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Processive catalysts remain attached to a substrate and perform multiple rounds of catalysis. They are abundant in nature. This review highlights artificial processive catalytic systems, which can be divided into (A) catalytic rings that move along a polymer chain, (B) catalytic pores that hold polymer chains and decompose them, (C) catalysts that remain attached to and move around a cyclic substrate via supramolecular interactions, and (D) anchored catalysts that remain in contact with a substrate via multiple catalytic interactions (see frontispiece)., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The kinetic enantio-recognition of chiral viologen guests by planar-chiral porphyrin cage compounds, measured in terms of ΔΔ G ‡on, is determined by the planar-chirality of the host and influenced by the size, as measured by ion mobility-mass spectrometry, but not the chirality of its substituents.

Complex speciation and exchange kinetics of labile ligands are critical parameters for understanding the reactivity of metal complexes in solution. We present a novel approach to determine ligand exchange parameters based on electrospray ionization mass spectrometry (ESI-MS). The introduction of isotopically labelled ligands to a solution of metal host and unlabelled ligands allows the quantitative investigation of the solution-phase equilibria. Furthermore, ion mobility separation can target individual isomers, such as ligands bound at specific sites. As a proof of concept, we investigate the solution equilibria of labile pyridine ligands coordinated in the cavity of macrocyclic porphyrin cage complexes bearing diamagnetic or paramagnetic metal centres. The effects of solvent, porphyrin coordination sphere, transition metal, and counterion on ligand dissociation are discussed. Rate constants and activation parameters for ligand dissociation in the solution can be derived from our ESI-MS approach, thereby providing mechanistic insights that are not easily obtained from traditional solution-phase techniques., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Here we describe a photoswitchable iron(III) salen phosphate catalyst, which is able to catalyze the enantiodivergent oxidation of prochiral aryl alkyl sulfides to chiral aryl alkyl sulfoxides. The stable (S)-axial isomer of the catalyst produced enantioenriched sulfoxides with the (R)-configuration in up to 75 % e.e., whereas the photoisomerized metastable (R)-axial isomer of the catalyst favored the formation of (S)-sulfoxides in up to 43 % e.e. The maximum Δe.e. value obtained in the enantiodivergent sulfoxidation was 118 %, which is identical to the maximum Δe.e. value that was measured in the enantiodivergent epoxidation of alkenes by a related recently described Mn1 catalyst. This iron-based catalyst broadens the scope of photoswitchable enantiodivergent catalysts and may be used in the future to develop a photoswitchable catalytic system that can write digital information on a polymer chain in the form chiral sulfoxide functions., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The development of enantiodivergent catalysts capable of preparing both enantiomeric products from one substrate in a controlled fashion is challenging. Introducing a switching function into the catalyst can address this challenge, allowing the chiral reaction environment to reversibly change during catalysis. Here we report a photoswitchable phosphate ligand, derived from 2,2'-biphenol, which axially coordinates as the counter ion to an achiral manganese(III) salen catalyst, providing the latter with the ability to switch stereoselectivity in the epoxidation of alkenes. The enantiomers of the chiral ligand exist as a pair of pseudo-enantiomers, which can be interconverted by irradiation with light of different wavelengths. The opposite axial chirality of these pseudo-enantiomers is efficiently transferred to the manganese(III) salen catalyst. With this switchable supramolecular catalyst, the enantioselectivity of the epoxidation of a variety of alkenes can be controlled, resulting in opposite enantiomeric excesses of the epoxide products. This transfer of chirality from a photoswitchable anionic ligand to a metal complex broadens the scope of supramolecular catalysts., Competing Interests: Competing Interests. The authors declare no competing interests.

