Modulating Electrostatic Interactions in Ion Pair Intermediates To Alter Site Selectivity in the C−O Deoxygenation of Sugars

Controlling which products one can access from the predefined biomass-derived sugars is challenging. Changing from CH₂Cl₂ to the greener alternative toluene alters which C−O bonds in a sugar are cleaved by the tris(pentafluorophenyl)borane/HSiR₃ catalyst system. This increases the diversity of high-value products that can be obtained through one-step, high-yielding, catalytic transformations of the mono-, di-, and oligosaccharides. Computational methods helped identify this non-intuitive outcome in low dielectric solvents to non-isotropic electrostatic enhancements in the key ion pair intermediates, which influence the reaction coordinate in the reactivity-/selectivity-determining step. Molecular-level models for these effects have far-reaching consequences in stereoselective ion pair catalysis.     

Theoretical investigation of ion pair SN2 reactions of alkali isothiocyanates with alkyl halides. Part 1. Reaction of lithium isothiocyanate and methyl fluoride with inversion mechanism

The gas‐phase ionic S_N2 reactions NCS^‐ + CH₃F and ion pair S_N2 reaction LiNCS + CH₃F with inversion mechanism were investigated at the level of MP2(full)/6‐311+G**//HF/6‐311+G**. Both of them involve the reactants complex, inversion transition state, and products complex. There are two possible reaction pathways in the ionic S_N2 reaction but four reaction pathways in the ion pair S_N2 reaction. Our results indicate that the introduction of lithium significantly lower the reaction barrier and make the ion pair displacement reaction more facile. For both ionic and ion pair reaction, methyl thiocyanate is predicted to be the major product, but the latter is more selective. More‐stable methyl isothiocyanate can be prepared by thermal rearrangement of methyl thiocyanate. The theoretical predictions are consistent with the known experimental results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Simultaneous Determination of Mixtures of Nitrite and Nitrate by Reversed‐Phase Ion‐Pair Liquid Chromatography

To overcome the relatively low resolution in the separation and quantitative analysis of mixtures of nitrite and nitrate, a reversed‐phase ion‐pair liquid chromatographic method is developed with advantages of high accuracy, good selectivity, high efficiency, and low cost. By employing cetyltrimethylammonium bromide (CTAB) as the ion‐pair reagent, this method can work excellently in situations where one component in the mixture is highly in excess (e.g., molar ratio of n( NO₂⁻):n(NO₃⁻) ranging from 1:99 to 95:5). The operation parameters were optimized on a Shim‐pack VP‐ODS(150 L × 4.6) analytical column using a methanol/water ratio of 50:50 (v/v) mobile phase containing 7.0 mmol/L CTAB and 3.1 mmol/L potassium dihydrogen phosphate (KH₂PO₄).The column works at a temperature of 35 °C with a flow rate of 1.5 mL/min. Such a protocol can be applied to monitor the formation of trace nitrous acid during the oxidative decomposition of nitric acid.     

On‐line Liquid‐liquid Extraction Coupled to a Reversed Micellar‐mediated Chemiluminescence Detection System: Application to the Determination of Amino/Nitroaromatic Compounds

A simple and fast flow method for the trace level determination of p‐toluidine, 2‐methyl‐5‐nitroaniline, and 2,4‐dinitroaniline in aqueous samples is reported. These amino/nitroaromatics are related to trinitrotoluene (TNT) and appear during the degradation process of the explosive. The chemical principles of ion‐pair formation and liquid‐liquid extraction are applied: In aqueous acidic medium, the protonated analyte [HA]⁺ makes an ion‐pair with the tetrachloroaurate(III) ion, followed by on‐line ion‐pair extraction into the dichloromethane carrier used. After membrane separation, the CH₂Cl₂ containing the ion‐pair, [HA]⁺[AuCl₄]⁻, is mixed with the reversed micellar luminescent reagent of luminol (in 0.3 M Na₂CO₃) prepared from cetyl‐trimethylammonium chloride in CH₂Cl₂‐cyclohexane and the [AuCl₄⁻‐luminol chemiluminescence (CL) output is recorded. The detection limits (S/N> 3) are: p‐toluidine, 1.0 × 10⁻⁴M; 2‐methyl‐5‐nitroaniline, 1.0 × 10⁻⁷ M; 2,4‐dinitroaniline, 1.0 × 10⁻⁷ M, while the calibration curves are linear between 1.0 × 10⁻⁴ — 1.0 × 10⁻² M for all the compounds. Although spectral studies indicated the formation and extraction of a very small amount of the ion‐pair species, the reversed micellar‐mediated CL detection system provides an alternative procedure for the determination of degradation products of the explosive TNT in environmental aqueous samples.     

