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1.
Polychalcogenide compounds with open polymeric frameworks are rare, and they represent a class of compounds in which microporosity might be achieved. Microporous frameworks that are not oxide-based are now attracting interest because of the combination of catalytic and electronic properties they may simultaneously possess. Three new compounds that may be forerunners to such materials have been discovered and are reported here. The reaction of gallium (Ga), indium (In), and thallium (TI) metal with (Ph(4)P)(2)Se(5) (Ph, phenyl) and an excess of elemental selenium (Se) in a sealed, evacuated Pyrex tube at 200 degrees C yielded small red crystals of (Ph(4)P)[Ga(Se(6))(2)] (I), (Ph(4)P)[In(Se(6))(2)] (II), and (Ph(4)P)[TI(Se(6))(2)] (III), respectively. The [M(Se(6))(2)](-) (M = Ga, In, TI) ions form a two-dimensional, open framework filled with Ph(4)P(+) ions. The [M(Se(6))(2)](n)(n-) structure consists of tetrahedral M(3+) centers and bridging Se(6)(2-) ligands, leading to an extended structure in two dimensions. These layers stack perfectly one on top of the other giving rise to one-dimensional channels running down the c axis that are filled with Ph(4)P(+) cations. These cations are situated in the layers, as opposed to between the layers, and the whole structure can be viewed as a template. Compound II shows remarkable thermal stability and melts congruently at 242 degrees C. Upon cooling to room temperature it gives a glassy phase that recrystallizes upon subsequent heating to 160 degrees C. 相似文献
2.
Three crystalline phases of xenon hexafluoride are based on tetrameric association of XeF(5)(+) and F(-) ions into eight-membered rings. Phase I (monoclinic, 8 XeF(6) units per cell) transforms at approximately 10 degrees C to phase II (orthorhombic, 16 XeF(6) units per cell), which in turn transforms at approximately -25 degrees C to phase 111 (monoclinic, 64 XeF(6) units per doubly primitive cell). The transformation from phase I to phase II requires gross reorientation of half of the tetramers in the structure. The transformation from phase II to phase III involves only an ordering of right-handed and left-handed configurations. 相似文献
3.
Lunar rock 66095 contains a hydrated iron oxide and has an unusual amount of water for a lunar rock (140 to 750 parts per million), 90 percent of which is released below 690 degrees C. The deltaof water released at these low temperatures varies from -75 to -140 per mil relative to standard mean ocean water (SMOW). The small amount of water released between 690 degrees and 1300 degrees C has a delta of about -175 +/-25 per mil SMOW. These delta values are not unusual for terrestrial water. The delta(18)O of water extracted from 110 degrees to 400 degrees C has a value of +5+/- I per mil SMOW, similar to the value for lunar silicates from rock 66095 and different from the value of -4 to -22 per mil found for samples of terrestrial rust including samples of rusted meteoritic iron. The amount of carbon varies from 11 to 59 parts per million with a delta(13)C from -20 to -30 per mil relative to Pee Dee belemnite. Only very small amounts of reduced species (such as hydrogen, carbon monoxide, and methane) were found, in contrast to the analyses of other lunar rocks. Although it is possible that most of the water in the iron oxide (goethite) may be terrestrial in origin or may have exchanged with terrestrial water during sample return and handling, evidence presented herein suggests that this did not happen and that some lunar water may have a deltaD that is indistinguishable from that of terrestrial water. 相似文献
4.
The survival of Escherichia coli B/r WP2 (tryptophan-requiring) from ultraviolet irradiation when suspended in 0.067M phosphate buffer (pH 7) has been studied over the temperature range 22 degrees to -269 degrees C. In unfrozen suspensions there was no appreciable change in sensitivity between 22 degrees and -10 degrees C. The sensitivity in the presence of ice progressively increased by a factor of 7 when the temperature was lowered to -79 degrees C. Between -79 degrees and -196 degrees C the sensitivity decreased to less than four times the sensitivity at 22 degrees C and was not appreciably different at -269 degrees C. Evidence from experiments with bacteriophage T1 and E. coli WP2 HCR(-) (a strain unable to excise thymine dimers) indicates that a new, qualitatively different lesion, less amenable to repair, may replace the thymine dimer in E. coli irradiated at -79 degrees C. 相似文献
5.
