Molecular imprinting of cyclodextrin to physiologically active oligopeptides in water

β-Cyclodextrin (β-CyD)-based polymeric receptors for γ-endorphin (γ-endor, an opioid heptadecapeptide) were prepared using the molecular imprinting method. When mono-3-(N-acrylamido)-3-deoxy-β-CyD bearing a vinyl group in the secondary hydroxyl side of the cavity of β-CyD was polymerised in water in the presence of γ-endor, the binding activity of the β-CyD polymer to this peptide in water was enormously promoted by the imprinting. By contrast, the bindings towards methionine–enkephalin (N-terminal pentapeptide of γ-endor) and its homologue leucine–enkephalin were suppressed. Thus, the binding of γ-endor by the imprinted polymer was highly selective. The imprinting towards γ-endor was also successful with the use of the β-CyD monomer bearing a vinyl group in the primary hydroxyl side of the cavity, although the recognition was less strict. Various factors affecting the imprinting efficiency (kinds of β-CyD vinyl monomer and template, as well as the pH of imprinting mixture) are discussed.     

Computational analysis of ligand recognition mechanisms by prostaglandin E2 (subtype 2) and D2 receptors

The eight members of the prostanoid receptor family belong to the class A G protein-coupled receptors. We investigated the evolutionary relationship of the eight members by a molecular phylogenetic analysis and found that prostaglandin E₂ receptor subtype 2 (EP₂) and prostaglandin D₂ receptor (DP) were closely related. The structures of the ligands for the two receptors are similar to each other but are distinguished by the exchanged locations of the carbonyl oxygen and the hydroxy group in the cyclopentane ring. The ligand recognition mechanisms of the receptors were examined by an integrated approach using several computational methods, such as amino acid sequence comparison, homology modeling, docking simulation, and molecular dynamics simulation. The results revealed the similar location of the ligand between the two receptors. The common carboxy group of the ligands interacts with the Arg residue on the seventh transmembrane (TM) helix, which is invariant among the prostanoid receptors. EP₂ uses a Ser on TM1 to recognize the carbonyl oxygen in the cyclopentane ring of the ligand. The Ser is specifically conserved within EP₂. On the other hand, DP uses a Lys on TM2 to recognize the hydroxy group of the ?? chain of the ligand. The Lys is also specifically conserved within DP. The interaction network between the D(E)RY motif and TM6 was found in EP₂. However, DP lacked this network, due to the mutation in the D(E)RY motif. Based on these observations and the previously published mutational studies on the motif, the possibility of another activation mechanism that does not involve the interaction between the D(E)RY motif and TM6 will be discussed.     

Electrokinetic supercharging with a system-induced terminator and an optimized capillary versus electrode configuration for parts-per-trillion detection of rare-earth elements in CZE

A further improvement of electrokinetic supercharging (EKS) methodology has been proposed, with the objective to enhance the sensitivity of the conventional CZE-UV method down to a single-digit part per trillion (ppt) level. The advanced EKS procedure is based on a novel phenomenon displaying the formation of a zone with an increased concentration of the hydrogen ion, capable to perform the function of a terminator, behind the sample zone upon electrokinetic injection. In combination with a visualizing co-ion of BGE, protonated 4-methylbenzylamine, acting as the leading ion, such system-induced terminator a effected the transient ITP state to efficiently concentrate cationic analytes prior to CZE. Furthermore, to amass more analyte ions within the effective electric field at the injection stage, a standard sample vial was replaced with an elongated vial that allowed the sample volume to be increased from 500 to 900 μL. Alongside, this replacement made the upright distance between the electrode and the capillary tips prolonged to 40.0 mm to achieve high-efficiency electrokinetic injection. The computer simulation was used for profiling analyte concentration, pH, and field strength in order to delineate formation of the terminator during sample injection. The proposed preconcentration strategy afforded an enrichment factor of 80,000 and thereby the LODs of rare-earth metal ions at the ppt level, e.g. 0.04 nM (6.7 ng/L) for erbium(III).     

Synthesis of skeletal analogues of saxitoxin derivatives and evaluation of their inhibitory activity on sodium ion channels Na(V)1.4 and Na(V)1.5

Skeletal analogues of saxitoxin (STX) that possess a fused-type tricyclic ring system, designated FD-STX, were synthesized as candidate sodium ion channel modulators. Three kinds of FD-STX derivatives 4a-c with different substitution at C13 were synthesized, and their inhibitory activity on sodium ion channels was examined by means of cell-based assay. (-)-FD-STX (4a) and (-)-FD-dcSTX (4b), which showed moderate inhibitory activity, were further evaluated by the use of the patch-clamp method in cells that expressed Na(V)1.4 (a tetrodotoxin-sensitive sodium channel subtype) and Na(V)1.5 (a tetrodotoxin-resistant sodium channel subtype). These compounds showed moderate inhibitory activity towards Na(V)1.4, and weaker inhibitory activity towards Na(V)1.5. Uniquely, however, the inhibition of Na(V)1.5 by (-)-FD-dcSTX (4b) was "irreversible".     