Theoretical Study on Reactivity of Electron Transfer in Model—System of Oxidation of α—Amino Carbon—centered Radical by O2

Electron transfer reaction between a simplified model model molecule of α－amino carbon-centered radical and O2 has studied with ab initio calculations at the MP2/6-31 G^**//UHF/6-31 G^** level,The reactant complex and the ion pair complex have been optimized and employed to perform calculation of the reaction heat and the reorganization energy,Solvent effects have been considered by applyning the conductor-like screening model,Theoretical results show that the highly endothermic charge separation process ,in which one electron transfers from the α－amino carbon-centered radical to O2,so as to form an ion pair complex,is difficult to occur in gas-phase,By apply-ing an external electronic field to prepare the charge-locallized molecular orbitals,the charge-separated state has been obtained using the initial-guess-induced self-consistent field technique,The theoretical investigations indicate that the solvent effect in the process of the oxidation of α-animo carbon-centered radical by O2 is remarkable.From the rate constant estima-tion ,it can be predicted that the oxidation of the model donor molecule by O2 can proceed,but not very fast.A peroxyl radi-cal compound has been found to be a competitive intermediate in the oxidation process.     

Reactions of Sulfanyl Chlorides with Thiocamphor and Thiofenchone: Wagner?Meerwein Rearrangement of an Intermediate Thiocarbonylium Ion

The reaction of sulfanyl and disulfanyl chlorides with thiocamphor ( 6 ) in the presence of Et₃N leads to unsymmetrical di‐ and trisulfanes, respectively (Schemes 2 and 4). A reaction mechanism via a thiocarbonylium ion, which is immediately deprotonated, is proposed. The formation of a minor product 10 in the absence of a base, resulting from a Wagner? Meerwein rearrangement, is an additional evidence for the intermediacy of a thiocarbonylium ion (Scheme 3). On the other hand, the non‐enolizable thiofenchone ( 13 ) reacts with sulfanyl chlorides in CH₂Cl₂/Et₃N to give exclusively products with a rearranged bicyclic skeleton (Scheme 5). A Wagner? Meerwein rearrangement of the intermediate thiocarbonylium ion is the key step. The structures of the products 10 and 14 , which have rearranged bicyclic systems, have been established by X‐ray crystallography.     

Ion‐pair cloud‐point extraction: A new method for the determination of water‐soluble vitamins in plasma and urine

A novel, simple, and effective ion‐pair cloud‐point extraction coupled with a gradient high‐performance liquid chromatography method was developed for determination of thiamine (vitamin B₁), niacinamide (vitamin B₃), pyridoxine (vitamin B₆), and riboflavin (vitamin B₂) in plasma and urine samples. The extraction and separation of vitamins were achieved based on an ion‐pair formation approach between these ionizable analytes and 1‐heptanesulfonic acid sodium salt as an ion‐pairing agent. Influential variables on the ion‐pair cloud‐point extraction efficiency, such as the ion‐pairing agent concentration, ionic strength, pH, volume of Triton X‐100, extraction temperature, and incubation time have been fully evaluated and optimized. Water‐soluble vitamins were successfully extracted by 1‐heptanesulfonic acid sodium salt (0.2% w/v) as ion‐pairing agent with Triton X‐100 (4% w/v) as surfactant phase at 50°C for 10 min. The calibration curves showed good linearity (r² > 0.9916) and precision in the concentration ranges of 1‐50 μg/mL for thiamine and niacinamide, 5–100 μg/mL for pyridoxine, and 0.5–20 μg/mL for riboflavin. The recoveries were in the range of 78.0–88.0% with relative standard deviations ranging from 6.2 to 8.2%.     

