Minimizing Side Reactions Research Articles

Indium-Mediated Stereoselective Allylation

Stereoselective indium-mediated organic reactions have enjoyed tremendous growth in the last 25 years. This is in part due to the insensitivity of allylindium to moisture, affording facile and practical reaction conditions coupled with outstanding functional group tolerance and minimal side reactions. Despite the plethora of articles about allylindium, there is much yet to be discovered and exploited for efficient and sustainable synthesis. In this Account, we describe indium-mediated synthetic methods for the preparation of chiral amines with the aim to present a balance of practical method development, novel asymmetric chemistry, and mechanistic understanding that impact multiple chemical and materials science disciplines. In 2005, we demonstrated the indium-mediated allylation of chiral hydrazones with complete diastereoselectivity (>99:1) and quantitative yields. Further, we revealed the first example of enantioselective indium-mediated allylation of hydrazones using catalytic (R)-3,3'-bis(trifluoromethyl)-BINOL ligands to afford homoallylic amines with high enantioselectivity. The use of enantiopure perfluoroalkylsulfonate BINOLs greatly improved the indium-mediated allylation of N-acylhydrazones with exquisite enantiocontrol (99% yield, 99% ee). This laboratory has also investigated indium-mediated asymmetric intramolecular cyclization in the presence of amino acid additives to deliver biologically relevant chromanes with excellent diastereoselectivity (dr >99:1). The effect of amino acid additives (N-Boc-glycine) was further investigated during the indium-mediated allylation of isatins with allyl bromide to yield homoallylic alcohols in excellent yields in a short time with a wide range of functional group tolerance. Critical mechanistic insight was gained, and evidence suggests that the additive plays two roles: (1) to increase the rate of formation of allylindium from allyl bromide and In(0) and (2) to increase the nucleophilicity of the allylindium reagent, probably through disruption of aggregates and coordination to the metal. We recently reported the palladium-catalyzed umpolung allylation of hydrazones with allyl acetates in the presence of indium(I) iodide (InI) with excellent diastereoselectivity (up to 99:1). The conversion was found to be inversely proportional to the phosphine concentration, providing insight into the mechanism of the critical redox transmetalation process that has implications for other Pd-catalyzed umpolung-type allylation processes. A detailed overview of the work in our lab is presented with the intention of stimulating further research interest in organoindium chemistry and its application in organic synthesis.

Automated High-Throughput Permethylation for Glycosylation Analysis of Biologics Using MALDI-TOF-MS

Monitoring glycoprotein therapeutics for changes in glycosylation throughout the drug's life cycle is vital, as glycans significantly modulate the stability, biological activity, serum half-life, safety, and immunogenicity. Biopharma companies are increasingly adopting Quality by Design (QbD) frameworks for measuring, optimizing, and controlling drug glycosylation. Permethylation of glycans prior to analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is a valuable tool for glycan characterization and for screening of large numbers of samples in QbD drug realization. However, the existing protocols for manual permethylation and liquid-liquid extraction (LLE) steps are labor intensive and are thus not practical for high-throughput (HT) studies. Here we present a glycan permethylation protocol, based on 96-well microplates, that has been developed into a kit suitable for HT work. The workflow is largely automated using a liquid handling robot and includes N-glycan release, enrichment of N-glycans, permethylation, and LLE. The kit has been validated according to industry analytical performance guidelines and applied to characterize biopharmaceutical samples, including IgG4 monoclonal antibodies (mAbs) and recombinant human erythropoietin (rhEPO). The HT permethylation enabled glycan characterization and relative quantitation with minimal side reactions: the MALDI-TOF-MS profiles obtained were in good agreement with hydrophilic liquid interaction chromatography (HILIC) and ultrahigh performance liquid chromatography (UHPLC) data. Automated permethylation and extraction of 96 glycan samples was achieved in less than 5 h and automated data acquisition on MALDI-TOF-MS took on average less than 1 min per sample. This automated and HT glycan preparation and permethylation showed to be convenient, fast, and reliable and can be applied for drug glycan profiling and clinical glycan biomarker studies.

