Amplification of acetylcholine-binding catenanes from dynamic combinatorial libraries

Directed chemical synthesis can produce a vast range of molecular structures, but the intended product must be known at the outset. In contrast, evolution in nature can lead to efficient receptors and catalysts whose structures defy prediction. To access such unpredictable structures, we prepared dynamic combinatorial libraries in which reversibly binding building blocks assemble around a receptor target. We selected for an acetylcholine receptor by adding the neurotransmitter to solutions of dipeptide hydrazones [proline-phenylalanine or proline-(cyclohexyl)alanine], which reversibly combine through hydrazone linkages. At thermodynamic equilibrium, the dominant receptor structure was an elaborate [2]-catenane consisting of two interlocked macrocyclic trimers. This complex receptor with a 100 nM affinity for acetylcholine could be isolated on a preparative scale in 67% yield.     

Controlled atomic doping of a single C60 molecule

We report a method for controllably attaching an arbitrary number of charge dopant atoms directly to a single, isolated molecule. Charge-donating K atoms adsorbed on a silver surface were reversibly attached to a C60 molecule by moving it over K atoms with a scanning tunneling microscope tip. Spectroscopic measurements reveal that each attached K atom donates a constant amount of charge (approximately 0.6 electron charge) to the C60 host, thereby enabling its molecular electronic structure to be precisely and reversibly tuned.     

人参水溶性蛋白的纯化工艺研究

为研究人参中几种水溶性蛋白的提取纯化工艺,采用中性缓冲液抽提和硫酸铵分级沉淀法提取人参总蛋白,应用超滤、亲和层析、离子交换层析、疏水层析、凝胶过滤层析等方法进行分离、纯化,得到5种水溶性人参蛋白。经SDS-PAGE电泳和高效凝胶过滤色谱分析,其分子量分别为65.8,65.5,24.7,15.1,7.6 kD。研究结果表明,本试验所确定的人参水溶性蛋白纯化工艺路线简便、可行。     

作物活体多探头测量仪的研制

采用TP—801单板机制作作物活体多探头测量仪。该机可在田间对生长状态下的农作物进行多点体内养分积累、运输、分配等测定,且结果可靠。     

Equilibrium information from nonequilibrium measurements in an experimental test of Jarzynski's equality

Recent advances in statistical mechanical theory can be used to solve a fundamental problem in experimental thermodynamics. In 1997, Jarzynski proved an equality relating the irreversible work to the equilibrium free energy difference, DeltaG. This remarkable theoretical result states that it is possible to obtain equilibrium thermodynamic parameters from processes carried out arbitrarily far from equilibrium. We test Jarzynski's equality by mechanically stretching a single molecule of RNA reversibly and irreversibly between two conformations. Application of this equality to the irreversible work trajectories recovers the DeltaG profile of the stretching process to within k(B)T/2 (half the thermal energy) of its best independent estimate, the mean work of reversible stretching. The implementation and test of Jarzynski's equality provides the first example of its use as a bridge between the statistical mechanics of equilibrium and nonequilibrium systems. This work also extends the thermodynamic analysis of single molecule manipulation data beyond the context of equilibrium experiments.     

Systematic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase

High-affinity nucleic acid ligands for a protein were isolated by a procedure that depends on alternate cycles of ligand selection from pools of variant sequences and amplification of the bound species. Multiple rounds exponentially enrich the population for the highest affinity species that can be clonally isolated and characterized. In particular one eight-base region of an RNA that interacts with the T4 DNA polymerase was chosen and randomized. Two different sequences were selected by this procedure from the calculated pool of 65,536 species. One is the wild-type sequence found in the bacteriophage mRNA; one is varied from wild type at four positions. The binding constants of these two RNA's to T4 DNA polymerase are equivalent. These protocols with minimal modification can yield high-affinity ligands for any protein that binds nucleic acids as part of its function; high-affinity ligands could conceivably be developed for any target molecule.     

Evolution of hormone-receptor complexity by molecular exploitation

According to Darwinian theory, complexity evolves by a stepwise process of elaboration and optimization under natural selection. Biological systems composed of tightly integrated parts seem to challenge this view, because it is not obvious how any element's function can be selected for unless the partners with which it interacts are already present. Here we demonstrate how an integrated molecular system-the specific functional interaction between the steroid hormone aldosterone and its partner the mineralocorticoid receptor-evolved by a stepwise Darwinian process. Using ancestral gene resurrection, we show that, long before the hormone evolved, the receptor's affinity for aldosterone was present as a structural by-product of its partnership with chemically similar, more ancient ligands. Introducing two amino acid changes into the ancestral sequence recapitulates the evolution of present-day receptor specificity. Our results indicate that tight interactions can evolve by molecular exploitation-recruitment of an older molecule, previously constrained for a different role, into a new functional complex.     

