Chiral switching in biomineral suprastructures induced by homochiral l-amino acid

Selective Chiral Interactions between Hydrophilic/Hydrophobic Amino Acids and Growing Gypsum Crystals

In nature, selective interactions between chiral amino acids and crystals are important for the formation of chiral biominerals and provide insight into the mysterious origin of homochirality. Here, we show that chiral amino acids with different hydrophilicities/hydrophobicities exhibit different chiral selectivity preferences in the dynamically growing gypsum [001] steps. Hydrophilic amino acids show a chiral selectivity preference for their d-isomers, whereas hydrophobic amino acids prefer their l-isomers. These differences in chiral recognition can be attributed to the different stereochemical matching between the hydrophilic and hydrophobic amino acids on the [001] steps of growing gypsum. These different chiral selectivities resulting from the amino acid hydrophilicity/hydrophobicity are confirmed by the experimental crystallization investigations from nano regulation on dynamic steps, to microscopic modification of gypsum morphology, and to macroscopic precipitation. Furthermore, as the hydrophilicity of amino acids increases, the disparity in chiral selection rises; conversely, the increase in the hydrophobicity of amino acids results in a decline in chiral selection. These insights improve our understanding of the interaction mechanism between amino acids and crystals and provide insights into the formation process of chiral biominerals and the origin of homochirality in nature.

Size Control of Biomimetic Curved-Edge Vaterite with Chiral Toroid Morphology via Sonochemical Synthesis

The metastable vaterite polymorph of calcium carbonate (CaCO3) holds significant practical importance, particularly in regenerative medicine, drug delivery, and various personal care products. Controlling the size and morphology of vaterite particles is crucial for biomedical applications. This study explored the synergistic effect of ultrasonic (US) irradiation and acidic amino acids on CaCO3 synthesis, specifically the size, dispersity, and crystallographic phase of curved-edge vaterite with chiral toroids (chiral-curved vaterite). We employed 40 kHz US irradiation and introduced L- or D-aspartic acid as an additive for the formation of spheroidal chiral-curved vaterite in an aqueous solution of CaCl2 and Na2CO3 at 20 ± 1 °C. Chiral-curved vaterites precipitated through mechanical stirring (without US irradiation) exhibited a particle size of approximately 15 μm, whereas those formed under US irradiation were approximately 6 μm in size and retained their chiral topoid morphology. When a fluorescent dye was used for the analysis of loading efficiency, the size-reduced vaterites with chiral morphology, produced through US irradiation, exhibited a larger loading efficiency than the vaterites produced without US irradiation. These results hold significant value for the preparation of biomimetic chiral-curved CaCO3, specifically size-reduced vaterites, as versatile biomaterials for material filling, drug delivery, and bone regeneration.

Chirality Supramolecular Systems: Helical Assemblies, Structure Designs, and Functions

Chirality, as one of the most striking characteristics, exists at various scales in nature. Originating from the interactions of host and guest molecules, supramolecular chirality possesses huge potential in the design of functional materials. Here, an overview of the recent progress in structure designs and functions of chiral supramolecular materials is present. First, three design routes of the chiral supramolecular structure are summarized. Compared with the template-induced and chemical synthesis strategies that depend on accurate molecular identification, the twisted-assembly technique creates chiral materials through the ordered stacking of the nanowire or films. Next, chirality inversion and amplification are reviewed to explain the chirality transfer from the molecular level to the macroscopic scale, where the available external stimuli on the chirality inversion are also given. Lastly, owing to the optical activity and the characteristics of the layer-by-layer stacking structure, the supramolecular chirality materials display various excellent performances, including smart response, shape-memorization, superior mechanical performance, and applications in biomedical fields. To sum up, this work provides a systematic review of the helical assemblies, structure design, and applications of supramolecular chirality systems.

