Structures of 17,19-hexatriacontadiyne monolayers on Au(111) studied by infrared reflection absorption spectroscopy and scanning tunneling microscopy

The aggregation and reaction of 17,19-hexatriacontadiyne molecules are studied on a Au(111) surface. The molecular orientation and arrangement are elucidated by infrared reflection absorption spectroscopy (IRAS) and scanning tunneling microscopy (STM). A vapor-deposited monolayer and a multilayered film formed by adsorption from the solution provide IRA spectra with bands due to the antisymmetric and symmetric stretching of methylenes in the gauche conformation. After the adsorbed film is rinsed with the solvent, however, the spectrum loses the gauche bands and is characterized by the enhanced C-H(distal) and C-H(proximal) stretching bands, which means that all-trans molecules are laid flat. Only STM images for the rinsed film display columnar structures on the herringbones of the reconstructed Au(111) surface; the alkyl chain direction is found to be parallel to the Au atom row. The results indicate that an ordered monolayer is formed first at the liquid-solid interface, and then, disordered overlayers with the gauche conformation are grown but removed by a rinse. Upon exposure to UV light, thus obtained monomer columns are converted into oligomers with flexible backbones and an increased gauche population in the alkyl chains, which resemble red phase polydiacetylenes in LB films.     

Two-dimensional fluorescence correlation spectroscopy IV: resolution of fluorescence of tryptophan residues in alcohol dehydrogenase and lysozyme

Generalized two-dimensional (2D) fluorescence correlation spectroscopy has been used to resolve the fluorescence spectra of two tryptophan (Trp) residues in alcohol dehydrogenase and lysozyme. In each protein, one Trp residue is buried in a hydrophobic domain of the protein matrix and the other Trp residue is located at a hydrophilic domain close to the protein-water interface. Fluorescence quenching by iodide ion, a hydrophilic quencher, was employed as a perturbation to induce the intensity change in the spectra. The Trp residue which is located at the hydrophilic domain is effectively quenched by the quencher, while the Trp residue located at the hydrophobic domain is protected from the quenching. Therefore, the fluorescence of these two Trp residues have a different sensitivity to the quenching, showing a different response to the concentration of the quencher. Fluorescence spectra of the two Trp residues in alcohol dehydrogenase, which are heavily overlapped in conventional one-dimensional spectra, have been successfully resolved by the 2D correlation technique. From the asynchronous correlation map, it was revealed that the quenching of Trp located at the hydrophobic part was brought about after that of Trp located at the hydrophilic part. In contrast, the fluorescence spectra of the two Trp residues could not be resolved after the alcohol dehydrogenase was denatured with guanidine hydrochloride. These results are consistent with the well-known structure of alcohol dehydrogenase. Furthermore, it was elucidated that the present 2D analysis is not interfered by Raman bands of the solvent, which sometimes bring difficulty into the conventional fluorescence analysis. Fluorescence spectra of the Trp residues in lysozyme could not be resolved by the 2D correlation technique. The differences between the two proteins are attributed to the fact that the Trp residue in the hydrophobic site of lysozyme is not sufficiently protected from the quenching.     

Facile Synthesis of Free‐Standing Polymer Brush Films Based on a Colorless Polydopamine Thin Layer

A free‐standing polymer brush film with tailored thicknesses based on a colorless polydopamine (PDA) thin layer is prepared and characterized. The surface‐initiated atom transfer radical polymerization (ATRP) of 2‐hydroxyethyl methacrylate (HEMA) is performed on a PDA layer with thickness of ca. 6 nm, which generated an optically transparent and colorless free‐standing PHEMA brush film (1.5 cm × 1.5 cm). Because the cross‐linked PDA layer is used as the base for the polymer brushes, the reported method does not require cross‐linking the polymer brushes. The free‐standing film thicknesses of ≈16–75 nm are controlled by simply changing the ATRP reaction time. The results show that the free‐standing PHEMA brush film transferred onto a plate exhibits a relatively smooth surface and is stable in any solvent.

     

Medical Application of Raman Spectroscopy

Abstract

In about the last 20 years, Raman spectroscopy has made phenomenal progress owing to technological innovations in lasers, detectors, and computers. Today, application of Raman spectroscopy spreads over large areas of science and technology. Medical science has also become one of the targets of Raman spectroscopy [1]; it has considerable promise as a diagnostic o r analytical tool in medicine since it is an excellent nondestructive structural probe for constituents of biological materials [2–6].     

