Unexpected right-handed helical nanostructures co-assembled from l-phenylalanine derivatives and achiral bipyridines

Chiral Induction in a Self-Assembled Pd4 Coordination Cage with Chiral Guests

The dynamic interplay of coordination bonds within metal-organic cages offers a unique avenue for structural evolution in response to external stimuli, presenting a promising strategy for the construction of chiral assemblies. This adaptability is crucial for the selective synthesis of homochiral assemblies and advancement of asymmetric catalysis. In this study, we report the self-assembly of an achiral square-planar Pd(II) acceptor with a C2-symmetric tetrapyridyl donor resulted in the formation of a racemic mixture of the chiral octahedral cage Pd4L2. The existence of this racemic mixture was confirmed using circular dichroism spectroscopy as well as single crystal X-ray diffraction analysis. We encoded chiral information into the asymmetric cavity of the cage by encapsulating chiral aromatic guests through efficient π-π stacking and hydrophobic interactions in aqueous media. The inclusion of a chiral guest induces a preference for one enantiomeric conformation of the cage over the other, effectively shifting the equilibrium towards a single, enantiopure host-guest complex. While the concept of chiral guest recognition by a chiral host is well-established, this work constitutes a remarkable example of guest-mediated chirality transfer leading to the formation of a single enantiopure coordination complex from achiral building blocks.

Bioinspired Amino Acid Based Materials in Bionanotechnology: From Minimalistic Building Blocks and Assembly Mechanism to Applications

Inspired by natural hierarchical self-assembly of proteins and peptides, amino acids, as the basic building units, have been shown to self-assemble to form highly ordered structures through supramolecular interactions. The fabrication of functional biomaterials comprised of extremely simple biomolecules has gained increasing interest due to the advantages of biocompatibility, easy functionalization, and structural modularity. In particular, amino acid based assemblies have shown attractive physical characteristics for various bionanotechnology applications. Herein, we propose a review paper to summarize the design strategies as well as research advances of amino acid based supramolecular assemblies as smart functional materials. We first briefly introduce bioinspired reductionist design strategies and assembly mechanism for amino acid based molecular assembly materials through noncovalent interactions in condensed states, including self-assembly, metal ion mediated coordination assembly, and coassembly. In the following part, we provide an overview of the properties and functions of amino acid based materials toward applications in nanotechnology and biomedicine. Finally, we give an overview of the remaining challenges and future perspectives on the fabrication of amino acid based supramolecular biomaterials with desired properties. We believe that this review will promote the prosperous development of innovative bioinspired functional materials formed by minimalistic building blocks.

A signal amplification for Trp isomers electrochemical recognition based on PEDOT:PSS and CS/PAA multilayers

In this work, enhanced tryptophan (Trp) isomers recognition was successfully demonstrated on (CS/PAA)3.5@PEDOT:PSS/GCE, a multilayer chiral sensor with good stability and reproducibility. The (CS/PAA)n multilayers chiral interface was first fabricated via alternating self-assembly of chiral chitosan (CS) and achiral polyacrylic acid (PAA). Conductive PEDOT:PSS was then compounded with (CS/PAA)n multilayers to obtain the chiral sensor for the electrochemical recognition of Trp isomers. The structure of the sensor and its chirality properties for Trp isomers were characterized by fourier transform infrared spectroscopy (FT-IR)，scanning electron microscopy (SEM) and electrochemical methods. The SEM images showed uniform distribution of PEDOT:PSS in the multilayer films, which changed the internal structure of the (CS/PAA)3.5. Consequently, (CS/PAA)3.5@PEDOT:PSS multilayers rendered more chiral centers in addition to improved good conductivity, which significantly amplified the oxidation peak current ratio of D-Trp to L-Trp (ID/IL) up to 6.71 at 25 °C. In addition, a linear relationship was observed between the peak current and Trp enantiomer concentration in the range of 0.002-0.15 mM, and the detection limits of D-Trp and L-Trp were 0.33 and 0.67 μM, respectively. More importantly, the percentage of D-Trp in non-racemic Trp enantiomers mixture solutions were successfully determined on the chiral interface, showing its effectiveness and promising potential in practical applications.

