Sodium and potassium activities in normal and "sodium-rich" frog skeletal muscle

In frog sartorius muscles immersed for 2 hours at 26 degrees C in normal Ringer solution, the intrafiber potassium concentration, C(K)(in millimoles per liter), was 123 +/- 2 (mean value plus or minus standard error), and the potassium activity, a(K) (in millimoles per liter), was 90 +/- 1.0. The corresponding sodium concentration and activity were 20 +/- 1 and 6.5 +/- 0.4, respectively. After overnight immersion in K+-free Ringer solution the values were: CK, 97 +/- 2; aK, 81.5 +/- 1.6; CNa, 47 +/- 2; and aNa, 11.2 +/- 0.6. The changes in aK and aNa during storage were not consistent with an exchange between predominantly "free" fiber K+ and external Na+. These results suggest that the Na+ taken up during overnight immersion largely replaced adsorbed or sequestered K+ in the fibers.     

"Hemoglobin alpha2beta2-121ys" chemical identification in an egyptian family

Stuidy of the amino acid composition and amino-terminal residue in the abnormal peptide of an electrophoretically slow hemoglobin revealed that the globin's structure was alpha(2)beta(2)(121 Lys) (Obeta). This hemoglobin had been provisionally classified as Hb E or as a new heemoglobin. The clinical significance of this abnormality is not yet defined.     

Size-Specific Infrared Spectra of Benzene-(H2O)n Clusters (n = 1 through 7): Evidence for Noncyclic (H2O)n Structures

Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C(6)H(6)-(H(2)O)n clusters with n = 1 through 7 in the O-H stretch region. The O-H stretch spectra show a dramatic dependence on cluster size. For the n = 3 to 5 clusters, the transitions can be divided into three types-attributable to free, pi hydrogen-bonded, and single donor water-water O-H stretches-consistent with a C(6)H(6)-(H(2)O)n structure in which benzene is on the surface of a cyclic (H(2)O)n cluster. In n = 6 and 7 clusters, the spectra show distinct new transitions in the 3500 to 3600 wave number region. After comparison of these results with the predictions of ab initio calculations on (H(2)O)n clusters, these new transitions have been assigned to double donor O-H stretches associated with the formation of a more compact, noncyclic structure beginning with (H(2)O)(6). This is the same size cluster for which ab initio calculations predict that a changeover to noncyclic (H(2)O)n structures will occur.     

Dianion Stabilization by (M(C5(CH3)5)2)+: Theoretical Evidence for a Localized Ring in (DDQ)2-

Organic dianions have been stabilized by (M(C(5)(CH(3))(5))(2))(+), where M is iron or cobalt. This has allowed the structural and spectroscopic characterization of these dianions. The structure of (M(C(5)(CH(3))(5))(2))(2)(+) (DDQ)(2-), where DDQ is 2,3-dichloro-5,6-dicyanobenzoquinone, has been determined by x-ray crystallography. The structure of (DDQ)(2-)is consistent with ab initio molecular orbital calculations that suggest a localizd as opposed to a delocalized (aromatic) ring structure.     

Monodisperse metal clusters 10 angstroms in diameter in a polymeric host: the "monomer as solvent' approach

A general methodology is presented for the dispersion of an inorganic compound within an organic polymer host through the use of solubilizing and polymerizable ligands. The dispersion of metal cluster cations 10 angstroms in diameter within a polymer host is achieved by free-radical polymerization of the hexafunctional metal cluster [Mo(6)Cl(8)(NVI)(6)](triflate)(4) with bound polymerizable ligands in N-vinylimidazole (NVI) solutions. Copolymerization of the activated cluster-bound ligands with the surrounding medium probably plays a key role in preventing aggregation and produces near monodisperse molecular clusters within the polymer matrix.     

