title: Solvent isotope effects on the phase-transition properties of lipid bilayers.
abstract: Highly sensitive differential scanning microcalorimetry (DSC) has been used to investigate the phase transition properties of lipid vesicles prepared from 1,2-distearoyl-L-3-glyceryl-phosphatidylcholine (DSPC) in H(2)O and D(2)O. The data show that the response of pre-transition properties to D(2)O-->H(2)O substitution is stronger than the main transition properties. We find that there is a small increase in the phase transition temperature (DeltaT approximately 0.5 K) and in the co-operative unit in the main transition. The increase in enthalpy (DeltaH congruent with1 kJ(.)mol(-1)) and in transition temperature (DeltaT congruent with2 K) observed in the pre-transition is comparable with that observed in quite different processes and systems, i.e. melting of nucleic acids and proteins and gel formation. It is suggested that D(2)O-->H(2)O substitution affects the thermal transition in these systems in such a way that the contributions of enthalpy and entropy to structural reorganization of water in these processes is modified.
authors.affiliation: Unità di Perugia, Istituto per la Fisica della Materia, I-06100, Perugia, Italy
authors.forename: S
authors.initials: S
authors.lastname: Cinelli
authors.forename: G
authors.initials: G
authors.lastname: Onori
authors.forename: A
authors.initials: A
authors.lastname: Santucci