Shu Watanabe

Efficient Characterization for Protein Crystals Using Confocal Raman Spectroscopy

Confocal Raman spectroscopy was applied to the characterization of various states emerging in the screening of protein crystallization. Four main characterized states, namely single crystals, microcrystals, precipitates, and clear drops without solid materials, appear in a droplet for crystallization; the first three states should be critically distinguished and characterized because of the limitations of visual observation under an optical microscope. Using lysozyme and other proteins, crystallization was performed by the hanging drop vapor diffusion technique and was monitored through an automated confocal Raman system. Prior to the spectroscopic analysis, an optical microscope with a charge-coupled device (CCD) camera and associated image processing software were used to rapidly identify the XY locations to be measured spectroscopically by focusing the laser beam on a test sample. Instead of the current image analysis by optical microscopy, confocal Raman spectroscopy with a high spatial resolution was used to identify the state of protein crystallization. Such real-time Raman monitoring also distinguished real protein crystals from pseudo-protein crystals emerging in a crystallization droplet.

A method for large-scale synthesis of Al-doped TiO2 nanopowder using pulse-modulated induction thermal plasmas with time-controlled feedstock feeding

A unique method of large-scale synthesis of Al-doped TiO2 nanopowder was developed, using 20 kW Ar–O2 pulse-modulated induction thermal plasmas (PMITP) with time-controlled feedstock feeding (TCFF). This PMITP–TCFF method is characterized by intermittent feedstock powder feeding synchronized with modulation of the power of the PMITP. The method enables heavy-load feeding of raw material powder to the thermal plasmas for complete evaporation. The nanopowder synthesized was analysed using different methods including field emission scanning electron microscopy, x-ray diffraction (XRD) spectroscopy, bright-field transmission electron microscopy (TEM), TEM/energy dispersive x-ray (EDX) mapping, x-ray photoelectron spectroscopy, and spectrophotometry. The results showed that Al-doped TiO2 nanopowder can be synthesized with mean diameters of 50–60 nm. The Al doping in TiO2 was confirmed from the constituent structure in the XRD spectra, the uniform presence of Al in the nanopowder in the TEM/EDX mapping, the chemical shift in the x-ray photoelectron spectra, and the absorption edge shift in the optical properties. The rate of production of the Al-doped TiO2 nanopowder was estimated as 400 g h−1.

A large amount synthesis of nanopowder using modulated induction thermal plasmas synchronized with intermittent feeding of raw materials

A large amount synthesis method for titanium dioxide (TiO2) nanopowder is proposed by direct evaporation of titanium powders using Ar-O2 pulse-modulated induction thermal plasma (PMITP). To realize a large amount synthesis of nanopowder, the PMITP method was combined with the intermittent and heavy load feeding of raw material powder, as well as the quenching gas injection. The intermittent powder feeding was synchronized with the modulation of the coil current sustaining the PMITP for complete evaporation of the injected powder. Synthesized particles by the developed method were analyzed by FE-SEM and XRD. Results indicated that the synthesized particles by the 20-kW PMITP with a heavy loading rate of 12.3 g min−1 had a similar particle size distribution with the mean diameter about 40 nm to those with light loading of 4.2 g min−1.

Protein Crystallization Using a High-Repetitive Low-Power Laser Beam Under Tightly Focused Condition

The feasibility of a simple laser irradiation scheme that utilizes a low-power laser beam emitted directly from a femtosecond laser oscillator was studied using lysozyme as an example for promoting protein crystallization. The various irradiation intensities required for crystallization promotion were surveyed by the hanging drop crystallization method under a tightly focused condition. The optimal irradiation condition was found to be 10 GW/cm2, and the rate of lysozyme crystallization increased five times compared with that for the nonirradiated sample. On the other hand, when an intensity of 45 GW/cm2 was applied, polycrystals were generated; the rate of crystallization was low with irradiation less than 5 GW/cm2.

Two-dimensional spectroscopic observation of a pulse-modulated induction thermal plasma torch for nanopowder synthesis

The two-dimensional distributions of spectral radiation intensities in the plasma torch were observed for the pulse modulated induction thermal plasmas (PMITP) with continuous or intermittent feedstock feeding for TiO2 nanopowder synthesis. For this observation, an imaging spectrophotometer with a high speed video camera were adopted. The evaporation of feedstock Ti powder, the formation of TiO and TiO transportation were investigated from the observation results of a Ti atomic spectral line and TiO molecule spectra as well as those of Ar and O atomic lines. An interpretation was suggested from the observation results for Ti feedstock evaporation and TiO formation in nanoparticle synthesis using a PMITP with intermittent feedstock feeding.