The cation complexation force of 18-crown-6 has been measured in ethanol by means of atomic force microscopy using probe tips and mica substrates modified chemically with 18-crown-6 and ammonium ion, respectively. The specific complexation force was suppressed by free potassium ion in the measurement solution, indicating a blocking effect based on the competitive complexation of the 18-crown-6 moiety between the free ion and the ammonium ion bound to the substrate. The single complexation force of 18-crown-6 with ammonium ion was evaluated to be about 60 pN in ethanol by autocorrelation analyses of the histograms for observed forces.

Tuning of localized surface plasmon resonance (LSPR) of metal nanostructures has attracted a great deal of interest, and the controlled syntheses of them have been extensively studied for fine tuning of their LSPR. In this paper, we report widely tunable LSPR from visible to near-infrared of hollow silver nanoshells synthesized by reduction of silver thiocyanate. The silver nanoshell exhibits size- and thickness-dependent LSPR for symmetric dipole mode from visible to near-infrared regions, while the antisymmetric dipole resonance is not changed. By combining characterization of the nanoshells by transmission electron microscopy and theoretical simulation based on discrete dipole approximation, we reveal that the LSPRs are controlled by the size and shell thickness of the nanoshells and also that dimples on the shell surfaces would significantly affect the LSPRs of symmetric dipole, and quadrupole mode for larger nanoshells.

Received 20th March 2000, Accepted 7th April 2000 Published on the Web 22nd May 2000Metal-ion complexation of crown ether derivatives incorporating one and two spirobenzopyran units was investigated by electrospray ionization mass spectrometry. The crowned spirobenzopyran derivatives exhibited very different metal ioncomplexing behavior from their corresponding parent crown ether rings, preferring multivalent to monovalent metal ions owing to the additional ionic interaction with the nitrophenolate anion of the merocyanine moiety. The on-line photochemical reaction for mass spectrometry indicated that the metal ion-complexing ability and ion selectivities of the crowned spirobenzopyrans can be switched photochemically, taking advantage of the difference between the spiropyran and merocyanine isomers.

We have measured the single intermolecular force of a typical photoionizable molecule, spirobenzopyran, by means of atomic force microscopy, which has proven to be useful in measuring directly single molecular forces. The spirobenzopyran moiety was immobilized covalently on both Au-coated probe tips and substrates by use of a self-assembled monolayer of a hexanethiol derivative incorporating a terminal spirobenzopyran moiety, 1'-(6'-mercaptohexyl)-3',3'-dimethylindolino-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline). Force curve measurements were carried out using the spirobenzopyran-modified probe tip and substrate under dark conditions and in situ UV light irradiation. The adhesion force observed in a polar solvent (i.e., ethanol) was increased substantially under in situ UV light irradiation, which caused photoisomerization of the spirobenzopyran moiety bound to both tip and substrate from its electrically neutral spiropyran form to the corresponding zwitterionic merocyanine one. Statistical analyses of the observed force by autocorrelation technique have revealed that the photoionization enhanced by UV light caused a remarkable increase in the single intermolecular force of the photochromic compound.

We have synthesised an inverse opal hydrogel functionalised with a thiourea moiety as an anion recognition site. The resulting hydrogel showed remarkable changes of its structural colour with respect to acetate and bicarbonate ions selectively in aqueous solution, indicating a potential as colorimetric sensing materials for hydrophilic anions.

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Single-molecule force spectroscopy was carried out using AFM force measurements for the purpose of direct observation of the stabilization of G-quadruplex DNA by a telomerase inhibitor, which is 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin tetrakis(p-toluenesulfonate) (TMPyP). In AFM force measurements, we used an AFM tip and an Au substrate modified chemically with terminal-biotinylated telomere DNA and streptavidin, respectively. The telomere DNA was fully stretched by the AFM tip based on the bridge formation between the AFM tip and the Au substrate through the streptavidin-biotin interaction. The force-extension curves, which reflected the stretching of a single DNA molecule, were distinguished from all of the curves, judging from the rupture force and the contour length. The selected curves were analyzed using a worm-like chain model, and one of the fitting parameters, persistence length (lp), was used as an index for the stabilization of the G-quadruplex structure. Consequently, the lp value was significantly increased by the addition of TMPyP under the experimental conditions where the G-quadruplex structure could be formed. On the other hand, the value was hardly changed by the addition of TMPyP under the conditions except the above. Furthermore, the methodology developed and demonstrated in this work was applied to evaluate the stabilization of G-quadruplex DNA by other telomerase inhibitors such as ethidium bromide and p-xylene-bis(N-pyridinium bromide).

The cation complexation behavior of dibenzocrown ethers adsorbed on highly oriented pyrolytic graphite substrates was investigated by means of atomic force microscopy using probe tips modified chemically with ammonium ion by silane coupling. The specific adhesion force based on the intermolecular force between dibenzocrown ether and ammonium ion was observed via force curve measurements in ethanol at the interface between the substrate and tip. The observed specific force decreased in the presence of the alkali metal ion in solution, indicating that the cation in solution interferes with the complexation of the crown ethers adsorbed on the substrate with the ammonium ion immobilized on the tip. The blocking effect of metal ions in solution on the observed force depended on the sizes of both the blocking cation and crown ether ring, suggesting that the surface-adsorbed dibenzocrown ethers possess a selective cation-complexing ability similar to that in their bulk state and that the adhesion force measurements using cation-modified tips allow evaluation of the cation-complexing ability of crown ethers under cation-competitive conditions.