DSC study of phase transition of anhydrous phospholipid DHPC and influence of water content

The phase transition behavior of 1,2-di-n-heptadecanoyl phosphatidylcholme (DHPC)with and without water has been studied by use of differential scanning calorimetry It was found by experiment that the glass transition occurred at first during the first heating of a sample of DHPC without water and then the sample underwent melting as an ordinary crystal.Therefore the sample of DHPC without water was a glassy crystal However,the DHPC sample crystallizing from melt was an ordinary crystal From the relationship between the total melting enthalpy Qf of freezable water and the water content h,it was concluded that the water contained in the DHPC samples might exist in three states recognizable thermodynamically.The water in the first state was an unfreezable water It was the water bound directly with the head groups of the phospholipid,i.e.the primary hydration water Every head group might bind seven such molecules of water.The water in the second state was the secondary hydration water,us melt ing point was

DSC study of phase transition of anhydrous phospholipid DHPC and influence of water content

The phase transition behavior of 1,2-di-n-heptadecanoyl phosphatidylcholme (DHPC)with and without water has been studied by use of differential scanning calorimetry It was found by experiment that the glass transition occurred at first during the first heating of a sample of DHPC without water and then the sample underwent melting as an ordinary crystal.Therefore the sample of DHPC without water was a glassy crystal However,the DHPC sample crystallizing from melt was an ordinary crystal From the relationship between the total melting enthalpy Qf of freezable water and the water content h,it was concluded that the water contained in the DHPC samples might exist in three states recognizable thermodynamically.The water in the first state was an unfreezable water It was the water bound directly with the head groups of the phospholipid,i.e.the primary hydration water Every head group might bind seven such molecules of water.The water in the second state was the secondary hydration water,us melt ing point was close to that of pure water and its specific melting enthalpy dQf/dh was lower than that of pure water Every molecule of DHPC might possess at most about six such molecules of water With the further increasing of the water content,the bulk water appeared in the system,its melting point and specific melting enthalpy were close to those of pure water.The experiments demonstrated that the melting peak of DHPC shifted toward the side of lower temperature with the increasing of water conlent.At h>16.2 (percent by weight),the temperature T and the en thalpy Ktr of the gel-liquid crystal phase transition of the lipid were unchanged substantially with the increasing of water content.The experimental values of the quantities,Ttr and Htr,and phase transition entropy Str were in good agreement with those calculated by the set of Huang equations (1981)