Carbenium ion trapping using sulfonamides: an acid-catalysed synthesis of pyrrolidines by intramolecular hydroamination

2-Chloromethyl-1-methylimidazole undergoes a pH-dependent aqueous hydrolysis with the neutral substrate being the reactive species, and the imidazole-protonated form (pKa = 5.7) unreactive. Addition of sodium chloride retards the hydrolysis, evidence that there is a free carbenium ion intermediate (the common ion effect). The rate constant ratio Kcl/Kw for the reactions of this cation with the added chloride and with the solvent is 7.4 M−1. Further evidence for a free cation is the observation of the 2-azidomethyl product when the hydrolysis is carried out with sodium azide present, but with no change in the rate constant. The Kaz/Kw ratio as determined by product analysis is 1.1 × 102 M−1 With the assumption that kaz represents a diffusion-controlled reaction and has a value of 7 × 109 M−1 s−1, the rate constant kw for the reaction of the cation with solvent is 6 × 107 s−1. A comparison with azide–water selectivity ratios reported for other cations shows that the imidazole-stabilized primary cation of this study is relatively long-lived. A possible explanation for this is given, in terms of the extensive resonance delocalization of the positive charge in this cation. Keywords: solvolysis, carbenium ion, heterocycle.

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Injector for a 100-500 kV Linac Electron Microscopy Source

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100061380 ◽

1967 ◽

Vol 25 ◽

pp. 274-275

Author(s):

John W. Coleman

Keyword(s):

Electron Microscopy ◽

Linear Accelerator ◽

Beam Current ◽

Ion Trapping ◽

University Of Virginia ◽

Electron Injector ◽

Illumination System ◽

Radio Corporation Of America ◽

The University ◽

Optical Integration

The injector to be described is a component in the Electron Injector-Linear Accelerator—Condenser Module for illumination used on the variable 100-500kV electron microscope being built at the Radio Corporation of America for the University of Virginia.The injector is an independently powered, autonomous unit, operating at a constant 6kV positive with respect to accelerator potential, thereby making beam current independent of accelerator potential. The injector provides for on-axis ion trapping to prolong filament lifetime, and incorporates a derived Einzel lens for optical integration into the overall illumination system for microscopy. Electrostatic beam deflectors for alignment are an integral part of the apparatus. The entire injector unit is cantilevered off a door for side loading, and is topped with a 4-filament turret released electrically but driven by a self-contained Negator spring motor.

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Aromatization of C2-C6 Aliphatic Hydrocarbons on Copper-Containing ZSM-5 Zeolites

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19922553 ◽

1992 ◽

Vol 57 (12) ◽

pp. 2553-2560

Author(s):

Zdravka Popova ◽

Katia Aristirova ◽

Christo Dimitrov

Keyword(s):

Copper Content ◽

Acid Strength ◽

The State ◽

Aliphatic Hydrocarbons ◽

Bronsted Acid ◽

Ion Formation ◽

Brönsted Acid ◽

Wide Range ◽

Carbenium Ion ◽

Acid Centers

The aromatization of a wide range of model aliphatic and cycloaliphatic hydrocarbons (ethene, ethane, propene, n-hexane, 1-hexene, methylcyclopentane, cyclohexane, cyclohexene) on copper-containing NaZSM-5 and HZSM-5 zeolites has been investigated. It was established that the degree of aromatization is related to carbenium ion formation and depends on the acid strength and copper content of zeolite. Experiments with copper-containing samples reduced prior to use indicated the possibility to enhance the selectivity to aromatization. The change of the state of Cu2+ ions during catalytic experiments confirmed the assumption about participation of Cu0 simultaneously with the Bronsted acid centers in the dehydrogenation/hydrogenation steps.

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Measurement of the effective electric field radius on Digital ion trap spectrometer

The Analyst ◽

10.1039/d1an00468a ◽

2021 ◽

Author(s):

Fuxing Xu ◽

Weimin Wang ◽

Bingjun Qian ◽

Liuyu Jin ◽

Chuanfan Ding

Keyword(s):

Electric Field ◽

Signal Intensity ◽

Ion Trap ◽

Great Influence ◽

Mass Range ◽

Ion Trapping ◽

Fundamental Parameter ◽

Digital Ion Trap ◽

Effective Electric Field

The effective electric field radius is a fundamental parameter of ion trap which has great influence on ion trapping capability, signal intensity, mass range and some other properties of ion...

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Influence of Rhamnolipids and Ionic Cross-Linking Conditions on the Mechanical Properties of Alginate Hydrogels as a Model Bacterial Biofilm

International Journal of Molecular Sciences ◽

10.3390/ijms22136840 ◽

2021 ◽

Vol 22 (13) ◽

pp. 6840

Author(s):

Natalia Czaplicka ◽

Szymon Mania ◽

Donata Konopacka-Łyskawa

Keyword(s):

Mechanical Properties ◽

Pure Water ◽

Testing Machine ◽

Bacterial Biofilm ◽

Ion Trapping ◽

Cross Linking ◽

Box Behnken Design ◽

Compression Load ◽

Alginate Hydrogels ◽

Biofilm Structure

The literature indicates the existence of a relationship between rhamnolipids and bacterial biofilm, as well as the ability of selected bacteria to produce rhamnolipids and alginate. However, the influence of biosurfactant molecules on the mechanical properties of biofilms are still not fully understood. The aim of this research is to determine the effect of rhamnolipids concentration, CaCl2 concentration, and ionic cross-linking time on the mechanical properties of alginate hydrogels using a Box–Behnken design. The mechanical properties of cross-linked alginate hydrogels were characterized using a universal testing machine. It was assumed that the addition of rhamnolipids mainly affects the compression load, and the value of this parameter is lower for hydrogels produced with biosurfactant concentration below CMC than for hydrogels obtained in pure water. In contrast, the addition of rhamnolipids in an amount exceeding CMC causes an increase in compression load. In bacterial biofilms, the presence of rhamnolipid molecules does not exceed the CMC value, which may confirm the influence of this biosurfactant on the formation of the biofilm structure. Moreover, rhamnolipids interact with the hydrophobic part of the alginate copolymer chains, and then the hydrophilic groups of adsorbed biosurfactant molecules create additional calcium ion trapping sites.

