Reaction and transport in active chemcal systems

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Active complex systems that use chemical reactions to drive their dynamics are ubiquitous in nature. The term “active systems” has a broad usage, but the focus of this research is on dense systems whose active solute or suspended species are either self-propelled or undergo conformational changes as a result of chemical reactions. Our aim is to discover the factors that control the behavior of active systems in order to understand, at a fundamental level, how they operate and how this knowledge can be translated into proposals for the construction of autonomous devices that can operate on molecular scales. Diffusion is the main mechanism that controls the motion of solute molecules in solution and brings them into contact where reactions can take place. This process is nonspecific and often slow. Although diffusion is essential in the biological realm, using molecular motors, biological systems have devised more efficient ways to transport species. There is no reason why our interest should be confined to these biological molecular motors and synthetic molecular machines and motors have been constructed in the laboratory. In particular, self-propelled micron and nano-scale motors that use chemical energy to produce directed motion have been made and used in proof-of-principle studies related to drug delivery, chemical sensing, pollutant removal and targeting cancer cells, among others. These studies have pointed to the many potential chemical, medical and materials science applications of these synthetic motors. Like their biological counterparts, these tiny motors are strongly buffeted by the surrounding medium and they must be able to function in spite of this. The design of such synthetic motors for use in applications requires knowledge of how they operate under various conditions, in complex environments and in concert through their collective motions. While most synthetic self-propelled motors studied to date have micron-scale dimensions, future applications will involve such synthetic motors with even smaller molecular dimensions. Fundamental theoretical challenges arise for the description of molecular-scale synthetic chemically-powered motors. Their resolution is a main goal of the proposed research. This knowledge is essential for applications on very small scales, even in the interior of the cell. Other types of active species are perhaps more familiar: enzymes undergoing catalytic cycles in the cell or in solution. Similar to the motors discussed above, these protein machines use chemical energy for their action and operate in the presence of very strong thermal fluctuations. Since the cell is crowded by various macromolecular species, including the active enzymes themselves, the nature of active non-thermal enzyme conformational motion will be explored in order to determine the roles it plays in transport and chemical dynamics.