Kinetic evidence for five-coordination in AlOH(aq)2+ ion

Trivalent aluminum ions are important in natural bodies of water, but the structure of their coordination shell is a complex unsolved problem. In strong acid (pH < 3.0), Al(III) exists almost entirely as the octahedral Al(H2O)6(3+) ion, whereas in basic conditions (pH > 7), a tetrahedral Al(OH)(4- structure prevails. In the biochemically and geochemically critical pH range of 4.3 to 7.0, the ion structures are less clear. Other hydrolytic species, such as AlOH(aq)2+, exist and are traditionally assumed to be hexacoordinate. We show, however, that the kinetics of proton and water exchange on aqueous Al(III), coupled with Car-Parrinello simulations, support a five-coordinate Al(H2O)4OH2+ ion as the predominant form of AlOH(aq)2+ under ambient conditions. This result contrasts Al(III) with other trivalent metal aqua ions, for which there is no evidence for stable pentacoordinate hydrolysis products.     

Spectroscopic determination of the OH- solvation shell in the OH-.(H2O)n clusters

There has been long-standing uncertainty about the number of water molecules in the primary coordination environment of the OH- and F- ions in aqueous chemistry. We report the vibrational spectra of the OH-.(H2O)n and F-.(H2O)n clusters and interpret the pattern of OH stretching fundamentals with ab initio calculations. The spectra of the cold complexes are obtained by first attaching weakly bound argon atoms to the clusters and then monitoring the photoinduced evaporation of these atoms when an infrared laser is tuned to a vibrational resonance. The small clusters (n 相似文献   

Eye-head coordination in monkeys: evidence for centrally patterned organization

Eye-head coordination was investigated by recording from the neck and eye muscles in monkeys. The results show that (i) during eye-head turning, neural activity reaches the neck muscles before the eye muscles, and (ii) all agonist neck muscles are activated simultaneously regardless of the initial head position. Since overt movement of the eyes precedes that of the head, it was concluded that the central neural command initiates the eye-head sequence but does not specify its serial order. Furthermore, it was determined that the compensatory eye movement is not initiated centrally but instead is dependent upon reflex activation arising from movement of the head.     

核桃隔开发利用的研究进 展

目的建立应用流式细胞术测定胡桃属植物基因组大小的方法,测定6种核桃种质资源的C值(即DNA含量),分析比较基因组大小,为胡桃属植物的遗传学、基因组学和进化学等研究提供参考依据。方法以深纹核桃野生种、漾濞泡核桃、三台核桃、云新云林核桃、普通核桃野生种和强特勒核桃的新鲜嫩叶为待检材料,以水稻日本晴新鲜嫩叶为标样,应用流式细胞术分别测定并计算6种核桃的基因组大小。结果测得6种核桃基因组大小分别为深纹核桃野生种(543.2±35.7) Mb、漾濞泡核桃(548.8±43.1) Mb、三台核桃(554.4±14.5) Mb、云新云林核桃(548.8±14.7) Mb、普通核桃野生种(551.6±39.0) Mb和强特勒核桃(520.8±38.5) Mb,6种核桃基因组大小无显著差异(P>0.05)。结论胡桃属核桃组植物无论物种分化、种内驯化和种间杂交都未引起基因组大小的变异。深纹核桃野生种、漾濞泡核桃、三台核桃和云新云林核桃都是首次报道其基因组大小,为中国特有种深纹核桃的深入研究提供了参考数据。同时丰富了胡桃属植物的C值库,并为胡桃属其他物种基因组大小测定提供了可以借鉴的方法。     

The structure of the first coordination shell in liquid water

X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen-bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen-bonded tetrahedral structure in ice. Upon heating from 25 degrees C to 90 degrees C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen-bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed.     

Synthesis of a stable compound with fivefold bonding between two chromium(I) centers

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.     

Hydrocarbon separations in a metal-organic framework with open iron(II) coordination sites

The energy costs associated with large-scale industrial separation of light hydrocarbons by cryogenic distillation could potentially be lowered through development of selective solid adsorbents that operate at higher temperatures. Here, the metal-organic framework Fe(2)(dobdc) (dobdc(4-) : 2,5-dioxido-1,4-benzenedicarboxylate) is demonstrated to exhibit excellent performance characteristics for separation of ethylene/ethane and propylene/propane mixtures at 318 kelvin. Breakthrough data obtained for these mixtures provide experimental validation of simulations, which in turn predict high selectivities and capacities of this material for the fractionation of methane/ethane/ethylene/acetylene mixtures, removal of acetylene impurities from ethylene, and membrane-based olefin/paraffin separations. Neutron powder diffraction data confirm a side-on coordination of acetylene, ethylene, and propylene at the iron(II) centers, while also providing solid-state structural characterization of the much weaker interactions of ethane and propane with the metal.     