Carboxylating stubborn alkyl chlorides

Organic Chemistry The utility of alkyl chlorides and carbon dioxide (CO2) as reagents in organic synthesis is often limited by the difficulty of activating these molecules. Borjesson et al. have overcome both these challenges with a nickel catalyst that adds CO2 at ambient pressures to unactivated alkyl chlorides (primary, secondary, and even tertiary). The nickel catalyst ligands that were most effective at minimizing side reactions were 1,10-phenanthrolines with ortho-substituents. The nickel center displaced chloride to create a nucleophile that could then react with electrophilic CO2. The reaction is tolerant of aliphatic alcohol or phenol groups, which helps minimize the need for protecting groups. J. Am. Chem. Soc. 10.1021/jacs.6b04088 (2016).

Stabilization of High Energy Cathodes By Introducing Conformal Passivating Shells on the Surface

Combined cycling stability at high energy density is required for lithium ion battery to meet the criteria for use in electric vehicles. In generally, material utilization and rate capability are enhanced at small particle sizes. [1] Reduced size of electrode materials can enhance the rate of lithium ions because of shortened diffusion pathway and increases surface area to induces facile access by the electrolyte. In contrast, chemical degradation at electrode-electrolyte interface is also facilitated by large contact area with nanoparticle electrode. Unfavorable interfacial reactions such as dissolution of active materials and decomposition of electrolyte mainly occur because the surface of active materials is energetically unstable. [2] In order to minimize side reactions that can negatively affect to electrochemical performance, replacing electrochemically inactive ions on the surface of active materials can improve the interfacial stability. However, this substitution should take place as thin passivating layers on individual particles to preserve storage capacity. [3] Herein, we demonstrate a strategy toward the stabilization of interfaces by introducing core-shell type of nanocrystals that is composed of electroactive transition metal oxide in core and ultra-thin inactive epitaxial oxide shell on the surface. To prove this concept, we introduce layered LixCoO2 nanocrystals as a core component, with Al-rich shells as passivation layer to minimize side reaction with electrolyte. The resulting materials shows stable cycling curves as well as higher capacity retention at high rate of charging and discharging reaction compared to bare LixCoO2.

Radical Coupling Allows a Fast and Tuned Synthesis of Densely Packed Polyrotaxanes Involving γ-Cyclodextrins and Polydimethylsiloxane

The first radical end-coupling synthesis of polydimethylsiloxane (PDMS)−γ-cyclodextrins (γ-CDs) based polyrotaxane is reported. Conversely to usual chemical way, the radical process leads to fast both controlled size and structure with minimal side reaction while exhibiting very high conversion rate (w/w, 80%). Pure PDMS−γ-CDs molecular necklaces were successfully isolated by preparative size exclusion chromatography and finely characterized both by 1D/2D/STD 1H and 13C NMR and MALDI-TOF mass spectrometry. The observations give clear evidence of the supramolecular assembly synthesis where the filling ratio (γ-CD/monomer unit) of PDMS chains is as high as 40% of γ-CDs. Combination of such radical-based coupling supported by detailed analytical characterizations appears at the forefront of a fast, suitable, and easily amenable scaling-up CDs-based polyrotaxane synthesis process.

(Invited) Hierarchical Inorganic Assemblies for the Photocatalytic Reduction of CO2 By H2o

The multi-electron processes of CO2 reduction and H2O oxidation, which constitute the essential reactions of sunlight to fuel conversion (artificial photosynthesis) require efficient coupling of light absorber and catalyst. Using all-inorganic heterobinuclear units such as ZrOCo anchored on high surface area silica, we have developed photodeposition methods for the directional assembly of nanometer sized catalyst clusters for H2O oxidation or CO2 reduction with proper coupling to the binuclear light absorber. Copper oxide nanoclusters were assembled adjacent to the Zr acceptor sites of the heterobinuclear unit, and light driven reduction of CO2 upon excitation of the ZrOCo unit demonstrated. Illumination of the ZrOCo chromophore coupled to a metal oxide nanocatalyst for H2O oxidation affords closing of the photocatalytic cycle in the absence of sacrificial agents. Time resolved FT-IR spectroscopy provided detailed mechanistic insight into the multi-electron reactions of H2O oxidation and CO2 reduction on the metal oxide catalyst surfaces under reaction conditions, with surface intermediates and their kinetics uncovered for the first time. To achieve CO2 photoreduction by H2O under product separation on the nanoscale, Co3O4-SiO2 core-shell nanotubes were developed in which the inner surface acts as efficient water oxidation catalyst while the nanoscale silica layer with embedded molecular wires serves as a proton conducting, gas impermeable separation membrane with tight control of electron transport. Completing the photocatalytic cycle on the nanoscale seeks to minimize side reactions and efficiency degrading transport processes. Characterization of the assembly by transient spectroscopy and photoelectrochemical measurements will be discussed. References Zhang, M.; de Respinis, M.; Frei, H. Nature Chem. 2014, 6, 362. Kim, W.; Yuan, G.; McClure, B. A.; Frei, H. J. Am. Chem. Soc. 2014, 136, 11034. McCure, B. A.; Frei, H. J. Phys. Chem. C 2014, 118, 11601. Kim. W.; Frei, H. ACS Catal. 2015, 5, 5627. Yuan, G.; Agiral, A.; Pellet, N.; Kim, W.; Frei, H. Faraday Discuss. 2014, 176. 233. Edri, E.; Frei, H. J. Phys. Chem. C 2015, 119, 000.