Chiral Supramolecular Assemblies: Controllable Construction and Biological Activity

Chiral supramolecular assemblies with helical structures (e. g., proteins with α-helix, DNA with double helix, collagen with triple-helix) as the central structure motifs in biological systems play a crucial role in various physiological activities of living organisms. Variations in chiral structure can cause many abnormal physiological activities. To gain insight into the construction, structural transition, and related physiological functions of these complex helix in natural systems, it is necessary to fabricate artificial supramolecular assemblies with controllable helix orientation as research platform. This review discusses recent advances in chiral supramolecular assembly, including the precise construction and regulation of assembled chiral nanostructures with tunable chirality. Chiral structure-dependent biological activities, including cell proliferation, cell differentiation, antibacterial activity and tissue regeneration, are also discussed. This review not only contributes to further understanding of the importance of chirality in the physiological environment, but also plays an important role in the development of chiral biomedical materials for the treatment of diseases (e. g., tissue engineering regeneration, stem cell transplantation therapy).

Metallophilic Interaction-Mediated Hierarchical Assembly and Temporal-Controlled Dynamic Chirality Inversion of Metal-Organic Supramolecular Polymers

The study of dynamic supramolecular chirality inversion (SMCI) not only helps to deepen the understanding of chiral transfer and amplification in both living organizations and artificially chemical self-assembly systems but also is useful for the development of smart chiral nanomaterials. However, it is still challenging to achieve the dynamic SMCI of the self-aggregation of metal-organic supramolecular polymers with great potential in asymmetric synthesis, chiroptical switches, and circular polarized luminescence. Here, we successfully developed a hierarchical coassembly system based on the mPAzPCC and various metal ions with effective chirality transfer and temporal-controlled SMCI. Due to the dynamic self-assembly and hierarchical chirality transfer of the Ag⁺/mPAzPCC complex driven by metallophilic interaction and coordination, morphological transition with nanoribbons, helical nanoribbons, and chiral nanotubules was successively obtained. Interestingly, the SMCI of chiral nanoaggregates was precisely regulated by solvents and metal ions in the Cu²⁺/mPAzPCC and Mn²⁺/mPAzPCC system. Besides, temporal-controlled dynamic SMCI switching from helix to bundled helix was clearly revealed in the aggregation of Cu²⁺/mPAzPCC, Mn²⁺/mPAzPCC, and Bi³⁺/mPAzPCC systems. This work provides a metallophilic interaction-mediated helical assembly pathway to dynamically modulate the chirality of metal-organic complex-based assemblies and deepen the understanding of the hierarchically dynamic self-assembly process, which would be of great potential in metal ion-mediated supramolecular asymmetric catalysis and bioinspired chiral sensing.

Tuning of the Supramolecular Helicity of Peptide-Based Gel Nanofibers

Helical supramolecular architectures play important structural and functional roles in biological systems. The helicity of synthetic molecules can be tuned mainly by the chiral manipulation of the system. However, tuning of helicity by the achiral unit of the molecules is less studied. In this work, the helicity of naphthalimide-capped peptide-based gel nanofibers is tuned by the alteration of methylene units present in the achiral amino acid. The inversion of supramolecular helicity has been extensively studied by CD spectroscopy and morphological analysis. The density functional theory (DFT) study indicates that methylene spacers influence the orientation of π-π stacking interactions of naphthalimide units in the self-assembled structure that regulates the helicity. This work illustrates a new approach to tuning the supramolecular chirality of self-assembled biomaterials.

