外施稀土在农田生态系中的生物地球化学循环与残留

选择已广泛使用稀土微肥的大兴县庞各庄小麦种植区内, 进行稀土喷施常规量、土施常规量及3倍常规量和对照4种处理的田间实验. 以各地块的耕层土壤为主体, 观测、收集和测定了与之相关各项源汇物质及它们所载带稀土的通量. 结果表明, 未施稀土的地块中, 由降雨、降雪、灌水、复合肥、尿素和降尘等主要源物质载带的稀土输入量极少, 每年共计仅有19.3 g·hm-2 左右; 而外施稀土的地块中, 稀土输入量显著增高. 喷施或土施常规量所输入的稀土分别为对照地块总输入量的9.7和106倍. 但在对照和施用不同量稀土的4个地块中, 由小麦植株的收获和雨水下渗所引起的稀土总输出量都很相近, 而且均以收获期的小麦植株为主要输出物质, 各部位的稀土输出量排序均为根>叶>茎>颍壳>籽粒. 由计算结果得知, 在对照地块的耕层土壤中稀土输出量与输入量基本平衡, 不会发生稀土累积; 而在外施稀土的地块中, 随着外施稀土量的增加, 耕层土壤中的稀土累积量有相应增高, 如果多年连续土施常规量稀土, 仅需159年就会使耕层土壤中稀土含量增加1倍, 发生环境污染有较大的潜在危险; 而采用喷施(常规量)的方法累积速度低得多, 需要2008年才能使耕层土壤中稀土含量增加1倍.     

华北模拟实验块地大气、降水、地表径流和土壤中的稀土浓度分布及施用农用稀土的影响

通过模拟实验块地，初步研究了在一个土壤生态系统中稀土的浓度分布以及施用稀土微肥的影响。结果表明：降水、地表径流水溶液中的稀土浓度均为μｇ／Ｌ量级（０１～１２μｇ／Ｌ），降水中的稀土主要来源于附近地表土壤。大气中的稀土含量随粒径分布有所不同，粒径越小含量越低，且其来源主要是附近的土壤，水可溶性的硝酸稀土微肥在施用后很快转化为水不溶性形态，施加稀土前后实验组表层土壤中稀土含量基本相同。与对照组相比，施加的稀土微肥对地表径流水溶性和悬浮物稀土浓度未产生明显影响。     

华北模拟实验块地大气,降水,地表径流和土壤中的稀土浓度分布及施…

通过模拟实验块地，初步了在一个土壤生态系统中稀土的浓度分布以及施用稀土微肥的影响，结果表明：降水、地表径流水溶液中的稀土浓度均为μｇ／Ｌ量级，降水中的稀土主要来源于附近地表土壤。大气中的稀土含量随粒径２有所不同，粒径越小一越低，且其来源主要是附近的水可溶性的硝酸稀土微肥在施用后很快转化为水不溶性形态，施加稀土前后实验组表层土壤中稀土含量基本相同，与对照组相比，施加的稀土微肥对地表径流水溶性和悬浮的     

稀土元素在土壤-水稻体系中的迁移与吸收累积特征

通过在天然水稻土中施用不同浓度稀土开展为期两年的水稻盆栽实验,在不同生长期系统观测了水稻植株样品的生物量,同时利用ICP-MS测定了土壤及水稻植株各器官中14种稀土元素的含量,并对植株体内稀土含量分布模式及各器官对土壤中稀土的富集与分异进行了对比研究。结果表明,无论苗期还是成熟期,当外施稀土量超过400 mg.kg-1时,水稻植株生物量即开始呈下降趋势,当外施稀土达500mg.kg-1时,生物量降低10%左右,水稻远低于旱作植物小麦对土壤中外施稀土的耐受能力。对照水稻各器官稀土分布模式与对照土壤相似,均呈轻稀土富集,中、重稀土相对亏损型,Eu轻度负异常;但与土壤不同,水稻根部的Tb及地上部各器官的Eu,Tb均出现正异常。土施大量稀土(400~1200 mg.kg-1)对水稻土及稻根的稀土分布模式有显著影响,对茎、叶略有影响,对籽粒影响不明显。植株各器官对土壤稀土的累积能力依次为根>叶>茎>穗轴、谷壳>籽粒。对照水稻根部对土壤中各稀土元素的吸收积累能力大致相同,仅对Tb有更强的选择性吸收。地上部各器官对中、重稀土的累积能力大于轻稀土,并多数对Eu及Tb有更强的累积。水稻的根部及叶、茎对外施稀土有更强的吸收累积能力,随外施稀土浓度增加,其富集系数随之增高,而穗轴和谷壳、籽粒的富集系数变化不大。植株各器官及籽粒对外施稀土中的Nd都表现出更强的吸收累积作用。     

土壤中稀土对有效氮形态分配和转化的影响

在土壤旱作和淹水培养两种方式下, 通过添加外源稀土研究了黄褐土中稀土对有效氮形态分配和转化的影响.结果表明, 在旱培条件下, 土壤中稀土含量的提高增加铵态氮和水解氮的含量, 减少硝态氮的含量, 两周内增加矿质态氮的含量, 八周以后则无显著影响; 有效氮的含量在稀土含量较低时升高, 高含量时则下降, 实验确定外源稀土对旱培土壤有效氮作用的无观察效应浓度(NOEC)为443.8 mg*kg-1. 在淹水培养条件下, 稀土含量较低时对土壤铵态氮和水解氮含量无显著影响, 含量较高时则降低铵态氮和水解氮含量, 外源稀土对淹水土壤铵态氮和水解氮含量影响的无观察效应浓度分别为 171.2, 256.9 mg*kg-1. 分析表明, 土壤中稀土含量的变化对氮素的影响在旱培条件下主要与稀土对土壤硝化过程作用有关, 淹水条件下与稀土对土壤氨化过程作用有关.     

