Showing papers on "Click chemistry published in 2015"

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

Abstract: 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.

“Click”-Inspired Chemistry in Macromolecular Science: Matching Recent Progress and User Expectations

Abstract: This year, it has been a decade that the concept of “click” chemistry was pioneered in polymer and material science by the exploration of the synthetic scope of copper-catalyzed azide/alkyne cycloaddition (CuAAC), the “click” benchmark. The impact on the endeavors of polymer chemists has been substantial because the power of this concept, featuring modularity, orthogonality, and versatility for the design and synthesis of polymeric materials, was recognized very soon in macromolecular research groups worldwide. After this first burst of research activity, challenging the boundaries of CuAAC in terms of attainable polymer constructs, ongoing method development, and implementation, in response to the need for metal-free alternatives, resulted in a valuable toolbox of “click”-inspired conjugation methods. Because of the large diversity of employable reactions, applied in various polymeric systems, the first-time or occasional “click” user will be confronted with a burden of choice. Therefore, the principal a...

Copper Nanoparticles in Click Chemistry.

Abstract: ConspectusThe challenges of the 21st century demand scientific and technological achievements that must be developed under sustainable and environmentally benign practices In this vein, click chemistry and green chemistry walk hand in hand on a pathway of rigorous principles that help to safeguard the health of our planet against negligent and uncontrolled production Copper-catalyzed azide–alkyne cycloaddition (CuAAC), the paradigm of a click reaction, is one of the most reliable and widespread synthetic transformations in organic chemistry, with multidisciplinary applications Nanocatalysis is a green chemistry tool that can increase the inherent effectiveness of CuAAC because of the enhanced catalytic activity of nanostructured metals and their plausible reutilization capability as heterogeneous catalystsThis Account describes our contribution to click chemistry using unsupported and supported copper nanoparticles (CuNPs) as catalysts prepared by chemical reduction Cu(0)NPs (30 ± 15 nm) in tetrahy

Isolation of bis(copper) key intermediates in Cu-catalyzed azide-alkyne "click reaction".

Abstract: The copper-catalyzed 1,3-dipolar cycloaddition of an azide to a terminal alkyne (CuAAC) is one of the most popular chemical transformations, with applications ranging from material to life sciences. However, despite many mechanistic studies, direct observation of key components of the catalytic cycle is still missing. Initially, mononuclear species were thought to be the active catalysts, but later on, dinuclear complexes came to the front. We report the isolation of both a previously postulated π,σ-bis(copper) acetylide and a hitherto never-mentioned bis(metallated) triazole complex. We also demonstrate that although mono- and bis-copper complexes promote the CuAAC reaction, the dinuclear species are involved in the kinetically favored pathway.

Recycling Tires? Reversible Crosslinking of Poly(butadiene)

Abstract: Furan-modified poly(butadiene) prepared by the thiol-ene click reaction is crosslinked with bismaleimides through the Diels-Alder reaction, giving rise to a novel recyclable elastomer. This is possible because of the thermal reversibility of the adducts responsible for the formation of the network. The use of this strategy provides the possibility to produce recyclable tires.

Chain‐Growth Click Polymerization of AB2 Monomers for the Formation of Hyperbranched Polymers with Low Polydispersities in a One‐Pot Process

Abstract: Hyperbranched polymers are important soft nanomaterials but robust synthetic methods with which the polymer structures can be easily controlled have rarely been reported. For the first time, we present a one-pot one-batch synthesis of polytriazole-based hyperbranched polymers with both low polydispersity and a high degree of branching (DB) using a copper-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization. The use of a trifunctional AB2 monomer that contains one alkyne and two azide groups ensures that all Cu catalysts are bound to polytriazole polymers at low monomer conversion. Subsequent CuAAC polymerization displayed the features of a “living” chain-growth mechanism with a linear increase in molecular weight with conversion and clean chain extension for repeated monomer additions. Furthermore, the triazole group in a linear (L) monomer unit complexed CuI, which catalyzed a faster reaction of the second azide group to quickly convert the L unit into a dendritic unit, producing hyperbranched polymers with DB=0.83.

CalFluors: A Universal Motif for Fluorogenic Azide Probes across the Visible Spectrum.

