Presence Of Tris Research Articles

Electrochemically mediated ATRP process intensified by ionic liquid: A “flash” polymerization of methyl acrylate

An electrochemically mediated atom transfer radical polymerization (eATRP) of methyl acrylate (MA) in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) ionic liquid (IL) was reported. Remarkably, the kinetic results revealed an extremely fast and well controlled polymerization in the presence of tris(2-(dimethylamino)ethyl)amine (Me6TREN). The monomer conversion reached more than 90% within a period of 300 s. Computational and simulation results indicated that the IL induced acceleration of polymerization can be attributed to the increased value of kt/kp2 compared to the associated literature value. Additionally, polymerizations under different conditions, including ligand types, monomer/IL ratios, catalyst loadings, and targeted degrees of polymerization were explored. All the kinetic plots suggested superfast polymerization rates with good control over molecular weight and dispersity. Furthermore, the livingness of MA polymerization was confirmed by chain extension experiment. This work provides a new insight into eATRP in IL through experimentation and simulation and thus enriches the knowledge of reaction features of eATRP.

The physical basis of fabrication of amyloid-based hydrogels by lysozyme.

The fabrication of amyloid-based hydrogels has attracted remarkable attention within the field of materials science and technology. These materials have a multitude of potential applications in the biomaterials field such as developing scaffolds for tissue engineering, drug delivery and hygiene products. Despite the potential new applications of these materials, the physical nature of their assembly is not well understood. In this study, we have investigated how the conformation of the amyloid precursor state (I) is formed and correlated with the assembly of amyloid-based hydrogels. A transparent hydrogel was fabricated at pH 7.4 by cooling of the temperature-induced unfolded state of hen egg white lysozyme (HEWL). The completely unfolded state (U) at the gelation concentration of HEWL was obtained around 90 °C in the presence of tris(2-carboxyethyl)phosphine (TCEP), with a TCEP/HEWL molar ratio of 4 : 1. The characterization of the hydrogel showed that it was composed of an amyloid fibril-like material. The physical nature of its assembly was examined in detail and it was found that the hydrogel formation reaction was a three-step, four-states process (U → I → F → H). We concluded that the properties of the pre-molten globule state (I) of the protein correlated only with the fibrillation process, whereas the assembly of the fibrils into an hydrogel was found to be almost independent of the I state. Thus, the study presented here provides a complete biophysical insight into the pathway of lysozyme hydrogel assembly.

Chemical Redox-Cycling for Improving the Sensitivity of Colorimetric Enzyme-Linked Immunosorbent Assay.

Herein, a redox-cycling was proposed to amplify the signal of enzyme-linked immunosorbent assay (ELISA), which was performed in a polystyrene microplate based on a classic sandwich-type. After the sandwich immunoreactions were finished, the alkaline phosphatase captured on a microplate triggered the hydrolyzation of l-ascorbic acid 2-phosphate to generate ascorbic acid (AA), which then reduced colorless tris(bathophenanthroline) iron(III) (Fe(BPT)33+) encapsulated in the micelle of TX-100 to pink red tris(bathophenanthroline) iron(II) (Fe(BPT)32+). In the presence of tris(2-carboxyethyl)phosphine, the oxidation product, dehydroascorbic acid, was transformed to AA quickly which then reduced Fe(BPT)33+ again and again, resulting in the generation of abundant Fe(BPT)32+ that could be read out conveniently by a commercial microplate reader or the naked eye. Because the negative charged TCEP with large size could hardly pass through the micelle, the reduction of Fe(BPT)33+ by TCEP directly was negligible. Experiment results for assay of alpha-fetoprotein (a model antigen) showed the cycling greatly improved the detection limit to 5 pg/mL, 2 orders of magnitude lower than that of conventional ELISA. The cycling also exhibited the advantages of simplicity and high reproducibility, implying its great potential for practical applications in biological and clinical diagnosis.

