Toyoki Kunitake

Molecular imprinting in ultrathin titania gel films via surface sol-gel process

Abstract Recent progresses of molecular imprinting in metal oxide matrices were summarized. Application of the surface sol–gel process to mixtures of organic carboxylic acids and titanium alkoxide provides ultrathin layers of titania gel (10–20xa0nm thick), in which molecule-sized cavities are kept intact upon removal of the organic templates. The imprinted cavity reflects the structural and functional features of the template molecule, and the enantioselective imprinting of dipeptide isomers is observed. Robustness and flexibility of the ultrathin titania layer is demonstrated by the formation of interconnected titania hollow structures. Possible practical applications and unsolved problems of this technique are discussed.

Remarkable enantioselectivity of molecularly imprinted TiO2 nano-thin films

TiO(2) nano-thin films with imprinted (R)- and (S)-enantiomers of propranolol, 1,1-bi-naphthol, and 2-(4-isobutylphenyl)-propionic acid were fabricated on quartz plates by spin-coating their solutions with Ti(O-(n)Bu)(4) in a toluene-ethanol mixture (1:1, v/v). After template removal, the imprinted films showed better binding for original templates than to the corresponding enantiomers. The assessment of template incorporation, template removal, and re-binding was conducted through UV-vis measurements. Significant enhancement of enantioselectivity was achieved by optimization of the film thickness and by heat-treatment of the imprinted films. After subtraction of non-specific binding, the optimized films provided chiral recognition with the enantioselectivity of almost 100% for (R)-propranolol and 95% for (S)-propranolol.

Self-assembly and imprinting of macrocyclic molecules in layer-by-layered TiO2 ultrathin films

Alternate TiO2 gel ultrathin films assembled with a macrocyclic carboxylic acids of tetrakis-4-carboxyphenyl porphine (TCPP) or tetra-4-carboxylphthalocyanine cobalt (II) (Co-TCPc) were prepared by the surface sol-gel process. To confirm the film growth and imprinting effect, quartz crystal microbalance (QCM) and UV-vis spectroscopy measurements were employed. The binding of TCPP was 1.2-14.3 times more selective compared to structurally related macrocyclic guest molecules. Among other findings, tetrakis-4-carboxymethyloxyphenyl porphine (TCMOPP) that has a spacer (-O-CH2-) between the phenyl rings and carboxylic acid moieties of TCPP showed a significantly lower binding efficiency equal to 0.07, regardless of its similar molecular structure to the template molecule. Structural difference of porphyrin and phthalocyanine analogs could be also selectively discriminated: the TCPP imprinted film showed ca. 13 times higher selectivity for recognition of TCPP itself from the mixture of TCPP and Co-TCPc. Characterization by AFM demonstrated that the TiO2/TCPP film has highly uniform surface and ultrathin thickness, while both TEM and SEM studies confirmed the immobilized structures of TCPP inside the film.

Landmine detection: Improved binding of 2,4-dinitrotoluene in a γ-CD/metal oxide matrix and its sensitive detection via a cyclic surface polarization impedance (cSPI) method

Highly sensitive and selective detection of 2,4-DNT, a representative explosive, was achieved by the synergic effect of molecular imprinting and host (cyclodextrin)-guest interaction in ultrathin layers of TiO(2) and SiO(2) gel; the detection limit using cSPI measurements reached nM concentration.

Nanocopying as a Means of 3D Nanofabrication: Scope and Prospects

The use of nanosized templates to fabricate three-dimensional architectures in the nanometer regime is still a largely unexplored field of nanotechnology. Positive and negative copying of molecules and nano-sized objects by the surface sol–gel process is useful for this purpose. The authors here give account of the techniques available to date, along with their advantages and disadvantages, is outlined.

A new electrochemical sensor for heavy-metal ions by the surface-polarization controlling method

A new electrochemical sensor with high sensitivity and selectivity for heavy-metal ions was proposed. The sensor was based on the electrochemical impedance spectroscopy (EIS) attributing to a constant phase element (CPE) behavior under dynamically controlled electrode potential. With the measurements of the CPE behavior by the surface-polarization controlling method, various heavy-metal ions could be easily detected and discriminated. No interference of counter anions such as Cl/sup -/, NO/sub 3//sup -/ and CH/sub 3/COO/sup

Polysaccharide–polynucleotide complexes. Part 12. Enhanced affinity for various polynucleotide chains by site-specific chemical modification of schizophyllan

/was observed, and the same metal ions gave similar sensor response patterns regardless of the counter anions. Especially, the present method offers a high sensitivity of ppb levels for the most highly toxic elements, i.e., Hg/sup 2+/ and Hg/sup +/.

Fabrication of optical gas sensors using porphyrin-based nano-assembled thin films: A comparison with bulk materials

Recently, we found that schizophyllan (SPG), which is a natural and neutral polysaccharide, can form macromolecular complexes with certain polynucleotides. In order to increase the stability and the affinity of the complexes, we synthesized a 2-aminoethanol-appended SPG (N-s-SPG) by utilizing periodate oxidation and reductive amination. Although the modification level was only 2.4 ± 0.3%, the melting temperature of the poly(C)–N-s-SPG complex was increased by 8 °C comparing with the poly(C)–s-SPG complex. In addition, the conformation of the complex was scarcely perturbed by the introduction of amino groups. When we formed complexes of N-s-SPG and other polynucleotides, the melting temperature of their complexes increased without exception. Moreover, the amino modification induced complexation with poly(U), which does not form a complex with SPG. The affinity for the short chain nucleotide was also enhanced. These results indicate that the present modification method is quite useful to improve complex stability and we believe, therefore, that this strategy will make it possible to apply SPG to a novel gene carrier.

Fabrication and Application of Enantioselective TiO2 Nanoflims by Molecular Imprinting

In this study two kinds of biological origins, porphyrin and bacteriorhodopsin that were embedded into polymer matrix and into inorganic sol-gel matrix, respectively, were employed as active elements for an optical sensor. To confirm the usefulness of the consequent nano-scale matrix in the detection of volatile organic compounds (VOCs), aromatics and amine compounds, anionic tetrakis-(4-sulfophenyl)porphine (TSPP) was alternately assembled with cationic poly(diallyldimethylammonium chloride) (PDDA) on quartz plates. The performance and sensor parameters of the nano-scale thickness porphyrin-based thin film and bacteriorhodopsin thick film are compared. The sensing principle is based on monitoring the optical changes of the Q-band at 700 nm for the porphyrin film and at 570 nm for the bacteriorhodopsin film. This work was a first step in the development of a fiber-optic gas sensor which employs thin films as sensitive elements for the detection of different gases.

Molecular Imprinting by the Surface Sol-Gel Process: Templated Nanoporous Metal Oxide Thin Films for Molecular Recognition

TiO2 nanofilms that are imprinted by spin-coating with (R)-and (S)-enantiomers of propranolol, 1,1-bi-naphthol, and 2-(4-isobutylphenyl)-propionic acid were prepared on quartz plates by spin-coating. After template removal, the imprinted films showed much better binding for template enantiomers than the corresponding enantiomers. Moreover, the improved enantioselectivity was obtained by controlling film thickness.