Chiral Mesostructured Inorganic Materials with Optical Chiral Response

Fabricating chiral inorganic materials and revealing their unique quantum confinement-determined optical chiral responses are crucial tasks in the multidisciplinary fields of chemistry, physics, and biology. The field of chiral mesostructured inorganic materials started from the synthesis of individual nanocrystals and evolved to include their assembly from metals, semiconductors, ceramics, and inorganic salts endowed with various chiral structures ranging from atomic to micron scales. This tutorial review highlights the recent research on chiral mesostructured inorganic materials, especially the novel expression of mesostructured chirality and endowed optical chiral response, and it may inspire us with new strategies for the design of chiral inorganic materials and new opportunities beyond the traditional applications of chirality. Fabrication methods for chiral mesostructured inorganic materials are classified according to chirality type, scale, and symmetry-breaking mechanism. Special attention is given to highlight systems with original discoveries, exceptional phenomena, or unique mechanisms of optical chiral response for left- and right-handedness.

Selective Chiral Recognition between Amino Acids and Growing Gypsum Crystals

In nature, selective chiral interactions between biomolecules and minerals provide insight into the mysterious origin of homochirality. Here, we show growing gypsum crystals in a nonequilibrium state can recognize chiral enantiomers of amino acids. The chiral selection for amino acids with different functional groups by growing minerals are distinct. For 11 amino acids, the d-isomer slows dynamic gypsum growth more than the l-isomer, whereas for another 7 amino acids, the opposite was observed. These differences in chiral recognition are attributed to the different stereochemical matching between the chiral amino acids and the dynamic steps of growing gypsum. These stereoselective interactions between amino acid enantiomers and dynamic growing crystals can be applied toward the fabrication of gypsum cements to regulate their structure and mechanical properties. These findings provide insight into understanding the mechanism of the origin of homochirality in nature and suggest a pathway for constructing advanced functional materials.

Mechanosensitive non-equilibrium supramolecular polymerization in closed chemical systems

Chemical fuel-driven supramolecular systems have been developed showing out-of-equilibrium functions such as transient gelation and oscillations. However, these systems suffer from undesired waste accumulation and they function only in open systems. Herein, we report non-equilibrium supramolecular polymerizations in a closed system, which is built by viologens and pyranine in the presence of hydrazine hydrate. On shaking, the viologens are quickly oxidated by air followed by self-assembly of pyranine into micrometer-sized nanotubes. The self-assembled nanotubes disassemble spontaneously over time by the reduced agent, with nitrogen as the only waste product. Our mechanosensitive dissipative system can be extended to fabricate a chiral transient supramolecular helix by introducing chiral-charged small molecules. Moreover, we show that shaking induces transient fluorescence enhancement or quenching depending on substitution of viologens. Ultrasound is introduced as a specific shaking way to generate template-free reproducible patterns. Additionally, the shake-driven transient polymerization of amphiphilic naphthalenetetracarboxylic diimide serves as further evidence of the versatility of our mechanosensitive non-equilibrium system.

Biomimetic Self-Assembled Chiral Inorganic Nanomaterials: A New Strategy for Solving Medical Problems

The rapid expansion of the study of chiral inorganic structures has led to the extension of the functional boundaries of inorganic materials. Nature-inspired self-assembled chiral inorganic structures exhibit diverse morphologies due to their high assembly efficiency and controlled assembly process, and they exhibit superior inherent properties such as mechanical properties, chiral optical activity, and chiral fluorescence. Although chiral self-assembled inorganic structures are becoming more mature in chiral catalysis and chiral optical regulation, biomedical research is still in its infancy. In this paper, various forms of chiral self-assembled inorganic structures are summarized, which provides a structural starting point for various applications of chiral self-assembly inorganic structures in biomedical fields. Based on the few existing research statuses and mechanism discussions on the chiral self-assembled materials-mediated regulation of cell behavior, molecular probes, and tumor therapy, this paper provides guidance for future chiral self-assembled structures to solve the same or similar medical problems. In the field of chiral photonics, chiral self-assembled structures exhibit a chirality-induced selection effect, while selectivity is exhibited by chiral isomers in the medical field. It is worth considering whether there is some correspondence or juxtaposition between these phenomena. Future chiral self-assembled structures in medicine will focus on the precise treatment of tumors, induction of soft and hard tissue regeneration, explanation of the biochemical mechanisms and processes of its medical effects, and improvement of related theories.

