Non-aqueous Conditions Research Articles

A new organic redox species-indole tetraone trapped MWCNT modified electrode prepared by in-situ electrochemical oxidation of indole for a bifunctional electrocatalysis and simultaneous flow injection electroanalysis of hydrazine and hydrogen peroxide

Indole and its derivatives are important core constituents of several natural, biological and pharmaceutical relevant compounds. In general, electrochemical oxidation of indole on solid electrodes in acid and non-aqueous conditions results in the formation of polyindole like compounds as an end product. Selective and controlled electrochemical oxidation of indole and its derivatives to redox active intermediate compound/s without over-oxidation to the polymeric product is a challenging research task. Herein, we report an electrochemical oxidation of electro-inactive indole to a multi-redox active Indole Tetraone (1H-Indole-2,3,4,7-Tetraone)-a new organic redox species (Ind-Tetraone) and entrapment as a surface-confined redox active species on multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNT@Ind-Tetraone) in physiological pH solution. GCE/MWCNT@Ind-Tetraone showed a well-defined surface-confined redox peaks at E1/2, −0.270 V (A1/C1) and +0.270 V (A2/C2) vs Ag/AgCl. From the physicochemical characterizations by Raman and IR spectroscopy, XPS, LC-MS (an ethanolic extract) and control electrochemical experiments with various substituted indole derivatives, it is confirmed the formation of Ind-Tetraone species without any polyindole formation upon the electrochemical oxidation of indole on MWCNT surface. Electrochemical oxidation of nitrogen atom as a radical species and subsequent electron-transfer/water addition reaction is proposed as a possible mechanism for the Ind-Tetraone product formation. A simultaneous electrocatalytic oxidation of hydrazine and reduction reaction of hydrogen peroxide at two discreet potentials has been demonstrated as a bifunctional application of the GCE/MWCNT@Ind-Tetraone system. In further, the GCE/MWCNT@Ind-Tetraone as a electrochemical detector, simultaneous flow injection analysis of hydrazine and hydrogen peroxide was also demonstrated as a proof of concept for the bifunctional application.

A Robust Oil-in-Oil Emulsion for the Nonaqueous Encapsulation of Hydrophilic Payloads.

Compartmentalized structures widely exist in cellular systems (organelles) and perform essential functions in smart composite materials (microcapsules, vasculatures, and micelles) to provide localized functionality and enhance materials' compatibility. An entirely water-free compartmentalization system is of significant value to the materials community as nonaqueous conditions are critical to packaging microcapsules with water-free hydrophilic payloads while avoiding energy-intensive drying steps. Few nonaqueous encapsulation techniques are known, especially when considering just the scalable processes that operate in batch mode. Herein, we report a robust oil-in-oil Pickering emulsion system that is compatible with nonaqueous interfacial reactions as required for encapsulation of hydrophilic payloads. A major conceptual advance of this work is the notion of the partitioning inhibitor-a chemical agent that greatly reduces the payload's distribution between the emulsion's two phases, thus providing appropriate conditions for emulsion-templated interfacial polymerization. As a specific example, an immiscible hydrocarbon-amine pair of liquids is emulsified by the incorporation of guanidinium chloride (GuHCl) as a partitioning inhibitor into the dispersed phase. Polyisobutylene (PIB) is added into the continuous phase as a viscosity modifier for suitable modification of interfacial polymerization kinetics. The combination of GuHCl and PIB is necessary to yield a robust emulsion with stable morphology for 3 weeks. Shell wall formation was accomplished by interfacial polymerization of isocyanates delivered through the continuous phase and polyamines from the droplet core. Diethylenetriamine (DETA)-loaded microcapsules were isolated in good yield, exhibiting high thermal and chemical stabilities with extended shelf-lives even when dispersed into a reactive epoxy resin. The polyamine phase is compatible with a variety of basic and hydrophilic actives, suggesting that this encapsulation technology is applicable to other hydrophilic payloads such as polyols, aromatic amines, and aromatic heterocyclic bases. Such payloads are important for the development of extended pot or shelf life systems and responsive coatings that report, protect, modify, and heal themselves without intervention.

