Structures and stabilities of higher coordinate onium-boronium dications (X(+)BH(3)+ and X(+)BH(5)+; X = NH(3), PH(3), H(2)O,and H(2)S)

Structures of higher coordinate onium-boronium dications (X(+)BH(3)+ 1-4a and X(+)BH(5)+ 1-4d; X = NH(3), PH(3), H(2)O, and H(2)S) were calculated by using the ab initio method at the MP2/6-311+G** level. All of the dications 1-4a contain a four-coordinate boron atom with a three-center two-electron bond involving boron and two hydrogens. On the other hand, all the dications 1-4d contain a six-coordinate boron atom with two three-center two-electron bonds. The thermodynamics of the complexations of 1-4a and H(2) to form 1-4d were computed. Deprotonations of 1-4d were found to be substantially endothermic.     

Elastic Properties and Energy Loss Related to the Disorder–Order Ferroelectric Transitions in Multiferroic Metal–Organic Frameworks [NH4][Mg(HCOO)3] and [(CH3)2NH2][Mg(HCOO)3]

Elastic properties are important mechanical properties which are dependent on the structure, and the coupling of ferroelasticity with ferroelectricity and ferromagnetism is vital for the development of multiferroic metal–organic frameworks (MOFs). The elastic properties and energy loss related to the disorder–order ferroelectric transition in [NH₄][Mg(HCOO)₃] and [(CH₃)₂NH₂][Mg(HCOO)₃] were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC curves of [NH₄][Mg(HCOO)₃] and [(CH₃)₂NH₂][Mg(HCOO)₃] exhibited anomalies near 256 K and 264 K, respectively. The DMA results illustrated the minimum in the storage modulus and normalized storage modulus, and the maximum in the loss modulus, normalized loss modulus and loss factor near the ferroelectric transition temperatures of 256 K and 264 K, respectively. Much narrower peaks of loss modulus, normalized loss modulus and loss factor were observed in [(CH₃)₂NH₂][Mg(HCOO)₃] with the peak temperature independent of frequency, and the peak height was smaller at a higher frequency, indicating the features of first-order transition. Elastic anomalies and energy loss in [NH₄][Mg(HCOO)₃] near 256 K are due to the second-order paraelectric to ferroelectric phase transition triggered by the disorder–order transition of the ammonium cations and their displacement within the framework channels, accompanied by the structural phase transition from the non-polar hexagonal P6₃22 to polar hexagonal P6₃. Elastic anomalies and energy loss in [(CH₃)₂NH₂][Mg(HCOO)₃] near 264 K are due to the first-order paraelectric to ferroelectric phase transitions triggered by the disorder–order transitions of alkylammonium cations located in the framework cavities, accompanied by the structural phase transition from rhombohedral R3¯c to monoclinic Cc. The elastic anomalies in [NH₄][Mg(HCOO)₃] and [(CH₃)₂NH₂][Mg(HCOO)₃] showed strong coupling of ferroelasticity with ferroelectricity.     

Strain Effects on the Electronic and Thermoelectric Properties of n(PbTe)-m(Bi2Te3) System Compounds

Owing to their low lattice thermal conductivity, many compounds of the n(PbTe)-m(Bi2Te3) homologous series have been reported in the literature with thermoelectric (TE) properties that still need improvement. For this purpose, in this work, we have implemented the band engineering approach by applying biaxial tensile and compressive strains using the density functional theory (DFT) on various compounds of this series, namely Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5. All the fully relaxed Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5 compounds are narrow band-gap semiconductors. When applying strains, a semiconductor-to-metal transition occurs for all the compounds. Within the range of open-gap, the electrical conductivity decreases as the compressive strain increases. We also found that compressive strains cause larger Seebeck coefficients than tensile ones, with the maximum Seebeck coefficient being located at −2%, −6%, −3% and 0% strain for p-type Bi2Te3, PbBi2Te4, PbBi4Te7 and Pb2Bi2Te5, respectively. The use of the quantum theory of atoms in molecules (QTAIM) as a complementary tool has shown that the van der Waals interactions located between the structure slabs evolve with strains as well as the topological properties of Bi2Te3 and PbBi2Te4. This study shows that the TE performance of the n(PbTe)-m(Bi2Te3) compounds is modified under strains.     

