Compartmentalization is an essential feature found in living cells to ensure that biological processes occur without being affected by undesired external influences. Over the years many scientists have designed self-assembled soft matter structures that mimic these natural catalytic compartments. The rationale behind this research is threefold. First of all, compartmentalization leads to the creation of a secluded environment for the catalytic species, which solves compatibility issues and which can improve catalyst efficiency and selectivity. Secondly, nano- and micro-compartments are constructed with the aim to obtain microenvironments that more closely mimic the cellular architecture. These biomimetic platforms are used to attain a better understanding of how cellular processes are executed. Thirdly, natural design rules are applied to create biomolecular assemblies with unusual functionality, which for example are used as artificial organelles. Here, recent developments will be discussed regarding these compartmentalized catalytic systems, with a selected number of illustrative examples to demonstrate which strategies have been followed, and to show to what extent the ambitious goals of this field of science have been reached. The focus here is on the field of soft matter science, covering the wide spectrum from polymeric assemblies to protein nanocages.

Polymers that possess lower critical solution temperature behavior such as poly(2-alkyl-2-oxazoline)s (PAOx) are interesting for their application as stimulus-responsive materials, for example in the biomedical field. In this work, we discuss the scalable and controlled synthesis of a library of pH- and temperature-sensitive 2-n-propyl-2-oxazoline P(nPropOx) based copolymers containing amine and carboxylic acid functionalized side chains by cationic ring opening polymerization and postpolymerization functionalization strategies. Using turbidimetry, we found that the cloud point temperature (CP) is strongly dependent on both the polymer concentration and the polymer charge (as a function of pH). Furthermore, we observed that the CP decreased with increasing salt concentration, whereas the CP increased linearly with increasing amount of carboxylic acid groups. Finally, turbidimetry studies in PBS-buffer indicate that CPs of these polymers are close to body temperature at biologically relevant polymer concentrations, which demonstrates the potential of P(nPropOx) as stimulus-responsive polymeric systems in, for example, drug delivery applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1573–1582

External small-molecule triggers were used to reversibly control dynamic protein–ligand interactions in giant vesicles. An alcohol dehydrogenase was employed to increase or decrease the interior pH upon conversion of two different small-molecule substrates, thereby modulating the pH-sensitive interaction between a Ni-NTA ligand on the vesicle membrane and an oligohistidine-tagged protein in the lumen. By alternating the small-molecule substrates the interaction could be reversed.

Delivery vehicles that are able to actively seek and precisely locate targeted tissues using concentration gradients of signaling molecules have hardly been explored. The directed movement toward specific cell types of cargo-loaded polymeric nanomotors along a hydrogen peroxide concentration gradient (chemotaxis) is reported. Through self-assembly, bowl-shaped poly(ethylene glycol)-b-polystyrene nanomotors, or stomatocytes, were formed with platinum nanoparticles entrapped in the cavity while a model drug was encapsulated in the inner compartment. Directional movement of the stomatocytes in the presence of a fuel gradient (chemotaxis) was first demonstrated in both static and dynamic systems using glass channels and a microfluidic flow. The highly efficient response of these motors was subsequently shown by their directional and autonomous movement towards hydrogen peroxide secreting neutrophil cells.

External small-molecule triggers were used to reversibly control dynamic protein–ligand interactions in giant vesicles. An alcohol dehydrogenase was employed to increase or decrease the interior pH upon conversion of two different small-molecule substrates, thereby modulating the pH-sensitive interaction between a Ni-NTA ligand on the vesicle membrane and an oligohistidine-tagged protein in the lumen. By alternating the small-molecule substrates the interaction could be reversed.