Solvent-Modulated Chiral Self-Assembly: Selective Formation of Helical Nanotubes, Nanotwists, and Energy Transfer

As the medium for self-assembly processes, solvents strongly influence the supramolecular assemblies via specific solute-solvent interactions, which may result in effective modulation of properties, self-assembled nanostructures, and functions through varying the solvent. Here, two kinds of pyridine-cyanostilbene functionalized chiral amphiphiles (l/d-PyPhG and l-PyG) were designed, and their self-assembly behaviors in different solvents were investigated. It was found that both amphiphiles formed gels in dimethyl sulfoxide (DMSO) and self-assembled into right-handed nanotwists, while they formed suspensions in ethanol consisting of left-handed nanotubes. Although the molecular chirality in the compounds remained unchanged in the two solvents, the nanoassemblies showed opposite handedness at the nanoscale together with opposite circular dichroism (CD) and circularly polarized luminescence (CPL) signals. Furthermore, when the amphiphiles were co-assembled with an achiral dye, it was found that efficient energy transfer took place in the systems composed of nanotubes rather than those composed of nanotwists. Therefore, by assembling molecules with the same molecular chirality in different solvents, a selective formation of helical nanotubes or nanotwists and the regulation of handedness as well as energy transfer efficiency were achieved.

Unexpected Role of Achiral Glycine in Determining the Suprastructural Handedness of Peptide Nanofibrils

Helical supramolecular architectures play important structural and functional roles in biological systems. Although their occurrence is widely perceived to correlate to fundamental chiral units including l-amino acids and d-sugars, the detailed relationship between molecular and supramolecular handedness is still unclear. At the same time, although achiral units are practically always in close proximity to chiral ones by covalent linkage along a polymeric chain, their effect on supramolecular handedness has received relatively less attention. Here, we designed a set of short amphiphilic peptides, in which an achiral glycine residue was incorporated at the interface between the hydrophobic and hydrophilic segments. We observed that glycine incorporation caused dramatic variations in suprastructural handedness in self-assembled peptide nanofibrils, and the effect of the hydrophilic charged residue at the C-terminus on supramolecular handedness was demolished, leading to chiral truncation. Furthermore, molecular dynamics simulations and quantum chemistry calculations revealed that the unanticipated role of the glycine residue in regulating supramolecular handedness originated from its effect on the conformational preference of single β-strands. Importantly, reduced density gradient analyses on single β-strands indicated that, due to the lack of a side chain in glycine, intricate noncovalent interactions were produced among the neighboring amino acid side chains of the incorporated glycine and its local backbone, resulting in diverse β-strand conformations.

Triple-Modulated Chiral Inversion of Co-Assembly System Based on Alanine Amphiphile and Cyanostilbene Derivative

The construction of chiroptical materials with controllable chirality is of special importance in biology and chemistry. Although tunable chirality can be realized in various systems, it remains a fundamental challenge to realize multimodulated chiral inversion. Herein, we report that chiral alanine derivative and fluorescent cyanostilbene derivative co-assemble to prepare supramolecular chiral systems, where twist nanofibers with totally inverted supramolecular chirality and circularly polarized luminescence are obtained through stoichiometric modulation. The supramolecular handedness can be inverted by means of altering the cooling rate and incorporating metal ions. The mechanism study reveals that the synergistic effect among hydrogen bonds, coordination interactions, and π-π stacking interactions contributes to the chirality inversion. This work establishes an effective strategy to precisely modulate supramolecular chirality in multiple ways, which shows great potential in developing smart chiroptical materials capable of achieving complex functionalities.

Supramolecular fibrous gels with helical pitch tunable by polarity of alcohol solvents

A sugar-based, low-molecular-weight gelator 16AG, can gelatinize primary alcohols by forming supramolecular fibers. We obtained non-helical, tape-like fibers in methanol and ethanol but helical fibers in alcohols with at least three carbons. The pitch of the helical fibers became shorter with increasing carbon number.

