On the main phase transition temperatures of highly asymmetric mixed-chain phosphatidylcholines

Abstract

The highly asymmetric mixed-chain phosphatidylcholines or C(X): C(Y) PC , which can self-assemble at T < T m into the mixed interdigitated gel-state bilayer in excess water, can be divided into two groups. Group I consists of C(X): C(Y) PC with X > Y, and Group II consists of C(X): C(Y) PC with X < Y. The main phase transition temperatures (T m ) of these C(X): C(Y) PC have been analyzed in terms of two structural parameters (δ and N f ). Specifically, these structural parameters are related to the packing geometry of the lipid's acyl chains as the lipid molecules are packed either in a mixed (δ) or a hypothetically partially (N f ) interdigitated packing motif at T < T m . Based on 28 and 29 T m values of Group I and II C(X): C(Y) PC , two general equations are derived, respectively, by multiple regression analyses. These equations correlate systematically the T m values of Group I and II phosphatidylcholines with their corresponding structural parameters. Using these two derived equations, the T m values of a total of 92 molecular species of C(X): C(Y) PC are generated, and these calculated T m values can be considered as the reliably predicted T m values for highly asymmetric C(X): C(Y) PC which have ΔC/CL values within the range of 0.42–0.66.