Kinetics of the reactions of Riftia pachyptila hemoglobin with oxygen were followed spectrophotometrically by stopped-flow and laser flash photolysis techniques. The rate of oxygen dissociation increases eightfold over the range of 5 degrees to 20 degrees C (k = 2.2 sec(-1)at 10 degrees C). Oxygen recombination after flash photolysis was biphasic. The rates of both slow and fast phases of the reaction were independent of temperature from 0 degrees to 20 degrees C(k'fast = 7 x 10(6); k'slow = 1 x 16(6) liter mole (-1) sec(-1)). As the oxygen affinity is relatively temperature independent, analysis in terms of the two-state model of cooperativity requires that the conformational equilibrium constant L decrease by about 50-fold between 3 degrees and 15 degrees C. 相似文献
6.
Crystalline semiconducting sulfide and selenide zeolite analogs were synthesized that possess four-connected, three-dimensional tetrahedral networks built from tetravalent (M4+ = Ge4+ or Sn4+, where M = meta) and trivalent (M3+ = Ga3+ or In3+) cations. Microporous materials were obtained in all four combinations of M4+ and M3+, and some of them were thermally stable up to at least 380 degrees C. These materials exhibit framework topologies with pore size ranging from 12 to 24 tetrahedral atoms, high surface area, high framework charge density and ion exchange capacity, and tunable electronic and optical properties. 相似文献
7.
Iwasa Y Arima T Fleming RM Siegrist T Zhou O Haddon RC Rothberg LJ Lyons KB Carter HL Hebard AF Tycko R Dabbagh G Krajewski JJ Thomas GA Yagi T 《Science (New York, N.Y.)》1994,264(5165):1570-1572
The fullerene C(60) can be converted into two different structures by high pressure and temperature. They are metastable and revert to pristine C(60) on reheating to 300 degrees C at ambient pressure. For synthesis temperatures between 300 degrees and 400 degrees C and pressures of 5 gigapascals, a nominal face-centered-cubic structure is produced with a lattice parameter a(o) = 13.6 angstroms. When treated at 500 degrees to 800 degrees C at the same pressure, C(60) transforms into a rhombohedral structure with hexagonal lattice parameters of a(o) = 9.22 angstroms and c(o) = 24.6 angstroms. The intermolecular distance is small enough that a chemical bond can form, in accord with the reduced solubility of the pressure-induced phases. Infrared, Raman, and nuclear magnetic resonance studies show a drastic reduction of icosahedral symmetry, as might occur if the C(60) molecules are linked. 相似文献
8.
A shear press has been used to determine the mechanical behavior of serpentinized dunite and forsterite at normal pressures to 50 kilobars, temperatures to 900 degrees C; and strain rates from 10(-1) to 10(-4) per second. The shear strength of dunite, containing less than 5 percent by volume of serpentine, is reduced by at least 30 percent as the temperature is raised from 300 degrees to 520 degrees C. Abundant kink bands develop at normal pressures above 35 kilobars at 27 degrees C and at lower pressures as the temperature is increased. 相似文献
9.
We have observed a red luminescence, qualitatively similar to that of enstatite achondrites, in unsorted fines, their separated mineral phases, and rock chips. The energy efficiency of the plagioclase fraction is approximately 1 percent. At -196 degrees C the effect is enhanced by a factor between 1 and 2. All fractions except ilmenite exhibit blue thermoluminescence with a glow peak near -135 degrees C and an energy efficiency approximately 4 x 10(-6). Unlike the thermoluminescence of terrestrial and meteoritic material, it is nonrepeatable even after annealing at 200 degrees C. Similar thermoluminescence is seen in rock chips, but in unsorted fines it is masked by the opaque fractions. 相似文献
10.