A Smart Glycol‐Directed Nanodevice from Rationally Designed Macroporous Materials

We have developed a smart nanodevice for the highly efficient and selective detection of glycoproteins. This polyfunctional device is fabricated through the rational functionalization of macroporous silica foam (MOSF) materials with a boron species (B‐MOSF) and amino groups (NH₂‐MOSF), and then the integration of MOSF, B‐MOSF and NH₂‐MOSF materials. In such a device, a macroporous structure with very large‐pore sizes (diameters≈100 nm) and high‐pore volumes (>0.65 cm³ g^?1) is advantageous to efficiently fasten the enzymatic reaction. The targeted specific glycopeptides of the products can be selectively isolated and enriched in B‐MOSF through the chemo‐affinity between boronic acid and glycol groups, while the non‐specific peptides are released to the solutions, or further purified by MOSF and NH₂‐MOSF, which have opposite charges. As a result, the protein digestion and glycol‐peptide isolation can be simultaneously achieved in the functionalized macroporous materials in one step, which is a great advantage compared to conventional multi‐procedure and time‐consuming techniques.     

Nitrogen‐Doped Carbon Embedded MoS2 Microspheres as Advanced Anodes for Lithium‐ and Sodium‐Ion Batteries

Rational design and synthesis of advanced anode materials are extremely important for high‐performance lithium‐ion and sodium‐ion batteries. Herein, a simple one‐step hydrothermal method is developed for fabrication of N‐C@MoS₂ microspheres with the help of polyurethane as carbon and nitrogen sources. The MoS₂ microspheres are composed of MoS₂ nanoflakes, which are wrapped by an N‐doped carbon layer. Owing to its unique structural features, the N‐C@MoS₂ microspheres exhibit greatly enhanced lithium‐ and sodium‐storage performances including a high specific capacity, high rate capability, and excellent capacity retention. Additionally, the developed polyurethane‐assisted hydrothermal method could be useful for the construction of many other high‐capacity metal oxide/sulfide composite electrode materials for energy storage.     

Kinetics and mechanism of oxidation of aurate(I) by peroxydisulphate in aqueous hydrochloric acid

The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm^?3 hydrochloric acid. The reaction proceeds with the formation of an ion‐pair between peroxydisulphate and chloride ion as the Michealis–Menten plot was linear with intercept. The ion‐pair thus formed oxidizes AuCl₂^? in a slow two‐electron transfer step without any formation of free radicals. The ion‐pair formation constant and the rate constant for the slow step were determined as 113 ± 20 dm^?3 mol^?1 and 5.0 ± 1.0 × 10^?2 dm³ mol^?1 s^?1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl₂, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 ± 0.1 dm³ mol^?1. The activation parameters were determined and the values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589–594, 2002     

Mechanistic Aspects of the Holmium‐Mediated,Reciprocal Hydrogen/Sulfur Exchange in the Gas Phase: C6H5CH3+CH2S→C6H5CHS+CH4

The thermal reaction of [Ho(CH₂S)]⁺ with toluene giving rise to [C₆H₅CHSHo]⁺ and CH₄ has been investigated using Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometry complemented by density functional theory (DFT) calculations. The high reactivity of [Ho(CH₂S)]⁺ which is in distinct contrast with the non‐reactivity of “bare” Ho⁺ has its origin in the presence of a carbon‐centered radical; the latter initiates hydrogen‐atom abstraction from the methyl group of toluene as the first step of a sequence of hydrogen and sulfur transfer mediated by cationic holmium.     

Unexpected Imidazoquinoxalinone Annulation Products in the Photoinitiated Reaction of Substituted‐3‐Methyl‐Quinoxalin‐2‐Ones with N‐Phenylglycine