An Inorganic Double Helix: Hydrothermal Synthesis, Structure, and Magnetism of Chiral [(CH3)2NH2]K4[V10O10(H2O)2(OH)4(PO4)7]{middle dot}4H2O

Very complicated inorganic solids can be self-assembled from structurally simple precursors as illustrated by the hydrothermal synthesis of the vanadium phosphate, [(CH(3))(2)NH(2)]K(4)[V(10)O(10)(H(2)O)(2)(OH)(4)(PO(4))(7)].4H(2)O, 1, which contains chiral double helices formed from interpenetrating spirals of vanadium oxo pentamers bonded together by P(5+). These double helices are in turn intertwined with each other in a manner that generates unusual tunnels and cavities that are filled with (CH(3))(2)NH(2)(+) and K(+) cations, respectively. The unit cell contents of dark blue phosphate 1, which crystallizes in the enantiomorphic space group P4(3) with lattice constants a = 12.130 and c = 30.555 angstroms, are chiral; only one enantiomorph is present in a given crystal. Magnetization measurements show that 1 is paramagnetic with ten unpaired electrons per formula unit at higher temperatures and that antiferromagnetic interactions develop at lower temperatures.     

Structural aspects of reversible molecular oxygen uptake

The system IrX(CO)[P(C(6)H(5))(3)](2) in benzene solution adds mo lecular oxygen reversibly if X is chlorine and irreversibly if X is iodine. The crystal structure of the complex IrIO(2)(CO)[P(C(6)H(5))(3)](2) * CH(2)Cl(2) is reported here and compared with a previous study of the structure of IrClO(2)(CO)[P(C(6)H(5))(3)](2). The O-O bond length is 1.47 +/- 0.02 angstroms in the irreversibly oxygenated iodo-compound and 1.30 +/- 0.03 angstroms in the reversibly oxygenated chloro compound.     

Hexagonal Domain-Like Charge Density Wave Phase of TaS2 Determined by Scanning Tunneling Microscopy

The structure of the room-temperature charge density wave (CDW) phase in octahedrally coordinated tantalum disulfide, 1T-TaS2, has been a controversial issue for over 15 years. Large-scale scanning tunneling microscope images of the intralayer structure of this phase exhibit a domain-like pattern defined by a variation in the maximum CDW amplitude. The circular domains, consisting of high-amplitude CDWs, are arranged in a regular hexagonal lattice (period 73+/-3 angstroms) that is rotated relative to the CDWs. In addition, from the analysis of atomic resolution images it was determined that there is a well-defined phase shift between the CDWs in adjacent domains, and that within a domain the CDW superlattice is commensurate with the atomic lattice. These results provide evidence for the hexagonal discommensurate CDW phase in 1T-TaS2 and also suggest an explanation for the long-standing controversy concerning the structure of this phase.     

The Effect of H2O on the 410-Kilometer Seismic Discontinuity

The 410-kilometer seismic discontinuity is generally considered to be caused by a phase transformation of the main constituent of the upper mantle, olivine, alpha-(Mg,Fe)(2)SiO(4), to beta-(Mg,Fe)(2)SiO(4). Recent data show that H(2)O dissolves in olivine and other nominally anhydrous mantle minerals and that the partitioning of H(2)O between olivine and beta-(Mg,Fe)(2)SiO(4) is about 1:10. Such behavior strongly affects the region over which the alpha to beta phase transformation occurs and hence the seismic discontinuity that results. The observed width of the discontinuity constrains the maximum H(2)O content of upper mantle olivine to about 200 parts per million by weight.     

A carbon-free sandwich complex [(P5)2Ti]2-

Reactions of highly reduced titanium complexes with white phosphorus, P4, at or below 25 degrees C yielded brown to deep red-brown salts of the first entirely inorganic metallocene, [(eta5-P5)2Ti](2-)(1). Like ferrocene and other carbon-based metallocenes, the structure of 1 has parallel and planar five-membered rings symmetrically positioned about the central metal atom. Despite its electron-deficient (16 electron) and formally zerovalent titanium character, salts of 1 are highly stable toward heat and air, both in solution and in the solid state. Computational studies show that the pentaphosphacyclopentadienyl unit, P5, functions as an unusually effective acceptor ligand, and this results in substantial stabilization of 1.     

