Cycloaddition Click Reaction Research Articles

Click Chemistry-Assisted Synthesis of a β-d-Galactose-Targeted SiO2@RC Shell-Core Structure as a Nanoplatform for Metal-Based Complex Delivery.

A facile reversed-phase microemulsion method was used to synthesize shell-core nanospheres of SiO2@RCs (SiO2-encapsuled rare-earth metal complexes). β-d-Galactose was then grafted onto the surfaces of the nanospheres through the copper(I)-catalyzed azide-alkyne cycloaddition click reaction for targeted delivery. The chemical characteristics and surface profiles of the nanocarriers were investigated by Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy. A high-efficiency microwave synthesis method was applied to prepare five complex cores by the reaction of different rare-earth metal salts with two isomeric ligands, o-CPA (2-chlorophenoxyacetic acid) and m-CPA (3-chlorophenoxyacetic acid). The crystal structures of the five synthesized RC cores were confirmed through X-ray diffraction, which revealed the formulas of five RCs, [Dy( o-CPA)3(H2O)]·H2O RC1, [Ho( o-CPA)3(H2O)]·H2O RC2, 2[Er( m-CPA)3(H2O)]·3H2O RC3, 2[Gd( m-CPA)3(H2O)]·3H2O RC4, and [Ce2( m-CPA)6(H2O)3]·2H2O RC5. An in vitro cell study revealed that all RCs exhibited certain anticancer activities. RC2, in particular, showed the strongest cytotoxicity against HepG2 cells. The enhanced cell permeability and drug retention considerably improved the cytotoxicity of all SiO2@RC2-gal relative to that of RC2. The selective uptake of the β-d-galactose-conjugated nanospheres by HepG2 cells through mechanisms mediated by cell surface receptors resulted in fewer side effects on extrahepatic tissues. Our contribution provides a novel design concept of a target SiO2@RCs-gal nanocarrier for delivering affordable antitumor complexes in cancer therapy.

Turning Off Transcription with Bacterial RNA Polymerase through CuAAC Click Reactions of DNA Containing 5-Ethynyluracil.

Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction in the major groove of DNA containing 5-ethynyluracil (UE ) with azides was used for turning off sequence-specific protein-DNA interactions. The concept was first demonstrated on switching off cleavage of short modified DNA by restriction endonuclease BamHI-HF. Finally, DNA template containing UE was used for in vitro transcription with E. coli RNA polymerase and the transcription was turned off by CuAAC with 3-azidopropane-1,2-diol or 3-azido-7-hydroxycoumarin.

Design, synthesis and evaluation of novel multi-target-directed ligands for treatment of Alzheimer's disease based on coumarin and lipoic acid scaffolds

A novel series of coumarin-lipoic acid conjugates were synthesized via cycloaddition click reaction to find out new multi-target-directed ligands (MTDLs) for treatment of Alzheimer's disease (AD). All of synthesized compounds were screened for neuroprotective and anti-cholinesterase activities. Based on primary screening, two compounds (5 and 11) were subjected to further biological evaluations. In particular, compound 11 which was the most potent AChE inhibitor showed good inhibitory effect on Aβ-aggregation and intracellular ROS (reactive oxygen species) formation, as well as the ability of selective bio-metal chelation and neuroprotection against H2O2- and Aβ1-42-induced cytotoxicity. In the light of these results, the applied hybridization approach introduced new promising lead compound with desired multifunctional properties, being useful in the treatment of Alzheimer's disease.

Ternary mixed-mode silica sorbent of solid-phase extraction for determination of basic, neutral and acidic drugs in human serum.