Delivery vehicles that are able to actively seek and precisely locate targeted tissues using concentration gradients of signaling molecules have hardly been explored. The directed movement toward specific cell types of cargo-loaded polymeric nanomotors along a hydrogen peroxide concentration gradient (chemotaxis) is reported. Through self-assembly, bowl-shaped poly(ethylene glycol)-b-polystyrene nanomotors, or stomatocytes, were formed with platinum nanoparticles entrapped in the cavity while a model drug was encapsulated in the inner compartment. Directional movement of the stomatocytes in the presence of a fuel gradient (chemotaxis) was first demonstrated in both static and dynamic systems using glass channels and a microfluidic flow. The highly efficient response of these motors was subsequently shown by their directional and autonomous movement towards hydrogen peroxide secreting neutrophil cells.

A laccase/(2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) mediated oxidation was combined with an aqueous, enantioselective copper-catalyzed Michael addition reaction of water in one pot. The copper catalyst was also immobilized onto DNA to induce enantioselectivity in the reaction. Low conversions were observed when the reactions were performed simultaneously, caused by an undesired reaction of an oxidised TEMPO intermediate. We increased the conversions by using a stepwise approach. Thus, after completion of the oxidation, the first reaction was stopped by inhibiting the enzyme with HCO₂K and reducing the reactive TEMPO intermediate. Next, the Michael addition reaction was started by adding the Cu catalyst. By applying this strategy, an efficient two-step one-pot sequence, proceeding with 20 % ee, was realized. The yield and ee of the second reaction were not affected by the oxidation reaction.

Enzyme-filled polystyrene-b-poly(3-(isocyano-L-alanyl-aminoethyl)thiophene) (PS-b-PIAT) nanoreactors are encapsulated together with free enzymes and substrates in a larger polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) polymersome, forming a multicompartmentalized structure, which shows structural resemblance to the cell and its organelles. An original cofactor-dependent three-enzyme cascade reaction is performed, using either compatible or incompatible enzymes, which takes place across multiple compartments.

Enzyme-filled polystyrene-b-poly(3-(isocyano-L-alanyl-aminoethyl)thiophene) (PS-b-PIAT) nanoreactors are encapsulated together with free enzymes and substrates in a larger polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) polymersome, forming a multicompartmentalized structure, which shows structural resemblance to the cell and its organelles. An original cofactor-dependent three-enzyme cascade reaction is performed, using either compatible or incompatible enzymes, which takes place across multiple compartments.

In this paper, we propose a “casting” strategy to prepare intrinsically fluorescent, uniform and porous gelatin microgels with multi-responsiveness. Gelatin microgels with tunable size were obtained by copying the structure of a porous CaCO₃ template. The diameter of the gelatin microgels was sensitive to salt concentration and pH. Doxorubicin and Rhodamine B as model drugs were loaded into the microgels via electrostatic interaction and release of the payload was triggered by changing the salt concentration and pH, respectively. Cell experiments demonstrated that the gelatin microgels had an excellent biocompatibility and biodegradability. The merits of gelatin microgels such as tunable size, biocompatibility, and stimulus responsive upload and release of positively charged small molecules will permit the microgels as excellent carriers for drug delivery. The whole manufacturing process is furthermore environmental-friendly involving no organic solvents and surfactants.

Der deutsche Chemiker Hermann Staudinger beschrieb 1919 als erster die Reaktion eines Azids mit einem Phosphan. Es war jedoch erst vor Kurzem, dass Bertozzi et al. das Potenzial dieser Reaktion als Biokonjugationsmethode erkannten und die so genannte Staudinger-Ligation einführten. Wegen des bioorthogonalen Charakters sowohl der Azid- als auch der Phosphan-Funktion ergaben sich für die Staudinger-Ligation zahlreiche Anwendungen in verschiedenen komplexen biologischen Systemen. Die Staudinger-Ligation wird beispielsweise zur Markierung von Glycanen, Lipiden, DNA und Proteinen genutzt. Darüber hinaus wird die Staudinger-Ligation zur Bildung von Glycopeptiden, Mikroarrays und funktionalen Biopolymeren eingesetzt. Im neu entstehenden Gebiet der bioorthogonalen Ligations-Strategien hat die Staudinger-Ligation einen hohen Standard gesetzt, mit dem die meisten neuen Methoden verglichen werden. In diesem Aufsatz werden jüngste Entwicklungen und neue Anwendungen der Staudinger-Ligation zusammengefasst.

