Noritaka Kato

Observations of merocyanine J-aggregate domains in mixed molecular monolayers using SHG/fluorescence and atomic force microscopes

Abstract Using a newly developed microscope, which enables us to obtain the optical second-harmonic and fluorescence (FL) images and the FL and absorption spectra of the same site of specimen, the monolayer of merocyanine dye (MD) mixed with arachidic acid (AA) was observed at the air–water interface. It was revealed that the cigar-shaped J-aggregate domains have a non-centrosymmetric structure with the polar axis inclined by ∼30° from the long axis of the domain. Complemental AFM observations of the Langmuir–Blodgett monolayer clarified that the monolayer consists of three topographically different phases: the MD J-aggregate domain, monomer MD, and AA.

Morphology and thermochromic phase transition of merocyanine J-aggregate monolayers at the air–water and solid–water interfaces

Thermal changes of the merocyanine dye (MD) monolayer at the air–water interface were investigated under various subphase conditions in order to elucidate the formation mechanism and to control morphological and chromatic properties of two-dimensional MD J-aggregate crystallites (JC) formed in the monolayer. The dissociation temperature (Td) of the JC to the monomer MD was measured for different counterions of MD molecules in the subphase. The JC size was found to be dependent on the subphase temperature; it becomes larger when the JC is formed at a temperature closer to Td. This phenomenon is qualitatively reproduced by the numerical simulation of the Cahn–Hilliard equation. In the case of the MD monolayer on the subphase which contains two kinds of counterions, it exhibits a reversible thermochromic transition between two different JC states. The chromatic change is discrete, and is attributed to the structural phase transition of the JC induced by the mutual recombination of two kinds of counterions to...

Three-dimensional observations of periodically poled domains in a LiTaO3 quasiphase matching crystal by second harmonic generation tomography

Second harmonic generation interference tomography which enables us to obtain three-dimensional images of ferroelectric antiparallel domain structures is devised. Periodically poled domains (PPDs) inside a LiTaO3 quasiphase matching crystal (QPM) are observed by this microscope. Section images perpendicular to the polar z axis show that the PPD structure is maintained throughout the top quarter of the sample but it starts to lose the periodic nature in the bottom half of the sample. Corresponding degradation of the QPM performance is observed along the z direction of the sample.

Optical second harmonic images of merocyanine J-aggregate monolayers at the air-water interface

Abstract By using the second harmonic generation (SHG) microscope, two-dimensional distribution of SHG-active domains of merocyanine J-aggregates at the air–water interface was successfully observed. It was found that the ionic compound of the subphase strongly influenced the form, size and anisotropy of the SHG-active domains.

Structural phase transition of merocyanine J-aggregate induced by ion-recombination in the aqueous sub-phase

Abstract By using the sub-phase, which contains two different kinds of counter-ions, we found a reversible thermochromic transition between different J -aggregate states of amphiphilic merocyanine dye (MD) molecules in the monolayer at the air–water interface. This chromatic change is attributed to the structural phase transition of MD J -aggregate crystallites induced by the mutual recombination of different counter-ions to MD molecules. The drastic morphological change of the MD monolayer during the transition is revealed by the in-situ observation using a multipurpose non-linear optical microscope.

Sensitive Detection of Protein―Lipid Interaction Change on Bacteriorhodopsin Using Dodecyl β-D-Maltoside

A light-driven proton pump bacteriorhodopsin (bR) forms a two-dimensional hexagonal lattice with about 10 archaeal lipids per monomer bR on purple membrane (PM) of Halobacterium salinarum. In this study, we found that the weakening of the bR-lipid interaction on PM by addition of alcohol can be detected as the significant increase of protein solubility in a nonionic detergent, dodecyl β-D-maltoside (DDM). The protein solubility in DDM was also increased by bR-lipid interaction change accompanied by structural change of the apoprotein after retinal removal and was about 7 times higher in the case of completely bleached membrane than that of intact PM. Interestingly, the cyclic and milliseconds order of structural change of bR under light irradiation also led to increasing the protein solubility and had a characteristic light intensity dependence with a phase transition. These results indicate that there is a photointermediate in which bR-lipid interaction has been changed by its dynamic structural change. Because partial delipidation of PM by CHAPS gave minor influence for the change of the protein solubility compared to intact PM in both dark and light conditions, it is suggested that specific interactions of bR with some lipids which remain on PM even after delipidation treatment have a key role for the change of solubility in DDM induced by alcohol binding, ligand release, and photon absorption on bR.

