Internal rotation and spin conversion of CH3OH in solid para-hydrogen

The quantum solid para-hydrogen (p-H2) has recently proven useful in matrix isolation spectroscopy. Spectral lines of compounds embedded in this host are unusually narrow, and several species have been reported to rotate in p-H2. We found that a p-H2 matrix inhibits rotation of isolated methanol (CH3OH) but still allows internal rotation about the C-O bond, with splittings of the E/A torsional doublet in internal rotation-coupled vibrational modes that are qualitatively consistent with those for CH3OH in the gaseous phase. This simplified high-resolution spectrum further revealed the slow conversion of nuclear spin symmetry from species E to species A in the host matrix, offering potential insight into nuclear spin conversion in astrophysical sources.     

The use of NMR spectroscopy for the understanding of disease

Nuclear magnetic resonance spectroscopy can now be used to investigate the biochemical energetics of human tissues and organs noninvasively. The method already has increased our understanding of some muscle diseases, has provided information from muscle metabolism about whole-body functions, control, and hormonal status, has helped in the elucidation of hitherto unrecognized causes of disease, and yielded new ideas about the control of bioenergetics in vivo. Studies on the biochemistry of human brain, liver, heart, and kidney are just beginning. Further investigations of well-selected patients are likely to bring biochemistry and clinical practice closer together.     

Chemoselective hydrogenation of nitro compounds with supported gold catalysts

The selective reduction of a nitro group when other reducible functions are present is a difficult process that often requires stoichiometric amounts of reducing agents or, if H2 is used, the addition of soluble metals. Gold nanoparticles supported on TiO2 or Fe2O3 catalyzed the chemoselective hydrogenation of functionalized nitroarenes with H2 under mild reaction conditions that avoided the accumulation of hydroxylamines and their potential exothermic decomposition. These chemoselective hydrogenation gold catalysts also provide a previously unknown route for the synthesis of the industrially relevant cyclohexanone oxime from 1-nitro-1-cyclohexene.     

Selective catalytic C-H alkylation of alkenes with alcohols

Alkenes and alcohols are among the most abundant and commonly used organic feedstock in industrial processes. We report a selective catalytic alkylation reaction of alkenes with alcohols that forms a carbon-carbon bond between vinyl carbon-hydrogen (C-H) and carbon-hydroxy centers with the concomitant loss of water. The cationic ruthenium complex [(C(6)H(6))(PCy(3))(CO)RuH](+)BF(4)(-) (Cy, cyclohexyl) catalyzes the alkylation in solution within 2 to 8 hours at temperatures ranging from 75° to 110°C and tolerates a broad range of substrate functionality, including amines and carbonyls. Preliminary mechanistic studies are inconsistent with Friedel-Crafts-type electrophilic activation of the alcohols, suggesting instead a vinyl C-H activation pathway with opposite electronic polarization.     

NMR技术在多糖研究中的应用

主要对NMR技术在结构研究、衍生化反应、多糖的水解反应中的应用进行了介绍。     

Chemical imaging of surfaces with the scanning electrochemical microscope

Scanning electrochemical microscopy is a scanning probe technique that is based on faradaic current changes as a small electrode is moved across the surface of a sample. The images obtained depend on the sample topography and surface reactivity. The response of the scanning electrochemical microscope is sensitive to the presence of conducting and electroactive species, which makes it useful for imaging heterogeneous surfaces. The principles and instrumentation used to obtain images and surface reaction-kinetic information are discussed, and examples of applications to the study of electrodes, minerals, and biological samples are given.     

Quantitation of hepatic glycogenolysis and gluconeogenesis in fasting humans with 13C NMR

The rate of net hepatic glycogenolysis was assessed in humans by serially measuring hepatic glycogen concentration at 3- to 12-hour intervals during a 68-hour fast with 13C nuclear magnetic resonance spectroscopy. The net rate of gluconeogenesis was calculated by subtracting the rate of net hepatic glycogenolysis from the rate of glucose production in the whole body measured with tritiated glucose. Gluconeogenesis accounted for 64 +/- 5% (mean +/- standard error of the mean) of total glucose production during the first 22 hours of fasting. In the subsequent 14-hour and 18-hour periods of the fast, gluconeogenesis accounted for 82 +/- 5% and 96 +/- 1% of total glucose production, respectively. These data show that gluconeogenesis accounts for a substantial fraction of total glucose production even during the first 22 hours of a fast in humans.     

人工林木材改性中核磁共振波谱的应用进展

阐述了核磁共振技术的基本原理;着重论述了核磁共振波谱在木材热处理、木材乙酰化、酯化、醚化及在木材纤维素、半纤维素和木素等木材改性方面的应用。     

The roles of subsurface carbon and hydrogen in palladium-catalyzed alkyne hydrogenation

Alkynes can be selectively hydrogenated into alkenes on solid palladium catalysts. This process requires a strong modification of the near-surface region of palladium, in which carbon (from fragmented feed molecules) occupies interstitial lattice sites. In situ x-ray photoelectron spectroscopic measurements under reaction conditions indicated that much less carbon was dissolved in palladium during unselective, total hydrogenation. Additional studies of hydrogen content using in situ prompt gamma activation analysis, which allowed us to follow the hydrogen content of palladium during catalysis, indicated that unselective hydrogenation proceeds on hydrogen-saturated beta-hydride, whereas selective hydrogenation was only possible after decoupling bulk properties from the surface events. Thus, the population of subsurface sites of palladium, by either hydrogen or carbon, governs the hydrogenation events on the surface.     