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Enhanced Osteogenesis of Dental Pulp Stem Cells In Vitro Induced by Chitosan–PEG-Incorporated Calcium Phosphate Cement

Polymers ◽

10.3390/polym13142252 ◽

2021 ◽

Vol 13 (14) ◽

pp. 2252

Author(s):

Jae Eun Kim ◽

Sangbae Park ◽

Woong-Sup Lee ◽

Jinsub Han ◽

Jae Woon Lim ◽

...

Keyword(s):

Stem Cells ◽

Calcium Phosphate ◽

Zeta Potential ◽

Mechanical Strength ◽

Calcium Phosphate Cement ◽

Dental Pulp ◽

Dental Pulp Stem Cells ◽

Ion Trapping ◽

Alizarin Red

The use of bone graft materials is required for the treatment of bone defects damaged beyond the critical defect; therefore, injectable calcium phosphate cement (CPC) is actively used after surgery. The application of various polymers to improve injectability, mechanical strength, and biological function of injection-type CPC is encouraged. We previously developed a chitosan–PEG conjugate (CS/PEG) by a sulfur (VI) fluoride exchange reaction, and the resulting chitosan derivative showed high solubility at a neutral pH. We have demonstrated the CPC incorporated with a poly (ethylene glycol) (PEG)-grafted chitosan (CS/PEG) and developed CS/PEG CPC. The characterization of CS/PEG CPC was conducted using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The initial properties of CS/PEG CPCs, such as the pH, porosity, mechanical strength, zeta potential, and in vitro biocompatibility using the WST-1 assay, were also investigated. Moreover, osteocompatibility of CS/PEG CPCs was carried out via Alizarin Red S staining, immunocytochemistry, and Western blot analysis. CS/PEG CPC has enhanced mechanical strength compared to CPC, and the cohesion test also demonstrated in vivo stability. Furthermore, we determined whether CS/PEG CPC is a suitable candidate for promoting the osteogenic ability of Dental Pulp Stem Cells (DPSC). The elution of CS/PEG CPC entraps more calcium ion than CPC, as confirmed through the zeta potential test. Accordingly, the ion trapping effect of CS/PEG is considered to have played a role in promoting osteogenic differentiation of DPSCs. The results strongly suggested that CS/PEG could be used as suitable additives for improving osteogenic induction of bone substitute materials.

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NMR Observation of Indanyl Carbenium Ion Intermediates in the Reactions of Hydrocarbons on Acidic Zeolites

Journal of the American Chemical Society ◽

10.1021/ja00101a044 ◽

1994 ◽

Vol 116 (22) ◽

pp. 10188-10195 ◽

Cited By ~ 48

Author(s):

Teng Xu ◽

James F. Haw

Keyword(s):

Carbenium Ion ◽

Acidic Zeolites

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Effect of Doping ofCd1−xZnxS/ZnS Core/Shell Quantum Dots in Negative Dielectric Anisotropy Nematic Liquid Crystal p-Methoxybenzylidene p-Decylaniline

Crystals ◽

10.3390/cryst11060605 ◽

2021 ◽

Vol 11 (6) ◽

pp. 605

Author(s):

Ayushi Rastogi ◽

Fanindra Pandey ◽

Rajiv Manohar ◽

Shri Singh

Keyword(s):

Quantum Dots ◽

Liquid Crystal ◽

Dielectric Permittivity ◽

Nematic Liquid Crystal ◽

Phase Shifters ◽

Ion Trapping ◽

Dielectric Anisotropy ◽

Core Shell ◽

Optical Parameters ◽

Dielectric Parameters

We report the effect of the doping of Cd1−xZnxS/ZnS core/shell quantum dots (CSQDs) in nematic liquid crystal p-methoxybenzylidenep-decylaniline (MBDA) at 0.05 wt/wt%, 0.1 wt/wt%, 0.15 wt/wt%, 0.2 wt/wt%, 0.25 wt/wt%, and 0.3 wt/wt% concentrations of CSQDs in MBDA. Dielectric parameters with and without bias with respect to frequency have been investigated. The change in electro-optical parameters with temperature has also been demonstrated. The increase in the mean dielectric permittivity was found due to the large dipole moment of CSQDs, which impose stronger interactions with the liquid crystal molecules. The dielectric anisotropy changes sign on doping CSQDs in MBDA liquid crystal. It was concluded that the CSQD doping noticeably increased the dielectric permittivity of nematic MBDA in the presence of an electric field. The doping of CSQDs in nematic MBDA liquid crystal reduced the ion screening effect effectively. This phenomenon is attributed to the competition between the generated ionic impurities during the assembling process and the ion trapping effect of the CSQDs. The rotational viscosity of nematic liquid crystal decreased with increasing concentration of the CSQDs, with a faster response time observed for the 0.05 wt/wt% concentration. The birefringence of the doped system increased with the inclusion of CSQDs in MBDA. These results find application in the field of display devices, phase shifters, LC – gratings, TIR waveguide, industries, and projectors.

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