Gas-Sensing Properties of B/N-Modified SnS2 Monolayer to Greenhouse Gases (NH3, Cl2, and C2H2)

The adsorption capacity of intrinsic SnS₂ to NH₃, Cl₂ and C₂H₂ is very weak. However, non-metallic elements B and N have strong chemical activity, which can significantly improve the conductivity and gas sensitivity of SnS₂. Based on density functional theory, SnS₂ was modified with B and N atoms to analyze its adsorption mechanism and gas sensitivity for NH₃, Cl₂ and C₂H₂ gases. The optimal structure, adsorption energy, state density and frontier molecular orbital theory are analyzed, and the results are in good agreement with the experimental results. The results show that the adsorption of gas molecules is exothermic and spontaneous. Only the adsorption of NH₃ and Cl₂ on B-SnS₂ belongs to chemical adsorption, whereas other gas adsorption systems belong to physical adsorption. Moderate adsorption distance, large adsorption energy, charge transfer and frontier molecular orbital analysis show that gas adsorption leads to the change of the conductivity of the modified SnS₂ system. The adsorption capacity of B-SnS₂ to these gases is Cl₂ > NH₃ > C₂H₂. The adsorption capacity of N-SnS₂ is NH₃ > C₂H₂ > Cl₂. Therefore, according to different conductivity changes, B-SnS₂ and N-SnS₂ materials can be developed for greenhouse gas detection of gas sensors.     

AACVD of Cu3N on Al2O3 Using CuCl2 and NH3

Cu₃N has been grown on m-Al₂O₃ by aerosol-assisted chemical vapor deposition using 0.1 M CuCl₂ in CH₃CH₂OH under an excess of NH₃ at 600 °C, which led to the deposition of Cu that was subsequently converted into Cu₃N under NH₃: O₂ at 400 °C in a two-step process without exposure to the ambient. The reaction of CuCl₂ with an excess of NH₃ did not lead to the growth of Cu₃N, which is different to the case of halide vapor phase epitaxy of III-V semiconductors. The Cu₃N layers obtained in this way had an anti-ReO₃ cubic crystal structure with a lattice constant of 3.8 Å and were found to be persistently n-type, with a room temperature carrier density of n = 2 × 10¹⁶ cm⁻³ and mobility of µ_n = 32 cm²/Vs. The surface depletion, calculated in the effective mass approximation, was found to extend over ~0.15 µm by considering a surface barrier height of ϕ_B = 0.4 eV related to the formation of native Cu₂O.     

Dose-dependent efficacy of the glucose-dependent insulinotropic polypeptide (GIP) receptor antagonist GIP(3-30)NH2 on GIP actions in humans

The glucose-dependent insulinotropic polypeptide (GIP) fragment GIP(3-30)NH₂ is a selective, competitive GIP receptor antagonist, and doses of 800 to 1200 pmol/kg/min inhibit GIP-induced potentiation of glucose-stimulated insulin secretion by >80% in humans. We evaluated the effects of GIP(3-30)NH₂ across a wider dose range in eight healthy men undergoing six separate and randomized 10-mmol/L hyperglycaemic clamps (A–F) with concomitant intravenous infusion of GIP (1.5 pmol/kg/min; A–E) or saline (F). Clamps A to E involved double-blinded, infusions of saline (A) and GIP(3-30)NH₂ at four rates: 2 (B), 20 (C), 200 (D) and 2000 pmol/kg/min (E), respectively. Mean plasma concentrations of glucose (A–F) and GIP (A–E) were similar. GIP-induced potentiation of glucose-stimulated insulin secretion was reduced by 44 ± 10% and 84 ± 10% during clamps D and E, respectively. Correspondingly, the amounts of glucose required to maintain the clamp during D and E were not different from F. GIP-induced suppression of bone resorption and increase in heart rate were lowered by clamps D and E. In conclusion, GIP(3-30)NH₂ provides extensive, dose-dependent inhibition of the GIP receptor in humans, with most pronounced effects of the doses 200 to 2000 pmol/kg/min within the tested range.     

