Coarse-grained lattice model for molecular recognition

We present a simple model which allows us to investigate the equilibrium aspects of molecular recognition between rigid biomolecules on a generic level. Using a two-stage approach, which consists of a design and a testing step, the role of cooperativity and of varying bond strength in molecular recognition is investigated. Cooperativity is found to enhance selectivity. In complexes which require a high binding flexibility, a small number of strong bonds seems to be favored compared to a situation with many but weak bonds.     

Enantioselective capillary electrophoresis for pharmacokinetic analysis of methadone and 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in equines anesthetized with ketamine and isoflurane

An enantioselective assay for the determination of methadone and its main metabolite 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in equine plasma based on capillary electrophoresis with highly sulfated γ‐cyclodextrin as chiral selector and electrokinetic analyte injection is described. The assay is based on liquid/liquid extraction of the analytes at alkaline pH from 0.1 mL plasma followed by electrokinetic sample injection of the analytes from the extract across a buffer plug without chiral selector. Separation occurs cationically at normal polarity in a pH 3 phosphate buffer containing 0.16% (w/v) of highly sulfated γ‐cyclodextrin. The developed assay is precise (intra‐ and interday RSD < 4% and < 7%, respectively), is capable to determine enantiomer levels of methadone and 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in plasma down to 2.5 ng/mL, and was successfully applied to monitor enantiomer drug and metabolite levels in plasma of a pony that was anesthetized with racemic ketamine and isoflurane and received a bolus of racemic methadone and a bolus followed by constant rate infusion of racemic methadone. The data suggest that the assay is well suited for pharmacokinetic purposes.     

Solvent-free self-assembly of C60 and cucurbit[7]uril using high-speed vibration milling

The synthesis of a cucurbit[7]uril-[60]fullerene supramolecular complex using a simple, green, and efficient pathway is reported for the first time. In the complex, which was found to be of the 1:2 type, the compounds interact weekly with each other. Since the complexation can be achieved by a solid-solid reaction without solvent both the waste and contact with harmful solvents can be reduced to a minimum. A significant increase of reaction rate and yield compared to the heterogeneous complexation was observed.     

Determination of resin acids in pulp mill EOP bleaching process effluent

Resin acids are tricyclic diterpenoids which are natural constituents of the wood from conifers. They are released from the wood during the manufacture of pulp and paper. These acids are very resistant to chemical degradation and survive the pulping and also the EOP bleaching process (EOP=alkaline extraction, oxygen and peroxide, the chemicals used in the bleaching process). Resin acids were extracted from alkaline medium using liquid–liquid extraction with t-butyl methyl ether and solid phase extraction with RP C18 adsorbent and a highly porous polystyrene-divinylbenzene polymer. After conversion of the acids to their pentafluorobenzyl esters, the extracts were analysed by GC/MS using a 25 m OV17 capillary column. Recovery values for single resin acids were determined by all three extraction methods. The solid phase extraction methods were applied to the analysis of the EOP effluent from a pulp mill bleaching process. 14 different resin acids and one resin acid methyl ester have been identified in the effluent. One of these was an oxo resin acid which might well be a product of the bleaching process.     

Formation and structure of the microemulsion phase in two-dimensional ternary AB+A+B polymeric emulsions

We present an analysis of the structure of the fluctuation-induced microemulsion phase in a ternary blend of balanced AB diblock copolymers with equal amounts of A and B homopolymers. To this end, graphical analysis methods are employed to characterize two-dimensional configuration snapshots obtained with the recently introduced field-theoretic Monte Carlo method. We find that a microemulsion forms when the mean curvature diameter of the lamellar phase coincides roughly with the periodicity of the lamellar phase. Further, we provide evidence to the effect of a subclassification of the microemulsion into a genuine and a defect-driven region.     

Indicator displacement assays as molecular timers

Dynamic mixtures of Rh-dye complexes can be used to determine the history of chemical events such as the addition of ATP and ADP by UV-vis spectroscopy.     

Enantioselective CE–MS analysis of ketamine metabolites in urine

The chiral drug ketamine has long-lasting antidepressant effects with a fast onset and is also suitable to treat patients with therapy-resistant depression. The metabolite hydroxynorketamine (HNK) plays an important role in the antidepressant mechanism of action. Hydroxylation at the cyclohexanone ring occurs at positions 4, 5, and 6 and produces a total of 12 stereoisomers. Among those, the four 6HNK stereoisomers have the strongest antidepressant effects. Capillary electrophoresis with highly sulfated γ-cyclodextrin (CD) as a chiral selector in combination with mass spectrometry (MS) was used to develop a method for the enantioselective analysis of HNK stereoisomers with a special focus on the 6HNK stereoisomers. The partial filling approach was applied in order to avoid contamination of the MS with the chiral selector. Concentration of the chiral selector and the length of the separation zone were optimized. With 5% highly sulfated γ-CD in 20 mM ammonium formate with 10% formic acid and a 75% filling the four 6HNK stereoisomers could be separated with a resolution between 0.79 and 3.17. The method was applied to analyze fractionated equine urine collected after a ketamine infusion and to screen the fractions as well as unfractionated urine for the parent drug ketamine and other metabolites, including norketamine and dehydronorketamine.     

Photochemically and thermally tunable planar defects in colloidal photonic crystals

We report a bottom-up synthesis of a photochemically and thermally active azobenzene-based polyelectrolyte multilayer (PEM) planar defect embedded in a colloidal photonic crystal (CPC). Both photoisomerization and thermal cycling lead to a precise tuning of an intragap transmitting state induced by the PEM structural defect.