Abstract. We report recent efforts to understand a broad range of experiments on confined water and protein hydration water, many initiated by a collaboration between workers at the University of Messina and MIT—the editors of this special issue. Preliminary calculations are not inconsistent with one tentative interpretation of these experiments as resulting from the system passing from the high-temperature high-pressure 'HDL' side of the Widom line (where the liquid might display non-Arrhenius behavior) to the low-temperature low-pressure 'LDL' side of the Widom line (where the liquid might display Arrhenius behavior). The Widom line—defined to be the line in the pressure–temperature plane where the correlation length has its maximum—arises if there is a critical point. Hence, interpreting the Messina–MIT experiments in terms of a Widom line is of potential relevance to testing, experimentally, the hypothesis that water displays a liquid–liquid critical point.

Print publication: Issue 50 (16 December 2009)
Received 19 August 2009, in final form 9 October 2009
Published 23 November 2009