The influence of unsaturation on the phase transition temperatures of a series of heteroacid phosphatidylcholines containing twenty-carbon chains.
A series of heteroacid sn-1,2 diacyl phosphatidylcholines (PC) with twenty-carbon fatty acyl chains has been synthesized. Each PC contained eicosanoate (20:0) in the sn-1 position and one of a group of eicosaenoic acids with increasing numbers of cis double bonds in the sn-2 position. The double bonds were at positions delta 11 (20:1), delta 11,14 (20:2), delta 11,14,17 (20:3), or delta 5,8,11,14 (20:4). The disaturated PC containing two eicosanoate chains was also studied. Aqueous dispersions of these PC were analyzed by differential scanning calorimetry, and data for the gel to liquid-crystalline transitions (given as PC: Tc (degrees C), Tmax (degrees C), delta H (kcal/mol)) were as follows - 20:0-20:0 PC: 66.8, 68.4, 15; 20:0-20:1 PC: 19.8, 22.2, 8; 20:0-20:2 PC: -4.3, 1.8, 5; 20:0-20:3 PC: 1.2, 4.4, 7; 20:0-20:4 PC: -10.7, -6.8, 3. Double bonds in excess of two per chain did not substantially change the transition temperatures of these heteroacid PC. There was a small effect of the location of the multiple double bonds on the transition temperature. The data is consistent with the model that the transition temperatures are determined by a balance between a decrease in the packing density in the gel and a decrease in the rotational freedom of the chains in the liquid crystal, both caused by the double bonds ((1983) Biochemistry 22, 1466-1473).
D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000032:analysis; D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D002621:Chemistry; D004537:Eicosanoic Acids / Q000032:analysis; D005231:Fatty Acids, Unsaturated / Q000032:analysis; D008081:Liposomes; D008560:Membrane Fluidity; D010713:Phosphatidylcholines / Q000032:analysis; D013696:Temperature; D013816:Thermodynamics
D001095:Arachidonic Acids; D004537:Eicosanoic Acids; D005231:Fatty Acids, Unsaturated; D008081:Liposomes; D010713:Phosphatidylcholines; D016718:Arachidonic Acid