Light-controlled tools

Elucidating and Optimizing the Photochemical Mechanism of Coumarin-Caged Tertiary Amines

Photoactivatable or "caged" pharmacological agents combine the high spatiotemporal specificity of light application with the molecular specificity of drugs. A key factor in all optopharmacology experiments is the mechanism of uncaging, which dictates the photochemical quantum yield and determines the byproducts produced by the light-driven chemical reaction. In previous work, we demonstrated that coumarin-based photolabile groups could be used to cage tertiary amine drugs as quaternary ammonium salts. Although stable, water-soluble, and useful for experiments in brain tissue, these first-generation compounds exhibit relatively low uncaging quantum yield (Φu < 1%) and release the toxic byproduct formaldehyde upon photolysis. Here, we elucidate the photochemical mechanisms of coumarin-caged tertiary amines and then optimize the major pathway using chemical modification. We discovered that the combination of 3,3-dicarboxyazetidine and bromine substituents shift the mechanism of release to heterolysis, eliminating the formaldehyde byproduct and giving photolabile tertiary amine drugs with Φu > 20%─a 35-fold increase in uncaging efficiency. This new "ABC" cage allows synthesis of improved photoactivatable derivatives of escitalopram and nicotine along with a novel caged agonist of the oxytocin receptor.

Triplet-Triplet Annihilation Upconversion-Based Photolysis: Applications in Photopharmacology

The emerging field of photopharmacology is a promising chemobiological methodology for optical control of drug activities that could ultimately solve the off-target toxicity outside the disease location of many drugs for the treatment of a given pathology. The use of photolytic reactions looks very attractive for a light-activated drug release but requires to develop photolytic reactions sensitive to red or near-infrared light excitation for better tissue penetration. This review will present the concepts of triplet-triplet annihilation upconversion-based photolysis and their recent in vivo applications for light-induced drug delivery using photoactivatable nanoparticles.

Deuteration-Driven Photopharmacology: Deuterium-Labeled for Controlling Alpha 7 Nicotinic Acetylcholine Receptors

Photopharmacology is a powerful approach to investigate biological processes and overcomes the common therapeutic challenges in drug development. Enhancing the photopharmacology properties of photoswitches contributes to extend their applications. Deuteration, a tiny structural modification, makes it possible to improve the photopharmacology and photophysical properties of prototype compounds, avoiding extra complex chemical changes or constructing multicomponent systems. In this work, we developed a series of D-labeled azobenzenes to expand the azobenzene photoswitchable library and introduced the D-labeled azobenzene unit into the photoagonist of α7 nicotinic acetylcholine receptors (α7 nAChRs) to investigate the effects of deuteration in photopharmacology. Spectral data indicated that deuteration maintained most of the photophysical properties of azobenzenes. The D-labeled photoagonist exhibited good control of the activity of α7 nAChRs than the prototype photoagonist. These results confirmed that deuteration is a promising strategy to improve the photopharmacological properties.

Cellular and Biophysical Applications of Genetic Code Expansion

Despite their diverse functions, proteins are inherently constructed from a limited set of building blocks. These compositional constraints pose significant challenges to protein research and its practical applications. Strategically manipulating the cellular protein synthesis system to incorporate novel building blocks has emerged as a critical approach for overcoming these constraints in protein research and application. In the past two decades, the field of genetic code expansion (GCE) has achieved significant advancements, enabling the integration of numerous novel functionalities into proteins across a variety of organisms. This technological evolution has paved the way for the extensive application of genetic code expansion across multiple domains, including protein imaging, the introduction of probes for protein research, analysis of protein-protein interactions, spatiotemporal control of protein function, exploration of proteome changes induced by external stimuli, and the synthesis of proteins endowed with novel functions. In this comprehensive Review, we aim to provide an overview of cellular and biophysical applications that have employed GCE technology over the past two decades.

Antigen Delivery Controlled by an On-Demand Photorelease

To eliminate infected and cancerous cells, antigen processing and presentation play a pivotal role through the recognition of antigenic peptides displayed on Major Histocompatibility Complex class I (MHC I) molecules. Here, we developed a photostimulated antigen release system that enables the temporal inception of antigen flux. Simple and effective photocaging of the human immunodeficiency virus (HIV)-Nef73-derived epitope, a representative high-affinity MHC I ligand, was provided by steric hindrance to block the recognition by the transporter associated with antigen processing (TAP) in the peptide loading complex (PLC). In response to light, a heteronomous release of antigens and subsequent translocation in various scenarios is demonstrated, including a TAP-related ATP-binding cassette (ABC) transporter reconstituted in liposomes and the native PLC in the endoplasmic reticulum (ER) membrane of human cells. The photochemically induced 'burst' of antigens opens new opportunities for a mechanistic analysis of the antigen translocation machinery and will help to provide insights into antigen processing pathways via an on-demand, subcellular pulse-chase release of antigens.

BODIPY-based photocages: rational design and their biomedical application

Photocages, also known as photoactivated protective groups (PPGs), have been utilized to achieve controlled release of target molecules in a non-invasive and spatiotemporal manner. In the past decade, BODIPY fluorophores, a well-established class of fluorescent dyes, have emerged as a novel type of photoactivated protective group capable of efficiently releasing cargo species upon irradiation. This is due to their exceptional properties, including high molar absorption coefficients, resistance to photochemical and thermal degradation, multiple modification sites, favorable uncaging quantum yields, and highly adjustable spectral properties. Compared to traditional photocages that mainly absorb UV light, BODIPY-based photocages that absorb visible/near-infrared (Vis/NIR) light offer advantages such as deeper tissue penetration and reduced bio-autofluorescence, making them highly suitable for various biomedical applications. Consequently, different types of photoactivated protective groups based on the BODIPY skeleton have been established. This highlight provides a comprehensive overview of the strategies employed to construct BODIPY photocages by substituting leaving groups at different positions within the BODIPY fluorophore, including the meso-methyl position, boron position, 2,6-position, and 3,5-position. Furthermore, the application of these BODIPY photocages in biomedical fields, such as fluorescence imaging and controlled release of active species, is discussed.

