Block copolymer synthesis in one shot: concurrent metal-free ATRP and ROP processes under sunlight

A completely metal-free strategy was developed by combining Atom Transfer Radical Polymerization (ATRP) and Ring Opening Polymerization (ROP) for the syntheses of block copolymers.

Photocatalytic copper-catalyzed azide–alkyne cycloaddition click reaction with Cu(ii) coordination polymer

Cu(ii) coordination polymers as photocatalysts for the copper-catalyzed azide–alkyne cycloaddition click reaction under household light irradiation in air.

A healable thermo-reversible functional polymer prepared via RAFT polymerization and ultrafast ‘click’ chemistry using a triazolinedione derivative

The synthesis of a thermo-reversible self-healable functional polymer based on the indole functionality via RAFT polymerization followed by an ultrafast Alder-ene ‘click’ reaction using 1,2,4-triazoline-3,5-dione (TAD) chemistry is reported.

Synthesis of self-curable polysulfone containing pendant benzoxazine units via CuAAC click chemistry

Synthesis, characterization, and properties of new thermally curable polysulfone containing benzoxazine moieties in the side chain were investigated. First, chloromethylation and subsequent azidation processes were performed to form polysulfone containing pendant clickable azide groups. Independently, antagonist 3,4-dihydro-3-(prop-2-ynyl)-2H-benzoxazine was prepared by using paraformaldehyde, phenol and propargylamine. The following copper(I) catalyzed azide-alkyne cycloaddition click reaction was applied to obtain self-curable polysulfone with pendant benzoxazine units. The polymer and intermediates at various stages were characterized by ¹H-NMR, ¹³C-NMR and FT-IR spectroscopies. The thermal properties and curing behavior of final polymer were investigated by differential scanning calorimetry and thermal gravimetric analysis. Compared to the neat polysulfone, the obtained polymers exhibited thermally more stable polymers.

Photochemistry of 1- and 2-Methyl-5-aminotetrazoles: Structural Effects on Reaction Pathways

The influence of the position of the methyl substituent in 1- and 2-methyl-substituted 5-aminotetrazoles on the photochemistry of these molecules is evaluated. The two compounds were isolated in an argon matrix (15 K) and the matrix was subjected to in situ narrowband UV excitation at different wavelengths, which induce selectively photochemical transformations of different species (reactants and initially formed photoproducts). The progress of the reactions was followed by infrared spectroscopy, supported by quantum chemical calculations. It is shown that the photochemistries of the two isomers, 1-methyl-(1H)-tetrazole-5-amine (1a) and 2-methyl-(2H)-tetrazole-5-amine (1b), although resulting in a common intermediate diazirine 3, which undergoes subsequent photoconversion into 1-amino-3-methylcarbodiimide (H₂N-N═C═N-CH₃), show marked differences: formation of the amino cyanamide 4 (H₂N-N(CH₃)-C≡N) is only observed from the photocleavage of the isomer 1a, whereas formation of the nitrile imine 2 (H₂N-C^-═N⁺═N-CH₃) is only obtained from photolysis of 1b. The exclusive formation of nitrile imine from the isomer 1b points to the possibility that only the 2H-tetrazoles forms can give a direct access to nitrile imines, while observation of the amino cyanamide 4 represents a novel reaction pathway in the photochemistry of tetrazoles and seems to be characteristic of 1H-tetrazoles. The structural and vibrational characterization of both reactants and photoproducts has been undertaken.

Sequential Photochemistry of Dibenzo[a,e]dicyclopropa[c,g][8]annulene-1,6-dione: Selective Formation of Didehydrodibenzo[a,e][8]annulenes with Ultrafast SPAAC Reactivity

An order of magnitude difference in photoreactivity between bis- (photo-DIBOD, 1) and mono-cyclopropenone-caged dibenzocyclooctadiynes (MC-DIBOD, 5) allows for selective monodecarbonylation of 1. Alternatively, 5 is prepared by selective mono-cyclopropanation of dibenzo[a,e]cyclooctadiyne (DIBOD). MC-DIBOD (5) permits efficient sequential SPAAC cross-linking of azide-derivatized substrates. Cycloaddition to 5 converts an azide moiety into a photocaged form of triazole-fused dibenzo[a,e]cyclooctyne (3). While the azide reactivity of MC-DIBOD (5) and DIBOD is similar to that of other dibenzocyclooctynes, fusion of triazole to the dibenzocyclooctyne system in 3 results in a 3 orders of magnitude enhancement in SPAAC rates. In methanol, 3 reacts with butyl azide at an astonishing rate of 34 M-1 s-1, thus representing the most reactive cyclooctyne analogue reported so far. MC-DIBOD (5) was utilized in the preparation of mixed bis-triazoles and derivatization of the protein BSA with fluorescent dye and polyethylene glycol.

