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In this study, we fabricated glass substrates covered with hydrophilic and hydrophobic silanes to investigate the effect of wettability of these surfaces on DNA molecular combing. As the hydrophilic and the hydrophobic silane, a mercapto-terminated (HS(CH 2 ) 3 Si(OCH 3 ) 3 ) and a methyl-terminated one (CH 3 (CH 2 ) 3 Si(OCH 3 ) 3 ) were used, respectively. The wettability was controlled by changing the molar ratio of the two components in the mixed monolayer. From the results of the DNA molecular combing, it was shown that the mercapto terminals on the surfaces were hardly dissociated into S - groups in aqueous buffers with pH 5.5 and 8.0. In addition, it was found that the length of the immobilized DNA molecules on the hydrophilic surfaces was shorter than that on the hydrophobic ones.

We first observed a unique pyrene (Py) emission from 10-(1-(6-hexyl)pyrenyl)decanoic acid (1,6-HPDA) Langmuir-Blodgett (LB) films. In the fluorescence spectra of the 1,6-HPDA LB films, the normal bands of monomer and excimer emission of Py were absent but the new structured emission band with peaks at 422, 448, and 473 nm was observed. Besides the intensity, the shape of the characteristic structured emission band at shorter wavelengths than normal excimers did not changed essentially on lowering the Py concentration in the LB monolayer from 100 to 1 mol%. The spectroscopic studies on HPDA LB films of a variety of Py concentrations suggested that a novel excimer responsible for the structured new emission would be efficiently formed by photo-excitation of a Py-Py pre-associated dimer in different manners than those of normal excimer formations. (c) 2005 Elsevier B.V. All fights reserved.

In studies of molecular devices, it is very important to estimate the electric conductivity of single molecules. This subject has recently been studied in various ways. Weiss and co-workers (J. Am. Chem. Soc. 120 (1998) 2721) estimated transconductance of a single molecule embedded in a self-assembled monolayer (SAM) using scanning tunneling microscopy (STM). In the present work, we studied the transconductance of various single molecules embedded in SAM matrices such as alkanethiolate and biphenylmethanethiolate derivatives. We formed one-component SAMs of decanethiolate (DT) and biphenylmethanethiolate (BPMT) on Au(111), and then inserted 4-carboxyterphenyl-4′-methanethiol (CTPMT) in the one-component SAMs of DT and BPMT. In addition, BPMT used as one of the matrices above was inserted as isolated single molecules in the other one-component SAM of DT. These SAMs enabled us to measure the transconductance of the isolated single molecules using STM. All the STM images of these three types of the mixed SAMs showed that the isolated single molecules were scattered in the one-component SAMs. The STM topographic height differences between the isolated single molecules and the matrices depended on differences in their electronic tunneling conductivities.

The light-harvesting function of the J-aggregate of the cyanine dye, N,N′-dioctadecyloxacyanine (Cy), in Langmuir–Blodgett (LB) monolayers containing the amphiphilic perylene derivative (Pe) as an energy acceptor was examined by varying the Cy:Pe molar ratio from 10:1 to 2000:1. A characteristic J-band considerably red-shifted from the corresponding monomer absorption band of Cy was intensely observed in the absorption spectra of the mixed Cy LB monolayers with Pe with the molar mixing ratios Cy:Pe=200:1, 500:1, 1000:1, and 2000:1. Although the contents of Pe in the mixed LB monolayers are such small fractions, the emission from excited Pe induced by energy transfer (ET) from photo-excited Cy was observed clearly. The highest sensitized emission intensity of Pe was observed on the mixed LB monolayer with the molar mixing ratio Cy:Pe=50:1 in which all excited energies of Cy were transferred to Pe. In this molar ratio, however, the ET from monomer or dimer Cy to Pe seemed to be dominant, and the antenna effect of Cy in this state is as low as ca. 50. In contrast, the antenna effect of J-aggregated Cy estimated for the mixed LB monolayers with low Pe ratios (Cy:Pe=500:1, 1000:1, and 2000:1) was such that ca. 250 molecules of Cy would harvest light for excitation of one Pe molecule. This can be attributed to the high rate of exciton migration in the J-aggregates, by which ET probability was increased.

Monolayers and multilayers from dipalmitoylphosphatidylethanolamine head labeled with nitrobenzoxadiazole (DPPE-NBD) were deposited as Langmuir–Blodgett (LB) films on silicon wafer or quartz glass plates at different deposition pressures at room temperature. The phase coexistence between the liquid and the solid phase was observed by atomic force microscopy, friction force microscopy, scanning surface potential microscopy (SSPM), scanning near-field optical microscopy (SNOM), and phase imaging by the tapping mode atomic force microscopy. The different methods reveal new features not imaged by a single method. There is no sharp boundary line between the liquid and the solid phase. Submicrometer solid domains are resolved above the phase transition together with multilayer needles. These needles are bilayer in thickness when deposition was carried below the equilibrium surface pressure of 19.6 mN m −1 and grow in height up to hundred nanometers upon increase of the deposition surface pressure. After some time, these very high needles equilibrate to bilayer height. SSPM and SNOM reveal big contrast between the liquid and the solid phase in the first case due to the large differences in the vertical component of the molecular dipoles in the two phases, and in the second case due to fluorescence self-quenching in the solid phase. Multilayer growth on top of a liquid phase in the center of the solid domains and liquid phase inside the solid domain could be resolved. Phase imaging of multilayers samples reveals features not seen in the AFM.