In this study, a ternary mixed-mode silica sorbent (TMSS) with octamethylene, carboxyl, and amino groups was prepared via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction and a subsequent reduction of azide to primary amine. While used in solid-phase extraction (SPE), the retention behavior of TMSS towards a total of nine kinds of basic, neutral, and acidic drugs was investigated in detail. The results revealed that hydrophobic, ion-exchange interaction, and electrostatic repulsion between TMSS and the analytes were closely related to the retention behavior of TMSS. Besides, the log Kow value of the analyte was also a factor influencing the retention behavior of analytes on TMSS. The nine analytes could be retained by TMSS simultaneously and then, were eluted into two fractions according to the acid-base property of the analytes for further determinations. The acidic and neutral analytes were in one fraction, and the basic ones in the other fraction. When used to treat the human serum spiked with the nine drugs, TMSS offered higher recoveries than BakerBond CBA and comparable recoveries to Oasis WCX. It should be noted TMSS had better purifying capability for human serum than Oasis WCX. Under the optimized SPE conditions, a method of SPE hyphenated to high-performance liquid chromatography-ultraviolet detection (HPLC-UV) for determination of the basic, neutral, and acidic drugs spiked in human serum was established. For the nine drugs, the linear ranges were all between 5.0 and 1000μgL-1 with correlation coefficients (R2) above 0.9990, and the limits of detection (LODs) were in the range of 0.8-2.3μgL-1. The intra-day and inter-day relative standard deviations (RSDs) were less than 5.3 and 8.8%, respectively. Graphical abstract Treating drugs in human serum by SPE with ternary mixed-mode silica sorbent.

Polyurethane tethering natural antibacterial substances for catheter applications

Antibacterial central venous catheters (CVC) have been in great demand in recent years. However, biomedical polyurethane (PU), the most used polymer for CVC extrusion, lacks antibacterial properties, surface coating after catheter extrusion or additives is generally required for fabricating antibacterial CVC. To develop antibacterial PU for CVC extrusion, a natural derived substance, benzoic acid, was thus grafted onto a PU with pendant alkynyl groups successfully through Cu(I)-catalyzed azide-alkyne cycloaddition click reaction in this research. The synthesized PU tethering benzoic acid (PUB) was fabricated into catheter which displays a suitable strength for CVC application. PUB tethering benzoic acid over 2 mmol/g has proved good antibacterial properties against Escherichia coli and Staphylococcus aureus based on a bacterial colony forming units test, and bone mesenchymal stem cells proliferation on PUB also demonstrate good cell compatibilities, suggesting PUB a promising polymer for CVC extrusion.

Ring-Expanded N-Heterocyclic Carbenes for Copper-Mediated Azide-Alkyne Click Cycloaddition Reactions.

A series of well‐defined copper(I) complexes bearing ring‐expanded N‐heterocyclic carbene (NHC) ligands has been applied to the azide–alkyne cycloaddition reaction. The obtained results notably showed that the six‐membered NHC ligands outperform well‐established five‐membered ones. [CuI(Mes‐6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.

Design, Synthesis, Antioxidant and Antibacterial Activities of Novel 2-((1-Benzyl-1H-1,2,3-Triazol-4-yl)methyl)-5-(2HChromen- 3-yl)-2H-Tetrazoles

1,4-Disubstituted 1,2,3-triazole derivatives of 2H-chromene-3-tetrazoles synthesized regioselectively by copper(I)-catalyzed alkyne–azide cycloaddition (CuAAC) click reaction were characterized by 1HNMR, 13C NMR, IR, and mass spectral data. These derivatives were screened for in vitro antioxidant activity using DPPH radical, H2O2 scavenging, and iron chelating activity methods and also evaluated for in vitro antibacterial activities against E. coli and S. aureus bacterial strains. The MIC and IC50 values for all these compounds were found to match the docking scores and relevant binding energies with the receptor active sites. These results allows one to consider the compounds as leads for a new generation of antioxidant and antibacterial agents.

Anchoring TGF-β1 on biomaterial surface via affinitive interactions: Effects on spatial structures and bioactivity.