Photoinduced electron transfer between N ‐phenylglycine (NPG) and electronically excited triplets of 7‐substituted‐3‐methyl‐quinoxalin‐2‐ones in acetonitrile generate the respective ion radical pair, where by decarboxylation the phenyl‐amino‐alkyl radical, PhNHCH₂?, is generated. This radical reacts with the 3‐methyl‐quinoxalin‐2‐ones ground states, leading to the product 2. Other, unexpected, 7‐substituted‐1,2,3,3a‐tetrahydro‐3a‐methyl‐2‐phenylimidazo[1,5‐a]quinoxalin‐4(5H)‐ones, annulation products, 3a–f, were generated; likely by the addition of two PhNHCH₂? radicals, to positions 3 and 4 of the quinoxalin‐2‐ones. The reaction mechanism includes a photoinduced one electron transfer initiation step, propagation steps involving radical intermediates and NPG with radical chain termination steps that lead to the respective products 2a–f and 3a–f and NPG by‐products. The proposed mechanism accounts for the strong dependency found for the initial photoconsumption quantum yields on the electron‐withdrawing power of the substituent. Therefore, photolysis of common reactants widely used such as NPG and substituted quinoxalin‐2‐ones may provide a simple synthetic way to the unusual, unreported tetrahydro‐imidazoquinoxalinones 3a–f.     

An ultrafast and clean method to manufacture poly(vinyl alcohol) bead foam products

Poly (vinyl alcohol) (PVA) foam is a promising environment‐friendly packaging material due to the good biodegradability and excellent mechanical properties. Besides, PVA can be produced on a large scale viathe non‐petroleum routes. However, the preparation of complex‐shaped PVA foam products has not been realized, because PVA is a water‐soluble and semi‐crystalline polymer with a high melting temperature (226°C), which cannot be welded through the conventional bead foaming technology. In this article, a clean and efficient strategy based on microwave foaming and sintering was innovatively developed to manufacture the PVA bead foam products. First, the expandable PVA beads were prepared through polar solvent‐plasticization, followed by supercritical carbon dioxide (scCO₂)‐impregnation in solid‐state. The impregnated beads were then surface plasticized with polar solvent by simple coating. Thus, the incorporated polar solvent in the internal and superficial regions of PVA beads was rapidly heated upon exposure to the microwave irradiation, which simultaneously induced the CO₂ foaming and interfacial melting, respectively. In this way, the expansion and welding of PVA beads were completed in a one‐step procedure. Meanwhile, the complex‐shaped PVA bead foam products with excellent elasticity and intra‐bead adhesive strength were prepared within a short period of 30 seconds. Therefore, the microwave heating can be considered as an efficient strategy for preparing the high‐performance polymer bead foam products, especially for these high‐melting temperature or glass‐transition temperature polymers.     

Preparation of Immobilized Metal Affinity Chromatographic Packings by Immobilization of Carboxymethylated Asparate (CM-Asp) Based on Monodisperse Hydrophilic Non-porous Beads and Their Application

The hydrophilic immobilized metal affinity chromatographic packing was prepared by immobilization of carboxymethylated asparate (CM‐Asp) as chelating ligand and Ni²⁺ as center ion on the base of monodispersed, 3.0 µm non‐porous monodisperse poly(glycidylmethacrylate‐co‐ethylenedimethacrylate) (P_GMA/EDMA) particles. The retention behavior of proteins and the effect of pH on the retention in the range from 4.0 to 9.0 were investigated on both the naked and metal ion chelated columns. Four proteins were quickly separated in 2.0 min with linear gradient elution at a flow rate of 3.0 mL·min^?1 by using the synthesized Ni²⁺‐CM‐Asp‐P_GMA/EDMA packings. The separation time was shorter than other immobilized metal affinity chromatography reported in the literature. The Ni²⁺‐CM‐Asp‐P_GMA/EDMA column was further investigated for the rapid separation and purification of copper‐zinc superoxide dismutase (Cu,Zn‐SOD) from the blood of pig in 3.0 min with only one step. The results obtained were satisfactory.     

Ruthenium‐Catalyzed meta‐Selective CH Bromination

The first example of a transition‐metal‐catalyzed, meta‐selective C? H bromination procedure is reported. In the presence of catalytic [{Ru(p‐cymene)Cl₂}₂], tetrabutylammonium tribromide can be used to functionalize the meta C? H bond of 2‐phenylpyridine derivatives, thus affording difficult to access products which are highly predisposed to further derivatization. We demonstrate this utility with one‐pot bromination/arylation and bromination/alkenylation procedures to deliver meta‐arylated and meta‐alkenylated products, respectively, in a single step.     