Solution polymerization of polybenzimidazole

ABSTRACTPolybenzimidazoles (PBI) are an important class of heterocyclic polymers that exhibit high thermal and oxidative stabilities. The two dominant polymerization methods used for the synthesis of PBI are the melt/solid polymerization route and solution polymerization using polyphosphoric acid as the solvent. Both methods have been widely used to produce high‐molecular weight PBI, but also highlight the obvious absence of a practical organic solution‐based method of polymerization. This current work explores the synthesis of high‐molecular weight meta‐PBI in N,N‐dimethyl acetamide (DMAc). Initially, model compound studies examined the reactivity of small molecules with various chemical functionalities that could be used to produce 2‐phenyl‐benzimidazole in high yield with minimal side reactions. 1H NMR and FTIR studies indicated that benzimidazoles could be efficiently synthesized in DMAc by reaction of an o‐diamine and the bisulfite adduct of an aromatic aldehyde. Polymerizations were conducted at various polymer concentrations (2‐26 wt % polymer) using difunctional monomers to optimize reaction conditions in DMAc which resulted in the preparation of high‐molecular weight m‐PBI (inherent viscosities up to 1.3 dL g−1). TGA and DSC confirmed that m‐PBI produced via this route has comparable properties to that of commercial m‐PBI. This method is advantageous in that it not only allows for high‐polymer concentrations of m‐PBI to be synthesized directly and efficiently, but can be applied to the synthesis of many PBI derivatives. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1795–1802

Diels–Alder and Dehydration Reactions of Biomass-Derived Furan and Acrylic Acid for the Synthesis of Benzoic Acid

Routes to benzoic acid starting from furan—obtained from hemicellulose in high yield—and methyl acrylate are reported. These routes involve Diels–Alder and dehydration reactions of furan and acrylic acid (or methyl acrylate) in a two-step reaction protocol that minimizes side reactions. The Diels–Alder reaction of furan and methyl acrylate (or acrylic acid) was run at 298 K and was catalyzed by Lewis acidic (Hf-, Zr-, and Sn-Beta) zeolite catalysts, and achieving a high turnover frequency (∼2 h–1) and no side reactions were observed. The oxanorbornene product was dehydrated at low temperatures (298 to 353 K) in mixtures of methanesulfonic acid and acetic anhydride in 96% yield. This is compared to an only 1.7% yield of methyl benzoate obtained for the dehydration of the oxanorbornene in neat methanesulfonic acid. The effect of oxanorbornene concentration and stereochemistry was found not to decrease the yield of aromatics, while dehydration of the carboxylic acid form of the oxanorbornene led to a decreas...

Application of a dynamic in vitro model with real-time determination of acetylcholinesterase activity for the investigation of tabun analogues and oximes