Macrocyclic metal porphyrin complexes can act as shape-selective catalysts mimicking the action of enzymes. To achieve enzyme-like reactivity, a mechanistic understanding of the reaction at the molecular level is needed. We report a mechanistic study of alkene epoxidation by the oxidant iodosylbenzene, mediated by an achiral and a chiral manganese(V)oxo porphyrin cage complex. Both complexes convert a great variety of alkenes into epoxides in yields varying between 20-88 %. We monitored the process of the formation of the manganese(V)oxo complexes by oxygen transfer from iodosylbenzene to manganese(III) complexes and their reactivity by ion mobility mass spectrometry. The results show that in the case of the achiral cage complex the initial iodosylbenzene adduct is formed on the inside of the cage and in the case of the chiral one on the outside of the cage. Its decomposition leads to a manganese complex with the oxo ligand on either the inside or outside of the cage. These experimental results are confirmed by DFT calculations. The oxo ligand on the outside of the cage reacts faster with a substrate molecule than the oxo ligand on the inside. The results indicate how the catalytic activity of the macrocyclic porphyrin complex can be tuned and explain why the chiral porphyrin complex does not catalyze the enantioselective epoxidation of alkenes., Competing Interests: The authors declare no conflict of interest., (© 2022 The Authors. European Journal of Organic Chemistry published by Wiley-VCH GmbH.)

The structure of the title salt, [Ag(C 7 H 12 N 2 ) 2 ][CdCl(C 44 H 28 N 4 )], at 150 K has triclinic symmetry. One of the phenyl rings bonded to the porphyrin mol-ecule and the propyl groups of both yl-idene mol-ecules coordinating to silver are disordered over two positions., (© Bruekers et al. 2022.)

Cadmium porphyrin cage compounds Cd1 and 113 Cd1 have been synthesized from the free base porphyrin cage derivative H 2 1 and Cd(OAc) 2  ⋅ 2 H 2 O or 113 Cd(OAc) 2  ⋅ 2 H 2 O, respectively. The compounds form allosteric complexes with the positively charged guests N,N '-dimethylimidazolium hexafluorophosphate ( DMI ) and N,N '-dimethylviologen dihexafluorophosphate ( Me 2 V ), which bind in the cavity of the cage, and tbupy , which coordinates as an axial ligand to the outside of the cage. In the presence of tbupy , the binding of DMI in Cd1 is enhanced by a factor of ∼31, while the presence of DMI or Me 2 V in the cavity of Cd1 enhances the binding of tbupy by factors of 55 and 85, respectively. The X-ray structures of the coordination complexes of Cd1 with acetone, acetonitrile, and pyridine, the host-guest complex of Cd1 with a bound viologen guest, and the ternary allosteric complex of Cd1 with a bound DMI guest and a coordinated tbupy ligand, were solved. These structures revealed relocations of the cadmium center in and out of the porphyrin plane, depending on whether a guest or a ligand is present. 113 Cd NMR could be employed as a tool to quantify the binding of guests and ligands to 113 Cd1 . 1D EXSY experiments on the ternary allosteric system Cd1-tbupy-Me 2 V revealed that the coordination of tbupy significantly slowed down the dissociation of the Me 2 V guest. Eyring plots of the dissociation process revealed that this kinetic allosteric effect is entropic in nature., Competing Interests: The authors declare no conflict of interest., (© 2022 The Authors. European Journal of Organic Chemistry published by Wiley-VCH GmbH.)

Paramagnetic metallohost systems can bind guest molecules and find application as biomimetic catalysts. Due to the presence of the paramagnetic metal center, rigorous characterization of these systems by NMR spectroscopy can be very difficult. We report here that metallohost-guest systems can be studied by using the paramagnetic relaxation enhancement (PRE) effect. Manganese(III) porphyrin cage compounds are shown through their PRE to thread and bind viologen guests, including a polymeric one. The binding constants and dethreading activation parameters are lower than those of the metal-free porphyrin cage compounds, which is proposed to be a result of charge repulsion of the trivalent metal center and dicationic viologen guest. The threading rate of the manganese(III) porphyrin cage onto the polymer is more than 10 times faster than that of the non-metallated one, which is ascribed to initial binding of the cage to the polymer chain prior to threading, and to an entron effect., (© 2022. The Author(s).)

