Electrochemical synthesis of dendritic diarylcarbenium ion pools

Dendritic diarylcarbenium ion pools were synthesized by the low temperature electrochemical oxidation of the corresponding dendritic (diarylmethyl)trimethylsilanes, which were prepared by use of the iterative method consisting of electrochemical activation and Friedel-Crafts type coupling. Time-course NMR studies revealed that thermal stability of dendritic diarylcarbenium ions depends both on the generation of the dendritic structure and on the para-substituents of the terminal phenyl groups. Dendritic diarylcarbenium ions up to the third generation exhibited high reactivity as a carbon electrophile.     

Direct dendronization of polystyrenes using dendritic diarylcarbenium ion pools

Dendritic diarylcarbenium ions exhibited sufficient electrophilicity to react with unfunctionalized polystyrenes. The polymers obtained by the reaction of the first and the second generation dendritic diarylcarbenium ions with polystyrenes were well characterized by MALDI-TOF MS and SEC-MALLS analyses and observed by AFM.     

Direct and indirect electrochemical generation of alkoxycarbenium ion pools from thioacetals

Thioacetals were found to be effective precursors to generate and accumulate alkoxycarbenium ions based on direct and indirect cation pool methods. Alkoxycarbenium ions thus generated reacted with carbon nucleophiles such as allylsilanes and enol silyl ethers to give C-C bond formation products in good yields.     

Indirect cation pool method. Rapid generation of alkoxycarbenium ion pools from thioacetals

A sequential one-pot indirect cation pool method has been developed. The method involves the electrochemical generation and accumulation of ArS(ArSSAr)+ at low temperature (step 1) and the follow-up reaction with a thioacetal to generate an alkoxycarbenium ion pool (step 2), which reacts with various carbon nucleophiles (step 3). Steps 2 and 3 are extremely fast. The electrogenerated ArS(ArSSAr)+ was well-characterized by 1H NMR and CSI-MS. The alkoxycarbenium ion pool generated by the present indirect method exhibited 1H and 13C NMR spectra and thermal stability similar to those of the alkoxycarbenium ion pool generated by the direct electrochemical method.     

Electrochemical generation of glycosyl triflate pools

Glycosyl triflates, which serve as important intermediates in glycosylation reactions, were generated and accumulated by the low-temperature electrochemical oxidation of thioglycosides such as thioglucosides, thiogalactosides, and thiomannosides in the presence of tetrabutylammonium triflate (Bu(4)NOTf) as a supporting electrolyte. Thus-obtained solutions of glycosyl triflates (glycosyl triflate pools) were characterized by low-temperature NMR measurements. The thermal stability of glycosyl triflates and their reactions with glycosyl acceptors were also examined.     

Intramolecular participation in alkoxycarbenium ion pools

[reaction: see text] Alkoxycarbenium ions having no substituents on the cationic carbon have been accumulated as "cation pools" by the introduction of an ether group in an appropriate position. Intramolecular participation of the ether oxygen is suggested to be responsible for stabilization of the alkoxycarbenium ions.     

Generation of alkoxycarbenium ion pools from thioacetals and applications to glycosylation chemistry

[reaction: see text] Alkoxycarbenium ions have been generated and accumulated as "cation pools" by the low-temperature electrochemical oxidation of alpha-phenylthioethers. Although an unsuccessful attempt to accumulate glycosyl cations was made, a one-pot method for electrochemical glycosylation, which involves anodic oxidation of thioglycosides to generate glycosyl cation equivalents followed by their reactions with glycosyl acceptors, has been developed.     

Mercaptocarborane-capped gold nanoparticles: electron pools and ion traps with switchable hydrophilicity

A simple single-phase method for the preparation of ca. 2 nm gold nanoparticles capped with mercaptocarborane ligands is introduced. The resultant monolayer protected clusters (MPCs) exhibit redox-dependent solubility and readily phase transfer between water and nonpolar solvents depending on the electronic and ionic charge stored in the metal core and in the ligand shell, respectively. The particles and their properties have been characterized by high angle annular dark field imaging in a scanning transmission electron microscope, elemental analysis, centrifugal particle sizing, UV-vis and FTIR spectroscopy, and thermogravimetric analysis and by (1)H, (11)B, and (7)Li NMR spectroscopy. Cellular uptake of the MPCs by HeLa cells has been studied by TEM, and the subsequent generation of reactive oxygen species inside the cells has been evaluated by confocal fluorescence microscopy. These MPCs qualitatively showed significant toxicity and the ability to penetrate into most cell compartments with a strong tendency of finally residing inside membranes. Applications in catalysis, electrocatalysis, and biomedicine are envisaged.     

