Some observations on monomer reactivity ratios in aqueous and non-aqueous media

Reactivity ratios have been determined for free radical copolymerization of n.butyl acrylate (BA) with N-vinyl-2-pyrrolidone (VP) at 65°C in bulk and in the presence of water. For 0 to 30% by weight of water in the feed, the value of r_VP was sensibly constant (∼ 0.03 ± 0.03). The value of r_BA also underwent virtually no change (∼ 0.90 ± 0.05) at water contents from 0 to 22% by weight but increased to 3.7 at 25% water and to 6.3 at 30% water. These findings are not amenable to satisfactory explanation but one aspect of possible relevance is proposed tentatively.     

The catalytic asymmetric Mannich-type reactions in aqueous media

The catalytic, diastereo- and enantioselective Mannich-type reaction of a hydrazono ester with silyl enol ethers in aqueous media has been successfully achieved with ZnF(2), a chiral diamine ligand, and trifluoromethanesulfonic acid.     

FIA titrations of phenothiazine derivatives in aqueous micellar and non-aqueous media

New methods of flow injection analysis (FIA) neutralization titrations of phenothiazine derivatives in aqueous micellar medium of a cationic surfactant using potentiometric and spectrophotometric detection were proposed; titrations with a mixing gradient chamber and high-speed titrations were compared. The FIA titration method in non-aqueous media based on an official method of determination (titration with perchloric acid in anhydrous acetic acid) was also developed. Under optimized reaction conditions and flow-through parameters, the calibration range and equations, the sensitivity, and the repeatability of all methods were found and discussed. All titrations were assayed for medicinal forms.     

Dichloramine-B as redox titrant in non-aqueous or partially aqueous media

Dichloramine-B is proposed as a redox titrant in glacial acetic acid medium. The general conditions for its use and the procedures for estimating hydrazine, ascorbic acid, ferrocyanide, hydroquinone, oxine, antimony(III) and thallium(I) potentiometrically and allyl, crotyl and cinnamyl alcohols by a back-titration procedure are described.     

The kinetics of charging and discharging of iridium oxide films in aqueous and non-aqueous media

Cyclic voltammetry and chronocoulometry have been used to investigate the kinetics of oxidation and reduction of electrochenucally generated Ir oxide films in H₂SO₄(aq), basic aqueous LiClO₄ solutions and LiClO₄ + acetonitrile solutions. In acidic aqueous solutions, the scan rate at which the main anodic peak potential begins to shift positively in cyclic voltammetry experiments has been used as a parameter to assess the charging and discharging kinetics of Ir oxide films grown under various conditions. In acidic and basic aqueous solutions, chronocoulometric measurements indicate that electron transport through the oxide is rate limiting for the main redox wave, whereas ion transport probably limits the charging/discharging kinetics in LiClO₄ + CH₃CN solutions. In this non-aqueous medium, it appears that ca. 35% of the oxide sites charge and discharge approximately an order of magnitude more rapidly than the remaining sites.     

Dichloramine-T as a new oxidimetric titrant in non-aqueous and partially aqueous media

A new oxidimetric titrant, dichloramine-T, is proposed for redox titrations in glacial acetic acid medium. The general analytical conditions for using this oxidant and the procedures for potentiometric determination of ascorbic acid, iodide, arsenic(III) and iron(II) are described.     

Thermometric titration of some monoprotic and diprotic acids in aqueous and non-aqueous media

Some mono- and diprotic acids have been titrated thermometrically with strong alkalis in aqueous and non-aqueous media. Thermograms with sharp arrest points were obtained, from which heats of neutralization were measured. Heats of neutralization in the media used were compared and an effect attributable to hydrogen bonding was found.     

Kinetic of catalytic sucrose esterification in aqueous media

The process of sucrose esterification in the presence of a homogeneous catalyst was developed directing the reaction to the production of weakly substituted esters. Esterification of sucrose was processed with octanoyl chloride in a discontinuous reactor, in presence of 4-dimethylaminopyridine as catalyst. The process was operated in a time interval ranging from 0 to 80 min, at temperatures from 288 to 303 K, pH=10 and at atmospheric pressure. The following conversion levels were obtained: octanoyl chloride 11-84%, primary monoester production of 9-67%, secondary monoesters of 1.3-17%. Activation energies ranging from 158 l to 300 kJ/mol characterized the stages of the process, among them the stage of formation of the DMAP/RCOCl complex (162.43 kJ/mol). The increase in primary monoesters yield due to the temperature rise, leads to an increase in the rate of the direct reaction as well as in the speed of secondary monoester conversion to primary monoesters, quantifying a selectivity in primary isomers in the following positions sequence: 6> 1" > 6".     

Amino-acid synthesis in aqueous media under ultrasonic irradiation

The now-famous “Miller-Urey experiment” used a reduced mixture of gases to form basic organic molecules, such as amino acids. Since then, several methods have tried to reproduce the synthesis of amino acids under unusual conditions. All authors agree that the formation mechanisms of amino acids under such conditions might be of radical origin. If so, sonochemistry, known to enhance or to promote radical pathways, should be a powerful tool to access the synthesis of these compounds. We explored the feasibility of amino acid synthesis under ultrasonic irradiation in aqueous medium under a reductive atmosphere. The effects of several experimental parameters such as incident ultrasound frequency, temperature, nature and concentration of initial reactants, reaction time, and acoustic energy were explored.     

