Surface vibrational spectroscopic studies of hydrogen bonding and hydrophobicity

Surface vibrational spectroscopy by sum-frequency generation was used to study hydrophobicity at the molecular level at various interfaces: water-surfactant-coated quartz, water-hexane, and water-air. In all cases, hydrophobicity was characterized by the appearance of dangling hydroxyl bonds on 25 percent of the surface water molecules. At the water-quartz interface, packing restrictions force the water surface layer to have a more ordered, ice-like structure. A partly wettable water-quartz interface was also studied.     

Water diffusion and clustering on Pd(111)

The adsorption, diffusion, and clustering of water molecules on a Pd(111) surface were studied by scanning tunneling microscopy. At 40 kelvin, low-coverage water adsorbs in the form of isolated molecules, which diffuse by hopping to nearest neighbor sites. Upon collision, they form first dimers, then trimers, tetramers, and so on. The mobility of these species increased by several orders of magnitude when dimers, trimers, and tetramers formed, and decreased again when the cluster contained five or more molecules. Cyclic hexamers were found to be particularly stable. They grow with further exposure to form a commensurate hexagonal honeycomb structure relative to the Pd(111) substrate. These observations illustrate the change in relative strength between intermolecular hydrogen bonds and molecule-substrate bonds as a function of water cluster size, the key property that determines the wetting properties of materials.     

保水剂在蔬菜基质育苗中的应用研究Ⅱ保水剂对黄瓜穴盘苗壮苗生理基础研究

保水剂通过提高穴盘育苗基质的持水量和保水性从而有效地解决育苗中需水严格与供水保水不足的矛盾。从已经得到的有关壮苗指数以及有关的生理变化可以初步判断,这种对于水分调控的效果已经远远超出“生长量”范畴,对蔬菜秧苗的生理活性也同时产生明显影响,保水剂的作用可以相对延长最佳持水量保持时间,植株保持较高的生理活性,因此,适宜的保水剂及用量将会由于影响秧苗质量而导致生产效果的改变。     

Disulfide-dependent multimeric assembly of resistin family hormones

Resistin, founding member of the resistin-like molecule (RELM) hormone family, is secreted selectively from adipocytes and induces liver-specific antagonism of insulin action, thus providing a potential molecular link between obesity and diabetes. Crystal structures of resistin and RELMbeta reveal an unusual multimeric structure. Each protomer comprises a carboxy-terminal disulfide-rich beta-sandwich "head" domain and an amino-terminal alpha-helical "tail" segment. The alpha-helical segments associate to form three-stranded coiled coils, and surface-exposed interchain disulfide linkages mediate the formation of tail-to-tail hexamers. Analysis of serum samples shows that resistin circulates in two distinct assembly states, likely corresponding to hexamers and trimers. Infusion of a resistin mutant, lacking the intertrimer disulfide bonds, in pancreatic-insulin clamp studies reveals substantially more potent effects on hepatic insulin sensitivity than those observed with wild-type resistin. This result suggests that processing of the intertrimer disulfide bonds may reflect an obligatory step toward activation.     

Interplay of intra- and intermolecular H-bonding in a progressively solvated macrocyclic peptide

Studying solvation of a large molecule on an atomic level is challenging because of the transient character and inhomogeneity of hydrogen bonding in liquid water. We studied water clusters of a protonated macrocyclic decapeptide, gramicidin S, which were prepared in the gas phase and then cooled to cryogenic temperatures. The experiment spectroscopically tracked fine structural changes of the clusters upon increasing the number of attached water molecules from 1 to 50 and distinguished vibrational fingerprints of different conformers. The data indicate that only the first two water molecules induce a substantial change of the gramicidin S structure by breaking two intramolecular noncovalent bonds. The peptide structure remains largely intact upon further solvation, reflecting the interplay between the strong intramolecular and weaker intermolecular hydrogen bonds.     

A single molecule of water encapsulated in fullerene C₆₀

Water normally exists in hydrogen-bonded environments, but a single molecule of H(2)O without any hydrogen bonds can be completely isolated within the confined subnano space inside fullerene C(60). We isolated bulk quantities of such a molecule by first synthesizing an open-cage C(60) derivative whose opening can be enlarged in situ at 120°C that quantitatively encapsulated one water molecule under the high-pressure conditions. The relatively simple method was developed to close the cage and encapsulate water. The structure of H(2)O@C(60) was determined by single-crystal x-ray analysis, along with its physical and spectroscopic properties.     