Ruthenium‐Catalyzed meta‐Selective C?H Bromination

The first example of a transition‐metal‐catalyzed, meta‐selective C H bromination procedure is reported. In the presence of catalytic [{Ru(p‐cymene)Cl₂}₂], tetrabutylammonium tribromide can be used to functionalize the meta C H bond of 2‐phenylpyridine derivatives, thus affording difficult to access products which are highly predisposed to further derivatization. We demonstrate this utility with one‐pot bromination/arylation and bromination/alkenylation procedures to deliver meta‐arylated and meta‐alkenylated products, respectively, in a single step.     

Isolation of an Imino‐N‐heterocyclic Carbene/Germanium(0) Adduct: A Mesoionic Germylene Equivalent

An autoionization of germanium dichloride/dioxane complex with an imino‐N‐heterocyclic carbene ligand ( L ) afforded a novel germyliumylidene ion, [( L )GeCl]⁺[GeCl₃]^?, which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [( L )Ge], which can be viewed as both a Ge⁰ species and a mesoionic germylene. X‐ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the π system on the GeC₂N₂ five‐membered ring. It was also confirmed that the nucleophilic behavior of [( L )Ge] as a two lone‐pair donor.     

Electrochemical Investigation for Cu2+ Oscillatory Phenomena at the Liquid/Liquid Interface with a Specific Adsorption of Ion Pair Model

In this paper, a novel current oscillatory phenomenon for Cu²⁺ at the water/1,2‐dichloroethane interface is reported with cyclic voltammetry and potential‐step chronoamperometry. The small irregular current spikes were only observed near the site of the oxidation peak of CuCl₂^? and were mainly related to the Cu²⁺concentration in the aqueous phase. Our experimental results demonstrated that the current oscillation is caused by specific adsorption of ion pairs at the W/DCE interface between Cu²⁺ in the aqueous phase and TPB^? in the organic phase. Therefore, a specific adsorption of ion pair model has been formulated for the current oscillation at the liquid/liquid interface. The DFT calculation method was used to explain the mechanism of ion pair formation. The calculation results suggested that the TPB^?Cu²⁺TPB^? ion pair has the lowest‐energy state, thus providing qualitative support for the ion pair model. A probable mechanism for the observed current oscillation was also discussed in this paper. At the same time, a spectrophotometric experiment was performed to evidence a strong attractive interaction between Cu²⁺ and TPB^?.     

Isolation of Functionalized Phenolic Monomers through Selective Oxidation and CO Bond Cleavage of the β‐O‐4 Linkages in Lignin

Functionalized phenolic monomers have been generated and isolated from an organosolv lignin through a two‐step depolymerization process. Chemoselective catalytic oxidation of β‐O‐4 linkages promoted by the DDQ/tBuONO/O₂ system was achieved in model compounds, including polymeric models and in real lignin. The oxidized β‐O‐4 linkages were then cleaved on reaction with zinc. Compared to many existing methods, this protocol, which can be achieved in one pot, is highly selective, giving rise to a simple mixture of products that can be readily purified to give pure compounds. The functionality present in these products makes them potentially valuable building blocks.     

Tetrafluoroborate Selective Electrodes on the Basis of Cations with Delocalized Charge

Screening of active substances based on styryl and trimethine cyanine dyes was carried out to prepare tetrafluoroborate ion‐selective electrodes. Correlations between the nature of the organic cation (pK_a) and working pH ranges of the sensors were studied. New tetrafluoroborate‐selective PVC membrane electrodes based on an active substance formed by the ion pair of 2‐(n‐ethylcarbazol‐3)‐ethenyl‐1,3,3‐trimethyl‐3H‐indolium and 2‐[3‐(5,6‐dimethyl‐3‐nonyl‐1,3‐benzothiazol‐2(3H)‐ylidene)propenyl]‐5,6‐dimethyl‐3‐nonyl‐1,3‐benzothiazolium with tetrafluoroborate ion were developed. The electrodes are non‐sensitive to pH in the range of 2–8 and can be used for boron determination in acidic media of 6–7 mol L^?1 H₂SO₄. The developed sensor was successfully applied for the determination of B₂O₃ in CdS(Se) nanocrystal‐doped glasses.