Catenane

About: Catenane is a research topic. Over the lifetime, 1149 publications have been published within this topic receiving 55725 citations. The topic is also known as: catenane.

Dynamic covalent chemistry.

Abstract: Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.

CH/π hydrogen bonds in crystals

Abstract: The nature and characteristics of the CH/π interaction are discussed by comparison with other weak molecular forces such as the CH/O and OH/π interaction. The CH/π interaction is a kind of hydrogen bond operating between a soft acid CH and a soft base π-system (double and triple bonds, C6 and C5 aromatic rings, heteroaromatics, convex surfaces of fullerenes and nanotubes). The consequences of CH/π hydrogen bonds in supramolecular chemistry are reviewed on grounds of recent crystallographic findings and database analyses. The topics include intramolecular interactions, crystal packing (organic and organometallic compounds), host/guest complexes (cavity-type inclusion compounds of cyclodextrins and synthetic macrocyclic hosts such as calixarenes, catenanes, rotaxanes and pseudorotaxanes), lattice-inclusion type clathrates (including liquid crystals, porphyrin derivatives, cyclopentadienyl compounds and C60 fullerenes), enantioselective clathrate formation, catalytic enantioface discriminating reactions and solid-state photoreaction. The implications of the CH/π concept for crystal engineering and drug design are evident.

A [2]Catenane-Based Solid State Electronically Reconfigurable Switch

Abstract: A solid state, electronically addressable, bistable [2]catenane-based molecular switching device was fabricated from a single monolayer of the [2]catenane, anchored with phospholipid counterions, and sandwiched between an n-type polycrystalline silicon bottom electrode and a metallic top electrode. The device exhibits hysteretic (bistable) current/voltage characteristics. The switch is opened at +2 volts, closed at −2 volts, and read at ∼0.1 volt and may be recycled many times under ambient conditions. A mechanochemical mechanism for the action of the switch is presented and shown to be consistent with temperature-dependent measurements of the device operation.

Cyclodextrin-based molecular machines.

Abstract: Cyclodextrins have been used as a cyclic component in the construction of supramolecular architectures. Recently they have been studied as a component in the construction of rotaxanes and catenanes. A cyclodextrin ring can translocate in some rotaxane and catenane structures. Therefore, much attention has been given to cyclodextrins as a component of molecular shuttles, motors, and machines. Attempts to design and synthesize molecular-level machines using cyclodextrins as a cyclic component are described.

Dynamic imine chemistry.

Abstract: Formation of an imine—from an amine and an aldehyde—is a reversible reaction which operates under thermodynamic control such that the formation of kinetically competitive intermediates are, in the fullness of time, replaced by the thermodynamically most stable product(s). For this fundamental reason, the imine bond has emerged as an extraordinarily diverse and useful one in the hands of synthetic chemists. Imine bond formation is one of a handful of reactions which define a discipline known as dynamic covalent chemistry (DCC), which is now employed widely in the construction of exotic molecules and extended structures on account of the inherent ‘proof-reading’ and ‘error-checking’ associated with these reversible reactions. While both supramolecular chemistry and DCC operate under the regime of reversibility, DCC has the added advantage of constructing robust molecules on account of the formation of covalent bonds rather than fragile supermolecules resulting from noncovalent bonding interactions. On the other hand, these products tend to require more time to form—sometimes days or even months—but their formation can often be catalysed. In this manner, highly symmetrical molecules and extended structures can be prepared from relatively simple precursors. When DCC is utilised in conjunction with template-directed protocols—which rely on the use of noncovalent bonding interactions between molecular building blocks in order to preorganise them into certain relative geometries as a prelude to the formation of covalent bonds under equilibrium control—an additional level of control of structure and topology arises which offers a disarmingly simple way of constructing mechanically-interlocked molecules, such as rotaxanes, catenanes, Borromean rings, and Solomon knots. This tutorial review focuses on the use of dynamic imine bonds in the construction of compounds and products formed with and without the aid of additional templates. While synthesis under thermodynamic control is giving the field of chemical topology a new lease of life, it is also providing access to an endless array of new materials that are, in many circumstances, simply not accessible using more traditional synthetic methodologies where kinetic control rules the roost. One of the most endearing qualities of chemistry is its ability to reinvent itself in order to create its own object, as Berthelot first pointed out a century and a half ago.