Self-healing dyes for super-resolution fluorescence microscopy

In recent years, optical microscopy techniques have emerged that allow optical imaging at unprecedented resolution beyond the diffraction limit. These techniques exploit photostabilizing buffers to enable photoswitching and/or the enhancement of fluorophore brightness and stability. A major drawback with the use of photostabilizing buffers, however, is that they cannot be used in live cell imaging. In this paper, we tested the performance of self-healing organic fluorophores, which undergo intramolecular photostabilization, in super-resolution microscopy examining both targeted (stimulated emission depletion (STED) microscopy) and stochastic readout (stochastic optical reconstruction microscopy (STORM)). The overall goal of the study was to identify dyes and conditions that lead to improved spatial and temporal resolution of both techniques without the need for mixtures of photostabilizing agents in the imaging buffer. As a result of previously shown superior performance, we identified an ATTO647N-photostabilizer conjugate as a potential candidate for STED microscopy. We have here characterized the photostability and resulting performance of this nitrophenylalanine (NPA) conjugate of ATTO647N on oligonucleotides in STED microscopy. We found that the superior photophysical performance resulted in optimal STED imaging and demonstrated that single-molecule fluorescent transients of individual fluorophores can be obtained with both the excitation- and STED-laser. In similar experiments, we also tested a nitrophenylacetic acid conjugate of STAR635P, another frequently used dye in STED microscopy, and present a characterization of its photophysical properties. Finally, we performed an analysis of the photoswitching kinetics of self-healing Cy5 dyes (containing trolox, cyclooctatetraene and NPA-based stabilizers) in the presence of Tris(2-carboxyethyl)phosphine and cysteamine, which are typically used in STORM microscopy. In line with previous work, we found that intramolecular photostabilization strongly influences photoswitching kinetics and requires careful attention when designing STORM-experiments. In summary, this contribution explores the possibilities and limitations of self-healing dyes in super-resolution microscopy of differing modalities.

Luminescent Silver–Copper “Hourglass” Hepta‐ and Decanuclear Alkynyl‐Phosphine Clusters

The heterometallic Ag–Cu compounds easily assemble from the corresponding metal triflates and alkynes in the presence of tris(diphenylphosphanyl)methane (tppm) under basic conditions. The formation of two types of cluster skeletons – heptanuclear [Ag6Cu(C2R)3{HC(PPh2)3}2(CF3SO3)3](CF3SO3) {R = C6H4‐4‐X (X = CF3, 1A; OMe, 2A; NMe2, 3A; NC10H20O4, 4A); CPh2OH, 5A} and decanuclear [Ag6Cu4(C2C6H4‐4‐X)8{HC(PPh2)3}2](CF3SO3)2 (X = CF3, 1B; H, 6B) species is governed by the electronic properties of the alkynyl ligands and the ratio of the starting components. All of the complexes, except 4A, were structurally characterized by single‐crystal XRD analysis. The solid‐state photophysical studies reveal room‐temperature phosphorescence (Φem = 0.3–42.5 %, λem = 556–756 nm), which is dependent on the electron‐donating ability of the alkynyl fragments and the nature of the metal core. Moreover, the geometry of the cluster framework is substantially influenced by the bridging counterions that, together with electronic modulation of organic blocks, allow near‐IR emission.

An investigation into nanohybrid states of europium (III) complex with hydroxyapatite nanocrystals

We synthesized the novel inorganic-organic nanohybrid systems in hydroxyapatite (HA) nanocrystal growth processes under the presence of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium (III) (EuTH) complex for the first time. The nanohybrid states were successfully controlled by the EuTH concentration to Ca ions in HA. The morphology of the HA was observed by a transmission electron microscope and the nanocrystalline aspect ratios were estimated to be 2.5–4.8. The segregated EuTH molecules on the HA nanocrystals covered over the a-plane in HA, leading to the effective crystal growth along with the uncovered c-plane. The luminescence properties of the nanohybrids were different from that of the EuTH itself in the solution and solid states, indicating the unique Eu3+ ion states on the HA nanocrystals because of the different ligand field symmetry. Moreover, the relative luminescence intensity ratio based on the 5D0 → 7F1 and 5D0 → 7F2 transitions in the nanohybrid became lower with increasing the EuTH concentration, suggesting that the hybridization lowered the coordination environment symmetry of Eu3+ ion. The luminescence intensity and quantum efficiency of the nanohybrids were higher than that of the EuTH itself. Therefore, the interaction at EuTH–HA interface as well as between EuTH–EuTH molecules significantly changed by the inorganic-organic hybridization under different EuTH concentrations. In future, the present hybridization technique can be applied for preparing the nanohybrids with various metallic complexes.