铬天青S-溴酸钾体系催化光度法测定水发食品中甲醛

在H2SO4介质中,甲醛对溴酸钾氧化铬天青S的褪色反应有催化作用,据此建立了催化光度法测定甲醛的新方法.该方法的线性范围为0.12～1.01 mg/L,检出限为0.012 mg/L.该方法用于腐竹、木耳和八渡笋等水发食品中甲醛的测定,测定结果的相对标准偏差RSD均小于5％(n=7),回收率为96.2％～103.8％,可满足食品中甲醛的测定要求.     

福美双的极谱催化波的检测方法

研究了酒石酸-酒石酸钾钠-K2S2O8体系中福美双的极谱催化波,拟定了测定福美双的新方法.结果表明在0.2 mol·L-1酒石酸-酒石酸钾钠(pH 5.5) 1.5×10-3 mol·L-1 K2S2O8底液中,极谱催化波峰电位Ep=-0.5 V(vs.SCE);二阶导数峰峰电流Ip″与福美双浓度在5.0×10-8～3.0×10-6 mol·L-1范围内呈良好的线性关系,检出限为1.0×10-8 mol·L-1,相对标准偏差为1.27%(n=11).福美双催化波灵敏度比相应的福美双还原波高25倍,对样品的平均检测回收率为90.29%～96.10%,该方法灵敏、简单、快速.     

钙钛矿催化剂用于氨选择性还原氮氧化物的研究进展

氨选择性催化还原氮氧化物(NO_x)技术是目前应用较为广泛的催化脱硝技术,钙钛矿材料因其独特的结构、良好的稳定性且环保无害的特点成为选择性催化还原NO_x领域的研究热点。本文综述了近年来国内外关于钙钛矿NH_3-SCR催化剂的研究进展,较为全面地对钙钛矿催化剂的主要类型、脱硝活性、构效关系进行了论述,同时介绍了钙钛矿在光辅助SCR技术这一全新领域的研究进展,并总结了钙钛矿催化剂的NH_3-SCR反应机制,对该领域未来可能的发展方向和研究目标进行了展望。     

Fluorescence imaging of cellular metabolites with RNA

Genetically encoded sensors are powerful tools for imaging intracellular metabolites and signaling molecules. However, developing sensors is challenging because they require proteins that undergo conformational changes upon binding the desired target molecule. We describe an approach for generating fluorescent sensors based on Spinach, an RNA sequence that binds and activates the fluorescence of a small-molecule fluorophore. We show that these sensors can detect a variety of different small molecules in vitro and in living cells. These RNAs constitute a versatile approach for fluorescence imaging of small molecules and have the potential to detect essentially any cellular biomolecule.     

Prediction of crop yields with the use of neural networks

The possibilities of the combined use of neural networks and fuzzy set theory in the form of constructing a so-called fuzzy neural network (FNN) or granular neural network (GNN) [1] for predicting crop yields in the Rostov oblast and Krasnodar and Stavropol krais are examined. The results of modeling plant growth on the basis of the CGMS simulation model as well as the values of the vegetation index NDVI, calculated from the SPOT VEGETATION satellite data, are the input parameters. As a result of training the neural network, the accuracy of predicting yields is on average about 75%.     

Video-rate molecular imaging in vivo with stimulated Raman scattering

Optical imaging in vivo with molecular specificity is important in biomedicine because of its high spatial resolution and sensitivity compared with magnetic resonance imaging. Stimulated Raman scattering (SRS) microscopy allows highly sensitive optical imaging based on vibrational spectroscopy without adding toxic or perturbative labels. However, SRS imaging in living animals and humans has not been feasible because light cannot be collected through thick tissues, and motion-blur arises from slow imaging based on backscattered light. In this work, we enable in vivo SRS imaging by substantially enhancing the collection of the backscattered signal and increasing the imaging speed by three orders of magnitude to video rate. This approach allows label-free in vivo imaging of water, lipid, and protein in skin and mapping of penetration pathways of topically applied drugs in mice and humans.     

Tracheal respiration in insects visualized with synchrotron x-ray imaging

Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.     

The catalytic role of the active site aspartic acid in serine proteases

The role of the aspartic acid residue in the serine protease catalytic triad Asp, His, and Ser has been tested by replacing Asp102 of trypsin with Asn by site-directed mutagenesis. The naturally occurring and mutant enzymes were produced in a heterologous expression system, purified to homogeneity, and characterized. At neutral pH the mutant enzyme activity with an ester substrate and with the Ser195-specific reagent diisopropylfluorophosphate is approximately 10(4) times less than that of the unmodified enzyme. In contrast to the dramatic loss in reactivity of Ser195, the mutant trypsin reacts with the His57-specific reagent, tosyl-L-lysine chloromethylketone, only five times less efficiently than the unmodified enzyme. Thus, the ability of His57 to react with this affinity label is not severely compromised. The catalytic activity of the mutant enzyme increases with increasing pH so that at pH 10.2 the kcat is 6 percent that of trypsin. Kinetic analysis of this novel activity suggests this is due in part to participation of either a titratable base or of hydroxide ion in the catalytic mechanism. By demonstrating the importance of the aspartate residue in catalysis, especially at physiological pH, these experiments provide a rationalization for the evolutionary conservation of the catalytic triad.     

Green, catalytic oxidation of alcohols in water

Alcohol oxidations are typically performed with stoichiometric reagents that generate heavy-metal waste and are usually run in chlorinated solvents. A water-soluble palladium(II) bathophenanthroline complex is a stable recyclable catalyst for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic water-alcohol system. The use of water as a solvent and air as the oxidant makes the reaction interesting from both an economic and environmental point of view.