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Using a Soxhlet-apparatus, we demonstrate that a conglomerate-forming clopidogrel precursor undergoing solution phase racemization can be deracemized through cyclic solvent removal and re-addition.

Acknowledgements: This work is part of the Dutch Research Council (NWO) and was performed at the NWO-Institute AMOLF. The authors would like to thank Daniël Koletzki for his contributions in enabling the in situ optical setup. L. S. D. A and E. A. L. acknowledge the D3N project (project no. 17972 of the research programme HTSM2019 from the NWO-TTW Domain), which is (partly) financed by the Dutch Research Council (NWO). S. v. D. acknowledges OCENW.KLEIN.155, which is financed by the Dutch Research Council (NWO). The work of G. G. and J. B. was supported by the EPSRC International Centre to Centre under grant no. EP/S030638/1. A. v. D. W. and W. L. N. acknowledges the Vernieuwingsimpuls Vidi research program “Shaping up materials” with project no. 016.Vidi.189.083, which is partly financed by the Dutch Research Council (NWO). B. E. and I. S. acknowledge OCENW.KLEIN.076, which is financed by the Dutch Research Council (NWO)., Two-dimensional (2D) lead halide perovskites are an exciting class of materials currently being extensively explored for photovoltaics and other optoelectronic applications. Their ionic nature makes them ideal candidates for solution processing into both thin films and nanostructured crystals. Understanding how 2D lead halide perovskite crystals form is key towards full control over their physical properties, which may enable new physical phenomena and devices. Here, we investigate the effects of the Pb oxidation state of the initial inorganic precursor on the growth of pure-phase (n = 1) - Popper 2D perovskite BA2PbI4 in single-step synthesis. We examine the different crystallisation routes in exposing PbO2 and PbI2 powders to a BAI : IPA organo-halide solution, by combining in situ optical microscopy, UV-VIS spectroscopy and time-resolved high performance liquid chromatography. So far, works using PbO2 to synthesise 3D LHPs introduce a preceding step to reduce PbO2 into either PbO or PbI2. In this work, we find that BA2PbI4 is directly formed when exposing PbO2 to BAI : IPA without the need for an external reducing agent. We explain this phenomenon by the spontaneous reduction/oxidation of PbO2/BAI that occurs under iodine-rich conditions. We observe differences in the final morphology (rectangles vs. octagons) and nanocrystal growth rate, which we explain through the different chemistry and iodoplumbate complexes involved in each case. As such, this work spans the horizon of usable lead precursors and offers a new turning knob to control crystal growth in single-step LHP synthesis.

Amplification of enantiomeric excesses (ee) is routinely observed during chiral crystallization of conglomerate crystals for which the enantiomers undergo racemization in solution. Although routes comprising a combination of crystal growth and dissolution are frequently used to obtain enantiopure molecules, crystal growth by itself has rather been considered as a source of enantiomeric erosion and discounted as a potential source of enantiomeric amplification. Counterintuitively, we here demonstrate striking enantiomeric amplification during crystal growth for clopidogrel and

The crystal growth behavior induced by small molecular additives is commonly assumed to be far less complex and rich in comparison to that obtained when using macromolecules. Herein, we demonstrate that the small organic molecule Acid Orange 7 can induce a large diversity of multi-layered barium carbonate structures. These multi-layered structures stem from the small molecule imperfectly blocking the fastest growing crystal face. By tuning the balance of growth and inhibition, we control the layer shape and thickness of the structures. Extending these strategies to strontium carbonate enables the precipitation of large quasi two-dimensional multi-layer sheets. Collectively, these findings highlight the unforeseen potential for using small organic molecules to induce the formation of complex inorganic structures., The crystal growth behavior induced by small molecular additives is assumed to be far less complex and rich than growth using macromolecular additives. Herein, the small organic molecule Acid Orange 7 induces a large diversity of multi-layered barium carbonate structures. Extending these strategies to strontium carbonate enables the precipitation of large quasi two-dimensional multi-layer sheets.

