Uranyl Ion Coordination

A review of the known crystal structures containing the uranyl ion shows that plane-pentagon coordination is equally as prevalent as planesquare or plane-hexagon. It is suggested that puckered-hexagon configurations of OH(-) or H(2)O about the uranyl group will tend to revert to plane-pentagon coordination. The concept oft of pentagonal coordination is invoked for possible explanations of the complex crystallography of the natural tiranyl hydroxides and the unusual behavior of polynuclear ions in hydrolyzed uranyl solutions.     

Metastable phases in polar stratospheric aerosols

Phase changes in stratospheric aerosols were studied by cooling a droplet of sulfuric acid (H(2)SO(4)) in the presence of nitric acid (HNO(3)) and water vapor. A sequence of solid phases was observed to form that followed Ostwald's rule for phase nucleation. For stratospheric partial pressures at temperatures between 193 and 195 kelvin, a metastable ternary H(2)SO(4)-HNO(3) hydrate, H(2)SO(4) . HNO(3) . 5H(2)O, formed in coexistence with binary H(2)SO(4) . kH(2)O hydrates (k = 2, 3, and 4) and then transformed to nitric acid dihydrate, HNO(3) . 2H(2)O, within a few hours. Metastable HNO(3) . 2H(2)O always formed before stable nitric acid trihydrate, HNO(3).3H(2)O, under stratospheric conditions and persisted for long periods. The formation of metastable phases provides a mechanism for differential particle growth and sedimentation of HNO(3) from the polar winter stratosphere.     

Synthesis of imido analogs of the uranyl ion

Here we describe the synthesis of two imido analogs of the uranyl ion, UO(2+)2, in which the oxygens are replaced by divalent alkyl or aryl nitrogen groups: U(NtBu)2I2(THF)2 (1) and U(NPh)2I2(THF)3 (2) (where tBu is tert-butyl and THF is tetrahydrofuran). Both compounds have been fully characterized by standard analytical techniques, including x-ray crystallography, and the chemical bonding between the metal center and the nitrogen ligands was quantified by using hybrid density functional theory calculations. As expected for a uranyl analog, these complexes exhibit linear N-U-N linkages and very short U-N bonds. In addition, the theoretical calculations show strong involvement of the 5f and 6d electrons in the U-N bonding.     

In situ observations of a high-pressure phase of H2O Ice

A previously unknown solid phase of H2O has been identified by its peculiar growth patterns, distinct pressure-temperature melting relations, and vibrational Raman spectra. Morphologies of ice crystals and their pressure-temperature melting relations were directly observed in a hydrothermal diamond-anvil cell for H2O bulk densities between 1203 and 1257 kilograms per cubic meter at temperatures between -10 degrees and 50 degreesC. Under these conditions, four different ice forms were observed to melt: two stable phases, ice V and ice VI, and two metastable phases, ice IV and the new ice phase. The Raman spectra and crystal morphology are consistent with a disordered anisotropic structure with some similarities to ice VI.     

Isotope selectivity of infrared laser-driven unimolecular dissociation of a volatile uranyl compound

Isotope-selective photodissociation of the volatile complex uranyl hexafluoroacetylacetonate . tetrahydrofuran [UO(2)(hfacac)(2) . THF] has been achieved with both a continuous-wave and a pulsed carbon dioxide laser. The photodissociation was carried out in a low-density molecular beam under collisionless conditions. Transitions of the laser are in resonance with the asymmetric O-U-O stretch of the uranyl moiety, a vibrational mode whose frequency is sensitive to the masses of the uranium and oxygen isotopes. Unimolecular dissociation is observed mass spectrometrically at an extremely low energy fluence, with no evidence of an energy fluence or intensity threshold. The dissociation yield increases nearly linearly with increasing energy fluence. At constant fluence the dissociation yield is independent of contact time between the radiation field and the molecule, indicating that the decomposition is driven by laser energy fluence and not laser intensity. The oxygen and uranium isotope selectivities measured in these experiments are nearly those predicted by the ratio of the linear absorption cross sections for the respective isotopes. Thus, essentially complete selectivity is observed for oxygen isotopes, while a selectivity of only about 1.25 is measured for the uranium isotopes. A model presented to describe these results is based on rapid intramolecular vibrational energy flow from the pumped mode into a limited number of closely coupled modes.     

