中国实验快堆生产同位素~(60)Co的优化设计研究

中国实验快堆(CEFR)是我国建设的第一座金属钠冷却快中子反应堆,其特点是比功率高、中子注量率高。由于CEFR能谱硬、中子泄漏多,本工作对利用这部分泄漏中子在快堆反射层生产~(60)Co同位素进行了可行性研究,并通过引入慢化剂设计适合的几何结构、选择合理的辐照位置和辐照时间等一系列措施对同位素生产进行优化,以提高~(60)Co比活度。优化中采用MCNP和ORIGEN2程序作为计算软件。计算结果表明,通过优化设计,~(60)Co比活度有显著提高,说明利用快堆反射层的泄漏中子生产~(60)Co是可行的。     

不同水汽源控制下的降水同位素分布特征

根据全球大气降水同位素网络中国33个站点降水与气象资料,结合已有中国各地区降水同位素的研究,系统分析了5种不同季风对中国大气降水同位素组成的影响。各个不同水汽来源区表现出的主要的同位素环境地理效应不同。对比分析冬夏稳定同位素分布规律,在夏季δ18O空间分布规律能够更好揭示水汽运移路线,尤其是东部沿海地区。对乌鲁木齐、石家庄、香港三个站点时间序列对比分析,发现不同季风控制下水汽来源对同位素变化具有决定性作用。     

徐家围子断陷深层天然气地球化学特征及成因

以试气井段为单位对徐家围子断陷深层天然气进行分析,探索各气藏天然气组成及碳同位素的分布规律。研究表明:乙烷碳同位素在平面上存在明显差异,断陷边部乙烷碳同位素较重,具有煤型气特征,断陷中部乙烷碳同位素较轻,达到油型气标准;天然气C_5以上的重烃碳同位素异常轻,可能来源于原油裂解;碳同位素反序的天然气不一定是无机成因,复杂的碳同位素序列可能是油型气和煤型气混合造成;无机成因烃气数量甚微,不可能单独成藏。     

南岭地区多金属矿床铅同位素组成差异分析

南岭地区是我国多金属矿床重要的基地,为了解该区多金属矿床成矿物质来源特点方面的差异,选择利用铅同位素示踪技术,对区内黄沙坪、宝山、凡口、大宝山、大厂5个不同多金属矿床成矿物质来源特征进行统计分析。结果表明,黄沙坪、宝山、大宝山3个多金属矿床中铅的来源相同且形成于燕山运动第一次成矿期高峰期(180~155 Ma),凡口、大厂2个多金属矿床铅的来源相同,形成于燕山运动第二成矿高峰期(115~90 Ma)。南岭地区多金属矿床形成的构造背景与华南地区中生代处于拉张构造背景一致,多金属矿床的形成是晚中生代以来华南地区岩石圈伸展作用的结果。     

新疆金山金矿床硫铅碳同位素组成及对成矿物质的示踪

新疆伊宁县金山金矿床是一正在进行勘探的大型金矿床,属于浅成低温热液型金矿床,金山金矿床产于下石炭统大哈拉军山组火山岩下部.对矿床的硫铅碳同位素组成研究表明:矿床中δ34S值变化较大(-12.7‰～l7.4‰),大部分硫同位素与中酸性岩浆硫同位素值接近,部分来自于地层中海相硫酸盐的溶解;矿石金属硫化物的206 Pb/20...     

金属氢化物法分离氢同位素研究进展

简要介绍了近50多年来金属氢化物法氢同位素分离研发进展和现状。基于金属氢化物法在化学吸附平衡上的差异,各国发展了多种增强该吸附差异的氢同位素分离方法,并对相关吸附材料进行了研究。本文主要介绍了金属氢化物分离氢同位素方法的产生、发展简史,以及各国相关研究的特点和最新进展,并对今后的氢同位素分离研究发展提出初步的想法。     

