Polymorphs, Proteins, and Nucleation Theory: A Critical Analysis

Full-Color and Switchable Circularly Polarized Light from a Macroscopic Chiral Dendritic Film through a Solid-State Supramolecular Assembly

Chiral materials displaying chirality across multiple length scales have attracted increasing interest due to their potential applications in diverse fields. Herein, we report an efficient approach for the construction of macroscopic crystal dendrites with hierarchical chirality based on an in situ solid assembly in a block copolymer film. Chiral fluorescent crystals are formed by enantiopure d-/l-dibenzoyl tartaric acid and pyrenecarboxylic acid in a poly(1,4-butadiene)-b-poly(ethylene oxide) film. The chiro-optical activity of the crystalline dendrites can be greatly amplified in the absorption and scattering regions and goes along with the dimension of dendrites. Notably, the chiral dendrites exhibited strong circularly polarized luminescence emission with a high dissymmetric factor (0.03). The enhancement of the quantum yield of the chiral film was up to 28%, which was 14 times higher that of the corresponding fluorescent molecules. The circularly polarized emission bands of the films can be fine-tuned by contriving the emissive bands of fluorescent molecules. More importantly, the chiral signals are able to be wiped when the fluorescent group photodimerizes under UV irradiation. This work provides an efficient way to develop functional materials through solid self-assembly.

Monitoring of CaCO3 Nanoscale Structuration through Real-Time Liquid Phase Transmission Electron Microscopy and Hyperpolarized NMR

Calcium carbonate (CaCO₃) is one of the most significant biominerals in nature. Living organisms are able to control its biomineralization by means of an organic matrix to tailor a myriad of hybrid functional materials. The soluble organic components are often proteins rich in acidic amino-acids such as l-aspartic acid. While several studies have demonstrated the influence of amino acids on the crystallization of calcium carbonate, nanoscopic insight of their impact on CaCO₃ mineralization, in particular at the early stages, is still lacking. Herein, we implement liquid phase-transmission electron microscopy (LP-TEM) in order to visualize in real-time and at the nanoscale the prenucleation stages of CaCO₃ formation. We observe that l-aspartic acid favors the formation of individual and aggregated prenucleation clusters which are found stable for several minutes before the transformation into amorphous nanoparticles. Combination with hyperpolarized solid state nuclear magnetic resonance (DNP NMR) and density functional theory (DFT) calculations allow shedding light on the underlying mechanism at the prenucleation stage. The promoting nature of l-aspartic acid with respect to prenucleation clusters is explained by specific interactions with both Ca²⁺ and carbonates and the stabilization of the Ca²⁺-CO₃^2-/HCO₃^- ion pairs favoring the formation and stabilization of the CaCO₃ transient precursors. The study of prenucleation stages of mineral formation by the combination of in situ LP-TEM, advanced analytical techniques (including hyperpolarized solid-state NMR), and numerical modeling allows the real-time monitoring of prenucleation species formation and evolution and the comprehension of their relative stability.

The influence of L-aspartic acid on calcium carbonate nucleation and growth revealed by in situ liquid phase TEM

In situ transmission electron microscopy has permitted the study of nanomaterials in liquid environments with high spatial and temporal resolutions, allowing chemical reaction visualization in real time. The aim of...

Deciphering shell proteome within different Baltic populations of mytilid mussels illustrates important local variability and potential consequences in the context of changing marine conditions

Molluscs defend themselves against predation and environmental stressors through the possession of mineralized shells. Mussels are widely used to predict the effects of abiotic factors such as salinity and pH on marine calcifiers in the context of changing ocean conditions. Shell matrix proteins are part of the molecular control regulating the biomineralization processes underpinning shell production. Under changing environmental conditions, differential expression of these proteins leads to the phenotypic plasticity of shells seen in many mollusc species. Low salinity decreases the availability of calcium and inorganic carbon in seawater and consequently energetic constraints often lead to thin, small and fragile shells in Mytilid mussels inhabiting Baltic Sea. To understand how the modulation of shell matrix proteins alters biomineralization, we compared the shell proteomes of mussels living under full marine conditions in the North Sea to those living in the low saline Baltic Sea. Modulation of proteins comprising the Mytilus biomineralization tool kit is observed. These data showed a relative increase in chitin related proteins, decrease in SD-rich, GA-rich shell matrix proteins indicating that altered protein scaffolding and mineral nucleation lead to impaired shell microstructures influencing shell resistance in Baltic Mytilid mussels. Interestingly, proteins with immunity domains in the shell matrix are also found to be modulated. Shell traits such as periostracum thickness, organic content and fracture resistance qualitatively correlates with the modulation of SMPs in Mytilid mussels providing key insights into control of biomineralization at molecular level in the context of changing marine conditions.

Prism substructures in the shell of Pinna nobilis (Linnaeus, 1758), Mollusca - Evidence for a three-dimensional pulsed-growth model

In the shells of the Pelecypods belonging to the Pinnidae family, the calcareous prismatic units of the outer layer are long-standing references for biomineralization studies. To elucidate how the mechanism of prism formation enables both shell elongation and thickness increase, a top-down structural analysis of these classical "simple prisms" has been carried out, taking advantage of shell sampling on actively mineralizing animals. Particular attention was paid to the morphological and structural patterns of the calcareous units sequentially produced at the margins of the growth lamellae. This pre-prismatic part of the shell allows for studying the mineralizing stages not taken into account in prism reconstructions based on samples taken from older areas of the shell. Examination of the microstructural sequence shows that within the actively mineralizing area of the shell, a step-by-step structuring process is continuously running, providing a renewed view of prism formation as it makes obvious the progressive occurrence of their specific patterns. Given the critically endangered status of the species, a better knowledge of the mineralization process associated to shell growth may become handy for future studies aimed at understanding the health status of individuals based on their shell records.