One-Pot Peptide Ligation-Oxidative Cyclization Protocol for the Preparation of Short-/Medium-Size Disulfide Cyclopeptides.

Native chemical ligation (NCL) employing the N-methylbenzimidazolinone (MeNbz) linker readily provided the linear precursor of a 16-mer peptide that is difficult to obtain by stepwise solid-phase peptide synthesis. NCL and the workup conditions were improved toward a protocol that allows for quantitative removal of the 4-hydroxymercaptophenol additive and subsequent formation of the disulfide bridge in the NCL cocktail by oxidation in air, tolerated by the presence of tris(hydroxypropyl)phosphine.

The Supramolecular and Coordination Chemistry of Cobalt(II) Extraction by Phosphinic Acids

A combination of mass spectrometry, DFT calculations and 31P{1H} NMR spectroscopy has been used to define the mode of action of the commercial cobalt extractant, bis(2,4,4‐trimethylpentyl)phosphinic acid (CYANEX®272, L1H) in Co recovery. The nature of the CoII complexes formed in the water‐immiscible phase is determined largely by the propensity of phosphinates to form strong interligand H‐bonds in the outer coordination sphere and also to form stable µ2‐Co–O–P–O–Co bridges. At low Co loading levels, the predominant species is the 4:1 complex, [Co(L1·L1H)2], in which coordinated neutral phosphinic acid ligands form strong H‐bonds to adjacent anionic phosphinates. At higher Co loading, oligomers such as [(L1·L1H)Co(L12Co)n(L1·L1H)] are formed with µ2‐phosphinate bridging, resulting in a substantial increase in the viscosity of the water‐immiscible phase. The presence of tris(2,4,4‐trimethylpentyl)phosphine oxide (L2) in the commercial formulation reduces the viscosity because its incorporation into oligomeric complexes such as [(L2)Co{L13CoL1CoL13Co}mL1] can terminate chains, resulting in a lower average molecular weight. The uptake of Zn by L1H shows a very similar dependence of viscosity on loading, and DOSY spectra and mass spectrometry demonstrate that higher molecular weight species are present at high Zn loading.

Cross-coupling of sulfonic acid derivatives via aryl-radical transfer (ART) using TTMSS or photoredox

The intramolecular cross-coupling of sulfonic acid derivatives occurs in the presence of tris(trimethylsilyl)silane (TTMSS) at room temperature and in air to form biaryl compounds. A photoredox-catalyzed procedure is also described. These protocols provide mild and convenient alternatives to standard tin-mediated reactions.

SET-LRP in the Neoteric Ethyl Lactate Alcohol.

Ethyl lactate (EtLa), a green and safe agrochemical solvent, is gifted with some properties that make it a good candidate for SET-LRP. It dissolves CuBr2, mediates an efficient disproportionation of CuBr in the presence of tris(2-(dimethylamino)ethyl)amine (Me6-TREN), and is capable to dissolve both aqueous (polar) and hydrocarbon (nonpolar) soluble monomers and polymers. Here, we report that EtLa is an excellent solvent for the Cu(0) wire-catalyzed SET-LRP to produce both hydrophilic and hydrophobic polyacrylates that exhibit precise chain end functionality. These results will expand the table of SET-LRP solvents with a new green member of biological origin that is also biodegradable and, therefore, are expected to contribute to continue expanding the use of SET-LRP in the field of biomacromolecules, bioconjugates, and other biology and medicine related disciplines.

