Direct current balancing algorithm for FLCOS binary phase holograms

The need for DC balancing phase pixels in ferroelectric liquid-crystal-on-silicon spatial light modulators leads to control schemes that limit their use in beam steering applications where a continuous display of a routing hologram is required. By analyzing the phase redundancy in binary phase holograms, a new DC balancing algorithm has been developed that allows more general beam splitting and multiple beam steering functions. The theoretical derivation of the algorithm and experimentally measured properties of the optical beams are presented and discussed.     

Kinetic lattice grand canonical Monte Carlo simulation for ion current calculations in a model ion channel system

An algorithm in which kinetic lattice grand canonical Monte Carlo simulations are combined with mean field theory (KLGCMC/MF) is presented to calculate ion currents in a model ion channel system. In this simulation, the relevant region of the system is treated by KLGCMC simulations, while the rest of the system is described by modified Poisson-Boltzmann mean field theory. Calculation of reaction field due to induced charges on the channel/water and membrane/water boundaries is carried out using a basis-set expansion method [Im and Roux, J. Chem. Phys. 115, 4850 (2001)]. Calculation of ion currents, electrostatic potentials, and ion concentrations, as obtained from the KLGCMC/MF simulations, shows good agreement with Poisson-Nernst-Planck (PNP) theory predictions when the channel and membrane have the same dielectric constant as water. If the channel and membrane have a lower dielectric constant than water, however, there is a considerable difference between the KLGCMC/MF and PNP predictions. This difference is attributed to the reaction field, which is missing in PNP theory. It is demonstrated that the reaction field as well as fixed charges in the channel play key roles in selective ion transport. Limitations and further development of the current KLGCMC/MF approach are also discussed.     

Development and validation of a rapid headspace gas chromatography-mass spectrometry method for the determination of diethyl ether and acetone residues in Tween extracts of shellfish intended for mouse bioassay for diarrhoetic toxins

A validated analytical method using headspace capillary gas chromatography with mass spectrometric detection, which utilises deuterated analogues of the target analytes as internal standards has been developed and applied to the determination of acetone and diethyl ether in Tween extracts of cockles (Cerastoderma edule) and mussels (Mytilus edulis) destined for mouse bioassay for lipophilic toxins. The optimal conditions for headspace incubation were 50 degrees C for 6 min. The limits of detection and quantitation for both DEE and acetone were 2 and 7 microg/mL, respectively, based on signal to noise ratios of 3 and 10, respectively. The linear dynamic range of the instrument was 0 to ca. 4000 microg/mL for both acetone (r(2)=0.995) and DEE (r(2)=0.999). Tween extracts of cockle spiked with acetone and DEE at 3925 and 3570 microg/mL, respectively, gave mean (n=3) recovery figures of 101% (RSD=13.1%) for acetone and 90% (RSD=7.3%) for DEE in cockle matrix. The corresponding figures obtained from spiked mussel matrix were 114% (RSD=5.7%) for acetone and 95% (RSD=6.7%) for DEE, respectively, which were within acceptable range.     

Balance between allylic C-H activation and cyclopropanation in the reactions of donor/acceptor-substituted rhodium carbenoids with trans-alkenes

Rhodium(II)-catalyzed reactions of aryldiazoacetates with (E)-aryl-substituted alkenes generate C-H insertion products and/or cyclopropanes. The product distribution is influenced by the nature of the donor group on the carbenoid, the structure of the (E)-aryl-substituted alkenes, and the rhodium catalyst.     

The role of dimension in multivalent binding events: structure-activity relationship of dendritic polyglycerol sulfate binding to L-selectin in correlation with size and surface charge density

L ‐, P ‐, and E ‐Selectin are cell adhesion molecules that play a crucial role in leukocyte recruitment from the blood stream to the afflicted tissue in an acute and chronic inflammatory setting. Since selectins mediate the initial contact of leukocytes to the vascular endothelium, they have evolved as a valuable therapeutic target in diseases related to inflammation by inhibition of the physiological selectin–ligand interactions. In a previous study, it was demonstrated that dPGS, a fully synthetic heparin analogue, works as an efficient inhibitor towards L ‐ and P ‐selectin in vitro as well as in vivo. Herein, the focus is directed towards the effect of size and charge density of the polyanion. The efficiency of L ‐selectin inhibition via an SPR‐based in vitro assay and a cell‐based flow chamber assay is investigated with dPGS ranging from approximately 4 to 2000 kDa. SPR measurements show that the inhibitory potential of highly sulfated dPGS increases with size and charge density. Thereby, IC₅₀ values from the micromolar to the low picomolar range are determined. The same tendency could be observed in a cell‐based flow chamber assay with three representative dPGS samples. This structure–affinity relationship of dPGS suggests that the strong inhibitory potential of dPGS is not only based on the strong electrostatic interaction with areas of cationic surface potential on L ‐selectin but is also due to a steric shielding of the carbohydrate binding site by large, flexible dPGS particles.

     

Crystal structures of ethylene glycol and ethylene glycol monohydrate

We have carried out a neutron powder diffraction study of deuterated ethylene glycol (1,2-ethanediol), and deuterated ethylene glycol monohydrate with the D2B high-resolution diffractometer at the Institut Laue-Langevin. Using these data, we have refined the complete structure, including all hydrogen atoms, of the anhydrous phase at 220 K. In addition, we have determined the structure of ethylene glycol monohydrate at 210 K using direct space methods. Anhydrous ethylene glycol crystallizes in space-group P2(1)2(1)2(1) with four formula units in a unit-cell of dimensions a = 5.0553(1) ?, b = 6.9627(1) ?, c = 9.2709(2) ?, and V = 326.319(8) ?(3) [ρ(calc)(deuterated) = 1386.26(3) kg m(-3)] at 220 K. Ethylene glycol monohydrate crystallizes in space-group P2(1)/c with four formula units in a unit-cell of dimensions a = 7.6858(3) ?, b = 7.2201(3) ?, c = 7.7356(4) ?, β = 92.868(3)°, and V = 428.73(2) ?(3) [ρ(calc)(deuterated) = 1365.40(7) kg m(-3)] at 210 K. Both the structures are characterized by the gauche conformation of the ethylene glycol molecule; however, the anhydrous phase contains the tGg' rotamer (or its mirror, g'Gt), whereas the monohydrate contains the gGg' rotamer. In the monohydrate, each water molecule is tetrahedrally coordinated, donating two hydrogen bonds to, and accepting two hydrogen bonds from the hydroxyl groups of neighboring ethylene glycol molecules. There are substantial differences in the degree of weak C-D···O hydrogen bonding between the two crystals, which calls into question the role of these interactions in determining the conformation of the ethylene glycol molecule.