Chiral-Solvent-Mediated Manganese-Based Hierarchical Supraparticles with Chiroptical Activity

In this study, manganese-based multiply hierarchical chiral supraparticles (SPs), with an anisotropy factor (g-factor) of 0.102 and circular dichroism (CD) intensity of 260 mdeg at 530 nm, are successfully synthesized with polar-solvent-mediated strategies. Notably, the g-factor of the SPs is further enhanced to 0.121 by the addition of an external chiral solvent, generating a chiral biased environment, which increases their CD intensity to 320 mdeg at 500 nm. The mechanism underlying the different chirality is proposed to be a difference in the angle of tilt of ±33° between the two enantiomers of the chiral SPs, which involves a difference of ±7° between the orientation of individual nanoplatelets. Chiral solvents induce the angle between adjacent nanoplatelets to get smaller than the original structure that leads to their higher anisotropic value. These findings potentially provide a practical method for the construction of complex chiral superstructures and the regulation of chiroptical activity.

Synchronous assembly of chiral skeletal single-crystalline microvessels

Skeletal or concave polyhedral crystals appear in a variety of synthetic processes and natural environments. However, their morphology, size, and orientation are difficult to control because of their highly kinetic growth character. We report a methodology to achieve synchronous, uniaxial, and stepwise growth of micrometer-scale skeletal single crystals from planar-chiral double-decker molecules. Upon drop-casting of a heated ethanol solution onto a quartz substrate, the molecules spontaneously assemble into standing vessel-shaped single crystals uniaxially and synchronously over the wide area of the substrate, with small size polydispersity. The crystal edge is active even after consumption of the molecules and resumes stereoselective growth with successive feeding. The resultant morphology can be packed into polycyclic aromatic hydrocarbon-like microarchitectures and behaves as a microscopic container.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.

Complex morphologies of biogenic crystals emerge from anisotropic growth of symmetry-related facets

Directing crystal growth into complex morphologies is challenging, as crystals tend to adopt thermodynamically stable morphologies. However, many organisms form crystals with intricate morphologies, as exemplified by coccoliths, microscopic calcite crystal arrays produced by unicellular algae. The complex morphologies of the coccolith crystals were hypothesized to materialize from numerous crystallographic facets, stabilized by fine-tuned interactions between organic molecules and the growing crystals. Using electron tomography, we examined multiple stages of coccolith development in three dimensions. We found that the crystals express only one set of symmetry-related crystallographic facets, which grow differentially to yield highly anisotropic shapes. Morphological chirality arises from positioning the crystals along specific edges of these same facets. Our findings suggest that growth rate manipulations are sufficient to yield complex crystalline morphologies.

Liquid-Liquid Phase Separation in Nucleation Process of Biomineralization

Biomineralization is a typical interdisciplinary subject attracting biologists, chemists, and geologists to figure out its potential mechanism. A mounting number of studies have revealed that the classical nucleation theory is not suitable for all nucleation process of biominerals, and phase-separated structures such as polymer-induced liquid precursors (PILPs) play essential roles in the non-classical nucleation processes. These structures are able to play diverse roles biologically or pathologically, and could also give inspiring clues to bionic applications. However, a lot of confusion and dispute occurred due to the intricacy and interdisciplinary nature of liquid precursors. Researchers in different fields may have different opinions because the terminology and current state of understanding is not common knowledge. As a result, our team reviewed the most recent articles focusing on the nucleation processes of various biominerals to clarify the state-of-the-art understanding of some essential concepts and guide the newcomers to enter this intricate but charming field.

Hierarchical self-assembly into chiral nanostructures

One basic principle regulating self-assembly is associated with the asymmetry of constituent building blocks or packing models. Using asymmetry to manipulate molecular-level devices and hierarchical functional materials is a promising topic in materials sciences and supramolecular chemistry. Here, exemplified by recent major achievements in chiral hierarchical self-assembly, we show how chirality may be utilized in the design, construction and evolution of highly ordered and complex chiral nanostructures. We focus on how unique functions can be developed by the exploitation of chiral nanostructures instead of single basic units. Our perspective on the future prospects of chiral nanostructures via the hierarchical self-assembly strategy is also discussed.