不同灌水处理下土壤水分动态及玉米水分利用效率研究

试验以"郑单958"和"浚单20"为试材,研究了田间不同灌水处理对土壤贮水量动态变化和玉米水分利用效率的影响。结果表明:表层土壤贮水量受降水影响较大,30～60 cm土壤水分含量在整个生育时期内变化最为剧烈,80～100 cm土壤整个生育时期水分含量稳定,无灌溉处理的耗水深度主要集中在60～100 cm土层。抗旱品种"郑单958"产量受灌水量的影响较小。"浚单20"灌水比不灌水处理平均增产8.02%。玉米2品种处理水分利用效率一般以不灌水处理较高,灌水处理水分利用效率均值比不灌水处理降低51.18%。因此,在水资源紧张的太行山山前平原区,选用抗旱玉米品种并灌水1次,即可减少农田耗水,又能保证较好的作物产量。     

In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+

The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.     

Insights into phases of liquid water from study of its unusual glass-forming properties

The vitrification of pure water is compared with that of molecular solutions rich in water, and gross differences are noted. Thermodynamic reasoning and direct observations on noncrystallizing nanoconfined water indicate that the glass transition in ambient-pressure water is qualitatively distinct from that found in the usual molecular liquids. It belongs instead to the order-disorder class of transition seen in molecular and ionic crystalline materials. The distinctive "folding funnel" energy landscape for this type of system explains the extreme weakness of the glass transition of water as well as the consequent confusion that has characterized its scientific history; it also explains the very small excess entropy at the glass transition temperature. The relation of confined water behavior to that of bulk is discussed, and the "fragile-to-strong" transition for supercooled water is interpreted by adding a "critical point-free" scenario to the two competing scenarios for understanding supercooled bulk water.     

Coordinated nonvectorial folding in a newly synthesized multidomain protein

The low-density lipoprotein receptor (LDL-R) is a typical example of a multidomain protein, for which in vivo folding is assumed to occur vectorially from the amino terminus to the carboxyl terminus. Using a pulse-chase approach in intact cells, we found instead that newly synthesized LDL-R molecules folded by way of "collapsed" intermediates that contained non-native disulfide bonds between distant cysteines. The most amino-terminal domain acquired its native conformation late in folding instead of during synthesis. Thus, productive LDL-R folding in a cell is not vectorial but is mostly posttranslational, and involves transient long-range non-native disulfide bonds that are isomerized into native short-range cysteine pairs.     

Water catalysis of a radical-molecule gas-phase reaction

There has been considerable speculation about the role of water and water complexes in chemical gas-phase reactions, including the conjecture that water may act as a molecular catalyst through its ability to form hydrogen bonds. Here, we present kinetic studies in which the effect of water on the rate of the reaction between hydroxyl radicals and acetaldehyde has been measured directly in Laval nozzle expansions at low temperatures. An increasing enhancement of the reaction rate by added water was found with decreasing temperatures between 300 and 60 kelvin. Quantum chemical calculations and statistical rate theory support our conclusions that this observation is due to the reduction of an intrinsic reaction barrier caused by specific water aggregation. The results suggest that even single water molecules can act as catalysts in radical-molecule reactions.     

A stable bicyclic compound with two Si=Si double bonds

In contrast to carbon, silicon does not readily form double bonds, and compounds containing silicon-silicon double bonds can usually be stabilized only by protection with bulky substituents. We have isolated a silicon analog of spiropentadiene 1, a carbon double-ring compound that has not been isolated to date. In the crystal structure of tetrakis[tri(t-butyldimethylsilyl)silyl]spiropentasiladiene 2, a substantial deviation from the perpendicular arrangement of the two rings is observed, and the silicon-silicon double bonds are shown to be distorted. Spectroscopic data indicate pronounced interaction between two remote silicon-silicon double bonds in the molecule. Silicon-silicon bonds may be more accessible to synthesis than previously assumed.     

Hydration of macromolecules

Frozen protein and nucleic acid solutions at -35 degrees C show relatively narrow (100 milligauss) proton nuclear magnetic resonance signals which are assignable to water that is sufficiently mobile to reduce the dipolar broadening normally associated with solids. Hydration was found to be 0.3 to 0.5 gram of water per gram of protein. Nucleic acids are three to five times as hydrated as proteins. Conformational changes in solution produce detectable changes in linewidth or amount of "bound" water, or both. The very fact that the water signals can be observed by high resolution nuclear magnetic resonance suggests that it is not "ice-like" in any literal sense, although it is clearly less mobile than liquid water at the same temperature. A simple model is described which considers both surface hydration and trapped water.     