Purification and functional analysis of the shell matrix protein N66 from the shell of the pearl oyster Pteria sterna

Mollusk biomineralization is a process controlled by a complex interplay of proteins, ions and external regulators. In spite of several studies, there is a lack of knowledge of who (molecules involved), how (mechanism) and why (evolution and adaptation) mollusk are designed as we know them. In this study, a shell matrix protein, N66, has been purified and characterized biochemically from the shell of Pteria sterna. Two protein bands with carbohydrates associated were separated with a molecular weight of ~60 and 64 kDa. It has carbonic anhydrase activity and it is able to form crystal polymorphs of calcium carbonate in vitro. The mRNA N66 was obtained from the mantle tissue of Pteria sterna and the deduced amino acid sequence contained a carbonic anhydrase (CA) domain and a Asn/Gly-rich domain (aa243-439). The CA domain contained three His residues acting as zinc ligands and the gate-keeper residues present in all α-CAs (Glu₁₆₆-Thr₅₂₅), being thus similar to the human isoform hCAVII. Also, to test whether the posttranslational modifications present on the native N66 affects the CA activity and its crystallization capability in vitro, a recombinant N66 was overexpressed in Escherichia coli and functionally characterized. Our results show that recombinant N66 has higher CA activity and produce larger size crystals in vitro than the native N66 protein, suggesting that intrinsic properties of the native N66, such as glycosylations and/or phosphorylations, might regulate its activity.

Biochemical and molecular characterization of N66 from the shell of Pinctada mazatlanica

Mollusk shell mineralization is a tightly controlled process made by shell matrix proteins (SMPs). However, the study of SMPs has been limited to a few model species. In this study, the N66 mRNA of the pearl oyster Pinctada mazatlanica was cloned and functionally characterized. The full sequence of the N66 mRNA comprises 1,766 base pairs, and encodes one N66 protein. A sequence analysis revealed that N66 contained two carbonic anhydrase (CA) domains, a NG domain and several glycosylation sites. The sequence showed similarity to the CA VII but also with its homolog protein nacrein. The native N66 protein was isolated from the shell and identified by mass spectrometry, the peptide sequence matched to the nucleotide sequence obtained. Native N66 is a glycoprotein with a molecular mass of 60-66 kDa which displays CA activity and calcium carbonate precipitation ability in presence of different salts. Also, a recombinant form of N66 was produced in Escherichia coli, and functionally characterized. The recombinant N66 displayed higher CA activity and crystallization capability than the native N66, suggesting that the lack of posttranslational modifications in the recombinant N66 might modulate its activity.

Composite Materials Design: Biomineralization Proteins and the Guided Assembly and Organization of Biomineral Nanoparticles

There has been much discussion of the role of proteins in the calcium carbonate biomineralization process, particularly with regard to nucleation, amorphous stabilization/transformation, and polymorph selection. However, there has been little if any discussion of the potential role that proteins might play in another important process: the guided assembly and organization of mineral nanoparticles into higher-ordered structures such as mesocrystals. This review discusses particle attachment theory and recent evidence of mineral-associated proteins forming hydrogels that assemble and organize mineral clusters into crystalline phase. From this discussion we postulate a mechanism by which biomineralization protein hydrogel aggregation assists in mineral nanoparticle assembly and organization within calcium carbonate skeletal elements and discuss potentials ways for harnessing this process in materials design.

Peculiarities of Protein Crystal Nucleation and Growth

This paper reviews investigations on protein crystallization. It aims to present a comprehensive rather than complete account of recent studies and efforts to elucidate the most intimate mechanisms of protein crystal nucleation. It is emphasized that both physical and biochemical factors are at play during this process. Recently-discovered molecular scale pathways for protein crystal nucleation are considered first. The bond selection during protein crystal lattice formation, which is a typical biochemically-conditioned peculiarity of the crystallization process, is revisited. Novel approaches allow us to quantitatively describe some protein crystallization cases. Additional light is shed on the protein crystal nucleation in pores and crevices by employing the so-called EBDE method (equilibration between crystal bond and destructive energies). Also, protein crystal nucleation in solution flow is considered.

How Can Additives Control the Early Stages of Mineralisation?

The interactions between additives and mineral precursors and intermediates are at the heart of additive-controlled crystallisation, which is of high importance for various fields. In this commentary, we reflect on potential modes of additive control according to classical nucleation theory on one hand, and from the viewpoint of the so-called pre-nucleation cluster pathway on the other. This includes a brief review of the corresponding literature. While the roles of additives are discussed generally, i.e., without specific chemical or structural details, corresponding properties are outlined where possible. Altogether, our discussion illustrates that “non-classical” nucleation pathways promise an improved understanding of additive-controlled scenarios, which could be utilised in targeted applications in various fields, ranging from scale inhibition to materials chemistry.