In situ monitoring of molecular aggregation using circular dichroism

Carboxymethyl chitosan coating infused with linalool-loaded molten globular β-Lactoglobulin nanoparticles for extended preservation of fresh-cut apples

This investigation employed molten globule state β-lactoglobulin nanoparticles (MG-BLGNPs) for encapsulating linalool (LN) combined with carboxymethyl chitosan (CMC) coating to enhance the shelf-life of fresh-cut apples. The effect of different MG structures on the encapsulation efficiency of BLGNPs and the properties of coating was studied. Structural characterization and molecular simulation showed structural differences between heat-induced MG state (70-BLGNPs, heated at 70 °C for 1 h) and sodium dodecyl sulfate-co-heat-induced MG state (SDS/70-BLGNPs, treated with 0.192 mg/mL SDS for 10 min, then heated at 70 °C for 1 h), with the latter being more unfolded. LN self-assembles into MG-BLGNPs, among the generated particles, SDS/70-BLG@LN exhibits stronger binding effect and higher LN loading capacity. Integration of MG-BLG@LN into CMC enhanced coating's mechanical properties and adhesion to fresh-cut apples. The SDS/70-BLG@LN/CMC coating showed superior preservation on fresh-cut apples during storage, reducing enzymatic browning, membrane lipid oxidation, and microbial growth while maintaining hardness and overall quality.

pH-Responsive Rhodamine Nanotube Capable of Self-Reporting the Assembly State

Nanomaterials that respond to intracellular signals, such as pH, have the potential for many biomedical applications, such as drug delivery, because the assembly/disassembly process can be tailored to respond to a stimulus characteristic of a specific subcellular location. In this work, two rhodamine-peptides that form stable nanotubes at physiological pH but dissociate into highly fluorescent monomers within the acidified interior of endosomal/lysosomal cellular compartments have been developed. The rhodamine dipeptide conjugates, NH2-KK(RhB)-NH2 (RhB-KK) and NH2-EK(RhB)-NH2 (RhB-KE) with rhodamine B chromophores appended at the ε-amino position of a lysine residue, were shown to assemble into well-defined nanotubes at pH values above ∼4-5 and to dissociate into a fluorescent monomer state at lower pH values. The pH dependence of the assembly process was investigated using circular dichroism (CD) and fluorescence spectroscopy along with transmission electron microscopy (TEM), atomic force microscopy (AFM), and confocal imaging. Although the ring opening/closing transition of the rhodamine chromophore took place at pH 4.1 for both peptides, the onset of assembly began at pH 4.6 for RhB-KE and at a comparatively more basic pH (5.8) for RhB-KK. Accordingly, the rhodamine-peptides interconverted between three pH-dependent states: an open-ring, monomeric state (λmax 580 nm, λex 550 nm) at pH values at or below ∼4.6; a closed-ring, nanotube form that exhibits AIEE (λmax 460 nm, λex = 330 nm) at higher pH values; a closed-ring, nonemissive monomeric state that emerged below the critical micelle concentrations (CMC). The pH-responsive features of the peptides were evaluated by live-cell imaging in three cancer cell lines using confocal laser scanning microscopy (CLSM). Visualizing the cells after incubation with either RhB-KE or RhB-KK produced CLSM images with a punctate appearance in the Texas Red channel that colocalized with the lysosomes. These experiments indicate that the nanotubes were rapidly trafficked into the acidic lysosomal compartments within the cells, which induced dissociation into a monomeric, open state. Uptake inhibition studies suggested that cellular uptake was mediated by either caveolae- or clathrin-mediated endocytosis, depending on the cell line studied.

Testing the Simplified Molecular Dynamics Approach to Improve the Reproduction of ECD Spectra and Monitor Aggregation

A simplified molecular-dynamics-based electronic circular dichroism (ECD) approach was tested on three condensed derivatives with limited conformational flexibility and an isochroman-2H-chromene hybrid, the ECD spectra of which could not be precisely reproduced by the conventional ECD calculation protocol. Application of explicit solvent molecules at the molecular mechanics (MD) level in the dynamics simulations and subsequent TDDFT-ECD calculation for the unoptimized MD structures was able to improve the agreements between experimental and computed spectra. Since enhancements were achieved even for molecules with limited conformational flexibility, deformations caused by the solvent molecules and multitudes of conformers produced with unoptimized geometries seem to be key factors for better agreement. The MD approach could confirm that aggregation of the phenanthrene natural product luzulin A had a significant contribution to a specific wavelength range of the experimental ECD. The MD approach has proved that dimer formation occurred in solution and this was responsible for the anomalous ECD spectrum. The scope and limitations of the method have also been discussed.

Structural effects of charge destabilization and amino acid substitutions in amyloid fragments of CsgA

The most studied functional amyloid is the CsgA, major curli subunit protein, which is produced by numerous strains of Enterobacteriaceae. Although CsgA sequences are highly conserved, they exhibit species diversity, which reflects the specific evolutionary and functional adaptability of the major curli subunit. Herein, we performed bioinformatics analyses to uncover the differences in the amyloidogenic properties of the R4 fragments in Escherichia coli and Salmonella enterica and proposed four mutants for more detailed studies: M1, M2, M3, and M4. The mutated sequences were characterized by various experimental techniques, such as circular dichroism, ATR-FTIR, FT-Raman, thioflavin T, transmission electron microscopy and confocal microscopy. Additionally, molecular dynamics simulations were performed to determine the role of buffer ions in the aggregation process. Our results demonstrated that the aggregation kinetics, fibril morphology, and overall structure of the peptide were significantly affected by the positions of charged amino acids within the repeat sequences of CsgA. Notably, substituting glycine with lysine resulted in the formation of distinctive spherically packed globular aggregates. The differences in morphology observed are attributed to the influence of phosphate ions, which disrupt the local electrostatic interaction network of the polypeptide chains. This study provides knowledge on the preferential formation of amyloid fibrils based on charge states within the polypeptide chain.

