Cölfen, Helmut
0000-0002-1148-0308 Berufsbeschreibung
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New Horizons of Non-Classical Crystallization
Non-Classical Crystallization (NCC) summarizes a number of crystallization pathways, which differ from the classical lay-er-by-layer growth of crystals involving atomic/molecular building units. Common to NCC is that the building units are larger and include nanoparticles, clusters or liquid droplets, providing multiple handles for their control at each elementary step. Therefore, many different pathways towards the final single crystals are possible and can be influenced by appropriate experimental parameters or additives at each step of crystal formation and growth. As a consequence, NCC allows for a plethora of crystallization strategies towards complex crystalline (hybrid)materials. In this perspective, we summarize the current state of the art with a focus on the new horizons for NCC with respect to mechanistic understanding, high-performance materials and new applications. This gives a glimpse on what will be possible in the future using these crystallization approaches: Examples are new electrode and storage materials, (photo)catalysts, building materials, porous or crystalline materials with complex shape, structural hierarchy and anisotropic single crystals.
Stabilization of Mineral Precursors by Intrinsically Disordered Proteins
Biogenic nucleation and crystallization occur in confined spaces with defined interfacial properties. However, the regulatory functions of organic players in the stabilization and transport of inorganic precursors such as ion clusters, liquid‐condensed phases, and amorphous particles are unclear. Given the prevalence of unstructured proteins in biogenic materials, the present study investigates the effects of biomineral‐associated, intrinsically disordered protein domains with simple and repetitive amino acid compositions on mineral nucleation and their capability to form distinct supramolecular assemblies. The quantitative assessment and structural evaluation of the nucleation process reveal that disordered regions confine hydrated mineral precursors within vesicles, transiently suppressing mineral precipitation. Stabilization of the amorphous mineral is attributed to protein self‐association and restructuration toward β‐configurations, triggered by specific bioinorganic interactions. In consequence, the conditioned macromolecules localize at phase boundaries formed upon liquid–liquid demixing of mineral precursors and stabilize the fluidic mineral precursors against crystallization. Thus, the conformational plasticity and self‐association of intrinsically disordered sequences in response to crystallization environments mediates the selection of functional macromolecular subensembles dedicated to biomaterial growth.
Additive Speciation and Phase Behavior Modulating Mineralization
Natural and synthetic composite materials as yet elude a complete understanding of their formation from organic and inorganic constituents. Addressing the interactions between organic additives and metastable inorganic precursors during mineral nucleation and growth is a critical challenge. In this study, we elucidate additive-controlled mineralization by a novel approach for the in situ continuous monitoring of a widely applied diffusion-based methodology, assisted by the quantitative assessment of mineral nucleation. The formation of amorphous superstructures is attributed to a complex interplay between additives and mineral species viz. ions, ion-clusters, and amorphous precursors as well as a unique phase behavior of the additive molecules relative to the maturing mineral phase. A pH-dependent conditioning of nucleation and demixing of transient liquid-like additive-ion complexes are shown to play critical roles in tuning mineral architecture. Thus, the modulation of mineral precursors and mineralization conditions by additive species determine material composition and morphology.
Mineralization Schemes in the Living World : Mesocrystals
With the expanding knowledge on structure–property relations in biogenic minerals, an emerging challenge is to decipher the underlying biochemical and physical mechanisms of material formation. For this purpose, the dependence of spatial properties of minerals including composition, structure, and orientation on dynamic processes such as the transport of mineral precursors as well as the nucleation and growth of particles requires elucidation. The aim of this chapter is to provide an overview of biomineralization processes in light of the nonclassical pathways of nucleation and crystallization. We address the mechanistic emergence of mesocrystallinity among diverse biomineral architectures as well as the associated checkpoints regulating particle nucleation, growth, and assembly.
On Biomineralization : Enzymes Switch on Mesocrystal Assembly
Cellular machineries guide the bottom-up pathways toward crystal superstructures based on the transport of inorganic precursors and their precise integration with organic frameworks. The biosynthesis of mesocrystalline spines entails concerted interactions between biomolecules and inorganic precursors; however, the bioinorganic interactions and interfaces that regulate material form and growth as well as the selective emergence of structural complexity in the form of nanostructured crystals are not clear. By investigating mineral nucleation under the regulation of recombinant proteins, we show that SpSM50, a matrix protein of the sea urchin spine, stabilizes mineral precursors via vesicle-confinement, a function conferred by a low-complexity, disordered region. Site-specific proteolysis of this domain by a collagenase initiates phase transformation of the confined mineral phase. The residual C-type lectin domain molds the fluidic mineral precursor into hierarchical mesocrystals identical to structural crystal modules constituting the biogenic mineral. Thus, the regulatory functions of proteolytic enzymes can guide biomacromolecular domain constitutions and interfaces, in turn determining inorganic phase transformations toward hybrid materials as well as integrating organic and inorganic components across hierarchical length scales. Bearing striking resemblance to biogenic mineralization, these hybrid materials recruit bioinorganic interactions which elegantly intertwine nucleation and crystallization phenomena with biomolecular structural dynamics, hence elucidating a long-sought key of how nature can orchestrate complex biomineralization processes.