磁式电感耦合等离子体质谱仪及其在核地质分析中的典型应用

磁式电感耦合等离子体质谱（ICP-SFMS）主要包括高分辨等离子体质谱（HR-ICP-MS）、多接收等离子体质谱（MC-ICP-MS）和全谱等离子体质谱（Spectro-ICP-MS）。HR-ICP-MS一般采用反向Nier-Johnson结构磁 电双聚焦布置,MC-ICP-MS采用正向Nier-Johnson结构电-磁双聚焦布置,而采用检测器阵列的全谱磁式ICP-MS则采用Mattauch Herzog结构布置。磁式电感耦合等离子体质谱仪性能改进主要体现在：调频ICP设计提高了对基体的耐受性及可靠性;采用J型采样锥和X型截取锥提高了灵敏度;大抽速接口泵可提高接口区真空度和仪器的灵敏度;改进的离子传输透镜系统可提高对锕系同位素的丰度灵敏度;改变接收器前的狭缝宽度可获得高分辨同位素比值;多个Daly检测器的使用可提高对低丰度同位素的检测能力;通过软件自动切换法拉第杯放大器高阻,能提高低丰度同位素测量的信号输出。磁式ICP-MS性能的改善,使其在核地质分析中的应用更广泛。使用激光烧蚀高分辨等离子体质谱（LA-HR-ICP-MS）可进行铀矿物微区原位U-Pb定年,使用MC-ICP-MS可高精密度地测定U同位素分馏,采用无熔剂制样LA-HR-ICP-MS可测定U、Th、Nb、Ta、Zr、Hf等难溶元素。     

Revisiting the Mechanism of β-O-4 Bond Cleavage During Acidolysis of Lignin. Part 6: A Review

ABSTRACT

This paper reviews our results on the acidolysis of dimeric non-phenolic β-O-4-type lignin model compounds in aqueous 82% 1,4-dioxane containing an acid at 85°C. It was shown that the mechanism of a C₆-C₂-type model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol IX, is fairly different from that of a C₆-C₃ analogue, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol XX, suggesting the significance of the presence of the γ-hydroxymethyl group. It was confirmed that the hydride transfer mechanism exists as a reaction route of the benzyl-cation-type intermediates derived from both compounds, and the contribution of this mechanism is greater than expected in the acidolysis of compound XX. An enol ether compound, 2-(2-methoxyphenoxy)-3-(3,4-dimethoxyphenyl)prop-2-en-1-ol, was first detected in the acidolysis of compound XX using the DBr/D₂O/1,4-dioxane system. It was confirmed in the acidolysis of compound XX using HBr that the mechanism is different from that in the system using either HCl or H₂SO₄ and an unknown mechanism contributes to the reaction. This unknown mechanism surprisingly contributed more with decreasing concentration of HBr or Br^?, provided that Br^? still existed in the system.     

Role of Long-Range Protein Dynamics in Different Thymidylate Synthase Catalyzed Reactions

Recent studies of Escherichia coli thymidylate synthase (ecTSase) showed that a highly conserved residue, Y209, that is located 8 Å away from the reaction site, plays a key role in the protein’s dynamics. Those crystallographic studies indicated that Y209W mutant is a structurally identical but dynamically altered relative to the wild type (WT) enzyme, and that its turnover catalytic rate governed by a slow hydride-transfer has been affected. The most challenging test of an examination of a fast chemical conversion that precedes the rate-limiting step has been achieved here. The physical nature of both fast and slow C-H bond activations have been compared between the WT and mutant by means of observed and intrinsic kinetic isotope effects (KIEs) and their temperature dependence. The findings indicate that the proton abstraction step has not been altered as much as the hydride transfer step. Additionally, the comparison indicated that other kinetic steps in the TSase catalyzed reaction were substantially affected, including the order of the substrate binding. Enigmatically, although Y209 is H-bonded to 3''-OH of 2''-deoxyuridine-5''-mono­phosphate (dUMP), its altered dynamics is more pronounced on the binding of the remote cofactor, (6R)-N⁵,N¹⁰-methylene-5,6,7,8-tetrahydrofolate (CH₂H₄folate), revealing the importance of long-range dynamics of the enzymatic complex and its catalytic function.     

稳定同位素标记妥布特罗-D9的合成

以自制的叔丁胺-D9为同位素标记前体,以邻氯苯乙酮为起始原料,溴化后,再与叔丁胺-D9经胺化、硼氢化钠还原后得到稳定同位素标记布特罗-D9。采用均匀设计对胺化步骤进行研究,实验数据通过多元回归分析,得出了优化的工艺条件:反应温度59℃,反应时间5 h,三氯甲烷为25 m L,n(溴代酮)∶n(叔丁胺-D9)=1∶2。目标产物结构经质谱(MS)、核磁(NMR)、高效液相色谱(HPLC)表征,产物纯度高于98.0%,同位素丰度高于97.5%(atom D),可作为食品安全领域检测用同位素内标试剂。