Terminal Azide Research Articles

Enhanced copper-catalyzed “click” reaction between homopolymers with terminal azide and alkyne groups in the presence of water

AbstractWe report here that the efficiency of the click chemistry between the terminal azide and alkyne groups of different polymer chains could be drastically increased with the addition of an optimum amount of water into a reaction system. That is, the efficiency was only slightly promoted by the addition of a small amount of water into the reaction mixture. However, the reaction efficiency was increased dramatically near the water volume fraction to lead the reaction mixture into nanosized phase separation. Further increasing in water content caused the polymer(s) to undergo macroscopic phase separation and the click reaction efficiency was decreased once again. The enhanced efficiency of click coupling reaction including conversion and rate was also demonstrated via in-situ 1H-NMR. The reaction kinetics as well as reaction rate constant for these reaction system with typical water content were also evaluated. This finding on enhanced click reaction is of practical value, because click reactions in polymer synthesis are generally more difficult to be carried out and proceed relative slowly at low yield in most case because of the strong steric hindrance effect from “large and long” polymer chains, as compared to “click” reactions which are employed for preparation of the low molecular weight organic compounds.

Copper on Iron: Catalyst and Scavenger for Azide–Alkyne Cycloaddition

Dipolar cycloaddition of terminal alkynes and azides catalyzed by the Cu/Fe bimetallic system is reported. In the presence of a readily accessible nanosized copper source, the cycloaddition reaction can be easily achieved at ambient temperature with high efficiency. The product obtained from the reaction catalyzed by Cu/Fe contains significantly lower copper contaminants compared to various active homogeneous copper complexes. Iron not only behaves as support for copper, but acts as a redox scavenger, and reduces the copper contamination of the organic product.

Synthesis and Micropatterning of Photocatalytically Reactive Self-Assembled Monolayers Covalently Linked to Si(100) Surfaces via a Si–C Bond

Selective generation of an amine-terminated self-assembled monolayer bound to silicon wafers via a silicon-carbon linkage was realized by photocatalytically reducing the corresponding azide-terminated, self-assembled monolayers (Az-SAMs). The Az-SAM was obtained by thermal deposition of 11-chloroundecene onto a hydrogen-terminated silicon wafer followed by nucleophilic substitution of the chloride with the azide ion in warm N,N'-dimethylformamide (DMF). The presence of the terminal azide group on the SAM was confirmed by reflection absorption infrared spectroscopy (RAIRS), by X-ray photoelectron spectroscopy (XPS), and by detecting the formation of a triazole upon reaction of the azide with an activated alkyne. The desired terminal amine groups were generated by photocatalytic reduction of the Az-SAM with cadmium selenide quantum dots (CdSe Qdots) using λ > 400 nm. Analysis of the reduced SAM by XPS gave results that were consistent with those obtained with an amine-terminated surface obtained by reducing the Az-SAM with triphenylphosphine. To demonstrate the feasibility of using the Az-SAM for surface patterning, a sample was coated with adsorbed CdSe Qdots and exposed to the output of a diode laser at λ = 407 nm through a micropatterned mask. Using a SEM, the pattern formed in this manner was revealed after removing the CdSe Qdots and subsequently adsorbing 10 nm gold nanoparticles (AuNPs) to the positively charged terminal-amine groups. The formation of the pattern by CdSe-photocatalyzed reduction of the azide demonstrates a novel route to create features by selective modification of organic monolayers on silicon wafers.

Azide- and Alkyne-Functionalised α- and β3-Amino Acids

The synthesis and full characterisation of bifunctional β³-amino acids that have side chains functionalised with terminal azides (<i>S</i>)-<b>4</b> and (<i>R</i>)-<b>4</b> or acetylenes <b>5</b> and <b>6</b> is reported for the first time. The building blocks incorporate a turn-inducing β³-segment and a side chain that can be functionalised further, for example, through copper-catalysed Huisgen cycloaddition. Moreover, the corresponding α-amino acids <b>1</b> and <b>3</b> have been synthesised and characterised. All amino acid building blocks were of high optical purity as demonstrated by derivatisation and subsequent NMR analysis.