The structure of the title hydrated salt, C 19 H 28 N 2 2+ ·2Cl - ·0.5H 2 O, at 150 K has monoclinic ( C 2/ c ) symmetry. The water mol-ecule is located on a twofold rotation axis., (© Bruekers et al. 2021.)

Chiral zirconium(IV) double cage sandwich complex Zr(1) 2 has been synthesized in one step from porphyrin cage H 2 1. Zr(1) 2 was obtained as a racemate, which was resolved by HPLC and the enantiomers were isolated in >99.5 % ee. Their absolute configurations were assigned on the basis of X-ray crystallography and circular dichroism spectroscopy. Vibrational circular dichroism (VCD) experiments on the enantiomers of Zr(1) 2 revealed that the chirality around the zirconium center is propagated throughout the whole cage structure. The axial conformational chirality of the double cage complex displayed a VCD fingerprint similar to the one observed previously for a related chiral cage compound with planar and point chirality. Zr(1) 2 shows fluorescence, which is quenched when viologen guests bind in its cavities. The binding of viologen and dihydroxybenzene derivatives in the two cavities of Zr(1) 2 occurs with negative allostery, the cooperativity factors α (=4 K 2 /K 1 ) being as low as 0.0076 for the binding of N,N' -dimethylviologen. These allosteric effects are attributed to a pinching of the second cavity as a result of guest binding in the first cavity., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. European Journal of Organic Chemistry published by Wiley-VCH GmbH.)

Dynamics in complexes of porphyrin cage compounds and viologen-derived guest molecules are investigated by selective exchange NMR spectroscopy (1D EXSY). Exchange rates were found to be independent of excess guest concentration, revealing a dissociative exchange mechanism, which is accompanied by negative activation entropies, indicating significant reorganization of the host-guest complex during dissociation. Nonsymmetric viologen guests with bulky head groups had more unidirectional binding and slower exchange rates than guests with less-bulky head groups. Thermodynamic and kinetic studies revealed that the exchange process is primarily driven by the thermodynamics of binding and that guest binding can be influenced by introducing steric and electronic groups on the host . Exchange studies with guests bearing a polymer chain revealed that both slippage and full dissociation takes place and the rate constants for both processes were determined. The slippage rate constant revealed that for smaller guests exchange takes place nearly exclusively under thermodynamic control., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The construction of macromolecular hosts that are able to thread chiral guests in a stereoselective fashion is a big challenge. We herein describe the asymmetric synthesis of two enantiomeric C 2 -symmetric porphyrin macrocyclic hosts that thread and bind different viologen guests. Time-resolved fluorescence studies show that these hosts display a factor 3 kinetic preference (ΔΔ G ‡ on = 3 kJ mol -1 ) for threading onto the different enantiomers of a viologen guest appended with bulky chiral 1-phenylethoxy termini. A smaller kinetic selectivity (ΔΔ G ‡ on = 1 kJ mol -1 ) is observed for viologens equipped with small chiral sec -butoxy termini. Kinetic selectivity is absent when the C 2 -symmetric hosts are threaded onto chiral viologens appended with chiral tails in which the chiral moieties are located in the centers of the chains, rather than at the chain termini. The reason is that the termini of the latter guests, which engage in the initial stages of the threading process (entron effect), cannot discriminate because they are achiral, in contrast to the chiral termini of the former guests. Finally, our experiments show that the threading and de-threading rates are balanced in such a way that the observed binding constants are highly similar for all the investigated host-guest complexes, i.e. there is no thermodynamic selectivity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The synthesis and characterization of double porphyrin cage compounds are described. They consist of two porphyrins that are each attached to a diphenylglycoluril-based clip molecule via four ethyleneoxy spacers, and are linked together by a single alkyl chain using "click"-chemistry. Following a newly developed multistep synthesis procedure we report three of these double porphyrin cages, linked by spacers of different lengths, i.e. 3, 5, and 11 carbon atoms. The structures of the double porphyrin cages were fully characterized by NMR, which revealed that they consist of mixtures of two diastereoisomers. Their zinc derivatives are capable of forming sandwich-like complexes with the ditopic ligand 1,4-diazabicyclo[2,2,2]octane ( dabco )., (© 2020 The Authors. European Journal of Organic Chemistry published by Wiley‐VCH GmbH.)