Abstract: Fluorescent bioorthogonal smart probes across the visible spectrum will enable sensitive visualization of metabolically labeled molecules in biological systems. Here we present a unified design, based on the principle of photoinduced electron transfer, to access a panel of highly fluorogenic azide probes that are activated by conversion to the corresponding triazoles via click chemistry. Termed the CalFluors, these probes possess emission maxima that range from green to far red wavelengths, and enable sensitive biomolecule detection under no-wash conditions. We used the CalFluor probes to image various alkyne-labeled biomolecules (glycans, DNA, RNA, and proteins) in cells, developing zebrafish, and mouse brain tissue slices.

Recent Advances in Click Chemistry Applied to Dendrimer Synthesis

Abstract: Dendrimers are monodisperse polymers grown in a fractal manner from a central point. They are poised to become the cornerstone of nanoscale devices in several fields, ranging from biomedicine to light-harvesting. Technical difficulties in obtaining these molecules has slowed their transfer from academia to industry. In 2001, the arrival of the "click chemistry" concept gave the field a major boost. The flagship reaction, a modified Huisgen cycloaddition, allowed researchers greater freedom in designing and building dendrimers. In the last five years, advances in click chemistry saw a wider use of other click reactions and a notable increase in the complexity of the reported structures. This review covers key developments in the click chemistry field applied to dendrimer synthesis from 2010 to 2015. Even though this is an expert review, basic notions and references have been included to help newcomers to the field.

A Mechanochemically Triggered "Click" Catalyst.

Abstract: "Click" chemistry represents one of the most powerful approaches for linking molecules in chemistry and materials science. Triggering this reaction by mechanical force would enable site- and stress-specific "click" reactions--a hitherto unreported observation. We introduce the design and realization of a homogeneous Cu catalyst able to activate through mechanical force when attached to suitable polymer chains, acting as a lever to transmit the force to the central catalytic system. Activation of the subsequent copper-catalyzed "click" reaction (CuAAC) is achieved either by ultrasonication or mechanical pressing of a polymeric material, using a fluorogenic dye to detect the activation of the catalyst. Based on an N-heterocyclic copper(I) carbene with attached polymeric chains of different flexibility, the force is transmitted to the central catalyst, thereby activating a CuAAC in solution and in the solid state.

Chemical Modification of Poly(Vinyl Alcohol) in Water

Abstract: Partial chemical modification of poly(vinyl alcohol) (PVA) was performed through tosylation followed by azidation. Amine functional PVA was also prepared by grafting propargylamine using click chemistry reaction. Through this approach, a tosyl group (a good leaving group), azide group (a group used in click chemistry) and amine group (a group used for amidation) were attached to PVA polymer chains. The three chemical modifications were performed in water. FTIR and XPS analysis confirmed the chemical modification after each step. Thermogravimetric analysis (TGA) was used to study the thermal stability of the modified PVA.

Metal‐Free Click Chemistry Reactions on Surfaces

Abstract: In the last decade, interest in the functionalization of surfaces and materials has increased dramatically. In this regard, click chemistry deserves a central focus because of its mild reaction conditions, high efficiency, and easy post-treatment. Among such novel click reactions, those that do not require any metal catalyst are of special interest, as metals may have undesirable effects in many fields. In this Review, the backgrounds and application of such metal-free click reactions for the modification of surfaces are highlighted.

The impact of 1,2,3-triazoles in the design of functional coatings

Abstract: In recent times 1,2,3-triazole rich molecules have gained much importance in the field of polymer and material science because of their excellent properties like strong anti-microbial and anti fouling nature of the triazole ring along with easy synthetic procedures and exceptionally high yield of end product. Generally these molecules are synthesized by azide–alkyne click reaction and this chemistry has potential application in the functionalization of a wide range of inorganic moieties like metal oxide nanoparticles, carbon nanotubes etc. to develop hybrid nanocomposites for high performance materials. Based on the previous reports, this particular review article provides a comprehensive overview of the application of 1,2,3-triazoles in the design of various high performance organic coatings such as anti-corrosive, anti-microbial, self-healing, hybrid nanocomposite, bio degradable etc.

Regioselective Sequential Modification of Chitosan via Azide-Alkyne Click Reaction: Synthesis, Characterization, and Antimicrobial Activity of Chitosan Derivatives and Nanoparticles.