Water Oxidation Reaction on Fe(III)-Cr(III) Mixed Oxide Under Electrochemical and Photochemical Condition

Introduction Water splitting into H2 and O2is attracted as one of useful strategies to produce hydrogen. This reaction is separated to two half redox reactions. 2H+ + 2e– → H2(0 V vs. RHE) 2H2O + 4h+ → O2 + 4H+(1.23 V vs. RHE) In general, water oxidation reaction is the rate determination step in water splitting because 4 electrons are involved in the reaction. Various catalysts aiming to enhance water oxidation have therefore been investigated. Metal oxides have been applied to such water oxidation catalysts for photochemical and electrochemical water oxidation. These metal oxide materials are also applied in the form of nanoparticles on the surface of a semiconductor, which are called cocatalyst. For example, IrO x , CoO x and RuO2are well known as not only bulk catalysts but also useful cocatalyst materials for water oxidation. Recently, our group has reported that Fe(III)-Cr(III) mixed oxide nanoparticles worked as cocatalysts for photocatalytic water oxidation, even better than pristine Fe2O3. However, the detail mechanism of the promotional effect caused by Cr(III) substitution has been still unclear. Nanoparticle cocatalysts loaded on a semiconductor photocatalyst worked as reaction sites for water oxidation or reduction by collecting holes/electron generated in the semiconductor. So they can be regarded as electrocatalysts for water splitting. To investigate the effect of Cr(III) substitution for Fe2O3, we focused material characteristics using bulk Fe(III) and Cr(III) mixed oxide particles as model compounds. In the present study, we examined the catalytic performance of Fe(III)-Cr(III) mixed oxide (Fe2-x Cr x O3) for water oxidation under photochemical and electrochemical condition as shown in Scheme 1, aiming to investigate the promotional effect of Cr(III) substitution for Fe2O3. Experimental Fe2-x Cr x O3 was prepared by a precipitation method. Appropriate amounts of Fe(NO3)3·9H2O and Cr(NO3)3·9H2O were dissolved in 20 mL of pure water. After addition of 1 mL NH3 aqueous solution, the precipitates were dried at 343 K for overnight. After grinding, the products were calcined at 823 K for 2 h after heating at 623 K for 2 h. Photochemical water oxidation activity was investigated under visible light irradiation (480 < λ < 500 nm) in the presence of tris(2,2’-bipyridyl)ruthenium(II) sulfate as a photosensitizer and sodium persulfate as a sacrificial electron acceptor. Electrochemical water oxidation was conducted in a phosphate buffered aqueous solution (pH 7.5) using three-electrode configuration, which consisted of a Ag/AgCl reference electrode, a Pt wire counter electrode and the Fe2–x Cr x O3/FTO working electrode. Result and discussion In photochemical water oxidation reaction, Fe2O3 showed catalytic performance for O2 evolution. Comparing to Fe2O3, the O2 evolution activity is dropped with increasing Cr ratio. Because the photochemical reaction proceeded on the surface of oxides, the property of Fe(III)-Cr(III) mixed oxide would have great influence on the O2 evolution activity. It is suggested that the catalytic activity that Fe2-x Cr x O3possessed for water oxidation is dropped by increasing the Cr ratio. Electrochemical water oxidation activity using Fe2-x Cr x O3/FTO electrode is investigated by controlled-potential electrolysis with gas detection and solution analysis. Faradaic efficiency of water oxidation and oxidative dissolution of Cr(III) to Cr(IV) during the electrolysis were determined by the amount of evolved O2 and dissolved Cr(IV) ion. Using Cr2O3 electrode, O2 was not detected, and the observed anodic current originated from oxidative dissolution of Cr(III). On the other hand, Fe2O3 electrode showed nearly 100% Faradaic efficiency for water oxidation, producing evolution of 0.2 μmol O2 after 50 min of electrolysis. In the case of Fe0.7Cr1.3O3 and Fe1.6Cr0.4O3, the amount of evolved O2 was improved about 5 times relative to Fe2O3, although Cr dissolution occurred to some extent (10–30% efficiencies). These results indicate that the activity of electrochemical water oxidation is improved by Cr substitution, although Cr dissolution occurred at the same time. Electrochemical impedance spectroscopy indicated that the promotional effect achieved by the Cr substitution resulted from improved charge transfer inside Fe2–x Cr x O3. We believe that this conclusion may be applied to nanoparticle-based photocatalytic overall water splitting system, where Fe2–x Cr x O3 nanoparticles were employed as water oxidation cocatalysts. Figure 1