Photochemically re-bridging disulfide bonds and the discovery of a thiomaleimide mediated photodecarboxylation of C-terminal cysteines

Described in this work is a novel method for photochemically manipulating peptides and proteins via the installation of cysteine-selective photoactive tags. Thiomaleimides, generated simply by the addition of bromomaleimides to reduced disulfide bonds, undergo [2 + 2] photocycloadditions to reconnect the crosslink between the two cysteine residues. This methodology is demonstrated to enable photoactivation of a peptide by macrocyclisation, and reconnection of the heavy and light chains in an antibody fragment to form thiol stable conjugates. Finally we report on an intriguing thiomaleimide mediated photochemical decarboxylation of C-terminal cysteines, discovered during this study.

Design of α-S-Neoglycopeptides Derived from MUC1 with a Flexible and Solvent-Exposed Sugar Moiety

The use of vaccines based on MUC1 glycopeptides is a promising approach to treat cancer. We present herein several sulfa-Tn antigens incorporated in MUC1 sequences that possess a variable linker between the carbohydrate (GalNAc) and the peptide backbone. The main conformations of these molecules in solution have been evaluated by combining NMR experiments and molecular dynamics simulations. The linker plays a key role in the modulation of the conformation of these compounds at different levels, blocking a direct contact between the sugar moiety and the backbone, promoting a helix-like conformation for the glycosylated residue and favoring the proper presentation of the sugar unit for molecular recognition events. The feasibility of these novel compounds as mimics of MUC1 antigens has been validated by the X-ray diffraction structure of one of these unnatural derivatives complexed to an anti-MUC1 monoclonal antibody. These features, together with potential lack of immune suppression, render these unnatural glycopeptides promising candidates for designing alternative therapeutic vaccines against cancer.

Rapid Bioorthogonal Chemistry Turn-on through Enzymatic or Long Wavelength Photocatalytic Activation of Tetrazine Ligation

Rapid bioorthogonal reactivity can be induced by controllable, catalytic stimuli using air as the oxidant. Methylene blue (4 μM) irradiated with red light (660 nm) catalyzes the rapid oxidation of a dihydrotetrazine to a tetrazine thereby turning on reactivity toward trans-cyclooctene dienophiles. Alternately, the aerial oxidation of dihydrotetrazines can be efficiently catalyzed by nanomolar levels of horseradish peroxidase under peroxide-free conditions. Selection of dihydrotetrazine/tetrazine pairs of sufficient kinetic stability in aerobic aqueous solutions is key to the success of these approaches. In this work, polymer fibers carrying latent dihydrotetrazines were catalytically activated and covalently modified by trans-cyclooctene conjugates of small molecules, peptides, and proteins. In addition to visualization with fluorophores, fibers conjugated to a cell adhesive peptide exhibited a dramatically increased ability to mediate contact guidance of cells.

Selective chemical labeling of proteins

Over the years, there have been remarkable efforts in the development of selective protein labeling strategies. In this review, we deliver a comprehensive overview of the currently available bioorthogonal and chemoselective reactions. The ability to introduce bioorthogonal handles to proteins is essential to carry out bioorthogonal reactions for protein labeling in living systems. We therefore summarize the techniques that allow for site-specific "installation" of bioorthogonal handles into proteins. We also highlight the biological applications that have been achieved by selective chemical labeling of proteins.

Near-Infrared-Sensitive Materials Based on Upconverting Nanoparticles

The near-infrared (NIR) region of the spectrum is called the "therapeutic window" because NIR light can penetrate deeply into tissue. Therefore, NIR-sensitive materials are attractive for biomedical applications. Recently, upconverting nanoparticles (UCNPs) were used to construct NIR-sensitive materials. UCNPs convert NIR light to UV or visible light, which can trigger photoreactions of photosensitive materials. Here, how to use UCNPs to construct NIR-sensitive materials is introduced, applications of NIR-sensitive materials with a focus on biomedical applications are highlighted, and the associated challenges are discussed.