Tabun-inhibited acetylcholinesterase (AChE) is rather resistant towards reactivation by oximes in vitro while in vivo experiments showed some protection of animals poisoned by this chemical warfare nerve agent after treatment with an oxime and atropine. In addition, AChE inhibited by close tabun analogues, N,N-diethyltabun and N,N-di-n-propyltabun was completely resistant towards reactivation by oximes. In order to get more insight into potential mechanisms of this oxime resistance experiments with these toxic agents and the oximes obidoxime, 2-PAM, MMB-4 and HI-6 were performed utilizing a dynamic model with real-time determination of AChE activity. This experimental setup allowed the investigation of reactivation with minimized side reactions. The determined reactivation constants with tabun-inhibited human AChE were in good agreement with previously reported constants determined with a static model. N,N-diethyl- and N,N-di-n-propyltabun-inhibited human AChE could not be reactivated by oximes which indicates that the inadequate oxime effect was not due to re-inhibition by phosphonyloximes. Additional experiments with tabun-inhibited human and Rhesus monkey AChE revealed that no reactivation occurred with HI-6. These data give further support to the assumption that an interaction of tabun with residues in the active site gorge of AChE prevents effective reactivation by oximes, a mechanism which may also be the reason for the total oxime resistance of N,N-diethyl- and N,N-di-n-propyltabun-inhibited human AChE.

(Invited) Atomic Layer Deposition of Core-Shell Nanowires for Solar Energy Conversion Devices

Semiconductor nanowires (NWs) have several advantages for solar energy conversion devices resulting from strong light absorption and anti-reflective properties, efficient charge transport properties, and large surface areas to drive chemical reactions. However, precise control of surfaces and interfacial properties is crucial to maximize charge-transfer efficiency across interfaces, while minimizing side reactions and recombination. One technique for surface and interfacial engineering is Atomic Layer Deposition (ALD), which allows for conformal deposition of a wide variety of materials with precision and tunable thickness and composition. Core-shell structures can be fabricated by coating NWs with ALD, facilitating precise tuning of the electronic, optical, and chemical properties to optimize their interfaces. We present several examples of ALD core-shell structures for energy conversion, with an emphasis on solar applications. Examples include quantum-dot sensitized NWs, earth abundant core-shell NWs, passivation layers and co-catalysts for photoelectrochemical water splitting, and control of heterogeneous interfaces in hierarchical nanomaterial synthesis.

Thermodynamic Properties of Nd in Liquid Nd-Bi Alloys Using Electrochemical Methods

Preliminary cyclic voltammograms performed on LiCl-KCl-NdCl3 electrolyte (1 mol% NdCl3) at 700°C show that the reduction of Nd3+/Nd(s) takes place at approximately -1.7V, which is equivalent to approximately -2.9V vs. Cl-/Cl2(g) in close agreement with the standard electrode potential based on the free energy of formation. The measurement was performed using an inert tungsten working electrode, graphite counter-electrode and Ag/Ag+ reference electrode with a thin-walled quartz tube (see Figure 1 in image file). With an aim to separate Nd using liquid bismuth electrode in LiCl-KCl molten salt electrolyte, it is important to understand the equilibrium redox potential of Nd in the liquid Bi. Thus, our work focuses on establishing the thermodynamic properties of Nd in liquid Nd-Bi alloys using electrochemical methods-electromotive force (emf) technique. We will present an electrochemical cell that measures the emf values of Nd in Bi at various mole fractions (0 < x Nd (in Bi) < 0.3) using the binary solid-state electrolyte CaF2-NdF3. The choice of CaF2-NdF3 is due to the thermodynamic stability of CaF2, which will minimize side reactions and electronic conduction providing accurate thermodynamic properties. The electrochemical cell for the Nd-Bi alloys is: Nd(s) |CaF2-NdF3| Nd (in Bi) where solid CaF2-NdF3 serves as the electrolyte, pure Nd as the reference electrode, and Nd-Bi alloys as the working electrode (see Figure 2 in image file). The electrode reactions are written below: Reference Electrode: Nd(s) + 3F- → NdF3 + 3e- Working Electrode: NdF3 + 3e- → Nd (in Bi) + 3F- ----------------------------------------------------------------------------- Cell Reaction: Nd(s) → Nd (in Bi) From the measured emf values for this cell, the thermodynamic activity of Nd is obtained using the Nernst equation (see Equation 1 in image file), where ΔGNd (in Bi) is the partial molar free energy of Nd in Bi, n is the number of electrons exchanged in the reaction (n = 3), F is the Faraday constant, R is the ideal gas constant, and T is the temperature. Using the temperature dependence of the emf, the partial molar entropy and enthalpy of Nd can be estimated using the Gibbs-Helmholtz equation (see Equations 2 and 3 in image file). The solid CaF2-NdF3 electrolyte will be prepared from high purity CaF2 powder (99.9%) and NdF3 powder (99.9%) uniaxially pressed at 30 MPa into a pellet 75 mm wide by 17 mm thick and sintered at 1000°C for 3 hrs. The Nd-Bi alloys (0.05 < x Nd < 0.30) will be prepared by melting high purity Nd (>99.1%) and Bi into ~10 mm diameter ingots using an arc melter and induction heater under an argon environment in order to eliminate reactions with air and water. The pure Nd reference electrodes will be similarly fabricated. The electrodes will then be placed into holes drilled into the CaF2-NdF3 pellet and electrical connections will be made with tungsten wires (see Figure 2 in image file). The cell will then be placed into an alumina crucible and loaded into a test chamber. The test chamber will be placed inside a crucible furnace, evacuated to ~1 Pa, heated to 80°C and 270°C, holding for 8 hrs at each temperature for removal of residual moisture, and then the chamber will be purged with argon gas flowing at ~10 mL/min and will be heated to 900°C to ensure thorough melting of the electrodes to establish the electrical contacts with the electrolyte and electrical leads. The emf values will be measured using an AUTOLAB PGSTAT-302N potentiostat-galvanostat at 450°C to 900°C in 30°C increments. At each temperature step, the emf E cell will be recorded for each working electrode and the measured data will be analyzed to calculate the temperature dependence to obtain thermodynamic properties of Nd in Bi electrode. Figure 1