Protein adsorption on biomaterial surfaces is clinically applied to increase therapeutic effects; however, this adsorption is possibly accompanied by conformational changes and results in loss of protein bioactivity or adverse reactions. In this research, a transforming growth factor β1 (TGF-β1) affinitive peptide HSNGLPL was grafted onto biopolymer surface to stabilize TGF-β1 spatial conformation after adhesion. The peptide with azide end group was combined with the propynyl pendant group on polyurethane via copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The final polymer was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy, which indicated that the affinitive peptide was introduced to the polymer. Quartz crystal microbalance with dissipation (QCM-D) was performed to monitor TGF-β1 adsorption and desorption on the surfaces coated with polyurethane with and without peptide combination. Results showed that TGF-β1 adhered on polyurethane surface and formed a compact and rigid layer. This layer showed spatial structural change but presented a loose and diffuse layer on the peptide-grafted polyurethane surface, indicating stable spatial conformation after adherence. Similar regulations were observed on the two surfaces where BSA layer was coated in advance. In vivo animal experiments revealed that immune reactions and tissue regenerations occurred earlier on peptide-modified polyurethane than on polyurethane, which did not undergo peptide grafting. This finding confirmed that affinitive interactions may preserve TGF-β1 bioactivity on polymer surface after adsorption.

Post modification of acetylene functional poly(oxindole biphenylylene) by photoinduced CuAAC

A novel strategy to obtain side chain modified poly(oxindole biphenylylene) (POXI) by photoinduced copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction is described. In the first step, an alkyne-functionalized poly(oxindolebiphenylylene) (POXI-alkyne) is synthesized by superacid-catalyzed condensation of isatin with aromatic hydrocarbons. Subsequently, poly(ethylene glycol) methyl ether (Me-PEG), 1-pyrenemethanol (Py-OH) and 1,3-dibromopropane (DBP) are functionalized by azide groups via simple nucleophilic substitution reaction. Visible-light-induced CuAAC reaction between POXI-alkyne and the corresponding azide functionalized click components employing dibenzoyldiethylgermane (DBDEG) as photoactivator resulted in the formation of POXI-PEG, POXI-Py and insoluble network, respectively. Successful modification of POXI was confirmed by the spectral, (1H NMR, FT-IR, Fluorescence), chromatographic (GPC) and thermal (DSC) investigations.

Hydrosoluble Cu(i)-DAPTA complexes: synthesis, characterization, luminescence thermochromism and catalytic activity for microwave-assisted three-component azide-alkyne cycloaddition click reaction.

New hydrosoluble and air-stable Cu(i) halide compounds, viz. [CuX(DAPTA)3] (1) and (2), and [Cu(μ-X)(DAPTA)2]2 (3) and (4) (X = Br or I, in this order), have been prepared by reacting Cu(i) halide (i.e., bromide or iodide) with 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) under mild conditions. They represent the first examples of Cu(i) halide complexes bearing the DAPTA ligand, which have been fully characterized by elemental analysis, IR, 1H, 13C{1H} and 31P{1H} NMR spectroscopies, ESI-MS+ and, for 4, also by single-crystal X-ray diffraction (SCXRD) analyses. Complexes 1-4 are efficient catalysts for the one-pot microwave assisted three-component (terminal alkyne, organic halide and NaN3) Huisgen cycloaddition reaction in aqueous media to afford the corresponding disubstituted triazoles. The catalysis proceeds with a broad alkyne substrate scope and according to "click rules". Photophysical studies of compound 4 showed an unusual reversible thermochromic behaviour exhibiting a blue emission at 298 K due to the halide-to-ligand charge transfer (3XLCT) and a red emission at 77 K because of the {Cu2I2} unit.

Poly(thymine)-Templated Selective Formation of Copper Nanoparticles for Alkaline Phosphatase Analysis Aided by Alkyne–Azide Cycloaddition “Click” Reaction

Alkaline phosphatase (ALP) is closely associated with many health disorders like liver diseases and bone diseases, which is a routine index of blood examination. In the current study, a fluorescent method for the detection of ALP is established based on poly(thymine)-templated selective formation of copper nanoparticles (CuNPs) and alkyne–azide cycloaddition “click” reaction. Generally, in the presence of ALP, l-ascorbic acid-2-phosphate is hydrolyzed, and the generated ascorbic acid reduces Cu2+ to Cu+, which further catalyzes alkyne–azide cycloaddition click reaction between two poly(thymine) segments. The two DNA fragments (18 thymine) are thus ligated, forming the DNA template (36 thymine), which is effective for the synthesis of CuNPs. Experimental results show that the fluorescence response of CuNPs increases with higher ALP concentration from 0.1 to 40 U/mL, and the limit of detection is as low as 0.05 U/mL. Furthermore, the proposed method is highly selective and is capable of detecting ALP in bio...