Chidsey CE 《Science (New York, N.Y.)》1991,251(4996):919-922
The rate constant of the electron-transfer reaction between a gold electrode and an electroactive ferrocene group has been measured at a structurally well-defined metal-electrolyte interface at temperatures from 1 degrees to 47 degrees C and reaction free energies from -1.0 to +0.8 electron volts (eV). The ferrocene group was positioned a fixed distance from the gold surface by the self-assembly of a mixed thiol monolayer of (eta(5)C(5)H(5))Fe(eta(5)C(5)H(4))CO(2)(CH(2))(16)SH and CH(3)(CH(2))(15)SH. Rate constants from 1 per second (s(-1)) to 2 x 10(4) s(-1) in 1 molar HClO(4) are reasonably fit with a reorganization energy of 0.85 eV and a prefactor for electron tunneling of 7 x 10(4) s(-1) eV(-1). Such self-assembled monolayers can be used to systematically probe the dependence of electron-transfer rates on distance, medium, and spacer structure, and to provide an empirical basis for the construction of interfacial devices such as sensors and transducers that utilize macroscopically directional electron-transfer reactions. 相似文献
11.
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. 相似文献
12.
Triops (Entomostraca) eggs killed only by boiling 总被引：1，自引：0，他引：1
D B Carlisle 《Science (New York, N.Y.)》1968,161(838):279-280
Temporary rainpools near Khartoum, Sudan, are inhabited by the notostracan crustacean Triops which completes its life cycle within 4 weeks. The annual rains fall in late summer, and throughout the winter and early summer the eggs of Triops remain in the dried mud or dust where they may be exposed to temperatures up to 80 degrees C. Laboratory experiments show that they can withstand temperatures up to within 1 degrees C of boiling, but are killed in partial vacuum by 70 degrees C, at atmospheric pressure by 100 degrees C, or under pressure by 105 degrees C. Exposure to high temperature seems to be necessary to break the egg diapause. 相似文献
13.
While the spring phytoplankton bloom in Newfoundland coastal waters is in progress during April and May, at water temperatures between -1 degrees and +2 degrees C, bacterial growth and respiratory rates remain low. Microbial community respiration is not measurable at -0.2 degrees C. Particulate materials that would be utilized by microorganisms in 2 to 3 days at 20 degrees to 25 degrees C require 11 days at 4 degrees C and 18 days at -0.2 degrees C. Thus, photosynthesis is active but microbial utilization of the products is suppressed. High secondary production in cold water may result from the low rate of microbial decomposition, enabling herbivores to utilize much of the primary production. 相似文献
14.
Carbon from the Allende meteorite is not graphite but carbyne (triply bonded elemental carbon), inasmuch as on heating to 250 degrees to 330 degrees C it releases mainly triply bonded fragments: -(C identical withC)(n),- with n = 1 to 5, and -(C identical withC)(n)-CN, with n = 1 to 3. Although carbynes have been known to form only by condensation of carbon vapor above 2600 K or by explosive shock of > 600 kilobars, it is found that they also form metastably by the reaction 2CO --> CO(2) + C (solid) at 300 degrees to 400 degrees C in the presence of a chromite catalyst. Such low-temperature formation by surface catalysis may be the dominant source of carbynes on the earth and in meteorites, and a major source of interstellar carbynes and cyanopolyacetylenes. 相似文献
15.
