Application of the Novel Tandem Process Diels‐Alder Reaction/Ireland‐Claisen Rearrangement to the Synthesis of rac‐Juvabione and rac‐Epijuvabione

The novel tandem process Diels‐Alder reaction/Ireland‐Claisen rearrangement shows a high diastereoselectivity for the Ireland‐Claisen rearrangement starting from the endo‐product of the Diels‐Alder reaction. Based on this mechanistic knowledge, the novel tandem process could be applied to the synthesis of rac‐juvabione.     

Shape memory natural rubber

Charles Goodyear discovered the vulcanization of natural rubber (NR) 170 years ago and transferred the gooey natural compound into the first representative of an entirely new class of materials; the elastomers. Thenceforth, NR was intensively explored and was used for countless products to date. All the more surprising, it was found recently that NR exhibits superior and unexpected properties whenever it is cross-linked to a degree smaller than 0.4% which is fairly below the commonly used 1%–2%. This article gives a brief overview on the exceptional properties of lightly cross-linked NR, named shape memory natural rubber (SMNR), including the cold programmable shape memory effect, storing of extremely large strain, energy and cold, and its capability to sense and memorize environmental parameters. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1381–1388     

Hybrids of silver nanoparticles with amphiphilic hyperbranched macromolecules exhibiting antimicrobial properties

Hybrids of silver particles of 1 to 2 nm in size with highly branched amphiphilically modified polyethyleneimines adhere effectively to polar substrates providing environmentally friendly antimicrobial coatings.     

Aerobic oxidation of 2,3,6-trimethylphenol to trimethyl-1,4-benzoquinone with copper(II) chloride as catalyst in ionic liquid and structure of the active species

TMQ is an important precursor in industrial vitamin E synthesis. We report a "green chemistry approach" with respect to the highly selective and environmentally friendly oxidation of 2,3,6-trimethylphenol (TMP) to trimethyl-1,4-benzoquinone (TMQ) with molecular oxygen as oxidant and a copper catalyst immobilized in a molten salt. n-Butanol as co-solvent has a positive effect on the activity and selectivity. The structurally characterized catalyst, a 1-n-butyl-3-methylimidazolium oxotetracuprat, is formed in situ via hydrolysis of CuCl2 in the presence of imidazolium chloride. We propose a mechanism of oxidative phenolate activation at a [Cu4(mu4-O)]6+ core as electronically coupled electron acceptor, formation of a copper-bound phenolate radical anion, spin delocalization into the aromatic ring, and attack by triplet oxygen at the para position. Attack of Cu(I) as reduction equivalent at the peroxy radical, proton-mediated elimination of a copper(II)-hydroxo species, will either substitute a copper(I) site in the reduced oxo cluster or take up an electron from the reduced mixed valent cluster [Cu4(mu4-O)]6+ to regenerate the oxidized cluster as the active electron acceptor.     

Electrical biochip technology—a tool for microarrays and continuous monitoring

Based on electrical biochips made in Si-technology cost effective portable devices have been constructed for field applications and point of care diagnosis. These miniaturized amperometric biosensor devices enable the evaluation of biomolecular interactions by measuring the redox recycling of ELISA products, as well as the electrical monitoring of metabolites. The highly sensitive redox recycling is facilitated by interdigitated ultramicroelectrodes of high spatial resolution. The application of these electrical biochips as DNA microarrays for the molecular diagnosis of viral infections demonstrates the measurement procedure. Self-assembling of capture oligonucleotides via thiol-gold coupling has been used to construct the DNA interface on-chip. Another application for this electrical detection principle is continuous measuring with bead-based biosensors. Here, paramagnetic nanoparticles are used as carriers of the bioanalytical interface in ELISA format. A Si-micromachined glucose sensor for continuous monitoring in interstitial fluid ex vivo shows the flexibility of the electrical platform. Here the novel approach is a pore membrane in micrometer-dimensions acting as a diffusion barrier. The electrochemical detection takes place in a cavity containing glucose oxidase and a Pt-electrode surface. The common hydrogen peroxide detection, together with Si technology, enable precise differential measurements using a second cavity.     

Immunoaffinity column cleanup with liquid chromatography using post-column bromination for determination of aflatoxin B1 in cattle feed: collaborative study

A collaborative study was conducted to evaluate the effectiveness of an immunoaffinity column cleanup liquid chromatography (LC) method for determination of aflatoxin B1 in cattle feed at a possible future European regulatory limit (1 ng/g). The test portion was extracted with acetone-water (85 + 15), filtered, diluted with water, and applied to an immunoaffinity column. The column was washed with water to remove interfering compounds, and the purified aflatoxin B1 was eluted with methanol. Aflatoxin B1 was separated and determined by reversed-phase liquid chromatography (RP-LC) and detected by fluorescence after post column derivatization (PCD) involving bromination. PCD was achieved with either pyridinium hydrobromide perbromide (PBPB), used by 14 laboratories, or an electrochemical cell and addition of bromide to the mobile phase, used by 7 laboratories. Both derivatization techniques were not significantly different when compared by the t-test; the method was statistically evaluated for all laboratories together (bromination and PBPB). The cattle feed samples, both spiked and naturally contaminated with aflatoxin B1, were sent to 21 laboratories in 14 different countries (United States, Japan, and Europe). Test portions were spiked at levels of 1.2 and 3.6 ng/g for aflatoxin B1. Recoveries ranged from 74 to 157%. Based on results for spiked samples (blind pairs at 2 levels) as well as naturally contaminated samples (blind pairs at 3 levels), the relative standard deviation for repeatability (RSDr) ranged from 5.9 to 8.7%. The relative standard deviation for reproducibility (RSDR) ranged from 17.5 to 19.6%. The method showed acceptable within- and between-laboratory precision for this matrix, as evidenced by HORRAT values, at the target levels of determination for aflatoxin B1. No major differences in RSD were observed, showing that the composition of the feeds was not a factor for the samples tested and that the method was applicable for all materials used.     

Influence of satellite groups on telechelic antimicrobial functions of polyoxazolines

The antimicrobial activity of poly(alkyloxazoline) telechelics with one quaternary N,N-dimethyldodecylammonium (DDA) end group was found to be greatly controlled by the non-bioactive distal end group, the so-called satellite group. In systematic investigations, the nature of the latter groups was varied to explore the mechanism of the satellite effect. To this end, poly(2-alkyl-1,3-oxazoline)s (alkyl = ethyl, methyl) with a DDA-group at the terminating end and varying alkyl, aminoalkyl, and polyphenyloxazoline block satellite groups, have been synthesized. Poly(oxazoline) derivatives with polydispersity indices of 1.06-1.20 and molecular weights from 2,200 to 12,800 g . mol(-1) could be obtained. The macromolecular structures have been confirmed by NMR spectroscopy and ESI-MS measurements. The polymers were investigated with regard to their antibacterial efficiency towards the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli. It was found that the introduction of alkyl chain satellites of 4-10 carbon atoms in length afforded antimicrobial activity of the polymers against both microbes that was about 2-3 times higher than that of the well-known structurally comparable low molecular weight biocide, dodecyltrimethylammonium chloride (DTAC). Based on the antimicrobial effects of the investigated polymers, a mechanism for the satellite effect was proposed.     

Mimicking dye-based functions of natural blue-light photoreceptors by studying photoinduced energy and electron transfer in a pyrene-isoalloxazine(flavin)-phenothiazine triad

An artificial system containing phenothiazine as electron donor, isoalloxazine as flavinoid redox-mediator and pyrene as antenna has been built up in order to model photoinduced energy and electron transfer processes of natural blue-light photoreceptors.