Threading of a polymer through a macrocyclic ring may occur directly, that is, by finding the end of the polymer chain, or by a process in which the polymer chain first folds and then threads through the macrocyclic ring in a hairpin-like conformation. We present kinetic and thermodynamic studies on the threading of a macrocyclic porphyrin receptor (H₂1) onto molecular threads that are blocked on one side and are open on the other side. The open side is modified by groups that vary in ease of folding and in bulkiness. Additionally, the threads contain a viologen binding site for the macrocyclic receptor, which is located close to the blocking group. The rates of threading of H₂1 were measured under various conditions, by recording as a function of time the quenching of the fluorescence of the porphyrin, which occurs when receptor H₂1 reaches the viologen binding site. The kinetic data suggest that threading is impossible if the receptor encounters an open side that is sterically encumbered in a similar way as a folded polymer chain. This indicates that threading of polymers through macrocyclic compounds through a folded chain mechanism is unlikely.

Nature’s enzymes are an ongoing source of inspiration for scientists. The complex processes behind their selectivity and efficiency is slowly being unraveled, and these findings have spawned many biomimetic catalysts. However, nearly all focus on the conversion of small molecular substrates. Nature itself is replete with inventive catalytic systems which modify, replicate, or decompose entire polymers, often in a processive fashion. Such processivity can, for example, enhance the rate of catalysis by clamping to the polymer substrate, which imparts a large effective molarity. Reviewed herein are the various strategies for processivity in nature’s arsenal and their properties. An overview of what has been achieved by chemists aiming to mimic one of nature’s greatest tricks is also included.

The synthesis and binding properties of new porphyrin cage compounds consisting of a rigid diphenylglycoluril part, which is connected via flexible bis(ethyleneoxy) spacers to a (metallo)porphyrin “roof”, are reported. Binding of viologen guests and pyridine ligands in these porphyrin cages are accompanied by significant conformational reorganizations of the hosts. Despite these structural changes, association constants are still very high, revealing that not only receptors that bind guests according to a lock-and-key mechanism but also those that bind guests by an induced-fit mechanism can exhibit strong binding.

We describe the synthesis of a series of interlocked structures from porphyrin–glycoluril cage compounds and bis(olefin)-terminated viologens by an olefin-metathesis protocol. The length of the chain connecting the olefin substituents with the viologen has a marked effect on the products of the ring-closure reaction. Long chains give [2]- and [3]catenane structures, whereas short chains give a mixture of [3]-, [4]-, and [5]catenanes. For comparison several [2]rotaxane compounds were prepared. The interlocked catenane and rotaxane structures display switching behavior, which can be controlled by the addition of acid and base. The kinetic and thermodynamic parameters of the switching processes have been determined by NMR spectroscopy.

Detailed information on the architecture of polyisocyanopeptides based on vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations is presented. It is demonstrated that the screw sense of the helical polyisocyanides can be determined directly from the CN-stretch vibrational region of the VCD spectrum. Analysis of the VCD signals associated with the amide I and amide II modes provides detailed information on the peptide side-chain arrangement in the polymer and indicates the presence of a helical β-sheet architecture, in which the dihedral angles are slightly different to those of natural β-sheet helices.

Rigid rod polyisocyanopeptides bearing phthalocyanines as pendant groups have been synthesised through CuAAC of polyisocyanopeptides containing acetylene groups with zinc(II) phthalocyanine azide. As confirmed by UV/Vis, fluorescence, and circular dichroism spectroscopies, the phthalocyanines are arranged in a helical fashion along the polymer backbone, forming the longest reported well-defined phthalocyanine assembly described to date.

The straightforward syntheses of polyisocyanides containing the alanine–cysteine motif in their side chains have been achieved. Detailed characterization of the polymers revealed a well-defined and highly stable helical conformation of the polyimine backbone responsible for the formation of rodlike structures of over one hundred nanometers. The 4₁ helix is further stabilized by β-sheet-like interactions between the peptide arms. As a result, the cysteine sulfur atoms are regularly aligned along the polymer axis, which provides a unique platform for the scaffolding of various entities by using versatile click-chemistry postmodification approaches. For instance, pyrene derivatives were introduced through thio-specific reactions involving either maleimide, iodoacetamide, or thioester groups, leading to arrays of stacked chromophores with excimer-like emission. A water-soluble cysteine-rich polyisocyanide was successfully biotinylated and coupled to streptavidin.

The design and synthesis of functional biomimetic water soluble polymers with a defined secondary structure has been developed using β-sheet polyisocyanopeptide scaffolds. Water soluble isocyanopolymers were prepared by random copolymerisation of the azido functionalized isocyanopeptides with nonfunctionalised methyl ester isocyanides derived from alanine. Upon saponification of the latter function a rigid rod water soluble polymer was obtained with an accessible azide for postfunctionalization. The potential of these biomimetic polymers was successfully demonstrated by using the click chemistry reaction of these polymers with an acetylene functionalised rhodamine dye. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4150–4164, 2009