Folli Andrea, Choi Heungjae, Barter Michael, Harari Jaafar, Richards Emma, Slocombe Daniel, Porch Adrian, Murphy Damien M
School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, UK.
School of Engineering, Cardiff University, The Parade, Cardiff CF24 3AA, UK.
J Magn Reson. 2020 Jan;310:106644. doi: 10.1016/j.jmr.2019.106644. Epub 2019 Nov 13.
A unique dual mode X-band Continuous Wave (CW) EPR resonator designed for simultaneous EPR measurement and rapid microwave (MW) induced sample heating is described. Chemical reactions subjected to a flow of energy and matter can be perturbed away from the thermodynamic equilibrium by imposing a rapid shock or physical change to the system. Depending on the magnitude of the perturbation, these changes can dictate the subsequent evolution of the entire system, allowing for instance to populate non-equilibrium reactive intermediate states. Temperature jump (T-jump) experiments are a common method to achieve such perturbations. Most T-jump experiments are based on Joule Heating methods or IR lasers. Here we demonstrate the principle of rapid sample heating based on microwaves. The benefits of MW heating include (i) rapid and efficient heating (i.e. using a tuned resonant cavity, >99% efficient power transfer to the sample can be achieved), and (ii) volumetric heating (i.e. the entire sample volume rises in temperature at once, since heat is generated in the sample instead of being transferred to it). Accordingly, the key concept of the design is the use of a cavity resonator allowing EPR detection (at 9.5 GHz) and simultaneous sample heating (at 6.1 GHz). Temperature increments of 50 °C within a few seconds are possible. This is evidenced and illustrated here by probing the temperature-induced variation of the rotational dynamics of 16-doxyl stearic acid methyl ester (16-DSE) spin probe grafted on the surface of sodium dodecyl sulphate (SDS) micelles in water, as well as copper (II) acetylacetonate in chloroform. Rapid changes in the rotational dynamics of the paramagnetic centres provide direct evidence for the in situ and simultaneous EPR measurement-heating capabilities of the resonator. Improvements afforded by the use of pulsed MW sources will enable faster heating time scales to be achieved. In the longer term, this current study demonstrates the simple and direct possibilities for using MW heating as a means of performing T-jump experiments.
本文描述了一种独特的双模式X波段连续波(CW)电子顺磁共振(EPR)谐振器,该谐振器设计用于同时进行EPR测量和快速微波(MW)诱导的样品加热。通过对系统施加快速冲击或物理变化,使经历能量和物质流动的化学反应偏离热力学平衡。根据扰动的大小,这些变化可以决定整个系统的后续演化,例如允许填充非平衡反应中间态。温度跃升(T-jump)实验是实现这种扰动的常用方法。大多数T-jump实验基于焦耳加热方法或红外激光。在此,我们展示了基于微波的快速样品加热原理。微波加热的优点包括:(i)快速高效加热(即使用调谐谐振腔,可实现>99%的高效功率传输到样品),以及(ii)体积加热(即整个样品体积同时升温,因为热量在样品中产生而不是传递到样品中)。因此,该设计的关键概念是使用一个腔谐振器,允许进行EPR检测(9.5 GHz)和同时进行样品加热(6.1 GHz)。在几秒钟内实现50°C的温度增量是可能的。通过探测接枝在水中十二烷基硫酸钠(SDS)胶束表面的16-二氧硬脂酸甲酯(16-DSE)自旋探针以及氯仿中的乙酰丙酮铜(II)的旋转动力学随温度的变化,在此得到了证明和说明。顺磁中心旋转动力学的快速变化为谐振器的原位和同时EPR测量-加热能力提供了直接证据。使用脉冲微波源带来的改进将能够实现更快的加热时间尺度。从长远来看?当前的这项研究证明了使用微波加热作为进行T-jump实验手段的简单直接可能性。 注:原文中“从长远来看?”这里的问号疑似多余字符,译文按正常理解翻译。