Raman spectra of aqueous dispersions of dipalmitoyl phosphatidylcholine (DPPC) were obtained at very high pressures, up to 32 kbar. A new structural phase transition was detected at 15 kbar, from the known GIV to a so far unknown GV gel phase. The acyl chains in the GV phase of DPPC are fully extended and their reorientational fluctuations are completely damped. More than two correlation field components for both the CH2bending mode and the asymmetric Cndash;C stretching mode are observed. According to the spectroscopic data and the results of a selection rules analysis, an interchain packing is suggested for the GV gel phase of DPPC which resembles that in a parallel orthorhombic cell with four nonequivalent chains.
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