Infrared Monitoring of Interlayer Water in Stacks of Purple Membranes

摘要: The thermodynamic behavior of films hydrated purple membranes from Halobacterium salinarum and the water confined in it was studied by Fourier transform infrared spectroscopy 180–280 K range. Unlike bulk water, thin layers sandwiched between biological does not freeze at 273 K but will be supercooled to ∼256 K. melting point is unaffected, leading hysteresis 250 273 K. In its heating branch, a gradually increasing light-scattering ice observed with rate-limiting kinetics tens minutes. Infrared (IR) spectra decomposition provided extinction coefficients for vibrational bands their changes upon freezing. Because hysteresis, any given temperature 255–270 K range, interbilayer could either liquid or frozen, depending on thermal history. We find that this difference affects dynamics bacteriorhodopsin photocycle range: decay M N states redistribution them are different whether initially precooled below freezing point. However, block transition. membrane lipids do undergo IR-detectable phase transition