SHG Microscopic Studies on Low Temperature Phase Transitions of SrTi 16 O 3 and SrTi 18 O 3

Marked field-induced second harmonic generation was observed in SrTi 16 O 3 at liquid. He temperature. The intensity decreased towards 35 K with the increase of temperature but it still remained significantly above 35 K and gradually diminished and vanished around 100 K. This indicates that ferroelectric nano-regions exist in higher temperature region and grow under electric field. On the other hand, 18 O-replaced SrTiO 3 (SrTi 18 O 3 ) exhibited SHG below 30 K without electric field and the intensity decreased steeply above the temperature. This corresponds to the appearance of ferroelectric phase. The point group of field-induced phase of SrTi 16 O 3 and ferroelectric phase of SrTi 18 O 3 is orthorhombic mm 2 with polar axis along the cubic {110} direction.

Partially induced transition from horizontal to vertical orientation of helical peptides at the air–water interface and the structure of their monolayers transferred on the solid substrates

To apply the Langmuir-Blodgett (LB) technique as a platform for investigating the fundamental properties of amphiphilic peptides (APs), we have investigated the structure of LB films using the APs. To vertically orient the helical APs like transmembrane proteins in the membrane, the primary structure of the APs was designed to have two domains: a hydrophilic domain (three amino acids) and a hydrophobic domain (ca. 20 amino acids). However, we are still far from having full control of their orientation. This study reports the contribution of the subphase temperature to the change in the orientation of helical APs. When the surface pressure-area isotherm of AP was observed at the subphase temperature at 41.5°C, the isotherm exhibited a plateau, implying that a phase transition of the monolayer at the air-water interface occurred. Circular dichroism (CD) spectra of the monolayers transferred on the solid substrates revealed that the orientation of the helices changed at the pressure, where the plateau of the isotherm was observed. This change was not observed at 21.5°C, i.e., the horizontal alignment of helixes was maintained. Atomic force microscopy (AFM) was used to systematically investigate the surface structure of the monolayers transferred at different surface pressures. A structural model of the monolayer that did not contradict with the results obtained by the three different techniques (the isotherm, CD spectroscopy, and AFM) was derived, and it was concluded that the horizontally oriented helices partially changed their orientation to vertical upon compression in the plateau region of the isotherm.

Characteristics of Halorhodopsin–Bacterioruberin Complex from Natronomonas pharaonis Membrane in the Solubilized System

Halorhodopsin is a retinal protein with a seven-transmembrane helix and acts as an inward light-driven Cl(-) pump. In this study, structural state of the solubilized halorhodopsin (NpHR) from the biomembrane of mutant strain KM-1 of Natronomonas pharaonis in nonionic detergent was investigated. A gel filtration chromatography monitored absorbances at 280 and 504 nm corresponding to the protein and a lipid soluble pigment of bacterioruberin (BR), respectively, has clearly detected an oligomer formation of the NpHRs and a complex formation between the NpHR and BR in the solubilized system. A molar ratio of NpHR:BR in the solubilized complex was close to 1:1. Further SDS-PAGE analysis of the solubilized NpHR cross-linked by 1% glutaraldehyde has revealed that the NpHR forms homotrimer in detergent system. Although this trimeric structure was stable in the presence of NaCl, it was dissociated to the monomer by the heat treatment at 45 °C in the desalted condition. The same tendency has been reported in the case of trimeric NpHR expressed heterologously on the E. coli membrane, leading to a conclusion that the change of strength of the trimeric association dependent on the ion binding is a universal feature of the NpHR. Interestingly, the trimer dissociation on the NpHR was accompanied by the complete dissociation of the BR molecule from the protein, indicated that the cavity formed by the NpHR protomers in the trimeric conformation is important for tight binding of the BR. Because the binding affinity for Cl(-) and the resistance to hydroxylamine under light illumination showed only minor differences between the NpHR in the solubilized state and that on the biomembrane, the influences of solubilization to the tertiary structure and function of the protein are thought to be minor. This NpHR-BR complex in the solubilized system has a potential to be a good model system to investigate the intermolecular interaction between the membrane protein and lipid.

Self-ordering of polar merocyanine dye molecules in Langmuir-Blodgett films

Abstract Mixed monolayers with merocyanine dye and arachidic acid were investigated by the atomic force microscope and the second harmonic generation microscope. From the observations, we found that the miscibility of these two molecules, the cluster size of merocyanine J-aggregates and the second harmonic images were strongly influenced by the ionic compound in subphase.