Effect of biological buffers on the colloidal behavior of sodium dodecyl sulfate (SDS)

This study investigates the influence of three commonly used buffers (TRIS, TES and TAPS) on the conductivities and the colloidal behavior of the aqueous solutions containing a surfactant, sodium dodecyl sulfate (SDS). To find the effect of these buffers on the aggregation behavior of the aqueous SDS solutions, we experimentally determined the conductivities of the solutions containing different concentrations of SDS (0.002M–0.025M) in water and in 0.2M, 0.5M, and 1.0M TRIS, TES, and TAPS buffers, respectively, at 298.2K under atmospheric pressure. To get insight into the effect of the buffers on the aggregation behavior of the aqueous SDS solutions, the critical micelle concentration (CMC) values of the aqueous solutions are estimated from the experimental results of conductivity measurements. Interestingly, in comparison with the CMC of SDS in water, the presence of TRIS is found to increase the CMC, whereas the addition of TES or TAPS is found to decrease the CMC, especially at higher concentration (1.0M). The influence of the buffers on the CMC or aggregation of the SDS is further characterized by calculating various aggregation parameters such as the degree of ionization of the micelle (αm), the degree of counter ion binding in micelle (fm), and the standard Gibbs free energy of micellization (ΔG°m) for all the studied systems. Moreover, the outcomes from the conductivities measurement are reconfirmed by using the fluorescence probe analysis.

Access to an abnormal position of N-heterocyclic carbene-Mn(II)-complex by pyrazolyl phosphane with a labile P[sbnd]N bond

Reaction of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with MnCl2 in presence of tris(3,5 dimethyl-1-pyrazolyl)phosphane in toluene under thermolytic condition afforded a four-coordinated Mn(II)-NHC-phosphane complex, 1 which represents an unprecedented example of Mn(II)-NHC complex having a phosphane unit attached to the abnormal position (C4) of NHC. Compound 1 has been characterized by mass spectrometry, elemental analysis, and 31P NMR spectroscopic analysis. The molecular structure of 1 has been unambiguously characterized by single crystal X-ray diffraction analysis. Further, its experimental magnetic moment value of 5.7 μB indicates its stable sextet configuration (S = 5/2) which was further confirmed by DFT study.

Estimation of the Rate Constants for the 2x2-Electron ORR by Combining the Voltammograms of O2 and H2O2 Reduction Reactions