Gels composed of sodium-aluminium silicate, lake magadi, kenya

Sodium-aluminum silicate gels are found in surficial deposits as thick as 5 centimeters in the Magadi area of Kenya. Chemical data indicate they are formed by the interaction of hot alkaline springwaters (67 degrees to 82 degrees C; pH, about 9) with alkali trachyte flows and their detritus, rather than by direct precipitation. In the process, Na(2)O is added from and silica is released to the saline waters of the springs. Algal mats protect the gels from erosion and act as thermal insulators. The gels are probably yearly accumulates that are washed into the lakes during floods. Crystallization of these gels in the laboratory yields analcite; this fact suggests that some analcite beds in lacustrine deposits may have formed from gels. Textural evidence indicates that cherts of rocks of the Pleistocene chert series in the Magadi area may have formed from soft sodium silicate gels. Similar gels may have acted as substrates for the accumulation and preservation of prebiological organic matter during the Precambrian.     

A small-molecule modulator of poly-alpha 2,8-sialic acid expression on cultured neurons and tumor cells

Poly-alpha2,8-sialic acid (PSA) has been implicated in numerous normal and pathological processes, including development, neuronal plasticity, and tumor metastasis. We report that cell surface PSA expression can be reversibly inhibited by a small molecule, N-butanoylmannosamine (ManBut). Inhibition occurs through a metabolic mechanism in which ManBut is converted to unnatural sialic acid derivatives that effectively act as chain terminators during cellular PSA biosynthesis. N-Propanoylmannosamine (ManProp), which differs from ManBut by a single methylene group, did not inhibit PSA biosynthesis. Modulation of PSA expression by chemical means has a role complementary to genetic and biochemical approaches in the study of complex PSA-mediated events.     

The Gelation of CO(2): A Sustainable Route to the Creation of Microcellular Materials

Compounds with strong thermodynamic affinity for carbon dioxide (CO(2)) have been designed and synthesized that dissolve in CO(2), then associate to form gels. Upon removal of the CO(2), these gels produced free-standing foams with cells with an average diameter smaller than 1 micrometer and a bulk density reduction of 97 percent relative to the parent material.     

A molecule carrier

We found that anthraquinone diffuses along a straight line across a flat, highly symmetric Cu111 surface. It can also reversibly attach one or two CO2 molecules as "cargo" and act as a "molecule carrier," thereby transforming the diffusive behavior of the CO2 molecules from isotropic to linear. Density functional theory calculations indicated a substrate-mediated attraction of approximately 0.12 electron volt (eV). Scanning tunneling microscopy revealed individual steps of the molecular complex on its diffusion pathway, with increases of approximately 0.03 and approximately 0.02 eV in the diffusion barrier upon attachment of the first and second CO2 molecule, respectively.     

Characteristics and Performance Of Novel Water-Absorbent Slow Release Nitrogen Fertilizers

In this article, a research on the characteristics and performance of water-absorbent slow release nitrogen fertilizer （WASRNF） using infrared spectroscopy （IR）, scanning electronic microscopy （SEM）, differential scanning calorimetry （DSC）, and thermogravimetry analysis （TGA）, was present. The results indicate that the water absorbency and nitrogen analysis of WASRNF is 103 g g^-1 and 30%, respectively, and WASRNF exhibits approximately neutral pH and very low salt index. WASRNF is a copolymer of nitrogen fertilizer and super absorbent polymer （SAP） monomers which is formed through hydrogen bond interaction, and the molecule contains hydrophilic groups, which is responsible for the absorption and water retention capacity of the molecule. WASRNF is a gel that exhibits the ability to swell, but does not dissolve in water. WASRNF shows non-homogenous nature as a whole, but in local zone it is homogenous, the copolymer molecule shows chain network that is the physical structure responsible for absorption and retention of water in WASRNF. The water retained in WASRNF exists as free and nonfreezing bound and freezing bound water states, with the free and the nonfreezing water accounting for more than 95% of water retained in WASRNF, and the nonfreezing bound water for less than 5%. WASRNF functions in delaying the release of nitrogen from it, thereby serving a novel slow release nitrogenous fertilizer.     

