「Spotlight Research」光切换亚胺驱动动态共价系统达到非平衡稳态

热点研究

「Spotlight Research」光切换亚胺驱动动态共价系统达到非平衡稳态

2024/7/25
热点研究
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Author: CS editor

作者：石油醚

本期热点研究，我们邀请到了本文第一作者来自德国维尔茨堡大学的博士生邬佳蓉为我们分享。

2024年7月18日，J. Am. Chem. Soc.在线发表了来自德国维尔茨堡大学Jake L. Greenfield教授团队题为「Photoswitchable Imines Drive Dynamic Covalent Systems to Nonequilibrium Steady States」的研究论文。该文中，将亚胺分子开关的光异构化过程与亚胺交换反应耦合，成功实现使用光照将热力学平衡态推向能量更高的状态，达到非平衡稳定态（NESS）。表面上看这是一个非常简单的系统，只有由一种醛和两种胺组成的两种亚胺分子，但是整个系统却包含非常多的信息，形成了一个“信息棘轮”。

“Photoswitchable Imines Drive Dynamic Covalent Systems to Nonequilibrium Steady States

Jiarong Wu，Jake L. Greenfield*

J. Am. Chem. Soc., 2024, DOI: 10.1021/jacs.4c03817”

Q1. 请对“Photoswitchable Imines Drive Dynamic Covalent Systems to Nonequilibrium Steady States”作一个简单介绍。

亚胺分子中包含一个动态化学键（C=N），在一定条件下可进行可逆的水解或缩聚反应，因此常常被使用在自组装或自修复材料的设计之中。作为偶氮（N=N）类分子开关的类似物，亚胺键在光照条件下也可以发生顺反异构，但是由于它们通常表现出欠佳的“分子开关”性能，比如热力学不稳定（表现为介稳态在室温下小于一分钟的半衰期），以及在光照下只有一小部分分子能发生异构，导致亚胺作为分子开关的潜力长期被忽视。

今年年初，我们在Chemical Science上报道了一种能显著提升亚胺分子作为分子开关性能的策略(https://doi.org/10.1039/D3SC05841G)，实现了可见光下E构型到Z构型的完全转化，热力学半衰期可达19.2小时。这也是我们课题组的第一篇文章。

基于这篇文章，我们最近在JACS上发表了我们的最新工作，将亚胺分子开关的光异构化过程与亚胺交换反应耦合，成功实现使用光照将热力学平衡态推向能量更高的状态，达到非平衡稳定态（NESS）。表面上看这是一个非常简单的系统，只有由一种醛和两种胺组成的两种亚胺分子，但是整个系统却包含非常多的信息，形成了一个“信息棘轮”。

Imines (C=N) are well-known for their dynamic-covalent properties and are widely used in the field of self-assembly and in designing self-healing materials due to their reversible condensation/hydrolysis behaviour. However, as analogues to azo-based photoswitches, which can undergo E/Z photoisomerization, their photoswitching properties have long been overlooked. This can be attributed to their poor photoswitching properties, for example, thermal half-lives of their metastable state being less than 1 minute at room temperature and low amounts of the metastable state being generated under photoirradiation.

Earlier this year, we discovered imines that exhibit much improved, and useful, photoswitching properties, and published the group’s first paper in Chemical Science (https://doi.org/10.1039/D3SC05841G). Specifically, we significantly optimized the photoswitching behavior of imines, achieving thermal half-lives of up to 19.2 hours and an almost quantitative conversion from E- to Z-isomer under visible light.

Building on this foundation, our recent work published in JACS showcases the coupling of the imine photoswitching process with a thermal transimination equilibrium. By utilizing light, we successfully drove the thermal equilibrium energetically uphill, to a non-equilibrium steady state (NESS). This system, remarkably simple with just one aldehyde and two different amine components forming a distribution of two imines, contains much more information within, making the entire system an “information ratchet.”

Q2. 有关本次研究的时候遇到过怎样的困难呢？又是怎样克服的呢

这个工作中最有挑战性的部分是动力学研究。虽然整个系统看起来很简单，但是在光照下情况会变得很复杂，有各种光异构和热力学反应同时进行，由于系统中胺始终是过量的，还会有无法检测到的胺缩醛中间体参与的顺反异构和亚胺交换反应（如图所示）。为了研究清楚这个系统中的每一条路径分别有怎样的贡献，我们把它拆分成了几个小部分，并且进行了一系列控制实验，最终成功分析了这个系统。

The most challenging part of this project was the kinetic studies. Although the system appears simple, under irradiation, several pathways can potentially occur, involving transient and undetectable aminal intermediates (as shown in the figure). To gain a proper understanding of this system, we broke it down into smaller bits and designed a series of control experiments to investigate the impact of each pathway on the overall system. Through this approach, we ultimately succeeded in analyzing the system.

Q3. 本次研究主体，有没有什么让您感觉特别辛苦和烧脑呢？

说实话这一整个工作都挺烧脑的（但很有趣！），因为明明是看起来很简单的系统，但是表现却很复杂。比如作为一个“棘轮”，应该可以计算棘轮常数来展示循环的通量，然而在我们的四组分系统（E-1, Z-1, E-2, Z-2）中，有两个循环，每个循环都有两个方向，导致不能使用简单的棘轮常数来表征循环通量。这是因为亚胺键既能够光响应，又是动态共价键，这在之前报道过的分子信息棘轮中是从未出现过的。

This entire project was quite brain-burning, with it being a simple system with complex behaviour, but also incredibly interesting! For instance, as a “ratchet,” it should be possible to calculate the ratcheting constant to demonstrate the flux of the cycles. However, in our four-component system (E-1, Z-1, E-2, Z-2), there are two cycles, each with two directions. This is unique in molecular information ratchets so far, as the imines are both light-responsive and dynamic-covalent motif simultaneously, which hasn’t been shown before.

Q4. 将来想继续研究化学的哪个方向呢？

系统化学，以及由动态共价化学制成的分子机器。我们正在尝试利用我们的亚胺开关在这些领域内拓展新的可能性。如果有合作想法也欢迎和我们联系！

Systems chemistry, and molecular machines made from dynamic covalent chemistry. We are actively working in these areas where we use our imine switches to achieve new properties. We are also open to collaborations so please get in touch with us!

Q5. 最后，有什么想对各位读者说的吗？

我们是一个对探索新领域有强烈热情的国际化课题组，如果您有能让亚胺开关实现更多有趣可能性的想法，欢迎联系我们！我们欢迎合作，也欢迎拥有同样热情的博士生和博士后！

对于那些同样刚开始独立职业生涯的人，我们的建议是，在设计、创造全新的东西之前仔细思考前人已经做过的事情，因为有趣的观察和新颖性会从这里产生。

We are an international research group with a very strong motivation to explore new frontiers. We are open to collaborations where we can see if our imine-switches can give added value (please get in contact), and we are also open to hosting highly motivated Post-Docs and PhD researchers.

Our advice to others also at the beginning of their independent career is to think carefully about what has already been done, and then design something significantly new, create something that hasn’t been achieved before as this is where the interesting observations, impact and novelty will surely come.