Pituitary gonadotrophs: nuclear concentration of radioactivity after injection of ( 3 H)testosterone

Gonadotrophs and castration cells in the male rat pituitary showed nuclear concentration of radioactivity 1 hour after [1,2,6,7-(3)H]testosterone injection. Thyrotrophs and acidophils did not retain radioactivity; also the cells of the intermediate and posterior lobes did not accumulate radioactivity. The autoradiographic results suggest a direct and selective action of androgen on gonadotrophs, which contrasts with the action of estradiol which was shown earlier to bind not only to basophils but to acidophils and chromophobes as well.     

陶粒负载生物滴滤塔净化恶臭气体研究(英文)

[目的]探讨净化单一恶臭气体H2S和NH_3工艺条件及影响因素。[方法]以陶粒作为生物滴滤塔的填料负载微生物,考察了生物滴滤塔于挂膜启动及稳定运行阶段对H_2S和NH_3的降解性能。[结果](1)净化H_2S废气的生物滴滤塔系统在9 d内即完成挂膜,在进口浓度100-1 000 mg/m~3,空床停留时间(EBRT)142-290 s的条件下,H_2S的去除率均可达到99%以上;(2)净化NH_3废气的生物滴滤塔在10 d内即完成挂膜,对NH_3去除率均达到94.61%。[结论]适宜条件下,生物滴滤塔对于H_2S和NH_3的去除率均较高。     

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.     

Disulfate ion as an intermediate to sulfuric Acid in Acid rain formation

The oxidation of the bisulfite ion by dissolved oxygen to produce sulfate ion involves the formation of a previously undetected intermediate. This intermediate has a fairly strong Raman band at 1090 wave numbers and a weak Raman band at 740 wave numbers, both of which are probably due to sulfur-oxygen stretches. The intermediate is proposed to be the disulfate ion S(2)O(7)(2-), which hydrolyzes into H(+) and either SO(4)(2-) or HSO(4)(2-) with a half-life of about 52 seconds at 25 degrees C.     

The Density of Hydrous Magmatic Liquids

Density measurements on several hydrous (相似文献   

A general synthetic procedure for heteropolyniobates

The heteropolyanions of W, Mo, and V, which have found numerous applications, are formed simply by acidification of solutions of their oxoanions. Under similar conditions, these oxoanion precursors are not available for Nb, and Nb-oxo chemistry is dominated by formation of the Lindquist ion [Nb6O19]8- only. However, heteropolyniobate formation is favored in hydrothermal reactions of aqueous, alkaline precursor mixtures. Here we give two examples of heteropolyniobates formed by this general reaction type: K12[Ti2O2][SiNb12O40].16H2O [1], which contains chains of silicododecaniobate Keggin ions, and Na14[H2Si4Nb16O56].45.5H2O [2], a new heteropolyanion structure type.     

Fenton试剂预处理有机磷农药废水的研究

利用Fenton试剂预处理有机磷农药废水,通过单因素和正交试验,考察H2O2投加量、[Fe2＋]/[H2O2]、初始pH值、反应时间等因素对废水COD去除率的影响。结果表明,Fenton试剂预处理甲胺磷模拟废水的反应符合一级反应模型,优化条件为H2O2投加量为9/5理论投加量,[Fe2＋]/[H2O2]（摩尔浓度比）=1∶3,pH=4,反应时间为40min。此条件下,废水COD去除率可达88.1%。     

Antarctic Ozone Depletion Chemistry: Reactions of N2O5 with H2O and HCl on Ice Surfaces

