Jun Haginaka

Separation and sensing based on molecular recognition using molecularly imprinted polymers

Molecular recognition-based separation and sensing systems have received much attention in various fields because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the development of such systems, where the molecule to be recognized is added to a reaction mixture of a cross-linker(s), a solvent(s), and a functional monomer(s) that possesses a functional groups(s) capable of interacting with the target molecule. Binding sites in the resultant polymers involve functional groups originating from the added functional monomer(s), which can be constructed according to the shape and chemical properties of the target molecules. After removal of the target molecules, these molecularly imprinted complementary binding sites exhibit high selectivity and affinity for the template molecule. In this article, recent developments in molecularly imprinted polymers are described with their applications as separation media in liquid chromatography, capillary electrophoresis, solid-phase extraction, and membranes. Examples of binding assays and sensing systems using molecularly imprinted polymers are also presented.

Protein-based chiral stationary phases for high-performance liquid chromatography enantioseparations

The enantioseparations of various compounds using proteins as the chiral selectors in high-performance liquid chromatography (HPLC) are considered in this review. The proteins used include albumins such as bovine serum albumin and human serum albumin, glycoproteins such as alpha1-acid glycoprotein, ovomucoid, ovoglycoprotein, avidin and riboflavin binding protein, enzymes such as trypsin, alpha-chymotrypsin, cellobiohydrolase I, lysozyme, pepsin and amyloglucosidase, and other proteins such as ovotransferrin and beta-lactoglobulin. This review deals with the properties of HPLC chiral stationary phases based on proteins, and the enantioselective properties and chiral recognition mechanisms of these stationary phases.

Enantiomer separation of drugs by capillary electrophoresis using proteins as chiral selectors

The separation of drug enantiomers using proteins as the chiral selectors in capillary electrophoresis (CE) is considered in this review. The proteins used include albumins such as bovine serum albumin, human serum albumin and serum albumins from other species, glycoproteins such as alpha1-acid glycoprotein, crude ovomucoid, ovoglycoprotein, avidin and riboflavin binding protein, enzymes such as fungal cellulase, cellobiohydrolase I, pepsin and lysozyme and other proteins such as casein, human serum transferrin and ovotransferrin. Protein-based CE is carried out in two modes: in one proteins are immobilized or adsorbed within the capillary, or protein-immobilized silica gels are packed into the capillary (affinity capillary electrochromatography mode), and in the other proteins are dissolved in the running buffer (affinity CE mode). Furthermore, the advantages and limitations of the two modes and the factors affecting the chiral separations of various drugs by protein-based CE are discussed.

Uniform-sized molecularly imprinted polymer for (S)-naproxen selectively modified with hydrophilic external layer

A uniform-sized molecularly imprinted polymer (MIP) for (S)-naproxen selectively modified with hydrophilic external layer has been prepared. First, the molecularly imprinted polymer for (S)-naproxen was prepared using 4-vinylpyridine and ethylene glycol dimethacrylate (EDMA) as a functional monomer and cross-linker, respectively, by a multi-step swelling and thermal polymerization method. Next, a 1:1 mixture of glycerol monomethacrylate (GMMA) and glycerol dimethacrylate (GDMA) was used for hydrophilic surface modification, and it was added directly to the molecularly imprinted polymer for (S)-naproxen 4 h after the start of molecular imprinting. The retention factors of all solutes tested were decreased with the surface modified molecularly imprinted polymer, compared with the unmodified molecularly imprinted polymer. However, chiral recognition of racemic naproxen was attained with the surface modified molecularly imprinted polymer as well as the unmodified molecularly imprinted polymer. Further, bovine serum albumin was completely recovered from the surface modified molecularly imprinted polymer. These results revealed that the chiral recognition sites of (S)-naproxen remained unchanged with hydrophilic surface modification, and that the molecularly imprinted polymer for (S)-naproxen was selectively modified with hydrophilic external layer. Preliminary results reveal that the surface modified molecularly imprinted polymer could be applicable to direct serum injection assays of (S)-naproxen.

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.