Hetero-metallic trinuclear nickel(II)–cadmium(II) complexes of a salicylaldimine ligand with thiocyanate, cyanate and azide ions: Isolation of a pair of polymorphs with thiocyanate ion

Four new trinuclear hetero-metallic nickel(II)–cadmium(II) complexes [(NiL)2Cd(NCS)2] (1A and 1B), [(NiL)2Cd(NCO)2] (2) and [(NiL)2Cd(N3)2] (3) have been synthesized using [NiL] as a so-called “ligand complex” (where H2L=N,N′-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Crystal structure analyses reveal that all four complexes contain a trinuclear moiety in which two square planar [NiL] units are bonded to a central cadmium(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1A and 1B), cyanate (in 2) and azide (in 3). Complexes 1A and 1B have the same molecular formula but crystallize in very different monoclinic unit cells and can be considered as polymorphs. On the other hand, the two isoelectronic complexes 2 and 3 are indeed isomorphous and crystallize only in one form. Their conformation is similar to that observed in 1A.

Selective Formation of 1,4-Disubstituted Triazoles from Ruthenium-Catalyzed Cycloaddition of Terminal Alkynes and Organic Azides: Scope and Reaction Mechanism

The catalytic activity of a series of ruthenium complexes lacking cyclopentadienyl ligands has been evaluated for the cycloaddition of terminal alkynes and azides to give selectively 1,4-disubstitu...

RuH2(CO)(PPh3)3Catalyzed Selective Formation of 1,4-Disubstituted Triazoles from Cycloaddition of Alkynes and Organic Azides

The ruthenium hydride complex RuH(2)(CO)(PPh(3))(3) was found to be an effective catalyst for the cycloaddition reactions of terminal alkynes and azides. In the presence of RuH(2)(CO)(PPh(3))(3), various azides reacted with a range of terminal alkynes to produce 1,4-disubstituted 1,2,3-triazoles with 100% selectivity and moderate to excellent yields.

Bis[μ-1-hexyl-3-(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl)urea]bis(azidosodium) chloroform disolvate

In the title compound, [Na2(N3)2(C21H34N2O6)2]·2CHCl3, the sodium cation is hepta­coordinated by five O atoms of the crown ether unit of the 1-hexyl-3-(2,3,5,6,8,9,11,12-octa­hydro-1,4,7,10,13-benzopenta­oxacyclo­penta­decin-15-yl)urea (L) ligand, the O atom of the urea group of the second, symmetry-related L ligand, and one N atom of the azide anion. The experimentally determined distance 2.472 (2) Å between the terminal azide N atom and the sodium cation is substanti­ally longer than that predicted from density functional theory (DFT) calculations (2.263 Å). The crown ethers complexing the sodium cation are related by an inversion centre and form dimers. The urea groups of the two L ligands are connected in a head-to-tail fashion by classical N—H⋯N hydrogen-bonding inter­actions and form a ribbon-like structure parallel to the b axis. Parallel ribbons are weakly linked through C—H⋯N, C—H⋯O and C—H⋯π inter­actions.

Efficient and Rapid Divergent Synthesis of Ethylene Oxide-Containing Dendrimers through Catalyst-Free Click Chemistry

Third and fourth generation ethylene oxide-containing dendrimers containing triazole units were prepared divergently through metal-free Huisgen 1,3-dipolar cycloaddition (“click”) reaction between activated disubstituted alkyne and terminal azide groups. The growth of the dendrimers was achieved in high yield with minimal purification effort and without the participation of toxic metal or excess of reagents. Preliminary in vitro testing on different cell lines indicates that this series of dendrimers is very promising for bio-related applications.

Rapid Preparation of Multifunctional Surfaces for Orthogonal Ligation by Microcontact Chemistry

Microcontact chemistry has been applied to patterned glass and silicon substrates by successive reaction of unprotected and monoprotected heterobifunctional linkers with alkene-terminated self-assembled monolayers (SAMs) to produce bi-, tri-, and tetrafunctional surfaces. Photochemical microcontact printing of an azide thiol linker followed by immobilization of an acid thiol linker on an undecenyl-terminated SAM results in a well-defined, micropatterned surface with terminal azide, acid, and alkene groups. Biologically relevant molecules (biotin, carbohydrates) have been selectively attached to the surface by means of orthogonal ligation chemistry, and the resulting microarrays display selective binding to fluorescently labeled proteins. An orthogonally addressable, tetrafunctional surface (azide, acid, alkene, and amine) can be prepared by an additional printing step of a tert-butyloxycarbonyl (Boc)-protected alkyne amine linker on the azide structures by using the copper(I)-catalyzed azide-alkyne Huisgen cycloaddition and subsequent removal of the protective group.