RNA Control via Redox-Responsive Acylation

Incorporating stimuli-responsive components into RNA constructs provides precise spatiotemporal control over RNA structures and functions. Despite considerable advancements, the utilization of redox-responsive stimuli for the activation of caged RNAs remains scarce. In this context, we present a novel strategy that leverages post-synthetic acylation coupled with redox-responsive chemistry to exert control over RNA. To achieve this, we design and synthesize a series of acylating reagents specifically tailored for introducing disulfide-containing acyl adducts into the 2'-OH groups of RNA ("cloaking"). Our data reveal that these acyl moieties can be readily appended, effectively blocking RNA catalytic activity and folding. We also demonstrate the traceless release and reactivation of caged RNAs ("uncloaking") through reducing stimuli. By employing this strategy, RNA exhibits rapid cellular uptake, effective distribution and activation in the cytosol without lysosomal entrapment. We anticipate that our methodology will be accessible to laboratories engaged in RNA biology and holds promise as a versatile platform for RNA-based applications.

Infrared neuromodulation-a review

Infrared (IR) neuromodulation (INM) is an emerging light-based neuromodulation approach that can reversibly control neuronal and muscular activities through the transient and localized deposition of pulsed IR light without requiring any chemical or genetic pre-treatment of the target cells. Though the efficacy and short-term safety of INM have been widely demonstrated in both peripheral and central nervous systems, the investigations of the detailed cellular and biological processes and the underlying biophysical mechanisms are still ongoing. In this review, we discuss the current research progress in the INM field with a focus on the more recently discovered IR nerve inhibition. Major biophysical mechanisms associated with IR nerve stimulation are summarized. As the INM effects are primarily attributed to the spatiotemporal thermal transients induced by water and tissue absorption of pulsed IR light, temperature monitoring techniques and simulation models adopted in INM studies are discussed. Potential translational applications, current limitations, and challenges of the field are elucidated to provide guidance for future INM research and advancement.

Supramolecular Assembly and Thermogelation Strategies Using Peptide-Polymer Conjugates

Peptide-polymer conjugates (PPCs) are of particular interest in the development of responsive, adaptive, and interactive materials due to the benefits offered by combining both building blocks and components. This review presents pioneering work as well as recent advances in the design of peptide-polymer conjugates, with a specific focus on their thermoresponsive behavior. This unique class of materials has shown great promise in the development of supramolecular structures with physicochemical properties that are modulated using soft and biorthogonal external stimuli. The temperature-induced self-assembly of PPCs into various supramolecular architectures, gelation processes, and tuning of accessible processing parameters to biologically relevant temperature windows are described. The discussion covers the chemical design of the conjugates, the supramolecular driving forces involved, and the mutual influence of the polymer and peptide segments. Additionally, some selected examples for potential biomedical applications of thermoresponsive PPCs in tissue engineering, delivery systems, tumor therapy, and biosensing are highlighted, as well as perspectives on future challenges.

All-photonic kinase inhibitors: light-controlled release-and-report inhibition

Light-responsive molecular tools targeting kinases affords one the opportunity to study the underlying cellular function of selected kinases. In efforts to externally control lymphocyte-specific protein tyrosine kinase (LCK) activity, the development of release-and-report LCK inhibitors is described, in which (i) the release of the active kinase inhibitor can be controlled externally with light; and (ii) fluorescence is employed to report both the release and binding of the active kinase inhibitor. This introduces an unprecedented all-photonic method for users to both control and monitor real-time inhibitory activity. A functional cellular assay demonstrated light-mediated LCK inhibition in natural killer cells. The use of coumarin-derived caging groups resulted in rapid cellular uptake and non-specific intracellular localisation, while a BODIPY-derived caging group predominately localised in the cellular membrane. This concept of release-and-report inhibitors has the potential to be extended to other biorelevant targets where both spatiotemporal control in a cellular setting and a reporting mechanism would be beneficial.

Intracellular delivery and deep tissue penetration of nucleoside triphosphates using photocleavable covalently bound dendritic polycations

Nucleoside triphosphates (NTPs) are essential in various biological processes. Cellular or even organismal controlled delivery of NTPs would be highly desirable, yet in cellulo and in vivo applications are hampered owing to their negative charge leading to cell impermeability. NTP transporters or NTP prodrugs have been developed, but a spatial and temporal control of the release of the investigated molecules remains challenging with these strategies. Herein, we describe a general approach to enable intracellular delivery of NTPs using covalently bound dendritic polycations, which are derived from PAMAM dendrons and their guanidinium derivatives. By design, these modifications are fully removable through attachment on a photocage, ready to deliver the native NTP upon irradiation enabling spatiotemporal control over nucleotide release. We study the intracellular distribution of the compounds depending on the linker and dendron generation as well as side chain modifications. Importantly, as the polycation is bound covalently, these molecules can also penetrate deeply into the tissue of living organisms, such as zebrafish.