Direct-type catalytic three-component Mannich reaction in aqueous media

Bismuth triflate catalyzed direct-type Mannich reaction of cyclohexanone, aromatic aldehyde, and aromatic amine proceeded smoothly in water to afford the corresponding β-amino ketone with very good yield and moderate to good anti selectivity.     

Dibromamine-B as a new redox titrant in non-aqueous or partially aqueous media

A new redox titrant, dibromamine-B (N,N'-dibromobenzene sulphonamide) is introduced for use in acetic acid medium. Direct potentiometric determinations of hydrazine, ascorbic acid, aniline, thiourea and its metal complexes and oxine and its metal complexes have been described.     

Photophysical and photochemical properties of tetrasulfonated silicon and germanium phthalocyanine in aqueous and non-aqueous media

The photophysical and photochemical properties of tetrasulfonated silicon and germanium phthalocyanine (SiPcS₄ and GePcS₄) in aqueous solution (phosphate-buffered saline (PBS) solution, pH 7.4) (in the presence and absence of cremophore EL (CEL)) and in dimethylsulphoxide (DMSO) were studied. The complexes have intense absorption in the visible/near-IR region though they highly aggregate in aqueous solution with a dimerization constant of 2 × 10⁴ dm³ mol⁻¹. The fluorescence excitation spectra however have only one band suggesting that only the monomer fluoresces. Both the quantum yields of the triplet state (Φ_T) and the triplet lifetimes (τ_T) were found to be higher in DMSO compared to in aqueous solution. Aggregation is hindered by addition of cremophore EL in aqueous solution and this induced disaggregation caused an increased Φ_T and τ_T probably due to the reduced interaction of the phthalocyanines with the aqueous medium in the presence of CEL.     

A comparison of redox processes for polypyrrole/dodecylsulfate films in aqueous and non-aqueous media

Polypyrrole/dodecylsulfate (PPy/DDS) films were synthesized in aqueous and ethanolic solutions and investigated in aqueous, ethanolic, methanolic and acetonitrile solutions by cyclic voltammetry (CV). The amounts of anions and cations in the films before and after electrochemical treatment were determined by electron probe microanalysis (EPMA); the film morphology was studied by scanning electron microscopy (SEM). The results prove that the mobility of bulky DDS^– ions in PPy increases in the order: water<acetonitrile<ethanol<methanol. It was found that dopant DDS^– ions can be easily removed from PPy matrix swollen in alcohols or acetonitrile by electrochemical reduction or by soaking in electrolyte solutions of these solvents. The influence of electrochemical treatment on the change of doping level in aqueous solution is essentially less and depends on the cations in the test solution. Although the electroneutrality of PPy/DDS films during redox cycling is realized mainly by movement of the cations in aqueous solution and by movement of the anions in organic solvents, nevertheless the participation of anions in aqueous and cations in organic solvents is also established. The redox properties of PPy/DDS are more dependent on the solvent of the test solutions than of the synthesis solutions. Electronic Publication     

Enhancement of lipase activity in non-aqueous media upon immobilization on multi-walled carbon nanotubes

Background  

Immobilization of biologically active proteins on nanosized surfaces is a key process in bionanofabrication. Carbon nanotubes with their high surface areas, as well as useful electronic, thermal and mechanical properties, constitute important building blocks in the fabrication of novel functional materials.     

Low-temperature polymer-assisted synthesis of shape-tunable zinc oxide nanostructures dispersible in both aqueous and non-aqueous media

We report the shape-controlled synthesis of zinc oxide (ZnO) nanostructures by a poly(vinyl methyl ether) (PVME)-assisted alkaline hydrolysis of zinc acetate at low temperature (20 °C). In this method, ZnO nanostructures of various morphologies including dumbbells, lances and triangles have been successfully prepared via a simple variation of different reaction parameters such as polymer concentration, pH of the reaction mixture and precursor concentration. However, without PVME, ZnO of such structurally uniform morphologies were not formed; rather ZnO of a mixture of defined and undefined morphologies were obtained indicating PVME-assisted the growth of such regular shaped ZnO nanostructures. HRTEM analysis of lance- and triangle-shaped samples as well as SAED patterns of all kinds of samples (dumbbell, lance and triangle) revealed that the ZnO nanostrcutures are single crystalline in nature and might form through oriented growth. XRD analysis also revealed the formation of well crystalline ZnO with a hexagonal structure. FTIR spectroscopy and TGA analysis confirmed the adsorption of PVME on the surface of ZnO nanostructures. Being a solvent adaptable polymer, the adsorbed PVME makes these shaped ZnO nanostructures highly dispersible in both polar and non-polar organic solvents including water. The extent of dispersibility in different solvents was studied by spectroscopic and microscopic techniques. Such solvent adoptability of PVME-coated ZnO nanostructures increases its ease of applications in device fabrication as well as in biological systems.     

The derivatization of fatty acids by (chloro)alkyl chloroformates in non-aqueous and aqueous media for GC analysis

Fatty acids can be conveniently derivatized in less than one minute with (chloro)alkyl chloroformates such as methyl chloroformate, 2-chloroethyl chloroformate and 2,2,2-trichloroethyl chloroformate. 2,2,2-Trichloroethyl chloroformate is the most reactive reagent, and yields a reaction product which can be sensitively detected by GC ECD (detection limit 50 ng/ml, i.e. 25 pg/injection, for C⁸, C¹⁰, and C¹² acids). In non-aqueous media 3-picoline, N-methylpiperidine, and dimethylaminopyridine show catalytic activity comparable with that of pyridine and can, therefore, replace it. N-methylpiperidine is the best basic catalyst in aqueous media (i.e. media containing up to 40 % water).