Tuning organic crystal chirality by the molar masses of tailored polymeric additives

Hierarchically ordered chiral crystals have attracted intense research efforts for their huge potential in optical devices, asymmetric catalysis and pharmaceutical crystal engineering. Major barriers to the application have been the use of costly enantiomerically pure building blocks and the difficulty in precise control of chirality transfer from molecular to macroscopic level. Herein, we describe a strategy that offers not only the preferred formation of one enantiomorph from racemic solution but also the subsequent enantiomer-specific oriented attachment of this enantiomorph by balancing stereoselective and non-stereoselective interactions. It is demonstrated by on-demand switching the sign of fan-shaped crystal aggregates and the configuration of their components only by changing the molar mass of tailored polymeric additives. Owing to the simplicity and wide scope of application, this methodology opens an immediate opportunity for facile and efficient fabrication of one-handed macroscopic aggregates of homochiral organic crystals from racemic starting materials.

Molecule-specific vibration-based chiral differentiation of Raman spectra using cysteine modified gold nanoparticles: the cases of tyrosine and phenylalanine

The chirality of amino acids plays a key role in many biochemical processes, with the development of spectroscopic analysis methods for the chiral differentiation of amino acids being significant. Normal Raman spectroscopy is blind to chirality; however, chiral discrimination of tyrosine (Tyr) (or phenylalanine, Phe) enantiomers using Raman spectra can be achieved assisted by the construction of a simple chiral selector (i.e., cysteine (Cys)-modified Au nanoparticles (NPs)). Due to the synergetic effect between Cys and the Au NPs, the characteristic Raman scattering intensities of the Tyr (or Phe) enantiomer with the same chirality of Cys are enantioselectively boosted by over four-fold compared with those of the counter enantiomer of Tyr (or Phe). The large differences in the Raman signals allow for the determination of enantiomeric excess. Interestingly, such enantiomeric discrimination is not revealed by the common chiral analysis method of circular dichroism spectroscopy. Consequently, it is anticipated that Raman spectroscopy based on molecular vibrations will find broad applications in chirality-related detection with high sensitivity and species specificity.

Tuning Sugar-Based Chiral and Flower-Like Microparticles

Unique supermolecular structures as chiral and flower-like microparticles and the precise tuning of the morphologies hold immense promise for a variety of applications. Examples of such structures deriving from monosaccharides are still rare, and a general understanding is also lacking. Herein, it is shown that chiral, flower-like, or solid microparticles can be tuned by only using monosaccharide esters without external stimuli. Chiral "left-handed" (counterclockwise) and "right-handed" (clockwise) morphologies can be induced by d- and l-glucose stearoyl esters. In comparison, other monosaccharides, i.e., galactose, mannose, and xylose, cannot formed chiral particles and generated diverse other morphologies of the supermolecular microparticles based on their distinct molecular configurations. Due to the numbers of side chains and the bond orientations, microparticles with solid and porous flower-like morphologies can be obtained. While glucose and xylose esters only lead to solid microparticles, mannose and galactose generate porous flower-like particles. These findings suggest a general method to design and control the superstructures by using monosaccharide backbones with diverse molecular configurations.

Helical polymer self-assembly and chiral nanostructure formation

This review surveys recent progress towards robust chiral nanostructure fabrication techniques using synthetic helical polymers, the unique inferred properties that these materials possess, and their intricate connection to natural, biological chirality.

