Atom-transfer radical polymerization of poly(ethylene oxide) macromonomers in aqueous media

Soluble comb-shaped and swelling network polymers based on monomethacrylate (M = 2080) and bismethacrylate (M = 4000) poly(ethylene oxide) macromonomers, have been synthesized by the controlled atom-transfer radical polymerization in aqueous media. PEG 2000 methyl ether ethyl-2-bromoisobutyrate and 2-bromoisobutyrate, in combination with CuBr, CuBr₂, and 2,2′-bipyridyl, have been used as initiators. The length of the main chain of comb-shaped polymers, as estimated with multidetector chromatography, is in good agreement with the calculated values in the 15–20 range at M _w /M _n = 1.42–1.89. The polymerization of the methacrylate macromonomer proceeds at a high rate and with a nearly quantitative conversion. The replacement of 10–80 mol % CuBr with CuBr₂ appreciably decelerates polymerization and decreases polydispersity to 1.14–1.21, while the experimental and calculated values of chain lengths remain equal. This finding indicates a higher level of process control. The polymer networks thus prepared manifest Gaussian elastic behavior, as is evident from the relationship between the elastic modulus G and the swelling degree Q that is consistent with the classical prediction G ～ Q ^m , where m = ?1/3. Within the framework of the accepted model of networks of this type, this fact suggests the short length of polymethacrylate chains. In addition, the relationship between the time of attainment of the gelation point and the composition of the initiation system agrees with the atomtransfer controlled polymerization mechanism. The efficiencies of various radical polymerization methods for controlling the network structure are compared.     

A Stopped-flow Study on the Kinetics and Mechanism of CO2 Uptake by the cis-[Cr(1,10-phenanthroline)2(OH2)2]3+ Complex Ion

The kinetics of the reaction between gaseous CO₂ and the cis-[Cr(phen)₂(OH₂)₂]³⁺ ion leading to the formation of the carbonato complex ion, have been studied over the pH and temperature ranges: 3 < pH < 6 and 5 < T < 25 °C, respectively, at a constant ionic strength of 1 m (NaClO₄). Investigations were carried out using the stopped-flow spectrophotometry technique in the UV–Vis range: 340–700 nm. The major reactant species in the pH range studied was cis-[Cr(phen)₂(OH)(OH₂)]²⁺ ion, which underwent reaction with CO₂ to form cis-[Cr(phen)₂(OH₂)(HCO₃)]²⁺ ion. Subsequently, slower ring closure of the latter species to form the bidentate carbonato chelate was observed. The possible mechanism has been discussed and the activation parameters ΔH^† and ΔS^† were also determined for the reaction studied.     

Preparation of thin SnO2 layers by inorganic sol-gel process

SnO₂ sols were prepared in the following way: (1) precipitation of metastannic acid with aqueous ammonia from aqueous solutions of SnCl₄, (2) washing the precipitates with NH₄NO₃ solution and water, (3) peptization of precipitates in water, sometimes with an addition of HNO₃, at elevated temperature using mechanical stirring. In those sols, sometimes diluted with water or ethanol, substrates (glass or silica derived wafers) were dipped and withdrawn at various rates. Gel coatings were converted into crystalline SnO₂ by thermal treatment at 600°C. Coatings with thickness between 300–2000 Å were prepared.     

Interferences in ultratrace speciation of organolead and organotin by gas chromatography with atomic spectrometric detection

Interferences in trace and ultratrace speciation analysis of organotin and organolead compounds in various samples by gas chromatography coupled with atomic absorption spectrometry (AAS) and/or microwave induced plasma atomic emission spectrometry (MIP AES) are investigated. Particular attention is given to the effects of matrix co-extractives and reagents impurities introduced during sample preparation. Their influence on the detection limits is discussed in terms of baseline noise level, blank value, formation of artefacts and signal suppression. Loss of column resolution during the analysis of some matrices is observed.     

Formation and thermal decomposition of aluminium nitroxy compounds

During the reactions of lithium oxide with aluminium nitride, and of lithium nitride with aluminium oxide, the formation has been observed of a previously unknown compound, of composition Li₂AlNO. The course of its thermal decomposition has also been determined.

---

Zusammenfassung Es wurde das Auftreten einer bisher unbekannten Verbindung der Zusammensetzung LiAlNO bei den Reaktionen von Lithiumoxid mit Aluminiumnitrid und Lithiumnitrid mit Aluminiumoxid beobachtet. Der Verlauf der thermischen Zersetzung dieser Verbindung wurde bestimmt.

---

Li₂AlNO. .

     

Miscibility of gramicidin A-ethyl nonadecanoate in langmuir monolayers in the presence of salts dissolved in the subphase

The behavior of binary mixed Langmuir monolayers from gramicidin A (GA) and ethyl nonadecanoate (EN), spread on aqueous subphases containing NaCl and CaCl2, was investigated on the basis of the analysis of surface pressure-average area per molecule (pi-A) isotherms complemented with Brewster angle microscopy (BAM) images. Compression modulus versus surface pressure (C(S-1)-pi) curves indicate the existence of interactions in the GA-EN mixed monolayers at low surface pressures (below 5 mN m(-1)). However, for mixtures in which the ester is the predominant component, both GA and EN are miscible within regions from fully expanded to collapse. To examine the interactions between both components in the studied system, values of the mean molecular area per molecule (A12) were plotted as a function of molar fraction of gramicidin A (X(GA)). A12-X(GA) plots exhibit negative deviations from ideality at high surface pressures, wherein beta-helices of GA are vertically oriented in respect to the interface. However, at surface pressures below the plateau transition, which is due to reorientation of GA, the binary system obeys the additive rule. Brewster angle microscopy (BAM) was applied for a direct visualization of the monolayers morphologies. The obtained images prove that for molar ratios of GA > or = 0.3 and at surface pressures above 5 mN m(-1), both components are immiscible at the interface. The observed negative deviations from the additively rule were attributed to the formation of a three-dimensional phase in the mixed film, which provokes its contraction at the interface.     

Studies on 16-Membered Azothia- and Azoxythiacrown Ethers as Ion Carriers in Ion Selective Membranes

16-Membered azothia- and azoxythiacrown ethers have been studied as ion carriers in ion-selective membranes. Their selectivities towards alkali, alkaline earth, transition and heavy metal cations were evaluated. The complex formation constants for these compounds with chosen cations have been determined using segmented sandwich membranes method.     

1,4‐Michael Addition – The Analytical Way for Quantitative Sensing of Neurotransmitter at Bare Gold Electrode in Physiological Solution in the Presence of Interfering Biogenic Compounds

Electrooxidation of norepinephrine in the presence a nucleophile was investigated on a bare gold electrode. Electrochemically produced norepinephrinequinone undergoes an attack by morpholine as nucleophile via 1,4‐Michael addition. The reaction products were identified by electrospray ionization mass spectrometry. The procedure used was suitable for quantitative norepinephrine determination in the concentration range from 1×10^?9 M to 8×10^?4 M with a detection limit of 8.7×10^?10 M in a samples containing an excess of ascorbic and uric acids. The proposed method is simple, green which means that it does not require the use of toxic compounds and solvents and thus is promising for detection of norepinephrine in physiological environment.