Photoelectrochemical cells that utilize water as a source of electrons are one of the most attractive solutions for the replacement of fossil fuels by clean and sustainable solar fuels. To achieve this, heterogeneous water oxidation catalysis needs to be mastered and properly understood. The search continues for a catalyst that is stable at the surface of electro(photo)anodes and can efficiently perform this reaction at the desired neutral pH. Here, we show how oligomeric Ru complexes can be anchored on the surfaces of graphitic materials through CH-π interactions between the auxiliary ligands bonded to Ru and the hexagonal rings of the graphitic surfaces, providing control of their molecular coverage. These hybrid molecular materials behave as molecular electroanodes that catalyse water oxidation to dioxygen at pH 7 with high current densities. This strategy for the anchoring of molecular catalysts on graphitic surfaces can potentially be extended to other transition metals and other catalytic reactions.

Molecular motors and switches change conformation under the influence of an external stimulus, e.g. light. They can be incorporated into functional systems, allowing the construction of adaptive materials and switchable catalysts. Here, we present two molecular motor-functionalized porphyrin macrocycles for future photo-switchable catalysis. They display helical, planar and point chirality, and are diastereomers, which differ in the relative orientation of the motor and macrocyclic components. Fluorescence, UV-vis, and 1 H NMR experiments reveal that the motor-functionalized macrocycles can bind and thread different variants of viologen guests, including a one-side blocked polymeric one of 30 repeat units. The latter feature indicates that the motor systems can find the open end of a polymer chain, thread on it, and move along the chain to eventually bind at the viologen trap, opening possibilities for catalytic writing on single polymer chains via chemical routes.

Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry. In this work we present the resolution of planar-chiral porphyrin cages and the determination of their absolute configuration by vibrational circular dichroism in combination with density functional theory calculations. The chiral porphyrin-cages form complexes with achiral and chiral viologen-guests and upon binding one of the axial enantiomorphs of the guest is bound selectively, as is indicated by induced-electronic-dichroism-spectra in combination with calculations. This host-guest binding also leads to unusual enhanced vibrational circular dichroism, which is the result of a combination of phenomena, such as rigidification of the host and guest structures, charge transfer, and coupling of specific vibration modes of the host and guest. The results offer insights in how the porphyrin cage-compounds may be used to construct a future molecular Turing machine that can write chiral information onto polymer chains.

In a liquid-STM setup environment, the redox behavior of manganese porphyrins was studied at various solid-liquid interfaces. In the presence of a solution of Mn(III)Cl porphyrins in 1-phenyloctane, which was placed at a conductive surface, large and constant additional currents relative to a set tunneling current were observed, which varied with the magnitude of the applied bias voltage. These currents occurred regardless of the type of surface (HOPG or Au(111)) or tip material (PtIr, Au or W). The additional currents were ascribed to the occurrence of redox reactions in which chloride is oxidized to chlorine and the Mn(III) center of the porphyrin moiety is reduced to Mn(II). The resulting Mn(II) porphyrin products were identified by UV-vis analysis of the liquid phase. For solutions of Mn(III) porphyrins with non-redox active acetate instead of chloride axial ligands, the currents remained absent., (Copyright © 2020, Habets et al.; licensee Beilstein-Institut.)

