自我介绍一下

gd526

我个人在英国某大学攻读博士学位

主要研究方向是无机化学反应机理推测

" h5 v! c$ N' W6 C; a, `- P

 

既然是机理，就要找关键中间体

我们用的主要就是nmr和para-hydrogen，中文叫做仲氢，我个人认为叫异氢更为合适些

/ m" A* T4 w8 b& r" K0 \; \: k

 

para-hydrogen最大的好处就是和金属发生氧化加成反应后的信号是增强的，理论上来说，金属氢化物的核磁信号要被放大31200倍

换句话说，三万分之一浓度的中间体，会和正常试样给出相同强度的nmr信号。

 

这个反应本身具有一定局限性，但是经过研究发现，para-hydrogen对nmr信号的增强效应，可以使得相关的氮谱和碳谱有效增强，最好的结果是

碳谱一次扫描得到的结果，相当于正常碳谱扫描58天的结果。同时，para-hydrogen的nmr增强效应，可以沿着氢的可逆转移，不衰减的转移到有机物上。在nmr信号上，具有anti-phase的信号，往往都是来自para-hydrogen上过来的。

 

实验室有五台nmr可供使用，600的常年用于DNP，一台400的用于激光光解反应，一台500的和两台400的用于日常科研。

日常运行由一个兼职的博士（大牛，博二发了science）管理，Bruker的客服人员几乎就常住这里了，因为整个学院，有12台他们的nmr。

* U/ M# Y1 u6 S) W6 c0 i& R- D- I

 

* |* U. E$ f$ J2 [

老板主要是搞DNP的，我这一级博士，三个DNP的博士，一个我，搞无机化学

/ N- A/ Z% s! m3 w% w Q / ]1 Y* S7 ~7 Q

celan

欢迎LZ来传经送宝。

celan

下面是一些这方面研究的文摘，这是个很有意义的工作。

Para-hydrogen enrichment and hyperpolarization

Enrichment of hydrogen gas into its para isomer (corresponding to nuclear spins in the singlet state); this is a necessary condition to obtain hyperpolarization from transfer of the relevant population excess. This transfer is generally mediated by a hydrogenation reaction such that the two protons become nonequivalent. The energy level populations of this new spin system can be calculated unambiguously using a density matrix formalism. This formalism is reviewed, and the authors propose a simple method that leads to the spin state after the hydrogenation reaction and the insertion of the sample in the NMR magnet. The effect of radio-frequency pulses is also considered.

[此贴子已经被作者于2010-6-16 9:17:59编辑过]

w q" C1 u `4 E4 y- k P( N, N( x

celan

Reversible Interactions with para-Hydrogen Enhance NMR Sensitivity by Polarization Transfer

The sensitivity of both nuclear magnetic resonance spectroscopy and magnetic resonance imaging is very low because the detected signal strength depends on the small population difference between spin states even in high magnetic fields. Hyperpolarization methods can be used to increase this difference and thereby enhance signal strength. This has been achieved previously by incorporating the molecular spin singlet para-hydrogen into hydrogenation reaction products. We show here that a metal complex can facilitate the reversible interaction of para-hydrogen with a suitable organic substrate such that up to an 800-fold increase in proton, carbon, and nitrogen signal strengths are seen for the substrate without its hydrogenation. These polarized signals can be selectively detected when combined with methods that suppress background signals.

celan

支持LZ,名词解释

# A) l$ o6 @- V/ B! s! q K" |

ortho-hydrogen and para-hydrogen正氢和仲氢，是双原子分子氢的两种量子态。它有两个质子，质子是费米子，具有半整数的自旋，氢分子中两个质子自旋平行的称为正氢，它可以取两自旋向上、向下或垂直纵轴，所以有三种状态，而两质子自旋反平行的称为仲氢，它只有一种状态。

fangjing

欢迎楼主，好深奥呢。

这个信号增强对普通的N谱或者C谱信号的增强有没有借鉴作用？

celan

Parahydrogen-Induced Polarization in Heterogeneous Hydrogenations Catalyzed by an Immobilized Au(III) Complex

 

" i( ]; S3 E0 @: m) R& C

Hydrogenation of unsaturated compounds with parahydrogen can lead to an enhancement of the NMR signals of reaction products by several orders of magnitude. Parahydrogen-induced polarization (PHIP) of nuclear spins is useful for developing both novel MRI applications as well as hypersensitive tools for operando studies in catalysis, but until recently, PHIP was observed only in homogeneous hydrogenations. To assess the potential of combining PHIP with heterogeneous catalysis, heterogeneous gas-phase hydrogenation of propene and propyne with parahydrogen was carried out using a Au(III) Schiff base complex immobilized within a metal?organic framework material IRMOF-3. Observation of PHIP in the ¹H NMR spectra of reaction products implies that both hydrogen atoms of a single H₂ molecule are transferred as a pair to the same product molecule and supports the conclusions made earlier that the well-defined isolated Au(III) centers of this catalyst are the active sites involved in hydrogen activation.

. C- c$ C/ ?: E6 n- ^6 `

[此贴子已经被作者于2010-6-16 9:56:42编辑过]

: F2 c0 A6 L; T' T

celan

Para-Hydrogen Induced Polarization without Incorporation of Para-Hydrogen into the Analyte

 Related methods are then used to facilitate the sensitization of the free pyridine ¹⁵N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.

[此贴子已经被作者于2010-6-16 10:06:31编辑过]

3 y$ V4 Y) @% t ?/ b! n/ x

syflu

  学习学习

rayanlcc

顶顶~~