Chiral Nanoceramics

The study of different chiral inorganic nanomaterials has been experiencing rapid growth during the past decade, with its primary focus on metals and semiconductors. Ceramic materials can substantially expand the range of mechanical, optical, chemical, electrical, magnetic, and biological properties of chiral nanostructures, further stimulating theoretical, synthetic, and applied research in this area. An ever-expanding toolbox of nanoscale engineering and self-organization provides a chirality-based methodology for engineering of hierarchically organized ceramic materials. However, fundamental discoveries and technological translations of chiral nanoceramics have received substantially smaller attention than counterparts from metals and semiconductors. Findings in this research area are scattered over a variety of sources and subfields. Here, the diversity of chemistries, geometries, and properties found in chiral ceramic nanostructures are summarized. They represent a compelling materials platform for realization of chirality transfer through multiple scales that can result in new forms of ceramic materials. Multiscale chiral geometries and the structural versatility of nanoceramics are complemented by their high chiroptical activity, enantioselectivity, catalytic activity, and biocompatibility. Future development in this field is likely to encompass chiral synthesis, biomedical applications, and optical/electronic devices. The implementation of computationally designed chiral nanoceramics for biomimetic catalysts and quantum information devices may also be expected.

Chiral Surface and Geometry of Metal Nanocrystals

Chirality is a basic property of nature and has great importance in photonics, biochemistry, medicine, and catalysis. This importance has led to the emergence of the chiral inorganic nanostructure field in the last two decades, providing opportunities to control the chirality of light and biochemical reactions. While the facile production of 3D nanostructures has remained a major challenge, recent advances in nanocrystal synthesis have provided a new pathway for efficient control of chirality at the nanoscale by transferring molecular chirality to the geometry of nanocrystals. Interestingly, this discovery stems from a purely crystallographic outcome: chirality can be generated on high-Miller-index surfaces, even for highly symmetric metal crystals. This is the starting point herein, with an overview of the scientific history and a summary of the crystallographic definition. With the advance of nanomaterial synthesis technology, high-Miller-index planes can be selectively exposed on metallic nanoparticles. The enantioselective interaction of chiral molecules and high-Miller-index facets can break the mirror symmetry of the metal nanocrystals. Herein, the fundamental principle of chirality evolution is emphasized and it is shown how chiral surfaces can be directly correlated with chiral morphologies, thus serving as a guide for researchers in chiral catalysts, chiral plasmonics, chiral metamaterials, and photonic devices.

Chiral Tartaric Acid Improves Fracture Toughness of Bioactive Brushite-Collagen Bone Cements

Brushite cements are promising bone regeneration materials with limited biological and mechanical properties. Here, we engineer a mechanically improved brushite-collagen type I cement with enhanced biological properties by use of chiral chemistry; d- and l-tartaric acid were used to limit crystal growth and increase the mechanical properties of brushite-collagen cements. The impact of the chiral molecules on the cements was examined with Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A 3-point bend test was utilized to study the fracture toughness, and cell attachment and morphology studies were carried out to demonstrate biocompatibility. XRD and SEM analyses showed that l-, but not d-tartaric acid, significantly restrained brushite crystal growth by binding to the {010} plane of the mineral and increased brushite crystal packing and the collagen interaction area. l-Tartaric acid significantly improved fracture toughness compared to traditional brushite by 30%. Collagen significantly enhanced cell morphology and focal adhesion expression on l-tartaric acid-treated brushite cements.

Polarized light through polycrystalline vaterite helicoids

Vaterite helicoids [W. Jiang et al., Nat. Commun., 2017, 8, 15066] are chiral, polycrystalline suprastructures grown in the presence of the amino acids, aspartic (Asp) or glutamic (Glu) acid, that are abundant in proteins regulating biomineralization. These complex objects are composed of hexagonal vaterite nanocrystals assembled as curved-edge platelets that form chiral ensembles. The sense stacked platelets is correlated with the stereochemistry of the amino acid additive: l-Asp gives counterclockwise architectures while d-Asp gives the clockwise enantiomorphs. As new layers stack, platelets become progressively inclined with respect to the substrate suface. The growth and structure of vaterite helicoids was originally evidenced by electron microscopy and atomic force microscopy. Here, we develop an optical model for describing polarized light transmission through helicoids as measured by Mueller matrix polarimetry. The close agreement between experimental measurements and simulation confirms that the propellor-like organization of inclined platelets creates optically active structures determined by growth additive stereochemistry. The microscopy employed demonstrates the information that can be obtained by complete polarimetry using a camera as a light detector, a technique that could be applied profitably to all manner of complex structures organized from anisotropic particles.