Phase transition of GvpU regulates gas vesicle clustering in bacteria

Gas vesicles (GVs) are microbial protein organelles that support cellular buoyancy. GV engineering has multiple applications, including reporter gene imaging, acoustic control and payload delivery. GVs often cluster into a honeycomb pattern to minimize occupancy of the cytosol. The underlying molecular mechanism and the influence on cellular physiology remain unknown. Using genetic, biochemical and imaging approaches, here we identify GvpU from Priestia megaterium as a protein that regulates GV clustering in vitro and upon expression in Escherichia coli. GvpU binds to the C-terminal tail of the core GV shell protein and undergoes a phase transition to form clusters in subsaturated solution. These properties of GvpU tune GV clustering and directly modulate bacterial fitness. GV variants can be designed with controllable sensitivity to GvpU-mediated clustering, enabling design of genetically tunable biosensors. Our findings elucidate the molecular mechanisms and functional roles of GV clustering, enabling its programmability for biomedical applications.

Detection of insulin oligomeric forms by a novel surface plasmon resonance-diffusion coefficient based approach

Insulin is commonly used to treat diabetes and undergoes aggregation at the site of repeated injections in diabetic patients. Moreover, aggregation is also observed during its industrial production and transport and should be avoided to preserve its bioavailability to correctly adjust glucose levels in diabetic patients. However, monitoring the effect of various parameters (pH, protein concentration, metal ions, etc.) on the insulin aggregation and oligomerization state is very challenging. In this work, we have applied a novel Surface Plasmon Resonance (SPR)-based experimental approach to insulin solutions at various experimental conditions, monitoring how its diffusion coefficient is affected by pH and the presence of metal ions (copper and zinc) with unprecedented sensitivity, precision, and reproducibility. The reported SPR method, hereby applied to a protein for the first time, besides giving insight into the insulin oligomerization and aggregation phenomena, proved to be very robust for determining the diffusion coefficient of any biomolecule. A theoretical background is given together with the software description, specially designed to fit the experimental data. This new way of applying SPR represents an innovation in the bio-sensing field and expanding the potentiality of commonly used SPR instruments well over the canonical investigation of biomolecular interactions.

Experimental techniques for detecting and evaluating the amyloid fibrils

Amyloid fibrils are insoluble proteins with intricate β-sheet structures associated with various human diseases, including Parkinson's, Alzheimer's, and prion diseases. Proteins can form aggregates when their structure is misfolded, resulting in highly organized amyloid fibrils or amorphous aggregates. The formation of protein aggregates is a promising research field for mitigating diseases and the pharmaceutical and food industries. It is important to monitor and minimize the appearance of aggregates in these protein products. Several methods exist to assess protein aggregation, that includes from basic investigations to advanced biophysical techniques. Physicochemical parameters such as molecular weight, conformation, structure, and dimension are examined to study aggregation. There is an urgent need to develop methods for the detection of protein aggregation and amyloid fibril formation both in vitro and in vivo. This chapter focuses on a comprehensive discussion of the methods used to characterize and evaluate aggregates and amyloid fibrils.

1,3-diene-based AIEgens: Stereoselective synthesis and applications

In recent years, significant advancements have been made in the synthesis and application of 1,3-dienes. This specific structural motif has garnered significant attention from researchers in materials science and biology due to its unique aggregation-induced emission (AIE) properties and extensive conjugation systems. The luminescent characteristics of these compounds are notably influenced by the geometry of the two double bonds. Therefore, it is essential to consolidate stereoselective synthetic strategies for 1,3-dienes. This comprehensive review seeks to elucidate the diverse techniques employed to attain stereo-control in the synthesis of 1,3-diene-based AIE luminogens (AIEgens). Particular emphasis is placed on comprehending the determinants of stereoselectivity and exploring the array of substrates amenable to these methods. Furthermore, the review underscores the AIE properties exhibited by these compounds and their extensive utility in organic light-emitting diodes (OLEDs), stimuli-responsive materials, sensors, bioimaging, and photodynamic therapy (PDT).

2,2'-Tethered Binaphthyl-Embedded One-Handed Helical Ladder Polymers: Impact of the Tether Length on Helical Geometry and Chiroptical Property

Synthetic breakthroughs diversify the molecules and polymers available to chemists. We now report the first successful synthesis of a series of optically-pure 2,2'-tethered binaphthyl-embedded helical ladder polymers based on quantitative and chemoselective ladderization by the modified alkyne benzannulations using the 4-alkoxy-2,6-dimethylphenylethynyl group as the alkyne source, inaccessible by the conventional approach lacking the 2,6-dimethyl substituents. Due to the defect-free helix formation, the circular dichroism signal increased by more than 6 times the previously reported value. The resulting helical secondary structure can be fine-tuned by controlling the binaphthyl dihedral angle in the repeating unit with variations in the 2,2'-alkylenedioxy tethering groups by one carbon atom at a time. The optimization of the helical ladder structures led to a strong circularly polarized luminescence with a high fluorescence quantum yield (28 %) and luminescence dissymmetry factor (2.6×10-3 ).

