Moteur moléculaire | EPFL Graph Search

Un moteur moléculaire est un objet de la taille d’une molécule ou d’un assemblage de molécules qui est capable de produire un travail mécanique ou un mouvement dirigé, ces buts ne pouvant être atteints que si de l’énergie est fournie au système. Les différences les plus importantes par rapport aux moteurs macroscopiques concernent la sensibilité des moteurs moléculaires à la viscosité de leur micro-environnement, et surtout à l’importance de l’agitation thermique. À l’échelle des picosecondes, ces machines sont soumises à un mouvement brownien et donc assez aléatoire. Le terme de « moteur moléculaire » est utilisé en biologie où ce terme s’applique aux moteurs protéiques, mais aussi en chimie pour décrire des structures relativement petites entièrement construites de novo, les moteurs synthétiques. À l’avenir, ces objets sont appelés à devenir les composants d’éventuelles nanomachines. Moteurs moléculaires synthétiques Les premiers exemples de moteurs synthétiques furent p

Coarse-grained entropy production with multiple reservoirs: Unraveling the role of time scales and detailed balance in biology-inspired systems

Daniel Maria Busiello, Deepak Gupta, Amos Maritan

A general framework to describe a vast majority of biology-inspired systems is to model them as stochastic processes in which multiple couplings are in play at the same time. Molecular motors, chemical reaction networks, catalytic enzymes, and particles exchanging heat with different baths, constitute some interesting examples of such a modelization. Moreover, they usually operate out of equilibrium, being characterized by a net production of entropy, which entails a constrained efficiency. Hitherto, in order to investigate multiple processes simultaneously driving a system, all theoretical approaches deal with them independently, at a coarse-grained level, or employing a separation of time scales. Here, we explicitly take in consideration the interplay among time scales of different processes and whether or not their own evolution eventually relaxes toward an equilibrium state in a given subspace. We propose a general framework for multiple coupling, from which the well-known formulas for the entropy production can be derived, depending on the available information about each single process. Furthermore, when one of the processes does not equilibrate in its subspace, even if much faster than all the others, it introduces a finite correction to the entropy production. We employ our framework in various simple and pedagogical examples, for which such a corrective term can be related to a typical scaling of physical quantities in play.

2020

Buckling instabilities and spatio-temporal dynamics of active elastic filaments

Tobias Schneider

Biological filaments driven by molecular motors tend to experience tangential propulsive forces also known as active follower forces. When such a filament encounters an obstacle, it deforms, which reorients its follower forces and alters its entire motion. If the filament pushes a cargo, the friction on the cargo can be enough to deform the filament, thus affecting the transport properties of the cargo. Motivated by cytoskeletal filament motility assays, we study the dynamic buckling instabilities of a two-dimensional slender elastic filament driven through a dissipative medium by tangential propulsive forces in the presence of obstacles or cargo. We observe two distinct instabilities. When the filament's head is pinned or experiences significant translational but little rotational drag from its cargo, it buckles into a steadily rotating coiled state. When it is clamped or experiences both significant translational and rotational drag from its cargo, it buckles into a periodically beating, overall translating state. Using minimal analytically tractable models, linear stability theory and fully nonlinear computations, we study the onset of each buckling instability, characterize each buckled state, and map out the phase diagram of the system. Finally, we use particle-based Brownian dynamics simulations to show our main results are robust to moderate noise and steric repulsion. Overall, our results provide a unified framework to understand the dynamics of tangentially propelled filaments and filament-cargo assemblies.

ROYAL SOC2020

Exploiting the chirality of intermetallic PdGa

Samuel Thomas Stolz

The intermetallic compound PdGa has recently attracted considerable interest for combining high catalytic activity with high reaction selectivity in symmetric heterogeneous catalysis, in particular semi-hydrogenation of acetylene and methanol steam reforming. However, its potential for asymmetric heterogeneous catalysis, for which its chiral bulk crystal structure predestines it, remained largely unexplored. The possibility to prepare clean, atomically well-defined, and bulk-truncated low Miller-index surfaces of chiral PdGa (Pd1Ga1) under ultra-high vacuum conditions paves the way to tackle several fundamental research questions in chemistry and physics under idealized conditions. In particular, the PdGa{111} surfaces and their unique properties are ideally suited to serve as model system to study ensemble (geometry) and ligand (electronic) effects and show the enormous potential of PdGa towards asymmetric heterogeneous catalysis. In this work, the focus is on obtaining fundamental insights into chirality transfer of intrinsically chiral surfaces on the electronic structure and on each of the principal steps of a catalytic reaction pathway by experimental surface analytical tools. With regard to the relation of the chiral crystal structure of PdGa and its electronic structure, crystals of the space group P213, such as PdGa, are predicted to exhibit peculiar symmetry-protected fermionic quasiparticles. Using ARPES, we were able to evidence such symmetry-protected fermionic quasiparticles in PdGa, to exhibit multifold band-crossings at the high-symmetry points G and R in the Brillouin zone are fermionic quasiparticles with topological charge of magnitude 4 The non-centrosymmetry of PdGa is not only manifested in the emergence of chiral Fermi-arcs, but its chirality governs also the interaction with molecules and its surfaces, which is expressed, for instance in unidirectional motion or enantioselective on-surface reactions. In particular, we have evidenced and induced directed rotation with a directionality of 98% of isolated small, achiral acetylene (C2H2) molecules on Pd3-terminated PdGa{111} surfaces by using LT-STM. The rotor of this exceptionally small motor consists of 4 atoms only and thus operates not only in the classical, electrically driven regime, but also in an unexpected quantum tunneling regime with persisting high directionality. This strong chirality transfer from the substrate to the molecule is also encountered in enantiospecific interactions with prochiral molecules which is a prerequisite for enantioselective control in on-surface reactions, i.e., asymmetric heterogeneous catalysis. With this focus, we have studied three different reactions on the two structurally different Pd1- and Pd3-terminated PdGa{111} surfaces with regard to enantiomeric excess and the relevance of ensemble effect (geometry) over the ligand effect (electronic structure): Enantioselective debromination of 5-Bromo-7Methylbenz(a)Anthracene (BMA) Nearly enantiopure homocoupling of 9-Ethynylphenanthrene (9-EP) Regio- and enantioselective azide-alkyne Huisgen cycloaddition between 3-(4-Azidophenyl)propionic azid (APA) and 9-EP Our results highlight the outstanding potential of intermetallic PdGa in numerous fields of research, specifically as a chiral topo-logical material with non-trivial bandstructure, as stator for molecular motors, or as template for asymmetric heterogeneous catalysis.

EPFL2020

Exploiting the chirality of intermetallic PdGa

Samuel Thomas Stolz

EPFL2020