Translational and rotational motions of a diatomic molecule enclosed in a solid matrix

The hamiltonian for a molecule enclosed in a cavity may be written H = H ^R(θ) + H ^T(r) + U ^RT(θ, r), where θ and r denote the molecular orientation and the displacement of the centre of mass. The crystalline potential seen by the guest molecule can be explicitly calculated on the basis of atom-atom and electrostatic multipolar interactions, by using an nth-order gradient formula in the spherical representation. We take a N ₂ molecule encaged in β-quinol clathrate as our model system, and solve variationally the Schrödinger equation for H to clarify the translation-rotation coupling. Energy levels of H are obtained as a function of the height of the hindering potential for rotation, by modifying the strength of the electrostatic multipolar interaction. Three limiting cases of H ^R are important: (a) libration around the Z-axis, (b) free rotation, and (c) an oscillational rotation whose equilibrium orientation is perpendicular to the Z-axis. The constrained translation under consideration is an anharmonic and almost spherically symmetric oscillation. The Pauli principle must be applied to the eigenstate of H. Excepting the case (a), translational states of H are different for different nuclear spin species, and higher-order effects of U ^RT on these states are significant. For p-N₂, some modes of motion interchange if the rotational motion changes from case (a) to case (c). If the constraining potential for translation is steeper, the effect of U ^RT will become smaller. The anharmonicity involved in H ^T is not negligible in discussing this effect.     

X‐ray fluorescence analysis of Co,Ni, Pd,Ag, and Au in the scrapped printed‐circuit‐board ash

A method for the quantitative analysis of Co, Ni, Pd, Ag, and Au in the scrapped printed‐circuit‐board ash by X‐ray fluorescence (XRF) spectrometry using loose powder was developed. The printed‐circuit‐board samples were converted to ash pyrolytically in porcelain crucibles by sequential heating using a gas burner and electric furnace, and then were ground with a ball mill. The calibrating standards were prepared by adding the appropriate amounts of NiO powder and aqueous standard solutions containing Co, Pd, Ag, and Au to the base mixtures of Al₂O₃ (5.0 mass%), SiO₂ (49 mass%), CaCO₃ (11 mass%), Fe₂O₃ (3.3 mass%), and CuO (30 mass%) as a matrix. Then, 10 g of the resulting mixtures were dried and homogenized for 90 min with a V‐type mixing machine. Specimens for XRF analysis were prepared from the so‐called loose‐powder method in which powder samples were compacted into a hole (12.0‐mm diameter and 5.0‐mm height) in an acrylic plate and covered with a 6‐µm thickness of polypropylene film. Matrix effects were corrected using the intensity value of Compton scattering for PdKα, AgKα, and AuLβ₂, and that of background scattering at 35.8° (2θ) for CoKα and NiKα. The detection limits corresponding to three times the standard deviation of the blank intensity were 2.5–45 µg g^?1. The proposed method was validated against the pressed‐powder‐pellet method by comparing the calibration curves. Moreover, the concentrations of Co, Ni, Pd, and Ag determined using the proposed XRF method were approximately the same as those resulting from an atomic‐absorption‐spectrometric analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Asymmetric [2,3]‐Wittig Rearrangement of Oxygenated Allyl Benzyl Ethers in the Presence of a Chiral di‐tBu‐bis(oxazoline) Ligand: A Novel Synthetic Approach to THF Lignans

We have accomplished highly enantioselective [2,3]‐Wittig rearrangements of functionalized allyl benzyl ethers in the presence of a chiral di‐tBu‐bis(oxazoline) ligand. In various oxygenated benzylic ethers, the reactions proceeded with excellent diastereo‐ and enantioselectivities, although the presence of a methoxy substituent at the ortho‐position on the benzyl group drastically decreased the enantioselectivity. Conversely, o‐ethyl and o‐phenyl substituents had no significant effect on the selectivity. We found that the C2‐substituent of the allylic moiety played an important role in producing high enantioselectivity. Highly enantioselective [2,3]‐Wittig rearrangement in the presence of catalytic amounts of the chiral ligands is also described.     

High-sensitivity capillary and microchip electrophoresis using electrokinetic supercharging preconcentration. Insight into the stacking mechanism via computer modeling

This review discusses recent progress in the application of one of the most effective in-line preconcentration techniques used in electrophoresis in capillaries and microchips, electrokinetic supercharging (EKS). Conventionally considered as a transient isotachophoresis (tITP) step put into effect after the electrokinetic sample injection (EKI), EKS presumes that the electrolyte filled into the capillary (or microchip channel) comprises a co-ion acting as a leading ion to stack the injected analytes. Subsequently, to create the tITP state, one needs an additional injection of a suitable terminating ion. As a resulting increase in sensitivity strongly depends on the performance of both EKS stages, two theoretical sections are focused on hints for proper arrangement of EKI and tITP elaborated by means of computer simulation. In particular, factors affecting the injected amount of analytes, different modes of introducing the sample, suitable combinations of leading and terminating ions, and optimization of supporting electrolyte compositions are discussed with an objective to increase the enrichment factors. A comprehensive coverage of recent EKS applications in capillary and microchip electrophoresis, including metal ions, pharmaceuticals, peptides, DNA fragments, and proteins, demonstrates attainable sensitivity enhancements up to two orders of magnitude. This should make this method exportable to other analytes and facilitate its more widespread use to applications that require low limits of detection.