Photoclick Reactions Research Articles

Peptide Bundlemer Networks or Lattices: Controlling Cross-Linking and Self-Assembly Using Protein-like Display of Chemistry.

Coiled-coil 'bundlemer' peptides were selectively modified with allyloxycarbonyl (alloc)-protected lysine, a non-natural amino acid containing an alkene on its side chain. The specific display of this alkene from the coiled-coil surface with protein-like specificity enabled this residue to be used as a covalent linkage for creating peptide networks with controllable properties or as a physical linkage for the self-assembly of bundlemers into unexpected, intricate lattices driven by the hydrophobic nature of the side chain. For network formation, peptides were modified with both alloc-protected lysine and cysteine amino acids for solution assembly into solvent-swollen films and subsequent covalent cross-linking via thiol-ene photo click reactions. The degree of network cross-linking, as determined by rheometry, was finely tuned by varying the specific spatial display of reactive groups on the bundlemer building block particles, transitioning between intrabundle and interbundle cross-linking. The designed display of alloc groups from the center of the bundlemer building block also prompted particle self-assembly into an unexpected intricate lattice with a porous morphology. The lattices were studied in a variety of solution conditions using transmission electron microscopy, cryotransmission electron microscopy, and small-angle X-ray scattering. The approximate particle arrangement in the lattice was determined by using coarse-grained modeling and machine learning optimization techniques along with experimental methods. The proposed truss-like face-centered cubic packing of the alloc-functionalized bundlemers agrees well with the experimental results.

Visible and near-infrared light-induced photoclick reactions.

Photoclick reactions combine the advantages offered by light-driven processes, that is, non-invasive and high spatiotemporal control, with classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photocrosslinking, protein labelling and bioimaging. Despite these advances, most photoclick reactions typically require near-ultraviolet (UV) and mid-UV light to proceed. UV light can trigger undesirable responses, including cellular apoptosis, and therefore, visible and near-infrared light-induced photoclick reaction systems are highly desirable. Shifting to a longer wavelength can also reduce degradation of the photoclick reagents and products. Several strategies have been used to induce a bathochromic shift in the wavelength of irradiation-initiating photoclick reactions. For instance, the extension of the conjugated π-system, triplet-triplet energy transfer, multi-photon excitation, upconversion technology, photocatalytic and photoinitiation approaches, and designs involving photocages have all been used to achieve this goal. Current design strategies, recent advances and the outlook for long wavelength-driven photoclick reactions are presented.

Cyclopropenes as Chemical Reporters for Dual Bioorthogonal and Orthogonal Metabolic Labeling of DNA.

Dual bioorthogonal labeling enables the investigation and understanding of interactions in the biological environment that are not accessible by a single label. However, applying two bioorthogonal reactions in the same environment remains challenging due to cross-reactivity. We developed a pair of differently modified 2'-deoxynucleosides that solved this issue for dual and orthogonal labeling of DNA. Inverse-electron demand Diels-Alder and photoclick reactions were combined to attach two different fluorogenic labels to genomic DNA in cells. Using a small synthetic library of 1- and 3-methylcyclopropenyl-modified 2'-deoxynucleosides, two 2'-deoxyuridines were identified to be the fastest-reacting ones for each of the two bioorthogonal reactions. Their orthogonal reactivity could be evidenced in vitro. Primer extension experiments were performed with both 2'-deoxyuridines investigating their replication properties as substitutes for thymidine and evaluating subsequent labeling reactions on the DNA level. Finally, dual, orthogonal and metabolic fluorescent labeling of genomic DNA was demonstrated in HeLa cells. An experimental procedure was developed combining intracellular transport and metabolic DNA incorporation of the two 2'-deoxyuridines with the subsequent dual bioorthogonal labeling using a fluorogenic cyanine-styryl tetrazine and a fluorogenic pyrene-tetrazole. These results are fundamental for advanced metabolic labeling strategies for nucleic acids in the future, especially for live cell experiments.