Dicyanorhodanine-Pyrrole Conjugates for Visible Light-Driven Quantitative Photoswitching in Solution and the Solid State

Small molecule photoswitches capable of toggling between two distinct molecular states in response to light are versatile tools to monitor biological processes, control photochemistry, and design smart materials. In this work, six novel dicyanorhodanine-based pyrrole-containing photoswitches are reported. The molecular design avails both the Z and E isomers from synthesis, where each can be isolated using chromatographic techniques. Inter- and intramolecular hydrogen bonding (H-bonding) interactions available to the E and Z isomers, respectively, uniquely impart thermal stability to each isomer over long time periods. Photoisomerization could be assessed by solution NMR and UV-vis spectroscopic techniques along with complementary ground- and excited-state computational studies, which show good agreement. Quantitative E → Z isomerization occurs upon 523 nm irradiation of the parent compound (where R = H) in solution, whereas Z → E isomerization using 404 nm irradiation offers a photostationary state (PSS) ratio of 84/16 (E/Z). Extending the π-conjugation of the pyrrole unit (where R = p-C6H4-OMe) pushes the maximum absorption to the yellow-orange region of the visible spectrum and allows bidirectional quantitative isomerization with 404 and 595 nm excitation. Comparator molecules have been prepared to report how the presence or absence of H-bonding affects the photoswitching behavior. Finally, studies of the photoswitches in neat films and photoinactive polymer matrices reveal distinctive structural and optical properties of the Z and E isomers and ultimately afford reversible photoswitching to spectrally unique PSSs using visible light sources including the Sun.

Crucial Roles of Leaving Group and Open-Shell Cation in Photoreaction of (Coumarin-4-yl)methyl Derivatives

Photoreactions of (coumarin-4-yl)methyl derivatives have been extensively studied in many fields of chemistry, including organic synthesis and photoinduced drug delivery systems. The identification of the reaction intermediates involved in the photoreactions is crucial not only for elucidating the reaction mechanism but also for the application of the photoreactions. In this study, the photoreactions of 7-diethylamino(coumarin-4-yl)methyl thioester 1a [-SC(O)CH3], thionoester 1b [-OC(S)CH3], and ester 1c [-OC(O)CH3] were investigated to clarify the intermediary species and their chemical behavior. While a radical pair [i.e., 7-diethylamino(coumarin-4-yl)methyl radical and CH3C(O)S•] plays an important role in the photoreactions of 1a and 1b, an ion pair [i.e., 7-diethylamino(coumarin-4-yl)methyl cation, and CH3CO2-] was the key in the photoreaction of 1c. 18O-isotope-labeling of 1c revealed a negligible recombination process within the ion pair. The unprecedented observation was rationalized by the open-shell character of the 7-diethylamino(coumarin-4-yl)methyl cation, whose formation was confirmed through product analysis and transient absorption spectroscopy.

Control of Photoisomerization Kinetics via Multistage Switching in Bimetallic Ru(II)-Terpyridine Complexes

In this study, we carried out detailed experimental and theoretical investigation on photophysical, electrochemical, and photoisomerization behaviors of a new array of luminescent binuclear Ru(II) complexes derived from a phenylene-vinylene-substituted terpyridyl ligand possessing RT lifetimes within 60.3-410.5 ns. The complexes experienced trans-to-cis isomerization in MeCN on irradiation with visible light, accompanied by significant changes in their absorption and emission spectral profiles. The reverse cis-to-trans process is also possible with the use of ultraviolet (UV) light. On conversion from trans to cis isomers, the emission intensity increases substantially, while for the reverse process, luminescence quenching occurs. Thus, "off-on" and "on-off" emission switching is facilitated upon treatment with visible and UV light alternatively. By the use of chemical oxidants (ceric ammonium nitrate and potassium permanganate) and reductants (metallic sodium) as well as light of appropriate wavelengths, multistate switching phenomena involving reversible oxidation-reduction and trans-cis isomerization have been achieved. Interestingly, the rate of this multistate photoswitching process becomes much faster compared to only two-state trans-cis isomerization of these complexes. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations are also performed to obtain a clear picture of the electronic environment of the complexes and also for the appropriate assignment of absorption and emission spectral bands.

Advances and Trends of Photoresponsive Hydrogels for Bone Tissue Engineering

The development of static hydrogels as an optimal choice for bone tissue engineering (BTE) remains a difficult challenge primarily due to the intricate nature of bone healing processes, continuous physiological functions, and pathological changes. Hence, there is an urgent need to exploit smart hydrogels with programmable properties that can effectively enhance bone regeneration. Increasing evidence suggests that photoresponsive hydrogels are promising bioscaffolds for BTE due to their advantages such as controlled drug release, cell fate modulation, and the photothermal effect. Here, we review the current advances in photoresponsive hydrogels. The mechanism of photoresponsiveness and its advanced applications in bone repair are also elucidated. Future research would focus on the development of more efficient, safer, and smarter photoresponsive hydrogels for BTE. This review is aimed at offering comprehensive guidance on the trends of photoresponsive hydrogels and shedding light on their potential clinical application in BTE.

O-nitrobenzyl Caged Molecule Enables Photo-controlled Release of Thiabendazole

Pesticides are essential in agricultural development. Controlled-release pesticides have attracted great attentions. Base on a principle of spatiotemporal selectivity, we extended the photoremovable protective group (PRPG) into agrochemical agents to achieve controllable release of active ingredients. Herein, we obtained NP-TBZ by covalently linking o-nitrobenzyl (NP) with thiabendazole (TBZ). Compound NP-TBZ can be controlled to release TBZ in dependent to light. The irradiated and unirradiated NP-TBZ showed significant differences on fungicidal activities both in vitro and in vivo. In addition, the irradiated NP-TBZ displayed similar antifungal activities to the directly-used TBZ, indicating a factual applicability in controllable release of TBZ. Furthermore, we explored the action mode and microcosmic variations by SEM analysis, and demonstrated that the irradiated NP-TBZ retained a same action mode with TBZ against mycelia growth.

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.