Organothiol monolayers on metal substrates (Au, Ag, Cu) and their use in a wide variety of applications have been extensively studied. Here, the growth of layers of organothiols directly onto muscovite mica is demonstrated using a simple procedure. Atomic force microscopy, surface X-ray diffraction, and vibrational sum-frequency generation IR spectroscopy studies revealed that organothiols with various functional endgroups could be self-assembled into (water) stable and adaptable ultra-flat organothiol monolayers over homogenous areas as large as 1 cm 2 . The strength of the mica-organothiol interactions could be tuned by exchanging the potassium surface ions for copper ions. Several of these organothiol monolayers were subsequently used as a template for calcite growth., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The study of artificial receptor molecules with the intention to mimic enzyme-substrate binding processes and catalysis in nature has always been a traditional area of research in supramolecular chemistry. Along this line, our group has developed a family of porphyrin cage compounds based on glycoluril and employed these in host-guest binding studies, as components of allosterically controlled self-assembled processes, in which structural changes in the cage upon complexation of a guest or a ligand change binding equilibria, and as enzyme mimics in supramolecular catalysis. In a recently started research program aimed at developing a new molecular approach to long-term data storage, porphyrin cage compounds are studied as molecular machines to encode information into synthetic polymer chains. In this Feature Article we will give an overview of the above aspects of our porphyrin cage compounds and place them in the context of related systems reported in the literature.

The synthesis and surface self-assembly behavior of two types of metal-porphyrin dimers is described. The first dimer type consists of two porphyrins linked via a rigid conjugated spacer, and the second type has an alkyne linker, which allows rotation of the porphyrin moieties with respect to each other. The conjugated dimers were equipped with two copper or two manganese centers, while the flexible dimers allowed a modular built-up that also made the incorporation of two different metal centers possible. The self-assembly of the new porphyrin dimers at a solid-liquid interface was investigated at the single-molecule scale using scanning tunneling microscopy (STM). All dimers formed monolayers, of which the stability and the internal degree of ordering of the molecules depended on the metal centers in the porphyrins. While in all monolayers the dimers were oriented coplanar with respect to the underlying surface ('face-on'), the flexible dimer containing a manganese and a copper center could be induced, via the application of a voltage pulse in the STM setup, to self-assemble into monolayers in which the porphyrin dimers adopted a non-common perpendicular ('edge-on') geometry with respect to the surface.

As part of a project aimed at the development of chiral processive catalysts that can write information on a polymer chain we describe the synthesis of two optically active porphyrin macrocycles, which are prepared in 3 steps from an achiral precursor compound. Fluorescence and 1 H-NMR studies show that one of the macrocycles displays selectivity in the binding of chiral viologen guest molecules.

Two-dimensional polymers (2DP) are a new class of materials that consist of a monolayer of ordered molecular building blocks, which have been covalently linked. One of these monomers was self-assembled on a flat muscovite mica scaffold and subsequently the organic layer was polymerized. The resulting flat and stable 2DP layer was used as a template for protein crystallization. Crystals of insulin were epitaxially grown on the template, whereas insulin crystals grown on clean muscovite mica had a random orientation. The template was selective, considering that no epitaxially ordered crystals formed of hen egg white lysozyme, bovine serum albumin, or talin., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Supramolecular approaches in transition-metal catalysis, including catalyst encapsulation, have attracted considerable attention. Compared to enzymes, supramolecular catalysts in general are less complex. Enzyme activity is often controlled by the use of smaller cofactor molecules, which is important in order to control reactivity in complex mixtures of molecules. Interested in increasing complexity and allowing control over supramolecular catalyst formation in response to external stimuli, we designed a catalytic system that only forms an efficient supramolecular complex when a small cofactor molecule is added to the solution. This in turn affects both the activity and selectivity when applied in a hydroformylation reaction. This contribution shows that catalyst encapsulation can be controlled by the addition of a cofactor, which affects crucial catalyst properties., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

We report the face-selective threading of a chiral porphyrin cage compound onto viologen guests that are provided on both ends with substituents of different sizes. Depending on the types of terminal groups on the guest the cage compound orients itself in one of two possible directions.