Antiferromagnetic Ordering and Paramagnetic Behavior of Ferromagnetic Cu6 and Cu18 Clusters in BaCuO2+x

Magnetization and neutron diffraction measurements on polycrystalline BaCuO2+x revealed a combination of magnetic behaviors. The Cu(6) ring clusters and Cu(18) sphere clusters in this compound had ferromagnetic ground states with large spins 3 and 9, respectively. The Cu(6) rings ordered antiferromagnetically below the Néel temperature T(N) = 15 +/- 0.5 kelvin, whereas the Cu(18) spheres remained paramagnetic down to 2 kelvin. The ordered moment below T(N) was 0.89(5) Bohr magnetons per Cu in the Cu(6) rings, demonstrating that quantum fluctuation effects are small in these atomic clusters. The Cu(18) clusters are predicted to exhibit ferromagnetic intercluster order below about 1 kelvin.     

Structural and Electronic Role of Lead in (PbBi)2Sr2CaCu2O8 Superconductors by STM

The structural and electronic effects of lead substitution in the high-temperature superconducting materials Pb(x)Bi(2-x)Sr(2)CaCu(2)O(8) have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)-O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)-O layers. STS data show that the electronic structure of the Bi(Pb)-O layers is insensitive to lead substitution within +/-0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at approximately 1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x 相似文献   

Sex Conversion in a Male Vitis vinifera L. by a Kinin

A synthetic (reputed) kinin, SD 8339, at 1000 parts per million in alcohol solution, applied to flower clusters of a male grapevine about 3 weeks before anthesis, completely converted the flower sex from male to hermaphrodite. Indolebutyric acid, 2,3,5-triiodobenzoic acid, 2-chloroethyltrimethylammonium chloride beta-naphthoxyacetic acid, beta-indoleacetic acid, alpha-naphthaleneacetic acid, and gibberellin A(3) failed to modify the sex.     

Isomers of Small Carbon Cluster Anions: Linear Chains with up to 20 Atoms

The structure of small carbon cluster anions, Cn(-) (4 相似文献   

Crystallinity of the double layer of cadmium arachidate films at the water surface

A crystalline counterionic layer at the interface between an electrolyte solution and a charged layer of insoluble amphiphilic molecules was observed with grazing incidence synchrotron x-ray diffraction. Uncompressed arachidic films spread over 10(-3) molar cadmium chloride solution (pH 8.8) spontaneously form crystalline clusters with coherence lengths of approximately 1000 angstroms at 9 degrees C. Ten distinct diffraction peaks were observed, seven of which were attributed to scattering only from a crystalline Cd(2+) layer and the other three to scattering primarily from the arachidate layer. The reflections from the Cd(2+) layer were indexed according to a 2 x 3 supercell of the arachidate lattice with three Cd(2+) ions per cadmium unit cell.     

The "Ozone Deficit" Problem: O2(X, v ge 26) + O(3P) from 226-nm Ozone Photodissociation

Highly vibrationally excited O(2)(X(3)sigmag(-), v >/= 26) has been observed from the photodissociation of ozone (O(3)), and the quantum yield for this reaction has been determined for excitation at 226 nanometers. This observation may help to address the "ozone deficit" problem, or why the previously predicted stratospheric O(3) concentration is less than that observed. Recent kinetic studies have suggested that O(2)(X(3)sigmag(-), v >/= 26) can react rapidly with O(2) to form O(3) + O and have led to speculation that, if produced in the photodissociation of O(3), this species might be involved in resolving the discrepancy. The sequence O(3) + hv --> O(2)(X(3)sigmag(-), v >/= 26) + O; O(2)(X(3)sigmag(-), v >/= 26) + O(2) --> O(3) + O (where hv is a photon) would be an autocatalytic mechanism for production of odd oxygen. A two-dimensional atmospheric model has been used to evaluate the importance of this new mechanism. The new mechanism can completely account for the tropical O(3) deficit at an altitude of 43 kilometers, but it does not completely account for the deficit at higher altitudes. The mechanism also provides for isotopic fractionation and may contribute to an explanation for the anomalously high concentration of heavy O(3) in the stratosphere.     

