizes in space group P3₁ with a = b = 15.744(4) Å, c = 24.002(6) Å, γ = 120°, and Z = 3. A highlight of the structure determination is the ready location of the Mg self-vector in a Harker section and the development of the entire structure by use of the tangent formula starting with the known position of the Mg atom.     

Structures 4-n-propyl Piperazines as Non-Imidazole Histamine H3 Antagonists

Seven new low-temperature structures of 4-n-propylpiperazine derivatives, potential H3 receptor antagonists, have been determined by X-ray crystallography, with the following symmetry and unit cell parameters: 2-(4-propyl-piperazin-1-yl)oxazolo[4,5-c]pyridine (compound 1), P-1, 5.9496 Å, 12.4570 Å, 12.8656 Å, 112.445°, 95.687°, 103.040°; 2-(4-propyl-piperazin-1-yl)thia-zolo[4,5-c]pyridine (compound 2), I2/a, 22.2087 Å, 7.5519 Å, 19.9225 Å, β = 92.368°; 2-(4-propyl-piperazin-1-yl)oxazolo[5,4-c]pyridine (compound 3), C2/c, 51.1351 Å, 9.36026 Å, 7.19352 Å, β = 93.882°; 2-(4-propyl-piperazin-1-yl)thiazolo[5,4-c]pyridine (compound 4), Pbcn, 19.2189 Å, 20.6172 Å, 7.4439 Å; 2-(4-propylpiperazin-1-yl)[1,3]oxazolo[4,5-b]pyridine, hydrate (structure 5), Pbca, 7.4967 Å, 12.2531 Å, 36.9527 Å; 2-(4-propylpiperazin-1-yl)[1,3]oxazolo[4,5-b]pyridine, first polymorph (structure 6), P-1, 7.2634 Å, 11.1261 Å, 18.5460 Å, 80.561°, 80.848°, 76.840°; 2-(4-propylpiperazin-1-yl)[1,3]oxazolo[4,5-b]pyridine, second polymorph (structure 7), P2₁, 8.10852 Å, 7.06025 Å, 12.41650 Å, β = 92.2991°. All the compounds crystallized out as hydrobromides. Oxazole structures show a much greater tendency to form twin crystals than thiazole structures. All the investigated structures display N—H···Br hydrogen bonding. (ADME) analysis, including the assessment of absorption, distribution, metabolism, and excretion, determined the physicochemical properties, pharmacokinetics, drug similarity, and bioavailability radar, and confirmed the usefulness of the compounds in question for pharmaceutical utility. This work is a continuation of the research searching for a new lead of non-imidazole histamine H3 receptor antagonists.     

Circulant orbitals for atoms and molecules

Circulant orbitals ϕ_n for a closed-shell system are the orbitals obtained when the N canonical orthonormal Hartree-Fock orbitals λ_[unk] are subjected to a unitary transformation which is the discrete Fourier transformation: ϕ_n = 1/√N Σ_[unk]λ_[unk]ω^{(n-1)([unk]-1)}, where ω = exp(2πi/N). Electron densities associated with the orbitals ϕ_n are each close to the average total electron density. The Fock matrix, diagonal for canonical orbitals, for circulant orbitals is a Hermitian circulant matrix, ε_{m, m+q} = 1/N Σ_[unk]ε_[unk]ω^q([unk]-1), where the ε_[unk] are the canonical orbital energies. The states ^Fϕ_n are uniformly distributed on the surface of a sphere in Hilbert space.     

Asymptotic Formula for the Coordinates of the Zeros of Sections of the Zeta Function, zeta(N)(s), Near s = 1

The sum, Σ1^Nn^-8 = ζN(s), s = σ + it, is called a section of the Riemann zeta function, ζ(s). Here an asymptotic formula, for large N, giving the location of the zeros of ζN(s) near s = 1 will be demonstrated. In particular these zeros will lie in σ < 1. Relationships between the location of the zeros of ζN(s) and the zeros of ζ(s) were discovered by Turán. The location in σ < 1 will also be demonstrated directly, without the asymptotic formula, together with results valid also when s - 1 is not small.     