Reversible combination of carbon monoxide with a synthetic oxygen carrier complex

Chlorocarbonyl-bis(triphenylphosphine)iridium(I), in solution, reacts reversibly with carbon monoxide under normal conditions, one molecule per metal atom. Formation of a 1 : 1 metal complex-CO adduct is verified by CO absorption measurements and the infrared spectrum of the adduct measured in situ. The spectrum suggests that the metal-C-O bonding is of the type found in conventional metal carbonyl.     

谷氨酸脱羧酶亲和层析介质制备

将 Sepharose 4B用环氧氯丙烷活化 ,接丁二胺臂 ,再用环氧氯丙烷活化 ,与谷氨酸的 N- 2氨基偶联。在 N ,N-二环己碳化二亚胺催化下 ,以接臂的胶与谷氨酸的 C- 5和 C- 1羧基基团偶联。结果表明 ,谷氨酸 N- 2氨基偶联和 C- 1羧基偶联的亲和介质对小麦谷氨酸脱羧酶有部分亲和作用 ,洗脱下的酶活低 ,而谷氨酸 C- 5羧基基团偶联的层析介质对小麦谷氨酸脱羧酶有完全亲和作用 ,洗脱的酶活高。谷氨酸能从亲和材料上洗脱掉脱羧酶 ,但它抑制酶活 ,而同等浓度的 4-氨基丁酸和谷氨酰胺梯度洗脱没有作用     

Oxygen equilibrium of brachiopod Lingula hemerythrin

In contrast to hemerythrin from five different species of sipunculid worms, ecardine brachiopod Lingula hemerythrin has an oxygen equilibrium which is reversibly altered by pH changes, both the oxygen affinity (Bohr effect) and the interactions between oxygen-binding centers being a function of pH. The significance of these phenomena is discussed in view of the phylogenetic distribution of hemerythrin and the function of respiratory pigments.     

管道上水方式的比选及应注意的问题

介绍了新建液体管道单点上水及多点上水方的适应性及特点,结合兰成渝成品油管道走向和沿途实际地质状况,分析比选了两种上水方式,指出了单点上水在大落差、多起伏管道应用的经济优势,并对其所面临的技术问题提出了相应的解决方法.     

The crystal structure of human Argonaute2

Argonaute proteins form the functional core of the RNA-induced silencing complexes that mediate RNA silencing in eukaryotes. The 2.3 angstrom resolution crystal structure of human Argonaute2 (Ago2) reveals a bilobed molecule with a central cleft for binding guide and target RNAs. Nucleotides 2 to 6 of a heterogeneous mixture of guide RNAs are positioned in an A-form conformation for base pairing with target messenger RNAs. Between nucleotides 6 and 7, there is a kink that may function in microRNA target recognition or release of sliced RNA products. Tandem tryptophan-binding pockets in the PIWI domain define a likely interaction surface for recruitment of glycine-tryptophan-182 (GW182) or other tryptophan-rich cofactors. These results will enable structure-based approaches for harnessing the untapped therapeutic potential of RNA silencing in humans.     

Lactic dehydrogenases: subfractionation of isozymes

Electrophoresis in polyacrylamide gel of homogenates of various organs from the mouse yields five major lactic dehydrogenase bands. If the gels are treated with beta-mercaptoethanol, subsequent electrophoresis produces 15 bands which show lactic dehydrogenase activity. This could be explained if one molecule of nicotinamide adenine dinucleotide (coenzyme) is attached to each of the monomeric subunits of lactic dehydrogenase and if mercaptoethanol can remove the coenzyme only from the muscle type. This is consistent with the hypothesis that intact lactic dehydrogenase is a tetramer.     

Norepinephrine uptake into cerebral cortical synaptosomes after one fight or electroconvulsive shock

Membrane affinity for the neurotransmitter norepinephrine is rapidly but reversibly decreased in nerve terminals of the cerebral cortex by intense nervous stimulation. This should adaptively facilitate alerting during acute emergency and stress. The Michaelis constant (K(m)) for the high-affinity active uptake of norepinephrine into crude synaptosome-rich homogenates of the cerebral cortices of mice was increased 68 percent after 15 minutes of intense fighting and 110 percent 5 minutes after a single electroconvulsive shock. These changes were no longer evident 18 to 20 hours later.