1. Introduction After the major discovery of the platinum based electro-catalysts for the cathodic reduction of the oxygen in the polymer electrolyte membrane fuel cells, commercialization of PEM fuel cells begins for automobile applications. However, it is necessary to replace the platinum-based electro-catalysts due to the high cost and scarcity by using other cheap and abundant non-precious metal catalysts. Fe-containing nitrogen-doped carbon catalysts (Fe-N-C) have been demonstrated as the potential alternative for the Pt-based catalysts for the last few years. However the poor understanding of the active sites of Fe-N-C catalysts prevents the development of highly active durable catalysts. Our recent studies[1] of the ORR on the Fe-N-C and N-C catalyst demonstrates that the ORR predominantly proceeds via the step wise reduction. Though the conventional Damjanovic model[2] (as shown in Scheme 1) concludes the direct 4-electron ORR, it actually overestimates the k 1 and underestimates the k 2 and k 3. Since the metal free catalysts are very active towards the reduction of O2 to H2O2, the role of the Fe on the reduction of H2O2 to H2O is studied and the estimated rate constants for the reduction of H2O2 to H2O will be used to estimate the real current for direct 4-electron ORR (I 1), 2-electron ORR to H2O2 (I 2) and 2-electron H2O2 reduction to H2O (I 3). 2. Methodology The precursor synthesis has been already discussed in the previous papers[3,4]. Briefly, the stoichiometric amount of pyromellitic acid dianhydride and 4,4’-oxydianiline was polymerized in the presence of tris(acetylacetonato) iron (III) (Fe(acac)3) yielding polyimides/Fe(acac)3 (the size of the polymer is controlled by maintaining low temperature during polymerization). The precursor was subjected to the multi-step pyrolysis reported earlier and the resulting catalyst is designated as Fe/PI. The Fe/PI-modified GC electrode with the loading density of 100 µg cm-2, carbon cloth and reversible hydrogen electrode was used as working, counter and reference electrodes, respectively. Both oxygen reduction reaction (ORR) and H2O2 reduction reaction was measured using rotating disk and rotating ring (Pt)-disk electrode voltammetry in 0.5 M H2SO4 solution. The H2O2 reduction rate constants (k 3) with potential were estimated using Koutecký‒Levich plot. From the ORR voltammograms, the value of I 1 , I2 and I 3 were determined by the following equations; I 2=0.5*{I r/N+ [(Ir/N)2(1+4k3/(Zω0.5)]0.5} (1) I 3=0.5*{-I r/N+ [(Ir/N)2(1+4k3/(Zω0.5)]0.5} (2) I 1=I d - [(Ir/N)2(1+4k3/(Zω0.5)]0.5 (3) where I d and I r represents disk and ring current of the oxygen reduction reaction, respectively, k 3 represents the rate constant of the H2O2 reduction reaction and ω refers the rotational speed of the ORR voltammogram. The value of the Z can be estimated from the kinematic viscosity (v) and diffusion coefficient (D) of H2O2 in 0.5 M H2SO4 (Z=0.62D 2/3 v -1/6) 3. Results and Discussion The H2O2-reduction steady-state voltammograms indicates that the Fe/PI catalyst is more active for both H2O2 oxidation and reduction indicated by the sharp intersection on the potential axis around 0.8 V vs. RHE. This simple method will be helpful separate the currents of many ORR voltammograms to describe the kinetics because this does not requires any parameters to be plotted against the rotation speed. The I 2 and I 3 values estimated using this method is significantly improved than the conventional Damjanovic model currents estimated form the rate constants (Figure 1). 4. Conclusion The newly developed methodology successfully separated I 1, I 2 and I 3 for ORR over Fe/N/C cathode catalysts. 5. Acknowledgements This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. 6.

Exploring the limitations of the Hantzsch method used for quantification of hydroxyl radicals in systems of relevance for interfacial radiation chemistry

In the presence of Tris or methanol, hydroxyl radicals in systems of relevance for interfacial radiation chemistry can be quantified indirectly via the Hantzsch method by determining the amount of the scavenging product formaldehyde formed. In this work, the influence of the presence of H2O2 on the Hantzsch method using acetoacetanilide (AAA) as derivatization reagent is studied. The experiments show that the measured CH2O concentration deviates from the actual concentration in the presence of H2O2 and the deviation increases with increasing [H2O2]0/[CH2O]0. The deviation is negative, i.e., the measured formaldehyde concentration is lower than the actual concentration. This leads to an underestimation of the hydroxyl radical production in systems containing significant amount of H2O2. The main reason for the deviation is found to be three coupled equilibria involving H2O2, CH2O and the derivative produced in the Hantzsch method.

Photoinduced metal-free diboration of alkynes in the presence of organophosphine catalysts

In sharp contrast to the transition metal-catalyzed diboration of alkynes with diboron species such as B2pin2, which affords vicinal cis-diborated alkenes, the organophosphine-catalyzed addition of B2pin2 to alkynes proceeds under metal-free conditions upon photoirradiation to give the corresponding vicinal trans-diborated alkenes with good stereoselectivity. For example, the photoinduced diboration of 1-octyne with B2pin2 in the presence of tris(o-methylphenyl)phosphine afforded 1,2-diborated octene with excellent trans selectivity (trans/cis=95/5). The influence of various organophosphines on the diboration is described in detail. The diboration does not occur in the dark or in the absence of an organophosphine catalyst. Moreover, ESR (electron spin resonance) measurements of the reaction mixture revealed a radical species around g=2.003, supporting a radical pathway for the organophosphine-catalyzed diboration. In addition, the photoinduced cis to trans isomerization of vicinal cis-diborated alkenes in the presence/absence of organophosphines is discussed.