Cyclopropene als Chemische Reporter für die Duale Bioorthogonale und Orthogonale Metabolische Markierung von DNA

AbstractDie duale bioorthogonale Markierung ermöglicht die Untersuchung und das Verständnis von Wechselwirkungen in der biologischen Umgebung, die mit einer einzigen Markierung nicht zugänglich sind. Eine Herausforderung bleibt jedoch die Anwendung von zwei bioorthogonalen Reaktionen in der gleichen Umgebung aufgrund von Kreuzreaktivität. Um dieses Problem für die duale und orthogonale Markierung von DNA zu lösen, haben wir zwei unterschiedlich modifizierte 2′‐Desoxynukleoside entwickelt. Mit Hilfe der Diels‐Alder‐Reaktion mit inversem Elektronenbedarf und Photoklick‐Reaktion wurde genomische DNA in Zellen mit zwei verschiedenen fluorogenen Markern verknüpft. Aus einer kleinen synthetischen Bibliothek aus 1‐ und 3‐methylcyclopropenyl‐modifizierten 2′‐Desoxynukleosiden wurden zwei 2′‐Desoxyuridine identifiziert, die am schnellsten in jeweils einer der beiden bioorthogonalen Reaktionen reagieren. Ihre orthogonale Reaktivität konnte in vitro nachgewiesen werden. Ihre Replikationseigenschaften als Ersatz für Thymidin wurden in Primerverlängerungsexperimenten untersucht, um die anschließenden Markierungsreaktionen an DNA abzuschätzen. Schließlich wurde eine duale, orthogonale und metabolische Fluoreszenzmarkierung von genomischer DNA in HeLa‐Zellen nachgewiesen. Es wurde ein experimentelles Protokoll entwickelt, das den intrazellulären Transport und den metabolischen DNA‐Einbau der beiden 2′‐Desoxyuridine mit der anschließenden dualen bioorthogonalen Markierung unter Verwendung eines fluorogenen Cyanin‐Styryl‐Tetrazins und eines fluorogenen Pyren‐Tetrazols kombiniert. Diese Ergebnisse sind von grundlegender Bedeutung für fortgeschrittene metabolische Markierungsstrategien für Nukleinsäuren in der Zukunft, insbesondere in lebenden Zellen.

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

AbstractPhotoclick 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.

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.

With or without a co-solvent? highly efficient ultrafast phenanthrenequinone-electron rich alkene (PQ-ERA) photoclick reactions.

The light-induced photocycloaddition of 9,10-phenanthrenequinone (PQ) with electron-rich alkenes (ERA), known as the PQ-ERA reaction, is a highly attractive photoclick reaction characterized by its operational simplicity and high biocompatibility. One essential aspect of photoclick reactions is their high rate, however the limited solubility of PQs often requires the use of a co-solvent. Evaluating the effect of different co-solvents on the PQ-ERA reaction and their influence on the reaction rate, we discovered that sulfur-containing compounds, in particular the frequently used solubilizing co-solvent DMSO, quench the triplet state of the PQ. These experimental results, supported by nanosecond-microsecond and ultrafast transient absorption data, show that even minimal amounts of DMSO result in a decreased lifetime of the reactive triplet state, essential for the photoclick reaction. Without DMSO as co-solvent, exceptionally high photoreaction quantum yields ( Φ P up to 93% with only 1 equivalent ERA) and complete conversion in seconds can be achieved. With these outstanding efficiencies, the PQ-ERA reaction can be used without excess ERA and at low light intensities, facilitating photoclick transformations in various future applications.

Efficient, Near‐Infrared Light‐Induced Photoclick Reaction Enabled by Upconversion Nanoparticles

AbstractPhotoclick reactions combine the selectivity of classical click chemistry with the high precision and spatiotemporal control afforded by light, finding diverse utility in surface customization, polymer conjugation, photocross‐linking, protein labeling, and bioimaging. Nonetheless, UV light, pivotal in prevailing photoclick reactions, poses issues, especially in biological contexts, due to its limited tissue penetration and cell‐toxic nature. Herein, a reliable and versatile strategy of activating the photoclick reactions of 9,10‐phenanthrenequinones (PQs) with electron‐rich alkenes (ERAs) with near infrared (NIR) light transduced by spectrally and structurally customized upconversion nanoparticles (UCNPs) is introduced. Under NIR irradiation, the UCNPs become UV/blue nanoemitters uniformly distributed in the reaction system. Enabled by the customized UCNPs, 800 or 980 nm light effectively activates the photocycloaddition reactions via radiative energy transfer in both general and triplet–triplet energy transfer (TTET)‐mediated PQ‐ERA systems. In particular, the novel sandwich structure UCNPs achieve the click reaction with up to 76% production yield in 10 min under NIR light irradiation. Meanwhile, the tricky side effect of photoclick product absorption‐induced quenching is successfully circumvented from the fine‐tuning of the upconversion spectrum. Moreover, through‐tissue irradiation experiments, the authors show that the UCNP‐PQ‐ERA reaction unlocks the full potential of photoclick reactions for in vivo applications.