Straightforward manufacturing pathways toward large-scale, uniformly layered composites may enable the next generation of materials with advanced optical, thermal, and mechanical properties. Reaction–diffusion systems are attractive candidates to this aim, but while layered composites theoretically could spontaneously arise from reaction–diffusion, in practice randomly oriented patches separated by defects form, yielding nonuniformly patterned materials. A propagating reaction front can prevent such nonuniform patterning, as is the case for Liesegang processes, in which diffusion drives a reaction front to produce layered precipitation patterns. However, while diffusion is crucial to control patterning, it slows down transport of reactants to the front and results in a steady increase of the band spacing as the front advances. Here, we circumvent these diffusive limitations by embedding the Liesegang process in mechanically responsive hydrogels. The coupling between a moving reaction front and hydrogel contraction induces the formation of a self-regulated transport channel that ballistically carries reactants toward the area where patterning occurs. This ensures rapid and uniform patterning. Specifically, large-scale ( > 5-cm) uniform banding patterns are produced with tunable band distance ( d = 60 to 160 µm) of silver dichromate crystals inside responsive gelatin–alginate hydrogels. The generality and applicability of our mechanoreaction–diffusion strategy are demonstrated by forming patterns of precipitates in significantly smaller microscopic banding patterns ( d = 10 to 30 µm) that act as self-organized diffraction gratings. By circumventing the inherent limitations of diffusion, our strategy unlocks the potential of reaction–diffusion processes for the manufacturing of uniformly layered materials.

Two-dimensional (2D) lead halide perovskites are an exciting class of materials currently being extensively explored for both photovoltaics and optoelectronic applications. The ionic nature of these materials makes them ideal candidates for solution processing into both thin films and nanostructured crystals. However, a complete mechanistic description of 2D perovskite crystallization in solution is still missing due to the intricacy of process parameters and intermediates. Here, we investigate the role of different solid lead precursors (PbO2, PbI2, PbCO3) on the crystallization of pure-phase, n=1, Ruddleson-Popper 2D perovskite BA2PbI4, during a two-step drop-cast-based synthesis. While BA2PbI4 is formed in all cases, the nucleation and resulting morphology are strongly dependent on the choice of precursor, where the three lead precursors differ from each other in terms of their Pb-ion oxidation state, crystal structure, and material class. We use in-situ optical live imaging during synthesis to reveal clear differences in crystallization kinetics of the same 2D perovskite as a function of the lead precursor. We discern three competing mechanisms in the Pb-precursor for the formation of BA2PbI4: dissolution/complexation, BAI intercalation, and solid-state conversion. The differences in the oxidation state and solubility of the starting lead precursor in halide-rich solution play a key role in defining the crystallization pathway(s). This work demonstrates the importance of lead precursors in defining the nucleation and growth of perovskites thereby advancing the existing solution-processing techniques. Understanding how 2D perovskite crystals form in solution is key towards full control over their growth and optoelectronic properties, which will enable new types of physical phenomena and devices.

The next generation of advanced functional materials can greatly benefit from methods for realizing the right chemical composition at the right place. Nanocomposites of amorphous silica and metal carbonate nanocrystals (BaCO3/SiO2) form an attractive starting point as they can straightforwardly be assembled in different controllable three-dimensional (3D) shapes, while the chemical composition of the nanocrystals can be completely converted via ion exchange. Nevertheless, it is still unknown-let alone predictable-how nanoscopic changes in the lattice volume of the nanocrystals translate to changes in the microscopic dimensions of 3D BaCO3/SiO2 structures during ion exchange. Here, we demonstrate that the microscopic shape adapts to contraction and expansion of the atomic spacing of nanocrystals. Starting from BaCO3/SiO2, we systematically decrease and increase lattice volumes by converting the BaCO3 nanocrystals into a range of chalcogenides and perovskites. Based on geometrical analysis, we obtain a precise prediction for how the microscopic nanocomposite volume follows the change in nanoscopic crystal volume. The silica matrix facilitates mechanical flexibility to adapt to nanoscopic volume changes, while preserving the 3D morphology and fine details of the original composite with high fidelity. The versatility and predictability of shape-preserving conversion reactions open up exciting opportunities for using nanocomposites as functional components.