Barbier-Negishi Coupling of Secondary Alkyl Bromides with Aryl and Alkenyl Triflates and Nonaflates.

A mild and practical Barbier-Negishi coupling of secondary alkyl bromides with aryl and alkenyl triflates and nonaflates has been developed. This challenging reaction was enabled by the use of a very bulky imidazole-based phosphine ligand, which resulted in good yields as well as good chemo- and site selectivities for a broad range of substrates at room temperature and under non-aqueous conditions. This reaction was extended to primary alkyl bromides by using an analogous pyrazole-based ligand.

Barbier–Negishi Coupling of Secondary Alkyl Bromides with Aryl and Alkenyl Triflates and Nonaflates

AbstractA mild and practical Barbier–Negishi coupling of secondary alkyl bromides with aryl and alkenyl triflates and nonaflates has been developed. This challenging reaction was enabled by the use of a very bulky imidazole‐based phosphine ligand, which resulted in good yields as well as good chemo‐ and site selectivities for a broad range of substrates at room temperature and under non‐aqueous conditions. This reaction was extended to primary alkyl bromides by using an analogous pyrazole‐based ligand.

Synthesis of five-membered unsaturated compounds from ketones via cyanophosphates under neutral conditions: [1,5]-C[sbnd]H insertion of alkylidene carbenes generated by tetrazole fragmentation

Cyanophosphates (CPs) can easily be prepared via the reactions of carbonyl compounds with diethyl phosphorocyanidate (DEPC) in the presence of LiCN (cat.) under non-aqueous conditions. Treatment of ketone-derived CPs with TMSN3/Bu2SnO (cat.) in toluene at reflux produces cyclopentenes or heterocyclic products in good yields under neutral conditions. In this two-step transformation, CPs may form tetrazolylphosphates, which subsequently undergo successive fragmentation to generate alkylidene carbenes, which undergo [1,5]-C–H insertions to yield five membered compounds.

Asymmetric Cyclometalated RuII Polypyridyl-Type Complexes with π-Extended Carbanionic Donor Sets.

A series of novel cyclometalated RuII complexes were investigated featuring the tridentate dqp ligand platform (dqp is 2,6-di(quinolin-8-yl)pyridine), in order to utilize the octahedral coordination mode around the Ru center to modulate the electrochemical and photophysical properties. The heteroleptic complexes feature C1 symmetry due to symmetry breaking by the peripheral five- or six-membered carbanionic chelate (phenyl, naphthyl, or anthracenyl units). The chelation mode is controlled by the steric effects and C-H activation selectivity of the ligand, which prompted the development of a general synthesis protocol. The optimized conditions to achieve high overall yields (55-75%) involve NaHCO3 as the base and an simplified purification protocol: i.e., facile chromatographic separation using commercially available amino-functionalized silica applying nonaqueous salt-free conditions to omit the necessity of counterion exchange. The structural, photophysical, and electrochemical properties were studied in depth, and the results were corroborated by density functional theory (DFT) calculations. Steady state and time-resolved spectroscopy revealed red-shifted absorption (up to 750 nm) and weak IR emission (800-1000 nm) combined with prolonged emission lifetimes (up to 20 ns) in comparison to classical tpy-based (tpy is 2,2':6',2″-terpyridine) complexes. An enhanced stability was observed by blocking the reactive positions of the carbanionic ligand framework, while the reactive positions may be exploited for further functionalization.

Controlled electrodeposition of gold nanoparticles onto copper-supported few-layer graphene in non-aqueous conditions

Graphene-Au hybrid materials show promise for applications ranging from biosensing to field emission devices. Electrodeposition is an inexpensive, fast and technically simple method for controlled deposition of nanoparticles but its use with graphene prepared by chemical vapor deposition (CVD) presents some problems. Cu foil is commonly used to catalyze the CVD process and the resulting graphene is most conveniently handled while retained on the Cu support. However Cu is able to spontaneously reduce Au salts in aqueous solution and hence deposition of nanoparticles via galvanic displacement occurs simultaneously with electrodeposition, and control of the growth process is lost. We show here that Au nanoparticles can be controllably electrodeposited onto Cu-supported few layer graphene (FLG) from N,N-dimethylformamide (DMF) solutions of a [AuCl4]− salt because spontaneous deposition of Au nanoparticles does not occur in this medium. Deposition occurs by the instantaneous nucleation mechanism when driven by an applied potential enabling the Au nanoparticle density to be controlled by the deposition conditions, predominantly the deposition potential. Following nucleation, nanoparticle growth is diffusion controlled. Our results demonstrate that the growth rate is similar in the presence and absence of an applied potential and control of growth time is key to controlling nanoparticle size.

