Yasumasa Kanekiyo

Mechanical Tuning of Molecular Recognition To Discriminate the Single-Methyl-Group Difference between Thymine and Uracil

Construction of enzyme-like artificial cavities is a complex and challenging subject. Rather than synthesizing complicated host molecules, we have proposed mechanical adaptation of relatively simple hosts within dynamic media to determine the optimum conformation for molecular recognition. Here we have applied this concept to one of the most challenging biomolecular recognition problems, i.e., that of discriminating thymine from uracil. We synthesized the novel cholesterol-armed triazacyclononane as a host molecule and subjected it to structural tuning by compression of its Langmuir monolayers in the absence and in the presence of Li(+) cations in the subphase. Experimental results confirm that the monolayer of triazacyclononane host selectively recognizes uracil over adenine (ca. 7 times based on the binding constant) and thymine (ca. 64 times) under optimized conditions ([LiCl] = 10 mM at surface pressure of 35 mN m(-1)). The concept of mechanical tuning of a host structure for optimization of molecular recognition offers a novel methodology in host-guest chemistry as an alternative to the more traditional molecular design strategies.

Novel nucleotide-responsive Hydrogels designed from copolymers of boronic acid and cationic units and their applications as a QCM resonator system to nucleotide sensing

Hydrogels comprised of boronic acid monomer (3), cationic monomer (4), and crosslinker monomer (5) were prepared by radical copolymerization. These hydrogels could efficiently bind nucleotides such as AMP and ATP by a cooperative action of the boronic acid-cis-diol complexation and the electrostatic interaction between the cationic unit and the phosphate group. The binding processes were conveniently monitored by the swelling and deswelling behaviors of these hydrogels in aqueous solution. For the hydrogel with the specific monomer composition an interesting charge inversion was observable: with increasing AMP or ATP concentration, the cation-rich hydrogel was gradually charge neutralized, once shrunken at the neutral stage, and then swollen again because of the anion-rich charge state. These nucleotide-induced swelling and deswelling phenomena were reproduced on the gold surface of a QCM resonator. Therefore, the present system is not only interesting to consider nucleotide-induced mechanochemical properties, but also applicable as a sensor to the nucleotide detection.

ORGANIC GELS ARE USEFUL AS A TEMPLATE FOR THE PREPARATION OF HOLLOW FIBER SILICA

A novel mesoporous silica with a tubular structure has been prepared using organic gel fibers as a template.

Chiroselective re-binding of saccharides to the fibrous aggregates prepared from organic gels of cholesterylphenylboronic acid

Abstract The xerogel fibers prepared from cholesterylphenylboronic acid or its D- or L-xylose complexes show the chiral discrimination ability in the re-binding of saccharides and partially retain the memory for the original imprinted saccharide. The novel findings indicate that the solgel phase transition in the organic gel is utilizable to the chiral discrimination and even to the molecular imprinting.

Mechanical tuning of molecular machines for nucleotide recognition at the air-water interface

Molecular machines embedded in a Langmuir monolayer at the air-water interface can be operated by application of lateral pressure. As part of the challenge associated with versatile sensing of biologically important substances, we here demonstrate discrimination of nucleotides by applying a cholesterol-armed-triazacyclononane host molecule. This molecular machine can discriminate ribonucleotides based on a twofold to tenfold difference in binding constants under optimized conditions including accompanying ions in the subphase and lateral surface pressures of its Langmuir monolayer. The concept of mechanical tuning of the host structure for optimization of molecular recognition should become a novel methodology in bio-related nanotechnology as an alternative to traditional strategies based on increasingly complex and inconvenient molecular design strategies.

‘Molecular-imprinting’ in polyion complexes which creates the ‘memory’ for the AMP template

The formation of a polyion complex precipitate was applied to molecular imprinting for the first time. Polyanion containing boronic acid units can sustain AMP by a boronate–cis-diol interaction. When this polyanion forms a polyion complex with polycation according to 1∶1 cation–anion stoichiometry, the phosphate anionic charges introduced into the polyanion by the AMP complexation are also counted. Thus, after removal of AMP from the polyion complex a ‘cleft’ which has the memory for the AMP template is created. It was proved that this cleft shows high affinity with AMP. We also noticed that the removal and re-binding processes for AMP coincide with the swelling and deswelling phenomena of this polyion complex.

Facile construction of an ultra-thin [60]fullerene layer from [60]fullerene–homooxacalix[3]arene complexes on a gold surface

A hexacationic homooxacalix[3]arene–[60]fullerene 2∶1 complex can be deposited on an anion-coated gold surface as a monolayer (or at least as a monolayer-like ultra-thin film); as expected, this membrane efficiently shows a redox response in cyclic voltammetry and a photoelectrochemical response under visible light irradiation.

'Molecular-imprinting' of AMP utilising the polyion complex formation process as detected by a QCM system

The formation of a polyion complex was applied for molecular imprinting of AMP on a QCM resonator surface. The gold electrode on the resonator surface was modified with anionic thiols. Subsequently, layers of polycations and boronic acid-containing polyanions were adsorbed onto the QCM anionic surface utilising an alternating adsorption process. When the polymer adsorption was conducted in the presence of AMP, the anionic charges of the phosphate group introduced into polyanion by a boronate–cis-diol interaction altered the film growth behaviour: viz., excess polycationic units were adsorbed onto the polyanionic surface. After removal of the AMP from the surface polyion complex, a swollen gel layer with excess cationic charge is created. It was proven that this QCM system sensitively responds to AMP. The responsiveness is derived from the mass decrease in relation to the shrinking of the surface gel layer.

Facile design of a metal-imprinted surface from a poly(vinyl chloride-co-acrylic acid) / poly(propylene glycol) blend

Abstract Porous thin films with memory for imprinted metals have been prepared by casting water-THF mixed solutions of a poly(vinyl chloride- co -acylic acid) / poly(propylene glycol) blend. When Cu 2+ and Pb 2+ ions are imprinted in the cast process, the films retain a memory for the original Cu 2+ and Pb 2+ ions. The imprinting processes can be thoroughly monitored by FT-IR spectroscopy.

Facile construction of a novel metal-imprinted polymer surface without a polymerisation process

Porous thin films have been prepared by casting water–THF mixed solutions of poly(vinyl chloride-co-acrylic acid): when Cu2+ ion is imprinted in the casting process, the film obtains a memory for the original Cu2+ ion. The imprinting processes can be closely monitored by FTIR spectroscopy.