Synthesis of biologically active nickelocenyl–amino acid conjugates using 1,3-dipolar cycloaddition click reactions

Herein we present the study of synthesis of novel bio-organometallic conjugates using 1,3-dipolar cycloaddition click reactions. Amino acid azides such as 4-azido-D-homoalanine, 5-azido-D-ornithine and 6-azido-D-lysine were reacted with ethynyl nickelocene to synthesize nickelocenyl-homoalanine conjugate (1), nickelocenyl-ornithine conjugate (2), and nickelocenyl–lysine conjugate (3) using Cu(I) compounds as catalysts. This synthetic strategy resulted in high yields (68–76%) of nickelocene-amino acid conjugates. Structure characterization of these purified bio-organometallic conjugates was performed using FT-IR, 1H, and 13C NMR spectroscopy. Antibacterial and antifungal activities of these products were tested against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Streptococcus pneumonia, Alternaria alternate, Aspergillus flavus, and Aspergillus niger using the disc diffusion method. Rifampicin (antibacterial) and fluconazole (antifungal) were used as standard drugs. Results of antimicrobial activities were found to be promising.

Longitudinally Controlled Modification of Cylindrical and Conical Track-Etched Poly(ethylene terephthalate) Pores Using an Electrochemically Assisted Click Reaction.

In this study, the longitudinally controlled modification of the inner surfaces of poly(ethylene terephthalate) (PET) track-etched pores was explored using an electrochemically assisted Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. Cylindrical or conical PET track-etched pores were first decorated with ethynyl groups via the amidation of surface -COOH groups, filled with a solution containing Cu(II) and azide-tagged fluorescent dye, and then sandwiched between comb-shaped and planar gold electrodes. Cu(I) was produced at the comb-shaped working electrode by the reduction of Cu(II); it diffused along the pores toward the other electrode and catalyzed CuAAC between an azide-tagged fluorescent dye and a pore-tethered ethynyl group. The modification efficiency of cylindrical pores (ca. 1 μm in diameter) was assessed from planar and cross-sectional fluorescence microscope images of modified membranes. Planar images showed that pore modification took place only above the teeth of the comb-shaped electrode with a higher reaction yield for longer Cu(II) reduction times. Cross-sectional images revealed micrometer-scale gradient modification along the pore axis, which reflected a Cu(I) concentration profile within the pores, as supported by finite-element computer simulations. The reported approach was applicable to the asymmetric modification of cylindrical pores with two different fluorescent dyes in the opposite directions and also for the selective visualization of the tip and base openings of conical pores (ca. 3.5 μm in base diameter and ca. 1 μm in tip diameter). The method based on electrochemically assisted CuAAC provides a controlled means to fabricate asymmetrically modified nanoporous membranes and, in the future, will be applicable for chemical separations and the development of sequential catalytic reactors.

CuAAC-Based Click Chemistry in Self-Healing Polymers.