Light-Activatable MBD-Readers of 5-Methylcytosine Reveal Domain-Dependent Chromatin Association Kinetics In Vivo

5-Methylcytosine (5mC) is the central epigenetic mark of mammalian DNA, and plays fundamental roles in chromatin regulation. 5mC is dynamically read and translated into regulatory outputs by methyl-CpG-binding domain (MBD) proteins. These multidomain readers recognize 5mC via an MBD domain, and undergo additional domain-dependent interactions with multiple additional chromatin components. However, studying this dynamic process is limited by a lack of methods to conditionally control the 5mC affinity of MBD readers in cells. Light-control of MBD association to chromatin by genetically encoding a photocaged serine at the MBD-DNA interface is reported. The authors study the association of MBD1 to mouse pericentromeres, dependent on its CxxC3 and transcriptional repressor domains (TRD) which interact with unmethylated CpG and heterochromatin-associated complexes, respectively. Both domains significantly modulate association kinetics, arguing for a model in which the CxxC3 delays methylation responses of MBD1 by holding it at unmethylated loci, whereas the TRD promotes responses by aiding heterochromatin association is studied. Their approach offers otherwise inaccessible kinetic insights into the domain-specific regulation of a central MBD reader, and sets the basis for further unravelling how the integration of MBDs into complex heterochromatin interaction networks control the kinetics of 5mC reading and translation into altered chromatin states.

Towards a Light-mediated Gene Therapy for the Eye using Caged Ethinylestradiol and the Inducible Cre/lox System

Increasingly, retinal pathologies are being treated with virus-mediated gene therapies. To be able to target viral transgene expression specifically to the pathological regions of the retina with light, we established an in vivo photoactivated gene expression paradigm for retinal tissue. Based on the inducible Cre/lox system, we discovered that ethinylestradiol is a suitable alternative to Tamoxifen as ethinylestradiol is more amenable to modification with photosensitive protecting compounds, i.e., "caging." Identification of ethinylestradiol as a ligand for the mutated human estradiol receptor was supported by in silico binding studies showing the reduced binding of caged ethinylestradiol. Caged ethinylestradiol was injected into the eyes of double transgenic GFAP-CreERT2 mice with a Cre-dependent tdTomato reporter transgene followed by irradiation with light of 450 nm. Photoactivation significantly increased retinal tdTomato expression compared to controls. We thus demonstrated a first step towards the development of a targeted, light-mediated gene therapy for the eyes.

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.

The fate of the contact ion pair determines the photochemistry of coumarin-based photocleavable protecting groups

Photocleavable protecting groups (PPGs) enable the precise spatiotemporal control over the release of a payload of interest, in particular a bioactive substance, through light irradiation. A crucial parameter that determines the practical applicability of PPGs is the efficiency of payload release, largely governed by the quantum yield of photolysis (QY). Understanding which parameters determine the QY will prove crucial for engineering improved PPGs and their effective future applications, especially in the emerging field of photopharmacology. The Contact Ion Pair (CIP) has been recognized as an important intermediate in the uncaging process, but the key influence of its fate on the quantum yield has not been explored yet, limiting our ability to design improved PPGs. Here, we demonstrate that the CIP escape mechanism of PPGs is crucial for determining their payload- and solvent-dependent photolysis QY, and illustrate that an intramolecular type of CIP escape is superior over diffusion-dependent CIP escape. Furthermore, we report a strong correlation of the photolysis QY of a range of coumarin PPGs with the DFT-calculated height of all three energy barriers involved in the photolysis reaction, despite the vastly different mechanisms of CIP escape that these PPGs exhibit. Using the insights obtained through our analysis, we were able to predict the photolysis QY of a newly designed PPG with particularly high accuracy. The level of understanding of the factors determining the QY of PPGs presented here will move the ever-expanding field of PPG applications forward and provides a blueprint for the development of PPGs with QYs that are independent of payload-topology and solvent polarity.

Exploiting Visible-Light Induced Radical to Cation Transformation Pathway for Reactivity Enhanced Electrophilic Aromatic Substitution Polymerization of Heteroaromatics

A straightforward approach is employed to synthesize methylene-bridged poly(hetero aromatic)s based on furan, pyrrole, thiophene, and thiophene derivatives. The process involves an electrophilic aromatic substitution reaction facilitated by a visible light-initiated system consisting of manganese decacarbonyl and an iodonium salt. The approach mainly relies on the formation of halomethylium cation, the attack of this cation to heteroaromatic, regeneration of methylium cation on the heteroaromatic, and reactivity differences between halomethylium and heteroaromatic methylium cations for successful polymerizations. This innovative synthetic strategy lead to the formation of polymers with relatively high molecular weights as the stoichiometric imbalance between the comonomers increased. Accordingly, these newly obtained polymers exhibit remarkable fluorescence properties, even at excitation wavelengths as low as 330 nm. Moreover, by harnessing the halogens at chain ends of homopolymers, block copolymers are successfully synthesized, offering opportunities for tailored applications in diverse fields.

Cation delocalization and photo-isomerization enhance the uncaging quantum yield of a photocleavable protecting group

Photocleavable protecting groups (PPGs) enable the light-induced, spatiotemporal control over the release of a payload of interest. Two fundamental challenges in the design of new, effective PPGs are increasing the quantum yield (QY) of photolysis and red-shifting the absorption spectrum. Here we describe the combination of two photochemical strategies for PPG optimization in one molecule, resulting in significant improvements in both these crucial parameters. Furthermore, we for the first time identify the process of photo-isomerization to strongly influence the QY of photolysis of a PPG and identify the cis-isomer as the superior PPG.

Effect of Two-Photon Excitation to 8-Azacoumarin Derivatives as Photolabile Protecting Groups

An improvement of the two-photon excitation was achieved using 8-azacoumarin-type caged compounds, which showed large values of the two-photon uncaging action cross-section (δu >0.1 Goeppert-Mayer (GM)). In particular, the 7-hydroxy-6-iodo-8-azacoumarin (8-aza-Ihc)-caged compound showed an excellent uncaging action cross-section value (δu = 1.28 GM). Therefore, 8-azacoumarin-type photolabile protecting groups (PPGs) can be used as two-photon excitation sources.