Ammonium/methylammonium transport (Amt) proteins facilitate diffusion of NH3 bidirectionally

The ammonium/methylammonium transport (Amt) proteins of enteric bacteria and their homologues, the methylammonium/ammonium permeases of Saccharomyces cerevisiae, are required for fast growth at very low concentrations of the uncharged species NH(3). For example, they are essential at low ammonium (NH(4)+ + NH(3)) concentrations under acidic conditions. Based on growth studies in batch culture, the Amt protein of Salmonella typhimurium (AmtB) cannot concentrate either NH(3) or NH(4)+ and this organism appears to have no means of doing so. We now show that S. typhimurium releases ammonium into the medium when grown on the alternative nitrogen source arginine and that outward diffusion of ammonium is enhanced by the activity of AmtB. The latter result indicates that AmtB acts bidirectionally. We also confirm a prediction that the AmtB protein would be required at pH 7.0 in ammonium-limited continuous culture, i.e., when the concentration of NH(3) is < or =50 nM. Together with our previous studies, current results are in accord with the view that Amt and methylammonium/ammonium permease proteins increase the rate of diffusion of the uncharged species NH(3) across the cytoplasmic membrane. These proteins are examples of protein facilitators for a gas.     

Thermochemical Study of CH3NH3Pb(Cl1−xBrx)3 Solid Solutions

Hybrid organic–inorganic perovskite halides, and, in particular, their mixed halide solid solutions, belong to a broad class of materials which appear promising for a wide range of potential applications in various optoelectronic devices. However, these materials are notorious for their stability issues, including their sensitivity to atmospheric oxygen and moisture as well as phase separation under illumination. The thermodynamic properties, such as enthalpy, entropy, and Gibbs free energy of mixing, of perovskite halide solid solutions are strongly required to shed some light on their stability. Herein, we report the results of an experimental thermochemical study of the CH₃NH₃Pb(Cl_1−xBr_x)₃ mixed halides by solution calorimetry. Combining these results with molecular dynamics simulation revealed the complex and irregular shape of the compositional dependence of the mixing enthalpy to be the result of a complex interplay between the local lattice strain, hydrogen bonds, and energetics of these solid solutions.     

碳酸铵-砷化氢法测尿中无机砷的可行性探讨

目的寻求一种简单、快速测定尿中无机砷的方法。方法用碳酸铵分离尿中的无机砷。于２５ｍｌ尿样中加入１５ｍｌ１％碳酸铵溶液,２４０次／ｍｉｎ振摇１ｈ;加入１ｍｌ浓硫酸,８０℃水浴１０ｍｉｎ;冷却后过滤,用ＡｇＤＤＣ法测定滤液中的无机砷。结果回收率为９７．６８％～１１０．８６％;重复试验的标准差和变异系数为０．０２７２μｇ和３．６６％。用此法测３８名健康人尿中的无机砷,结果为７．９９×１０－３±４．１９×１０－３ｍｇ／Ｌ,无机砷占尿总砷的百分比为５．１２％～２８．３０％,Ｐ５０为１５．３８％。结论该法能有效地测出尿中的无机砷     

Human Rhesus-associated glycoprotein mediates facilitated transport of NH(3) into red blood cells

Rhesus (Rh) antigens are carried by a membrane complex that includes Rh proteins (D and CcEe), Rh-associated glycoproteins (RhAG), and accessory chains (LW and CD47) associated by noncovalent bonds. In heterologous expression systems, RhAG and its kidney orthologs function as ammonium transporters. In red blood cells (RBCs), it is generally accepted that NH(3) permeates by membrane lipid diffusion. We have revisited these issues by studying RBC and ghosts from human and mouse genetic variants with defects of proteins that comprise the Rh complex. In both normal and mutant cells, stopped-flow analyses of intracellular pH changes in the presence of inwardly directed methylammonium (CH(3)NH(+)(3)+CH(3)NH(2)) or ammonium (NH(+)(4)+NH(3)) gradients showed a rapid alkalinization phase. Cells from human and mouse variants exhibited a decrease in their kinetic rate constants that was strictly correlated to the degree of reduction of their RhAG/Rhag expression level. Rate constants were not affected by a reduction of Rh, CD47, or LW. CH(3)NH(2)/NH(3) transport was characterized by (i) a sensitivity to mercurials that is reversible by 2-mercaptoethanol and (ii) a reduction of alkalinization rate constants after bromelain digestion, which cleaves RhAG. The results show that RhAG facilitates CH(3)NH(2)/NH(3) movement across the RBC membrane and represents a potential example of a gas channel in mammalian cells. In RBCs, RhAG may transport NH(3) to detoxifying organs, like kidney and liver, and together with nonerythroid tissue orthologs may contribute to the regulation of the systemic acid-base balance.     

