The detection of formaldehyde in textiles using interdigitated microelectrode array diffusion layer titration with electrogenerated hypobromite

An interdigitated microelectrode array (IDA) was applied to the determination of formaldehyde released from textiles produced in industry. The proposed method is based on formaldehyde reaction with hypobromite which is formed in weakly basic media by control current electrooxidation of bromide on the generator segment of the IDA array. The unreacted hypobromite diffuses through the gap between individually polarisable IDA segments and it is amperometrically detected on the collector segment of the IDA. The efficiency of this nonconvective transfer process in the absence of formaldehyde was substantially higher (78%) in comparison with that when using the rotating ring disc electrode. The influence of the added formaldehyde on the transfer process can be utilised to develop a simple and sensitive analytical procedure for formaldehyde detection with a detection limit of 4×10⁻⁶ mol dm⁻³.     

Reversible protein adsorption and bioadhesion on monolayers terminated with mixtures of oligo(ethylene glycol) and methyl groups

Surface-grafted, environmentally responsive polymers have shown great promise for controlling adsorption and desorption of macromolecules and cells on solid surfaces. In the paper, we demonstrate that certain mixed self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG) and methyl-terminated alkanethiolates on gold form surfaces with switchable hydrophobicity and tendency for protein adsorption and cellular attachment. At temperatures above 32 degrees C, SAMs with a surface density of approximately 50% OEG adsorbed significant amounts of pyruvate kinase and lysozyme, whereas below this temperature, these same SAMs were resistant to the adsorption of these proteins. Furthermore, protein layers adsorbed to these SAMs above 32 degrees C were removed upon rinsing with water below this temperature. Similar results were seen for attachment and release of the marine bacterium, Cobetia marina. The change from nonresistance to adsorptive state of the SAMs was concomitant with a change in advancing water contact angle. Vibrational sum frequency generation spectroscopy suggests that the temperature-induced changes coincide with a disorder-to-partial order transition of the hydrated methylene chains of the OEG moieties within the SAMs. Mixed OEG-methyl SAMs represent both a convenient means of controlling macromolecular and cellular adsorption within the laboratory and a useful tool for relating adsorption properties to molecular structures within the SAMs.     

Extremal k *-Cycle Resonant Hexagonal Chains

Denote by ^* _n the set of all k ^*-cycle resonant hexagonal chains with n hexagons. For any B _n ^* _n , let m(B _n ) and i(B _n ) be the numbers of matchings (=the Hosoya index) and the number of independent sets (=the Merrifield–Simmons index) of B _n , respectively. In this paper, we give a characterization of the k ^*-cycle resonant hexagonal chains, and show that for any B _n ^* _n , m(H _n )m(B _n ) and i(H _n )i(B _n ), where H _n is the helicene chain. Moreover, equalities hold only if B _n =H _n .     

The effect of minor-groove hydrogen-bond acceptors and donors on the stability and replication of four unnatural base pairs

The stability and replication of DNA containing self-pairs formed between unnatural nucleotides bearing benzofuran, benzothiophene, indole, and benzotriazole nucleobases are reported. These nucleobase analogues are based on a similar scaffold but have different hydrogen-bond donor/acceptor groups that are expected to be oriented in the duplex minor groove. The unnatural base pairs do not appear to induce major structural distortions and are accommodated within the constraints of a B-form duplex. The differences between these unnatural base pairs are manifest only in the polymerase-mediated extension step, not in base-pair stability or synthesis. The benzotriazole self-pair is extended with an efficiency that is only 200-fold less than a correct natural base pair. The data are discussed in terms of available polymerase crystal structures and imply that further modifications may result in unnatural base pairs that can be both efficiently synthesized and extended, resulting in an expanded genetic alphabet.     

Stereoselective routes to substituted β-amino carbonyl compounds via heterodiene [4π+2π] cycloadditions of auxiliary-based C2 symmetric ketene acetals

Heterodiene [4π+2π] cycloadditions of (S,S)-4,5-diaryl-2-methylene-1,3-dioxolanes 1 to a series of β-amido-α,β-unsaturated carbonyl compounds are diastereoselective (d.r.≥4:1). The products can be purified by trituration or crystallisation and hydrolysed with acid to generate the corresponding β-amido carbonyl compounds, the overall sequence effecting an auxiliary-based enantioselective conjugate addition of an acetate enolate, leading to β-aminoacid derivatives.     