Aqueous and non-aqueous microchip electrophoresis with on-chip electrospray ionization mass spectrometry on replica-molded thiol-ene microfluidic devices

This work describes aqueous and non-aqueous capillary electrophoresis on thiol-ene-based microfluidic separation devices that feature fully integrated and sharp electrospray ionization (ESI) emitters. The chip fabrication is based on simple and low-cost replica-molding of thiol-ene polymers under standard laboratory conditions. The mechanical rigidity and the stability of the materials against organic solvents, acids and bases could be tuned by adjusting the respective stoichiometric ratio of the thiol and allyl (“ene”) monomers, which allowed us to carry out electrophoresis separation in both aqueous and non-aqueous (methanol- and ethanol-based) background electrolytes. The stability of the ESI signal was generally ≤10% RSD for all emitters. The respective migration time repeatabilities in aqueous and non-aqueous background electrolytes were below 3 and 14% RSD (n=4-6, with internal standard). The analytical performance of the developed thiol-ene microdevices was shown in mass spectrometry (MS) based analysis of peptides, proteins, and small molecules. The theoretical plate numbers were the highest (1.2–2.4×104m−1) in ethanol-based background electrolytes. The ionization efficiency also increased under non-aqueous conditions compared to aqueous background electrolytes. The results show that replica-molding of thiol-enes is a feasible approach for producing ESI microdevices that perform in a stable manner in both aqueous and non-aqueous electrophoresis.

Asymmetric epoxidation of chromenes mediated by iminium salts: Synthesis of mollugin and (3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin

Organocatalytic asymmetric epoxidation of chromenes mediated by iminium salt catalysts under non-aqueous conditions provided ees as high as 99%. Contrastingly, reaction under aqueous conditions can form the corresponding diol products with ees as high as 71%. The process has been used for the synthesis of the East African medicinal plant metabolite (3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin.

Determining the Fate of a Non-Heme Iron Oxidation Catalyst Under Illumination, Oxygen, and Acid.

We analyze the stability of the non-heme water oxidation catalyst (WOC), Fe(bpmcn)Cl2 toward oxygen and illumination under nonaqueous and acidic conditions. Fe(bpmcn)Cl2 has been previously used as a C-H activation catalyst, a homogeneous WOC, and as a cocatalyst anchored to WO3 for photoelectrochemical water oxidation. This paper reports that the ligand dissociates at pH 1 with a rate constant k = 19.8(2) × 10-3 min-1, resulting in loss of catalytic activity. The combination of UV-vis experiments, 1H NMR spectroscopy, and cyclic voltammetry confirm free bpmcn and Fe2+ present in solution under acidic conditions. Even under nonaqueous conditions, both oxygen and illumination together show slow oxidation of iron over the course of a few hours, consistent with forming an Fe3+-O2- intermediate as corroborated by resonance-enhanced Raman spectroscopy, with a rate constant of k = 3.03(8) × 10-3 min-1. This finding has implications in both the merits of non-heme iron complexes as WOCs as well as cocatalysts in photoelectrochemical schemes: the decomposition mechanisms may include both anchoring group hydrolysis and instability under illumination.

Evaluation of solvation free energies for small molecules with the AMOEBA polarizable force field.

