Reversible Photocontrol of Biological Systems by the Incorporation of Molecular Photoswitches

Pyrene Functionalized Norbornadiene-Quadricyclane Fluorescent Photoswitches: Characterization of their Spectral Properties and Application in Imaging of Amyloid Beta Plaques

This study presents the synthesis and characterization of two fluorescent norbornadiene (NBD) photoswitches, each incorporating two conjugated pyrene units. Expanding on the limited repertoire of reported photoswitchable fluorescent NBDs, we explore their properties with a focus on applications in bioimaging of amyloid beta (Aβ) plaques. While the fluorescence emission of the NBD decreases upon photoisomerization, aligning with what has been previously reported, for the first time we observed luminescence after irradiation of the quadricyclane (QC) isomer. We deduce how the observed emission is induced by photoisomerization to the excited state of the parent isomer (NBD) which is then the emitting species. Thorough characterizations including NMR, UV-Vis, fluorescence, X-ray structural analysis and density functional theory (DFT) calculations provide a comprehensive understanding of these systems. Notably, one NBD-QC system exhibits exceptional durability. Additionally, these molecules serve as effective fluorescent stains targeting Aβ plaques in situ, with observed NBD/QC switching within the plaques. Molecular docking simulations explore NBD interactions with amyloid, unveiling novel binding modes. These insights mark a crucial advancement in the comprehension and design of future photochromic NBDs for bioimaging applications and beyond, emphasizing their potential in studying and addressing protein aggregates.

Photochromic luminescence of organic crystals arising from subtle molecular rearrangement

Photoluminescence (PL) colour-changing materials in response to photostimulus play an increasingly significant role in intelligent applications for their programmability. Nevertheless, current research mainly focuses on photochemical processes, with less attention to PL transformation through uniform aggregation mode adjustment. Here we show photochromic luminescence in organic crystals (e.g. dimethyl terephthalate) with PL varying from dark blue to purple, then to bright orange-red, and finally to red. This change is attributed to the emergence of clusters with red emission, which is barely achieved in single-benzene-based structures, thanks to the subtle molecular rearrangements prompted by light. Crucial to this process are the through-space electron interactions among molecules and moderate short contacts between ester groups. The irradiated crystals exhibit reversible PL transformation upon sufficient relaxation, showing promising applications in information storage and smart optoelectronic devices. This research contributes to the development of smart photochromic luminescent materials with significant PL colour transformations through molecular rearrangement.

Photocontrolled Reversible Amyloid Fibril Formation of Parathyroid Hormone-Derived Peptides

Peptide fibrillization is crucial in biological processes such as amyloid-related diseases and hormone storage, involving complex transitions between folded, unfolded, and aggregated states. We here employ light to induce reversible transitions between aggregated and nonaggregated states of a peptide, linked to the parathyroid hormone (PTH). The artificial light-switch 3-{[(4-aminomethyl)phenyl]diazenyl}benzoic acid (AMPB) is embedded into a segment of PTH, the peptide PTH25-37, to control aggregation, revealing position-dependent effects. Through in silico design, synthesis, and experimental validation of 11 novel PTH25-37-derived peptides, we predict and confirm the amyloid-forming capabilities of the AMPB-containing peptides. Quantum-chemical studies shed light on the photoswitching mechanism. Solid-state NMR studies suggest that β-strands are aligned parallel in fibrils of PTH25-37, while in one of the AMPB-containing peptides, β-strands are antiparallel. Simulations further highlight the significance of π-π interactions in the latter. This multifaceted approach enabled the identification of a peptide that can undergo repeated phototriggered transitions between fibrillated and defibrillated states, as demonstrated by different spectroscopic techniques. With this strategy, we unlock the potential to manipulate PTH to reversibly switch between active and inactive aggregated states, representing the first observation of a photostimulus-responsive hormone.

Complete amide cis-trans switching synchronized with disulfide bond formation and cleavage in a proline-mimicking system

A typical naturally occurring disulfide structure in proteins is an 8-membered disulfide ring formed between two adjacent cysteine (Cys-Cys) residues. Based on this structure, we designed 7- to 9-membered disulfide ring molecules, embedded in the 7-azabicyclo[2.2.1]heptane skeleton, that switch their conformation from exclusively trans-amide to exclusively cis-amide upon redox transformation from dithiol to disulfide, and vice versa. Constrained shape of disulfide rings is rare in nature, and the present molecular structure is expected to be a useful fundamental component for the construction of new conformation-switching systems.

Optical Control of Insect Behavior and Receptors with Azobenzene-Bridged Fipronil and Imidacloprid

Photopharmacology can be implemented in a way of regulating drug activities by light-controlling the molecular configuations. Three photochromic ligands (PCLs) that bind on one or two sites of GABARs and nAChRs were reported here. These multiphoton PCLs, including FIP-AB-FIP, IMI-AB-FIP, and IMI-AB-IMI, are constructed with an azobenzene (AB) bridge that covalently connects two fipronil (FIP) and imidacloprid (IMI) molecules. Interestingly, the three PCLs as well as FIP and IMI showed great insecticidal activities against Aedes albopictus larvae and Aphis craccivora. IMI-AB-FIP in both trans/cis isomers can be reversibly interconverted depending on light, accompanied by insecticidal activity decrease or increase by 1.5-2.3 folds. In addition, IMI-AB-FIP displayed synergistic effects against A. craccivora (LC50, IMI-AB-FIP = 14.84-22.10 μM, LC50, IMI-AB-IMI = 210.52-266.63 μM, LC50, and FIP-AB-FIP = 36.25-51.04 μM), mainly resulting from a conceivable reason for simultaneous targeting on both GABARs and nAChRs. Furthermore, modulations of wiggler-swimming behaviors and cockroach neuron function were conducted and the results indirectly demonstrated the ligand-receptor interactions. In other words, real-time regulations of receptors and insect behaviors can be spatiotemporally achieved by our two-photon PCLs using light.

Titanium catalyzed [2σ + 2π] cycloaddition of bicyclo[1.1.0]-butanes with 1,3-dienes for efficient synthesis of stilbene bioisosteres

Natural stilbenes have shown significant potential in the prevention and treatment of diseases due to their diverse pharmacological activities. Here we present a mild and effective Ti-catalyzed intermolecular radical-relay [2σ + 2π] cycloaddition of bicyclo[1.1.0]-butanes and 1,3-dienes. This transformation enables the synthesis of bicyclo[2.1.1]hexane (BCH) scaffolds containing aryl vinyl groups with excellent regio- and trans-selectivity and broad functional group tolerance, thus offering rapid access to structurally diverse stilbene bioisosteres.