Molecular Engineering To Enhance Reactivity and Selectivity in an Ultrafast Photoclick Reaction

AbstractLight‐induced 9,10‐phenanthrenequinone‐electron‐rich alkene (PQ‐ERA) photocycloadditions are an attractive new type of photoclick reaction, featuring fast conversions and high biocompatibility. However, the tunability of the reaction was hardly investigated up to now. To this end, we explored the influence of substituents on both reaction partners and the reaction rate between the PQs and ERAs. We identified new handles for functionalization and discovered that using enamines as ERAs leads to drastically enhanced rates (>5400 times faster), high photoreaction quantum yields (ΦP, up to 65 %), and multicolor emission output as well as a high fluorescence quantum yield of the adducts (ΦF, up to 97 %). Further investigation of the photophysical and photochemical properties provided insights to design orthogonal reaction systems both in solution and on nanoparticle surfaces for ultrafast chemoselective functionalization by photoclick reactions.

Molecular Engineering To Enhance Reactivity and Selectivity in an Ultrafast Photoclick Reaction.

Light-induced 9,10-phenanthrenequinone-electron-rich alkene (PQ-ERA) photocycloadditions are an attractive new type of photoclick reaction, featuring fast conversions and high biocompatibility. However, the tunability of the reaction was hardly investigated up to now. To this end, we explored the influence of substituents on both reaction partners and the reaction rate between the PQs and ERAs. We identified new handles for functionalization and discovered that using enamines as ERAs leads to drastically enhanced rates (>5400 times faster), high photoreaction quantum yields (ΦP , up to 65 %), and multicolor emission output as well as a high fluorescence quantum yield of the adducts (ΦF , up to 97 %). Further investigation of the photophysical and photochemical properties provided insights to design orthogonal reaction systems both in solution and on nanoparticle surfaces for ultrafast chemoselective functionalization by photoclick reactions.

Photo-induced defluorination acyl fluoride exchange as a fluorogenic photo-click reaction for photo-affinity labeling.

Photo-click chemistry has emerged as a powerful tool for revolutionizing bioconjugation technologies in pharmacological and various biomimetic applications. However, enriching the photo-click reactions to expand the bioconjugation toolkit remains challenging, especially when focusing on spatiotemporal control endowed by light activation. Herein, we describe a photo-induced defluorination acyl fluoride exchange (photo-DAFEx) as a novel type of photo-click reaction that is mediated through acyl fluorides produced by the photo-defluorination of m-trifluoromethylaniline to covalently conjugate with primary/secondary amines and thiols in an aqueous environment. (TD)-DFT calculations, together with experimental discovery, indicate that the m-NH2PhF2C(sp3)-F bond in the excited triplet state is cleaved by water molecules, which is key to inducing defluorination. Intriguingly, the benzoyl amide linkages built by this photo-click reaction exhibited a satisfactory fluorogenic performance, which allowed visualization of its formation in situ. Accordingly, this photo-controlled covalent strategy was exploited not only for the decoration of small molecules, peptide cyclization and functionalization of proteins in vitro, but also for designing photo-affinity probes targeting endogenous carbonic anhydrase II (hCA-II) in living cells.

Establishing PQ-ERA photoclick reactions with unprecedented efficiency by engineering of the nature of the phenanthraquinone triplet state.

The light-induced photocycloaddition of 9,10-phenanthrenequinone (PQ) with electron-rich alkenes (ERA), known as the PQ-ERA reaction, is a highly attractive photoclick reaction characterized by high selectivity, external non-invasive control with light and biocompatibility. The conventionally used PQ compounds show limited reactivity, which hinders the overall efficiency of the PQ-ERA reaction. To address this issue, we present in this study a simple strategy to boost the reactivity of the PQ triplet state to further enhance the efficiency of the PQ-ERA reaction, enabled by thiophene substitution at the 3-position of the PQ scaffold. Our investigations show that this substitution pattern significantly increases the population of the reactive triplet state (3ππ*) during excitation of 3-thiophene PQs. This results in a superb photoreaction quantum yield (ΦP, up to 98%), high second order rate constants (k2, up to 1974 M-1 s-1), and notable oxygen tolerance for the PQ-ERA reaction system. These results have been supported by both experimental transient absorption data and theoretical calculations, providing further evidence for the effectiveness of this strategy, and offering fine prospects for fast and efficient photoclick transformations.

Multiconfigurational photodynamics simulations reveal the mechanism of photodecarbonylations of cyclopropenones in explicit aqueous environments.

