Quantitative evaluation of blinking in surface enhanced resonance Raman scattering and fluorescence by electromagnetic mechanism

We analyze blinking in surface enhanced resonance Raman scattering (SERRS) and surface enhanced fluorescence (SEF) of rhodamine 6G molecules as intensity and spectral instability by electromagnetic (EM) mechanism. We find that irradiation of intense NIR laser pulses induces blinking in SERRS and SEF. Thanks to the finding, we systematically analyze SERRS and SEF from stable to unstable using single Ag nanoparticle (NP) dimers. The analysis reveals two physical insights into blinking as follows. (1) The intensity instability is inversely proportional to the enhancement factors of decay rate of molecules. The estimation using the proportionality suggests that separation of the molecules from Ag NP surfaces is several angstroms. (2) The spectral instability is induced by blueshifts in EM enhancement factors, which have spectral shapes similar to the plasmon resonance. This analysis provides us with a quantitative picture for intensity and spectral instability in SERRS and SEF within the framework of EM mechanism.     

Optimizing T2-weighted magnetic resonance sequences for surface coil microimaging of the eye with regard to lid, eyeball and head moving artifacts

PURPOSE: To acquire high-resolution magnetic resonance (MR) images, we developed a new blinking artifact reduced pulse (BARP) sequence with a surface coil specialized for microscopic imaging (47 mm in diameter). MATERIALS AND METHODS: To reduce eye movement, we ascertained that the subjects' eyes were kept open and fixated to the target in the 1.5-T MR gantry. To reduce motion artifacts from blinking, we inserted rest periods for blinking (1.5 s within every 5 s) during MR scanning (T2-weighted fast spin echo; repetition time, 5 s; echo time, 100 ms; echo train, 11; matrix, 256 x 128; field of view, 5 cm; 1-mm thickness x 30 slices). Three scans (100 s x 3) were performed for each normal subject, and they were added together after automatic adjustment for location to reduce quality loss caused by head motion. RESULTS: T2-weighted MR images were acquired with a high resolution and a high signal-to-noise ratio. Motion artifacts were reduced with BARP, as compared with those with random blinking. Intraocular structures such as the iris and ciliary muscles were clearly visualized. Because the whole eye can be covered with a 1-mm thickness by this method, three-dimensional maps can easily be generated from the obtained images. CONCLUSION: The application of BARP with a surface coil of the human eye might become a useful and widely adopted procedure for MR microimaging.     

Residual pump light as a probe of self-pulsing instability in an ytterbium-doped fiber laser

Self-pulsing instability in the ytterbium-doped fiber (YDF) laser is investigated with the pump-bypassed cavity configuration. The residual pump light acts as a probe of the intracavity dynamics, and the temporal behavior of the light shows correlations with the self-mode locking instability in the original cavity and the sustained self-pulsing instability in the modified cavity of the YDF laser. The results suggest that the interactions among stimulated emission, pump absorption and/or reabsorption could account for self-pulsing instability in the YDF laser. The pump-bypassed laser cavity configuration can be used to investigate the instabilities of various kinds of fiber lasers.     

One-step advanced preparation of surface-functional peptide nanospheres by the polymerization of L-phenylalanine N-carboxyanhydride with dual initiators

Surface-grafted peptide nanospheres consisting of hydrophobic poly(L-phenylalanine) with hydrophilic poly(ethylene glycol) (PEG) grafts were successfully prepared by the one-step polymerization of L-phenylalanine N-carboxyanhydride with the dual initiators of hydrophobic n-butylamine and hydrophilic NH2-monoterminated PEG (NH2-PEG). The monodispersed peptide nanospheres were stably self-assembled during polymerization in a mixture of water/dimethyl sulfoxide to create a colloidal solution, but only aggregated in water or organic solvents. When n-butylamine or NH2-PEG was used as a solitary initiator, the peptide nanospheres were not formed. The peptide nanospheres showed high dispersion-stability in water, and their diameter was approximately 300 nm. Furthermore, the peptide nanospheres were well-redispersed in water, retaining the same diameter and monodispersity even after lyophilization. Peptide nanospheres with the functional carboxylic acid on their graft layer were also successfully prepared by the one-step preparation method. This one-step preparation method of surface-grafted peptide nanospheres will be useful as an advanced technology to develop biodegradable functional nanospheres.     