Abstract: Recently, the attention of researchers has been drawn toward the synthesis of chitosan derivatives and their nanoparticles with enhanced antimicrobial activities. In this study, chitosan derivatives with different azides and alkyne groups were synthesized using click chemistry, and these were further transformed into nanoparticles by using the ionotropic gelation method. A series of chitosan derivatives was successfully synthesized by regioselective modification of chitosan via an azide-alkyne click reaction. The amino moieties of chitosan were protected during derivatization by pthaloylation and subsequently unblocked at the end to restore their functionality. Nanoparticles of synthesized derivatives were fabricated by ionic gelation to form complexes of polyanionic penta-sodium tripolyphosphate (TPP) and cationic chitosan derivatives. Particle size analysis showed that nanoparticle size ranged from 181.03 ± 12.73 nm to 236.50 ± 14.32 nm and had narrow polydispersity index and positive surface charge. The derivatives and corresponding nanoparticles were evaluated in vitro for antibacterial and antifungal activities against three gram-positive and gram-negative bacteria and three fungal strains, respectively. The minimum inhibitory concentration (MIC) of all derivatives ranged from 31.3 to 250 µg/mL for bacteria and 188 to1500 µg/mL for fungi and was lower than that of native chitosan. The nanoparticles with MIC ranging from 1.56 to 25 µg/mLfor bacteria and 94 to 750 µg/mL for fungi exhibited higher activity than the chitosan derivatives. Chitosan O-(1-methylbenzene) triazolyl carbamate and chitosan O-(1-methyl phenyl sulfide) triazolyl carbamate were the most active against the tested bacterial and fungal strains. The hemolytic assay on erythrocytes and cell viability test on two different cell lines (Chinese hamster lung fibroblast cells V79 and Human hepatic cell line WRL68) demonstrated the safety; suggesting that these derivatives could be used in future medical applications. Chitosan derivatives with triazole functionality, synthesized by Huisgen 1,3-dipolar cycloaddition, and their nanoparticles showed significant enhancement in antibacterial and antifungal activities in comparison to those associated with native, non-altered chitosan.

SuFEx on the Surface: A Flexible Platform for Postpolymerization Modification of Polymer Brushes

Abstract: Polymer brushes present a unique architecture for tailoring surface functionalities due to their distinctive physicochemical properties. However, the polymerization chemistries used to grow brushes place limitations on the monomers that can be grown directly from the surface. Several forms of click chemistry have previously been used to modify polymer brushes by postpolymerization modification with high efficiency, however, it is usually difficult to include the unprotected moieties in the original monomer. We present the use of a new form of click chemistry known as SuFEx (sulfur(VI) fluoride exchange), which allows a silyl ether to be rapidly and quantitatively clicked to a polymer brush grown by free-radical polymerization containing native -SO2F groups with rapid pseudo-first-order rates as high as 0.04 s(-1). Furthermore, we demonstrate the use of SuFEx to facilely add a variety of other chemical functional groups to brush substrates that have highly useful and orthogonal reactivity, including alkynes, thiols, and dienes.

In situ prepared copper nanoparticles on modified KIT-5 as an efficient recyclable catalyst and its applications in click reactions in water

Abstract: A novel heterogeneous copper nano catalyst supported on modified silica mesopore KIT-5 was successfully prepared. The 3-aminopropyltriethoxysilane (APTES) on KIT-5 was coordinated with copper(I) and accurately characterized. In addition a comparative survey on the metal-ligand interactions in the syntheses of catalyst in two different solvents via density functional theory calculations was performed. A one-pot procedure for syntheses of 1,4-disubstituted 1,2,3-triazole derivatives via a three-component reaction between terminal alkynes, alkyl halides, and sodium azide, namely click reaction in the presences of 3 mol% nanoparticles copper/APTES-KIT-5 (Cu/AK) as a catalyst was developed to give the products in good to excellent yields. This catalyst showed high catalytic activity in water as a “green” solvent. This reaction was performed under open air conditions and required no special reaction conditions and chromatographic separation for purification.

