Triphasic nanocolloids

Triphasic nanocolloids, that is, nanocolloids with three distinct compartments, were successfully produced by use of electrified co-jetting. Simultaneous manipulation of the three parallel liquid with laminar flows yielded a liquid droplet with three interfaces between the jetting liquids. Under a high electric potential, a single liquid jet was produced from the triple point of the droplet. Separation between the phases was maintained throughout the jetting process and resulted in triphasic nanocolloids. Poly(ethylene oxide), poly(acrylic acid), and poly(acrylamide-co-acrylic acid) solutions were used and verified to be compatible with the process. Fluorescent-labeled biomolecules were selectively incorporated in each phase of the nanocolloids, and confocal laser scanning microscopy was employed for the characterization. Scanning electron microscopy results verified that the sizes of the colloids are in the range of nanocolloids. This simple and versatile technique to fabricate multicompartment nanocolloids is expected to have great impact on drug delivery, molecular imaging, and smart displays.     

Deracemization By Simultaneous Bio‐oxidative Kinetic Resolution and Stereoinversion

Deracemization, that is, the transformation of a racemate into a single product enantiomer with theoretically 100 % conversion and 100 % ee, is an appealing but also challenging option for asymmetric synthesis. Herein a novel chemo‐enzymatic deracemization concept by a cascade is described: the pathway involves two enantioselective oxidation steps and one non‐stereoselective reduction step, enabling stereoinversion and a simultaneous kinetic resolution. The concept was exemplified for the transformation of rac‐benzylisoquinolines to optically pure (S)‐berbines. The racemic substrates were transformed to optically pure products (ee>97 %) with up to 98 % conversion and up to 88 % yield of isolated product.     

Determination of aflatoxin B1 in medical herbs: interlaboratory study

A method was developed for the determination of aflatoxin B1 in medical herbs (senna pods, botanical name Cassia angustifolia; devil's claw, botanical name Harpagophytum procumbens; and ginger roots, botanical name Zingiber officinale). The method, which was tested in a mini-collaborative study by 4 laboratories, is based on an immunoaffinity cleanup followed by reversed-phase high-performance liquid chromatography separation and fluorescence detection after post-column derivatization. It allows the quantitation of aflatoxin B1 at levels lower than 2 ng/g. A second extractant (acetone-water) was tested and compared to the proposed methanol-water extractant. Several post-column derivatization options (electrochemically generated bromine, photochemical reaction, and chemical bromination) as well as different integration modes (height versus area) were also investigated. No differences were found depending on the choice of derivatization system or the signal integration mode used. The method was tested for 3 different matrixes: senna pods, ginger root, and devil's claw. Performance characteristics were established from the results of the study and resulted in HorRat values ranging from 0.12 to 0.75 with mean recoveries from 78 to 91% for the extraction with methanol-water and HorRat values ranging from 0.10-1.03 with mean recoveries from 98 to 103% for the extraction with acetone-water. As a result, the method, with all tested variations, was found to be fit-for-purpose for the determination of aflatoxin B1 in medical herbs at levels of 1 microg/kg and above.     

Chemical Cross‐linking of Polypropylenes Towards New Shape Memory Polymers

In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross‐linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x‐iPP is stable for many cycles, x‐sPP ruptures after the first shape‐memory cycle. It is shown by wide‐angle X‐ray scattering (WAXS) experiments that cross‐linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals.

     

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.     

A New Fluorescence Resonance Energy Transfer Pair and Its Application to Oligonucleotide Labeling and Fluorescence Resonance Energy Transfer Hybridization Studies

We describe two new fluorescence resonance energy transfer (FRET) compatible labels, their covalent linkage to oligonucleotides, and their use as donor and acceptor, respectively, in FRET hybridization studies. The dyes belong to the cyanine dyes, and water solubility is imparted by a phosphonate which represents a new solubilizing group in DNA labels. They were linked to amino-modified synthetic oligonucleotides via oxysuccinimide (OSI) esters. The studies performed include binding assays, determinations of molecular distances, homogeneous competitive assays, and limits of detection, which are in the order of 5 pmol/L for a 15-mer.     

Relevance of sub-surface chip layers for the lifetime of magnetically trapped atoms

We investigate the lifetime of magnetically trapped atoms above a planar, layered atom chip structure. Numerical calculations of the thermal magnetic noise spectrum are performed, based on the exact magnetic Green function and multi layer reflection coefficients. We have performed lifetime measurements where the center of a side guide trap is laterally shifted with respect to the current carrying wire using additional bias fields. Comparing the experiment to theory, we find a fair agreement and demonstrate that for a chip whose topmost layer is metallic, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a much smaller conductivity; essentially the same magnetic noise would be obtained with a metallic membrane suspended in vacuum. Based on our theory we give general scaling laws of how to reduce the effect of surface magnetic noise on the trapped atoms.