From Solute, Fluidic and Particulate Precursors to Complex Organizations of Matter
The organization of matter from its constitutive units recruits intermediate states with distinctive degrees of self-association and molecular order. Existing as clusters, droplets, gels as well as amorphous and crystalline nanoparticles, these precursor forms have fundamental contributions towards the composition and structure of inorganic and organic architectures. In this personal account, we show that the transitions from atoms, molecules or ionic species to superstructures of higher order are intertwined with the interfaces and interactions of precursor and intermediate states. Structural organizations distributed across different length scales are explained by the multistep nature of nucleation and crystallization, which can be guided towards functional hybrid materials by the strategic application of additives, templates and reaction environments. Thus, the non-classical pathways for material formation and growth offer conceptual frameworks for elucidating, inducing and directing fascinating material organizations of biogenic and synthetic origins.
On Mineral Retrosynthesis of a Complex Biogenic Scaffold
Synergistic relations between organic molecules and mineral precursors regulate biogenic mineralization. Given the remarkable material properties of the egg shell as a biogenic ceramic, it serves as an important model to elucidate biomineral growth. With established roles of complex anionic biopolymers and a heterogeneous organic scaffold in egg shell mineralization, the present study explores the regulation over mineralization attained by applying synthetic polymeric counterparts (polyethylene glycol, poly(acrylic acid), poly(aspartic acid) and poly(4-styrenesulfonic acid-co-maleic acid)) as additives during remineralization of decalcified eggshell membranes. By applying Mg2+ ions as a co-additive species, mineral retrosynthesis is achieved in a manner that modulates the polymorph and structure of mineral products. Notable features of the mineralization process include distinct local wettability of the biogenic organic scaffold by mineral precursors and mineralization-induced membrane actuation. Overall, the form, structure and polymorph of the mineralization products are synergistically affected by the additive and the content of Mg2+ ions. We also revisit the physicochemical nature of the biomineral scaffold and demonstrate the distinct spatial distribution of anionic biomolecules associated with the scaffold-mineral interface, as well as highlight the hydrogel-like properties of mammillae-associated macromolecules.
Mineral Nucleation : Stabilization of Mineral Precursors by Intrinsically Disordered Proteins
Biogenic crystallization reactions produce hybrid nanostructured materials under physiological conditions. In article 1802063, Helmut Cölfen and co‐workers identify the disorder to order transitions of biomacromolecules as a regulatory feature of additive‐controlled mineralization. This molecular conditioning generates conformational sub‐ensembles and supramolecular assemblies adept at controlling the pathways of nucleation and crystallization.
Modulating Nucleation by Kosmotropes and Chaotropes : Testing the Waters
Water is a fundamental solvent sustaining life, key to the conformations and equilibria associated with solute species. Emerging studies on nucleation and crystallization phenomena reveal that the dynamics of hydration associated with mineral precursors are critical in determining material formation and growth. With certain small molecules affecting the hydration and conformational stability of co-solutes, this study systematically explores the effects of these chaotropes and kosmotropes as well as certain sugar enantiomers on the early stages of calcium carbonate formation. These small molecules appear to modulate mineral nucleation in a class-dependent manner. The observed effects are finite in comparison to the established, strong interactions between charged polymers and intermediate mineral forms. Thus, perturbations to hydration dynamics of ion clusters by co-solute species can affect nucleation phenomena in a discernable manner.
Comprehensive Supramolecular Chemistry II : Facet Control in Nanocrystal Growth
Morphology is a critical aspect determining the physical behavior of crystals especially at small-length scales. Insights into the fundamental aspects of nucleation and particle growth enable tuning of crystals with respect to shape, size, crystallography, and composition. With a brief introduction on recent developments concerning nucleation and crystal growth, this article presents diverse methods for nanoparticle synthesis and highlights the individual roles of additives, solvents, templates, surfactants, and seeds. Each route is exemplified with interesting examples that facilitate a lucid understanding of underlying methods.