Enzymatic flow-injection determination of urea in blood serum using potentiometric gas sensor with internal nonactin based ISE

Ion-selective electrode with cellulose triacetate membrane containing nonactin is employed for the potentiometric detection of ammonia produced in biocatalytic reaction in flow-injection system with enzyme reactor. The elimination of interferences occurring in the presence of alkali metal ions was achieved by covering a nonactin membrane with outer hydrophobic gas permeable membrane. The obtained flow-injection response to ammonia indicates a possibility of ammonia determination down to 10 microM ammonia. In the flow-injection system for urea determination 200 microl of 10-fold diluted blood serum sample was injected into carrier stream of distilled water merged with TRIS buffer, passed through the urease flow-through reactor and then after merging with NaOH stream delivered to the detector. It was found in several series of natural blood serum samples, that the correction for endogenous ammonia in such a determination is not indispensable.     

Comparison of the thermal behavior of three cellulose fibers mercerized or submitted to solar degradation

Comparison of Lyocell, modal and viscose fibers was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. Thermal analysis was performed in air atmosphere. Samples were mercerized (21.3 g 100 mL-1) or submitted to solar radiation (seven months). Solar degraded samples presents a higher thermal stability and are initially less degraded. Furthermore, Lyocell fiber is the most stable under thermal degradation conditions. Heating produces a reduction of the fiber diameter (about 50%). This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of macrocyclic tetraamides derived from α-amino acids and their investigations using ESI-MS technique

Chiral α,ω-diesters react under high-pressure conditions (10 kbar) with α,ω-diamines to give chiral cyclic tetraamides of C₂-symmetry. The complexation properties of tetraamides towards alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) were estimated on the basis of ESI-MS spectra.     

Evaluation of a purge-and-trap injection system for capillary gas chromatography-microwave induced plasma-atomic emission spectrometry for the determination of volatile selenium compounds in water

A method is presented for the selective determination of the volatile selenium species dimethylselenide and dimethyldiselenide, using a commercially available purge-and-trap injection system coupled to capillary gas chromatography-microwave induced plasma-atomic emission spectrometry. The efficiency of the purging step was evaluated and the parameters affecting the purge and trap processes were optimized. The method was applied to the determination of volatile selenium compounds in lake water. Relative detection limits of 2ng/l for dimethylselenide and dimethyldiselenide, corresponding to an absolute detection limit of 10 pg, were achieved.     

Thiol-ene chemistry as an effective tool for hydrophobization of cotton fabrics

In this paper, several methods of hydrophobization of cotton fabrics using the thio-ene click reaction were compared. Durable, superhydrophobic textiles were obtained in an easy way. Various variants of functionalized silsesquioxanes were used for the hydrophobization of fabrics. The synthesis of bifunctional silsesquioxanes (RSiMe₂O)₄(ViSiMe₂O)₄Si₈O₁₂ and (RSiMe₂O)₄(R’SiMe₂O)₄Si₈O₁₂ were performed via hydrothiolation of silsesquioxane derivative (ViSiMe₂O)₈Si₈O₁₂. Alkoxysilyl, alkyl and fluoroalkyl moieties were introduced as functional groups. Samples were prepared using four methods, differing in the modification method and the number of stages. During the research, fabrics were modified via (a) the dip-coating process, (b) carrying out thiol-ene click reactions directly on the surface of the fabric and (c) using both of these methods. The hydrophobicity of the fabric was evaluated by measuring the Water contact angle (WCA). The obtained samples were also examined using infrared analysis (FT-IR), Scanning electron microscope (SEM), and Elemental analysis (SEM–EDS). All analyses were performed before and after the washing process in order to verify the stability of the performed modifications.

Graphical abstract

     

The stereochemistry of quaternary N-methyl sparteinium cations, their derivatives, stereoisomers and analogues : Part II. Molecular and crystal structure, and IR spectra of methiodide and methperchlorate of 2-oxosparteine

The crystal and molecular structures of two quarternary salts of 2-oxosparteine (II), the methiodide (IICH⁺₃ • I⁻) and the methperchlorate (IICH⁺₃ • ClO⁻₄) have been determined on the basis of X-ray and IR data. The studies were performed by analogy to previously investigated quaternary salts of sparteine (I), the methiodide (ICH⁺₃ • I⁻) and the methperchlorate (ICH⁺₃ • ClO⁻₄). As expected, the configurations and conformations of cationic parts within the two pairs of quaternary salts are identical, except for the structure of their A/B fragments, which in ICH⁺₃ cations have the character of tertiary amines, but in IICH⁺₃ that of lactams.

