Kimihiro Yoshizako

Molecularly imprinted uniform-size polymer-based stationary phase for high-performance liquid chromatography structural contribution of cross-linked polymer network on specific molecular recognition

Abstract Non-covalently molecularly imprinted, uniform-size, polymer-based, stationary phases were prepared by a two-step swelling technique using isomers of diaminonaphthalene or a chiral amide derived from ( S )- α -methylbenzylamine as the template molecule. Methacrylic acid worked as an effective host molecule for diaminonaphthalene templates, however, an imprinted, cross-linked, polymer-based, stationary phase without such a relatively strong host functionality unexpectedly showed moderate molecular recognition, which suggested that the cross-linked polymer network could memorize the shape of a template. In chiral separation of amide derivatives, a cross-linked polymer network also memorized the shape of a chiral template, resulting in chiral resolution. In addition, a chiral cross-linking agent having similar functionality to the chiral amide template could enhance molecular recognition drastically. Further studies suggested that this enhancement in chiral recognition was due to a favorable structural interaction within the specific recognition sites.

Molecular recognition towards coplanar polychlorinated biphenyls based on the porogen imprinting effects of xylenes

Molecularly imprinted, uniformly sized polymeric separation media were prepared using o-, m- or p-xylene as a porogenic template to investigate recognition ability towards coplanar polychlorinated biphenyls (PCBs). PCBs having chlorine atoms at meta positions of biphenyl were preferably retained on stationary phase with m-xylene as porogenic template and PCBs having chlorine atoms at para positions of biphenyl were found to be retained longer on the stationary phase imprinted by the porogenic template, p-xylene. It was found that positional relationship between substituted chlorine atoms was also important for chromatographic recognition.

Preparation of uniformly sized polymeric separation media potentially suitable for small-scale high-performance liquid chromatography and/or capillary electrochromatography

Uniformly sized polymer particles were prepared by either a two-step swelling and polymerization method or a Shirasu porous glass (SPG) emulsification technique to compare their suitability as a uniformly sized packing material for small-scale high-performance liquid chromatography (HPLC) or capillary electrochromatography (CEC). The SPG emulsification technique afforded slightly worse size uniformity compared to the two-step swelling and polymerization technique. However, fairly nice spherical shapes with reproducible outward appearance and internal pore size distribution were obtained for both of 3- or 6-micron sized particles. On the other hand, the two-step swelling and polymerization method afforded broken particles with quite different outward appearances due to the polymeric porogen effects of seed polymer utilized as the shape template. In HPLC, the column packed with the 3-micron particles prepared with the SPG emulsification technique proved to have a fairly high column efficiency with good column stability, as assessed under repeated use in gradient elution. On the other hand, the column packed with the packing material obtained through the two-step swelling and polymerization method showed much poorer column stability, while initial column efficiency was compatible to that obtained using the SPG emulsification method. In addition, the packing material prepared with the SPG emulsification technique could be modified with ion-exchangeable monomers and showed fairly good column efficiency in the CEC mode.

An Unexpected Molecular Imprinting Effect for a Polyaromatic Hydrocarbon, Anthracene, Using Uniform Size Ethylene Dimethacrylate Particles

A non-covalent type of molecular imprinting effect toward a polyaromatic hydrocarbon (PAH), viz. anthracene, was studied utilizing uniformly sized ethylene dimethacrylate (EDMA) polymer particles without functional host monomers. Although polymerization at 0°C initiated by a redox initiation system was expected to afford larger molecular imprinting effect due to stronger and more effective intermolecular interaction between the template and surface functional groups of the polymer, almost no imprinting effect was observed, while a much higher polymerization temperature of 70°C unexpectedly afforded a larger molecular imprinting effect for the template anthracene. In order to determine the unexpected imprinting effects observed, uniformly sized, macroporous un-imprinting EDMA polymer particles (base particles) were prepared by various polymerization techniques at different polymerization temperature as well as with different initiation systems. The careful studies proved that each kind of base polymer particle showed different molecular recognition ability, especially toward anthracene, which is depends upon the physical properties of each kind of base polymer particle. On the basis of these facts, we would propose that the potential molecular recognition ability of the un-imprinted base polymer particles is another important factor for realization of effective molecular imprinting alongside the factors reported previously.