Luminescent Radicals

Organic radicals are attracting increasing interest as a new class of molecular emitters. They demonstrate electronic excitation and relaxation dynamics based on their doublet or higher multiplet spin states, which are different from those based on singlet-triplet manifolds of conventional closed-shell molecules. Recent studies have disclosed luminescence properties and excited state dynamics unique to radicals, such as highly efficient electron-photon conversion in OLEDs, NIR emission, magnetoluminescence, an absence of heavy atom effect, and spin-dependent and spin-selective dynamics. These are difficult or sometimes impossible to achieve with closed-shell luminophores. This review focuses on luminescent organic radicals as an emerging photofunctional molecular system, and introduces the material developments, fundamental properties including luminescence, and photofunctions. Materials covered in this review range from monoradicals, radical oligomers, and radical polymers to metal complexes with radical ligands demonstrating radical-involved emission. In addition to stable radicals, transiently formed radicals generated in situ by external stimuli are introduced. This review shows that luminescent organic radicals have great potential to expand the chemical and spin spaces of luminescent molecular materials and thus broaden their applicability to photofunctional systems.

Protein Nanotubes as Advanced Material Platforms and Delivery Systems

Protein nanotubes (PNTs) as state-of-the-art nanocarriers are promising for various potential applications both in the food and pharmaceutical industries. Derived from edible starting sources like α-lactalbumin, lysozyme, and ovalbumin, PNTs bear properties of biocompatibility and biodegradability. Their large specific surface area and hydrophobic core facilitate chemical modification and loading of bioactive substances, respectively. Moreover, their enhanced permeability and penetration ability across biological barriers such as intestinal mucus, extracellular matrix, and thrombus clot, make it promising platforms for health-related applications. Most importantly, their simple preparation processes enable large-scale production, supporting applications in the biomedical and nanotechnological fields. Understanding the self-assembly principles is crucial for controlling their morphology, size, and shape, and thus provides the ground to a multitude of applications. Here, the current state-of-the-art of PNTs including their building materials, physicochemical properties, and self-assembly mechanisms are comprehensively reviewed. The advantages and limitations, as well as challenges and prospects for their successful applications in biomaterial and pharmaceutical sectors are then discussed and highlighted. Potential cytotoxicity of PNTs and the need of regulations as critical factors for enabling in vivo applications are also highlighted. In the end, a brief summary and future prospects for PNTs as advanced platforms and delivery systems are included.

Aggregation‐enabled alkene insertion into carbon–halogen bonds

Molecular aggregation affects the electronic interactions between molecules and has emerged as a powerful tool in material science. Aggregate effect finds wide applications in the research of new physical phenomena; however, its value for chemical reaction development has been far less explored. Herein, we report the development of aggregation‐enabled alkene insertion into carbon–halogen bonds. The spontaneous cleavage of C–X (X = Cl, Br, or I) bonds generates an intimate ion pair, which can be quickly captured by alkenes in an aggregated state. Additional catalysts or promoters are not necessary under such circumstances, and solvent quenching experiments indicate that the aggregated state is critical for achieving such sequences. The ionic insertion mode is supported by mechanistic studies, density functional theory calculations, and symmetry‐adapted perturbation theory analysis. Results also show that the non‐aggregated state may quench the transition state and terminate the insertion process.

Protein aggregation: Consequences, mechanism, characterization and inhibitory strategies

Proteins play a major role in the regulation of various cellular functions including the synthesis of structural components. But proteins are stable under physiological conditions only. A slight variation in environmental conditions can cost them huge in terms of conformational stability ultimately leading to aggregation. Under normal conditions, aggregated proteins are degraded or removed from the cell by a quality control system including ubiquitin-proteasomal machinery and autophagy. But they are burdened under diseased conditions or are impaired by the aggregated proteins leading to the generation of toxicity. The misfolding and aggregation of protein such as amyloid-β, α-synuclein, human lysozyme etc., are responsible for certain diseases including Alzheimer, Parkinson, and non- neuropathic systemic amyloidosis respectively. Extensive research has been done to find the therapeutics for such diseases but till now we have got only symptomatic treatment that will reduce the disease severity but will not target the initial formation of nucleus responsible for disease progression and propagation. Hence there is an urgent need to develop the drugs targeting the cause of the disease. For this, a wide knowledge related to misfolding and aggregation under the same heading is required as described in this review alongwith the strategies hypothesized and implemented till now. This will contribute a lot to the work of researchers in the field of neuroscience.

Tailor-Made Pdn L2n Metal-Organic Cages through Covalent Post-Synthetic Modification

Post-synthetic modification (PSM) is an effective approach for the tailored functionalization of metal-organic architectures, but its generalizability remains challenging. Herein we report a general covalent PSM strategy to functionalize Pd_n L_2n metal-organic cages (MOCs, n=2, 12) through an efficient Diels-Alder cycloaddition between peripheral anthracene substituents and various functional motifs bearing a maleimide group. As expected, the solubility of functionalized Pd₁₂ L₂₄ in common solvents can be greatly improved. Interestingly, concentration-dependent circular dichroism and aggregation-induced emission are achieved with chiral binaphthol (BINOL)- and tetraphenylethylene-modified Pd₁₂ L₂₄ , respectively. Furthermore, Pd₁₂ L₂₄ can be introduced with two different functional groups (e.g., chiral BINOL and achiral pyrene) through a step-by-step PSM route to obtain chirality-induced circularly polarized luminescence. Moreover, similar results are readily observed with a smaller Pd₂ L₄ system.

