Highly enantioselective conjugate addition of diethylzinc to acyclic enones with fine-tunable phosphite-pyridine ligands

A new series of fine-tunable phosphite-pyridine (P,N) ligands derived from (S)-2-amino-T-hydroxy-6,6'-dimethyl-1,1'-biphenyl and (S)-2-amino-2'-hydroxy-4,4',6,6'-tetramethyl-1,1'-biphenyl was employed in Cu(I)-catalyzed conjugate addition of diethylzinc to acyclic enones. Excellent enantioselectivities (up to 98% ee) and highly catalytic activities were achieved for a variety of acyclic enones.

Structural probing of D-fructose derived ligands for asymmetric addition of diethylzinc to aldehydes

A series of new chiral ligands derived from D-fructose have been synthesized and applied in the enantioselective addition of diethylzinc to aldehydes. Comparison of the enantioselectivities obtained with these ligands demonstrated that the catalytic properties are highly dependent upon the structure of ligands, a rational explanation of the structural effects on the catalytic properties is provided. (C) 2003 Elsevier Science Ltd. All rights reserved.

A 2-kW COIL with a square pipe-array JSOG and nitrogen buffer gas

A 2-kW-class chemical oxygen-iodine laser (COIL) using nitrogen buffer gas has been developed and tested since industrial applications of COIL devices will require the use of nitrogen as the buffer gas. The laser, with a gain length of 11.7 cm, is energized by a square pipe-array jet-type singlet oxygen generator (SPJSOG) and employs a nozzle bank with a designed Mach number of 2.5. The SPJSOG has advantages over the traditional plate-type JSOG in that it has less requirements on basic hydrogen peroxide (BHP) pump, and more important, it has much better operational stability. The SPJSOG without a cold trap and a gas-liquid separator could provide reliable operations for a total gas flow rate up to 450 mmol/s and with a low liquid driving pressure of around 0.7 atm or even lower. The nozzle bank was specially designed for a COIL using nitrogen as the buffer gas. The cavity was designed for a Mach number of 2.5, in order to provide a gas speed and static temperature in the cavity similar to that for a traditional COIL with helium buffer gas and a Mach 2 nozzle. An output power of 2.6 kW was obtained for a chlorine flow rate of 140 mmol/s, corresponding to a chemical efficiency of 20.4%. When the chlorine flow rate was reduced to 115 mmol/s, a higher chemical efficiency of 22.7% was attained. Measurements showed that the SPJSOG during normal operation could provide a singlet oxygen yield Y greater than or equal to 55%, a chlorine utilization U greater than or equal to 85%, and a relative water vapor concentration w = [H2O]/([O-2] + [Cl-2]) less than or equal to 0.1.

Effect of addition of Zn on the catalytic activity of a Co/HZSM-5 catalyst for the SCR of NOx with CH4

The selective catalytic reduction (SCR) of NOx by methane in the presence of excess oxygen was studied on a Zn-Co/HZSM-5 catalyst. It was found that the addition of Zn could improve effectively the selectivity of methane towards NOx reduction. When prepared by a coimpregnation method, the Zn-Co/HZSM-5 catalyst showed much higher catalytic activity than the two catalysts of a Zn/Co/HZSM-5 and Co/Zn/HZSM-5 prepared by the successive impregnation method. It is considered that there exists a cooperative effect among the Zn, Co and zeolite, which enhances the reduction of NO to NO2 reaction and the activation of methane. (C) 2002 Elsevier Science B.V. All rights reserved.

聚丙烯酰胺防治水土流失的效果

Field plots observations indicate that applying polyacrylamide to soil can reduce surface runoff by 18 4%～46 8%,decrease soil erosion by 13%～55%,and increase soil organic matter,alkali-hydrolyzable nitrogen,available phosphate,available potassium in different degrees compared with not application.In addition,applying polyacrylamide can also increase corn yield by 540 5kg·ha -1 ,and net income by 240 5ha.

A systematic approach to standard addition methods in instrumental analysis

Nine cases of standard addition methods in instrumental analysis, including linear instruments, a non-linear response, the electrochemical Nernst equation, and radiochemical techniques.

有机肥对土壤剖面硝态氮淋失影响的模拟研究

利用三种不同长度的土柱 ,模拟研究了有机肥对土壤剖面中土壤硝态氮淋失的影响。结果表明 ,有机肥对KNO3氮肥中 NO- 3 — N的淋失有一定抑制作用 ;施加有机肥可提高土壤碱解态氮含量 ;有机肥本身亦可产生NO- 3 — N淋失。

水分和氮磷水平对小麦碳同位素分辨率和水分利用效率的影响

依据盆栽试验数据 ,利用植物稳定性碳同位素分辨率的理论模型 ,研究了水分和氮磷营养对小麦叶片碳同位素分辨率 (Carbon- isotope discriminationΔ)的影响。结果表明 :水分差异引起碳同位素分辨率较大变异 ,碳同位素分辨率随土壤相对含水量 (Soil relative water content)的提高而提高 ,在土壤相对含水量为 6 0 %～ 70 %条件下碳同位素分辨率最高。缺水时磷水平提高 ,碳同位素分辨率提高。水分利用效率 (Water use efficiency)与碳同位素分辨率关系受土壤水分和养分水平的影响。缺水条件下水分利用效率与碳同位素分辨率之间为负相关 ,充分供水下为正相关 ;在低氮水平下的关系不明显 ,施氮 15 0 kg· hm- 2时相关性显著。

Nitrogen-15 signals of leaf-litter-soil continuum as a possible indicator of ecosystem nitrogen saturation by forest succession and N loads