One-pot preparation method for a uniform-sized polymer-based chiral stationary phase for high-performance liquid chromatography with polymethacrylamide as a chiral selector

Abstract A simple one-pot method for the preparation of a uniform-sized polymer-based chiral stationary phase (PCSP) for high-performance liquid chromatography was investigated with polymethacrylamide as a chiral selector. During the polymerization process of uniform-sized base particles prepared by a two-step swelling method, solid chiral methacrylamide monomer was added directly to the aqueous polymerization medium of the base particles. The methacrylamide polymerized and was incorporated on the surface of the base polymer particles quantitatively without losing the size uniformity of the base particles. When the methacrylamide was added stepwise, the polymer-based chiral stationary phase obtained gave complete resolution of 2,2′-dihydroxy-1,1′-binaphthyl, whereas lower resolution was observed with PCSPs prepared by the traditional copolymerization method.

A polymeric chiral surface functionality immobilized on uniformly sized macroporous polymer beads

Uniformly sized functionalized macroporous polymer beads were prepared by either a classical copolymerization method or recently reported in situ surface modification method utilizing chiral methacrylamide as a functional modifier. To evaluate conformational and/or specific differences in their surface chiral functionality, we applied chromatographic evaluation techniques. The prepared modified beads were utilized as chiral stationary phase in high-performance liquid chromatography (HPLC). Those prepared by the in situ surface modification method tended to show higher chiral recognition ability than those by the classical copolymerization method, even if the equivalent amount of the chiral functional group was involved within polymer beads. Detailed chromatographic studies exhibited the in situ surface modification method could lead to polymeric methacrylamide functionality on the surface within relatively large pore size regions of the macroporous polymer beads, while the classical copolymerization method tended to form less polymeric surface functionality. The difference in the chiral surface functionality on both of macroporous polymer beads afforded drastic change in chromatographic chiral recognition ability. Complete resolution of a drug, thalidomide could be achieved on the chiral stationary phase with the polymeric chiral surface functionality, while no resolution was found on that with the monomeric one even if the same chiral methacrylamide was used as a modifier to prepare the chiral stationary phases.

Uniform-sized polymer-based separation media prepared using vinyl methacrylate as a cross-linking agent Possible powerful adsorbent for solid-phase extraction of halogenated organic solvents in an aqueous environment

Abstract Uniform-sized macroporous polymer-based separation media were prepared through a typical two-step swelling method utilizing vinyl methacrylate or other ordinary cross-linking agents to investigate their properties as packing materials in HPLC. A simple and less hydrophobic cross-linking agent, vinyl methacrylate, afforded stable macroporous packing materials unexpectedly affording the largest retention volume towards hydrophobic solutes in reversed-phase liquid chromatography with good column efficiency. The retention ability towards seven halogenated organic solvents from chloroform to tetrachloroethylene was found to be much higher than that with a typical hydrophobic polymer-based packing material, poly(styrene-divinylbenzene) particles, and also a typical C 18 silica-based hydrophobic station phase.

Effect of polymer-supported catalytic moiety on an asymmetric ethylation of aldehyde by diethylzinc

In order to investigate their effects on an asymmetric alkylation of aldehyde by diethylzinc, two types of polymer-supported asymmetric catalysts derived from chiral amino alcohols were prepared by two different preparation techniques. As reference catalysts, corresponding monomeric and unbound polymeric catalysts were also prepared. The monomeric catalysts showed moderate enantioselectivities in hexane, however, the unbound polymeric catalysts prepared by polymerization of the monomeric catalysts afforded quite low enantioselectivities in hexane. Immobilized catalysts prepared by classical copolymerization technique showed similar catalytic selectivities as the monomeric catalysts, on the other hand, anchored-type polymer-supported catalysts afforded similar catalytic selectivities to those of the unbound polymeric catalysts. These observations suggested that difference in preparation techniques should afford immobilized catalysts involving different catalytic moieties just like monomeric catalyst or unbound polymeric catalyst which somehow affects asymmetric reactions.