Shifting the equilibrium of a biocatalytic cascade synthesis to enantiopure epoxides using anion exchangers

Hydroxide-loaded anion exchangers have been successfully employed to shift the equilibrium of a one-pot, two-step, two-enzyme cascade reaction affording enantiopure epoxides starting from prochiral α-chloroketones. The α-chloroketones were asymmetrically reduced employing an alcohol dehydrogenase and then transformed further to the corresponding epoxides employing halohydrin dehalogenases. Each epoxide enantiomer could be obtained with up to 93% conversion in enantiomerically pure form (>99% ee). In contrast to previous studies the amount of hydride donor (2-propanol) could be reduced due to favoured halohydrin formation in the reduction of α-chloroketones.     

A simple quantum gate with atom chips

We present a simple scheme for implementing an atomic phase gate using two degrees of freedom for each atom and discuss its realization with cold rubidium atoms on atom chips. We investigate the performance of this collisional phase gate and show that gate operations with high fidelity can be realized in magnetic traps that are currently available on atom chips.     

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.     

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.     

Taxol Inclusion Complexes with a Cyclodextrin Dimer: Possibilities to Detoxify Chemotherapeutics and to Target Drugs Specifically to Tumors?

The natural drug, paclitaxel (taxol), is highly effectiveas a tumor chemotherapeuticwith a low probability of inducing chemoresistance,but shows severe toxic side effectsat the therapeutic dose. How can this toxicitybe overcome? Here we report the synthesisof cyclodextrin dimers connected at thesecondary face by amide-bonded aliphatic spacers. The spacer length of one of the dimers referred to asdiβCD(2N-A4C5A4) or dimer 7cmatches the distance between the twobenzoic acid residues of paclitaxel. We investigated the physical inclusion of taxol into this dimer using the TNS-label competition method. Affinity constants with the dimer in comparison to free β-cyclodextrin are found to be of the order of 10⁷ l/mole.When included into the cyclodextrin dimer, the drug shows a considerable time delay of incorporation into human tumor cell cultures (OAT SCLC cells) or a total exclusion from the cells. This is the prerequisite to avoid intoxication of other organs of a patient. Possibilities are discussed to detoxify chemotherapeutics and to target their inclusioncomplexes specifically to tumors using specific biological signals.     

Gas chromatographic-mass spectrometric analysis of acrylamide and acetamide in cigarette mainstream smoke after on-column injection

A method is described for the simultaneous determination of two short-chained amides, acrylamide and acetamide (classified by the International Agency for Research on Cancer as probable and possible human carcinogens, respectively), in total particulate matter using gas chromatography-on-column injection and mass spectrometric detection. Sample preparation is kept to a minimum, and the proposed analytical procedure proves to be fast, sensitive, and precise. Validation studies show good linearity with a regression coefficient of r2=.000 for both compounds. Quantitation limits are 32 ng/mL for acrylamide and 70 ng/mL for acetamide. In the particulate phase of mainstream smoke from the University of Kentucky Reference Cigarette 2R4F, 2.3 microg/cig acrylamide and 4.7 microg/cig acetamide are found; no acetamide and only .0074 microg/cig acrylamide is found in the gas phase. Possible mechanisms of formation in cigarette smoke are discussed.