Oxidation of 2‐Phenylethylamine with N‐Bromosuccinimide in Acid and Alkaline Media: A Kinetic and Mechanistic Study

A kinetic study of oxidation of 2‐phenylethylamine (PEA), a bioactive compound, with potent oxidant, N‐bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimental rate laws obtained are: ‐d [NBS] /dt = k[NBS][PEA][H⁺] in hydrochloric acid medium and ‐d [NBS]/dt = k[NBS][PEA]^x[OH^?]^y in alkaline medium where x and y are less than unity. Accelerating effect of [Cl^?], and retardation of the added succinimide on the reaction rate have been observed in acid medium. Variation of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The reactions were studied at different temperatures and the activation parameters have been evaluated. The reaction constants involved in the proposed mechanisms were computed. The reaction was found to be faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the observed experimental results.     

Polyurethane/polyethyl acrylate interpenetrating polymer networks

The thermal decomposition kinetics of polyurethane/polyethyl acrylate interpenetrating polymer networks (PU/PEA IPN) were studied by means of thermogravimetry and derivative thermogravimetry (TG-DTG), and compared with those of polyurethane (PU) and polyethyl acrylate (PEA). The decomposition temperature (T _i) of PU/PEA IPN was found to be higher thanT _i of PEA, but lower thanT _i of PU. Thermal decomposition kinetic parameters,n andE, estimated using Coats-Redfern method, are found for PU/PEA IPN, PU and PEA to be 1.6, 1.9 and 1.1, and 196.6, 258.6 and 139.2 kJ mol^–1, respectively. The results show that PU/PEA IPN is neither a simple mixture of PU and PEA nor a copolymer of them. The mechanism of thermal decomposition of PU/PEA IPN is different from those of PU and PEA. The special network in PU/PEA IPN effectually protects weak bonds in the molecular chain of PU and PEA.We express our thanks to Dr. Yaxiong Xie and Zhiyuong Ren for their help in this work,     

Novel Biodegradable and pH‐Sensitive Poly(ester amide) Microspheres for Oral Insulin Delivery

Biodegradable and pH‐sensitive PEAs based on dual amino acids are designed, synthesized, and characterized. Insulin can be loaded into the PEA microspheres by a solid‐in‐oil‐in‐oil technique with high encapsulation efficiency. The feasibility of PEA microspheres as oral insulin delivery carriers is evaluated in vitro and in vivo. The hydrophobic leucine groups on PEA seem to play an important role in the pH‐dependent release mechanism and cytotoxicity of PEA microspheres. Oral administration of insulin‐loaded PEA microspheres to streptozotocin‐induced diabetic rats at 60 IU kg^?1 is able to reduce fasting plasma glucose levels to 49.4%. These results indicate that PEA microspheres are potential new vehicles for insulin oral delivery.

     

Adsorptive recovery of an essential rose oil component from aqueous solution by nanoporous carbon (CMK-3)

A nanoporous carbon (CMK-3) was synthesized and used to adsorb 2-phenylethanol (PEA) from aqueous solutions. The characterization of CMK-3 by N₂ adsorption isotherm revealed the formation of a nanoporous carbon with average pore diameter and surface area of 3.34 nm and 1268 m² g^?1, respectively. Column-like particle morphology of CMK-3 was observed from scanning electron microscope images. To evaluate the feasibility of CMK-3 as a potential PEA adsorbent, batch adsorption experiments were conducted for aqueous PEA solutions. The results showed that CMK-3 is an efficient sorbent for the separation of PEA from water. The optimized adsorbent doses were found to be 0.3 and 2.2 g L^?1 for 30 and 300 mg L^?1 PEA, respectively. Our studies about the effect of pH on CMK-3 adsorption capacity revealed that the adsorption capacity increased at lower pH due to the protonation of PEA. Three adsorption models, Langmuir, Freundlich and Temkin were used to describe the adsorption isotherms. Thermodynamic parameters such as ΔG ⁰, ΔH ⁰, and ΔS were also evaluated, and it was found that the sorption process was spontaneous, endothermic, and physical in nature. The adsorption kinetics was investigated in detail and the pseudo-second-order kinetic equation fitted the experimental data very well. The mechanistic study by Weber-Morris model revealed that the overall adsorption process was simultaneously governed by external mass transfer and intraparticle diffusion. Almost all (97 %) adsorbed PEA was successfully recovered into ethanol which is a common solvent in fragrance industry. CMK-3 was proved to be a promising adsorbent for the adsorption-recovery of PEA from aqueous solution.     

Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol

A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO₄ and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO₄ and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of detection of 10 g 1^–1 foro-cresol and 30 g 1^–1 form-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absorbance wavelengths obtained for the reaction products of PAP witho-cresol (614 nm) andm-cresol (632 nm), both compounds can be simultaneously determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.     

Temperature and shear dependencies of rheology of poly(acrylonitrile‐co‐itaconic acid) dope in DMF

Poly(acrylonitrile‐co‐itaconic acid) (poly(AN‐co‐IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN‐co‐IA) polymer solutions in N,N‐dimethylformamide (DMF), in the range of 1 × 10⁵–1 × 10⁶ g mol^?1, has been investigated in the shear rate (γ′) range of 1 × 10¹–5 × 10⁴ min^?1. The zero shear viscosity (η₀) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius–Frenkel–Eyring model. The free energy of activation of viscous flow (ΔG_V) values were in the range 5–32 kJ mol^?1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔG_V value of the polymer solution of any and concentration (c) is suggested. The power law fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and was found to exist at constant shear rate, concentration and temperature. For each , the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.     

Contact Interactions between Individual Fibers of Cellulose and Its Derivatives: Mechanism of Cationic Surfactant Action

The effect of cationic surfactants (cetyltrimethylammonium bromide and tetrabutylammonium iodide) and cationic polyelectrolyte polyethylenimine on the coefficient of friction and adhesion force p(during shear and tensile testing, respectively) at the point contacts between the individual fibers of cellulose, viscose, and cellulose acetate was studied. The comparison of these data with the results of -potential and adsorption measurements enabled us to relate the nonmonotonic dependence of parameters and pon the surfactant concentration to the changes in electrosurface properties and the hydrophilicity or hydrophobicity of the fibers. The specific free energy of interaction U[mJ/m²] was estimated for cellulose acetate fibers.     

RPLC retention of 1,ω-di(alkoxy)-polysulphides

Summary A simple and reliable method for routine measurement of ammonia in ambient air is described. It is based on the collection of ammonia on H₃PO₃-coated annular denuders and its subsequent derivatization withm-toluoyl chloride (MTC) in alkaline acetonitrile. The resultingm-toluamide is determined by reversed phase HPLC with UV detection at 230 nm. The limit of dotection is about 0.3g m^–3 for NH₃ in air samples collected at 151 min^–1 for one hour.     

Structure and reactivity of 3-hydroxypyridine N-oxide

It has been established by UV spectroscopy that 3-hydroxypyridine N-oxide in aqueous and acid solutions exists in the form of the conjugate acid, and in an alkaline medium in the anionic form; no bipolar form has been detected in aqueous solution. Using Huckel's MO LCAO method the indices of the -electronic structure have been calculated for various forms of 3-hydroxypyridine N-oxide. The values of the localization energies L _r ⁺ obtained agree with the experimentally observed sequence of electrophilic substitution in 3-hydroxypyridine N-oxide in acid and alkaline media.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 92–95, January, 1974.     

Spectrophotometric Determination of Polyoxyethylene Nonionic Surfactants in Ground Waters Using Triple-Stage Solid-Phase Extraction Followed by an Improved Ferric Thiocyanate Complexation Method

A practical spectrophotometric determination method for polyoxyethylene nonionic surfactants in ground waters was established, which is based on a ferric thiocyanate complexation colorimetric method preceded by a triple-stage solid-phase extraction technique using SCX, SAX, and C18 cartridges interconnected. Cationic and anionic surfactants interfere with the determination and were therefore effectively trapped and isolated by the SCX and SAX solid phases, respectively. Nonionic surfactants (NSs) were finally introduced and concentrated in the C18 cartridge. The analyte was quantitatively eluted from the C18 sorbent, and the residue was subjected to the colorimetric determination. The calibration line was linear (r² = 0.9997) up to 200µgL^–1 of heptaoxyethylenedodecylether when analyzing sample sizes of 100mL. Overall recoveries were 95–97% with an RSD of less than 3%. The method was applied to the analysis of river water, and 6.4µgL^–1 of NSs as heptaoxyethylenedodecylether was found by means of the standard addition method. The proposed method is very practical and features minimum consumption of chemicals.     