Polyion complexed mixed LB films of amphiphiles with long FC chains (PFECA [CF 3 (CF 2 ) 8 (CH 2 ) 2 O(CH 2 ) 2 COOH] or perfluorodecanoic acid (PFDA) [CF 3 (CF 2 ) 8 COOH]) and those with long hydrocarbon (HC) chains, 3-, 6-, 9- or 12-(9-anthroyloxy) stearic acids (3-, 6-, 9- or 12-ANSTAs) deposited on Si substrates were characterized by atomic force microscopy/friction force microscopy (AFM/FFM). AFM/FFM images of 1:1 mixed LB films of PFDA and 6-, 9-, or 12-ANSTA showed phase separated structures, while those of PFDA and 3-ANSTA did not. AFM/FFM images of 1:1 mixed LB films of PFECA and 3-, 6-, or 9-ANSTA did not show phase separated structure. These results show that the amphiphile molecules with long HC chain which have a bulky probe unit at the position in the methylene chain close to head group (e.g. 3-ANSTA) can mix well with the amphiphile molecules with long fluorocarbon (FC) chains (PFDA or PFECA). Similar results were also observed in the mixed LB films of PFDA (or PFECA) and doxylstearic acids. According to the π – A isotherms for these amphiphiles with bulky probe unit, the molecular sectional area in the monolayers for these amphiphile molecule increased as the position of the probe unit approached to the head group. Since the cohesion energy for molecules decrease with the increase in the inter-molecular distance, the molecular mixing between the amphiphile with FC chain and that with HC chain which have a bulky probe unit at the position closer to head group can be attributed to the decrease of cohesion energy due to the increase in the inter-molecular distance. In the AFM/FFM image for 1:1 mixed LB films of PFDA and 12-ANSTA, the following interesting phenomenon were observed. After a scanning with large load over the part of an island composed of 12-ANSTA, which is higher than the sea area before these scanning, the height of the whole area of the island became lower than the sea area. From this result, it was confirmed that this mixed LB film has a ‘side by side’ structure.

We have studied the phase-separation of self-assembled monolayers (SAMs) of dialkyl disulfides on Au surface. Initially, the heat-induced phase-separation of SAMs consisting of unsymmetric disulfide molecules (CF 3 (CF 2 ) 5 (CH 2 ) 2 SS(CH 2 ) 7 CH 3 ) of hydrocarbon and fluorocarbon chains was investigated. We proved that the dimer structure cleaved on the Au surface. Subsequently, we formed one-dimensional nanostructures utilizing an anisotropic phase-separation of SAMs consisting of a mixture of the above unsymmetric disulfide and a symmetric disulfide of hydrocarbon (CH 3 (CH 2 ) 7 SS(CH 2 ) 7 CH 3 ). The wire-like structure with a width of 5 nm and a length ≈100 nm was observed by scanning tunneling microscopy.

Electron spin resonance (ESR) spectra for cast films and spin-coated films of stearic acid (STA), dioctadecyldimethylammonium chloride (DODAC) or didodecyldimethylammonium bromide (DDAB) mixed with spin probes, 5-doxylstearic acid (5-DXSTA) or 16-doxylstearic acid (16-DXSTA), were measured. The anisotropy of the ESR spectra was determined by varying the angle Θ, between the direction of the applied magnetic field and the direction normal to the sheet. The temperature dependence of the ESR spectra was measured to examine the effect of molecular motion on the ESR spectra. For the cast and spin-coated DODAC and DDAB films, a clear Θ dependence of the ESR spectra was observed, especially at higher temperature when 5-DXSTA was used as a spin probe, while the ESR spectra for these films were almost isotropic at higher temperature when 16-DXSTA was used as a spin probe. From this result, it was confirmed that the methylene chains close to the head groups in cast and spin-coated films of DODAC and DDAB were carrying out anisotropic rotational Brownian motion around the axis perpendicular to the film plane, while the tail parts of the methylene chains were doing almost isotropic rotational motion at higher temperature. The temperature dependence of the ESR spectra for cast and spin-coated films of DODAC and DDAB showed that the flexibility of methylene chains in DDAB films was larger than that in DODAC films, and this difference was ascribed to the difference in the gel-to-liquid crystal transition temperatures of DODAC and DDAB films. On the other hand, the ESR spectra for cast and spin-coated films of STA mixed with 5-DXSTA or 16-DXSTA did not show clear anisotropy anywhere in the temperature range used in this study. From this result, it was shown that amphiphiles in these films had a less ordered structure compared with those in DODAC and DDAB films.