Click chemistry has emerged as a significant tool for materials science, organic chemistry, and bioscience. Based on the initial concept of Barry Sharpless in 2001, the copper(I)-catalyzed azide/alkyne cycloaddition (CuAAC) reaction has triggered a plethora of chemical concepts for linking molecules and building blocks under ambient conditions, forming the basis for applications in autonomous cross-linking materials. Self-healing systems on the other hand are often based on mild cross-linking chemistries that are able to react either autonomously or upon an external trigger. In the ideal case, self-healing takes place efficiently at low temperatures, independent of the substrate(s) used, by forming strong and stable networks, binding to the newly generated (cracked) interfaces to restore the original material properties. The use of the CuAAC in self-healing systems, most of all the careful design of copper-based catalysts linked to additives as well as the chemical diversity of substrates, has led to an enormous potential of applications of this singular reaction. The implementation of click-based strategies in self-healing systems therefore is highly attractive, as here chemical (and physical) concepts of molecular reactivity, molecular design, and even metal catalysis are connected to aspects of materials science. In this Account, we will show how CuAAC reactions of multivalent components can be used as a tool for self-healing materials, achieving cross-linking at low temperatures (exploiting concepts of autocatalysis or internal chelation within the bulk CuAAC and systematic optimization of the efficiency of the used Cu(I) catalysts). Encapsulation strategies to separate the click components by micro- and nanoencapsulation are required in this context. Consequently, the examples reported here describe chemical concepts to realize more efficient and faster click reactions in self-healing polymeric materials. Thus, enhanced chain diffusion in (hyper)branched polymers, autocatalysis, or internal chelation concepts enable efficient click cross-linking already at 5 °C with a simultaneously reduced amount of Cu(I) catalyst and increased reaction rates, culminating in the first reported self-healing system based on click cycloaddition reactions. Via tailor-made nanocarbon/Cu(I) catalysts we can further improve the click cross-linking reaction in view of efficiency and kinetics, leading to the generation of self-healing graphene-based epoxy nanocomposites. Additionally, we have designed special CuAAC click methods for chemical reporting and visualization systems based on the detection of ruptured capsules via a fluorogenic click reaction, which can be combined with CuAAC cross-linking reactions to obtain simultaneous stress detection and self-healing within polymeric materials. In a similar concept, we have prepared polymeric Cu(I)-biscarbene complexes to detect (mechanical) stress within self-healing polymeric materials via a triggered fluorogenic reaction, thus using a destructive force for a constructive chemical response.

Multifunctional triazolylferrocenyl Janus dendron: Nanoparticle stabilizer, smart drug carrier and supramolecular nanoreactor

Owing to their unique broken symmetry, amphiphilic Janus dendrimers and dendons provide fascinating properties for material, biological, pharmaceutical and biomedical applications. The integration of various organometallic moieties into these macromolecules will further offer the opportunity to form complex and intelligent architectures and materials. Here, we report a novel, simple and multifunctional Janus dendron containing redox‐reversible hydrophobic ferrocene (Fc) unit, complexing‐effective 1,2,3‐triazole ligand and biocompatible hydrophilic triethylene glycol termini. Silver and gold nanoparticles were firstly successfully prepared by using the Janus dendron as the reducing agent of Au(III) and Ag(I), and the stabilizer of the corresponding nanoparticles. The redox response of the Fc moiety was then employed to trigger the release of model drug, rhodamine B, encapsulated in supramolecular micelles formed by the self‐assembly of the Janus dendron. Finally, the precise and excellent metal‐complexing ability of the triazole group in this dendron was fully utilized to stabilize a water‐soluble Cu(I) catalyst, forming supramolecular nanoreactors for the catalysis of the copper(I)‐catalyzed azide alkyne cycloaddition click reaction in only water. The multifunctional characteristics of this dendron highlight the potential for organometallic Janus dendrimers and dendrons in the fields of functional materials and nanomedicines.

Dynamic covalent chemistry enables formation of antimicrobial peptide quaternary assemblies in a completely abiotic manner.

Naturally occurring peptides and proteins often use dynamic disulfide bonds to impart defined tertiary/quaternary structures for the formation of binding pockets with uniform size and function. Although peptide synthesis and modification are well established, controlling quaternary structure formation remains a significant challenge. Here, we report the facile incorporation of aryl aldehyde and acyl hydrazide functionalities into peptide oligomers via solid-phase copper-catalysed azide-alkyne cycloaddition (SP-CuAAC) click reactions. When mixed, these complementary functional groups rapidly react in aqueous media at neutral pH to form peptide-peptide intermolecular macrocycles with highly tunable ring sizes. Moreover, sequence-specific figure-of-eight, dumbbell-shaped, zipper-like and multi-loop quaternary structures were formed selectively. Controlling the proportions of reacting peptides with mismatched numbers of complementary reactive groups results in the formation of higher-molecular-weight sequence-defined ladder polymers. This also amplified antimicrobial effectiveness in select cases. This strategy represents a general approach to the creation of complex abiotic peptide quaternary structures.