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.

Photoswitchable and long-lived seven-membered cyclic singlet diradicals for the bioorthogonal photoclick reaction

Annularly 1,3-localized singlet diradicals are energetic and homolytic intermediates, but commonly too short-lived for widespread utilization. Herein, we describe a direct observation of a long-lived and seven-membered singlet diradical, oxepine-3,6-dione-2,7-diyl (OXPID), via spectroscopic experiments and also theoretical evidence from computational studies, which is generated via photo-induced ring-expansion of 2,3-diaryl-1,4-naphthoquinone epoxide (DNQO). The photo-generated OXPID reverts to the thermally stable σ-bonded DNQO with t1/2 in the μs level, thus constituting a novel class of T-type molecular photoswitches with high light-energy conversion efficiency (η = 7.8-33%). Meanwhile, the OXPID is equilibrated to a seven-membered cyclic 1,3-dipole as an electronic tautomer that can be captured by ring-strained dipolarophiles with an ultrafast cycloaddition rate (k2CA up to 109 M-1 s-1). The T-type photoswitchable DNQO is then exploited to be a highly selective and recyclable photoclick reagent, enabling spatiotemporal-resolved bioorthogonal ligation on living cell membranes via a tailored DNQO-Cy3 probe.

Visible-light-mediated synthesis of oxime esters via multicomponent reactions of aldehydes, aryl amines, and N-hydroxyphthalimide esters

Oxime esters are useful scaffolds in many organic chemistry transformations. Herein, a novel visible-light-mediated three-component reaction for synthesis of oxime esters is reported. Aldehydes, aniline, and N-hydroxyphthalimide (NHPI) esters were used as substrates in this three-component reaction, and eosin Y was used as a crucial photocatalyst for the reaction. Wide ranges of aldehydes and NHPI esters were well tolerated in this reaction method, generating various oxime esters with high efficiency under mild reaction conditions. This visible-light-mediated methodology will be a promising approach to synthesize useful oxime esters in a single step.

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.

Controlled destabilization of caged circularized DNA oligonucleotides predicted by replica exchange molecular dynamics simulations

Spatiotemporal control is a critical issue in the design of strategies for the photoregulation of oligonucleotide activity. Efficient uncaging, i.e., activation by removal of photolabile protecting groups (PPGs), often necessitates multiple PPGs. An alternative approach is based on circularization strategies, exemplified by intrasequential circularization, also denoted photo-tethering, as introduced in [Seyfried et al., Angew. Chem., Int. Ed., 2017, 56, 359]. Here, we develop a computational protocol, relying on replica exchange molecular dynamics (REMD), in order to characterize the destabilization of a series of circularized, caged DNA oligonucleotides addressed in the aforementioned study. For these medium-sized (32 nt) oligonucleotides, melting temperatures are computed, whose trend is in good agreement with experiment, exhibiting a large destabilization and, hence, reduction of the melting temperature of the order of ΔTm ∼ 30 K as compared with the native species. The analysis of free energy landscapes confirms the destabilization pattern experienced by the circularized oligonucleotides. The present study underscores that computational protocols that capture controlled destabilization and uncaging of oligonucleotides are promising as predictive tools in the tailored photocontrol of nucleic acids.

Synthesis of an Ortho-Functionalized Tetrafluorinated Azobenzene Phosphoramidite for Incorporation into a Tetrafluorinated Azobenzene-Containing siRNA for Photocontrolled Gene Silencing

This article presents the detailed synthesis and characterization protocols for an ortho-functionalized tetrafluorinated azobenzene containing siRNA, which has photoswitchable properties. To design this tetrafluorinated azobenzene scaffold, several synthetic steps are performed to generate a symmetrical tetrafluorinated azobenzene diol. This diol is treated with dimethoxytrityl chloride (DMT-Cl) to protect one of the alcohols. Next, the DMT-protected tetrafluorinated monoalcohol is phosphitylated to afford the DMT-phosphoramidite building block used for solid-phase synthesis. This paper also contains the detailed biophysical characterization, biological testing, and photo-switching protocols of an ortho-functionalized fluorinated azobenzene containing siRNA (F-siRNA), which has photoswitchable properties that can be controlled with visible light. First, the F-siRNA was characterized by annealing the sense and antisense strands together and then measuring the circular dichroism (CD) profile and melting temperature (Tm ) of the duplexes. Second, biological testing of the F-siRNA is performed in cell culture to determine their gene silencing efficacy. Finally, their gene-silencing activities are measured after exposure to green light to inactivate the F-siRNA, followed by blue light, which reactivates the F-siRNA. The F-siRNA can be kept inactive for up to 72 hr and reactivated at any time within this 72-hr window. © 2023 Wiley Periodicals LLC.

Light-regulated RNA interference induced by p-hydroxyphenacyl-modified siRNA in mammalian cells

siRNA is an important tool for modulating gene expression in current biomedical research. It would be highly desirable for siRNA to respond to an external stimulus. In this paper, we report a convenient, photolabile caging agent to regulate siRNA functions. 2-bromo-4'-hydroxyacetophenone (BHAP) can readily modify phosphorothioate backbones and inhibit siRNAs. Mild UV irradiation will cleave the modifying moiety to generate natural nucleic acid backbones, thus activating siRNA functions. Such modification is conveniently conducted in an aqueous solution with high efficiency and is cost-effective and scalable. This approach provides a convenient tool for the controlled regulation of gene expression by deploying minimal usage of complex organic synthesis for site-specific installation of the caging group to siRNA unlike previous reported works that required a series of intricate organic synthesis and cumbersome purification techniques to achieve similar aims. This study will open new doors for optochemical regulation of a variety of genes by pHP caging group in mammalian cell culture.

