Artificial nano-and microcapsules that seek to mimic their natural counterparts can be constructed in different ways, leading to a variety of properties, as will be discussed in this review. [6][7][8] Enzymatic conversions can take place in the lumen of such capsules, and their membranes can be used to confine and tune reaction pathways. Synthetic capsules are also attracting a lot of attention because of their promising applications in the controlled release of pharmaceuticals. Capsules that bear recognition elements have been targeted to specific tissues or organs, providing a desirable vehicle for the aforementioned release of drugs. 9 For a chemist, the successful exploitation of capsules begins with their tailormade design and synthesis, for which cells and their organelles are the primary source of inspiration. In order to be able to do so, one needs insight into the design principles of nature to endow function to a molecule and to direct its self-assembly to a preset architecture. Although spectacular progresshasbeenmadeinthefieldofbioinspiredself-assembly, [10][11][12][13] unfortunately, the construction of an artificial cell is still not much more than a fantasy. Fortunately, more simple systems such as micelles, vesicles, and other assemblies of molecules may already partly solve the problem by providing a capsule that can be geared toward a desired application, e.g. the controlled release of drugs, as was demonstrated in the literature already quite a long time ago. [14][15][16] The view of life as being the result of a nanoscale phenomenon 17 is of more recent date and should rouse the interest in capsules for any chemist. Stijn F. M. van Dongen (group, center) was born in Goirle, The Netherlands, and studied chemistry at the Radboud University Nijmegen. He received his master's degree in 2006 after traineeships in the physical organic chemistry group of Prof. R. J. M. Nolte and the synthetic biology group of Prof. D. M. Hilvert at the ETH in Zu ¨rich, Switzerland. He is currently a Ph.D. student in the group of Profs.' R. J. M. Nolte and J. C. M. van Hest, working on the exploration of polymersomes as nanoreactors in a biological setting. Hans-Peter M. de Hoog (group, second from left) was born in Arnhem, The Netherlands, and graduated in chemistry at Utrecht University in 1998, specializing in the analysis of complex biomolecules. After a short stay at The Netherlands Organisation for Applied Scientific Research (TNO), he moved to the Radboud University Nijmegen in 2005 to pursue a Ph.D. in supramolecular and physical organic chemistry in the group of Prof. R. J. M. Nolte and J. J. L. M. Cornelissen. His research involves a collaborative project with Delft University of Technology (Prof. I. W. C. E. Arends) on the applicationdriven encapsulation of enzymes in polymersomes. Ruud J. R. W. Peters (group, right) obtained his bachelor's degree in molecular life sciences at the Radboud University Nijmegen in 2008. He is currently performing his master's research on the interactions between polymersomes a...

Porous polymersomes based on block copolymers of isocyanopeptides and styrene have been used to anchor enzymes at three different locations, namely, in their lumen (glucose oxidase, GOx), in their bilayer membrane (Candida antarctica lipase B, CalB) and on their surface (horseradish peroxidase, HRP). The surface coupling was achieved by click chemistry between acetylene-functionalised anchors on the surface of the polymersomes and azido functions of HRP, which were introduced by using a direct diazo transfer reaction to lysine residues of the enzyme. To determine the encapsulation and conjugation efficiency of the enzymes, they were decorated with metal-ion labels and analysed by mass spectrometry. This revealed an almost quantitative immobilisation efficiency of HRP on the surface of the polymersomes and a more than statistical incorporation efficiency for CalB in the membrane and for GOx in the aqueous compartment. The enzyme-decorated polymersomes were studied as nanoreactors in which glucose acetate was converted by CalB to glucose, which was oxidised by GOx to gluconolactone in a second step. The hydrogen peroxide produced was used by HRP to oxidise 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to ABTS(.+). Kinetic analysis revealed that the reaction step catalysed by HRP is the fastest in the cascade reaction.

With the advent of supramolecular chemistry and later nanotechnology a great deal of research has been focused on new types of molecular structures, which are not held together by covalent bonds but by non-covalent mechanical interactions. Examples include the catenane, rotaxane, and knot interlocked structures. The design and synthesis of these architectures is an art by itself and as such is worth being reviewed. In this tutorial review we will focus, however, on the functional aspects of interlocked molecules and discuss how these can find applications, e.g. as artificial muscles, as molecular valves, as components of electronic devices, and as catalysts.

The controlled introduction of azides in proteins provides targetable handles for selective protein manipulation. We present here an efficient diazo transfer protocol that can be applied in an aqueous solution, leading to the facile introduction of azides in the side chains of lysine residues and at the N-terminus of enzymes, e.g. horseradish peroxidase (HRP) and the red fluorescent protein DsRed. The effective introduction of azides was verified by mass spectrometry, after which the azido-proteins were used in Cu(I)-catalyzed [3 + 2] cycloaddition reactions. Azido-HRP retained its catalytic activity after conjugation of a small molecule. This modified protein could also be successfully immobilized on the surface of an acetylene-covered polymersome. Azido-DsRed was coupled to an acetylene-bearing protein allowing it to act as a fluorescent label, demonstrating the wide applicability of the diazo transfer procedure.

There's an APP for that: cell-repellent APP (azido-[polylysine-g-PEG]) is used to create substrates for spatially controlled dynamic cell adhesion. The simple addition of a functional peptide to the culture medium rapidly triggers cell adhesion. This highly accessible yet powerful technique allows diverse applications, demonstrated through tissue motility assays, patterned coculturing and triggered cell shape change.

In processive catalysis, a catalyst binds to a substrate and remains bound as it performs several consecutive reactions, as exemplified by DNA polymerases. Processivity is essential in nature and is often mediated by a clamp-like structure that physically tethers the catalyst to its (polymeric) template. In the case of the bacteriophage T4 replisome, a dedicated clamp protein acts as a processivity mediator by encircling DNA and subsequently recruiting its polymerase. Here we use this DNA-binding protein to construct a biohybrid catalyst. Conjugation of the clamp protein to a chemical catalyst with sequence-specific oxidation behaviour formed a catalytic clamp that can be loaded onto a DNA plasmid. The catalytic activity of the biohybrid catalyst was visualized using a procedure based on an atomic force microscopy method that detects and spatially locates oxidized sites in DNA. Varying the experimental conditions enabled switching between processive and distributive catalysis and influencing the sliding direction of this rotaxane-like catalyst.

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.

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