Triplet-Triplet Energy Transfer: A Simple Strategy for an Efficient Visible Light-Induced Photoclick Reaction

Photoclick reactions combine the advantages offered by light-driven processes and classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photo-crosslinking, and protein labeling. Despite these advances, the dependency of most of the photoclick reactions on UV light poses a severe obstacle for their general implementation, as this light can be absorbed by other molecules in the system resulting in their degradation or unwanted reactivity. However, the development of a simple and efficient system to achieve bathochromically shifted photoclick transformations remains challenging. Here, we introduce triplet-triplet energy transfer as a fast and selective way to enable visible light-induced photoclick reactions. Specifically, we show that 9,10-phenanthrenequinones (PQs) can efficiently react with electron-rich alkenes (ERAs) in the presence of a catalytic amount (as little as 5 mol %) of photosensitizers. The photocycloaddition reaction can be achieved under green (530 nm) or orange (590 nm) light irradiation, representing a bathochromic shift of over 100 nm as compared to the classical PQ-ERAs system. Furthermore, by combining appropriate reactants, we establish an orthogonal, blue and green light-induced photoclick reaction system in which the product distribution can be precisely controlled by the choice of the color of light.

Arylazopyrazoles for Conjugation by CuAAC Click Chemistry

Molecular photoswitches are increasingly being implemented in bioactive compounds and responsive materials. For this purpose, photoswitches must be coupled to a wide variety of substrates and scaffolds. We present a library of "clickable" arylazopyrazoles (AAPs), which can be conjugated by Cu-catalyzed alkyne azide cycloaddition (CuAAC). All synthesized AAP alkynes show good photostationary states (at least 88%) and long half-life times of the Z-isomer (18 to 108 h). The AAP azides decompose upon exposure to ultraviolet (UV) irradiation, but after CuAAC, all AAPs exhibit good photophysical properties.

Meta-Substituted Asymmetric Azobenzenes: Insights into Structure-Property Relationship

This article presents a comprehensive investigation into the functionalization of methoxyphenylazobenzene using electron-directing groups located at the meta position relative to the azo group. Spectroscopic analysis of meta-functionalized azobenzenes reveals that the incorporation of electron-withdrawing units significantly influences the absorption spectra of both E and Z isomers, while electron-donating functionalities lead to more subtle changes. The thermal relaxation process from Z to E result in almost twice as prolonged for electron-withdrawing functionalized azobenzenes compared to their electron-rich counterparts. Computational analysis contributes a theoretical understanding of the electronic structure and properties of meta-substituted azobenzenes. This combined approach, integrating experimental and computational techniques, yields significant insights into the structure-property relationship of meta-substituted asymmetrical phenolazobenzenes.

Light-Activatable Photocaged UNC2025 for Triggering TAM Kinase Inhibition in Bladder Cancer

Photopharmacology is an emerging field that utilizes photo-responsive molecules to enable control over the activity of a drug using light. The aim is to limit the therapeutic action of a drug at the level of diseased tissues and organs. Considering the well-known implications of protein kinases in cancer and the therapeutic issues associated with protein kinase inhibitors, the photopharmacology is seen as an innovative and alternative solution with great potential in oncology. In this context, we developed the first photocaged TAM kinase inhibitors based on UNC2025, a first-in-class small molecule kinase inhibitor. These prodrugs showed good stability in biologically relevant buffer and rapid photorelease of the photoremovable protecting group upon UV-light irradiation (<10 min.). These light-activatable prodrugs led to a 16-fold decrease to a complete loss of kinase inhibition, depending on the protein and the position at which the coumarin-type phototrigger was introduced. The most promising candidate was the N,O-dicaged compound, showing the superiority of having two photolabile protecting groups on UNC2025 for being entirely inactive on TAM kinases. Under UV-light irradiation, the N,O-dicaged compound recovered its inhibitory potency in enzymatic assays and displayed excellent antiproliferative activity in RT112 cell lines.

A Portrait of the Chromophore as a Young System-Quantum-Derived Force Field Unraveling Solvent Reorganization upon Optical Excitation of Cyclocurcumin Derivatives

The study of fast non-equilibrium solvent relaxation in organic chromophores is still challenging for molecular modeling and simulation approaches, and is often overlooked, even in the case of non-adiabatic dynamics simulations. Yet, especially in the case of photoswitches, the interaction with the environment can strongly modulate the photophysical outcomes. To unravel such a delicate interplay, in the present contribution we resorted to a mixed quantum-classical approach, based on quantum mechanically derived force fields. The main task is to rationalize the solvent reorganization pathways in chromophores derived from cyclocurcumin, which are suitable for light-activated chemotherapy to destabilize cellular lipid membranes. The accurate and reliable decryption delivered by the quantum-derived force fields points to important differences in the solvent's reorganization, in terms of both structure and time scale evolution.

Responsive Supramolecular Polymers for Diagnosis and Treatment

Stimuli-responsive supramolecular polymers are ordered nanosized materials that are held together by non-covalent interactions (hydrogen-bonding, metal-ligand coordination, π-stacking and, host-guest interactions) and can reversibly undergo self-assembly. Their non-covalent nature endows supramolecular polymers with the ability to respond to external stimuli (temperature, light, ultrasound, electric/magnetic field) or environmental changes (temperature, pH, redox potential, enzyme activity), making them attractive candidates for a variety of biomedical applications. To date, supramolecular research has largely evolved in the development of smart water-soluble self-assemblies with the aim of mimicking the biological function of natural supramolecular systems. Indeed, there is a wide variety of synthetic biomaterials formulated with responsiveness to control and trigger, or not to trigger, aqueous self-assembly. The design of responsive supramolecular polymers ranges from the use of hydrophobic cores (i.e., benzene-1,3,5-tricarboxamide) to the introduction of macrocyclic hosts (i.e., cyclodextrins). In this review, we summarize the most relevant advances achieved in the design of stimuli-responsive supramolecular systems used to control transport and release of both diagnosis agents and therapeutic drugs in order to prevent, diagnose, and treat human diseases.

Design of Functional Globular β-Sheet Miniproteins

The design of discrete β-sheet peptides is far less advanced than e. g. the design of α-helical peptides. The reputation of β-sheet peptides as being poorly soluble and aggregation-prone often hinders active design efforts. Here, we show that this reputation is unfounded. We demonstrate this by looking at the β-hairpin and WW domain. Their structure and folding have been extensively studied and they have long served as model systems to investigate protein folding and folding kinetics. The resulting fundamental understanding has led to the development of hyperstable β-sheet scaffolds that fold at temperatures of 100 °C or high concentrations of denaturants. These have been used to design functional miniproteins with protein or nucleic acid binding properties, in some cases with such success that medical applications are conceivable. The β-sheet scaffolds are not always completely rigid, but can be specifically designed to respond to changes in pH, redox potential or presence of metal ions. Some engineered β-sheet peptides also exhibit catalytic properties, although not comparable to those of natural proteins. Previous reviews have focused on the design of stably folded and non-aggregating β-sheet sequences. In our review, we now also address design strategies to obtain functional miniproteins from β-sheet folding motifs.