Redox-Driven In Situ Helix Reversal of Graphene-Based Hydrogels

Controlling the handedness of dynamic helical nanostructures of supramolecular assemblies by external stimuli is of great fundamental significance with appealing morphology-dependent applications. Significantly, access to in situ chirality transformation of dynamic multistimuli-responsive systems can provide channels for real-time monitoring of the transfer processes in biological systems. However, efforts to achieve helix inversion in an all-gel-state and to comprehend the phenomena at a molecular scale are scarce. Herein, we introduce an example of supramolecular hydrogel in which graphene oxide (GO) incorporation leads to opposite helicity of the l-phenylalanine derivative (LPFEG) upon UV irradiation. The gelator modulates different degrees of packing that are responsible for the initial construction of right-handed nanofibers in GO surfaces and for the change in helix to preferred left-handedness in RGO surfaces caused by GO reduction. Specifically, LPFEG shows a mixture of right- and left-handed nanofibers with an appropriate exposure to UV light. A thermal-reversible transformation of chirality is also discovered in the supramolecular assemblies, allowing a dynamic and invertible flip of helicity upon heating and cooling. The morphology transformation makes the hybrid an ideal candidate for application in a precisely controlled drug delivery process. It can unexpectedly serve as a photosensitizer and a carrier for enantioselective absorption of specific chiral drugs enantiomer (l-dopa and S-naproxen sodium) and also exhibit on-demand drug release due to the helix reversal induced by light irradiation. Our results illustrate how the surface reactivity can direct the helical organization of adsorbed fibers, which in turn provide control over enantioselective absorption of chiral drug enantiomers, further giving rise to on-demand drug release due to handedness inversion upon UV irradiation.

Supramolecular organogels fabricated with dicarboxylic acids and primary alkyl amines: controllable self-assembled structures

Supramolecular organogels are soft materials comprised of low-molecular-mass organic gelators (LMOGs) and organic liquids. Owning to their unique supramolecular structures and potential applications, LMOGs have attracted wide attention from chemists and biochemists. A new "superorganogel" system based on dicarboxylic acids and primary alkyl amines (R-NH2) from the formation of organogels is achieved in various organic media including strong and weak polar solvents. The gelation properties of these gelators strongly rely on the molecular structure. Their aggregation morphology in the as-obtained organogels can be controlled by the solvent polarity and the tail chain length of R-NH2. Interestingly, flower-like self-assemblies can be obtained in organic solvents with medium polarity, such as tetrahydrofuran, pyridine and dichloromethane, when the gelators possess a suitable length of carbon chain. Moreover, further analyses of Fourier transformation infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy reveal that the intermolecular acid-base interaction and van der Waals interaction are critical driving forces in the process of organogelation. In addition, this kind of organogel system displays excellent mechanical properties and thermo-reversibility, and its forming mechanism is also proposed.

Chirality Transfer in Carbon Dot-Composited Sol-Gel Systems for Excitation-Dependent Circularly Polarized Luminescence

In situ control of a circularly polarized luminescent (CPL) signal is desirable but rarely addressed. Even to compare with traditional chemical regulations, controlling the CPL signal at the material level using simple physical manipulation (such as photoexcitation) can be more convenient and preferable. In this work, we have constructed carbon dot-based composite luminescent materials with CPL activity. The materials can exist in the sol-gel state in a mixture solvent by chiral co-assembly, and chirality transfer occurred in the supramolecular assemblies and induced the CPL activity. Owing to the unique luminescent properties of the carbon dot component, the obtained CPL signal of the composite system is therefore excitation-dependent. The control ability of the CPL signal may allow the composite materials to find potential usage in advanced chirality-related fields.

Self-Assembly Evolution of N-Terminal Aromatic Amino Acids with Transient Supramolecular Chirality

Deep understanding and fine tailoring of spontaneous structural evolution of self-assembled arrays are pivotal in the rational design of advanced soft materials. However, an indistinct structure-property relationship and pathway complexity in self-assembly lead to a considerable challenge. Herein, we reveal the self-assembly pathway complexity in spontaneous aggregation of several N-terminated aromatic amino acids. By primarily tuning the incubation time, building blocks appended with alanine and serine selectively form 1:1 hydrated clathrates, enabling the microfiber to transition to crystals. The dynamic water intercalation process was studied by incubation time-dependent morphological changes, powder X-ray diffraction, and single-crystal structure analysis. A pronounced amino acid residue effect on the self-assembly evolution was reflected by supramolecular chirality inversion of the building block having the phenylalanine residue, accomplishing dynamic M- to P-helicity transition within a confined time scale.