High strength brushite bioceramics obtained by selective regulation of crystal growth with chiral biomolecules

Chirality seems to play a key role in mineralization. Indeed, in biominerals, the biomolecules that guide the formation and organization of inorganic crystals and help construct materials with exceptional mechanical properties, are homochiral. Here, we show that addition of homochiral l-(+)-tartaric acid improved the mechanical properties of brushite bioceramics by decreasing their crystal size, following the classic Hall-Petch strengthening effect; d-(-)-tartaric acid had the opposite effect. Adding l-(+)-Tar increased both the compressive strength (26 MPa) and the fracture toughness (0.3 MPa m^1/2) of brushite bioceramics, by 33% and 62%, respectively, compared to brushite bioceramics without additives. In addition, l-(+)-tartaric acid enabled the fabrication of cements with high powder-to-liquid ratios, reaching a compressive strength and fracture toughness as high as 32.2 MPa and 0.6 MPa m^1/2, respectively, approximately 62% and 268% higher than that of brushite bioceramics prepared without additives, respectively. Characterization of brushite crystals from the macro- to the atomic-level revealed that this regulation is attributable to a stereochemical matching between l-(+)-tartaric acid and the chiral steps of brushite crystals, which results in inhibition of brushite crystallization. These findings provide insight into understanding the role of chirality in mineralization, and how to control the crystallographic structure of bioceramics to achieve high-performance mechanical properties. STATEMENT OF SIGNIFICANCE: Calcium-phosphate cements are promising bone repair materials. However, their suboptimal mechanical properties limit their clinical use. Natural biominerals have remarkable mechanical properties that are the result of controlled size, shape and organization of their inorganic crystals. This is achieved by biomineralization proteins that are homochiral, composed of l- amino acids. Despite the importance of chiral l-biomolecules in biominerals, using homochiral molecules to fabricate bone cements has not been studied yet. In this study, we showed that homochiral l-(+)-tartaric acid can regulate the crystal structure and improve the mechanical properties of a calcium-phosphate cement. Hence, these findings open the door for a new way of designing strong bone cement and highlight the importance of chirality in bioceramics.

Emergence of chirality and structural complexity in single crystals at the molecular and morphological levels

Naturally occurring single crystals having a multidomain morphology are a counterintuitive phenonomon: the macroscopic appearance is expected to follow the symmetry of the unit cell. Growing such crystals in the lab is a great challenge, especially from organic molecules. We achieve here uniform metallo-organic crystals that exhibit single crystallinity with apparently distinct domains and chirality. The chirality is present at both the molecular and macroscopic levels, although only achiral elements are used. "Yo-yo"-like structures having opposite helical handedness evolve from initially formed seemingly achiral cylinders. This non-polyhedral morphology coexists with a continuous coordination network forming homochiral channels. This work sheds light on the enigmatic aspects of fascinating crystallization processes occurring in biological mineralization. Our findings open up opportunities to generate new porous and hierarchical chiral materials.

Homochirality in biomineral suprastructures induced by assembly of single-enantiomer amino acids from a nonracemic mixture

Since Pasteur first successfully separated right-handed and left-handed tartrate crystals in 1848, the understanding of how homochirality is achieved from enantiomeric mixtures has long been incomplete. Here, we report on a chirality dominance effect where organized, three-dimensional homochiral suprastructures of the biomineral calcium carbonate (vaterite) can be induced from a mixed nonracemic amino acid system. Right-handed (counterclockwise) homochiral vaterite helicoids are induced when the amino acid L-Asp is in the majority, whereas left-handed (clockwise) homochiral morphology is induced when D-Asp is in the majority. Unexpectedly, the Asp that incorporates into the homochiral vaterite helicoids maintains the same enantiomer ratio as that of the initial growth solution, thus showing chirality transfer without chirality amplification. Changes in the degree of chirality of the vaterite helicoids are postulated to result from the extent of majority enantiomer assembly on the mineral surface. These mechanistic insights potentially have major implications for high-level advanced materials synthesis.