Selective ablation of atherosclerotic lesions with less thermal damage by controlling the pulse structure of a quantum cascade laser in the 5.7-µm wavelength range

Cholesteryl esters are the main components of atherosclerotic plaques, and they have an absorption peak at the wavelength of 5.75 µm. To realize less-invasive ablation of the atherosclerotic plaques using a quasi-continuous wave (quasi-CW) quantum cascade laser (QCL), the thermal effects on normal vessels must be reduced. In this study, we attempted to reduce the thermal effects by controlling the pulse structure. The irradiation effects on rabbit atherosclerotic aortas using macro pulse irradiation (irradiation of pulses at intervals) and conventional quasi-CW irradiation were compared. The macro pulse width and the macro pulse interval were determined based on the thermal relaxation time of atherosclerotic and normal aortas in the oscillation wavelength of the QCL. The ablation depth increased and the coagulation width decreased using macro pulse irradiation. Moreover, difference in ablation depth between the atherosclerotic and normal rabbit aortas using macro pulse irradiation was confirmed. Therefore, the QCL in the 5.7-µm wavelength range with controlling the pulse structure was effective for less-invasive laser angioplasty.     

Third-order aberration analysis of an off-axial optical system

The aberration theory applied to co-axial optical systems is extended to off-axial systems, for which third-order aberration coefficients are considered. The derived aberrations are analyzed using three-dimensional ray bundles, spot diagrams, and image charts, and classified in relation to the system symmetry. This theory is very useful for optical designers, allowing them to clarify the relationship between the structures of off-axial optical systems and the corresponding off-axial aberrations.     

Second-harmonic-generation microscope using eight-segment polarization-mode converter to observe three-dimensional molecular orientation

We developed a compact polarization-mode converter for microscopy to control three-dimensional polarization at the focus. The converter consisted of two homogeneously aligned liquid-crystal spatial light modulators with eight independently controllable electrodes (segments), and a quarter-waveplate. The converter converted a linearly polarized beam to three polarization modes: two orthogonal linear polarizations and a pseudo-radial polarization. We applied the converter to second-harmonic-generation microscopy and demonstrated the detection of three-dimensional molecular orientation.     

Blue emission from InGaN/GaN hexagonal pyramid structures

Cathodoluminescence (CL) from InGaN grown on GaN hexagonal pyramid structures has been investigated. The facet structure can be controlled by the growth temperature and reactor pressure. GaN pyramid structures surrounded with facets were grown at 1020 C at a pressure of 500 Torr by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The indium mole fraction in the InGaN film depends on the facet structure. The thickness of the InGaN and the peak wavelength and intensity of the CL from the InGaN gradually increased from the bottom to the top of the facets.     

pH-responsive non-surface-active/surface-active transition of weakly ionic amphiphilic diblock copolymers

The weakly ionic amphiphilic diblock copolymer polystyrene-b-poly(acrylic acid) was synthesized by nitroxy radical-mediated living radical polymerization with precise control of block length, block ratio, and polydispersity. Systematical surface tension experiments and foam formation observations revealed that this polymer was non-surface active under neutral and alkaline (pH 10) conditions, while it was surface active under an acidic condition (pH 3). This result supports our proposed origin of non-surface activity; the image charge repulsion at the air/water interface is essential in addition to very stable micelle formation in the bulk solution. At a higher pH (pH 12), the polymer showed slight surface activity since the added NaOH played a role as an added salt. The critical micelle concentration (cmc) was estimated by static light scattering. Cmc increased with increasing added salt (NaCl) concentration as was observed for other strongly ionic non-surface-active polymers. Hence, this trend is characteristic for non-surface-active polymers. The pH dependence of cmc was minimum at pH 8–10. Since the acrylic acid block is fully ionized under this condition, the strong image charge repulsion at this condition accelerated micelle formation at a low polymer concentration, which consequently decreased cmc. Micelles in bulk solution were confirmed by dynamic light scattering, and the salt concentration and pH dependencies of the hydrodynamic radius of the micelles were also estimated. The pH-responsive non-surface-active/surface-active transition observed in this study strongly supports the fact that the image charge repulsion is an essential factor for non-surface activity in addition to stable micelle formation in solution.     

Enhanced collective optical response of vast numbers of silver nanoparticles assembled on a microbead

We investigated the optical response of a huge number of silver nanoparticles (AgNPs) densely assembled on an organic microsphere, i.e., AgNP-fixed bead, under the collective phenomena of localized surface plasmons. For this purpose, various optical properties of such a AgNP-fixed bead were analyzed in aqueous solution by dark-field optical microscopy and laser Raman microscopy. In particular, in comparison with the optical spectrum of single AgNPs, significant spectral broadening and redshift were observed due to plasmonic superradiance with decreasing interparticle distance to the subnanoscale when using small binder molecules in the AgNP-fixed bead. Furthermore, we observed surface-enhanced Raman scattering and clarified the sensitivity of the signal intensity to the size of the binder molecules between the AgNPs, which can be explained based on optical response theory using a discrete integral with spherical cells. These results and discussion provide a guiding principle for broadband plasmonic light absorbers and for highly sensitive detection of small molecules and nanoscale biomaterials based on vast numbers of nanogaps produced by a bottom-up self-assembly process.     

Mechanical and tribological properties of DLC coatings deposited by plasma-based ion implantation and deposition method on polyoxymethylene

Polyoxymethylene (POM, polyacetal) is one of the most popular plastics for machine elements, especially in Japan. However, it is difficult to use it under severe operating conditions such as high speed and high contact pressure. Diamond-like carbon (DLC) coatings were well known to be tribological and functional coatings. However, both POM and DLC coatings are difficult to adhere them each other. In the present paper, DLC coatings are deposited by plasma-based ion implantation and deposition (PBIID) method on POM substrate, and validity of DLC coatings on POM was investigated through friction and mechanical tests. When gas pressure was 0.2 and 0.8 Pa, hardness and adhesion properties of DLC coating deposited under gas pressure of 0.5 Pa were lower compared with under 0.2 and 0.8 Pa. For preparing DLC coatings having hard and good adhesion properties, relatively thin substrate was suitable. A correlation between relative humidity in the laboratory and friction coefficient was confirmed while DLC coatings remain on the substrate.     

Intramolecular Benzyne–Phenolate [4+2] Cycloadditions

An intramolecular benzyne–phenolate [4+2] cycloaddition is reported. Benzyne precursors, having vicinal halogen‐sulfonate functionalities, linked with a phenol(ate) by various tether groups undergo efficient intramolecular [4+2] cycloaddition by treatment with either Ph₃MgLi or nBuLi for halogen–metal exchange to form various benzobarrelenes.     

Catalytic Carbonylation and Carboxylation of Organosulfur Compounds via C−S Cleavage

Transition‐metal‐catalyzed carbonylation with CO gas occupies a privileged position in organic synthesis for the synthesis of carbonyl compounds. Although this attractive and useful chemistry has led many researchers to investigate carbonylative transformations of various organic (pseudo)halides, C?S‐cleaving carbonylation of organosulfur compounds has been fairly limited. Recently, a broad spectrum of C?S‐cleaving transformations has been emerging in the field of cross‐coupling. In light of the importance of carbonyl compounds as well as considerable advancement for employing organosulfur compounds as competent surrogates of (pseudo)halides, carbonylative transformations of C?S bonds should be of high value. This Minireview focuses on catalytic C?S carbonylation of organosulfur compounds with CO or its equivalents. In addition, reductive carboxylation of C?S bonds with CO₂ is described.