Discovering privileged topologies of molecular knots with self-assembling models

Despite the several available strategies to build complex supramolecular constructs, only a handful of different molecular knots have been synthesised so far. Here, in response to the quest for further designable topologies, we use Monte Carlo sampling and molecular dynamics simulations, informed by general principles of supramolecular assembly, as a discovery tool for thermodynamically and kinetically accessible knot types made of helical templates. By combining this approach with the exhaustive enumeration of molecular braiding patterns applicable to more general template geometries, we find that only few selected shapes have the closed, symmetric and quasi-planar character typical of synthetic knots. The corresponding collection of admissible topologies is extremely restricted. It covers all known molecular knots but it especially includes a limited set of novel complex ones that have not yet been obtained experimentally, such as 10124 and 15n41185, making them privileged targets for future self-assembling experiments

Mechanical Bonds and Topological Effects in Radical Dimer Stabilization

While mechanical bonding stabilizes tetrathiafulvalene (TTF) radical dimers, the question arises: what role does topology play in catenanes containing TTF units? Here, we report how topology, together with mechanical bonding, in isomeric [3]- and doubly interlocked [2]catenanes controls the formation of TTF radical dimers within their structural frameworks, including a ring-in-ring complex (formed between an organoplatinum square and a {2+2} macrocyclic polyether containing two 1,5-dioxynaphthalene (DNP) and two TTF units) that is topologically isomeric with the doubly interlocked [2]catenane. The separate TTF units in the two {1+1} macrocycles (each containing also one DNP unit) of the isomeric [3]catenane exhibit slightly different redox properties compared with those in the {2+2} macrocycle present in the [2]catenane, while comparison with its topological isomer reveals substantially different redox behavior. Although the stabilities of the mixed-valence (TTF2)^(•+) dimers are similar in the two catenanes, the radical cationic (TTF^(•+))_2 dimer in the [2]catenane occurs only fleetingly compared with its prominent existence in the [3]catenane, while both dimers are absent altogether in the ring-in-ring complex. The electrochemical behavior of these three radically configurable isomers demonstrates that a fundamental relationship exists between topology and redox properties

QUENCHING EFFECTS IN A Fe40Ni40P14B6 AMORPHOUS ALLOY STUDIED BY MAGNETIC ANISOTROPY MEASUREMENTS

Kinetics for the establishment of the magnetic anisotropy has been found to be a reversible function of the equilibrium structural state quenched in from different temperatures (activation energy : 0.28 ± 0.02 eV

STRUCTURAL RELAXATION AND ATOMIC MOBILITY BY MAGNETIC ANISOTROPY MEASUREMENTS IN SOME METALLIC GLASSES

We compare the magnetic anisotropy induced by thermomagnetic treatments in some amorphous metallic alloys, considered in three different states : as-received, annealed, annealed and subsequently quenched. The atomic mobility is shown to decrease during an anneal, and to be partially restored by a quench. It is concluded that some processes involved in what is called "structural relaxation" are reversible, at least in part

Evidence for carbon mobility in the amorphous alloy Fe81B 13.5Si3.5C2 from magnetic anisotropy measurements

The amorphous alloy Fe81B13.5Si3.5C 2 shows an additional induced magnetic anisotropy, as compared with the alloy Fe81.5B 14.5Si4, attributed to a rearrangement of the carbon atoms. These atoms migrate faster than the other components, through a particular mechanism, probably interstitial in character. Their mobility is comparable to that of interstitial carbon in the crystalline iron-nickel alloys.L'alliage amorphe Fe81B13,5Si3,5C 2 présente, par rapport à l'alliage Fe81,5B14,5Si 4, une anisotropie magnétique induite supplémentaire, attribuée au réarrangement des atomes de carbone; ceux-ci migrent plus vite que les autres constituants, et par un mécanisme distinct, sans doute interstitiel. Leur mobilité est comparable à celle du carbone interstitiel dans les alliages cristallins fer-nickel de structure cfc