The reactions of dinitrogen pentoxide (N(2)O(5)) with H(2)O and hydrochloric acid (HCl) were studied on ice surfaces in a Knudsen cell flow reactor. The N(2)O(5) reacted on ice at 185 K to form condensed-phase nitric acid (HNO(3)). This reaction may provide a sink for odd nitrogen (NO(x)) during the polar winter, a requirement in nearly all models of Antarctic ozone depletion. A lower limit to the sticking coefficient, gamma, for N(2)O(5) on ice is 1 x 10(-3). Moreover, N(2)O(5) reacted on HCl-ice surfaces at 185 K, with gamma greater than 3 x 10(-3). This reaction, which produced gaseous nitryl chloride (ClNO(2)) and condensed-phase HNO(3), proceeded until all of the HCl within the ice was depleted. The ClNO(2), which did not react or condense on ice at 185 K, can be readily photolyzed in the Antarctic spring to form atomic chlorine for catalytic ozone destruction cycles. The other photolysis product, gaseous nitrogen dioxide (NO(2)), may be important in the partitioning of NO(x) between gaseous and condensed phases in the Antarctic winter.     

草莓果实采后NAD激酶活性与NAD（H）、NADP（H）含量及活性氧代谢的关系

【目的】研究草莓采后成熟衰老过程中NADK活性与NAD（H）、NADP（H）及活性氧代谢和膜氧化产物变化的关系，以探讨NADK在非跃变型果实成熟衰老过程中的作用，为调控果实的成熟衰老提供理论依据。【方法】将从果园采回的草莓果实贮藏于不同的温度下并进行每天取样，研究草莓果实在低温（4℃）、常温（20℃）贮藏期间成熟衰老过程中NAD激酶（NADK）活性及其底物NAD（H）、产物NADP（H）以及超氧阴离子O2- •过氧化氢（H2O2）、膜氧化产物丙二醛（MDA）含量的变化并分析NADK 与上述指标的关系。【结果】草莓果实在低温（4℃）贮藏时，其NADK活性比常温（20℃）贮藏的高，NAD（H）含量则相应比常温贮藏的低，NADP（H）含量则高于常温下的；同时，在常温贮藏期间果实O2- •生成速率和H2O2含量、膜氧化产物MDA含量均比低温贮藏的高，暗示NADK可能通过影响NAD（H）、NADP（H）的含量及比例来调控O2- •生成速率和H2O2含量，从而调控果实的成熟衰老。【结论】非跃变型果实草莓采后成熟衰老过程中，保持较高的NADK活性有利于延缓果实的成熟衰老，降低NADK活性可导致NAD和NAD（H）含量的积累，进而加速电子传递，产生大量的活性氧O2- •和H2O2，从而促进膜过氧化作用和积累较多的MDA，最终导致果实衰老变质。     

Hydrous sodium silicates from lake magadi, kenya: precursors of bedded chert

Two new hydrous sodium silicates, NaSi(7)O(13)(OH)(3).3H(2)O (magadiite) and NaSi(11)O(20.5)(OH)(4).3H(2)O (kenyaite), were found in lake beds at Lake Magadi, Kenya. Both are well-crystallized layered silicates with large basal spacings. Concretions within the magadiite bed consist of kenyaite or quartz (chert) in the center, surrounded by kenyaite. In dilute acids magadiite and kenyaite are converted to 6SiO(2).H(2)O (SH), the first known crystalline hydrate of silica. The magadiite bed probably represents a chemical precipitate from alkaline brines. Percolating waters convert magadiite to kenyaite and eventually to chert. Thus a mechanism has been outlined for the formation of bedded chert deposits through inorganic precipitation. Alternations between silica-rich and iron-rich bands of iron formations may be due to concentration cycles in alkaline lakes.     