The supramolecular assembly of metal-porphyrin hexamers with bidentate ligands in chloroform solutions is demonstrated by UV/Vis and 1H NMR-titrations, and Small Angle Neutron Scattering (SANS) experiments. Titrations of zinc porphyrin hexamer Zn1 with 1,4-diazabicyclo[2,2,2]octane (DABCO) revealed that at a DABCO/Zn1 molar ratio of 3, intermolecular sandwich complexes are formed, which can be considered as "circular-shaped porphyrin ladders". These supramolecular complexes further aggregate into larger polymeric stacks, as a result of a combination of cooperativity effects, π-π stacking interactions, and chelate effects. The presence of rodlike assemblies in solution, formed by assembly of Zn1 and DABCO, is confirmed by SANS-experiments. Using a model for cylindrical assemblies, curve fitting calculations reveal that rods with an average length of 26 nm and a radius of 30-35 Å were formed, corresponding to columnar stacks of approximately 30 hexamer molecules. In contrast, the metal-free hexamer H21 did not form extended assemblies due to the absence of coordinative intermolecular interactions.

Nitration of tetraphenylporphyrin cage compound 1, at -40 °C, leads to the regioselective formation of the chiral mononitro compound 2 (75% isolated yield) and, at -30 °C, to the achiral syn-dinitro-derivative 3 and the chiral anti-dinitro derivative 4 in a diastereomeric ratio of 5:2, which were separated by chromatography (46 and 20% yields, respectively). The structures of the compounds were confirmed by X-ray crystallography.

We describe a manganese porphyrin-α-cyclodextrin conjugate as a catalyst for the epoxidation of cis-polybutadiene with trans-epoxide preference, which is a reverse stereoselectivity as compared to normal porphyrin catalysts. A clamp-like mechanism is proposed based on a combination of circular dichroism analysis, molecular modeling, and a series of epoxidation experiments.

Surfaces with controllable topography and chemistry were prepared to act as substrates for protein crystallization, in order to investigate the influence of these surface properties on the protein crystallization outcome. Three different methods were investigated to deposit 1,3,5-tris(10-carboxydecyloxy)benzene (TCDB) on a muscovite mica substrate to find the best route for controlled topography. Of these three, sublimation worked best. Contact angle measurements revealed that the surfaces with short exposure to the TCDB vapor (20 min or less) are hydrophilic, while surfaces exposed for 30 min or longer are hydrophobic. The hydrophilic surfaces are flat with low steps, while the hydrophobic surfaces contain macrosteps. Four model proteins were used for crystallization on the surfaces with controlled topography and chemistry. Hen egg white lysozyme crystals were less numerous on the surface with macrosteps than on smoother surfaces. On the other hand, insulin nucleated faster on the hydrophobic surfaces with macrosteps, and therefore, the crystals were more abundant and smaller. Bovine serum albumin and talin protein crystals were more numerous on all TCDB functionalized surfaces, compared to the reference clean muscovite mica surfaces. Overall, this shows that surface topography and chemistry is an important factor that partly determines the outcome in a protein crystallization experiment., Competing Interests: The authors declare no competing financial interest.

To comply with the rapidly increasing demand of information storage and processing, new strategies for computing are needed. The idea of molecular computing, where basic computations occur through molecular, supramolecular, or biomolecular approaches, rather than electronically, has long captivated researchers. The prospects of using molecules and (bio)macromolecules for computing is not without precedent. Nature is replete with examples where the handling and storing of data occurs with high efficiencies, low energy costs, and high-density information encoding. The design and assembly of computers that function according to the universal approaches of computing, such as those in a Turing machine, might be realized in a chemical way in the future; this is both fascinating and extremely challenging. In this perspective, we highlight molecular and (bio)macromolecular systems that have been designed and synthesized so far with the objective of using them for computing purposes. We also present a blueprint of a molecular Turing machine, which is based on a catalytic device that glides along a polymer tape and, while moving, prints binary information on this tape in the form of oxygen atoms.