The effects of electronic polarization in biomolecular interactions will differ depending on the local dielectric constant of the environment, such as in solvent, DNA, proteins, and membranes. Here the performance of the AMOEBA polarizable force field is evaluated under nonaqueous conditions by calculating the solvation free energies of small molecules in four common organic solvents. Results are compared with experimental data and equivalent simulations performed with the GAFF pairwise‐additive force field. Although AMOEBA results give mean errors close to “chemical accuracy,” GAFF performs surprisingly well, with statistically significantly more accurate results than AMOEBA in some solvents. However, for both models, free energies calculated in chloroform show worst agreement to experiment and individual solutes are consistently poor performers, suggesting non‐potential‐specific errors also contribute to inaccuracy. Scope for the improvement of both potentials remains limited by the lack of high quality experimental data across multiple solvents, particularly those of high dielectric constant. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Thermal Stability of RNA Structures with Bulky Cations in Mixed Aqueous Solutions

Bulky cations are used to develop nucleic-acid-based technologies for medical and technological applications in which nucleic acids function under nonaqueous conditions. In this study, the thermal stability of RNA structures was measured in the presence of various bulky cations in aqueous mixtures with organic solvents or polymer additives. The stability of oligonucleotide, transfer RNA, and polynucleotide structures was decreased in the presence of salts of tetrabutylammonium and tetrapentylammonium ions, and the stability and salt concentration dependences were dependent on cation sizes. The degree to which stability was dependent on salt concentration was correlated with reciprocals of the dielectric constants of mixed solutions, regardless of interactions between the cosolutes and RNA. Our results show that organic solvents affect the strength of electrostatic interactions between RNA and cations. Analysis of ion binding to RNA indicated greater enhancement of cation binding to RNA single strands than to duplexes in media with low dielectric constants. Furthermore, background bulky ions changed the dependence of RNA duplex stability on the concentration of metal ion salts. These unique properties of large tetraalkylammonium ions are useful for controlling the stability of RNA structures and its sensitivity to metal ion salts.

Separation of Isomers of JWH-122 on Porous Graphitic Carbon Stationary Phase with Non-Aqueous Mobile Phase Using Intelligent Software.

Cannabimimetic compounds have gained an increasing attention from the forensic community during the past few years. The present study was aimed to develop a liquid chromatographic separation method for the analysis of JWH-122 and its methyl isomers. In Hungary, JWH-122 is scheduled as a narcotic compound and its methyl isomers fall into the new psychoactive substance category, attracting significantly milder punishment than JWH-122 does. According to our best knowledge, gas chromatography or reversed phase liquid chromatography coupled with mass spectrometry could not be applied for separation and selective determination of methyl-naphthoyl indol isomers. In this study, we aimed to develop a high performance liquid chromatography method with UV and mass spectrometric detection for the separation of JWH-122 and all its possible isomers, depending on the position of methyl group on the naphthyl frame. Different reversed phase columns were used. Alkyl-modified silica with different selectivity and morphology with different mobile phase composition cannot be applied for separation of JWH-122 isomers. Porous graphitic carbon (PGC) column was used for separation of banned JWH-122 and each of its methyl isomers. In method development, a Quality by Designapproach is presented for modeling the retention of the compounds. According to our knowledge, this is the first time reporting the use of intelligent software to estimate the retention on PGC material and using non-aqueous conditions. Retention times predicted by two program packages (STATISTICA® and DryLab®) are compared. The possibilities and limitations of the software modeling in the conditions described above are also evaluated.

Vinyl-functionalized poly(borosiloxane) as precursor for SiC/SiBOC nanocomposite

Vinyl-functionalized borosiloxane oligomers were synthesized by reacting boric acid and vinyltris(2-methoxyethoxy)silane (VTMEOS) in the mole ratio 1:2, 1:1.5 and 1:1 under non-aqueous conditions using diglyme as solvent. Use of vinyltris(2-methoxyethoxy)silane instead of vinyltriethoxysilane overcomes the premature gelation of borosiloxane oligomer. The effect of monomer feed ratio on the molecular weight, microstructure, thermal stability and ceramic residue of the oligomers was studied. The oligomers were characterized by FT-IR and NMR spectroscopy, GPC and TGA. The oligomers on heat treatment at 900°C in inert atmosphere give amorphous SiBOC ceramic which on further heating at 1500°C forms SiC/SiBOC nanocomposite. The extent of conversion of SiBOC to SiC is influenced by both carbon and boron content of SiBOC which in turn is controlled by the monomer feed ratio. This is evident from the observation that the extent of formation of β-SiC nano crystals follow the trend BSiVME-2>BSiVME-1>BSiVME-3.

