Hiroshi Kitano

Efficient 355-nm generation in CsB3O5 crystal.

We demonstrate UV generation in CSB3O5 (CBO) crystals grown by the top-seeded solution growth technique. 355-nm UV light was generated by use of a type II CBO crystal as a sum frequency of the fundamental light and the second harmonic of a nanosecond Nd:YVO4 laser. A 3.0-W output of the third-harmonic was obtained at a repetition rate of 31 kHz. The conversion efficiency from the fundamental light to the third harmonic reached 30%, which was 1.5 times higher than that obtained with a type II LiB3O5 crystal under the same experimental conditions.

Protein Crystal Processing Using a Deep-UV Laser

We propose a new protein crystal processing technique, pulsed UV laser soft ablation (PULSA). This is the first report on the successful processing of protein crystals using an optical light source without causing significant damage to the crystal. Photoablation without thermal degradation of the protein crystal structure was achieved using deep-UV laser pulses at a wavelength of 193 nm. The PULSA technique did not affect the quality of the crystals used for X-ray data collection. Moreover, complicated and precise processing of protein crystals, which is difficult using conventional mechanical tools, has been achieved using PULSA. This technique will undoubtedly be a powerful tool for processing protein crystals.

Femtosecond Laser Processing of Protein Crystals in Crystallization Drop

We have developed a novel processing technique for protein crystals using femtosecond laser irradiation. We call this technique the femtosecond-laser-induced cut and cleave operation (fs-CACO). By precisely controlling the laser fluence and the position of the laser focal point, we are able to perform accurate and reproducible processing of protein crystals with little damage without troublesome treatment such as the unsealing of vessels and removal of solutions surrounding the crystals. To our knowledge, this is the first report on processing protein crystals using ultra-short-pulse laser ablation. Fs-CACO will be a powerful tool for making problematic protein crystals suitable for X-ray diffraction measurements.

Universal Processing Technique for Protein Crystals Using Pulsed UV Laser

We demonstrated the laser processing of three types of soft protein crystals using a 193 nm deep-UV pulsed laser. In particular, high-solvent-content crystals, phosphoenolpyruvate carboxylase (PEPC) crystals, were successfully processed without causing significant damage. An unchanged resolution limit between pre- and post-processings in X-ray diffraction measurements showed that laser irradiation has little influence on crystallinity. These results reveal that the processing using a deep-UV laser is effective for various protein crystals and will be very useful in accelerating protein structural analysis.

On the phase transition in α-NH4HgCl3, a two-dimensional version of ammonium chloride

Abstract Heat capacity of α-NH4HgCl3 crystal has been measured with an adiabatic calorimeter from 11 to 300 K. A sharply peaked anomaly due to an order-disorder change of the ammonium ions was found at 54.97 ± 0.04 K. The entropy and enthalpy changes were estimated to be ΔS = 5.2 ± 1.0JK−1 mol−1 and ΔH = 342 ± 65 J mol−1. In accordance withthe structural two-dimensionality of α-NH4HgCl3 crystal, Onsagers solution of the two-dimensional Ising model was used in calculation of the transition temperature. On the assumption that the octopole-octopole interaction is responsible for the ordering of the ammonium ions in the present crystal and in ammonium chloride, the calculation gives 74.44 K for the transition temperature. Several possibilities were discussed for explaining the remaining discrepancy between the observed and calculated transition temperatures.

Application of UV-Laser Ablation to Detaching Protein Crystal from Growth Vessel

We propose a new procedure for detaching protein crystals from a growth vessel, which we call harvesting adhered crystals by laser irradiation (HACLI). A single laser shot at a wavelength of 193 nm successfully detaches hen egg-white lysozyme crystals from a fused-silica glass plate or capillary tube. X-ray diffraction measurements demonstrate that laser irradiation has little influence on the crystallinity. The HACLI technique will be a powerful tool for handling fragile protein crystals, especially those grown in a glass capillary tube.

New Approach to Improve X-Ray Diffraction Pattern of Protein Crystal Using UV-Laser Ablative Processing

A newly proposed processing technique for protein crystals, Pulsed UV Laser Soft Ablation (PULSA), is found to be practically useful for X-ray diffraction analysis. We experimentally confirmed that a diffraction pattern from a cracked protein crystal was considerably improved by eliminating the damaged section with the PULSA processing. This technique will enable us to easily process protein crystals mounted on X-ray diffraction equipments without any extra mechanical handling of the crystals.

Corneal ablation with new 193 nm solid-state laser: preliminary experiments.

PURPOSE: To assess the ability of a newly developed 193 nm solid‐state laser to ablate the cornea. SETTING: Osaka University, Osaka, Japan. METHODS: A prototype laser engine was developed by combining a 1547 nm laser diode, fiber amplifiers, and 5 stages of a frequency‐conversion system using CsLiB6O10 crystals as the last stage. Poly(methyl methacrylate) (PMMA) plates were exposed to the prototype laser beam to determine the relationship between the fluence and ablation rate. Laser irradiation of porcine corneas was performed to induce morphological changes, and the quality of the lesions was determined by light and scanning electron microscopy. RESULTS: The relationship between the fluence and ablation rate of the 193 nm solid‐state laser was comparable to that of the argon–fluoride excimer laser. Light and scanning electron microscopy of the porcine corneas showed that the linear and square lesions had sharp, clean edges. CONCLUSIONS: Smooth ablations of PMMA plates and porcine corneas were obtained by the laser. Further investigations must be conducted to determine whether this laser can be an alternative laser source for keratorefractive surgery.

Effect of Laser Irradiation on Enzyme Activity

We previously developed a protein crystallization technique using a femtosecond laser and protein crystal processing and detaching techniques using a pulsed UV laser. In this study, we examine the effect of laser irradiation on protein integrity. After several kinds of laser were irradiated on part of a solution of glycerol-6-phosphate dehydrogenase from Leuconostoc mesenteroides, we measured the enzyme activity. Femtosecond and deep-UV laser irradiations have little influence on the whole enzyme activity, whereas the enzyme lost its activity upon high-power near-infrared laser irradiation at a wavelength of 1547 nm. These results suggest that suitable laser irradiation has no remarkable destructive influence on protein crystallization or crystal processing.

Protein Crystal Growth Using Laser-Processed Seed Crystals

We demonstrate the use of crystals processed by a pulsed UV laser as seeds for protein crystallization. A hen-egg-white lysozyme crystal, which was successfully laser-processed without causing significant damage, was seeded and grown larger than its original size. Polarized light microscopy and X-ray diffraction analysis showed that the crystal grown by seeding was a single crystal of suitable quality for X-ray crystallography. The results support the effectiveness of UV-laser processing for protein crystals. Furthermore, this seeding technique, which we call laser-cut seeding, will be useful for the production of a seed of suitable size and shape in macroseeding, for the elimination of a damaged section in a growing crystal, and for removing useless crystals from polycrystals.