新的水溶性~(13)C NMR弛豫试剂的性质研究

合成了Gd~(3+)与2,3-二羟基-对-二甲苯胺四乙酸(DPTA)的固体配合物,研究了该化合物作为水溶性~(13)NMR弛豫试剂的性质,证明该试剂对增强各种氨基酸(苏氨酸、半胱氨酸、精氨酸、组氨酸、色氨酸和抗坏血酸)季碳原子的谱峰强度是十分有效的。精氨酸的自旋-晶格弛豫时间(T_1)测量表明,Gd-DPTA可使精氨酸分子中季碳T_1缩短200倍以上,效果优于Gd-DTPA。

用~(13)C-NMR法研究酚酞/双酚T型聚芳醚砜的序列结构

利用~(13)C核磁共振法研究了酚酞/双酚T型聚芳醚砜共聚物((PP/Bis-T)PES)的序列结构,分析了将双酚T单元引入酚酞型聚芳醚砜(PES-C)聚合物分子中对其酚酞单元的核磁共振谱的影响,并证实了(PP/BiS-T)PES属于无规共聚物。

异戊二烯稀土催化聚合过程中配合物结构及其转化的~(13)C-NMR研究

本文用~(13)C-NMR研究了异戊二烯(IP)在均相催化剂(CF_3CO_2)_2LnCl·EtOH—(i-Bu)AlH—o-C_6D_4Cl_2作用下的聚合过程。单体首先被活化同稀土配位生成η~4-IP稀土配合物(反式和顺式),然后η~4-IP的C-3和C-4插入Ln-H键生成η~3-烯丙基稀土配合物——η~3-(2-甲基)丁烯基稀土配合物(同式和对式)。二维~(13)C-NMR交换谱表明η~4-IP和0η~3-烯丙基的每对异构体在常温下分别进行慢交换反应(互变异构),这一过程使插入反应在常温下得以进行。

应用~(13)C—NMR研究大豆籽粒成熟期间糖油的变化

本文应用碳—13核磁共振技术监测大豆籽粒在成熟期间糖、油化学组份变化动态,从而揭示了种子在不同发育阶段能量的输运过程。连续记录谱指定峰的信噪比(S/N)曲线表明脂肪和糖在成熟中期就已形成。这种方法与经典化学方法的结果趋势是一致的。

水溶液中羟脯氨酸稀土配合物的NMR研究

测定了在11种稀土离子(La~(3+)、Pr~(3+)、Nd~(3+)、Eu~(3+)、Tb~(3+)、Dy~(3+)、Ho~(3+)、Er~(3+)、Tm~(3+)、Yb~(3+)和Lu~(3+)存在下羟脯氨酸~(13)C的诱导位移和抗磁性稀土配合物体系的~(1)H化学位移与偶合常数。对配合物构象分析表明,在水溶液中羟脯氨酸以空间位阻小的“外向”构象存在,通过羧基与稀土离子形成双齿配位结构,Ln~(3+)-O键长为2.1。在水溶液中巳配位的与游离的氨基酸和水分子间的快速配位交换平衡导致稀土氨基酸配合物具有有效轴对称性。

~(13)C-NMR化学位移与聚合物的构象——Ⅱ.1,2-聚丁二烯仲碳(—CH_2—)的~(13)C-NMR谱研究

在1,2-聚丁二烯链分子中,导致仲碳(—CH_2—)谱峰分裂的原因是存在着两种gauche排列。在这样一个复杂体系中,由于主链仲碳与叔碳的gauche排列占有重要的位置,因此主链叔碳对化学位移的贡献对于仲碳谱有着决定性的影响。相比之下,乙烯基的贡献要小得多。两种贡献分别是γ_1=—6.37——6.41ppm与γ_2=0.0——1.56ppm。在不计入侧基的影响或同时考虑乙烯基的贡献这两种情况下,均方误差MSE分别是0.166×10~(-2)和0.364×10~(-2)ppm~2。本文同时讨论了模型链的种类、链长以及温度对键概率的影响。并指出有个别反常的情况发生。文中还对间同1,2-聚丁二烯的链结构进行了分析。