DELFI: a computer oracle for recommending density functionals for excited states calculations

Density functional theory (DFT) is the workhorse of computational quantum chemistry. One of its main limitations is that choosing the right functional is a non-trivial task left for human experts. The choice is particularly hard for excited state calculations when using its time-dependent formulation (TD-DFT). This is due to the approximations of the method, but also because the photophysical properties of a molecule are defined by a manifold of states that all need to be properly described. This includes not only the relative energy of the states, but also capturing the correct character, order, and intensity of the transitions. In this work, we developed a neural network to recommend functionals to be used on molecules for TD-DFT calculations, by simultaneously considering all these properties for a manifold of states. This was possible by developing a scoring system to define the accuracy of an excited state's calculation against a higher-accuracy reference. The scoring system is generalizable to any level of theory; we here applied it to evaluate the performance of common functionals of different rungs against a higher accuracy method on a large set of organic molecules. The results are collected in a database that we released and made open, providing four million data points to the community for future applications. The scoring system assigns a value between zero and one hundred to each functional for each molecule, transforming the complicated task of learning photophysical properties into a simpler regression task. We used the dataset to train a graph attention neural network to predict the scores for unseen molecules. We call this oracle DELFI (Data-driven EvaLuation of Functionals by Inference), which can be used to quickly screen and predict the ranking of functionals to calculate the optical properties of organic molecules. We validated DELFI in two in silico experiments: choosing a common functional for a series of spiropyran-merocyanine isomers and a unique functional to screen a large dataset of over 50 000 organic photovoltaic molecules, for which an extensive benchmark would be unfeasible. A corresponding web application allows DELFI to be easily run and the results to be analyzed, alleviating the hurdle of choosing the right functional for TD-DFT calculations.

Photoswitchable Temperature Nanosensors Based on the Chemical Kinetics of Photochromic Naphthopyran for Live Cell Imaging

Microscopic temperature imaging holds significant importance in various fields, particularly in the development of nanomaterials for photothermal therapy (PTT). In this study, we present an analytical method to probe cellular temperature based on chemical kinetics and additional luminescence quenching by photoswitchable naphthopyrans. Taking advantage of the rapid ring-closing reaction of naphthopyran, temperature sensing was realized with a linear relationship between the logarithmic decay time constant (ln τ) and the reciprocal temperature (T-1). To create luminescent temperature nanosensors, we harnessed the ability of ring-opened naphthopyran to quench the luminescence of a semiconducting polymer, resulting in a diverse array of probes. Structural modifications on the naphthopyran also provided a way to fine-tune the sensitivity and response window of the nanosensors. The method allowed cellular temperature imaging on a cost-effective fluorescence microscopic setup. As an application, the temperature increase induced by gold nanorods (AuNRs) in cell lysosomes was successfully monitored, laying the foundation for a new class of photoswitchable nanosensors with promising biological applications.

Well-Defined Oligo(azobenzene-graft-mannose): Photostimuli Supramolecular Self-Assembly and Immune Effect Regulation

The immune system can recognize and respond to pathogens of various shapes. Synthetic materials that can change their shape have the potential to be used in vaccines and immune regulation. The ability of supramolecular assemblies to undergo reversible transformations in response to environmental stimuli allows for dynamic changes in their shapes and functionalities. A meticulously designed oligo(azobenzene-graft-mannose) was synthesized using a stepwise iterative method and "click" chemistry. This involved integrating hydrophobic and photoresponsive azobenzene units with hydrophilic and bioactive mannose units. The resulting oligomer, with its precise structure, displayed versatile assembly morphologies and chiralities that were responsive to light. These varying assembly morphologies demonstrated distinct capabilities in terms of inhibiting the proliferation of cancer cells and stimulating the maturation of dendritic cells. These discoveries contribute to the theoretical comprehension and advancement of photoswitchable bioactive materials.

Synthetic Biology Meets Ca2+ Release-Activated Ca2+ Channel-Dependent Immunomodulation

Many essential biological processes are triggered by the proximity of molecules. Meanwhile, diverse approaches in synthetic biology, such as new biological parts or engineered cells, have opened up avenues to precisely control the proximity of molecules and eventually downstream signaling processes. This also applies to a main Ca2+ entry pathway into the cell, the so-called Ca2+ release-activated Ca2+ (CRAC) channel. CRAC channels are among other channels are essential in the immune response and are activated by receptor-ligand binding at the cell membrane. The latter initiates a signaling cascade within the cell, which finally triggers the coupling of the two key molecular components of the CRAC channel, namely the stromal interaction molecule, STIM, in the ER membrane and the plasma membrane Ca2+ ion channel, Orai. Ca2+ entry, established via STIM/Orai coupling, is essential for various immune cell functions, including cytokine release, proliferation, and cytotoxicity. In this review, we summarize the tools of synthetic biology that have been used so far to achieve precise control over the CRAC channel pathway and thus over downstream signaling events related to the immune response.

Photochromic Nucleosides and Oligonucleotides

Photochromism is a reversible phenomenon wherein a material undergoes a change in color upon exposure to light. In organic photochromes, this effect often results from light-induced isomerization reactions, leading to alterations in either the spatial orientation or electronic properties of the photochrome. The incorporation of photochromic moieties into biomolecules, such as proteins or nucleic acids, has become a prevalent approach to render these biomolecules responsive to light stimuli. Utilizing light as a trigger for the manipulation of biomolecular structure and function offers numerous advantages compared to other stimuli, such as chemical or electrical treatments, due to its non-invasive nature. Consequently, light proves particularly advantageous in cellular and tissue applications. In this review, we emphasize recent advancements in the field of photochromic nucleosides and oligonucleotides. We provide an overview of the design principles of different classes of photochromes, synthetic strategies, critical analytical challenges, as well as structure-property relationships. The applications of photochromic nucleic acid derivatives encompass diverse domains, ranging from the precise photoregulation of gene expression to the controlled modulation of the three-dimensional structures of oligonucleotides and the development of DNA-based fluorescence modulators. Moreover, we present a future perspective on potential modifications and applications.

Bidirectional Regulation of Intracellular Enzyme Activity Using Light-Driven Nano-Inhibitors

Photochemical regulation provides precise control over enzyme activities with high spatiotemporal resolution. A promising approach involves anchoring "photoswitches" at enzyme active sites to modulate substrate recognition. However, current methods often require genetic mutations and irreversible enzyme modifications for the site-specific anchoring of "photoswitches", potentially compromising the enzyme activities. Herein, we present a pioneering reversible nano-inhibitor based on molecular imprinting technique for bidirectional regulation of intracellular enzyme activity. The nano-inhibitor employs a molecularly imprinted polymer nanoparticle as its body and azobenzene-modified inhibitors ("photoswitches") as the arms. By using a target enzyme as the molecular template, the nano-inhibitor acquires oriented binding sites on its surface, resulting in a high affinity for the target enzyme and non-covalently firm anchoring of the azobenzene-modified inhibitor to the enzyme active site. Harnessing the reversible isomerization of azobenzene units upon exposure to ultraviolet and visible light, the nano-inhibitor achieves bidirectional enzyme activity regulation by precisely docking and undocking inhibitor at the active site. Notably, this innovative approach enables the facile in situ regulation of intracellular endogenous enzymes, such as carbonic anhydrase. Our results represent a practical and versatile tool for precise enzyme activity regulation in complex intracellular environments.

