Oscillating fluorescence in an unstable colloidal dispersion of CdSe/ZnS core/shell quantum dots

Fluorescence oscillation is observed in an ensemble of colloidal CdSe/ZnS core/shell quantum dots (QDs) dispersed in nonpolar solvent under continuous irradiation. The QDs dispersed in toluene gradually aggregate and change their fluorescence intensity, even in the dark. During the aggregation, the QD/toluene suspension is unstable, that is, overdispersed. The fluorescence oscillation is found only in this unstable state before the system reaches steady state. In addition, the aggregation rate is promoted by irradiation and strongly correlates with the oscillation amplitude. Our experimental results indicate that the dispersion instability plays an important role in both linear and nonlinear dynamics of the fluorescence. It is inferred from the experimental results and previous studies that the complex time evolution of fluorescence in the QD/toluene dispersion is possibly due to adsorption and desorption of surface ligand molecules over the course of QD aggregation.     

Lateral displacement by transient mobility in chemisorption of CO on Pt(997)

We investigated adsorbed states of CO on Pt(997) at 11 K using infrared reflection absorption spectroscopy. At 11 K, thermal migration is suppressed and thus the initial chemisorption at terrace sites and step sites is controlled by the transient mobility of the adsorbing molecule. The initial occupation ratio between atop CO on the terrace and atop CO at the step is directly determined to be 3.6:1. With a simple isotropic migration model, we estimated the mean lateral displacement from the first impact point to the initial chemisorption site to be 6.8 A. We also discuss the origin of transient mobility of CO on metal surfaces.     

Analysis of cigarette smoke by an online thermal desorption system and multidimensional GC-MS

Single puffs of cigarette smoke with a wide continuous range of volatility are directly analyzed using a new system. The system consists of a smoking machine, an online thermal desorption system (TDS), and a multidimensional gas chromatograph-mass spectrometer (MDGC-MS) system. The online TDS with the smoking machine collects the single-puff cigarette smoke with glass beads as the cryogenic adsorbent. The MDGC is composed of three capillary columns, Poraplot Q, and DB-WAX for separation and a deactivated capillary column for pressure balance, which enables simultaneous separation of the two different phases. The smoke desorbed from the TDS is divided into vapor and semivolatile phases and analyzed individually with each column by the MDGC. Thus, the system enables the overall analysis of the two phases simultaneously, including acetaldehyde and 1,4-benzenediol. This system also provides more appropriate analysis for compounds crossing the two phases such as toluene and pyridine. For the approach of introducing internal standards, a gas mixture of toluene-d(8) and o-xylene-d(10) is applied and the compounds are detected in the vapor and semivolatile phases, respectively.     

High-brightness 138-W green laser based on an intracavity-frequency-doubled diode-side-pumped Q-switched Nd:YAG laser

Green power of 138 W was generated at an estimated beam quality of M(2) = 11 by intracavity frequency doubling of a diode-pumped Nd:YAG laser. The laser employs a diffusive close-coupled diode-pumping design and a bifocusing-compensation resonator design to ensure stable operation.     

Development of novel pyrrole synthesis for the preparation of intermediates of bioactive pyrrole alkaloids

We have developed a novel method for the synthesis of 3,4-diarylpyrrole-2,5-dicarboxylates via α-diazo esters, which are easily obtained from phenylalanine derivatives. Utilizing this method, intermediates of bioactive compounds having the structure of 3,4-diarylpyrrole-2,5-dicarboxylates were synthesized.     

Formation of formal compounds in reaction of dimethyl phenols with formaldehyde

Formaldehyde was reacted with both 2,4-dimethylphenol(2,4-xyenol) and 2,6-dimethylphenol(2,6-xylenol), which are model compounds of monofunctional phenols, and the reaction products were subjected to HLC analysis to elucidate details of the formation process and bonding manner of a formal group, which can greatly affect the performance of phenol–formaldehyde resins. As a result, formal compounds of dimethylphenols were successfully separated by HLC. It was further found, as a result of tracing the reactions by HLC, that the formation of a formal group occurs at either position of the ortho and para positions, and that methylol compounds were formed following formation of the formal compounds. Furthermore, as a result of NMR analysis as well as consideration of solvation on the basis of the relative elution volumes of the nonacetylated and acetylated reaction products it was found that the formal group was added to the phenol nuclei.     