Picosecond kinetics of fluorescence and absorbance changes in photosystem II particles excited at low photon density

Oxygen-evolving photosystem II particles (from Synechococcus) with about 80 chlorophyll molecules per primary electron donor (P₆₈₀) were used for a correlated study of picosecond kinetics of fluorescence and absorbance changes, detected by the single-photon-timing technique and by a pump-probe apparatus, respectively. Chlorophyll fluorescence decays were biexponential with lifetimes τ₁ = 80 ± 20 ps and τ₂ = 520 ± 120 ps in open reaction centers and τ₁ = 220 ± 30 ps and τ₂ = 1.3 ± 0.15 ns in closed reaction centers. The corresponding fluorescence yield ratio F_max/F_o was 3-4. Absorbance changes were monitored in the spectral range of 620-700 nm after excitation at 675 nm with 10-ps pulses sufficiently weak (<7 × 10¹² photons/cm² per pulse) to avoid singlet-singlet annihilation. With open reaction centers, the absorbance changes could be fit to the sum of three exponentials. The associated absorbance difference spectra were attributed to (i) exciton trapping and charge separation (τ = 100 ± 20 ps), (ii) the electron-transfer step P₆₈₀⁺ I^- Q_A → P₆₈₀⁺ I Q_A^- (where I is the primary electron acceptor and Q_A is the first quinone acceptor) (τ = 510 ± 50 ps), and (iii) the reduction of P₆₈₀⁺ by the intact donor side (τ > 10 ns). With closed reaction centers, the absorbance changes were biexponential with lifetimes τ₁ = 170-260 ps and τ₂ = 1.6-1.75 ns. The results are explained in terms of a kinetic model that assumes P₆₈₀ to constitute a shallow trap. The results show that Q_A reduction in these photosystem II particles decreases both the apparent rate and the yield of the primary charge separation by a factor of 2-3 and increases the mean lifetime of excitons in the antenna by a factor of 3-4. Thus, we conclude that the long-lived, nanosecond chlorophyll fluorescence is not charge-recombination luminescence but rather emission from equilibrated excited states of antenna chlorophylls.     

An atomic kinetic energy functional with full Weizsacker correction

A functional is proposed for representing the electronic kinetic energy of the ground state of an N-electron atom or ion in terms of its electron density, [Formula: see text] Here T_w is the Weizsacker quantity (⅛)∫(ρ·ρ/ρ)dτ and T₀ is the Thomas-Fermi quantity C_F ∫ ρ^{5 / 3}dτ. From Hartree-Fock data on 55 neutral atoms, C = 1.412 ± 0.033; for 1200 atoms and ions, C = 1.332 ± 0.053. The proposed functional gives the derivative δT/δρ its most important correct properties. The term T_w is shown to give the kinetic energy of the K shell, whereas the term (C/N^⅓)T₀ gives an incorrect statistical estimate of that energy. An alternative correction -(C/N^⅓)T gives even better results.     

Structural and functional analysis of the yeast N-acetyltransferase Mpr1 involved in oxidative stress tolerance via proline metabolism

Mpr1 (sigma1278b gene for proline-analog resistance 1), which was originally isolated as N-acetyltransferase detoxifying the proline analog l-azetidine-2-carboxylate, protects yeast cells from various oxidative stresses. Mpr1 mediates the l-proline and l-arginine metabolism by acetylating l-Δ¹-pyrroline-5-carboxylate, leading to the l-arginine–dependent production of nitric oxide, which confers oxidative stress tolerance. Mpr1 belongs to the Gcn5-related N-acetyltransferase (GNAT) superfamily, but exhibits poor sequence homology with the GNAT enzymes and unique substrate specificity. Here, we present the X-ray crystal structure of Mpr1 and its complex with the substrate cis-4-hydroxy-l-proline at 1.9 and 2.3 Å resolution, respectively. Mpr1 is folded into α/β-structure with eight-stranded mixed β-sheets and six α-helices. The substrate binds to Asn135 and the backbone amide of Asn172 and Leu173, and the predicted acetyl-CoA–binding site is located near the backbone amide of Phe138 and the side chain of Asn178. Alanine substitution of Asn178, which can interact with the sulfur of acetyl-CoA, caused a large reduction in the apparent k_cat value. The replacement of Asn135 led to a remarkable increase in the apparent K_m value. These results indicate that Asn178 and Asn135 play an important role in catalysis and substrate recognition, respectively. Such a catalytic mechanism has not been reported in the GNAT proteins. Importantly, the amino acid substitutions in these residues increased the l-Δ¹-pyrroline-5-carboxylate level in yeast cells exposed to heat stress, indicating that these residues are also crucial for its physiological functions. These studies provide some benefits of Mpr1 applications, such as the breeding of industrial yeasts and the development of antifungal drugs.     