Spectrophotometric Determination of Trace Amounts of Chromium with Citrazinic Acid

A sensitive and selective spectrophotometric method for the determination of trace amounts of chromium(VI) is described, based on diazotization and coupling reactions. Chromium(VI) oxidizes hydroxylamine in acetate buffer of pH 4.0 ± 0.5 to nitrite, which then diazotizes p-aminoacetophenone to form diazonium salt. The diazonium salt is then coupled with a new coupling agent, citrazinic acid in an alkaline medium, which gives an azo dye with an absorption maximum at 470 nm, a molar absorptivity of 2.12 × 10⁴L mol^–1cm^–1, and a Sandell's sensitivity of 0.00246 g/cm². The color is stable for 6 h and the system obeys Beer's law in the range 2–15 g chromium(VI) in a final volume of 10 mL. The detection limit of chromium(VI) is 0.04 g/mL. Chromium(III) can be determined after it is oxidized with bromine water in an alkaline medium to chromium(VI). The developed method has been successfully applied to the analysis of chromium in alloy steels, industrial effluents, and pharmaceutical preparations.     

The conflict between hole delocalisation and static plus dynamic polarisation in molecular cations: illustration on Mg n + clusters

In a filled band problem, like an alkaline earth or a rare gas cluster, the positive ion is stabilised by both the hole delocalisation and by polarisation effects. The variational monoelectronic pictures take into account the first factor and the static polarisation, disregarding the dynamic or instantaneous polarisation, which is a correlation effect. This unbalance of SCF treatments underestimates the binding energy and unduly favors the structures in which the hole is concentrated on an atom surrounded by numerous neighbors. Taking into account the dynamic polarisation through CI or effective VB approaches restores the relative stability of structures where the hole is spread over a large number of atoms, as illustrated on the Mg ₄ ⁺ problem. This remark is shown to have general implications for covalent molecules.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

In-situ FTIR spectroscopy of iron electrodes

The reactions of an iron electrode in alkaline electrolytes of different concentrations are studiedin-situ using internal reflection and external reflection FTIR spectroscopy. Fe(OH)₂ is formed during the reaction Fe(O) Fe(II) at all investigated concentrations. The product of the reaction Fe(II) Fe(III) is-FeOOH in concentrated and-FeOOH in diluted alkaline solutions.     

Effects of Aromatic Fluorine Substitution on Protonated Neurotransmitters: The Case of 2‐Phenylethylamine

Fluorination of pharmaceutical compounds is a common tool to modulate their physiochemical properties. We determine the effects of site‐specific aromatic fluorine substitution on the geometric, energetic, vibrational, and electronic properties of the protonated neurotransmitter 2‐phenylethylamine (xF‐H⁺PEA, x=ortho, meta, para) by infrared multiphoton photodissociation (IRMPD) in the fingerprint range (600–1750 cm^?1) and quantum chemical calculations at the B3LYP‐D3/aug‐cc‐pVTZ level. The IRMPD spectra of all ions are assigned to their folded gauche conformers stabilized by intramolecular NH⁺???π hydrogen bonds (H‐bonds) between the protonated amino group and the aromatic ring. H→F substitution reduces the symmetry and allows for additional NH⁺???F interactions in oF‐H⁺PEA, leading to three distinct gauche conformers. In comparison to oF‐H⁺PEA, the fluorination effects on the energy landscape (energy ordering and isomerization barriers) in pF‐H⁺PEA and mF‐H⁺PEA with one and two gauche conformers are less pronounced. The strengths of the intramolecular NH⁺???F and NH⁺???π bonds are analyzed by the noncovalent interaction (NCI) method.     

Indirect flame atomic absorption detection for the liquid chromatographic separation of alkaline metals

Alkaline metals and ammonium ion are separated by cationic exchange liquid chromatography using a 60 g ml^–1 aqueous copper solution as the mobile phase at 1.5 ml min^–1. Detection is carried out by measuring copper with an atomic absorption spectrometer directly interfaced to the chromatograph. A simple T-piece is used to compensate the difference between the nebulizer uptake rate and the chromatographic flow-rate with air. The method is applicable to the analysis of alkaline metals and ammonium in waters. Average recovery (n = 16) was 100.3 ± 4.0%.     

Mechanistic study of the oxidation of N-phenyldiethanolamine by <Emphasis Type="Italic">bis</Emphasis>(hydrogen periodato)argentate(III) complex anion

The kinetics of oxidation of phenyldiethanolamine (PEA) by a silver(III) complex anion, [Ag(HIO₆)₂]⁵⁻, has been studied in an aqueous alkaline medium by conventional spectrophotometry. The main oxidation product of PEA has been identified as formaldehyde. In the temperature range 20.0–40.0 °C , through analyzing influences of [OH⁻] and [IO ₄ ⁻ ]_tot on the reaction, it is pseudo-first-order in Ag(III) disappearance with a rate expression: k _obsd = (k ₁ + k ₂[OH⁻]) K ₁ K ₂[PEA]/{f([OH⁻])[IO ₄ ⁻ ]_tot + K ₁ + K ₁ K ₂ [PEA]}, where k ₁ = (0.61 ± 0.02) × 10⁻² s⁻¹, k₂ = (0.049 ± 0.002) M⁻¹ s⁻¹ at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k ₁ and k ₂ have also been derived. A reaction mechanism is proposed involving two pre-equilibria, leading to formation of an Ag(III)-periodato-PEA ternary complex. The ternary complex undergoes a two-electron transfer from the coordination PEA to the metal center via two parallel pathways: one pathway is spontaneous and the other is assisted by a hydroxide ion.     