黄土高原表层土壤中稀土元素含量及其对稀土农用效果的影响

用中子活化法（ＩＮＡＡ）测定了黄土高原地区主要类型土壤（表层）１０４个样品中８个稀土元素（Ｌａ，Ｃｅ，Ｎｄ，Ｓｍ，Ｅｕ，Ｔｂ，Ｙｂ，Ｌｕ），初步探讨了该区土壤中稀土元素的区域分布及对稀土农用效果的影响。结果表明，黄土高原土壤中稀土元素的含量接近全国土壤中的平均含量：主要类型土壤的稀土元素含量分布规律为：灰褐土，娄土＞黑垆土，黄绵土＞灰钙土，与土壤粘粒含量相似，由东南向西北呈下降趋势：该区较适合于农用稀土的推广应用。     

离子吸附型稀土矿稀土提取过程中天然放射性核素分布调查分析

离子吸附型稀土矿中含有天然放射性核素U、Ra-226和Th-232。我国每年生产该类稀土精矿6万t左右,产生大量的废渣、废水,若不加以重视,含放射性核素的冶炼废料可能对环境造成污染,存在危害工人健康的隐患。本文针对该类矿物稀土提取过程天然放射性核素分布进行了初步的调查分析。不同离子吸附型稀土矿矿山中放射性核素的含量不同,不但和原岩性质有关、还与其成矿环境有关。在该类矿物的提取过程中,放射性核素大部分残留在浸出尾矿中,而浸出母液中的少量天然放射性核素经过除杂、沉淀、焙烧工艺后在除杂渣和稀土精矿中得到富集,但其放射性比活度在105Bq·kg~(-1)内。而稀土提取过程中浸出母液、除杂母液、沉淀母液等液体样品中天然放射性核素含量都低于0.3 mg·L~(-1)。本文对稀土提取过程中天然放射性核素分布的初步调查分析,为探讨南方离子吸附型稀土矿放射性核素的迁移富集、分布规律以及放射性污染防治工作提供了基础。     

小麦对稀土元素吸收、分布及积累规律的研究

本文介绍应用示踪原子法研究小麦对镧、铈、钕和钇等稀土元素的吸收和积累规律,并对影响小麦吸收铈的几个因素进行了研究。结果表明,稀土化合物的种类对小麦吸收的影响最大,铈在小麦籽粒中的残留量甚微。     

自然土壤环境下脐橙植物体稀土累积特征

在赣南稀土高背景区(稀土矿区)和稀土低背景区不同土壤脐橙果园分别取岩、土、植物样32组,用ICP-MS法测定样品中15个稀土元素的含量,并对稀土元素在土壤和脐橙植物体内的分布、迁移、累积特征进行研究.结果表明,稀土元素在脐橙植物体内的分布特征是:根>叶>枝>果皮>果肉;稀土元素从A层土→A层土可溶态→根→枝→叶(以及枝→果皮,枝→果肉)的演化、迁移过程中,总的趋势是轻稀土元素所占百分比逐渐增高,重稀土元素所占百分比逐渐降低;高、低稀土背景区脐橙植物体各器官的稀土含量差别由根至果实逐渐缩小,根的稀土含量差别很大,到果肉则差别很小,高、低稀土背景区脐橙果肉的稀土含量均低于限量标准.     

酸雨胁迫及稀土农用条件下菠菜及其土壤中稀土元素的赋存

利用盆栽实验研究了酸雨胁迫、稀土农用条件下 ,菠菜及其土壤中稀土元素的含量及分布特征。结果表明 :菠菜地上部分的REE含量为 0 .5 2 7～ 0 .696μg·g- 1 之间 ,地下部 2 .668～ 3 .0 0 3 μg·g- 1 。土壤 2 2 9.0 9～ 2 5 0 .3 μg·g- 1 。酸雨明显地影响作物对REE的吸收和利用 ,酸度越大 ,影响越明显。随着酸雨酸度的增大、植株体内、土壤中的REE受淋洗的作用加强而表现出REE的总量随着pH的减小而逐渐减少。施用稀土后 ,植株的地上或地下部分及其土壤中的REE含量均与对照的土壤中的REE分配模式基本相同 ,遵循稀土元素分布丰度的奇偶 (Oddo Harkins)规则、轻稀土富集 ,Eu弱负异常 ,富铈配分型 ,表明稀土元素仍然主要来自土壤并受其影响。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.