Separation of styrene and ethylbenzene on metal-organic frameworks: analogous structures with different adsorption mechanisms

The metal-organic frameworks MIL-47 (V(IV)O{O(2)C-C(6)H(4)-CO(2)}) and MIL-53(Al) (Al(III)(OH)·{O(2)C-C(6)H(4)-CO(2)}) are capable of separating ethylbenzene and styrene. Both materials adsorb up to 20-24 wt % of both compounds. Despite the fact that they have identical building schemes, the reason for preferential adsorption of styrene compared to ethylbenzene is very different for the two frameworks. For MIL-47, diffraction experiments reveal that styrene is packed inside the pores in a unique, pairwise fashion, resulting in separation factors as high as 4 in favor of styrene. These separation factors are independent of the total amount of adsorbate offered. This is due to co-adsorption of ethylbenzene in the space left available between the packed styrene pairs. The separation is of a non-enthalpic nature. On MIL-53, the origin of the preferential adsorption of styrene is related to differences in enthalpy of adsorption, which are based on different degrees of framework relaxation. The proposed adsorption mechanisms are in line with the influence of temperature on the separation factors derived from pulse chromatography: separation factors are independent of temperature for MIL-47 but vary with temperature for MIL-53. Finally, MIL-53 is also capable of removing typical impurities like o-xylene or toluene from styrene-ethylbenzene mixtures.     

Calibrations and T–Duality

For a subclass of Hitchin’s generalised geometries we introduce and analyse the concept of a structured submanifold which encapsulates the classical notion of a calibrated submanifold. Under a suitable integrability condition on the ambient geometry, these generalised calibrated submanifolds minimise a functional occurring as D–brane energy in type II string theories. Further, we investigate the behaviour of calibrated cycles under T–duality and construct non–trivial examples.     

Determination of fructose using immobilized glucose isomerase in an on-line analyzer

The determination of fructose using a continuous analyzer based on analyte conversion in enzyme reactors followed by amperometric oxygen measurement is described. Two experimental setups were compared, allowing determinations in the ranges 0–180 and 0–25 mM fructose. In the former, fructose was continuously dialyzed versus a buffer stream conducting fructose to an enzyme reactor. This reactor contained two immobilized enzyme preparations, one with immobiized glucose isomerase (E.C. 5.3.1.5) that isomerized fructose to glucose and another that subsequently oxidized the former glucose by immobilized glucose oxidase (E.C. 1.1.3.4) with the consumption of dissolved oxygen. In the latter set-up, fructose was first isomerized in a glucose isomerase reactor, then glucose was continuously dialyzed and oxidized by glucose oxidase as above. This set-up was run in continuous operation for 1000 measurement cycles with a total decrease in response less than 15%.     

Sulfoxide hemithioindigo tweezers – visible light addressable capture and release

Introducing responsive elements into supramolecular recognition systems offers great advantages for the control of intermolecular interactions and represents an important stepping stone towards multi-purpose and reprogrammable synthetic systems. Of particular interest is implementation of light-responsiveness because of the unique ease and precision of this signal. Here we present visible light responsive hemithioindigo-based molecular tweezers that bear a highly polar sulfoxide function as an additional recognition unit inside their binding site. Sulfur oxidation allows to simultaneously enhance all crucial properties of this receptor type i.e. photoswitching capability, thermal stability of individual switching states, binding affinity, and binding modulation upon switching. With a novel titration method the thermodynamic binding parameters were determined using reduced sample amounts. Employing these strongly enhanced molecular tweezers allowed to demonstrate photocontrol of intermolecular charge transfer in a reversible manner.

Hemithioindigo based molecular tweezers with a comprehensively improved property profile are obtained by simple oxidation of the sulfur atom.     

Improved thin-layer chromatographic method for the separation of cholesterol,egg phosphatidylcholine,and their degradation products

Degradation products of egg phosphatidylcholine (EPC) and cholesterol were analyzed with different normal- and reversed-phase thin-layer chromatography (TLC) systems. The best separation, in terms of the highest number of degradation products from both analytes, was obtained with a reversed-phase system, using butanol-methanol-water-96-98% (v/v) acetic acid (40 + 40 + 20 + 4, v/v/v/v) as the mobile phase after overnight saturation at 25 degrees C. A special development technique was used. After a first development, the plate was dried and a second development was performed in the same direction. This method enabled us to separate lysophosphatidylcholine, several free fatty acids and hydroperoxides, and several undefined degradation products of EPC and cholesterol. All products were visualized after the plate was dipped in a 1% (v/v) solution of 4-methoxybenzaldehyde in 98% sulfuric acid-96-98% (v/v) acetic acid-ethanol-water (2 + 10 + 60 + 30), presenting a blue color or a white spot against a colored background. After activation at 110 degrees C, a stable color for both analytes was reached after 12 min. Precision of <5% was obtained at 2 levels of analysis. Good linearity was obtained in the range of 5-30 microg for EPC (r = 0.991) and 5-40 microg for cholesterol (r = 0.991). These results show that TLC can be an inexpensive and easy alternative for the analysis of EPC and cholesterol.     

Processing and characterization of porous electrochemical cells for flue gas purification

In the present work, porous electrode materials lanthanum strontium manganate (LSM)-gadolinium-doped cerium oxide (CGO) and electrochemical cells LSM-CGO + CGO were fabricated via the processes of slurry preparation, tape casting and lamination, and sintering. Graphite, wheat starch, and polyamide powders were used as pore formers, respectively, in order to investigate their effects on shrinkage, flow rate, porosity, and average pore size of the sintered samples. The observation from scanning electronic microscope (SEM) revealed different microstructures caused by different pore formers. Porous, flat, and crack-free electrochemical cells were successfully achieved using the present ceramic processing route. The produced cells could potentially be used for flue gas purification.     

Multiple high-level QM/MM reaction paths demonstrate transition-state stabilization in chorismate mutase: correlation of barrier height with transition-state stabilization

Multiple profiles for the reaction from chorismate to prephenate in the enzyme chorismate mutase calculated with hybrid density functional combined quantum mechanics/molecular mechanics methods (B3LYP/6-31G(d)-CHARMM27) agree well with experiment, and provide direct evidence of transition-state stabilization by this important enzyme, which is at the centre of current debates about the nature of enzyme catalysis.