Cooperative Network Formation via Two-Colour Light-Activated λ-Orthogonal Chromophores

Independently addressing photoreactive sites within one molecule with two colours of light is a formidable challenge. Here, we combine two sequence independent λ-orthogonal chromophores in one heterotelechelic dilinker molecule, to exploit their disparate reactivity utilizing the same reaction partner, a maleimide-containing polymer. We demonstrate that polymer network formation only proceeds if two colours of light are employed. Upon single colour irradiation, linker-decorated post-functionalized polymers are generated at either wavelength and in either sequence. Network formation, however, is only achieved by sequential or simultaneous two colour irradiation. The herein introduced photoreactive system demonstrates the power of wavelength orthogonal chemistry in macromolecular synthesis.

Proton-Coupled Photochromic Hemithioindigo: Toward Photoactivated Chemical Sensing and Imaging

We report photoswitchable fluorescent hemithioindigos (HTIs) where the metastable E isomers were stabilized by the proton-bridged intramolecular hydrogen bond. Titration experiments and computational analysis indicated that the E isomers were much more basic than the Z isomers, which enabled photoactivated colorimetric and fluorescent pH response in solvents and polypropylene films. The HTIs exhibited reversibly switchable fluorescence with the Z isomers being the most fluorescent. Moreover, the HTIs were lysosomotropic and the kinetic fluorescence evolution during photoswitching was able to differentiate subcellular compartments with different pH. The combination of photoenhanced basicity, switchable fluorescence, and proton-coupled photochromism lay the groundwork for a broad range of chemical and biological applications.

Photoisomerization of 2-Arylazoimidazoles under Visible Light: Identifying a Predictive Tool to Anticipate and Tune Likely Photoswitching Performance and Cis Half-Life

Azopyrazoles are an emerging class of photoswitches, whereas analogous azoimidazole-based switches are unable to draw much attention because of their short cis half-lives, poor cis-trans photoreversion yields, and toxic ultraviolet (UV) light-assisted isomerization. A series of 24 various aryl-substituted N-methyl-2-arylazoimidazoles were synthesized, and their photoswitching performances and cis-trans isomerization kinetics were thoroughly investigated experimentally and theoretically. Para-π-donor-substituted azoimidazoles with highly twisted T-shaped cis conformations showed nearly complete bidirectional photoswitching, whereas di-o-substituted switches exhibited very long cis half-lives (days-years) with nearly ideal T-shaped conformations. This study demonstrates how the electron density in the aryl ring affects cis half-life and cis-trans photoreversion via twisting of the NNAr dihedral angle that can be used as a predictive metric for envisaging and tuning the likely switching performance and half-life of any given 2-arylazoimidazole. By applying this tool, two better-performing azoimidazole photoswitches were engineered. All switches permitted irradiation by violet (400-405 nm) and orange (>585 nm) light for forward and reverse isomerization, respectively, and displayed comparatively high quantum yields and impressive resistance to photobleaching.

Visible and NIR light photoactivatable o-hydroxycinnamate system for efficient drug release with fluorescence monitoring

Photoactivatable protecting groups (PPGs) have become powerful materials for controlling the activity of biologically important molecules in the biomedical field. However, designing PPGs that can be efficiently activated by biologically benign visible and NIR light with fluorescence monitoring is still a great challenge. Herein, we report o-hydroxycinnamate-based PPGs that can be activated by both visible (one-photon) and NIR (two-photon) light for controlled drug release with real-time monitoring. Thus, a photoremovable 7-diethylamino o-hydroxycinnamate group is covalently attached to an anticancer drug, gemcitabine, to establish a photoactivatable prodrug system. Upon excitation by visible (400-700 nm) or NIR (800 nm) light, the prodrug efficiently releases drug which is quantified by monitoring the formation of a strongly fluorescent coumarin reporter. The prodrug is taken up by the cancer cells and interestingly accumulates within mitochondria as determined by FACS and fluorescence microscopy imaging. Further, the prodrug demonstrates photo-triggered, dose-dependent, and temporally controlled cell death upon irradiation with both visible and NIR light. This photoactivatable system could be useful and adapted in the future for the development of advanced therapies in biomedicine.

Reversible Control of RNA Splicing by Photoswitchable Small Molecules

Dynamics are intrinsic to both RNA function and structure. Yet, the available means to precisely provide RNA-based processes with spatiotemporal resolution are scarce. Here, our work pioneers a reversible approach to regulate RNA splicing within primary patient-derived cells by synthetic photoswitches. Our small molecule enables conditional real-time control at mRNA and protein levels. NMR experiments, together with theoretical calculations, photochemical characterization, fluorescence polarization measurements, and living cell-based assays, confirmed light-dependent exon inclusion as well as an increase in the target functional protein. Therefore, we first demonstrated the potential of photopharmacology modulation in splicing, tweaking the current optochemical toolkit. The timeliness on the consolidation of RNA research as the driving force toward therapeutical innovation holds the promise that our approach will contribute to redrawing the vision of RNA.

Mitochondria-Targeted COUPY Photocages: Synthesis and Visible-Light Photoactivation in Living Cells

Releasing bioactive molecules in specific subcellular locations from the corresponding caged precursors offers great potential in photopharmacology, especially when using biologically compatible visible light. By taking advantage of the intrinsic preference of COUPY coumarins for mitochondria and their long wavelength absorption in the visible region, we have synthesized and fully characterized a series of COUPY-caged model compounds to investigate how the structure of the coumarin caging group affects the rate and efficiency of the photolysis process. Uncaging studies using yellow (560 nm) and red light (620 nm) in phosphate-buffered saline medium have demonstrated that the incorporation of a methyl group in a position adjacent to the photocleavable bond is particularly important to fine-tune the photochemical properties of the caging group. Additionally, the use of a COUPY-caged version of the protonophore 2,4-dinitrophenol allowed us to confirm by confocal microscopy that photoactivation can occur within mitochondria of living HeLa cells upon irradiation with low doses of yellow light. The new photolabile protecting groups presented here complement the photochemical toolbox in therapeutic applications since they will facilitate the delivery of photocages of biologically active compounds into mitochondria.