Small-angle X-ray scattering studies of the open and closed conformations of aspartate aminotransferase

Summary Aspartate aminotransferase was investigated by X-ray small-angle scattering. A small difference was found between the open (active) and the closed (liganded) conformation of the enzyme. The results were compared with X-ray crystallography data.

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Untersuchungen zur Röntgenkleinwinkelstreuung der offenen und geschlossenen Konformation von Aspartat-Aminotransferase

Zusammenfassung Aspartat-Aminotransferase wurde mittels Röntgenkleinwinkelstreuung untersucht. Ein kleiner Unterschied zwischen der offenen (aktiven) und der geschlossenen (ligandierten) Konformation wurde gefunden. Die Ergebnisse wurden mit Röntgenkristallstrukturdaten verglichen.

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Abbreviations AspAT aspartate aminotransferase     

Immunological method for the detection of nitroaromatic residues covalently bound to humic acids

The potential of the earlier reported sandwich-immunoassay principle for the detection of nitroaromatic residues bound to humic acids was examined. A synthetic conjugate derived by coupling a 2,4,6-trinitrotoluene derivative to humic acid was used as a model substance for bound nitroaromatic residues. Spectrophotometric determination gave a content of 14 ± 1.6 μmol/g TNT-derivative in the synthetic conjugate, which was used as a calibration standard. Extensive blocking optimization was necessary to establish the sandwich-immunoassay. Experiments were carried out to check the selectivity of the developed test system. Trace amounts of 2,4,6-trinitrotoluene (25 μg/L) suppressed the assay signal completely by blocking the antibody binding sites. This was a proof for the excellent selectivity of the assay. The potential of quantitative determinations was examined with dilution experiments. During assay optimization strong non-immunological interactions between various proteins and humic acids were observed. This led to a significant improvement of the original sandwich-immunoassay, where the humic acid antibody was substituted by basic proteins. More sensitive calibration curves with higher signal intensities were achieved. This new immunoassay seems to be the method of choice for further immunological investigations of bound residues.     

1,6-Eliminationsreaktionen an Spirocoleonon; Charakterisierung der ersten Spiro[(methylcyclopropan)-phenanthren]-1,3-dion-Derivate

Preparation of the First Spiro[(methylcyclopropan)-phenanthrene]-1,3-dione Derivatives by 1,6-Elimination Reactions of Spirocoleons Spirocoleons, e.g. coleon J ( 1 ), on treatment with 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) in aprotic solvents, undergo enolization followed by a rapid 1,6-elimination with formation of the hitherto unknown 2-methyl-spiro[cyclopropane-1,2′(1′H)-phenanthrene]-1′,3′(4′bH)-dione system, e.g. 3 . In protic solvents, base-catalyzed solvolysis of the spirocyclopropane predominates.     

Chemical studies on antioxidant mechanisms and free radical scavenging properties of lignans

The antioxidant activity, in terms of radical scavenging capacity, of altogether 15 different lignans was measured by monitoring the scavenging of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The effect of differences in skeletal arrangement or the degree of oxidation of the lignans was investigated in a structure-activity relationship study. A large variety in the radical scavenging capacities of the different lignans was observed and related to some structural features. Lignans with catechol (3,4-dihydroxyphenyl) moieties exhibited the highest radical scavenging capacity, while the corresponding guaiacyl (3-methoxy-4-hydroxyphenyl) lignans showed a slightly weaker scavenging capacity. In addition, the butanediol structure was found to enhance the activity, whereas a higher degree of oxidation at the benzylic positions decreased the activity. Additionally, the readily available lignans (-)-secoisolariciresinol, a mixture of hydroxymatairesinol epimers and (-)-matairesinol were studied in more detail, including kinetic measurements and identification of oxidation products in the reactions with DPPH and ABAP (2,2-azobis(2-methylpropionamidine) dihydrochloride. The identification of reaction products, by GC-MS, HPLC-MS and NMR spectroscopy, showed that dimerisation of the two aromatic moieties was the major radical termination reaction. Also, the formation of adducts was a predominant reaction in the experiments with ABAP. The kinetic data obtained from the reactions between the lignans and DPPH indicated a complex reaction mechanism.