Beneficial effect of butyrate,Lactobacillus casei and L-carnitine combination in preference to each in experimental colitis

AIM: To investigate the beneficial effect of the combination of butyrate, Lactobacillus casei, and L-carnitine in a rat colitis model.METHODS: Rats were divided into seven groups. Four groups received oral butyrate, L-carnitine, Lactobacillus casei and the combination of three agents for 10 consecutive days. The remaining groups included negative and positive controls and a sham group. Macroscopic, histopathological examinations, and biomarkers such as tumor necrosis factor-alpha (TNF-α) and interlukin-1β (IL-1β), myeloperoxidase (MPO), thiobarbituric acid reactive substances (TBARS), and ferric reduced ability of plasma (FRAP) were determined in the colon.RESULTS: The combination therapy exhibited a significant beneficial effect in alleviation of colitis compared to controls. Overall changes in reduction of TNF-α (114.66 ± 18.26 vs 171.78 ± 9.48 pg/mg protein, P < 0.05), IL-1β (24.9 ± 1.07 vs 33.06 ± 2.16 pg/mg protein, P < 0.05), TBARS (0.2 ± 0.03 vs 0.49 ± 0.04 μg/mg protein, P < 0.01), MPO (15.32 ± 0.4 vs 27.24 ± 3.84 U/mg protein, P < 0.05), and elevation of FRAP (23.46 ± 1.2 vs 15.02 ± 2.37 μmol/L, P < 0.05) support the preference of the combination therapy in comparison to controls. Although the monotherapies were also effective in improvement of colitis markers, the combination therapy was much better in improvement of colon oxidative stress markers including FRAP, TBARS, and MPO.CONCLUSION: The present combination is a suitable mixture in control of experimental colitis and should be trialed in the clinical setting.     

Aloe vera attenuated gastric injury on indomethacin-induced gastropathy in rats

AIM: To evaluate the protective effects of Aloe vera on gastric injury in rats with indomethacin (IMN)-induced gastropathy.METHODS: Male Sprague-Dawley rats were randomly divided into three groups. Group 1 (control, n = 6) was given distilled water (DW) orally. Group 2 (IMN, n = 6) was given oral IMN (150 mg/kg) dissolved in 5% sodium bicarbonate (NaHCO₃^-) at time 0 and 4 h. Group 3 (Aloe vera-treated, n = 6) was given oral Aloe vera (150 mg/kg) dissolved in DW and IMN at time 0 and 4 h. Eight hours later, the stomach was removed to determine gastric malondialdehyde (MDA), the number of interleukin (IL)-18 positive stained cells (%) by immunohistochemistry, and for histopathological examination. Then, the serum was collected to determine tumor necrosis factor (TNF)-α and cytokine-induced neutrophil chemoattractant (CINC)-1 by sandwich enzyme linked immunosorbent assay method.RESULTS: In the IMN group, serum TNF-α, CINC-1 and gastric MDA were significantly increased when compared to the control group (27.78 ± 1.52 pg/mL vs 85.07 ± 49.11 pg/mL, P = 0.009; 104.55 ± 45.80 pg/mL vs 1054.70 ± 20.38 pg/mL, and 1.74 ± 0.21 nmol/mg vs 9.36 ± 1.07 nmol/mg protein, P = 0.000, respectively). The mean level of TNF-α, CINC-1 and gastric MDA in the Aloe vera-treated group were improved as compared with the IMN group (85.07 ± 49.11 pg/mL vs 35.19 ± 1.61 pg/mL, P = 0.021; 1054.70 ± 20.38 pg/mL vs 813.56 ± 239.04 pg/mL, P = 0.025; and 9.36 ± 1.07 nmol/mg vs 2.67 ± 0.64 nmol/mg protein, P = 0.000, respectively). The number of IL-18 positive stained cells (%) in the gastric epithelial cells of the IMN group was significantly higher than the control group (5.01% ± 3.73% vs 30.67% ± 2.03%, P = 0.000, respectively). In contrast, Aloe vera treatment decreased the number of IL-18 positive stained cells (%) significantly when compared with the IMN group (30.67% ± 2.03% vs 13.21% ± 1.10%, P = 0.000, respectively). Most rats in the IMN group developed moderate to severe gastric inflammation and erosions. The gastric erosions and neutrophil infiltration scores were significantly reduced in the Aloe vera-treated group.CONCLUSION: Aloe vera attenuated IMN-induced gastropathy in rats by the reduction of oxidative stress, inflammation, and improvement of gastric histopathology.     