Solid-state deracemization via temperature cycles is a technique that has been shown to be effective to isolate the pure enantiomer of a conglomerate-forming compound. This process has a large number of operating parameters that can be adjusted according to system-specific properties. On the one hand, this feature makes the process flexible and prone to optimization. On the other hand, the design space is so large that experimental optimization of the process can become long and cumbersome. In this work, we achieve two results. First, we show that deracemization via temperature cycles works very effectively for two new experimental systems, namely, the chiral compounds 2-(benzylideneamino)-2-(2-chlorophenyl)acetamide (CPG) and 3,3-dimethyl-2-((naphthalen-2-ylmethylene)amino)butanenitrile (tLEU). Second, we propose a new approach for the design of an effective deracemization process via temperature cycles for a new compound. Therefore, in this work, we investigate the effect of different operating conditions, namely, the initial enantiomeric excess, the cooling rate, the temperature range, and the catalyst concentration, on the performance of deracemization via temperature cycles for the new compounds CPG and tLEU and for N-(2-methylbenzylidene)phenylglycine amide (NMPA), which was already studied in a previous paper. On the basis of these outcomes, we conclude by proposing a model-free screening strategy for the design of an effective deracemization process via temperature cycles for a new compound., Organic Process Research & Development, 24 (8), ISSN:1083-6160, ISSN:1520-586X

All biological systems are composed of molecules of a single chirality. Although many different scenarios can lead to chiral symmetry breaking, the transmission of the absolute configuration of one compound to another one remains challenging. We here demonstrate that during crystallization-induced chiral symmetry breaking by Viedma ripening, a cascade of different and counteracting processes can occur: solid-solution formation and dissolution inhibition favor symmetry breaking towards the same absolute configuration, while enantioselective growth inhibition favors symmetry breaking towards the opposite absolute configuration. These insights offer a new playground for controlling symmetry breaking processes that are of fundamental and practical importance.

Biological assembly processes offer inspiration for ordering building blocks across multiple length scales into advanced functional materials. Such bioinspired strategies are attractive for assembling supported catalysts, where shaping and structuring across length scales are essential for their performance but still remain tremendously difficult to achieve. Here, we present a simple bioinspired route toward supported catalysts with tunable activity and selectivity. We coprecipitate shape-controlled nanocomposites with large specific surface areas of barium carbonate nanocrystals that are uniformly embedded in a silica support. Subsequently, we exchange the barium carbonate to cobalt while preserving the nanoscopic layout and microscopic shape, and demonstrate their catalytic performances in the Fischer–Tropsch synthesis as a case study. Control over the crystal size between 10 and 17 nm offers tunable activity and selectivity for shorter (C5–C11) and longer (C20+) hydrocarbons, respectively. Hence, these results open simple, versatile, and scalable routes to tunable and highly reactive bioinspired catalysts., Bioinspired strategies offer tremendous inspiration for ordering building blocks across multiple length scales into advanced functional materials. Herein, a bioinspired strategy is introduced for assembling catalytic nanocomposites with independently programmable microscopic shape and nanoscopic crystal size. To show the versatility and functionality potential, the synthesis is scaled up and tunable reactivity and selectivity are demonstrated for the Fischer−Tropsch synthesis.

Shape-preserving conversion offers a promising strategy to transform self-assembled structures into advanced functional components with customizable composition and shape. Specifically, the assembly of barium carbonate nanocrystals and amorphous silica nanocomposites (BaCO3/SiO2) offers a plethora of programmable three-dimensional (3D) microscopic geometries, and the nanocrystals can subsequently be converted into functional chemical compositions, while preserving the original 3D geometry. Despite this progress, the scope of these conversion reactions has been limited by the requirement to form carbonate salts. Here, we overcome this limitation using a single-step cation/anion exchange that is driven by the temporal pH change at the converting nanocomposite. We demonstrate the proof of principle by converting BaCO3/SiO2 nanocomposites into tin-containing nanocomposites, a metal without a stable carbonate. We find that BaCO3/SiO2 nanocomposites convert in a single step into hydroromarchite nanocomposites (Sn3(OH)2O2/SiO2) with excellent preservation of the 3D geometry and fine features. We explore the versatility and tunability of these Sn3(OH)2O2/SiO2 nanocomposites as a precursor for functional compositions by developing shape-preserving conversion routes to two desirable compositions: tin perovskites (CH3NH3SnX3, with X = I or Br) with tunable photoluminescence (PL) and cassiterite (SnO2)—a widely used transparent conductor. Ultimately, these findings may enable integration of functional chemical compositions into advanced morphologies for next-generation optoelectronic devices., The combination of self-assembly and ion exchange offers a facile route to sculpt complex architectures with tunable composition. Here, self-assembled BaCO3/SiO2 nanocomposites are converted into tin-containing nanocomposites via a temporal local reaction zone. This conversion strategy gives direct access to nanocomposites of tin perovskites and tin oxides with tunable three-dimensional shapes.

