Pressure studies on the bilayer phase transitions of ester-linked diacylphosphatidylcholines (diacyl-PCs) and ether-linked dialkyl-PCs are reviewed. Comparing the bilayer phase diagrams and the thermodynamic quantities of phase transitions for diacyl-PCs with those for dialkyl-PCs, the difference in lateral interaction between polar head groups of diacyl-PC and dialkyl-PC was elucidated. The mechanism of bilayer interdigitation induced by high-pressure, which is characteristic of phospholipids with a choline head group, is discussed on the basis of molecular interaction in lipid bilayer membranes.
There have been innovative high-pressure studies on biological processes applying modern techniques of genetics and molecular biology in model microorganisms such as bacterium Escherichia coli and yeast Saccharomyces cerevisiae. Recent advanced investigations in this field have been systematically done in the genome-wide level to identify genes and proteins required for microbial growth and survival under high hydrostatic pressure. This article is an overview of studies on the effect of high pressure on microbial physiology and the challenges in piezophysiology, which has been proposed to discover whether the responses of living cells to high pressure are relevant to their growth and viability.
Studies of pressure-adapted (piezophilic) protein have lagged behind the investigation of other extremophilic proteins, however the recent characterization of proteins from deep-sea organisms has substantially accelerated the field. Recent experiments on proteins from deep-sea sources have contributed to our understanding of protein adaptation to high pressure. These studies have also complemented previous work that had investigated the effect of pressure on the activity and stability of “normal”, unadapted proteins. Together this research has lead to the conclusion that volume changes due to the hydration effects of exposed side chains and large internal cavities drive protein unfolding under high pressure.
Food (i.e. vegetables, tofu, egg-custard gel, agar gel or kon-nyaku) was pressurized at 0.1∼686 MPa and -20°C. Texture and structure were compared with the untreated control or food frozen in freezers (-20°C, -30°C or -80°C) at 0.1 MPa. At 200∼400 MPa, food was supercooled and froze rapidly with released pressure. Therefore, the size of ice crystals was small. Thus, pressure-shift-freezing at 200∼400 MPa was effective in improving the quality of frozen food with the exception of kon-nyaku. With an increase of sugars, the appearance, texture and structure of all gels improved.
In recent years, significant progress has been made in research into applications of the high-pressure treatment method. This is because it has been demonstrated that the effects of high-pressure treatment can induce additionally new phenomena when used in combination with other physical, biological, biochemical effects. Incrementation or extraction of food composition and selective inactivation of microbe by using the difference of pressure tolerance are enumerated in the concrete example. Therefore, food products using high-pressure induced transformation (Hi-pit) will contribute to various food industries such as the medical treatment, health food, brewing, fermented food, and food service industry.
For a better understanding of the molecular transport mechanism in fluids, it is important to study the density dependence in the intermediate region between liquid and gas. The hydrodynamic theory is considered to explain the molecular transport coefficients at high liquid densities, while the binary collision theory is valid in dilute gases. In this article, we report the density dependence of the electrolyte conductivities of alkali-metal halides in liquid methanol near the liquid-vapor coexistence curve up to the critical temperature (240°C) and those of tetraalkylammonium bromides up to about 180°C, and discuss the application limit of the hydrodynamic theory (Hubbard-Onsager’s dielectric friction theory) for the ionic transport process in liquids.
High-pressure solubility of sodium chloride in water and fullerene C60 in toluene, two typical pairs of solute and solvent, was measured. Bird’s-eye views of their solubility-pressure-temperature surfaces are shown. Each view consists of two surfaces of non-solvate and solvate solutes; NaCl and NaCl • 2H2O, and C60 and C60• 2C6H5CH3, respectively. Their high-pressure phenomena are thermodynamically discussed.
This is a review talk presented as a “Bridgman Award Lecture” at the AIRAPT21 held in Catania, Italy, in September 2007. History of the developments of high-pressure and high-temperature experiments to clarify the nature of seismic discontinuities of the Earth’s deep interior is briefly reviewed, together with the scientific contributions of the author. Extension of the pressure range and developments of new techniques, particularly high pressure in situ X-ray diffraction, played important role for better understanding the Earth’s deep interior.
In this short communication, we report neutron diffractions under high pressure from lead powder in a Paris-Edinburgh cell on the High Resolution Powder Diffractometer (HRPD) installed at JRR-3, Ibaraki, Japan. This is the kick-off experiment in Japan as a high pressure powder diffraction study using the reactor neutron source. The obtained data enable us to estimate how long beam time is necessary for the potential experiments.
Gas hydrates are crystalline inclusion compounds in which guest molecules (e.g. methane and carbon dioxide) stabilize the cages formed by hydrogen bonded H2O molecules at low temperature and suitable pressure. Since these materials are interested in various research fields, the understanding of their unique properties sometimes requires the collaborations beyond the research fields. This review shows some interesting phenomena of gas hydrates, which have been recently studied actively.
Energy-related materials are expected to reinforce energy security and solve worldwide environmental problems. We are currently focusing on the developments of advanced hydrogen storage materials for fuel cell technologies. Actually we have studied new metal-, complex- and perovskite-hydrides composed of light elements using high pressure technique and microwave process. In addition, hydrides researches connected with secondary battery and neutron shield have being also progressed, aiming at searching new functional materials. In this article, we introduce our recent studies of various hydrides for energy-related applications.