Speckle observations of Jupiter's satellite Io at a wavelength of 5 micrometers during July 1984 resolved the disk and showed emission from a hot spot in the Loki region. The hot spot contributed a flux approximately equal to 60 percent of that from the disk. Images reconstructed by means of the Knox-Thompson algorithm showed the spot moving across the disk as the satellite rotated. It was located at 301 degrees +/- 6 degrees west longitude, 10 degrees +/- 6 degrees north latitude, and had a radiance of (2.96 +/- 0.54) x 10(22) ergs sec(-1) cm(-1) sr(-1)/A where A is the area of the spot. For an assumed temperature of 400 K, the area of the source would be 11,400 square kilometers. An active "lava lake" similar to that seen by Voyager may be the source of the infrared emission. 相似文献
16.
Viscosity of fluids in subduction zones 总被引：2，自引：0，他引：2
The viscosities of aqueous fluids with 10 to 80 weight percent dissolved silicates have been measured at 600 degrees to 950 degrees C and 1.0 to 2.0 gigapascals by in situ observation of falling spheres in the diamond anvil cell. The viscosities at 800 degrees C range from 10(-4) to 10(0.5) pascal seconds. The combination of low viscosities with a favorable wetting angle makes silicate-rich fluid an efficient agent for material transport at low-volume fractions. Our results therefore suggest that there may be a direct relationship between the position of the volcanic front and the onset of complete miscibility between water and silicate melt in the subducting slab. 相似文献
17.
The melting curve of tintelluride (Sn(0.496)Te(0.504) was determined by differential thermal analysis at pressures between 5 and 40 kilobars. Near 844 degrees +/-4 degrees C and 12.0+/-1.0 kb, the liquid and two solid polymorphscoexist. 相似文献
18.
Thyroxine-binding globulin: characterization of the binding site with a fluorescent dye as a probe 总被引：1，自引：0，他引：1
The fluorescent dye 1,8-anilinonaphthalenesulfonate competed with thyroxine for binding to thyroxine-binding globulin. Fluorescence analysis indicated that the dye bound to the globulin in a molar ratio of 1:1 and with an association constant (at 23 degrees C) of 4.19 x10(6)M(-1), and that thyroxine bound to the globulin in a molar ratio of 1:1 and with an association constant (at 23 degrees C) of 2.35x10(10)M(-1). Displacement of globulin-bound dye by thyroxine was shown by fluorescence quenching, and displacement of globulin-bound thyroxine by dye was demonstrated by ultrafiltration. 相似文献
19.
Nguyen T Sutton AD Brynda M Fettinger JC Long GJ Power PP 《Science (New York, N.Y.)》2005,310(5749):844-847
Although in principle transition metals can form bonds with six shared electron pairs, only quadruply bonded compounds can be isolated as stable species at room temperature. Here we show that the reduction of {Cr(mu-Cl)Ar'}2 [where Ar' indicates C6H3-2,6(C6H3-2,6-Pri2)2 and Pr indicates isopropyl] with a slight excess of potassium graphite has produced a stable compound with fivefold chromium-chromium (Cr-Cr) bonding. The very air- and moisture-sensitive dark red crystals of Ar'CrCrAr' were isolated with greater than 40% yield. X-ray diffraction revealed a Cr-Cr bond length of 1.8351(4) angstroms (where the number in parentheses indicates the standard deviation) and a planar transbent core geometry. These data, the structure's temperature-independent paramagnetism, and computational studies support the sharing of five electron pairs in five bonding molecular orbitals between two 3d5 chromium(I) ions. 相似文献
20.
Phosphatase mutants in Aspergillus nidulans 总被引：1，自引：0，他引：1
G Dorn 《Science (New York, N.Y.)》1965,150(700):1183-1184
Three mutants at three different phosphatase loci produce inactive enzymes at 35 degrees C but partially or fully active enzynmes at 25 degrees C. Furthermore, a suppressor mutant (su5palA1) which restores alkaline phosphatase activity in the palA1 mtutant is an allele of palcC4, a mzutant with a simultaneous reduction in alkaline and acid phosphatase activity. These data suggest that the phosphataseproteins may be made up of two or more different polypeptide chains, and that some of the polypeptide chains are common to two or more of these enzymes. 相似文献