Gas-evolving photochemical reactions use light and mild conditions to access strained organic compounds irreversibly. Cyclopropenones are a class of light-responsive molecules used in bioorthogonal photoclick reactions; their excited-state decarbonylation reaction mechanisms are misunderstood due to their ultrafast (<100 femtosecond) lifetimes. We have combined multiconfigurational quantum mechanical (QM) calculations and non-adiabatic molecular dynamics (NAMD) simulations to uncover the excited-state mechanism of cyclopropenone and a photoprotected cyclooctyne-(COT)-precursor in gaseous and explicit aqueous environments. We explore the role of H-bonding with fully quantum mechanical explicitly solvated NAMD simulations for the decarbonylation reaction. The cyclopropenones pass through asynchronous conical intersections and have dynamically concerted photodecarbonylation mechanisms. The COT-precursor has a higher quantum yield of 55% than cyclopropenone (28%) because these trajectories prefer to break a σCC bond to avoid the strained trans-cyclooctene geometries. Our solvated simulations show an increased quantum yield (58%) for the systems studied here.

Click Chemistry Mediated by Photochemical Energy

AbstractLight mediated chemical reactions have emerged as an important class of reactions known as photoclick reactions. These reactions have allowed synthesis of complex molecular structures to be performed under mild conditions. The spatiotemporal control offered by photoclick reactions cannot be achieved by thermal processes. This review captures the advances in the area of photoclick chemistry and highlights the importance of light induced cycloaddition reactions, thiol‐ene/yne reactions and hetero‐Diels–Alder reactions.

Click Chemistry: copper, ruthenium catalyzed and photoinduced

Click chemistry is an extremely powerful method for covalent conjugation of molecular entities quickly and efficiently. Click chemistry knitted the threads between two different molecular entities that have created interesting structures for more than 15 years with a wide range of applications, including in interesting fields such as synthetic chemistry, medicinal science, biochemistry, material science, pharmacology and catalysis. Due to the schematic modification and incorporation of azide and alkyne groups within biological scaffolds, azide-alkyne cycloaddition (AAC) is still the leading methodology among click chemistry. This review focuses on the mechanism, scope, and applications of the CuAAC reaction, RuAAC reaction, and the recent development of photo-click reactions, and their applications cover the literature from the last ten years.

Visible Light Chemical Micropatterning Using a Digital Light Processing Fluorescence Microscope.

Patterning chemical reactivity with a high spatiotemporal resolution and chemical versatility is critically important for advancing revolutionary emergent technologies, including nanorobotics, bioprinting, and photopharmacology. Current methods are complex and costly, necessitating novel techniques that are easy to use and compatible with a wide range of chemical functionalities. This study reports the development of a digital light processing (DLP) fluorescence microscope that enables the structuring of visible light (465–625 nm) for high-resolution photochemical patterning and simultaneous fluorescence imaging of patterned samples. A range of visible-light-driven photochemical systems, including thiol–ene photoclick reactions, Wolff rearrangements of diazoketones, and photopolymerizations, are shown to be compatible with this system. Patterning the chemical functionality onto microscopic polymer beads and films is accomplished with photographic quality and resolutions as high as 2.1 μm for Wolff rearrangement chemistry and 5 μm for thiol–ene chemistry. Photoactivation of molecules in living cells is demonstrated with single-cell resolution, and microscale 3D printing is achieved using a polymer resin with a 20 μm xy-resolution and a 100 μm z-resolution. Altogether, this work debuts a powerful and easy-to-use platform that will facilitate next-generation nanorobotic, 3D printing, and metamaterial technologies.

Synthesis of oleic-based primary glycol with high molecular weight for bio-based waterborne polyurethane

Oleic acid, as a renewable resource, exists in almost every vegetable oil, especially olive and camellia oils, which has promising prospects for the preparation of bio-based polymers. In this study, a novel oleic-based primary glycol (OPG) was synthesized from methyl oleate (MO, derived from vegetable oil) via Claisen condensation and thiol-ene photo-click reactions and used as an alternative to petroleum-based glycol for the preparation of bio-based waterborne polyurethane (BWPU), and the differences in reactivity between the OPG and petroleum-based polypropylene glycol (PPG) and properties between BWPU and petroleum-based waterborne polyurethane (PWPU) were investigated. The yield of OPG was approximately 90%, the degree of functionality was 2.0, the hydroxyl value was about 155 mg KOH g−1 and the molecular weight (Mw) varied from 296 g mol−1 to 560 g mol−1 and 716 g mol−1 after the chain extension of Claisen condensation and thiol-ene photo-click reactions. In comparison with PPG, OPG exhibited lower activation energy towards IPDI, and the values showed an order of OPG (Ea/Eo=71.25/74.20 kJ mol−1) < PPG600 (Ea/Eo=106.83/108.03 kJ mol−1) < PPG1000 (Ea/Eo=129.20/129.37 kJ mol−1). Correspondingly, the end point of pre-polymerization appeared in 80 min for OPG and 420 min, 840 min for PPG600 and PPG1000 at 80 °C without catalyst, demonstrating that OPG had higher reactivity. Because of the difference in hydrophobicity, the minimum amount of hydrophilic extender used to obtain stable WPU emulsions was 7 wt% for OPG and 3.5 wt% for PPG respectively. The resulting BWPU films possessed good mechanical properties, including higher tensile strength (19.78 MPa) and Young’s modulus (206.61 MPa). But the thermal stability (Td5% ≤ 250 ℃) and low temperature resistance (Tg ≥ 28 ℃) of BWPU films were inferior to that of PWPU films.