Novel Aqueous Fabrication and Characterization of Gold Coated Cobalt Nanoparticles

Background: Biological applications such as imaging and targeted drug delivery and many others require non-toxic, stable, inert and biocompatible nanoparticles. Coating the nanoparticles with inert materials is one of the ways that is used to enhance the stability and biocompatibility of nanoparticles. In particular, gold coating is very attractive as it reduces the toxicity of the magnetic nanoparticles, enhances their stability in biological systems and provides stable and inert platforms for further functionalization. However, current methods for the fabrication of gold-coated magnetic nanoparticles are carried out in non-aqueous media with toxic organic solvents at very high temperatures. In this article, we demonstrate a novel procedure for the fabrication of gold-coated cobalt nanoparticles. Unlike previous procedures that are performed in nonaqueous conditions at elevated temperatures, this method can be carried out exclusively in aqueous media at ambient conditions. Methods: Cobalt nanoparticles were prepared by the reduction of a cobalt precursor and subsequently coated with gold by an electroless plating procedure. The Co NPs and the gold-coated Co NPs were characterized by ultraviolet-visible (UVVis) spectroscopy, X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry, scanning electron (SEM) and transmission electron (TEM) microscopy. Results: Results from SEM and TEM imaging indicated that the resulting gold-coated Co NPs had a Co core and an Au shell, were well dispersed and within the nanoscale range in terms of size (45 ± 8 nm in diameter). EDX confirmed the presence of both Co and Au in the coated sample. XRD data demonstrated a pattern with diffraction peaks indicating presence of gold and cobalt. SQUID results indicated that the magnetic properties of the nanoparticles were maintained even after coating with gold. Conclusion: All these results confirmed the fabrication of stable, well dispersed magnetic gold-coated Co NPs in aqueous media making them potentially ideal for downstream applications such as in vivo imaging, therapeutics and biological applications. Keywords: Nanoparticles, magnetic nanoparticles, cobalt nanoparticles, characterization, gold-coated, shell, core.

Response to Comment on “Cycling Li-O 2 batteries via LiOH formation and decomposition”

Lithium-oxygen (Li-O 2 ) batteries cycle reversibly with lithium iodide (LiI) additives in dimethoxyethane (DME) to form lithium hydroxide (LiOH). Viswanathan et al. argue that because the standard redox potential of the four-electron (e − ) reaction, 4OH – ↔ 2H 2 O + O 2 + 4 e – , is at 3.34 V versus Li + /Li, LiOH cannot be removed by the triiodide ion (I 3 – ). However, under nonaqueous conditions, this reaction will occur at a different potential. LiOH also reacts chemically with I 3 – to form IO 3 – , further studies being required to determine the relative rates of the two reactions on electrochemical charge.

Production of Omega-3 Fatty Acid Ethyl Esters from Menhaden Oil Using Proteus vulgaris Lipase-Mediated One-Step Transesterification and Urea Complexation.

An organic solvent-stable lipase from Proteus vulgaris K80 was used to produce the omega-3 polyunsaturated fatty acid ethyl esters (ω-3 PUFA EEs). First, the lyophilized recombinant lipase K80 (LyoK80) was used to perform the transesterification reaction of menhaden oil and ethanol. LyoK80 produced the ω-3 PUFA EEs with a conversion yield of 82% in the presence of 20% water content via a three-step ethanol-feeding process; however, in a non-aqueous condition, LyoK80 produced only a slight amount of the ω-3 PUFA EEs. To enhance its reaction properties, the lipase K80 was immobilized on a hydrophobic bead to derive ImmK80; the biochemical properties and substrate specificity of ImmK80 are similar to those of LyoK80. ImmK80 was then used to produce ω-3 PUFA EEs in accordance with the same transesterification reaction. Unlike LyoK80, ImmK80 achieved a high ω-3 PUFA EE conversion yield of 86% under a non-aqueous system via a one-step ethanol-feeding reaction. The ω-3 PUFA EEs were purified up to 92% using a urea complexation method.

