Template synthesis of molecular knots

Knot theory realizations in nematic colloids

Nematic braids are reconfigurable knots and links formed by the disclination loops that entangle colloidal particles dispersed in a nematic liquid crystal. We focus on entangled nematic disclinations in thin twisted nematic layers stabilized by 2D arrays of colloidal particles that can be controlled with laser tweezers. We take the experimentally assembled structures and demonstrate the correspondence of the knot invariants, constructed graphs, and surfaces associated with the disclination loop to the physically observable features specific to the geometry at hand. The nematic nature of the medium adds additional topological parameters to the conventional results of knot theory, which couple with the knot topology and introduce order into the phase diagram of possible structures. The crystalline order allows the simplified construction of the Jones polynomial and medial graphs, and the steps in the construction algorithm are mirrored in the physics of liquid crystals.

A [2]rota[2]catenane, constructed from a pillar[5]arene-crown ether fused double-cavity macrocycle: synthesis and structural characterization

A [2]rota[2]catenane, based on a pillar[5]arene-crown ether fused bicycle, was constructed and its structure was determined crystallographically.

Controlling the assembly of cyclotriveratrylene-derived coordination cages

Ligand-functionalised cyclotriveratrylene derivatives self-assemble to afford coordination cages and topologically non-trivial constructs, including controlled assembly of M₃L₂ metallo-cryptophane and M₆L₈ cages.

Discrete and polymeric complexes formed from cobalt(ii), 4,4′-bipyridine and 2-sulfoterephthalate: synthetic, crystallographic and magnetic studies

Five discrete and polymeric complexes have been prepared and characterised from the reaction of different ratios of Co(ii), 4,4′-bipyridine and 2-sulfoterephthalate.

Molecular Mechanochemistry: Engineering and Implications of Inherently Strained Architectures

Mechanical activation of chemical bonds is usually achieved by applying external forces. However, nearly all molecules exhibit inherent strain of their chemical bonds and angles as a result of constraints imposed by covalent bonding and interactions with the surrounding environment. Particularly strong deformation of bonds and angles is observed in hyperbranched macromolecules caused by steric repulsion of densely grafted polymer branches. In addition to the tension amplification, macromolecular architecture allows for accurate control of strain distribution, which enables focusing of the internal mechanical tension to specific chemical bonds and angles. As such, chemically identical bonds in self-strained macromolecules become physically distinct because the difference in bond tension leads to the corresponding difference in the electronic structure and chemical reactivity of individual bonds within the same macromolecule. In this review, we outline different approaches to the design of strained macromolecules along with physical principles of tension management, including generation, amplification, and focusing of mechanical tension at specific chemical bonds.

Constructing supramolecular grids: from 4f square to 3d–4f grid

Novel supramolecular 4f and 3d–4f grids were constructed using dihydrazone based ligands, where the 3d–4f grid represents the first example of this type and shows SMM behavior.

The self-sorting behavior of circular helicates and molecular knots and links

We report on multicomponent self-sorting to form open circular helicates of different sizes from a primary monoamine, Fe(II) ions, and dialdehyde ligand strands that differ in length and structure by only two oxygen atoms. The corresponding closed circular helicates that are formed from a diamine--a molecular Solomon link and a pentafoil knot--also self-sort, but up to two of the Solomon-link-forming ligand strands can be accommodated within the pentafoil knot structure and are either incorporated or omitted depending on the stage that the components are mixed.

Catenanes from catenanes: quantitative assessment of cooperativity in dynamic combinatorial catenation

A series of dynamic combinatorial [2] and [3]catenanes have been prepared. Formation of the [3]catenanes occurs with positive or negative cooperativity, depending on the cyclodextrin homologue. Systems level analysis allows cooperativity to be quantified and MD simulations reveal that cooperativity derives from the extents to which hydrophobic surface area is exposed to the aqueous surroundings.

Self-assembly of a M4L6 complex with unexpected S4 symmetry

In a one-pot reaction 1,4-diaminobenzene and 2-formylpyridine, as the reacting subcomponents, self-assemble to a small supramolecular M₄L₆ pseudo-tetrahedron with unexpected S₄ symmetry in the presence of Fe(ii) ions.

Anion-controlled formation of an aminal-(bis)imine Fe(ii)-complex

The subcomponent self-assembly of 1,2-diaminobenzene and 2-formylpyridine with iron(ii) salts yields an unprecedented complex containing both the aminal and imine groups and can be controlled by the choice of counter-anion.

Mechanochemistry of Topological Complex Polymer Systems

Although existing since the concept of macromolecules, polymer mechanochemistry is a burgeoning field which attracts great scientific interest in its ability to bias conventional reaction pathways and its potential to fabricate mechanoresponsive materials. We review here the effect of topology on the mechanical degradation of polymer chains and the activation of mechanophores in polymer backbones. The chapter focuses on both experimental and theoretical work carried out in the past 70 years. After a general introduction (Sect. 1), where the concept, the history, and the application of polymer mechanochemistry are briefly described, flow fields to study polymer mechanochemistry are discussed (Sect. 2), results of mechanochemistry study are presented for linear polymers (Sect. 3), cyclic polymers (Sect. 4), graft polymers (Sect. 5), star-shaped polymers (Sect. 6), hyperbranched polymers and dendrimers (Sect. 7), and systems with dynamic topology (Sect. 8). Here we focus on (1) experimental results involving the topological effect on the coil-to-stretch transition and the fracture of the polymer chains, (2) the underlying mechanisms and the key factor that determines the mechanical stability of the macromolecules, (3) theoretical models that relate to the experimental observations, and (4) rational design of mechanophores in complex topology to achieve multiple activations according to the existing results observed in chain degradation.

Au nanoparticle/DNA rotaxane hybrid nanostructures exhibiting switchable fluorescence properties

The preparation of a DNA rotaxane consisting of a circular nucleic acid interlocked, through hybridization, on a nucleic acid axle and stoppered by two 10-nm-sized Au nanoparticles (NPs) is described. By the tethering of 5-nm- or 15-nm-sized Au NPs on the ring, the supramolecular structure of the rotaxane is confirmed. Using nucleic acids as "fuels" and "anti-fuels", the cyclic and reversible transition of the rotaxane ring across two states is demonstrated. By the functionalization of the ring with fluorophore-modified nucleic acids in different orientations, the transitions of the rings between the sites are followed by fluorescence quenching or surface-enhanced fluorescence. The experimental results are supported by theoretical modeling.

Getting tubed: mechanical bond in endohedral derivatives of carbon nanotubes?

We present a brief overview of some of the most prominent examples of encapsulation of molecules inside carbon nanotubes. We then relate them to mechanically interlocked molecules, and in particular rotaxanes, by examining the most prominent features of the mechanical bond (topology, dynamic properties, and stability) and comparing them to those of endohedral derivatives of nanotubes. Our analysis shows that there is a surprisingly clear link between these two apparently disparate species.