Fluorescent cellulose nanocrystals via supramolecular assembly of terpyridine-modified cellulose nanocrystals and terpyridine-modified perylene

Due to their natural origin, biocompatibility, and non-toxicity, cellulose nanocrystals are promising candidates for applications in nanomedicine. Highly fluorescent nanocellulosic material was prepared via surface modification of cellulose nanocrystals with 2,2′:6′,2″-terpyridine side chains followed by supramolecular assembly of terpyridine-modified perylene dye onto the terpyridine-modified cellulose nanocrystals (CTP) via RuIII/RuII reduction. The prepared terpyridine-modified cellulose-RuII-terpyridine-modified perylene (CTP-RuII-PeryTP) fluorescent nanocrystals were characterized using cross-polarized/magic angle spin 13C nuclear magnetic resonance (CP/MAS 13C NMR), Fourier transform infrared (FTIR), UV–visible, and fluorescence spectroscopy. In addition, further self-assembly of terpyridine units with azide functional groups onto CTP-RuII-PeryTP was possible via repeating the RuIII/RuII reduction protocol to prepare supramolecular fluorescent nanocrystals with azide functionality (CTP-RuII-PeryTP-RuII-AZTP). The prepared derivative may have potential application in bio-imaging since the terminal azide groups can be easily reacted with antigens via “Click” chemistry reaction.

One-pot synthesis of photosensitive dendrimer-like polystyrenes from simultaneous copper(I)-catalyzed azide-alkyne cycloaddition and atom transfer radical polymerization

Dendrimer-like polystyrenes (PSs) containing azobenzene moieties/core were prepared by one-pot copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) and atom transfer radical polymerization (ATRP) in the presence of PS with terminal azide groups, styrene monomers, 2,4-dibromoisobutyrate-4′-propynyloxyazobenzene, copper(I) bromide and ligand. The successful preparation of the dendrimer-like PSs was confirmed using gel permeation chromatography and 1H NMR and Fourier transform infrared spectroscopy. The dendrimer-like PSs prepared from one-pot CuAAC and ATRP exhibit a well-defined and controlled molecular structure in both whole macromolecules and the branches, which is attributed to the controlled character of ATRP and the quantitative yield of click chemistry. The dendrimer-like PSs prepared also exhibit good photo-isomerization properties due to the incorporation of azobenzene units within the dendrimers. Copyright © 2012 Society of Chemical Industry

An unprecedented “linear-bent” isomerism in tri-nuclear Cu2IIZnII complexes with a salen type di-Schiff base ligand

Two new trinuclear hetero-metallic copper(II)-zinc(II) complexes [(CuL)(2)Zn(N(3))(2)] (1A and 1B) have been synthesized using [CuL] as a so-called "metalloligand" (where H(2)L = N,N'-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Complexes 1A and 1B have the same molecular formula but crystallize in different crystal systems (triclinic for 1A and monoclinic for 1B) with space group P1 for 1A and P2(1)/c for 1B. 1A is an angular trinuclear species, in which two terminal four-coordinate square planar "metalloligand" [CuL] are coordinated to a central Zn(II) through double phenoxido bridges. The Zn(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually cis nitrogen atoms of terminal azide ions. In complex 1B, in addition to the double phenoxido bridge, the two terminal Cu(II) ions are linked to the central Zn(II) via a μ(-l,l) azido bridge giving rise to a square pyramidal environment around the Cu(II) ions and consequently the structure becomes linear. These two species can be considered as "linear-bent" isomers. EPR spectra and ESI mass spectra show that the two isomers are identical in solution. The DFT calculation reveals that the energy of 1A is 7.06 kcal mol(-1) higher than that of 1B. The existence of both isomers in the solid state suggests that crystal packing interactions in are more efficient and probably compensate for the difference in energy.

Synthesis of the first heterometalic star-shaped oxido-bridged MnCu3complex and its conversion into trinuclear species modulated by pseudohalides (N3−, NCS−and NCO−): Structural analyses and magnetic properties