Towards Optical Information Recording: A Robust Visible-Light-Driven Molecular Photoswitch with the Ring-Closure Reaction Yield Exceeding 96.3

Diarylethene molecular photoswitches hold great fascination as optical information materials due to their unique bistability and exceptional reversible photoswitching properties. Conventional diarylethenes, however, rely on UV light for ring-closure reactions, typically with modest yields. For practical application, diarylethenes driven by visible lights are preferred but achieving high ring-closure reaction yield remains a significant challenge. Herein, we synthesized a novel all-visible-light-driven photoswitch, TPAP-DTE, by facilely endcapping the dithienylethene (DTE) core with triphenylamine phenyl (TPAP) groups. Owing to the electron-donating conjugation effect of TPAP, the open-form TPAP-DTE responds strongly to short-wavelength visible lights with considerable photocyclization quantum yields and molar absorption coefficient. Upon 405 nm visible-light irradiation, TPAP-DTE achieves a ring-closure reaction yield exceeding 96.3 % (confirmed by both nuclear magnetic resonance spectroscopy and high-performance liquid chromatography). Its ring-opening reaction yield is 100 % upon irradiation with long-wavelength visible light. TPAP-DTE could be regarded as a bidirectional "quasi"-quantitative conversion molecular switch. Furthermore, TPAP-DTE exhibits robust fatigue resistance over 100 full photoswitching cycles and great anti-aging property under 85 °C and 85 % humidity for at least 1000 h. Consequently, its rewritable QR-code, multilevel data storage, and anti-counterfeiting/encryption applications are successfully demonstrated exclusively using visible lights, positioning TPAP-DTE as a highly promising medium for information recording.

Visible Light Control over the Cytolytic Activity of a Toxic Pore-Forming Protein

Enabling control over the bioactivity of proteins with light, along with the principles of photopharmacology, has the potential to generate safe and targeted medical treatments. Installing light sensitivity in a protein can be achieved through its covalent modification with a molecular photoswitch. The general challenge in this approach is the need for the use of low energy visible light for the regulation of bioactivity. In this study, we report visible light control over the cytolytic activity of a protein. A water-soluble visible-light-operated tetra-ortho-fluoro-azobenzene photoswitch was synthesized by utilizing the nucleophilic aromatic substitution reaction for installing a solubilizing sulfonate group onto the electron-poor photoswitch structure. The azobenzene was attached to two cysteine mutants of the pore-forming protein fragaceatoxin C (FraC), and their respective activities were evaluated on red blood cells. For both mutants, the green-light-irradiated sample, containing predominantly the cis-azobenzene isomer, was more active compared to the blue-light-irradiated sample. Ultimately, the same modulation of the cytolytic activity pattern was observed toward a hypopharyngeal squamous cell carcinoma. These results constitute the first case of using low energy visible light to control the biological activity of a toxic protein.

What Happens to a Pyrrole Hemithioindigo Photoswitch Trapped in a Fluorescent Protein?

Artificial molecular photoswitches that can be reversibly controlled into different configurations by external light stimulation have broad application prospects in various fields, such as materials and chemical biology. Among them, the pyrrole hemithioindigo (PHT) photoswitch has a geometric structure similar to that of the fluorescent protein chromophore. What happens when the chromophore is replaced by PHT, and does it achieve similar functions to the original one? To answer these questions, we carried out ONIOM(QM/MM) and classical molecular dynamics studies on the photoisomerization mechanism and spectroscopic properties of PHT in the fluorescent protein. The results showed that in the protein environment, the fate of excited PHT is governed by the competition between fluorescence emission and hula-twist isomerization. Due to the strong steric hindrance effects caused by the interlacing residues in the protein that restrict the PHT conformation transformation, the cis-to-trans isomerization process of PHT needs to overcome a barrier of at least 4.9 kcal/mol; thus, fluorescence emission is more dominant in competition. It is also found that the intermolecular interaction between LYS67 and the carbonyl oxygen of PHT has a significant effect on the fluorescence emission. These results revealed the photochemical reaction mechanism of a light-driven molecular switch in the fluorescent protein and provided further theoretical support for the field of chemical biology.

A Complete Unveiling of the Mechanism and Chirality in Photoisomerization of Arylazopyrazole 3pzH: Combined Electronic Structure Calculations and AIMS Dynamic Simulations

The arylazopyrazole 3pzH as a novel photoswitch exhibits quantitative switching and high thermal stability. In this work, combined electronic structure calculations and ab initio multiple spawning (AIMS) dynamic simulations were performed to systemically investigate the cis ↔ trans photoisomerization mechanism and the chiral preference after photoexcitation of 3pzH to the first excited singlet state (S1). Unlike most of the azoheteroarene photoswitches reported previously, many twisted and T-shaped cis isomers were found to be stable for 3pzH in the S0 state, owing to the moderate interaction between the hydrogen atom and π electrons of the aromatic ring. Two twisted cis isomers with different chirality ((M)-Z1 and (P)-Z1), the most stable T-shaped cis isomer ((T)-Z2), and the most stable planar trans isomer (E2) were selected as the initial structures to carry out the AIMS nonadiabatic dynamic simulations. Following excitation to the S1 state, all of the cis isomers decayed to conical intersection (CI) regions via the same bicycle pedal mechanism, while the evolution of the trans isomers to their CI regions was achieved via rotation around the N═N bond. More importantly, chiral preferences were found for the twisted cis isomers in the S1 state through the AIMS dynamic simulations due to the steric effect and static electronic repulsion. Notably, chirality was also observed in S1 isomerization starting from the planar E2 isomer because of the dynamic effect. After the nonadiabatic transition to the S0 state, the bicycle pedal mechanism was found to play a crucial role in cis ↔ trans photoisomerization. The simulated photoisomerization productivities were generally consistent with past experimental observations. Our calculations not only uncover the underlying reason for the excellent photoswitching properties of 3pzH but also enrich the knowledge of photoisomerization for azoheteroarene photoswitches, which will surely benefit their rational design.

Activation of Anthraquinone's Electrophilicity by Light for a Dynamic C-O Bond

Coupling of photoswitching with dynamic covalent chemistry enables control of the formation and cleavage of covalent bonds by light irradiation. peri-Aryloxyanthraquinones feature an exclusive ability to switch electrophilicity by interconversion between para- and ana-quinone isomers, which was used for the first time for the implementation of a dynamic C-O bond. Photogenerated ana-isomers undergo a concerted oxa-Michael addition of phenols to give hitherto unknown 4-hydroxy-10,10-diaryloxyanthracen-9-ones. These species were found to be in equilibrium with the corresponding ana-quinones, thus forming a dynamic covalent system of a new type. Withdrawal of the colored ana-quinones from the equilibria by visible light irradiation resulted in two para-quinones with "locked" aryloxy groups.

