Shoichi Toyabe

Experimental demonstration of information-to-energy conversion and validation of the generalized Jarzynski equality

In 1929, Leo Szilard invented a feedback protocol[? ] in which a hypothetical intelligence called Maxwell’s demon pumps heat from an isothermal environment and transduces it to work. After an intense controversy that lasted over eighty years; it was finally clarified that the demon’s role does not contradict the second law of thermodynamics, implying that we can convert information to free energy in principle[? ? ? ? ? ]. Nevertheless, experimental demonstration of this information-to-energy conversion has been elusive. Here, we demonstrate that a nonequilibrium feedback manipulation of a Brownian particle based on information about its location achieves a Szilard-type information-energy conversion. Under real-time feedback control, the particle climbs up a spiral-stairs-like potential exerted by an electric field and obtains free energy larger than the amount of work performed on it. This enables us to verify the generalized Jarzynski equality[? ], or a new fundamental principle of “information-heat engine” which converts information to energy by feedback control.

Thermodynamic efficiency and mechanochemical coupling of F1-ATPase.

F1-ATPase is a nanosized biological energy transducer working as part of FoF1-ATP synthase. Its rotary machinery transduces energy between chemical free energy and mechanical work and plays a central role in the cellular energy transduction by synthesizing most ATP in virtually all organisms. However, information about its energetics is limited compared to that of the reaction scheme. Actually, fundamental questions such as how efficiently F1-ATPase transduces free energy remain unanswered. Here, we demonstrated reversible rotations of isolated F1-ATPase in discrete 120° steps by precisely controlling both the external torque and the chemical potential of ATP hydrolysis as a model system of FoF1-ATP synthase. We found that the maximum work performed by F1-ATPase per 120° step is nearly equal to the thermodynamical maximum work that can be extracted from a single ATP hydrolysis under a broad range of conditions. Our results suggested a 100% free-energy transduction efficiency and a tight mechanochemical coupling of F1-ATPase.

Fabrication and Placement of a Ring Structure of Nanoparticles by a Laser-Induced Micronanobubble on a Gold Surface

We have developed a new fabrication method for a ring structure of assembled nanoparticles on a gold surface by the use of continuous Nd:YAG laser light. A micronanobubble on a gold surface, created by laser local heating, acts as a template for the formation of the ring structure. Both Marangoni convection flow and capillary flow around the micronanobubble are responsible for the driving force to assemble nanoparticles such as CdSe Q-dots into the ring structure from the solution. Because a single micronanobubble was generated by the Nd:YAG laser focusing point, the precise positioning of the ring structure was feasible directly on the gold surface, which makes it possible to fabricate various patterns of rings such as arrays and letters and even a double-ring structure without any photomasks or any templates.

Recovery of state-specific potential of molecular motor from single-molecule trajectory

We have developed a novel method to evaluate the potential profile of a molecular motor at each chemical state from only the probes trajectory and applied it to a rotary molecular motor F1-ATPase. By using this method, we could also obtain the information regarding the mechanochemical coupling and energetics. We demonstrate that the position-dependent transition of the chemical states is the key feature for the highly efficient free-energy transduction by F1-ATPase.

Single molecule thermodynamics of ATP synthesis by F1-ATPase

FoF1-ATP synthase is a factory for synthesizing ATP in virtually all cells. Its core machinery is the subcomplex F1-motor (F1-ATPase) and performs the reversible mechanochemical coupling. The isolated F1-motor hydrolyzes ATP, which is accompanied by unidirectional rotation of its central . When a strong opposing torque is imposed, the -shaft rotates in the opposite direction and drives the F1-motor to synthesize ATP. This mechanical-to-chemical free-energy transduction is the final and central step of the multistep cellular ATP-synthetic pathway. Here, we determined the amount of mechanical work exploited by the F1-motor to synthesize an ATP molecule during forced rotations using a methodology combining a nonequilibrium theory and single molecule measurements of responses to external torque. We found that the internal dissipation of the motor is negligible even during rotations far from a quasistatic process.

Experimental test of a new equality: measuring heat dissipation in an optically driven colloidal system.

Measurement of energy dissipation in small nonequilibrium systems is generally a difficult task. Recently, Harada and Sasa [Phys. Rev. Lett. 95, 130602 (2005)] derived an equality relating the energy dissipation rate to experimentally accessible quantities in nonequilibrium steady states described by the Langevin equation. Here, we show an experimental test of this new relation in an optically driven colloidal system. We find that this equality is validated to a fairly good extent, thus the irreversible work of a small system is estimated from readily obtainable quantities.

Experimental thermodynamics of single molecular motor

Molecular motor is a nano-sized chemical engine that converts chemical free energy to mechanical motions. Hence, the energetics is as important as kinetics in order to understand its operation principle. We review experiments to evaluate the thermodynamic properties of a rotational F1-ATPase motor (F1-motor) at a single-molecule level. We show that the F1-motor achieves 100% thermo dynamic efficiency at the stalled state. Furthermore, the motor reduces the internal irreversible heat inside the motor to almost zero and achieves a highly-efficient free energy transduction close to 100% during rotations far from quasistatic process. We discuss the mechanism of how the F1-motor achieves such a high efficiency, which highlights the remarkable property of the nano-sized engine F1-motor.

Nonequilibrium Fluctuations in Biological Strands, Machines, and Cells

Can physics provide a quantitative methodology and unified view to elucidate rich and diverse biological phenomena? Nonequilibrium fluctuations are key quantities. These fluctuations have universal symmetries, convey essential information about systems’ behaviors, and are experimentally accessible in most systems. We review experimental developments to extract information from the nonequilibrium fluctuations of biological systems. In particular, we focus on the three major hierarchies in small scales: strands, molecular machines, and cells.

Observation of DNA pinning at laser focal point on Au surface and its application to single DNA nanowire and cross-wire formation

We report a new technique for fabricating a single DNA nanowire at a desired position in a sequential manner using the micronanobubble generated by laser local heating at the Au/water interface. In our previous report, we found the reversible pull-in/shrinkage of one end immobilized DNA strands near a Nd:YAG laser focal point on an Au surface. In further experiments, the pinning of DNA strands in the stretched state was observed on the Au surface only when the bubble has touched the free end of DNA. This pinning phenomenon was observed even on the alkane thiol modified Au surface as self-assembled monolayers (SAMs) such as hexanethiol, mercaptohexanol, and hexadecanethiol. However, no pinning was observed on the bovine serum albumin (BSA) modified surface. Since optical tweezers can manipulate a DNA modified bead (radius=1.87 μm), the bead was firstly fixed on a solid surface by being compressed with the optical tweezers, and the pulling and pinning of DNA on the bead were achieved. As a consequence, the laser local heating on the Au surface enables us to control the number and position of the one end immobilized DNA strands as DNA nanowires.

Information-to-free-energy conversion: Utilizing thermal fluctuations.

Maxwell’s demon is a hypothetical creature that can convert information to free energy. A debate that has lasted for more than 100 years has revealed that the demon’s operation does not contradict the laws of thermodynamics; hence, the demon can be realized physically. We briefly review the first experimental demonstration of Maxwell’s demon of Szilard’s engine type that converts information to free energy. We pump heat from an isothermal environment by using the information about the thermal fluctuations of a Brownian particle and increase the particle’s free energy.