Hydrogen-bonding effects in calix

The synthesis and spectroscopic characterization of self-assembling calix[4]arene based capsules 1a.1a and 1b.1b are described. These compounds feature four urea substituents at the upper rims and four secondary amide fragments at the lower rims that can participate in inter- and intramolecular hydrogen bonding in apolar solution. Communication between the calixarene rims in 1a, b influences the self-assembled cavity's size and shape. Specifically. dimerization results in a perfect cone conformation of the calixarene skeleton in 1a, b and stabilizes a seam of intramolecular amide C=O...H-N hydrogen bonds at the lower rim. This seam is cycloenantiomeric, with either clockwise or counterclockwise arrangements of the head-to-tail amides. Complexation of Na+-cation breaks hydrogen bonds at the lower rim but maintains the capsular assembly. Encapsulation properties of 1a.1a and 1b.1b were studied in nonpolar solvents and their binary mixtures as well as through heterodimerization experiments. The presence of amide groups at the lower rim causes notable differences in the capsule's binding affinities when compared to the corresponding tetraester capsules 1c.1c and 1d.1d. In the monomeric state calixarenes 1a, b are in a pinched cone conformation. The solid state X-ray crystallographic studies with monomeric 1a reveal only two intramolecular C=O...H-N hydrogen bonds between the adjacent amides at the lower rim, and an extensive network of intermolecular hydrogen bonds between urea groups at the upper rim.     

Study on the electroreduction process of oxygen to superoxide ion by using acetylene black powder microelectrode

In this paper, the powder microelectrode technique was employed in studying the voltametric response of the O₂/₂⁻ couple, which demonstrated a nearly reversible redox process at an acetylene black powder microelectrode in N,N-dimethylformamide (DMF). A well-developed steady state current plateau for the electrochemical reduction of oxygen was obtained in this system. The electron transfer number (n) and heterogeneous electron transfer rate constant k _s were measured by steady-state voltametric response, and the results were 1.08, 3.4 × 10⁻³ cm s⁻¹, respectively. Additionally, the scavenging activity of O₂⁻ with biological antioxidant (ascorbic acid) was evaluated by cyclic voltammetry; IC₅₀ came to 5 × 10⁻⁴ mol/l. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1040–1044. The text was submitted by the authors in English.     

Voltammetric determination of malachite green in fish samples based on the enhancement effect of anionic surfactant

In this work, an electrochemical method for the determination of malachite green was developed on the basis of enhancement effect of an anionic surfactant: sodium dodecyl benzene sulfonate. It is found that the oxidation peak current of malachite green at carbon paste electrode significantly increases in the presence of low concentration of sodium dodecyl benzene sulfonate in pH 6.5 phosphate buffer, suggesting that sodium dodecyl benzene sulfonate shows obvious enhancement effect for the determination of malachite green. The experimental parameters, such as supporting electrolyte, kind of surfactant, concentration of sodium dodecyl benzene sulfonate and accumulation time, were optimized, and then a sensitive and convenient electrochemical method was proposed for the determination of malachite green. The oxidation peak current is proportional to the concentration of malachite green over the range from 8.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol l⁻¹, and the detection limit is 4.0 × 10⁻⁹ mol l⁻¹ after 5 min of accumulation. Finally, this new method was successfully employed to detect malachite green in fish samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1019–1024. The text was submitted by the authors in English.     

Thermal degradation of copolymers from vinyl acetate and vinyl alcohol

The thermal degradation of poly(vinyl acetate) (PVA), poly(vinyl alcohol) (PVAL), vinyl acetate-vinyl alcohol (VAVAL), vinyl acetate-vinyl-3,5-dinitrobenzoate (VAVDNB) and vinyl alcohol-3,5-dinitrobenzoate (VALVDNB) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal analysis indicates that PVA and PVAL are thermally more stable than VAVAL copolymers, being PVAL the most stable polymer. The presence of small amounts of vinyl-3,5-dinitrobenzoate (VDNB) in PVA or PVAL produces a marked decrease in the thermal stability of both homopolymers, being VALVDNB copolymers the less stable materials. The apparent activation energy of the degradative process was determined by the Kissinger and Flynn-Wall methods which agree well.     

Carboxyl groups in pre-treated regenerated cellulose fibres

The influence of peroxide bleaching and slack-mercerization on the amount of acidic groups in regenerated fibres (viscose, modal and lyocell) were studied. Conductometric titration was used to determine the total content of acidic carboxylic groups. Polyelectrolyte titration was used for surface and total charge determination, and to obtain information about the charge distribution and accessibilities of charged groups. Changes in fibre crystallinity to pre-treatment processes were characterized using iodine sorption (Schwertassek method) and correlated to treatments and the amount of carboxylic groups. For all three types of fibres the amount of accessible carboxyl groups was lowered by an increase in the degree of crystallinity. Bleaching with hydrogen peroxide causes some oxidative cellulose damage and, therefore, a larger amount of carboxyl groups (presumably formed at the end of cellulose chains). Slack-mercerization did not significantly change the total amount of acidic groups in the fibres, but their accessibility to cationic polyelectrolytes, in particular to polymers with high molecular weight was substantially lowered. Lidija Fras Zemljič, Zdenka Peršin, and Karin Stana Kleinschek are the members of the European Polysaccharide Network of Excellence (EPNOE).     