Photocontrol of the β-Hairpin Polypeptide Structure through an Optimized Azobenzene-Based Amino Acid Analogue

A family of neurodegenerative diseases, including Huntington's disease (HD) and spinocerebellar ataxias, are associated with an abnormal polyglutamine (polyQ) expansion in mutant proteins that become prone to form amyloid-like aggregates. Prior studies have suggested a key role for β-hairpin formation as a driver of nucleation and aggregation, but direct experimental studies have been challenging. Toward such research, we set out to enable spatiotemporal control over β-hairpin formation by the introduction of a photosensitive β-turn mimic in the polypeptide backbone, consisting of a newly designed azobenzene derivative. The reported derivative overcomes the limitations of prior approaches associated with poor photochemical properties and imperfect structural compatibility with the desired β-turn structure. A new azobenzene-based β-turn mimic was designed, synthesized, and found to display improved photochemical properties, both prior and after incorporation into the backbone of a polyQ polypeptide. The two isomers of the azobenzene-polyQ peptide showed different aggregate structures of the polyQ peptide fibrils, as demonstrated by electron microscopy and solid-state NMR (ssNMR). Notably, only peptides in which the β-turn structure was stabilized (azobenzene in the cis configuration) closely reproduced the spectral fingerprints of toxic, β-hairpin-containing fibrils formed by mutant huntingtin protein fragments implicated in HD. These approaches and findings will enable better deciphering of the roles of β-hairpin structures in protein aggregation processes in HD and other amyloid-related neurodegenerative diseases.

Optical modulation of cell nucleus penetration and singlet oxygen release of a switchable platinum complex

The activation of anticancer molecules with visible light constitutes an elegant strategy to target tumors and to improve the selectivity of treatments. In this context, we report here a visible-light activatable bis-platinum complex (DHP-Pt2) incorporating an organic photo-switchable ligand based on the dimethyldihydropyrene moiety. Illumination of this metal complex with red light (660 nm) under air readily produces the corresponding endoperoxide form (CPDO2-Pt2). These two metal complexes exhibit different DNA binding properties and, more importantly, we show that only the photogenerated CPDO2-Pt2 is able to penetrate into cancer cell nuclei, where it is then capable of releasing cytotoxic singlet oxygen. This study represents the first proof-of-concept showing that dimethyldihydropyrene derivatives can be used to transport and deliver singlet oxygen into cancer cell nuclei upon visible-light activation.

Internal Heavy-Atom Effect on Visible-Light-Induced Cyclization Reaction in Diarylethene-Perylenebisimide Dyads

All-visible-light switchable diarylethene-perylenebisimide (DAE-PBI) dyads having bromine heavy atoms in the molecule were designed and synthesized. Very recently, we found a unique visible-light-induced cyclization reaction in a DAE-PBI dyad. The dyad exhibited reversible cyclization and cycloreversion reactions upon alternate irradiation with green (500-550 nm) and red (>600 nm) light. From the experimental results, it was suggested that the triplet state of DAE unit was generated via multiplicity conversion based on intramolecular energy transfer from the singlet excited state of PBI unit and that the cyclization reaction of DAE unit proceeded from the triplet state. In addition, it was revealed that the reactivity remarkably increased in a solvent containing heavy atoms such as carbon tetrachloride and iodoethane (i.e., external heavy-atom effect). Based on such results, in this study, we attempted to design and synthesize novel DAE-PBI dyads introducing bromine heavy atoms at different positions in the molecule. The synthesized dyads exhibited higher quantum yields of photocyclization reaction under visible-light irradiation even in a heavy-atom-free solvent compared to the previous dyad having no heavy atoms. The magnitude of enhancement well correlated to the contribution ratio of atomic orbital of bromine to the molecular orbital in LUMOs. These results indicated that the internal heavy atom effectively contributed to the visible-light-induced cyclization reaction in DAE-PBI dyads. Such an internal heavy-atom effect will pave the way for new molecular design to develop all-visible-light-activatable molecular switches.

Photoluminescence switching in quantum dots connected with fluorinated and hydrogenated photochromic molecules

We investigate switching of photoluminescence (PL) from PbS quantum dots (QDs) crosslinked with two different types of photochromic diarylethene molecules, 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (1H) and 4,4'-(1-perfluorocyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (2F). Our results show that the QDs crosslinked with the hydrogenated molecule (1H) exhibit a greater amount of switching in photoluminescence intensity compared to QDs crosslinked with the fluorinated molecule (2F). With a combination of differential pulse voltammetry and density functional theory, we attribute the different amount of PL switching to the different energy levels between 1H and 2F molecules which result in different potential barrier heights across adjacent QDs. Our findings provide a deeper understanding of how the energy levels of bridge molecules influence charge tunneling and PL switching performance in QD systems and offer deeper insights for the future design and development of QD based photo-switches.

Photo-Controlled Gating of Selective Bacterial Membrane Interaction and Enhanced Antibacterial Activity for Wound Healing

Reversible biointerfaces are essential for on-demand molecular recognition to regulate stimuli-responsive bioactivity such as specific interactions with cell membranes. The reversibility on a single platform allows the smart material to kill pathogens or attach/detach cells. Herein, we introduce a 2D-MoS2 functionalized with cationic azobenzene that interacts selectively with either Gram-positive or Gram-negative bacteria in a light-gated fashion. The trans conformation (trans-Azo-MoS2 ) selectively kills Gram-negative bacteria, whereas the cis form (cis-Azo-MoS2 ), under UV light, exhibits antibacterial activity against Gram-positive strains. The mechanistic investigation indicates that the cis-Azo-MoS2 exhibits higher affinity towards the membrane of Gram-positive bacteria compared to trans-Azo-MoS2 . In case of Gram-negative bacteria, trans-Azo-MoS2 internalizes more efficiently than cis-Azo-MoS2 and generates intracellular ROS to kill the bacteria. While the trans-Azo-MoS2 exhibits strong electrostatic interactions and internalizes faster into Gram-negative bacterial cells, cis-Azo-MoS2 primarily interacts with Gram-positive bacteria through hydrophobic and H-bonding interactions. The difference in molecular mechanism leads to photo-controlled Gram-selectivity and enhanced antibacterial activity. We found strain-specific and high bactericidal activity (minimal bactericidal concentration, 0.65 μg/ml) with low cytotoxicity, which we extended to wound healing applications. This methodology provides a single platform for efficiently switching between conformers to reversibly control the strain-selective bactericidal activity regulated by light.

Photochemically Activated 3D Printing Inks: Current Status, Challenges, and Opportunities

3D printing with light is enabled by the photochemistry underpinning it. Without fine control over the ability to photochemically gate covalent bond formation by the light at a certain wavelength and intensity, advanced photoresists with functions spanning from on-demand degradability, adaptability, rapid printing speeds, and tailored functionality are impossible to design. Herein, recent advances in photoresist design for light-driven 3D printing applications are critically assessed, and an outlook of the outstanding challenges and opportunities is provided. This is achieved by classing the discussed photoresists in chemistries that function photoinitiator-free and those that require a photoinitiator to proceed. Such a taxonomy is based on the efficiency with which photons are able to generate covalent bonds, with each concept featuring distinct advantages and drawbacks.