ESIPT-, AIE-, and AIE + ESIPT-Based Light-Activated Drug Delivery Systems and Bioactive Donors for Targeted Disease Treatment

Targeted release of bioactive molecules for therapeutic purposes is a key area in the biomedical field that is growing quickly, where bioactive molecules are released passively or actively from drug delivery systems (DDSs) or bioactive donors. In the past decade, researchers have identified light as one of the prime stimuli that can implement the efficient spatiotemporally targeted delivery of drugs or gaseous molecules with minimal cytotoxicity and a real-time monitoring ability. This perspective emphasizes recent advances in the photophysical properties of ESIPT- (excited-state intramolecular proton transfer), AIE- (aggregation-induced emission), and AIE + ESIPT-attributed light-activated delivery systems or donors. The three major sections of this perspective describe the distinctive features of DDSs and donors concerning their design, synthesis, photophysical and photochemical properties, and in vitro and in vivo studies demonstrating their relevance as carrier molecules for releasing cancer drugs and gaseous molecules in the biological system.

Photoswitchable Oxidopyrylium Ylide for Photoclick Reaction with High Spatiotemporal Precision: A Dynamic Switching Strategy to Compensate for Molecular Diffusion

We describe a novel type of photoclick reaction between 2,3-diaryl indenone epoxide (DIO) and ring-strained dipolarophiles, in which DIO serves as a P-type photoswitch to produce mesoionic oxidopyrylium ylide (PY) to initiate an ultra-fast [5+2] cycloaddition (k_2hν =1.9×10⁵  M^-1  s^-1 ). The photoisomerization between DIO and PY can be tightly controlled by either 365 or 520 nm photo-stimulation, which allows reversion or regeneration of the reactive PY dipole on demand. Thus, this reversible photoactivation was exploited to increase the chemoselectivity of the [5+2] cycloaddition in complex environments via temporal dual-λ stimulation sequences and to recycle the DIO reagent for batch-wise protein conjugation. A dynamic photoswitching strategy is also proposed to compensate for molecular diffusion of PY in aqueous solution, enhancing the spatial resolution of lithographic surface decoration and bioorthogonal labeling on living cells via a spatiotemporal dual-λ photo-modulation.

Arylazopyrazole-Based Photoswitchable Inhibitors Selective for Escherichia coli Dihydrofolate Reductase

Selective inhibitors of Escherichia coli dihydrofolate reductase (eDHFR) are crucial chemical biology tools that have widespread clinical applications. We developed a set of eDHFR-selective photoswitchable inhibitors by derivatizing the structure of our previously reported methotrexate (MTX) azolog, azoMTX. Substitution of the skeletal p-phenylene group of azoMTX with bulky bis-alkylated arylazopyrazole moieties significantly increased its selectivity toward eDHFR over human DHFR. Owing to the physical properties of arylazopyrazoles, the new ligands exhibited nearly complete Z-to-E photoconversion and high thermostability of Z-isomers. In addition, real-time photoreversible control of eDHFR activity was achieved by alternatively switching the illumination light wavelengths.

Rhodamine-Sensitized Two-Photon Activation of a Red Light-Absorbing BODIPY Photocage

Two-photon (2P) activatable probes are of high value in biological and medical chemistry since near infrared (NIR) light can penetrate deeply even in blood-perfused tissue and due to the intrinsic three-dimensional activation properties. Designing two-photon chromophores is challenging. However, the two-photon absorption qualities of a photocage can be improved with an intramolecular sensitizer, which transfers the absorbed light onto the cage. We herein present the synthesis and photophysical characterization of a 2P-sensitive uncaging dyad based on rhodamine 101 as donor fluorophore and a redshifted BODIPY as acceptor photocage. Liberation of p-nitroaniline (PNA) upon one-photon photolysis was confirmed by HPLC analysis. The photoreaction was found to be accompanied by a considerable change of the fluorescence properties of the chromophores. The possibility of a fluorescent read-out enabled the detection of two-photon induced uncaging by confocal fluorescence microscopy.

Visible light responsive photoacids for subcellular pH and temperature correlated fluorescence sensing

Liao's photoacids (PAs) are a well-known type of visible light-responsive photoswitches. Here, taking advantage of the temperature-dependent thermal relaxation from the ring-closed to the ring-opened forms, PAs are proposed for the first time as a fluorescent temperature sensor in cells. The logarithmic lifetime (ln τ) of the ring-closed spiro-form exhibited an excellent linear response to the reciprocal of the temperature. In addition, the fluorescent ring-opened PAs were able to highlight lysosomes and responded to lysosomal pH changes. These properties made the PAs promising fluorescent probes in the sensing of subcellular pH and temperature.

A Caged In-Source Laser-Cleavable MALDI Matrix with High Vacuum Stability for Extended MALDI-MS Imaging

Insufficient vacuum stability of matrix chemicals is a major limitation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) of large tissue sample cohorts. Here, we designed and synthesized the photo-cleavable caged molecule 4,5-dimethoxy-2-nitrobenzyl-2,5-dihydroxyacetophenone (DMNB-2,5-DHAP) and employed it for lipid MALDI-MSI of mouse brain tissue sections. DMNB-2,5-DHAP is vacuum-stable in a high vacuum MALDI ion source for at least 72 h. Investigation of the uncaging process suggested that the built-in laser (355 nm) in the MALDI ion source promoted the in situ generation of 2,5-DHAP. A caging group is used for the first time in designing a MALDI matrix that is vacuum-stable, uncaged upon laser irradiation during the measurement process, and that boosts lipid ion intensity with MALDI-2 laser-induced postionization.

