从铁(II) -tris[2,2'-bi(tetrahydropyrimidine) ]到TEMPO的原子转移:由马库斯方程预测的负度的激活
Elizabeth A Mader1, Anna S Larsen, James M Mayer
1Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700.
Journal of the American Chemical Society
|July 1, 2004
概括
研究了铁复合体和TEMPO之间的质子合电子转移 (PCET). 该反应表现出异常的负激活度,支持马库斯理论对原子转移反应的预测.
科学领域:
- 无机化学 无机化学 有机化学
- 化学动力学 化学动力学
- 物理化学 物理化学
背景情况:
- 质子合电子转移 (PCET) 是化学和生物学的一个基本反应机制.
- 了解PCET的动力学和热力学对于设计新的催化剂和储能系统至关重要.
- 铁复合物和氧化物激素如TEMPO在各种催化和氧化还原过程中都很重要.
研究的目的:
- 为了研究从铁 (II) 复合体转移到TEMPO的原子转移的动力学和热力学.
- 为了确定前向和反向PCET反应的速率常数和激活参数.
- 评估马库斯理论在预测这种PCET反应的行为中的适用性.
主要方法:
- 停止流动的紫外线视频光度测量被用来实时监测反应.
- 分析了动力数据,以确定298K的速率常数.
- 计算了热力学参数,包括激活和.
主要成果:
- 前期速率常数 (k1) 确定为260 ± 30 M−1s−1,反向速率常数 (k-1) 为150 ± 20 M−1s−1.1.
- 在前置反应中观察到异常的负激活度 (ΔH1 = -2.7 ± 0.4 kcal mol-1).
- 马库斯理论使用独立测量的自我交换参数成功预测了观察到的温度依赖.
结论:
- 这项研究表明,马库斯理论对于分析复杂的PCET反应具有实用性.
- 负激活度主要是由反应的有利度驱动的,而不是自我交换.
- 这项研究提供了关于铁-TEMPO系统中原子转移机制的见解.
相关概念视频
Radioactivity and Nuclear Equations
Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for hydrogen, neutrons. The number of protons in the nucleus is called the atomic number (Z) of the element, and the sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are isotopes of the same element.
A nuclide of an element has a specific number of protons and...
A nuclide of an element has a specific number of protons and...
Nuclear Transmutation
Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with another particle. The first manmade nucleus was produced in Ernest Rutherford’s laboratory in 1919 by a transmutation reaction, the bombardment of one type of nuclei with other nuclei or with neutrons. Rutherford bombarded nitrogen-14 atoms with high-speed α particles from a natural radioactive isotope of radium and observed protons being...
Atomic Nuclei: Nuclear Spin State Population Distribution
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
Atomic Nuclei: Nuclear Relaxation Processes
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...
Transmission Electron Microscopy
In 1931, physicist Ernst Ruska—building on the idea that magnetic fields can direct an electron beam just as lenses can direct a beam of light in an optical microscope—developed the first prototype of the electron microscope. This development led to the development of the field of electron microscopy. In the transmission electron microscope (TEM), electrons are produced by a hot tungsten element and accelerated by a potential difference in an electron gun, which gives them up to 400 keV in...
Transition State Theory
Transition-state theory, also known as activated-complex theory, provides a molecular-level explanation of reaction rates in both gas-phase and solution-phase reactions. It extends earlier kinetic models by considering the formation of a short-lived, high-energy configuration during a reaction.The progress of a chemical reaction can be represented using a reaction profile, which plots potential energy against the reaction coordinate. As two reactant molecules approach one another, their...