Controlled sequential in situ self-assembly and disassembly of a fluorogenic cisplatin prodrug for cancer theranostics

Temporal control of delivery and release of drugs in tumors are important in improving therapeutic outcomes to patients. Here, we report a sequential stimuli-triggered in situ self-assembly and disassembly strategy to direct delivery and release of theranostic drugs in vivo. Using cisplatin as a model anticancer drug, we design a stimuli-responsive small-molecule cisplatin prodrug (P-CyPt), which undergoes extracellular alkaline phosphatase-triggered in situ self-assembly and succeeding intracellular glutathione-triggered disassembly process, allowing to enhance accumulation and elicit burst release of cisplatin in tumor cells. Compared with cisplatin, P-CyPt greatly improves antitumor efficacy while mitigates off-target toxicity in mice with subcutaneous HeLa tumors and orthotopic HepG2 liver tumors after systemic administration. Moreover, P-CyPt also produces activated near-infrared fluorescence (at 710 nm) and dual photoacoustic imaging signals (at 700 and 750 nm), permitting high sensitivity and spatial-resolution delineation of tumor foci and real-time monitoring of drug delivery and release in vivo. This strategy leverages the advantages offered by in situ self-assembly with those of intracellular disassembly, which may act as a general platform for the design of prodrugs capable of improving drug delivery for cancer theranostics.

Insights into Self-Assembly of Nonplanar Molecules with Aggregation-Induced Emission Characteristics

Utilizing nonplanar conjugated molecules as building blocks facilitates the development of self-assembly but is fundamentally challenging. To study the self-assembly behavior, we herein demonstrate the self-assembly process of a nonplanar conjugated molecule with aggregation-induced emission (AIE) feature from an isolated molecule to an irregular cluster to a well-defined vesicle driven by amphiphiles. The superhigh aggregation-sensitive emission affords more precise and detailed information about the self-assembly process than traditional dyes. Meanwhile, the arrangements of the AIE-active molecule change from disordered to well-organized forms by reducing the twisted configuration during the transformation process, and the strong hydrophobicity of amphiphiles is crucial for such configuration and morphology transformations. Owing to the thermophilic bacteria-mimetic membranes, the obtained vesicles exhibit a property of superhigh thermal stability. They also display promising light-harvesting applications. This work not only deciphers the self-assembly of AIE molecules but also provides a strategy for nonplanar molecules to build well-organized self-assemblies.

Bioprocessing of recombinant proteins from Escherichia coli inclusion bodies: insights from structure-function relationship for novel applications

The formation of inclusion bodies (IBs) during expression of recombinant therapeutic proteins using E. coli is a significant hurdle in producing high-quality, safe, and efficacious medicines. The improved understanding of the structure-function relationship of the IBs has resulted in the development of novel biotechnologies that have streamlined the isolation, solubilization, refolding, and purification of the active functional proteins from the bacterial IBs. Together, this overall effort promises to radically improve the scope of experimental biology of therapeutic protein production and expand new prospects in IBs usage. Notably, the IBs are increasingly used for applications in more pristine areas such as drug delivery and material sciences. In this review, we intend to provide a comprehensive picture of the bio-processing of bacterial IBs, including assessing critical gaps that still need to be addressed and potential solutions to overcome them. We expect this review to be a useful resource for those working in the area of protein refolding and therapeutic protein production.

A nonconjugated radical polymer with stable red luminescence in the solid state

Organic radicals are unstable and stable radicals usually display non-luminescent properties. Luminescent radicals possess the all-in-one properties of optoelectronics, electronics, and magnetics. To date, the reported structures of luminescent radicals are limited to triphenylmethyl radical derivatives and their analogues, which are stabilized with extended π-conjugation. Here, we demonstrate the first example of a nonconjugated luminescent radical. In spite of the lack of delocalized π-stabilization, the radical polymer readily emits red luminescence in the solid state. A traditional luminescent quencher, 2,2,6,6-tetramethylpiperidin-1-yl turned into a red chromophore when grafted onto a polymer backbone. Experimental data confirm that the emission is associated with the nitroxide radicals and is also affected by the packing of the polymer. This work discloses a novel class of luminescent radicals and a distinctive pathway for luminescence from open-shell materials.

Toward high-throughput oligomer detection and classification for early-stage aggregation of amyloidogenic protein

Aggregation kinetics of proteins and peptides have been studied extensively due to their significance in many human diseases, including neurodegenerative disorders, and the roles they play in some key physiological processes. However, most of these studies have been performed as bulk measurements using Thioflavin T or other fluorescence turn-on reagents as indicators of fibrillization. Such techniques are highly successful in making inferences about the nucleation and growth mechanism of fibrils, yet cannot directly measure assembly reactions at low protein concentrations which is the case for amyloid-β (Aβ) peptide under physiological conditions. In particular, the evolution from monomer to low-order oligomer in early stages of aggregation cannot be detected. Single-molecule methods allow direct access to such fundamental information. We developed a high-throughput protocol for single-molecule photobleaching experiments using an automated fluorescence microscope. Stepwise photobleaching analysis of the time profiles of individual foci allowed us to determine stoichiometry of protein oligomers and probe protein aggregation kinetics. Furthermore, we investigated the potential application of supervised machine learning with support vector machines (SVMs) as well as multilayer perceptron (MLP) artificial neural networks to classify bleaching traces into stoichiometric categories based on an ensemble of measurable quantities derivable from individual traces. Both SVM and MLP models achieved a comparable accuracy of more than 80% against simulated traces up to 19-mer, although MLP offered considerable speed advantages, thus making it suitable for application to high-throughput experimental data. We used our high-throughput method to study the aggregation of Aβ40 in the presence of metal ions and the aggregation of α-synuclein in the presence of gold nanoparticles.