National Key Research and Development Program [2010CB833502]; National Natural Science Foundation of China [30600071, 40601097, 30590381]; Chinese Academy of Sciences [KZCX2-YW-432, O7V70080SZ, LENOM07LS-01]; GUCAS [O85101PM03]

Short-term effect of increasing nitrogen deposition on CO2, CH4 and N2O fluxes in an alpine meadow on the Qinghai-Tibetan Plateau, China

National Key Research and Development Program [2010CB833500]; Natural Science Foundation of China [30590381]; Knowledge Innovation Project of Chinese Academy of Sciences [KZCX2-YW-432]

Drivers of soil net nitrogen mineralization in the temperate grasslands in Inner Mongolia, China

Soil net nitrogen mineralization (NNM) of four grasslands across the elevation and precipitation gradients was studied in situ in the upper 0-10 cm soil layer using the resin-core technique in Xilin River basin, Inner Mongolia, China during the growing season of 2006. The primary objectives were to examine variations of NNM among grassland types and the main influencing factors. These grasslands included Stipa baicalensis (SB), Aneulolepidum Chinense (AC), Stipa grandis (SG), and Stipa krylovii (SK) grassland. The results showed that the seasonal variation patterns of NNM were similar among the four grasslands, the rates of NNM and nitrification were highest from June to August, and lowest in September and October during the growing season. The rates of NNM and nitrification were affected significantly by the incubation time, and they were positively correlated with soil organic carbon content, total soil nitrogen (TN) content, soil temperature, and soil water content, but the rates of NNM and nitrification were negatively correlated with available N, and weakly correlated with soil pH and C:N ratio. The sequences of the daily mean rates of NNM and nitrification in the four grasslands during the growing season were AC > SG > SB > SK, and TN content maybe the main affecting factors which can be attributed to the land use type.

Radiation-use efficiency and the harvest index of winter wheat at different nitrogen levels and their relationships to canopy spectral reflectance

Radiation-use efficiency (RUE, g/MJ) and the harvest index (HI, unitless) are two helpful characteristics in interpreting crop response to environmental and climatic changes. They are also increasingly important for accurate crop yield simulation, but they are affected by various environmental factors. In this study, the RUE and HI of winter wheat and their relationships to canopy spectral reflectance were investigated based on the massive field measurements of five nitrogen (N) treatments. Crop production can be separated into light interception and RUE. The results indicated that during a long period of slow growth from emergence to regreening, the effect of N on crop production mainly showed up in an increased light interception by the canopy. During the period of rapid growth from regreening to maturity, it was present in both light interception and RUE. The temporal variations of RUEAPAR (aboveground biomass produced per unit of photosynthetically active radiation absorbed by the canopy) during the period from regreening to maturity had different patterns corresponding to the N deficiency, N adequacy and N-excess conditions. Moreover, significant relationships were found between the RUEAPAR and the accumulative normalised difference vegetation index (NDVI) in the integrated season (R-2 = 0.68), between the HI and the accumulative NDVI after anthesis (R-2 = 0.89), and between the RUEgrain (ratio of grain yield to the total amount of photosynthetically active radiation absorbed by the canopy) and the accumulative NDVI of the whole season (R-2 = 0.89) and that after anthesis (R-2 = 0.94). It suggested that canopy spectral reflectance has the potential to reveal the spatial information of the RUEAPAR, HI and RUEgrain. It is hoped that this information will be useful in improving the accuracy of crop yield simulation in large areas.

Effects of inoculated Microcoleus vaginatus on the structure and function of biological soil crusts of desert

Microcoleus vaginatus Gom., the dominant species in biological soil crusts (BSCs) in desert regions, plays a significant role in maintaining the BSC structure and function. The BSC quality is commonly assessed by the chlorophyll a content, thickness, and compressive strength. Here, we have studied the effect of different proportions of M. vaginatus, collected from the Gurbantunggut Desert in northwestern China, on the BSC structure and function under laboratory conditions. We found that when M. vaginatus was absent in the BSC, the BSC coverage, quantified by the percentage of BSC area to total land surface area, was low with a chlorophyll a content of 4.77 x 10(-2) mg g(-1) dry soil, a thickness of 0.86 mm, and a compressive strength of 12.21 Pa. By increasing the percentage of M. vaginatus in the BSC, the BSC coverage, chlorophyll a content, crust thickness, and compressive strength all significantly increased (P < 0.01). The maximum chlorophyll a content (13.12 mg g(-1)dry soil), the highest crust thickness, and the compressive strength (1.48 mm and 36.60 Pa, respectively) occurred when the percentage of inoculated M. vaginatus reached 80% with a complex network of filaments under scanning electron microscope. The BSC quality indicated by the above variables, however, declined when the BSC was composed of pure M. vaginatus (monoculture). In addition, we found that secretion of filaments and polymer, which stick sands together in the BSC, increased remarkably with the increase of the dominant species until the percentage of M. vaginatus reached 80%. Our results suggest that not only the dominant species but also the accompanying taxa are critical for maintaining the structure and functions of the BSC and thus the stability of the BSC ecosystems.

A strategy for synthesis of ion-bonded supramolecular star polymers by reversible addition-fragmentation chain transfer (RAFT) polymerization

We have developed a novel strategy for the preparation of ion-bonded supramolecular star polymers by RAFT polymerization. An ion-bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert-butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by H-1 NMR and GPC. The results show that the polymerization possesses the character of living free-radical polymerization and the ion-bonded supramolecular star polymers PSt, PtBA, and PSt-b-PtBA, with six well-defined arms, were successfully synthesized.