Recent advances in crosslinking chemistry of biomimetic poly(ethylene glycol) hydrogels

Abstract: The designs and applications of biomimetic hydrogels have become an important and integral part of modern tissue engineering and regenerative medicine. Many of these hydrogels are prepared from synthetic macromers (e.g., poly(ethylene glycol) or PEG) as they provide high degrees of tunability for matrix crosslinking, degradation, and modification. For a hydrogel to be considered biomimetic, it has to recapitulate key features that are found in the native extracellular matrix, such as the appropriate matrix mechanics and permeability, the ability to sequester and deliver drugs, proteins, or nucleic acids, as well as the ability to provide receptor-mediated cell–matrix interactions and protease-mediated matrix cleavage. A variety of chemistries have been employed to impart these biomimetic features into hydrogel crosslinking. These chemistries, such as radical-mediated polymerizations, enzyme-mediated crosslinking, bio-orthogonal click reactions, and supramolecular assembly, may be different in their crosslinking mechanisms but are required to be efficient for gel crosslinking and ligand bioconjugation under aqueous reaction conditions. The prepared biomimetic hydrogels should display a diverse array of functionalities and should also be cytocompatible for in vitro cell culture and/or in situ cell encapsulation. The focus of this article is to review recent progress in the crosslinking chemistries of biomimetic hydrogels with a special emphasis on hydrogels crosslinked from poly(ethylene glycol)-based macromers.

Rewritable Polymer Brush Micropatterns Grafted by Triazolinedione Click Chemistry.

Abstract: Triazolinedione (TAD) click reactions were combined with microcontact chemistry to print, erase, and reprint polymer brushes on surfaces. By patterning substrates with a TAD-tagged atom-transfer radical polymerization initiator (ATRP-TAD) and subsequent surface initiated ATRP, it was possible to graft micropatterned polymer brushes from both alkene- and indole-functionalized substrates. As a result of the dynamic nature of the Alder-ene adduct of TAD and indole at elevated temperatures, the polymer pattern could be erased while the regenerated indole substrate could be reused to print new patterns. To demonstrate the robustness of the methodology, the write-erase cycle was repeated four times.

Construction of Versatile and Functional Nanostructures Derived from CO2 -based Polycarbonates.

Abstract: The construction of amphiphilic polycarbonates through epoxides/CO2 coupling is a challenging aim to provide more diverse CO2 -based functional materials. In this report, we demonstrate the facile preparation of diverse and functional nanoparticles derived from a CO2 -based triblock polycarbonate system. By the judicious use of water as chain-transfer reagent in the propylene oxide/CO2 polymerization, poly(propylene carbonate (PPC) diols are successfully produced and serve as macroinitiators in the subsequent allyl glycidyl ether/CO2 coupling reaction. The resulting ABA triblock polycarbonate can be further functionalized with various thiols by radical mediated thiol-ene click chemistry, followed by self-assembly in deionized water to construct a versatile and functional nanostructure system. This class of amphiphilic polycarbonates could embody a powerful platform for biomedical applications.

Dinuclear Copper Intermediates in Copper(I)-Catalyzed Azide- Alkyne Cycloaddition Directly Observed by Electrospray Ionization

Abstract: The mechanism of the CuAAC reaction has been investigated by electrospray ionization mass spectrometry (ESI-MS) using a combination of the neutral reactant approach and the ion-tagging strategy. Under these conditions, for the first time, putative dinuclear copper intermediates were fished out and characterized by ESI(+)-MS/MS. New insight into the CuAAC reaction mechanisms is provided and a catalytic cycle is proposed. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) (1) can be seen as the most prominent example of the so-called click chemistry. (2) The robustness of this Cu I - mediated transformation has boosted its interest, making it the most straightforward strategy for the regiospecific prep- aration of 1,2,3-triazoles. To date, this reaction is widely employed in organic synthesis, medicinal chemistry, surface and polymer science, and in bioconjugation strategies. (1c, d) Despite the apparent simplicity and widespread use of the reaction, its mechanism has emerged as particularly complex, being still a matter of debate. Cu I stands out as the only active oxidation state for the catalyst. A second-order rate law with respect to Cu I has been experimentally observed. (3-5) Others observed both first-order and third-order kinetics, but relate both observations to a common binuclear Cu mechanism. (6) Moreover, DFT calculations of the reaction pathway showed a more favorable energetic pathway when dinuclear Cu I intermediates are considered, as compared to mononuclear intermediates. (7-9) However, as only mononuclear copper acetylides and copper triazolides can be isolated, (10) the implication of truly dinuclear Cu I intermediates could not be claimed out of any doubt, until a paper by Fokin et al. appeared. (11) Indeed, they inferred for the CuAAC the