Adsorption of Cu(II) on humic acids derived from different organic materials

The adsorption of Cu(II) from aqueous solution onto humic acid(HA) which was isolated from cattle manure(CHA), peat(PHA), and leaf litter(LHA) as a function of contact time, p H, ion strength, and initial concentration was studied using the batch method. X-ray absorption spectroscopy(XAS) was used to examine the coordination environment of the Cu(II) adsorbed by HA at a molecular level. Moreover, the chemical compositions of the isolated HA were characterized by elemental analysis and solid-state 13 C nuclear magnetic resonance spectroscopy(NMR). The kinetic data showed that the adsorption equilibrium can be achieved within 8 h. The adsorption kinetics followed the pseudo-second-order equation. The adsorption isotherms could be well fitted by the Langmuir model, and the maximum adsorption capacities of Cu(II) on CHA, PHA, and LHA were 229.4, 210.4, and 197.7 mg g–1, respectively. The adsorption of Cu(II) on HA increased with the increase in p H from 2 to 7, and maintained a high level at p H>7. The adsorption of Cu(II) was also strongly influenced by the low ionic strength of 0.01 to 0.2 mol L–1 Na NO3, but was weakly influenced by high ionic strength of 0.4 to 1 mol L–1 Na NO3. The Cu(II) adsorption on HA may be mainly attributed to ion exchange and surface complexation. XAS results revealed that the binding site and oxidation state of Cu adsorbed on HA surface did not change at the initial Cu(II) concentrations of 15 to 40 mg L–1. For all the Cu(II) adsorption samples, each Cu atom was surrounded by 4 O/N atoms at a bond distance of 1.95 ? in the first coordination shell. The presence of the higher Cu coordination shells proved that Cu(II) was adsorbed via an inner-sphere covalent bond onto the HA surface. Among the three HA samples, the adsorption capacity and affinity of CHA for Cu(II) was the greatest, followed by that of PHA and LHA. All the three HA samples exhibited similar types of elemental and functional groups, but different contents of elemental and functional groups. CHA contained larger proportions of methoxyl C, phenolic C and carbonyl C, and smaller proportions of alkyl C and carbohydrate C than PHA and LHA. The structural differences of the three HA samples are responsible for their distinct adsorption capacity and affinity toward Cu(II). These results are important to achieve better understanding of the behavior of Cu(II) in soil and water bodies in the presence of organic materials.     

Flaxedil (gallamine triethiodide): evidence for a central action

A central action of gallamine triethiodide has been demonstrated in cats with permanently implanted electrodes that permit direct repetitive stimulation and recording of afterdischarges from cerebral cortex. Systemically administered gallamine produced a consistent and reproducible augmentation of duration of afterdischarge at doses just sufficient to produce skeletal muscle paralysis. Simultaneous examination of expiratory carbon dioxide, blood pressure, body temperature, blood glucose, and direct cortical response to brief single stimuli failed to reveal any consistent peripheral change to which the centrally observed effecte Could be attributed.     

Djurleite (Cu1.94S) and Low Chalcocite (Cu2S): New Crystal Structure Studies

Additional x-ray structure studies on low chalcocite generally confirm the previously reported structure but show that either disorder is present or the true space group is not P2(1)/c but Pc, four of the 96 copper atoms in the monoclinic unit cell taking on twofold (linear) coordination. The crystal structure of djurleite has been solved in space group P2(1)/n, the monoclinic cell having parameters a = 26.897, b = 15.745, and c = 13.565 angstroms; beta = 90.13 degrees ; and a content of 248 copper and 128 sulfur atoms. Of the 62 different copper atoms in the structure, 52 are in threefold, triangular coordination with sulfur, nine in tetrahedral, and one in linear coordination.     

玉米秸秆生物炭处理含铜废水效果研究

在环境监测过程中,水污染问题一直备受关注。该文以农业生产中产生的废弃物玉米秸秆为原料,采用限氧控温炭化法制得生物炭,研究其吸附废水中铜离子的性能,考察了生物炭投加量、振荡时间、铜离子初始浓度、以及初始pH值对吸附效果的影响,并作正交实验。实验结果表明:出玉米秸秆生物质炭吸附去除废水中铜离子是可行的;正交试验得出玉米秸秆生物炭吸附铜离子的影响因素大小为振荡时间pH初始浓度投加量,最佳水平组合为振荡时间为3h、投加量为0.6g、铜离子初始浓度为10mg/L、pH为6.3,去除率可达95.5%。