Synthesis and spectroscopic properties of furyl-phenyl-acrylates and naphthofurans and their interaction with ct-<Emphasis Type="Italic">DNA</Emphasis>

A series of novel substituted derivatives related to furyl-phenyl-acrylates and naphthofurans, was synthesized and characterized by UV/Vis and fluorescence spectroscopy. Acyclic compounds can undergo photochemical dehydrocyclization by visible light irradiation in order to obtain their cyclic derivatives. The interactions of the prepared compounds with calf thymus DNA was investigated by means of electronic absorption and fluorescence spectra. It is intriguing that addition of ct-DNA induced a fluorescence increase of acyclic derivatives, exactly the opposite of the strong fluorescence quenching observed for cyclic derivatives 10 and 12. Compound 11 showed decreasing fluorescence intensity for lower concentrations of ct-DNA, while increasing of fluorescence is observed for high excess of added ct-DNA. Correspondence: Grace Karminski-Zamola, Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 20, HR-10000 Zagreb, Croatia.     

Monitoring enzyme reaction and screening of inhibitors of acetylcholinesterase by quantitative matrix-assisted laser desorption/ionization fourier transform mass spectrometry

A matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS)-based assay was developed for kinetic measurements and inhibitor screening of acetylcholinesterase. Here, FTMS coupled to MALDI was applied to quantitative analysis of choline using the ratio of choline/acetylcholine without the use of additional internal standard, which simplified the experiment. The Michaelis constant (K _m) of acetylcholinesterase (AChE) was determined to be 73.9 μmol L⁻¹ by this approach. For Huperzine A, the linear mixed inhibition of AChE reflected the presence of competitive and noncompetitive components. The half maximal inhibitory concentration (IC₅₀) value of galantamine obtained for AChE was 2.39 μmol L⁻¹. Inhibitory potentials of Rhizoma Coptidis extracts were identified with the present method. In light of the results the referred extracts as a whole showed inhibitory action against AChE. The use of high-resolution FTMS largely eliminated the interference with the determination of ACh and Ch, produced by the low-mass compounds of chemical libraries for inhibitor screening. The excellent correlation with the reported kinetic parameters confirms that the MS-based assay is both accurate and precise for determining kinetic constants and for identifying enzyme inhibitors. The obvious advantages were demonstrated for quantitative analysis and also high-throughput characterization. This study offers a perspective into the utility of MALDI-FTMS as an alternate quantitative tool for inhibitor screening of AChE.     

Brugnanin,a new syn-2,3-dihydrobenzofuran neolignan dioate from the mangrove <Emphasis Type="Italic">Bruguiera gymnorrhiza</Emphasis>

Brugnanin (1), a neolignan dioate, was isolated from a mangrove plant Bruguiera gymnorrhiza. Based on spectroscopic interpretation of MS, IR, and NMR data, 1 was elucidated as (7R*,8S*,E)-3-hydroxy-5,5′-dimethoxy-7-O-4′,8-3′-neolignan-7′-ene-9,9′-dioic acid dioctadecyl ester. MTT assay showed that 1 had weak inhibitory activity against growth of CNE-1 nasopharyngeal carcinoma cell line. Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 147–149, March–April, 2008.     

Heritability and linkage study on heart rates in a Mongolian population

Elevated heart rate has been proposed as an independent risk factor for cardiovascular diseases, but their interrelationships are not well understood. In this study, we performed a genome-wide linkage scan in 1,026 individuals (mean age 30.6 years, 54.5% women) from 73 extended families of Mongolia and determined quantitative trait loci that influence heart rate. The DNA samples were genotyped using deCODE 1,039 microsatellite markers for 3 cM density genome-wide linkage scan. Correlation analysis was carried out to evaluate the correlation of the covariates and the heart rate. T-tests of the heart rate were also performed on sex, smoking and alcohol intake. Consequently, this model was used in a nonparametric genome-wide linkage analysis using variance component model to create a multipoint logarithm of odds (LOD) score and a corresponding P value. In the adjusted model, the heritability of heart rate was estimated as 0.32 (P<.0001) and a maximum multipoint LOD score of 2.03 was observed in 77 cM region at chromosome 18. The second largest LOD score of 1.52 was seen on chromosome 5 at 216 cM. Genes located on the specified locations in chromosomes 5 and 18 may be involved in the regulation of heart rate.     

Identification of rat urinary glycoproteome captured by three lectins using gel and LC-based proteomics

Many different types of urine proteome studies have been done, but urine glycoprotein studies are insufficient. Therefore, we studied the glycoproteins from rat urine, which could be used to identify biomarkers in an animal model. First, urinary proteins were prepared by using the dialysis and lyophilizing methods from rat urine. Glycoproteins enriched with lectin affinity purification, concanavalin A, jacalin and wheat germ agglutinin from the urinary proteins were separated by means of reverse-phase fast protein LC (FPLC) or 1-D PAGE. Each FPLC fraction and 1-D PAGE gel band were trypsin-digested and analyzed by means of nanoLC-MS/MS. LC-MS/MS analyses were carried out by using linear ion trap MS. A total of 318 rat urinary glycoproteins were identified from the FPLC fractions and gel bands; approximately 90% of identified proteins were confirmed as glycoproteins in Swiss-Prot. Many glycoproteins, known as biomarkers, including C-reactive protein, uromodulin, amyloid beta A4 protein, alpha-1-inhibitor 3, vitamin D-binding protein, kallikrein 3 and fetuin-A were identified in this study. By studying urinary glycoproteins collected from rat, these results may help to assist in identifying urinary biomarkers regarding various types of disease models.