Investigation of the Mechanism of Mg Insertion in Birnessite in Nonaqueous and Aqueous Rechargeable Mg-Ion Batteries

Magnesium batteries are an energy storage system that potentially offers high energy density, but development of new high voltage cathode materials and understanding of their electrochemical mechanism are critical to realize its benefits. Herein, we synthesize the layered MnO2 polymorph (the birnessite phase) as a nanostructured phase supported on conductive carbon cloth and compare its electrochemistry and structural changes when it is cycled as a positive electrode material in a Mg-ion battery under nonaqueous or aqueous conditions. X-ray photoelectron spectroscopy and transmission electron microscopy studies show that a conversion mechanism takes place during cycling in a nonaqueous electrolyte, with the formation of MnOOH, MnO, and Mg(OH)2 upon discharge. In aqueous cells, on the other hand, intercalation of Mg2+ ions takes place, accompanied by expulsion of interlayer water and transformation to a spinel-like phase as evidenced by X-ray diffraction. Both systems are structurally quasireversible. The ...

Characterization of a novel cold active and salt tolerant esterase from Zunongwangia profunda

A novel cold active esterase, EstLiu was cloned from the marine bacterium Zunongwangia profunda, overexpressed in E. coli BL21 (DE3) and purified by glutathione-S transferase (GST) affinity chromatography. The mature esterase EstLiu sequence encodes a protein of 273 amino acids residues, with a predicted molecular weight of 30KDa and containing the classical pentapeptidase motif from position 156 to 160 with the catalytic triad Ser158-Asp211-His243. Although, EstLiu showed 64% similarity with the hypothetical esterase from Chryseobacterium sp. StRB126 (WP_045498424), phylogenetic analysis showed it had no similarity with any of the established family of lipases/esterases, suggesting that it could be considered as a new family. The purified enzyme showed broad substrate specificity with the highest hydrolytic activity against p-nitrophenyl butyrate (C4). EstLiu showed remarkable activity (75%) at 0°Cand the optimal activity at pH 8.0 and 30°C with good thermostability and quickened inactivation above 60°C. EstLiu retained 81, 103, 67 and 78% of its original activity at 50% (v/v) in ethanol, isopropanol, DMSO and ethylene glycol, respectively. In the presence of Tween 20, Tween 80 and Triton X-100, EstLiu showed 88, 100 and 117% of relative activity. It is also co-factor independent. The high activity at low temperature and desirable stability in organic solvents and salts of this novel family esterase represents a good evidence of novel biocatalyst. Overall, this novel enzyme showed better activity than previously reported esterases in extreme reaction conditions and could promote the reaction in both aqueous and non-aqueous conditions, indicating its great potential for industrial applications.

Mechanistic studies of pyridinium electrochemistry: alternative chemical pathways in the presence of CO2.

Protonated heterocyclic amines, such as pyridinium, have been utilized as catalysts in the electrocatalytic reduction of carbon dioxide. While these represent a new and exciting class of electrocatalysts, the details of the mechanism and faradaic processes occurring in solution are unclear. We report a series of cyclic voltammetry experiments involving Pt, Ag, Au, and Cu electrodes, under both aqueous and nonaqueous conditions, directed towards gaining an improved mechanistic understanding of pyridinium electrochemistry. Surface-enhanced Raman (SER) spectroelectrochemistry was also performed on Cu film-over-nanosphere electrodes in order to identify adsorbed species. It was found that the reduction potential of pyridinium (-0.58 V vs. SCE) and its electrochemical reversibility are unique features of platinum electrodes. In contrast, the reduction potentials on Ag, Au, and Cu electrodes are ∼400 mV more negative than Pt in both the presence and the absence of CO2. SER spectroelectrochemistry of pyridinium solutions shows no evidence for a pyridinium radical or a pyridinium ion. Increased cathodic current in the presence of CO2 is only detected at scan rates less than 10 mV s(-1) in aqueous solutions. The addition of CO2 resulted in a shift in the potential for the hydrogen evolution reaction. Pyridinium electrochemistry was observed under nonaqueous conditions; however no increase in cathodic current was observed when CO2 was added to the solution. Based on this set of results it is concluded that the reduction potential of pyridinium is surface dependent, CO2 acts as a pseudo-reserve of H(+), and pyridinium and CO2 create an alternative mechanism for hydrogen evolution.