Oxidative decomposition of oxalate ion with ozone in aqueous solution

The oxidation of oxalate ions with ozone in aqueous solution has been studied, and the effects of pH, temperature, and reactant concentrations on the reaction rate and efficiency have been estimated. The oxidative decomposition is most effective in alkaline medium (pH ≥ 10) at 50°C. Under these conditions, the consumption of ozone is 0.6±0.1 g per gram of oxalate or 1.1±0.1 mol per mole of oxalate, which corresponds to the stoichiometry (COO^–)₂ + O₃ + H₂O → 2CO₃^2– + O₂ + 2H⁺.     

Solvolyses of diarylmethyl chlorides. A comprehensive stability scale for diarylcarbenium ions.

Eleven donor substituted diarylmethyl chlorides have been solvolyzed in ethanol. The rate constants, determined at 25°C, and additional ethanolysis data taken from the literature have been connected with solvolvsis rate constants, determined in other solvents, to construct a stability scale for 74 diarylcarbenium ions, covering a rate range of > 10¹². Correlation equations are given which allow the calculation of solvolysis rates in other solvents, of equilibrium constants, and of rate constants for reactions involving diarylcarbenium ions.     

An electrode for the coulometric generation of hydrogen ion

The anodic generation of hydrogen ion on bright platinum in 1.0M sodium perchlorate is not quantitative owing to the formation of a chemical species With oxidizińg properties, presumably a peroxydiperchlorate, but 100% current efficiency can be obtained in the anodic generation of hydrogen in 0.25M sodium hydrazinium sulphate, Na(N(2)H(5))SO(4). Five hydrogen ions are formed for each four electrons passed. The efficiency of this "hydrazine-platinum anode" has been demonstrated by the high-precision coulometric titration of tris(hydroxymethyl)aminomethane.     

Cationization of organic molecules under pulsed laser induced ion generation

Mass spectra of various involatile organic compounds, obtained by surface analysis with a laser microprobe mass analyser are reported. Metal-cationized quasimolecular ions of adenine, adenosine, 5-adenylic acid and sucrose supported on metal foils were observed. Metal attachment can also be detected from mixtures of metal salts and the organic compounds. Silver-cationized sugar molecules and atomic silver ions solvated by (H₂O)_x and (NH₃)_x (x = 1,2) have been found. The mass spectra are compared with those obtained by secondary ion mass spectrometry and similar techniques, discussing the processes of ion generation involved.     

Role of electron-transfer processes in reactions of diarylcarbenium ions and related quinone methides with nucleophiles

Second-harmonic alternating current voltammetry has been used to determine one-electron reduction potentials of 15 diarylcarbenium ions and 5 structurally analogous quinone methides, which have been employed as reference electrophiles for the development of nucleophilicity scales. A linear correlation (r(2) = 0.993) between the empirical electrophilicity parameters E and the reduction potentials in acetonitrile (E = 14.091E degrees (red) - 0.279) covering a range of 1.64 V (or 158 kJ mol(-)(1)) has been observed. For a large number of nucleophiles, it has been demonstrated that the observed activation free energies of the electrophile-nucleophile combinations are 61-195 kJ mol(-)(1) smaller than the free energy change of electron transfer from nucleophile to electrophile, which definitely excludes outer-sphere electron transfer occurring during these reactions.     