Restricted access media-molecularly imprinted polymer for propranolol and its application to direct injection analysis of β-blockers in biological fluids

A restricted access media-molecularly imprinted polymer (RAM-MIP) for propranolol (PRP) has been prepared for direct injection analysis of beta-blockers in biological fluids. First, the MIP for PRP was prepared using methacrylic acid and ethylene glycol dimethacrylate as the functional monomer and cross-linker, respectively, by a multi-step swelling and polymerization method. Next, a 1:1 mixture of glycerol monomethacrylate and glycerol dimethacrylate was used for hydrophilic surface modification, and added directly to the MIP for PRP after 4 h from the start of polymerization. Then further polymerization was carried out for 20 h. The obtained RAM-MIP for PRP showed excellent molecular recognition ability for PRP, good ones for alprenolol (ALP) and pindolol, and fair ones for other beta-blockers. The RAM-MIP was applied for direct injection analysis of ALP enantiomers in a rat plasma sample by a column-switching HPLC system using a beta-cyclodextrin phenylcarbamate-bonded silica column as the analytical column. The calibration graph, constructed from peak area versus each ALP enantiomer concentration, was linear with a correlation coefficient of > 0.999 over the concentration ranges of 12.5-250 ng ml(-1). The limit of quantitation was 12.5 ng ml(-1) with a 50 microl injection. This method could be applicable for the assay of ALP enantiomers at the therapeutic plasma levels, and have wide applicability for the assay of beta-blockers in biological fluids.

Uniformly sized molecularly imprinted polymer for (S)-naproxen: Retention and molecular recognition properties in aqueous mobile phase

A uniformly sized molecularly imprinted polymer (MIP) for (S)-naproxen has been prepared by a multi-step swelling and polymerization method using 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate (EDMA) as a functional monomer and cross-linker, respectively. We optimized the preparation method of the MIP by changing the molar amounts of the template molecule and functional monomer. Further, we examined the effects of organic modifier type, column temperature and flow-rate on the retentivity and enantioselectivity for naproxen using a mixture of phosphate buffer and organic modifier (acetonitrile, ethanol and 2-propanol) as an eluent. When the amounts of (S)-naproxen, 4-VPY and EDMA used were 4, 6 and 25 mmol, respectively, the enantioselectivity and resolution for naproxen were good despite the shorter retention. When acetonitrile was used as an organic modifier, the highest column efficiency was obtained for the separation of naproxen enantiomers. With regard to the effects of column temperature and flow-rate, the column performance was improved by elevating a column temperature and decreasing a flow-rate.

Drug determination in serum by liquid chromatography with restricted access stationary phases

Abstract Drug determination in serum with restricted access stationary phases is described. With such phases, large molecules such as proteins are eluted in the void volume without destructive accumulation because they have restricted access to some surfaces, but small molecules such as drugs and their metabolites can reach the hydrophobic sites and be separated. Thus, assay of drugs by direct serum injection can be achieved without a sample preparation step such as deproteinization and/or extraction. The restricted access stationary phases include internal-surface reversed-phases (ISRP), shielded hydrophobic phases (SHP), semi-permeable surfaces (SPS), dual zone (DZ) and mixed functional phases (MFP). The characteristics of these stationary phases and their application to the assay of drugs in serum are discussed.

Facilitated nitration and oxidation of LDL in cigarette smokers

Background  Cigarette smoking increases the risk of developing atherosclerosis and ischaemic heart disease. Smoking‐induced oxidative stress is considered to favour oxidation of low‐density lipoprotein (LDL) and subsequently promotes the atherogenic process. We investigated whether peroxynitrite, a reaction product of cigarette smoke, is involved in facilitated oxidation of LDL in smokers.

Uniform-sized molecularly imprinted polymer for (S)-ibuprofen: Retention properties in aqueous mobile phases

A uniform-sized molecularly imprinted polymer for (S)-ibuprofen has been prepared by a multi-step swelling and thermal polymerization method using 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate (EDMA) as a host functional monomer and cross-linker, respectively. The obtained (S)-ibuprofen imprinted 4-VPY-EDMA materials were evaluated using aqueous eluents by HPLC. Hydrophobic and hydrogen bonding interactions between ibuprofen enantiomers and 4-VPY-EDMA materials could play an important role in the retentivity and enantioselectivity. Further, partial resolution of the enantiomers of ibuprofen metabolites, 2-hydroxy- and 2-carboxyibuprofen, was attained with the (S)-ibuprofen imprinted 4-VPY-EDMA materials.