Layer structure estimation of three‐dimensional crystal and two‐dimensional molecular film for fluorinated comb copolymers

Comb copolymers containing both hydrogenated and fluorinated side‐chains were prepared by copolymerization using acrylic or methacrylic monomers in several ratios. The crystal structures of these copolymers and layer structures of their organized molecular films were investigated by wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and out‐of plane X‐ray diffraction. Further, to selectively estimate the regularity of shorter fluorocarbon side‐chains, organized molecular films of copolymers were investigated by polarized near‐edge X‐ray adsorption fine structure (NEXAFS) spectroscopy. From the results of these measurements, it was inferred that these copolymers formed highly ordered layer structures, and a long spacing was predominantly determined by the arrangement of hydrogenated side‐chains, except in copolymers having extremely high fluorocarbon contents. In the case of the organized molecular films, the fluorinated side‐chains of methacrylate copolymers cannot form a highly ordered arrangement, whereas those of acrylate copolymers were oriented on monolayers. However, in both cases, the hydrogenated side‐chains predominantly formed layer structures in the organized films, and the fluorinated side‐chains did not contribute to the formation of the layer structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 534–546, 2008     

Nonlinear resonances and self-excited oscillations of a rotor caused by radial clearance and collision

This paper investigates oscillations in a flexible rotor system with radial clearance between an outer ring of the bearing and a casing by experiments and numerical simulations. The mathematical model considers the collisions of the bearing with the casing. The following phenomena are found: (1) Nonlinear resonances of subharmonic, super-subharmonic and combination oscillation occur. (2) Self-excited oscillation of a forward whirling mode occurs in a wide range above the major critical speed. (3) Entrainment phenomena from self-excited oscillation to nonlinear forced oscillation occur at these nonlinear resonance ranges. Moreover, this study analyzes periodic solutions of the mathematical model by the Harmonic Balance Method (HBM). As the results, the nonlinear resonances of subharmonic oscillation and its entrainment phenomenon can be explained theoretically by investigating the stability of the periodic solutions. The influence of the static force and the bearing damping on these oscillation are also clarified.     

Test compounds for detecting the silanol effect on the elution of ionized amines in reversed‐phase LC

The effectiveness of several basic compounds for testing silica‐based stationary phases was reviewed by applying them to recent columns for reversed‐phase HPLC. Most octadecylsilylated (C18) stationary phases, prepared as a base‐deactivated material from high‐purity silica gel with endcapping, provided excellent peak shape and column efficiency for the bases including benzylamine and amitriptyline that once caused problems and were subsequently employed for testing silanol activities. However, a cyclic tertiary amine, dextrometorphan, was eluted as an acceptable peak from only a few columns at neutral pH. Such a more sensitive probe is expected to contribute to further improvement of the stationary phase for reversed‐phase HPLC.     

Determination of Ubiquinone in Blood by High-Performance Liquid Chromatography with Post-Column Fluorescence Derivatization Using 2-Cyanoacetamide

It was shown that ubiquinone (CoQ₁₀) and ubiquinol (CoQ₁₀H₂) produce fluorescence products under alkaline conditions when reacted with 2-cyanoacetamide. The reaction mixture from CoQ₁₀ gave fluorescence with excitation and emission maximum wavelengths at 442 nm and 549 nm, respectively. This reaction was considered to proceed via Craven’s reaction. Moreover, 2-cyanoacetamide was shown to be a useful reagent for high-performance liquid chromatography (HPLC) with post-column fluorescence derivatization of CoQ₁₀ and CoQ₁₀H₂ in blood. CoQ₁₀ showed a linear response in the range of 0.32–1276 ng, and the detection limit (S/N = 3) was 0.16 ng. Moreover, the sample pretreatment by deproteinization and extraction of CoQ₁₀ and CoQ₁₀H₂ from plasma using 1-propanol with potassium formate was effective for excellent separation of CoQ₁₀ and CoQ₁₀H₂ from other fluorescent substances in the blood. This simple and rapid pretreatment was considered to minimize the oxidation of CoQ₁₀H₂. On the other hand, CoQ₁₀ and CoQ₁₀H₂ in plasma samples obtained by finger prick were detected, as in venous blood obtained by venipuncture. Our method involving the simple and rapid collection of plasma by finger prick and sample pretreatment is thought to be applicable for the determination of CoQ₁₀H₂/total CoQ₁₀ ratio as a biomarker of oxidative stress.