Enhancing hydrogen evolution activity in water splitting by tailoring Li⁺-Ni(OH)₂-Pt interfaces

Improving the sluggish kinetics for the electrochemical reduction of water to molecular hydrogen in alkaline environments is one key to reducing the high overpotentials and associated energy losses in water-alkali and chlor-alkali electrolyzers. We found that a controlled arrangement of nanometer-scale Ni(OH)(2) clusters on platinum electrode surfaces manifests a factor of 8 activity increase in catalyzing the hydrogen evolution reaction relative to state-of-the-art metal and metal-oxide catalysts. In a bifunctional effect, the edges of the Ni(OH)(2) clusters promoted the dissociation of water and the production of hydrogen intermediates that then adsorbed on the nearby Pt surfaces and recombined into molecular hydrogen. The generation of these hydrogen intermediates could be further enhanced via Li(+)-induced destabilization of the HO-H bond, resulting in a factor of 10 total increase in activity.     

A sharp peak of the zero-temperature penetration depth at optimal composition in BaFe2(As(1-x)P(x))2

In a superconductor, the ratio of the carrier density, n, to its effective mass, m*, is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration depth, λ(L). In two-dimensional systems, this ratio n/m* (~1/λ(L)(2)) determines the effective Fermi temperature, T(F). We report a sharp peak in the x-dependence of λ(L) at zero temperature in clean samples of BaFe(2)(As(1)(-x)P(x))(2) at the optimum composition x = 0.30, where the superconducting transition temperature T(c) reaches a maximum of 30 kelvin. This structure may arise from quantum fluctuations associated with a quantum critical point. The ratio of T(c)/T(F) at x = 0.30 is enhanced, implying a possible crossover toward the Bose-Einstein condensate limit driven by quantum criticality.     

Orientational Disorder of C60 in Li2CsC60

The x-ray diffraction of the nonsuperconducting ternary fulleride Li(2)CsC(60) reveals at room temperature a face-centered-cubic (Fm3m) disordered structure that persists to a temperature of 13 Kelvin. The crystal structure is best modeled as containing quasispherical [radius of 3.556(4) angstroms] C(60)(3-) ions, in sharp contrast to their orientational state in superconducting face-centered-cubic K(3)C(60) (merohedral disorder) and primitive cubic Na(2)CsC(60) (orientational order). The orientational disorder of the carbon atoms on the C(60)(3-) sphere was analyzed with symmetry-adapted spherical-harmonic functions. Excess atomic density is evident in the <111> directions, indicating strong bonding Li(+)-C interactions, not encountered before in any of the superconducting alkali fullerides. The intercalate-carbon interactions and the orientational state of the fullerenes have evidently affected the superconducting pair-binding mechanism in this material.     

Crystal Structure of Tl2Ba2Ca2Cu3O10, a 125 K Superconductor

There is now a new series of high-temperature superconductors that may be represented as (A(III)O)(2)A(2)(II)Can-1CunO2+2n where A(III) is Bi or Tl, A(II) is Ba or Sr, and n is the number of Cu-O sheets stacked consecutively. There is a general trend toward higher transition temperatures as n increases. The highest n value for a bulk phase is three and is found when A(III) is Tl. This compound, Tl(2)Ba(2)Ca(2)Cu(3)O(10), has the highest transition temperature( approximately 125 K) of any presently known bulk superconductor. The structure of Tl(2)Ba(2)Ca(2)Cu(3)O(10) has been determined from single-crystal x-ray diffraction data and is tetragonal, with a = 3.85 A and c = 35.9 A. No superstructure is observed, and the material is essentially twin-free. Electron microscopy in the Tl/Ba/Ca/Cu/O system has revealed intergrowths where n = 5; such regions may well be responsible for the superconducting onset behavior observed in this system at about 140 K.