In 1919 the German chemist Hermann Staudinger was the first to describe the reaction between an azide and a phosphine. It was not until recently, however, that Bertozzi and co-workers recognized the potential of this reaction as a method for bioconjugation and transformed it into the so-called Staudinger ligation. The bio-orthogonal character of both the azide and the phosphine functions has resulted in the Staudinger ligation finding numerous applications in various complex biological systems. For example, the Staudinger ligation has been utilized to label glycans, lipids, DNA, and proteins. Moreover, the Staudinger ligation has been used as a synthetic method to construct glycopeptides, microarrays, and functional biopolymers. In the emerging field of bio-orthogonal ligation strategies, the Staudinger ligation has set a high standard to which most of the new techniques are often compared. This Review summarizes recent developments and new applications of the Staudinger ligation.

The generally accepted benefits of small lateral dimensions of microreactors (1 μm to 1 mm) enable a different way of performing synthetic chemistry: Extremely short contact times in the millisecond range can circumvent the need for performing highly exothermic and fast reactions at very low temperatures. In order to fully exploit this technology, such fast processes need to be redesigned and investigated for optimal reaction conditions, which can differ drastically from the ones traditionally applied. In a comprehensive study, we optimized the selective Swern–Moffatt oxidation of benzyl alcohol to benzaldehyde by varying five experimental parameters, including reaction time and temperature. Employing an ultrashort mixing and reaction time of only 32 ms, the optimal temperature was determined to be 70 °C, approximately 150 °C higher than in the conventional batch conditions. This remarkable difference shows both the potency of continuous-flow chemistry as well as the urgency of a paradigm shift in reaction design for continuous-flow conditions.

De algemeen geaccepteerde voordelen van de zijdelingse dimensies van microreactoren (1 µm tot 1 mm) maken een nieuwe manier van het uitvoeren van synthetische reacties mogelijk: extreem korte contacttijden in de orde van milliseconden kunnen de noodzaak van het uitvoeren van zeer exotherme reacties bij lage temperaturen omzeilen. Om deze technologie ten volle te benutten, moeten dergelijke snelle processen opnieuw worden ontworpen, en moet opnieuw worden gezocht naar optimale reactiecondities, die nu drastisch kunnen verschillen van de conventionele omstandigheden. In een uitgebreide studie hebben we de selectieve Swern–Moffatt oxidatie van benzylalcohol naar benzaldehyde geoptimaliseerd door vijf experimentele parameters te variëren, waaronder reactietijd en temperatuur. Door gebruik te maken van zeer korte meng- en reactietijden, zoals 32 ms, is vastgesteld dat de optimale reactietemperatuur 70 °C bedraagt, ongeveer 150 °C hoger dan onder gebruikelijke condities. Dit opmerkelijke verschil reflecteert enerzijds het potentieel van flowchemie, maar toont anderzijds ook de noodzaak aan van een drastische verandering in denkwijze bij het ontwerpen van continue flowchemie.

The copper-catalyzed azide–alkyne 1,3-dipolar cycloaddition (CuAAC) is extensively used for the functionalization of well-defined polymeric materials. However, the necessity for copper, which is inherently toxic, limits the potential applications of these materials in the area of biology and biomedicine. Therefore, the first entirely copper-free procedure for the synthesis of clickable coatings for the immobilization of functional molecules is reported. In the first step, azide-functional coatings are prepared by thermal crosslinking of side-chain azide-functional polymers and dialkyne linkers. In a second step, three copper-free click reactions (i.e., the Staudinger ligation, the dibenzocyclooctyne-based strain-promoted azide–alkyne [3+2] cycloaddition, and the methyl-oxanorbornadiene-based tandem cycloaddition−retro-Diels−Alder (crDA) reaction) are used to functionalize the azide-containing surfaces with fluorescent probes, allowing qualitative comparison with the traditional CuAAC.

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.