Behavior of Biological Substances in Near- and Supercritical Water
S. Deguchi, R.G. Alargova, D. Alargov, K. Tsujii, and K. Horikoshi
The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15 Natsushima-cho, Yokosuka 237-0061 Japan
Water at high temperatures and pressures is intriguing from view points of physical chemistry. When both the temperature and pressure exceed the critical point (374℃, 22.1 MPa), water becomes supercritical water (SCW), where liquid and gas are no longer distinguishable (Fig. 1). SCW would exist in the vicinity of a hydrothermal vent or over a volcano. Particularly interesting aspect of SCW is that it behaves remarkably differently from water at ambient conditions.
We have developed a high temperature and high pressure cell for an optical microscope, and studied various biopolymers and microorganisms in SCW. Cellulose dissolved in water at 320-350℃. Chitin, on the other hand, was found to be more stable than cellulose in water at high temperatures, and dissolved slowly at 390℃. Microorganisms were studied as well. The cell structure of a deep-sea yeast, Cryptococcus sp. N6, was destroyed at 250℃ and 25 MPa, to give a residue that remained up to 300℃. In the case of a mycerial cord of Flammulina velutipes, it shrank at 250-310℃, and dissolved slowly at 390℃.
SCW is also interesting as a reaction medium. We have studied the reactions that supposedly take place in a hydrothermal vent and are relevant to the origin of life. When glycine solution was injected to SCW, formation of short oligomers was observed within 10 seconds. The result suggests that a hydrothermal vent might have served as a very effective chemical reactor for the origin of life.
