Molecular imprinted polymers for separation science: A review of reviews

Molecular imprinted polymer is an artificial receptor made by imprinting molecules of a template in a polymer matrix followed by removing the template molecules via thorough washing to give the permanent template grooves. They show favored affinity to the template molecule compared to other molecules, and this property is the basic driving force for such diverse application of this techniques. Such techniques have been increasingly employed in a wide scope of applications such as chromatography, sample pretreatment, purification, catalysts, sensors, and drug delivery, etc., mostly in bioanalytical areas. A major part of them is related to development of new stationary phases and their application in chromatography and sample pretreatment. Embodiments of molecular imprinted polymer materials have been carried out in a variety of forms such as irregularly ground particles, regular spherical particles, nanoparticles, monoliths in a stainless steel or capillary column, open tubular layers in capillaries, surface attached thin layers, membranes, and composites, etc. There have been numerous review articles on molecular imprinted polymer issues. In this special review, the reviews in recent ca. 10 years will be categorized into several subgroups according to specified topics in separation science, and each review in each subgroup will be introduced in the order of date with brief summaries and comments on new developments and different scopes of prospects. Brief summaries of each categories and conclusive future perspectives are also given.     

Simultaneous Determination of α- and γ-Mangostins in Mouse Plasma by HPLC–MS/MS Method: Application to a Pharmacokinetic Study of Mangosteen Extract in Mouse

Recently, extracts from the pericarp of mangosteen, Garcinia mangostana L., exhibited various pharmacological properties such as anti-oxidative, anti-inflammatory, anti-bacterial and chemopreventive activities. Albeit it has diverse application, there is little information about its pharmacokinetic aspects. Thus, the present study was undertaken to develop the simultaneous determination of α- and γ-mangostins (α- and γ-MG), major and active compounds, from extracts for the application of pharmacokinetic studies in mice using combined liquid chromatography–tandem mass-spectrometry and microsampling systems. The intra- and inter-validation, precision, accuracy, stability, recovery and matrix effects of α- and γ-MG were conducted in mouse plasma. Based on the developed analytical methods, pharmacokinetic parameters of α- and γ-MG after intravenous and oral administration of mangosteen extract were calculated. In sample preparation steps, the biological samples were deproteinized by acetonitrile and chromatographic separation was accomplished on a C₁₈ column. The detection was accomplished by multiple-reaction monitoring scanning after electrospray ionization source in the positive ionization mode. The optimized mass transition ion pairs (m/z) for quantitation were 411.062 → 354.900, 397.384 → 340.900, and 808.379 → 527.200 for α- and γ-MG and docetaxel (internal standard), respectively. The total run time was 5 min. The results provided a meaningful basis for the preclinical and clinical application of mangosteen extract.     

New Cyclization Route to the Skeletons of Lennoxamine and Chilenine

A new cyclization route, triggered by epoxide opening, has been performed to provide the key intermediates for isoindolobenzapine alkaloids, lennoxamine and chilenine. The epoxide was prepared by the Stille reaction using vinyltributylstannane and the following dioxirane treatment. Cyclization under the treatment of BF₃ · OEt₂ provided an azepine moiety, and the oxidative cyclization toward the known precursor for the alkaloids has been achieved by reaction with a stoichiometric amount of Pd(OAc)₂. This formal synthesis suggests a new route to the alkaloids.     

Analysis of cell gap-dependent driving voltage in a fringe field-driven homogeneously aligned nematic liquid crystal display

We have studied cell gap-dependent driving voltage characteristics in a homogeneously aligned nematic liquid crystal (LC) cell driven by a fringe electric field, termed the fringe field switching (FFS) mode. The results show that for the FFS mode using a LC with positive dielectric anisotropy, the operating voltage decreases as the cell gap decreases, whereas it increases with a decreasing cell gap when using a LC with negative dielectric anisotropy. The difference between LCs is explained by simulation and experiment.     

Silaffin Peptides as a Novel Signal Enhancer for Gravimetric Biosensors

Application of biomimetic silica formation to gravimetric biosensors has been conducted for the first time. As a model system, silaffin peptides fused with green fluorescent protein (GFP) were immobilized on a gold quartz crystal resonator for quartz crystal microbalances using a self-assembled monolayer. When a solution of silicic acid was supplied, silica particles were successfully deposited on the Au surface, resulting in a significant change in resonance frequency (i.e., signal enhancement) with the silaffin–GFP. However, frequency was not altered when bare GFP was used as a control. The novel peptide enhancer is advantageous because it can be readily and quantitatively conjugated with sensing proteins using recombinant DNA technology. As a proof of concept, this study shows that the silaffin domains can be employed as a novel and efficient biomolecular signal enhancer for gravimetric biosensors.     

Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.     

Preparation of 2,2-difluoro-1-trialkylsilylethenylstannanes and their cross-coupling reactions

Reaction of 2 with bis(tributyltin) in the presence of 3 mol % Pd₂(dba)₃, 6 mol % XPhos, and 30 equiv of LiBr in wet and air bubbled THF at reflux for 8 h afforded the desired products 3 in 73–74% yields. The cross-coupling reaction of 3a with aryl iodides in the presence of 10 mol % Pd(PPh₃)₄ and 10 mol % CuI afforded the coupled products 4a–p in 47–90% yields. The coupling reaction of 3b with various alkynyl bromides having aryl-, alkyl, or trialkylsilyl group also afforded the corresponding 1,3-enynes 5a–g in 61–77% yields.