水分胁迫诱导平邑甜茶叶片衰老期间内肽酶与活性氧累积的关系

 在水分胁迫下,平邑甜茶叶片3种不同底物内肽酶活性的变化可分为缓升期和速升期,分别对应于叶绿素含量的缓降期和速降期。水分胁迫使平邑甜茶叶片SOD活性先升后降, ASA含量大幅度降低, O2-·、H2O2、1O2含量增高,膜脂过氧化产物 MDA含量大幅度增加,且 Chl、O2-·、H2O2、1O2、MDA上升和下降的幅度与内肽酶活性的降低均呈显著相关。表明水分胁迫下活性氧代谢失调而累积的活性氧(O2-·、H2O2、1O2)导致内肽酶活性大幅度上升。     

Neurons of the hypothalamus concentrate (3H)progesterone or its metabolites

Selective concentration of [(1)H]progesterone or its metabolites is observed in nuclei of neurons in certain hypothalamic regions of the guinea pig 15 minutes after injection of [1,2,6,7-(3)H]progesterone, by use of dry-mount autoradiography. Highest concentrations of progestin target neurons exist in the nucleus arcuatus, the nucleus preopticus periventricularis, and the nucleus preopticus suprachiasmaticus. Previous administration of unlabeled progesterone inhibits the nuclear concentration of radioactivity, but cortisol has no effect. Estradiol priming enhances the nuclear uptake of radioactivity. The results demonstrate the existence of progestin target sites in the hypothalamus and suggest a direct action of progestin on certain hypothalamic structures.     

X-ray-induced dissociation of H2O and formation of an O2-H2 alloy at high pressure

When subjected to high pressure and extensive x-radiation, water (H2O) molecules cleaved, forming O-O and H-H bonds. The oxygen (O) and hydrogen (H) framework in ice VII was converted into a molecular alloy of O2 and H2. X-ray diffraction, x-ray Raman scattering, and optical Raman spectroscopy demonstrated that this crystalline solid differs from previously known phases. It remained stable with respect to variations in pressure, temperature, and further x-ray and laser exposure, thus opening new possibilities for studying molecular interactions in the hydrogen-oxygen binary system.     

乳清蛋白抗氧化肽对H_2O_2所致人胚肺成纤维细胞MRC-5过氧化损伤的保护作用

【目的】探讨纯化后的乳清蛋白抗氧化肽P4对人胚肺成纤维细胞(human lung fibroblast)MRC-5过氧化损伤的保护作用及可能的作用机制。【方法】采用H2O2诱导建立细胞氧化损伤模型,应用四唑蓝快速比色法(MTT法)检测细胞存活率,通过检测细胞培养液中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GSH-Px)活性及丙二醛(MDA)含量,来确定P4对过氧化损伤MRC-5细胞的保护作用,并利用电镜观察细胞形态学变化。【结果】1mmol·L-1H2O2孵育24h可显著诱导MRC-5细胞损伤,使细胞存活力下降到22.47%,细胞经不同浓度的抗氧化肽P4(4、20、100μg·mL-1)与H2O2共孵育后,特别是100μg·mL-1(高剂量组)抗氧化肽P4可使细胞存活率达到44.77%。同时,提高乳清蛋白抗氧化肽P4的浓度,可促进受损的MRC-5细胞修复,提高了SOD、CAT、GSH-Px酶活性,降低MDA含量。扫描电镜和透射电镜观察结果也表明,一定浓度的乳清抗氧化肽对MRC-5细胞具有保护作用。【结论】乳清抗氧化肽通过拮抗H2O2而对MRC-5的过氧化损伤具有保护作用。     

Metal oxide chemistry in solution: the early transition metal polyoxoanions

Many of the early transition elements form large polynuclear metal-oxygen anions containing up to 200 atoms or more. Although these polyoxoanions have been investigated for more than a century, detailed studies of structure and reactivity were not possible until the development of modern x-ray crystallographic and nuclear magnetic resonance spectroscopic techniques. Systematic studies of small polyoxoanions in inert, aprotic solvents have clarified many of the principles governing their structure and reactivity, and also have made possible the preparation of entirely new types of covalent derivatives such as CH(2)Mo(4)O(15)H(3-), C(5)H(5)TiMo(5)O(18)(3-), and (OC)(3)Mn(Nb(2)W(4)O(19))(3-). Since most early transition metal polyoxoanions have structures based on close-packed oxygen arrays containing interstitial metal centers, their chemistry offers a rare opportunity to study chemical transformations in detail on well-defined metal oxide surfaces.