Thermochemical and thermal analysis on N-(p-methylphenyl)-N '-(2-pyridyl)urea

Low temperature heat capacities of N-(p-methylphenyl)-N'-(2-pyridyl)urea were determined by adiabatic calorimetry method in the temperature range from 80 to 370 K. It was found that there was not any heat anomaly in this temperature region. Based on the experimental data, some thermodynamic function results were obtained. Thermal stability and decomposition characteristics analysis of N-(p-methylphenyl)-N'-(2-pyridyl)urea were carried out by DSC and TG. The results indicated that N-(p-methylphenyl)-N'-(2-pyridyl)urea started to melt at ca. 426 K (153degreesC) and the melting peak located at 447.01 K (173.86degreesC). The melting enthalpy was 204.445 kJ mol(-1) (899.6 J g(-1)). The decomposition peak of N-(p-methylphenyl)-N'-(2-pyridyl)urea was found at 499.26 K (226.11degreesC) from DSC curve. This result was similar with that from TG and DTG experiment, in which the mass loss peak was determined as 500.4 K (227.2degreesC).

保护性耕作对土壤线虫c-p类群及功能团的影响

以辽宁彰武县保护性耕作示范推广基地土壤为研究对象,通过实地调查和取样分析,对比研究了传统犁耕和6a保护性耕作(免耕秸秆覆盖)条件下的土壤线虫c-p(colonizer-persister)类群及功能团,为评价保护性耕作的土壤生态效应提供理论依据。研究发现,与犁耕相比,保护性耕作显著增加了土壤线虫各c-p类群及绝大多数功能团的多度,但显著减少了Ba4和Om5功能团多度。此外,保护性耕作还改变了土壤线虫生活史和功能团的结构特征:在大部分研究土层,c-p1和c-p2线虫的相对多度显著提高,而c-p3、c-p4以及c-p3-5类群显著降低;Ba1、Ba2、Ba3、Fu4和H5功能团的相对多度显著提高,而Ba4、H3和Om5的相对多度显著降低,Fu2、H2和Om4相对多度的变化较复杂,在表土层表现为显著抑制,在15~30cm土层则为促进作用。土壤线虫c-p类群和功能团的多度及结构特征可能适合作为评价保护性耕作对土壤质量影响的生物学指标。

策勒绿洲4种杨树的生理生态学特性的研究——P-V曲线和持水力的研究

通过对策勒绿洲的 4种杨树 (新疆杨、箭杆杨、胡杨和灰胡杨 )的P -V曲线和持水力的测定分析 ,得出了初步结论 :人工栽培种新疆杨和箭杆杨的抗旱性能低于乡土树种胡杨和灰胡杨

Comparison of steroid substrates and inhibitors of P-glycoprotein by 3D-QSAR analysis

Steroid derivatives show a complex interaction with P-glycoprotein (Pgp). To determine the essential structural requirements of a series of structurally related and functionally diverse steroids for Pgp-mediated transport or inhibition, a three-dimensional quantitative structure activity relationship study was performed by comparative similarity index analysis modeling. Twelve models have been explored to well correlate the physiochemical features with their biological functions with Pgp on basis of substrate and inhibitor datasets, in which the best predictive model for substrate gave cross-validated q(2) = 0.720, non-cross-validated r(2) = 0.998, standard error of estimate SEE = 0.012, F = 257.955, and the best predictive model for inhibitor gave q(2) = 0.536, r(2) = 0.950, SEE = 1.761 and F = 45.800. The predictive ability of all models was validated by a set of compounds that were not included in the training set. The physiochemical similarities and differences of steroids as Pgp substrate and inhibitor, respectively, were analyzed to be helpful in developing new steroid-like compounds. (C) 2004 Elsevier B.V. All rights reserved.

潮棕壤不同利用方式pH和Olsen-P的垂直变化特征

对潮棕壤4种土地利用方式经过14年后土壤pH和Olsen-P在0～150cm土体10个土层中的垂直分布情况进行的比较研究表明,不同利用方式下土壤pH和Olsen-P含量的剖面分布差异显著,说明不同利用方式对土壤pH和Olsen-P有较大影响。林地和撂荒地0～5cm土层pH分别为>7.0和6.5～7.0,玉米地0～20cm各土层土壤pH基本为6.0以下;20cm以下各土层中的pH,水稻田土壤呈微碱性,玉米地和撂荒地接近中性,林地呈微酸性。土体中Olsen-P平均含量为撂荒地>林地>水稻田>玉米地。水稻田和玉米地0～20cm的3个土层Olsen-P含量明显高于20～80cm的4个土层,表明耕地土壤由于施P肥而导致的P素表聚性;林地和撂荒地0～5cm土层的Olsen-P含量大大高于5～80cm的6个土层,这可能与林地和撂荒地的P素生物归还及基本不受人为扰动有关。4种土地利用方式下土壤各层次Olsen-P含量垂直分布的散点折线图呈现出较为相似的特征。80cm以下的3个土层Olsen-P含量接近或超过表层土壤,主要是受母质层相对较高的全P含量影响所致,也可能与地下水作用有关,不过具体原因还有待于进一步研究。

Synthesis of novel P-ketimine bidentate ferrocenyl ligands with central and planar chirality and comparsion in the catalytic activity between P-ketimine and P-aldimine

A series of novel ferrocenylphosphine-ketimine ligands 6 were prepared by reaction of (R,S-p)-PPFNH2-R or (S,S-p)-PPFNH2 with a variety of m-substituted acetophenones. A different catalytic activity was observed between ferrocenylphosphine-ketimine ligands and corresponding aldimine ligands. The efficiency and diastereomeric impact of these ferrocenylphosphine-ketimine ligands in Pd-catalyzed asymmetric allylic alkylation were first investigated, and higher enantioselectivity of over 98% e.e. with 95% yield was obtained by the use of ferrocenylphosphine-ketimine ligands. However, in Rh-catalyzed asymmetric hydrosilylation of aryl ketones, only 42% e.e. was obtained by the use of ferrocenylphosphine-ketimine ligands compared to 90% e.e. with the use of aldimine ligands. (C) 2003 Elsevier Ltd. All rights reserved.

东北地区不同纬度梯度农田土壤Olsen-P的分布特征

本文研究了中国东北地区不同纬度梯度农田土壤Olsen-P在0～100cm剖面中的分布特征。结果表明,除公主岭和大石桥外,其他各点土壤Olsen-P含量在0～20cm土层较高,20～40cm土层迅速下降,40～100cm各土层又逐渐升高,但底层要远低于表层。不同纬度梯度下各点0～20cm土层Olsen-P含量为暗棕壤>黑土>棕壤,高纬度地点Olsen-P含量具有高于低纬度地点的趋势;20～100cm各土层Olsen-P含量总体表现为黑土和暗棕壤相对较高,棕壤区偏低,没有明显的纬度分异现象。施肥等农田管理措施对0～20cm土壤Olsen-P含量有明显影响,其他土层Olsen-P含量可能主要受磷素运移特点和成土母质等因素影响。