Mechanical Tuning of Aggregated States for Conformation Control of Cyclized Binaphthyl at the Air-Water Interface

An air-water interface enables molecular assemblies and conformations to be controlled according to their intrinsic interactions and anisotropic stimuli. The chirality and conformation of binaphthyl derivatives have been controlled by tuning molecular aggregated states in solution. In this study, we have tuned molecular aggregated states of monobinaphthyldurene (MBD) by applying different mechanical stimuli to control the conformation at the air-water interface. Density functional theory calculations indicate that MBD exists essentially in two conformations, namely, 1-MBD (most stable) and 2-MBD (less stable). MBD was mechanically dissolved in appropriate lipid matrices using the Langmuir-Blodgett (LB) method, while pure MBD was self-assembled at the dynamic air-water interface in the absence of or by applying vortex motions (vortex LB method). In MBD mixed monolayer, surface pressure-molecular area measurements and atomic force microscopy observations suggest that separate lipids and MBD phases transform to mixed phases induced by the dissolution of MBD into the lipid matrices during mechanical compression at the air-water interface. Circular dichroism measurements indicate that molecular conformation changes from 1-MBD to 2-MBD in passing from a separated phase to a mixed MBD/lipid phase. In addition, the molecular aggregated states and conformations of MBD depend on the spreading volume and vortex flow rate when applying the vortex LB method. Molecular conformations and aggregated states of MBD could be controlled continuously by applying a mechanical stimulus at the air-water interface.

Azimuth-Resolved Circular Dichroism of Metamaterials

Chiral optical metamaterials have attracted a great deal of attention due to their intriguing properties with respect to fundamental research and practical applications. For metamaterials with achiral structures, the system composed of metamaterials and obliquely incident light has extrinsic chirality and can produce circular dichroism (CD) effect. However, there have been few studies on the azimuth-dependent CD spectra of achiral metamaterials that have greatly improved our understanding of optical phenomena caused by external chirality. In this work, we experimentally studied the azimuth-dependent CD that originated from the extrinsic chirality of the metamaterials in an asymmetric-U shape and a U-bar-shape gold unit structure, separately. We explain the origin of the CD in the coupling of the macro-electric dipole and magnetic dipole, and the simulation results are in good agreement with the experiment. Our results provide a possible way to build an on-chip azimuth sensor based on azimuth-dependent CD spectra of metamaterials.

Aggregation-induced emission (AIE) from poly(1,4-dihydropyridine)s synthesized by Hantzsch polymerization and their specific detection of Fe2+ ions

As an important metal element widely existing in nature and the human body, the simple and specific detection of Fe2+ ions has always been of interest.

Regulating the Excited State Chirality to Fabricate High-Performance-Solid-State Circularly Polarized Luminescence Materials

Developing solid-state materials and greatly improving the luminescence dissymmetry factors (g_lum) are the key issues for the future oriented practical application in the field of circularly polarized luminescence (CPL). However, most of the solid-state CPL-active materials suffer from aggregation caused emission quenching and relatively small g_lum values, which intensively restrict the development and application. In this work, high-performance CPL-active solid-state materials were achieved by regulating the excited state chirality of a series of bi-pyrene based chiral emitters. Due to the reversible mechanochromic luminescence under external stimuli, their excited state chirality can also be switched. It was found that the pristine amorphous powder possessed weak but obvious chiroptical properties because of the inherently chiral structures. Mechanical grinding could switch the fluorescence color and eliminate the CPL activity. Subsequently, by carrying out solvent fumigation, instant crystallization with well-defined microcrystal formation occurred, which could activate the CPL emission. Due to the chiral supramolecular arrangement of chromophores in the crystalline state, the resulting excimer emission in microcrystals showed chirality amplification not only in the excited state but also in the ground state. These findings not only provide a new method to fabricate high-performance CPL-active solid-state materials, but also clarify the chirality origin of pyrene-excimer-based chiral luminophores in various states which showed the importance of CPL as a probe of excited state chirality.

In situ instant crystallization significantly boosts the CPL performance in which both large circular polarization and high luminescence efficiency are achieved due to the chiral supramolecular arrangement of chromophores in the crystalline state.

Challenges in Experimental Methods

Experimental studies of amyloids encounter many challenges. There are many methods available for studying proteins, which can be applied to amyloids: from basic staining techniques, allowing visualization of fibers, to complex methods, e.g., AFM-IR used to their detailed biochemical and structural characterization in nanoscale. Which method is appropriate depends on the goal of an experiment: verification of aggregational properties of a peptide, distinguishing oligomers from mature fibers, or kinetic studies. Insolubility, rapid aggregation, and the need of using a high-purity peptide may be a limiting factor in studies involving amyloids. Moreover, the results obtained by various experimental methods often differ significantly, which may lead to misclassification of amyloid peptides. Due to ambiguity of experimental results, laborious and time-consuming analysis, bioinformatical methods become more widely used for amyloids.