Pilot scale (10 kg) production and characterization of epoxidized sucrose soyate

The objective of this study was to develop and characterize the performance of a reactor and refining units that would produce 10kg of epoxidized sucrose soyate (ESS) with a process timeframe and resin quality similar to the 300g laboratory scale in order to meet the increasing demand for multiple applications in coatings and composite materials. Scale up challenges involve maintaining suitable reaction temperature and time, achieving high double-bond conversion, minimizing side reactions, and avoiding excessive refining time. To accomplish this, a 38L stainless steel steam-jacketed GROEN kettle was modified for use as an epoxidation reactor. The modifications helped achieve adequate mixing, heat transfer and temperature control. Consequently, the reaction temperature was successfully controlled between 55 and 65°C by varying the H2O2 addition rate and the fluid temperature in the reactor’s jacket. Twenty 7–10kg batches were produced which had similar resin quality as the lab scale, an overall 84.9% resin yield, and >98% conversion of double bonds after batch three. The total production days were reduced from 8 to 4 after a 40L refining funnel was fabricated for washing, gravity phase separation, and filtration, and an explosion-proof solvent extraction unit was adapted for devolatilizing hexane used during refining. The overall heat transfer coefficient of the jacket was determined to be 1069Wm−2K−1.

Characterization of top-down ETD in a travelling-wave ion guide

Top-down sequencing methods are becoming increasingly relevant for protein characterization, in particular electron capture (ECD) and electron transfer dissociation (ETD) which allow for extensive backbone cleavage with minimal side reactions. The ability to obtain sequence-specific fragments while maintaining aspects of the higher-order structure, as well as the position of deuterium labels in H/D exchange, has attracted interest from scientists in the field of structural proteomics. Recently, ETD has also been combined with ion mobility on commercially available quadrupole/time-of-flight instruments, and this implementation paves the way to novel structural studies and investigation of the ETD process itself. In the current work, we investigate the use of ETD for fragmentation of standard peptides and proteins and provide a detailed description of the effect of the parameters controlling the time and efficiency of the reaction. We also highlight how the combination with ion mobility separation after electron transfer provides extended analytical benefits, such as assignment of fragments to a specific charge-reduced state of the precursor.

Polyether–maleimide‐based crosslinked self‐healing polyurethane with Diels–Alder bonds

ABSTRACTThe Diels–Alder (DA) reaction is particularly desirable for the preparation of heat‐stimuli self‐healing polymeric materials because of its thermal reversibility, high yield, and minimal side reactions. Some attempts were conducted to synthesize polyether–maleimide‐based crosslinked self‐healing polyurethane with DA bonds (C‐PEMIPU–DA) through the reactions of the prepolymer (polymeric MDI/PBA‐1000) functionalized by furfuryl amine and polyether–maleimide without benzene in this study. The structures of intermediates and C‐PEMIPU–DA were first confirmed by 1H‐NMR, Fourier transform infrared spectroscopy, and differential scanning calorimetry. Next, the thermal reversibility and the self‐healing performance of C‐PEMIPU–DA were studied by 1H‐NMR, polarizing optical microscopy, tensile testing, and a sol–gel process. The results show that C‐PEMIPU–DA exhibited interesting properties of thermal reversibility and self‐healing. The polymers could be applied to self‐healing materials or recyclable materials in the fields of the repair of composite structures and aging parts because of their thermosetting properties at room temperature and thermoplasticity at higher temperatures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41944.