Spatiotemporal Resolved Live Cell Membrane Tracking through Photo-click Reactions Enriched in Lipid Phase.

A set of photo-switchable monopeptides derived from cis-β-dibenzodiazocine-l-alanine (cis-DBDAA) have been designed and synthesized, which are capable of photo-click reacting with diaryltetrazoles or diarylsydnones in a hydrophobic phospholipid bilayer environment. The DBDAA monopeptides include both a hydrophobic tail on C-terminal, providing high affinity toward lipid membrane, and a modularized functional moiety on N-terminal, enabling rapid optimization of the self-assembly strength to form multifunctional supramolecules. With the cis-DBDAA monopeptides photo-switched into trans-configuration, we were able to disrupt the supramolecular assembly through an efficient photo-click reaction across the lipid bilayer of liposomes. We reveal that the performance of the photo-click reactions between the monopeptides and photo-generated nitrile imine intermediates is significantly enhanced by enrichment of both reactants in the hydrophobic membrane lamel of liposomes. Enrichment of the DBDAA monopeptide in lipid phase serves as a convenient method to introduce bioorthogonal chemical handles on live cell membranes, which enables fluorescence labelling of single cell's membrane with high spatiotemporal resolution to facilitate the studies on cell membrane dynamics.

Nano-3D-Printed Photochromic Micro-Objects.

Molecular photoswitches that can reversibly change color upon irradiation are promising materials for applications in molecular actuation and photoresponsive materials. However, the fabrication of photochromic devices is limited to conventional approaches such as mold casting and spin-coating, which cannot fabricate complex structures. Reported here is the first photoresist for direct laser writing of photochromic 3D micro-objects via two-photon polymerization. The integration of photochromism into thiol-ene photo-clickable resins enables rapid two-photon laser processing of highly complex microstructures and facile postmodification using a series of donor-acceptor Stenhouse adduct (DASA) photoswitches with different excitation wavelengths. The versatility of thiol-ene photo-click reactions allows fine-tuning of the network structure and physical properties as well as the type and concentration of DASA. When exposed to visible light, these microstructures exhibit excellent photoresponsiveness and undergo reversible color-changing via photoisomerization. It is demonstrated that the fluorescence variations of DASAs can be used as a reporter of photoswitching and thermal recovery, allowing the reading of DASA-containing sub-micrometric structures in 3D. This work delivers a new approach for custom microfabrication of 3D photochromic objects with molecularly engineered color and responsiveness.

Photoclick Chemistry: A Bright Idea.

At its basic conceptualization, photoclick chemistry embodies a collection of click reactions that are performed via the application of light. The emergence of this concept has had diverse impact over a broad range of chemical and biological research due to the spatiotemporal control, high selectivity, and excellent product yields afforded by the combination of light and click chemistry. While the reactions designated as "photoclick" have many important features in common, each has its own particular combination of advantages and shortcomings. A more extensive realization of the potential of this chemistry requires a broader understanding of the physical and chemical characteristics of the specific reactions. This review discusses the features of the most frequently employed photoclick reactions reported in the literature: photomediated azide-alkyne cycloadditions, other 1,3-dipolarcycloadditions, Diels-Alder and inverse electron demand Diels-Alder additions, radical alternating addition chain transfer additions, and nucleophilic additions. Applications of these reactions in a variety of chemical syntheses, materials chemistry, and biological contexts are surveyed, with particular attention paid to the respective strengths and limitations of each reaction and how that reaction benefits from its combination with light. Finally, challenges to broader employment of these reactions are discussed, along with strategies and opportunities to mitigate such obstacles.