A tetra-nuclear, star-shaped hetero-metallic copper(II)-manganese(II) complex, [{CuL(H(2)O)}(2)(CuL)Mn](ClO(4))(2) (1) has been synthesized by reacting the "complex as ligand" [CuL] with Mn(ClO(4))(2) where H(2)L is the tetradentate di-Schiff base derived from 1,3-propanediamine and 2-hydroxyacetophenone. Upon treatment with the polyatomic anions azide, cyanate, or thiocyanate in methanol medium, complex 1 transforms into the corresponding trinuclear species [(CuL)(2)Mn(N(3))(2)] (2), [(CuL)(2)Mn(NCO)(2)] (3) and [(CuL)(2)Mn(NCS)(2)] (4). All four complexes have been structurally and magnetically characterized. In complex 1 the central Mn(II) ion is encapsulated by three terminal [CuL] units through the formation of double phenoxido bridges between Mn(II) and each Cu(II). In complexes 2-4 one of the CuL units is replaced by a couple of terminal azide, N-bonded cyanate or N-bonded thiocyanate ions respectively and the central Mn(II) ion is connected to two terminal Cu(II) ions through a double asymmetric phenoxido bridge. Variable temperature magnetic susceptibility measurements show the presence of moderate ferrimagnetic exchange interactions in all the cases mediated through the double phenoxido bridges with J values (H = -JS(i)S(i + 1)) of -41.2, -39.8 and -12.6 cm(-1) (or -40.5 and -12.7 cm(-1) if we use a model with two different exchange coupling constants) for the tetranuclear MnCu(3) cluster in compound 1 and -20.0, -17.3 and -32.5 cm(-1) for the symmetric trinuclear MnCu(2) compounds 2-4. These ferrimagnetic interactions lead to spin ground states of 1 (5/2 - 3*1/2) for compound 1 and 3/2 (5/2 - 2*1/2) for compounds 2-4.

Evaluation of bicinchoninic acid as a ligand for copper(i)-catalyzed azide–alkyne bioconjugations

The Cu(I)-catalyzed cycloaddition of terminal azides and alkynes (click chemistry) represents a highly specific reaction for the functionalization of biomolecules with chemical moieties such as dyes or polymer matrices. In this study we evaluate the use of bicinchoninic acid (BCA) as a ligand for Cu(I) under physiological reaction conditions. We demonstrate that the BCA-Cu(I)-complex represents an efficient catalyst for the conjugation of fluorophores or biotin to alkyne- or azide-functionalized proteins resulting in increased or at least equal reaction yields compared to commonly used catalysts like Cu(I) in complex with TBTA (tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine) or BPAA (bathophenanthroline disulfonic acid). The stabilization of Cu(I) with BCA represents a new strategy for achieving highly efficient bioconjugation reactions under physiological conditions in many application fields.

Molecularly imprinted magnetic materials prepared from modular and clickable nanoparticles

We report a new strategy toward construction of functional composite materials for fast molecular separation. Molecularly imprinted nanoparticles containing surface-exposed alkyne groups were synthesized by one-pot precipitation polymerization. Magnetic Fe3O4 nanoparticles were first coated with a silica shell, and then modified with terminal azide groups. The two types of clickable nanoparticles were conjugated through a Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction to give composite magnetic particles, which displayed high molecular recognition selectivity and could be easily separated using a simple magnet.

Anomalous Staudinger reaction at intramolecular frustrated P–B Lewis pair frameworks

The FLP-mesityl azide addition products 5, formed by FLP-addition to the terminal azide nitrogen atom, undergo N-N bond cleavage in an unusual variant of the Staudinger reaction upon thermolysis or photolysis to give an internally borane stabilized [P]=NH phosphinimine and a dimethylindazole derivative.

ChemInform Abstract: Polysaccharides: The “Click” Chemistry Impact

AbstractReview: 82 refs.

Preparation of 18F-labeled peptides using the copper(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition

An optimized procedure for preparing fluorine-18 ((18)F)-labeled peptides by the copper-catalyzed azide-alkyne 1,3-dipolar cyloaddition (CuAAC) is presented here. The two-step radiosynthesis begins with the microwave-assisted nucleophilic (18)F-fluorination of a precursor containing a terminal p-toluenesulfonyl, terminal azide and polyethylene glycol backbone. The resulting (18)F-fluorinated azide-containing building block is coupled to an alkyne-decorated peptide by the CuAAC. The reaction is accelerated by the copper(I)-stabilizing ligand bathophenanthroline disulfonate and can be performed in either reducing or nonreducing conditions (e.g., to preserve disulfide bonds). After an HPLC purification, (18)F-labeled peptide can be obtained with a 31 ± 6% radiochemical yield (n = 4, decay-corrected from (18)F-fluoride elution) and a specific activity of 39.0 ± 12.4 Ci μmol(-1) within 77 ± 4 min.

Polysaccharides: The “Click” Chemistry Impact

Polysaccharides are complex but essential compounds utilized in many areas such as biomaterials, drug delivery, cosmetics, food chemistry or renewable energy. Modifications and functionalizations of such polymers are often necessary to achieve molecular structures of interest. In this area, the emergence of the “click” chemistry concept, and particularly the copper-catalyzed version of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides, had an impact on the polysaccharides chemistry. The present review summarizes the contribution of “click” chemistry in the world of polysaccharides.