Mechanism of Cu(I)/Cu(0)-Mediated Reductive Coupling Reactions of Bromine-Terminated Polyacrylates, Polymethacrylates, and Polystyrene.

The mechanism of the Cu(I)/Cu(0)-mediated reductive coupling reactions of bromine-terminated polymer chain-end radicals, so-called atom-transfer radical coupling (ATRC), is studied. Poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), and polystyrene (PSt), prepared by atom-transfer radical polymerization (ATRP), were activated by an excess amount of Cu(I)Br and Cu(0) in the presence of tris[2-(dimethylamino)ethyl]amine (Me6TREN), and the structural analyses of the resulting polymer products and deuterium-labeling experiments unambiguously determined the mechanism. While PMMA and PSt reacted by a radical mechanism as expected, PMA-bromide was reduced to an anionic species, which was most likely an organocopper species. Trapping experiments with TEMPO suggested that the polymer chain-end radicals were generated in all cases by the reduction of the bromine-terminated polymers by low-valent Cu species. However, the PMA chain-end radical was further reduced to the anionic species from which coupling products formed in low yield.

Model Studies of Alkyl Halide Activation and Comproportionation Relevant to RDRP in the Presence of Cu0

Model studies of alkyl halide activation by Cu0 and comproportionation between CuII/L and Cu0 in the presence of tris[2-(dimethylamino)methyl]amine (Me6TREN), tris(2-pyridylmethyl)amine (TPMA) and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as ligands were conducted and quantified in dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN). When more active alkyl halides such as ethyl α-bromophenylacetate (EBPA) were used, the rate coefficients of activation by Cu0, ka0app, were the same as the rate coefficients of comproportionation, kcompapp indicating that desorption of the newly formed CuI species from the Cu0 surface could be a rate-determining step. When less active alkyl halides, such as methyl 2-bromopropionate (MBrP) were used, the activation was 2.5 orders of magnitude slower than for EBPA and slower than comproportionation. This indicates that atom transfer between alkyl halide and Cu0 is slower than desorption of CuI from the surface. Under the same conditions (solven...

Kinetics and Mechanism of the Reaction between H2O2 and Tungsten Powder in Water

In this work, the reaction between H2O2 and tungsten powder in the presence of Tris(hydroxymethyl) aminomethane was studied experimentally. The production of hydroxyl radicals can be quantified indirectly by quantifying the scavenging product formaldehyde (CH2O). XRD, XPS, and SEM analysis shows that no significant structural or compositional changes occur after reaction. We compared H2O2 consumption and CH2O formation in both heterogeneous W(s)/H2O2/Tris system and homogeneous W(aq)/H2O2/Tris system. Increasing the amount of W powder leads to the increase in dissolution rate of W species, insignificant increase of H2O2 consumption rate and the decrease of final CH2O production. By contrast, the consumption rate of H2O2 increases as increasing the concentration of dissolved W species. Based on the experimental results, a mechanism of H2O2 reacting with W powder in the presence of Tris is proposed. The mechanism well explained the relationship between surface reactions and homogeneous Haber–Weiss peroxide ...

Practical Peptide Synthesis Mediated by a Recyclable Hypervalent Iodine Reagent and Tris(4-methoxyphenyl)phosphine.

6-(3,5-Bis(trifluoromethyl)phenyl)-1H,4H-2aλ(3)-ioda-2,3-dioxacyclopenta[hi]indene-1,4-dione (p-BTFP-iodosodilactone, 1a) was synthesized and demonstrated to be an efficient hypervalent iodine(III) reagent for the synthesis of dipeptides from various standard amino acids, including sterically hindered amino acids, in good to high yields within 30 min in the presence of tris(4-methoxyphenyl)phosphine. In addition, the combined system of 1a/(4-MeOC6H4)3P was used to synthesize the pentapeptide leu-enkephalin in protected form. It is worth noting that 1a can be regenerated readily after reaction.