Au-coated carbon electrodes for aprotic Li–O2 batteries with extended cycle life: The key issue of the Li-ion source

Despite having the capability of achieving high energy densities, Li–O2 batteries still suffer from many inherent disadvantages such as electrolyte stability, sluggish kinetics of the oxygen reduction/evolution reactions in the aprotic environment and electrodes stability.Our research demonstrates by combining electrochemical and analytical techniques that the performances of Li–O2 batteries based on LiTFSI-Tetraglyme electrolyte and Au-coated carbon electrodes are manly hindered by the instability of the lithium metal anode in the oxygen-saturated environment. Although the Au-coated carbon electrodes are able to minimize side reactions arising from electrolyte decomposition, oxygen crossover on the lithium metal results in the formation of decomposition products (LiOH, Li2CO3) that are clearly detrimental for the battery performance. Finally it is demonstrated that the Au-coated carbon electrodes in combination with the LiTFSI-Tetraglyme electrolyte can sustain extended cycling (100 cycles) when a more stable source of Li-ion, namely lithium iron phosphate (LFP), is used.

Kinetics and mechanism of styrene epoxidation by chlorite: role of chlorine dioxide.

An investigation of the kinetics and mechanism for epoxidation of styrene and para-substituted styrenes by chlorite at 25 °C in the pH range of 5-6 is described. The proposed mechanism in water and water/acetonitrile includes seven oxidation states of chlorine (-I, 0, I, II, III, IV, and V) to account for the observed kinetics and product distributions. The model provides an unusually detailed quantitative mechanism for the complex reactions that occur in mixtures of chlorine species and organic substrates, particularly when the strong oxidant chlorite is employed. Kinetic control of the reaction is achieved by the addition of chlorine dioxide to the reaction mixture, thereby eliminating a substantial induction period observed when chlorite is used alone. The epoxidation agent is identified as chlorine dioxide, which is continually formed by the reaction of chlorite with hypochlorous acid that results from ClO produced by the epoxidation reaction. The overall stoichiometry is the result of two competing chain reactions in which the reactive intermediate ClO reacts with either chlorine dioxide or chlorite ion to produce hypochlorous acid and chlorate or chloride, respectively. At high chlorite ion concentrations, HOCl is rapidly eliminated by reaction with chlorite, minimizing side reactions between HOCl and Cl2 with the starting material. Epoxide selectivity (>90% under optimal conditions) is accurately predicted by the kinetic model. The model rate constant for direct reaction of styrene with ClO2(aq) to produce epoxide is (1.16 ± 0.07) × 10(-2) M(-1) s(-1) for 60:40 water/acetonitrile with 0.20 M acetate buffer. Rate constants for para substituted styrenes (R = -SO3(-), -OMe, -Me, -Cl, -H, and -NO2) with ClO2 were determined. The results support the radical addition/elimination mechanism originally proposed by Kolar and Lindgren to account for the formation of styrene oxide in the reaction of styrene with chlorine dioxide.

Toward a Lithium-‘air’ Battery: The Effect of CO2 on the Chemistry of a Lithium-Oxygen Cell

Lithium-oxygen chemistry offers the highest energy density for a rechargeable system; such a system is known as a “lithium-air battery”. Most studies of lithium-air batteries have focused on demonstrating battery operations in an environment of pure oxygen; such a battery should technically be described as a “lithium-dioxygen (O2) battery”. Consequently, the next step for the lithium-“air” battery is to understand how the reaction chemistry is affected by the constituents of ambient air. Among the components of air, CO2 is of particular interest because its solubility in organic solvents is about fifty times higher than that of O2, and it can react actively with O2 - ·, which is the key intermediate species in Li-O2 battery reactions. In this work, we investigated the reaction mechanisms in the Li-O2/CO2 cell under various electrolyte conditions using quantum mechanical simulations combined with experimental verification. Our most important finding is that the subtle balance among various reaction pathways influencing the potential energy surfaces can be modified by the electrolyte solvation effect. Thus, a low dielectric electrolyte tends to primarily form Li2O2, while a high dielectric electrolyte is effective in electrochemically activating CO2, yielding only Li2CO3. Most surprisingly, we further discovered that a high dielectric medium such as DMSO can result in the reversible reaction of Li2CO3 within a Li-air cell (contrary to conventional belief) over multiple cycles. We believe that the current mechanistic understanding of the chemistry of CO2 in a Li-air cell and the interplay of CO2 with electrolyte solvation will provide an important guideline for developing Li-air batteries. Furthermore, the newly discovered possibility for a rechargeable Li-O2/CO2 battery based on Li2CO3 formation chemistry may have merits in enhancing cyclability by minimizing side reactions.