A simple route to enantiomerically pure (S)-2-aminobutyramide – the chiral component of the anti-epileptic drugs Levetiracetam and Brivaracetam has been developed. This approach is based on the rational design and application of a Viedma ripening process. The practical potential of the process is demonstrated on a large scale.

An efficient deracemization method for conversion of the racemate to the desirable (R)-enantiomer of Praziquantel has been developed by coupling incompatible racemization and crystallization processes. By a library approach, a derivative that crystallizes as a conglomerate has been identified. Racemization occurs via reversible hydrogenation over a palladium on carbon (Pd/C) packed column at 130 0C, whereas deracemization is achieved by alternating crystal growth/dissolution steps with temperature cycling between 5-15 0C. These incompatible processes are combined by means of a flow system resulting in complete deracemization of the solid phase to the desired (R)-enantiomer (98 % ee ). Such an unprecedented deracemization by a decoupled crystallization/racemization approach can readily be turned into a practical process and opens new opportunities for the development of essential enantiomerically pure building blocks that require harsh methods for racemization.

Forging customizable compounds into arbitrary shapes and structures has the potential to revolutionize functional materials, where independent control over shape and composition is essential. Current self-assembly strategies allow impressive levels of control over either shape or composition, but not both, as self-assembly inherently entangles shape and composition. Herein, independent control over shape and composition is achieved by chemical conversion reactions on nanocrystals, which are first self-assembled in nanocomposites with programmable microscopic shapes. The multiscale character of nanocomposites is crucial: nanocrystals (5-50 nm) offer enhanced chemical reactivity, while the composite layout accommodates volume changes of the nanocrystals (approximate to 25, which together leads to complete chemical conversion with full shape preservation. These reactions are surprisingly materials agnostic, allowing a large diversity of chemical pathways, and development of conversion pathways yielding a wide selection of shape-controlled transition metal chalcogenides (cadmium, manganese, iron, and nickel oxides and sulfides). Finally, the versatility and application potential of this strategy is demonstrated by assembling: 1) a scalable and highly reactive nickel catalyst for the dry reforming of butane, 2) an agile magnetic-controlled particle, and 3) an electron-beam-controlled reversible microactuator with sub-micrometer precision. Previously unimaginable customization of shape and composition is now achievable for assembling advanced functional components.

Propagation of homochirality plays a crucial role in the discussion on the origin of life. We investigated the role of structurally related enantiopure additives in chiral symmetry breaking during reactive crystallizations. We demonstrate that symmetry breaking can be driven towards the same absolute configuration as the additive if this additive forms an enantiospecific solid solution with the racemate. We observe two antagonistic processes: enantiospecific growth inhibition directs symmetry breaking to the opposite enantiomer following "the rule of reversal", and enantiospecific solid solution formation that favors homochiral outcome. During continuous grinding, contributions of solid solution formation override contributions of enantiospecific growth inhibition, directing the process towards the absolute configuration of the additive. Collectively, our findings offer a potential mechanism for the propagation of homochirality.

Controlling self-assembly of nanocomposites is a fundamental challenge with exciting implications for next-generation advanced functional materials. Precursors for composites can be generated photochemically, but limited insight in the underlying processes have hindered precise hands-on guidance. In this study, light-controlled nucleation and growth is demonstrated for self-assembling composites according to precise user-defined designs. Carbonate is generated photochemically using ultraviolet (UV) light to steer the precipitation of nanocomposites of barium carbonate nanocrystals and amorphous silica (BaCO3 /SiO2 ). Using a custom-build optical setup, the self-assembly process is controlled by optimizing the photogeneration, diffusion, reaction, and precipitation of the carbonate species, using the radius and intensity of the UV-light irradiated area and reaction temperature. Exploiting this control, nucleation is induced and the contours and individual features of the growing composite are sculpted according to micrometer-defined light patterns. Moreover, moving light patterns are exploited to create a constant carbonate concentration at the growth front to draw lines of nanocomposites with constant width over millimeters with micrometer precision. Light-directed generation of local gradients opens previously unimaginable opportunities for guiding self-assembly into functional materials. This article is protected by copyright. All rights reserved.