Functional interaction between native G protein-coupled purinergic receptors in Xenopus follicles

Purinergic receptors are expressed in the membrane of the follicular cell layer that communicates with the Xenopus oocyte. Adenosine (Ado) generates a cAMP-dependent K⁺ current (I_K,cAMP), whereas ATP activates a Cl⁻ current (F_Cl) and has a dual effect on I_K,cAMP, provoking both its activation and inhibition. Here, purinergic responses were studied electrophysiologically, first in the whole follicle (w.f.), and then in the same follicle after removal of its epithelium/theca layers (e.t.r. follicle). Responses were analyzed as the ratio of the current amplitudes (i_etr/i_wf) in the two preparations. For ATP activation of I_K,cAMP and F_Cl, the ratios i_etr/i_wf were 0.053 and 22, respectively, whereas that for Ado was 0.75. Thus, epithelium/theca removal drastically altered the ATP response, suggesting a change in the signaling pathway that correlated with changes in the pharmacological characteristics: the half-maximal effective concentration for activation of the main current in w.f. (I_K,cAMP) was 14 ± 3.8 μM [Hill coefficient (nH) = 2.7 ± 0.61], and that in e.t.r. follicles (F_Cl) was 1.8 ± 0.68 μM (nH = 0.76 ± 0.09), whereas Ado-response parameters did not change. Responses to UTP and β,γ-methylene-ATP, specific agonists for I_K,cAMP inhibition and activation, respectively, indicated that in e.t.r. follicles inhibition increased and activation decreased drastically. Thus, purinergic responses were not independent; instead, they were functionally linked. We hypothesize that this property was due to direct interactions between receptors for Ado (A2 subtype) and ATP (P2Y subtype) in the Xenopus follicle.     

Crystal and Electronic Structures,Photoluminescence Properties of Eu2+-Doped Novel Oxynitride Ba4Si6O16-3x/2Nx

The crystal structure and the photoluminescence properties of novel green Ba_4-yEu_ySi₆O_16-3x/2N_x phosphors were investigated. The electronic structures of the Ba₄Si₆O₁₆ host were calculated by first principles pseudopotential method based on density functional theory. The results reveal that the top of the valence bands are dominated by O-2p states hybridized with Ba-6s and Si-3p states, while the conduction bands are mainly determined by Ba-6s states for the host, which is an insulator with a direct energy gap of 4.6 eV at Γ. A small amount of nitrogen can be incorporated into the host to replace oxygen and forms Ba_4-yEu_ySi₆O_16-3x/2N_x solid solutions crystallized in a monoclinic (space group P2₁/c, Z = 2) having the lattice parameters a = 12.4663(5) Å, b = 4.6829(2) Å, c = 13.9236(6) Å, and β = 93.61(1)°, with a maximum solubility of nitrogen at about x = 0.1. Ba₄Si₆O_16-3x/2N_x:Eu²⁺ exhibits efficient green emission centered at 515–525 nm varying with the Eu²⁺ concentration when excited under UV to 400 nm. Furthermore, the incorporation of nitrogen can slightly enhance the photoluminescence intensity. Excitation in the UV-blue spectral range (λ_exc = 375 nm), the absorption and quantum efficiency of Ba_4-yEu_ySi₆O_16-3x/2N_x (x = 0.1, y = 0.2) reach about 80% and 46%, respectively. Through further improvement of the thermal stability, novel green phosphor of Ba_4-yEu_ySi₆O_16-3x/2N_x is promising for application in white UV-LEDs.     

Peculiarities of DRX in a Highly-Alloyed Austenitic Stainless Steel

The features of discontinuous dynamic recrystallization (DRX) in a highly-alloyed austenitic stainless steel were studied at temperatures of 800 °C to 1100 °C. Hot deformation accompanied by DRX was characterized by an activation energy of 415 kJ/mol. The frequency of the sequential DRX cycles depended on the deformation conditions; and the largest fraction of DRX grains with small grain orientation spread below 1° was observed at a temperature of around 1000 °C and a strain rate of about 10⁻³ s⁻¹. The following power law relationships were obtained for DRX grain size (D_DRX) and dislocation density (ρ) vs. temperature-compensated strain rate (Z) or peak flow stress (σ_P): D_DRX ~ Z^−0.25, ρ ~ Z^0.1, σ_P ~ D_DRX^−0.9, σ_P ~ ρ^1.4. The latter, i.e., σ_P ~ ρ^1.4, was valid in the flow stress range below 300 MPa and changed to σ_P ~ ρ^0.5 on increasing the stress. The obtained dependencies suggest a unique power law function between the dislocation density and the DRX grain size with an exponent of −0.5.