Switching energy dissipation pathway: in situ proton-induced transformation of AIE-active self-assemblies to boost photodynamic therapy

With the morphological transformation of fluorescent self-assembled nanostructures, their functions can be varied simultaneously. However, little attention has been paid to the function variation in this process. Herein, we present aggregation-induced emission (AIE)-active self-assembled nanospheres to investigate the transformation-induced function variation by switching the energy dissipation pathway. The self-assembled nanospheres showed strong emission under neutral conditions, indicating that radiative decay dominates the energy dissipation. Under acidic conditions, the spheres transformed to vesicles and nanotubes, in which the excited energy was largely consumed by the intersystem crossing pathway and highly efficient reactive oxygen species (ROS) generation was afforded. In particular, this morphological transformation and function variation can smoothly proceed in acidic lysosomes, thus drastically boosting photodynamic cancer therapy.

Design and Development of Axially Chiral Bis(naphthofuran) Luminogens as Fluorescent Probes for Cell Imaging

Designing chiral AIEgens without aggregation-induced emission (AIE)-active molecules externally tagged to the chiral scaffold remains a long-standing challenge for the scientific community. The inherent aggregation-caused quenching phenomenon associated with the axially chiral (R)-[1,1'-binaphthalene]-2,2'-diol ((R)-BINOL) scaffold, together with its marginal Stokes shift, limits its application as a chiral AIE-active material. Here, in our effort to design chiral luminogens, we have developed a design strategy in which 2-substituted furans, when appropriately fused with the BINOL scaffold, will generate solid-state emissive materials with high thermal and photostability as well as colour-tunable properties. The excellent biocompatibility, together with the high fluorescence quantum yield and large Stokes shift, of one of the luminogens stimulated us to investigate its cell-imaging potential. The luminogen was observed to be well internalised and uniformly dispersed within the cytoplasm of MDA-MB-231 cancer cells, showing high fluorescence intensity.

Real-Time Visual Monitoring of Kinetically Controlled Self-Assembly

The construction of artificial structures through hierarchical self-assembly based on noncovalent interactions, as well as monitoring during the self-assembly process, are important aspects of dynamic supramolecular chemistry. Herein we describe the complex dynamics of chiral N,N'-diphenyl dihydrodibenzo[a,c]phenazine derivatives (S)/(R)-DPAC, whose different assemblies were found to have distinct optical and morphological characteristics. With ratiometric fluorescence originating from vibration-induced emission (VIE), the self-assembly process from kinetic traps to the thermodynamic equilibrium state could be monitored in real time by optical spectrometry. During the morphology transformation from particles to nanobricks, strong circularly polarized luminescence was induced with g_lum =1.6×10^-2 . The excited-state characteristics of the self-assemblies enabled investigation of the relationship between molecular aggregation and conformational change, thus allowing effective monitoring of the sophisticated supramolecular self-assembly process.

Aggregation-Induced Emission Properties in Fully π-Conjugated Polymers, Dendrimers, and Oligomers

Aggregation-Induced Emission (AIE) in organic molecules has recently attracted the attention of the scientific community because of their potential applications in different fields. Compared to small molecules, little attention has been paid to polymers and oligomers that exhibit AIE, despite having excellent properties such as high emission efficiency in aggregate and solid states, signal amplification effect, good processability and the availability of multiple functionalization sites. In addition to these features, if the molecular structure is fully conjugated, intramolecular electronic interactions between the composing chromophores may appear, thus giving rise to a wealth of new photophysical properties. In this review, we focus on selected fully conjugated oligomers, dendrimers and polymers, and briefly summarize their synthetic routes, fluorescence properties and potential applications. An exhaustive comparison between spectroscopic results in solution and aggregates or in solid state has been collected in almost all examples, and an opinion on the future direction of the field is briefly stated.

Helicity Manipulation of a Double-Paddled Binaphthyl in a Two-Dimensional Matrix Field at the Air-Water Interface

Molecular behavior and functionality are affected by their prevailing immediate environment. Molecular machines function according to conformational variations and have been studied largely in solution states. In order to access more highly complex functional molecular machines, it is necessary to analyze and control them in various environments. We have designed and synthesized a bisbinaphthyldurene (BBD) molecule that has two binaphthyl groups connected through a central durene moiety, allowing for the formation of several conformers. In density functional theory (DFT) calculations, BBD has five major conformers, denoted anti-1/anti-2/syn-1/syn-2/flat. It has been demonstrated that BBD exhibits different conformations in solution (anti-1 and syn-1) than on a gold surface (syn dimer and flat). In this work, the ratio of BBD conformations has been controlled in mixed monolayers with several different lipids at an air-water interface in order to compare conformational activity under different conditions. The conformations of BBD in transferred films obtained by using Langmuir-Blodgett techniques were estimated from circular dichroism spectra and DFT calculations. It has been found that the conformation of BBD in the mixed monolayer depends on its aggregated state, which has been controlled here by the mechanical properties and miscibility. In mixed monolayers with "hard" lipids having less miscibility with BBD as well as in cast film, BBD is self-aggregated and mostly forms stable anti-1 and syn-1 conformations, while unstable anti-2 and syn-2 conformers dominated in the more dispersed states involving "soft" lipids, which show good miscibility with BBD. Conformational changes in BBD are due to the formation of different aggregated states in each mixed monolayer according to the miscibility. Overall, BBD molecular conformations (and the resulting spectra) could be tuned by controlling the environment whether in solution, on a solid substrate, or in an admixture with lipids at the air-water interface.