Enzyme Fragment Complementation Driven by Nucleic Acid Hybridization

A modified protein fragment complementation assay has been designed and validated as a gain-of-signal biosensor for nucleic acid:nucleic acid interactions. The assay uses fragments of NanoBiT, the split luciferase reporter enzyme, that are esterified at their C-termini to steramers, sterol-modified oligodeoxynucleotides. The Drosophila hedgehog autoprocessing domain, DHhC, served as a self-cleaving catalyst for these bioconjugations. In the presence of ssDNA or RNA with segments complementary to the steramers and adjacent to one another, the two NanoBiT fragments productively associate, reconstituting NanoBiT enzyme activity. NanoBiT luminescence in samples containing nM ssDNA or RNA template exceeded background by 30-fold and as high as 120-fold depending on assay conditions. A unique feature of this detection system is the absence of a self-labeling domain in the NanoBiT bioconjugates. Eliminating that extraneous bulk broadens the detection range from short oligos to full-length mRNA.

Visible light-induced switching of soft matter materials properties based on thioindigo photoswitches

Thioindigos are visible light responsive photoswitches with excellent spatial control over the conformational change between their trans- and cis- isomers. However, they possess limited solubility in all conventional organic solvents and polymers, hindering their application in soft matter materials. Herein, we introduce a strategy for the covalent insertion of thioindigo units into polymer main chains, enabling thioindigos to function within crosslinked polymeric hydrogels. We overcome their solubility issue by developing a thioindigo bismethacrylate linker able to undergo radical initiated thiol-ene reaction for step-growth polymerization, generating indigo-containing polymers. The optimal wavelength for the reversible trans-/cis- isomerisation of thioindigo was elucidated by constructing a detailed photochemical action plot of their switching efficiencies at a wide range of monochromatic wavelengths. Critically, indigo-containing polymers display significant photoswitching of the materials' optical and physical properties in organic solvents and water. Furthermore, the photoswitching of thioindigo within crosslinked structures enables visible light induced modulation of the hydrogel stiffness. Both the thioindigo-containing hydrogels and photoswitching processes are non-toxic to cells, thus offering opportunities for advanced applications in soft matter materials and biology-related research.

Development of Photoswitchable Tethered Ligands that Target the μ-Opioid Receptor

Converting known ligands into photoswitchable derivatives offers the opportunity to modulate compound structure with light and hence, biological activity. In doing so, these probes provide unique control when evaluating G-protein-coupled receptor (GPCR) mechanism and function. Further conversion of such compounds into covalent probes, known as photoswitchable tethered ligands (PTLs), offers additional advantages. These include localization of the PTLs to the receptor binding pocket. Covalent localization increases local ligand concentration, improves site selectivity and may improve the biological differences between the respective isomers. This work describes chemical, photophysical and biochemical characterizations of a variety of PTLs designed to target the μ-opioid receptor (μOR). These PTLs were modeled on fentanyl, with the lead disulfide-containing agonist found to covalently interact with a cysteine-enriched mutant of this medically-relevant receptor.

Photoresponsive peptide materials: Spatiotemporal control of self-assembly and biological functions

Peptides work as both functional molecules to modulate various biological phenomena and self-assembling artificial materials. The introduction of photoresponsive units to peptides allows the spatiotemporal remote control of their structure and function upon light irradiation. This article overviews the photoresponsive peptide design, interaction with biomolecules, and applications in self-assembling materials over the last 30 years. Peptides modified with photochromic (photoisomerizable) molecules, such as azobenzene and spiropyran, reversibly photo-controlled the binding to biomolecules and nanostructure formation through self-assembly. Photocleavable molecular units irreversibly control the functions of peptides through cleavage of the main chain and deprotection by light. Photocrosslinking between peptides or between peptides and other biomolecules enhances the structural stability of peptide assemblies and complexes. These photoresponsive peptides spatiotemporally controlled the formation and dissociation of peptide assemblies, gene expressions, protein-drug interactions, protein-protein interactions, liposome deformation and motility, cytoskeleton structure and stability, and cell functions by appropriate light irradiation. These molecular systems can be applied to photo-control biological functions, molecular robots, artificial cells, and next-generation smart drug delivery materials.

PSW-Designer: An Open-Source Computational Platform for the Design and Virtual Screening of Photopharmacological Ligands

Photoswitchable (PSW) molecules offer an attractive opportunity for the optical control of biological processes. However, the successful design of such compounds remains a challenging multioptimization endeavor, resulting in several biological target classes still relatively poorly explored by photoswitchable ligands, as is the case for G protein-coupled receptors (GPCRs). Here, we present the PSW-Designer, a fully open-source computational platform, implemented in the KNIME Analytics Platform, to design and virtually screen novel photoswitchable ligands for photopharmacological applications based on privileged scaffolds. We demonstrate the applicability of the PSW-Designer to GPCRs and assess its predictive capabilities via two retrospective case studies. Furthermore, by leveraging bioactivity information on known ligands, typical and atypical strategies for photoswitchable group incorporation, and the increasingly structural information available for biological targets, the PSW-Design will facilitate the design of novel photoswitchable molecules with improved photopharmacological properties and increased binding affinity shifts upon illumination for GPCRs and many other protein targets.

Photoswitchable Probes of Oxytocin and Vasopressin

Oxytocin (OT) and vasopressin (VP) are related neuropeptides that regulate many biological processes. In humans, OT and VP act via four G protein-coupled receptors, OTR, V1aR, V1bR, and V2R (VPRs), which are associated with several disorders. To investigate the therapeutic potential of these receptors, particularly in the receptor-dense areas of the brain, molecular probes with a high temporal and spatial resolution are required. Such a spatiotemporal resolution can be achieved by incorporating photochromic moieties into OT and VP. Here, we report the design, synthesis, and (photo)pharmacological characterization of 12 OT- and VP-derived photoprobes using different modification strategies. Despite OT's and VP's sensitivity toward structural changes, we identified two photoprobes with good potency and photoswitch window for investigating the OTR and V1bR. These photoprobes should be of high value for producing cutting-edge photocontrollable peptide probes for the study of dynamic and kinetic receptor activation processes in specific regions of the brain.

Molecular design and synthesis of methoxy-substitued spiropyrans with photomodulated NIR-fluorescence

This study focuses on the molecular design and synthesis of salt spiropyrans with near-IR fluorescence. The structure of the obtained compounds was confirmed by NMR, IR and mass spectroscopy. In the course of studying the spectral and photoluminescent characteristics, it was possible to reveal the effect of some substituents in various positions on the properties of spiropyran dyes. Due to the structural similarity of one of the isomers to cyanine dyes, the obtained compounds are of interest as potential fluorescent probes for bioimagimg, in particular, for DNA studies. To reveal their ability of binding to DNA molecules molecular docking was carried out. Toxic effects of compounds demonstrating NIR fluorescence were studied on biofilms, as well as using bacterial lux-biosensors.