Block copolymer materials from the organocatalytic ring-opening polymerization of a pentaerythritol-derived cyclic carbonate

9-Phenyl-2,4,8,10-tetraoxaspiro[5,5]undecanone (PTO) was synthesized from pentaerythritol via the acid-catalyzed acetal formation reaction with benzaldehyde and subsequent ring closure with ethyl chloroformate. The cyclic carbonate monomer was subsequently polymerized by ring-opening polymerization (ROP) initiated from 1,4-butanediol (1,4-BDO) using the 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea and 1,8-diazabicyclo[5.4.0]undec-7-ene dual organocatalytic system. It was found that the organocatalyst allowed for the synthesis of well-defined polymers with minimal adverse side reactions and low dispersities. This system was then employed in the ROP of PTO initiated from an α,ω-dihydroxy poly(caprolactone) (PCL) macroinitiator, with varying molecular weights, to yield a series of A-B-A block copolymers. These materials were characterized by 1H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis and tensile analysis. It was found that the chain extension from PCL with poly(PTO) (PPTO) blocks yielded a thermoplastic material with superior tensile properties (elongation and Young's modulus) to that of the PCL homopolymer. Furthermore, it was noted that the addition of PPTO could be employed to alter the crystallization properties (crystallization temperature (Tc), and percentage crystallization) of the central PCL block. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2279–2286

A facile route to tailoring peptide-stabilized gold nanoparticles using glutathione as a synthon.

The preparation of gold nanoparticles (AuNPs) of high purity and stability remains a major challenge for biological applications. This paper reports a simple synthetic strategy to prepare water-soluble peptide-stabilized AuNPs. Reduced glutathione, a natural tripeptide, was used as a synthon for the growth of two peptide chains directly on the AuNP surface. Both nonpolar (tryptophan and methionine) and polar basic (histidine and dansylated arginine) amino acids were conjugated to the GSH-capped AuNPs. Ultracentrifugation concentrators with polyethersulfone (PES) membranes were used to purify precursor materials in each stage of the multi-step synthesis to minimize side reactions. Thin layer chromatography, transmission electron microscopy, UV-Visible, 1H-NMR, and fluorescence spectroscopies demonstrated that ultracentrifugation produces high purity AuNPs, with narrow polydispersity, and minimal aggregation. More importantly, it allows for more control over the composition of the final ligand structure. Studies under conditions of varying pH and ionic strength revealed that peptide length, charge, and hydrophobicity influence the stability as well as solubility of the peptide-capped AuNPs. The synthetic and purification strategies used provide a facile route for developing a library of tailored biocompatible peptide-stabilized AuNPs for biomedical applications.

Anion Exchange Fuel Cell Membranes Prepared from C–H Borylation and Suzuki Coupling Reactions

Of the polymer materials investigated as anion exchange membranes, trimethylbenzylammonium-containing polysulfones are the most extensively studied. They are commonly prepared by chloromethylation of the aromatic backbone or radical bromination of benzylic carbons, followed by a Menshutkin reaction between a tertiary amine and the benzyl halide. To overcome synthetic limitations involved with these two methods, we report the preparation of an anion exchange membrane by means of iridium-catalyzed C–H borylation followed by palladium-catalyzed Suzuki coupling. Owing to the use of mild reaction conditions and high efficiency of these metal-catalyzed reactions, we were able to minimize side reactions and easily control the degree of functionalization for a series of trimethylbenzylammonium-containing polysulfones. The resulting membranes exhibited lower water uptake while maintaining similar hydroxide conductivity and functional group stability as compared to the corresponding chloromethylation-prepared anion exchange membrane materials.