Aggregate Science: From Structures to Properties

Molecular science entails the study of structures and properties of materials at the level of single molecules or small interacting complexes of molecules. Moving beyond single molecules and well-defined complexes, aggregates (i.e., irregular clusters of many molecules) serve as a particularly useful form of materials that often display modified or wholly new properties compared to their molecular components. Some unique structures and phenomena such as polymorphic aggregates, aggregation-induced symmetry breaking, and cluster excitons are only identified in aggregates, as a few examples of their exotic features. Here, by virtue of the flourishing research on aggregation-induced emission, the concept of "aggregate science" is put forward to fill the gaps between molecules and aggregates. Structures and properties on the aggregate scale are also systematically summarized. The structure-property relationships established for aggregates are expected to contribute to new materials and technological development. Ultimately, aggregate science may become an interdisciplinary research field and serves as a general platform for academic research.

TICT-Based Near-Infrared Ratiometric Organic Fluorescent Thermometer for Intracellular Temperature Sensing

Fluorescent thermometers with near-infrared (NIR) emission play an important role in visualizing the intracellular temperature with high resolution and investigating the cellular functions and biochemical activities. Herein, we designed and synthesized a donor-Π-acceptor luminogen, 2-([1,1'-biphenyl]-4-yl)-3-(4-((E)-4-(diphenylamino)styryl) phenyl) fumaronitrile (TBB) by Suzuki coupling reaction. TBB exhibited twisted intramolecular charge transfer-based NIR emission, aggregation-induced emission, and temperature-sensitive emission features. A ratiometric fluorescent thermometer was constructed by encapsulating thermosensitive NIR fluorophore TBB and Rhodamine 110 dye into an amphiphilic polymer matrix F127 to form TBB&R110@F127 nanoparticles (TRF NPs). TRF NPs showed a good temperature sensitivity of 2.37%·°C^-1, wide temperature response ranges from 25 to 65 °C, and excellent temperature-sensitive emission reversibility. Intracellular thermometry experiments indicated that TRF NPs could monitor the cellular temperature change from 25 to 53 °C for Hep-G2 cells under the photothermal therapy agent heating process, indicating the considerable potential applications of TRF NPs in the biological thermometry field.

Sunlight and UV driven synthesis of Ag nanoparticles for fluorometric and colorimetric dual-mode sensing of ClO

A photo-responsive compound BINOL-LA (1) having a rigid backbone ending up with two 5-membered cyclic disulfide moieties was designed. BINOL-LA capped Ag nanoparticles (1@Ag NPs) with a network structure were synthesized in a green way by sunlight or UV lamp irradiation. 1@Ag NPs exhibit a selective recognition towards ClO^- in aqueous solution with a switch-on fluorescence response and a visual color change, with detection limits of 0.17 μM and 1.54 μM, respectively. The sensing mechanism is based on the ClO^--mediated oxidation of AgS bond, resulting in a disaggregation of 1@Ag NPs assembly. With the strategy demonstrated here, ClO^- in tap water and lake water can be detected quantitatively in 5 s.

Ultrathin circular polarimeter based on chiral plasmonic metasurface and monolayer MoSe2

Two-dimensional materials are ideal platforms for intriguing physics and optoelectronic applications because of their ultrathin thicknesses and excellent properties in optics and electronics. Further studies on enhancing the interaction between light and two-dimensional materials by combining metallic nanostructures have generated broad interests in recent years, such as enhanced photoluminescence, strong coupling and functional optoelectronics. In this work, an ultrathin circular polarimeter consisting of chiral plasmonic metasurface and monolayer semiconductor is proposed to detect light with different circular polarization within a compact device. A designed chiral plasmonic metasurface with sub-wavelength thickness is integrated with monolayer MoSe₂, and the circular-polarization-dependent photocurrent responses of right and left circularly polarized light for both left- and right-handed metasurfaces are experimentally demonstrated. The photoresponse circular dichroism is also obtained, which further indicates the remarkable performance of the proposed device in detecting and distinguishing circularly polarized light. This design offers a great potential to realize multifunctional measurements in an ultrathin and ultracompact two-dimensional device for future integrated optics and optoelectronic applications with circularly polarized light.

Synthesis and Self-Assembly Behavior of Chlorophyll Derivatives for Ratiometric Photoacoustic Signal Optimization

Self-assembly provides researchers powerful tools for creating ordered functional structures and complex architectures. Investigation of in vivo self-assembly reveals the assembly/aggregation-induced retention (AIR) effect and enhanced targeting effect, which can be applied to promising biomedical applications by enhancing molecular accumulation in the target region. These unique bioeffects inspire the interest of researchers in construction of self-assembled nanomaterials in biological systems. Although many efforts have been achieved, the in-depth analysis of the relationship between assemblies and functions is rarely reported. Here, we focus on the relationship of chlorophyll-derivative assemblies and their photoacoustic signals and attempt to establish a method for monitoring the aggregation efficiency in vivo based on photoacoustic signals. Three arginine-rich peptide-purpurin molecules were designed and synthesized. The assembled capabilities and assembly processes of these molecules were characterized and monitored by UV, fluorescence, and CD spectra images of gradually changing polarities in mixed solvents, and the morphologies of the assemblies were observed by TEM. Furthermore, the relationship between the aggregation ratios of the molecules and the ratiometric photoacoustic signals was systemically studied. We prospect that the fundamental research in revealing objective laws will be useful for future guidance in optimizing photoacoustic detection windows and assembled molecule design.