The design of small-molecule prodrugs and activatable phototherapeutics for cancer therapy

Cancer remains as one of the most significant health problems, with approximately 19 million people diagnosed worldwide each year. Chemotherapy is a routinely used method to treat cancer patients. However, current treatment options lack the appropriate selectivity for cancer cells, are prone to resistance mechanisms, and are plagued with dose-limiting toxicities. As such, researchers have devoted their attention to developing prodrug-based strategies that have the potential to overcome these limitations. This tutorial review highlights recently developed prodrug strategies for cancer therapy. Prodrug examples that provide an integrated diagnostic (fluorescent, photoacoustic, and magnetic resonance imaging) response, which are referred to as theranostics, are also discussed. Owing to the non-invasive nature of light (and X-rays), we have discussed external excitation prodrug strategies as well as examples of activatable photosensitizers that enhance the precision of photodynamic therapy/photothermal therapy. Activatable photosensitizers/photothermal agents can be seen as analogous to prodrugs, with their phototherapeutic properties at a specific wavelength activated in the presence of disease-related biomarkers. We discuss each design strategy and illustrate the importance of targeting biomarkers specific to the tumour microenvironment and biomarkers that are known to be overexpressed within cancer cells. Moreover, we discuss the advantages of each approach and highlight their inherent limitations. We hope in doing so, the reader will appreciate the current challenges and available opportunities in the field and inspire subsequent generations to pursue this crucial area of cancer research.

Controlling antifungal activity with light: Optical regulation of fungal ergosterol biosynthetic pathway with photo-responsive CYP51 inhibitors

Invasive fungal infections (IFIs) have been associated with high mortality, highlighting the urgent need for developing novel antifungal strategies. Herein the first light-responsive antifungal agents were designed by optical control of fungal ergosterol biosynthesis pathway with photocaged triazole lanosterol 14α-demethylase (CYP51) inhibitors. The photocaged triazoles completely shielded the CYP51 inhibition. The content of ergosterol in fungi before photoactivation and after photoactivation was 4.4% and 83.7%, respectively. Importantly, the shielded antifungal activity (MIC₈₀ ≥ 64 μg/mL) could be efficiently recovered (MIC₈₀ = 0.5-8 μg/mL) by light irradiation. The new chemical tools enable optical control of fungal growth arrest, morphological conversion and biofilm formation. The ability for high-precision antifungal treatment was validated by in vivo models. The light-activated compound A1 was comparable to fluconazole in prolonging survival in Galleria mellonella larvae with a median survival of 14 days and reducing fungal burden in the mouse skin infection model. Overall, this study paves the way for precise regulation of antifungal therapy with improved efficacy and safety.

Stimulus-Responsive Amino Acids Behind In Situ Assembled Bioactive Peptide Materials

In situ self-assembly of peptides into well-defined nanostructures represents one of versatile strategies for creation of bioactive materials within living cells with great potential in disease diagnosis and treatment. The intimate relationship between amino acid sequences and the assembling propensity of peptides has been thoroughly elucidated over the past few decades. This has inspired development of various controllable self-assembling peptide systems based on stimuli-responsive naturally occurring or non-canonical amino acids, including redox-, pH-, photo-, enzyme-responsive amino acids. This review attempts to summarize the recent progress achieved in manipulating in situ self-assembly of peptides by controllable reactions occurring to amino acids. We will highlight the systems containing non-canonical amino acids developed in our laboratory during the past few years, primarily including acid/enzyme-responsive 4-aminoproline, redox-responsive (seleno)methionine, and enzyme-responsive 2-nitroimidazolyl alanine. Utilization of the stimuli-responsive assembling systems in creation of bioactive materials will be specifically introduced to emphasize their advantages for addressing the concerns lying in disease theranostics. Eventually, we will provide the perspectives for the further development of stimulus-responsive amino acids and thereby demonstrating their great potential in development of next-generation biomaterials.

Visible Light Induced High Resolution and Swift 3D Printing System by Halogen Atom Transfer

3D printing technology offers solutions for numerous needs in industry and the daily life of individuals. In recent years, most research efforts have focused on this technology as the market share has grown and requirements have become specified in their related fields. In this work, a novel visible light induced 3D printing system with high resolution and short printing time using dimanganese decacarbonyl (Mn₂ (CO)₁₀ ) in combination with organic halides is reported. The radicals formed through halogen abstraction by photochemically generated manganese pentacarbonyl from organic halides with high quantum efficiency initiate the polymerization of acrylic resins. The kinetics of the process using various halide-containing molecules in the photoinitiaiting system are investigated with real-time fourrier transform infrared spectroscopy and photo-differential scanning calorimetry analyses, and the characteristics of 3D printouts are presented and compared with that of the commercial photoinitiator, 2,4,6-trimethylbenzoyl)phosphine oxide without Mn₂ (CO)₁₀ . The results obtained confirm that the combination of Mn₂ (CO)₁₀ and structurally diverse organic halides is a class of promising 3D system for various applications.

Photo-regulated genetic encoding of dibenzo[c,g][1,2]diazocine on proteins via configuration switching

We report two evolved Methanosarcina mazei pyrrolysine tRNA synthetases to genetically incorporate the isomers of dibenzo[c,g][1,2]diazocine-alanine (DBDAA) into proteins either in the dark or under regulation of 405 nm photo-stimulation. The genetic-encoded DBDAA realizes photo-tuning of enzymatic activity via the host-guest recognition of cucurbit[7]uril.