Water inversed helicity of nanostructures from ionic self-assembly of a chiral gelator and an achiral component

The ionic self-assemblies (ISAs) formed by a cationic chiral organogelator (l-glutamide amphiphile, abbreviated as PULG) and anionic dyes exhibited helical nanostructures. And the formed helical structures can be tuned by water amount in the ethanol/water solvent. In pure ethanol, the chirality of the gelator was successfully transferred to the achiral components, which was confirmed by the appearance of an induced CD signal in the achiral components. Meanwhile, the electrostatic interaction between the gelator and achiral dyes contributed to the chirality amplification, causing the nanofibrous structures of the gelator to be transformed to uniform left-handed helices. Upon adding water to ethanol, the induced CD signal exhibited inversion from positive to negative. Interestingly, the left-handed helices formed by ISA of PULG/anionic dyes in ethanol were inverted to right-handed helices with the addition of water. Based on detailed investigations of the XRD patterns, CD and UV/Vis spectra, the mechanism of helicity inversion was proposed: left-handed helices were dominated by hydrogen bonding and right-handed helices were dominated by π-π stacking. This work exemplifies a feasible method to invert the helicity of chiral nanostructures in co-assembly and gives an insight into the conformation change of biomacromolecules in a biological system.

Self-Assembled Helical and Twisted Nanostructures of a Preferred Handedness from Achiral π-Conjugated Oligo( p-phenylenevinylene) Derivatives

The formation of chiral nanostructures from the self-assembly of achiral building blocks without external symmetry breaking inducing factors is believed to associate with the origin of chirality. Herein, we reported the synthesis and self-assembly of oligo( p-phenylenevinylene)- b-poly(ethylene glycol) (OPV₃- b-PEG₁₇, the subscripts represent the number of repeat unit of each block) in solution. We systematically examined the influence of solvent, heating temperature, and concentration of OPV₃- b-PEG₁₇ on the self-assembly of OPV₃- b-PEG₁₇ by UV/vis absorption and fluorescence spectrometry, circular dichroism technique, and transmission electron and atomic force microscopy. Interestingly, helical and twisted nanoribbons and nanotubes of a preferred handedness can be formed from achiral OPV₃- b-PEG₁₇ in the mixture of water/ethanol (v/v = 1/1) and the solution showed an obvious exciton-coupled bisignated signal, which indicated that symmetry breaking occurred during the formation of these nanostructures without external inducing factors. Our results showed that the occurrence of symmetry breaking is subtle to the experimental factors including solvent, heating temperature, and concentration of OPV₃- b-PEG₁₇. The directional π-π stacking along with steric repulsion between PEG domains should be the driving force for the formation of these chiral nanostructures. The occurrence of statistical fluctuations in the initial stage of self-assembly led to an accidental excess of helical or/and twisted structures, that is, symmetry breaking. Subsequently, the autocatalysis effect resulted in the formation of helical or/and twisted nanoribbons with a preferred handedness.

Tuning the Handedness: Role of Chiral Component in Peptide-Appended Bolaamphiphile-Based Coassembled Hydrogels

Chirality is the intrinsic property of a molecule that can be tuned by the change in chirality of a molecule or by the addition of a chiral component as an external stimulus. An l-leucine-based dipeptide-appended succinic acid-based bolaamphiphile coassembled with d-tartaric acid to form supramolecular right-handed nanostructured hydrogel, whereas l-tartaric acid coassembled to form supramolecular left-handed nanostructured hydrogel. Scanning electron microscopy and transmission electron microscopy experiments revealed the right- and left-handed helical nanofibers that are responsible for the formation of supramolecular nanostructured hydrogels. The synergistic chiral effect of l-leucine in peptide bolaamphiphile and d/l-tartaric acid plays a significant role in bicomponent gelation with helical nanofibers. The first two amino acids attached to both sides of succinic acid moiety act as a tuning button for supramolecular chirality of amino acids/peptides attached with succinic acid-based bolaamphiphiles. The second amino acid plays the role of modulating supramolecular chirality if the first two amino acids act neutrally to the chirality of bolaamphiphiles, which was confirmed by circular dichroism spectroscopy.