The axial chirality hidden in vitamin D and its application in cocrystal prediction

An ECD titration method was developed to detect hydrogen-bonding interaction in solution and to predict cocrystal formation in the solid state.

Visualization and Manipulation of Molecular Motion in the Solid State through Photoinduced Clusteroluminescence

The development of molecular machines has long been a dream of scientists and is expected to revolutionize many aspects of technology and medicine. As the prerequisite of a practicable molecular machine, studies on the solid-state molecular motion (SSMM) are not only of scientific importance but also practically useful. Herein, two nonconjugated molecules, 1,2-diphenylethane (s-DPE) and 1,2-bis(2,4,5-trimethylphenyl)ethane (s-DPE-TM), are synthesized, and their SSMM is investigated. Experimental and calculation results reveal that s-DPE and s-DPE-TM are capable of performing light-driven SSMM to form excited-state through-space complexes (ESTSC). The radiative decay of ESTSC generates an unexpected visible emission termed clusteroluminescence, which serves as a tool to visualize the process of SSMM. Meanwhile, the original packing structure can be recovered from ESTSC after the removal of light irradiation. This work provides a new strategy to manipulate and "see" the SSMM and gains new insights into clusteroluminescence.

Super-Resolution Visualization of Self-Assembling Helical Fibers Using Aggregation-Induced Emission Luminogens in Stimulated Emission Depletion Nanoscopy

Organic fluorophores for stimulated emission depletion (STED) nanoscopy usually suffer from quenched emission in the aggregate state and inferior photostability, which largely limit their application in real-time, in situ, and long-term imaging at an ultrahigh resolution. Herein, an aggregation-induced emission (AIE) luminogen of DP-TBT with bright emission in solid state (photoluminescence quantum yields = 25%) and excellent photostability was designed to meet the requirements in STED nanoscopy. In addition to its excellent fluorescence properties, DP-TBT could also easily form self-assembling helixes and finally be well-visualized by super-resolution STED nanoscopy. The observations showed that helical fibers of DP-TBT as dashed lines had a much decreased fiber width with also a full width at half-maximum value of only 178 nm, which is ∼6 times higher than solid lines obtained by confocal microscopy (1154 nm). The STED nanoscopic data were also used to reconstruct 3D images of assembled helixes. Finally, by long-term tracking and dynamic monitoring, the formation and growth of helical fibers by DP-TBT in self-assembly processes were successfully obtained. These findings imply that highly emissive AIEgens with good photostability are highly suitable for real-time, in situ, and dynamic imaging at super-resolution using STED nanoscopy.

Non-aromatic annulene-based aggregation-induced emission system via aromaticity reversal process

Aggregation-induced emission (AIE) is a photophysical phenomenon correlated closely with the excited-state intramolecular motions. Although AIE has attracted increasing attention due to the significant applications in biomedical and optoelectronics, an in-depth understanding of the excited-state intramolecular motion has yet to be fully developed. Here we found the non-aromatic annulene derivative of cyclooctatetrathiophene shows typical AIE phenomenon in spite of its rotor-free structure. The underlying mechanism is investigated through photoluminescence spectra, time-resolved absorption spectra, theoretical calculations, circular dichroism as well as by pressure-dependent fluorescent spectra etc., which indicate that the aromaticity reversal from ground state to the excited state serves as a driving force for inducing the excited-state intramolecular vibration, leading to the AIE phenomenon. Therefore, aromaticity reversal is demonstrated as a reliable strategy to develop vibrational AIE systems. This work also provides a new viewpoint to understand the excited-state intramolecular motion behavior of lumiongens.

Axially chiral 1,4-dihydropyridine derivatives: aggregation-induced emission in exciplexes and application as viscosity probes

By combining the fluorophores of axially chiral 1,1′-binaphthol (BINOL) and 1,4-dihydropyridine derivatives, axially chiral 1,4-dihydropyridine derivatives ((R)-/(S)-2) with aggregation-induced emission (AIE) in exciplexes were designed and synthesized. (R)-/(S)-2 emitted low fluorescence in THF solutions of their locally excited states; however, they emitted red-shifted fluorescence in the aggregate state upon exciplex formation. Moreover, (R)-/(S)-2 showed linear and multi-exponential relationships between their local excited and exciplex fluorescence intensities and the viscosity of the medium, which allowed us to determine the viscosities of different mixed solvents. In addition, as an axially chiral viscosity probe, (R)-/(S)-2 show excellent CD signals and have potential applications in the fields of chiral recognition and fluorescence imaging, which will broaden the new family of AIE fluorophores. To the best of our knowledge, there are few reports of axially chiral intramolecular exciplex-mediated AIE molecules.

Axially chiral 1,4-dihydropyridine derivatives ((R)-/(S)-2) with aggregation-induced emission (AIE) in exciplex were designed and synthesized. They have excellent CD signals and can determine the different viscosity in mixed solvents.