On tame pro-p Galois groups over basic {\mathbb{Z}_p}-extensions

For a prime number p and a finite set S of prime numbers congruent to 1 modulo p, we consider the Galois group of the maximal pro-p-extension unramified outside S over the ${\mathbb Z_p}$ -extension of the rational number field. In this paper, we give a family of S for which the Galois group is a metacyclic pro-p group with an application to Greenberg’s conjecture.     

Dielectric and calorimetric studies on 1BC1EPOPB feroelectric liquid crystal having a large spontaneous polarization

Experimental investigations on the ferroelectric liquid crystal, R-4′(1-butoxycarbonyl-1-ethoxy) phenyl 4-(4-octyloxy phenyl) benzoate (1BC1EPOPB) of large spontaneous polarization (P _S(+) = 240?nC?cm^?2), using dielectric and calorimetric techniques, are reported. The temperature range of 25.0–125.0°C has been chosen for dielectric measurements. Dielectric dispersion studies are carried out in the temperature range 45.0–75.0°C and in the frequency range 2?Hz to 2?MHz for the smectic A, smectic C* and smectic X phases. A new phase called ‘smectic X’ has been found around 56.3°C. The transition temperatures identified by the dielectric dispersion studies for different phases and those given by DSC techniques are in close agreement.     

Chemical Interactions of Cryptic Actinomycete Metabolite 5‐Alkyl‐1,2,3,4‐tetrahydroquinolines through Aggregate Formation

Organisms often produce secondary metabolites as a mixture of biosynthetically related congeners. However, why are metabolites with minor chemical variations produced simultaneously? 5‐Alkyl‐1,2,3,4‐tetrahydroquinolines (5aTHQs) are small, lipophilic metabolites produced by Streptomyces nigrescens HEK616 when cultured with Tsukamurella pulmonis TP‐B0596. A mixture of 5aTHQs forms aggregates that show enhanced membrane affinity and biological activity. The ability to form aggregates and membrane‐binding activity is regulated by the length of the alkyl chains. Aggregates with long alkyl chains were too stable to fuse with lipid membranes. However, if inactive 5aTHQ congener was mixed with active congener, the mixture showed increased membrane affinity, enabling cellular entry and biological activity. Therefore, it is shown that sloppiness in a biosynthetic pathway, by which minor structural variations can be produced, is functionally rational, as the metabolites show synergistic action.     

Local structural analysis of In-doped Bi2Se3 topological insulator using X-ray fluorescence holography

We performed X-ray fluorescence holography measurements on an In-doped Bi₂Se₃ topological insulator and obtained an in-plane atomic image in the vicinity of In. We found that atomic images at the positions of the first nearest neighbors (NNs) are very weak whereas those at the positions of the second and the third NNs are relatively strong. On the basis of the fact that In is half of the atomic number of Bi, we attributed the origin of this feature to the clustering of the In atoms in the Bi plane. We calculated the intensity of the atomic images and confirmed that the formation of In cluster results in a decrease by 30% in the first NN atomic image intensity. However, the decrease in the magnitude is not enough to explain the experimental results, suggesting another contribution such as the lattice distortions. The effect of the lattice distortion on the atomic image intensity is discussed on the basis of the simulation including the positional fluctuation of In atoms.     

SPR and SERS characteristics of gold nanoaggregates with different morphologies

In this study, surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) characteristics of gold nanoaggregates with different morphologies are examined to elucidate the correlation between SPR and SERS of the object. Nanoaggregates, defined as random aggregates (hereafter RA), elongated aggregates (hereafter EA) and two-dimensional layered aggregates (hereafter 2DLA) are fabricated by immobilizing colloidal gold nanoparticles on glass substrates. The color variation observed in the RA and EA samples indicates the variation in localized SPR excitations excited on the samples. The RA sample mostly shows a broadened and shifted SPR peak centered at 570 nm in addition to another peak in the longer wavelength region (∼700 nm), whereas in the EA sample a weak blue-shifted peak is observed near 450 nm in addition to a broadened peak centered at 570 nm covering a trail for another one near 700 nm. In the case of the 2DLA sample, more than one SPR peaks are observed in the longer wavelength region. The SERS observation confirms million times higher enhancement at least in Raman intensity using the gold nanoaggregates adsorbed by dye molecules. The EA sample of gold nanoparticles shows ∼5 times higher enhancement in Raman signal compared to that of the RA and 2DLA sample.