Stoichiometry-controlled inversion of circularly polarized luminescence in co-assembly of chiral gelators with an achiral tetraphenylethylene derivative

A supramolecular circularly polarized luminescence (CPL) system was constructed based on the co-gelation of an achiral tetraphenylethylene derivative and chiral organic gelators of glutamic acid in chloroform. And the handedness of CPL can be inverted by stoichiometric ratio.

Photocontrolled morphological conversion and chiral transfer of a snowflake-like supramolecular assembly based on azobenzene-bridged bis(dibenzo-24-crown-8) and a cholesterol derivative

A snowflake-like supramolecular clockwise-helical assembly was fabricated via the host–guest interaction, while a snowflake-like supramolecular non-helical assembly can be obtained upon UV-irradiation.

Chalcogen-substitution modulated supramolecular chirality and gas sensing properties in perylenediimides

The supramolecular helicity and gas response of perylene dyes can be well modulated by chalcogen atoms in the perylene core.

Controlling Supramolecular Chirality in Multicomponent Self-Assembled Systems

Chirality exists as a ubiquitous phenomenon in nature, from molecular level l-amino acids, d-sugar, secondary structures of proteins, DNA, RNA, and nanoscale helices to macroscopic conch and even galaxy. The aggregation of molecular building blocks with or without chiral centers might bring about asymmetric spatial stacking, which further results in the appearance of nonsymmetry in extended scales like helical nanofibers. This phenomenon, known as supramolecular chirality, is an important branch of supramolecular and self-assembly chemistry, which relates intimately with biomimetics, asymmetric catalysis, and designing chiroptic advanced materials. One of the important research focuses among supramolecular chirality is about rational manipulation of chirality amplification and handedness, presenting a profound influence on the performance of resulting soft materials such as circularly polarized luminescence and cell adhesion on hydrogels. The control over supramolecular chirality normally relies on two factors, i.e., thermodynamic and kinetic variables dependent on molecular structural parameters and environmental contributions, respectively. Supramolecular chirality in two or more component-based systems places an emphasis on thermodynamic control as it occurs from either integrated coassembly or separated self-sorting, which is more sophisticated than that of single component systems. Thus, the study on supramolecular chirality in multicomponent systems could mimic complicated biosystems, allowing for better understanding about the origin of natural chirality and extended applications as biomimetics. To date, the exploration of supramolecular chirality in multicomponent systems is restricted on both fundamental and application aspects when compared to more matured single component systems. Over the past few years, we have carried out systematic studies on several systems expressing supramolecular chirality from chiral amplification or symmetry breaking. We emphasized more the thermodynamic control by introducing a second component to form noncovalent bonding like hydrogen bonding or coordination interactions. In this Account, we would specifically discuss rational manipulation of the occurrence, transfer, and inversion of supramolecular chirality by taking several of the latest representative examples. In the multicomponent systems, in addition to the building blocks with chiral centers, the second or third components could be structural analogues and achiral small molecules such as bipyridines, melamine, metal ions, inorganic nanomaterials, and even solvents. These second or third components are able to incorporate during the aggregation to form coassembly via noncovalent bonds, influencing spatial arrangements of building blocks within various dimensions from vesicles and nanofibers to organic/inorganic hybrids. Other than chirality, morphology, stimulus responsiveness, and properties could also be well tailored by controlling interactions between different components.