Synthesis, characterization and surface properties of star-shaped polymeric surfactants with polyhedral oligomeric silsesquioxane core

Star-shaped amphiphilic polymeric surfactants comprising a hydrophobic polyhedral oligomeric silsesquioxane (POSS) core and hydrophilic poly(ethylene glycol) (PEG) arms with various chain lengths are successfully synthesized using copper(I)-catalysed azide–alkyne cycloaddition (CuAAC) click reaction. Their chemical structures and molecular characteristics are clearly confirmed using Fourier transform infrared and 1H NMR spectroscopies and gel permeation chromatography, and no homopolymer is found after CuAAC click reaction. Aqueous solutions of these star-shaped polymers have been investigated using atomic force and transmission electron microscopies and dynamic light scattering studies and it is found that they can self-assemble into micelles. The sizes of the micelles can be adjusted by the length of the PEG arms, where longer chains not only lead to increased micelle sizes, but also reduce the contact angle values. Moreover, the melting points and root mean square roughness of the obtained star-shaped polymers are slightly increased on increasing the chain length of the PEG arms. © 2017 Society of Chemical Industry

Triazole/Triazine-Functionalized Mesoporous Silica As a Hybrid Material Support for Palladium Nanocatalyst.

Noble and precious metal catalysts are sought for their remarkable efficiency in catalyzing numerous reactions in heterogeneous phase. However, they are costly and require the development of high-surface-area supports that favor their strong immobilization, dispersion, and stability. Toward this end, mesoporous silica-based materials can be regarded as unique supports for nanometric-sized noble metal catalysts provided they are functionalized with appropriate ligands. In this work, mesoporous silica SBA-15 was prepared and modified with 3-azidopropyltriethoxysilane and then clicked with alkyne derivatives of 1,3,5-triazine complex ligand. The resulting hybrid material contains triazole and triazine moieties covalently bound to the mesoporous silica network. The triazole/triazine minidendron was immobilized through a 1,3-dipolar cycloaddition click reaction, which was monitored by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The heterocyclic ligand-functionalized SBA-15 material served as a hybrid reactive platform for in situ deposition of palladium nanoparticles whose size is 3.154 ± 0.49 nm as assessed by X-ray diffraction and confirmed by transmission electron microscopy. The catalytic performance of the final palladium-decorated hybrid triazole/triazine-functionalized SBA-15 support was evaluated in the model reduction of 4-nitrophenol to 4-aminophenol by catalytic hydrogenation and stoichiometric reduction. Excellent catalytic performances were achieved, with reduction rate constant (Kapp) of 16.8 × 10-3 s-1 for this model reaction. Moreover, the hybrid catalyst can be produced in high yield and recycled.

Clicked graphene oxide as new support for the immobilization of peroxophosphotungstate: Efficient catalysts for the epoxidation of olefins

Peroxophosphotungstate (PW) anions were successfully immobilized on the surface of clicked graphene oxides and used as heterogeneous catalysts for the epoxidation of various olefins using H2O2 as oxidant. Graphene oxide (GO) was functionalized with azide groups through both grafting and tethering methods Then, supported ionic liquids were formed on the surface of GO through the Cu (I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The clicked GO supported ionic liquids were used as appropriate supports for the immobilization of PW anions. Characterization of the prepared materials by various physicochemical methods showed that PW anions have been successfully immobilized on the surface of clicked GOs. Catalytic activities of these heterogeneous catalysts were evaluated in the epoxidation of olefins which showed that not only the catalysts are active, but also they could be reused several times without significant loss of their activities.

Molecular Weight Distribution of Living Chains in Polystyrene Prepared by Atom Transfer Radical Polymerization.

Living and dead chains of a polystyrene synthesized by atom transfer radical polymerization were separated and characterized by high performance liquid chromatography (HPLC), size exclusion chromatography (SEC), NMR, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The bromine end group in the living chain was quantitatively converted to a hydroxyl end group via first azidation and subsequent copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with propargyl alcohol. The living chains bearing a polar end group are fully resolved from the unmodified dead chains by HPLC separation using a bare silica stationary phase. Molecular weight distributions (MWD) of the living and dead chain are characterized by SEC and MALDI-MS. The MWD of the living chains is close to a Poisson distribution. Interestingly, the elution peak of the living chains in the HPLC separation split into two. The peak split is attributed to the diastereomeric structure of the chain end by NMR and MALDI-MS analyses.