Non-reciprocal interactions between molecules have long been an enigmatic phenomenon that defies our understanding of fundamental forces. In a recent groundbreaking study, researchers from the University of Maine and Penn State have shed light on this puzzle, uncovering a mechanism by which molecules can interact non-reciprocally without the need for external forces. This discovery not only challenges previous explanations but also opens up new avenues of research in understanding complex behavior in living organisms.
Gravity and electromagnetism, two of the fundamental forces governing the universe, are regarded as reciprocal forces. They dictate that two objects will either be attracted to or repelled by each other. However, in our everyday experiences, we witness countless instances where interactions do not conform to this reciprocal law. For instance, a predator may be attracted to its prey, while the prey attempts to flee from its predator. Such non-reciprocal interactions are vital for the complex behavior exhibited by living organisms.
Until now, the mechanism behind non-reciprocal interactions in microscopic systems such as bacteria has been attributed to hydrodynamic or other external forces. It was widely believed that similar types of forces accounted for the interactions between single molecules. However, the study published in Chem by UMaine physicist R. Dean Astumian and collaborators unveil a groundbreaking new mechanism.
The researchers propose that non-reciprocal interactions between single molecules can be explained by the local gradients of reactants and products facilitated by chemical catalysts. These catalysts, such as enzymes in biological systems, exhibit a property known as kinetic asymmetry. This property controls the direction of response to a concentration gradient, causing one molecule to be repelled by another while attracting a different molecule. The “Eureka moment” occurred when the authors realized that this kinetic asymmetry is an inherent property of the catalyst itself, allowing for evolution and adaptation.
The implications of this discovery are far-reaching. Non-reciprocal interactions, made possible by kinetic asymmetry and catalysts, play a vital role in the interaction of molecules with each other. These interactions may have played a pivotal role in the emergence of complex matter from simple molecules. Previous research in the field of “active matter” has introduced non-reciprocal interactions through ad hoc forces. However, this study provides a fundamental molecular mechanism for the occurrence of such interactions between single molecules.
The researchers’ work builds upon their earlier findings on the directional motion of catalyst molecules in a concentration gradient. The role of kinetic asymmetry in determining non-reciprocal interactions has also been observed in biomolecular machines and has even been incorporated into the design of synthetic molecular motors and pumps.
This collaboration between Astumian, Sen, and Mandal aims to uncover the organizational principles behind the loose associations of different catalysts that may have contributed to the formation of early metabolic structures. Understanding kinetic asymmetry holds the potential to unravel the mystery of how life evolved from simple molecules.
“We’re at the very beginning stages of this work, but I see understanding kinetic asymmetry as a possible opportunity for understanding how life evolved from simple molecules,” says Astumian.
The discovery of a mechanism by which molecules can interact non-reciprocally without external forces marks a significant milestone in our understanding of complex behavior in living organisms. The role of catalysts and their inherent property of kinetic asymmetry sheds new light on the puzzling phenomenon of non-reciprocal interactions. As research in this field progresses, we inch closer to comprehending the intricate processes that shaped the evolution of life.
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