Electronic structures of Pt-Co and Pt-Ru alloys for CO-tolerant anode catalysts in polymer electrolyte fuel cells studied by EC-XPS

CO tolerance at pure Pt, Pt-Co, and Pt-Ru alloys was investigated by X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-XPS) in order to discover a hint for designing higher performance anode catalysts. After the electrochemical stabilization and/or CO adsorption, these electrodes were immediately transferred to the XPS chamber without exposure to air to avoid contamination of the surfaces. It was revealed that alloying with Co or Ru modified the electronic structures of Pt atoms, resulting in a positive core level (CL) shift of Pt 4f(7/2) which could weaken the Pt-CO interaction. For the Pt-Co alloy electrode, the Pt 4f(7/2) CL shift remained after the electrochemical stabilization despite Co dissolution and formation of a Pt skin layer. Changes in surface core level shifts (DeltaSCLSs) induced by CO adsorption were evaluated and related to the CO adsorption energy. The values of DeltaSCLS at these alloys were smaller than that of pure Pt, indicating that Ru and Co are effective elements to weaken the bond strength of Pt-CO.     

Effects of thermoresponsive coacervation on the hydrolytic degradation of amphipathic poly(gamma-glutamate)s

Hydrolytic properties of thermoresponsive biopolymers with amphiphilic structures, gamma-PGA-P, were investigated. Hydrolysis was monitored in terms of molecular weight changes using GPC and spectroscopic measurements. The hydrolytic degradation of gamma-PGA-P was controlled by a change in the degree of propyl group conversion, reaction temperature, and/or reaction pH. The degradation was classified as the rapid elimination of propyl side chains and the moderate cleavage of peptide linkages in the backbone. Furthermore, hydrophobic environments established by the thermoresponsive coacervation of gamma-PGA-P60 solutions inhibited hydrolytic degradation reactions. Inversely, hydrolytic degradations increased coacervation temperatures. Kinetic studies of hydrolytic reactions suggest that the degradation rate of gamma-PGA-P60 solutions can be controlled by their thermoresponsivity. The hydrolysis reported here represents the first degradation rate controlled by thermoresponsive coacervation.     

Formation of Ge-diffusion-suppressed GaAs layers and InAs quantum dots on Ge/Si substrates

Crystal growth of GaAs layers and InAs quantum dots (QDs) on the GaAs layers was investigated on Ge/Si substrates using ultrahigh vacuum chemical vapor deposition. Ga-rich GaAs with anti-site Ga atoms grown at a low V/III ratio was found to suppress the diffusion of Ge into GaAs. S-K mode QD formation was observed on GaAs layers grown on Ge/Si substrates with Ga-rich GaAs initial layers, and improved photoluminescence from 1.3 μm-emitting InAs QDs was demonstrated.     

Formation of regioregular head‐to‐tail poly[3‐(4‐butylphenyl)thiophene] by an oxidative coupling polymerization with vanadium acetylacetonate

The mechanism for the formation of head‐to‐tail (H–T) poly[3‐(4‐butylphenyl)thiophene] by oxidative coupling polymerization with a catalytic amount of vanadium acetylacetonate was investigated. Polymerization was carried out in the presence of vanadium acetylacetonate, trifluoromethane sulfonic acid, and trifluoroacetic anhydride under an oxygen atmosphere in 1,2‐dichloroethane at room temperature. Polymers and oligomers obtained after several polymerization times were characterized by gel permeation chromatography, IR, and NMR spectroscopies. With these findings and the reactivity of monomer and dimers based on ab initio density functional theory, the polymerization was found to proceed mainly through the formation of H–T linkages due to the high spin density at the 2‐position of 3‐(4‐butylphenyl)thiophene and the calculated total energy of dimers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2287–2295, 2001     

Preparation of 1,6‐naphthyridine‐2,5(1H,6H)‐diones

Novel method for the synthesis of 3‐acyl‐1,6‐dialkyl‐7‐methyl‐1,6‐naphthyridine‐2,5(1H,6H)‐diones (2) was developed. The reaction of 2‐acyl‐1‐alkylamino‐1‐ethoxyethylenes (1) with acetyl chloride or β‐keto amide 3 with acetyl chloride in the presence of p‐toluenesulfonic acid gave 2 in moderate yield (14‐59% yield).     

Synthesis and functionalities of poly(N-vinylalkylamide). IV. Synthesis and free radical polymerization of N-vinylisobutyramide and thermosensitive properties of the polymer

Pyrolysis of (N-α-isopropoxyethyl)isobutyramide, which was obtained by the reaction of isobutyramide, 2-propanol, and acetaldehyde in the presence of conc. sulfuric acid, produced N-vinylisobutyramide (NVIBA). The free radical polymerization of NVIBA was carried out in various solvents in the presence of a radical initiator. It was found that the polymerizability of NVIBA is similar to that of N-vinylacetamide. The resulting polyNVIBA showed a lower critical solution temperature (LCST) sharply at 39°C. Thermosensitive properties of polyNVIBA were investigated in comparison with poly(N-isopropylacrylamide). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1763–1768, 1997