Light-Induced Dyotropic Rearrangement of Diarylethenes: Scope, Mechanism, and Prospects

Irreversible two-photon photorearrangement of 1,2-diarylethenes is a unique process providing access to complex 2a1 ,5a-dihydro-5,6-dithiaacenaphthylene (DDA) heterocyclic core. This reaction was serendipitously discovered during studies on photoswitchable diarylethenes and was initially considered as a highly undesired process. However, in recent years, it has been recognized as an efficient photochemical reaction, interesting by itself and as a promising synthetic method for the synthesis of challenging molecules. Herein, we discuss the state-of-the-art in studies on this notable process.

Light-driven modulation of electrical conductance with photochromic switches: bridging photochemistry with optoelectronics

Photochromic conducting molecules have emerged because of their unique capacity to modulate electrical conductivity upon exposure to light, toggling between high and low conductive states. This unique amalgamation has unlocked novel avenues for the application of these materials across diverse areas in optoelectronics and smart materials. The fundamental mechanism underpinning this phenomenon is based on the light-driven isomerization of conjugated π-systems which influences the extent of conjugation. The photoisomerization process discussed here involves photochromic switches such as azobenzenes, diarylethenes, spiropyrans, dimethyldihydropyrenes, and norbornadiene. The change in the degree of conjugation alters the charge transport in both single molecules and bulk states in solid samples or solutions. This article discusses a number of recent examples of photochromic conducting systems and the challenges and potentials of the field.

Photocaging of Carboxylic Function Bearing Biomolecules by New Thiazole Derived Fluorophore

The design and synthesis of a new fluorophore containing an arylidene thiazole scaffold resulted in a compound with good photophysical characteristics. Furthermore, the thiazole C5-methyl group was easily modified into specific functional groups (CH2 Br and CH2 OH) for the formation of a series of photocourier molecules containing model compounds (benzoic acids), as well as prodrugs, including salicylic acid, caffeic acid, and chlorambucil via a "benzyl" linker. Spectral characteristics (1 H, 13 C NMR, and high-resolution mass spectra) corresponded to the proposed structures. The photocourier molecules demonstrated absorption with high values of coefficient of molar extinction, exhibited contrasting green emission, and showed good dark stability. The mechanism of the photorelease was investigated through spectral analysis, HPLC-HRMS, and supported by TD-DFT calculations. The photoheterolysis and elimination of carboxylic acids were proved to occur in the excited state, yielding a carbocation as an intermediate moiety. The fluorophore structure provided stability to the carbocation through the delocalization of the positive charge via resonance structures. Viability assessment of Vero cells using the MTT-test confirmed the weak cytotoxicity of prodrugs without irradiation and it increase upon UV-light.

Singlet and Triplet Pathways Determine the Thermal Z/E Isomerization of an Arylazopyrazole-Based Photoswitch

Understanding the thermal isomerization mechanism of azobenzene derivatives is essential to designing photoswitches with tunable half-lives. Herein, we employ quantum chemical calculations, nonadiabatic transition state theory, and photosensitized experiments to unravel the thermal Z/E isomerization of a heteroaromatic azoswitch, the phenylazo-1,3,5-trimethylpyrazole. In contrast to the parent azobenzene, we predict two pathways to be operative at room temperature. One is a conventional ground-state reaction occurring via inversion of the aryl group, and the other is a nonadiabatic process involving intersystem crossing to the lowest-lying triplet state and back to the ground state, accompanied by a torsional motion around the azo bond. Our results illustrate that the fastest reaction rate is not controlled by the mechanism involving the lowest activation energy, but the size of the spin-orbit couplings at the crossing between the singlet and the triplet potential energy surfaces is also determinant. It is therefore mandatory to consider all of the multiple reaction pathways in azoswitches in order to predict experimental half-lives.

The Power of Action Plots: Unveiling Reaction Selectivity of Light-Stabilized Dynamic Covalent Chemistry

Exploiting the optimum wavelength of reactivity for efficient photochemical reactions has been well-established based on the development of photochemical action plots. We herein demonstrate the power of such action plots by a remarkable example of the wavelength-resolved photochemistry of two triazolinedione (TAD) substrates, i.e., aliphatic and aromatic substituted, that exhibit near identical absorption spectra yet possess vastly disparate photoreactivity. We present our findings in carefully recorded action plots, from which reaction selectivity is identified. The profound difference in photoreactivity is exploited by designing a 'hybrid' bisfunctional TAD molecule, enabling the formation of a dual-gated reaction manifold that demonstrates the exceptional and site-selective (photo)chemical behavior of both TAD substrates within a single small molecule.

On the Simulation of Thermal Isomerization of Molecular Photoswitches in Biological Systems

Molecular photoswitches offer precise, reversible photocontrol over biomolecular functions and are promising light-regulated drug candidates with minimal side effects. Quantifying thermal isomerization rates of photoswitches in their target biomolecules is essential for fine-tuning their light-controlled drug activity. However, the effects of protein binding on isomerization kinetics remain poorly understood, and simulations are crucial for filling this gap. Challenges in the simulation include describing multireference electronic structures near transition states, disentangling competing reaction pathways, and sampling protein-ligand interactions. To overcome these challenges, we used multiscale simulations to characterize the thermal isomerization of photostatins (PSTs), which are light-regulated microtubule inhibitors for potential cancer phototherapy. We employed a new ab initio multireference electronic structure method in a quantum mechanics/molecular mechanics setting and combined it with enhanced sampling techniques to characterize the cis to trans free-energy profiles of three PSTs in a vacuum, aqueous solution, and tubulin dimer. The significant advantage of our novel approach is the efficient treatment of the multireference character in PSTs' electronic wavefunction throughout the conformational sampling of protein-ligand interactions along their isomerization pathways. We also benchmarked our calculations using high-level ab initio multireference electronic structure methods and explored the competing isomerization pathways. Notably, calculations in a vacuum and implicit solvent models cannot predict the order of the PSTs' thermal half-lives in the aqueous solution observed in the experiment. Only by explicitly treating the solvent molecules can the correct order of isomerization kinetics be reproduced. Protein binding perturbs free-energy barriers due to hydrogen bonding between PSTs and nearby polar residues. Our work generates comprehensive, high-quality benchmark data and offers guidance for selecting computational methods to study the thermal isomerization of photoswitches. Ab initio multireference free-energy calculations in explicit molecular environments are crucial for predicting the effects of substituents on the thermal half-lives of photoswitches in biological systems.

2,3-Diarylmaleate salts as a versatile class of diarylethenes with a full spectrum of photoactivity in water

There is incessant interest in the transfer of common chemical processes from organic solvents to water, which is vital for the development of bioinspired and green chemical technologies. Diarylethenes feature a rich photochemistry, including both irreversible and reversible reactions that are in demand in organic synthesis, materials chemistry, and photopharmacology. Herein, we introduce the first versatile class of diarylethenes, namely, potassium 2,3-diarylmaleates (DAMs), that show excellent solubility in water. DAMs obtained from highly available precursors feature a full spectrum of photoactivity in water and undergo irreversible reactions (oxidative cyclization or rearrangement) or reversible photocyclization (switching), depending on their structure. This finding paves a way towards wider application of diarylethenes in photopharmacology and bioinspired technologies that require aqueous media for photochemical reactions.