Modulating Supramolecular Chirality in Alanine Derived Assemblies by Multiple External Stimuli

Having control over the supramolecular chirality through multiexternal stimulators provides many possibilities in realizing functional chiral materials. Herein, the supramolecular chirality of nanotwists comprising PA centered with 1,4-phenyldicarboxamide bearing two l/d-helicogenic alanine motifs and achiral COOH at each terminus of the alanine arms is modulated by solvent, temperature, and ultrasound. The modulations are mainly due to the hydrogen bonds among gelators and solvent-gelator interactions, resulting in changes of the molecular arrangement and subsequent self-assembled nanostructures. Typically, the gel of PA in ethyl acetate prepared by ultrasonication method exhibits thixotropic property due to the participation of ethyl acetate in the self-assembly process, resulting in relatively flexible and tolerant networks. This study provides a simplistic way to control the handedness of chiral nanostructures and a rational design of the self-assembly system with multistimuli-responsive supramolecular chirality.

The Cooperative Effect of Both Molecular and Supramolecular Chirality on Cell Adhesion

Although helical nanofibrous structures have great influence on cell adhesion, the role played by chiral molecules in these structures on cells behavior has usually been ignored. The chirality of helical nanofibers is inverted by the odd-even effect of methylene units from homochiral l-phenylalanine derivative during assembly. An increase in cell adhesion on left-handed nanofibers and weak influence of cell behaviors on right-handed nanofibers are observed, even though both were derived from l-phenylalanine derivatives. Weak and negative influences on cell behavior was also observed for left- and right-handed nanofibers derived from d-phenylalanine, respectively. The effect on cell adhesion of single chiral molecules and helical nanofibers may be mutually offset.

Investigations of Peptide-Based Biocompatible Injectable Shape-Memory Hydrogels: Differential Biological Effects on Bacterial and Human Blood Cells

Here, we report the self-assembly of Amoc (9-anthracenemethoxycarbonyl)-capped dipeptides, which self-assemble to form injectable, self-healable, and shape-memory hydrogels with inherent antibacterial properties. Amoc-capped dipeptides self-assemble to form nanofibrillar networks, which are established by several spectroscopic and microscopic techniques. The inherent antibacterial properties of hydrogels are evaluated using two Gram-positive Staphylococcus aureus, Bacillus subtilis and three Gram-negative Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhi bacteria. These hydrogels exhibit potent antibacterial efficacy against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentrations (MIC₅₀) for the hydrogels on Gram-positive bacteria are in the range of 10-200 μM hydrogelator concentrations. The biocompatibility and cytotoxicity of the hydrogels are evaluated using 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), hemolysis, and lipid peroxidation (LPO) assay on human blood cells. The hydrogels are hemocompatible and they decrease LPO values on human red blood cells probably via increased cellular stability against oxidative stress. Furthermore, MTT data show that the hydrogels are biocompatible and promote cell viability and proliferation on cultured human white blood cells. Taken together, these results may suggest that our designed injectable hydrogels could be useful to prevent localized bacterial infections.

Water induced morphological transformation of a poly(aryl ether) dendron amphiphile: helical fibers to nanorods, as light-harvesting antenna systems

Self-assembly of suitable molecular building blocks is an efficient and convenient approach to generate nanomaterials with various morphologies and functions. Moreover, understanding the nature of molecules and controlling factors of their self-assembly process is crucial in fundamental aspects of molecular self-assembly which provide insights into the design of new assemblies with functional nano-architectures. To this end, the present study reports water induced self-assembled multifaceted morphology formation and the plausible pathway of the morphology transformation of a single poly(aryl ether) dendron amphiphile 1(D). In THF, 1(D) self-assembles into helical fibers. However, with an increase in the water fraction in its THF solution, the morphology changes to nanorods through an intermediate scroll-up pathway of exfoliated fibers. The nanorod formation and transformation of 1(D) are investigated using various microscopy and spectroscopy techniques, which indicate that it has highly ordered multilayered arrays of 1(D) molecules. Finally, these multilayered arrays of 1(D) nanorods are exploited for constructing a model light-harvesting system via the incorporation of small quantities of two newly designed BODIPY based molecules as energy acceptors and 1(D) as an antenna chromophore.