Thermomechanical Formation-Structure-Property Relationships in Photopolymerized Copper-Catalyzed Azide-Alkyne (CuAAC) Networks

Bulk photopolymerization of a library of synthesized multifunctional azides and alkynes was carried out toward developing structure-property relationships for CuAAC-based polymer networks. Multifunctional azides and alkynes were formulated with a copper catalyst and a photoinitiator, cured, and analyzed for their mechanical properties. Material properties such as the glass transition temperatures (T_g) show a strong dependence on monomer structure with T_g values ranging from 41 to 90 °C for the series of CuAAC monomers synthesized in this study. Compared to the triazoles, analogous thioether-based polymer networks exhibit a 45-49 °C lower T_g whereas analogous monomers composed of ethers in place of carbamates exhibit a 40 °C lower T_g. Here, the formation of the triazole moiety during the polymerization represents a critical component in dictating the material properties of the ultimate polymer network where material properties such as the rubbery modulus, cross-link density, and T_g all exhibit strong dependence on polymerization conversion, monomer composition, and structure postgelation.

Cu-Catalyzed Click Reaction in Carbohydrate Chemistry

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

Cyclopropenone-caged Sondheimer diyne (dibenzo[a,e]cyclooctadiyne): a photoactivatable linchpin for efficient SPAAC crosslinking

The first fully conjugated bis-cyclopropenone (photo-DIBOD), a derivative of dibenzo[a,e][8]annulene, has been synthesized. 350-420 nm irradiation of this robust compound results in the efficient formation of dibenzo [a,e] cyclooctadiyne, an unstable, but useful SPAAC cross-linking reagent. Since photo-DIBO doesn't react with organic azides, this method allows for the spatiotemporal control of the ligation of two azide-tagged substrates.

LED and visible light-induced metal free ATRP using reducible dyes in the presence of amines

A new photoinitiating system involving electron acceptor dyes, namely, eosin Y and erythrosin B, in conjunction with alkyl halides and amines for photoinduced ATRP of (meth)acrylates and vinyl monomers in the absence of inorganic catalysts is reported.

Insertion of organometallic moieties into peptides and peptide nucleic acids using alternative “click” strategies

Application of alternative “click” strategies (metal-free photoclick and one-pot click) to cymantrene and ferrocene derivatives yielded novel metal-containing conjugates.

Copper(i) chloride catalysed room temperature Csp–Csp homocoupling of terminal alkynes mediated by visible light

An eco-friendly approach to the C_sp–C_sp homocoupling of terminal alkynes (including electron-withdrawing groups) was achieved at room temperature via a copper(i) chloride catalysed process mediated by visible light.

Catalyst free visible light induced cycloaddition as an avenue for polymer ligation

The current study introduces a tetrazole species able to perform a rapid, visible light induced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC).

Wavelength selective polymer network formation of end-functional star polymers

A wavelength selective technique for light-induced network formation is introduced, combining RAFT for precursor and DLW for 3D-structure generation.

Copper-catalysed azide-alkyne cycloadditions (CuAAC): an update

The reactions of organic azides and alkynes catalysed by copper species represent the prototypical examples of click chemistry. The so-called CuAAC reaction (copper-catalysed azide-alkyne cycloaddition), discovered in 2002, has been expanded since then to become an excellent tool in organic synthesis. In this contribution the recent results described in the literature since 2010 are reviewed, classified according to the nature of the catalyst precursor: copper(I) or copper(II) salts or complexes, metallic or nano-particulated copper and several solid-supported copper systems.

Access to Multiblock Copolymers via Supramolecular Host-Guest Chemistry and Photochemical Ligation

We combine supramolecular host-guest interactions of β-cyclodextrin (CD) with light-induced Diels-Alder reactions of 2-methoxy-6-methylbenzaldehyde (photoenol, PE) for the formation of multiblock copolymers. Via the synthesis of a new bifunctional chain transfer agent (CTA) and subsequent reversible addition-fragmentation chain transfer (RAFT) polymerization, we introduce a supramolecular recognition unit (tert-butyl phenyl) and a photoactive unit (photoenol) to a polymer chain in order to obtain an α,ω-functionalized polymeric center block, having orthogonal recognition units at each chain end. Multiblock copolymers are formed via the light-induced reaction of the photoenol with a maleimide-functionalized polymer chain and the supramolecular self-assembly of the tert-butyl phenyl group with the β-CD end group of a third polymer chain. By employing the fast and efficient photoinduced Diels-Alder reaction in combination with supramolecular host-guest interactions, a novel method for macromolecular modular ligation is introduced.