On the basis of accumulated X-ray and IR data the similarities and differences in the modes of interaction of perchlorate and iodide anions with quaternary cations, and especially with their N⁺---CH₃ groups are discussed. In this discussion are also included the methiodide and methperchlorate of -isosparteine: IIICH⁺₃ • X⁻ (X⁻ = I⁻ or ClO⁻₄) where N⁺---CH₃ groups are cisoidally oriented to the basic nitrogen atoms. The most interesting observations are as follows: (i) When N⁺---CH₃ groups are easily accessible for direct quasi hydrogen bonding interactions with counter anions and when other positive charged groups, for instance lactam groups, are absent in quaternary cations, perchlorate anions interact more strongly than the iodide anions and in consequence introduce conformational changes into the ring with N⁺---CH₃ group as well as into further rings. (ii) Perchlorate and iodide anions interact with N⁺---CH₃ groups similarly and very weakly if at all, when the N⁺---CH₃ groups are for steric reasons inaccessible to counter anions or when in quaternary cations there are additional groups which attract the counter anions electrostatically. The last mechanism operates in both quaternary salts of 2-oxosparteine and this is the reason why their monocrystals are isosteric and IR spectra almost identical. (iii) The sterically hindered N⁺---CD₃ groups in both IIICD⁺₃ • X⁻ salts give rise in their IR spectra to two doubles of sharp, well resolved bands which indicate the presence of two different rotamers stabilized by two modes of weak intramolecular hydrogen bonds with basic N atoms. (iv) In IIICH⁺₃ • X⁻ and IIICD⁺₃ • X⁻ salts the perchlorate and iodide anions do not interact at all with the rotating and vibrating N⁺---CH₃ (N⁺---CD₃) group but the structures of these salts are not isosteric since the perchlorate anions interact more strongly than iodide anions with the A/B fragment of the IIICH⁺₃ cations. This is visible from the shapes and intensities of the so-called “trans” band in the IR spectra of both salts.     

Electrooxidation of phenol at exfoliated graphite electrode in alkaline solution

The present paper reports on exfoliated graphite (EG) used for the cyclic electrochemical process of phenol oxidation in alkaline solution. It is shown that the electrochemical activity of anode-produced EG decreases considerably in the second cycle due to the deposition of an oligomer film, composed of the products of phenol oxidation, on the EG surface. Thermal treatment of the inactive graphite anode in air at 500 °C provided a regenerated material of activity three times higher for the first cycle and 2.6 times higher for three cycles as compared to the original anode. The reason for such a behavior is assigned to a carbon film formed on the EG surface during the carbonization/oxidation processes involving the products of phenol oxidation. Comparative studies showed that electroactivity of the original EG can also be enhanced if before the process of phenol oxidation the original EG is activated by heat treatment. Unfortunately, the electrochemical activity of the product of such a treatment is higher only for the first cycle of phenol oxidation and drops dramatically in the following cycles.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdask-Sobieszewo, 23–26 April 2003. Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Copolymer of Di (methacryloyloxymethyl) naphthalene and divinylbenzene as a column packing for high-performance liquid chromatography

Summary A new porous polyaromatic ester packing was synthetized for high performance liquid chromatography. The relationship between retention and chain length of the members of homologous series of alkylbenzenes, N-alkylanilines, alkylarylethers, alkylbenzoates and alkylarylketones on this new stationary phase using different eluents was investigated. Using the alkylarylketone scale the retention indices of the homologues and test compounds were calculated. The results were compared with those obtained for poly (styrene-divinylbenzene) polymers. For both types of packing the first members of each homologous series gave non-linear behaviour. The methylene group index increments are different for the studied homologous series; thus there is no simple additivity of the retention indices. The efficiency of the porous polymeric columns is a function of the capacity factor of the solute and the organic component of the eluent.