Department of Chemistry, Brandeis University, MS 015, Waltham, Massachusetts 02454-9110, USA.
Acc Chem Res. 2012 Dec 18;45(12):2160-8. doi: 10.1021/ar200251j. Epub 2011 Dec 28.
Evolution is a characteristic feature of living systems, and many fundamental processes in life, including the cell cycle, take place in a periodic fashion. From a chemistry perspective, these repeating phenomena suggest the question of whether reactions in which concentrations oscillate could provide a basis and/or useful models for the behavior of organisms, and perhaps even their ability to evolve. In this Account, we examine several aspects of the behavior of the prototype oscillating chemical reaction, the Belousov-Zhabotinsky (BZ) system, carried out in microemulsions, arrays of micrometer-sized aqueous droplets suspended in oil, or hydrogels. Each of these environments contains elements of the compartmentalization that likely played a role in the development of the first living cells, and within them we observe behaviors not found in the BZ reaction in simple aqueous solution. Several of these phenomena resemble traits displayed by living organisms. For example, the nanodroplets in a BZ microemulsion "communicate" with each other through a phenomenon analogous to quorum sensing in bacteria to produce a remarkable variety of patterns and waves on length scales 10(5) times the size of a single droplet. A photosensitive version can "remember" an imposed image. Larger, micrometer-sized droplets exhibit similarly rich behavior and allow for the observation and control of individual droplets. These droplets offer promise for building arrays capable of computation by varying the strength and sign of the coupling between drops. Gels that incorporate a BZ catalyst and are immersed in a solution containing the BZ reactants change their shape and volume in oscillations that follow the variation in the redox state of the catalyst. Using this phenomenon, we can construct phototactic gel "worms" or segments of gel that attract one another. Whether such systems will provide more realistic caricatures of life, and whether they can serve as useful materials will largely depend on the successful integration of various properties, including communication, motion, and memory, which we observed in separate experiments. Theoretical approaches that couple reaction and diffusion processes to mechanical and other material properties are likely to play a key role in this integration, and we describe one such approach. The evolution of systems of coupled chemical oscillators presents another challenge to the development of these systems, but one that we expect to be solved.
进化是生命系统的一个特征，生命中的许多基本过程，包括细胞周期，都是周期性发生的。从化学的角度来看，这些重复出现的现象引发了一个问题，即浓度振荡的反应是否可以为生物体的行为提供基础和/或有用的模型，甚至为它们的进化能力提供基础和/或有用的模型。在本报告中，我们研究了在微乳液、微米级水滴滴阵列悬浮在油中或水凝胶中进行的原型振荡化学反应、Belousov-Zhabotinsky（BZ）系统的几个方面。这些环境中的每一个都包含了可能在第一个生命细胞的发展中发挥作用的分隔元素，在这些环境中，我们观察到了在简单水溶液中的 BZ 反应中没有发现的行为。其中一些现象类似于生物体表现出的特征。例如，BZ 微乳液中的纳米液滴通过类似于细菌群体感应的现象相互“通信”，在比单个液滴大 10^5 倍的长度尺度上产生各种图案和波。光敏版本可以“记住”施加的图像。更大的微米级液滴表现出类似的丰富行为，并允许观察和控制单个液滴。这些液滴有望通过改变液滴之间的耦合强度和符号来构建能够进行计算的阵列。将包含 BZ 催化剂的凝胶浸入含有 BZ 反应物的溶液中，凝胶的形状和体积会随催化剂氧化还原状态的变化而发生振荡变化。利用这一现象，我们可以构建趋光凝胶“蠕虫”或凝胶段，它们相互吸引。这些系统是否会提供更现实的生命漫画，以及它们是否可以作为有用的材料，在很大程度上取决于各种性质的成功整合，包括我们在单独实验中观察到的通信、运动和记忆。将反应和扩散过程与机械和其他材料性质耦合的理论方法可能在这种整合中发挥关键作用，我们描述了其中一种方法。耦合化学振荡器系统的进化给这些系统的发展带来了另一个挑战，但我们预计这个挑战将得到解决。