Application of intelligent responsive DNA self-assembling nanomaterials in drug delivery

Smart nanomaterials are nano-scaled materials that respond in a controllable and reversible way to external physical or chemical stimuli. DNA self-assembly is an effective way to construct smart nanomaterials with precise structure, diverse functions and wide applications. Among them, static structures such as DNA polyhedron, DNA nanocages and DNA hydrogels, as well as dynamic reactions such as catalytic hairpin reaction, hybridization chain reaction and rolling circle amplification, can serve as the basis for building smart nanomaterials. Due to the advantages of DNA, such as good biocompatibility, simple synthesis, rational design, and good stability, these materials have attracted increasing attention in the fields of pharmaceuticals and biology. Based on their specific response design, DNA self-assembled smart nanomaterials can deliver a variety of drugs, including small molecules, nucleic acids, proteins and other drugs; and they play important roles in enhancing cellular uptake, resisting enzymatic degradation, controlling drug release, and so on. This review focuses on different assembly methods of DNA self-assembled smart nanomaterials, therapeutic strategies based on various intelligent responses, and their applications in drug delivery. Finally, the opportunities and challenges of smart nanomaterials based on DNA self-assembly are summarized.

Isomerization of bioactive acylhydrazones triggered by light or thiols

The acylhydrazone unit is well represented in screening databases used to find ligands for biological targets, and numerous bioactive acylhydrazones have been reported. However, potential E/Z isomerization of the C=N bond in these compounds is rarely examined when bioactivity is assayed. Here we analysed two ortho-hydroxylated acylhydrazones discovered in a virtual drug screen for modulators of N-methyl-D-aspartate receptors and other bioactive hydroxylated acylhydrazones with structurally defined targets reported in the Protein Data Bank. We found that ionized forms of these compounds, which are populated under laboratory conditions, photoisomerize readily and the isomeric forms have markedly different bioactivity. Furthermore, we show that glutathione, a tripeptide involved with cellular redox balance, catalyses dynamic E⇄Z isomerization of acylhydrazones. The ratio of E to Z isomers in cells is determined by the relative stabilities of the isomers regardless of which isomer was applied. We conclude that E/Z isomerization may be a common feature of the bioactivity observed with acylhydrazones and should be routinely analysed.

How do donor and acceptor substituents change the photophysical and photochemical behavior of dithienylethenes? The search for a water-soluble visible-light photoswitch

Dithienylethenes are a type of diarylethene and they constitute one of the most widely studied classes of photoswitch, yet there have been no systematic studies of how electron-donor or -acceptor substituents affect their properties. Here we report eight dithienylethenes bearing push-push, pull-pull and push-pull substitution patterns with different lengths of conjugation in the backbone and investigate their photophysical and photochemical properties. Donor-acceptor interactions in the closed forms of push-pull dithienylethenes shift their absorption spectra into the near-infrared region (λmax ≈ 800 nm). The push-pull systems also exhibit low quantum yields for photochemical electrocyclization, and computational studies indicate that this can be attributed to stabilization of the parallel, rather than anti-parallel, conformations. The pull-pull systems have the highest quantum yields for switching in both directions, ring-closure and ring-opening. The chloride salt of a pull-pull DTE, with alkynes on both arms, is the first water-soluble dithienylethene that can achieve >95% photostationary state distribution in both directions with visible light. It has excellent fatigue resistance: in aqueous solution on irradiation at 365 nm, the photochemical quantum yields for switching and decomposition are 0.15 and 2.6 × 10-5 respectively, i.e. decomposition is more than 5000 times slower than photoswitching. These properties make it a promising candidate for biological applications such as super-resolution microscopy and photopharmacology.

Gonçalves DP, Zhu C, Tilki T, Prévôt ME, Hegmann T. Controlling the Structure and Morphology of Organic Nanofilaments Using External Stimuli

In our continuing pursuit to generate, understand, and control the morphology of organic nanofilaments formed by molecules with a bent molecular shape, we here report on two bent-core molecules specifically designed to permit a phase or morphology change upon exposure to an applied electric field or irradiation with UV light. To trigger a response to an applied electric field, conformationally rigid chiral (S,S)-2,3-difluorooctyloxy side chains were introduced, and to cause a response to UV light, an azobenzene core was incorporated into one of the arms of the rigid bent core. The phase behavior as well as structure and morphology of the formed phases and nanofilaments were analyzed using differential scanning calorimetry, cross-polarized optical microscopy, circular dichroism spectropolarimetry, scanning and transmission electron microscopy, UV-vis spectrophotometry, as well as X-ray diffraction experiments. Both bent-core molecules were characterized by the coexistence of two nanoscale morphologies, specifically helical nanofilaments (HNFs) and layered nanocylinders, prior to exposure to an external stimulus and independent of the cooling rate from the isotropic liquid. The application of an electric field triggers the disappearance of crystalline nanofilaments and instead leads to the formation of a tilted smectic liquid crystal phase for the material featuring chiral difluorinated side chains, whereas irradiation with UV light results in the disappearance of the nanocylinders and the sole formation of HNFs for the azobenzene-containing material. Combined results of this experimental study reveal that in addition to controlling the rate of cooling, applied electric fields and UV irradiation can be used to expand the toolkit for structural and morphological control of suitably designed bent-core molecule-based structures at the nanoscale.

Light-Based Anti-Biofilm and Antibacterial Strategies

Biofilm formation and antimicrobial resistance pose significant challenges not only in clinical settings (i.e., implant-associated infections, endocarditis, and urinary tract infections) but also in industrial settings and in the environment, where the spreading of antibiotic-resistant bacteria is on the rise. Indeed, developing effective strategies to prevent biofilm formation and treat infections will be one of the major global challenges in the next few years. As traditional pharmacological treatments are becoming inadequate to curb this problem, a constant commitment to the exploration of novel therapeutic strategies is necessary. Light-triggered therapies have emerged as promising alternatives to traditional approaches due to their non-invasive nature, precise spatial and temporal control, and potential multifunctional properties. Here, we provide a comprehensive overview of the different biofilm formation stages and the molecular mechanism of biofilm disruption, with a major focus on the quorum sensing machinery. Moreover, we highlight the principal guidelines for the development of light-responsive materials and photosensitive compounds. The synergistic effects of combining light-triggered therapies with conventional treatments are also discussed. Through elegant molecular and material design solutions, remarkable results have been achieved in the fight against biofilm formation and antibacterial resistance. However, further research and development in this field are essential to optimize therapeutic strategies and translate them into clinical and industrial applications, ultimately addressing the global challenges posed by biofilm and antimicrobial resistance.

Genetic Encoding of Arylazopyrazole Phenylalanine for Optical Control of Translation

An arylazopyrazole was explored for its use as an enhanced photoswitchable amino acid in genetic code expansion. This new unnatural amino acid was successfully incorporated into proteins in both bacterial and mammalian cells. While photocontrol of translation required pulsed irradiations, complete selectivity for the trans-configuration by the pyrrolysyl tRNA synthetase was observed, demonstrating expression of a gene of interest selectively controlled via light exposure.