Low-Pressure H2, NH3 Microwave Plasma Treatment of Polytetrafluoroethylene (PTFE) Powders: Chemical,Thermal and Wettability Analysis

Functionalization of Polytetrafluoroethylene (PTFE) powders of ~6 μm particle size is carried out using low-pressure 2.45 GHz H₂, NH₃ microwave plasmas for various durations (2.5, 10 h) to chemically modify their surface and alter their surface energy. The X-ray Photoelectron Spectroscopy (XPS) analyses reveal that plasma treatment leads to significant defluorination (F/C atomic ratio of 1.13 and 1.30 for 10 h NH₃ and H₂ plasma treatments, respectively vs. 1.86 for pristine PTFE), along with the incorporation of functional polar moieties on the surface, resulting in enhanced wettability. Analysis of temperature dependent XPS revealed a loss of surface moieties above 200 °C, however, the functional groups are not completely removable even at higher temperatures (>300 °C), thus enabling the use of plasma treated PTFE powders as potential tribological fillers in high temperature engineering polymers. Ageing studies carried over a period of 12 months revealed that while the surface changes degenerate over time, again, they are not completely reversible. These functionalised PTFE powders can be further used for applications into smart, high performance materials such as tribological fillers for engineering polymers and bio-medical, bio-material applications.     

Polymerization and solubility of recombinant hemoglobins alpha 2 beta 2 (6Val) (Hb S) and alpha 2 beta 2(6Leu) (Hb Leu).

In an effort to clarify the role of amino acid hydrophobicity at the beta 6 position in sickling we have made recombinant hemoglobin tetramers containing beta 6 Val (Hb S) and beta 6 Leu (Hb Leu). Recombinant Hb S and Hb Leu had the same electrophoretic mobility, chromatographic behavior, and absorption spectrum. The deoxy form of both tetramers polymerized in high phosphate buffer (1.8 M) and exhibited distinct delay times prior to polymerization. The kinetics of polymerization for recombinant and native Hb S were similar, while recombinant Hb Leu polymerized more readily. The solubility of deoxy Hb Leu was less than deoxy Hb S, indicating that rapid polymerization and decreased solubility of deoxyhemoglobin is accelerated with increasing hydrophobicity at the beta 6 position.     

Anomalous dispersion of sulfur in quinidine sulfate, (C(20)H(25)N(2)O(2))(2)SO(4).2H(2)O: Implications for structure analysis

A Patterson-type map computed with Bijvoet differences squared as coefficients, (|F_h| - |F_-h|)², as recommended by Rossmann, readily yielded the position of the S atom. The experiment was performed with Cu Kα radiation which is far from the absorption edge for sulfur. The coordinates of the remainder of the 54C, N, and O atoms were derived by means of partial structure development by use of the tangent formula. The latter was used only to effect phase extension, not phase refinement. A main purpose of this experiment was to reaffirm, as first shown in the investigation of the protein crambin by Hendrickson and Teeter, that, in the presence of a large number of lighter atoms, sulfur atoms can be located by use of anomalous dispersion at wave-lengths far from the absorption edge. The space group is P2₁ with a = 26.718(8) Å, b = 6.987(3) Å, c = 10.857(6) Å, and β = 99.51(4)° and contains two quinidyl ions, one sulfate ion, and two water molecules per asymmetric unit. The conformations of the two independent quinidyl ions differ mainly in the torsional angle of the bond between the vinyl side chain and the quinuclidine moiety. The R factor is 4.9% for all 2869 data.     

Intracellular pH transients induced by Co2 or NH3.

Experiments are reviewed in which intracellular pH (pHi), during exposure of a cell to CO2- or NH3-containing solutions, not only undergoes an acidification of alkalinization, respectively, but tends to return toward its original value and, upon removal of the test solution, rebounds to a value more alkaline or acid, respectively, than the initial one. A simple physiochemical model is discussed which interprets these observations both qualitatively and quantitatively. In the case of NH3-induced transients, only passive movements seem to take place; in the CO2-induced transients one must postulate an active 'proton pump'. Experimentally verifiable predictions can be made from these models. It is suggested that many physiological effects follow exposure to CO2 or NH3 may be subject to similar transients and rebounds.