Results of a transient simulation of a drift tube ion mobility spectrometer considering charge repulsion, ion loss at metallic surfaces and ion generation

With optimized geometry and operating parameters both IMS selectivity and sensitivity can be significantly increased. However, finding these parameters and geometry requires an accurate knowledge of the electrical field and the ion concentration within the IMS at any time of operation. Furthermore, the ion loss at metallic surfaces and space charge effects caused by the moving ion cloud must be considered. This is particularly true when using non-radioactive electron emitters which generate a comparably high space charge density at electron currents similar to radioactive beta-sources due to their smaller ionization volume. This can lead to a reduced IMS resolution mainly caused by coulomb repulsion. In this work a transient model which enables a detailed view on the electric field within the IMS considering ion diffusion and migration as well as ion loss and coulomb repulsion is presented. This finite element model provides excellent agreement between simulated IMS spectra and experimental data especially when considering space charge effects and coulomb repulsion respectively. The model is used to design a short drift tube IMS with significantly improved resolution. Furthermore, this model allows considering ion-ion and ion-neutral reactions, such as ion generation, charge transfer reactions and ion-ion recombination. Moreover, fluid dynamics can be considered as required for modeling aspiration type IMS.     

Parameters contributing to efficient ion generation in aerosol MALDI mass spectrometry

The Bioaerosol Mass Spectrometry (BAMS) system was developed for the real-time detection and identification of biological aerosols using laser desorption ionization. Greater differentiation of particle types is desired; consequently MALDI techniques are being investigated. The small sample size ( approximately 1 microm3), lack of substrate, and ability to simultaneously monitor both positive and negative ions provide a unique opportunity to gain new insight into the MALDI process. Several parameters known to influence MALDI molecular ion yield and formation are investigated here in the single particle phase. A comparative study of five matrices (2,6-dihydroxyacetophenone, 2,5-dihydroxybenzoic acid, alpha-cyano-4-hydroxycinnamic acid, ferulic acid, and sinapinic acid) with a single analyte (angiotensin I) is presented and reveals effects of matrix selection, matrix-to-analyte molar ratio, and aerosol particle diameter. The strongest analyte ion signal is found at a matrix-to-analyte molar ratio of 100:1. At this ratio, the matrices yielding the least and greatest analyte molecular ion formation are ferulic acid and alpha-cyano-4-hydroxycinnamic acid, respectively. Additionally, a significant positive correlation is found between aerodynamic particle diameter and analyte molecular ion yield for all matrices. SEM imaging of select aerosol particle types reveals interesting surface morphology and structure.     

Direct generation of ion beam images with a two-dimensional charge injection device

The use of a two-dimensional charge injection device (CID) to directly image the spatial profile of impingent positively charged ions is described. By this approach, no prior conversion from an ion beam to a photon image is required. Because of the positive response of the device to plasma photons, ions that emanated from the radiofrequency glow discharge source were diverted around a photon stop and focused onto the CID. The resultant ion images were digitized via an external image processor and corrected for dark current contributions. Two-dimensional ion images and single pixel line profiles are presented.     

Self-transforming stainless-steel into the next generation anode material for lithium ion batteries

Here,an extremely cost-effective and simple method is proposed in order to morphologically selftransform stain less steel from a completely inactive material to a fully operati onal,nanowire-structured,3D anode material for lithium ion batteries.The reagentless process of a single heating step of the plain stainless steel in a partially reduci ng atmosphere,converts the stain less steel into an active anode via metal-selective oxidation,creating vast spinel-structured nanowires directly from the electrochemically in active surface.The simple process allows the complete utilizati on of the 3D mesh structure as the electrochemically-active spinel nanowires greatly enhance the active surface area.The novel material and architecture exhibits high capacities(-1000 mAh/g after-400 cycles),long cycle life(>1100 cycles)and fast rate performance(>2C).Simple modulation of the substrate can result in very high areal and volumetric capacities.Thus,areal capacities greater than 10 mAh/cm² and volumetric capacities greater than 1400 mAh/cm³ can be achieved.Using the proposed method,the potential reduction in cost from the use of battery-grade graphite is at least an order of magnitude,with considerable better results achieved in terms of capacity and intrinsic structural benefits of the substrate,which include direct contact of the active material with the current collector,lack of delamination and binder-free performance.This work provides a new paradigm and a key step in the long route to replace the commercial graphite anode as the next-geneation anode material.