模式识别在有机化合物碳—13核磁共振波谱中的应用

本文介绍了以碳—13 NMR 谱为基础,运用模式识别方法对于取代苯类有机化合物的分类情况。数据源为 CIAC-碳-13数据库。特征选择为简单的机率比率法。模式识别方法为Fisher 意义下的判别函数、KNN 及非线性映射。所得结果比较满意。

YP_5O_(14):Er~(3+),Tm~(3+)晶体的合成

研究了水热法合成晶体,浓度配比、生长温度对晶体生长习性的影响.合成了一系列化学计量比的Y_(1-x-0.3)Er_(0.3)Tm_xP_5O_(14)(x=0.01～0.1)晶体,观察和分析了晶体的缺陷及成因,测定和讨论了晶体结构.

1,2-聚丁二烯~(13)C-NMR弛豫的溶剂效应

本文测定了一系列具有不同微观结构的1,2-聚丁二烯样品在四种溶剂的50.3MHz ~(13)C自旋-晶格弛豫时间(T_1)和核Overhauser效应(NOE)值。并用Schaefer logx~2相关时间分布模型对实验数据进行了拟合。研究了1,2-聚丁二烯在溶液中的~(13)C-NMR弛豫的溶剂效应及其与结构的关系。发现聚合物与溶剂的溶解度参数之差△δ越大,聚合物在溶液中协同链段运动趋向越明显,~(13)C自旋-晶格弛豫速率(1/T_1)越大;1,2-链节较少,分子链较柔顺时,~(13)C-NMR弛豫受溶剂影响较显著。NMR弛豫参数对结构变化的反应在良溶剂中比在不良溶剂中敏感。

Vertical distribution of bacterial and archaeal communities along discrete layers of a deep-sea cold sediment sample at the East Pacific Rise (similar to 13 degrees N)

The community structure and vertical distribution of prokaryotes in a deep-sea (ca. 3,191 m) cold sediment sample (ca. 43 cm long) collected at the East Pacific Rise (EPR) similar to 13 degrees N were studied with 16SrDNA-based molecular analyses. Total community DNA was extracted from each of four discrete layers EPRDS-1, -2, -3 and -4 (from top to bottom) and 16S rDNA were amplified by PCR. Cluster analysis of DGGE profiles revealed that the bacterial communities shifted sharply between EPRDS-1 and EPRDS-2 in similarity coefficient at merely 49%. Twenty-three sequences retrieved from DGGE bands fell into 11 groups based on BLAST and bootstrap analysis. The dominant groups in the bacterial communities were Chloroflexi, Gamma proteobacteria, Actinobacterium and unidentified bacteria, with their corresponding percentages varying along discrete layers. Pairwise Fst (F-statistics) values between the archaeal clone libraries indicated that the archaeal communities changed distinctly between EPRDS-2 and EPRDS-3. Sequences from the archaeal libraries were divided to eight groups. Crenarchaea Marine Group I (MGI) was prevalent in EPRDS-1 at 83%, while Uncultured Crenarchaea group II B (UCII B) abounded in EPRDS-4 at 61%. Our results revealed that the vertically stratified distribution of prokaryotic communities might be in response to the geochemical settings and suggested that the sampling area was influenced by hydrothermalism. The copresence of members related to hydrothermalism and cold deep-sea environments in the microbial community indicated that the area might be a transitional region from hydrothermal vents to cold deep-sea sediments.

A new naphthoquinoneimine derivative from the marine algal-derived endophytic fungus Aspergillus niger EN-13

Cultivation of an endophytic fungus Aspergillus niger EN-13 that was isolated from the inner tissue of the marine brown alga Colpomenia sinuosa resulted in the characterization of a new naphthoquinoneimine derivative, namely, 5,7-dihydroxy-2-[1-(4methoxy-6-oxo-6H-pyran-2-yl)-2-phenylethylaniino]-[1,4]naphthoquinone. The structure of the new compound was established on the basis of various NMR spectroscopic analyses including 2D NMR techniques, EI-MS, and HR-ESI-MS. This compound displayed moderate antifungal activity. (c) 2007 Bin Gui Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.