ON THE MAIN PHASE-TRANSITION TEMPERATURES OF HIGHLY ASYMMETRIC MIXED-CHAIN PHOSPHATIDYLCHOLINES

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 (delta 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 (delta) 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 Delta C/CL values within the range of 0.42-0.66.