In recent years, two dimensional (2D) perovskites have attracted growing interest as a material for optoelectronic applications, combining the defect tolerance and strong absorption of bulk perovskites with enhanced material stability. Moreover, the possibility to tune their bandgap via control of the thickness of the perovskite layers allows precise optimization of the energy levels in these materials, making them ideal candidates for rationally designed semiconductor heterojunctions. However, despite the advances in the synthesis of 2D perovskites, typical fabrication strategies produce either uniform thin-films or isolated single crystals, severely hindering the prospect of patterning these materials. We demonstrate an ion-exchange synthesis of 2D perovskites, starting from a lead carbonate host material and converting it to 2D perovskites via a solution-based treatment. The process allows for the fabrication of 2D perovskites spanning a range of halide compositions and 2D layer thicknesses and yields highly crystalline luminescent materials. We demonstrate the potential of this approach for 2D perovskite patterning, spatially localizing 2D perovskite structures via the conversion of pre-patterned lead carbonate structures. These results significantly expand the possibilities of 2D perovskite material design toward controllable integration of 2D perovskites in complex device architectures. (C) 2021 Author(s).

Herein we introduce a “chiral switch” – a sequence of operations that alternate between equilibrium and non-equilibrium conditions to switch the absolute configuration of a chiral center. The generality and practical potential of the technique are demonstrated with three unnatural α-amino acid precursors.

Patterning materials with different properties in a single film is a fundamental challenge and essential for the development of next-generation (opto)electronic functional components. This work introduces the concept of ion exchange lithography and demonstrates spatially controlled patterning of electrically insulating films and semiconductors with tunable optoelectronic properties. In ion exchange lithography, a reactive nanoparticle “canvas” is locally converted by printing ion exchange “inks.” To demonstrate the proof of principle, a canvas of insulating nanoporous lead carbonate is spatioselectively converted into semiconducting lead halide perovskites by contact printing an ion exchange precursor ink of methylammonium and formamidinium halides. By selecting the composition of the ink, the photoluminescence wavelength of the perovskite semiconductors is tunable over the entire visible spectrum. A broad palette of conversion inks can be applied on the reactive film by printing with customizable stamp designs, spray-painting with stencils, and painting with a brush to inscribe well-defined patterns with tunable optoelectronic properties in the same canvas. Moreover, the optoelectronic properties of the converted canvas are exploited to fabricate a green light-emitting diode (LED), demonstrating the functionality potential of ion exchange lithography.

Bottom‐up assembly can organize simple building blocks into complex architectures for light manipulation. The optical properties of self‐assembled polycrystalline barium carbonate/silica double helices are studied using fluorescent Fourier and Mueller matrix microscopy. Helices doped with fluorescein direct light emission along the long axis of the structure. Furthermore, light transmission measured normal and parallel to the long axis exhibits twist sense‐specific circular retardance and waveguiding, respectively, although the measurements suffer from depolarization. The helices thus integrate highly directional emission with enantiomorph‐specific polarization. This optical response emerges from the arrangement of nanoscopic mineral crystallites in the microscopic helix, and demonstrates how bottom‐up assembly can achieve ordering across multiple length scales to form complex functional materials. 1 Introduction

The Strecker reaction is broadly used for the preparation of α-amino acids. However, control of enantioselectivity remains challenging. We here couple the Strecker reaction to Viedma ripening for the absolute asymmetric synthesis of highly sterically hindered α-amino acids. As proof-of-principle, the enantiomerically pure α-amino acids tert-leucine and α-(1-adamantyl)glycine were obtained.

Biological and bio-inspired mineralization processes yield a variety of three-dimensional structures with relevance for fields such as photonics, electronics and photovoltaics. However, these processes are only compatible with specific material compositions, often carbonate salts, thereby hampering widespread applications. Here we present a strategy to convert a wide range of metal carbonate structures into lead halide perovskite semiconductors with tunable bandgaps, while preserving the 3D shape. First, we introduce lead ions by cation exchange. Second, we use carbonate as a leaving group, facilitating anion exchange with halide, which is followed rapidly by methylammonium insertion to form the perovskite. As proof of principle, pre-programmed carbonate salt shapes such as vases, coral-like forms and helices are transformed into perovskites while preserving the morphology and crystallinity of the initial micro-architectures. This approach also readily converts calcium carbonate biominerals into semiconductors, furnishing biological and programmable synthetic shapes with the performance of artificial compositions such as perovskite-based semiconductors.