基于尺度推绎法的生态脆弱区粮食作物耕作适宜性评价（摘要）

[目的]对以生态脆弱及半干旱气候为典型特征的寿阳县进行农作物土地适宜性评价,以期为农田的可持续发展提供理论依据。[方法]针对研究区寿阳县的当地作物玉米、小麦、高粱和大麦,通过尺度推绎方法开展了传统及机械种植两种情景下的土地耕作适宜性评价。尺度推绎在一个土地系统中完成,该系统由土地单元、土地面和土地点几级空间系统组成。并通过气候调整指数修正了IAO（意大利海外农业研究所）的土地适宜性评价方法。[结果]4种作物种植适宜性出现了两极化现象：4种作物的最适宜等级（S1）和最不适宜等级（N2）在研究区占大部分地区。玉米、大麦和小麦在传统模式下更适宜耕作。[结论]未来的耕作政策应更加注重在非宜耕区实现耕地向林地与草地的转变,在宜耕区加大农业生产的投入,注意提高牧民生活与环境保护的平衡,以维持一个健康、稳定的生态系统。     

Identification of the molecular defect in a family with spondyloepiphyseal dysplasia

Spondyloepiphyseal dysplasias (SED) are a heterogeneous group of inherited disorders characterized by disproportionate short stature and pleiotropic involvement of the skeletal and ocular systems. Evidence has suggested that SED may result from structural defects in type II collagen. To confirm the validity of this hypothesis, the structure of the "candidate" type II collagen gene (COL2A1) has been directly examined in a relatively large SED family. Coarse scanning of the gene by Southern blot hybridization identified an abnormal restriction pattern in one of the affected members of the kindred. Analysis of selected genomic fragments, amplified by the polymerase chain reaction, precisely localized the molecular defect and demonstrated that all affected family members carried the same heterozygous single-exon deletion. As a consequence of the mutation, nearly 90 percent of the assembled type II collagen homotrimers are expected to contain one or more procollagen subunits harboring an interstitial deletion of 36 amino acids in the triple helical domain.     

含水率对樟子松细胞壁弹性模量和硬度的影响规律

为探明水分对木材细胞壁力学性能的影响，选取樟子松为对象，利用热水、1%氢氧化钠以及苯-乙醇溶液在80 ℃、6 h、固液比1:20的工艺条件下对试样进行抽提处理，抽提后的木材样品加工成金字塔形，然后对试样进行吸湿处理并且调控试样含水率，借助纳米压痕测试研究含水率对木材细胞壁力学性能的影响，并建立机理模型做进一步分析。结果表明，随着含水率的增加，木材的纵向弹性模量与硬度，均出现了一定程度的下降。分析发现，水分子进入细胞壁后与游离羟基形成氢键，随着含水率增加，会被部分原有的氢键破坏，并与之前进入的水分子形成氢键，在内部形成水分子簇，增大了细胞壁分子链之间的距离，使空隙增多，进而降低木材的弹性模量，且水分会使木材细胞壁主成分逐渐软化，硬度降低。     

Catalytic activation of carbon-fluorine bonds by a soluble transition metal complex

Homogeneous catalytic activation of the strong carbon-fluorine bonds under mild conditions was achieved with the use of rhodium complexes as catalysts. The catalytic reactions between polyfluorobenzenes and hydrosilanes result in substitution of fluorine atoms by hydrogen atoms and are chemo- and regioselective. With individual stoichiometric steps observed and combined, and with intermediates isolated and fully characterized (including crystal structures), these systems demonstrate the effectiveness of a rational approach to catalytic design.     

柱型苹果杂交后代果实性状遗传

对威赛克(Wijcik)与嘎拉(Gala)杂交后代的植株类型及果实的成熟期、大小、形状、色泽、风味和质地的研究结果表明,威赛克与嘎拉正反交组合中,杂交后代植株柱型株型符合1∶1的分离比例,亲本成熟期具有较强的遗传力,果实大小大多数倾向于亲本类型,果形大多数表现为圆锥形,亲本果面片红遗传力较强,果实风味遗传变异较大且分离较广泛,果实质地表现为双亲型和中间型,以中间型的比例较高.     

Structure of water in microemulsions: electrical, birefringence, and nuclear magnetic resonance studies

Microemulsions, which are optically transparent oil-water dispersions, were produced by mixing hexadecane, hexanol, potassium oleate, and water. As the amount of water is increased, the microemulsion exhibits a clear to turbid to clear transition. In contrast to the clear regions, the turbid region possesses birefringence. The development of birefringence is also accompanied by a sharp decrease in the electrical resistance. The high-resolution (220 megacycle) nuclear magnetic resonance data suggest that water exists in two distinct molecular environments in the birefringent region; the first environment is characterized by relatively less mobile water molecules than oil molecules, whereas in the second environment oil molecules are less mobile than water molecules. The electrical, birefringence, and nuclear magnetic resonance data are in agreement with the proposed mechanism of change in the structure of water from water spheres to water cylinders to water lamellae. The chemical shift of water protons suggests that the molecular environment of water in spheres is different from that of water in cylinders or that of water in lamellae.