Light-triggered self-assembly of a cyanostilbene-conjugated glutamide from nanobelts to nanotoroids and inversion of circularly polarized luminescence

UV irradiation regulated transformation of chiral nanostructures and inversion of circularly polarized luminescence.

Helicity Inversion of Supramolecular Hydrogels Induced by Achiral Substituents

Probing the supramolecular chirality of assemblies and controlling their handedness are closely related to the origin of chirality at the supramolecular level and the development of smart materials with desired handedness. However, it remains unclear how achiral residues covalently bonded to chiral amino acids can function in the chirality inversion of supramolecular assemblies. Herein, we report macroscopic chirality and dynamic manipulation of chiroptical activity of hydrogels self-assembled from phenylalanine derivatives, together with the inversion of their handedness achieved solely by exchanging achiral substituents between oligo(ethylene glycol) and carboxylic acid groups. This helicity inversion is mainly induced by distinct stacking mode of the self-assembled building blocks, as collectively confirmed by scanning electron microscopy, circular dichroism, crystallography, and molecular dynamics calculations. Through this straightforward approach, we were able to invert the handedness of helical assemblies by merely exchanging achiral substituents at the terminal of chiral gelators. This work not only presents a feasible strategy to achieve the handedness inversion of helical nanostructures for better understanding of chiral self-assembly process in supramolecular chemistry but also facilities the development of smart materials with controllable handedness in materials science.

Self-assembly of water-soluble silver nanoclusters: superstructure formation and morphological evolution

Supramolecular self-assembly, based on non-covalent interactions, has been employed as an efficient approach to obtain various functional materials from nanometer-sized building blocks, in particular, [Ag₆(mna)₆]^6-, mna = mercaptonicotinate (Ag₆-NC). A challenging issue is how to modulate the self-assembly process through regulating the relationship between building blocks and solvents. Herein, we report the controlled self-assembly of hexanuclear silver nanoclusters into robust multilayer vesicles in different solvents, DMSO, CH₃CN, EG and MeOH. Their unique luminescence enables them to be bifunctional probes to sense Fe³⁺ and dl-dithiothreitol (DTT). By protonating the Ag₆-NC to Ag₆-H-NC using hydrochloric acid (HCl), the multilayer vesicles survive in aprotic solvents, DMSO and CH₃CN, but are transformed to nanowires in protic solvents, water, EG and MeOH. Our results demonstrated that the solvent-bridged H-bond plays a key role in the evolution of the morphologies from vesicles to nanowires. Moreover, the nanowires could further hierarchically self-assemble in water into hydrogels with high water content (99.5%), and with remarkable mechanical strength and self-healing properties. This study introduces a robust cluster-based building block in a supramolecular self-assembly system and reveals the significance of aprotic and protic solvents for the modulation of the morphologies of cluster-based aggregates.

Switching between Phosphorescence and Fluorescence Controlled by Chiral Self-Assembly

Helical self-assembly plays a unique role in regulating the localized excitations of π functional systems, which can also bring highly multi-scale orders, and show a special effect to tune the energy of electronics, vibration, and rotation of molecules. Due to controllable and dynamic property of chiral self-assembly, highly ordered and helical assemblies can be obtained to exhibit amplification effect and fascinating photophysical properties in photoluminescence. However, an effective control of singlet-triplet emissive switching in a unimolecular platform remains a great challenge. Recently, switchable singlet-triplet emission induced by helical self-assembly in a unimolecular platform has been developed. By taking advantage of the helical self-assembly driven by multiple intermolecular hydrogen bonding and strong π-π stacking interactions, reversible switching between fluorescence and phosphorescence could be efficiently achieved both in N,N-dimethylformamide/H2O solution and the solid state. The results will inspire the design of other intelligent luminescent materials through chiral self-assembly and be valuable for interdisciplinary development of supramolecular self-assembly and related materials science.

Molecular packing and the handedness of the self-assemblies of C17H35CO-Ala-Phe sodium salts

Molecular packing structure dominates the handedness of the self-assemblies of a series of lipodipeptide sodium salts.