Deamination and decarboxylation in the chromium(III)-catalysed oxidation of L-valine by alkaline permanganate and analysis of chromium(III) in microscopic amounts by a kinetic method

The kinetics of Cr^III-catalysed oxidation of L-valine by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and L-valine in alkaline medium exhibits 2:1 stoichiometry (KMnO₄:l-valine). The reaction shows first order dependence on [permanganate] and [chromium(III)], and less than unit order dependence each in [L-valine] and alkali concentrations under the experimental conditions. However the order in [L-valine] and [alkali] changes from first order to zero order as the concentrations change from lower to higher respectively. The results suggest the formation of a complex between L-valine and the hydroxylated species of Cr^III. The complex reacts further with 1 mol of alkaline permanganate species in a rate-determining step, resulting in the formation of a free radical, which again reacts with 1 mol of alkaline permanganate species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were obtained and discussed. The title reaction has been utilised to analyse chromium(III) in the 26.0 ng cm^–3–1.0 g cm^–3 range.     

黄麻基碳纤维/MnO/C锂离子电池负极材料的制备及其电化学性能

利用黄麻碳化后的纤维和吡咯单体作为还原剂,高锰酸钾作为氧化剂,通过原位氧化还原反应法合成了碳纤维/MnO/C一维复合物。扫描电子显微镜(SEM)结果显示,MnO/C纳米颗粒分布在碳纤维的外壁上,MnO被包裹在由聚吡咯碳化而来的碳中,MnO/C纳米颗粒大小为50~150 nm。将制备的产物作为锂离子电池负极材料进行充放电测试,结果表明当电流密度为100mA·g~(-1)时,循环50次后仍具有410 mAh·g~(-1)的比容量,同时也展现了良好的倍率性能。     

Simultaneous determination of radionuclides separable into natural decay series by use of time-interval analysis

A delayed coincidence method, time-interval analysis (TIA), has been applied to successive – decay events on the millisecond time-scale. Such decay events are part of the ²²⁰Rn²¹⁶Po (T_1/2 145 ms) (Th-series) and ²¹⁹Rn²¹⁵Po (T_1/2 1.78 ms) (Ac-series). By using TIA in addition to measurement of ²²⁶Ra (U-series) from -spectrometry by liquid scintillation counting (LSC), two natural decay series could be identified and separated. The TIA detection efficiency was improved by using the pulse-shape discrimination technique (PSD) to reject -pulses, by solvent extraction of Ra combined with simple chemical separation, and by purging the scintillation solution with dry N₂ gas. The U- and Th-series together with the Ac-series were determined, respectively, from alpha spectra and TIA carried out immediately after Ra-extraction. Using the ²²¹Fr²¹⁷At (T_1/2 32.3 ms) decay process as a tracer, overall yields were estimated from application of TIA to the ²²⁵Ra (Np-decay series) at the time of maximum growth. The present method has proven useful for simultaneous determination of three radioactive decay series in environmental samples.     

Diffusion in concentrated dispersions: a study with fiber-optic quasi-elastic light scattering (FOQELS)

A fiber-optic, quasi-elastic light-scattering instrument is described using single-mode fiber optical components, including a novel slanted exit face optode. The setup operates with homodyne signal detection. It enables the characterization of diffusion processes in concentrated dispersions up to volume concentrations of 50%.The performance of the instrument is exemplified with results obtained from latex spheres with diameters of 226 nm and 404 nm at volume fractions from =0.01 to =0.5. The correlation functions are analyzed according to the second order cumulants method and the Contin-procedure yielding an average and a distribution function of the short-time self-diffusion coefficient,D _eff ^s , respectively.At high ionic strength the concentration dependence ofD _eff ^s /D ₀ is found to be in close agreement with theoretical predictions based on a multi-body interaction model of hard spheres up to =0.45. With decreasing ionic strength the negative slope of the virial expansion tends to increase, presumably due to enhanced repulsive electrostatic interactions.The described technology offers new experimental means for on-line remote control sensing of particle size in concentrated disperse systems.Presented at the 34. Hauptversammlung der Kolloidgesellschaft e.v., Bochum, Oct. 1–4, 1989