Insertion Compounds of 2H-TaS(2).NH(3)

A new method of intercalating metals into layer compounds has been developed using electrolytic generation from the salt solution in ammonia. The results suggest that metals that are soluble in ammonia will form a homogeneous metal-ammonia intercalate layer, NH₃·M_x, when x is less than the limiting solubility of M in NH₃. The superconducting transition temperature (T_c) was found to increase as the c-axis expansion [2δ = c(TaS₂·NH₃·M_x) - c(2H-TaS₂)] decreased when M = lithium, sodium, and potassium. Of all the alkali metals, potassium gave the most stable compounds and the highest T_c, 4.7°K.     

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.     

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.     

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.     

新疆蚤类畸形实例(三)

报告新疆地区发现的蚤类畸形27例,其中叶状切唇蚤Coptopsylla lamellifer三受精囊畸形及方形黄鼠蚤Citellophilus tesquorum典型而清晰的双受精囊畸形是罕见的。发现并讨论了线虫寄生与蚤类雄性阉割及雌性卵巢退化之间的密切关系。     

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.     

A Comparative Mini-Review on Transition Metal Oxides Applied for the Selective Catalytic Ammonia Oxidation (NH3-SCO)

The selective catalytic oxidation of NH₃ (NH₃-SCO) into N₂ and H₂O is an efficient technology for NH₃ abatement in diesel vehicles. However, the catalysts dedicated to NH₃-SCO are still under development. One of the groups of such catalysts constituted transition metal-based catalysts, including hydrotalcite-derived mixed metal oxides. This class of materials is characterized by tailored composition, homogenously dispersed mixed metal oxides, exhibiting high specific surface area and thermal stability. Thus, firstly, we give a short introduction to the structure and composition of hydrotalcite-like materials and their applications in NH₃-SCO. Secondly, an overview of other transition metal-based catalysts reported in the literature is given, following a comparison of both groups. The challenges in NH₃-SCO applications are provided, while the reaction mechanisms are discussed for particular systems.     

The protein-folding speed limit: intrachain diffusion times set by electron-transfer rates in denatured Ru(NH3)5(His-33)-Zn-cytochrome c

The kinetics of electron transfer from the triplet-excited Zn-porphyrin to a Ru(NH(3))(5)(His-33)(3+) complex have been measured in Zn-substituted ruthenium-modified cytochrome c under denaturing conditions. In the folded protein, the electron-tunneling rate constant is 7.5 x 10(5) s(-1). As the protein is denatured with guanidine hydrochloride, a faster adiabatic electron-transfer reaction appears (4.0 x 10(6) s(-1), [guanidine hydrochloride] = 5.4 M) that is limited by the rate of intrachain diffusion to bring the Zn-porphyrin and Ru complex into contact. The 250-ns contact time for formation of a 15-residue loop in denatured cytochrome c is in accord with a statistical model developed by Camacho and Thirumalai [Camacho, C. J. & Thirumalai, D. (1995) Proc. Natl. Acad. Sci. USA 92, 1277-1281] that predicts that the most probable transient loops formed in denatured proteins are comprised of 10 amino acids. Extrapolation of the cytochrome c contact time to a 10-residue loop sets the folding speed limit at approximately 10(7) s(-1).     

THE VARIATION IN SERUM TRIIODOTHYRONINE (T3) ACHIEVED DURING SUPPRESSION TESTING IN THYROTOXICOSIS

Regular measurement of thyroidal radioiodine uptake has been widely used as a means of monitoring continued extrapituitary stimulation of the thyroid during the treatment of thyrotoxicosis with carbimazole and triiodothyronine (T3). However, it is unclear to what extent the serum T3 level may vary at the time of testing, nor what effect this might have on the uptake of radioiodine. Two studies have been undertaken. In the first, serum T3 levels in twenty-four thyrotoxic patients were measured at intervals during an 18-month course of carbimazole combined with T3, 20 μg qid. Considerable variations in the highest and lowest levels of serum T3 were found both between and within individuals. The second study was on twenty-three thyrotoxic patients thought to be entering remission because the iodine uptake after 5 months of drug treatment had fallen to less than 50% of the pretreatment value (suppressors). The changes in uptake of radioiodine after 5 and then 6 months of treatment were compared in seven patients, who received carbimazole and T3 throughout, with the corresponding changes in the remaining sixteen patients, whose T3 alone was withdrawn prior to the uptake test at month 6. The mean degree of suppression remained unchanged by month 6 in the first group. In the second group, however, the mean uptake rose significantly, and nine of the sixteen patients would have been classified as non-suppressors at the sixth month (i.e. uptake greater than 50% the pretreatment value) had their failure to maintain high serum levels of T3 gone undetected. The first study indicated this could well happen in routine circumstances, and it is suggested that the reliability of suppression tests be checked with simultaneous measurement of serum T3.     

FREE THYROXINE (FT4) AND FREE TRIIODOTHYRONINE (FT3) IN AUTONOMOUS THYROID NODULES

Total and free thyroid hormones (T3, T4, FT3 and FT4), TSH and its response to TRH were determined in sixty-three patients affected by autonomous thyroid nodules: mean concentrations of free T3 (FT3) were significantly higher in hot nodules (suppressing extranodular tissue on the scan) as compared to warm ones, even in those cases where total T3 and T4 were within normal ranges (hot nodules, group as a whole: 8.8 +/- 3.5 pg/ml; warm nodules: 5.3 +/- 1.2; hot nodules with normal total T3 and T4 concentrations: 7.5 +/- 3). Also the clinical condition of thyrotoxicosis appeared to be correlated with FT3 concentrations (toxic patients, group as a whole: 9.6 +/- 4.0 pg/ml; euthyroid patients: 6.8 +/- 3.1; toxic patients with normal values of T3 and T4; 8.3 +/- 2.8). On the contrary the correlation of total and free thyroid hormone concentrations with the response of TSH to TRH was not significant.     

THE ROLE OF TRIIODOTHYRONINE (T3) IN THE MAINTENANCE OF EUTHYROIDISM IN ENDEMIC GOITRE

Serum concentrations of triiodothyronine (T3), thyroxine (T4) and thyroid stimulating hormone (TSH) have been measured in subjects from an endemic goitrous area of New Guinea. An increase in TSH concentration and a decrease in T4 concentration was found in both goitrous and non-goitrous subjects, both abnormalities being more frequent in the goitrous group. In the majority of subjects (93%) the T3 level fell within the normal range. Euthyroidism appears to be preserved in the iodine deficient state by the continued production of normal amounts of T3, the intrinsic metabolic activity of T4 being relatively unimportant.